Geologic Characteristics And Prtrogenesis Of The Wajilitag Mafic-ultramafic Intrusion From The Permian Tarimlarge Igneous Province,NW China

The TarimLarge Igneous Province?TLIP?is recognized as the second largest LIP in China after the Emeishan Large Igneous Province?ELIP?.Compared with typical LIPs such as the Deccan,Siberian and Emeishan,the TLIP has three distinct features:highly complex lithology,long duration of magmatism?300²70Ma?and significant volumes of ferrobasalts.However,little is known about its causes,and the key to solving this confusion is to reveal its source characteristics.This paper systematically studies the different stages of olivine in the mafic-ultramafic intrusion in the Wajilitag Fe-Ti-V oxide deposit in the northwestern Tarim large igneous province.Combined with the Zn isotope of the whole rock,we evaluated the characteristics of the mantle source and the geodynamic process of the TLIP.In this study,we report the chemical compositions of olivine in two types of olivine pyroxenites?porphyritic and coarse-grained?from the Wajilitag mafic-ultramafic intrusion in the northwestern TLIP,aiming to characterize the mantle sources of magmas.Olivine in the porphyritic olivine pyroxenites shows low100*Mn/Fe?¹.3?and Mn/Zn?<13?ratios,whereas that in the coarse-grained olivine pyroxenites is characterized by markedly higher ratios of 100*Mn/Fe?>1.9?and Mn/Zn?>14?,suggesting a heterogeneous mantle source beneath the Wajilitag area.The two type of olivines show relatively consistent high Ti and Ca contents,indicating that the mantle source probably has undergone carbonatitic metasomatism.The low olivine V/Sc values?<1.5?in the two types of olivine pyroxenites reflect high oxygen fugacity conditions during magma crystallization.The maximum temperatures of crystallization of porphyritic olivine pyroxenites and olivine pyroxenites estimated based on the Al-in-olivine thermometer are 1350°C and 1190°C,respectively.The Wajilitag mafic-ultramafic intrusion has a heavy?⁶⁶Zn values?0.27±0.03‰⁰.48±0.02‰?compared to the normal mantle values.Meanwhile,previous stydies reported that Wajilitag mafic-ultramafic intrusion has a light?²⁶Mg values?-1.93‰^-0.65‰?,which suggets that the material causing the increase of?⁶⁶Zn in the Wajilitag mafic-ultramafic intrusion is carbonatite.Comprehensive research shows that the complex lithology,long duration of magmatism and voluminous ferrobasalts in the TLIP are attributed to the carbonatitic metasomatism and the incorporation of differing proportions of pyroxenite components into the mantle.A comparison of the results from our study in terms of mantle source and oxygen fugacity suggests less potential for metallogeny in this region,as against the Panxi area in the Emeishan Large Igneous Province.