Qaidam block situated in the interior of Rodinia and Gondwana: New magmatic and metamorphic constraints

Some Precambrian microcontinental blocks, generally embedded in the Phanerozoic orogenic belts, are keys to constrain supercontinent assembly and dispersal as well as play an important role in the ocean-continent transition. The Qaidam block is considered as a Precambrian continental fragment surrounded by Paleozoic orogens. The previous reconstruction models commonly placed the Qaidam block in the peripheries rather than the interiors of the Rodinia and Gondwana supercontinents due to the lack of two global events at 1.2–1.0 Ga and 0.65–0.5 Ga. In this study, we present new zircon U–Pb–Hf isotope data and whole-rock geochemical data for the high-grade orthogneisses and low-grade metavolcanic rocks in the western Qaidam block. Zircon U–Pb dating displays three age groups at approximately 0.55 Ga, 0.75 Ga, and 1.1 Ga. The Ediacaran to early Cambrian age in zircon rims from orthogneisses is interpreted as a metamorphic origin, consistent with the timing of the latest Ediacaran–early Cambrian ultrahigh temperature metamorphism recorded in Mg-Al and mafic granulites. The late Mesoproterozoic age in magmatic zircons of orthogneisses and the middle Neoproterozoic age of metavolcanic rocks reflect two magmatic events. Combining with wide magmatic and metamorphic records of 1.0–0.9 Ga in the Qaidam block, we suggest that the Qaidam block experienced a prolonged subduction–collision process during the late Mesoproterozoic to early Neoproterozoic, followed by a 0.8–0.75 Ga anorogenic event related to the continental rifting environment within an already assembled Rodinia. These data show that the Qaidam block likely maintained a long-term connection with East Gondwana from the late Mesoproterozoic to the latest Cambrian and occupied interior positions in Rodinia and Gondwana rather than in their periphery. It probably did not separate from East Gondwana until the latest Ediacaran–early Cambrian.