Zircon U-Pb age, Hf isotopic compositions and geochemistry of the Silurian Fengdingshan I-type granite Pluton and Taoyuan mafic-felsic Complex at the southeastern margin of the Yangtze Block

This work presents an integrated study of zircon U-Pb ages and Hf isotope along with whole-rock geo-chemistry on Silurian Fengdingshan I-type granites and Taoyuan mafic-felsic intrusive Complex located at the southeastern margin of the Yangtze Block, filling in a gap in understanding of Paleozoic l-type granites and mafic-intermediate igneous rocks in the eastern South China Craton (SCC). The Fengdingshan granite and Taoyuan hornblende gabbro are dated at 436 +/- 5 Ma and 409 +/- 2 Ma, respectively. The Fengdingshan granites display characteristics of calc-alkaline I-type granite with high initial Sr-87/Sr-86 ratios of 0.7093-0.7127, low epsilon Nd(t) values ranging from -5.6 to -5.4 and corresponding Nd model ages (T-2DM) of 1.6 Ga. Their zircon grains have epsilon Hf(t) values ranging from -2.7 to 2.6 and model ages of 951-1164 Ma. The Taoyuan mafic rocks exhibit typical arc-like geochemistry, with enrichment in Rb, Th, U and Pb and depletion in Nb, Ta. They have initial Sr-87/Sr-86 ratios of 0.7053-0.7058, epsilon Nd(t) values of 0.2-1.6 and corresponding T-2DM of 1.0-1.1 Ga. Their zircon grains have epsilon Hf(t) values ranging from 3.2 to 6.1 and model ages of 774-911 Ma. Diorite and granodiorite from the Taoyuan Complex have initial Sr-87/Sr-86 ratios of 0.7065-0.7117, epsilon Nd(t) values from -5.7 to -1.9 and Nd model ages of 1.3-1.6 Ga. The petrographic and geochemical characteristics indicate that the Fengdingshan granites probably formed by reworking of Neoproterozoic basalts with very little of juvenile mantle-derived magma. The Taoyuan Complex formed by magma mixing and mingling, in which the mafic member originated from a metasomatized lithospheric mantle. Both the Fengdingshan and Taoyuan Plutons formed in a post-orogenic collapse stage in an intracontinental tectonic regime. Besides the Paleozoic Fengdingshan granites and Taoyuan hornblende gabbro, other Neoproterozoic and Indosinian igneous rocks located along the southeastern and western margin of the Yangtze Block also exhibit decoupled Nd-Hf isotopic systemics, which may be a fingerprint of a previous late Mesoproterozoic to early Neoproterozoic oceanic subduction. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.