The Baishigang Pluton is located at the eastern end of the E-W-trending Fogang granite belt, and has an outcrop area of about 440 km2. It intruded into the Lower Jurassic Lantang Group and is made up mainly of medium- to coarse-grained biotite granites. The major mineral phases of the granites are quartz (25%-35%), microperthite (45%-50%), plagioclase (An=20-30, 15%-20%) and biotite (5%-10%). Zircon U-Pb isotopic dating yields an age of 148.5 ± 1.6 Ma, indicating that it was formed in the Late Jurassic. Chemical analyses show that the granites have high SiO2 (= 73.37%-76.05%) and moderate Al2O3 (12.00%-13.16%). They are slightly peraluminous with A/NKC values ranging mainly from 1.0 to 1.1 and normative corundum <1%. The rocks also have moderate to low alkaline contents (K2O + Na2O = 7.44%-8.48%, NK/A [molecular (K2O + Na2O)/ Al2O3] = 0.75-0.88) and high potassium contents (K2O = 4.22%-5.29%, K2O/Na2O = 1.31-1.70), thus can be ascribed to the rocks of the high-K calc-alkaline series. Trace and rare earth elements of the granites are characterized by rich Rb, Th, U, Pb and LREE, and poor Ba, Sr, P, Ti, and have high Rb/Sr (2.36-20.82) and low K/Rb ratios (<150 for most of the samples). Chondrite-normalized REE patterns are right-inclined and display significant negative europium anomalies (δEu = 0.05-0.28). Their HFSE (e. g., Nb, Ta, Zr, Hf) concentrations and Ga/Al ratios are lower than that of the respective values of A-type granites. The granites have a more enriched Nd isotopic composition with initial εNd values from -5.99 to -7.51, and show younger depleted-mantle model ages (TDM = 1.42-1.54 Ga). Integrated geochemical data suggest that the rocks are highly fractionated I-type granites. By combining with comprehensively analyses of the tectonic settings, we suggest that the Baishigang pluton was formed in a post-collisional tensile environment, and the granites were generated by a two-stage process including mixing of underplating basaltic magma with the induced felsic melts in the source region and subsequent high-degree fractional crystallization.
|Number of pages||12|
|Journal||Acta Geologica Sinica|
|Publication status||Published - 15 Aug 2005|
- Baishigang pluton
- Crust-mantle interaction
- Guangdong Province
- Highly fractionated I-type granite