Advanced Applied Geology

Advanced Applied Geology

Petrogenesis and Geochemistry of Neo-Tethyan Subduction-related Adakites in the Sabzevar Zone: Evidence from Magma-Fluid Interactions

Authors
1 Department of Geology, Tab.C., Islamic Azad University,Tabas, Iran
2 Department of Geology, Ma.C., Islamic Azad University, Mashhad, Iran
Abstract
This study presents a detailed petrological and geochemical investigation of adakites from the Cheheldokhtar and Firuzeh regions. We demonstrate that both suites originate from partial melting of subducted Neo-Tethyan oceanic crust but under distinct pressure-temperature conditions and melting regimes. Geochemical modeling indicates that the Cheheldokhtar adakites were generated by <10% partial melting of a garnet-amphibolite source, resulting in silica-poor compositions. These magmas subsequently underwent fluid-dominated metasomatism. In contrast, the Firuzeh adakites were produced by ~5% melting of a garnet-eclogite residue, yielding silica-rich melts that experienced enrichment from both subduction-derived fluids and sediment melts. The fundamental petrogenetic difference correlates with a tectonic transition: Cheheldokhtar adakites are characteristic of an oceanic arc setting, whereas Firuzeh adakites are diagnostic of a subsequent continental arc environment. Collectively, these findings document a clear temporal and spatial evolution in the Sabzevar zone from an oceanic to a continental arc, directly mirroring the advanced subduction and eventual closure of the Neo-Tethys Ocean. This study quantitatively links changing slab melting depths and metasomatic agents to the progressive maturation of an orogenic system.
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