Crystallization kinetics of olivine‐phyric shergottites
Crystallization kinetics of olivine‐phyric shergottites
复制标题
橄榄石-镁橄榄石的结晶动力学
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
H. McSween
中科院分区：
文献类型：
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作者：
M. Ennis;H. McSween
本文采用晶体尺寸分布（CSD）和空间分布模式（SDP）分析了从火星喷发年龄推断的每个采样地点的橄榄石-辉石辉长岩（Elephant moraine [EET] 79001A， Dar al Gani [DaG] 476和dhofar [Dho] 019）的早期结晶阶段，橄榄石和辉石。橄榄石中的微量元素分带模式（P和Cr）也被用来表征这些火星玄武岩的结晶历史。先前报道的这些陨石的2 - D CSDs使用一种新的立体校正方法重新评估。橄榄石CSD图中的扭结表明在不同条件下结晶的几个种群。DaG 476和EET 79001A中辉石的CSDs显示在稳态条件下生长的单种群；Dho 019的辉石过于杂交，无法进行CSD分析。根据前人实验数据推断的CSD斜率和生长速率，计算出小颗粒的岩浆房停留时间为几天到橄榄石巨晶的几个月不等。DaG 476和Dho 019中橄榄石的磷成像显示，骨状、扇形或斑块状岩心快速生长，可能是对延迟成核的反应，随后缓慢生长，最后快速树突生长，并形成边缘的振荡带。SPD分析表明橄榄石和辉石晶体以簇状生长或积累，而不是随机分布的颗粒。这些数据揭示了火星玄武岩复杂的凝固历史，并且总体上与橄榄石巨晶岩心的深度形成一致，橄榄石巨晶岩心被包裹在上升的岩浆中，这些岩浆结晶了辉石、小橄榄石和巨晶上的振荡边缘。
Crystal size distribution (CSD) and spatial distribution pattern (SDP) analyses are applied to the early crystallizing phases, olivine and pyroxene, in olivine‐phyric shergottites (Elephant moraine [EET] 79001A, Dar al Gani [DaG] 476, and dhofar [Dho] 019) from each sampling locality inferred from Mars ejection ages. Trace element zonation patterns (P and Cr) in olivine are also used to characterize the crystallization history of these Martian basalts. Previously reported 2‐D CSDs for these meteorites are re‐evaluated using a newer stereographically corrected methodology. Kinks in the olivine CSD plots suggest several populations that crystallized under different conditions. CSDs for pyroxene in DaG 476 and EET 79001A reveal single populations that grew under steady‐state conditions; pyroxenes in Dho 019 were too intergrown for CSD analysis. Magma chamber residence times of several days for small grains to several months for olivine megacrysts are calculated using the CSD slopes and growth rates inferred from previous experimental data. Phosphorus imaging in olivines in DaG 476 and Dho 019 indicate rapid growth of skeletal, sector‐zoned, or patchy cores, probably in response to delayed nucleation, followed by slow growth, and finally rapid dendritic growth with back‐filling to form oscillatory zoning in rims. SPD analyses indicate that olivine and pyroxene crystals grew or accumulated in clusters rather than as randomly distributed grains. These data reveal complex solidification histories for Martian basalts, and are generally consistent with the formation at depth of olivine megacryst cores, which were entrained in ascending magmas that crystallized pyroxenes, small olivines, and oscillatory rims on megacrysts.