Mineralogy, composition, and alteration of Mars Pathfinder rocks and soils: Evidence from multispectral, elemental, and magnetic data on terrestrial analogue, SNC meteorite, and Pathfinder samples
Mineralogy, composition, and alteration of Mars Pathfinder rocks and soils: Evidence from multispectral, elemental, and magnetic data on terrestrial analogue, SNC meteorite, and Pathfinder samples
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火星探路者岩石和土壤的矿物学、成分和蚀变：来自陆地类似物、SNC 陨石和探路者样本的多光谱、元素和磁性数据的证据
DOI：
10.1029/1999je001059
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发表时间：
2000
影响因子：
--
通讯作者：
D. Britt
中科院分区：
文献类型：
--
作者：
R. Morris;D. Golden;J. Bell;T. Shelfer;Andreas C Scheinost;N. Hinman;G. Furniss;S. Mertzman;J. Bishop;D. Ming;C. Allen;D. Britt
在火星探路者使命期间，在战神谷获得了主要元素、多光谱和磁性数据。为了了解这些数据的成分，矿物学和过程的影响，我们获得了主要元素，矿物学和磁性数据的结晶和纳米相铁矿物，陆地模拟样品与已知的地质背景，SNC陨石。沉积岩样品包括莫纳克亚火山的未蚀变、古闪质和硫酸盐火山灰（水解和酸性硫酸盐蚀变）、基拉韦厄火山的蒸汽喷口物质（水解蚀变）和陨石坑的撞击岩（再石化）。火星探路者的显着结果包括：（1）谱带深度BD 530 b和BD 600以及反射率比R800/R750与主要铁矿物一致，该铁矿物是纳米相三氧化二铁，与未知量的H2O相关，并且存在于复合颗粒中，沿着少量其他铁矿物。赤铁矿和赤铁矿加纳米相针铁矿是最符合的数据，但磁赤铁矿，akaganeite，施威特曼石，纳米相纤铁矿也是可能的解释。铁氧化物作为唯一蚀变产物一直不受数据青睐，是黄钾铁矾和结晶良好的针铁矿和纤铁矿。(2)三价铁吸附边的强度（R750/R445）意味着探路者岩石和土壤的Fe ~（3+）/Fe ~（2+）值分别在0.7-3和3-20范围内。(3)硅酸亚铁适用于开拓者岩石和土壤的子集。一个子集具有可归因于低钙辉石的930 nm附近的带最小值。或者，该带可能是某些氧化铁的第二种表现形式，包括纳米相针铁矿、磁赤铁矿、赤霞铁矿和施韦特曼铁矿。另一个子集有一个负的光谱斜率，从1000到1005纳米，这可能是由于高钙辉石和/或橄榄石带的高能翼，明亮和黑暗的材料的混合物，以及岩石，在黑暗的岩石上的明亮的尘埃薄涂层。(4)探路者岩石和土壤的化学数据与具有低MgO和SO 3浓度的“安山质”岩石（无土岩石）和具有高MgO和SO 3浓度的全球玄武岩土壤（无土土壤）之间的双组分混合物一致。探路者无岩土壤可以模拟为SNC陨石和探路者无土岩石的化学混合物。(5)探路者土壤不能通过我们研究的任何水解和酸硫酸盐蚀变过程的探路者岩石的化学蚀变获得。据推测，全球混合已经掩盖并可能消除了化学变化的元素特征。(6)在斜长石质和硫酸盐质火山灰中的强磁性相是钛磁铁矿和可能是其氧化产物钛磁赤铁矿（Fe-Ti尖晶石）。火山灰样品的饱和磁化强度（0.5-2.0 Am 2/kg）等于或低于推断的火星尘埃范围的低端（4±2 Am 2/kg），这意味着岩石成因的Fe-Ti尖晶石可能是火星强磁性相的候选者。(7)火星土壤和尘埃的主要的斜长石光谱特征和磁性性质与嵌入Fe-Ti尖晶石颗粒的玻璃状前体一致。与月球玻璃生产率的比较表明，火星上火山和撞击过程产生的足够数量的玻璃质物质足以解释这些观测结果。
Major element, multispectral, and magnetic properties data were obtained at Ares Vallis during the Mars Pathfinder mission. To understand the compositional, mineralogical, and process implications of these data, we obtained major element, mineralogical, and magnetic data for well-crystalline and nanophase ferric minerals, terrestrial analogue samples with known geologic context, and SNC meteorites. Analogue samples include unaltered, palagonitic, and sulfatetic tephra from Mauna Kea Volcano (hydrolytic and acid-sulfate alteration), steam vent material from Kilauea Volcano (hydrolytic alteration), and impactites from Meteor Crater (relithification). Salient results for Mars Pathfinder include: (1) Band depths BD530b and BD600 and the reflectivity ratio R800/R750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of H2O and occurring in composite particles along with subordinate amounts of other ferric minerals. Hematite and hematite plus nanophase goethite are most consistent with the data, but maghemite, akaganeite, schwertmannite, and nanophase lepidocrocite are also possible interpretations. Ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well-crystalline goethite and lepidocrocite. (2) The strength of the ferric adsorption edge (R750/R445) implies the Fe3+/Fe2+ values for Pathfinder rock and soil are within the ranges 0.7–3 and 3–20, respectively. (3) Ferrous silicates are indicated for subsets of Pathfinder rocks and soils. One subset has a band minimum near 930 nm that can attributed to low-Ca pyroxene. Alternatively, the band could be a second manifestation of certain ferric oxides, including nanophase goethite, maghemite, akaganeite, and schwertmannite. Another subset has a negative spectral slope from ∼800 to 1005 nm which could result from the high-energy wing of a high-Ca pyroxene and/or olivine band, a mixture of bright and dark materials, and, for rocks, thin coatings of bright dust on dark rocks. (4) Chemical data on Pathfinder rocks and soils are consistent with two-component mixtures between an “andesitic” rock with low MgO and SO3 concentrations (soil-free rock) and a global, basaltic soil with high MgO and SO3 concentrations (rock-free soil). Pathfinder rock-free soil can be modeled as a chemical mixture of SNC meteorites and the Pathfinder soil-free rock. (5) Pathfinder soil cannot be obtained by chemical alteration of Pathfinder rocks by any of the hydrolytic and acid-sulfate alteration processes we studied. Presumably, global mixing has obscured and possibly erased the elemental signatures of chemical alteration. (6) The strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite (Fe-Ti spinels). The saturation magnetization of the tephra samples (0.5–2.0 Am2/kg) is at or below the low end of the range inferred for Martian dust (4±2 Am2/kg), implying that lithogenic Fe-Ti spinels are a possible candidate for the Martian strongly magnetic phase. (7) The predominantly palagonitic spectral signature and magnetic nature of Martian soil and dust are consistent with glassy precursors with imbedded Fe-Ti spinel particles. Comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on Mars by volcanic and impact processes is sufficient to account for these observations.