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Compositional variations of peridotites from the Cretaceous ophiolites in southern Turkey and Northern Cyprus are presented to document the nature of partial melting and possible effects of reactive dissolution of primary mantle phases during fore-arc spreading. The peridotites overall exhibit a range of 187Os/188Os ratios from 0.1171 to 0.1266 and appear to represent a mantle region that preserves a record of ancient melt depletion. The samples are depleted in 187Os/188Os compared to the ambient oceanic upper mantle (187Os/188Os ~0.127), suggesting that they are representatives of a shallow fore-arc mantle where transport of radiogenic 187Os during slab dehydration was limited. Chemical variations of primary mantle minerals indicate that the peridotites are the residues of moderate to high degrees (>16%) of partial melting and have experienced significant modal and chemical compositional modification through interaction with oxidizing hydrous basaltic melts. Interacting melts, which appear to be similar in composition to primitive arc tholeiite, are likely to have originated from sub-lithospheric lower part of the mantle wedge during early stages of fore-arc spreading and migrated upward to react with variably depleted harzburgites to induce further melting in the overlying lithospheric mantle through open-system reactive flow. This second stage melting resulted in (1) common occurrence of reactive harzburgites and dunites by incongruent melting of orthopyroxene and crystallization of olivine through interaction with olivine saturated melt; and (2) local development of refertilized peridotites by shallower melt impregnation that involves interaction with olivine + clinopyroxene saturated melt. The dissolution of orthopyroxene caused the reacting melt to be enriched in silica and diluted in incompatible elements which led to the production of the final melts similar in composition to fore arc basalt and boninite. Involvement of compositionally variable mantle and melt components with different rates of melt influx therefore appears to explain the generation of fore-arc crust with a range of diverse rock suites including temporally and spatially associated arc tholeiites and boninites with significant depletion in incompatible elements.

The Central Anatolian Crystalline Complex (CACC) is a large continental domain exposed in central Turkey that was affected by high temperature metamorphism during the Late Cretaceous. As a result of this event, Paleozoic sediments became metamorphosed, initially under Barrovian conditions, then overprinted locally by high temperature–low pressure metamorphism, and intruded by widespread batholiths. In this study we focus on the crystalline Hirkadag Massif located in the central part of the CACC, where we applied an integrated approach involving metamorphic, structural and geochronological analysis in order to elucidate its tectonic history from burial to exhumation. Our metamorphic study reveals that conditions of metamorphism reached ~ 7–8 kbar/700 °C and were relatively homogeneous at the scale of the Hirkadag Massif. Coeval with the regional metamorphism, the rocks were intensely deformed as reflected by isoclinal folding, the development of a pervasive foliation and top-to-the-SE shearing. This was followed by decompression to pressures of ~ 3–4 kbar at 800 °C, which may be linked to the emplacement of local granodioritic intrusions at ~ 77 Ma. Subsequent cooling of the Hirkadag high-grade metamorphic and intrusive rocks is indicated by 40Ar/39Ar cooling ages of 68.8 ± 0.9 Ma (biotite) and 67.0 ± 1.2 Ma (potassium feldspar). Evidence for tectonic exhumation has been identified within the marbles at the NE margin of the Hirkadag Massif, in the form of discrete protomylonitic and mylonitic shear bands showing a consistent N40–60 top-to-NE sense of shear. Further east, the contact between brecciated mylonitic marbles and non-metamorphic conglomerates preserves the typical structural features of an upper-crustal detachment fault. Restoration of the Hirkadag Massif and the CACC to their late Cretaceous configuration suggests that the LP–HT metamorphism, magmatism and extensional structures evolved as a result of the development and exhumation of a ~ N–S trending magmatic arc experiencing regional E–W extension above an active subduction zone.