AUTHOR=Chen Si , Chen Yi , Guillot Stéphane , Li Qiuli 

TITLE=Change in Subduction Dip Angle of the Indian Continental Lithosphere Inferred From the Western Himalayan Eclogites

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 9 - 2021

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.790999

DOI=10.3389/feart.2021.790999

ISSN=2296-6463

ABSTRACT=The occurrence of ultrahigh-pressure (UHP) and high-pressure (HP) rocks in the Himalayan orogen has been conventionally attributed to the different subduction angles along strike. However, the present-day geophysical data shows low subduction angles of the Indian Plate beneath southern Tibet and Karakoram, implying that a shift from steep to low-angle subduction happened in the western Himalaya. The timing and processes of such a subduction-angle change are still unknown. Here we present a combined analysis of zircon geochronology and geochemistry of eclogites and gneiss in the Stak massif, western Himalaya. Metamorphic zircons equilibrated with garnet and omphacite show flat heavy rare earth element patterns without Eu anomalies and thus yield similar eclogite-facies ages of ca. 31 Ma. The Stak HP eclogite-facies metamorphism is at least 15 Ma younger than those measured in the western Himalayan UHP eclogites, but broadly contemporaneous with other Himalayan HP rocks. Therefore, all the Himalayan HP rocks record higher peak geothermal gradients and younger ages than those of the UHP rocks. Our new data, combined with the magmatic lull observed in the Kohistan-Ladakh-Gangdese arc and with the convergent rate of the Indian plate, suggest a change in subduction dip angle over time. Consequently, we suggest that the entire Indian continental plate experienced an approximately coherent shift from steep to low-angle subduction after the breakoff of the Neo-Tethyan slab since the middle Eocene.