An 850–820 Ma LIP dismembered during breakup of the Rodinia supercontinent and destroyed by Early Paleozoic continental subduction in the northern Tibetan Plateau, NW China

Abstract

Neoproterozoic intraplate magmatism is widely distributed in NW China and generally thought to be related to the breakup of the Rodinia supercontinent. Here we report a fragmented Large Igneous Province (LIP) formed at 850–820Ma in the northern margin of the Qaidam block, northern Tibetan Plateau (named herein as the “North Qaidam LIP”). The associated rocks have undergone various grades of metamorphism from greenschist to ultrahigh-pressure (UHP) eclogite facies, including the greenschist-facies Yingfeng dolerite dikes and basalts (846–821Ma), the amphibolite- to HP granulite-facies Aolaoshan meta-volcanic sequence (protolith age of 832Ma and metamorphic age of 439Ma), and the North Qaidam UHP eclogites (protolith age of 847–828Ma and metamorphic age of 440–420Ma). Geochemical data reveal that they resemble present-day E-MORB/OIB and typical continental flood basalts. These features, together with high potential temperatures (Tp=1434–1524°C) for “primary” magmas, suggest that these basaltic rocks were most likely derived from a mantle plume source and were emplaced in a continental extensional environment.Their varying metamorphic facies record a range of locations along the underthrust continental slab from near-surface (Yingfeng dolerites/basalts), middle (Aolaoshan amphibolites) to deep (N. Qaidam UHP eclogites) sites with depths greater than 120km. The large spatial distribution (potentially >0.1Mkm2), short duration (<30Myr) and intraplate geochemical character suggest that these igneous rocks are remnants of the North Qaidam LIP caused by the upwelling of a mantle plume during 850–820Ma. We consider that the North Qaidam LIP represents the onset of a protracted break-up history and precedes subsequent multiple episodes of rifting. These Neoproterozoic igneous rocks in the Qaidam block were separated from the contemporaneous magmatic suites over Australia, South China and Tarim by the breakup of Rodinia, and were further destroyed by the subduction of the passive continental margin of the Qaidam block in the Early Paleozoic (440–420Ma).