Search

The Xinxing granitic pluton is a large batholith cropping out in southern South China with its long axis parallel to the regional NE–trending faults. We conduct the first comprehensive study of zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb chronology and trace element chemistry, rock-forming mineral chemistry and whole-rock element and Sr–Nd isotope geochemistry for this pluton. Our new data indicate that the pluton was emplaced during the interval 234–232 Ma, i.e. early Indosinian rather than late Mesozoic as previously considered. The southern pluton consists of syenogranite and monzogranite, which are composed of K-feldspar, oligoclase, quartz and ferri-biotite. The northern pluton consists of monzogranite and granodiorite, which are composed of andesine, K-feldspar, quartz and magnesio-biotite. The southern granites have high SiO2 contents (72.5–79.2 wt%) and high FeOT/(FeOT + MgO) (T refers to total) ratios with low Mg# [atomic Mg/(Mg + FeT)]. They are enriched in rare earth elements and depleted in Sr and Ba with Zr + Y + Ce + Nb >350 ppm and 10,000 × Ga/Al >2.6. Their initial magma temperatures are unusually high (>886 °C). All those features strongly suggest an affinity with A-type granites. The northern granites have lower SiO2 contents (63.4–72.5 wt%) and lower FeOT/(FeOT + MgO) ratios as well as higher Mg# than the southern granites. They are also enriched in rare earth elements and depleted in Sr and Ba, with high Ga/Al ratios and high Zr + Y + Ce + Nb contents. Geochemical data and major element modeling confirm that the southern A-type granites were generated by the moderate degree (~49%) shallow (ca. 15–20 km depth) dehydration melting of the early Paleozoic granitoids triggered by intraplating of basaltic magmas. Subsequent moderate degree (~57%) fractionation of such crustal melts produced the more felsic granites in the southern pluton, whereas subsequent mixing of such crustal melts with about 8 to 48% intraplated mafic magmas generated the less felsic granites in the northern pluton. Interaction of mafic magmas with A-type crustal melts causes the northern granites to lose some diagnostic geochemical features of A-type granites such as high FeOT/(FeOT + MgO) ratios and to be transitional towards I-type granites. We further suggest their origin to have been related to the transtension of the regional NE–trending strike-slip faults coupled with the early Indosinian continental collisions. [ABSTRACT FROM AUTHOR]

Late Paleozoic granites have rarely been reported in South China. We present the first detailed zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating and in situ Hf isotopic and whole-rock element geochemical and Sr-Nd isotopic data for two late Permian granitic plutons (Napeng and Shicun) recently identified in the Yunkai massif, South China. In addition, we assess their origin and relationship to the geodynamics of late Paleozoic to early Mesozoic magmatism in South China. The Napeng pluton consists of cordierite- and/or garnet-bearing biotite granites, and the Shicun pluton is composed of two-mica granites and muscovite granites. Detailed LA-ICP-MS zircon U-Pb dating shows that both plutons were emplaced in the late Permian and contain abundant inherited zircons with a spread of ages, including Neoarchean-Paleoproterozoic, Neoproterozoic-Cambrian, Ordovician-Silurian, Devonian, Carboniferous, and early Permian. The cordierite- and/or garnet-bearing biotite granites are strongly peraluminous and have higher maficity than experimental melts of metasedimentary rocks. Both the two-mica and muscovite granites are also strongly peraluminous but have similar maficity to experimental melts of metasedimentary rocks. All the granites have high initial 87Sr/86Sr, negative ε Nd(t), and ε Hf(t) (in situ zircon). Detailed petrographic and geochemical characteristics of the studied granites suggest that they are S-type granites and were formed by partial melting of subducted oceanic sediments of the eastern Paleo-Tethys Ocean within the depth of mantle region to normal lower crust in the continental collision zone. Our new data suggest that the origin of the Napeng and Shicun granites might mark the onset of the continental collision between the Indochina and South China Blocks with the initial closure of the eastern Paleo-Tethys Ocean at the beginning of the late Permian. [ABSTRACT FROM AUTHOR]

A-type granites are widespread in most orogenic belts, and their petrogenesis has played an important role in reconstructing orogenic events. However, their sources, even today, are a subject of considerable controversy. At least four models have been proposed for their formation, namely, melting of a previously melted source, fractionation of basaltic magma, anatexis of crustal igneous sources, and magma mixing. Here we present Early Jurassic A-type granites in southeast (SE) China as an example of a shallow (ca. 15-20-km depth), igneous, crust-derived A-type granite. We present detailed laser ablation ICP-MS zircon U-Pb dating and major- and trace-element and Sr-Nd isotopic data for these granites and assess their origin and relationship to the geodynamics of the late Mesozoic extensive magmatism in SE China. The associated granites include the Zhaibei, Keshubei, Zhulanbu, and Guangze plutons, which were emplaced during the interval 191-188 Ma and occur in a northeast-trending belt, parallel to the present coastline. They consist mainly of syenogranite and alkali-feldspar granite, with minor monzogranite, in which biotite and amphibole are anhedral and interstitial to both feldspar and quartz. The granites have high SiO2 (71.3-78.4 wt%) and K2O + Na2O and low Al2O3 and CaO contents, with high (K2O + Na2O)/Al2O3 ratios. They are enriched in rare earth elements (except Eu) and depleted in Ba and Sr. They display 10,000Ga/Al > 2.6 and Zr + Nb + Ce + Y > 350 ppmand have high zircon saturation temperatures (up to 900°C). Their Sr-Nd isotopic compositions (initial 87Sr/86Sr ranges from 0.7070 to 0.7283 and #949;Nd(T) ranges from 0.1 to -10.2) are variable but consistent with those of the early Paleozoic granitoids in SE China. Geochemical data suggest that the Early Jurassic A-type granites were derived by dehydration melting of early Paleozoic hornblende- and biotite-bearing granitoids in the middle crust (ca. 15-20 km), induced by intraplating of mantle-derived basaltic magmas. We further suggest that they formed in an extensional tectonic regime caused by slab break-off of the Paleo-Pacific Plate. [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]

This paper presents the first detailed zircon U–Pb chronology, major and trace element, and Nd–Hf isotope geochemistry of two Neoproterozoic plutons (Shanhou and Jiangshan) along the northwest side of the Jiangshan–Shaoxing suture, Zhejiang province, South China. The Shanhou pluton consists of gabbros, dioritic rocks and monzogranites. SHRIMP and LA-ICP-MS zircon U–Pb dating indicates that the gabbros (∼846 Ma), dioritic rocks (∼845 Ma) and monzogranites (∼847 Ma) were emplaced simultaneously. The Jiangshan pluton consists mainly of dioritic rocks that were also emplaced in the middle Neoproterozoic with a SHRIMP zircon U–Pb age of ca. 842 Ma. The Shanhou gabbros are mainly high-K calc-alkaline, and are enriched in LREE and LILE and depleted in HFSE with marked negative Ta–Nb anomalies. They have positive ɛ Nd (T) (2.0–3.5) and ɛ Hf (T) ( in-situ zircon) (3.3). The Shanhou and Jiangshan dioritic rocks as well as the Shanhou granites are also high-K calc-alkaline, enriched in LREE and LILE and depleted in HFSE with marked negative Ta–Nb anomalies. They also show positive ɛ Nd (T) (0.1–4.7) and ɛ Hf (T) ( in-situ zircon) (0.8–5.0). Detailed elemental and isotopic data suggest that both plutons were formed in a continental arc setting with gabbros derived from partial melting of subduction-modified mantle wedge. Such gabbroic magmas underwent fractionation crystallization of clinopyroxene + amphibole, forming the less felsic dioritic rocks. Progressive fractionation crystallization of amphibole + plagioclase from the evolved melts with a little crustal assimilation produced the more felsic dioritic rocks and granites. Our new data suggest that final amalgamation between the Yangtze and Cathaysia blocks postdated 842 Ma. [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]

The western Tibet Plateau comprises a series of crustal terranes that were successively accreted to the southern margin of Eurasia attending the transition of the Palaeo- to Neo-Tethys. We present the first detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotope geochemistry of three Cretaceous plutons (Kalaqigu, Aranbaotai, and Hongqilapu) from this area. SHRIMP zircon U–Pb dating shows that the three plutons were emplaced in the Early Cretaceous. The 114 Ma Kalaqigu pluton is composed of strongly peraluminous high-K calc-alkaline monzogranite and granodiorite. These rocks consist of plagioclase, K-feldspar, quartz, and biotite, and show variable Sr–Nd and Hf (in situzircon) isotopic compositions [87Sr/86Sr (T) = 0.7098–0.7157, ϵNd(T) = –8.1 to –15.6, and ϵHf(T) = –10.2 to –19.8 (mean –14.8)]. Elemental and isotopic data suggest that the granitoids were generated by partial melting of metasedimentary basement in the normal to thickened lower-crust triggered by underplating or injection of hot mantle-derived magmas in a continental arc setting. The 110 Ma Aranbaotai pluton consists of strongly peraluminous high-K calc-alkaline two-mica monzogranites. These rocks are composed of K-feldspar, plagioclase, quartz, biotite, and muscovite, and also show variable Sr–Nd and Hf (in situzircon) isotopic compositions [87Sr/86Sr (T) = 0.7075–0.7144, ϵNd(T) = –9.4 to –13.3, and ϵHf(T) = –5.4 to –16.4 (mean –10.0)]. Elemental and isotopic data suggest that the granites were formed by partial melting of subducted sediments at a depths of <40 km to ∼40–50 km in the collision (overthrust) zone during continental collision. The 102 Ma Hongqilapu pluton consists of metaluminous high-K calc-alkaline granodiorites. These rocks are composed of plagioclase + K-feldspar + quartz + amphibole + biotite ± clinopyroxene, and show uniform Sr–Nd and Hf (in situzircon) isotopic compositions [87Sr/86Sr (T) = 0.7078, ϵNd(T) = –7.6 to –8.0, and ϵHf(T) = –7.2 to –11.2 (mean –9.4)]. Elemental and isotopic data suggest that the granitoids were generated by crystal fractionation of basaltic magmas in a continental arc setting. Our new data suggest that at 114 Ma, the Karakorum terrane was still an active continental arc fuelled by the northword slab subduction of the Mesozoic Tethys; collision of the Kohistan terrane with the Karakorum terrane most likely occurred at 110 Ma, resulting in the closure of the Mesozoic Tethys; since 102 Ma, the southern Karakorum terrane hosted to a new continental arc coupled with the northward slab subduction of the Neo-Tethys. [ABSTRACT FROM PUBLISHER]

The Jiangnan Orogen is located at a key tectonic position along the junction between the Yangtze and Cathaysia blocks. We obtained detailed major and trace elements, whole-rock Nd + zircon Hf isotope data, and U–Pb age data from several Mesozoic granites, including the Fuling (FL), Taiping–Huangshan (TH), Lingshan (LS), Sanqingshan (SQS), and Baijuhuajian intrusions in order to investigate their sources and petrogeneses related to extension in South China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon from the FL, TH, SQS, and LS bodies yield Early Cretaceous ages of 124–135 Ma. These plutons are alkali-feldspar granites to syenogranites–monzogranites, and show A-type affinities. They have high K2O and total alkali contents, and are enriched in rare earth elements (except for Eu), Zr, and other high-field-strength elements as well as high Ga/Al ratios, and are depleted in Ba and Sr. These granites are metaluminous to weakly peraluminous (ACNK from 0.81 to 1.27). The whole-rockϵNd(T) values of −5.34 to −0.96 are coupled with zirconϵHf(T) values (from −5.3 to +4.24), and all samples plot along the mantle array. Field observations, geochronology, geochemistry, Nd isotopic, and zircon Hf isotopic compositions suggest that they formed by the partial melting of Mesoproterozoic metamorphic basement, with input from juvenile, mantle-derived materials in the shallow (<30 km) crust at high temperatures (756–965°C). These melts underwent crystal fractionation of biotite, plagioclase, and K-feldspar. The upwelling of asthenosphere triggered partial melting of the metamorphic protolith in a back-arc or intra-arc rift setting, reflecting rollback of the Pacific plate. Our research adds new geochronologic constraints on Cretaceous (135–120 Ma) A-type granites from the NE sector of the Jiangnan Orogen. Combined with previous research, we suggest that three main episodes of late Mesozoic extensional tectonism took place in South China: (1) 190–170 Ma (mainly inland), (2) 165–120 Ma (including 165–150 Ma in SE Shi-Hang, 135–120 Ma in NE Shi-Hang, and ∼125 Ma in the Lower Yangtze River Belt), and (3) 100–90 Ma (coastal area), showing an oceanwards younging trend due to the subduction of the Palaeo-Pacific plate. [ABSTRACT FROM AUTHOR]

The western Kunlun orogen occupies a key position along the tectonic junction between the Pan-Asian and Tethyan domains, reflecting Proto- and Palaeo-Tethys subduction and terrane collision during early Palaeozoic to early Mesozoic time. We present the first detailed zircon U–Pb chronology, major and trace element, and Sr–Nd–O–Hf isotope geochemistry of the Qiukesu pluton and its microgranular enclaves from this multiple orogenic belt. SHRIMP zircon U–Pb dating shows that the Qiukesu pluton was emplaced in the early Silurian (ca. 435 Ma). It consists of weakly peraluminous high-K calc-alkaline monzogranite and syenogranite, with initial87Sr/86Sr ratios of 0.7131–0.7229, ϵNd(T) of –4.1 to –5.7, δ18O of 8.0–10.8‰, and ϵHf(T) (in situzircon) of –4.9. Elemental and isotopic data suggest that the granites formed by partial melting of lower-crustal granulitized metasedimentary-igneous Precambrian basement triggered by underplating of coeval mantle-derived enclave-forming intermediate magmas. Fractional crystallization of these purely crustal melts may explain the more felsic end-member granitic rocks, whereas such crustal melts plus additional input from coeval enclave-forming intermediate magma could account for the less felsic granites. The enclaves are intermediate (SiO257.6–62.2 wt.%) with high K2O (1.8–3.6 wt.%). They have initial87Sr/86Sr ratios of 0.7132–0.7226, ϵNd(T) of –5.0 to –6.0, δ18O of 6.9–9.9‰, and ϵHf(T) (in situzircon) of –8.1. We interpret the enclave magmas as having been derived by partial melting of subduction-modified mantle in the P–T transition zone between the spinel and spinel-garnet stability fields. Our new data suggest that subduction of the Proto-Tethyan oceanic crust was continuous to the early Silurian (ca. 435 Ma); the final closure of the Proto-Tethys occurred in the middle Silurian. [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]

The origin of microgranitoid enclaves in granitic plutons has long been debated (hybrid magma blobs vs. refractory restites or cognate fragments). This article presents detailed petrography, SHRIMP zircon U–Pb chronology, bulk-rock major and trace element analyses, and Sr–Nd isotope and in situ zircon Hf isotopic geochemistry for microgranitoid enclaves within two Late Triassic granitic plutons in the Qinling orogen. Zircon U–Pb dating shows that the enclaves formed during the Carnian (222.5 ± 2.1 to 220.7 ± 1.9 Ma) coeval with their host granitoids (220.0 ± 2.0 to 218.7 ± 2.4 Ma). Field and petrological observations (e.g. double enclaves, xenocrysts, acicular apatite, and poikilitic K-feldspar or quartz) suggest that the enclaves are globules of a mantle-derived more mafic magma that was injected into and mingled with the host magma. The enclaves are mainly ultrapotassic, distinct from the host granitoids that have high-K calc-alkaline bulk-rock compositions. Although the enclaves have closely similar bulk-rock Sr–Nd isotope [initial 87Sr/86Sr = 0.7046–0.7056, ϵNd (T) = –0.3 to –5.0] and in situ zircon Hf isotope [ϵHf (T) = –1.5 to +2.9] ratios as the granitoids [initial 87Sr/86Sr = 0.7042–0.7059, ϵNd (T) = –0.6 to –6.3, ϵHf (T) = –2.2 to +1.6], chemical relationships including very different bulk-rock compositions at a given SiO2 content lead us to interpret the isotopic similarities as reflecting similar but separate isotopic source rocks. Detailed elemental and isotopic data suggest that the enclaves and the host granitoids were emplaced in a continental arc environment coupled with northward subduction of the Palaeo-Tethyan oceanic crust. Partial melting of subducted sediments triggered by dehydration of the underlying igneous oceanic crust, with melts interacting with the overlying mantle wedge, formed high-K calc-alkaline granitic magmas, whereas partial melting of diapiric phlogopite-pyroxenites, solidified products of the same subducting sediment-derived melts, generated ultrapotassic magmas of the microgranitoid enclaves. Our new data further confirm that in the Late Triassic time the Qinling terrane was an active continental margin rather than a post-collisional regime, giving new insights into the tectonic evolution of this orogen. [ABSTRACT FROM AUTHOR]

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: 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]

Two suites of granitoids, the Late Jurassic (158 ± 3 Ma) Linglong suite and the Early Cretaceous (130-126 Ma) Guojialing suite, crop out in the northwestern Jiaodong Peninsula, eastern China. The Linglong suite is a monzogranite, comprising alkali feldspar, plagioclase, quartz and Ferich biotite. The Guojialing suite includes at least five plutonic bodies of both granodiorite and monzogranite. The rocks are composed of plagioclase, alkali feldspar, quartz, Mg-rich amphibole and Mg-rich biotite. Both the Linglong and Guojialing suites have adakitic affinity. They are enriched in LREE with high La/Yb ratios and show positive Eu anomalies. The rocks are also enriched in LILE and depleted in HFSE with high Sr/Y ratios. The Linglong granite shows very uniform Sr--Nd isotopic compositions with initial 87Sr/86Sr ratios of 0.7119-0.7126 and εNd (T) values of -21.3 to -21.6, which are similar to those of the local Neoarchaean basement. The Guojialing suite has variable initial 87Sr/86Sr ratios (0.7108-0.7120) and εNd (T) values (-10.8 to -17.2), which are distinct both from those of the Neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area. Detailed petrological and geochemical data indicate that the Linglong suite was derived by partial melting of Neoarchaean metamorphic lower-crustal rocks at depth of > 50 km with a eclogite residue, whereas the Guojialing suite was formed by the reaction of delaminated eclogitic crust-derived melt with the upwelling asthenospheric mantle. The petrogenesis of these two contrasting adakitic granitoids suggests intensive lower-crustal delamination during Early Cretaceous times, following a crustal thickening process from the late stage of the Early Jurassic to early stage of the Late Jurassic with crustal thickness of < 32 km to > 50 km, respectively. [ABSTRACT FROM AUTHOR]

Abstract: SHRIMP zircon U–Pb dating, mineral chemical, element geochemical and Sr–Nd–Pb–Hf isotopic data have been determined for the Yulong monzogranite-porphyry in the eastern Tibet, China. The Yulong porphyry was emplaced into Triassic strata at about 39 Ma. The rocks are weakly peraluminous and show shoshonitic affinity, i.e., alkalis-rich, high K2O contents with high K2O/Na2O ratios, enrichment in LREE and LILE. They also show some affinities with the adakite, e.g., high SiO2 and Al2O3, and low MgO contents, depleted in Y and Yb, and enrichment in Sr with high Sr/Y and La/Yb ratios, and no Eu anomalies. The Yulong porphyry has radiogenic 87Sr/ 86Sr (0.7063–0.7070) and unradiogenic 143Nd/ 144Nd (ε Nd =−2.0 to −3.0) ratios. The Pb isotopic compositions of feldspar phenocrysts separated from the Yulong porphyry show a narrow range of 206Pb/ 204Pb ratios (18.71–18.82) and unusually radiogenic 207Pb/ 204Pb (15.65–15.67) and 208Pb/ 204Pb (38.87–39.00) ratios. In situ Hf isotopic composition of zircons that have been SHRIMP U–Pb dated is characterized by clearly positive initial ε Hf values, ranging from +3.1 to +5.9, most between +4 and +5. Phenocryst clinopyroxene geothermometry of the Yulong porphyry indicates that the primary magmas had anomalously high temperature (>1200 °C). The source depth for the Yulong porphyry is at least 100 km inferred by the metasomatic volatile phase (phlogopite–carbonate) relations. Detailed geochemical and Sr–Nd–Pb–Hf isotopic compositions not only rule out fractional crystallization or assimilation-fractional crystallization processes, but also deny the possibility of partial melting of subducted oceanic crust or basaltic lower crust. Instead, low degree (1–5%) partial melting of a metasomatized lithosphere (phlogopite–garnet clinopyroxenite) is compatible with the data. This example gives a case study that granite can be derived directly by partial melting of an enriched lithospheric mantle, which is important to understand the source and origin of diverse granites. [Copyright &y& Elsevier]

The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U-Pb dating, and Sr-Nd-Hf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2 Myrs. The stratigraphically oldest rhyodacite yielded a zircon U-Pb age of 135 ± 1 Ma and the overlying rhyodacitic porphyry has an age of 135 ± 1 Ma. Three porphyritic lava samples yielded zircon U-Pb ages of 136 ± 1 Ma, 132 ± 1 Ma, and 135 ± 1 Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U-Pb ages of 137 ± 1 Ma and 137 ± 1 Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U-Pb age of 136 ± 1 Ma. All these newly obtained precise U-Pb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr-Nd-Hf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ε(T) value higher than the other rocks, may indicate involvement of a subordinate younger mantle-derived magma in its origin. Geochemical data indicate that the various rocks show variable REE patterns and negative anomalies of Ba, Nb, Sr, P, Eu and Ti in the trace element spidergrams, suggesting that these rocks may have undergone advanced fractional crystallization with separation of plagioclase, K-feldspar and accessory minerals such as allanite. We suggest that this Cretaceous volcanic-intrusive complex formed in an extensional environment, and the formation of the Xiangshan mafic microgranular enclaves can be explained by the injection of mafic magma from a deeper seated mantle magma chamber into a hypabyssal felsic magma chamber at the crustal emplacement levels. [ABSTRACT FROM AUTHOR]

Mafic microgranular enclaves (MMEs) are common in the monzogranites from the Yangba pluton in the Bikou Terrane of central China. Zircon LA-ICP-MS U–Pb dating yields ages of 208.7 ± 0.7 Ma and 209.3 ± 0.9 Ma for the host monzogranites, and 211.9 ± 0.8 Ma for the MMEs, indicating formation from coeval magmas. The field occurrence and textures including spheroidal shapes, transitional contacts, igneous mineral assemblages, acicular apatites, and oscillatory zoning with repeated resorption surfaces in plagioclase, indicate that the MMEs crystallized from mafic magma that was injected into and mingled with the host felsic magma. The host monzogranites are intermediate-felsic, metaluminous, and lack typical peraluminous minerals or alkaline mafic minerals, suggesting their I-type affinity. The monzogranites display depletion in high field strength elements, with Nb and Ta anomalies, and enrichment in large ion lithophile elements and light rare earth elements (LREE), with slightly negative Eu anomalies (Eu/Eu ∗ = 0.72–0.93). The MMEs from the Yangba pluton are intermediate, metaluminous, and have higher K 2 O, Al 2 O 3 , Fe 2 O 3 T , MgO, Ni, and Cr contents than the pluton. The MMEs also display much higher total rare earth element (REE) concentrations and REE patterns that are sub-parallel to those of the host rocks, enrichments in Rb, Th, U, K, and LREE, and depletions in Ba, Nb, Ta, and Ti. These features are similar to those of the host rocks, indicating crust–mantle interaction during their petrogenesis. Zircons from the MMEs have highly variable ε Hf ( t ) values (−5.5 to +8.7) with corresponding two-stage Hf model ages ( T DM2 ) of 1.14 to 1.42 Ga, indicating they were derived from depleted mantle with crustal contamination. In contrast, zircons from host monzogranite show ε Hf ( t ) values ranging from −1.7 to +2.7, with T DM2 of 1.13 to 1.21 Ga, corresponding to that of the basement rocks in the Bikou Terrane, which indicates that these granitic magmas were probably derived from the Neoproterozoic juvenile lower crust with minor contribution of Mesoproterozoic ancient lower crust. The integrated petrology and elemental and isotopic geochemistry suggest that the MMEs and host monzogranites were generated by the interaction of a granitic magma and a mafic magma in the lower crust. We envisage that Neoproterozoic subcontinental lithosphere mantle-derived mafic magma intruded the lower continental crust during Late Triassic, following the Late Permian to Early Triassic collision between the South China and North China Blocks. [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 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]

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]