Geochronology, geochemistry, and associated tectonics of Permian-Triassic magmas in NW Truong Son Fold Belt

Research was conducted on plutonic rocks, previously referred to as the Hai Van granitic rocks, distributed in Da Nang and Quang Nam provinces in Central Vietnam. The granitic rocks in Da Nang Province have low magnetic susceptibilities and have geochemical signatures typical of S-type. Additionally, a negative Eu anomaly suggests that the source rock is an organic matter-bearing sedimentary rock. The granitic rocks were likely formed during the collision between the Indochina and South China blocks. In contrast, plutonic rocks in Quang Nam Province have high magnetic susceptibilities and have geochemical signatures of I-type. No Eu anomaly was observed, and they are adakitic rocks in nature. Based on these findings, the plutonic rocks in Quang Nam Province are distinctly different from the Hai Van granitic rocks in Da Nang Province, but they are Van Canh plutonic rocks. The Hai Van granitic rocks in Da Nang Province and the Van Canh plutonic rocks in Quang Nam Province are located in the Truong Son Fold Belt. The Van Canh plutonic rocks are located farther away from the Song Ma Suture Zone than the Hai Van granitic rocks. The Van Canh plutonic rocks were generated due to the subduction of the hot Song Ma Ocean beneath the Indochina Block. The Hai Van granitic rocks are understood to have been generated in a compressional field where the Song Ma Ocean was pushing against the Indochina Block; however, the Van Canh plutonic rocks are supposed to have been generated in an extensional field, like in a back-arc-like environment generated by the subduction of the Song Ma Ocean beneath the Indochina Block.

Propagation tectonics and multiple accretionary processes of the Qinling Orogen

<p>Early Mesozoic development of Southeast Asia involved oceanic subduction, closure, accretion and collision of discrete terranes rifted from Gondwana. South China, as an important continental terrane, is bound to the north by the Qinling-Dabie collisional orogenic belt, to the south by the Indochina Block, and to the east by the Pacific Plate. The role of continental collision and subduction during the Early Mesozoic development of South China has sparked the interest of geologists worldwide and stimulated considerable research. The Triassic tectonic history of the southwestern South China Block is marked by the Indosinian orogeny that records amalgamation of the Indochina and South China blocks during the late Permian to Triassic as a result of closure of the eastern branch of the Paleo-Tethys Ocean. In South China, there is widespread granitic magmatism, metamorphism and deformation. The closure of eastern Paleo-Tethys Ocean and subsequent collision between the South China block and Indochina Block has caused the collision zone metamorphism and formation of granites during the Permo-Triassic, with the Song Ma fault zone as the collision boundary. The Indosinian magmatism in the Pingxiang region was the magmatic products in this period. We report the new results of bulk-rock major and trace element, Nd, Hf isotopic compositions and zircon U–Pb dating of granites and rhyolites in the Pingxiang region in Guangxi Province, Southwest China, to decipher their petrogenesis and tectonic settings. The granites and rhyolitics in the Pingxiang area have low Mg<sup>#</sup> values (11.1–36.7), low Nb/Ta ratios (9.26–13.74) exhibiting a both affinity from S-type to I-type granaite. The isotopic features of these rocks show negative ε<sub>Hf</sub>(t) with the values ranging from -9.89 to -6.09, negative ε<sub>Nd</sub>(t) values ranging from -12.89 to -12.02 and T<sub>2DM</sub> values of 1.8–3.3 Ga, suggesting that the Pingxiang granites and rhyolites was derived from partial melting of paleoproterozoic crust rocks. The granites yielded <sup>206</sup>Pb/<sup>238</sup>U ages ranging from 243 to 241 Ma, and the rhyolites yielded <sup>206</sup>Pb/<sup>238</sup>U ages ranging from 247 to 245 Ma, which are both within the age range of the subduction to collision. Combine the regional geology, we suggest these granitoids and rhyolites were formed by the partial melting of crustal rocks during a transition from subduction to post-collisional environment with closure of Paleo-Tethys Ocean between the South China block and Indochina Block.</p><p>This study was financially supported by Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).</p>

Petrogenesis of ca. 830 Ma Lushan bimodal volcanic rocks at the southeastern margin of the Yangtze Block, South China: Implications for asthenospheric upwelling and reworking of juvenile crust

Early Paleozoic tectonic evolution of the South China Block: Constraints from geochemistry and geochronology of granitoids in Hunan Province

Revisiting the high temperature Darongshan-Shiwandashan granitoids in the South China: A response to slab tearing associated with diachronous collision between Indochina and South China blocks

Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

Southeast Asia consists of several microcontinents that detached from the northeastern margin of Gondwanaland. The Song Ma belt in northern Vietnam consists of ophiolite, metabasite, metasedimentary rocks and eclogite, and it is thought to be a suture zone between the Indochina and South China blocks. However, the nature and boundaries of the Song Ma belt and the collision age of the two blocks have long been debated. In this article, petrological and geochemical studies on the Song Ma ophiolite and eclogite and first sensitive high‐resolution ion microprobe (SHRIMP) age dating of eclogite provide new light to resolve such debate. Eclogite consisting of garnet, omphacite, phengite, quartz, barroisite and rutile is closely associated with garnet–phengite–quartz schist in the ‘Nam Co antiform’, a northern subunit of the Song Ma belt. The eclogite experienced a three‐stage metamorphic evolution: (I) pre‐eclogite stage (amphibolite facies) defined by inclusions of taramite, barroisite, quartz, zoisite/epidote, mica, rutile & rare chlorite in garnet, (II) eclogite stage and (III) retrograde stage of amphibolite to greenschist facies. The P–T conditions of the three stages are of 14–16 kbar and 520–550 °C (I), 24–27 kbar and 650–750 °C (II), and 3–7 kbar and 430–510 °C (III), and show a clockwise P–T path based on their mineral assemblages and stability fields in the P–T pseudosection. Thermobarometric results yield similar peak pressure and temperature (26–28 kbar and 650–710 °C). These data suggest that the Song Ma eclogite underwent high‐pressure metamorphism in subduction zone with a low thermal gradient ∼8 °C km−1. The Song Ma ophiolite is composed of serpentinized peridotite, gabbro, basalt, mafic dyke and chert, and experienced ocean‐floor metamorphism. Metabasalt and gabbro of ophiolite suite and eclogite all have MORB‐type geochemical affinities. Zircon separates from eclogite have very low Th/U ratios of 0.01–0.05, indicating a metamorphic origin. SHRIMP U–Pb isotopic analyses of this zircon yield a 206Pb/238U weighted mean age of 230.5 ± 8.2 Ma. This age is interpreted as the closure age of the Paleotethys Ocean that separated the South China and Indochina blocks, and the subsequent collision of the two blocks that took place at the Middle Triassic corresponding to the major episode of the Indosinian Orogeny.

Early Paleozoic intracontinental felsic magmatism in the South China Block: Petrogenesis and geodynamics

U–Pb zircon geochronology and geochemistry from NE Vietnam: A ‘tectonically disputed’ territory between the Indochina and South China blocks

Petrogenesis of the early Paleozoic strongly peraluminous granites in the Western South China Block and its tectonic implications

Crustal formation in the Nanling Range, South China Block: Hf isotope evidence of zircons from Phanerozoic granitoids

Origin of the Heping granodiorite pluton: Implications for syn-convergent extension and asthenosphere upwelling accompanying the early Paleozoic orogeny in South China

Large granitoid complexes within the continental crust are believed to be closely linked to mantle-derived magmas based on field observations and isotopic studies. However, details on the contribution of mantle-derived magmas in the generation of felsic magmas deep in the lower to middle crust, especially the interaction between the mantle-derived mafic magmas and the generated felsic melts, are not well constrained by petrological and mineralogical studies. Here we present a detailed study of an early Paleozoic monzonorite–granite suite from the South China Block and comparison with the other coeval magmatic rocks (~22,000km2) in the region, to provide more details on the underplating/intraplating of mantle-derived magmas and the generation of felsic magmas in intracontinental settings. It is shown that the monzonorite has signatures of both mantle-derived magmas (substantial contents of MgO, Cr, and Ni; presence of olivine and orthopyroxene) and crust-derived magmas (substantial contents of SiO2, K2O, Rb, Ba, and light rare-earth elements; presence of K-feldspar, quartz and low-calcium plagioclase). Interestingly, the monzonorite, granite and the mafic microgranular enclaves (MME) are remarkably uniform in Sr–Nd–Hf isotopic compositions, with high initial 87Sr/86Sr ratios (0.7081–0.7098), low eNd (t) values (−6.8 to −6.3) and low zircon eHf (t) values (−8.0 to −7.4). An integrated study of petrological, mineralogical, and geochemical data of the monzonorite–granite suite and coeval magmatic rocks from the same region makes it clear that the input of crustal components is essential to explain the unusual signatures of the monzonorite. Petrogenetic modelling and isotopic compositions suggest that the contribution of mantle-derived mafic magmas in the generation of crust-derived felsic magmas is represented by heat input and minor mass input, and in the meantime, we prefer to explain the unusual geochemical signatures of the monzonorite by selective contamination of crust-derived felsic melts.

Linking ocean subduction with early Paleozoic intracontinental orogeny in South China: Insights from the Xiaying complex in eastern Guangxi Province