Origin of exotic blocks in Himalaya: a case study from Zildat ophiolitic mélange, Indus suture zone, Ladakh, India

Abstract

The Zildat ophiolitic mélange lies in the eastern part of Ladakh and represents the part of the Indus Suture Zone. This ophiolitic mélange constitutes low-grade metasediments, ultramafic rocks, and exotic limestone blocks. The exotic blocks are comprised of calcite, which shows various type of twinning patterns that indicates dynamic recrystallization up to 300 °C. The carbon and oxygen isotope ratio of the exotic block is 3.2 ± 1.1‰VPDB and 21.7 ± 2.8 ‰VSMOW, respectively, suggestive of marine/platform origin. Furthermore, the stable isotope (carbon and oxygen) ratio of CO₂ and H₂O fluid also advocates the platform type origin of the fluid. Two types of fluid inclusions were observed in these exotic blocks: carbonic and aqueous-carbonic entrapped between 435 and 370 °C at 386–323 MPa and advocates for deep-seated marine carbonates and exhumed from 13 km depth below the sea surface which become got deposited in the Zanskar shelf. The exotic blocks in ophiolitic mélange were probably derived from the Zanskar shelf (platform), having salinity between 20.37 and 11.22 wt % NaCl, similar to the Permian time seawater.