Metamorphic PT path, U-Pb zircon dating and tectonic implications of High-pressure Pelitic Granulites from the Kharta region, Southern Tibet, China

HP pelitic granulites associated with eclogites from the Kharta Gneiss are found in the Thongmon area, central Himalaya, which provides significant constraints for the tectonic evolution of the Himalayan orogeny. Three generations of garnets are identified in pelitic granulites (DR15P15). The first generation of garnet is core sections of euhedral to subhedral porphyroblasts (Grt-I core) followed by growth of Grt-I mantle during the heating stage. The third generation of garnet is represented by thin rims of Grt-I and small grains (Grt-II) in the matrix, which likely nucleated and grew in response to peritectic reaction during exhumation. Petrographic evidence and P-T pseudosection calculation reveal a four-stages metamorphic evolution: 1) a prograde metamorphic stage (M1) represented by Grt-I core and its mineral inclusions rutile, ilmenite and quartz with metamorphic conditions of 740-760 degrees C and 13-16 kbar; 2) a near isobaric heating stage with slightly decompression to HP granulite-facies (M2, 820-840 degrees C, 13-14 kbar) indicated by the composition of Grt-I mantle and the increase of Zr concentrations of rutile in it; 3) a heating decompression stage (M3) supported by a decrease in grossular content in the Grt-I rim and higher X-An in plagioclase, yielding T > 860 degrees C and P = 10-11 kbar in the sillimanite stability field; 4) a final decompression stage followed by cooling (M4, T similar to 800 degrees C and P = 6-8 kbar) indicated by biotite replacing sillimanite and lower Ti content in biotite in the matrix. Based on the zircon trace element geochemistry, zircon inclusions, and the REE partitioning between garnet and zircon, the metamorphic zircon rims with middle Miocene age (16-13 Ma) probably grew during Grt-I rim/Grt-II formation at granulite facies stage (M3). The P-T history of the pelitic granulites of the Kharta Gneiss indicates that they were subducted beneath the Asian plate and exhumed to middle-lower crustal depths prior to 14-13 Ma due to the activity of STDS. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

This study provides detailed insights into the metamorphic evolution and tectonic history of the HP pelitic granulites associated with eclogites from the Kharta Gneiss in the central Himalaya, shedding light on the overall evolution of the Himalayan orogeny.