Evidence for multiple dynamic events and subsequent decompression stage recorded in a shock vein
Evidence for multiple dynamic events and subsequent decompression stage recorded in a shock vein
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DOI：
10.1016/j.epsl.2011.05.010
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发表时间：
2011-07
影响因子：
5.3
通讯作者：
M. Miyahara;E. Ohtani;M. Kimura;S. Ozawa;T. Nagase;M. Nishijima;K. Hiraga
中科院分区：
文献类型：
--
作者：
M. Miyahara;E. Ohtani;M. Kimura;S. Ozawa;T. Nagase;M. Nishijima;K. Hiraga
我们研究了大和 791384 L6 球粒陨石的激波脉，以阐明激波事件引起的动态过程的性质和顺序。 Y-791384的球粒状母岩主要由橄榄石（Fa24-25）、低钙辉石（Fs18-22）、钠长石（An9-10Ab84-86Or5-7）、硫铁长石和金属Fe-Ni组成。激波脉含有多数铁榴石（或多数铁榴石）和镁方石（+少量硬玉）作为高压多晶型物。在冲击静脉中记录了两种不同的动态事件。大部分晶粒含有玻璃化(Mg,Fe)SiO3-钙钛矿夹杂物。 (Mg,Fe)SiO3-钙钛矿是从球粒状熔体中结晶出来的，是第一次动态事件的残余物。镁铁矿和镁镁铁矿也直接从球粒陨石熔体中结晶，但由第二次动态事件诱导。第一个和第二个动态事件的压力条件分别为 >~24 GPa 和 <~22 GPa。普遍存在的羽毛状橄榄石（Fa16）在镁方石和镁铁矿上成核。这种羽毛状的橄榄石是与冲击事件相关的熔体中快速生长的橄榄石的证据。从阿连德陨石和橄榄岩的高压熔化实验推导出的相关系表明，镁方石和镁橄榄石对不能在平衡条件下共存。不平衡组合反映了减压阶段。这些特征展示了自然动态过程中事件的复杂性。
We investigated a shock vein of the Yamato 791384 L6 chondrite to clarify the nature and sequence of the dynamic processes that resulted from the shock events. The chondritic host-rock of Y-791384 mainly consists of olivine (Fa24–25), low-Ca pyroxene (Fs18–22), albitic feldspar (An9–10Ab84–86Or5–7), troilite and metallic Fe–Ni. The shock vein contains majorite (or majorite-pyropess) and magnesiowüstite (+ minor jadeite) as high-pressure polymorphs. Two different dynamic events were recorded in the shock vein. The majorite grain contained vitrified (Mg,Fe)SiO3-perovskite inclusions. The (Mg,Fe)SiO3-perovskite was crystallized from a chondritic melt, and is a remnant of a first dynamic event. The majorite and magnesiowüstite were also crystallized directly from a chondritic melt but induced by a second dynamic event. The pressure condition for the first and second dynamic events would be >~24 GPa and <~22 GPa, respectively. Pervasive feather-shaped olivine (Fa16) nucleated on the magnesiowüstite and majorite. This feather-shaped olivine is evidence for rapidly grown olivine from the melt related to the shock event. Phase relations deduced from high-pressure melting experiments of the Allende meteorite and peridotite indicate that the magnesiowüstite and majorite + olivine pair cannot coexist at equilibrium condition. The disequilibrium assemblage reflects a decompression stage. These features demonstrate the complexity of events during a natural dynamic process.