阿尔泰造山带晚古生代高温变质作用与塔里木地幔柱活动的成因联系：来自泥质和镁铁质麻粒岩的证据  

The petrogenetic link between the Late Paleozoic high-temperature metamorphism in the Altay orogen and the Tarim mantle plume: Evidence from metapelitic and mafic granulites

作　　者：刘兆[1,2] 仝来喜[1] 

机构地区：[1]中国科学院广州地球化学研究所、同位素地球化学国家重点实验室,广州510640 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2015年第6期1761-1773,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划973项目(2011CB808901)资助

摘　　要：阿尔泰造山带是中亚造山带（CAOB）的重要组成部分,在其南缘出露有高温泥质和镁铁质麻粒岩,确定其P-T轨迹对于理解阿尔泰造山带南缘在晚古生代的构造演化历史具有重要意义。通过对该区乌恰沟泥质和镁铁质麻粒岩样品精细的岩相学观察,显示其变质矿物组合分别为石榴石＋堇青石＋黑云母＋斜长石＋石英＋磁铁矿＋钛铁矿±斜方辉石±尖晶石±钾长石,斜方辉石＋单斜辉石＋角闪石＋黑云母＋斜长石＋钾长石＋石英＋钛铁矿＋磁铁矿。使用传统温压计和平均温压计算方法对其变质峰期及峰期后的P-T条件进行了计算,并利用Thermocalc软件对其中两个泥质麻粒岩进行了P-T视剖面图模拟,确定了其峰期变质条件为770~865℃和3.0~5.1kbar,并得到了两条峰期后近等压冷却（IBC）的P-T演化轨迹。这样近等压冷却的P-T轨迹表明高温变质作用可能发生于一个总体伸展的大地构造背景之下。已有年代学数据支持该区高温变质事件发生于二叠纪（270-280Ma）,与塔里木地幔柱活动的时间（-275Ma）高度一致。这说明阿尔泰二叠纪高温变质事件可能与塔里木地幔柱有着密切的成因联系。因此,我们认为二叠纪地幔柱活动引起的幔源岩浆底侵和加热可能提供了阿尔泰南缘高温-超高温变质作用所需的热源。The Altay orogen is an important part of the Central Asian Orogenic Belt（ CAOB）,and several high-temperature metapelitic and mafic granulites occur on its southern margin. Constructing their P-T paths is of great significance to understand the Late Paleozoic tectonic evolution history of the southern Chinese Altay. Detailed petrographic observations on the metapelitic and mafic granulites at Wuqiagou area show that their metamorphic assemblages are garnet ＋ cordierite ＋ biotite ＋ plagioclase ＋ quartz ＋ magnetite＋ ilmenite ± orthopyroxene ± spinel ± k-feldspar and orthopyroxene ＋ clinopyroxene ＋ biotite ＋ plagioclase ＋ k-feldspar ＋ amphibole ＋magnetite ＋ ilmenite ＋ quartz,respectively. Peak and post-peak metamorphic P-T conditions are estimated using conventional thermobarometers and average P-T approach. P-T pseudosections are calculated for two metapelitic granulites via the Thermocalc program,yielding peak metamorphic P-T conditions of 770 ~ 865℃ /3. 0 ~ 5. 1kbar and two post-peak near-isobaric cooling（ IBC） P-T paths. Such IBC P-T paths suggest that high-temperature metamorphism likely occurred in an overall extensional tectonic setting. The available age results support that the high-temperature metamorphism in the region occurred in the Permian（ 270 - 280Ma） which is coeval with the time of the Tarim mantle plume activity（ - 275Ma）. This indicates that the Altay Permian high-temperature metamorphism is likely associated tightly with the Permian Tarim mantle plume activity. We consider that the heat source necessary for the Permian high-temperature metamorphism in the southern Altay was most probably provided by underplating and heating of mantlederived mafic magma as a result of the Tarim mantle plume.

关 键 词：高温变质作用 泥质和镁铁质麻粒岩 阿尔泰造山带 P-T轨迹 塔里木地幔柱活动 

分 类 号：P588.347[天文地球—岩石学]