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A combined investigation of geochemistry and geochronology was carried out for Early Cretaceous magmatic rocks in Tongling, centre of the Middle and Lower Yangtze River. The magmatic activity can be divided into two stages, peaking at ~140 Ma and ~127 Ma. The previous show high Sr and Sr/Y, low Y, and the later have low Sr, Sr/Y and La/Yb. There are correlation patterns between Sr-Nd isotopes and SiO2, and samples show little variation of V and Cr with large variation of Rb, which suggest the effects of partial melting of the diverse source and magma mixing/crustal assimilation were more important than fractional crystallization. The broad variation of εNd(t) and εHf(t) values can be attributed to binary mixing of YC lower crust with slab-derived or enriched mantle melts. The TDM2 of Nd and Hf, Zr saturation temperature, and magma oxygen fugacity display increased trend from ~140 Ma to ~127 Ma. Based on these signatures, origin model of the Early Cretaceous intrusions in Tongling was proposed. Affected by Pacific Plate subduction, following metasomatism by slab-derived fluid/melts, basaltic magma derived from lithospheric mantle underplated the lower crust. Meanwhile, partial melting of the lower crust formed the intermediate-felsic rocks of the first stage. As subduction continued, roll-back of the subducted slab resulted in extension, causing lithospheric thinning and the upwelling of hot asthenosphere. The second stage intrusions were the result of the reworking of the Meso-Neoproterozoic crust in the extension tectonic setting. [ABSTRACT FROM AUTHOR]

The Takestan area is in the western part of the Alborz magmatic arc. Magmatic rocks of the area consist of plutonic rocks (e.g. granitoids), effusive volcanic, and pyroclastic rocks. Using U-Pb zircon LA ICP-MS dating, we conclude that major parts of Takestan plutonic rocks were emplaced at 41–39 Ma (Late Eocene, Bartonian), but a small part of these rocks have ages of ~37 Ma (Late Eocene, Priabonian). The dacitic rocks have an age of ~39 Ma (Late Eocene, Bartonian) and the rhyolitic rocks are the youngest part of the magmatic rocks of the region with ages of 37–35 Ma (Late Eocene, Priabonian). Old zircons are present in all of granitoid and volcanic samples, except for a dacitic sample. They are interpreted both as earlier components in a long-lived magma chamber and inherited zircons from older continental crust. The age of magmatic rocks in the western part of the Alborz magmatic arc decreases from east to west, but the ages of the majority of them are limited to Palaeogene. The studied rocks like other Palaeogene magmatic rocks of Iran were possibly formed in a subduction related tectonic environment. Indeed, the Palaeogene magmatism of Iran is akin to geodynamic events related to Neotethyan subduction beneath Iranian micro-continent at the southern part of Eurasia. [ABSTRACT FROM AUTHOR]

This study presents U-Pb zircon ages and Lu-Hf zircon isotope data for Cretaceous-Paleocene plutonic rocks along a W-E transect in northwestern Mexico. These data are combined with tectonic reconstruction that restores Late Cenozoic extensional deformation and shows the position of magmatism at 36 Ma. Zircon U-Pb ages results span from 142 to 58 Ma and demonstrate that the continental arc migrated northeastward at 1–2.5 km/Myr. These rates are slower than previously interpreted, but consistent with landward arc migration rates observed in the Andes. Weighted mean initial epsilon hafnium (εHf(t)) values of plutonic rocks along the transect range from + 8.8 to −9.1. The heterogeneity in the zircon εHf(t) is spatially related to the pre-Cretaceous basement provinces that the intrusive rocks were emplaced into. Zircon εHf(t) values of western Baja California display positive values ranging from + 8.8 to + 2.6 suggesting they were formed from a moderately depleted mantle and were emplaced into the Guerrero-Alisitos-Vizcaino terrane. Zircon εHf(t) values in the eastern part of Baja California and most of Sonora are heterogeneous ranging between −0.7 and −9.1 and may be formed from a relatively slightly more evolved mantle source and end up more evolved after crustal assimilation of metasediments. Zircon εHf(t) values ranging from + 8.7 to + 2.9 in Chihuahua are consistent with a depleted-mantle derived melt and assimilation of Grenville lithospheric province. Our results highlight how Hf isotopic signatures help to constrain the pre-Cretaceous basement configuration in northwestern Mexico despite the few exposed outcrops along the transect. [ABSTRACT FROM AUTHOR]

Magmatic rocks distributed along the western part of the Po Ko fault, which documented tectono-thermal evolution of the Indochina block, when and how they formed are less constrained. Our new geochronological and geochemical data reveal that they were generated at 488–457 Ma and display a variety of SiO2 concentrations (SiO2 = 50.7–72.8 wt%). They also generally show slightly negative Eu anomalies (Eu/Eu* = 0.65–0.98) and enrich in LILEs (e.g. Rb and K) but deplete in HFSEs (e.g. Nb and Ta), consistent with arc-related signatures. Combined with their relatively high Mg# values (Mg# = 56–40) and initial87Sr/86Sr ratios (0.7085–0.7167) but negative εNd(t) values (−2.5 to −3.7), we consider those magmatic rocks originated from an enriched mantle source (e.g. EMII), which was metasomatized in the past. In comparing our data with tectono-thermal events in the southern Truong Son belt, we infer that there existed an ocean (a branch of the proto-Tethys Ocean) between the Truong Son belt and the Kontum massif during Late Cambrian, which subsequently underwent southeast subduction beneath the Kontum mass if initiated at ~488 Ma and terminated at ~457 Ma. [ABSTRACT FROM AUTHOR]

The evolution of the Gondwana along the flank of the West African Craton was complex and is far from understood. Subduction-related activity along this margin spanned between c. 750 and 500 Ma. Sections close to African cratons record the earliest stages, while Autochthonous and Allochthonous domains of the Variscan Belt preserve the latest stages of the arc system, essentially between c. 540 and 500 Ma. The geochemistry of the Ediacaran-early Cambrian siliciclastic series deposited along this Cadomian active margin preserves the evolutionary history of their sources, which are related to activity in the arc and nearby continental areas. In this sense, the SW Iberian Massif (Ossa-Morena Complex) preserves a section of this Ediacaran-early Cambrian peri-Gondwanan arc. Its evolution can be tracked through the characterization of the subduction-related magmatism (including the Mérida Massif) and coeval metasedimentary record (Serie Negra Group and Malcocinado Formation) during a time interval spanning almost 100 m.y., from pre-602 Ma to at least c. 534 Ma. This study reveals that arc magmatism is closely linked with synorogenic deposition in a complex way so far unexplored. Arc recycling is revealed by the isotopic equivalence of synorogenic strata to the first magmatic event (pre-602 Ma), and by geochronological data of the arc-building pulses. The earliest magmatic pulses (c. 602–550 Ma) are characterized by significant crustal input, likely favoured by subduction erosion. Subsequently, magmatism evolved towards larger mantle involvement (c. 540–534 Ma), likely associated with progressive variation in the slab angle. These slab-mantle-upper plate interactions generated changes in the arc dynamics leading to an extensional setting with alkaline magmatism during the Cambrian. This review proposes a model of petrogenetic and geodynamic arc evolution between the Ediacaran and the Early Cambrian. The gathered data could improve the accuracy of future palaeogeographic reconstructions for the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]

The Okinawa Trough is an incipient back-arc basin formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate and is a natural laboratory for studying basin evolution, magmatism, and crust-mantle interactions during the early stages of back-arc spreading. Back-arc spreading and recent magmatism are occurring mainly in the Middle Okinawa Trough (MOT) and Southern Okinawa Trough (SOT). In order to investigate the magmatism in the Okinawa Trough, volcanic rock samples from the MOT and SOT were analysed for Fe – Sr – Nd – Pb – Hf isotopic compositions. The Fe isotopic compositions of basaltic andesite samples from the SOT are similar to or lower than MORBs. The fluid/melt derived from the subducted slab, especially the fluid dehydrated from slab serpentinites and sediment-derived melts, entered the overlying depleted mantle wedge and participated in magma generation, which resulted in the low δ56Fe values of the SOT basaltic magmas. The δ56Fe values of volcanic rocks from the MOT increase with increasing SiO2 contents, suggesting a gradual enrichment of heavy Fe isotopes during the evolution of the magma as it ascended to the surface. While the Sr – Nd – Pb – Hf isotopic compositions do not vary significantly, suggesting that the different samples are the products of different degrees of crystal fractionation of comagma. The fractional crystallization of olivine, pyroxene, and ilmenite minerals, which enrich in light Fe isotopes, resulted in the gradual increase in Fe isotopic values of magma during its evolution. The dacites and rhyolites from the southernmost Okinawa Trough have the similar δ56Fe values with the basaltic andesite and the basalt from the SOT and MOT, accompanied by significantly lower Nd and Hf isotope ratios relative to basalts, reflecting that the contamination of crustal materials would not change the magma in Fe isotope compositions evidently. Compared with the MOT, the volcanic rocks from the SOT was more affected by subduction components on their underlying mantle, and those from the southernmost experienced more contamination by crustal materials in the evolving magma. [ABSTRACT FROM AUTHOR]

The Late Mesozoic subduction of Izanagi slab beneath East Asia formed large-scale intraplate magmatism in SE South China and subduction mélanges outcropped in SW Japan to eastern Taiwan Island, but the accompanying arc remains uncertain. We conducted LA-ICP-MS U–Pb zircon dating and trace element analyses of proximal sandstones from the SW East China Sea to trace a Jurassic to Cretaceous magmatic arc. Newly acquired data reveal that arc magmatism mostly developed in episodes of 150–124 and 124–102 Ma, exhibiting characteristics of low-T, high Th/U, U/Yb, Sc/Yb, Th/Nb, and low Nb/Yb, Nb/Hf ratios. This magmatic arc, combined with the SE South China intraplate and residual subduction mélanges, spatially forms a Late Mesozoic trench–arc–intraplate architecture responding to the Izanagi subduction. Its identified tectonic scenarios mainly include slab strike-slip subduction (200–170 Ma), slab stagnation and intraplate foundering (170–150 Ma), slab rollback and arc-root removal (150–102 Ma), and arc migration (102–86 Ma). Both the western East China Sea and Cathaysia block share a unified Paleoproterozoic basement that formed at ca. 1.85 Ga, and the Cathaysia-based magmatic arc occurred then. [ABSTRACT FROM AUTHOR]

The Punta del Este Terrane, located in southeastern Brazil and eastern Uruguay, is a tectonostratigraphic terrane recognized in the Dom Feliciano Belt, the southern segment of Mantiqueira Province (Brasiliano Orogen). The northern sector of the terrane, called here by the Jaguarão Domain, is constituted by Arroio Telho, Arroio Grande, Matarazzo metamorphic complexes, and the Arroio Pedrado Gneisses. The first is composed of low to medium-grade metasedimentary rocks. Metasiliciclastic schists and marbles constitute the second, with serpentinites, magnesian schists, amphibolites, and metagabbros. The Matarazzo Complex comprises pure and siliceous dolomitic marble, metadolerite, and metagabbro. Arroio Pedrado unit comprises granodioritic to monzogranitic augen-gneisses. The rocks of the complexes were poly-deformed and intruded by high-K calc-alkaline peraluminous and metaluminous granitoids. The Pedro Osório, Arroio Grande, and Cerro Amaro dextral shear zones delimited the domain to the north. To the south and east, the units of the Jaguarão Domain were covered by coastal plain sediments. In gravimetric maps, the domain shows a high-density relief in contrast with the rocks of the granite belt (Pelotas Batholith). U-Pb zircon data from garnet-muscovite granites present crystallization ages of 587–568 Ma, which point to a widespread Ediacaran magmatism in the northern Punta del Este Terrane. U-Pb zircon provenance data of the metasedimentary sequences indicate main Meso- to Paleoproterozoic contribution, with subordinate Tonian to Cryogenian age populations. The geochronological results of the supracrustal rocks indicate a sedimentary deposition in an extensional setting, in which posterior deformation and metamorphism/magmatism compatible with a syn-orogenic setting in the context of the Dom Feliciano Belt framework. [ABSTRACT FROM AUTHOR]

During the Late Cretaceous, a magmatic arc extended from the Lesser Caucasus through the northern margin of the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans for a distance of 2700 km. We studied the arc volcanic rocks in three regions in the Western Pontides and reviewed the geological data on the Lesser Caucasus-Pontide-ABTS magmatic arc, which shows several common features. Prior to the start of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data show that magmatism in the Lesser Caucasus-Pontide-ABTS arc started in the Turonian (ca. 93 Ma) peaked in the middle Campanian (80–78 Ma) and became rare and sporadic after the late Campanian (ca. 75 Ma). Magmatism was dominantly calc-alkaline to high-K calc-alkaline and shows typical subduction geochemical signatures. Late Cretaceous volcanism took place in a submarine and extensional environment. In the Lesser Caucasus-Pontide-ABTS belt, the arc volcanic rocks are overlain by Maastrichtian to Palaeocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Kefken region in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The Maastrichtian volcanic rocks show a more varied geochemistry than the older arc volcanic rocks, and include alkaline basalts, calc-alkaline basalts, and adakites. The coeval start of arc magmatism in the 2700-km-long Lesser Caucasus-Pontide-ABTS belt is related to the inception of the Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of sub-ophiolite metamorphic rocks in Anatolia. The end of magmatism is linked to a marked decrease in the convergence rate during the Campanian, which was also partitioned between the northern and southern Tethyan subduction zones. [ABSTRACT FROM AUTHOR]

During the Permian-Triassic transition, dramatic environmental changes occurred, including the segmentation of Pangaea and the beginning of the Alpine orogenic cycle with widespread magmatism and tectonic activity. The Permian-Triassic succession deposited in the northern (palaeo-) Gondwana is now exposed in the inner Northern Apennines where it crops out discontinuously in the Middle Tuscan Ridge, a NS-oriented morphotectonic feature mainly formed by blue-schist and green-schist facies metamorphic rocks. In this paper, we describe a previously unreported late Palaeozoic succession exposed in the central part of the Middle Tuscan Ridge: the Montagnola Senese Ridge. This succession provides information concerning the enigmatic late Palaeozoic units exposed in southern Tuscany, and permits the age constraint of continentalization at the Permian-Triassic boundary with associated magmatism. Specifically, by integrating stratigraphic, structural, and petrographic data, we describe a siliciclastic, volcanoclastic-to-carbonate succession which recorded the transition from marine sedimentation to the typical continental, red-beds of the Verrucano tectofacies. Additionally, deformational features, metamorphism and age of the succession are discussed in terms of its tectono-sedimentary evolution and implications for the Palaeozoic-Triassic setting of the central Pangaea sector currently exposed in southern Tuscany. The results allow us to recognize a middle-late Permian pre-Verrucano succession, and to date the transition to continental facies as latest Permian. The microflora permits correlation of the pre-Verrucano succession to the late Palaeozoic units of the inner Northern Apennines, and establishes the diachronous nature of the Verrucano tectofacies exposed in the inner Northern Apennines. Finally, the thermal maturity of the organic matter indicates a maximum temperature of 387 ± 30°C attained during metamorphism. [ABSTRACT FROM AUTHOR]

Across western and northern Chukotka, a region spanning 400 000 km2, we have defined three different tectono-magmatic systems that were active during the Aptian-Albian (123–100 Ma) time span: (1) the Tytylveem post-collisional belt (123–105 Ma); (2) the Chaun province of extension-related magmatism (109–100 Ma); and (3) the earliest eruptive units (106–100 Ma) of the subduction-related Okhotsk-Chukotka volcanic belt (OCVB). The observed tectono-magmatic systems are characterized by their location and by their different chemical and isotopic compositions. The general enrichment of magma sources successively increases from the OCVB to the Tytylveem belt and then to the Chaun province. While the Tytylveem belt was active, the volcanic loci shifted northwest along the strike of the belt, perhaps because of diachronous delamination of the lithosphere of the once present, but extinct, South Anyui ocean. On the scale of the entire region of NE Asia, the tectonic re-arrangement that controlled magmatism in the Early Cretaceous was marked by the extinction of major subduction zones on the periphery of the closing Oimyakon and South Anyui oceanic basins followed by magmatic events likely caused by lithospheric delamination and/or extension. Along the Pacific margin of Asia, subduction-related volcanism was nearly continuous during the entire Cretaceous. [ABSTRACT FROM AUTHOR]

The North China Craton (NCC), notably the southeastern margin of the NCC, hosts the most typical example of decratonic gold deposits. However, the factors controlling the intensity of decratonic gold mineralization and the relation between the geodynamic model of decratonization and gold mineralization still deserve to be well elucidated. The Bengbu and the Jiaobei uplifts are located at the southeastern margin of the NCC and the two uplifts have similar tectonic positions and metamorphic basements, yet the intensity of gold mineralization is quite distinct. Mesozoic mineralization and magmatism in both uplifts are controlled by the same deep geodynamic process. Accordingly, in this review, we make an effort to find solutions to these problems by integrating the whole-rock geochemical and Sr-Nd-Pb isotopic data as well as zircon U-Pb-Hf-O isotopic data from late Mesozoic magmatic rocks from the Bengbu uplift and the Jiaobei uplift. The late Mesozoic magmatism of the two uplifts can be divided into three stages, i.e. Late Jurassic (stage I), middle Early Cretaceous (stage II), and late Early Cretaceous (stage III). Comparative studies of the gold-related rocks in these two areas indicate that the intensity of the decratonic gold mineralization is controlled by magmatic source composition (i.e. the affinity of the upper crust of the South China Block), intrinsic magmatic variables of gold-related rocks (i.e. redox state and volatiles content), as well as lithospheric architecture (i.e. lithospheric thickness). Additionally, the integrated data of magmatic rocks in the three stages suggest that plate subduction acts as the recycling engine factory responsible for the decratonic mineral systems. In the early stage (Triassic), continental subduction of the South China Block induced pre-enrichment of ore-forming nutriments in magma sources, whereas in the late stage (Early Cretaceous), oceanic subduction of the paleo-Pacific plate led to the craton destruction, thereby triggering related magmatism and gold mineralization in the eastern NCC. [ABSTRACT FROM AUTHOR]

In eastern Anatolia, the Divriği-Hekimhan Magmatic Province (DHMP) includes ~77–69 Ma alkaline rock units which are located to the NW of the Baskil Arc of ~85–74 Ma. The magmatic rocks are composed of nepheline (Ne)–to quartz (Q)–normative alkaline basaltic to trachytic/syenitic units. Among them, the basaltic rocks are composed of plagioclase (Or2–11Ab32–51An39–64) + clinopyroxene (Wo47–51En35–42Fs9–16) + Fe-Ti oxide ± alkali feldspar (Or57–98Ab2–42An1) ± biotite ± olivine. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70591–0.70871 and−3.2–1.6, respectively. The subvolcanic trachytic rocks are composed of perthitic alkali feldspar phenocryst in a matrix of feldspar (Or45–61Ab38–54An0–2), biotite, and Fe-Ti oxides. The trachytic volcanic rocks are made up of feldspar (Or38–63Ab34–59An1–4) in a fine-grained matrix. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70532–0.70952 and−3.2–0.7, respectively. The syenitic rocks in the region contain both quartz- and nepheline-sodalite-bearing syenites. Geochemical features reveal that the Ne-normative basaltic magmas have undergone mafic mineral fractionation coupled with crustal contamination to produce the Q-normative derivatives. Enhanced differentiation of the Ne- and Q-normative fractionated magmas via feldspar-dominated fractionation created the silica-undersaturated and -oversaturated trachytic magmas, respectively. During the feldspar-dominated differentiation, the re-melting of accumulated alkali feldspars in the magma chamber likely gave rise to the formation of trachytic rocks with alkali feldspar-like whole rock compositions. The final products of the Ne-normative magmas are represented by the phonolites and foid-syenites with silica-undersaturated eutectic compositions. A geochemical evaluation of the basaltic rocks revealed that the alkaline magmatism mainly originated from a shallow asthenospheric mantle source which had previously been metasomatized by oceanic to continental subduction. We suggest that the DHMP was formed in response to STEP fault-controlled rolling back of the northward subducting slab of the Baskil Arc, which created a localized gap for asthenospheric upwelling. [ABSTRACT FROM AUTHOR]

The Mabujina Complex exposed in south-central Cuba consists of an elongated body of metamorphosed volcanic and subvolcanic mafic rocks and tonalitic gneisses. The complex is largely composed of greenschist facies rocks (Porvenir Formation) directly below the Cretaceous volcanic arc section and of a deeper sequence of deformed amphibolite facies rocks (Mabujina Amphibolite Complex). The origin of the protolith of the Mabujina Complex has been the subject of intense debate in the past. While some authors consider the Mabujina Complex to represent the deepest and oldest (Early Cretaceous) exposed section (root) of the Cretaceous Caribbean volcanic arc others suggested an exotic (non-Caribbean related) Early Cretaceous volcanic arc section. The later proposal implies the tectonic emplacement underneath the Caribbean arc of a segment of the Pacific-related Early Cretaceous Mexican Guerrero volcanic arc terrane. A new set of whole-rock geochemical analyses presented in this study shows that the protoliths of the Mabujina Amphibolite Complex constitute an island-arc sequence with a) less abundant island-arc tholeiitic mafic rocks similar to the Early Cretaceous tholeiitic island arc of the Caribbean and b) dominant transitional to calc-alkaline mafic and felsic igneous rocks that resemble the Early to Late Cretaceous magmatism of the Caribbean arc. The high initial Nd ratios of the rocks from the Mabujina Amphibolite Complex are indistinguishable from the tholeiitic to calc-alkaline sequences from the Caribbean arc, reflecting a depleted MORB mantle source with limited subduction-related component input. The present data, together with published geochemical and geochronological data of the protoliths, allow identifying a Caribbean origin for the Mabujina Complex instead of an exotic provenance in the Guerrero Arc of western Mexico. However, even if the interpretation of the geochemical data favours a Caribbean origin, the Mabujina Amphibolite Complex cannot represent the root of the volcanic arc. Here, we propose that the Mabujina Amphibolite Complex is a fragment of the Early to Mid-Cretaceous Caribbean arc that was tectonically emplaced below this same arc as a likely consequence of arc segmentation and strike-slip trans-compression triggered by oblique subduction during the mid-Cretaceous. [ABSTRACT FROM AUTHOR]

The classic Neotethyan Ankara Melange formed within the Triassic-Eocene İzmir-Ankara-Erzincan ocean ('N Neotethys'), bordered in central Anatolia by the Kırşehir and Tauride-Anatolide continental units to the south and by the discontinuous Sakarya continent to the northwest. Farther north, the separate Intra-Pontide ocean probably remained partly open until the early Cenozoic. The Neotethyan Ankara Melange developed via phases of intra-oceanic accretion (mainly pre-Aptian), initial continental accretion (i.e. Coniacian (?)), arc magmatism (Upper Cretaceous) and continent-continent collision (Maastrichtian-Early Eocene). Variably dismembered ophiolitic rocks of Early-Middle Jurassic age within the Ankara Melange formed by supra-subduction zone (SSZ) spreading above a generally northward-dipping subduction zone. Volcanic-sedimentary lithologies of Triassic-Cretaceous age represent fragments of oceanic crust including variably sized oceanic seamounts. The oceanic volcanics and sediments accreted from the downgoing plate, whereas the ophiolites represent fragments of the overriding plate. The main driver of accretion in the Ankara area was collision of a large Upper Jurassic-Lower Cretaceous oceanic seamount (probably plume related) and its capping carbonate platform, with Middle-Late Jurassic fore-arc oceanic lithosphere. Intra-oceanic arc and proximal-distal fore-arc basin units developed above the accretionary complex and within remnant Neotethyan ocean to the north during the Upper Cretaceous. After docking with the Sakarya continent, the Ankara Melange was transgressed by continental margin fore-arc and syn-collisional foreland basin sediments (Campanian-Early Eocene). Comparisons with Neotethyan melanges across Anatolia to the Caucasus indicate exceptional development in the type Ankara area. [ABSTRACT FROM AUTHOR]

The Bohemian Massif of Central Europe is a Variscan collage of lithospheric fragments that formed at the northern margin of Gondwana during the late Neoproterozoic. A key geodynamic process that shaped this margin before it became involved in the Variscan orogen was the Cambro–Ordovician rifting that opened the Rheic Ocean. This rifting event has been studied extensively, yet a number of issues remain unresolved, among which are its geodynamic causes. New U–Pb zircon ages of orthogneisses from the mid-crustal Moldanubian unit, in combination with available information on magmatism and basin subsidence in the upper-crustal Teplá–Barrandian unit of the Bohemian Massif, are here used to reconstruct in detail the mechanism of the Cambro–Ordovician rifting. We argue that extension occurred in three phases defined by (1) protracted ~524–480 Ma intermediate to felsic plutonism (including the dated ~490–480 Ma orthogneisses), (2) basaltic submarine volcanism at ca. 470 Ma, and (3) rapid subsidence at ca. 458–452 Ma. This relative timing is interpreted to reflect stretching of the lower lithosphere before upper lithospheric rifting. In a broader context, these inferences are compatible with contrasting, rheologically controlled modes of northern Gondwana break-up during the early Ordovician, in which the westerly Avalonian-type terranes were rifted away from Gondwana, whereas the easterly Cadomian-type terranes formed a hyperextended Gondwanan shelf. [ABSTRACT FROM AUTHOR]

Mesozoic igneous rocks are widely distributed in the South China Sea (SCS) and its adjacent areas and are exposed in the SCS, South China, Hainan, Indochina, Taiwan, the Philippines, and Borneo; these rocks are mostly dominated by granitoids. This paper presents a complete map of the Mesozoic igneous rocks of the SCS and its adjacent areas. This paper also presents an analysis of geological survey and published data in terms of seismic profiles, ages, geochemistry and isotopic systematics of the Mesozoic igneous complexes of the SCS and its adjacent areas. Three periods of igneous activity can be distinguished: (1) Permian – Triassic that spans from 250–201 Ma; (2) Jurassic (201–145 Ma); and (3) Latest Jurassic/Cretaceous to Maastrichtian (145–66 Ma), of which the Cretaceous is the best preserved and could possibly be the most widespread. Triassic igneous rocks are distributed in the northwestern and southern SCS (Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, the Dangerous Grounds, and the Reed Bank); Jurassic igneous rocks are distributed in the northern and southern SCS (Pearl River Mouth Basin, Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, and the Reed Bank); and Cretaceous igneous rocks are distributed in the northern, western and southern SCS. The igneous activity of the SCS is mostly distributed in the continent slope. Mesozoic igneous rocks of the SCS include at least 350 rock masses: the smallest being 0.182 km2, the largest being 5,5,502 km2, and the total area covering 688,539 km2. Mesozoic magmatism in the SCS and its adjacent areas migrated oceanward (southeastward). Our new seismic profiles and the wells from the literature highlight that Jurassic granites occur not only inland of South China but also in coastal South China and the northern and southern SCS. The YING6 well in the northern SCS encountered andesite with an age of 68.24 Ma, which is the youngest age found for the SCS Mesozoic volcanic rocks. The XY1 well in the western SCS encountered granite with an age of 68.9 Ma, which is the youngest age found for the SCS Mesozoic intrusive rocks. The WZ12-3-1 well in the northern SCS encountered granite with an age of 243.3 Ma, which is the oldest age found for the SCS Mesozoic intrusive rocks. The encountered dacite ages (219.1 ± 1.4 Ma) of the NK-1 well in the southern SCS were the oldest ages found for the SCS Mesozoic volcanic rocks. The thickest Mesozoic igneous rocks (>1022.5 m) were encountered in the NK-1 well. Igneous rocks in the SCS and its adjacent areas are closely related to tectonic movements such as faults, plate movement, and mantle-derived igneous fluid ascent. They are controlled by the subduction of the Tethys lithospheric and Paleo-Pacific domains. [ABSTRACT FROM AUTHOR]

The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the evolution of Triassic magmatism in the Northern Mediterranean. The magmatic rocks from Jabuka, Brusnik, Vis Islands and the submerged Brusnik plateau have been investigated to define their age and genetic affinity, identifying their role in the geodynamics of the Adria Plate. The plutonic and lava flow samples have been characterized for their petrography, mineral chemistry, whole rock major and trace elements, and Sr and Nd isotopic compositions. The two samples with the freshest plagioclase crystals have been selected for 40Ar/39Ar analysis, which gave ages of 221.5 ± 2.5 Ma (Brusnik) and 227 ± 5 Ma (Jabuka), similar to those of the Triassic magmatism from the northern part of the Adria Plate and neighbouring territories. Geochemical and isotopic data suggest that the magmatism dominantly sourced from spinel peridotites variously metasomatized during pre-Mesozoic subduction events. Furthermore, the investigated rocks evidence interactions of the magmas with Mid-Late Triassic evaporites. The comparison with other coeval magmatic occurrences from the Adria Plate and its edges shows that the subduction signature of the Triassic within-plate magmatism is mainly related to the evolution of the upper mantle of the Adria Plate. [ABSTRACT FROM AUTHOR]

Arc magmatism plays a key-role in the growth and differentiation of continental crust. In particular, the prolonged magmatic flux events control the genesis of deep crustal hot zones where magma accumulation and fractionation favour the continental arc crust evolution and geochemical stratification. In this view long-lived magmatic systems located in arc domains, with their erupted products spanning from basalts to rhyolites are formidable archive for the understanding the evolution of transcrustal magmatic plumbing systems and the construction of a stratified continental crust. This study focuses on the long-lived (ca. 9 Ma) Miocene-Holocene Cordillera de San Buenaventura volcanic system in the Southern Puna Plateau (NW Argentina), a unique natural laboratory where exploring the building up of MASH-zones (or deep crustal 'hot zones') and related sustained volcanism. Synthesis of new and published data, together with new thermobarometry and fractional crystallization modelling, indicates a cyclic scenario with mantle melts undergoing fractional crystallization dominated incipient and waning stages alternate to major mafic magma recharge events during the building up phase of the MASH-zone. This magmatic scenario is also discussed in the light of the coeval geodynamic framework dominated by the subduction of the Nazca plate and the eastward migration of the frontal arc magmatism. [ABSTRACT FROM AUTHOR]

The West Junggar terrane (WJT) is known to tectonically correlate with the Central and East Kazakhstan terrane; however, the Middle Palaeozoic magmatism has rarely been reported in the southern WJT, leading to significant uncertainties on the tectonic evolution and correlation of the southwestern Central Asian Orogenic Belt (CAOB). Here, we present the adakitic quartz diorites with zircon U-Pb ages of 390–394 Ma in the Alashankou region to demonstrate the presence of Early-Middle Devonian magmatism in the southern WJT for the first time. They are characterized by low Yb (1.00–1.41 ppm) and Y (8.9–14.4 ppm) but high Sr (301.5–475.9 ppm), Sr/Y (23–41), and (La/Yb)N (8.1–11) values, typical of modern adakites. As suggested by the relatively high SiO2 (64.96–67.71 wt.%), moderate K2O (1.53–3.19 wt.%), but low MgO (1.56–2.31 wt.%), TiO2 (0.28–0.42 wt.%), Cr (≤13.7 ppm), Co (2.7–9.9 ppm), Ni (8.0–18.7 ppm), and Th (3.7–4.8 ppm) concentrations as well as the high positive ɛHf(t) values (+5.6 to +10.3) and low Nb/Ta ratios, the adakitic quartz diorites were probably generated by the partial melting of a slightly thickened lower crust, which consisted mainly of the Ediacaran-Middle Palaeozoic intra-oceanic arc rocks in the southern WJT. Combined with regional data, our new results support that the southern WJT probably evolved as the eastern extension of the Kazakhstan Early-Middle Devonian outer volcanic belt during the Middle Palaeozoic. The Early-Middle Devonian tectonic extension and resultant lower crust melting may thus be related to the slab retreat of the Junggar-Balkhash Ocean. [ABSTRACT FROM AUTHOR]

Various types of early Palaeogene calderas indicating transtensional (strike-slip fault-related extensional structure and extensional strike-slip duplex) and transpressional (contractional) structures have been identified in southern Sikhote-Alin (northeastern Asia). These volcanic structures formed due to the NNW-oriented (345–355°) stress during left-lateral displacements within a zone of dynamic interaction between the main tectonic units of the territory: the Central Sikhote-Alin and Vostochny Faults. These faults form a large-scale fault zone, where strike-slip displacements and magmatic activity propagated from boundary faults to the central area of the fault zone. The analysis of regional faulting morphology and kinematics within this fault zone and its vicinity shows that the NNE-trending strike-slip faults bend into NE-trending thrust zones on its southern and northern flanks. These changes reveal a regional S-shaped structure that we named the 'sinistral kink band of southern Sikhote-Alin'. The activation of the subparallel NNE-trending sinistral faults in the central part of the kink band accounts for the increased permeability of the basement and terrigenous strata. The early Palaeogene magmatic activity should be regarded as a marker of left-lateral displacements from at least ~61–55 Ma due to oblique interactions between continental and oceanic plates along the northeastern Asian margin. [ABSTRACT FROM AUTHOR]

The Late Cretaceous Mata da Corda Formation, located in the eastern part of the Alto Paranaíba Igneous Province (APIP), Central Brazil, is one of the few places on Earth where kamafugite melts reached the surface generating large volumes of lava, pyroclastic rocks and shallow intrusions over an area of 4,500 km2. The western part of the APIP, however, is dominated by hundreds of diatreme-like kamafugites and shallow kimberlite intrusions and by the occurrence of multi-stage alkaline-carbonatite complexes. These complexes feature silica-undersaturated K-rich alkaline rocks, such as aillikite, that closely resemble the mineralogy and geochemistry of kamafugite, albeit lacking feldspathoids. The spatial and temporal distribution of kamafugite and aillikite within the APIP suggests a connection between them. In addition, on a regional scale, airborne magnetic data show three highly magnetic dipole-like structures to the south of the Mata da Corda Formation of an undisclosed nature, which bear geophysical similar responses to the neighbouring alkaline-carbonatite complexes. Links between kamafugite and aillikite are evaluated by the following chemical and isotopic evidence: (1) kamafugite and aillikite compositions plot in the kamafugite field of Foley's ultrapotassic rock classification; (2) similar CI chondrite-normalized REE distribution, with aillikite enriched up to 2 times in REE compared to kamafugite; (3) both lithologies share almost the same rock-forming minerals; and (4) similar 143Nd/144Nd(i) and 87Sr/86Sr(i) ratios for all the APIP alkaline-carbonatite rocks, indicating a common source from an enriched lithospheric mantle. Therefore, silica-undersaturated rocks from alkaline-carbonatite complexes display an evolved ultrapotassic affinity indicative of a genetic link. [ABSTRACT FROM AUTHOR]

The evolution history of the Hegenshan Ocean is an important part of studying the evolution of the Xingmeng orogenic belt, but it is still controversial. Here we present an integrated study of petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotopes on a series of intrusive rocks from the Baiyinguole area, Xiwuqi, central Inner Mongolia, NE China. Chronological data indicate that the intrusive rocks can be divided into three stages: 326–317, 297–295, and 259–254 Ma. The 326–317-Ma gabbros and diorites belong to the calc-alkaline series, and are characterized by positive whole-rock εNd(t) values (+1.1–+6.7), relatively low La/Ba ratios (0.04–0.10), and high La/Nb ratios (1.82–3.18), indicating that the magma source is from a subduction-modified lithospheric mantle. These samples have arc features owing to the southward subduction of the Hegenshan oceanic crust. The 297–295-Ma granodiorites and monzogranites show positive εNd(t) values (+1.9–+2.4), low 87Sr/86Sri ratios (0.704185–0.705234), and young Nd two-stage model ages (TDM2), which is consistent with typical I-type granites. On various tectonic setting discrimination diagrams, the granodiorites and monzogranites are plotted in the syn-collisional field. The 259–254-Ma syenogranites have low abundances of mafic minerals, low contents of Zr/Hf (18.31–31.35) and Nb/Ta (6.80–11.80) values, high SiO2 (76.36–78.54 wt.%) content, A/CNK (1.08–1.76), and D.I. of 96.8–97.4 (average 97.1), and notable negative Eu anomalies (δEu* = 0.07–0.17) and weakly tetrad-effects in REE pattern, which is affinity to the characteristics of highly differentiated granites. Moreover, they have positive εNd(t) values (+2.0–+2.1) with scattered TDM2 of 730–1217 Ma and low Nb/U ratios. This study suggests that the syenogranites are formed in a post-collisional tectonic setting, which is related to the closure of the Hegenshan Ocean. In addition, based on a review of the pre-existing literature data, a model of southward ridge subduction is proposed to explain the tectonic evolution of the Hegenshan Ocean. [ABSTRACT FROM AUTHOR]

Tracing coupled ocean closure and intra-continental orogenic processes using tectonomagmatic thermal events is important for performing plate reconstructions. In this study, we collected geochronological data obtained from Jurassic–Early Cretaceous volcanic sequences in the Great Xing apos; an Range (GXR) and compared and merged the data to obtain a better understanding of the timing of volcanism in the GXR. Jurassic–Early Cretaceous volcanism, which is mainly represented by the Tamulangou, Manketouebo, and Manitu formations, are ubiquitous in the GXR and do not contain a magmatic hiatus. Thus, 'diachronous' volcanism did not occur in the GXR. The volcanic sequences in these formations are also slightly ambiguous and therefore cannot be used to determine the timing of volcanism. However, absolute ages and rock assemblages can provide better constraints on this timing. Combined with data from Jurassic–Early Cretaceous tectonomagmatic thermal events in Mongolia, Siberia, and NE China, we re-evaluated the influences of the Jurassic–Early Cretaceous closure of the Mongol–Okhotsk Ocean (MOO), as well as the subduction and rollback of the Izanagi Plate, at different times in the GXR. The GXR likely underwent flat-slab subduction during the Late Jurassic–early Cretaceous as the MOO closed in an irregular 'scissor-like' fashion (i.e. not in a progressive west to east manner). Large-scale lithospheric delamination likely led to a large pulse of magmatism and mineralisation in the GXR during the late Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative εHf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites. [ABSTRACT FROM AUTHOR]

The study of Permian-Triassic granitoids, which widely occur within the East Kunlun Orogenic Belt (EKOB), is relevant for a better understanding of the evolution of the Paleo-Tethys Ocean and regional crustal evolution. This study focuses on the Permian-Triassic granitoids from the Nagengkangqieer region, east segment of EKOB. The Late Permian granodiorite (ca. 252 Ma) shows high-K calc-alkaline and metaluminous features with moderate SiO2 (63.31–67.04 wt.%), relatively high Mg# (48–52), and low Sr/Y ratios. The granodiorite is enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) and shows enriched isotopic compositions (εNd (t) = −5.53 to −5.14, εHf (t) = −5.6 to −1.1). These geochemical characteristics imply that the Late Permian granodiorite was derived from a mixing source of mafic lower crust and mantle materials (<30%). The Middle Triassic porphyritic monzogranite (ca. 239 Ma) and monzogranite (ca. 239 Ma) are high-K calc-alkaline to shoshonitic and weak peraluminous with high SiO2 (70.58–76.54 wt.%) contents and low Mg# (19–36). They display relatively higher FeOT/MgO ratios, lower P2O5 contents, and more enriched isotopic compositions (εNd (t) = −7.87 to −6.71, εHf (t) = −13.7 to −1.2) than those of granodiorites. These findings indicate that the Triassic granites belong to fractionated granites derived from partial melting of the lower continental crust. In combination with the results of this study and the spatio-temporal distribution of regional magmatic, metamorphic, and sedimentary events, we conclude that Late Permian granodiorite formed in a subduction setting, whereas the Middle Triassic granites were formed in a syn-collision setting. Closing of the Paleo-Tethys Ocean occurred in the Middle Triassic (ca. 240 Ma). Additionally, only a small proportion of juvenile materials (<30%) was involved in magmatism and contributed to continental crustal growth during Late Permian subduction, whereas crustal reworking dominated regional magmatism and resulted in a higher crustal maturity. [ABSTRACT FROM AUTHOR]

Compositional changes of successively emplaced magmatites can be used to infer changes in their petrogenetic evolution and geodynamic setting. The central-northern Lhasa terrane hosts extensive Late Cretaceous magmatism, however, the mechanism that triggered the magmatism and its relationship to the directly preceding Late Cretaceous tectonic transition in the central Tibetan Plateau is still unresolved. Therefore, we conducted a detailed petrological, geochronological, geochemical, and isotopic study on recently identified Late Cretaceous doleritic and granodioritic rocks in the Xiongmei area, northern Lhasa subterrane. The potassic (K2O/Na2O ratios >1) dolerites (ca. 80 Ma) display a post-collisional basaltic shoshonitic signature with uniform moderately enriched whole-rock Sr–Nd and zircon–Hf isotopic compositions ((87Sr/86Sr)t = 0.7070 to 0.7095, whole-rock εNd(t) = – 2.4 to – 1.3, and zircon εHf(t) = – 5.9 to +1.9), suggesting that they evolved from a similar parental magma and were likely derived by partial melting of an enriched lithospheric mantle metasomatized by hydrous fluids. The granodiorites are geochemically divided into medium-K and high-K calc-alkaline rocks. The medium-K samples (ca. 80 Ma) are generally characterized by low K2O/Na2O ratios <1, whereas the high-K samples (78–76 Ma) display high K2O/Na2O ratios >1. The medium-K samples have positive zircon εHf(t) values from +4.8 to +6.5 and uniform whole-rock ɛNd(t) values from – 2.4 to – 1.3, which significantly differ from those of the high-K samples that have negative to positive zircon εHf(t) values from – 1.9 to +2.8 and negative whole-rock ɛNd(t) values from – 8.4 to – 5.1. The medium-K samples are characterized by high Sr contents and Sr/Y ratios, coupled with low Y and HREE contents, similar to adakitic compositions, and were interpreted to have been derived from deep partial melting of the foundering juvenile garnet-bearing mafic lower crust at relatively low temperatures. Compared to the medium-K samples, the high-K samples have lower Sr/Y and (La/Yb)N ratios, coupled with flat HREE patterns and distinct negative Eu, Sr and Ti anomalies and are most likely derived from shallower partial melting of the K-rich juvenile lower crust at relatively high temperatures. Considering the occurrence of variable magmatism in the central-northern Lhasa subterrane during the Late Cretaceous, the change in magma composition and lower crustal melting conditions (cold-deep vs. hot-shallow) suggest that the lithospheric mantle keel was partially detached by small-scale mantle convection in response to the low-angle Neo-Tethys-associated subduction between 85 and 70 Ma. [ABSTRACT FROM AUTHOR]

The newly identified earliest part of the Sanligang bimodal volcanic succession in the Dahongshan area of the northern Yangtze Block provides insight into the role of this block in the evolution of the Rodinia supercontinent. Field contact relationships and dating indicate that these rocks are contemporaneous and formed at 840–820 Ma. The Sanligang mafic rocks have low SiO2 (40.33–48.17 wt.%) and K2O (0.07–1.65 wt.%), high TiO2 (2.64–3.52 wt.%) contents, and low U/Th (0.33–0.38), Th/Zr (0.001–0.002), and Nb/Y (0.059–0.064) ratios with positive εNd(t) (+5.08 to +7.59). This suggests that they are formed from magmas derived from an asthenospheric mantle source that had not been modified by slab-derived materials, with a low degree of crustal contamination during their eruption. Contemporaneous felsic rocks in the study area have high SiO2 (73.1–80.0 wt.%), variable K2O (0.63–4.39 wt.%) and Na2O (1.73–6.54 wt.%), and low MgO (0.1–0.58 wt.%) contents and are light rare earth element enriched, with (La/Yb)N values of 1.37–2.65 and significantly negative Eu anomalies. They have A2-type granite affinities, as evidenced by their high 10,000 Ga/Al values (3.51–4.55) and Zr contents (285–620 ppm), and positive whole-rock εNd(t) (+6.16–+6.52), zircon εHf(t) (+9.69–+12.29) and δ18O (+4.82–+6.11) values, suggesting they formed by partial melting of juvenile crustal material caused by heating associated with contemporaneous mantle-derived mafic magmatism. Combining the data for these bimodal volcanic successions with other rock assemblages in the Dahongshan area indicates that this magmatism occurred in a back-arc extensional setting. This magmatism was caused by slab detachment and separation along a vertical tear during the Neoproterozoic evolution of the arc to arc–back-arc system of the northern margin of the Yangtze Block. [ABSTRACT FROM AUTHOR]

There is considerable debate regarding the petrogenesis of K-rich magma, which are believed to occur in subduction settings. The districts of the potassic rocks in the rear-arc of the Cenozoic Iran have not been thoroughly investigated. In this study, we investigate Late Eocene K-rich rocks of the Roshtkhar area of NE Iran. We employ whole-rock geochemistry, Sr-Nd-Hf-isotopes and zircon U-Pb age data of intrusive rocks to identify the mantle signature, evaluate the timing of emplacement, and determine the geodynamic setting. The Roshtkhar intrusive rocks (RIR) encompass a narrow compositional spectrum from syenite to monzonite, belonging to K-rich series, and are enriched in light rare earth elements and large ion lithophile elements such as Cs, Rb, Ba, Th, and U, with positive K, Pb, and Sr anomalies. U-Pb LA-ICP-MS dating of zircon from two samples yielded ages of ca. 38 Ma. Epsilon Hf values for investigated Eocene zircons display a variable range from +0.3 to +6.5. The RIR show relatively homogeneous initial epsilon Nd values ranging from +0.64 to −1.31 and modest variation in initial 87Sr/86Sr from 0.7048 to 0.7052. The data show mantle contribution with small involvement of Cadomian upper crustal material of up to 12% and an approximately 3% contribution fluid derived from subducted sediment into the mantle source. The lack of rocks that are purely derived from the lower crust in the study area further argues against the partial melting of lower crust that delaminated into the mantle. We suggest slab retreat, extension, and mantle upwelling as the main mechanisms for the generation of the primitive melts of RIR. Accordingly, decompression melting of metasomatized lithospheric mantle (e.g. phlogopite, apatite, and/or pargasite-bearing lherzolite) would be a plausible mechanism for the forming of K-rich basic melt in the mantle source. [ABSTRACT FROM AUTHOR]

Whether the northern margin of the North China Craton (NCC) was a continental arc or in a lithospheric extensional setting during the Carboniferous is the primary divergence among different tectonic models about the terminal evolutionary history of the southeastern Central Asian Orogenic Belt (CAOB). The Alxa block is the western segment of the northern NCC and contiguous to the southeastern CAOB, and therefore the tectonic setting of the Carboniferous magmatic intrusions in this block can shed light on this controversy. In this contribution, new zircon U–Pb ages, elemental geochemistry, and Sr-Nd isotopes are presented for thirteen Late Carboniferous (~318–300 Ma) magmatic intrusions in the southwestern Alxa block. Among them, seven calc-alkaline I-type granites and one aluminous A2-type granite were probably generated by the partial melting and crystallization differentiation of various crustal sources (perhaps including earlier orogenic materials) under different temperature conditions. Four quartz diorites and one hornblende gabbro may be the partial melts of subduction-modified basaltic lower crust sources and sub-continental lithospheric mantle sources, respectively. According to the integration of the new results and regional geological correlations, the Alxa block and the southeastern CAOB were most likely in a uniform tectonic regime during the Carboniferous. At that time, this region was characterized by the lithospheric extension-related magmatic rock associations, the increasing mantle inputs over time, the clockwise P–T paths of high temperature-low pressure metamorphic rocks, and the transgression sedimentary sequences. All these lines of evidence suggest an intra-continental lithospheric extensional setting rather than a continental arc setting for the southeastern CAOB during the Carboniferous. [ABSTRACT FROM AUTHOR]

The Archaean crustal evolution of the northern São Francisco Craton (SFC) reveals significant similarity with Kaapvaal-Zimbabwe and Pilbara, cratons, especially before 3.0 Ga. Likewise, compiled geochronological and Nd-Sr-Hf isotope data suggest that the Archaean blocks of the northern part of SFC (e.g. Gavião, Uauá and Serrinha) shared similar crustal evolution since 3.15 Ga. The 3.42–3.35 Ga TTGs of the southern and western Gavião Block have negative and slightly positive ɛNd(t) and ɛHf(t) values and TDM(Hf) ages between 3.50 and 3.90 Ga, indicating that they were produced by partial melting of Eoarchaean to Palaeoarchaean crust, with minor mantle sources. The ca. 3.30 Ga high-silica plutonic-volcanic system, which is related to intraplate magmatism and intracrustal differentiation processes, would represent processes of continental rifting and break-up. In the northern Gavião Block, the 3.64 Ga migmatite-gneiss paleosomes with negative ɛHf(t), 176Hf/177Hf ratio between 0.2802 and 0.2805 and TDM(Hf) ages between 3.75 and 4.15 Ga of the Mairi Complex represent the oldest dated rocks of the whole São Francisco Craton, suggesting late Hadean and Eoarchaean sources. The 3.15 and 3.00 Ga rocks of the Serrinha Block have positive ɛNd(t) values, suggesting a predominant juvenile source. Likewise, coeval 3.15 and 3.00 Ga Uauá Block rock assemblage has slightly positive to negative ɛNd(t) values, which indicate mixing of crustal and juvenile sources. The 2.90 to 2.77 Ga period in the SFC is characterized by pervasive crustal anatexis with high-K granite generation, similar to Kaapvaal and Pilbara cratons. Therefore, Archaean migmatite-gneiss terrains recorded four crustal differentiation intervals (e.g. 3.66–3.51, 3.45–3.30, 3.15–3.00 and 2.90–2.77 Ga) in the São Francisco Craton. [ABSTRACT FROM AUTHOR]

S-type granites constitute an important component of the Paleoproterozoic Khondalite Belt in the North China Craton. Here we present results from petrography, geochemistry and isotope geochronology on the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite samples in the Jining-Liangcheng area. The geochemical characteristics of these samples indicate formation through partial anatexis of the khondalites, with heat and material input from mantle-derived magma. Geochemical similarities between the porphyritic garnet-bearing syenogranite, garnet-bearing monzogranite, and metapelitic gneiss suggest their broad affinity. Sensitive high-resolution ion microprobe zircon U–Pb dating revealed that the S-type granites formed at ca. 1.92–1.90 Ga and were subsequently metamorphosed at ca. 1.85 Ga. The ca. 1.92–1.91 Ga porphyritic garnet-bearing syenogranite shows zircon εHf(t) values of −1.94–+3.38 with two-stage Hf crustal model ages (TDM2) ages of ca. 2.42–2.59 Ga. The 1.91–1.90-Ga garnet-bearing monzogranites show zircon εHf(t) values ranging from −4.36 to +0.38, with TDM2 ranging from ca. 2.57 to ca. 2.82 Ga. The geochemical isotopic compositions suggest that the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite originated from the partial melting of pre-existing crust of heterogeneous compositions with the addition of mantle-derived material. On the basis of our results, combined with geological data on the Paleoproterozoic structural evolution of the Khondalite Belt, we assume that the timing of the metamorphism and anatexis in the Jining–Liangcheng area is correlated with a regional metamorphism and mantle-derived magmatism. [ABSTRACT FROM AUTHOR]

Anorogenic magmatism in the northern Arabian-Nubian Shield occurred during a long-lasting crustal extension event (<580 Ma), which succeeded the formation of the Pan-African orogenic belt in NE Africa and Arabia. Late Neoproterozoic anorogenic felsic volcanic-subvolcanic rocks, along with post-collisional granitoid suites, are exposed in the Gabal Abu Durba mountain range along the eastern flank of the Gulf of Suez in Sinai. These rocks include granite and rhyolite porphyries, metaluminous to weakly peralkaline with distinct potassic alkaline and ferroan affinities. Major and trace element characteristics such as K2O/MgO >16, total alkalis >8.5 wt.%, (K2O + Na2O)/CaO >10, agpaitic index (NK/A) >0.85 and Zr (>250 ppm), Nb (>20 ppm), Y (>80 ppm), Zn (>100 ppm) and Ce (>100 ppm), and 10,000 × Ga/Al >2.6 and [Zr + Nb + Y + Ce] >350 ppm are suggestive of an A-type granite genesis. Zircon U-Pb dating of two representative samples returned crystallization ages of 569 ± 2.6 Ma and 561.7 ± 3.2 Ma for granite and rhyolite porphyries, respectively. The melting temperatures estimated at 997–1020°C are consistent with high-temperature liquidus conditions. Fractional crystallization, coupled with less significant crustal assimilation, was likely the main mechanism of formation of these rocks from a common primitive asthenospheric mantle-derived trachytic magma in an anorogenic intra-plate setting. The A-type alkali granite and rhyolite porphyries of Gabal Abu Durba are manifestations of mantle upwelling and lower crust underplating in the late Ediacaran anorogenic stage. These felsic subvolcanic intrusions (≈ 569–562 Ma) along with their volcanic counterparts constitute a new unmatched rock unit that most probably represent the last chapter of the anorogenic magmatism in the Neoproterozoic Arabian-Nubian Shield crust before the beginning of Phanerozoic era. [ABSTRACT FROM AUTHOR]

Mantle magmatism is active in the southern Central Asian Orogenic Belt (CAOB) in the early Permian. This paper discusses contributions from mantle pyroxenite and the onset of the early Permian mantle magmatism based on the whole-rock major elements and Sr-Nd isotopes of the early Permian basalts and mafic gabbroic rocks as well as olivine chemistries. The clinopyroxene-orthopyroxene barometer yields 1.0–3.7 kbar of emplacement pressure for these mafic-ultramafic intrusions. The Ca-in-olivine hydrometer using compositions of the most primitive olivine (Fo≥86 mol.%) yields 2.7–4.1 wt.% H2O for the parental magmas. Thus, the early Permian mafic-ultramafic intrusions formed from hydrous magmas at shallow crusts. The bulk-rock evolution of most of these mafic gabbroic rocks is consistent with the liquid lines of descent of basaltic magmas in the Hark diagrams of MgO, CaO, Al2O3, and Na2O+K2O versus SiO2, suggesting that these gabbroic rocks have melt-like compositions. The gabbroic rocks and associated basalts are characterized by low CaO, high Fe/Mn ratios, and high FC3MS values (FeO/CaO-3*MgO/SiO2), and the primitive olivines (Fo >80 mol.%) have low Ca and Mn contents with expected high Ni contents without sulphide segregation, implying that pyroxenite-derived melts (46–71 wt.%) contributed to the early Permian mantle magmatism. In addition, Sr-Nd isotopic compositions of these early Permian intrusions suggest a mixing mantle source of the enriched mantle I (EMI) and high U/Pb mantle (HIMU) components, recording geochemical signatures of the previously subducted slabs. Mantle pyroxenite formed from reactions between slab-derived (eclogite-derived) melts and peridotite at high pressure. The onset of the early Permian mantle magmatism is possibly related to the lower solidus temperature and higher melt production of mantle pyroxenite (forming a mantle plume) relative to peridotite at high pressure. [ABSTRACT FROM AUTHOR]

The North Tianshan Ocean represents a critical southwestern segment of the Paleo-Asian Ocean and is crucial for understanding accretionary and collisional processes of the southwestern Central Asian Orogenic Belt. The Dananhu arc belt, an important porphyry Cu deposit metallogenic belt in the eastern North Tianshan, records Paleozoic episodic magmatism. However, the tectonic affinity and evolution processes of the Dananhu arc belt are still open to debate. Here, geochronology, major and trace elements, and Sr-Nd-Hf isotope compositions for magmatic rocks are conducted to reveal the ages, petrogenesis, and tectonic settings of these magmatic rocks in the Dannanhu arc belt. The Carboniferous dacite (328 Ma) and gneissic granite (310 Ma) show high-K calc-alkaline, enriched in large ion lithophile elements (LILEs; e.g. Rb, Th, and U), depleted in high field strength elements (HFSEs; e.g. Nb, Ta, and Ti), depleted isotopic compositions (εNd(t) = 1.3-3.4; εHt(t) = 0.5-12.5) and juvenile Nd-Hf model ages. Combining these Carboniferous magmatic rocks with the features of high Sr-Ba granitoid and Sr-Nd isotopic decoupling, we suggest that these Carboniferous rocks were probably formed through fractional crystallization of partial melting of mantle wedge that had been metasomatized by melts from subducted sediments in a forearc setting. The early Permian granites (289-276 Ma) show high K2O+Na2O (6.9-8.9 wt.%), low MgO (0.06-0.15 wt.%) contents, high positive zircon εHt(t) (10.5 to 12.1) and whole-rock εNd(t) (4.4-5.5) values, suggesting that the early Permian granites were derived from juvenile lower crust in a post-collisional setting. Our geochronological and geochemical data, together with published data, reveal that high flux arc magmatism with age peaks at ca. 431 and 332 Ma is consistent with porphyry copper mineralization in the Dananhu arc belt, implying a close genetic relationship. The final closure of the North Tianshan Ocean was constrained to the late Carboniferous and early Permian. [ABSTRACT FROM AUTHOR]

The late Paleozoic tectonic evolution of the Lhasa terrane and subduction of Sumdo Paleo-Tethys ocean remains controversial due to limited data and variable Permian magmatism in central and southern Lhasa. We report new zircon U–Pb ages and Hf-isotope ratios as well as whole-rock major element, trace element, and Sr–Nd isotope data from middle Permian (266 ~ 257 Ma) arc-related magmatism, including high-Mg quartz diorite and trondhjemite in the Tangjia-Sumdo area. The quartz diorite has high SiO2 (53.92–57.90 wt.%), MgO (3.69–8.03 wt.%) and low TiO2 (0.60–1.01 wt.%) contents. It is enriched in the large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and depleted in the high field strength elements (HFSEs, e.g. Nb, Ta, Ti). We interpreted these chemical features, in combination with uniform whole-rock (87Sr/86Sr)i (0.70375–0.70452), εNd(t) (+4.48 – +5.55), and zircon εHf(t) (+11.2 – +13.7) values, as indicative of dioritic melt derived by the interaction of fluids expelled from the subducting slab with the overlying mantle wedge in an island arc setting. The trondhjemite has high SiO2 (71.16–73.52 wt.%), Al2O3 (14.92–16.24 wt.%) and K2O + Na2O (7.34–8.27 wt.%) contents, is enriched in the light rare-earth elements (LREEs) and is depleted in Th and heavy rare-earth elements (HREEs). These rocks are characterized by positive εNd(t) (+5.91 – +6.68) and εHf(t) (+12.0 – +16.1) values and may have been derived from partial melting of subducted oceanic crust. Based on the elemental and isotopic composition of the quartz diorite and trondhjemite, we suggest that middle Permian magmatism occurred in an intra-oceanic subduction setting in the Sumdo Paleo-Tethys ocean. The Sumdo Paleo-Tethys ocean was probably a small ocean basin within the eastern Lhasa terrane and not a vast ocean basin that completely separated central Lhasa from the southern Lhasa subterrane. [ABSTRACT FROM AUTHOR]

The North Qaidam subduction-collision zone is a typical Alpine-type ultra-high pressure (UHP) metamorphic zone due to the Early Palaeozoic subduction of the Qaidam Block beneath the Oulongbuluke Block, with an integrated record of oceanic subduction, continental subduction, collision, and exhumation to post-collisional extensional collapse. In this study, systemic petrology, zircon U-Pb geochronology, Hf isotopic data and whole-rock geochemical analyses have been carried out for granitoids in the North Qaidam UHP metamorphic units to determine their petrogenesis and further reveal the tectonic evolution of the continental collision orogen. Zircon U-Pb dating yields weighted mean ages of 433 ± 2 Ma, 351 ± 8 Ma, 416 ± 4 Ma, 389 ± 3 Ma and 383 ± 1 Ma, with the εHf(t) values of the latter three ages ranging from −2.4 to 3.3, −5.9 to 1.1 and −3.3 to 2.4, respectively. Based on field relationship, petrological, geochronological, and geochemical results, these granitoids could be divided three groups. The early group granodiorites (~433 Ma) show a marked chemical resemblance to adakites: (1) high La/Yb and Sr/Y ratios, with low Y and HREE values; (2) high Al2O3 and low Mg#, Cr, and Ni values with obvious positive Eu anomalies. Petrological and geochemical characters indicate that the early group adaktic granodiorites may be derived from partial melting of metabasite in a thickened mafic lower crust. The middle group granites (~416 Ma) have an affinity to I-type granitoids, characterized by high Na2O contents (>4.18 wt.%) and low A/CNK values, which were probably generated by partial melting of felsic gneiss of subducted continental crust. The late group granites (389 ~ 351 Ma) are also I-type granitoids, which were originated from partial melting of Mesoproterozoic crust, with minor mantle material input. According to a comprehensive study of these granitoids, along with regional geological background and HP-UHP metamorphism, a four-stage evolutionary process of the North Qaidam UHP metamorphic belt from oceanic subduction, continental subduction, collision to extensional collapse is proposed. After the final closure of the Proto-Tethys Ocean, the subducted continental crust experienced HP-UHP eclogite-faces metamorphism (460 ~ 430 Ma), and thickening of the lower crust lead to generation of adakites and S-type granites. Following break-off of the subducting oceanic slab (425 ~ 400 Ma), the reduction in negative buoyancy caused the exhumation of deeply subducted continental crust accompanied by associated anataxis and syn-collisional I-type granitoids, representing the transition in tectonic regime from compression to extension. Due to the tectonic transition, mantle-derived intrusions and post-collisional granitoids were emplaced during 400 ~ 350 Ma. Simultaneously, the pronounced decreasing in La/Yb and Sr/Y ratios of magmatic rocks (age of 460 ~ 350 Ma) suggested that the crustal thickness decreased gradually from syn-collisional to post-collisional stage. [ABSTRACT FROM AUTHOR]

The Tianshui area is located at the junction of the Qinling and Qilian Orogens, the evolution of which is crucial in understanding the Early Palaeozoic tectonic evolution of the Central China Orogenic System. We present here geochronological, geochemical, and Sr-Nd isotopic data for four representative Silurian magmatic rocks, termed the Dangchuan, Huamiao, Yanjiadian, and Hongtupu, along a cross section across the main rock units of the Tianhui area. The 432 Ma Dangchuan syenogranites are peraluminous with negative εNd(t) values, high initial 87Sr/86Sr ratios, and low Rb/Sr and high CaO/Na2O ratios. We interpret the syenogranites to be generated by partial melting of metagreywackes during a Silurian orogenic event. The 436 Ma Huamiao diorites are high-Mg diorites with high MgO contents and Mg# (63–65) and enriched Sr-Nd isotopic compositions. The 445 Ma Yanjiadian diorites are high-Mg adakitic rocks with high Sr and Mg# and low Y and Yb contents. They were both generated by the interaction between sediment/slab-derived fluids/melts and mantle peridotite in the subduction-related setting. The 445 Ma Hongtupu basalts include E-MORB and IAB with depleted Sr-Nd isotopic compositions. They were derived from enriched mantle and sediment-modified mantle, respectively, and formed in a back-arc basin setting. Synthesizing our new and published data, we propose a tectonic model involving generation of Baihua-Huluhe arc-back-arc system, subduction of the Huluhe back-arc oceanic basin, and collision between the North Qinling arc terrane and North China Block, which is closely associated with the closure of the Proto-Tethys Ocean. [ABSTRACT FROM AUTHOR]

We present newly acquired data on the trace element composition and Sr–Nd–Pb-O isotopes of Pliocene – Holocene basalts of the Medvezhiy caldera located on the Iturup Island, Kuril arc. With its unique rhenium mineralization and high-Mg basalt volcanism, it is the largest caldera on the volcanic front of the Kurile Island arc. The calc-alkaline suite of rocks spanning the range from high-Mg basalts to high-Al basalts, has typical arc rock features, such as Nb-Ta depletion and LILE enrichment. The whole set of the caldera geochemical data is divided into two age units, pre- and postcaldera basalts. The precaldera basalts typify low-K, high-Al, basaltic suite of the frontal zones of «cold» subduction. PRIMACALC2 code and Arc Basalt Simulator version 3.1 forward model points to ~21.7% of partial melting of moderately depleted mantle peridotite with relatively high water content (~0.34 wt%) at the pressure of ~1.37 GPa. With similar isotope and trace element signatures, Late Pleistocene–Holocene basalts are marked by the high abundances of MgO (up to 11 wt %), but low Al2O3. The primary magmas were generated from depleted mantle with lower H2O content (~0.13%) and degree of partial melting (~9.5%), but at higher pressure (~1.77 GPa). The decompression scheme reproduces the fractionation trends of postcaldera magnesian basalts for most major elements but fails to explain the composition variations of the precaldera lavas. Their origin has been the matter of some complex processes in the shallow magma chamber. The abrupt change in the type of eruptions and magma composition of the caldera in Late Pleistocene–Holocene were related to a transformation of both the magma-feeding and melt generation systems as the result of geodynamic reorganization of the vast territory adjacent to the Sea of Japan and Kamchatka. [ABSTRACT FROM AUTHOR]

Thickened crust is of great significance for tectonic evolution and mineralization and generally occurs in collisional orogenic belts. Whether accretionary orogenic belts, such as the Central Asian Orogenic Belt (CAOB), are able to create remarkably thickened crusts and what the mechanism is, remain to be determined. In the southwestern of CAOB, the Eastern Tianshan with broad magmatism and integrated arc-continental system is an excellent area for understanding the crustal evolution. Here, we report geochronological, geochemical and Nd-Hf-O isotope data for Middle Triassic Baishandong granites in the Eastern Tianshan, which exhibit three stages: Group 1 (ca. 237 Ma) granodiorites, Group 2 (ca. 234 Ma) monzogranites, and Group 3 (ca. 229 Ma) highly fractionated I-type granites. The Group 1 and 2 granites exhibit high-K, calc-alkaline, and metaluminous characteristics, weak negative Eu anomalies, and low (K2O+Na2O)/CaO and FeOT/MgO ratios with high Na2O/K2O, Sr/Y, and (La/Yb)N values and low MgO, Y, and Yb contents, which are indicative of adakitic affinity. The Group 3 rocks have extremely high SiO2 contents, notable Eu and Sr depletions, lower Mg# values, and the 'tetrad effect' of REEs, indicating that they are highly fractionated I-type granites. All the granites have similar depletion in Sr, Nd, Hf, and O isotope compositions (εNd(t) = 3.1–5.5, (87Sr/86Sr)i = 0.7036–0.7051, εHf(t) = 11.3–13.4, δ18O = 6.61–7.21) with young Nd, Hf second-stage model age (565–755 Ma, 425–541 Ma). It indicates that they are all the remelting of thickened juvenile lower crust that was initially derived from Neoproterozoic crust-mantle differentiation. Based on the discussion, we proposed that the granitic pluton intruded in an intraplate extensional setting, which indicates that thickened crust had existed before the Triassic and that the final amalgamation of the Paleo-Asian Ocean occurred in late Palaeozoic. Geochemical features indicate tectonic compression played a more important role in significant lower crust thickening. [ABSTRACT FROM AUTHOR]

The origin and formation of the continental collision-related magmas remain elusive. The volcanic rocks erupted during India-Asia continental collision offer an ideal opportunity to explore their genesis and geodynamic process. Here, we report new zircon U-Pb dating results and Hf isotope, whole-rock element and Sr-Nd isotope data of volcanic rocks in Linzhou Basin, central Lhasa Terrane, southern Tibet. These volcanic rocks are mainly comprised of andesites and belong to Dianzhong Formation. The timing of their formation is ca. 63–66 Ma, coeval with the India-Asia continental initial collision in the central part of southern Tibet. All these rocks show an arc-like geochemical affinity and they have more depleted Sr-Nd-Hf isotopic compositions (87Sr/86Sri = 0.705006–0.705963, εNd(t) = −1.78 to 3.52, zircon εHf(t) = 1.2–7.0) than the Cretaceous pre-collisional andesites and Eocene ancient lithospheric mantle-derived melts beneath the central Lhasa Terrane. The correlation between Mg# and CaO, TiO2, Al2O3, Sr/Y, 87Sr/86Sr, εNd(t) suggests that they were likely hybrid production between an isotopically depleted end-member and the enriched lithospheric mantle (ELM). The oceanic crust-derived melts would be the best candidate for the former end-member according to their depleted Sr-Nd isotopic compositions. The andesitic rocks of Dianzhong Formation in the central Lhasa Terrane were most likely stemmed from partial melts of altered Neo-Tethyan crust and then mixed with the ELM-derived melts. Given the Cretaceous-Tertiary upper crustal shortening, back-arc extension, and voluminous volcanism in the Lhasa Terrane, along with abrupt increasing in the magma temperature and the convergence rate between India and Asia during Palaeocene, the occurrence of the Dianzhong Formation volcanic rocks can be well explained by the Neo-Tethyan slab roll-back. The mixing between the oceanic crust- and the continental lithospheric mantle-derived melts induced by the oceanic slab roll-back would be a complimentary scenario for the formation of the syn-collisional magmatism in collisional orogeny belts. [ABSTRACT FROM AUTHOR]

We present a review of the Maastrichtian-Miocene tectono-stratigraphic evolution of the southern Apennines. Starting from the Late Cretaceous, a large part of the Africa-Adria domain, from Lybia to Italy, was affected by an abortive rift event. In the Maastrichtian-Eocene interval, it caused the dismembering of the Apennine and Apulian platforms. The rifting, accompanied by anorogenic magmatism and a severe extension, triggered the drowning of some shallow-water realms with the sedimentation of slope-to-basin deposits. Synchronously, the surrounding pre-existing slope-basin areas were the location of a widespread calciclastic supply. We described the stratigraphic records of this event in several key places of the southern Apennines and compared them to the corresponding rocks in Sicily, central Apennines, and Dinarids. The reconstructed Maastrichtian-Eocene palaeogeographic map shows remnants of the Apennine and Apulian platforms again in shallow-water conditions or forming emerged areas, surrounded by slope-to-deep basin sectors. We propose a depositional model where the exposed Mesozoic carbonates were eroded, producing a calciclastic supply deposited in the drowned carbonate domains and the pre-existing surrounding basins. Along the slope, the calciclastic sediments deposited as aprons at the toe of fault scarps and as isolated debris and channel-fan deposits up to the deep basin. Scaglia-type successions are also present, characterized by a mix of calcareous and clayey sediments. Finally, calciclastic turbidites and isolated calciruditic bodies are intercalated with widespread clayey deposits in the deep basin. [ABSTRACT FROM AUTHOR]

The Bressanone (Brixen) pluton, cropping out at the culmination of the Southalpine indenter between the North Giudicarie and the Pustertal-Gailtal faults, is mainly composed of Permian granodiorite to granite, with minor gabbros and diorites in its southern part. New U–Pb SHRIMP zircon ages reveal two distinct crystallization episodes at 289.7 ± 3.2 and 280 ± 2.2 Ma, respectively. The pluton is affected by a hydrothermal potassic to sodic + Cu metasomatic alteration, which has long been ascribed to a late phase of the Permian magmatism. In contrast with this hypothesis, we report new 39Ar–40Ar data for different generations of metasomatic K-feldspar, which indicate formation ages between 35.3 ± 0.3 and 27.8 ± 0.5 Ma. This interval overlaps with the ages of the widespread 'Periadriatic' calc-alkaline magmatism, which extends from the Western to the Eastern Alps straddling the Periadriatic Fault System. The observed hydrothermalism has geochemical characteristics compatible with those of the coeval calc-alkaline Periadriatic magmatism. These data altogether suggest the release of fluids from a hidden intrusion during the main stage of the Alpine orogenic magmatism. Our results provide the first evidence of Oligocene magmatic activity in the Southern Alps east of the Giudicarie Line, bridging the gap between the western-central and eastern Alpine magmatic plutons. A fairly continuous Oligocene magmatic belt straddling the Periadriatic Fault System is consistent with a triggering of the magmatism by slab steepening or slab break-off, either of which are considered to be an essential driver for the Miocene lithospheric rearrangement in the Eastern Alps. Our finding is particularly relevant given that the outcropping area of the Bressanone pluton is centred above the imaged subducting lithosphere gap that separates the Western-Central and the Eastern Alps, hence at a location where mantle upwelling should have been easier although no relevant magmatism was found to date. [ABSTRACT FROM AUTHOR]

The Nodoushan plutonic complex in the central part of the Urumieh–Dokhtar Magmatic Belt developed mainly in the Cenozoic in response to the final stages of subduction-related magmatism that preceded the post-Oligocene collision between the Arabian and Eurasian Plates. Despite numerous recent studies examining the deformation and related exhumation history of the Arabia–Eurasia collision zone, the exhumation history of the Urumieh–Dokhtar Magmatic Belt (making up the majority of the Iranian Plateau) is largely unknown. In this work, apatite and zircon (U-Th)/He thermochronometry and thermal modelling analysis are applied to the (mainly) granitoid intrusive bodies in the Nodushan Plutonic complex in order to unravel the exhumation history of this region in the context of collisional tectonics. The results document two main phases of exhumation in the early Miocene (~ 22–20 Ma) and middle Miocene (~ 11 Ma). The distribution of (U-Th)/He ages suggests that these deformation episodes are related to the collision between the Arabian and Eurasian Plates. The 'soft' initial stages of Arabia–Eurasia collision in the Nodoushan plutonic complex occurred when the stretched Arabian passive margin reached the subduction zone in the early Miocene. Subsequently, the final 'hard' collision with the harder continental margin occurred in the middle Miocene. The results of this work mark the first thermochronometric data related to SE Iranian Plateau evolution and identify exhumation that initiated in the early Miocene and developed regionally during middle Miocene times. [ABSTRACT FROM AUTHOR]

The Wanbaogou granitic plutons are exposed along with coeval volcanic rocks, and provide an opportunity to investigate Silurian tectonism in the South Kunlun belt, northwest China. This study presents new whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for Silurian intrusive rocks of the Wanbaogou area. We analysed four samples: a porphyritic monzogranite and dioritic dike from the Wanbaogou pluton and a granodiorite and monzogranite from the Wudaogou pluton. Zircon U–Pb dating yielded similar ages of 423.8 ± 1.9, 422.9 ± 1.9, 424.9 ± 2.0, and 425.3 ± 2.6 Ma, respectively. indicating that the intrusions were coeval. The granitic samples are mostly transitional between the high-K and shoshonite series. The Wanbaogou monzogranite is metaluminous and has features typical of A-type granites in terms of trace element geochemistry, whereas the Wudaogou granitoids are metaluminous to weakly peraluminous I-type granites. The Wanbaogou dikes are intermediate to mafic in composition and belong to the low- to medium-K series. The four intrusive samples have εHf(t) values of −10.62 to +0.99 (average = −2.52), similar to the εHf(t) values of intraplate volcanic rocks (−6.35 to +2.89; average = −1.82) and, combined with the geochemical data, indicate the 430–420 Ma magmatism could have been generated by crustal melting with input from mantle-derived materials, followed by crustal contamination. Data for the Wanbaogou and Wudaogou plutons, dikes, and volcanic rocks from the same area suggest rapid orogenic uplift at 430–420 Ma. Our data and the results of previous research on the Kunlun high- to ultra-high-pressure metamorphic belt and coeval volcanic and intrusive rocks elsewhere in the region suggest that collisional tectonism ceased abruptly at 430–420 Ma. Slab break-off may be responsible for this termination of tectonism and rapid uplift. [ABSTRACT FROM AUTHOR]

The Cadomian Orogeny was active along the northern margin of Gondwanaland during the Late Neoproterozoic–Early Cambrian period. Remains of this orogenic activity are traced from Western Europe to the Himalayas, including some metamorphic basement rocks of Turkey. In this study, we provide new whole-rock and mineral chemistry, and zircon U–Pb age data for the metagabbro and metagranites in the Armutlu Peninsula, north of the Intra Pontide suture zone (IPSZ), which are the equivalent of the Cadomian basement of the İstanbul Zone (İZ). Geochemically, the metagabbros show an extreme depletion in Nb, Zr, Th, and Hf; low TiO2 contents; and high Mg# values exhibiting boninitic affinity, which are commonly associated with fore-arc settings. The metagranites are calc-alkaline and high-K calc-alkaline in character. They are slightly enriched in LREE and have similar features to shear-type plagiogranites. The yielded zircon U-Pb crystallization ages are 564 ± 4.4 Ma for metagabbros and 561 ± 9.5 Ma (Late Ediacaran) for metagranites. In this study, we provide additional information for the Cadomian basement of the İZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products. [ABSTRACT FROM AUTHOR]

Cadomian (Ediacaran–Cambrian) magmatic rocks have been reported in the eastern (e.g. the Çatalca and İhsaniye plutons) and western (e.g. the Binkılıç and Safaalan plutons) parts of the Istranca (Strandja) Massif. This paper aims to investigate the tectonic setting and the magma evolution history of the Cadomian magmatic rocks using both new and previously existing geochemical and geochronological data. The meta-granitoid rocks with intermediate to felsic composition are the main magmatic activity in the region. They intrude into metamorphic basement rocks composed of gneiss, schist, amphibolite, calc-schist, and quartzites (the Tekedere group). These plutons show strong foliation and traces of the polyphase metamorphism. All plutons are peraluminous and slightly metaluminous, mostly calc-alkaline and high-K calc-alkaline, and plot into the volcanic arc granites (VAG) field on the tectono-magmatic discrimination diagrams. The zircon U–Pb crystallization ages of the plutons are between 525.3 ± 3.5 Ma and 548.7 ± 2.3 Ma. Initial εNd values vary from −0.02 to 1.86. Nd-TDM model ages range between 1.08 and 1.24 Ga and indicate that the primitive magmas were originated and/or assimilated by the remelting of Neoproterozoic juvenile crustal rocks. New geochemical and geochronological data suggest a magma generation within a subduction-related magmatic arc setting in response to the southward subduction of the Proto-Tethys Ocean during the Late Precambrian-Early Palaeozoic period in the Istranca Massif. [ABSTRACT FROM AUTHOR]

New U-Pb zircon geochronology using high-spatial resolution secondary ion mass spectrometry fills a data gap and provides crystallization ages for granitoids from the Asir composite terrane in the southernmost Arabian Shield of Saudi Arabia. Ages of c. 810–685 Ma, c. 663–636 Ma, and 625–610 Ma reflect oceanic island arc genesis, subduction-related arc accretion (syn-collisional), and post-collisional stabilization, respectively. All samples have juvenile εNd(t) compositions with no evidence of older material being involved in their genesis, indicating that this part of the Arabian Shield grew through juvenile magmatic addition and that assimilation by syn- and post-tectonic magmatism involved an isotopically juvenile component(s). The crustal thickness derived from the (La/Yb)N proxy indicates significant thickening from 10–20 km to c. 70 km at c. 650 Ma, consistent with timing of orogenic uplift and increasing crustal thickness post-dating peak Nabitah orogeny. The age of an intrusion cross-cutting the Atura formation, when combined with other data, provides a well-constrained depositional age of c. 646–625 Ma for the Atura formation and indicates that erosion of the orogenic edifice in this part of the Arabian Shield began at latest by 625 Ma. Our new data indicate that denudation occurred 80–100 m.y. before the development of the prominent sub-Cambrian peneplain, consistent with previous assertions that major pulses of denudation occurred prior to the waning stages of Nabitah orogenesis. [ABSTRACT FROM AUTHOR]

Subduction zones are the gateways of large-scale material and energy exchange. The SW Japan region is one of the important regions to understand ongoing convergent margin processes with continuous island arc magmatism. Here we investigate the bimodal magmatic suites from the Tsukuba area in Japan based on petrology, geochemistry and zircon U-Pb-Hf isotopes. Magmatic rocks in the Tsukuba area comprise two compositionally different groups: 1) a mafic group comprising Hbl-gabbros of ~66 Ma and 2) a felsic group represented by two pulses of granitoids at ~66 Ma and ~78 Ma, respectively. All these rocks display calc-alkaline affinity and negative Nb, and Ta anomalies, with a bimodal classification represented by a significant silica gap between the mafic and felsic members. The Hbl-gabbro witnessed plagioclase and amphibole fractionation as evidenced by the humped REE pattern and positive Eu and Sr anomalies. Zircon grains from the Hbl-gabbros show ƐHf (t) values in the range of −7.7 to −4.0 with a peak at −6.4, indicating an enriched mantle source modified by slab-derived fluids. The petrological and geochemical characteristics of Hbl-gabbros are similar to those in the magmatic suite of SW Japan, suggesting that Cretaceous arc magmatism in Tsukuba is an extension of the coeval magmatic belt in SW Japan. Two pulses of granitoids identified in this study are similar in composition and are both classified as I-type granite. The relative uniform high SiO2 (70–75%) and large variation of Hf isotope (−21.0 to −4.0) indicates the granitoids formed by lower crustal melting. The Hf model ages (2479–1392 Ma) of granitoids are significantly older than those of coeval granitoids in SW Japan which show Nd model ages at 1435–748 Ma. This indicates that the arc magmatism in the Tsukuba area involved older lower crust linked to a possible micro-continent derived from the Southern Korean Peninsula. [ABSTRACT FROM AUTHOR]

This study investigates relicts of some granitic Gondwanan basement unexpectedly outcropping in the northwest of Central-East Iranian Microcontinent (CEIM) and incorporated into an ophiolitic mélange. Based on petrographical (e.g. high modal content of muscovite (~10 vol.%), absence of hornblende, inherited zircons (>541 Ma)), geochemical (peraluminous and calc-alkaline S-type affinity, high silica, high 'light rare earth element (LREE)/heavy rare earth element (HREE)' ratios, negative Nb and Ti anomalies), and geochronological (magmatic zircon age ~448 Ma) results, it is an Ordovician anatectic granite formed from a sedimentary source during crustal thickening in a syn-collisional setting. It shows some signatures of metamorphic deformation (cataclastic fabric, quartz bulging recrystallization, and foliation) likely developed in the Devonian (~410 Ma). The U-Pb zircon ages from this granite are analogous to the other Ordovician collision-related magmatic events in the CEIM (Chahak to Airekan, Balvard). Our results confirm that Cadomian subduction and closure of the Proto-Tethys Ocean to the north of the Gondwana supercontinent resulted in crustal thickening during Ordovician collision-related magmatism and Devonian-Carboniferous regional metamorphism in the CEIM. [ABSTRACT FROM AUTHOR]