Sr and Nd isotopic systematics in ALHA 77005: Age of shock metamorphism in shergottites and magmatic differentiation on Mars
Sr and Nd isotopic systematics in ALHA 77005: Age of shock metamorphism in shergottites and magmatic differentiation on Mars
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ALHA 77005 中的 Sr 和 Nd 同位素系统学：shergottites 的冲击变质作用年龄和火星上的岩浆分异
DOI：
10.1016/0016-7037(89)90363-3
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发表时间：
1989
影响因子：
5
通讯作者：
E. Jagoutz
中科院分区：
文献类型：
--
作者：
E. Jagoutz
ALHA 77005陨石属于SNC陨石群，被认为是火星的碎片。新的Sr和Nd同位素数据报告ALHA 77005全岩和岩相学上不同的矿物分离。斜长石从斜长石冲击熔体结晶，分馏的Rb Sr比在冲击事件的时间。用此Rb Sr分馏法测得该地震的Rb/Sr年龄为15 ± 15Ma。在误差范围内，这一冲击年龄与2.5 Ma的暴露年龄相同。用普通辉石和褐变岩测得Rb-Sr结晶年龄为154 ± 6Ma，与Shergotty中斜长岩的结晶年龄一致。岩相学证据表明，ALHA 77005中的积云橄榄石与使辉石和斜长石结晶的积云间液体的来源不同。所有SNC陨石的岩相学比较表明，大多数SNC陨石是正积云，其中积云相来自不同的来源比积云间液体。不同同位素系统的相互关系表明，SNC陨石可以通过混合三种同位素不同的来源来解释。这三个来源在火星历史早期就被区分开来。在月球上，斜长石分馏是主要的岩浆过程，火星上的主要岩浆过程是镁铁质岩浆作用和混合。火星和地球同位素系统学的比较表明，火星吸积的物质化学性质类似于C1和普通的钙钛矿，而地球的硅镁和铷铅比低于钙钛矿。当将C2、C3和CV陨石与Cl或普通陨石进行比较时，观察到类似的特征：C2、C3、CV陨石和地球的表观Pb存量中Rb较少。
The meteorite ALHA 77005 belongs to the group of SNC meteorites which are thought to be fragments of the planet Mars. New Sr and Nd isotopic data are reported for ALHA 77005 whole rock and petrographically distinct mineral separates. Plagioclase crystallized from a plagioclase shock melt, fractionating the Rb Sr ratio at the time of the shock event. A Rb/Sr age of 15±15 Ma for the shock event is measured using this Rb Sr fractionation. This shock age is, within error, identical to the exposure age of 2.5 Ma. Using augite and pigeonite a Rb Sr crystallization age of 154±6 Ma is measured, which is identical to the crystallization age of the Shergotty mesostasis-plagioclase. Petrographic evidence indicates that the cumulus olivine in ALHA 77005 is derived from a different source than the intercumulus liquid which crystallized the pyroxenes and the plagioclases. Petrographic comparison of all SNC meteorites suggests that most SNC meteorites are orthocumulates in which the cumulus phase comes from a different source than the intercumulus liquid. The interrelation of the different isotopic systems indicates that the SNC meteorites can be explained by mixing three isotopically distinct sources. These three sources were differentiated early in Martian history. In contrast to the Moon, where plagioclase fractionation is the dominant magmatic process, the major magmatic processes on Mars are mafic magmatism and mixing. Comparison of Martian and terrestrial isotopic systematics suggests that Mars accreted from a material chemically similar to C1 and ordinary chondrites, whereas the Earth has lower than chondritic Si Mg and Rb Pb ratios. A similar feature is observed when comparing C2, C3 and CV chondrites with Cl or ordinary chondrites: C2, C3, CV meteorites and the Earth have less Rb for their apparent Pb inventory.