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Research Progress in the Petrogenesis of the Proterozoic Anorthosite Massifs

CHEN Wei1,2, ZHAO Taiping1   

  1. 1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 2. Graduate School of Chinese Academy of Sciences, Peking 100039, China
  • Received:2007-03-20 Revised:2007-03-20 Online:2007-03-20 Published:2007-03-20

Abstract: 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.