青海省治多县扎那日根岩体特征及构造意义

Characteristics and tectonic significance of the Zhanarigen rock masses in Zhidoi, Qinghai

关键词:  治多  中酸性岩体  构造意义  青海

Key words:  Zhidoi  intermediate to acidic rock mass  tectonic significance  Qinghai

摘要:

扎那日根岩体主要由早期的黑云母石英闪长岩和晚期的花岗闪长岩组成。花岗闪长岩中单颗粒锆石U-Pb年龄值为216 ±2Ma和217±7Ma (晚三叠世)。岩石富碱贫钛,属钙碱性岩系。微量元素特征表现为:富集大离子亲石元素K、Ba、Rb及高场强元素Th,相对于其它相邻元素而言,Sr、Nb、Ta略显亏损,Ti、P较强亏损,(⁸⁷Sr/⁸⁶Sr)_i为0.70403~0.70463,ε_Nd(t)为2.7~ 3.4。构造背景为火山弧花岗岩,成岩物质源于壳幔混合产物。

Abstract:

The Zhanarigen rock masses in Zhidoi, Qinghai consist of early biotite quartz diorite and late granodiorite. The granodiorite gives U-Pb zircon ages ranging between 216 ±2 Ma and 217 ±7 Ma (Late Triassic). The Zhanarigen rock masses are enriched in alkali and depleted in Ti, suggesting the calc-alkaline series. They also exhibit the enrichment of the macro-ion lithophile elements K, Ba and Rb, and high field strength elements Th, while slight depletion in Sr, Nb and Ta, marked depletion in Ti and P relative to their adjacent elements. The initial ⁸⁷Sr/⁸⁶Sr ratios vary from 0.70403 to 0.70463, and the ε_Nd(t) values from 2.7 to 3.4. Judged from the trace element discrimination diagrams, the Zhanarigen rock masses should be assigned to the volcanic arc granites derived from the mixed crust-mantle products.