Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on “Mt. Sharp” in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences crosscut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient Martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near‐infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse‐grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine‐grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain‐size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time.

中文翻译：

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火星盖尔陨石坑维拉鲁宾山脊的成岩作用，来自桅杆摄像机多光谱图像


火星科学实验室 (MSL) 任务拍摄的“Mt. 山”维拉鲁宾山脊的湖泊沉积岩图像。火星盖尔陨石坑中的“夏普”显示出从红色到紫色到灰色的鲜明颜色变化。这些颜色差异横切地层学，可能是由于沉积后沉积物的成岩变化所致。然而，这些流体相互作用的化学性质和时间尚不清楚。确定成岩过程如何改变古代火星环境的化学和矿物学特征对于了解火星过去的宜居性和实现 MSL 任务的目标至关重要。在这里，我们使用 Mastcam 和 ChemCam 的可见/近红外光谱来确定山脊颜色变化的矿物学起源。颜色变化与赤铁矿结晶度、晶粒尺寸和结构相关的光谱特性的变化一致。粗粒灰色赤铁矿在灰色斑块中占主导地位，并存在于紫色区域中，而纳米相和细粒红色结晶赤铁矿在光谱中占主导地位，在红色和紫色区域中。我们假设这些差异是由成岩流体导致的赤铁矿粒度粗化造成的，正如在陆地类似物中观察到的那样。在这个模型中，在埋藏期间或埋藏之后，通过氧化附近的液体而导致早期的初级红化，随后通过漂白形成灰色斑块，在挖掘后可能会出现有限的二次红化。成岩作用的改变可能减少了生物特征的保存，并改变了沉积物的成分，使得解释古湖中的条件如何随着时间的推移而演变变得更加困难。