Intermineral oxygen three-isotope systematics of silicate minerals in equilibrated ordinary chondrites
Intermineral oxygen three-isotope systematics of silicate minerals in equilibrated ordinary chondrites
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平衡普通球粒陨石中硅酸盐矿物的矿间氧三同位素系统学
DOI：
10.1111/maps.12932
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发表时间：
2017
影响因子：
2.2
通讯作者：
Noguchi, Takaaki
中科院分区：
文献类型：
--
作者：
McDougal, David;Nakashima, Daisuke;Tenner, Travis J.;Kita, Noriko T.;Valley, John W.;Noguchi, Takaaki
三维X射线层析重建和岩石学研究表明，PułTusk H球粒陨石中有大量的金属堆积。在这些堆积物的接触处，球粒陨石岩石富含硫铁矿。这块岩石含有富含斜长石的条带，其结构表明是熔融结晶。异常大的磷酸盐与斜长石共生，由黄闪石、氟磷灰石和氯磷灰石组合组成。金属堆积是由冲击熔融、金属-硫化物熔体的快速分离以及熔体并入破裂的火山口基底形成的。这种影响很可能发生在H球粒陨石母体的早期演化中，当时撞击后的热与辐射成因的热重叠。这使得金属熔体能够缓慢冷却并分离成富金属和富硫化物的部分。这导致与金属堆积接触的球粒陨石重结晶和冲击熔体的结晶。由于缓慢冷却时的氧化条件，磷从金属中释放出来，并被硅酸盐冲击熔体吸收。熔体也是挥发物的宿主。在进一步冷却时，磷与硅酸盐反应，形成滑石，而挥发物则分配到残留的富含卤素的干燥流体中。在晚期，流体将黄晶石蚀变为片状的氯/氟磷灰石。上述变化序列表明，在球粒陨石母体早期演化过程中的影响可能导致了局部金属偏析和硅酸盐熔融。此外，震后条件支持二次过程：成分/结构平衡、挥发分重新分布和流体改变。
Three‐dimensional X‐ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in Pułtusk H chondrite. At the contact of these accumulations, the chondritic rock is enriched in troilite. The rock contains plagioclase‐rich bands, with textures suggesting crystallization from melt. Unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite, and fluorapatite and chlorapatite. The metal accumulations were formed by impact melting, rapid segregation of metal‐sulfide melt and the incorporation of this melt into the fractured crater basement. The impact most likely occurred in the early evolution of the H chondrite parent body, when post‐impact heat overlapped with radiogenic heat. This enabled slow cooling and separation of the metallic melt into metal‐rich and sulfide‐rich fractions. This led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts. Phosphorus was liberated from the metal and subsumed by the silicate shock melt, owing to oxidative conditions upon slow cooling. The melt was also a host for volatiles. Upon further cooling, phosphorus reacted with silicates leading to the formation of merrillite, while volatiles partitioned into the residual halogen‐rich, dry fluid. In the late stages, the fluid altered merrillite to patchy Cl/F‐apatite. The above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting. In addition, postshock conditions supported secondary processes: compositional/textural equilibration, redistribution of volatiles, and fluid alterations.