Search

Outcrops of early Palaeozoic mafic rocks are limited in the South China Block (SCB), which become a barrier to unlock the related tectonic evolutionary history. We present a new report of early Palaeozoic Pengxi hornblendite at Xiajiang County, Jiangxi Province, in this paper. The Pengxi hornblendite has a concordant zircon U–Pb age of 433 ± 2 Ma (40 grains) which could represent its formation time. It is characterized by high MgO content (16.8–19.6 wt.%) and Mg# (78–80), compatible elements concentration (Ni = 280–506 ppm, Cr = 1,580–1,780 ppm), and evident depletions of Nb, Ta, and Ti which are similar to the arc‐related magmatism. Combining with the enriched Nd (εNd(t) = −5.3 to −7.8) isotopic feature, we suggest that the hornblendite was derived from partial melting of metasomatized subcontinental lithospheric mantle (SCLM). The lack of other field geological evidences in the study and adjacent areas, such as volcanic rocks, pyroclastic sedimentary rocks, and turbidites, did not support the contemporaneous subduction model. The study area is located near the boundary of the Yangtze and Cathaysia blocks which was a Neoproterozoic subduction belt characterized by ophiolites, volcanic rocks, and turbidites. Mafic rocks formed at different periods (e.g., 800, 500, and 430 Ma) in the SCB have similar enriched Nd isotopic compositions and La/Nb ratios which suggest that the Silurian hornblendite with arc‐like geochemical features may not be the result of contemporaneous subduction but likely inherited from the Neoproterozoic subduction. During Silurian post‐orogenic collapse event, the partial melting of enriched SCLM generated the Pengxi hornblendite. This work can provide new data to the further discussion of the controversies in the tectonic background of the SCB. [ABSTRACT FROM AUTHOR]

The Banjing tungsten deposit, which has been discovered recently, is located in the northernmost part of the Dabu pluton, southern Jiangxi Province, China. In this study, zircon LA‐ICP‐MS U–Pb dating of the fine‐grained porphyritic biotite granite indicate that it was formed in the early Yanshanian (159.4 ± 2.5 Ma–161.6 ± 0.8 Ma). Whole‐rock geochemical studies have shown the fine‐grained porphyritic biotite granite has SiO2 of 75.82%–76.84%, Al2O3 12.50%–12.87%, MgO 0.07%–0.20%, and CaO 0.64%–1.09%, with A/CNK of 1.017–1.038. It has a total rare earth elements content of 93.9–118.9 ppm with strong negative Eu anomalies (δEu = 0.021–0.081). The biotite granite is enriched in Rb, Th, U, Nd and depleted in Ba, Sr, Nb, Ti. These data suggest the Dabu pluton belongs to S‐type granite. This pluton has ISr of 0.71212–0.72929 and εNd(t) from −9.60 to −10.62 with Nd model ages concentrated in 1732–1838 Ma. These isotopic data in combination with zircon Hf isotopes suggest the biotite granite originated from partial melting of the Middle Proterozoic metamorphic supracrustal rocks in South China, with a minor contribution from juvenile crust. Meanwhile, this study has obtained Re–Os isochron ages of the intrusion‐related and quartz vein‐type molybdenum mineralization are 156.3 ± 2.7 Ma and 157.0 ± 1.1 Ma in the Banjing tungsten deposit, respectively. Sericite from the greisen‐type tungsten‐molybdenum ore has an 40Ar–39Ar plateau age of 156.4 ± 1.0 Ma, interpreted as the formation age of this deposit. Collectively, the Banjing tungsten deposit is considered as a product of the early Yanshanian large‐scale peak mineralization in South China, which was formed in an extensional intracontinental environment caused by the subduction of the Palaeo‐Pacific Plate. [ABSTRACT FROM AUTHOR]

The southern Jiangxi Province is an important part of the fluorite mineralization belt in South China. Fluorite ore bodies are primarily in the contact zone between the Devonian Huitong granitic complex and the Late Cretaceous Ganzhou Formation, controlled by the NE‐trending faults. Zircon U–Pb dating of the Huitong granitic complex yields emplacement ages of 410.7 ± 1.4 Ma and 400.7 ± 4.6 Ma, while the Sm–Nd dating of the fluorite yields an isochron age of 94 ± 2 Ma, suggesting that the Huitong granitic complex is the host rock. Fluid inclusions in the fluorite show low homogenization temperatures (136–207°C), salinities (1.23–3.87 wt% NaCl), and densities (0.87–0.95 g/cm3), suggesting that the ore‐forming fluid is an NaCl‐H2O system of low temperature, salinity, and density. Raman spectroscopy showed that the fluid phase is dominated by water. The δDVSMOW values of the fluid inclusions in the Tongda fluorite ranged between −59.5 and −55.2‰, while the δ18OVSMOW values of the fluorite ranged from −7.2 to −5.6‰. Collectively, the ore‐forming fluid is dominated by meteoric water, possibly with a minor contribution of hydrothermal fluid. Both the interaction with host rocks and the cooling of hydrothermal fluids are the likely mechanisms of underlaying fluorite precipitation at low temperatures. The mineralization occurred in extensional faults during the Late Cretaceous related to the subduction of the Palaeo‐Pacific Oceanic Plate. [ABSTRACT FROM AUTHOR]

The Permian–Triassic mass extinction (PTME), the most devastating extinction event in Phanerozoic history, has witnessed the demise of almost 80% of marine gastropod genera. Despite the vast scale of the extinction event, the recovery of some groups of marine gastropods has been curiously fast, contrasting with the delayed recovery of many other marine clades. Understanding the rapid recovery of gastropods after the PTME represents a major palaeobiological conundrum, since oxygen‐dependent taxa are expected to have been severely impacted by anoxic oceanic conditions of the PTME. The controversial microbialite refuge hypothesis has been proposed as a potential explanation of this pattern, arguing that marine invertebrates were associated with oxygen‐producing microbial mats during the PTME, which provided a suitable microhabitat for survival within hostile anoxic conditions. To better understand the dynamics of gastropod recovery after the PTME, we studied a gastropod fauna collected from the basal Daye Formation (earliest Triassic) at the Yangou section in Leping County, Jiangxi Province, south China, allowing us to capture a snapshot of the marine fauna immediately after the PTME. Altogether, 13 microgastropod species belonging to 12 genera were recorded, representing the most diverse Induan (earliest Triassic) gastropod fauna in the world known to date. The fact that the Yangou assemblage, along with the second most diverse Griesbachian gastropod fauna from the Wadi Wasit section in Oman, is not associated with microbial buildups implies that microbial mats probably did not play a key role as refuges for marine invertebrates during the PTME. On the other hand, the Yangou fauna suggests that non‐anoxic shallow lagoon systems were more likely to have acted as refuges for marine invertebrates during the PTME. [ABSTRACT FROM AUTHOR]