Oceanic lithosphere heterogeneity in the eastern Paleo-Tethys revealed by PGE and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite

Platinum group elements (PGE) and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite (SWChina) were investigated in this study, in order to constrain the evolution of the lithospheric mantle beneath the Jinshajiang-Ailaoshan Ocean, which was a branch of the eastern Paleo-Tethys. The Jinshajiang peridotites have whole-rock compositions (e.g., MgO = 32.7-38.1 wt.%; Al2O3 = 0.67-1.30 wt.%) and spinels with moderate Cr# values (0.4-0.6) similar to those of abyssal peridotites, which indicate moderate degrees of partial melting (15%-20%). These peridotites exhibit U-shaped chondrite-normalized REE patterns that could be caused by hydrothermal alteration or melt-rock interaction after mantle melting. In addition, Pd concentrations and (Pd/Ir) N ratios of the Jinshajiang peridotites increases with decreasing Al2O3 concentrations. These negative correlations cannot be explained by simple partial melting but record a melt-rock reaction event after mantle melting. This study therefore demonstrates the efficiency of PGE in detecting themelt-rock reaction process relative to whole-rock major and trace elements. The suprachondritic Os-187/Os-188 ratios (0.1272-0.1374) further indicate that the later percolating melt derived from a mantle domain with distinct Os-187-enriched isotopic compositions. In comparison with peridotites in the Ailaoshan ophiolite belt, which were not significantly affected by melt percolation, this study further highlights that the lithosphericmantle compositions beneath different segments of the same ocean basin are highly variable and might be controlled by distinct mantle processes in response to different rifting mechanisms. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Automated summary

This study investigates the PGE and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite, shedding light on the evolution of the lithospheric mantle beneath the region. Peridotites in the area show features of moderate partial melting and distinctive rock characteristics. Furthermore, the study reveals a melt-rock reaction event in the peridotites after mantle melting, as evidenced by the negative correlations between Pd concentrations and Al2O3 concentrations.