北祁连山清水沟蓝片岩带中含硬柱石蓝片岩和榴辉岩的岩石学﹑^(40)Ar/^(39)Ar年代学及其意义  

Petrology and ^(40)Ar/^(39)Ar Geochronology of the Lawsonite-Bearing Blueschist and Eclogite from the Qingshuigou Blueschist Belt in North Qilian Mountains in NW China and Their Tectonic Implication

作　　者：林宜慧[1,2] 张立飞[1] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京100871 [2]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2012年第9期1503-1524,共22页Acta Geologica Sinica

基　　金："973"课题(编号2009CB825007);国家自然科学基金项目(编号410090371;41121062)资助的成果

摘　　要：本文在北祁连造山带清水沟高级蓝片岩中发现了硬柱石,硬柱石作为包体出现在石英颗粒中,颗粒细小(9.5～4μm),无自形晶。在与其伴随的榴辉岩中也发现了硬柱石包体。利用矿物内部一致性热力学数据和Domino/Theriak软件计算了清水沟含硬柱石榴辉岩、百经寺白石崖绿帘石蓝片岩、清水沟绿帘石蓝片岩和阿柔煤矿含硬柱石蓝片岩的温压条件分别是:495～519℃,2.24～2.39GPa;530～600℃,1.35～2.15GPa;520～545℃,2.20～2.35GPa;544～576℃,1.92～2.08GPa。反映清水沟高级蓝片岩带经历了硬柱石蓝片岩相到绿帘石蓝片岩相的变质转化,与含硬柱石榴辉岩的温压条件相似,代表了古祁连山洋向北俯冲发生高压低温变质作用的产物。40Ar/39Ar同位素年代学研究表明,绿帘石蓝片岩的变质年龄分别为447±1.7～447±5Ma和453±2～454±2Ma;低温榴辉岩中蓝闪石得到的蓝片岩相退变年龄为392±12～400±3Ma。综合以上岩石学﹑地球化学和同位素年代分析等资料,进一步探讨了北祁连造山带早古生代大地构造演化过程。This study reports the discovery of lawsonite, which was for the first time identified in the Oingshuigou high-grade blueschist belt in the North Qilian Mountains and was also discovered in accompanying eclogite. It occurs as enclaves in quartz grains. There are no euhedra crystals observed, with size ranging from 9. 5 to 4μm. Using internally consistent mineral thermodynamic detabase of Holland and Powell （1998）, and Domino/Theriak calculation software by de Capitani and Brown （1987）, we calculated metamorphicρT conditions of the HP/LT metamorphic belt. 2.24～2.39 GPa and 495～519℃ for the lawsonite-bearing eclogite in Qingshuigou;1.35～2.15 GPa and 530～600℃ for the epidote blueschistin Baijingsi; 2.20～2.35 GPa and 520～545℃ for the epidote blueschist in Oingshuigou; 1.924～ 2.08 GPa and T=544～576℃for the lawsonite-bearing blueschist in Arou coal mine. Results show that the Qingshuigou high-degree blueschist experienced metamorphic transformation from lawsonite glueschist to epodite blueschist, and has the similar pT condition to that of lawsonite-bearing eclogite, indicating that they were the product of high temperature and low pressure metamorphism triggered by the northward subduction of the ancient Qilian Mountain Ocean. The high quality laser 40 Ar/39 Ar dating of the epidote blueschist yields the metamorphic ages of 447±1.7～447±5 Ma and 453±2～454±2 Ma. The age of 392 ±12 ～ 400 ± 3 Ma can be interpreted as retrograde metamorphism age for low temperature eclogite. Combined with the lithological, geochemical and isotopic data above, Early Paleozoic tectonic evolution process of North Qilian orogeny was further discussed.

关 键 词：北祁连山 蓝片岩 榴辉岩 视剖面图 40Ar/39Ar定年 

分 类 号：P588.3[天文地球—岩石学]