We have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian-aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim: the Shoemaker and Matijevic formations. The Shoemaker formation consists of two types of polymict impact breccia: clast-rich with coarser clasts in upper units; clast-poor with smaller clasts in lower units. Comparisons with terrestrial craters show that the lower units represent more distal ejecta from at least two earlier impacts, and the upper units are proximal ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition with subtle compositional variations caused by differences in post-impact alteration. The Matijevic formation and lower Shoemaker units represent pre-Endeavour geology, which we equate with the regional Noachian subdued cratered unit. An alteration style unique to these rocks is formation of smectite and Si- and Al-rich vein-like structures crosscutting outcrops. Post-Endeavour alteration is dominated by sulfate formation. Rim-crossing fracture zones include regions of alteration that produced Mg-sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium-sulfate vein formation occurred over extended time, including before the Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate that mobilization of salts by transient water has occurred recently and may be ongoing.

中文翻译：

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Noachian 基岩和蚀变事件的地质和地球化学，Meridiani Planum，火星：MER 机会观测

我们使用火星探测车机遇号数据来调查子午平面上诺亚时代奋进陨石坑西缘的岩屑类型的起源和变化。沿边缘确定了两个地质单元：Shoemaker 和 Matijevic 地层。Shoemaker 地层由两种类型的多晶冲击角砾岩组成：富含碎屑的上部单元具有较粗的碎屑；碎屑较差，较低单位的碎屑较小。与地球陨石坑的比较表明，下部单元代表来自至少两次早期撞击的更远侧喷射物，而上部单元是来自奋进陨石坑的近端喷射物。两者都是玄武岩成分的目标岩石与因撞击后蚀变差异引起的细微成分变化的混合物。Matijevic 地层和较低的 Shoemaker 单元代表了奋进前的地质，我们将其等同于区域性的诺亚克陨石坑单元。这些岩石特有的蚀变方式是形成蒙脱石和富含硅和铝的脉状结构横切露头。奋进后的改变主要是硫酸盐的形成。边缘交叉断裂带包括产生硫酸镁作为主要相的蚀变区域，可能与奋进号撞击在时间上密切相关。硫酸钙矿脉的形成发生在很长一段时间内，包括奋进号撞击之前和奋进号边缘已经大幅退化之后，很可能是在环绕和包围边缘的烧伤地层沉积之后。岩石表面和内部 Mg、Ca 和 Cl 浓度的差异表明，最近发生了瞬变水对盐分的迁移，并且可能还在继续。