Chemical, microstructural and chronological record of phosphates in the Ksar Ghilane 002 enriched shergottite
Chemical, microstructural and chronological record of phosphates in the Ksar Ghilane 002 enriched shergottite
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Ksar Ghilane 002 富集的六角辉石中磷酸盐的化学、微观结构和年代记录
DOI：
10.1016/j.gca.2018.11.015
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发表时间：
2019
影响因子：
5
通讯作者：
Hiyagon H.
中科院分区：
文献类型：
--
作者：
Roszjar J.;Whitehouse M.J.;Terada K.;Fukuda K.;John T.;Bischoff A.;Morishita Y.;Hiyagon H.
2010年发现的富玄武质（火星）shergottite Ksar Ghilane（KG）002异常丰富，共存但离散的磷灰石和merrilite晶体。它已被选择，以更好地约束形成条件和后结晶过程，从而基于钙磷酸盐的火星岩石的演变。岩石学，化学，年代学和显微结构的方法，使用一系列高空间分辨率的技术，包括拉曼光谱，电子显微镜（SEM，EPMA，CL成像）和二次离子质谱（西姆斯）分析已被应用到一个有代表性的磷酸钙颗粒。磷灰石和钠长石的分析结果表明：（i）F、Cl、Br和I浓度的分区，（ii）Cl浓度升高，范围为11，900 - 35，300 µg/g，卤素比率，即，Cl/Br和Cl/I，以及稳定的氯同位素组成，报告为δ 37 Cl值rel。标准平均海洋氯化物（SMOC，定义为0‰），值为+0.67 ± 0.14‰（1σ），将KG 002磷酸盐与其他富集和贫化的辉绿云母区分开来。卤素和较重的δ 37 Cl记录表明，与其他富集的shergottites相比，火星上富含Cl和同位素较重的地壳储层的同化程度略高，约为3.5%。(iii)结构的调查，连同化学和岩石学方面的颗粒证实羟基贫merrilite的发生，表明弱，如果任何蚀变作用引起的变质作用，只有轻微的结构修改，由于冲击变质，和没有替代反应。因此，从分馏，含水和含铁地幔源，富含挥发物，包括卤素和钠和亲石稀土元素，和没有与地壳流体/样品盐水的相互作用的钙磷酸盐的火成岩结晶推断。(iv)其中6个磷灰石和3个镁黄长石的Pb同位素组成为非放射成因，238 U-206 Pb记录的磷酸盐结晶时间为395 ± 240 Ma（2σ），与其它富集的镁黄长石相似。
The enriched basaltic (martian) shergottite Ksar Ghilane (KG) 002, discovered in 2010, is exceptionally rich in coexisting but discrete apatite and merrillite crystals. It has been selected to better constrain the formation conditions and post-crystallization processes, and thus the evolution of martian rocks based on Ca-phosphates. A petrological, chemical, chronological and microstructural approach using a series of high-spatial resolution techniques including Raman spectroscopy, electron microscopy (SEM, EPMA, CL-imaging) and secondary ion mass spectrometry (SIMS) analysis has been applied to a representative number of Ca-phosphate grains. Analytical results for apatite and merrillite reveal: (i) zoning in F, Cl, Br and I concentrations, (ii) elevated Cl concentrations in the range of ∼11,900–35,300 µg/g and halogen ratios, i.e., Cl/Br and Cl/I, as well as stable chlorine isotope composition, reported as δ37Cl values rel. to Standard Mean Ocean Chloride (SMOC, defined as 0‰) with a value of +0.67 ± 0.14‰ (1σ), distinguishing KG 002 phosphates from that of other enriched and depleted shergottites. The halogen and heavier δ37Cl record indicate a slightly higher degree of ∼3.5% assimilation of Cl-rich and isotopically heavier crustal reservoir on Mars when compared to other enriched shergottites. (iii) Structural investigations together with the chemical and petrological context of the grains confirm the occurrence of hydroxyl-poor merrillite, indicate weak if any alteration effects induced by metamictization, only minor structural modifications due to shock metamorphism, and absence of replacement reactions. Therefore, igneous crystallization of Ca-phosphates from a fractionated, hydrous and ferrous mantle source, rich in volatiles including the halogens and Na and lithophile rare earth-elements, and absence of interaction with crustal fluids/brines of the sample is deduced. (iv) The Pb isotopic composition of six apatite and three merrillite grains is highly unradiogenic and the238U-206Pb record yields a phosphate crystallization time at 395 ± 240 Ma (2σ), which is similar to those of other enriched shergottites.