Did the carbonaceous chondrites evolve in the crustal regions of partially differentiated asteroids
Did the carbonaceous chondrites evolve in the crustal regions of partially differentiated asteroids
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碳质球粒陨石是否在部分分化小行星的地壳区域演化
DOI：
10.1029/2010je003757
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发表时间：
2011
影响因子：
--
通讯作者：
G. Gupta
中科院分区：
文献类型：
--
作者：
S. Sahijpal;G. Gupta
[1]碳质陨石被认为是最原始的陨石，包含一些最早形成的太阳系阶段，例如，富钙铝包体和球粒。传统上已知碳质方解石的母体经历了水蚀变。然而，最近的古地磁记录的CV球粒陨石，阿连德，表明剩余的磁性，这表明这些球粒陨石可能演变的地壳区域的部分分化的小行星具有对流熔融铁的核心。我们提出的结果的基础上，我们全面的数值模拟的情况下，涉及融化和行星分化的小行星。探讨了在这些分异体上存在相当大的碳质结壳的可能性。模拟结果表明，用对流熔融铁核产生的动力磁场来解释古地磁记录是可能的。除了缓慢的线性吸积的情况下，我们设想的情况下，涉及两个小行星的吸积插曲。小行星在初始阶段的早期快速吸积，可能在最初的1200万年内，将在分化后产生相当大的熔融铁核，以产生所需的磁场。这将是一个缓慢的固结南极地壳增生，也许超过几百万年。水化/脱水反应期间释放的气体所产生的内部压力也有可能破坏南极地壳的排出。
[1] Carbonaceous chondrites are considered to be the most primitive meteorites that contain some of the earliest formed solar system phases, e.g., Ca-Al-rich inclusions and chondrules. The parent bodies of the carbonaceous chondrites are traditionally known to have experienced aqueous alteration. However, the recent paleomagnetic records of the CV chondrite, Allende, indicate remnant magnetism that suggests that these chondrites possibly evolved on the crustal region of a partially differentiated asteroid having a convective molten iron core. We present results based on our comprehensive numerical simulations of the scenario involving melting and planetary differentiation of asteroids. The possibility of a sizable carbonaceous chondritic crust on these differentiated bodies is explored. The simulations indicate that it could be possible to explain the paleomagnetic records of the chondrites by the dynamo-generated magnetic field from the convective molten iron core. Apart from the slow linear accretion scenario, we envisage a scenario involving two episodes of accretion of the asteroids. An early rapid accretion of the asteroids in the initial stage, perhaps within the initial ∼2 Myr, would produce a sizable molten iron core subsequent to differentiation to produce the required magnetic fields. This would be followed by a slow accretion of consolidated chondritic crust, perhaps over several million years. There is also a possibility of the disrupted expulsion of the chondritic crust by the internal pressures generated by gases released during hydration/dehydration reactions.