Early Paleozoic granodiorites and gabbros related to asthenosphere upwelling in the eastern Wuyi-Yunkai Orogen, South China

Abstract

The early Paleozoic Wuyi-Yunkai Orogen (WYO) developed in the inner part of the South China Block (SCB) and underwent large scale felsic magmatism. Different tectonic models have been proposed to explain the evolution of the WYO, including intracontinental and collisional orogenesis. The debates focus on whether the asthenospheric materials were involved during evolution of the WYO. We conducted detailed petrographic and geochemical analyses on gabbros from the Qiaotou pluton and granodiorites and the hosted MMEs from the Xinsi pluton in the eastern WYO, and present the first evidence of asthenosphere upwelling that induced significant lithosphere remobilization in the SCB during early Paleozoic. Granodiorites from the Xinsi pluton (441 ± 2 Ma) contain abundant amphibole and are metaluminous, which originated from the igneous basement in the Cathaysia Block. The hosted MMEs (440 ± 2 Ma) have variable SiO2 and enriched Sr-Nd isotopic compositions with high zircon δ18O values, which were formed through hybridization of felsic melts and mafic magmas from the enriched lithosphere mantle. Gabbros from the Qiaotou pluton (448 ± 8 Ma) have low K2O with insignificant Nb-Ta-Ti anomalies and show variable Sr-Nd-O isotopic compositions. They were derived from the depleted asthenosphere and underwent crustal assimilation. The asthenosphere upwelling may be induced by slab breakoff during the collision between the western Cathaysia Block and an unknown block near northern Gondwana. The continental collision possibly transferred compressional stress and caused crustal uplifting along the weak zone in the inner SCB. The asthenosphere upwelling provided tremendous heat for the lithosphere remobilization and voluminous magmatism in the WYO.