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江浪穹窿位于扬子西缘松潘一甘孜造山带东南缘,本次研究对江浪穹窿南部江浪岩组黑云石英片岩进行LA-ICP-MS U-Pb碎屑锆石测年。结果显示,这些锆石的年龄主要介于2 925~537 Ma之间。对比分析揭示沉积物源应来自扬子板块西北缘的元古代地层,且多为岩浆事件的产物,活动时期主要集中于2 479 Ma、810 Ma和548 Ma左右,变质事件则可能发生于918 Ma、608 Ma和100 Ma左右。2925~2462 Ma的老年龄锆石暗示区内可能存在古元古代甚至太古代的老基底。6个年轻年龄集中于559~537 Ma,加权平均值(548±9)Ma(MSWD=1.4,2σ),因而本文将该年龄(新元古代)作为江浪组最老的沉积时限。
The Jianglang dome is located on the southeast margin of the Songpan-Garzê orogenic belt in the western margin of the Yangtze River. The zircon dating of the biotite quartz schist from the Jianglangyan Formation in the southern part of the Jianglang Formations was measured by LA-ICP-MS U-Pb detrital zircon. The results show that these zircons are mainly aged between 2925 and 537 Ma. The comparative analysis reveals that the source of sediments should come from the Proterozoic strata in the northwestern margin of the Yangtze plate and are mostly the products of magmatic events. The active periods are mainly concentrated at about 2 479 Ma, 810 Ma and 548 Ma, and the metamorphic events may occur at 918 Ma, 608 Ma and 100 Ma or so. The zircon ages of 2925 ~ 2462 Ma indicate that there may be ancient basement or even ancient basement in the area. The six young age centers on 559-537 Ma and the weighted mean value (548 ± 9) Ma (MSWD = 1.4, 2σ). Therefore, this age (Neoproterozoic) is regarded as the oldest depositional period of the Jianglang Formation.