Chen W.,Wuhan University |
Chen W.,Institute of Geological Survey of Hubei |
Ma C.-Q.,Wuhan University |
Bian Q.-J.,Wuhan University |
And 5 more authors.
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2010
Granitoids occurred in Demingding region,east of middle Gangdise volcanic magma arc in Tibet, was composed of quartz diorite, quartz monzodiorite, leucotonalite, biotite granodiorite and porphyrite biotite adamellite with alkaline calcium-calcium characteristics. SiO2 content of the rocks ranged from 57.19% to 71. 78% , the ratio of K2)O/Na2O equals 0. 39-0. 98,with relatively rich sodium,and A/CNK was equals to 0. 80 -1. 02. The content of Al2O3 of 13. 64%-18. 74% indicated that the rocks were of the aluminium type. Granite aggregate summation signREE for rare earth elements ranges from 95. 11 X 10-6 to 187. 21 X 10-6 with enrichment of light REE. Negative Eu anomaly changed from no obviousness to obviousness. The rocks were rich in K,Rb,Ba,Th and other large-ion stone elements and poor in high field strength elements of Nb, Y, Yb. Study of petrology and geochemistry showed that the granite subjected a magma evolution from acid to neutral and was of characters of I type granite. They formed in the island arc environment during the plate subduction. SHRIMP U-Pb age of the granodiorite in the eastern section of Gangdise was 70. 4 Ma±2. 2 Ma,implying that the magmatism in Gangdise acted throughout Cretaceous and the magmatic activity was the product of northward subduction of new Tethys.