Petrogenesis and geodynamic implications of Neoproterozoic gabbro-diorites, adakitic granites, and A-type granites in the southwestern margin of the Yangtze Block, South China

Published on Oct 1, 2019in Journal of Asian Earth Sciences2.76
· DOI :10.1016/j.jseaes.2019.103977
Yu Zhu1
Estimated H-index: 1
(Northwest University (United States)),
Shaocong Lai19
Estimated H-index: 19
(Northwest University (United States))
+ 4 AuthorsBaoping Gan1
Estimated H-index: 1
(Northwest University (United States))
Abstract The occurrence of A-type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone. This paper presents a comprehensive study of zircon U-Pb-Hf isotopes and whole-rock geochemistry on the Neoproterozoic gabbro-diorites, biotite granites, and K-feldspar granites in the southwestern margin of the Yangtze Block, South China. Zircon U-Pb dating of three distinctive intrusions yield concordant ages of 810.4 ± 2.0 Ma for gabbro-diorites, 800.3 ± 2.1 Ma for biotite granites, and 749.1 ± 2.0 Ma for K-feldspar granites. The gabbro-diorites are sodic and calc-alkaline rocks with low SiO2 (52.62–53.87 wt%), medium MgO (2.67–3.41 wt%), high Fe2O3T (7.18–7.49 wt%) and CaO (5.68–7.50 wt%) contents. They display high Th/Zr and Rb/Y ratios but low Nb/Zr and Nb/Y ratios. Together with their positive whole-rock eNd(t) (+1.0 to +1.5) and zircon eHf(t) values (+3.66 to +8.18), we suggest that these gabbro-diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction-related fluids. The biotite granites display relatively high Sr contents (335–395 ppm), Sr/Y ratios (38.9–54.3), low Y (7.04–9.71 ppm) and Yb contents (0.78–1.08 ppm), resembling the adakitic granites. Their low Mg# (36–41) values, Cr (2.94–3.59 ppm) and Ni (1.32–1.55 ppm) contents as well as positive eNd(t) (+0.5 to +0.6) and eHf(t) values (+1.62 to +8.07) indicate that they were formed by partial melting of thickened juvenile mafic lower crust, probably within the existence of garnet. The K-feldspar granites have high SiO2 (76.61–77.14 wt%) and alkalis (Na2O + K2O = 8.55–9.69 wt%) contents, high 10,000 * Ga/Al (2.56–2.80) ratios and differentiation index (95.3–96.9), indicating the affinity to highly fractionated A-type granites. We suggest that these A-type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant. Taking into account previous studies from the western Yangtze Block, South China, we propose that the gabbro-diorites, adakitic granites and A-type granites in this study were formed in persistent subduction process during the Neoproterozoic.
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#1Yu Zhu (Northwest University (United States))H-Index: 1
#2Shaocong Lai (Northwest University (United States))H-Index: 19
Last.Zezhong Zhang (Northwest University (United States))H-Index: 1
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#1Jun-Hong Zhao (China University of Geosciences)H-Index: 24
#2Mei-Fu Zhou (China University of Geosciences)H-Index: 69
Last.Wei Wang (China University of Geosciences)
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#1Jun-Hong Zhao (China University of Geosciences)H-Index: 24
#2Qi-Wei Li (China University of Geosciences)H-Index: 1
Last.Wei Wang (China University of Geosciences)H-Index: 43
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#1Yuejun Wang (SYSU: Sun Yat-sen University)H-Index: 48
#2Chengshi Gan (SYSU: Sun Yat-sen University)H-Index: 2
Last.Y. Zhang (CSIRO: Commonwealth Scientific and Industrial Research Organisation)H-Index: 25
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#1Orhan Karsli (Recep Tayyip Erdoğan University)H-Index: 10
#2Faruk Aydin (Karadeniz Technical University)H-Index: 20
Last.Murat Ketenci (ITU: Istanbul Technical University)H-Index: 3
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