Alteration trends and geochemical source region characteristics preserved in the fluviolacustrine sedimentary record of Gale crater, Mars
Alteration trends and geochemical source region characteristics preserved in the fluviolacustrine sedimentary record of Gale crater, Mars
复制标题
DOI：
10.1016/j.gca.2018.11.031
复制
发表时间：
2019-02-01
影响因子：
5
通讯作者：
Gasda, P. J.
中科院分区：
文献类型：
--
作者：
Bedford, C. C.;Bridges, J. C.;Gasda, P. J.
火星科学实验室的化学和相机（ChemCam）仪器套件上的Currency漫游者分析了类似的1200沉积目标在使命到溶胶1482。这些目标包括沉积岩、成岩特征（例如，与火山岩有关的蚀变晕、矿脉、结核和抗侵蚀隆起的山脊）、活性风成细粒、土壤和漂浮物。我们已经隔离ChemCam的地球化学趋势有关的成岩功能和蚀变产物的沉积岩，以确定大风火山口的沉积物源区的成分特征。通过对地质单元的粒度分组和分析，考虑了粒度变化对沉积单元地球化学的影响。从数据库中删除了明显的成岩特征，并推断夏普山组样品主要是等化学水蚀变，我们建议源区组成是一个更强的布拉德伯里和夏普山组之间的地球化学变化的来源比开放系统的蚀变。此外，化学蚀变指数（CIA）值和二氧化硅，氧化镁或FeOT之间缺乏相关性表明，夏普山组沉积物的化学风化的轻微增加是不足以覆盖沉积物源成分签名。这导致了五个独特的火成岩端元成分，我们假设有贡献的盖尔陨石坑的地层记录的识别。这些端元是：（1）亚碱性玄武岩，成分类似于古谢夫陨石坑的拉斑玄武岩阿迪朗达克类玄武岩，主要分布在夏普山底部的细粒单元中;（2）粗面玄武岩，主要分布在从达尔文航点到夏普山底部的砾岩单元中;（3）富钾火山岩源;从强烈的钾富集和高丰度透长石确定，透长石在金伯利的河流砂岩和砾岩中占主导地位形成;（4）一种高度演化的、富含二氧化硅的火成岩源，与鳞石英的存在相关，并记录在夏普山玛丽亚山口地区的湖相泥岩中;（5）一种分馏的、相对富含SiO2的亚碱性玄武岩，被认为影响了夏普山群下部沉积泥岩的成分。端元（1）、（2）、（3）和（4）之前已经在漫游车行进过程中的特定航点处被识别出来，但我们表明它们的影响延伸到盖尔的整个地层记录中。沿着漫游车的行进。检测到的端元的出现也强烈相关的地层位置，这表明随着时间的推移改变沉积物源区。我们的结论是大风沉积物的来源更多样的比建议的基本上是同质的，全球分布的火星玄武岩从轨道推断，表明复杂的岩浆组合存在于古老的高地地壳周围大风。(C)2018作者爱思唯尔有限公司出版
The Mars Science Laboratory's Chemistry and Camera (ChemCam) instrument suite on-board the Curiosity rover has analysed similar to 1200 sedimentary targets during the mission up to sol 1482. These targets have included sedimentary rock, diagenetic features (e.g., fracture-associated alteration halos, mineral veins, nodules, and erosion resistant raised ridges), active aeolian fines, soils and float. We have isolated ChemCam geochemical trends relating to diagenetic features and alteration products from those of the sedimentary rock in order to identify the compositional characteristics of Gale crater's sediment source regions. The effects of grain size variation on sedimentary unit geochemistry have been taken into account by grouping and analysing geological units according to grain size. With obvious diagenetic features removed from the database, and predominately isochemical aqueous alteration inferred for the Mt Sharp Group samples, we propose that source region composition is a stronger source of geochemical change between the Bradbury and Mt Sharp Groups than open-system alteration. Additionally, a lack of correlation between the Chemical Index of Alteration (CIA) values and SiO2, MgO or FeOT indicates that the slight increase in chemical weathering of the Mt Sharp Group sediments was insufficient to overprint sediment source compositional signatures. This has led to the identification of five unique igneous endmember compositions which we hypothesise to have contributed to Gale crater's stratigraphic record. These endmembers are: (1) a subalkaline basalt, compositionally similar to the tholeiitic Adirondack Class basalts of Gusev crater, and dominant within the finer grained units up to the base of Mt Sharp; (2) a trachybasalt, mostly identified within conglomerate units from the Darwin waypoint to the base of Mt Sharp; (3) a potassium-rich volcanic source, determined from strong potassium enrichment and a high abundance of sanidine that is most dominant in the fluvial sandstones and conglomerates of the Kimberley formation; (4) a highly evolved, silica-rich igneous source that correlates with the presence of tridymite, and is recorded in the lacustrine mudstone of Mt Sharp's Marias Pass locality; and, (5) a fractionated, relatively SiO2-rich subalkaline basalt, seen to have influenced the composition of mudstone deposited in the lower part of the Mt Sharp Group. Endmembers (1), (2), (3), and (4) have previously been identified at specific waypoints along the rover's traverse, but we show that their influence extends throughout Gale's stratigraphic record. The occurrence of detected endmembers is also strongly correlated with stratigraphic position, which suggests changing sediment source regions with time. We conclude that Gale sediment provenances were much more varied than suggested by the largely homogenous, globally-distributed Martian basalt inferred from orbit, showing that complex magmatic assemblages exist within the ancient highland crust surrounding Gale. (C) 2018 The Authors. Published by Elsevier Ltd.