Study On Zircon Inclusions Of Longtou Shan Kimberlite In Siziwangqi,Inner Mongolia

Kimberlite is a kind of alkaline ultrabasic rock with rich in volatile and potassium,which originates from the deep mantle and rises rapidly to the shallow part of the crust.Its inclusions carry the information of the deep earth and are an important medium for us to better understand the deep earth.This study collects zircon inclusions of Longtou Shan kimberlite to study the relationship between zircon and its inclusions occurring within kimberlite,to further explore the primary zircon characteristics of kimberlite.In addition,it provides a basis study on the formation age of kimberlite.Longtou Shan kimberlite consists of abundant of zircon minerals.The inclusion minerals within zircons are identified by electron probe technique,which is composed of the diamond,olivine,pyroxene,corundum,and quartz minerals.The inclusions have a good indicative significance for the genesis and formation setting of zircons,we can restrict directly and effectively the formation setting of zircons,and the zircon formed in different settings has the corresponding inclusions' mineral composition.Diamond is the primary mineral of kimberlite,whereas the olivine and pyroxene may be either primary minerals or captive minerals of kimberlite.The ages are suggested to divide into five following groups by using the LA-ICP-MS zircon U-Pb dating that containing mineral inclusions:(1)the first group(2398~2121 Ma)is captive zircon,which may be related to extensional tectonic events in the region;(2)the second group(1943~1856 Ma)is also captive zircon,which may be related to the collision event between the North China craton and the northern continental block,i.e.,Siberia craton;(3)the third group(1798~1476 Ma)is magmatic zircon may be related to the breakup of Colombia supercontinent;(4)the fourth group(1298~1273 Ma)is metamorphosed zircon may be related to the occurrence of mafic large igneous province events in the region;and(5)the fifth group(408~342 Ma)is metamorphosed zircon that is possible related to the closure of the Paleo-Asian Ocean.By discussing the relationship between zircon and inclusion,the magmatic zircon consisting of the diamond inclusion plays an important role as the primary zircon of kimberlite,and the formation age of Longtou Shan kimberlite is interpreted as 1476 +49 Ma.