Western Anatolia, one of the world's best-known extensional terrains, is characterized by the presence of several moderate- to high-enthalpy geothermal fields. Geothermal fluids have helium isotope compositions reflecting mixing between mantle and crustal helium components, the former ranging between 0.58% and 45% of the total helium in a given sample. Regarding the distribution of heat and mantle He and their correlation with tectonic structure and volcanism in western Anatolia, the prominent features are as follows: (1) the association between highest heat and highest 3 He lies along the eastern segment of the Büyük Menderes graben, (2) the high heat and high 3 He occur in the vicinity of the Quaternary Kula volcanism, (3) high-enthalpy fields exist in close vicinity to the young alkaline volcanics, (4) relatively high mantle He contributions occur in areas of not only the young alkaline, but also the old calc-alkaline volcanics, and (5) there is a lack of volcanic exposures along the Büyük Menderes graben (except at its western and southeastern terminations), where the highest values are recorded for both heat and helium. The first three features collectively suggest that the transfer mechanism for both heat and helium is probably mantle melting accompanying the current extension in western Anatolia, yet the latter two further indicate that this may be accomplished via subsurface plutonic activities. The large range observed in the helium isotope compositions may be linked with differential (local) extension rates and associated melt generation in the respective areas. This suggestion can be substantiated by He isotope data from more of the region.

Abstract The Tauride–Anatolide continent, stretching for c . 900 km across western and central Turkey, is one of the world's best example of a subducted, exhumed passive margin within a collisional orogen. Twelve widely separated areas were studied and correlated to develop a new plate-tectonic model. A metamorphosed, rifted continental margin of Triassic–Lower Cretaceous age (Tauride–Anatolide platform) is overlain by Upper Cretaceous (Cenomanian-Lower Maastrichtian) pelagic sediments and then by both tectonic melange (subduction complexes) and sedimentary melange (foredeep gravity complexes). The melanges are overthrust by unmetamorphosed ophiolitic rocks, commonly peridotites with swarms of diabase/gabbro dykes, and are underlain by metamorphic soles. New geochemical evidence from basaltic blocks in the melange indicates predominantly subduction influenced, within-plate and mid-ocean ridge-type settings. The dykes cutting the ophiolites were probably intruded during early-stage intra-oceanic arc genesis. The metamorphosed continental margin, melanges and ophiolites in the north (Anatolides) are correlated with unmetamorphosed equivalents in the Taurides further south (e.g. Beyşehir and Lycian nappes). Oceanic crust of Triassic–Late Cretaceous age formed between the Gondwana-related Tauride–Anatolide continent in the south and the Eurasia-related Sakarya microcontinent in the north. Following Late Triassic–Early Cretaceous passive margin subsidence, the continental margin was covered by Cenomanian-Turonian pelagic carbonates ( c . 98–90 Ma). Ophiolites formed in an intra-oceanic subduction zone setting in response to northward subduction, probably within a two-stranded ocean, with the Inner Tauride ocean in the SE and the İzmir–Ankara–Erzincan ocean in the north/NW. Metamorphic soles relate to intra-oceanic subduction ( c . 95–90 Ma). Oceanic sedimentary/igneous rocks accreted to the advancing supra-subduction oceanic slab. The Tauride–Anatolide continental margin then underwent diachronous collision with the trench ( c . 85 Ma), deeply subducted and metamorphosed at HP/LT ( c . 80 Ma). Accretionary, ophiolitic and exhumed HP/LT rocks were gravity reworked into a southward-migrating flexural foredeep and progressively overridden ( c . 70–63 Ma). Slices of the upper part of the platform and its margin detached and were thrust southwards as the (Tauride) Lycian and Beyşehir nappes, together with regional-scale ophiolites. The continental margin and melange were simultaneously exhumed during Maastrichtian–Early Paleocene (70–63 Ma) and transgressed by shallow-water sediments, beginning in the Late Maastrichtian in the east ( c . 64 Ma) and the Mid?-Late Paleocene ( c . 60 Ma) further west. Remnant oceanic crust was consumed during Early Cenozoic time, followed by Mid Eocene (45–40 Ma) diachronous continental collision and a second phase of regional deformation. Rather than being progressive there were two stages of collision: first, Upper Cretaceous ophiolite emplacement driven by continental margin-subduction trench collision, and secondly Eocene collision of the Tauride and Sakarya/Eurasian continents.

Abstract The development of the central Tauride region was dominated by rifting and passive margin development during Triassic–Early Cretaceous. The Tauride continental margin was later destabilized, followed by subsidence and collapse to form a flexurally controlled foredeep. Volcanic–sedimentary mélange and ophiolitic rocks were thrust onto the northern margin of the Tauride carbonate platform (Geyik Dağ) during Campanian–Maastrichtian. The remaining non-emplaced Tauride shelf subsided to form a second-stage foredeep during the Eocene. This basin was finally over-ridden by large thrust slices of Tauride shelf sediments, represented by the Hadim and Bolkar nappes, together with previously emplaced continental margin and ophiolitic units. Large- and small-scale field kinematic data indicate regional emplacement towards the west or SW. The ophiolitic rocks and related mélange were emplaced directly onto the Tauride autochthon (Geyik Dağ) in response to regional-scale out-of-sequence thrusting. Localized backthrusting to the NE took place in a transpressive setting. In the south, the relatively distal Bolkar nappe was emplaced over the more proximal Hadim nappe to produce the present thrust stacking order. The two-phase emplacement reflects initial northward subduction, which culminated in trench-continental margin collision (Campanian–Maastrichtian). This was followed by continent–continent collision (Eocene) related to suturing of a Mesozoic ocean basin to the north.