Hanna Romy D, Hamilton Victoria E, Putzig Nathaniel E
Jackson School of Geological Sciences, University of Texas at Austin, Austin, Texas, USA.
Department of Space Studies, Southwest Research Institute, Boulder, Colorado, USA.
J Geophys Res Planets. 2016 Jul;121(7):1293-1320. doi: 10.1002/2015JE004924. Epub 2016 Jul 4.
We examine four olivine-bearing regions at a variety of spatial scales with thermal infrared, visible to near-infrared, and visible imagery data to investigate the hypothesis that the relationship between olivine abundance and thermal inertia (i.e., effective particle size) can be used to infer the occurrence of olivine chemical alteration during sediment production on Mars. As in previous work, Nili Fossae and Isidis Planitia show a positive correlation between thermal inertia and olivine abundance in Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) data, which could be interpreted as indicating olivine chemical weathering. However, geomorphological analysis reveals that relatively olivine-poor sediments are not derived from adjacent olivine-rich materials, and therefore, chemical weathering cannot be inferred based on the olivine-thermal inertia relationship alone. We identify two areas (Terra Cimmeria and Argyre Planitia) with significant olivine abundance and thermal inertias consistent with sand, but no adjacent rocky (parent) units having even greater olivine abundances. More broadly, global analysis with TES reveals that the most typical olivine abundance on Mars is ~5-7% and that olivine-bearing (5-25%) materials have a wide range of thermal inertias, commonly 25-600 J m K s. TES also indicates that the majority of olivine-rich (>25%) materials have apparent thermal inertias less than 400 J m K s. In summary, we find that the relationship between thermal inertia and olivine abundance alone cannot be used in infer olivine weathering in the examined areas, that olivine-bearing materials have a large range of thermal intertias, and therefore that a complex relationship between olivine abundance and thermal inertia exists on Mars.
我们利用热红外、可见光至近红外以及可见光图像数据，在各种空间尺度上对四个含橄榄石区域进行了研究，以探究这样一个假设：橄榄石丰度与热惯量（即有效粒径）之间的关系可用于推断火星沉积物形成过程中橄榄石化学蚀变的发生情况。与之前的研究一样，在热发射光谱仪（TES）和热发射成像系统（THEMIS）的数据中，尼利槽沟和伊希地平原显示出热惯量与橄榄石丰度之间存在正相关关系，这可能被解释为表明橄榄石发生了化学风化作用。然而，地貌分析表明，相对贫橄榄石的沉积物并非源自相邻的富橄榄石物质，因此，不能仅基于橄榄石 - 热惯量关系推断化学风化作用。我们识别出两个区域（西默里亚地和阿吉尔平原），其橄榄石丰度显著且热惯量与沙子一致，但没有相邻的岩石（母岩）单元具有更高的橄榄石丰度。更广泛地说，利用TES进行的全球分析表明，火星上最典型的橄榄石丰度约为5 - 7%，含橄榄石（5 - 25%）的物质具有广泛的热惯量范围，通常为25 - 600 J m K s。TES还表明，大多数富橄榄石（>25%）的物质表观热惯量小于400 J m K s。总之，我们发现仅热惯量与橄榄石丰度之间的关系不能用于推断所研究区域内的橄榄石风化情况，含橄榄石物质具有大范围的热惯量，因此火星上橄榄石丰度与热惯量之间存在复杂的关系。
