Geochemistry and tectonic setting of Neoproterozoic mafic rocks from the northern Tarim craton, NW China: Constraints for the evolution of the Rodinia supercontinent

The Neoproterozoic mafic-ultramafic rocks exposed along the northern margin of the Tarim craton record the evolution of the Rodinia supercontinent and have been extensively studied. However, there has been long-lasting debates regarding the geodynamic processes responsible for these rocks. Some researchers suggested that the Neoproterozoic mafic-ultramafic intrusive rocks in northern Tarim may be the product of an independent mantle plume, whereas recent studies proposed that subduction process also contributed to the formation of these rocks. Different models have varying implications for the reconstruction of the Rodinia supercontinent, which further leads to the ambiguous paleogeographic position of the Tarim craton within the Rodinia supercontinent. Therefore, investigating the petrogenesis and tectonic setting of the Neoproterozoic intrusive rocks in the northern Tarim craton is crucial for constraining the paleogeographic location of the Tarim craton.

In this paper, we report whole-rock geochemical data of the ~810 Ma Quruqtagh mafic rocks and 660-600 Ma Aksu mafic rocks at the northeastern and northwestern margins of the Tarim craton, respectively, to evaluate their petrogenesis and tectonic setting. New findings provide constraints on the role and paleogeographic position of the Tarim craton during the Neoproterozoic evolution of the Rodinia supercontinent. The Quruqtagh Group I mafic rocks have OIB (oceanic island basalt) characteristics, including enrichments in light rare earth elements (LREEs; [La/Yb]_N=11.6-12.2), no obvious Eu anomalies (Eu^*=0.96-1.10), and relative enrichments in large ion lithophile elements (LILEs, e.g., Ba, Rb, Sr) and high field strength elements (HFSEs, e.g., Nb, Ta, Ti). Meanwhile, they show the relatively high Th/Yb (1.22-1.61), Nb/Yb (11.5-21.1), and low TiO₂/Yb (0.51-0.66) ratios of the samples, within the OIB fields on the relevant discrimination diagrams. Accordingly, the Group I mafic rocks might have formed in an intracontinental extensional environment. In contrast, the Quruqtagh Group II mafic rocks have the characteristics of CAB (continental arc basalt). They are characterized by slight LREEs enrichments ([La/Yb]_N = 1.25-2.49), relative enrichments of LILEs (e.g., Rb, Ba, Sr), and significant depletions in the HFSEs (e.g., Nb), suggesting that a continental arc setting.

Similar to the Quruqtagh Group I mafic rocks, the ~660-600 Ma Aksu mafic rocks exhibit OIB-like geochemical characteristics. They show significant LREEs enrichments ([La/Yb]_N = 7.56-8.84) and slightly positive Eu anomalies (Eu^* = 1.02-1.12). Their high Th/Yb (0.88-1.15) and TiO₂/Yb (1.15-1.75) ratios and low Th/Nb (~0.1) ratios are akin to the OIB affinities. The Aksu mafic rocks display elevated Zr/Y ratios (6.58-8.89) and plot within the within-plate basalt fields on Ti-Zr-Y and Nb-Zr-Y discrimination diagrams, suggesting derivation from magmas generated in an intracontinental extensional setting.

The ~810 Ma Quruqtagh mafic rocks with both OIB and CAB characteristics, were probably subjected to subduction processes, and the 660-600 Ma Aksu OIB-like mafic rocks originated in an intracontinental extensional setting. Therefore, the northern margin of the Tarim craton likely experienced multiple episodes of subduction in the Neoproterozoic in response to the peripheral evolution of the Rodinia supercontinent.

This study was financially supported by the National Key Research and Development Program of China project (grant 2024YFF0808000).