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江浪穹窿位于扬子陆块西缘,其间的甲坝岩组发育一套顺层产出的角闪岩,主要由角闪石(80%~85%)、斜长石(10%~15%)与少量石英(<3%)组成。为查明角闪岩的原岩性质、成岩时代及构造背景,对其进行岩石地球化学分析及LA-ICP-MS锆石U-Pb定年研究。主微量元素测试结果表明:(1)角闪岩w(SiO_2)介于48.10%~54.44%,具有较高的Al_2O_3(平均13.82%)、Fe_2O_3~T(平均10.56%)、MgO(平均8.07%)、CaO(平均9.09%)含量;(2)轻、重稀土元素具中等程度分异((La/Yb)N平均3.57),无明显Ce异常与Eu异常;(3)富集大离子亲石元素(如Rb,Th和Sr),亏损高场强元素(如Nb,P,Zr,Hf和Ti),多数微量元素含量与N-MORB相当。原岩恢复及构造背景判别显示,角闪岩原岩可能是弧后盆地玄武岩。锆石U-Pb年代学分析表明,角闪岩中锆石具有清晰的振荡环带及较高的Th/U值(平均0.51),应属岩浆成因;锆石~(207)Pb/~(206)Pb加权平均年龄分为2 385Ma及2 211 Ma两组,前者应为捕获锆石的年龄,后者可以代表原岩结晶年龄。这一结果暗示,至少有部分甲坝岩组地层形成于古元古代。综合分析,江浪穹窿很可能发育古元古代基底,且部分地层时代亟待重新厘定。
Jianglang Dome is located at the western margin of the Yangtze Block. In the meantime, a series of amphibolite rocks are developed in the Kaiba Formation, which are mainly composed of amphibole (80% -85%), plagioclase (10% -15% ) And a small amount of quartz (<3%). In order to find out the protolith characteristics, diagenetic age and tectonic setting of amphibolite, the lithogeochemical analysis and zircon U-Pb dating of LA-ICP-MS were carried out. The main trace elements test results show that: (1) w (SiO 2) of amphibolite is between 48.10% and 54.44% with high contents of Al 2 O 3 (average 13.82%), Fe 2 O 3 T (average 10.56%), MgO ), And CaO (average 9.09%). (2) Light and heavy rare earth elements have a moderate degree of differentiation (La / Yb) N average 3.57), with no obvious Ce anomalies and Eu anomalies; (3) Stone elements (such as Rb, Th and Sr), depleted high field strength elements (such as Nb, P, Zr, Hf and Ti), most of the content of trace elements and N-MORB. The restoration of the original rock and the discrimination of tectonic setting show that the original amphibole rock may be the basalt in the backarc basin. The zircon U-Pb chronological analysis shows that the zircons in amphibolite have a clear oscillatory zone and a high Th / U value (average 0.51), which should be of magmatic origin. The zircon ~ (207) Pb / ~ 206) The Pb-weighted average ages are divided into 2 385 Ma and 2 211 Ma groups. The former should be the age of the zircons captured and the latter may represent the age of the original rock. This result suggests that at least some of the formations in the Archean Formation formed during the Paleoproterozoic. Comprehensive analysis, Jiang Long dome is likely to develop ancient basement of the ancient palaeontology, and some stratigraphic era urgent redefined.