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The development of orientated symplectites during deformation
Author(s) -
BRODIE K. H.
Publication year - 1995
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1995.tb00237.x
Subject(s) - granulite , geology , shear zone , geochemistry , plagioclase , facies , deformation (meteorology) , shear (geology) , metamorphic rock , petrology , geomorphology , paleontology , quartz , tectonics , oceanography , structural basin
Orientated symplectites have been observed in deformed granulite facies metabasic rocks from the Ivrea‐Verbano zone in northern Italy. The area underwent lower crustal extension, accommodated by movement on localized high‐ T shear zones. In areas of relatively low strain, such as at the margins of shear zones, symplectites of orthopyroxene, plagioclase and spinel have formed. The symplectites are vermiform and orientated parallel to the main foliation and in the regional stretching direction. The reaction was synkinematic with the deformation, and only developed in potentially dilatant grain boundaries in the rock. It was presumably inhibited in grain boundaries subjected to higher normal stress due to the relatively large volume increase involved in the reaction. The observations support the interpretation that the deformation was related to regional extension under high‐ T granulite facies conditions, the symplectites forming as a result of decreasing pressure.