Genesis And Tectonic Significance Of Basic-intermediate Dyke Swarms In Tianquan County,Sichuan Province

The basic-intermediate dyke swarms are a type of rock combination formed by basic magma along the early fissures in the extensional tectonic setting.It has basaltlike chemical composition,stable attitude,and typical structural characteristics.Records and good signs of supercontinental reconstruction.During the Proterozoic period,earth tectonic-magmatic activity was frequent,and a large number of basicintermediate dyke swarms developed.A large number of neo-proterozoic dyke swarms developed in the western margin of the Yangtze craton where research area is located.The basic-intermediate dyke swarms in the Tianquan area are mainly distributed in the Neoproterozoic monzonitic granite and syenite granites in the Baoxing complex,The distribution range is wide and the number is large,but most of the width is not large,unconformable contact intrusive with granite,most of the occurrences are relatively steep,clearly demarcated from the surrounding rock,The width is mainly between tens of centimeters and tens of meters,and move towards is mainly near SN and NE.The rock types of these dyke swarms are diabase,porphyrite and pyroxene diorite,dyke swarms alteration have occurred in varying degrees.The diabase has a typical diabase texture,dense block structure,and the metamorphism is not obvious.Its mineral combination is plagioclase,pyroxene,magnetite and a small amount of accessory mineral,for example apatite,;porphyrite has a typical diabase texture and porphyritic texture,dense block structure,phenocrysts are mainly pyroxene and magnetite,and plagioclase phenocrysts are rarely seen,which is the reason for the complete alteration of plagioclase phenocrysts;pyroxene diorite have a uniform grain structure,dense block structure,mainly It is composed of plagioclase and hornblende,and also contains some biotite,magnetite and a small amount of quartz.The dark mineral content is basically about 50%.The hornblende content is very high and is clearly divided into two categories,one type of automorphic extent is better,another type of poor automorphic extent is the product of pyroxene alteration.According to facieology and geochemical analysis,the pyroxene in this type of rock has completely eroded into hornblende and chlorite.The geochemical characteristics of the dyke swarms show that the magma originated from the depleted mantle source region of the asthenosphere and was assimilation and contamination of the crust;its formation environment was an intraplate rift environment;its consolidation index and magnesium index indicate the magma evolution,there is a certain degree of crystallization differentiation.The field geological investigation found that the dyke swarms invasion is located in Neoproterozoic granite,and the overlying rock layer is Sinian period limestone,this indicates that the emplacement age of the dyke swarms are Neoproterozoic,and the UPb chronology of zircon shows that the emplacement age of the dyke swarms are about 760 Ma-770 Ma.This result is similar to the age of most basic dyke swarms in the western margin of the Yangtze craton.Based on the above analysis,the dyke swarms in the study area is high-iron pulled porphyry basalt,formed in the rift valley environment,and related to a geological event of crust-mantle interaction in the western margin of the Neoproterozoic Yangtze craton.Combined with the tectonic-magmatic evolution in the area,the formation of the dyke swarms in the area should be related to the of the Rodinia supercontinent breakup event,which is the product of the supercontinent breakup.