Geochronological and geochemical feature of the Cenozoic adakites in Hoh Xil, Tibetan Plateau

Abstract

The volcanic rocks in the Tibetan Plateau have undergone complex evolution, as the collision between the Indian and Eurasian Plates proceeds. The volcanic rock samples collected from a volcanic edifice in the Hoh Xil, Tibetan Plateau, are studied in this paper. The geochemistry and zircon U-Pb chronology of the volcanic rock samples are determined. Our results indicate that the volcanic rocks in this area are mostly alkali-rich intermediate-acidic ones, and consist of quartz trachyandesite, andesite, pyroxene andesite, and andesitic tuff. Geochemically, these rocks feature high light rare earth elements and large-ion lithophile elements concentration, with low Nb, Ta, and Ti concentration, and significant Pb positive anomaly. Based on our analysis, we conclude that the volcanic rocks are adakites. The eruption ages of the volcanic rocks in this area are determined for the first time in the literature: 45.23 ± 0.35 Ma for the hornblende trachyandesite; 41.36 ± 0.45 Ma for the biotite trachyandesite; and 42.97 ± 0.23 Ma for the biotite-quartz trachyandesite. This suggests that the volcanic rocks studied in this paper were formed in the Lutetian (Eocene). It is further concluded that the volcanic rocks originated from a mantle provenance that have assimilated large amount of crustal materials. The formation of the volcanic rocks is attributable to the breakoff of oceanic lithospheric slab.