The Gutian-Xiaotao granitic Complex is composed of the Xiaotao, Gutian, Huajia, Jiaoyang and Gutian units. The Xiaotao, Gutian and Huajia units are biotite-bearing monzogranite, and the Jiaoyang and Gutian units are homblende-bearing biotite quartz-monzonite. The Xiaotao and Gutian granites are characterized by high SiO2 (> 71.77%), K2 O (> 4.67%) and low CaO (< 1.71 %), belonging to weakly to strongly peraluminous. They have high Rb, Nb, Ta, Th, U contents and low Sr, Ba. Their REE concentrations and differentiation extents are variable with middle to strong Eu depletion (Eu/Eu* = 0.52 ∼ 0.08). The Jiaoyang and Gutian quartz monzonites have low SiO2 (62.88% ∼ 66.38%) and high Al2O3 contents (15.44% ∼ 16.51%). The former has high REE content and later low REE contents, both have weak Eu depletion (0.65 ∼ 0.80) and high La/Yb ratios. The Huajia granites have geochemical characteristics ranging between above-mentioned two suites of granites. LA-ICPMS zircon U-Pb dating indicates that the Xiaotao granite formed at 222 ± 3Ma and Gutian granite at 161 ± 1Ma. The Xiaotao and Gutian granites and Gutian monzonite have similar initial 87Sr/86Sr ratios (0.7089 ∼ 0.7099) and ε Nd(t) values (-11.1 ∼ -11.5), and zircons from the Xiaotao and Gutian granites show similar Hf isotopic compositions, suggesting that they originated from same source, although they were generated at different time. Geochemistry and Sr-Nd-Hf isotopes indicate that that the source consists of metasedimentary rocks with 1.7 ∼ 1.5Ga model age. The Huajia granite in the southern Complex has marked high initial 87Sr/86Sr ratio (0.7310) and lower εNd(t) values (-16.4), indicating that its parental magma derived from Paleoproterozoic crustal materials, which implies different basements under the northern and southern parts of the Complex. The Gutian granite formed in early Yanshanian and the Xiaotao granite formed in late Indosinian. Geochemical features, rock assemblage and structure stress analyses indicate that early Yanshanian granitic magmas generated in the extensional tectonic setting within plate, and late Indosinian ones in post-orogeny tectonic setting.
|Number of pages||15|
|Journal||Acta Petrologica Sinica|
|Publication status||Published - 2007|
- Element geochemistry
- Gutian-Xiaotao granitic Complex
- La-ICPMS Zircon U-Pb dating
- Sr-ND-Hf isotope tracer