皖东张八岭群主期变质温度评价及结构框架探究

皖东张八岭群处于郯庐断裂带南段，构造位置极为独特和和关键，其是大别造山带和苏鲁造山带之间最重要的变质块体之一。前人主要侧重于构造地质学、年代学及岩石地球化学等方面研究，而对张八岭群的峰期变质条件、岩石单元划分和构成以及时间序列并不明晰。故而，本文将通过对张八岭群的区域变质岩石学、岩相学、热力学及年代学等研究，进一步确定其峰期变质条件、岩性特征，并对其岩石单元划分和构成进行深入解析。本次主要对张八岭群应用了白云母温度计进行峰期变质温度评价，单元-Ⅰ和单元-Ⅱ的温度范围分别为：T = 368 ℃～494 ℃和T = 331 ℃～394 ℃，主要经历了绿片—绿帘角闪岩相变质。锆石U-Pb年代学分析表明单元-Ⅰ和单元-Ⅱ原岩结晶年龄分别为749±8 Ma～738±8 Ma和738±9 Ma，该结果与前人研究结果基本一致。单元-Ⅲ的碎屑年龄范围为908±29 Ma～685±30 Ma，最大沉积年龄为685±30 Ma，沉积时限应属于新元古代，沉积物源主要来自扬子板块。据野外特征、岩相学差异、热力学评价和年代学分析，本文将张八岭群自下而上划分为3个单元，其中，单元-Ⅰ主要由石英—长石片岩组成，单元-Ⅱ主要由云母石英片岩和少量变基性岩组成，单元-Ⅲ主要由千枚岩、大理岩及少量片岩组成。本文认识对于理解华北板块与扬子板块沿郯庐断裂汇聚提供一定的岩石学支撑，张八岭群并没有经历高压低温蓝片岩相变质。

Evaluation of the main stage metamorphism temperature of the Zhangbaling Group in eastern Anhui and its structural framework

The Zhangbaling Group in eastern Anhui is located in the southern part of the Tan-Lu fault zone. It is one of the most important metamorphic blocks between the Dabie orogenic belt and the Sulu orogenic belt, and the tectonic position is very unique and important. Previous studies mainly focus on tectonic geology, chronology and petrogeochemistry. The study of main metamorphic conditions, rock units and time series are relatively indistinct. This paper conducts a detailed research on peak metamorphic conditions, lithology characteristic and rock unit division on the basic of regional metamorphic petrology, lithofacies thermodynamics and chronology studies. Combined with muscovite thermometer and previous studies, the results of peak metamorphic temperature of unite-Ⅰ and unite-Ⅱ are T = 368 ℃～494 ℃ and T = 331 ℃～394 ℃, respectively. It shows that Zhangbaling Group mainly gone through greenschist-epidote amphibolite facies. The study of LA-ICP-MS zircon U-Pb reveals the crystallization age of unit-Ⅰ and unit-Ⅱ are 749±8 Ma～738±8 Ma and 738±9 Ma and basically consistent with previous studies. However, the clastic age of unit-Ⅲ is ranging from 908±29 Ma to 685±30 Ma. The source of unit-Ⅲ is relatively single and sedimentary provenance is mainly from unit-Ⅰ and unit-Ⅱ. The maximum sedimentary age is 685±30 Ma. The sedimentary time should belong to Neoproterozoic, and the source of sedimentary material is mainly from Yangtze plat. According to the above research, we divide Zhangbaling Group into three units from bottom to top. Unit-Ⅰ, unit-Ⅱ and unit-Ⅲ are respectively composed of quartz-feldspar schist mica quartz schist and a small amount of metabase, phyllite, marble and a small number of schist. The result of this paper provides a certain petrological support for understanding the convergence of the North China plate and the Yangtze plate along the Tan-Lu fault. The Zhangbaling Group does not experience high-pressure, low-temperature blue schist facies metamorphism.