摘要
在缺少糜棱岩形成温度资料的情况下,糜棱岩的形成深度、与所叠加岩石的关系、变质演化、抬升-剥露历史、矿物的变形机制、同位素年龄数据的解释等一系列问题就很难得到正确合理的解释。适用于低温条件下的白云母-绿泥石地质温度计、白云母-黑云母地质温度计和绿泥石成分温度计仅在区域变质岩中应用过,从未在糜棱岩中使用。本文利用郯庐断裂带南段(安徽段)韧性剪切带内糜棱岩中同构造新生的白云母、黑云母和绿泥石,首次尝试上述3种地质温度计在糜棱岩中的应用。糜棱岩中新生矿物组合及长石变形行为显示,糜棱岩的变形温度为350℃～450℃。利用白云母-黑云母地质温度计和绿泥石地质温度计获得的温度值分别为672℃～1116℃和470℃～520℃,高于糜棱岩的形成温度,指示这2个地质温度计不适用于计算低温糜棱岩的形成温度。而利用白云母-绿泥石地质温度计获得的温度值与糜棱岩的形成温度相吻合,这表明在上述3种低温地质温度计中,只有白云母-绿泥石地质温度计适用于低温糜棱岩的形成温度测定。
Owing to lack of formation temperature data of mylonites, such problems as the formation depth, metamorphic evolution, deformation mechanism, exhumation history of mylonites, relation with host rocks and explanation of isotopic age data are difficult to interpret correctly and reasonably. The muscovite-chlorite geothermometer, muscovite-biotite geothermometer and chlorite compositional geothermometer that are suited to the low-temperature conditions have only been used in the interpretation of regional metamorphism of sedimentary rocks and have never been used for mylonites of ductile shear zones. In this paper an attempt is first made to apply the above-mentioned three geothermometers in mylonite by using syn-tectonic neogenic muscovite, biotite and chlorite of mylonites in a ductile shear zone in the southern segment （Anhui segment） of the Tanlu fault zone. According to the neogenic mineral assemblages and deformation behaviors of feldspars, the deformation temperatures of the Tanlu fault zone range between 350℃ and 450℃. The temperatures obtained using the muscovite-biotite geothermometer and chlorite compositional geothermometer range between 672℃ and 1116℃ and between 470℃ and 520℃ respectively, being higher than the deformation temperatures of mylonites in the ductile shear zone, which suggests that the two geothermometers are not applicable to calculation of the formation temperatures of low-temperature mylonite. The temperatures obtained using the muscovitechlorite geothermometer coincide with the deformation temperatures of mylonites in the Tanlu ductile shear zone, which suggests that among the above-mentioned three geothermometeres, only the muscovite-chlorite geothermometer is applicable to the measurements of the formation temperatures of low-temperature mylonites.
出处
《中国地质》
CAS
CSCD
2005年第4期625-633,共9页
Geology in China
基金
国家自然科学基金项目(40272094)资助
