Intraoceanic Subduction System Within the Neo‐Tethys: Evidence From Late Cretaceous Arc Magmatic Rocks of the Eastern Himalaya

Abstract

AbstractThe tectonic evolution of the Neo‐Tethys Ocean remains highly controversial, with several models existing in the community that conflict with each other. Here, we present new geochronologic and geochemical data for orthogneisses and amphibolites from the Greater Himalayan Sequence, eastern Himalayan orogen, which indicate that these rocks have Cenozoic metamorphic ages (∼52–3 Ma), but were derived from Late Cretaceous (∼89 Ma) magmas with arc‐like and depleted mantle geochemical signatures. Considering that northern India was a passive continental margin during the Mesozoic, and the previously reported Late Cretaceous magmatic rocks in the eastern Himalaya formed in a continental rifting setting, we suggest that the studied Late Cretaceous arc‐type magmatic rocks formed in an intraoceanic arc setting within the Neo‐Tethys, and accreted onto the passive margin of the Indian continent prior to the terminal continental collision. When combined with the existence of Late Mesozoic and intraoceanic arc‐type magmatic rocks in the western Himalaya, we suggest that a huge Late Cretaceous subduction system operated within the eastern Neo‐Tethys Ocean. This study supports two subduction zones having been responsible for the consumption and closure of the Neo‐Tethys basin, and a two‐stage collision history between India, Asia, and the intermediate island arc system. Our data therefore provide important constraints on the evolution of the Neo‐Tethys Ocean and India‐Asia collisional orogeny in southern Tibet.