Subduction-related Eocene shoshonites from the Cenozoic Urumieh-Dokhrat magmatic arc (Qaleh-Khargooshi area, West of the Yazd province, Iran)


Abstract: The fifth phase of Eocene volcanism in the central part of the Urumieh-Dokhtar magmatic arc (UDMA), comprises lavas with shoshonitic characteristics, ranging from trachybasalt to trachydacite. In shoshonites of the Qaleh-Khargooshi area, leucite changes to analcime, analcime to albite, sanidine to albite and anorthoclase, and clinopyroxene to albite. These reactions, together with other field, petrographic and geochemical features, are evidence of an original absarokitic magma which was changing to generate the different rock units. The parental magma of these shoshonites was produced by a low degree of partial melting from a metasomatized enriched mantle source. During the ascent of shoshonitic magma through the continental crust, crustal contamination, chemical changes and mineralogical transformations took place. The geochemistry of these shoshonitic rocks is similar to potassic volcanic rocks of continental arcs or convergent margins.

Keywords: shoshonite, Eocene, Urumieh-Dokhtar, Qaleh-Khargooshi, Iran

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