Mineralogy of coexisting pyroxenes in magnesian ureilites and their formation conditions
Mineralogy of coexisting pyroxenes in magnesian ureilites and their formation conditions
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镁质脲岩中共生辉石的矿物学及其形成条件
DOI：
10.1016/0012-821x(89)90067-8
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发表时间：
1989
影响因子：
5.3
通讯作者：
H. Takeda
中科院分区：
文献类型：
--
作者：
H. Takeda
用电子探针和单晶X射线衍射方法证实了在南极洲发现的Yamato（Y）791538和LEW 85440两种镁钠闪石中存在斜方辉石。在Y 791538中发现了第一个共存的平衡褐帘石-斜方辉石对。LEW 85440斜方辉石与少量普通辉石共存。Y 791538、Y 74659和LEW 85440中的斜方辉石和橄榄石成分几乎相同，但它们共存的单斜辉石的Ca含量有很大差异。这些相组合可以用1220°C以上不同温度下具有相似成分的镁铁质硅酸盐结晶、氧逸度和氧同位素异常来解释。耐火富镁硅酸盐的高温结晶和可能保存的前体碳质方解石类物质的氧同位素异常可能与它们的形成过程相一致，可能是通过局部熔融的基质比富镁硅酸盐和晶体生长引起的星子规模的碰撞。
The occurrence of orthopyroxene in two magnesian ureilites found in Antarctica, Yamato (Y)791538 and LEW85440 has been confirmed by electron probe microanalysis and by single-crystal X-ray diffraction. The first coexisting equilibrium pigeonite-orthopyroxene pair has been found in Y791538. The LEW85440 orthopyroxene coexists with minor augite. The orthopyroxenes and olivines in Y791538, Y74659 and LEW85440 have almost identical compositions, but the Ca contents of their coexisting clinopyroxenes differ considerably. These phase assemblages can be explained by crystallization of mafic silicates with a similar composition, oxygen fugacity and oxygen isotope anomaly at different temperature above 1220°C. The high-temperature crystallization of refractory Mg-rich silicates and the possible preservation of the oxygen isotope anomaly of precursor carbonaceous chondrites-like materials may be consistent with their formation processes probably through local melting of more matrices than Mg-rich silicates and crystal growth induced by the planetesimal-scale collision.