新疆尾亚地区石英二长闪长岩的岩浆混合成因

新疆东天山的尾亚钒钛磁铁矿矿区,在花岗岩中含有大量闪长岩包体,而且花岗岩与闪长岩相互包裹、渗透,并在花岗岩与闪长岩接触带形成二者混合的产物——岩浆混合岩。通过野外特征、岩相学和矿物成分对比,发现矿区中部的石英二长闪长(斑)岩体与岩浆混合岩完全相同,表明该岩体系岩浆混合成因。各类参与岩浆混合作用岩石的岩相学和矿物学表现出典型的岩浆混合作用特征。矿物不平衡组构主要有:钾长石的更长环斑结构、斑晶的环边结构、针状磷灰石发育、暗色矿物的聚晶团块、岩浆混合岩中出现钾长石"变晶"等等。各类岩石中斜长石和角闪石的主要氧化物成分对SiO_2(%)表现出类似全岩哈克图解的线性关系。主要造岩矿物的化学成分以及钾长石巨晶的化学成分剖面,反映出本区岩浆混合作用有化学混合的参与。黑云母的化学成分表明,本区岩浆混合为以壳慢混源为基础的混合作用。

Magma-mixing genesis of quartz monzodiorite in the Weiya, Xinjiang

There wildly occurs magma mixing in the Weiya vanadium-bearing titianomagnetite ore district,which evidenced by not only lots of diorite enclaves in granitoid rocks,granitoid enclaves in diorite and dispersion each other,but also forming a mixing product in the contact zone of granite and diorite:magma mixed rocks.Based on comparison of field characteristics,lithology and mineralogy, it is found that the quartz monzodiorit rockbody in the middle part of the ore district is identical petrography with the magma mixed rocks and thus the rockbody might belong to magma-mixing genesis.All rock types present typical magma mixing characteristics in petrography and mineral chemistry.There are wide spread disequilibrium mineral textures in these rocks such as rapakivi texture of Kf (potassium feldspar),circum-phenocrast structure,acicular apatite texture,glomerogranular crumb structure by hornblende and biotite,plagioclase"crystalloblast"with a lot of capture crystals.Plot data of main oxides versus SiO_2(wt %)from plagioclase and hornblende compose of well linearity similar to Hake diagram of bulk-rock analysis.Composition of essential rock-forming minerals and huge Kf phenocrast section indicate that exchange of the chemical compositions exist in magma mixing.It is suggested by composition of biotite that the magma mixing in this area is derived from crust-mantle mixing source.