Clues to Martian brines based on halogens in salts from nakhlites and MER samples
Clues to Martian brines based on halogens in salts from nakhlites and MER samples
复制标题
根据nakhlites 和 MER 样品中的盐中的卤素来寻找火星盐水的线索
DOI：
10.1029/2005je002470
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发表时间：
2005
影响因子：
--
通讯作者：
G. Dreibus
中科院分区：
文献类型：
--
作者：
M. Rao;S. Sutton;D. Mckay;G. Dreibus
[1]氯和溴丰度在Nakhla脉中确定在本研究中，同步辐射X射线微探针（Br）和电子微探针（Cl）技术相比，以及最近确定的卤素在土壤和岩石外皮在古谢夫和子午线站点的APXS仪器。这些火星岩石中的盐来自火星盐水，这些盐水经历了蒸发或冷冻浓缩。对这些盐中的卤素丰度进行了“稀释效应”（由于与贫卤素相混合）校正，以获得其“真实”丰度，这似乎接近于陆地海水中的卤素丰度。与碳酸盐-硫酸盐-岩盐蒸发盐沉积序列的岩相学证据一致，Nakhla脉产生高Br Lafayette iddingsite具有低Br（11 ppm）和高Cl/Br比（10-50），表明可能来自浓盐水的盐沉积，而Lafayette iddingsite具有低Br（11 ppm）和高Cl/Br比，（250-300），表明盐沉积从火星上的稀盐水。从古谢夫和梅里迪亚尼的岩石外壳中提取的盐中，Cl/Br的比例很低（20 ~ 80），这表明它们可能来自火星地下的浓缩盐水。在拉斐特和阿迪朗达克的稀溶液中沉积的盐中的高Cl/Br比（10270）类似于南极的Cl/Br比，这似乎是火星上稀盐水的特征（在岩盐沉淀之前），包括“早期火星沃茨”（诺亚纪或更早）。我们的研究结果似乎是一致的Burt-Knauth模型，涉及在蒸发/冻结的盐水溶液在火星风化层的密度分层。
[1] Chlorine and Br abundances in fracture-filling secondary salts in Nakhla veins determined in this study by Synchrotron X-ray Microprobe (Br) and Electron Microprobe (Cl) techniques compare well to the halogens determined recently by APXS instruments in soils and rock rinds at the Gusev and Meridiani sites. The salts in these Mars rocks arise from Martian brines that have undergone evaporative or freezing concentration. The halogen abundances in these salts are corrected for “dilution effect” (because of mixing with halogen-poor phases) to obtain their “true” abundances, which seem to be close to the halogen abundances in terrestrial sea brines. Consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate-sulfate-halite in nakhlite meteorites, Nakhla veins yield high Br (∼250 ppm) and low Cl/Br ratios (∼10–50), suggesting possible salt deposition from concentrated brines, whereas Lafayette iddingsite, with low Br (11 ppm) and high Cl/Br ratios (∼250–300), indicates salt deposition from dilute brines on Mars. The low Cl/Br ratios (∼20 to 80) in salts from Gusev and Meridiani rock rinds indicate that they presumably originate from concentrated subsurface Martian brines. The high Cl/Br ratio (∼270) in salts deposited by dilute solutions in Lafayette and Adirondack is similar to the chondritic Cl/Br ratio, which seems to characterize the dilute brines on Mars (prior to halite precipitation) including “Early Mars Waters” (Noachian or earlier). Our results seem to be consistent with the Burt-Knauth model involving density stratification during evaporation/freezing of brine solutions in Martian regolith.