The construction mechanism of the Neoproterozoic S-type Sanfang-Yuanbaoshan granitic plutons in the Jiangnan Orogenic Belt, South China: Insights from geological observation, geochronology, AMS and Bouguer gravity modeling

Abstract

The Neoproterozoic S-type granitic plutons, distributed along the suture zone of the Yangtze and Cathaysia blocks, play an important role in the tectonic evolution of the Jiangnan Orogeny.However, few researchers had focused on the scientific issues on the physical construction process of these plutons. Therefore, we carried out multidisciplinary approaches on the Sanfang and Yuanbaoshan plutons in the western Jiangan Orogenic Belt to figure out the construction mechanism of these plutons. Zircon Hf and U-Pb dating indicates that the magma, originated from the crustal partial melting, was crystallized at ca. 830 Ma. Field investigation shows that the plutons are dome shaped, and the bedding/foliation of the country rocks, the Sibao group, conform plutons boundaries and their inclinations gradually decrease away from the contact zone. A topto-the-E kinematic sense was observed in the eastern margin of Yuanbaoshan pluton. Both the textural analysis and AMS measurement reveal primary magmatic and secondary general top-tothe-W/NW post-solidus fabrics. The Bouguer gravity modeling reveals that the feeder zone probably locates in the southern part of each pluton and these two plutons are connected at depth.According to the primary magmatic fabric patterns, deep geometric shape as well as structural features of the country rocks, we propose that crustal partial melting magma probably intruded into the pre-existing mechanically weak (fold/fault) zone of the Sibao group, then lateral and upward accreted to construct the dome-shape plutons. The timing and mechanism of the postsolidus deformation are not well constrained, the interpretations are remain hypothetical.

Caledonian Tin Mineralization in the Jiuwandashan Area, Northern Guangxi, South China

“…The Yuanbaoshan granitic pluton is a N-S-trending, elliptically shaped batholith that intrudes the Yuxi Formation and yields an age of 838 ± 5 Ma [33]. In addition, there are five NW-SE-trending gabbroic dikes in the mining area, which are thought to be Neoproterozoic in age, although precise ages are not available for these rocks.…”

“…The granites in the Jiuwandashan area are mainly middle Neoproterozoic in age [20,22,[25][26][27][28]. After folding of the Neoproterozoic Sibao Group, magma was intruded along faults, which formed mafic-ultramafic intrusions and the Motianling, Yuanbaoshan, and other large granitic plutons in the Jiuwandashan area [33]. Previous studies have shown that Neoproterozoic subduction materials were reactivated and formed a series of mafic igneous rocks during late Mesozoic extension [42].…”

Neoproterozoic to Palaeozoic tectonic deformation history of the western Jiangnan Orogen, South China: Insights from new structural and geochronological data from northern Guangxi

“…L. Wang et al, , 2014X. L. Wang, Zhou, et al, 2007;Yan et al, 2021). The faults in the region are divided into two sets based on their strikes: NNE-SSW strike and NW-SE-to WNW-ESE-strike.…”

“…These granitoids have S-type geochemical affinities, suggesting that they were emplaced from magmas generated by crustal thickening as a result of the collision between the Yangtze and Cathaysia blocks (Shu et al, 2021;Yan et al, 2021). The first deformation event D1 occurred after the deposition of the Sibao Group and was contemporaneous with granitoid emplacement within the Sibao Group, before the deposition of the Danzhou Group.…”

“…L. Wang, Zhou, et al, 2007;X. L. Wang, Zhou, Chen, Zhang, & Sun, 2017;Yan, Shu, Chen, Faure, & Feng, 2021;Yao, Shu, Santosh, & Zhao, 2014;G. L. Zhang, 2004;J.…”