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The Central Anatolian Crystalline Complex (CACC) is a microcontinent in the Alpine±Himalayan belt. It has previously been considered as a coherent structural entity, but, although the entire CACC is comprised of similar rocks (primarily metasedimentary rocks and granitoids), it consists of at least four tectonic blocks characterized by different P±T±t paths. These blocks are the Kõrs Ëehir (north-west), Akdag AE (northeast), Nig AEde (south) and Aksaray (west) massifs. The northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion; metamorphic rocks are characterized by clockwise P±T paths at moderate P±T and local low-P±high-T (LP±HT) overprinting in the highest grade rocks. Apatite ®ssion track ages are Eocene to Oligocene (47±32 Ma). The Aksaray block represents the hot, shallow mid-crust of a Late Cretaceous±early Tertiary arc. It is dominated by intrusions; rare metapelitic rocks record low-P (<4 kbar) regional metamorphism overprinted by LP±HT contact metamorphism. Apatite ®ssion track ages are 50±45 Ma. The Nig AEde massif is different from the other CACC blocks because it evolved as a core complex in a wrench-dominated setting. It is characterized by clockwise P±T paths at moderate P±T followed by widespread LP±HT metamorphism. Apatite ®ssion track ages are Miocene (12±9 Ma), signi®cantly younger than those in the northern massifs. Nig AEde rocks resided in the mid-crust at a time when the rest of the CACC was at or near the Earth's surface. Variations in P±T±t and tectonic histories Ð especially timing of exhumation Ð between the northern and southern CACC re¯ect the difference between head-on collision vs. mid-crustal wrenching.

Metamorphic terranes comprised of blueschist facies and regional metamorphic (Barrovian) rocks in apparent structural continuity may represent subduction complexes that were partially overprinted during syn-to post-subduction heating or may be comprised of unrelated tectonic slices. An excellent example of a composite blueschist-to-Barrovian terrane is the southern Sivrihisar Massif, Turkey. Late Cretaceous blueschist facies rocks are dominated by marble characterized by rod-shaped calcite pseudomorphs after aragonite and interlayered with blueschist that contains eclogite and quartzite pods. Barrovian rocks, which have 40 Ar ⁄ 39 Ar white mica ages that are >20 Myr younger than those of the blueschists, are also dominated by marble, but rod-shaped calcite has been progressively recrystallized into massive marble within a 200-m transition zone. Barrovian marble is interlayered with quartzite and schist in which isograds are closely spaced and metamorphic conditions range from chlorite to sillimanite zone over 1 km present-day structural thickness. Andalusite, kyanite and prismatic sillimanite are present in muscovite-rich quartzite; in one location, all three are in the same rock. Andalusite pre-dates Barrovian metamorphism, kyanite is both pre-and syn-Barrovian and sillimanite is entirely Barrovian. Muscovite with phengitic cores and relict kyanite in quartzite below the staurolite-in isograd are evidence for pre-Barrovian subduction metamorphism preserved at the low-T end of the Barrovian domain; above the staurolite isograd, all evidence for subduction metamorphism has been erased. Some regional metamorphism may have occurred during exhumation, as indicated by synkinematic high-T minerals defining the fabric of L-tectonite. Quartz microstructures in lineated quartzite reveal a strong constrictional fabric that may have formed in a transtensional bend in the plate boundary. Transtension accounts for the closely spaced isograds and development of a strong constrictional fabric during exhumation.

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Decompression of deep, hot continental crust is the primary mechanism of crustal melting, with major consequences for the geodynamics of orogens. Decompression within thickened continental crust may be initiated by processes driven from above (erosion, tectonic denudation) and/or below (crust/lithosphere thinning, buoyant rise of deep crust). On a larger scale, decompression of subducted continental crust may add material, including melt, to the overlying, non-subducting plate. This mechanism has the potential to produce large amounts of melt because fertile material is continually conveyed into the mantle, where it eventually buoyantly ascends and melts. Decompression-driven melting of continental crust may account for the high melt fractions (≥20 vol.%) and great thickness (20–30 km) inferred for the partially molten layer in orogenic crust. When high melt volumes are present in the crust and/or the thickness of the partially molten layer is large, the subsequent thermo-mechanical evolution of orogens is strongly influenced by lateral (channel) and vertical (buoyant) crustal flow. For both lateral and vertical flow, the presence of melt decouples deep crust from upper crust, and continental crust from mantle lithosphere.A major consequence of vertical crustal flow is the generation of migmatite-cored gneiss domes that riddle most orogens. High-grade rocks in many domes record pressure-temperature-time (P-T-t) paths indicating near-isothermal decompression followed by cooling from T > 700 °C to T < 350 °C in <2–5 Ma. Diapiric ascent of partially molten crust accounts for the decompression rate and magnitude required to maintain a near-isothermal path. We propose that gneiss domes are a signature of decompression and crustal melting, and are therefore fundamental structures for understanding the thermo-mechanical evolution of continental crust during orogeny.