Experimental investigation of shock metamorphic effects in a metapelitic granulite: The importance of shock impedance contrast between components
Experimental investigation of shock metamorphic effects in a metapelitic granulite: The importance of shock impedance contrast between components
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变泥质麻粒岩冲击变质效应的实验研究：成分之间冲击阻抗对比的重要性
DOI：
10.1111/j.1945-5100.2011.01250.x
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发表时间：
2011
影响因子：
2.2
通讯作者：
U. Hornemann
中科院分区：
文献类型：
--
作者：
P. Ogilvie;R. Gibson;W. Reimold;A. Deutsch;U. Hornemann
冲击恢复实验是在12.5、25、34、40和56 GPa25 °C下以及18和25 GPa400 °C下对苏格兰Etivéaureole中的高品位混合岩型石榴石-堇青石变辉石进行的。这项研究的目的是(1)表征复杂的多矿物岩石中含有大量含水铁镁矿物的冲击效应，作为可变冲击压力和震前温度的函数，以及(2)探索组成矿物之间的冲击阻抗对比对这些特征的各自丰度和分布的影响。在任何冲击压力下，各相冲击变质作用强度的大小顺序为：堇青石(Crd)→黑云母(BT)→斜长石(Pl)→钾长石(KFS)→石英(QTZ)→石榴石(Grt)→斜方辉石(OPx)。冲击压力低于40 GPA(25 °C)的样品在晶内和晶间尺度上的冲击效应具有明显的不均匀分布的典型特征。冲击不均匀主要归因于相邻相之间的冲击阻抗反差，表现为冲击阻抗反差最大的局部激波放大和阻抗反差最小的冲击抑制。冲击变质效应在实验岩石和天然岩石中的不均匀分布是亚毫米尺度上极端不平衡的标志。冲击变质效应的不均匀分布缓解了仅在矿物中使用冲击效应作为区域冲击压力晴雨表的情况，应该通过数值模型对冲击压力的额外限制来增强。
Shock recovery experiments were performed at 12.5, 25, 34, 40, and 56 GPa at 25 °C, and at 18 and 25 GPa at 400 °C, on a high‐grade, migmatitic, garnet‐cordierite metapelite from the Etivé aureole, Scotland. Objectives for this study were to (1) characterize shock effects in a complex polymineralic rock with a significant proportion of hydrous ferromagnesian minerals, both as a function of variable shock pressure and preshock temperature, and (2) to explore the effects of shock impedance contrast between component minerals on the respective abundances and distribution of these features. At any shock pressure, the order of decreasing intensity of shock metamorphic effects in component phases is: cordierite (Crd)→biotite (Bt)→plagioclase (Pl)→K‐feldspar (Kfs)→quartz (Qtz)→garnet (Grt)→orthopyroxene (Opx). Samples shocked to pressures below 40 GPa (25 °C) were typically characterized by marked heterogeneous distribution of shock effects on both intragranular and intergranular scales. Shock heterogeneity is mainly attributed to shock impedance contrast between contiguous phases, and manifests as shock amplification locally where shock impedance contrast is greatest, and shock suppression where impedance contrast is least. The heterogeneous distribution of shock metamorphic effects in both experiments and natural rocks is a signature of extreme disequilibrium at the submillimeter scale. The heterogeneous distribution of shock metamorphic effects mitigates against the use of shock effects in minerals exclusively as regional shock pressure barometers, and ought to be augmented by additional constraints on shock pressure from numerical models.