Geology and Tectonic Significance of the Paleproterozoic Ophio1itic Melange in Goukouquan, Northern Margin of Altun

After regional geological surveys in recent years, a new ophiolitic melange of Paleproterozoic Era was identified in Goukouquan, northern margin of Altun, which consists of oceanic crust block, overlying rock series and exotic blocks. The oceanic crust rock is a complete sequence of ophiolite including metamorphic peridotite-ultramafic cumulates, gabbroic complex rock, anorthosite, plagiogranite, diabase, mafic volcanic lava and other components. Studies of the rock combination, petrology, geochemistry, isotopic geochronology and Zircon U-Pb SHRIMP dating on metamorphic iherzolite, anorthosite, gabbro, basalt specify their average ages as (1 889±27)Ma, (1 869±27)Ma, (1 836±40)Ma, (1 818±25)Ma and several 2 200 Ma-2 600 Ma age data as isolated points, confirming that there is an ocean basin from late Neoarchean Era to Paleproterozoic Era in northern Altun area, which then dived, collided and closed to form the ophiolitic melange of Goukouquan, which can be speculated as mantle plume (P-Type) origin. This discovery provided a sufficient basis for tectonic evolution from late Neoarchean Era to Paleproterozoic Era in Dunhuang block and Altun orogenic belt and will be of great significance for the research on Cambrian crustal evolution.