Paleo- to Mesoproterozoic magmatic and tectonic evolution of the southwestern Yangtze Block, south China: New constraints from ca. 1.7-1.5 Ga mafic rocks in the Huili-Dongchuan area

Paleo- to early Mesoproterozoic rocks in the Yangtze Block are extremely sparse and are predominately exposed along the southwestern margin. Their petrogenesis and tectonic significance remain unclear, resulting in a limited understanding of the tectonic evolution of the southwestern Yangtze Block during this period. Therefore, we report here detailed geochronological and geochemical analyses of newly discovered Paleo- to early Mesoproterozoic mafic intrusive rocks in the Huili-Dongchuan area, southwestern Yangtze Block and interpret their petrogenesis and tectonic significance. Secondary ion mass spectroscopy (SIMS) zircon and baddeleyite U-Pb dating yielded crystallization ages of ca. 1716-1714 Ma for gabbros and diabases (referred to as the 1.72-1.71 Ga group), ca. 1705-1700 Ma for gabbros and a diabase-porphyrite (the 1.70 Ga group), and ca. 1519-1504 Ma for a gabbro and a diabase (the 1.52-1.50 Ga group), which effectively constrain the minimum depositional age of the Tong'an and Dongchuan groups that they intrude to 1.72 Ga. The three groups (or episodes) of intrusive rocks differ from each other in their chemical compositions and isotopic characteristics, most likely because of varying degrees of melting in a convective upper mantle (probably the asthenosphere), which had been metasomatized by melts with enriched components input by a plume from the lower mantle. Modeling calculations suggest that fractional crystallization (FC) and assimilation and fractional crystallization (AFC) were the most important processes involved in modifying the chemical compositions of these rocks. These magmatic activities are interpreted to have been related to mantle plumes and continental rifting that occurred in the Huili-Dongchuan area near the southwestern margin of the Yangtze Block. (C) 2020 international Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.