C-复合小行星上的放射性热液活动
Hydrothermal activities on C-complex asteroids induced by radioactivity
摘要：
富含碳质物质的C-复合小行星是地球挥发性物质的潜在来源。它们的光谱很暗，类似于原始的碳质陨石，因此，C-复合小行星被认为是碳质陨石的潜在母体。然而，相当数量的C-复合小行星的表面光谱比富含水的碳质陨石具有较弱的羟基吸收。相反，它们最好对应于显示脱水证据的陨石，通常归因于撞击加热。在这里，我们报告一个老的放射性年龄4564.7万年前的钙碳酸盐从Jbilet Winselwan陨石类似于脱水的C-复杂的小行星。碳酸盐被高温多晶型的钙硫酸盐包裹，表明在水蚀变后随后在>300°C下发生热变质。这种古老的年龄表明，早期发生的水蚀变和随后的热变质作用的驱动下，短寿命的放射性核素的衰变，而不是影响加热。最初的小行星由于内部受到放射性加热而解体，应会产生主要由热变质物质组成的小行星族。这解释了脱水的C-复合小行星的常见现象。
英文摘要：
C-complex asteroids, rich in carbonaceous materials, are potential sources of Earth's volatile inventories. They are spectrally dark resembling primitive carbonaceous meteorites, and thus, C-complex asteroids are thought to be potential parent bodies of carbonaceous meteorites. However, the substantial number of C-complex asteroids exhibits surface spectra with weaker hydroxyl absorption than water-rich carbonaceous meteorites. Rather, they best correspond to meteorites showing evidence for dehydration, commonly attributed to impact heating. Here, we report an old radiometric age of 4564.7 million years ago for Ca-carbonates from the Jbilet Winselwan meteorite analogous to dehydrated C-complex asteroids. The carbonates are enclosed by a high-temperature polymorph of Ca-sulfates, suggesting thermal metamorphism at >300°C subsequently after aqueous alteration. This old age indicates the early onset of aqueous alteration and subsequent thermal metamorphism driven by the decay of short-lived radionuclides rather than impact heating. The breakup of original asteroids internally heated by radioactivity should result in asteroid families predominantly consisting of thermally metamorphosed materials. This explains the common occurrence of dehydrated C-complex asteroids.
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