The formation of boundary clinopyroxenes and associated glass veins in type B1 CAIs
The formation of boundary clinopyroxenes and associated glass veins in type B1 CAIs
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B1 型 CAI 中边界单斜辉石和相关玻璃脉的形成
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发表时间：
2009
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通讯作者：
J. Bradley
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作者：
J. Paque;J. Beckett;H. Ishii;A. Aléon‐Toppani;D. Burnett;N. Teslich;Z. Dai;J. Bradley
翻译后摘要-我们使用聚焦离子束薄切片制备和扫描透射电子显微镜（FIB/STEM）检查尖晶石和主机黄长石之间的界面区域的尖晶石晶粒的B1型夹杂物从阿连德和利奥维尔碳质方解石。边界单斜辉石装饰尖晶石表面的组合物相似的粗单斜辉石从同一地区的包裹体，表明形成后很少运动。寄主黄长石在界面附近没有显示出异常成分，也没有观察到晚期矿物，这表明边界辉石不是由残余液体结晶形成的。阿连德尖晶石显示出直接的尖晶石-黄长石接触或两个相之间的介入边界单斜辉石。利奥维尔B1中的尖晶石-黄长石界面区域更复杂，具有边界单斜辉石，如在阿连德中观察到的，但也有不同量的玻璃、次生方解石、钙钛矿和富含Mg-、Al-、OH-和贫Ca-、Si-的结晶相，其可能是层状双水合物。玻璃脉形成的一种可能情况是黄长石的开放系统蚀变产生了Mg-carpholite或sudoite +铝透辉石的多孔水合聚集体，其被冲击熔化并淬火成玻璃。我们观察到的水合结晶相可能是前体相组合的冲击残留物，但更有可能是后来通过玻璃的改变形成的。
Abstract— We used focused ion beam thin section preparation and scanning transmission electron microscopy (FIB/STEM) to examine the interfacial region between spinel and host melilite for spinel grains in type B1 inclusions from the Allende and Leoville carbonaceous chondrites. Boundary clinopyroxenes decorating spinel surfaces have compositions similar to those of coarser clinopyroxenes from the same region of the inclusion, suggesting little movement after formation. Host melilite displays no anomalous compositions near the interface and late‐stage minerals are not observed, suggesting that boundary pyroxenes did not form by crystallization of residual liquid. Allende spinels display either direct spinel‐melilite contact or an intervening boundary clinopyroxene between the two phases. Spinel‐melilite interfacial regions in a Leoville B1 are more complex, with boundary clinopyroxene, as observed in Allende, but also variable amounts of glass, secondary calcite, perovskite, and an Mg‐, Al‐, OH‐rich and Ca‐, Si‐poor crystalline phase that may be a layered double hydrate. One possible scenario of formation for the glass veins is that open system alteration of melilite produced a porous, hydrated aggregate of Mg‐carpholite or sudoite + aluminous diopside that was shock melted and quenched to a glass. The hydrated crystalline phase we observed may have been a shocked remnant of the precursor phase assemblage, but is more likely to have formed later by alteration of the glass.