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Alkaline intrusions such as ultrapotassic syenites are typically formed in extensional tectonic settings including continental rift, post-orogenic and post-collisional regimes. Here we present two early Mesozoic ultrapotassic syenite plutons (Tieshan and Yangfang) in South China that were formed in a continent collisional setting. LA-ICP-MS zircon U Pb chronological, major and trace elemental, and Sr Nd isotopic data of these syenites are used to explore their origin and to further constrain the geodynamics of early Mesozoic magmatism in South China. Our new data indicate that the Tieshan and Yangfang plutons were formed in Early Triassic (249 Ma) and Middle Triassic (240 Ma), respectively. The Tieshan and Yangfang syenites have SiO 2 contents of 50.84–56.95 wt% and 59.13–68.34 wt%, respectively, both are enriched in alkalis with very high K 2 O (5.60–9.68 wt%) and K 2 O/Na 2 O (1.8–15.7) and in LILE (Ba = 2464–8813 ppm; Sr = 652–3499 ppm), REE (498–1355 ppm) and HFSE (Zr = 264–766 ppm). They show enriched Sr Nd isotopic compositions with 87Sr/86Sr (t) and ε Nd (t) of 0.7096–0.7102 and − 5.2 to −6.5, respectively for Tieshan and of 0.7112–0.7119 and − 8.8 to −9.7, respectively for Yangfang. Geochemical data suggest that the studied ultrapotassic syenites were derived by partial melting of ancient subduction-modified lithospheric mantle including slab-derived melt hybridization and slab-derived carbonate fluid metasomatism, with the source depth of 60–90 km for Tieshan and at least 90 km for Yangfang. We further suggest that their origins are related to the transtension of the regional NE–trending strike-slip faults caused by continental collisions during the early Mesozoic amalgamation in East Asia. • Tieshan and Yangfang ultrapotassic syenites emplaced during Early to Middle Triassic. • Both syenites formed by partial melting of ancient subduction-modified mantle. • Their origin was related to transtension of regional NE–trending strike-slip faults. • Their formation was coupled with Late Permian to Triassic amalgamation in East Asia. [ABSTRACT FROM AUTHOR]

The widespread occurrence of late Mesozoic volcanic rocks in the Gan-Hang Belt in South China is associated with similarly widespread mineralization, but many important questions surrounding these volcanic rocks have not been clearly answered. The Tianhuashan basin located in the northern Wuyi Mountain volcanic belt is one of the most important volcanic basins in the Gan-Hang Belt, and it is primarily composed of the Daguding and Ehuling Formations and their intrusive counterparts. LA-ICP-MS zircon U–Pb dating shows that the Daguding Formation erupted in the Late Jurassic (152–160 Ma), whereas the Ehuling Formation erupted in the Early Cretaceous (131–139 Ma) in the Tianhuashan basin. Volcanic rocks are rhyolite and share similar trace and rare earth element patterns with an enrichment of LREEs and a depletion in Sr, Ba, Nb, Ta, P, Eu and Ti. They are also characterized by negative whole rock ε Nd (t) and zircon ε Hf (t) values with Paleoproterozoic t 2DM ages, suggesting that they were derived primarily from the remelting of ancient crustal materials. Daguding volcanic rocks are strongly peraluminous and show a higher Mg# than pure crustal melts, implying that they were likely derived from Paleoproterozoic metasedimentary basement materials. However, Ehuling volcanic rocks are weakly peraluminous and have a pronounced A 2 -type geochemical signature. Detailed elemental and isotopic data suggest that they were formed by the partial melting of the Paleoproterozoic metamorphic basement (including metasedimentary and metaigneous rocks) at a high temperature (~ 840 °C), followed by fractional crystallization. These results imply that during the Late Jurassic, South China on the Gan-Hang Belt was a continental arc coupled with the subduction of the Paleo-Pacific plate. Since the beginning of the Early Cretaceous, an intra-arc rift has formed along the Gan-Hang Belt as a consequence of slab rollback. These results also indicate that the extension in the Gan-Hang Belt began later than the southwestern part of the Shi-Hang Zone and lasted from 139 Ma to 122 Ma. [ABSTRACT FROM AUTHOR]

The western Tibet Plateau comprises a series of crustal terranes that were successively accreted to the southern margin of Eurasia associated with the evolution of Paleo- and Neo-Tethys. This paper presents the first detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotope geochemistry of three Mesozoic plutons (South Kudi, Arkarz and Mazha) and their microgranular enclaves in the western Kunlun and Tianshuihai terranes. SHRIMP zircon U–Pb dating shows that the three plutons were emplaced in the Late Triassic (215–209 Ma) and show a southward-younging trend. The South Kudi pluton (215 Ma) is composed of high-K calc-alkaline granodiorite and monzogranite, with initial 87 Sr/ 86 Sr ratios of 0.7093–0.7099, ε Nd (T) of − 4.9 to − 5.4, and ε Hf (T) (in-situ zircon) of 0.3. Elemental and isotopic data suggest that the granitoids were generated by partial melting of the Precambrian metasedimentary–igneous basement in the normal lower-crust (< 40 km) of the western Kunlun terrane triggered by underplating of basaltic magma. The Arkarz pluton (213 Ma) consists of high-K calc-alkaline monzogranite, syenogranite and alkali-feldspar granite and contains abundant microgranular enclaves. The host granites have initial 87 Sr/ 86 Sr ratios of 0.7071–0.7085, ε Nd (T) of –3.7 to − 4.8, and ε Hf (T) of − 0.7, and were also generated by partial melting of the Precambrian metasedimentary–igneous basement in the normal lower-crust (< 40 km) of the western Kunlun terrane triggered by underplating of enclave-forming potassic magma. Fractional crystallization of these pure crustal melts may explain the more felsic end-member granite. The enclaves are mainly basic (SiO 2 48.0–54.9 wt.%) with high K 2 O (1.4–3.8 wt.%). They have initial 87 Sr/ 86 Sr ratios of 0.7071–0.7080 and ε Nd (T) of − 2.6 to − 4.5. We interpret the enclave magmas as having been derived by partial melting of the metasomatized mantle wedge in the spinel–garnet transition zone (~ 60–80 km). The Mazha pluton (209 Ma) is composed of high-K calc-alkaline tonalite and granodiorite, with initial 87 Sr/ 86 Sr ratios of 0.7087–0.7097, ε Nd (T) of − 6.3 to − 6.5, and ε Hf (T) of − 2.8. Elemental and isotopic data suggest that the granitoids were generated by mixing of mantle-derived basaltic magma with felsic melt derived by partial melting of lower crust of the Tianshuihai terrane. Our new data suggest that during the Late Triassic (215–209 Ma) the Tianshuihai terrane and the southern part of the western Kunlun terrane were a continental arc in response to the northward subduction of the Paleo-Tethys between the Tianshuihai and Karakorum terranes; the collision of the Karakorum terrane with the Tianshuihai terrane is not earlier than the age of 209 Ma, and most likely occurred during the Early Jurassic. [ABSTRACT FROM AUTHOR]

Abstract: Mesozoic lamprophyres are widely present in gold province in the Jiaodong Peninsula. In this study, we analyzed major and trace elements and Sr–Nd–Pb isotopic compositions of lamprophyres from the Linglong and Penglai Au-ore districts in the Jiaodong Peninsula, in an attempt to better understand Mesozoic lithospheric evolution beneath the eastern North China Craton. These lamprophyre dikes are calc-alkaline in nature, and are characterized by low concentrations of SiO2, TiO2 and total Fe2O3, high concentrations of MgO, Mg# and compatible element, enriched in LREE and LILE but variably depleted in HFSE. They display initial 87Sr/86Sr ratios of 0.709134–0.710314, εNd(t) values of −13.2 to −18.3, 206Pb/204Pb of 17.364–17.645, 207Pb/204Pb of 15.513–15.571 and 208Pb/204Pb of 37.995–38.374. Interpretation of elemental and isotopic data suggests that the Linglong and Penglai lamprophyres were derived from partial melting of a phlogopite- and/or amphibole-bearing lherzolite in the spinel–garnet transition zone. The parental magma might have experienced fractionation of olivine and clinopyroxene, and minor crustal materials were incorporated during ascent of these mafic magmas. Before ~120Ma of emplacement of these calc-alkaline lamprophyres, the ancient lithospheric mantle was variably metasomatized by hydrous fluids rather than melts from subducted/foundered continental crust. It is proposed that continuous modification by slab-derived hydrous fluids from the Paleo-Pacific plate converted the old cratonic lithospheric mantle to Mesozoic enriched lithospheric mantle. Geodynamic force for generation of these lamprophyres may be related to large scale lithospheric thinning coupled with upwelling of the asthenosphere beneath the North China Craton. Continental arc-rifting related to the Paleo-Pacific plate subduction is favored as a geodynamic force for the cratonic lithosphere detachment. [Copyright &y& Elsevier]

Abstract: The Central Tianshan zone is located between the Turpan–Hami and Tarim blocks and played a pivotal role in crustal evolution and collisional tectonics of the southern Altaids (or the Central Asian orogenic belt). The Xingxingxia granodiorite in the eastern Central Tianshan is an Early Paleozoic (424.9±5.8Ma) intrusion. Petrography, geochemistry and Sr–Nd–Hf isotopes suggest that the Xingxingxia granodiorite was genetically related to a volcanic arc, emplaced above a subduction zone. Thus, the Central Tianshan zone was a magmatic arc above an early Paleozoic subduction zone of the Paleoasian ocean. We present LA-ICP-MS zircon U–Pb dating and Hf isotope determinations of Precambrian zircon grains trapped in the Xingxingxia granodiorite. Three populations of inherited zircons indicate that Neoproterozoic (809±41Ma; ε Hf(t)=0.10–5.73), Mesoproterozoic (~1400Ma; ε Hf(t) 8.71–10.05) and Paleoproterozoic (~1750Ma; ε Hf(t) 0.11 and 4.80) tectonomagmatic events in the Central Tianshan zone, which are comparable with those in the Tarim block. Combined with a series of similar geological characteristics between these two blocks, it is suggested that the Central Tianshan zone might have been originally a part of the Tarim block, and was separated from it during the Early Paleozoic time due to pull-apart caused by southward subduction of the Northern Tianshan ocean, a branch of the Paleoasian ocean. [Copyright &y& Elsevier]

Abstract: The Gan-Hang rift, trending at least 450km in a NE–SW direction, is a part of a Mesozoic Basin and Range Province in southeastern China. Detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotope data of three granitic plutons and a diabasic dike in the northwest of the Gan-Hang rift, are used to explore the origin of these granites and their relationship to the evolution of the Gan-Hang rift. SHRIMP zircon U–Pb dating shows that the granitic plutons and diabasic dike were emplaced in the Early Cretaceous (122–129 Ma). The Tongshan and Damaoshan plutons, close to the Gan-Hang rift, consist mainly of weakly peraluminous granitic rocks, which show A2 subtype affinity. These granites have initial 87Sr/86Sr ratios of 0.7080–0.7103, εNd (T) values of−1.4 to−5.6 and εHf (T) (in-situ zircon) values of −3.8 to +1.2. Detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized Mesoproterozoic metamorphic basement (including metasedimentary and metaigneous rocks) in the shallow (<30km) crust at a high temperature (~823°C). These pure crustal melts underwent crystal fractionation of biotite, plagioclase and K-feldspar, forming the more felsic end-member of granitic rocks. The Ehu pluton, more distant from the Gan-Hang rift, is composed of two-mica granites, which are strongly peraluminous and are S-type granites. These granites have higher initial 87Sr/86Sr ratios (0.7162−0.7191) and lower εNd (T) (−7.1 to −7.4) and εHf (T) (−6.8; in-situ zircon) values than the Tongshan and Damaoshan granites. Detailed elemental and isotopic data suggest that the Ehu granites were formed by partial melting of Paleoproterozoic metasedimentary basement in the deep (~40–50km) crust at a relatively low temperature (~757°C), with no fractional crystallization and mantle-derived magma mixing in their evolution. The coeval diabasic dike is calc-alkaline and has initial 87Sr/86Sr ratio of 0.7085, εNd (T) value of +0.9 and εHf (T) (in-situ zircon) value of −7.1, suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment-derived melt with monazite in the residual phase. The association of Early Cretaceous (122–129Ma) S- and A-type granites in the northwest of the Gan-Hang rift marks the onset of back-arc extension or intra-arc rift. With ongoing extension the crust and lithospheric mantle became progressively thinned. The upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the Gan-Hang rift, forming the A-type granitic magmas such as Tongshan and Damaoshan, whereas partial melting of metasedimentary rocks in the less thinned crust farther from the Gan-Hang rift formed the S-type granitic magmas such as Ehu. The red sediments with the total thickness more than 10,000m have been successively deposited in the Gan-Hang rift valley since the late Early Cretaceous (~105Ma), suggesting that this region experienced the most back-arc extension. [Copyright &y& Elsevier]

Abstract: The Qinling–Dabie–Sulu orogen marks the junction between the North and South China Blocks. However, the exact timing of the final coalescence of the North and South China Blocks in the Qinling orogen is poorly constrained. This paper presents new SHRIMP zircon U–Pb chronology, major and trace elements, and Sr–Nd–Hf isotope data for five early Mesozoic granitic plutons across the Qinling orogen. SHRIMP zircon U–Pb dating shows that four plutons were emplaced in the Carnian (227–218Ma) of Late Triassic with a southward-younging trend and one pluton was emplaced in the Norian (∼211Ma) of Late Triassic. The Carnian plutons consist of high-K calc-alkaline granitoids (quartz monzodiorite, quartz monzonite, granodiorite and monzogranite) and calc-alkaline diorite. These rocks are mainly metaluminous and are characterized by high Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios, and by high Mg#, higher than pure crustal melts. The Norian pluton is composed of high-K calc-alkaline two-mica granites, which are peraluminous. These granites have low Sr and high Y and Yb contents and show similar Mg# to pure crustal melts. Detailed elemental and isotopic data suggest that the Carnian plutons were emplaced in a continental arc setting coupled with the northward subduction of the Paleo-Tethyan oceanic crust. Partial melting of subducted sediments triggered by dehydration of the underlying igneous oceanic crust, with subsequent melts interacting with the overlying mantle wedge, formed the high-K calc-alkaline granitic magmas. Partial melting of the hybridized peridotitic mantle wedge induced by slab melts generated the calc-alkaline dioritic magma. The Norian pluton was emplaced during continental collision between the South Qinling terrane and South China Block, which marks the final integration of the North and South China Blocks. Partial melting of subducted sediments at a shallow depth (<30km) in the collision (overthrust) zone could account for the origin of the Norian peraluminous granites. Our new data suggest that the final coalescence of the North and South China Blocks in the Qinling orogen is not synchronous with that in the Dabie–Sulu orogen, and thus, the Paleo-Tethyan oceanic basin between the North and South China Blocks most likely occurred as a ‘scissors-like’ shape, with closure in the Anisian (∼240Ma) of Middle Triassic in the eastern part (Dabie–Sulu) and in the Norian (∼211Ma) of Late Triassic in the western part (Qinling). [Copyright &y& Elsevier]

Abstract: Lithospheric thinning and destruction of the North China Craton have been topics of active discussion throughout the last two decades, but the specific processes associated with lithospheric thinning remains controversial. Here we report co-occurrence of low-Ti (TiO2 <1.1wt.%, Ti/Y<270) and high-Ti (TiO2 >2wt.%, Ti/Y>370) types of lamprophyres in the Jiaodong Peninsula, eastern North China Craton in order to address this issue. Low-Ti lamprophyres are depleted in HFSE and enriched in Pb, both typical subduction signatures. We suggest they were derived from partial melting of an ancient and enriched lithospheric mantle, which was previously modified by slab-derived hydrous fluids. In contrast, the high-Ti lamprophyre has trace element patterns similar to many oceanic basalts with depletion of Pb but little or no HFSE depletion. We infer that they originated from partial melting of a convective asthenospheric mantle. Zircon U–Pb dating shows that both types of lamprophyres intruded the eastern North China Craton about 121Myr ago. Their indistinguishable ages thus appear to record a rapid transition from lithospheric to asthenospheric mantle source, suggesting further that the lithosphere beneath the eastern North China Craton was removed, potentially delaminated ca. 121Myr ago beneath Jiaodong Peninsula. The detachment of cratonic lithosphere is likely related to continental arc-rifting which resulted from Palaeo-Pacific plate subduction in the Mesozoic. [Copyright &y& Elsevier]

Early Cretaceous felsic intrusions and volcanic rocks are widespread in the Gan-Hang Belt, SE China. In this study, we report a distinctive high-Zr rhyolite (802–1145ppm Zr) from the Dazhou uranium district in the eastern Gan-Hang Belt. SHRIMP zircon U–Pb dating shows that the Dazhou rhyolite erupted at 127.3±1.7Ma. Geochemical data indicate A-type characteristics for the Dazhou rhyolite, such as high contents of alkali elements, high and high Ga/Al ratios, enrichment in some LILEs, HFSEs, and REEs, and depletion in Sr, Ba, P, and Ti. Compared to other A-type granitoids reported previously in the same belt, the Dazhou high-Zr rhyolite shows only a slight enrichment in other HFSE elements and LREE, but has similar whole-rock Nd and zircon Hf isotopic compositions to those A-type granitoids with relatively lower Zr concentrations, indicating that all these A-type rocks may have similar magma sources. Hence, the difference of Zr contents in these rocks is not due to their different source rocks. We found that zircon grains in the Dazhou high-Zr rhyolite are generally inheritance-poor, and the calculated zircon saturation temperatures are extremely high at ∼1000°C. It is therefore suggested that the distinctive high-Zr characteristic of the Dazhou rhyolite was a result of high-temperature suppression of zircon crystallization by ambient mafic magmas correlative with the upwelling of the asthenospheric mantle. The fundamental difference in magma temperature and magmatic evolution mechanism between the Dazhou high-Zr rhyolite and other A-type granitoid suites in the eastern Gan-Hang Belt brought about their different Zr concentrations. [ABSTRACT FROM AUTHOR]

Highlights: [•] First reported Neoproterzoic (∼740Ma) igneous rock in Chinese Central Tianshan. [•] The granite is an A1-type granite developed in a rift-like environment. [•] Central Tianshan recorded Neoproterozoic rift-related igneous events related to the breakup of Rodinia. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of boron and its isotopes in fluid-dominant processes and hydrothermal alteration of granites is examined using fresh and altered granite samples from the Qitianling granite and associated hydrothermal tin deposits in South China. Boron concentrations are highest in the fresh granite (37ppm) and depleted as a result of two stages of fluid mobility and fluid–rock interaction within the granite. Constraints provided both by δ 11 B and δ 18 O data suggest that the first stage was related to exsolution of aqueous fluids from the granite magma at a temperature of >450°C. This was followed by further boron depletion in the granite by hydrothermal circulation of meteoric water at lower temperatures (~350°C) and low water/rock ratios. The sensitivity of coupled boron and oxygen isotope systematics to these processes suggests that they can provide valuable constraints on of fluid mobility in granite and associated mineralization. [Copyright &y& Elsevier]

• The Jurassic porphyries at Chuankeng were formed at intra-plate extensional setting. • Magma source are Neoproterozoic juvenile crust with minor Paleoproterozoic ancient crust. • More contributions of ancient crust, lower oxygen fugacity and water contents reduce Cu fertility. • Nd-Hf isotopes, zircon Ce4+/Ce3+and T ti-zr can be used together to assess the potential of Cu mineralization. Large-scale Jurassic porphyry–skarn Cu mineralization in the Qin-Hang metallogenic belt of South China has attracted much attention, but comparative studies of porphyries in large- and small-scale deposits are lacking. In this paper, we present new zircon U–Pb ages, trace element composition and Hf isotopic composition as well as whole-rock geochemical and Sr–Nd isotopic compositions for the porphyries associated with mineralization in the small-scale Chuankeng Cu deposit. Drawing on our data for the Chuankeng deposit and existing data for the nearby giant Dexing Cu deposit, we aim to identify factors controlling the mineralization potential of both deposits. Granodiorite porphyries of Chuankeng deposit were emplaced at ca. 161–158 Ma. They have moderate SiO 2 contents of 61.9–66.1 wt% and high Sr/Y (59–135) and (La/Yb) N (4–14) ratios. Their high MgO contents (0.2–2.9 wt%), lack of negative Eu anomaly, depletion in Y and Yb, relatively high initial 86Sr/87Sr ratios (0.7076–0.7078), and low ε Nd (t) values (−4.5 to −4.9), indicating that the Chuankeng porphyries were derived from partial melting of delaminated lower crust. The Middle–Late Jurassic Chuankeng porphyries are considered to have been formed in a localized intra-continental extension environment along the Jiangshao Fault in response to far-field stress from Paleo-Pacific Plate subduction. Although no Middle–Late Jurassic magmatic arc rocks have been found in the study area, the Chuankeng porphyries display similar characteristics to arc rocks. On the basis of their zircon ε Hf (t) values (−2.6 to +0.9), two-stage Hf model ages (1.4–1.1 Ga), and regional geological history, we infer that magma source of Chuankeng porphyries were mainly Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. Thus their arc-like features were inherited from the Neoproterozoic juvenile crust that formed by subduction of oceanic crust during the Jiangnan orogeny. Chuankeng porphyries have lower zircon Ce4+/Ce3+ and higher Ti-in-zircon temperatures and lower whole rock ε Nd and zircon ε Hf values than the Dexing porphyries, indicating they are less oxidized and less hydrous and with more involvement of the ancient crustal material in the magma source, which could explain the relatively small-scale Cu mineralization in Chuankeng. This study highlights the values of integrated studies of whole rock Nd and zircon trace element and Hf isotopic compositions in assessing the potential for Cu mineralization. [ABSTRACT FROM AUTHOR]