Multistage evolution of the Aladağ mantle peridotites (S-Türkiye): Processes of partial melting and melt-peridotite interaction in Mid-Ocean Ridge and Subduction Zones

The Aladağ ophiolite is located in the eastern Taurides, north of the city of Adana, southern Türkiye and, from bottom to top, is composed of mantle peridotites, ultramafic-mafic cumulates, isotropic (massive) gabbro and diabase dykes. Mantle peridotites are represented by varying degrees of serpentinized dunite, harzburgite and lherzolite. We studied 100 lherzolite, harzburgite and dunite samples representing the entire Aladağ ophiolite mantle. Whole rock major and trace element analysis were performed for all samples, and mineral chemistry analysis were carried out on selected mineral phases.

According to geochemical characteristics, mantle peridotites are divided into two sub-groups: abyssal (Group-1) and suprasubduction zone peridotites (Group-2). Group-1 mantle peridotites are represented by high clinopyroxene modal abundances, whole-rock and clinopyroxene heavy Rare Earth Element (REE) contents and low spinel Cr# values (13–47). Whole-rock heavy REE patterns indicate that these rocks are 5–18 % unhydrous partial melting residues. In contrast, Group-2 mantle peridotites are represented by lower clinopyroxene modal abundances, whole-rock and clinopyroxene heavy REE contents, and higher spinel Cr# values (44–74) than Group-1 samples, reflecting higher partial melting degrees of up to 33 %. Light REE and LILE enriched whole-rock and clinopyroxene contents of Group-2 samples reflect that, in addition to depletion, they were enriched with fluids/melts and underwent both cryptic and modal metasomatism in the subduction zone.

Aladağ peridotites have formed originally by low degree partial melting at mid-ocean spreading ridge (MOR) and later re-melted and metasomatized/refertilized in a suprasubduction zone (SSZ) environment.