Search

We present the whole‐rock and mineral chemical data of the Khasi meta‐mafic/basic‐trondhjemite intrusives (KMI) and meta‐tonalite‐trondhjemite (MTT) that coevally emplaced the Proterozoic Shillong Group (SG) of Shillong Plateau, northeast (NE) India and discuss their petrogenetic‐tectonic origin. The calc‐alkaline to tholeiite KMI are compositionally transitional between hornblende‐gabbro; hornblende‐diorite and minor‐hornblendite. They show Ta–Nb troughs and strong decoupling large‐ion lithophile/high field strength elements (HFSE) signature consistent with subduction zone‐related basic magmas. The calcic to calc‐alkaline, low‐Al2O3, and I‐type metaluminous Fe‐hedenbergite‐trondhjemite (KMT) exhibits similar trace and rare earth elements (REE) distribution to the KMI. The MTT on the other hand are depleted in trace elements and REE, and correspond with the I‐type granitoids, and are comparable to Proterozoic to Phanerozoic tonalite‐trondhjemite‐granodiorites. Gentle negative sloping of REE in KMI ([La/Lu]CN = 4.04 to 6.35) with moderate LREE, suggests partial melting or, fractional crystallization from a transitional source between garnet and spinel lherzolite. Although almost a flat pattern ([La/Lu]CN = 3.70 to 4.05) for MTT entails a high degree of partial melting from sources similar to Archaean Mafic Composite or Archaean Tholeiite. Trace elemental modellings ([Sr/Y] vs. Y and [La/Yb]N vs. YbN) for MTT infer low pressure (<15 kbar) and high degree partial melting of >50% in equilibrium with 10% garnet +90% amphibole residue. A relatively flat REE pattern with some elevated HREE of MTT compared to KMI suggests for depleted source. Bimodal plutonism and the prevalence of meta‐dacite‐rhyolite in SG invokes for tonalite‐trondhjemite‐dacite setting of a continental arc or, active continental margin tectonic setting. Emplacement of KMI initiated in a temporary relax‐extensional phase and MTT in a compressional regime. This is possibly caused by an over‐thickened crust later subjected to orogenic collapse, exhumation‐metamorphism, and decompressional melting. This event might have taken place between 1.0 to 0.5 Ga during the Pan‐African Orogenic crustal growth, linked to the amalgamation of Gondwana. [ABSTRACT FROM AUTHOR]

The Heilongjiang Complex records the evolution history of the Mudanjiang Ocean, which is of great significance to constrain the amalgamation process of the Jiamusi and Songnen‐Zhangguangcai Range massifs. We carried out petrological, chronological, geochemical, mineral chemical and electron backscatter diffraction (EBSD) fabric analyses on the Heilongjiang Complex in the Yilan area. The latest zircon U–Pb dating results show that the protolith ages of the amphibolite are 261.3 ± 3.0 Ma and 261.8 ± 3.3 Ma, while that of the granodioritic mylonite is 207.8 ± 2.2 Ma. The amphibolites and granodioritic mylonite are enriched in large‐ion lithophile elements (e.g., Rb, Ba, and Sr) and light rare earth elements, with depletion in high‐field‐ strength elements (e.g., Nb, Ta, Zr, and Hf), indicating that the formation of the protoliths of the amphibolites and granodioritic mylonite is related to the subduction of the Mudanjiang oceanic plate under the Songnen‐Zhangguangcai Range Massif. The amphibolites and granodioritic mylonite both experienced two periods of metamorphic and deformation events. The metamorphic degree of the early period of metamorphism is low amphibolite facies, which records a clockwise P–T path from early increased temperature and pressure to a late isothermal depressurization. The P–T path reveals that this period of metamorphism is associated with the collision between two massifs. The later period of metamorphism reaches low greenschist facies, accompanied by deformation, which may be related to the rapid exhumation of the Heilongjiang Complex. This study provides a new perspective for exploring the collision and collage process of the Jiamusi and Songnen‐Zhangguangcai Range massifs. [ABSTRACT FROM AUTHOR]

An ophiolite suite, predominantly composed of residual mantle peridotites, mid-ocean-ridge basalt (MORB)--like ultramafic rocks, and oceanic plagiogranites, has been identified in the Zhenghe-Dapu fault zone, Cathaysia block, South China. The peridotites experienced strong serpentinization and are characterized by low 187Os/188Os ratios of 0.11621-0.12008 and very low 187Re/188Os values of 0.031-0.129, similar to those from highly refractory mantle residues. The meta-ultramafic rocks, mainly amphibolites, can be classified into two groups. Group I is characterized by high Ni and Cr and low K2O contents. Their spoon-like rare earth element (REE) patterns, along with lower concentrations of highly incompatible elements, indicate that the protolith was of cumulate origin. Group II displays depleted REE patterns and low Nb/Yb, Th/Yb, and Ti/V ratios, which are geochemically similar to normal (N) MORB. Both groups exhibit positive εNd(t) values (1.2-4.1) and relatively high (87Sr/86Sr)i ratios (0.7046-0.7096), suggesting their origin from partial melting of depleted mantle sources in a mid-ocean-ridge setting that experienced a greater extent of fluid-rock alteration. The meta-plagiogranites intercalated with the mylonitic amphibolites are characterized by low K2O (0.09-0.21 wt%) and total REE contents along with low K2O/Na2O and Rb/Sr ratios, which are consistent with those of typical oceanic plagiogranite. They exhibit strongly positive zircon εHf(t) values (+9.5 to +15.1) and positive whole-rock εNd(t) values (+2.8 to +3.6). Their extremely low MgO (0.6-1.65 wt%), Cr (0.22-6.26 ppm), and Ni (0.77-4.74 ppm) compositions and low Mg# (22.4-31.9) preclude their origination from mantle-derived primary magma but favor oceanic crust. Low zircon δ18O values (4.02‰-5.4‰) and decoupled Sr-Nd isotope features imply the involvement of high-temperature seawater alteration in their source region. The enriched light rare earth element (LREE) patterns with strongly positive Eu anomalies, similar to the East Karmøy--type plagiogranite in western Norway, imply that the plagiogranites were derived from anatexis of amphibolite in an active shear zone near the mid-ocean ridge. The magmatic and metamorphic zircons from the meta-plagiogranites yield nearly identical secondary ion mass spectrometry (SIMS) U-Pb ages ranging from 523 to 521 Ma and from 522 to 518 Ma, respectively. The simultaneous magmatism and metamorphism also signify an active high-temperature shear zone, where the plagiogranites were formed slightly later than the oceanic crust. The age of ca. 520 Ma represents the formation age of the oceanic crust rather than its emplacement age. The identification of the ca. 520 Ma ophiolite suite along the Zhenghe-Dapu fault zone indicates that the Cathaysia block consisted of at least two different terranes rather than a single tectonic unit in the Cambrian, and the final amalgamation of the eastern and western Cathaysia block may have occurred far later than ca. 520 Ma, most likely during the late early Paleozoic. [ABSTRACT FROM AUTHOR]

Zircon from spatially and temporally distinct igneous rock units across the Gawler Craton, Australia, show subtle differences in trace and rare earth element ratios. These igneous suites range in composition from granite, rhyolite to gabbro and originate from the ca 2450 Ma Sleaford Complex, the ca 1850 Ma Donington Suite, the ca 1633–1608 Ma St Peter Suite, the ca 1595–1587 Ma Gawler Range Volcanics and the ca 1595–1575 Ma Hiltaba Suite granites. The geochemical characterisation of zircon is carried out on relatively unaltered samples in order to establish primary signatures and to understand the processes controlling the geochemical signatures of the igneous suites. A range of zircon morphologies and internal textures that are preserved in these igneous suites infer the geological history of the host rock, including metamorphism and multiple episodes of zircon saturation suggesting a complex magma evolution. Despite differences in whole-rock geochemistry between igneous suites, zircon largely overlaps geochemically. However, subtle differences in Th/U, U/Hf and (Nb + Ta)/P ratios are evident between the Donington Suite, Gawler Range Volcanics and Hiltaba Suite. This is likely due to the tectonic setting, composition of the crystallising magma and timing of zircon crystallisation in the magma evolution. The subtle geochemical differences in zircon show the potential of using these ratios to aid in provenance studies with large populations of zircon that are of similar age. However, as the dataset is limited and focused only on unaltered samples, further work needs to be undertaken to look at the altered counterparts of these igneous suites. Zircon recovered from unaltered samples of spatially and temporally distinct igneous suites in the Gawler Craton is used here. Th/U, U/Hf and (Nb + Ta)/P ratios of zircon can discriminate the Donington Suite, Gawler Range Volcanics and Hiltaba Suite. Zircon morphologies, internal textures and geochemical characteristics are a value aid to provenance studies. [ABSTRACT FROM AUTHOR]

The Kunyushan granitic complex in the Jiaodong Peninsula, East China, is located in the northeast part of the Sulu UHP metamorphic belt. It is the transition belt of the North China Craton and Sulu UHP metamorphic belt. Field relationship and dating results revealed five intrusive phases of the Kunyushan granitic complex were modified into gneissic fine‐grained garnet‐bearing monzogranite (G1), gneissic medium‐ to fine‐grained monzogranite (G2), medium‐ to coarse‐grained monzogranite (G3), medium‐grained monzogranite (G4), and porphyritic coarse‐ to medium‐grained monzogranite (G5). All these phases have similar rock assemblages of peraluminous, calc‐alkaline, I‐type monzogranites. The monzogranites had primitive mantle‐normalized patterns enriched in light rare earth elements (LREE) and lithophile elements (Sr, Ba, and Rb), but depleted in heavy rare earth elements (HREE) and high‐field‐strength elements (Nb, P, and Ti). LA‐ICP‐MS zircon U–Pb dating shows that the crystallization age of the Kunyushan granitic complex extends at least from 157.7–142.0 Ma. The weighted average ages of G1‐G5 were 145.6 ± 1.9 Ma, 145.8 ± 0.5 Ma, 147.2 ± 0.7 Ma, 154.2 ± 0.6 Ma, and 155.0 ± 0.7 Ma, respectively. G5 to G1, from the middle to the edge shows a trend of gradually becoming younger. Zircon grains from different phases have similar 176Hf/177Hf values from 0.281917 to 0.282298, and εHf(t) values from −27.6 to −14.0, with a weighted average of −22.6 ± 0.5, typical of crustal‐derived origin. The corresponding two‐stage model ages TCDM are from 2,910 to 2,066 Ma, with a weighted average of 2,603 ± 31 Ma. Hf–Sr–Nd–Pb isotopes and inherited zircons suggest that the parental magma of the Kunyushan granitic complex was derived from melting of basement rocks of the North China Craton and the Yangtze Craton. The magmatism presumably took place under the background of subduction and back‐arc extension of the Palaeo‐Pacific plate. We infer that the Kunyushan granitic complex was produced by partial melting of the thickened lower crust, through delamination of the thickened lower crust during the Late Jurassic. This magmatic event may mark the beginning of the extensive Mesozoic thinning of the lithosphere in East China. [ABSTRACT FROM AUTHOR]

The Lower Jurassic clastic rocks in the Qiangtang Basin, northern Tibet, are generally regarded as the early sediments of the new Mesozoic Qiangtang Basin (Late Triassic to Early Cretaceous). However, little attention has been paid to the palaeoenvironment, provenance, and tectonic setting of this unit. The QZ‐16 well, located in the east of the northern Qiangtang Basin, firstly recovered the Lower Jurassic strata (Quemo Co Formation) in the Qiangtang Basin. In this paper, the whole‐rock major‐trace elemental characteristics of 34 mudstone samples and detrital zircon geochronology of one sandstone, collected from the Quemo Co Formation of the QZ‐16 well, are reported in order to infer the palaeoenvironment, provenance, and tectonic setting. Quemo Co mudstones are dominated by SiO2 and Al2O3, while Fe2O3, CaO, K2O, and MgO are the second most abundant oxides. They are generally characterized by high REE concentrations, enrichment in light rare earth elements (LREEs), marked negative Eu and Ce anomalies. The REE contents of the mudstones are mainly controlled by terrigenous detrital minerals input. The Lower Jurassic mudstones have relatively high chemical index of alteration (79.1–83.6) values, indicating moderate to high degree of chemical weathering conditions of the source area. Sr/Ba and Rb/K ratios reflect that the marine transgression impact was limited and the mudstones were generally deposited in a brackish water environment. Major, trace, and REE contents indicate that the mudstones were mainly derived from intermediate igneous rocks with subordinate felsic igneous rocks. Prominent age peaks at ca. 200 ~ 400 Ma, 700 ~ 970 Ma, 1,700 ~ 1,900 Ma, and 2,100 ~ 2,700 Ma of the detrital zircon grains suggest that the Lower Jurassic clastic rocks were derived from the Central Qiangtang and Songpan–Ganzi complex. Moreover, tectonic discrimination diagrams based on major and trace elements show that the source of the Lower Jurassic sediments were most likely derived from a collision tectonic setting. [ABSTRACT FROM AUTHOR]

The Dongliushuquanzi magmatism contains two units: granitic intrusion and multiple intrusive dioritic veins. LA‐ICP‐MS zircon dating results have revealed that the magmatism developed in two distinct episodes: the first episode, which occurred in the Late Carboniferous–Early Permian, is characterized by the main granitic intrusion and the Phase I dioritic veins, Phase II dioritic veins developed during the second magmatic episode in the late Early Permian. The analysing results of major and trace elements indicate that the granitic intrusion are enriched in light rare earth elements and large‐ion lithophile elements such as Rb, Ba, K, but depleted in high‐field‐strength elements, such as Nb, Ta, P, and Ti. These geochemical signatures, in addition to their weak negative Eu anomalies, are similar to those of continental arc magmatic rocks. The main body of the granitic intrusion and the Phase I dioritic veins are characterized by negative and inhomogeneous ε Hf (t) values (include ε Hf (t) < −10 and −10 < ε Hf (t) < −5 two subgroups), they were derived from mixture of decompression melting basaltic juvenile lower crustal materials and partial melting ancient materials in middle‐upper crust. Phase II dioritic veins are characterized by positive and homogeneous zircon εHf(t) values (~ + 10), record predominantly juvenile crustal sources, formed by partial melting of basaltic juvenile lower crustal materials. The two magmatic episodes are in response to slab rollback, slab break‐off and final amalgamation of the Palaeo‐Asian Ocean. The ages of inherited zircons record ~499 and ~365 Ma magmatic activity, imply that there also exist Cambrian and Devonian magmatism in the west section of the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

Late Neoproterozoic gabbroic-diabasic sills are widely distributed in the eastern part of the South Qinling block. Here, a comprehensive geochronological and geochemical study of these mafic sills has been conducted. LA-ICP-MS zircon U-Pb results indicate that the gabbroic-diabasic sills were formed at 632 ± 2 Ma. The sills consist mainly of tholeiitic basaltic rocks with relatively low TiO2 contents (0.81–1.07 wt.%) and high Fe2O3T/MgO ratios. These rocks display relatively flat to moderate light rare earth elements (LREE) enrichment patterns and positive Eu anomalies (Eu/Eu* = 1.15–1.41). On the primitive mantle normalized spider diagram, the samples show E-MORB-like geochemical features. All of the studied samples display similar Sm-Nd isotopic compositions with negative εNd (t) values ranging from −6.2 to −5.5. Most clinopyroxenes from the mafic sills have relatively low Al/Ti ratios similar to those of typical rift-related cumulates. Therefore, Whole-rock and mineral geochemical features of the studied samples suggest that the mafic sills might have been derived from partial melting of a metasomatised subcontinental lithospheric mantle source in a continental rift setting. It can be advocated that the break-up of the Rodinia supercontinent in the northern part of the Yangtze craton might have been a long-lasting process. By comparison of the coherent Neoproterozoic magmatic events in the northern Yangtze craton and the Tarim block, it can be suggested that the Yangtze craton might have been adjacent to the Tarim block in the reconstruction model of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

The Eastern Kunlun Orogenic Belt (EKOB) in Northwest China, is an ideal area for understanding the tectonic evolution of the Palaeo-Tethys Ocean. The EKOB is marked by widespread Palaeozoic to Early Mesozoic magmatism. However, the Late Permian–Early Mesozoic tectonic evolution of the Palaeo-Tethys Ocean tectonic regime is poorly understood. Here, we report new zircon LA-ICP-MS U–Pb dating and geochemical analyses of Late Permian–Early Triassic intrusive rocks in the Xiangyanggouxi and Dageledong areas in the EKOB, Northwest China, to discuss their petrogenesis and geodynamic setting and reconstruct the tectonic evolution of Palaeo-Tethys oceanic tectonic regime. Zircon U-Pb dating results indicate that these granitoids crystallized during ca. 256–248 Ma, i.e. the Late Permian to Early Triassic. These granitoids are mainly comprised of granodiorites and monzonitic granites that possess high concentrations of SiO2 (66.81–75.98 wt.%), K2O+Na2O (6.21–7.92 wt.%), and low contents of MgO, CaO, Cr, Ni, and Mg# (<0.44). They are classified as medium- to high-K calc-alkaline and metaluminous I-type granitoids. These granitoids are rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. In addition, combined with the εHf(t) values of −2.4 to +2.4 with two-stage model ages ranging from 1409 Ma to 1027 Ma, and the εNd(t) values from −3.73 to −2.95, it is suggested that the primary magma of these granitoids was derived from the partial melting of the Late Meso–Proterozoic mafic lower crust. These findings, combined with spatio-temporal distributions of regional magmatism, reveal that the Late Permian and Early Triassic granitoids formed in a continental magmatic arc setting related to the northward subduction of the Palaeo-Tethys Ocean plate beneath the EKOB-Qaidam terrane. [ABSTRACT FROM AUTHOR]

This study presents the results of geochemical investigations of early to middle Eocene sandstones belonging to the Dalbuing Formation of Yinkiong Group, occurring in and around Yamne valley of Arunachal Pradesh. Geochemically, these sandstones are wacke and lithic arenite, with the former being dominant than the other. The various indices of weathering (CIA, CIW, PIA) suggest intense chemical weathering of the source rock. Moreover, the average Th/U ratio (mean = 6.97) also indicates intense chemical weathering in the source areas and derivation of the sediments from the upper continental crust. However, the plot of chemical index of alteration (CIA) vs. index of compositional variability (ICV) shows that most of the sandstones are geochemically mature and were derived from intensively weathered source rock. The sandstones were deposited dominantly in semi-arid condition. Tectonically, these sandstones are found to have affinities towards both the passive margin (PM) and the active continental margin (ACM) settings, which further implies existence of multiple tectonic activities during their deposition. Moreover, the elemental ratios of Eu/Eu*, La/Sc, Th/Sc, La/Co, Th/Co, Th/Cr and chondrite normalized REE distribution pattern suggest their derivation from sources of felsic composition. The high ratio of Zr/Sc indicates the enrichment of heavy mineral zircon supplemented by sediment recycling. [ABSTRACT FROM AUTHOR]

Although it is generally accepted that the Kazakhstan Block is an assemblage of Precambrian microcontinents and Early Palaeozoic island arcs, the details and timing constraint of the collage process need to be precisely studied in local regions. Thus, we conducted combined studies of geochemistry, zircon U–Pb geochronology and Sr–Nd–Hf isotopes upon the Awusiqi alkali‐feldspar granite and volcanic rocks from the Saur area in northern West Junggar. The Awusiqi volcanic rocks are mainly composed of andesites, rhyolites, and pyroclastic rocks. The alkali‐feldspar granite directly intrudes into the surrounding volcanic strata. Zircon U–Pb ages of the Awusiqi andesites, rhyolites, and alkali‐feldspar granite are 431 ± 3 Ma, 428 ± 5 Ma, and 426 ± 6 Ma, respectively. These new age data imply for the existence of Silurian magmatism in the Saur area. The alkali‐feldspar granite and rhyolites with high silica and alkali contents belong to metaluminous to weakly peraluminous and alkaline series and show seagull‐type REE patterns with strongly negative Eu anomalies. They are relatively enriched in the light rare earth elements (LREEs), K, Rb, Ba, Cs and other large‐ionic lithophile elements (LILEs), and are poor in P, Sr, and Eu, geochemically similar to those of A2‐type granites. The alkali‐feldspar granites have positive zircon εHf(t) values varying from +11.03 to +16.87 and young Hf model ages (TDM2 = 686 – 425 Ma). These features suggest that the Awusiqi alkali‐feldspar granite and rhyolites (except sample 18XJSF22C) were generated by partial melting of the juvenile lower crust with fractional crystallization, whereas sample 18XJSF22C shows mantle‐derived features. Awusiqi andesites show typical sanukitic high‐Mg andesites characteristics(Mg# = 48.08 – 65.52). The andesites are enriched in LREEs and LILEs, and are depleted in Nb, Ta, and Ti. They also have relatively high initial 87Sr/86Sr ratios (0.70543 – 0.70547), positive εNd(t) values (+2.5 – +5.7), and ancient Nd model ages (TDM1 = 1,093 – 815 Ma). These features suggest the andesites were likely derived from partial melting of a depleted mantle source previously metasomatized by slab‐derived fluids and melts. The discovery of Silurian magmatism in the Saur area has further confirmed the existence of Early Palaeozoic Tarbagtay arc basement and widespread Middle Palaeozoic A2‐type granitoids. We favor a post‐collisional setting in the Silurian in northern West Junggar, which also is the local embodiment of the Middle Palaeozoic amalgamation of the Kazakhstan Block. [ABSTRACT FROM AUTHOR]

Mineralogical and geochemical (major, trace and rare earth elements) studies were carried out on the clay samples of the Terani Formation, South India to investigate the paleoweathering, source rocks characteristics and tectonic setting. The chemical index of alteration (CIA), plagioclase index of alteration (PIA) values and A-CN-K diagram indicate that clays were generated from source rocks of the upper continental crust affected by intense chemical weathering. The chondrite-normalized REE patterns show considerable LREE enrichment, HREE depletion with significant negative Eu anomalies. The REE patterns, elemental ratios like Al2O3/TiO2 Cr/Ni, Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, discriminant function diagram, various bivariate and ternary plots indicate the contribution of sediments from felsic and intermediate source rocks. The discriminant-function-based tectonic setting diagrams reveal passive margin setting for the source area of the Terani Formation. [ABSTRACT FROM AUTHOR]

During the Late Cretaceous period, massive magmatism occurred in South China. Eastern Hunan Province is situated in the inland part of South China. Comparing with the coastal area, the inland of South China is characterized by the absence of intermediate‐acid intrusive rocks, but the occurrence of multiple mafic rocks. To date, the emplacement and triggering mechanism of magmatism of inland South China is still very puzzling. In this article, we address this question by concentrating on the basalt exposed in eastern Hunan Province. Geochronologically, three stages of zircon grains, which include xenocrysts and authigenic crystals (rare), are recognized, and the last stage of zircon grains with a concordant age of 79.93 ± 0.47 Ma (MSWD = 1.9) represents the actual crystallization age of basaltic magma. Geochemically, the basalt in eastern Hunan Province has low TiO2 and K2O contents (1.11–2.63 and 0.28–2.88 wt%) but high alkali contents (3.75–6.58 wt%) and K2O/Na2O ratios (0.05–0.56). The basalts from eastern Hunan Province are enriched in large‐ion lithophile elements and light rare earth elements and obviously depleted in heavy rare earth elements with weak negative Eu anomalies (Eu/Eu* = 0.87–1.26); they lack significant Ti, Nb, Ta, etc., depletions. These features are much different from those of coastal basalt with strong arc‐related signatures. The incompatible element ratios and Sr–Nd–Pb isotope compositions commonly imply significant EMII‐type OIB‐like source region and within‐plate basalt characteristics. The basalt may have suffered from earlier partial melting of garnet‐spinel peridotite and later rapid fractional crystallization of mafic minerals (olivine and pyroxene). Significant geochemical and petrological discrepancies between inland basalt and coastal basalt suggest a subduction‐absent within‐plate setting for inland basalt but a strong subduction‐related signature for coastal basalt. The magmatic age of mafic rocks from inland South China hold a significant tendency to become younger to the west. The spatial and temporal distribution and variation of components of basalt in South China indicated a mantle plume model which is derived from the 670 km thermal boundary layer (670 TBL) between the lower and upper mantle. The trigger mechanism of this model could be attributed to the westward steep rollback subduction of the Palaeo‐Pacific Plate in the Late Cretaceous. [ABSTRACT FROM AUTHOR]

The evolution of the South China continental crust and its linkage to the assembly and rifting of eastern Gondwana are key issues in the understanding of the early Paleozoic evolution of eastern Asia. We report U-Pb zircon ages and geochemical and Lu-Hf isotopic data for the South Fufang and Yingshang granitoids and the Mayuan diabases from the Wuyishan of eastern South China. The zircons yielded U-Pb ages of ca. 414-404 and ca. 409-401 Ma for the granitoids and diabases, respectively. Petrographic and geochemical features indicate that the granitoids are peraluminous A-type granites, expressed by high Ga/Al ratios and high Zr, Nb, Ce, Y, and rare earth element contents. They show negative zircon eHf(t) values (-15.4 to -5.8), consistent with the derivation from a crustal source. The granitoids likely originated from partial melting of dry granulite residues in the lower crust. The diabases show depletion in Ti, and negative correlations between FeOt and Mg#, and SiO2 and TiO2/FeOt, reflecting clinopyroxene, olivine, and Fe-Ti oxide fractionation. Their negative zircon eHf(t) values (-4.5 to -0.4) indicate an ancient enriched-mantle origin. The diabases likely originated from partial melting of a subcontinental lithospheric mantle. We interpret these A-type granitoids and diabases as postorogenic, formed during extensional collapse of thickened crust. Their generation indicates that South China experienced crustal extension during the Early Devonian. The extension occurred coevally with global rifting that led to the separation of the continental blocks of eastern Asia from eastern Gondwana, which was associated with the Early Devonian opening of the paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

Geological, petrological, isotope-geochemical (40Ar/39Ar analysis, petrochemical data, and geochemistry of trace elements and REE), and mineralogical researches testify that the formation of the early Paleozoic basalt and picrite complexes of the West Siberian Plate basement was related to the development of the Cambrian subduction zone of the Paleo-Asian Ocean. Using the compositions of clinopyroxenes and amphiboles (and also programs of computational modeling), we have established the P-T conditions of formation of early Paleozoic picrite complexes. Crystallization of clinopyroxenes began at significant depths (25-20 km) and at high temperatures (1300-1275 °C). Olivine might have formed at elevated pressures (8-7 kbar) and temperatures of 1540-1490 °C. Amphiboles formed, most likely, at 6.1-4.5 kbar and much lower temperatures, 1105-1060 °C. Petrochemical analysis and data on trace elements and REE in the rocks of the studied early Paleozoic complexes in West Siberia testify to their intricate formation involving magmatic systems with basalt (island arc and back-arc basins), picrite, and shoshonite (and also WPB type) melt characteristics. Taking into account the similar geochemical characteristics of the early Paleozoic basaltoids and picrites of the West Siberian Plate basement and the Kamchatka volcanics, we suggest that a considerable part of the studied ancient complexes formed by the model implying (as in the case of the Sredinnyi Ridge in Kamchatka) the action of enriched magmatic systems during the development of a destructive window ("slab-window") under rupture of subducted plate on the background of common island arc magmatism. [ABSTRACT FROM AUTHOR]

In this study, we present new zircon U-Pb and Hf isotope data and geochemical analyses for Jurassic igneous rocks from the southern Zhangguangcai Range, NE China. In the context of our new U/Pb data together with other published data (n = 165), we recognize three major magmatic pulses in the eastern Songnen Block during the Jurassic: earliest Jurassic (200–195 Ma), late Early Jurassic (183–175 Ma) and early Late Jurassic (ca. 163 Ma). According to the petrological classification scheme, rocks are divided into two categories of andesite and I-type granitoids. Generally, Early Jurassic monzogranites have more evolved compositions with SiO2, Al2O3, and K2O+Na2O concentrations of 67–74 wt.%, 13.28–17.04 wt.% and 7.25–9.31 wt.%, respectively than Late Jurassic granodiorite. Early Jurassic andesite has SiO2, Al2O3, Na2O+K2O contents of 54.64–56 wt.%, 17.27–17.44 wt.% and 3.47–4.06 wt.%, respectively with low Mg# values of 0.18–0.26. In addition, all samples show enrichment in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depletion in high strength field elements (HSFEs, such as Nb, Ta, P and Ti) and low Sr/Y and (La/Yb)N ratios, all of which are characteristic of arc-type magmatic signatures. In view of the Hf isotope signatures, these rocks show high initial 176Hf/177Hf ratios (0.282711–0.283069) corresponding to positive εHf(t) values (+0.39 to +13.66) and Neoproterozoic two-stage model ages (1154–550 Ma). In summary, the geochemical results suggest that the primary magmas of Jurassic granitoids were derived from variable degrees of partial melting of juvenile lower crust, whereas Early Jurassic andesite was derived from the partial melting of mantle wedge peridotite metasomatized by hydrous melts from subducting sediments and/or oceanic crust. The Jurassic arc-type magmatism in the eastern Songnen Block indicates that the Mudanjiang oceanic plate was still subducting in the Jurassic. [ABSTRACT FROM AUTHOR]

The Ayishan Group in the Lajishan area is sandwiched between the South Qilian Belt and the Qilian Block, which is transitionally interpreted to represent the products of the post‐collision setting or the continental marginal arc during the Early Ordovician or Silurian and is associated with the evolution of the Proto‐Tethyan Ocean. While the detailed information about the age, geochemistry, and tectonic setting of the Ayishan Group is lacking, our geological mapping and analyses demonstrates that the Ayishan Group consists of andesites, rhyolites, ignimbrites, sandstones, and conglomerates, which unconformably overlies the Cambrian–Ordovician arc‐ophiolite complex. Zircon U–Pb dating of the rhyolites demonstrated that the Ayishan Group formed between 447 and 442 Ma and is Late Ordovician. Geochemical analyses demonstrated that rhyolites have high and variable SiO2 contents of 69.6–76.5 wt% and an aluminium saturation index (A/CNK) of 0.85–1.45, belonging to calc‐alkaline to high K calc‐alkaline series. They are subdivided into two subtypes of high‐Sr/Y rhyolites (HSRs) and normal rhyolites (NRs) based on the geochemical characteristics. The HSRs show lower total rare earth elements (34.77–62.78 ppm), lower Yb (0.19–0.21 ppm) and Y (1.77–1.99 ppm) contents, and relatively higher Sr contents (159–193 ppm), compared with NRs, and with positive Eu anomalies. Both subtypes exhibit extremely high whole‐rock δ18O values of 12.63–13.21‰, but various initial 87Sr/86Sr ratios and εNd(t) values, indicating a dominant origin of terrigenous sediments and the HSRs exhibit a more terrestrial composition than the NRs. Various magma sources further caused the assorted residual phase leading to the different geochemistry between the HSRs and the NRs. Combined with the previous data, these results imply that the rhyolites of the Ayishan Group were produced in the process of the amalgamation of the Qilian Block with the Qaidam Block during the Late Ordovician, which further indicated that the Proto‐Tethyan Ocean closed 450 Ma ago. [ABSTRACT FROM AUTHOR]

Located in the eastern part of the Tethyan tectonic domain, the Jinshajiang Suture Belt (JSB), northwestern Yunnan, China, is notable for its large-scale distribution of Jurassic to Triassic granitoids that are genetically related to the evolution of the Paleo-Tethys Ocean and polymetallic mineralization. In this study, geochronological and geochemical analyses were conducted on three samples of these granite porphyries (GPs) using laser ablation inductively coupled plasma mass spectrometry and zircon U–Pb aging to reveal ages of 213 ± 15 , 198.4 ± 8.6 , and 195.3 ± 6.4 M a , respectively. These ages are younger than the emplacement ages of the granodiorites, at 208–239 Ma, suggesting that magmatic activities in the Yangla mining district likely continued for ~44 Ma. These GPs are rich in large-ion lithophile elements such as Rb, Ba, Th, U, K, and La but are deficient in high field strength elements such as Ta, Nb, Ce, Zr, Hf, and Ti. Significant Pb enrichment and P depletion were noted, as were varying degrees of metallogenic element enrichment in the order of Cu > Pb > Zn. The total content of rare earth elements (ΣREEs) of the GPs is in the range of 50.41–127.27 ppm and the LREE/HREE ratio is in the rage of 4.46–10.54. The GPs are rich in LREEs, with a high degree of differentiation noted between the LREEs and HREEs. The δ Eu (EuN/Eu ∗) and δ Ce (CeN/Ce ∗) values, at 0.53–0.86 and 0.79–0.98, indicate weak and slightly weak negative anomalies, respectively. The geochemical characteristics of the GPs indicate that these bodies are slightly metaluminous to peraluminous S-type granites in a calc–alkaline series that formed in a late-collisional or postcollisional tectonic setting. Three-component mixing of magmas including those of upper crust, lower crust, and mantle materials in addition to subsequent partial melting could have been responsible for the generation of these GPs in an epithermal low-pressure setting at <5 kbar. [ABSTRACT FROM AUTHOR]

Abundant Neogene adakitic magmatism occurred in the southern Lhasa subterrane after the onset of the India-Asia collision while convergence continued. However, the tectonic setting and magmatic evolution of the adakitic rocks are still under discussion. This study includes new mineral chemical and whole-rock geochemical data as well as zircon U-Pb and Lu-Hf isotopes of adakitic intrusive rocks from the Gyaca and Nyemo locations in the southern Lhasa subterrane. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb dating yielded crystallization ages of ca. 30 Ma for the Gyaca and Nyemo monzogranite and ca. 15 Ma for the Nyemo granodiorite. Both have common chemical signatures such as low MgO and heavy rare earth element contents as well as low compatible element abundances, indicating that these rocks result from partial melting of thickened lower crust with residual eclogite and garnet amphibolite. Furthermore, these rocks are characterized by variable positive zircon Hf(t) values, suggesting a juvenile magma source with variable ancient crustal contributions. Taking previous data into account, the adakitic magmatism concurs with an early late Eocene to Oligocene (ca. 38- 25 Ma) and a late Miocene (ca. 20-10 Ma) phase. The adakitic rocks of the two phases are characterized by different fractionation evolutions of light and medium rare earth elements. We propose that the early-phase adakitic rocks were generated by the anatexis of Lhasa terrane lower crust owing to crustal shortening and thickening subsequent to the onset of the India-Asia collision and the upwelling of hot asthenosphere beneath the Lhasa terrane caused by the break-off of the Neo-Tethyan oceanic slab. The latest phase of adakitic rocks, however, relates to upwelling asthenosphere following the delamination and/or break-off of the subducting Indian continental slab. [ABSTRACT FROM AUTHOR]

Miocene postcollisional potassic and adakitic rocks are widely distributed in the southern Lhasa terrane and western central Lhasa terrane. However, coeval potassic and adakitic rocks in eastern central Lhasa terrane were rarely recognized, and their origins and formation mechanism remain controversial. In this paper, we provide new geochronological and geochemical data for the Miocene postcollisional potassic and adakitic intrusions exposed in the Qingdu area, eastern central Lhasa terrane, southern Tibet. The Qingdu Miocene intrusions consist of quartz monzonite porphyry and biotite granite with coeval zircon U–Pb ages of 14.1 Ma and 14.0 Ma, respectively. They have high SiO2 (67.98–75.32 wt.%), Al2O3 (14.13–14.78 wt.%), and K2O (4.06–6.18 wt.%) and low MgO (0.25–1.46 wt.%) contents. They are both enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with high (La/Yb)N (25.37–42.32) ratios. The biotite granite samples have low Y (7.10–9.96 ppm) and Yb (0.61–0.85 ppm) contents, and high Sr (229–384 ppm) contents and high Sr/Y (30–41) ratios, which show adakitic geochemical characteristics, whereas the quartz monzonite porphyry samples show potassic geochemical characteristics. They display initial (87Sr/86Sr)i ratios of 0.7083–0.7103, εHf(t) values of −6.7 to −0.1, εNd(t) values of −8.96 to −7.44, (208Pb/204Pb)i ratios of 39.028–39.110, (207Pb/204Pb)i ratios of 15.662–15.684, and (206Pb/204Pb)i ratios of 18.541–18.577. These signatures indicate that both the potassic and adakitic intrusions are more likely to originate from partial melting of a thickened lower crust, which were mainly the products of the binary mixing between the juvenile and ancient crust components. Based on the spatial distributions and isotopic features of the postcollisional potassic and adakitic rocks in the Lhasa terrane, we suggest that the differences of the lower crustal composition played a crucial role in causing the geochemical variations of the Miocene postcollisional adakitic and potassic rocks in Lhasa terrane. [ABSTRACT FROM AUTHOR]

We present systematic U–Pb age data collected by laser ablation multi-collector inductively coupled plasma mass spectrometry, precise geochemical data, and Nd isotope data for igneous rocks from the southeastern Lesser Xing'an Range (SE LXR). The results indicate that the formation ages as follows: Maojiatun alkaline granite, 207.2 ± 0.84 Ma and 204.6 ± 0.93 Ma; Diorite porphyrite, 164.5 ± 0.97 Ma; and Tieli syenogranite, 186.7 ± 1.50 Ma. The alkaline granite has high silicon, potassium, alkali, and FeOT contents; it is enriched in high field strength elements, Zr, Hf, Th, Rb, and U; is depleted in Ba, Sr, Nb, Ta, P, Ti, etc.; and has high ratios of 10000Ga/Al. It shows an A2-type granite affinity. The Tieli alkali-feldspar granite has high total alkali contents and is enriched in high field strength elements and rare earth elements and depleted in Sr, Ba, Ti, and P, and shows varying degrees of alkalinity. Rocks from SE LXR display similar εNd (t) values with corresponding to Nd model ages of 1095 to 813 Ma. The igneous rocks from the SE LXR are proposed to be derived from melting of the Neoproterozoic lower crust and potential magma mixing with ancient crystalline basement. The formation of the Maojiatun alkaline granite occurred in response to a postorogenic event following the closure of the Paleo-Asian Ocean. However, the SE LXR exhibited an extensional back-arc tectonic setting in the Early Jurassic. The Middle Jurassic diorite porphyrite could be related to the temporary stagnation of the westward subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

In the Trollfjord–Rybachy–Kanin fault zone, the major convergent suture between the East European and West Arctic platforms, on the isthmus of Cape Vestnik located between the Sredny and Rybachy peninsulas, in the Riphean terrigenous sequence, massifs of disintegrated granitoids have been identified, primarily belonging to the Archean crystalline basement and which subsequently underwent tectonic extrusion to the upper horizons in the form of protrusions. Petrographic studies of disintegrated rocks from the Vestnik granitoid massif and the surrounding rocks indicate their high permeability and porosity in shattering zones. The positive Eu anomaly and decrease in content of light rare earth elements indicates the reducing nature of the fluids that affected disintegrated rocks, contributing to their formation under decompression conditions. The buried massifs of disintegrated granites may have reservoir properties. U–Pb and Sm–Nd isotopic studies of disintegrated plagiogranites with a model age of 2966 Ma has made it possible to correlate them with the rocks from the Murmansk block of the Baltic Shield. According to Sm–Nd data, the dolerite dike that cuts the plagiogranite massif has an age of 1333 ± 160 Ma (Middle Riphean) on pyrite and plagioclase, which corresponds to fragmentation of the basement at the initial continental rifting stage, which led to the formation of the White Sea paleorift system. East of Cape Vestnik, within the water area of the Barents Sea, a chain of linear–arched contrasting negative anomalies has been recorded in the gravity field. They are interpreted with high probability as reflections of the plate-shaped massifs of disintegrated granitoids included in the Riphean sedimentary sequence along the Trollfjord–Rybachy–Kanin shear zone, which may suggest a promising hydrocarbon potential of this zone under certain conditions. [ABSTRACT FROM AUTHOR]

The mafic igneous activities in the late Triassic play an important role in the tectonic evolution of the South China Block (SCB). In this paper, relevant data of the bojites in Yajiangqiao area, eastern Hunan Province, South China were provided, including zircon U–Pb ages, whole‐rock geochemical data, Sr–Nd–Pb isotopic data, and zircon Hf isotope data. These data indicate that the bojites were crystallized at ~ 215.7 Ma, and thus are coeval with biotite monzonitic granites of Yajiangqiao pluton. The bojite samples feature a low SiO2 content of 48.84–49.94 wt%, a low ALK (K2O + Na2O) content of 5.13–6.13 wt%, a relatively high Al2O3 content of 17.64–21.22 wt%, a moderate MgO content of 4.32–7.07 wt%, and a moderate FeOT content of 5.66–7.33 wt%. In addition, the samples have a total rare earth element (REE) content of 108–163 ppm. They display right‐declined REE patterns, enriched in light rare earth elements and large‐ion lithophile elements (such as Rb, K, Th, and U) and depleted in high field strength elements (such as Nb, Ta, P, and Ti). All the samples have homogeneous Sr–Nd–Pb and zircon Hf isotopic compositions, with the (87Sr/86Sr)i ratio varying from 0.708 202 to 0.709 515, (143Nd/144Nd)i ratio from 0.512 156 to 0.512 229, (206Pb/204Pb)t ratio from 18.185 to 18.264, (207Pb/204Pb)t ratio from 15.667 to 15.672, (208Pb/204Pb)t ratio from 38.510 to 38.587, and initial 176Hf/177Hf ratio ranging from 0.282 428 to 0.282 530. Meanwhile, the calculated εNd(t) and εHf(t) values range from −4.0 to −2.6 and from −7.9 to −4.1, respectively, with two‐stage Nd model ages of 1.20–1.32 Ga and two‐stage Hf model ages of 1.35–1.56 Ga, respectively. As indicated by geochemical data, the primitive magmas of the bojites in Yajiangqiao area were derived from lithospheric mantle in post‐collisional extensional environment, which underwent low‐degree partial melting (1–5 %) of spinel‐garnet lherzolites (spinel > garnet) and was subjected to metasomatism of slab‐derived fluids. Furthermore, it can be concluded from these data and previous data that the SCB was transformed from syn‐collisional compression to post‐collisional extension in the late Triassic (~ 234 Ma) and the post‐collisional extension lasted until 215 Ma. [ABSTRACT FROM AUTHOR]

Metasomatites of the White Sea mobile belt of the Fennoscandian (Baltic) shield are considered. Metasomatites are traced from southeast to northwest for a distance of ≥550 km. In mineral composition, metasomatites correspond to the paragenesis of amphibolite facies of regional high-pressure metamorphism. To determine the tectonic position of metasomatites and their place in the sequence of geological events, we carried out isotope-geochemical studies of zircons, isolated both from metasomatites and their enclosing gneisses. It was established that the host metamorphic formations formed in the Neoarchean and metasomatites formed in the Late Paleoproterozoic (≈1.9 Ga). The rare-earth spectra of the studied zircons indicate that they formed from a fluid in a retrograde branch of regional metamorphism. Fluids were discharged along the deep thrust planes, thereby marking the zones of their exits to the modern surface. The results obtained indicate tectonothermal reworking of Archean complexes in the Late Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The geochemistry of the clastic sedimentary units of the Suonahu Formation from the QD17 well in the northern Qiangtang basin, Tibet, was studied using various chemical analyses. SiO2/Al2O3 ratios indicated that compositional maturity and recycling of the sediments were low to moderate. The total rare earth element (∑REE) contents of the clastic sediments ranged from 29.28 to 191.92 ppm. Element abundances suggest that the studied clastic sediments in the northern Qiangtang Basin were mainly sourced from felsic rocks mixed with small amounts of intermediate rocks, and that they were mostly developed in a continental setting. The REE geochemistry of the clastic sediments suggests that these different lithological samples were derived from a similar terrigenous source and that the Eu anomaly was inherited from the source rocks. The paleoclimate index (C-value) varied from 0.01 to 0.36, reflecting generally arid to semiarid conditions. In addition, Rb/Sr (about 0.41) and Sr/Cu (about 37.02) ratios support the idea that arid conditions prevailed during the deposition of the Suonahu Formation. Sr/Ba ratios (0.48–3.23) suggest a paleoenvironment with variable salinity. The covariation among this factor and paleoclimate indicators suggests that variations in climatic conditions exerted a primary control on salinity. The chemical index of alteration (CIA), A–CN–K ternary diagram, and low Th/U ratios indicate that the parent rocks of the clastic sediments experienced weak chemical weathering. Two multidimensional tectonic discrimination diagrams based on major elements show that the Suonahu Formation was deposited in a rift-related basin. The TiO2 versus Zr, La/Th versus Hf, and Co/Th versus La/Sc bivariate diagrams and multi-major elements discrimination diagram indicate that the detritus was primarily derived from felsic igneous rocks with less contribution from intermediate igneous rocks. [ABSTRACT FROM AUTHOR]

The diabase and granite porphyry outcrop in the Baijiagou section within the Meso-Cenozoic Liupanshan fault zone at the southwestern margin of the North China Craton (NCC), and they have been regarded previously as Meso-Cenozoic dykes according to their occurrence. Zircon U-Pb LA-ICP-MS age determining for the diabase and granite porphyry yield respectively 1804 ±21 and 1792 ± 16 Ma, and they form a bimodal magmatic assemblage of Paleoproterozoic. The diabase can be classified into two major geochemical types, which are low-Ti (LT) and high-Ti (HT) in nature. The former is characterized by relatively high SiO2 (48.81 - 54.01 wt.%), P2O5, and A12O3, and low TiO2 (1.41 -1.54 wt.%),FeO,MnO, and CaO, and enriched whole-rock Sr and Nd isotopic composition [(87Sr/86Sr), - 0.703 - 0.708; eNd= -3.76 to -4.37]. The latter has lower SiO2 (45.9 - 51.19 wt.%), P2O5, and A12O3, and higher TiO2 (1.61 - 2.26 wt.%) and FeO than that of the former, and depleted Sr and Nd isotopic composition [(87Sr/86Sr), = 0.691 - 0.708; eNd = 3.27 - 5.03]. Both types of diabase exhibit light rare earth element enrichment and flat middle-heavy rare earth element patterns. The LT diabase has negative Eu anomalies and higher total REE contents than the HT diabase. Th/Nb ratios of the LT and HT diabases are 0.28 - 0.29 and 0.08 - 0.10, respectively, which are similar to basalts formed in an intraplate spreading setting in association with a mantle plume. The regional geology suggests that intracontinental rifting occurred at the southwestern margin of the NCC in the Paleoproterozoic, and that the rifting was related to a mantle plume. This rifting event was part of the break-up of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The Gangdese magmatic belt, located along the southern margin of the Lhasa terrane, plays a critical role in understanding the tectonic framework associated with the Indian–Asian slab collision. In this paper, a chronology of zircon U–Pb and geochemical analysis of the rock of the Cuobulaguo granitic mass in the southern of the Gangdese, Tibet, revealed a series of results. The results show that the LA-ICP-MS monzonitic granite zircon U–Pb ages are 61–59 Ma, which corresponds to the same period as the magmatic arc of the southern limit of Gangdese. In terms of geochemical composition, the granite is rich in ω(SiO2) 70.09% to 72.64%, with a high ω(Al2O3) 14.40% to 15.99%, a low ω(TiO2) 0.08% to 0.24%, ω(MgO) 0.41% to 0.76%, ω(Fe2O3T) 6.82% to 29.9%, ω(P2O5) 0.07% to 0.12%, and ω(CaO) 1.06% to 1.75%. The granite mainly belongs to the high-K calc-alkaline series. The light rare earth element (LREE) content of skeletal granite is between 133.69 × 10−6 ~ 226.64 × 10−6 and the heavy rare earth element (HREE) content is between 17.36 × 10−6 and 32.11 × 10−6. LREE/HREE is between 5.05 and 7.83. It is enriched in light rare earth elements (LREE) and large ion lithophile elements, such as Rb, K, U, etc., depletes high field strength elements, such as P, Nb, and Ta, and has the geochemical composition of arc magmatic rocks. In addition, the aluminum saturation index (A/CNK = 1.06 to 1.11) of Cuobulaguo granite, belongs to I-type granite. The comprehensive analysis showed that with the beginning of the collision between the Indian–Asian continental, the subduction ocean plate was separated from the continental plate due to gravity, resulting in an increase in the asthenosphere, which made partial fusion of the lithospheric mantle. It invaded the bottom of the lower crust, which in turn induced a partial melting of the lower crust to form granite. [ABSTRACT FROM AUTHOR]

To constrain the timing from the accretion to the subduction-related metamorphism of the protolith in the Sanbagawa eclogites, we performed zircon U–Pb datings and REE composition analyses on pelitic schist of the Seba eclogite-facies region in the Besshi area in central Shikoku, Japan. The detrital igneous cores of the zircons show ages from ca. 2000 to 100 Ma, and the metamorphic rims show ca. 90 Ma. These results show that the protolith was accreted at ca. 100–90 Ma, which is significantly younger than the previously reported accretion age of ca. 130 Ma of other eclogite-facies regions in this area. And, the metamorphic rim domains show HREE decrease without Eu anomalies, suggesting that they were formed at ca. 90 Ma eclogite-facies metamorphism. Our results combined with previous reports for the tectonics of the Sanbagawa metamorphic rocks suggest that there are at least two eclogite-facies units with different accretion ages in the Besshi area; ca. 130 Ma unit (Besshi unit) and ca. 100–90 Ma unit (Asemi-gawa unit), which structurally contact with each other. It is likely that the older unit was subducted into a depth of over 50 km and stagnated until the younger unit was subducted to the same depth. Probably, both units were juxtaposed at a mantle depth and began to exhume to the surface at the same timing after ca. 90 Ma. The juxtaposition and exhumation process might have relation to multi-factors such as tectonic erosion along the subduction zone, shallowing subduction angle of the hotter slab, backflow in the mantle and fluid infiltration along exhumation route. [ABSTRACT FROM AUTHOR]

The Dalma metavolcanic belt is composed of ultramafics at the base, tuffs on top and basalts in-between. It extends for about 200kms east-west in the middle of the Proterozoic Singhbhum Mobile Belt. Ultramafics are chiefly composed of actinolite, hornblende, relic pyroxene and olivine. The main mineral constituents of basalts are actinolite, hornblende, chlorite, epidote, clinozoisite and plagioclase whereas; tuffs are composed of xenocrysts of biotite, quartz, k-feldspar, plagioclase and iron oxides. Ultramafic samples have high MgO (> 21 wt.%) and low SiO2 (< 42 wt.%), Al2O3 (< 10 wt.%) and Na2O+K2O (< 1 wt.%). CaO shows large variation in these samples from 3.91 to 7.77 wt. %. In studied basalt samples SiO2, TiO2, Al2O3, MgO and alkalis (Na2O+K2O) show variation like (45.7–48.3 wt.%), (0.64–0.97 wt.%), (9.3–13.9 wt.%), (8.5–13.6 wt.%) and (0.95–4.64 wt.%) respectively. In studied tuffs the SiO2, TiO2, Al2O3, MgO and alkalis show variation from (48.9–49.8 wt.%), (0.7–0.8 wt.%), (13.6–13.9 wt.%), (8.4–9.1 wt.%) and (2.39–2.85 wt.%) respectively. In general, studied samples show light rare earth element depleted patterns and flat patterns for heavy rare earth elements similar to MORBs on chondrite normalized REE diagrams. The overall enrichment of LILEs (e.g., Rb, K and Th) and depletion of HFSEs (e.g., Nb-Ta trough) on primitive mantle normalized multi-element diagrams are similar to subduction zone or islamd arc basalts. Ratios like Ti/Y, Ti/Zr, Zr/Nb and Ti/V are also similar to those found in arc related volcanic suites. Sm/Yb vs La/Sm diagram indicates generation of melts from the spinel lherzolite mantle source. On tectonic setting discrimination diagrams like Zr vs Zr/Y, Zr vs Ti and Ti vs V majority of studied samples clearly show island arc tectonic affinity. [ABSTRACT FROM AUTHOR]

Detailed geochronological, geochemical, and Sr-Nd-Hf isotopic data are presented for early Paleozoic volcanic rocks in the Karadaban area from the northern Altyn region, NW China, with the aim to constrain their petrogenesis and tectonic implications. The Karadaban volcanic rocks show a bimodal distribution in composition, with rhyolite and basalt. The LA-ICP-MS zircon U-Pb age indicates that the volcanic rocks were erupted at 512 Ma. The mafic rocks are calc-alkaline, enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; Ba and U) and depleted in high-field strength elements (HFSE; Nb and Ta). These features together with their depleted isotopic signature (initial 87Sr/86Sr=0.70413–0.70817, εNdt=2.7 to 3.7) suggest that they were likely derived from a depleted mantle source but mixed with crustal components while upwelling. The felsic rocks show an A-type affinity, with high alkalis and Rb/Sr and Ga/Al ratios; enriched in LILE (e.g., Rb, K, Th, U, and REE) and depleted in Ba, Sr, Nb, P, and Ti; and with fractionated REE patterns with strong negative Eu anomalies. The combination of the decoupling of εNdt values (−2.5 to −6.3) and εHft values (+5.5 to +14.7) in the setting of subduction indicates that the felsic rocks were generated by partial melting of the juvenile crustal as a result of magma upwelling. The geochemical and Sr-Nd-Hf isotopic characteristics, coupled with regional geology, indicate that the formation of the Karadaban bimodal volcanic rocks involves an extensional regime associated with a subduction-related environment. The rifting of the back arc in response to the retreat of the subducting northern Altyn oceanic lithosphere may account for the Karadaban bimodal volcanic rocks. [ABSTRACT FROM AUTHOR]

The Ekmekçi granodiorite porphyry is a unit in the E-W trending, postcollisional Eocene magmatic rocks of northern Anatolia. It occurs as a relatively small stock, but represents a link between plutonic and volcanic rocks. This Early Eocene granodiorite porphyry intruded into the Upper Triassic rocks of the Karakaya complex in the Sakarya Zone. In this study we present geochemical and zircon U-Pb LA-ICP-MS age data to contribute to understanding the Early Tertiary postcollisional tectonic setting of NW Anatolia. The granodiorite porphyry includes plagioclase, quartz, hornblende, K-feldspar, biotite, and minor zircon, apatite, sphene, and opaque minerals. The stock displays medium-K calc-alkaline I-type and metaluminous affinity. Similar to other Eocene magmatic rocks, it displays characteristic features of subduction-related magmatism, such as enrichment in large-ion lithophile elements relative to highfield strength elements and enrichment of light rare earth elements relative to heavy rare earth elements with a lack of significant Eu anomalies. They are characterized by homogeneous initial Sr and Nd isotopic compositions of 0.7044-0.7049 and 0.51255-0.51260, respectively. Zircon U-Pb data indicate that the Ekmekçi granodiorite porphyry was emplaced at 5.1 ± 1 Ma (2s Ypresian). Geochemically, the Ekmekçi granodiorite porphyry is similar to mafic volcanic rocks rather than the plutonic rocks of the same age. It was emplaced to the north of the İzmir-Ankara-Erzincan Suture (northern plutonic belt of NW Anatolia) and can be correlated with southern plutons such as Orhaneli, Topuk, Tepeldağ, Gürgenyayla, and Sivrihisar in the Anatolide-Tauride block in terms of age. [ABSTRACT FROM AUTHOR]

The Wuhaolai mafic complex is situated at the middle part of the northern margin of the North China Craton (NCC), Inner Mongolia. LA‐ICP‐MS zircon U–Pb ages, geochemical, and Sr–Nd isotopic data are presented to confirm the formation age of the complex, the nature of Paleozoic lithospheric mantle, and the tectonic evolution of the northern margin of the NCC. The mafic complex is composed of pyroxenite, gabbro, and diorite, which are derived from the same parental magma. The geochronological results show that this mafic complex was emplaced at 265.9 ± 3.3 Ma. All three different rock types are characterized by calc‐alkaline series with enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion of high field strength elements (HFSEs) and high rare earth elements (HREEs), and show negative Nb–Ta anomalies. Besides, they exhibit a low (87Sr/86Sr)i (0.7059–0.7065) and high εNd(t) (−13.35 to −8.19) values. These geochemical features also indicate that the parental magma of this complex was derived from an EM I‐like lithospheric mantle, which has undergone subduction‐related metasomatism. Combined with the previous studies on the Late Carboniferous to Late Permian intrusions from the northern margin of the NCC, the Wuhaolai mafic complex belongs to the Within‐Plate Basalt, representing a tectonic setting of continental extension environment, and the final closure time of the Paleo‐Asian Ocean (PAO) should be earlier than the Middle Permian. [ABSTRACT FROM AUTHOR]

The origin of A-type granites is purely circumstantial. Granitic complexes are quite common and generally composed of different type granites. I- and A-type granite association in a granitic complex is often described in the literature. Here we present a granitic complex, i.e. the Pitou complex in southern Jiangxi province, South China that is composed of different varieties of A-type granites. Detailed zircon LA-ICP-MS U Pb chronology and in situ Hf isotope, mineral chemistry and whole-rock element and Sr Nd isotope data of this granitic complex are used to explore their origin and to further constrain the geodynamics of Mesozoic magmatism in South China. Our new data indicate that the Pitou complex was emplaced during the Late Triassic (237 Ma) (central to northern part) and Early Jurassic (188–185 Ma) (southern part), respectively and that both the Late Triassic and Early Jurassic granites belong to A-type but show contrasting origins. The Late Triassic granites show an association of alkali-feldspar granite-syenogranite-monzogranite and the rock type of the Early Jurassic granites is alkali-feldspar granite. All the granites are composed mainly of K-feldspar, quartz, plagioclase and biotite (ferri-biotite or annite) with biotite occurring as anhedral crystal, interstitial to quartz and feldspar. Both the Late Triassic and Early Jurassic granites have high SiO 2 (>70 wt%) and total alkalis (K 2 O + Na 2 O > 8 wt%) with high FeO T /(FeO T + MgO) and low Mg#. They are enriched in rare earth elements (except Eu) and depleted in Sr and Ba. They display Zr + Y + Ce + Nb >350 ppm, 10,000 × Ga/Al >2.6 and have high zircon saturation temperatures (>800 °C). Biotites in the granites are Fe-rich with very low Fe3+/Fe2+, indicating fairly reducing conditions. However, the Late Triassic and Early Jurassic granites also show some geochemical differences. The Late Triassic granites have lower FeO T /(FeO T + MgO) and higher Mg# than the Early Jurassic granites, with the Mg# of the former consistent with pure crustal melts and the Mg# of the latter much lower than pure crustal melts. In addition, the Late Triassic granites have lower zircon saturation temperatures (up to 843 °C, average 823 °C) than the Early Jurassic granites (up to 946 °C, average 875 °C). Furthermore, the Late Triassic granites have high 87Sr/86Sr (t) (0.7132–0.7226) and negative ε Nd (t) (−10.3 to −10.9) and ε Hf (t) (in situ zircon) (−11.5 to −11.6) that are similar to those of the early Paleozoic granitoids in the region whereas the Early Jurassic granites have low 87Sr/86Sr (t) (down to 0.7034) and positive ε Nd (t) (up to +3.0) and ε Hf (t) (in situ zircon) (up to +8.3) that are similar to those of the Early Jurassic gabbroic rocks in the region. Geochemical data and major element modeling suggest that the Late Triassic A-type granites were formed by shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas and the Early Jurassic A-type granites were produced by extensive fractionation (ca. 90% to 95%) from gabbroic magmas by removal of plagioclase, amphibole, K-feldspar, clinopyroxene and magnetite. We further suggest the origin of the Late Triassic A-type granites was related to the transtension of the regional NE–trending strike-slip faults caused by the early Indosinian continental collisions and the Early Jurassic A-type granites were emplaced in a back-arc extensional setting coupled with the slab rollback and subsequent slab break-off of the subducted Palaeo-Pacific plate. Our new data confirm that the early Mesozoic magmatism in South China was controlled by continental collisions during the Late Permian to Triassic amalgamation in Southeast Asia whereas the late Mesozoic magmatism was related to the northwestward subduction of the Palaeo-Pacific plate. A transition in the dominant tectonic regime from the Tethyan to the Pacific tectonic domain most likely took place during the Rhaetian. • The Pitou granitic complex emplaced during the Late Triassic and Early Jurassic. • Both Late Triassic and Early Jurassic granites are A-type but show contrasting origin. • Late Triassic granites formed by shallow dehydration melting of Paleozoic granitoids. • Early Jurassic granites formed by extensive fractionation from gabbroic magmas. • Origin of both A-type granites suggests different geodynamic mechanisms. [ABSTRACT FROM AUTHOR]

This paper is a part from a running project aiming at optimizing the permanganate coating treatment for rare-earth (RE) containing magnesium alloys. Alloying of Mg alloys with RE elements enhances the galvanic corrosion and decreases the overall resistance. The objective of this paper is to optimize the permanganate treatment time that can provide the highest protection, so that permanganate coating can be engineered for Mg alloys. Electrochemical characteristics, morphology, and microstructure examination were investigated as a function of permanganate treatment time. EIS and polarization testing correlated to macroand microscopic surface examinations and visual inspection. Taking into account the industrial applicability and the economic aspects, the optimum treatment time was determined to be 10 min and this value is critical where increasing or decreasing it has a detrimental effect on the overall performance. Accordingly, processes active during permanganate treatment are kinetically dependent and strongly influenced by the treatment time. [ABSTRACT FROM AUTHOR]

The Late Neoproterozoic basement is exposed in the Mahabad area of northwest Iran, and it is classified into three main groups. The first is metamorphic rocks that include gneiss, schist, phyllite, and slate. The second is sedimentary rocks, which comprise shale, sandstone, and dolomite and the third is igneous rocks including granite, rhyolite, felsic tuff, and ignimbrite, which are the subject of this research. Zircon U Pb ages for three igneous samples show that crystallization occurred at 558–552 Ma in the late Neoproterozoic (Ediacaran). The felsic magmatic rocks have SiO 2 contents of 64.3 to 78.9 wt%, Al 2 O 3 contents of 12.0 to 16.8 wt%, low TiO 2 contents (0.08 to 0.69 wt%), and large variations in K 2 O (0.05 to 5.46 wt%) and Na 2 O (1.17 to 6.70 wt%). The felsic magmatic rocks are enriched in light rare earth elements (REEs) such as La and Sm, have flat heavy REE patterns, and strong negative Eu anomalies. They are mainly weakly to strongly peraluminous and calc-alkalic to alkali-calcic rocks. A wide range of initial 87Sr/86Sr (556Ma) ratios (0.7056 to 0.7203) and negative εNd(t) values (−6.0 to −2.9) do not show clear trends of mixing/contamination among mantle, slab fluids, and/or altered oceanic crust. The Mahabad magmatic rocks were produced mainly by partial melting of graywacke, psammite, and shale at high temperatures (~800 °C), based on the zircon saturation index. S-type like granites usually form in syn - to post-collisional systems, but the Mahabad felsic rocks, which have almost the same ages as the associated sedimentary rocks, were generated in an extensional regime according to geochemical discrimination diagrams. This can be explained as follows: sediments were deeply buried during the late Neoproterozoic amalgamation of microcontinents at a subduction zone along the northern boundary of Gondwana, and then erosion of the roof and/or thinning owing to extension led to upwelling of the asthenosphere and intrusion of mafic magma, which was responsible for partially melting the buried metasedimentary rocks to generate S-type like granites and felsic volcanic rocks. [Display omitted] • S-like felsic rocks with 550 Ma ages are presented in NW Iran. • Immature sediments such as greywacke were the source of magma. • Sediments were buried during the accretion of microcontinents to N-Gondwana. • The partial melting of buried sediments occurred in an extensional regime. [ABSTRACT FROM AUTHOR]

In order to further enhance the properties of lead-free solder alloys such as SnAgCu, SnAg, SnCu and SnZn, trace amount of rare earths were selected by lots of researchers as alloys addition into these alloys. The enhancement include better wettability, physical properties, creep strength and tensile strength. For Sn3.8Ag0.7Cu bearing rare earths, when the rare earths were La and Ce, the creep-rupture life of solder joints can be remarkably improved, nine times more than that of the original Sn3.8Ag0.7Cu solder joints at room temperature. In addition, creep-rupture lifetime of RE-doped solders increases by over four times for SnAg and seven times for SnCu. This paper summarizes the effects of rare earths on the wettability, mechanical properties, physical behavior and microstructure of a series of lead-free solders. [ABSTRACT FROM AUTHOR]

We report SHRIMP U-Pb, rare earth element, Hf isotope, and laser Raman spectroscopic data on zircons from ultrahigh-temperature (UHT) granulites from the Jining Complex of the Khondalite Belt in the Western Block of the North China Craton (NCC). These UHT rocks form part of an ultrahot orogen that formed along the collisional margin of the NCC associated with the tectonics of assembly of the Paleoproterozoic supercontinent Columbia. Despite the core-rim textures displayed by some of the UHT zircons, their age values sharply converge within error, yielding weighted mean 207Pb/206Pb ages of ca. 1.92 Ga, indicating growth by recrystallization under extreme thermal conditions. in general, the zircons show moderate heavy rare earth element enrichment with sharp positive Ce and negative Eu anomalies. The Hf isotope data from the UHT zircons also display a fairly uniform character, with the majority of them characterized by positive ϵHf values, without any indication of mixing between reworked crust and juvenile material. The majority of mineral inclusions in the UHT zircons, as revealed by laser Raman study, also support a magmatic source. Our results confirm extreme crustal metamorphism in the NCC and suggest asthenospheric up-welling, magmatic underplating, and plume activity in response to the collision-extension events during the final assembly of the Paleoproterozoic supercontinent Columbia. [ABSTRACT FROM AUTHOR]

Slab breakoff originally denotes the detachment of dense subducted oceanic slab from the light subducted continental slab, which is driven by opposing buoyancy forces during continental collision (Davies and von Blanckenburg, 1995; von Blanckenburg and Davies, 1995). The breakoff of subducted oceanic slab can induce the upwelling of sub‐slab asthenosphere through the slab window, and then heat the overriding lithospheric mantle resulting in the melting of its fertile layer within the metasomatic mantle wedge. The decompression partial melting of uprising asthenospheric mantle commonly produce mafic magma with depleted MORB‐like geochemical signatures (Davies and von Blanckenburg, 1995; Cole et al., 2006; Wang et al., 2018), whereas the partial melting of enriched lithospheric mantle will produce mafic magma with alkaline, calc‐alkaline or ultrapotassic features (von Blanckenburg and Davies, 1995). These mafic magmas rise into overlying lower crust and trigger crustal melting to generate the granitic magma. The North Qaidam tectonic belt (NQTB) records the evolutionary process of the South Qilian Ocean from subduction to closure. The subduction of oceanic and continental lithosphere to mantle depths is proven by the identification of oceanic‐type and continental‐type eclogites enclosed in crustal metapelite and gneiss from the North Qaidam tectonic belt (Song et al., 2006; Zhang et al., 2008; Zhang et al., 2010; Zhang et al., 2017). However, details of this process are not exactly constrained, in particularly, the closure timing of South Qilian Ocean. The study of characteristic mafic magmatism, combined with the previous studies of ultra‐high pressure metamorphism, give us an excellent opportunity to trace the detailed processes associated with the transition from oceanic subduction to continental subduction, and assess the feasibility of slab breakoff in the North Qaidam tectonic belt. In this contribution, an integrated study of petrology, geochemistry, geochronology and Sr‐Nd‐Hf isotopes is performed on the mafic igneous rocks from Chahanhe area in the North Wulan gneiss complex. These mafic igneous rocks can be divided into two groups, namely, arc‐like type and E‐MORB type based on their trace element patterns. Arc‐like mafic rocks (441–428 Ma) were characterized by enrichment of light rare earth elements (LREEs), large ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs), high field strength elements (HFSEs). Combined with variable zircon ∊Hf(t) values of −6.17 to +1.58, it is suggested that arc‐like mafic rocks are predominantly derived from the partial melting of the enriched lithospheric mantle, and minor juvenile materials have contributed to their sources. The E‐MORB mafic rocks (440 Ma) exhibit relatively flatted REE patterns and positive ∊Nd(t) values of +1.63 to +4.28, but high (87Sr/86Sr)i ratios of 0.706825 to 0.708979, indicting a derivation from partial melting of asthenospheric mantle, with involvement of enriched components probably derived from ambient lithospheric mantle or stagnant subducted oceanic crust. Collectively, it is proposed that the break‐off of the subducted South Qilian oceanic slab triggered the decompression melting of asthenospheric mantle, and the upwelling of asthenosphere provided heat and induced partial melting of the enriched lithospheric mantle and pre‐existing crust, resulting in generation of arc‐like mafic rocks and widespread granites. [ABSTRACT FROM AUTHOR]

Syn- to post-collisional magmatism in the Chinese western Tianshan Orogen is recorded in the Late Carboniferous to Early Permian magmatic rocks of the Awulale Mountains. However, the orogen's tectono-magmatic evolution remains controversial. In particular, two contrasting genetic models have been proposed, i.e., post-collisional extension vs. mantle plume. Here, we report zircon U-Pb ages, whole-rock geochemical data and Nd-Hf isotopic data from the mafic dikes and granitoids of the western Awulale Mountains. These data better constrain the rock's petrogenesis and geodynamic processes following the amalgamation of the Tianshan Orogen. In combination with previous data, we have identified two magmatic episodes in the Awulale Mountains. The Late Carboniferous (ca. 319–307 Ma) episode emplaced the mafic gabbro dikes and intermediate-acidic granitoids with I-type and adakitic affinity. The latest Carboniferous-Permian (ca. 302–286 Ma) episode emplaced bimodal intrusions containing mafic diabase dikes, acidic adakite and I- and A-type granites. Mafic dikes and granitoids of both episodes show depleted whole-rock Nd and zircon Hf isotopic compositions (εNd (t) : +2.21 ~ +7.54, εHf (t) : +6.48 ~ +15.97), indicating a juvenile magmatic source. However, the mafic dikes have variable geochemical features that clearly suggest their derivation from two distinct mantle sources during the two magmatic episodes. The earlier gabbro dikes have lower Th/Yb (0.08–0.12) and Zr/Yb ratios (15.32–25.45) that resemble a normal mid-ocean ridge basalt (N-MORB) from a depleted mantle source. In contrast, the later diabase dikes show enrichment in the light rare earth elements (LREE) with relatively higher Th/Yb (0.22–0.86) and Zr/Yb ratios (38.05–68.97) that are similar to an enriched mid-ocean ridge basalt (E-MORB) mantle source. Also, the Nb/Ta ratios from the earlier adakitic granitoids (21.26–23.28) differ markedly from the later acidic adakites (0.41–19.50), which implies the transition from a thicker to a thinner crust. Integrating our results with the previous geological records, leads us to propose a two-stage tectonic model for the Chinese western Tianshan Orogen's transition from syn - to post-collision. The Late Carboniferous stage of magmatism was triggered by the break-off of the North Tianshan Oceanic slab as the Yili Block and Junggar Terrane collided. The subsequent latest Carboniferous-Permian stage followed the switch to a post-collisional setting with delamination of the thickened lower crust and the intrusion of voluminous lithospheric mantle-induced bimodal magmatism. • Two episodes of contrasting magmatism have been identified in Awulale. • Early magmatism was triggered by slab break-off in a syn -collisional setting. • Late magmatism was linked to post-collisional crustal delamination. [ABSTRACT FROM AUTHOR]

The Dibamba River (DR) basin is one of the major fluvial basins of the Cameroon coastal area. The current work presents the very first systematic study of elemental geochemical characteristics, including REE, of surface sediments collected from the river bed at different parts of the river courses to determine the intensity of weathering, provenance, and tectonic settings, and evaluate the features that most faithfully mirror the nature of the source terrane. The sediments are dominantly fine and coarse sands. The framework components mainly consist of quartz. The clay minerals comprise kaolinite and illite. Opaque minerals, associated with kyanite, zircon, sillimanite, garnet, and hypersthene, are present as common accessory minerals. The DR sediments are classified geochemically as Fe-shale and Fe-sand. The CIA (72.04 ± 7.1), PIA (66.1–89.2), CIW, and the A–CN–K and (A-K)-C-N plots indicate moderate to high intensity of chemical weathering in the source areas. The SiO 2 /Al 2 O 3 , Al 2 O 3 /Na 2 O, K 2 O/Na 2 O ratios, and ICV indicate that the samples were predominantly texturally and compositionally mature. The ZTR index and the ternary Al 2 O 3 –TiO 2 –Zr and binary Th/Sc versus Zr/Sc diagrams suggest recycling and sorting of almost all the sediments. The REE patterns and the size of Eu, and various ternary and bivariate plots such as Zr versus TiO 2 , Th/Co versus La/Sc, and Cr/V versus Y/Ni indicate the contribution of sediments from intermediate and felsic source rocks. The tectonic discriminant-function-based diagrams revealed a rift or a passive margin setting for the source region. This is consistent with the tectonic history of the Pan-African domain and the Douala Cretaceous sub-basin, which are the probable source terranes of the studied stream sediments. • The Dibamba River sediments consist mainly of mature fine and coarse sands. • These sediments and their sources underwent a moderate to high degree of chemical weathering. • They derived from intermediate and felsic rocks, and recycled detritus. • Tectonic discrimination diagrams indicate rift and passive margin settings for source terrains. • Geochemical data of the studied stream sediments provide additional constraints regarding the tectonic history of the Pan-African belt. [ABSTRACT FROM AUTHOR]

• Dismembered gabbroid and wehrlite found emplaced in North Singhbhum Mobile Belt. • LA-ICP MS U-Pb zircon from gabbroid rocks yield 1.88 Ga crystallization age. • Petrographical and geochemical features indicate origin in oceanic magma chamber. • Sr-Nd isotopes show influence of a depleted and an enriched mantle component. • Evidence of rift-drift transition in Chaibasa rift-basin of Singhbhum Craton. Dismembered, kilometer-scale slices of gabbroid and serpentinized wehrlite rocks are found emplaced within metapelites of Chaibasa Formation, belonging to the North Singhbhum Mobile Belt, Singhbhum Craton, India. Zircon grains from the gabbroid body yield an average U-Pb crystallization age of 1881.1 ± 8.4 Ma. The undeformed gabbroid body exhibits modal and cryptic layering, and both units exhibit cumulate texture. The presence of dismembered cumulate and layered mafic–ultramafic rocks within a mobile belt assemblage is enigmatic and has potentially far-reaching implications. The gabbroid rocks are moderately evolved with Mg# (100 Mg/Mg + Fe) ranging from 48 to 63, low alkali, TiO 2 , U, Th, Zr, and high Al 2 O 3 , Pb, Ba, Rb, with unfractionated rare earth elements patterns. The serpentinized wehrlite (Mg# 65–71) hosts secondary minerals (clinopyroxene rims, amphibole blebs and interstitial Mg-chlorite) and has LREE enriched rare earth element patterns, which suggest complex fluid-rock interaction history. The gabbroid rocks have 87Sr/86Sr (t) 0.70600–0.71099, 143Nd/144Nd (t) 0.510130–0.510294, and Ɛ Nd(t) 1.8 to −1.4. The serpentinized wehrlite displays extreme enrichment with 87Sr/86Sr (t) 0.71045–0.72640, 143Nd/144Nd (t) 0.509120–0.509706, and almost upper crust-like Ɛ Nd(t) of −9.7 to −21.2. The cumulate nature of the mafic–ultramafic rocks with other petrographical and geochemical evidences suggest formation in a magma chamber. Additionally, their field characteristics, stratigraphic constraints and E-MORB like character of calculated equilibrium melts of the gabbroid rocks, indicates affinity towards formation in an oceanic magma chamber and possible emplacement by obduction. Mineral chemistry, whole-rock geochemistry and clinopyroxene trace elements of the serpentinized wehrlite reveal progressive fluid-rock interaction from very high-temperature to low-temperature regimes, and deep crustal affinity of the modeled metasomatic fluid. Isotopic character of the gabbroid rocks can be explained by 30%-50% mixing between a depleted and an enriched domain in the lithospheric mantle, whereas isotopic nature of the wehrlite has been perturbed by the prolonged metasomatic event. Their occurrence within the Chaibasa intra-continental rift basin indicates rift-drift transition and formation of incipient oceanic crust at 1.88 Ga. A 1.86 Ga orogenic event caused closure of the basin and obduction of these remnant oceanic fragments onto the mobile belt assemblage. This is the first discovery of oceanic crustal fragments in Singhbhum Craton, which fits into the model of rift-dominated tectonics, widespread continental amalgamation, and ophiolite emplacement during the Columbia supercontinent cycle in Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The Early Silurian source rock of the Qusaiba shale from Saudi Arabia was analyzed for its mineralogical and geochemical compositions to investigate its provenance, depositional environment, and tectonic setting, which still has not been studied. The shale is approximately 85 m thick gray to dark gray to black shale intercalated with siltstone and sandstone. The non-clay minerals are quartz and dolomite, while the clay minerals are kaolinite, illite, and smectite in some samples. An intermediate igneous source is suggested for the Qusaiba shale based on the Al 2 O 3 /TiO 2 ratio, calculated SiO 2 , and Zr–TiO 2 , Al 2 O 3 –TiO 2 , SiO 2 –Al 2 O 3 /TiO 2 and Ce n –La/Yb n binary plots. The Zr/Sc versus Th/Sc cross plot indicate that the Qusaiba shale was not subjected to sedimentary recycling. The abundance of kaolinite, C–values [Σ(Mn + Fe + Ni + Cr + Co + V)/Σ(Mg + Ca + Sr + Ba + Na + K)], Sr/Cu ratios and high chemical index of alteration (CIA) values indicate humid and warm conditions for the period of deposition. Geochemical proxies such as V–Al 2 O 3 and P 2 O 5 –Al 2 O 3 binary plots suggest a shallow marine depositional environment for the Qusaiba shale was prevailing during the Paleozoic in northeastern Gondwana. The Qusaiba shale represents a transgressive phase in the Early Silurian followed the Late Ordovician regressive event marked by the glacial non-marine sandstone of the Sarah Formation. The Qusaiba Formation shows another regressive event characterized by storm deposits at its top. The tectonic setting interpreted from major oxides, ratios of immobile–trace elements and rare earth elements (REE) parameters such as (La/Y) n , (La/Y) n , (Gd/Yb) n and Eu/Eu* depicts a passive margin matching with the regional setting for the northeastern Gondwana. Illite contents (13 %–33%) and IC values (0.52°–0.75° Δ2θ) suggest a late diagenesis stage for the Qusaiba shale. [Display omitted] • Geochemical proxies suggested intermediate igneous source rock for the hot shales. • Warm and humid conditions prevailed during the deposition of the hot shales. • Shallow marine depositional environment was interpreted for the hot shales. • Three transgressive-regressive cycles were defined within the studied section. • A passive margin setting is deduced for the hot shales based on their geochemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Yaoertu mineralization occurred at the Early Cretaceous. • The magma derived from the mixing of juvenile crust and mantle-derived materials. • The extensional tectonic settings resulted in extensive magmatism and mineralization. The newly discovered Yaoertu Cu–Pb–Zn–Ag deposit in the southern Great Xing'an Range (SGXR), NE China, is spatially associated with late Yanshanian intrusions. The Cu mineralization occurs within a fine-grained granite, whereas the Pb–Zn–Ag orebodies are developed within country rocks of the Linxi Formation, and are spatially associated with monzogranite or fine-grained granite. The monzogranite and fine-grained Cu-bearing granite have zircon ages of 137.1 ± 0.4 and 137.4 ± 0.5 Ma, indicating that mineralization occurred in the Early Cretaceous, consistent with the formation of extensive skarn or hydrothermal Pb–Zn–Ag deposits in the SGXR. The monzogranite is enriched in SiO 2 (69.91–67.87 wt%) and Na 2 O + K 2 O (8.43–7.92 wt%), contains 15.20–14.85 wt% Al 2 O 3 , and has a mean A/CNK value of 1.01, indicating the monzogranites are weakly-peraluminous high-K calc-alkaline granites. The fine-grained granites contain 77.18–75.14 wt% SiO 2 , 5.44–4.73 wt% K 2 O, 13.14–12.16 wt% Al 2 O 3 , 0.62–0.52 wt% CaO, and belong to the high-K calc-alkaline series. The monzogranite is enriched in light rare earth elements (REEs), exhibits fractionation of light over heavy REEs (LREE/HREE = 10.58–9.78), and has Eu/Eu* values of 0.74–0.61, whereas the fine-grained granite has LREE/HREE of 8.34–7.07 and more marked negative Eu anomalies (Eu/Eu* = 0.17–0.11). Zircon δ18O values in the monzogranite range from 6.61‰ to 6.87‰, and from 6.67‰ to 7.14‰ in the fine-grained Cu-bearing granite. The chemical composition and zircon Hf–O isotopic data suggest that the Early Cretaceous granites are formed by mixing between the juvenile crust and mantle-derived materials. Post-orogenic extensional settings related to the closure of the Mongol–Okhotsk Ocean resulted in extensive magmatism and large-scale mineralization. [ABSTRACT FROM AUTHOR]

Compared with the statement of the mantle plume hypothesis for large-scale plus high-volume intraplate magmatism, a series of OIB-like mafic rocks which are low-volume and spatially closely related to subduction zones still remain mysterious and inapposite to be explained by using traditional mantle plume hypothesis. In the North Qaidam, most previous studies have focused on ultra-high pressure metamorphic rocks and have paid little attention to mafic magmatism as a mechanism of generating magma with a mantle signature. The Kendelong (KDL) metagabbro with consistently intrusive ages of 485–490 Ma within the Olongbuluke microblock that is overriding plate above the subduction zone is analogous to Oceanic Island Basalts (OIBs) in geochemistry and formed contemporaneously with oceanic subduction. Analyzed samples of the KDL metagabbro have sporadic (87Sr/86Sr) i ratios of 0.7008–0.7063 that have been influenced by paulopost alteration, relatively uniform positive ε Nd (t) values of +0.3 to +1.4, zircon ε Hf (t) values of +1.5 to +6.8, and coupled Nd–Hf isotopes that lie on the terrestrial array. After ruling out the possibility of contributions from subducted enriched components and mantle metasomatites, geochemical features and isotopic compositions indicate that the magmas were derived from a relatively primitive asthenosphere without prior large-volume melt extraction. Rare earth element modeling shows that a low degree of partial melting (<10%) of an asthenospheric mantle source in the garnet stability field should be responsible for the magmatic origin of the KDL OIB-like metagabbro. Considering the temporal and spatial correlations between the KDL metagabbro and other types of mafic rock in adjacent regions, we propose that decompression melting of upwelling asthenosphere triggered by rollback of subducted oceanic slab is a plausible regime to explain the petrogenesis of the early Paleozoic KDL OIB-like metagabbro and to trace a fortuitous tectonic transition event. Moreover, even if the OIB-like magmatism is spatially related to subduction zones, the participation of subduction materials could not be an exclusive prerequisite to sentence its genesis. [Display omitted] • OIB-like magmation is reported in the North Qaidam. • OIB-like magmation in the North Qaidam is related to plate tectonics. • Magmas were derived from decompression-induced melting of upwelling asthenosphere. • Slab only provided geodynamic regime for the Kendelong OIB-like metagabbro. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Nanling W-Sn mineralization is linked to crust-derived highly fractionated granites. • Multiple cycles of W-Sn mineralization occurred from Neoproterozoic to Cretaceous. • The Wuyi Au-Cu mineralization is related to moderately evolved arc magma. • Significant mantle contributions for the Au-Cu mineralization magmatic rocks. • Yanshanian W-Sn and Au-Cu mineralization formed in contrasting tectonic settings. The Cathaysia Block in South China is characterized by extensive Yanshanian felsic magmatism and related large-scale W-Sn-Au-Cu polymetallic mineralization. The Nanling area, a large granite province in the western Cathaysia Block, represents the largest W–Sn metallogenic province in the world. By contrast, the Wuyi area in the eastern Cathaysia Block is characterized by volcanic-subvolcanic rocks associated with porphyry-epithermal Au-Cu mineralization. We summarize the published reliable rock-forming and ore-forming dating data, petrogeochemistry, zircon Hf isotopes, Re contents in molybdenite, and He-Ar isotopes of fluid inclusions in ore minerals to better understand the ore-related magmatism and corresponding metallogenic settings in these two contrasting metallogenic belts. Multiple cycles of W-Sn mineralization occurred from Neoproterozoic to Cretaceous in the Nanling area. The Yanshanian W-Sn mineralization related granites were primarily emplaced during Late Jurassic (160–150 Ma). Geochemically, these granites generally belong to highly fractionated granite, with high SiO 2 and K 2 O contents, and 'V-shape' rare earth elements (REE) patterns. The lack of arc volcanic rocks and the widespread presence of highly fractionated granites in the Nanling area is likely consistent with the intra-continental extensional setting in response to the far-field effects of subduction of the paleo-Pacific plate. In addition, W-Sn mineralization related granites in the Nanling area have low epsilon Hf isotopic values, together with low Re contents in molybdenite and low Ra values for He-Ar isotopes of sulfide minerals, suggesting that they were principally derived from crustal materials, with few involvements of mantle materials. The Yanshanian volcanic-subvolcanic rocks in the Wuyi area share similar geochemical features with typical arc magmatism, such as the enrichment in large ion lithophile elements (LILEs), and the depletion in high field strength elements (HFSEs, Nb, Ta and Ti). The Middle-Late Jurassic (165–150 Ma) Au-Cu mineralization is related to initial subduction of the paleo-Pacific plate, whereas the late Early Cretaceous to early Late Cretaceous (110–90 Ma) Au-Cu mineralization is linked to retreat of the subducted slab. The high Mg# and relatively higher zircon ε Hf (t) values suggest that metasomatized mantle was incorporated into ore related volcanic-subvolcanic rocks. Moreover, the relatively high Re contents in molybdenite and high Ra values for He-Ar isotopes of sulfide minerals support a significant contribution from the mantle to the Au-Cu mineralization in the Wuyi area. To sum up, we tentatively suggest a two-stage model to explain the spatio-temporal distribution of the ore-related granites and volcanic-subvolcanic rocks in the Nanling W-Sn and Wuyi Au-Cu metallogenic belts, respectively. The initial subduction of the paleo-Pacific plate produced volcanic arc rocks and related Au-Cu mineralization along the margin of the Cathaysia Block during 165–150 Ma, followed by the intra-plate extensional granite association and related W-Sn mineralization in the interior of the Cathaysia Block during 160–150 Ma. Late stage Au-Cu mineralization in the Wuyi belt is formed by remelting of metasomatized mantle wedge in a back-arc setting during 110–90 Ma in response to rollback of the paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

• Peraluminous granites in the southern NCC formed at ~ 1.86 Ga, ~1.90 Ga and ~ 1.96 Ga. • The Paleoproterozoic granitic magmatism was likely due to the collision between the Eastern and Western Blocks of the NCC. • The granites recorded heterogeneous Paleoproterozoic crust in the southern NCC. As one of the oldest cratons on Earth, the North China Craton (NCC) is a frequent area for geological research due to its complex crustal evolution. Regarding the Paleoproterozoic crustal evolution of the craton, most studies have focused on continental amalgamation (i.e. horizontal crustal evolution), but few on the vertical crustal evolution. Here we report whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotope geochemistry for the Xinyang granites to constraint the vertical crustal structure and evolution of the southern NCC. The studied granites comprise two-mica K-feldspar granite and garnet-bearing K-feldspar granite. All the rocks have high SiO 2 and total alkali, but low CaO, MgO and Fe 2 O 3 T contents. Their A/CNK values (1.05–1.28) suggest that they are peraluminous rocks. These granites are enriched in LILE (Rb, Th and K), depleted in Sr, P and HFSE (Nb and Ti). The two-mica K-feldspar granites show obviously fractionated REE patterns ((La/Yb) N = 18.3–387) with negative or positive Eu anomalies (δEu = 0.47–1.03, 4.85–6.72), while the garnet-bearing K-feldspar granites have flat REE patterns ((La/Yb) N = 1.69–4.89) with extraordinary negative Eu anomalies (δEu = 0.22–0.42). The magmatic zircons of the two-mica K-feldspar granites yield crystallization ages ranging from ~ 1.86 Ga to ~ 1.90 Ga, and those of the garnet-bearing K-feldspar granites give crystallization ages of ~ 1.90 Ga. Previous work also reported a biotite K-feldspar granite pluton formed at ~ 1.96 Ga in the Xinyang area. Taken together, three major episodes of Paleoproterozoic granitoid events (~1.86 Ga, ~1.90 Ga and ~ 1.96 Ga) are recognized in the area. Combined with regional geochronological investigations, the peraluminous granitic magmatic activities occurring during 1.96–1.86 Ga in the Xinyang area could be linked to the collision between the Eastern and Western Blocks of the NCC. Alternatively, zircon Hf isotopic compositions suggest that these rocks derived from partial melting of pre-existing crust with heterogeneous compositions. Zircons from the ~ 1.86 Ga two-mica K-feldspar granites yield ε Hf (t) values of −5.2–1.7 with T crust of 2.40–2.86 Ga, compared to zircons from the ~ 1.90 Ga two-mica K-feldspar granites which yield wide range of ε Hf (t) values of −13.5–1.0 with T crust of 2.50–3.42 Ga. In contrast, the ~ 1.90 Ga garnet-bearing K-feldspar granites have homogeneous negative zircon ε Hf (t) values ranging from −11.8 to −10.4, with T crust ranging from 3.23 to 3.30 Ga. Moreover, zircons from the biotite K-feldspar granites have ε Hf (t) values of −0.6–2.6, corresponding to T crust of 2.44–2.77 Ga. Based on abovementioned geochemical signals, we propose that the Paleoproterozoic crust in the southern NCC likely consisted of two parts in vertical, the upper Middle-Late Archean crust and the lower early Paleoproterozoic crust with Eo-Paleoarchean crustal remnants. During the Paleoproterozoic, the southern NCC experienced multi-stage crustal reworking, indicating that a stable continental crust likely had been formed by the end of Archean. [ABSTRACT FROM AUTHOR]

The Paleoproterozoic Orosirian period of ca. 2.05–1.8 Ga saw unique magmatic manifestations of Andean-type arc to Caledonian-style post-collisional batholiths, anorthosite–mangerite–charnockite– granite suites and mafic dyke swarms. Chronicling their timeline in North Korea presents a pivotal task in the palinspatic reconstruction of the Korean Peninsula relative to the North China Craton (NCC) and the supercontinent Columbia. Here we document episodic late Orosirian tectono-thermal events from the northern Nangrim Massif, spanning from ca. 1871–1851 Ma tonalitic intrusions through ca. 1856 Ma granites and ca. 1839 Ma gabbroic diorites to ca. 1830 Ma mafic dykes and ca. 1828 Ma metamorphism. Meta-gabbroic/doleritic rocks range in SiO 2 from 46.6 to 57.8 % and in MgO from 6.46 to 11.5 %, with moderately enriched light rare earth elements (La N /Yb N = 3.55–12.3) and depleted high field strength elements. Together with their variable zircon ε Hf (t) values from −10.0 to +5.2, these rocks tend to call for a heterogeneous lithospheric mantle that experienced prior melt depletion and subsequent fluid refertilization. Pyroxene-bearing tonalite–granite suite spans in SiO 2 from 59.0 to 76.4 % and exhibits transitional character from magnesian and alkalic to ferroan and calc-alkalic. These elemental features and zircon ε Hf (t) values of −7.9 to −1.0 are consistent with partial melting of newly- underplated mafic middle crustal protoliths. By combining these newly identified tectono-thermal events with massif-scale coeval syenite-granite suites as well as anatexis-induced metamorphic pulses, we updated the profile of Orosirian tectono-thermal episodes in the Nangrim Massif, which present successive snapshots into post-collisional geodynamic processes from orogenic collapse to lithospheric delamination. This renewed profile not only provides convincing evidence for demarcating the influence scope of the giant Paleoproterozoic Jiao-Liao-Ji-Korean (JLJK) orogeny in the Korean Peninsula, but also offers key reference for applying analogous Phanerozoic accretionary to collisional orogenic processes to their ancient tectono-magmatic expressions. The JLJK case of Orosirian orogeny exemplifies the importance of Phanerozoic-style Wilson orogenic cycle in the amalgamation of the Sino-Korean craton and its incorporation into the Paleoproterozoic supercontinent Nuna–Columbia. • This study documents multiple Orosirian tectono-thermal events in Nangrim Massif. • High-Mg mafic magmas call for a prior melt-depleted then fluid-fertilized mantle. • Tonalite-granite suite stems from the fusion of mafic crustal protoliths. • These episodes chronicle typical post-collisional geodynamic processes. [ABSTRACT FROM AUTHOR]

The petrographic and geochemical compositions of the Campanian-Maastrichtian siliciclastic sediments in the northern Bida Basin, North-central Nigeria were investigated with the aim to determine the petrofacies, their provenance and tectonic settings. The mineral composition of the samples selected from the 10 sub-facies in the study area is characterized by abundant quartz (predominantly of monocrystalline quartz) and minor feldspar, rock fragments and heavy minerals. The framework grains are angular, sub-angular to sub-rounded and well sorted with the quartz varieties exhibiting euhedral to subhedral, non-undulose to undulose characteristics. The modal composition reveals the sediments as quartzarenite to sublitharenite with minor sub-arkoses and also reflects felsic rocks derived within passive margin paleotectonics as provenance. Geochemical proxies obtained based on major, trace and rare earth elements data; Al 2 O 3 /TiO 2 , SiO 2 /Al 2 O 3 , K 2 O/Al 2 O 3 , La/Th, La/Co, Th/Co, La/Sc, Cr/Th, Zr/Nb and Zr/Th with chondrite-normalized REE patterns, light REE enrichment, heavy REE flat pattern and negative Eu anomalies revealed sediments derivation mainly from felsic source rocks. A higher Zr/Sc and Zr/Hf ratio with Th/Sc and Zr/Sc binary plot suggest considerable zircon enrichment in the source areas. Discrimination plots; log(K 2 O/Na 2 O) versus SiO 2 , TiO 2 versus (Fe 2 O 3 +MgO), Al 2 O 3 /SiO 2 versus (Fe 2 O 3 +MgO) and SiO 2 /20-(K 2 O+Na 2 O)-(TiO 2 +Fe 2 O 3 +MgO), La/Y versus Sc/Cr, La-Th-Sc, Th-Sc-Zr/10 of the analyzed sandstones suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the basin by fluvial modes. This study suggests a passive paleotectonic setting for the Precambrian Basement Complex consisting of two igneous source materials from which the sediments are derived and supplied to the study area. • Petrofacies, provenance and tectonic settings of Bida Basin investigated. • Quartzarenite to sublitharenite are the main petrofacies. • Geochemical proxies revealed sediments derivation from felsic source rocks. • Study suggest a passive paleotectonic setting. [ABSTRACT FROM AUTHOR]