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The tectonic setting of Indosinian magmatism in West Qinling Orogen and the tectonic evolution of the Paleo-Tethys remain hotly debated. Here we present SHRIMP zircon U Pb dating, major-trace elemental and Sr-Nd-Pb-Hf isotopic data for four granitic and gabbroic plutons across the eastern West Qinling Orogen, from north to south including Guanshan, Fengxian, Mishuling and Miba. Our new data indicate that the Fengxian granitoids, emplaced at 238 Ma in a continental arc setting, show adakitic affinity and were formed by partial melting of subducted sediments. The southern Guanshan granitoids, emplaced at 235–229 Ma in a continental arc setting, also show adakitic affinity but were generated by partial melting of thickened (>50 km) lower crust. The northern Guanshan granites and gabbros were emplaced at 217–216 Ma in a back-arc setting, with the former generated by partial melting of normal (40–50 km) lower crust and the latter derived from asthenospheric mantle. The Mishuling granitic pluton contains abundant mafic microgranular enclaves, both emplaced at 214 Ma in a back-arc setting with the host granitoids formed by partial melting of normal (40–50 km) lower crust and the enclave magmas derived from asthenospheric-lithospheric mantle. The Miba granitoids, emplaced at 216 Ma in a continental arc setting, show adakitic affinity and were generated by partial melting of thickened (>50 km) lower crust. We suggest that the Paleo-Tethyan oceanic crust had subducted near the Shangdan suture by 238 Ma and successively advanced northward, approaching southeastern Qilian Orogen at 235–229 Ma. Then slab rollback initiated and gradually migrated southward. The slab subduction did not cease before 214 Ma. • We have investigated four Triassic granitic-gabbroic plutons in West Qinling Orogen. • The granitoids formed in a continental-arc setting during the Ladinian-Carnian. • The granitoids, enclaves and gabbros formed in a back-arc setting during the Norian. • The origin of these rocks recorded the Paleo-Tethyan oceanic crust advance to retreat. [ABSTRACT FROM AUTHOR]

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

A comprehensive study of zircon U–Pb dating and in situ Hf isotopes, whole-rock major and trace element geochemistry and Sr–Nd isotopes was carried out for three late Mesozoic granitic plutons (Waitun, Shipi and Taiyuan) in northwestern Fujian province, SE China. We assess the origin of the granites and their relationship to the evolution of the late Mesozoic volcanic–intrusive complex belt in SE China. LA-ICP-MS zircon U–Pb dating shows that three plutons were emplaced in the Middle Jurassic to Early Cretaceous (168–109 Ma), in which the Waitun and Shipi plutons are intrusive complexes. All the plutons are composed of high-K calc-alkaline I-type granites with a great diversity in elemental and isotopic compositions. The granites have SiO 2 contents of 68.3–78.5 wt.%, showing a gradual decrease in initial 87 Sr/ 86 Sr (0.7181 to 0.7091) and increase in ε Nd (T) (− 16.7 to − 8.1) and ε Hf (T) (in-situ zircon) (− 20.6 to − 6.9) with decreasing emplacement ages. Geochemical data suggest that the Middle Jurassic (~ 168 Ma) Waitun granites are of purely crustal origin, derived by partial melting of a mixed source of Paleoproterozoic metaigneous (~ 78%) and metasedimentary (~ 22%) rocks at a depth of 30–40 km triggered by underplating of basaltic magma. Mixing of such crustal melts with about 10% basaltic magma could account for the origin of the Late Jurassic (~ 161 Ma) Waitun granites. The Late Jurassic (~ 156 Ma) Shipi and Early Cretaceous (~ 134 Ma) Taiyuan granites were produced by extensive fractional crystallization of primary crustal melts, the source of which show relatively high proportion (~ 82%) of metaigneous rocks. The Early Cretaceous (~ 109 Ma) Shipi granites were generated by partial melting of a mixed source of Paleoproterozoic metaigneous (~ 92%) and metasedimentary (~ 8%) rocks at a depth of ~ 30 km plus additional (~ 15%) input from coeval basaltic magma. The granites were formed in a continental arc setting induced by northwestward subduction of the Paleo-Pacific plate. Progressive slab rollback since the Middle Jurassic from inland to the coastal area is the most likely mechanism for the generation of the granites. [ABSTRACT FROM AUTHOR]

The early Paleozoic orogen of South China is possibly one of the few examples of intraplate orogeny in the world. It is characterized by an angular unconformity between post-Silurian cover and pre-Devonian strata and by the intensive and extensive early Paleozoic granitic plutonism. However, synchronous mafic–ultramafic rocks have not been well-studied, but they are crucial for understanding the nature and evolution of the orogen. In this paper, we present the first detailed LA-ICP-MS zircon U–Pb dating, major and trace element geochemical and Sr–Nd–Hf isotopic data for a Silurian gabbroic pluton (Dakang) and a coeval granitic pluton (Guiyang), that have recently been identified in central Fujian, in the southeastern part of the orogen. We assess the origin of these mafic and granitic rocks and their relationship to the evolution of the early Paleozoic orogen in South China. LA-ICP-MS zircon U–Pb dating shows that the Dakang and Guiyang plutons were emplaced at 441–438 Ma and 431 Ma, respectively. The Dakang pluton consists of gabbros and minor intermediate rocks (diorite, monzodiorite and monzonite). These rocks are all metaluminous and potassic, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They have initial 87 Sr/ 86 Sr of 0.7066–0.7098, ε Nd (T) of − 7.0 to − 3.3 and ε Hf (T) (in-situ zircon) of − 5.2 to − 4.4. Geochemical data suggest that the Dakang gabbroic magmas were derived by partial melting of previously subduction-modified lithospheric mantle in the spinel–garnet transition zone at a high temperature (~ 1300 °C). These primary magmas underwent fractionation crystallization of clinopyroxene and amphibole, forming the evolved gabbros and intermediate rocks. The Guiyang pluton consists of weakly peraluminous granites, which show low Ga/Al ratios (10,000*Ga/Al < 2.6) and so can be classed as I-type granites. They have initial 87 Sr/ 86 Sr of 0.7095–0.7113, ε Nd (T) of − 6.7 to − 5.9 and ε Hf (T) (in-situ zircon) of − 7.7 to − 0.8. Geochemical data suggest that the Guiyang granites were generated by partial melting of a mixed source of Paleoproterozoic metaigneous and metasedimentary rocks in the lower crust. Our new data, together with published data, confirm that lithospheric delamination occurred along the metamorphic core of the early Paleozoic orogen of South China during the Silurian (442–420 Ma), and that this represents a post-orogenic tectonic regime in the orogen core. [ABSTRACT FROM AUTHOR]

Abstract: The western Kunlun orogen, the northwest Tibet Plateau, occupies a key tectonic position at the junction between the Pan-Asia and the Tethyan tectonic domains. It is related to subduction of Proto- and Paleo-Tethys and terrane collision from early Paleozoic to early Mesozoic. This paper presents the first detailed SHRIMP zircon U–Pb chronology, mineral chemistry, major and trace element, and Sr–Nd–Hf isotope geochemistry of three Middle Triassic plutons (Yuqikapa, Muztaga and Taer) and their microgranular enclaves in the western Kunlun orogen. SHRIMP zircon U–Pb dating shows that the Yuqikapa pluton was emplaced in the Anisian (~243Ma) and the Muztaga and Taer plutons that contain microgranular enclaves were emplaced in the Ladinian (234–227Ma). The Yuqikapa pluton is composed of peraluminous high-K calc-alkaline two-mica granites (monzogranite–syenogranite–alkali-feldspar granite), with initial 87Sr/86Sr ratios of 0.7071–0.7077, ε Nd (T) of −4.4 to −6.3 and ε Hf (T) (in-situ zircon) of −3.3. Elemental and isotopic data suggest that they were formed by “wet” anatexis of the Precambrian metasedimentary and metaigneous rocks in the continental collision (overthrust) zone. The Muztaga and Taer plutons consist of metaluminous to weakly peraluminous high-K calc-alkaline granitoids (granodiorite–monzogranite), with initial 87Sr/86Sr ratios of 0.7052−0.7104, ε Nd (T) of −3.6 to −7.3 and ε Hf (T) (in-situ zircon) of −3.1 to −1.0. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metasedimentary and metaigneous rocks in the normal lower-crust (<40km) for the Muztaga pluton and in the thickened lower-crust (~40–50km) for the Taer pluton, triggered by underplating of coeval (233–226Ma) mantle-derived enclave-forming magmas. The enclaves are basic (SiO2 48.0–51.6wt.%) to intermediate (SiO2 53.0–54.6wt.%) with high K2O (1.4–4.2wt.%). They generally have lower initial 87Sr/86Sr ratios (0.7034–0.7084) and high initial ε Hf (−1.1 to +1.2) than their respective host granitoids. The enclave magmas are considered to have been derived from the partial melting of subduction-modified mantle in the spinel stability field (<60km) (enclaves in the Muztaga pluton) and the spinel-garnet transition zone (~60–80km) (enclaves in the Taer pluton). Final closure of the Paleo-Tethys occurred in the Middle Triassic Anisian (~243Ma). The Middle Triassic Ladinian (234–227Ma) dates the post-collisional regime caused by Paleo-Tethyan oceanic slab break-off. [Copyright &y& Elsevier]

Abstract: This paper presents detailed SHRIMP zircon U–Pb chronology, mineral chemistry, major and trace element, and Sr–Nd–Hf isotope geochemistry of two Cenozoic plutons (Karibasheng and Kuzigan) in western Tibetan Plateau, China. The Karibasheng pluton is composed of monzogranite, and the Kuzigan pluton consists of syenogranite, diopside-bearing syenite and diopside syenite. SHRIMP zircon U–Pb dating on monzogranite, syenogranite and diopside syenite shows that they were emplaced in Miocene (12–10Ma). These rocks are metaluminous and show the affinities with shoshonitic rocks, i.e., alkali-rich (K2O+Na2O=8.6–13.4wt.%), high K2O contents (4.7–10.6wt.%) with high K2O/Na2O ratios (1.2–4.6), enrichment in large ion lithophile elements (LILE) (e.g., Ba=2200–9100ppm; Sr=840–3100ppm, most >1100ppm) and rare earth elements (REE), especially light REE (LREE) (La/Yb up to 168). The rocks are depleted in high field strength elements (HFSE) but show high Nb/Ta ratios (13.3–30.7). The granites have lower initial 87Sr/86Sr ratios (0.7091–0.7099) and higher εNd (T) values (−7.1 to −9.5) than the syenites that have initial 87Sr/86Sr ratios of 0.7095–0.7117 and εNd (T) values of −8.6 to −12.2. Their zircon εHf (T) values (−7.2 to −9.7) are coupled with their whole-rock εNd (T) values, and plot along the mantle array. The amphibole–plagioclase thermometer and estimation of apatite saturation temperature indicate that the primary magmas had high temperatures (up to 880°C for the granites and up to 1100°C for the syenites). The source depth for the granites and syenites is <70–100km inferred by the metasomatic volatile phase (amphibole–phlogopite) relation, and thus most probably within the upper part of lithospheric mantle. Detailed elemental and isotopic data and major element modeling suggest that the granites and syenites were derived directly by partial melting of the veined lithospheric mantle that had been hybridized by the continental slab-derived melts. Continental slab break-off was most likely the mechanism associated with the generation of these granites and syenites. [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: Extensive middle to late Jurassic felsic and mafic magmatism occurred in the southern Hunan province, southeast China. SHRIMP zircon U–Pb dating, mineral chemical, element geochemical and Sr–Nd–Hf isotopic data have been determined for these rocks. The results indicate that the middle Jurassic (178–170 Ma) Changchengling and Ningyuan basaltic rocks belong to tholeiitic series and alkaline series, respectively, and were formed by fractional crystallization of the parent magmas that were derived from partial melting of asthenospheric mantle triggered by the slab-released fluids of the subducted Paleo-Pacific plate. The late Jurassic (152–146 Ma) Daoxian basalts and Guiyang lamprophyre dikes are low-Ti, high-Mg potassic rocks. They were derived directly by partial melting of shallower (60–100 km) lithospheric mantle composed of amphibole- and phlogopite-bearing lherzolite in response to thermal perturbations associated with the rifting of continental arc. The middle Jurassic (164 Ma) Tongshanling granitic rocks belong to calc-alkaline series and are strongly peraluminous. They were formed by partial melting of Palaeoproterozoic metasedimentary basement in the lower-crust plus additional input from coeval basaltic magma. The late Jurassic (156 Ma) Jinjiling and Xishan granitic rocks show A2 subtype affinity. They were generated by partial melting of granulitized Palaeoproterozoic metamorphic basement in the lower crust in response to injection of coeval low-Ti, high-Mg potassic magmas. A moderate degree (56–58%) of fractionation of these pure crustal melts could account for more felsic end-member of granitic rocks. Detailed petrologic and geochemical data for the middle to late Jurassic felsic and mafic rocks from the southern Hunan imply that during the middle Jurassic time SE China on the southeast of the Shi-Hang zone was a continental arc coupled with the subduction of the Palaeo-Pacific plate and since the beginning of late Jurassic time an intra-arc rift has been formed along the Shi-Hang zone as a consequence of slab roll-back. [Copyright &y& Elsevier]

Abstract: This paper presents detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotope geochemistry of three intrusive plagiogranite bodies formed in an island arc setting within the Oytag ophiolite suite of the Oytag–Kuda Suture Zone. SHRIMP zircon U–Pb dating of two of these intrusions shows that they were emplaced into the Oytag volcanic rocks at 337.5±4.1 Ma and 327.7±4.9 Ma, and that the younger intrusion contains inherited zircons ranging from 435.3 to 480.8 Ma. Both intrusions are composed of low-Al trondhjemite and tonalite. The rocks have low K2O and Sr and high Y contents with low Sr/Y ratios. They have relatively low rare earth element (REE) concentrations and are depleted in light REE (LREE) and relatively enriched in heavy REE (HREE), with marked negative Eu anomalies in the chondrite-normalized REE patterns. They have initial 87Sr/86Sr ratios of 0.7048 to 0.7068 and ε Nd (T) values of 6.2 to 7.6, which are lower than those of typical MORB. In situ Hf isotopic compositions of zircons with Early Carboniferous age from both intrusions are characterized by positive initial ε Hf values, ranging from +12.5 to +19.5, similar to typical MORB. The inherited Ordovician zircons in the younger intrusion have initial ε Hf values of −1.9 to +3.1, similar to zircons from Ordovician granitoids in the region. Detailed elemental and isotopic data suggest that the Oytag plagiogranites were formed in an oceanic island arc setting, by differentiation of arc tholeiitic magmas that formed in response to the intra-oceanic subduction. The inherited zircons are interpreted as the xenocrysts captured from the incipient oceanic crust that contains relicts of discrete fragments of continental crust with Ordovician zircons, through which the plagiogranite was emplaced. The Oytag ophiolite suite might be the remnants of an ancient island arc, the basement of which was the incipient oceanic crust. The Oytag–Kuda Suture Zone is suggested to be a multiple suture zone that represents the remnants of both the Proto-Tethyan and Paleo-Tethyan oceans. The western Kunlun orogen was therefore not a long-lived active continental margin during the early and late Paleozoic times. It most likely underwent at least two orogenic cycles and thus might represent a multiple orogenic belt. [Copyright &y& Elsevier]

A series of granitoids from Proterozoic to Cenozoic age occurred in the western Kunlun orogenic belt, Xinjiang, northwestern China. Several intrusions such as the West Datong (Middle Caledonian age), North Kuda (Late Caledonian age) and Kuzigan, Karibasheng, Zankan (Himalayan age) plutons have shoshonitic affinity. Their rock assemblages include (quartz) monzodiorite–(quartz) monzonite–quartz syenite (Middle Caledonian) or monzonitic granite–granite (Late Caledonian) or biotite (monzonitic) granite–diopside granite–diopside syenite (Himalayan). Generally, biotite is iron–phlogopite, with some eastonite and high Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. Amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende, with some edenite and higher Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. The rocks show SiO2 contents of 52.77–71.85% and high K2O+Na2O (mostly >8%, average 9.14%), K2O/Na2O (mostly >1, average 1.50) and Fe2O3/FeO (0.85–1.51, average 1.01) and low TiO2 contents (0.15–1.12%, average 0.57%). Al2O3 contents (13.01–19.20%) are high but variable. The granitoids are prominently enriched in LILE, LREE and volatiles such as F. However, the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations, suggesting their different geneses: the origin of the West Datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source; the North Kuda and Himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late-orogenic slab break-off or lithospheric thinning. [Copyright &y& Elsevier]

Abstract: The Huziyan basalts, occurring in the southern Hunan province, contain abundant mafic xenoliths. These xenolith and the basalt samples offer a unique opportunity to investigate the origin and nature of the lower crust beneath the inland area of the South China Block and to shed new light on the study of the early crustal evolution in the region. We carried out combined SHRIMP U–Pb geochronology and Hf isotope analyses on zircons from both the Huziyan mafic xenoliths and the host basalts. We have also carried out mineral chemistry, whole-rock geochemical, and Sr–Nd isotopic analyses on these mafic xenoliths. Our data show that these xenoliths were once seated in the lower crust according to petrographic examination and P–T estimation. We discovered one of the oldest zircon (207Pb/206Pb age=3.73 Ga, and T DM =4.08 Ga) in the Cathaysia Block in the Huziyan basalts, which implies the existence of a crustal remnant as old as 3.7 Ga. Three representative xenoliths yield consistent U–Pb ages of about 220 Ma (220±9 Ma for H4-2 determined through two baddeleyites, 230±8 Ma for H4-3 and 233±5 Ma for H4-5-2). Some of the zircons with ages of about 220 Ma display depleted mantle-like Hf isotopic compositions. It is thus deduced that some juvenile crust formed at 220 Ma when the mafic melt, derived from depleted mantle, underplated the lower crust. Such a thermal event in the deep crust might have induced intensive crust–mantle interaction and contributed to the formation of contemporaneous Indosinian granitoids in peripheral areas. Another thermal event leading to crustal growth at about 800 Ma can also be identified both from U–Pb ages (770–850 Ma) of xenocrystic zircons in the basalts and xenoliths, and from upper intercept ages of discordia in two xenoliths (933±65 Ma and 828±80 Ma). Episodic crustal growths might also have taken place at 2.7 Ga and 1.9 Ga. This is implied by Hf isotope model ages of some of the zircons. Large variation in Hf isotopic compositions among zircons of the same age (ɛ Hf(t)=−5.4 to 20.8 for 220 Ma zircons, and −8.3 to 10.9 for 800 Ma zircons) suggests mixing and interaction between DM-derived melt and old crustal components at both of these times. Furthermore, petrographic and geochemical characteristics suggest that these xenoliths were formed through accumulation of pyroxene and plagioclase, and were then metamorphosed in the lower crust. Multiple episodes of juvenile growth, crustal reworking, and mafic underplating resulted in complexity and heterogeneity in the lower crust, as demonstrated by diversities in bulk geochemistry, Sr–Nd isotopic compositions and zircon Hf isotopic composition of these xenoliths. [Copyright &y& Elsevier]

Abstract: The Linglong granite is one of the most important Mesozoic plutons in the Shandong Peninsula, eastern China, and its petrogenesis has long been controversial, particularly with regard to the nature of source region and geodynamic setting. Our new precise zircon U–Pb dating results reveal that the Linglong granite was emplaced in the Late Jurassic (157–160Ma). In addition, abundant inherited zircons are identified in the granite with four groups of age peaked at ~208, ~750, ~1800 and ~2450Ma. Geochemical studies indicate that the Linglong granite is weakly peraluminous I–type granite, and is characterized by high SiO2, Sr and La, but low MgO, Y and Yb contents, strongly fractionated REE pattern and high Sr/Y and La/Yb ratios. It also exhibits high initial 87Sr/86Sr ratios (0.7097 to 0.7125), low εNd(t) (−17.7 to −20.3) and variable zircon εHf(t) (−22.2 to −8.7) values. Calculation of the zircon saturation temperature (TZr) reveals that the magma temperatures are 760±20°C, and the lowest TZr value of 740°C may be close to initial magma temperature of this inheritance-rich rock. Interpretation of the elemental and isotopic data suggests that the Linglong granite has some affinities with the adakite, and was most likely derived from partial melting of thickened lower crust without any significant contribution of mantle components. The presence of a large number of inherited zircons and variable Sr–Nd–Hf isotopic compositions reveal that the Linglong granite probably has multiple sources consisting of the lower crust of both South China Block and North China Block, as well as the collision-related alkaline rocks and UHP metamorphic rocks. The continental arc-rifting related to the Izanagi plate subduction was the most likely geodynamic force for formation of the Jurassic Linglong adakatic granite in the Shandong Peninsula. [Copyright &y& Elsevier]

Abstract: The widespread occurrence of Mesozoic granites in the Gan-Hang Belt in Southeast China is associated with similarly widespread, economically important mineralization, but the precise timing, origin, and plate tectonic significance of these granites are not well understood. We have studied two of these (Early Cretaceous) granite bodies, the Yangmeiwan granite and the Daqiaowu granitic porphyry, from the northeastern part of the Gan-Hang Belt in western Zhejiang Province by zircon U-Pb geochronology, major and trace element analyses, and Nd–Hf isotopic analyses. LA-ICP-MS and SHRIMP U–Pb dating of zircon grains from these two granites yield ages of 133–136Ma, representing a Early Cretaceous magmatic event. These granitic rocks are metaluminous to weakly peraluminous and have a pronounced A-type geochemical signature with high Na2O+K2O, Fe2O3*/MgO and Ga/Al ratios. They show low CaO, MgO and TiO2 contents, enrichment in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y), depletion in Sr, Ba, P, Eu and Ti. They also show A2 subtype affinity and were probably formed at a high temperature (~810°C for Yangmeiwan granite and ~850°C for Daqiaowu granitic porphyry). These A-type granitic rocks show bulk rock εNd(t) values in the range of −6.5 to −3.6 and zircon εHf(t) values from −7.8 to −0.9, with Mesoproterozoic TDM c ages for both Nd and Hf isotopes. Geochemical and isotopic data suggest that these A-type granitic rocks were generated largely by partial melting of granulitized Mesoproterozoic metamorphic basement rocks (including parametamorphic and orthometamorphic rocks), with a possible input of mantle-derived materials and followed by subsequent fractional crystallization. Our new data together with previous published data suggest that the Cretaceous A-type granitic rocks with ages between 137Ma and 122Ma occurred along the Gan-Hang Belt, indicating an important Mesozoic extensional event in Southeast China. This event represents either a back-arc extension or an intra-arc rift due to the roll-back of the paleo-Pacific plate, and it started as early as ~137Ma in Xiangshan and Xinlu basins. It is earlier than ~130Ma as previously suggested in the studied region and later than that along the south part of the Shi-Hang Zone. With ongoing extension during slab roll-back of paleo-Pacific plate, the crust and lithospheric mantle became progressively thinned. The upwelling of asthenosphere would have triggered crustal rocks to partially melt, generating granitic magmas. Our new geochemical data also suggest that mantle-crust interaction in the formation of the A-type granitic magma along the Gan-Hang Belt gradually intensified from early to late stages between ca. 137 and ca. 122Ma. [Copyright &y& Elsevier]