Geochemical Characteristics And Significance Of Mafic Rocks From Batang Zhubalong Area Along Jinshajiang Suture Zone

The mafic rocks in Batang Zhubalong are located in the middle piece of Jinshajiang suture zone in Sanjiang area,they belong to the component of tectonic mélange zone.The mafic rocks exposed in the area include gabbro,diabase,basalt,and andesitic-basalt etc.By a study in mafic rocks’field geological characteristics、geochemical characteristics,isotopic age in Jinshajiang mélange zone,we providded reliable date for mafic geological research,and obtained the following knowledge:Mafic rocks in Batang Zhubalong area are native to the middle piece of the Jinsha Jiang tectonic mélange zone,which are output in tectonic block and tectonic slices,the matrix is a set of silt flysch formation.Mafic intrusive rocks in the study area are rich in titanite,and these rocks mostly experienced deformation and metamorphism that include cataclastic lithification,mylonitization,etc.and hydrothermal alteration such as carbonatation,chloritization,epidotization,etc.Besides,the rocks in this area experienced more than two periods of tectonic metamorphism.In tho role of late collision orogenesis,the fault occurrence and schistositys are reformed to wastward.The rocks in the study area are rich in Na,low in K,high in alkali and low in Mg#value（0.42⁰.56）.The volcano rocks in eastern part of the study area are with low TiO₂（0.76%⁰.98%）;middle and high K₂O（0.67%¹.28%）,high Al₂O₃（16.77%¹9.94%）,MgO（5.76%⁷.65%）,and with Nb,Ta,Ti loss and rare earth element situation map right deviation,the LREE/HREE,La_N/Yb_N andδEu are4.83%⁵.68%,4.26%⁵.63%and 0.94¹.07 respectively,without Eu anomaly,which are the typical characteristics of continental marginal arc volcanic rocks.The rocks located in the western of study area have medium and high content of K₂O（0.13%-0.76%）,TiO₂（1.28%².27%）,P₂O₅（0.13%-0.30%）,the content of Al₂O₃is higher（12.80%²0.82%）,and the rare earth elements are of weak right deviation and no obvious Eu anomaly,which is similar to the chemical composition of Sanjiang ocean ridge-alike ocean ridge basalt.The result of the experiment shows that the age of the zircon from diabase gabbro sample is 246.5+1.3 Ma（95%confidence coefficient,MSWD=2.1）,which also represents the crystallization age of magmatic crystallization.In early triassic,Jinsha Jiang Ocean is still in a expanded state and accompanied by the role of subduction.The collision happened in western section and southern section is earlier than the collision happened in northern section.So it is concluded that the Jinsha Jiang Ocean is closed in concave arc.The mafic rock magma in the study area is evolutionary magma,the basalt magma in western part of the study area comes from mantle source,the continental arc volcanic in eastern study area comes form the mantle plume source（related to the role of subduction fluid）,which is which is contaminated by the continental crust.The magma has undergone various degrees of sulfide detachment and the loss of copper elements.In this area of the Jinsha Jiang ocean,there may be the a subduction from oceanic ridge to the continental plate...