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On hematite as a target for dating aqueous conditions on Mars

机译：以赤铁矿为火星测水条件的目标

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摘要

Hematite spherules, identified by the Opportunity Mars Exploration Rover (MER), have been interpreted as in situ evidence for past aqueous conditions on the Martian surface. Hematite has also been demonstrated as a reliable (U-Th)/He chronometer, although it is not widely used. In the absence of post-formational diffusive He loss, (U-Th)/He ages measured from Martian hematite spherules should yield the time since water was present on Mars. Using published morphologic constraints and He diffusion kinetics for hematite we model He diffusive loss to assess whether Martian hematite spherules will retain original (U-Th)/He ages during long residence times (4.0 Ga) at surface conditions (22℃). Fractional loss calculations predict < 2% diffusive loss at 22℃ over 4.0 Ga, indicating Martian hematite will preserve ages within analytical precision of the (U-Th)/He technique. If present Mars conditions persisted since the Noachian (e.g. 4.0 Ga), hematite spherules likely record ages reflecting the timing of aqueous mineralization. For the 'wetting-upwards' Burn Formation at Meridiani Planum, hematite from the lower eolian dune subunit would be postdepositional providing a minimum age on deposition, while hematite from the upper interdune/playa unit may be syndepositional thus yielding the age of the deposit. Therefore (U-Th)/He hematite ages obtained from samples collected along a vertical profile could potentially constrain the timing and rates of water saturation of the rock column, and the timing of the transition from wet to dry conditions at Meridiani Planum. Determining an absolute paleohydrologic timescale on Mars may reveal if water was available for sufficient durations required for the development of life.
机译：由机会火星探测漫游者（MER）识别的赤铁矿小球已被解释为火星表面过去含水状况的原位证据。赤铁矿虽然未被广泛使用，但也已被证明是一种可靠的（U-Th）/ He天文钟。在没有形成后扩散性He损失的情况下，从火星赤铁矿小球测得的（U-Th）/ He年龄应该能得出自火星上存在水以来的时间。利用已公布的形态学限制条件和赤铁矿的He扩散动力学，我们对He扩散损失进行建模，以评估火星赤铁矿球体在表面条件（22℃）下长时间停留（4.0 Ga）时是否会保留原始（U-Th）/ He年龄。分数损失计算预测，在22 Ga和4.0 Ga下的扩散损失<2％，这表明火星赤铁矿将在（U-Th）/ He技术的分析精度范围内保留年龄。如果自Noachian（例如4.0 Ga）以来目前的火星状况持续存在，赤铁矿球体可能记录了反映水成矿时间的年龄。对于Meridiani Planum的“向上润湿”燃烧组，下风成沙丘亚单元的赤铁矿将进行沉积后沉积，以提供最小的沉积年龄，而上中间/普拉亚单元的赤铁矿可能是同沉积的，从而产生沉积年龄。因此，从沿垂直剖面收集的样品获得的（U-Th）/赤铁矿年龄可能会限制岩石柱水饱和度的时间和速率，以及Meridiani Planum从湿到干的过渡时间。确定火星上的绝对古水文时间尺度可能会揭示出是否有足够的水可用于生命发展。

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  • 来源
    《Planetary and space science》 |2012年第1期|p.101-108|共8页
  • 作者

    Joseph Kula; Suzanne L. Baldwin;

  • 作者单位

    Earth Sciences Department, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States;

    Earth Sciences Department, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    hematite; helium; mars; (U-TH)/He;

    机译：赤铁矿氦;火星;（U-TH）/他;

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