江西相山碎斑熔岩成因和钾长石亚显微结构  

Genesis of the Xiangshan Porphyroclastic Lava and Submicroscopic Structure of Its K-feldspar Phenocrysts

作　　者：刘昌实[1] 薛纪越[1] 张根娣[1] 沈渭洲[1] 陈繁荣[1] 张富生[2] 

机构地区：[1]南京大学地球科学系,南京210008 [2]南京大学现代测试中心

出　　处：《岩石矿物学杂志》1992年第3期243-251,T001,共10页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金委48970173

摘　　要：相山碎斑熔岩含铁铝榴石(1340g/T)、红柱石等岩浆结晶副矿物,具S型火山岩地球化学和Nd、Sr、O同位素组成的特征。据光学测定和X光粉晶衍射测定,斑晶钾长石主要是高正长石或低透长石,有序参数δ′=-0.32—-0.01。在透射电镜下,出溶的细钠长石页片由共格拐点分解形成,成分波长约50—100nm;出溶的宽钠长石页片由无应力离溶作用形成,页片宽50—200nm。结果表明,碎斑熔岩是在火山环境下形成,而不是在深成环境下形成。The Upper Jurassic. porphyroclastic lava exposed in Xiangshan area,Jiangxi Province, usually contains certain amounts of almandite and andalusitewhich crystallized from magma as accessory constituents. Geochemically, itshows many characteristics of S-type volcanic rocks and has Nd, Sr, O iso-topic compositions. Optical and X-ray powder diffraction determinations indicate that theK-feldspar in porphyroclastic lava is mainly high orthoclase or low sanidine,with optic angles (-2V) ranging from 40°to 53°, All occupancies at t_1(O)sites from 0.36 to 0.38 and. degree of order δ′from -0.32 to 0.11. It isseen under TEM that exsolved fine albite lamellae are formed by the decom-position process of coherent: spinodal with the compositional wave-lengthabout 50--100 nm, whereas wide albite lamellae are formed by strain-freeexsolution with lamella width some 50--200 nm. These data suggest that theXiangshan porphyroclastic lava was formed in volcanic environment ratherthan plutonic environment.

关 键 词：碎斑熔岩 钾长石有序度 亚显微结构 

分 类 号：P642.25[天文地球—工程地质学]