苏鲁造山带古元古代超高温麻粒岩及其构造意义  

Paleoproterozoic UHT granulite in the Sulu orogen and its tectonic implications

作　　者：雷恒聪 向华[2] 张泽明[2] 祁敏[2] 董昕[2] 林彦蒿[3] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037 [3]中国地质大学研究生院,武汉430074

出　　处：《岩石学报》2014年第8期2435-2445,共11页Acta Petrologica Sinica

基　　金：深部探测项目(Sinoprobe-05-04);国家自然科学基金项目(41302040);中国地质调查局工作项目(12120114079801)联合资助

摘　　要：本文报道了在苏鲁超高压变质带北端威海地区识别出的古元古代超高温泥质麻粒岩。泥质麻粒岩与大理岩、钙硅酸盐岩和片麻岩等变质表壳岩伴生。这些表壳岩以透镜体的形式产于经历了三叠纪超高压变质的新元古代正片麻岩中。泥质麻粒岩由石榴石、夕线石、斜长石、钾长石、反条纹长石、石英、黑云母、白云母和金红石组成。黑云母和白云母呈石榴石和夕线石的冠状体产出,为退变质矿物。相平衡模拟结果表明,麻粒岩峰期变质的温度和压力条件为～940℃和～1.2GPa。泥质麻粒岩中的锆石近等粒状或椭圆形,具有扇状或冷杉状分带,大多数具有平坦甚至亏损的重稀土配分模式,并有Eu负异常,为典型的麻粒岩相变质锆石。锆石的LA-ICP-MS U-Pb定年结果给出了1845±9Ma的207Pb/206Pb加权平均年龄,表明超高温麻粒岩形成于古元古代。结合现有的其他研究结果,我们推测扬子板块北缘经历了古元古代的增生造山作用。In this paper, we report the Paleoproterozoic ultrahigh-temperature pelitic granulites from the northern segment of Snlu ultrahigh-pressure metamorphic belt. The pelitic granulites occur as interlayer within other metamorphic supraerustal rocks, such as marble, cale-silicate rock and gneiss. In turn, these rocks together occur as larger lens within the Triassic ultrahigh-pressure metamorphic orthogneisses with the Neoproterozoic protolith ages. The pelitic granulites show the porphyroblast texture, massive structure or weak gneissic foliation, and are composed of garnet, sillimanite, plagioclase, K-feldspar, antiperthite, quartz, biotite, muscovite and rutile. The porphyroblastic garnet set in the matrix of sillimanite, plagioclase, K-feldspar, antiperthite, quartz, biotite, muscovite and rutile. The biotite and muscovite commonly occur as the symplectitic corona around garnet and sillimanite, representing the retrograde phase of the granulite. Garnet shows a homogenous core compositions with XFo = 0. 508 ～ 0. 587, XMg = 0. 394 ～0. 453 and Mg^# = 0. 408 ～ 0. 471. Phase equilibria modeling in the MnNCFKMASHTO system indicates that the pelitie granulites were metamorphosed under P-T conditions of -1.2GPa and～940℃. Zircons from the granulites are nearly isometric granular, and have the sector or fir-like zoning. Most zircons are characterized by fiat or even depleted HREE patterns with negative Eu anomalies, typical of granulite-facies metamorphic zircon. LA-ICP-MS U-Pb dating of the zircons yields a weighted mean 207Pb/206Pb age of 1845 ± 9Ma （MSWD = 0. 77 ）, indicating the peak-metamorphic age of the pelitic granulites. Considering the widespread occurrence of Paleoproterozoic （1.9～1.8Ga） magmatism and metamorphism in the n0rthern.margin of the Yangtze plate, we speculate that these tectonothermal events may have derived from an accretionary orogeny during or after the Columbia supercontinent assembly.

关 键 词：古元古代 超高温麻粒岩 扬子板块北缘 增生造山作用 苏鲁造山带 

分 类 号：P588.347[天文地球—岩石学] P597.3[天文地球—地质学]