Genesis of trondhjemite by low-pressure low-melt fraction anatexis of hornblende-gabbro at Alvand Plutonic Complex (Hamedan, NW Iran): insights from geochemical modelling

Abstract

Amphibole-dominated dehydration melting of gabbro is the primary process responsible for the genesis of adakites, low-K tonalites, modern trondhjemites, and plagiogranites as well as Archean tonalite-trondhjemite-granodiorite suites that represent the earliest examples of continental crust. Previous literature has mostly focused on the role of Al-rich amphibole during anatexis of a mafic source and many of these studies have investigated this process through experimental melting runs. However, due to experimental boundary conditions, little is known about partial melting of amphibole-bearing mafic rock at temperatures < 800°C for upper crustal conditions (pressure < 500 MPa). Classic and forward thermobarometric modelling suggests that in situ trondhjemite leucosomes, hosted by Cheshmeh-Ghasaban mafic metatexites (Alvand Plutonic Complex, Hamedan, NW Iran), represent a rare natural case study of a low-temperature incipient amphibole-dominated anatectic event of a mafic source with a primary assemblage (Pl+Hbl+Cpx+Bt+Opx) typical of a hornblende-bearing gabbroic rock.

A comprehensive re‐look into Jurassic‐Cretaceous Neotethyan active margin in Iran: Evidence of deep mantle flow into subduction magma factory and formation of transitional basalts

“…Melt derived from an asthenospheric mantle source (Yang et al, 2018) or partial melting of a metasomatized sub‐continental lithospheric mantle following upwelling asthenosphere (H. Zhang, Chen, et al, 2018) are the main models proposed for the alkaline gabbros. Formation of the A‐ and I‐type granites by melting of the arc crust (Yang et al, 2018; H. Zhang, Chen, et al, 2018) and migmatization of both mafic and pelitic protoliths (Lucci et al, 2021; Saki et al, 2020, 2022) are the products of magmatic underplating.…”