The origin and microstructures of metamorphic felsic dykes emplaced during brittle-ductile extension (southeast Sinai)

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Abstract
Structural, petrographic and chemical analyses of a set of northeast-trending quartzofeld-spathic dykes in Wadi Kid area (southeastern Sinai) show that they are the product of anatexis of pelitic rocks. Metamorphic P-T data indicate that anatexis could have occurred only 2 km below the present erosion level. The partial melts intruded into overlying rocks during regional metamorphism along a set of northeast-oriented extensional fractures, thereby recrystallizing and in some cases obtaining tectonite fabrics. The fractures were formed perpendicular to the regional mineral lineation and show that the area was within the deeper parts of the brittle–ductile transition zone. The original depth of the presently exposed crustal level corresponds well with the theoretical and experimentally derived depths of the brittle-ductile transition zone in high heat flow regimes. The emplacement of a granitoid pluton or gneiss dome, possibly of dioritic composition, could be responsible for both melting and tensile fracturing of the overlying rocks.