摘要:
本文将哀牢山变质岩划分为三个建造类型,描述了它们的矿物成分及组构特征;选择代表性变质岩石种类,进行了岩石化学全分析及恢复原岩的研究;并根据同位素年龄和区域地质情况,对哀牢山深断裂带自晚元古代至中、新生代以来的发展演化历史,以及与其相伴随的不同期次区域变质作用、变质相分布、侵入岩浆活动及混合岩化、区域地质构造性质等,均作了详细的分析和论证。
Abstract:
The Ailaoshan metamorphic belt, striking N4OW parallel to the Ailaoshan fault, occurs as an arc convex southwestwards in plan. According to the mineral assemblages, petrochemical characteristics, fabrics and metamorphic features, the Ailaoshan metamorphic rocks can be classified into 3 main formation types: （1） hornblende-plagioclase gneiss-granulite form- ation （CⅠ）, （2） migmatite-granite formation （c Ⅱ）. （3） muscovite-biotite schist-phyllonite formation （C Ⅲ）. The Ailaoshan metamorphic belt is paired metamorphic ones, which mainly formed in the Carboniferous to Middle Triassic and the Middle Jurassic to the end of the Early Cretaceous. The high-temperature and low-pressure metamorphic belt consists of amphibolite-granulite facies, while the low-temperature and high-pressure one consists of greenschist-blue- schist facies. According to the diagrams of （al+fm）-（c+alk） versus si, （al=alk） versus c and （FeO）/MgO versus SiO2. （FeO） and TiO2 and Rb-Sr isotope ages, the protoliths of the Ailaoshan metamorphic rocks are mainly volcanic rocks and less commonly sedimentary rocks. The metavolcanic rocks in C Ⅰ and C Ⅲ, which are characterized by high （FeO） and low SiO2, （FeO）/MgO, K2O, Na2O and(87Sr/86Sr)0 and low （FeO）, are composed mainly of calc-alkaline （CA） series and, possibly, partly tholeiite. The protoliths show that there was a wide oceanic basin （a part of the East Tethys） along the Jinsha River-Ailaoshan fault during the Precambrian to Devon- ian. Due to the shrinkage of the oceanic basin during the Carboniferous to Middle Triassic （Variscan to Indosinian） the Ailaoshan area was situated in island-arc and active continental-margin tectonic environments, which led to the evolution of the continental crust with subduction of the oceanic basin in the Upper Triassic （Indosinian）. Strong thrusting in the Carboniferous to Middle Triassic and the Middle Jurassic to the end of the Early Cretaceous （Yanshanian） resulted in the formation of the Ailaoshan paired metamorphic belts.
下载:
