Geochemistry and Petrogenesis of the Degamankesh Gabbroic Bodies (SW of Astara city)

Abstract

In the northern ranges of Guilan in Degarmankesh, alkali gabbroic bodies have been outcropped. Based on petrographic studies, the essential minerals are plagioclase, pyroxene and± Olivine. Chlorite, termolite-actinolite, serpentine, sosorite are secondary and opaque is accessory mineral of the rocks studied. Based on geochemistry data, the rocks studied are plotted on gabbro domain. Normalized trace element patterns relative to MORB and primitive mantle show LREE enriched and HREE depleted. K, Th, Rb positive anomaly as well as negative anomaly of Ta, Nb and Ti point to continental crust contaminated by the rocks under discussion. In terms of tectonic setting, the studied rocks lie in continental intraplate and continental arc environment. The parent magma generated by 5% to 14% partial melting of garnet lehrzolite mantle source possibly at the depth of approximately 80 km. The overall petrographic and geochemical criteria indicate that the studied gabrros originated from magmatism related to Paleogene pull apart basin, in the course of partial melting of asthenosphere arisen under continental lithosphere and contaminated with derived subducted fluids in supraduction zone.

Keywords

• Gabbro
• Alkaline series
• Astara city
• Talesh zone