Citation: | NONG Junnian, ZOU Yu, QIU Enlu, GUO Shangyu, YE Xusong, XIANG Feng, WEN Ming, LU Shiyi. Petrogenesis of Dacun and Gulong plutons in southeast Guangxi: Constraints from geochemistry, zircon U-Pb ages and Hf isotope[J]. Geological Bulletin of China, 2017, 36(2-3): 224-237. |
The Dacun and Gulong plutons were found in the southwest orogenic belt of the Yangtze block and the Cathaysia block, and the pluton has important geological significance in analyzing the regional tectonic evolution of South China. In this paper, two quartz diorite samples were collected from Dacun pluton and Gulong pluton for LA-ICP-MS zircon U-Pb dating, respectively, which yielded U-Pb ages of 438±1Ma and 435±2Ma, indicating that the Dacun pluton and Gulong pluton were both formed in Caledonian orogeny. The data show that the Dacun pluton and Gulong pluton belong to I-type granite which has calc-alkaline and aluminous-peraluminous features. The Hf isotopic compositions of zircons show that the rocks have εHf(t) values from 0 to +4, and TDM2(Hf) model ages are mainly concentrated in the range of 1.15~1.45Ga, implying that the magma was derived from the basic lower crust material, and the lower crust was formed in the Mesoproterozoic. According to geochemical features of the Dacun and Gulong plutons, Hf isotopic composition, and the dark particles-bearing pluton, in combination with regional geological conditions, the authors hold that, after the intracontinental collision orogenic period, the Dacun and Gulong plutons were formed along with the local lithosphere stretching-thinning, the upwelling of high temperature mantle materials from the asthenosphere, and the partial melting of the basic lower crust in the Mesoproterozoic. In the process of melting, there existed mixture of the upwelling mantle-derived magma formed in the source area at different levels, thus leading to the generation of parental magma. And then the magma experienced a certain degree of differentiation and evolution, finally forming rocks through solidification.
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Geological sketch map of the study area and sampling locations
Photograph and photomicrographs of the Gulong pluton
CL images of representative zircons from Dacun and Gulong plutons
Concordia diagrams showing LA-ICP-MS zircon U-Pb age dating results for the Dacun pluton
Concordia diagrams showing LA-ICP-MS zircon U-Pb age dating results for the Gulong pluton
SiO2-K2O diagram
A/CNK-A/NK diagram
Chondrite-normalized REE patterns (a) and primitive-mantle-normalized incompatible-element spidergrams for Dacun and Gulong plutons (b)
εHf(t) histogram of zircons from the Dacun and Gulong plutons
TDM2(Hf) histogram of zircons from the Dacun and Gulong plutons
Histogram of the late Early Paleozoic intermediate to acidic magmatic rocks in South China
C/MF-A/MF diagram