秦岭柞水岩体和东江口岩体的锆石U-Pb年代学及其意义

LA-ICP-MS Zircon U-Pb Geochronology and Geological Significance of Zhashui Granitoids and Dongjiangkou Granitoids from Qinling,Central China

柞水岩体和东江口岩体位于秦岭造山带南秦岭构造域,主要由似斑状花岗闪长岩和二长花岗岩组成。通过LA-ICP-MS锆石U-Pb同位素定年,结合锆石阴极发光图像,揭示柞水岩体的似斑状二长花岗岩(样品ZS01-01)存在两个谐和年龄,分别为209±2和199±2 Ma;东江口岩体似斑状二长花岗岩(样品ZS04-01)也存在两个谐和年龄,分别为219±2和209±2 Ma。结合前人的地球化学和区域构造背景研究,判定这两个岩体属于同一岩浆事件的不同阶段侵位,东江口岩体的似斑状二长花岗岩侵位结晶略早于柞水岩体,柞水岩体主期岩浆侵位时,东江口岩体也有同期岩浆侵位结晶。这两个岩体年龄的准确测定,表明在219～199 Ma期间沿商丹断裂有3个阶段的构造-岩浆活动。

Zhashui granitoids and Dongjiangkou granitoids in the South Qinling tectonic domain of the Qinling orogen, ShanXi province, are composed of porphyry-like granodiorites and porphyry-like monzogranites. LA-ICP-MS zircon U-Pb dating , in conjunction with CL-imagery, reveals that the Zhashui porphyry-like monzogranite （sample ZS01-01 ） emplaced from 209 ± 2 Ma to 199 ±2 Ma, and Dongjiangkou porphyry-like monzogranite （sample ZS04-01） from 219 ±2 Ma to 209 ±2 Ma. Integrated with the previous studies in regional tectonic setting and geochemical characteristics, the two granitoids formed in one geological event. Emplacement of the Dongjiangkou instrusion is slightly earlier than Zhashui intrusion, and second emplacement of the Dongjiangkou intrusion occurred at synchronous time with the main emplacement of the Shashui intrusion. These new dating data of these two intrusions indicates existing three stages of the tectono-magma activities during -219 Ma to -199 Ma along Shangdan suture belt in the north margin of the South Qinling tectonic domain.