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Localized and Areally Extensive Alterations in Marathon Valley, Endeavour Crater Rim, Mars

机译：马拉松山谷，奋进火山口边缘，火星的本地化和区域性广泛变化

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Mars Exploration Rover Opportunity is exploring the rim of 22 km diameter, Noachian-aged Endeavour crater. Marathon Valley cuts through the central region of the western rim providing a window into the local lower rim stratigraphic record. Spectra from the Compact Reconnaissance Imaging Spectrometer for Mars show evidence for the occurrence of Fe-Mg smectite in this valley, indicating areally extensive and distinct lithologic units and/or styles of aqueous alteration. The Alpha Particle X-ray Spectrometer has determined the compositions of 59 outcrop targets on untreated, brushed and abraded surfaces. Rocks in the Marathon Valley region are soft breccias composed of mm- to cm-sized darker clasts set in a lighter-toned, finegrained matrix. They are basaltic in non-volatile-element composition and compositionally similar to breccias investigated elsewhere on the rim. Alteration styles recorded in the rocks include: (1) Enrichments in Si, Al, Ti and Cr in more reddish-colored rock, consistent with leaching of more soluble cations and/or precipitation of Si +/- Al, Ti, Cr from fluids. Coprecipitation of Ge-rich phases with Si occurred in the western area only; high water:rock is indicated. Pancam multispectral observations indicate higher nanophase ferric oxide contents, but the rocks have lower Fe contents. The highly localized nature of the red zones indicate they cannot be the source of the widespread smectite signature observed from orbit. (2) Outcrops separated by approximately 65 m show common compositional changes between brushed and abraded (approximately 1 mm deep) targets: increases in S and Mg; decreases in Al, Cl and Ca. These changes are likely due to relatively recent, surface-related alteration of valley rocks and formation of surface coatings under low water:rock. (3) One target, from the center of a region of strong CRISM smectite signature, shows modest differences in composition (higher Si, K; lower Mn) compared to most Marathon Valley rocks, while another target approximately 40 cm away on the same outcrop does not; a change towards smectite bulk compositions is not observed. The smectite signature likely resulted from alteration under low water:rock such that primary minerals were partially altered to phyllosilicates, but wholesale leaching of cations by fluids did not occur.
机译：火星探索漫游者号机遇号正在探索直径22公里的边缘，即Noachian时代的Endeavor陨石坑。马拉松山谷穿过西部边缘的中部地区，为了解当地较低边缘的地层记录提供了一个窗口。来自火星的紧凑侦察成像光谱仪的光谱显示了该山谷中铁镁镁蒙脱石的存在证据，表明区域上广泛而独特的岩性单元和/或水蚀变样式。 Alpha粒子X射线光谱仪已经确定了59个露头目标在未经处理，磨砂和磨蚀表面上的成分。马拉松河谷地区的岩石是软角砾岩，由浅色细颗粒基质中毫米至厘米大小的深色碎屑组成。它们的非挥发性元素成分是玄武岩，其成分类似于在轮辋其他位置研究的角砾岩。岩石中记录的蚀变样式包括：（1）较红的岩石中的Si，Al，Ti和Cr富集，这与溶出更多可溶性阳离子和/或从流体中析出的Si +/- Al，Ti，Cr一致。富锗相与硅共沉淀仅发生在西部地区。高水位：有岩石。 Pancam多光谱观测表明，纳米相三氧化二铁含量较高，但岩石中的铁含量较低。红色区域的高度局部化性质表明它们不能成为从轨道上观察到的广泛蒙皂石特征的来源。 （2）露头相距约65 m，表明刷和磨的（约1 mm深）靶之间的共同成分变化是：S和Mg的增加； Al，Cl和Ca含量降低。这些变化可能是由于相对较新的谷地岩石表面相关的蚀变和低水位岩石下表面涂层的形成所致。 （3）与大多数马拉松河谷岩石相比，一个目标位于CRISM绿土特征强烈的区域中心，其成分之间存在适度差异（较高的Si，K，较低的Mn），而另一个目标距同一露头约40 cm才不是;没有观察到向蒙脱石本体组成的变化。绿土特征很可能是由于在低水位：岩石下的蚀变所致，从而使主要矿物部分地转变为层状硅酸盐，但没有发生流体整体浸出阳离子的现象。

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