Yamato nakhlites: Petrography and mineralogy
Yamato nakhlites: Petrography and mineralogy
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Yamato nakhlites：岩相学和矿物学
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发表时间：
2003
期刊：
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通讯作者：
N. Iwata
中科院分区：
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作者：
N. Imae;Y. Ikeda;K. Shinoda;H. Kojima;N. Iwata
利用电子探针显微分析仪和傅里叶变换红外光谱仪对新发现的Yamato ***/3（Y***/3-）、Y***1.3和Y***2*进行了岩相学和矿物学研究。自面体辉石（En,*）* Fs,,。* Wo-2。*)为主要相，模态比为1/ 2* vol，呈细长晶粒（+mm *）。/毫米)与薄富铁轮辋。构成这些辉石晶体大部分体积的辉石岩心的化学成分是均匀的，与其他钠长石的化学成分几乎相同。富铁轮辋与中稳态接触。菱形铁橄榄石（Fa0, 12; 2 +2 vol, *）。/mm)和亚面体钛磁铁矿(+ vol，小于*。+mm)为小的斑晶。其余陨石物质为中稳态（2 +/ vol），主要由斜长石（An,0 -,Ab00/ Or. 2）组成。小相为磁黄铁矿（Fe*.20 *. 22s，小于× × mm）、磷灰石（小于× × mm）、钛磁铁矿、贫钙辉石、铁晶橄榄石（Fa 2/）、三晶石和硅晶石。根据橄榄石和辉石斑晶的岩心和岩缘的化学成分范围，将这些山野斑晶与其他斑晶区分开来。我们认为Yamato硅石的这些矿物的化学变化介于NWA2+1和其他（Nakhla， Governador Valadares和Lafayette）之间。傅里叶变换红外显微光谱仪对橄榄石斑晶边缘和裂缝及中间平衡的蚀变相进行了研究，发现存在含oh矿物，可能是蒙脱石（1*）和针铁矿（-*）的混合物。与融合地壳接触的橄榄石颗粒中含oh相的气泡的存在表明，蚀变发生在进入大气层之前（即火星起源）。关键词：nakholite，火星陨石，Y***/3-, Y***1.3, Y***2*, +。nakhlites是一种火成岩陨石，是基于氧同位素（Clayton, +33-）的SNC （shergotites， nakhlites和Chassigny）组的一部分。Nakhlites是一种以斜辉石岩（奥辉岩）为主的积云超镁质岩石，主要化学成分为玄武岩。从南极的角度来看，SNCs可能来自火星。陨石资源，+0,+——，，**国家极地研究所
We carried out the petrographical and mineralogical study of new Yamato nakhlites, Yamato ***/3(Y***/3-), Y***1.3 and Y***2*,, with electron probe microanalyzer and Fourier transform infrared microspectrometer. Euhedral pyroxenes (En,* .*Fs,, .*Wo-2 .*) are the predominant phase with a modal proportion of 1/ 2* vol and occur as elongated grains ( +mm *./mm) with thin Fe-rich rims. The chemical composition of the augite cores comprising most of the volume of these pyroxene crystals is homogeneous and nearly identical with those in other nakhlites. Fe-rich rims are present in contact with the mesostasis. Anhedral ferroan olivines (Fa0, 12; 2 +2 vol , *./mm) and subhedral titanomagnetites ( + vol , smaller than *.+mm) are minor phenocrysts. The remainder of the meteoritic material is mesostasis (2 +/ vol ), which predominantly consists of plagioclase (An,0 -,Ab00/ Or. 2). Minor phases in the mesostasis are pyrrhotite (Fe*.20 *.22S; smaller than ,* mm), apatite (smaller than ,* mm), titanomagnetite, Ca-poor pyroxene, fayalitic olivine (Fa 2/), tridymite and iddingsite. We distinguish these Yamato nakhlites from other nakhlites based on the chemical compositional ranges of the cores and rims of olivine and pyroxene phenocrysts. We suggest that the chemical variations of these minerals for the Yamato nakhlites are intermediate between those of NWA2+1 and others (Nakhla, Governador Valadares, and Lafayette). The study by Fourier transform infrared microspectrometer of altered phases both on rims and fractures in olivine phenocrysts and in mesostasis revealed the existence of OH-bearing minerals, which might be mixtures of montmorillonite (1* ) and goethite (-* ). The existence of bubbles in an OH-bearing phase in olivine grains in contact with the fusion crust suggests that the alteration occurred before atmospheric entry (i.e. Martian origin). key words: nakhlites, Martian meteorites, Y***/3-, Y***1.3, Y***2*, +. Introduction The nakhlites are one of igneous meteorites, and are part of the SNC (shergottites, nakhlites, and Chassigny) group based on oxygen isotopes (Clayton, +33-). Nakhlites are cumulus ultramafic rocks mainly consisting of clinopyroxenes (augites), and the bulk chemical composition is basaltic. SNCs may have come from Mars based on the +Antarct. Meteorite Res., +0, +--, ,**National Institute of Polar Research