石鼓-黎明地区变沉积岩系的深熔时代和物源

以出露于石鼓-黎明地区的黑云母石英片岩及其深熔脉体为重点研究对象,对其中的锆石进行了阴极发光图像分析、SHRIMP和LA-ICP-MS U-Pb年代学研究。阴极发光图像显示,黑云母石英片岩中大部分锆石保留清晰的振荡环带;深熔脉体中大部分锆石具有核-边结构,核部保留清晰的振荡环带或呈灰色无分带结构,边部较窄呈黑色。对黑云母石英片岩及其深熔脉体中锆石核部进行定年,得到年龄范围为2 637～743 Ma,具有858～852 Ma的主要年龄峰值,表明其主要物质来源为扬子板块西缘新元古代岩浆岩,同时也有太古代-古元古代基底岩石的加入,沉积时代应晚于852 Ma。深熔脉体锆石边部的Th/U值较小(0. 1),得到206Pb/238U年龄变化于225～197 Ma之间,可能代表了变沉积岩的变质-深熔时代,该年龄与金沙江-点苍山-哀牢山变质带二叠纪-三叠纪变质事件的时代相一致。

Timing of anatexis and provenance of meta-sedimentary rocks in Shigu-Liming area

Based on cathodoluminescence (CL) images, the authors present LA-ICP-MS and SHRIMP U-Pb zircon data of biotite-quartz schist and granitic leucosomes in the Shigu-Liming area. Most zircon grains separated from biotite-quartz schist show clear oscillatory zoning, and most of them from granitic leucosomes are characterized by core-rim structure with strongly or weakly oscillatory zoned cores and narrow black rims. Analysis of zircon cores from biotite-quartz schist and granitic leucosomes yielded U-Pb ages of 2 637~743 Ma with age peak at 858~852 Ma, indicating that their sediments were mainly transported from Neoproterozoic magmatic rocks of western Yangtze Block and also from Archean to Paleoproterozoic basement rocks and deposited after~852 Ma. These zircon rims have low Th/U ratios (<0.1) indicating the timing of anatexis. U-Pb analysis spots yielded ages of 225~197 Ma, and this age population is completely consistent with the age range of the Permian-Triassic metamorphic events of Jinshajiang-Diancangshan-Ailaoshan complex.