Late Triassic E-MORB/OIB-like basalts in a continental arc, eastern Tibet, formed by the subduction of a conservative plate boundary?

The ~1500-km-long, (N)NW–(S)SE-trending, Yushu–Yidun Arc delineates the configuration of subducted Paleo-Tethyan oceanic lithosphere in the central–eastern Tibetan Plateau. At its southern termination, widespread Late Triassic arc-like rocks are associated with coeval, minor amounts of E-MORB/OIB-like basalts (EOB) and porphyry Cu (±Mo, ±Au) deposits developed to the north of the southwestern extension of the Longmenshan Fault. This association of tectonic, magmatic, and ore deposit features, along with the coeval dextral slip of the Longmenshan Fault and NE–SW-trending granitic belt to the northwest, were likely related to the active proto-Longmenshan Fault. This was a weakened conservative plate boundary located between the subducted Garze–Litang oceanic lithosphere and Yangtze Craton. Upwelling asthenospheric mantle along the subducted conservative plate boundary underwent decompression partial melting and formed the parental melts of the EOB, which triggered partial melting of the subducted slab and metasomatized mantle wedge and formed the ore-forming magmas and arc-like andesites, respectively.