Indosinian Magmatism Research Articles

Indosinian magmatism in NE Vietnam: Petrogenesis and geodynamic implications of Triassic mafic suites from the Song Hien region

The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and SrNd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and SrNd isotopic compositions ((La/Yb)CN = 0.4–4.6; Dy/Dy⁎ = 0.7–1.3; (87Sr/86Sr)i = 0.7053–0.7125; εNd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and SrNd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic syn-collisional magmatism has an important metallogenic context, controlling NiCu sulfide and Sn(Cu) mineralizations.

Middle to Late Triassic felsic and mafic magmatism in the eastern West Qinling Orogen, Central China: A record of the Paleo-Tethyan oceanic crust advance to retreat

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 UPb 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.

Indosinian magmatism and mineralization in the Banjiaoyuan tin deposit, middle Nanling Range, South China: Constraints from zircon and cassiterite U-Pb ages, geochemistry and Sr-Nd-Hf isotopic compositions

Indosinian W-Sn metallogeny associated with granites in South China has been reported in recent years by many researchers. However, the refined genetic relations between these deposits and the related granites remain unclear in most areas, and the tectonic setting of Indosinian magmatism and W-Sn mineralization are still widely controversial. The Banjiaoyuan tin deposit is located in the east vicinity of Yangmingshan pluton in the middle Nanling Range, South China. The granitic stocks in this deposit comprise two intrusive episodes, i.e., the first episode of medium-coarse-grained porphyritic tourmaline-biotite monzogranite (G1), and the second episode of micron-fine-grained tourmaline-muscovite monzogranite (G2). LA-ICP-MS zircon U-Pb dating gives weighted ages of 226.9 ± 1.6 Ma to 223.8 ± 1.9 Ma for G1, and 224.3 ± 2.0 Ma for G2, respectively. LA-MC-ICP-MS cassiterite U-Pb dating yields Tera-Wasserburg concordia age of 216.7 ± 2.4 Ma for tin mineralization. These ages indicate that both the granitic magmatism and related mineralization were initiated in the late Indosinian period. All the granites have high SiO2, Al2O3, P2O5 contents, and low TFeO, CaO, MgO, TiO2 contents, indicating that the granites are highly differentiated S-type granites, and furthermore, the high DI and Rb, K, U, Hf, Sm, low SI and Ba, Sr, Ti, TREE further show that the granites have undergone high extent of differentiation and evolution. High Rb/Nb and K/Nb ratios, low Nb/Ta and Zr/Hf ratios, widely varying CaO/Na2O ratios, low and uniform εNd(t) values, and dominantly negative and relatively dispersed εHf(t) values jointly indicate that the granites were derived from a heterogeneous mixture of calcium-poor mudstone and calcium-rich psammite (or metamorphic igneous rocks) in the crust. The known Indosinian W-Sn deposits in South China are more closely related to S-type granites than to I-type granites, suggesting that their ore-forming materials are mainly derived from the crust. In addition, individual positive εHf(t) values indicate that a small amount of newborn crustal components were involved in the formation of granitic magma. Compared with G1, G2 differs distinctly in petrological, chemical and isotopic characteristics, especially it is more richer in F content and contains magmatic cassiterite and wolframite crystals, suggesting that G2 have undergone higher extent of differentiation and evolution, and are much more closely related to the Sn-W mineralization than G1. The late Indosinian granites in this deposit were formed in post-collisional extensional tectonic environment, while the early Indosinian granites intruded in the Yangmingshan area were formed in syn-collision compression environment. Based on the statistics, the metallogenic ages of Indosinian W-Sn deposits in South China are between 212 and 230 Ma, and the petrogenetic ages of related granites are between 211 and 230 Ma, both age groups belong to the late Indosinian period, representing a regional large-scale granitic magma intrusion and mineralization event that initiated in post-collisional extensional tectonic environment.

Inspiration of magma source and intrusion of Niukutou polymetallic ore area: evidence from audio frequency magnetotelluric(AMT)

Niukutou research area is located in the north slope of Qimantage mountain in the east Kunlun, which is an important part of the lead, zinc, copper and iron metallogenic belt. The regional mineralization is inseparable from Indosinian magmatism. However, the research area is covered by Quaternary stratum area and the trace of magmatic activity is difficult to find. In order to further understand the underground structure, the spatial distribution characteristics of magmatic rocks and the relationship with polymetallic mineralization of the research area, the audio-frequency magnetotelluric (AMT) survey is deployed. Through the comprehensive analysis based on the electrical structure, we found that the granites encountered in the research area are from the magma source corresponding to the deep F3 channel, the granites are occurred as the veins from multi-channels. There are no granites base in the profiles and the regional metallogeny are controlled by the magma activity and the fault F3.In geologic modeling process of groundwater system, block modeling needs to be established.

Late Triassic Magma Mixing and Fractional Crystallization in the Qingchengzi Orefield, Eastern Liaoning Province: Regional Petrogenetic and Metallogenic Implications

The Qingchengzi orefield is an important Pb-Zn-Au-Ag polymetallic orefield in NE China. The Indosinian magmatism has formed the Shuangdinggou batholith and the Xinling stock, as well as dikes of quartz monzonite porphyry and lamprophyre. According to petrographic characteristics, the Shuangdinggou intrusion can be divided into the main suite and the central suite. Zircon U-Pb dating yielded crystallization ages of 215.0–220.9 Ma for these various Qingchengzi magmatic units, which are within analytical error and represent coeval magmatism. The Shuangdinggou main suite contains abundant mafic microgranular enclaves (MMEs) and shows features of magma mixing. Geochemically, the major oxide contents of the MMEs and their quartz monzonite host show well-defined linear fractionation trends. The REE and trace element patterns of the MMEs and their host are similar, which demonstrates certain degree of geochemical homogenization between the two during magma mixing. The Shuangdinggou main suite shares similar geochemical characteristics with typical high Ba-Sr granites (Ba=1 082 ppm–2 051 ppm, Sr=803 ppm-886 ppm), and was likely originated from the mixing between a melt derived from partial melting of the thickened lower crust and the enriched mantle. The central suite was likely formed by fractional crystallization of the main-suite magma. The Xinling intrusion may represent a branch of the Shuangdinggou intrusion and has the same genesis as the central suite. The quartz monzonite porphyries geochemically mimic the Shuangdinggou main suite, and may also be an epioic facies of the Shuangdinggou intrusion. The MMEs and lamprophyres may have been derived from incomplete magma mixing. Formation of the Pb-Zn and Au-Ag deposits in the Qingchengzi orefield may have been related to the granite/quartz monzonite porphyries near the Shuangdinggou intrusion, which were formed by magma mixing and fractional crystallization.

Genesis of Middle Triassic high-Mg# quartz diorites from the Xiahe area, West Qinling Orogen, Central China, and their geodynamic implications

The West Qinling Orogen (WQO) features widespread Triassic granitic rocks, which are crucial to constrain the tectonic evolution of the WQO. Here, we conducted an integrated petrological, geochronological, geochemical, and Sr-Nd-Hf isotope study on quartz diorites and mafic microgranular enclaves (MMEs) from the Ren’ai and Daerzang plutons, Hezuo area, WQO. The quartz diorites and MMEs have crystallization ages between 244 and 241 Ma. The quartz diorites display intermediate SiO2, high Mg# values (62–66) and evolved S-Nd-Hf isotope compositions, indicating an origin from magma mixing process. The MMEs display mineral compositions similar to those of the host rocks, only with more mafic minerals. The The Ren’ai and Daerzang plutons were part of the early Indosinian magmatic belt mainly distributed in the western and middle parts of the northern WQO. In comparison, late Indosinian magmatic rocks are mainly exposed in the eastern WQO. The asymmetric distribution of Early Mesozoic magmatism in the WQO might have been caused by a specific subduction pattern of the A’nimaque-Mianlue oceanic crust. The western and middle WQO experienced a period of flat or low angle subduction in the early stage, followed by slab rollback of the oceanic crust, which accounted for the flare-up of early Indosinian magmatism in the northern WQO. However, the distribution of late Indosinian magmatism might have been caused by asymmetric crustal delamination in the WQO.

Geochemistry, zircon U–PB ages and HF isotopes of the Muong Luan granitoid pluton, Northwest Vietnam and its petrogenetic significance

AbstractThe Indosinian Orogeny plays a significant role in tectonic background and magmatic evolution in Indochina and surrounding regions. Being a part product of the Indosinian magmatism in northwest Vietnam during late Permian–middle Triassic period, Muong Luan granitoid pluton dominantly consists of granodiorite, less diorite and granite. This pluton is located in the Song Ma suture and assigned to the Dien Bien complex. Geochemically, the Muong Luan granitoid rocks are characterized by a wide range of SiO2 contents (59.9–75.1 wt%) and high K2O contents. They display typical features of I‐type granites. The presence of hornblende and no muscovite and cordierite in the rocks further supports for I‐type character of granitoids. The emplacement age of the Muong Luan pluton obtained by LA–ICP–MS U–Pb zircon is at 242–235 Ma, corresponding to Indosinian time. Zircon εHf values of –5.6 to –10.4, in combination with moderate Mg values of 34–45 suggested that the Muong Luan granitoid was derived from partial melting of mafic crustal source rocks, which are probably Paleoproterozoic in age as revealed by Hf model ages (TDM2 = 1624–1923 Ma).

Subduction-related middle Permian to early Triassic magmatism in central Hainan Island, South China

There was extensive Permian to Triassic magmatism in Hainan Island, southern part of the South China Block (SCB), which began earlier and exhibits different rock types and geochemical characteristics compared to the Indosinian magmatism in the hinterland of the SCB. Two stages of magmatism have been identified in central Hainan Island in this study. The first-stage magmatism (253–262Ma) is characterized by strongly deformed granites. These gneissic granites exhibit SiO2 (64.0–69.8wt%), MgO (0.97–1.60wt%), Fe2O3T (2.68–6.78wt%), A/CNK (most <1.1), zircon εHf(t) values (−2.08 to −0.41), the geochemical features of I-type granites. These early granites can be subdivided into high-REE and low-REE groups. Compared to the low-REE granites, the high-REE ones have higher K2O, Ba, K2O/Na2O, Gd/Yb and Th/Ta, low U, Rb/Ba, Nb/La and U/Pb. The low-REE granites show whole-rock εNd(t) (−4.33 to −3.96) and ISr (ca 0.7074), while the high-REE granites have lower εNd(t) (−7.34 to −6.33) and higher ISr (0.7096–0.7109). The gneissic granites probably derived from the partial melting of the Baoban Complex at different crustal levels. The second-stage magmatism (245–256Ma) is characterized by weakly deformed to massive gabbroic-dioritic rocks. They exhibit relatively low SiO2 (48.9–59.7wt%), high Fe2O3T (6.57–11.6wt%), total alkalies (Na2O+K2O) (3.91–7.35wt%), and variable MgO (2.74–7.05wt%), Ni (3.84–60.1ppm) and Cr (7.22–299ppm) concentrations. They also have low whole-rock εNd(t) values (−7.92 to −5.11) and high ISr (0.7083–0.7118), and a range of zircon εHf(t) values (−5.55 to −1.11), suggesting that their parental magmas were derived from heterogeneous enriched-mantle sources, and experienced AFC processes. The rock assemblages and their geochemical features indicate that both granites and gabbroic-dioritic rocks were formed in a back-arc extensional environment, which was probably related to the subduction of Paleo-Pacific oceanic plate. Hence, the Indosinian intracontinental orogeny in the hinterland of the SCB probably was triggered by this subduction in the southeast, rather than the collision between the SCB and the Indochina Block in the southwest.

Mineralogy and trace element geochemistry of the Co- and Cu-bearing sulfides from the Shilu Fe–Co–Cu ore district in Hainan Province of South China

Hosted within the metamorphosed, neritic siliciclastic rocks and sedimentary carbonates of the Proterozoic Shilu Group, the Shilu Fe–Co–Cu ore district in Hainan Province of South China comprises the upper Fe- and the lower Co–Cu ore layers. Combined with the field observation, the mineralogical and geochemical studies of sulfides using electron microprobe and laser ablation ICP-MS analyses recognized three types of Co–Cu ores. Type I is represented by massive ores and mainly comprises the first generation of pyrite (PyI) which occurred either as recrystallized, subhedral to euhedral microcrystal aggregates (PyIa) or as elongated, fine-grained euhedral grains (PyIb) with an orientated alignment parallel to S1 foliation. Type II is banded, disseminated and brecciated ores, and composed of the second generation of pyrite (PyII) which displays internal rhythmic growth zoning, the first generations of chalcopyrite (CcpI) and pyrrhotite (PoI), and associated Co–(Ni)–(As)–sulfide minerals. Type III occurring as veins or veinlets mainly consists of the third generation of pyrite (PyIII) and the second generations of chalcopyrite (CcpII) and pyrrhotite (PoII), of which PyIII appears as subhedral to euhedrall grains or as rims of composite pyrite. The moderate Co and As, and high Ni contents as well as the low Co/Ni ratios (∼2–5) in PyI indicate a sedimentary–metamorphic origin for Type I ores. The higher Co, Ni and As concentrations in PyIb relative to PyIa likely was related to an inhomogeneous deformation–metamorphism. The highest Co (av. 51,195ppm) in PyII and Ni (av. 3374ppm) in PoI most likely were linked to the preferred incorporation of Co into pyrite and Ni into pyrrhotite. Combined with the high Ag concentrations in CcpI (av. 266ppm) and PyII (av. 13.32ppm), the high Co/Ni ratios in PyII (av. 1241) suggest the derivation of Type II ores from a Co–Cu–Ni–Ag-rich hydrothermal fluid. Further, up to 9wt.% Co concentrations in PyII show a temperature condition of 310–400°C. In contrast, the depletion of trace elements in CcpII and PyIII, and the lower Co/Ni ratios (av. 46) in PyIII suggest a Co-poor but Cu-bearing hydrothermal fluid for origin of Type III ores. The complex texture and chemical composition of sulfides combined with previous work confirm a four-stage metallogenesis for the Shilu Co–Cu ores. From early to late, these include: (1) the ca. 1075–880Ma deposition of the primary Co–Cu ore source beds which most likely were derived from submarine, metalliferous hydrothermal fluids, (2) the syn-structural metamorphism which led to Type I ores due to the South China Caledonian Orogeny, (3) the first stage of hydrothermalism which produced Type II ores and most likely was associated with Indosinian magmatism, and (4) the second stage of hydrothermalism which yielded Type III ores and likely was related to Yanshanian magmatism. The first stage of hydrothermalism was considered to be significant for the Co–Cu enrichment. The Shilu Co–Cu ores thus are better attributed to a BIF origin, but greatly reworked and enriched by late structural deformation and hydrothermal activities.

Geochronology and geochemistry of the Late Triassic Longtan pluton in South China: termination of the crustal melting and Indosinian orogenesis

The Indosinian orogeny is recorded by Triassic angular unconformities in Vietnam and South China and by widely occurring granitoids in the Yunkai-Nanling and the Xuefengshan belts of South China. The Longtan pluton in the northwestern part of the Xuefengshan belt is a typical high-K, calc-alkaline, I-type granitoid, which can shed light on the relationship between the Indosinian tectonic and magmatic activity in the region. Three precise zircon U–Pb ages yielded a mean of 218 ± 0.8 Ma, which is taken as the age of crystallization. The pluton consists of both granodiorite (64.59–68.01 % SiO2 and 3.25–4.22 % K2O) and granite (70.49–71.80 % SiO2 and 4.07–4.70 % K2O). The granodiorites are characterized by relatively high Mg# (54–57), low contents of Na2O (3.2–4.3 wt%), low abundances of incompatible elements (LILE, Nb and P), high initial 87Sr/86Sr (0.7175–0.7184) and negative eNd(t) (−9.98 to −9.72). REE patterns show moderate fractionation ((La/Yb)cn = 8.07–18.80) with negative Eu anomalies (Eu/Eu* = 0.62–0.86). Compared with the granodiorite, the granite has a wider range of Mg# (49–59), lower contents of Na2O (2.8–4.2 wt%), higher initial 87Sr/86Sr (0.7232–0.7243) and more negative eNd(t) (−12.07 to −11.24) values. REE patterns are relatively flat ((La/Yb)cn = 14.73–29.37) with smaller negative Eu anomalies (Eu/Eu* = 0.48–0.63). The granodiorite has lower K2O/Na2O and Al2O3/(MgO + FeOTot) values than the granite. Based on major and trace element geochemistry and Sr–Nd isotopes, we interpret the Longtan granodioritic magma to have been derived by partial melting of interlayered Proterozoic metabasaltic to metatonalitic source rocks, whereas the granite was probably derived from a mixture of Proterozoic metagraywackes and metaigneous rocks. Field, petrographic and geochemical evidence indicate that partial melting and fractional crystallization were the dominant mechanism in the evolution of the pluton. The Longtan granodiorites and granites are petrologically and geochemically similar to typical Indosinian varieties and are considered to have been produced in a similar manner. The Indosinian granitoids in the region show a magmatic peak age of ~238 Ma from the Yunkai-Nanling belt in the southeast and a magmatic peak age of ~218 Ma of the Xuefengshan belt to the northwest. These early and late magmatic episodes of the Indosinian granitoids also display slight variations of regular compositions, eNd(t) values and T DM ages. Thus, we propose a syncollisional extension model that Indosinian granitoids were generated by decompressional partial melting of crustal materials triggered by two extensions during collision of the Indochina and South China blocks. The Longtan pluton in the northwesternmost part of the orogenic belt marks the termination of the Indosinian magmatism and orogenesis.

U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions of Early Indosinian intrusive rocks in West Qinling, central China: petrogenesis and tectonic implications

The Qinling–Dabie–Sulu orogenic belt is the junction between the North and South China blocks, which resulted from the final amalgamation of China continents during the Indosinian. Indosinian granitoids are widespread in the Qinling orogen, and their geneses can thus constrain the evolution of China continent. We carried out a combined U–Pb zircon dating and geochemical study for the Shuangpengxi granodiorite pluton and the Xiekeng diorite–granodiorite pluton in the middle part of the West Qinling orogen. U–Pb zircon dating shows that the magma crystallization ages of 242 ± 3 Ma for the Shuangpengxi pluton and ~244–242 Ma for the Xiekeng pluton. Geochemical and Sr–Nd–Hf isotopic compositions reveal that the magma of the Shuangpengxi granodiorite was derived from partial melting of crustal materials. The Xiekeng diorites can be divided into high-Al diorite and high-Mg diorite. Both of them resulted from partial melting of enriched lithospheric mantle, but their mantle source had been modified by previous slab-derived melt. The high-Al diorite was formed by fractional crystallization of olivine, pyroxene and/or preferential accumulation of plagioclase, and the high-Mg diorite was formed by fractional crystallization of olivine and/or preferential accumulation of pyroxene. The Xiekeng granodioritic porphyry was formed by mixing of crust-derived and mantle-derived melts. We propose that the Early Indosinian magmatism resulted from break-off of subducted oceanic slab after collision. The slab break-off model can well explain the linear distribution of the Early Indosinian plutons and rapid crustal uplift during the Middle Triassic in the West Qinling.

SHRIMP zircon U-Pb ages and tectonic implications for Indosinian granitoids of southern Zhuguangshan granitic composite, South China

The large southern Zhuguangshan granitic batholith composite consists of granites with ages varying from the Caledonian through Indosinian to Yanshanian. Based on K-Ar dating data, the ages of the major parts of this composite were previously regarded as Yanshanian. In this study, the SHRIMP zircon U-Pb dating method has been adopted for six plutons, Ledong, Longhuashan, Dawozi, Zhaidi, Baiyun and Jiangnan, in the southern Zhuguangshan composite, in which the four plutons other than Baiyun and Jiangnan were previously regarded as Yanshanian granites. Magmatic zircons from these six plutons, dated by this study, have yielded ages of 239±5 Ma (MSWD = 2.5), 239±5 Ma (MSWD = 2.5), 239±2 Ma (MSWD = 1.7), 239±4 Ma (MSWD = 3.2), 231±2 Ma (MSWD = 0.81) and 231±3 Ma (MSWD = 1.8), respectively. The results indicate that these plutons were formed by early Indosinian magmatism. Geochemical characteristics suggest that these granites were formed in an extensional tectonic environment. Therefore, the Indosinian period granites in the southern Zhuguangshan composite were formed by partial melting of the Paleo-Mesoproterozoic crustal components during the collapse of thickened lithosphere after the collision between the South China and Indosinian plates.

Characteristics and geodynamic evolution of Indosinian magmatism in South China: A case study of the Guikeng pluton

We examined the geochronology, petrology, and geochemistry of the two-stage Guikeng pluton, Wuyi Mountain Range, South China, with the aim of assessing the influence on Indosinian magmatism in South China of collision/amalgamation between the Sibumasu Block and the Indo-China and South China blocks, and between the North China and Yangtze blocks. An additional aim was to summarise the characteristics and geodynamic evolution of Indosinian magmatism in South China. The Guikeng pluton was then compared with the Indosinian Fucheng–Hongshan and Shiwandashan–Darongshan plutons in the Wuyi–Yunkai Mountain Range Belt, two groups of Indosinian granites in Hunan Province (South China Inland Belt), and Indosinian granitoids in the Sulu–South Korea Belt.The Guikeng pluton consists of medium- to fine-grained biotite monzogranites and biotite granites in its marginal belt, medium- to coarse-grained K-feldspar phenocryst-rich biotite granites in its interior part, and late-stage fine-grained muscovite granites. The granites have high Rb, Cs values, (87Sr/86Sr)i, and Rb/Sr ratios, low Sr, Ba, and εNd(t) values, and slightly to moderately negative Eu anomalies. These geochemical characteristics suggest that the granites were derived from late Paleo-proterozoic meta-sedimentary basement (1.7–2.0Ga).The rocks of the marginal belt and the main part of the pluton originated from two distinct magma sources. The fine-grained muscovite granites were produced by intensive differentiation of K-feldspar phenocryst-rich biotite granites. The granites from the marginal belt and the main part of the pluton yield SHRIMP U–Pb zircon ages of 234±3 and 220.4±3Ma, respectively, consistent with early and late Indosinian magmatism in South China. The early Indosinian metaluminous to weakly peraluminous foliated biotite granites were formed in a collision/compressional setting, whereas late Indosinian strongly peraluminous massive granites were formed in a post-collision setting.The rock assemblage, source region of Indosinian granites, and tectonic setting differ between South China and Sulu–South Korea, indicating the metamorphic basement of the Ogcheon Metamorphic Belt in North China is different to that of the Nanhua Rift in South China.

Tectonic setting discrimination and40Ar/39Ar isotope geochronology of the Miba granite

The Miba granite is located in the juncture of Kang County in eastern Gansu Province and Lueyang County in Shanxi Province. It is considered to be the post-orogenic granite (POG-type) by major element discrimination method of Maniar.40Ar/39Ar dating indicates that its emplacement time is about 240—230 Ma and it is the result of the Indo-Sinian magmatism. In the early Yanshan period (about 193.8 Ma), a thermal event resulted in the partial opening of the argon isotope system of the biotite.