Type 1 aqueous alteration in CM carbonaceous chondrites: Implications for the evolution of water-rich asteroids
Type 1 aqueous alteration in CM carbonaceous chondrites: Implications for the evolution of water-rich asteroids
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CM 碳质球粒陨石中的 1 型水蚀变：对富水小行星演化的影响
DOI：
10.1111/maps.12872
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发表时间：
2017
影响因子：
2.2
通讯作者：
King A
中科院分区：
文献类型：
--
作者：
King A
CM碳质球粒陨石在太阳系早期经历了水蚀变。它们的范围从轻度蚀变的2型到几乎完全水合的1型陨石，并提供了富含水的小行星的地球化学条件的记录。我们发现，CM 1方解石含有丰富的（84-91体积%）页硅酸盐，加上橄榄石（4-8体积%），磁铁矿（2-3体积%），硫化铁（<5体积%），方解石（<2体积%）。CM 1 - 2方解石含有页硅酸盐（71-88体积%）、橄榄石（4-20体积%）、顽火辉石（2-6体积%）、磁铁矿（2-3体积%）、硫化铁（1-2体积%）和方解石（~1体积%）。随着水蚀变的进行，CM辉长岩中镁蛇纹石和磁铁矿的丰度增加。相比之下，CM 1/2和CM 1方解石中的方解石丰度往往相对于CM 2s被耗尽。模态数据支持该模型，即金属和富铁基质是CM母体上首先发生变化的组分，然后进一步水化攻击球粒和碎片中发现的较粗的富镁硅酸盐。基于缺乏托基利尼石，我们认为，CM 1钙钛矿经历了由于高温（>120 °C）而增加的蚀变，尽管更高的水/岩比也可能发挥了作用。模态数据为解释小行星的组成和从这些天体返回的样品的矿物学提供了限制。我们预测，“CM 1-like”小行星，如Bennu所提出的OSIRIS-雷克斯任务的目标，将具有丰富的富镁层状硅酸盐和铁氧化物，但缺乏方解石。
The CM carbonaceous chondrite meteorites experienced aqueous alteration in the early solar system. They range from mildly altered type 2 to almost completely hydrated type 1 chondrites, and offer a record of geochemical conditions on water‐rich asteroids. We show that CM1 chondrites contain abundant (84–91 vol%) phyllosilicate, plus olivine (4–8 vol%), magnetite (2–3 vol%), Fe‐sulfide (<5 vol%), and calcite (<2 vol%). The CM1/2 chondrites contain phyllosilicate (71–88 vol%), olivine (4–20 vol%), enstatite (2–6 vol%), magnetite (2–3 vol%), Fe‐sulfides (1–2 vol%), and calcite (~1 vol%). As aqueous alteration progressed, the abundance of Mg‐serpentine and magnetite in the CM chondrites increased. In contrast, calcite abundances in the CM1/2 and CM1 chondrites are often depleted relative to the CM2s. The modal data support the model, whereby metal and Fe‐rich matrix were the first components to be altered on the CM parent body(ies), before further hydration attacked the coarser Mg‐rich silicates found in chondrules and fragments. Based on the absence of tochilinite, we suggest that CM1 chondrites experienced increased alteration due to elevated temperatures (>120 °C), although higher water/rock ratios may also have played a role. The modal data provide constraints for interpreting the composition of asteroids and the mineralogy of samples returned from these bodies. We predict that “CM1‐like” asteroids, as has been proposed for Bennu—target for the OSIRIS‐REx mission—will have a high abundance of Mg‐rich phyllosilicates and Fe‐oxides, but be depleted in calcite.