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Experimental investigation of shock metamorphic effects in a metapelitic granulite: The importance of shock impedance contrast between components
Author(s) -
OGILVIE Paula,
GIBSON Roger L.,
REIMOLD W. Uwe,
DEUTSCH Alexander,
HORNEMANN Ulrich
Publication year - 2011
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2011.01250.x
Subject(s) - shock (circulatory) , plagioclase , geology , metamorphic rock , mineralogy , geochemistry , quartz , medicine , paleontology
– 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.