Geochemistry of the Granites in the Tamuqi Area on the Southern Margin of Tarim Block

This study shows that the intrusive rocks distributed in the Aoyiqieke-Tamuqi area on the southern margin of the Tarim Block are composed of gabbro, diorite, granodiorite and granite, which constitute regionally a nearly EW-trending tectono-magmatic belt. Petrochemically the diorite, granodiorite and granite belong to the calc-alkaline, high-K series, with Na 2O/K 2O ratios varying between 0.83 and 2.63. M/F ratios in the diorite are within the range of 0.44- 0.70 and those of the granodiorite (granite) are 0.45- 0.87. Petrochemistry data show that the intrusive complexes are of the I type and their ΣREE is slightly variable, within the range of 178.31- 229.01×10 -6. The LREE/HREE ratios of the diorite and granite are 3.78- 5.13 and 6.69- 7.66, respectively. The plutons usually show moderate negative Eu anomalies with δEu values ranging from 0.53 to 0.82, showing almost no difference among different rocks. The (La/Yb) N values of diorite and granite are 12.39- 14.86 and 22.07- 26.03, respectively. The diorite and granite possess very similar REE distribution patterns, indicating that they were both derived from the same source. As for their trace element ratios, the diorite has higher Nb/Ta ratios than the granite, which are 15.73- 17.16 and 12.03- 15.01, respectively. It can be seen that the Nb/Ta ratios of the diorite are much closer to the average mantle ( 17.5). Their Zr/Hf ratios are very close to each other, within the range of 29-34. Th/Y ratios in the diorite are 0.42- 0.80 (all less than unity) while those of the granite are 1.02- 2.04. Some difference is also noticed in Ti/V between the diorite and the granite ( 52.6- 54.2 for the former and 52.6- 54.2 for the latter). As compared with ocean ridge granites, both diorite and granite are characterized by remarkable LILE enrichment, as well as by moderate negative Ba and postive Ce anomalies. The contents of Nb and Ta in the diorite and granite are equivalent to those of the ocean ridge granites, but the contents of Zr, Hf, Sm, Y, and Yb are all lower than those of the ocean ridge granites, indicating that these granites are similar to the island-arc granites of Chile. From their geochemical characteristics, it is considered that the intrusive rocks in the area studied were formed in an island-arc environment at the continental margin.