Petrogenesis Of The Zhuopan Alkaline Complex In West Yunnan Province And Its Metallogenesis Significance

Zhuopan alkaline complex is the important part of the Jinshajiang-Ailaoshan alkali-rich intrusive rocks,which is located in the western part of strike-slip extensional basin of Lanping.Based on the recent extensive researches and field investigations,this article systematically studies on mineralogy and geochemistry,we discussed its formation and evolution.The complex is characterized by alkali-rich,high K,lower TiO2 and high Al2O3.The pyroxenes in the rocks are diopside,belong to calcic-pyroxenes.The appearance of calcic-pyroxenes was closely related to the high content of Ca and K.According to pyroxene thermometer,the crystallization temperature of the pyroxene is estimated to 1070-1490?.Electron microprobe analysis(EMPA)shows that the biotites belong to Mg-biotites,biotites composition suggest that zhuopan alkaline complex is characterized by high Fe contents and high oxygen fugacity,which may be the reason why the complex has an iron deposit.The hornblende in the rock are pargasite.The pargasite were characterized by high Si,high Ca,high Mg and alkali-low.The biotite and pyroxene both are non-alkaline dark minerals.The feldspar in the rock are alkali-feldspar.The main characteristics of rare earth elements are following: different sample have similar REE patterns and others feature such as clear enrichment light REE,obvious LREE differentiation but relatively weaker heavy REE.There is no Eu anomaly or there are only weakly positive and negative europium anomaly.Trace element analysis show that the rock mass concentration of K,Rb,Sr,Ba and other large ion lithophile elements,relatively depletion Nb?Ta?Ti and other high field strength elements.Characteristics of trace element indicate that the source region is enriched mantle or metasomatic mantle,and subjected to intense crustal assimilation and contamination.According to the study of zircon U-Pb age,the rock diagenetic age of Zhuopan alkaline complex is 34.88-35.50 Ma,formed in Cenozoic,belong to the Himalayan tectonic stage.The age is consistent with the age of the other alkaline complex which also located in this belt.The Sr-Nd-Pb isotope:87Sr/86 Sr from 0.708011 to 0.709619?143Nd/144 Nd from 0.512209 to 0.512297?206Pb/204 Pb from 18.7248 to 19.2883,207Pb/204 Pb from 15.6749 to15.7202,208Pb/204 Pb from 39.0759 to 40.8077,that showed the source area have obvious characteristics of contamination by crustal materials and the crust-mantle transitional zone between EM?enriched mantle and lower crust.Considering the reach results of discrimination diagram for tectonic settings of biotite and the geochemical characteristics,we conclude that zhuopan alkaline complex formed in post-collision extrusion to stretch transformation tectonic setting,which coincide with the time background of the intrusions,the diagenetic process of zhuopan alkaline complex and the tectonic activities of the district has obvious coupling relationship.The Zhuopan alkaline complex which is located in the central part of Jinsa River-Ailaoshan-Honghe fault zone,due to the shear-extensional,the magma erupted into the strike-slip extensional,lead to the characteristics of the rock is different from other magma.