PGE and isotopic characteristics of Shergol and Suru Valley Ophiolites, Western Ladakh: Implications for supra-subduction tectonics along Indus Suture Zone

Present study reports the PGE-geochemistry of mantle peridotites and Nd-isotope geochemistry of arc related mafic rocks from the Indus Suture Zone (ISZ), western Ladakh. The total PGE concentration of the Shergol and Suru Valley peridotites (Sigma PGE = 96-180 ppb) is much higher than that of the primitive mantle and global ophiolitic mantle peridotites. The studied peridotites show concave upward PGE-distribution patterns with higher palladium-group PGE/Iridium-group PGE ratios (i.e., 0.8-2.9) suggesting that the partial melting is not the sole factor responsible for the evolution of these peridotites. The observed PGE-distribution patterns are distinct from residual/refractory mantle peridotites, which have concave downward or flat PGE-distribution patterns. Relative enrichment of palladium-group PGE as well as other whole-rock incompatible elements (e.g., LILE and LREE) and higher Pd/Ir ratio (1.1-5.9) reflects that these peridotites have experienced fluid/melt interaction in a supra-subduction zone (SSZ) tectonic setting. Also, the Shergol mafic intrusives and Dras mafic volcanics, associated with the studied peridotites, have high Nd-143/Nd-144 ratios (i.e., 0.512908-0.513078 and 0.512901-0.512977, respectively) and positive epsilon(Nd(t)) (calculated for t = 140 Ma) values (i. e., +5.3 to +8.6 and + 5.1 to +6.6, respectively), indicating derivation from depleted mantle sources within an intra-oceanic arc setting, similar to Spongtang and Nidar ophiolites from other parts of Ladakh Himalaya. The transition from SSZ-type Shergol and Suru Valley peridotites to Early Cretaceous tholeiitic Shergol mafic intrusives followed by tholeiitic to calc-alkaline Drasmafic volcanics within the Neo-Tethys Ocean exhibit characteristics of subduction initiation mechanism analogous to the Izu-Bonin-Mariana arc system within western Pacific. (c) 2021 ChinaUniversity of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Automated summary

The study of PGE geochemistry of mantle peridotites and Nd-isotope geochemistry of arc-related mafic rocks in the Indus Suture Zone (ISZ) in western Ladakh shows distinct characteristics indicating interaction between subduction zone tectonic settings and arc environments.