We present here the first geochemical data from adakitic rocks from an extensional system—the U.S. East Coast rifted margin. Adakitic magmas are high-K melts that have been petrogenetically interpreted to be partial melts of subducting slab and/or lower crustal lithologies in delamination events. The adakitic rocks presented here are from a small volcanic region in the Valley and Ridge province in Virginia and were probably emplaced around the time of continent rupture and Central Atlantic magmatic province activity. They are bimodal in character (high Si and low Si) and have the typical high- and low-Si adakitic geochemical characteristics such as high K 2 O (up to 9.88 wt%) abundances, steep rare earth element patterns, and significantly high Sr (2473 ppm) and relatively low Rb (35 ppm) contents for high-Si adakitic rocks. The petrogenetic relation of these melts to partial melting of metagabbroic rocks (high-Si adakites) and interaction of these melts with ambient peridotite (low-Si adakites) suggests that the geodynamic process for the formation of the studied Jurassic central Virginia igneous rock succession is delamination of mantle lithosphere and lower crust below the volcanic rifted margin. We present with geodynamic models that negatively buoyant mantle lithosphere instabilities developed below this passive margin during continent rupture. After foundering, warm asthenosphere welled up and heated the lower crust of the East Coast margin. This lithosphere was interspersed in our study area with fragmented hydrated metamorphic mafic to ultramafic lithologies. In situ and/or dripping melting of such meta-igneous rocks reproduces the observed geochemistry of the studied high-Si adakitic rocks. Further recycling processes within the convecting mantle of delaminated floating fertile meta-igneous rock packages could be responsible for Atlantic melting anomalies such as the Azores or Bermuda.

Lithospheric foundering or delamination has been long recognized as an important process in the formation of the Andes, but the scale, timing, and surface uplift consequences remain controversial. We use recently completed ambient noise tomography and finite-frequency P-wave tomography results and other geologic and geophysical information to identify two ~200-km-diameter regions of piecemeal delamination in the Puna region between 21°S and 27°S. One location in the northern Puna Plateau is centered under the 11–1 Ma large-volume silicic Altiplano-Puna volcanic center, and the other in the southern Puna Plateau is centered approximately between the Arizaro Basin and 6–2 Ma Cerro Galan volcanic field. The foundering in the northern location has progressed to the point where the main thermal anomaly resides in the middle and upper crust, and the surface volcanic flare-up and mantle thermal anomalies are both in a waning stage. In the southern location, the main thermal anomaly is still in its waxing stage in the lower crust and upper mantle, and the foundering mantle material is imaged in the mantle wedge. The differing patterns of back-arc volcanism in the two foundering centers suggest different styles and timing of delamination, with the foundering process coming to completion earlier in the north than in the south. Based on plate-motion reconstructions, the NE-SW–aligned Juan Fernandez Ridge swept southward through this area starting about ca. 14 Ma in the north and ca. 10 Ma in the south. Although we do not think the passage of the Juan Fernandez Ridge initiated foundering, it played an important role in facilitating delamination by increasing interplate coupling, and weakening and perhaps hydrating the upper plate, and its passage allowed the delaminated material to sink into the expanding space of the mantle wedge. Another important factor in this evolution is the upper-plate lithospheric strength variations inherited from the different geologic basements underlying the northern and southern Puna regions. As the larger-scale delamination progressed, leaving behind thin lithosphere and a mantle wedge with a mixture of continental lithospheric fragments and hot asthenosphere, smaller secondary Rayleigh-Taylor instabilities occurred beneath the southern Puna Plateau, influencing basin development, and subsequent melting of this “drip” material was the source of the ensuing low-volume mafic volcanism.

The relative importance of crustal thickening, lithospheric delamination, and climate change in driving surface uplift and the associated changes in accommodation space and depositional facies in the adjacent foreland basin in the central Andes has been a topic of vigorous debate over the past decade. Interpretation of structural, geochemical, geomorphic, and geobiologic field data has led to two proposed end-member Tertiary surface uplift scenarios for the Eastern Cordillera and Subandes in the vicinity of the Bolivian orocline. A “gradual uplift” model proposes that the rate of surface uplift has been relatively steady since deformation propagated into the Eastern Cordillera during the late Eocene. In this scenario, the mean elevation of the region was >2 km above mean sea level (msl) by the late Miocene or earlier. Alternatively, a “rapid uplift” model suggests that the mean elevation of the Altiplano was <1 km above msl, and the peaks of the Eastern Cordillera were more than 2 km below their modern elevations until rapid uplift began ca. 10 Ma. Determining which of these uplift scenarios is most consistent with the stratigraphic record is complicated by the potentially confounding effects of global climate changes and lithospheric delamination in the stratigraphic record. In this study, we use a coupled mountain-belt–sediment-transport model to predict the foreland basin stratigraphic response to these end-member surface uplift scenarios. Our model results indicate that the location and height of the migrating deformation front play the dominant roles in controlling changes in accommodation space and grain size within the foreland basin. Changes in accommodation space and rates of sediment supply related to climate change and lithospheric delamination play secondary roles. Our results support the conclusion that the Eastern Cordillera likely gained most of its modern elevation prior to 10 Ma, in contrast with recent proposals that most of the modern elevation was obtained during the late Miocene. This conclusion is consistent with the most comprehensive paleoaltimetric analysis of the region to date.

Abstract In the central Andes of South America, a combination of crustal shortening and thickening, lithospheric densification and delamination, and surficial and climate interactions have resulted in development of the 3–5 km-high central Andean plateau and flanking 6–7 km peaks of the Eastern and Western cordilleras. Questions remain concerning the timing and rate of surface uplift and the relative roles of these mechanisms in producing and supporting these extreme elevations. End-member models attempting to answer these questions propose either a large-magnitude, rapid late Miocene uplift event, or rather slow and steady topographic growth initiating in the late Oligocene–early Miocene. The former model is based primarily on climate- and temperature-sensitive stable isotope analysis of carbonate material as a paleo-elevation proxy and is consistent with an uplift mechanism involving large-scale delamination and foundering of negatively buoyant lower crust and mantle lithosphere. The latter model is consistent with surface uplift driven directly by crustal shortening and is supported by climate simulations that suggest a nonlinear climate response to topographic uplift, indicating instead that there are threshold changes in temperature and isotopic composition of precipitation with rising topography, and highlighting that the use of such proxies may overestimate uplift rate and magnitude.

The Vermont Appalachians expose metamorphosed magmatic rocks ranging in age from Late Proterozoic to Cretaceous. Geochemistry, in concert with stratigraphic, structural, and metamorphic studies, reveals the origins of the magmatic rocks. Late Proterozoic–Early Cambrian dikes and greenstones in western Vermont formed during rifting of the Laurentian continent to form the Iapetus Ocean. Cambrian serpentinized peridotite represents forearc suprasubduction zone ophiolitic fragments. Cambrian to Ordovician amphibolites and felsic gneisses were formed as part of the Shelburne Falls volcanic arc. The Early Ordovician Mount Norris intrusive suite formed in an extensional setting in the vicinity of the Shelburne Falls arc. Silurian extensional magmatism at ca. 420 Ma is represented by the Comerford intrusive suite of dikes and small metamorphosed gabbro/diorite bodies in northeastern Vermont. Extension in the Silurian occurred behind a volcanic arc, perhaps because of slab detachment. Late Devonian granitoid bodies cut metamorphosed Silurian sedimentary units in northeastern Vermont. They probably formed as a result of delamination of lithosphere and consequent partial melting of mantle lithosphere and lower crust following continental collision. The last episode of magmatism in Vermont is represented by lamprophyric dikes and small alkaline bodies, which intruded at 130–110 Ma. Formation of the Late Proterozoic to Late Devonian magmatic rocks is explained in plate models involving continental rifting to produce the Iapetus Ocean in the Late Proterozoic, followed by subduction processes to close that ocean in stages from the Early Ordovician to Devonian time.

Late Paleozoic granitic rocks have been identified in two drill holes south of the proposed Alleghanian suture separating the Suwannee terrane from terranes to the north. These granites are the only known expression of magmatism on the accreted Gondwanan plate during the Alleghanian collision of Laurentia and Gondwana, an event that represents the final episode in the assembly of Pangea. Zircons from samples of granite from drill holes in southwestern Georgia and northern Florida were analyzed by ion probe, yielding igneous crystallization ages of 294 ± 6 and 296 ± 4 Ma (2σ), respectively. Xenocrystic zircons with ages of ca. 1.0–1.2 Ga and ca. 560 Ma were also obtained from one sample. The Proterozoic ages of these grains are consistent with previous proposals of a Gondwanan origin for the Suwannee terrane, particularly those proposals involving the Orinoquian or Sunsas-Rondonian provinces of South America. The major- and trace-element geochemical compositions of the granites are inconsistent with generation in a subduction environment. Instead, the data support models of the Alleghanian event in the Southern Appalachians involving an oblique collision between Laurentia and Gondwana followed by a late-stage, postorogenic episode of magmatism related to a postcollisional, lithospheric collapse event that may have included delamination.

Integrated magmatic, structural, and geophysical data provide a basis for modeling the Neogene lithospheric evolution of the high Central Andean Puna-Altiplano Plateau. Reconstruction of three transects south of the Bolivian orocline in the Altiplano and Puna Plateau shows processes in common, including subduction characterized by relatively shallow and changing slab dips, crustal shortening, delamination of thickened lower crust and lithosphere, crustal melting, eruption of giant ignimbrites, and deep crustal flow. Temporal similarities in events in the three transects can be correlated with changes in the rate of westward drift of South America and slab rollback. Temporal differences between the three transects can be attributed to variations in Nazca plate geometry in response to southward subduction of the aseismic Juan Fernandez Ridge. Subduction of the north-south arm of the ridge can explain an Oligocene flat slab under the Altiplano, and subduction of a northeast arm of the ridge can explain a long period of relatively shallow subduction characterized by local steepening and shallowing. Major episodes of ignimbrite eruption and delamination have occurred over steepening subduction zones as the ridge has passed to the south. Late Miocene to Holocene delamination of dense lithosphere is corroborated by published seismic images. The southern Altiplano transect (17°S–21°S) is notable for high, structurally complex Western and Eastern Cordilleras flanking the Altiplano Basin, the eastern border of which is marked by late Miocene ignimbrites. The broad Subandean fold-and-thrust belt lies to the east. The Neogene evolution can be modeled by steepening of a shallowly subducting plate, leading to mantle and crustal melting that produced widespread volcanism including large ignimbrites. Major uplift of the plateau at 10–6.7 Ma was dominantly a response to crustal thickening related to Subandean shortening and peak lower-crustal flow into the Altiplano from the bordering cordilleras as the ignimbrites erupted, and partly a response to delamination along the eastern Altiplano border. A smaller ignimbrite volume than in the northern Puna suggests the Altiplano lithosphere never reached as high a degree of melting as to the south. An Oligocene flat-slab stage can explain extensive Oligocene deformation of the high plateau region. The northern Puna transect at ~21°S–24°S is notable for voluminous ignimbrites (>8000 km 3 ) and a narrower Subandean fold-and-thrust belt that gives way southward to a thick-skinned thrust belt. The evolution can be modeled by an early Miocene amagmatic flat slab that underwent steepening after 16 Ma, which led to mantle melting that culminated in widespread ignimbrite eruptions beginning at 10 Ma, peaking in the backarc at ca. 8.5–6 Ma, restricted to the near arc by 4.5 Ma, and ending by 3 Ma. The formation of eclogitic residual crust caused periodic lower-crustal and lithospheric mantle delamination. Late Miocene uplift was largely due to crustal thickening in response to crustal shortening, magmatic addition, and delamination. Crustal flow played only a minor role. The high degree of mantle and crustal melting can be explained as a response to steepening of the early Miocene flat slab. The southern Puna transect at ~24°S–~28°S is notable for eastward frontal arc migration at 8–3 Ma, intraplateau basins bounded by high ranges, long-lived Miocene stratovolcanic-dome complexes, voluminous 6–2 Ma ignimbrites, 7–0 Ma backarc mafic flows, and the latest Miocene uplift of the reverse-faulted Sierras Pampeanas ranges to the east. Its evolution can be modeled by a moderately shallow slab producing widespread volcanism with subsequent steepening by 6 Ma, leading to delamination of dense lithosphere culminating in the eruption of the voluminous Cerro Galan ignimbrite at 2 Ma.

The magmatic and tectonic processes of the pre–2.5 Ga hot, young Earth differed profoundly from those of the modern planet. The ancient rocks differ strikingly in individual and collective composition, occurrence, association, and structure from modern rocks. Widespread forcing of Archean geology into plate-tectonic frameworks reflects unwarranted faith in uniformitarianism and in inappropriate chemical discriminants, and disregard for the lack of features that characterize plate interactions. Archean crust records extreme and prolonged internal mobility and was far too weak and mobile to behave as rigid plates, required, by definition, for plate tectonics. None of the geologic indicators of subduction, arc magmatism, and continental sundering, separation, and convergence have been documented. No Archean oceanic crust or mantle has been recognized, and the only known basement to supra-crustal rocks, including the thick basalts, high-Mg basalts, and ultramafic lavas that typify greenstone successions, consists of tonalite-trondhjemite-granodiorite (TTG) migmatites and gneisses. A thick global melabasaltic protocrust likely formed by ca. 4.45 Ga, and from it TTG suites were extracted by partial melting over the next 2 b.y. Delamination of the increasingly dense restitic protocrust enabled rise of lighter and hotter depleted mantle and hence more melting. The oldest known crustal materials are zircons, which scatter in age back to 4.4 Ga and are recycled in migmatites whose final crystallization was after 3.8 Ga, and in ancient sediments. Earth may have had a dense greenhouse atmosphere, not a hydrosphere, before 3.6 Ga, for the oldest proved supracrustal rocks are of that age, and older felsic crust may have been too hot to permit rise of dense melts. Rigid plates of lithosphere did not stabilize until a billion years after that and then were mostly small and local. Dense lavas erupted atop mobile felsic crust after 3.6 Ga produced a density inversion that was partly righted by sinking of the volcanic rocks and rising of the subjacent TTG. In some places, the early dense rocks retained cohesion and sank as synclinal keels between rising domiform diapiric batholiths. In others, the early dense rocks sank deep into mobile TTG crust, and only later in Archean time was the felsic substrate strong enough to enable dome-and-keel style. The TTG substrate rose slowly, with variable amounts of partial melting to generate more-fractionated melts and with additions of new TTG from the underlying protocrust, for hundreds of millions of years. The mantle beneath preserved cratons generated ultramafic melts that required a temperature ∼300°C hotter than modern asthenosphere ca. 3.5 Ga. Severe and prolonged lateral deformation was superimposed on large parts of some cratons during the era of volcanism and diapirism, obscuring dome-and-keel geology over broad tracts. Lower crust was at high temperature for prolonged periods and flowed pervasively, coupled discontinuously to the upper crust to produce lateral deformation therein. Rifting, separation, rotation, and collision of internally more rigid lithosphere fragments began ca. 2.1 Ga, but may have been dominantly intracontinental deformation, quite distinct from modern plate tectonics. The products of this regime differ greatly from those of Phanerozoic plate tectonics, and reflect a transitional era of erratically stiffening lithosphere. An early-depleted upper mantle has been progressively re-enriched, by delamination and subduction of crustal materials, while new “juvenile” crust derived from it has become progressively more depleted, during Pro-terozoic and Phanerozoic time.

The Atakor massif is a part of the Hoggar volcanic province, which was emplaced on top of a basement swell initiated during the Cretaceous. There have been three main episodes of volcanic activity since the Miocene, separated by long periods of quiescence. The lava flows and domes were emitted along lithosphere-scale fault zones. With its famous scenery, the Atakor massif is one of the largest (2150 km 2 ) volcanic districts of the province. Mafic volcanic rocks are abundant in the center of the massif, but become scarce to the south, where only few scarps are observed. Phonolites occur only in the Assekrem area, whereas trachytes occur everywhere, with a marked enrichment in quartz to the south and the southeast (Tahifet area), where rhyolites are also exposed. Two magmatic groups have been identified based on field and petrological observations. The mafic group has a basanite-phonotephrite association, forming uplifted plateaus, scoria cones, and valley-filling lava flows. The presence of mantle-derived amphibole ± biotite megacrysts and peridotite mantle xenoliths together with the nonprimary chemical compositions of the magmatic rocks suggest that magmatic differentiation may have occurred within the upper mantle. The felsic group is composed of two diverging trends, a silica-saturated benmoreite-trachyte-rhyolite trend and a silica-undersaturated trachyte-phonolite trend. The primary magmas are considered to have been produced as a consequence of lithospheric mantle delamination along linear megashear zones inducing low degrees of decompression partial melting at variable depths (110–40 km) in the upwelling asthenosphere. The discrete volcanic episodes correspond to periods of reactivation of the major fault zones in response to discrete Neogene extensional tectonic events associated with Alpine orogenesis in the Western Mediterranean region induced by Africa-Eurasia collision.

Neogene to Quaternary volcanism of the Carpathian-Pannonian region is part of the extensive volcanic activity in the Mediterranean and surrounding regions. Using the spatial and temporal distribution of the magmatic rocks, their major- and trace-element features, and Sr-Nd-Pb isotope characteristics, we suggest that lithospheric extension in the Pannonian Basin had a major role in the generation of the magmas. Dehydration of subducting slab should have resulted in thorough metasomatism in the mantle wedge during Cretaceous to early Miocene that would have lowered the melting temperature, therefore playing an indirect role in the generation of magmas later on. Mixing between mantle-derived magmas and lower-crustal melts was an important process at the first stage of the silicic and calc-alkaline magmatism in the Northern Pannonian Basin. However, the crustal component gradually decreased with time, which is consistent with magmatic activity in a continuously thinning continental plate. Calc-alkaline volcanism along the Eastern Carpathians was mostly postcollisional and could have been related to slab break-off processes. However, the fairly young (<1.5 Ma) potassic magmatism at the southeasternmost segment of the Carpathian volcanic arc could be explained by lithospheric delamination under the Vrancea zone. Alkaline basaltic volcanism began at the end of rifting of the Pannonian Basin (11 Ma) and continued until recently. We suggest that a mantle plume beneath the Pannonian Basin is highly unlikely and the mafic magmas were formed by small degree partial melting in a heterogeneous asthenospheric mantle, which has been close to the solidus temperature due to the lithospheric extension in the Miocene. Magmatism appears to have been in a waning phase for the last 2 m.y., but recent volcanic eruptions (<200 k.y.) indicate that future volcanic activity cannot be unambiguously ruled out.

In the Mediterranean area, four major lamproitic provinces with uniform geological, geochemical, and petrographic characteristics are recognized: Spain, Italy, Balkans, and Turkey. Mediterranean lamproites are SiO 2 -rich lamproites, characterized low CaO, Al 2 O 3 , and Na 2 O, and high K 2 O/Al 2 O 3 and Mg-number. They are enriched by in large ion lithophile elements relative to high field strength elements and in Pb, and show depletion in Ti, Nb, and Ta. The Mediterranean lamproites are characterized by a wide range of 87 Sr/ 86 and 143 Nd/ 144 Sr i Nd i . Both intra- and interprovince variations are significant. In contrast, the Pb isotope compositions of all Mediterranean lamproite provinces are almost identical, falling within the pelagic sediment field and resembling local upper-crustal sediments and Mesozoic flysch sediments from the Tethyan Ocean. Using the Serbian lamproites as an example, we develop constraints on the mantle melting processes and geodynamic environment of the whole Mediterranean lamproitic province. Partial melting of refractory mantle material previously enriched in incompatible elements is considered to be the most likely explanation for Mediterranean lamproites. The depleted-mantle component is probably multiply depleted peridotite from above the subducting plate during Mesozoic subduction processes, which preceded collision and orogenesis. The considerable variations of Sr-Nd isotopes are explained as having been produced by vein + wall-rock melting involving metasomatic veins that were out of isotopic equilibrium with the peridotite wall rock during melting. The uniformity of the Pb isotope compositions of all Mediterranean provinces is a result of the presence of a common crustal isotopic end member in their mantle source similar to flysch sediments from the Vardar Tethyan Ocean. No generic geodynamic scenario can explain lamproites, but neither mantle plume nor subduction is essential for the initiation of the volcanism. Most of the evidence implies postcollisional tectonics, including delamination of lithospheric mantle and/or orogenic collapse, as the major causes for the volcanism.

The late Mesozoic–early Tertiary evolution of the Mediterranean region was defined by a series of collisions between Gondwana-derived continental blocks and Eurasia as the intervening ocean basins closed. The late Tertiary–Quaternary evolution of the region was controlled by the generally northward motion of Afro-Arabia and the compressional tectonics induced by the convergence between Eurasia and Afro-Arabia. Earlier collisional events caused the formation of thick orogenic crust, high-standing plateaus, and heterogeneous mantle, and resulted in slab break-offs that were collectively crucial for the onset of postcollisional collapse of the mountain belts, tectonic extension, and magmatism. The diachronous collision of Adria (Apulia), as an appendage of Africa, with Europe along its irregular margins created the Alps, the Apennines, and the Dinaride-Albanide-Hellenide mountain belt at different times and affected the formation of the Carpathians in the east. The collision of theArabian promontory with Eurasia ca. 13 Ma facilitated the westward tectonic escape of Anatolia and caused intense deformation taken up by crustal shortening and conjugate strike-slip fault systems in a zone of ∼1000 km stretching from the Bitlis-Zagros suture zone in the south to the Greater Caucasus in the north. The Anatolia plate has been rotating counterclockwise relative to Eurasia during its escape to the west and hence has been experiencing internal deformation through a combination of strike-slip and normal faulting, including metamorphic core complex formation. Subduction roll-back along the Hellenic trench has likely been the driving force for this southwest motion of Anatolia and the extensional tectonics affecting the Aegean province in the upper plate throughout the late Tertiary. The widespread alkaline volcanism both in the Aegean extensional province and in the Turkish-Iranian plateau since the late Miocene shows chemical evidence for an enriched asthenospheric mantle melt source; in both regions postcollisional slab break-off events have played a major role in providing this asthenospheric material and weakening the orogenic crust significantly. Young basins (Tyrrhenian, Aegean?) are in the process of opening above strongly arcuate subduction zones in a broadly convergent system of the Mediterranean region. The mantle response to the discrete collisional events, the geometry of colliding continental margins, and the scale of collisions strongly controlled the syn- to postcollisional tectonics and magmatism in the Mediterranean region.

The relationship between Cenozoic igneous rocks and the geodynamic evolution of the Aegean region is synthesized. A simplified palinspastic reconstruction of the region is attempted for the last 50 m.y., on the basis of published syntheses of paleomagnetic data and estimates of amounts of extension and of shortening in nappes. Variability in magma genesis results from hydrous melting of the asthenospheric mantle wedge during subduction, thermal melting of enriched subcontinental lithospheric mantle as a result of rising asthenosphere, and decompression melting of rising asthenosphere. Break-off of a subducting slab or lithospheric delamination occurred several times during the earlier Cenozoic as a result of Late Cretaceous and Paleogene closure of several Neo-Tethyan Ocean basins, triggering the rise of hot asthenosphere. Magmas underwent assimilation and fractional crystallization during passage through subcontinental lithosphere and crust; these processes were less effective where strike-slip faults provided efficient pathways for magma rise. Available data on the trace elements and radiogenic isotopes are used to identify the magmatic affinities of Cenozoic igneous rocks. Unusual features of the Cenozoic igneous activity of the Aegean region are the wide range of rock types in “back-arc” settings and the exposure of both upper-crustal and middle-crustal rocks. This is a consequence of (1) the numerous microcontinental blocks within the Aegean area, separated by Neo-Tethyan Ocean strands that were destroyed by subduction; (2) orogen-parallel strike-slip faulting resulting from the progressive collision of Arabia with Anatolia; and (3) the extensional collapse and roll-back of the Hellenic subduction zone over subducting oceanic crust. Magmatism directly related to hydrous melting of subarc asthenosphere lay south of the present south Aegean arc in the Paleogene; it influenced the Cyclades plutons in the Miocene and then moved southward again as a result of extension and roll-back to its present position. Calc-alkaline volcanism in Rhodope may be related to the subduction of the Intra-Pontide Ocean. Lithospheric delamination or slab break-off produced thermal melting of the sub-continental lithospheric mantle inhomogeneously enriched by earlier subduction, resulting in voluminous shoshonitic volcanism in the Miocene of the northeast Aegean and the Oligocene of Rhodope. In both cases, shoshonitic volcanism was followed by minor alkaline magmatism related to the decompression melting of upwelling asthenosphere. The thermal effects of upwelling asthenosphere, coupled with increased geothermal gradient from extension, also contributed to the thermal melting of sub-continental lithospheric mantle. The plutonic rocks of the Cyclades and northern Greece resulted from crustal melting by magmas largely derived from the melting of lithospheric mantle.

Western Anatolia (Turkey) has experienced discrete pulses of widespread volcanism since the collision of the Sakarya and Tauride continental blocks in the early Eocene. Underplating of the leading edge of the Tauride platform at a north-dipping subduction zone beneath the Sakarya continent resulted in crustal thickening and detachment of the Neo-Tethyan oceanic lithosphere from continental lithosphere, causing slab break-off and the development of an asthenospheric window. Thermal perturbation caused by this asthenospheric upwelling led to melting of the metasomatized overriding mantle lithosphere that produced volcanism and granitic plutonism across the suture zone and the Sakarya continent. The products of this first episode of postcollisional volcanism in western Anatolia were subalkaline in character, with rocks ranging in composition from basalt, basaltic andesite, and andesite to dacite; they show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements and display the highest 87 Sr/ 86 Sr (i) (0.7087 to 0.7071) and the lowest ϵNd (i) (−6.5 to −3.5) values in comparison to the rocks of the following volcanic episodes. Geochemical features and compositional variations of this subalkaline volcanic group indicate increasing amounts of crustal contamination and a decreasing subduction signature during their evolution from the Eocene through the Oligo-Miocene. Following the initial phases of orogenic collapse, collision-induced compression in western Anatolia was replaced by north-south extension in the early to middle Miocene that produced metamorphic core complexes and NNE-trending horst-graben structures in the region. The second major volcanic episode from 16 to 14 Ma produced mildly alkaline rocks ranging in composition from basalt, trachy-basalt, and trachy-andesite to trachyte, showing enrichment in LILE and LREE (although less pronounced in comparison to the subalkaline lavas), with 87 Sr/ 86 Sr (i) (0.7075 to 0.7062) and ϵNd (i) (−3.6 to −1.6) values that are transitional between the earlier subalkaline and the later alkaline group lavas. Melting of a subduction-modified lithospheric mantle and asthenospheric melts appear to have contributed to the magma budget of the mildly alkaline group, which shows the effects of less crustal contamination or assimilation as a result of advanced crustal thinning associated with tectonic extension in the region. The asthenospheric melt contribution likely resulted from lithospheric delamination or partial convective removal of the subcontinental lithospheric mantle. Alkaline volcanism, which started around 12 Ma and continued until the latest Quaternary, produced rocks in the tephrite, basanite, and foidite fields that show ocean island basalt–type trace-element patterns and 87 Sr/ 86 Sr (i) (0.7033 to 0.7030) and ϵNd (i) (+6.5 to +2.5) values. These features suggest enriched asthenospheric mantle–derived melts as their main magma source. Crustal contamination or assimilation was not an important process in the evolution of the alkaline group, suggesting that magma transport was facilitated by lithospheric-scale extensional fault systems that acted as natural conduits. Establishment of the Hellenic subduction zone and the associated slab roll-back from the middle Miocene onward produced arc volcanism on the south Aegean islands (Milos, Santorini, and Methana) and in southwestern Turkey (Bodrum). The postcollisional volcanism in western Anatolia thus displays compositionally distinct magmatic episodes controlled by slab break-off, lithospheric delamination, asthenospheric upwelling and decompressional melting, and oceanic lithospheric subduction as part of the geodynamic evolution of the eastern Mediterranean region throughout the Cenozoic.