【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。更多还原

【Abstract】 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 t₁（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.更多还原