坡缕石晶体化学和成因研究现状与进展

综述了坡缕石(凹凸棒石)矿物晶体化学和成因研究的新进展和存在问题,最新研究表明:坡缕石是分布广泛很有成因意义的标型矿物。还着重介绍了我国坡缕石石棉和苏皖一带坡缕石晶体化学研究以及坡缕石成因研究的新成果和存在问题。     

Scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite-grade phyllites, SE Vermont

Detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south‐eastern Vermont show that grain‐scale zoning is common, and sympathetic zoning in adjacent minerals is nearly universal. We interpret this to reflect a pressure‐solution mechanism for cleavage development, where precipitation from a very small fluid reservoir fractionated that fluid. Multiple analyses along single muscovite, biotite and chlorite grains (30–200 μm in length) show zoning patterns indicating Tschermakitic substitutions in muscovite and both Tschermakitic and di/trioctahedral substitutions in biotite and chlorite. Using cross‐cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite‐grade, chlorite‐grade overprinted by biotite‐grade and biotite‐grade. Zoning patterns are comparable in all three settings, requiring a similar cleavage‐forming mechanism independent of metamorphic grade. Moreover, the use of ⁴⁰Ar/³⁹Ar geochronology demonstrates this is true regardless of age. Furthermore, samples with chlorite‐grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of Al, Si, Mg and Fe ions are greater than the temperature of the biotite isograd (>～400 °C). Parallel and smoothly fanning tie lines produced by coexisting muscovite–chlorite, and muscovite–biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization. These results do not support theories suggesting cleavages form in fluid‐dominated systems. If crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir, then the compositions of individual grains defining these cleavages would be uniform. On the contrary, the fine‐scale chemical zoning observed probably reflects a grain‐scale process consistent with a pressure‐solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation. Thus the role of fluids was probably limited to one of catalysing pressure‐solution and fluids apparently did not drive cleavage development.     

攀枝花岩体辉石的矿物学研究

本文对攀枝花辉长岩体中共存的单斜、斜方辉石进行了系统的矿物学及晶体化学研究。首次查明该岩体中斜方辉石的成分,光性及结构特征。研究表明:单斜种属为次透辉石,其化学式为Ca_（0.831）Na_（0.027）K_（0.002）Mg_（0.811）Fe_（0.213）~（2+）Fe_（0.054）~（3+）AlⅥ_（0.030）Ti_（0.013）Mn_（0.008）AlⅣ_（0.082）Si_（1.918）O_6,晶胞参数为α=9.7443—9.7617,b=8.9174—8.9431,c=5.2353—5.2653,β=105°56＇～106°8＇,空间群C2/c,Z=4;斜方辉石为紫苏辉石,化学式为Ca_（0.044）Na_（0.012）K_（0.005）Mg_（1.335）Fe_（0.584）~（2+）Ti_（0.007）Mn_（0.014）Al_（0.029）Si_（1.969）O_6,晶胞参数α=18.2720,b=8.8734,c=5.2078,空间群Pbca,Z=8,该岩体辉石的成分与布什维尔德和斯卡尔嘎得两侵入体中辉石的成分趋向一致。     

某碳酸岩-超碱性岩杂岩体中磷灰石的晶体化学研究

本文用电子探针成分分析,Ｘ射线单晶结构分析,振动光谱等手段对意大利武图列火山地区碳酸岩－超碱性岩杂岩体中磷灰石的晶体化学特征进行了研究。结果表明：该磷灰石的晶体化学式为：（Ｃａ９．８１Ｓｒ０．０５Ｍｎ０．０１ＬＲＥＥ０．０４Ｎａ０．０９）「Ｐ５．５０Ｓｉ０．０１５Ｓ０．０５Ｃ０．３０」Ｏ２３．７（Ｆ０．８０Ｃｌ０．０３ＯＨ１．１７）,属氟羟磷灰石,其结构中在钙多面体与磷氧四面体位置上出现广泛的类质