Plagioclase breakdown as an indicator for shock conditions of meteorites
Plagioclase breakdown as an indicator for shock conditions of meteorites
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DOI：
10.1038/ngeo704
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发表时间：
2010-01-01
影响因子：
18.3
通讯作者：
Funakoshi, Ken-ichi
中科院分区：
文献类型：
--
作者：
Kubo, Tomoaki;Kimura, Makoto;Funakoshi, Ken-ichi
当它们的母体经历冲击变质作用时形成的冲击陨石通常含有无定形形式或高压相的矿物斜长石。冲击变质作用的峰值压力可以通过确定斜长石非晶化压力的冲击恢复实验来限制（1-3）。然而，在这些实验中，温度低得不切实际，时间尺度比自然事件短得多。本文介绍了两种斜长石在加压升温条件下的原位X射线衍射测量结果。我们发现斜长石的非晶化压力随着温度的升高而降低，这表明以前的研究高估了这个参数（1-3）。我们还发现，矿物硬玉的形成首先从无定形斜长石，而其他矿物，如斯铁橄榄石或石榴石的成核显着延迟。因此，硬玉在不含斯铁闪石（4-8）的冲击陨石中的出现可以解释为结晶动力学的结果。斜长石破裂的研究可以约束冲击事件的压力-温度-时间历史，从而有助于重建太阳系早期小行星的碰撞历史。
Shocked meteorites that were formed when their parent body underwent shock metamorphism often contain the mineral plagioclase either in an amorphous form or in its high-pressure phase. The peak pressures in shock metamorphism can be constrained by shock-recovery experiments that determine the amorphization pressures of plagioclase(1-3). However, in these experiments temperatures have been unrealistically low and timescales much shorter than those in natural events. Here we present in situ X-ray diffraction measurements of two kinds of plagioclase feldspar in conditions of increasing pressures and temperatures. We find that the amorphization pressure of plagioclase decreases with increasing temperature, suggesting that previous studies overestimated this parameter(1-3). We also found that the mineral jadeite forms first from amorphous plagioclase, whereas the nucleation of other minerals such as stishovite or garnet is significantly delayed. The occurrence of jadeite in shocked meteorites that do not contain stishovite(4-8) can therefore be explained as a result of the crystallization kinetics. We conclude that the study of plagioclase breakdown can constrain the pressure-temperature-time history of shock events, and thus help to reconstruct the collisional history of asteroids in the early Solar System.