Origin and evolution of the Neoproterozoic Dengganping Granitic Complex in the western margin of the Yangtze Block, SW China: Implications for breakup of Rodina Supercontinent

摘要

A better understanding of the origin and evolution of widespread Neoproterozoic granites along the western margin of the Yangtze Block is important in locating the position of South China within the Rodinia Supercontinent, and the mechanism by which the supercontinent was fragmented. Published and our new detailed geochronological and geochemical data from the Dengganping Complex show that it formed during an extended magmatic event during the Neoproterozoic. This was during the emplacement of a fractionated ca. 815 Ma syenogranite, which was followed by partial melting during ca. 740 Ma and the emplacement of a biotite monzogranite. The geochemistry of the syenogranite indicates it is: (1) a peraluminous high-K type of granite; (2) calc-alkaline; (3) fractionated; (4) enriched in Th, U, Zr, Hf and LREE (LREE/HREE values of 5.3-9); (5) depleted in Nb and Sr; (6) has a negative Eu anomaly (delta Eu = 0.3-0.5); (7) has whole rock epsilon(Nd)(t) value of -0.7 to +0.5; (8) has zircon epsilon(Hf)(t) value of -1.7 to +5.2; and (9) has zircon O-18 values ranging from 5.13 to 7.38 parts per thousand. These characteristics are indicative of a source derived from the partial melting of crustal material. The biotite monzogranite is: (i) peraluminous calc-alkaline to high-K calc-alkaline; (ii) enriched in LREE (LREE/HREE = 9.9-14.6), Rb, Ba, Th and U; (iii) depleted in Nb and Ta; (iv) has weak negative delta Eu and delta Ce anomalies; (v) has whole rock epsilon(Nd)(t) value of between -3.2 and -1.8; has relatively high positive zircon epsilon(Hf)(t) values of +4.1 to +13; and has zircon O-18 values ranging from 3.44 to 6.75 parts per thousand. These features are indicative of partial melting of a juvenile mafic crust that might have experienced a high-temperature water-rock interaction. By comparing the geochronology of Neoproterozoic magmatic rocks along the faulted western margin of the Yangtze Block, it is suggested that the region was part of the Rodinia Supercontinent when it started to breakup during widespread rifting between ca. 825 and 710 Ma. We believe the fault zone formed in response to an opening ocean was induced by the presence of a mantle plume during this period. (C) 2020 Elsevier B.V. All rights reserved.