中文摘要：

中-晚侏罗世和早白垩世2期伸展作用最终形成了医巫阁山变质核杂岩。有限应变分析结果显示，早期（中-晚侏罗世）伸展作用形成的韧性剪切带中付林指数㈤为0．5-6．06，平均值约为2．78；晚期（早白垩世）伸展作用形成的韧性剪切带中付林指数为0．21-2．39，平均值约为1．23。结合有限应变及运动学涡度分析可知，医巫闾山地区2期伸展变形具有不均匀性，中-晚侏罗世伸展变形表现为早期拉长应变、晚期平面应变，纯剪切组分大于简单剪切；早白垩世伸展变形表现为平面应变，早期简单剪切组分与纯剪切相等，晚期纯剪切组分大于简单剪切。对比2期伸展变形环境及古应力的差异，发现早期伸展变形温度高、差应力小、应变速率较大；晚期伸展变形温度低、差应力大、应变速率较小。医巫闾山地区中-晚侏罗世在近水平的伸展背景下，中下地壳发生减压熔融；在晚侏罗世末期短暂的挤压作用后，早白垩世先发生近水平的伸展滑移，之后转为以垂向隆升为主的变形,并最终形成变质核杂岩。

英文摘要：

The Yiwultishan metamorphic core complex was formed by two stages of extension that occurred in Middle-Late Jurassic and Early Cretaceous respectively. Finite strain measurement shows that the Flinn exponent of the earlier extension （Middle-Late Jurassic） and the later extension（Early Cretaceous） are 0.50-6.06 （2.78 on average） and 0.21-2.39 （1.23 on average） respectively. The kinematic vorticity （Wk） estimated by Polar Mohr Circle diagram of earher extension is 0.00-0.82 （0.56 on average）, whereas the later extension＇s Wk is 0.5-0.93 （0.75 on average）. The Wk of the extensional crenulation cleavage （C＇） estimated by C＇ method ranges from 0.31 to 0.72. The analysis of finite strain and kinematic vorticity suggests that the two stages of extension in Yiwultishan area were asymmetrical, and the strain type of Middle-Late Jurassic deformation is pure dominated general shearing with elongation at earlier extension and plane strain at later extension. Plane strain with equally simple and pure shearing at earlier extension and pure dominated at later extension constitute the strain type of Early Cretaceous deformation. A comparison of the deformation conditions and paleo-stresses of two stages of extension indicates that the earlier extension is characterized by higher deformation temperature, lower differential stress and higher strain rate, whereas the later extension is characterized by lower temperature, higher differential stress and lower strain rate. All these characteristics, combined with the modes of occurrence and deformation features of syn-extensional dikes, plutons and their wall rocks, suggest that decompressed melting occurred in the middle and lower crust under an approximately horizontal extension in Yiwulushan area in Middle-Late Jurassic period; after a short compression at the end of Late Jurassic, the area underwent an approximately hori- zontal extension in early Early Cretaceous and then the deformation turned into perpendicular uplift, and finally led to th