MESOZOIC MULTIPLE INTRA-OCEANIC SUBDUCTION SYSTEMS OF THE NEOTETHYS WITHIN THE INDUS-YARLUNG TSANGPO SUTURE AND GANGDESE BELT, SOUTHERN TIBET

The Tibetan Plateau was built up through sequential accretion of Gondwana-derived terranes to the southern margin of the Eurasian continent. The Indo-Asian collision took place at ca. 50 Ma, triggering the closure of the Neotethys (Ma et al., 2017a; Wang, 2017; Zhu et al., 2015). The ophiolites of the Indus-Yarlung Tsangpo suture zone was suggested to be the remnants of the Neotethyan oceanic lithosphere (Yang et al., 2014), whose formation ages fall into the range of 130-120 Ma (Liu et al., 2016). However, more lines of evidence indicate that the Neotethys was opened at Early Triassic at least. These lines of evidence include the identified multiple intra-oceanic subduction systems of the Neotethys within the Indus-Yarlung Tsangpo suture zone and the Gangdese magmatic belt, southern Tibet. From old to young, the identified intra-oceanic arcs are represented by the ca. 240 Ma Zhongga arc-affinity diorite, the ca. 220 Ma Daga arc-affinity appinite, the ca. 190-170 Ma Xiongcun intra-oceanic arc (Lang et al., 2014; Ma et al., 2017b; Tafti et al., 2014; Tang et al., 2015), the ca. 160 Ma Dazhuka and Zedong arc-affinity rock assemblage (Aitchison et al., 2000; Wang et al., 2012; Wei et al., 2007), the ca. 125 Ma intra-oceanic supra-subduction-related Zhongba ophiolites (Dai et al., 2011, 2012). Furthermore, voluminous Middle Triassic to Early Paleogene subduction-related magmatic rocks occurred in the Gangdese magmatic belt, revealing a long-standing active continental margin along the southern margin of the Lhasa terrane (Mo et al., 2005; Wang et al., 2016). In combination with published results, we suggest that multiple intra-oceanic subduction systems existed within the Neotethys during the Mesozoic, and the Neotethys was opened at Early Triassic or more earlier.