元古宙岩体型斜长岩的特征及研究现状

斜长岩是指斜长石含量>90%的岩浆岩，可分为6类。其中，岩体型斜长岩仅赋存于前寒武纪变质地体中，形成时代主要为元古宙（2.1~ 0.9 Ga），代表地球演化史上很重要的构造-热事件。岩体呈穹隆状或层状产出，具典型堆晶结构，有含钾长石和斜长石出溶片晶的巨晶斜长石和富铝辉石。巨晶的出溶指示了岩浆由高压至低压的变压结晶过程，体现了斜长岩体深成、浅侵位的特点。关于斜长岩的源区，之前普遍认为源于幔源玄武质岩浆，而近10年来更趋向于源区为下地壳，母岩浆的成分为纹长苏长岩和铁闪长岩等新认识；其成因模式以底侵模式和地壳舌状物熔融模式最具代表性。岩体型斜长岩时空上常与奥长环斑花岗岩共生，构成AMCG（Anorthosite Mangerite Charnockite Granite）岩石组合，被认为属非造山岩浆作用的产物，可能代表大陆裂谷环境。然而，新近一些年龄结果显示，它们形成于造山作用的后期阶段，暗示岩体产出于碰撞后环境。斜长岩体中常赋存有Fe Ti V氧化物矿床，有的富含P及Cu，Ni硫化物等，属典型的岩浆矿床。对此，目前主要有结晶分异过程、早期堆晶过程及不混熔分离3种成因机制解释。由此对今后研究中值得关注的问题提出了一些看法。

Research Progress in the Petrogenesis of the Proterozoic Anorthosite Massifs

Anorthosite refers to igneous rocks consisting of over 90% plagioclase. Massif-type anorthosite is the most common type of anorthosite and with distinct characteristics. Most massif-type anorthosite bodies are Proterozoic ranging from 2.1 Gato 0.9 Ga in formation ages, representing an important tectono-thermal event in the earth evolution. The anorthosite massifs are usually dome-shaped or layered. Anorthosites often show cumulate texture composed of high-Al pyroxene and plagioclase megacrysts containing exsolution lamellaes of plagioclase and K-feldspar. The exsolution of the megacrysts indicates a polybaric crystallization process, which indicates the feature of deep generation and shallow emplacement. There exist different points of view in the petrogenesis of massif-type anorthosite. Many workers considered that the anorthosite massifs were generated from the upper mantle-derived basaltic magma. Whereas, especially in recent decade,some geologists argued that they were formed from the lower crust. The composition of the parental magma of anorthosite is considered to be more like jotunite and ferrodiorite. Two models are very common to interpret the formation of anorthosite massifs: the underplating model and the crustal tongue melting model.Most massif-type anorthosite bodies are spatially and temporally associated with rapakivi-granites, constituting an AMCG suite (anorthosite-mangerite-charnockite-granite), as a result of anorogenic magmatism in a continental-rift setting. However, some massifs might be formed at the late stage of orogeny, representing a post-collisional setting. Proterozoic massif-type anorthosite bodies are also hosts of P-rich Fe-Ti oxide deposits and a few of Cu-Ni sulfide deposits. These deposits are considered to be formed by fractional crystallization, primary cumulates or immiscible oxide melts.