四川丹巴地区斜长角闪岩的地球化学特征及其大地构造意义

丹巴地区位于川西松潘－甘改造山带东缘，出露较多的斜长角闪岩类。这些岩石通常呈透镜状与碳酸盐岩，泥质岩相伴生。地球化学研究表明，这类斜长角闪岩为正斜长角闪的岩主要为钙碱性玄武岩类。

GEOCHEMICAL CHARACTERS AND TECTONIC SIGNIFICANCE OF PLAGIOCLASE AMPHIBOLITE IN DANBA AREA, SICHUAN PROVINCE

Danba area is located in the eastern margin of the main body of Songpan-Gauze orogenic belt. As acomplex basement of orogenic belt, the matamorphic rocks of Danba area attaining up to high-grade amphibolite factes, seem to be the highest in the entire orogenic belt. In terms of difference of metamorphism amphibolite of Danba area can be subdivided into epidote amphibolite, biotite amphibolite and plagioclase amphibolite. All these amphibolites occurred as lens and are associated with carbonatite, pelite and silicolites. Themineralogy of amphibolite is rather simple. Major minerals are bornblende and plagioclase which formed lepidoblastic structure. Zircon is one of the accessory minerals. which occurred as prism-developing bipyramide.U-Pb isotopic dating on single zircon from plagioclase amphibolites gives an age of 800 Ma ;it is suggested thatamphibolites are the products of the late Proterozoic volcanism. Based on petrochemistry, trace element andREE data, this paper discusses petrogenesis of plagioclase amphibolite in Danba area. A combination of geochemical characters. such as high contents of Fe, Mg, Ca and Ti in rock, enrichment of lithophile elements(Sr,B,Th,Nb,Ta etc. ). slight enrichment of LREE and deption of Eu, may indicate that plagioclase amphibolite is similiar to island arc basalt. They formed at active continental margin and are contaminated by continental crustal in process of uplift.