Paleoproterozoic tectonic evolution of the northern Yangtze craton from oceanic subduction through continental collision to continental rifting: Geochronological and geochemical records of metabasites from the Tongbai orogen in central China

摘要

We report for the first time the existence of multistage Paleoproterozoic collision- and rift-related tectonothermal events in the northern margin of the Yangtze craton. This is achieved through an integrated study of geochronology and geochemistry for Phanerozoic metabasites from the Tongbai orogen in central China. Zircon U-Pb dating and trace element analysis reveal two episodes of magmatism and one episode of metamorphism from ca. 1.96 Ga to 1.63 Ga. Whole-rock geochemistry indicates that the 1.96 Ga metabasite shows typical arc-like trace elemental distribution patterns with enrichment in LREE but depletion in HFSE, whereas the 1.63 Ga metabasites are characterized by enriched mid-ocean ridge basalts (MORB)- or ocean island basalts (OIB)-like trace element distribution patterns with enrichment in LREE but no depletion in HFSE. In addition, a 1.84 Ga granulite facies metamorphic event is recorded by sector zoned domains of zircon from the 1.96 Ga metabasites, showing flat HREE patterns with markedly negative Eu anomalies and a high formation temperature of 825 degrees C. Integrating the available data from the northern Yangtze craton, we suggest that the 1.96 Ga metabasite was produced by decompressional melting of the metasomatic mantle domain subsequent to exhumation of the high-pressure metamorphic rocks, the 1.84 Ga granulite facies metamorphism was induced by asthenospheric upwelling in response to post-collisional extension, and the 1.63 Ga magmatism was associated with lithospheric extension due to continental rifting. Therefore, the Paleoproterozoic metabasites in the Tongbai orogen witness the tectonic evolution from oceanic subduction through continental collision to continental rifting, indicating that the northern margin of the Yangtze craton was involved in the assembly and breakup of supercontinent Columbia. In comparison to the coeval rift-related igneous rocks in other blocks, the geochemical features of 1.63 Ga metabasites in the northern Yangtze craton are similar to those in the northern Australia, but are significantly different from those in the southern Siberia and the northern Laurentia. This indicates a possible connection between the northern Yangtze and the northern Australia before the Columbia breakup.