Nd, Sr and Pb isotopic characteristics of the alkaline_rich porphyries in western Yunnan and its compression strike_slip setting

Abstract

Distributed along the Jinshajiang-Ailaoshan fault zone, the alkaline_rich porphyry zone was formed in Paleogene (from 62 Ma to 23.18 Ma). The petrochemical and isotopic geochemical characteristics of the porphyriessuggest that the tectonic setting is predominantly shear_compression and locally extension, uplifting (diapir) of the Protererzoic basement metamorphic rocks of Mt. Cangshan is also a product of the same setting. The alkaline_rich porphyry results from upward erosion of deep EMⅡ fluid contaminated in different degrees by crustal components. Porphyries keep a trace of both Yangtze block and Gandwana continent, as shown by lead isotopes.