Structural OH in mantle-derived clinopyroxene megacrysts from Nushan

Thirteen clinopyroxene megacrysts from Nushan Cenozoic basalts have been investigated by Fourier transform infrared spectrometer(FTIR). The results demonstrate that all samples contain trace amount of structural OH. Clinopyroxenes from Nushan show four groups of absorption bands, in which, 3 472–3 506 cm⁻¹ is the major characteristic one. It is suggested that the position of major band is probably related to AI content: the position of major characteristic band for high-AI samples is around 3 470 cm⁻¹, whereas that for low-AI samples around 3 620 cm⁻¹.     

青藏北羌塘新第三纪玄武岩单斜辉石地球化学

目的通过玄武岩中单斜辉石成分及微量元素地球化学的研究,探讨岩浆源区性质及其大陆动力学意义。方法利用电子探针和激光探针剥蚀技术,分析了北羌塘半岛湖新第三纪粗面玄武岩中单斜辉石斑晶的常量、微量及稀土元素特征。结果单斜辉石主要为透辉石和顽透辉石种属,是玄武岩浆上升过程中逐步结晶的产物;矿物中富集Rb,Sr,Ba,Zr,Hf,Nb和Th,U,Pb,并存在Sc,Ti,V等铁族元素的低度富集,稀土元素总量平均857×10-6,轻重稀土分异显著,轻稀土强烈富集,无明显铕异常。结论单斜辉石是玄武质岩石中痕量及稀土元素的重要赋存矿物相。     

胶州大西庄晚中生代玄武岩中单斜辉石巨晶

胶州大西庄晚白垩世碱性玄武岩中发现有单斜辉石巨晶,其矿物化学成分较为均一,SiO2含量在46．2％～47．6％之间,A1203为8．4％～9．0％,MgO为12．8％～14．6％,CaO为16．9％～17．5％,Mg^11值在72～76之间。除了SiO：含量稍低以外,和中国东部新生代玄武岩中单斜辉石巨晶化学成分的变化范围内一致。Wo值〈459／5,属于为铝普通辉石。辉石巨晶的KD（Fe-Mg）值为0．2～0．4,和碱性玄武岩浆平衡,平衡温压分别为1396～1422℃和2．4～2．6GPa,表明其是寄主岩浆在高压下结晶的产物。大西庄单斜辉石巨晶和中国东部中新生代玄武岩中单斜辉石巨晶成分及成因上的相似性,揭示了该地区晚白垩世至新生代处于一致的动力学背景。     

Oxygen isotopic heterogeneity in the mantle: Evidence from clinopyroxene megacrysts of Nüshan, eastern China

Major element, REE and oxygen isotopic compositions of fourteen clinopyroxene megacrysts from Nushan, eastern China have been obtained. They are believed to represent crystallization products of one mantle-derived alkali basaltic magma. Oxygen isotopic ratios are homogeneous within the same sample, but heterogeneous among different samples, 18O values of these megacrysts are from 4.86‰ to 6.48‰. We suggest that the oxygen isotopic variation of clinopyroxene megacrysts should be inherited from their source magma, and the heterogeneity of source magma results from contamination of subducted oceanic materials.     

Glass melt inclusion in clinopyroxene from Linqu Cenozoic basalt, Shandong Province, China

Melt inclusions or glasses usually occur in spinel- facies peridotitic xenoliths entrained in the global ba- salts[1―4], and olivine phenocrysts and/or xenocrysts carried in the intermediate-mafic volcanic rocks (such as basalts, basaltic andesites and h…     

Trace-element of Tuoyun clinopyroxene: Implication for the deep processes of lithospheric mantle beneath the southwest Tianshan, West China

Based on the LAM-ICPMS analytic results on the trace elements of clinopyroxenes in peridotitic xenoliths occurring in early-Cretaceous basalts from western Xinjiang, the properties and the deep processes, including partial melting and mantle metasomatism, of the subcontinental lithospheric mantle beneath the Tuoyun Basin are analyzed. In the northern edge of the Tarim Basin (southwest Tianshan), the Mesozoic subcontinental lithosphere which has experienced the effect of partial melting (<10%) and intricate mantle metasomatism is characterized by Phanerozoic ‘ocean-type’ mantle. The superposed influence of SiO₂-unsaturated silicate melt and carbonate melt probably results in the metasomatic medium which resembles the hydrous silicated carbonate melt in some aspects. By comparing Tuoyun mantle with Cenozoic main mantle beneath eastern China, the properties are similar, while the former shows finer grain and higher diopside content of the peridotites and more conspicuous modal metasomatism.     

湖南益阳玄武岩质科马提岩鬣刺结构的基本特征

湖南益阳玄武岩质科马提岩的鬣刺结构是橄榄石、单斜辉石的中空骸晶呈放射状、束状、平行状、毛发状、丛状等晶团或晶群,排列于极细小的橄榄石、辉石、火山玻璃等物质组成的基质之中.橄榄石已蛇纹石化、滑石化、碳酸盐化等;单斜辉石变化较弱或已被透闪石化、绿泥石化等,基质已脱玻化,故此为鬣刺结构假象。橄榄石骸晶长0.25—0.75mm,宽约0.025mm;单斜辉石骸晶长0.1—0.5mm,宽0.025—0.05mm,属显微鬣刺结构.