Detrital zircon data have recently become available from many different portions of the Tibetan–Himalayan orogen. This study uses 13,441 new or existing U‐Pb ages of zircon crystals from strata in the Lesser Himalayan, Greater Himalayan, and Tethyan sequences in the Himalaya, the Lhasa, Qiangtang, and Nan Shan–Qilian Shan–Altun Shan terranes in Tibet, and platformal strata of the Tarim craton to constrain changes in provenance through time. These constraints provide information about the paleogeographic and tectonic evolution of the Tibet–Himalaya region during Neoproterozoic to Mesozoic time. First‐order conclusions are as follows: (1) Most ages from these crustal fragments are <1.4 Ga, which suggests formation in accretionary orogens involving little pre‐mid‐Proterozoic cratonal material; (2) all fragments south of the Jinsa suture evolved along the northern margin of India as part of a circum‐Gondwana convergent margin system; (3) these Gondwana‐margin assemblages were blanketed by glaciogenic sediment during Carboniferous–Permian time; (4) terranes north of the Jinsa suture formed along the southern margin of the Tarim–North China craton; (5) the northern (Tarim–North China) terranes and Gondwana‐margin assemblages may have been juxtaposed during mid‐Paleozoic time, followed by rifting that formed the Paleo‐Tethys and Meso‐Tethys ocean basins; (6) the abundance of Permian–Triassic arc‐derived detritus in the Lhasa and Qiangtang terranes is interpreted to record their northward migration across the Paleo‐ and Meso‐Tethys ocean basins; and (7) the arrival of India juxtaposed the Tethyan assemblage on its northern margin against the Lhasa terrane, and is the latest in a long history of collisional tectonism. Key Points Tibet is underlain mainly by juvenile terranes Tethyan realm consisted of three separate ocean basins Detrital zircons record changing provenance
Zircon U‐Pb geochronological data on over 900 zircon grains for Cambrian to Silurian sandstone samples from the South China Block constrain the pre‐Devonian tectonic setting of, and the interrelationships between, the constituent Cathaysia and Yangtze blocks. Zircons range in age from 3335 to 465 Ma. Analyses from the Cathaysia sandstone samples yield major age clusters at ∼2560, ∼1850, ∼1000, and 890–760 Ma. Zircons from the eastern and central Yangtze sandstone samples show a similar age distribution with clusters at ∼2550, ∼1860, ∼1100, and ∼860–780 Ma. A minor peak at around 1450 Ma is also observed in the Cathaysia and central Yangtze age spectra, and a peak at ∼490 Ma represents magmatic zircons from Middle Ordovician sandstone in the eastern Yangtze and Cathaysia blocks. The Cambrian and Ordovician strata show a transition from a carbonate‐dominated succession in the central Yangtze Block, to an interstratified carbonate‐siliciclastic succession in the eastern Yangtze Block, to a neritic siliciclastic succession in the Cathaysia Block. Paleocurrent data across this succession consistently indicate directions toward the W‐NNW, from the Cathaysia Block to the Yangtze Block. Our data, together with other geological constraints, suggest that the Cathaysia Block constitutes a fragment on the northern margin of east Gondwana and both Cathaysia and east Gondwana constituted the source for the analyzed early Paleozoic samples. The similar age spectra for the Cambrian to Silurian sandstone samples from the Yangtze and Cathaysia blocks argue against the independent development and spatial separation of these blocks in the early Paleozoic but rather suggest that the sandstone units accumulated in an intracontinental basin that spanned both blocks. Subsequent basin inversion and Kwangsian orogenesis possibly at 400–430 Ma also occurred in an intracontinental setting probably in response to the interaction of the South China Block with the Australian‐Indian margin of east Gondwana.
Late Mesozoic extension in NE Asia resulted in the development of a large extensional province. Metamorphic core complexes (MCCs) are the major features in this province and have 40Ar/39Ar ages of 130–110 Ma for the mylonites and U‐Pb zircon ages of 150–110 Ma for the integral granitic intrusions. Based on this and previous studies, this paper summarizes major characteristics of these MCCs and recognizes a regional kinematic shear sense. Most MCCs in the Transbaikalia region, Sino‐Mongolia border tract, and the northwest‐central portion of the North China craton (NCC) show a top‐to‐the‐southeast (SE) shear, whereas those in the eastern and southern NCC locally underwent top‐to‐the‐northwest (NW) shear. The three largest basins (Songliao, Huabei and Ordos) in North China are located in the transitional zone between domains of opposing shear sense. We interpret the extension in the Transbaikalia, Sino‐Mongolia tract and northwestern part of the NCC to reflect late‐orogenic collapse of thickened crust following Middle‐Late Jurassic collision along the Okhotsk suture. The southeastward extension is probably controlled by crustal‐scale top‐to‐the‐SE tangential shear. The transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage (ecc, i.e., C′) in sub‐horizontal ductile shear zones late in orogenic crustal thickening. The combined effect of gravitational loading and thermal‐uplifting is considered to be the origin of the late‐or post‐orogenic collapse. The top‐to‐the‐NW extension in the NE of the NCC might reflect antithetic sub‐extensional zones or Mesozoic back‐arc extension as a far‐field effect of Cretaceous Pacific plate subduction. Key Points Characteristics of late Mesozoic metamorphic core complexes (MCCs) in NE Asia Kinematic pattern with shear‐sense polarity for MCCs and basins Transition from the contraction to extension is marked by extensional detachment
A long‐standing problem in the geological evolution of the India‐Asia collision zone is how and where convergence between India and Asia was accommodated since collision. Proposed collision ages vary from 65 to 35 Ma, although most data sets are consistent with collision being underway by 50 Ma. Plate reconstructions show that since 50 Ma ∼2400–3200 km (west to east) of India‐Asia convergence occurred, much more than the 450–900 km of documented Himalayan shortening. Current models therefore suggest that most post‐50 Ma convergence was accommodated north of the Indus‐Yarlung suture zone. We review kinematic data and construct an updated restoration of Cenozoic Asian deformation to test this assumption. We show that geologic studies have documented 600–750 km of N‐S Cenozoic shortening across, and north of, the Tibetan Plateau. The Pamir‐Hindu Kush region accommodated ∼1050 km of N‐S convergence. Geological evidence from Tibet is inconsistent with models that propose 750–1250 km of eastward extrusion of Indochina. Approximately 250 km of Indochinese extrusion from 30 to 20 Ma of Indochina suggested by SE Asia reconstructions can be reconciled by dextral transpression in eastern Tibet. We use our reconstruction to calculate the required size of Greater India as a function of collision age. Even with a 35 Ma collision age, the size of Greater India is 2–3 times larger than Himalayan shortening. For a 50 Ma collision, the size of Greater India from west to east is ∼1350–2600 km, consistent with robust paleomagnetic data from upper Cretaceous‐Paleocene Tethyan Himalayan strata. These estimates for the size of Greater India far exceed documented shortening in the Himalaya. We conclude that most of Greater India was consumed by subduction or underthrusting, without leaving a geological record that has been recognized at the surface.
Measurements at ∼400 campaign‐style GPS points and another 14 continuously recording stations in central Asia define variations in their velocities both along and across the Kyrgyz and neighboring parts of Tien Shan. They show that at the longitude of Kyrgyzstan the Tarim Basin converges with Eurasia at 20 ± 2 mm/yr, nearly two thirds of the total convergence rate between India and Eurasia at this longitude. This high rate suggests that the Tien Shan has grown into a major mountain range only late in the evolution of the India‐Eurasia collision. Most of the convergence between Tarim and Eurasia within the upper crust of the Tien Shan presumably occurs by slip on faults on the edges of and within the belt, but 1–3 mm/yr of convergence is absorbed farther north, at the Dzungarian Alatau and at a lower rate with the Kazakh platform to the west. The Tarim Basin is thrust beneath the Tien Shan at ∼4–7 mm/yr. With respect to Eurasia, the Ferghana Valley rotates counterclockwise at ∼0.7° Myr−1 about an axis at the southwest end of the valley. Thus, GPS data place a bound of ∼4 mm/yr on the rate of crustal shortening across the Chatkal and neighboring ranges on the northwest margin of the Ferghana Valley, and they limit the present‐day slip rate on the right‐lateral Talas‐Ferghana fault to less than ∼2 mm/yr. GPS measurements corroborate geologic evidence indicating that the northern margin of the Pamir overthrusts the Alay Valley and require a rate of at least 10 and possibly 15 mm/yr.
Arc volcanism across Iran is dominated by a Paleogene pulse, despite protracted and presumably continuous subduction along the northern margin of the Neotethyan ocean for most of Mesozoic and Cenozoic time. New U‐Pb and 40Ar/39Ar data from volcanic arcs in central and northern Iran constrain the duration of the pulse to ∼17 Myr, roughly 10% of the total duration of arc magmatism. Late Paleocene‐Eocene volcanic rocks erupted during this flare‐up have major and trace element characteristics that are typical of continental arc magmatism, whereas the chemical composition of limited Oligocene basalts in the Urumieh‐Dokhtar belt and the Alborz Mountains which were erupted after the flare‐up ended are more consistent with derivation from the asthenosphere. Together with the recent recognition of Eocene metamorphic core complexes in central and east central Iran, stratigraphic evidence of Eocene subsidence, and descriptions of Paleogene normal faulting, these geochemical and geochronological data suggest that the late Paleocene‐Eocene magmatic flare‐up was extension related. We propose a tectonic model that attributes the flare‐up to decompression melting of lithospheric mantle hydrated by slab‐derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. We suggest that Paleogene magmatism and extension was driven by an episode of slab retreat or slab rollback following a Cretaceous period of flat slab subduction, analogous to the Laramide and post‐Laramide evolution of the western United States. Key Points Iranian arc volcanism is dominated by a Paleogene flare‐up The volcanic flare‐up overlaps in time with a phase of extensional tectonism The extensional flare‐up is ascribed to Neotethyan slab rollback
Along the northern border of Africa, Pangea breakup has been diachronic. During the Jurassic, the Alpine Tethys propagated northeastward from the Atlantic to the Alps. During the Permian, the Neo‐Tethys propagated westward from Oman to northwestern Arabia. Then a secondary and late branch of Neo‐Tethys gave birth to the East Mediterranean basin. Finally the two oceans connected at end of Jurassic times, achieving the development of Africa northern plate boundary. By the Late Cretaceous, convergence between Africa and Eurasia led to the progressive closure of the Tethys realm. The continental collision is not completely achieved, and the different segments of the confrontation zone (Maghreb, central and East Mediterranean, Zagros, and Oman) expose different stages of the process. However, we emphasize the existence of synchronous geodynamic events from one end of the system to the other, although they do not have the same meaning. Two of them are particularly important. The Campanian‐Santonian (C‐S) event corresponds to (1) obduction and exhumation of high‐pressure–low‐temperature metamorphic rocks around the Arabian promontory, (2) inversion along the margins of the East Mediterranean basins, and (3) lithosphere buckling in the Atlas system (Maghreb) and adjacent Sahara platform. The middle‐late Eocene (MLE) event corresponds to (1) the onset of collision at the northern corner of Arabia, (2) the onset of slab retreat in the Mediterranean, and (3) inversion along the margin of the East Mediterranean as well as in the Atlas. The C‐S event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity. The MLE event coincides with a period of strong coupling between the Africa and Eurasia plates and an abrupt decrease of convergence velocity. In the middle of the system, the central Mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the Triassic. Key Points Evolution of the south Tethys paleomargin
The Aegean region (Greece, western Turkey) is one of the best studied continental extensional provinces. Here, we provide the first detailed kinematic restoration of the Aegean region since 35 Ma. The region consists of stacked upper crustal slices (nappes) that reflect a complex paleogeography. These were decoupled from the subducting African‐Adriatic lithospheric slab. Especially since ∼25 Ma, extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes. We reconstruct up to 400 km of trench‐perpendicular (NE‐SW) extension in two stages. From 25 to 15 Ma, the Aegean forearc rotated clockwise relative to the Moesian platform around Euler poles in northern Greece, accommodated by extensional detachments in the north and an inferred transfer fault SE of the Menderes massif. The majority of extension occurred after 15 Ma (up to 290 km) by opposite rotations of the western and eastern parts of the region. Simultaneously, the Aegean region underwent up to 650 km of post‐25 Ma trench‐parallel extension leading to dramatic crustal thinning on Crete. We restore a detachment configuration with the Mid‐Cycladic Lineament representing a detachment that accommodated trench‐parallel extension in the central Aegean region. Finally, we demonstrate that the Sakarya zone and Cretaceous ophiolites of Turkey cannot be traced far into the Aegean region and are likely bounded by a pre‐35 Ma N‐S fault zone. This fault became reactivated since 25 Ma as an extensional detachment located west of Lesbos Island. The paleogeographic units south of the İzmir‐Ankara‐Sava suture, however, can be correlated from Greece to Turkey. Key Points We present a detailed kinematic restoration of the Aegean deformation since the Eocene The Aegean region underwent 400 km of NE‐SW extension Formation of the Aegean orocline involved up to 650 km of arc‐parallel extension
The present‐day topography of the Tian Shan range is considered to result from crustal shortening related to the ongoing India‐Asia collision that started in the early Tertiary. In this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event. Apatite fission track analysis and (U‐Th)/He dating on apatite and zircon indicate that inherited Paleozoic structures were reactivated in the late Paleozoic‐early Mesozoic during a Cimmerian orogenic episode and also in the Late Cretaceous‐Paleogene (around 65–60 Ma). These reactivations could have resulted from the accretion of the Kohistan‐Dras arc or lithospheric extension in the Siberia‐Mongolia zone. Activity resumed in the late Mesozoic prior to the major Tertiary orogenic phase. Finally, the ongoing deformation, which again reactivates inherited tectonic structures, tends to propagate inside the endoreic basins that were preserved in the range, leading to their progressive closure. This study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas.
Studies conducted in present‐day magma‐poor rifted margins reveal that the transition from weakly thinned continental crust (∼30 km) in proximal margins to hyper‐extended crust (≤10 km) in distal margins occurs within a narrow zone, referred to as the necking zone. We have identified relics of a necking zone and of the adjacent distal margin in the Campo, Grosina and Bernina units of the fossil Alpine Tethys margins and investigated the deformation and sedimentary processes associated with extreme crustal thinning during rifting. Within the basement rocks of the necking zone, we show that: (1) Grosina basement represents pre‐rift upper/middle crust, while the underlying Campo unit consists of pre‐rift middle/lower crust that was exhumed and cooled below ∼300°C by ca. 180 Ma, when rifting started to localize within the future distal margin; (2) the juxtaposition of the Campo and Grosina units was accommodated by the Eita shear zone, which is interpreted as a decollement/decoupling horizon active at mid‐crustal depth at 180–205 Ma; (3) the Grosina unit hosts a large‐scale brittle detachment fault. Our observations suggest that crustal thinning, accommodated through the necking zone, is the result of the interplay between detachment faulting in the brittle layers and decoupling and thinning in ductile quartzo‐feldspatic middle crustal levels along localized ductile decollements. The excision of ductile mid‐crustal layers and the progressive embrittlement of the crust enables major detachment faults to cut into the underlying mantle, exhuming it to the seafloor. This structural evolution can explain the first‐order crustal architecture of many present‐day rifted margins. Key Points The necking of the continental crust in rifted margins Description of rift‐related structures in fossil Adriatic margin New conceptual model to explain crustal thinning during the rifting
U‐Pb (zircon) crystallization ages of 52 late‐Variscan granitoid intrusions from NW Iberia (19 from new data, 33 from previous studies) constrain the lithospheric evolution of this realm of the Variscan belt of Western Europe and allow assessment of the relationship between oroclinal development and magmatism in late‐Carboniferous‐early Permian times. The U‐Pb ages, in conjunction with a range of geological observations, are consistent with the following sequence of events: (i) oroclinal bending starts at 310–305 Ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts; (ii) between 305 and 300 Ma, melting continues under the outer arc of the orocline (Central Iberian Zone of the Iberian Variscan belt) and mid‐crustal melting is initiated. Coevally, the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure; (iii) between 300 and 292 Ma, foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle; (iv) cooling of the lithosphere between 292 and 286 Ma resulting in a drastic attenuation of lower crustal high‐temperature melting. By 285 Ma, the thermal engine generated by orocline‐driven lithospheric thinning/delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts. The model proposed explains the genesis of voluminous amounts of granitoid magmas in post‐orogenic conditions and suggests that oroclines and similar post‐orogenic granitoids, common constituents of numerous orogenic belts, may be similarly related elsewhere. Key Points Lithospheric delamination related magmatism Orocline triggered lithospheric delamination Granitoid emplacement in space and time
We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex through an integrated geophysical approach involving multichannel and single‐channel seismic data at different scales. Pre‐stack depth migrated crustal‐scale seismic profiles have been used to reconstruct the overall geometry of the subduction complex, i.e., depth of the basal detachment, geometry and structural style of different tectonic domains, and location and geometry of major faults. High‐resolution multichannel seismic (MCS) and sub‐bottom CHIRP profiles acquired in key areas during a recent cruise, as well as multibeam data, integrate deep data and constrain the fine structure of the accretionary wedge as well as the activity of individual fault strands. We identified four main morpho‐structural domains in the subduction complex: 1) the post‐Messinian accretionary wedge; 2) a slope terrace; 3) the pre‐Messinian accretionary wedge and 4) the inner plateau. Variation of structural style and seafloor morphology in these domains are related to different tectonic processes, such as frontal accretion, out‐of‐sequence thrusting, underplating and complex faulting. The CA subduction complex is segmented longitudinally into two different lobes characterized by different structural style, deformation rates and basal detachment depths. They are delimited by a NW/SE deformation zone that accommodates differential movements of the Calabrian and the Peloritan portions of CA and represent a recent phase of plate re‐organization in the central Mediterranean. Although shallow thrust‐type seismicity along the CA is lacking, we identified active deformation of the shallowest sedimentary units at the wedge front and in the inner portions of the subduction complex. This implies that subduction could be active but aseismic or with a locked fault plane. On the other hand, if underthrusting of the African plate has stopped recently, active shortening may be accommodated through more distributed deformation. Our findings have consequences on seismic hazard, since we identified tectonic structures likely to have caused large earthquakes in the past and to be the source regions for future events. Key Points Overall geometry, tectonic processes, and kinematics of the subduction complex Segmentation of the continental margin in two different lobes Location and geometry of active faults absorbing plate motion
The Pyrenean peridotites (lherzolites) form numerous small bodies of subcontinental mantle, a few meters to 3 km across, exposed within the narrow north Pyrenean zone (NPZ) of Mesozoic sediments paralleling the north Pyrenean Fault. Recent studies have shown that mantle exhumation occurred along the future NPZ during the formation of the Albian‐Cenomanian Pyrenean basins in relation with detachment tectonics. This paper reviews the geological setting of the Pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the Béarn region. Only two types of geological settings have to be distinguished among the Pyrenean ultramafic bodies. In the first type (sedimented type or S type), the lherzolites occur as clasts of various sizes, ranging from millimetric grains to hectometric olistoliths, within monogenic or polymictic debris flow deposits of Cretaceous age, reworking Mesozoic sediments in dominant proportions as observed around the Lherz body. In the second type (tectonic type or T type), the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses. Both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed Triassic rocks and have fault contacts with units of deformed Jurassic and Lower Cretaceous sediments belonging to the cover of the NPZ. These deformed Mesozoic formations are not older that the Aptian‐early Albian. They are unconformably overlain by the Albian‐Cenomanian flysch formations and have experienced high temperature‐low pressure mid‐Cretaceous metamorphism at variable grades. Such a tectonic setting characterizes most of the lherzolite bodies exposed in the western Pyrenees. These geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the Mesozoic cover in the preorogenic evolution of the Pyrenean realm. In the light of such evidence, a simple model of basin development can be inferred, involving extreme thinning of the crust, and mantle uprising along a major detachment fault. We demonstrate coeval development of a crust‐mantle detachment fault and generalized gravitational sliding of the Mesozoic cover along low‐angle faults involving Triassic salt deposits as a tectonic sole. This model accounts for the basic characteristics of the precollisional rift evolution in the Pyrenean realm.
Multimethod chronology was applied on intrusives bordering the Kyrgyz South Tien Shan suture (STSs) to decipher the timing of (1) formation and amalgamation of the suturing units and (2) intracontinental deformation that built the bordering mountain ranges. Zircon U/Pb data indicate similarities between the Tien Shan and Tarim Precambrian crust. Caledonian (∼440–410 Ma) and Hercynian (∼310–280 Ma) zircon U/Pb ages were found at the edge of the STSs, related to subduction and closure of the Turkestan Ocean and the formation of the suture itself. Permian‐Triassic (∼280–210 Ma) titanite fission track and zircon (U‐Th)/He data record the first signs of exhumation when the STSs evolved into a shear zone and the adjacent Tarim basin started to subside. Low‐temperature thermochronological (apatite fission track, zircon and apatite (U‐Th)/He) analyses reveal three distinct cooling phases, becoming younger toward the STSs center: (1) Jurassic‐Cretaceous cooling ages provide evidence that a Mesozoic South Tien Shan orogen formed as a response to the Cimmerian orogeny; (2) Early Paleogene (∼60–45 Ma) data indicate a renewed pulse of STSs reactivation during the Early Cenozoic; (3) Neogene ages constrain the onset of the modern Tien Shan mountain building to the Late Oligocene (∼30–25 Ma), which intensified during the Miocene (∼10–8 Ma) and Pliocene (∼3–2 Ma). The Cenozoic signals may reflect renewed responses to collisions at the southern Eurasian border (i.e., the Kohistan‐Dras and India‐Eurasia collisions). This progressive rejuvenation of the STSs demonstrates that deformation has not migrated steadily into the forelands, but was focused on pre‐existing basement structures. Key Points The South Tien Shan suture formed before ~310‐280 Ma Jurassic and Early Cretaceous ages date a Mesozoic Tien Shan orogen Paleogene and Neogene reactivations rejuvenated towards the suture
The large number and distribution of rollback systems in Mediterranean orogens infer the possibility of interacting extensional back-arc deformation driven by different slabs. The formation of the Pannonian back-arc basin is generally related to the rapid Miocene rollback of a slab attached to the European continent. A key area of the entire system that is neglected by kinematic studies is the connection between the South Carpathians and Dinarides. In order to derive an evolutionary model, we interpreted regional seismic lines traversing the entire Serbian part of the Pannonian Basin. The observed deformation is dominantly expressed by the formation of Miocene extensional detachments and (half) grabens. The extensional geometries and associated synkinematic sedimentation that migrated in time and space allow the definition of a continuous and essentially asymmetric early to late Miocene extensional evolution. This evolution was followed by the formation of few uplifted areas during the subsequent latest Miocene–Quaternary inversion. The present-day extensional geometry changing the strike across the basin is an effect of the clockwise rotation of the South Carpathians and Apuseni Mountains in respect to the Dinarides. Our study infers that the Carpathian rollback is not the only mechanism responsible for the formation of the Pannonian Basin; an additional middle Miocene rollback of a Dinaridic slab is required to explain the observed structures. Furthermore, the study provides constraints for the pre-Neogene orogenic evolution of this junction zone, including the affinity of major crustal blocks, obducted ophiolitic sequences and the Sava suture zone.
This paper aims at summarizing the current extent and architecture of the former Mesozoic passive margin of North Africa from North Algeria in the west up to the Ionian‐Calabrian arc and adjacent Mediterranean Ridge in the east. Despite that most paleogeographic models consider that the Eastern Mediterranean Basin as a whole is still underlain by remnants of the Permo‐Triassic or a younger Cretaceous Tethyan‐Mesogean ocean, the strong similarities documented here in structural styles and timing of inversion between the Saharan Atlas, Sicilian Channel and the Ionian abyssal plain evidence that this portion of the Eastern Mediterranean Basin still belongs to the distal portion of the North African continental margin. A rim of Tethyan ophiolitic units can be also traced more or less continuously from Turkey and Cyprus in the east, in onshore Crete, in the Pindos in Greece and Mirdita in Albania, as well as in the Western Alps, Corsica and the Southern Apennines in the west, supporting the hypothesis that both the Apulia/Adriatic domain and the Eastern Mediterranean Basin still belong to the former southern continental margin of the Tethys. Because there is no clear evidence of crustal‐scale fault offsetting the Moho, but more likely a continuous yet folded Moho extending between the foreland and the hinterland beneath the Mediterranean arcs, we propose here a new model of delamination of the continental lithosphere for the Apennines and the Aegean arcs. In this model, only the mantle lithosphere of Apulia and the Eastern Mediterranean is still locally subducted and recycled in the asthenosphere, most if not all the northern portion of the African crust and coeval Moho being currently decoupled from its former, currently delaminated and subducted mantle lithosphere. Key Points Current architecture of the African margin Discussing a delamination model
A series of sharp bends (oroclines) are recognized in the Paleozoic to early Mesozoic New England Orogen of eastern Australia. The exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated. Here we present zircon U‐Pb ages that confirm the lateral continuation of early Permian (296–288 Ma) granitoids and shed new light on the oroclinal structure. Orogenic curvature is defined by the alignment of early Permian granitoids parallel to the structural grain of the orogen, as well as the curved geometry of sub‐vertical deformation fabrics, forearc basin terranes, and serpentinite outcrops. Alternative geometrical interpretations may involve two bends (Texas and Coffs Harbour Oroclines), three bends (+Manning Orocline), or even four bends (+Nambucca Orocline). We argue that the model involving four bends is most consistent with available data, although further kinematic constraints are required to confirm the existence of the Manning and Nambucca Oroclines. A subsequent phase of younger magmatism (<260 Ma) cuts across the curved structural grain, providing a minimum age constraint for orocline development. Assuming a structure of four oroclines, we suggest a tentative tectonic model that involves an early stage of subduction curvature during slab rollback at 300–285 Ma, followed by bending associated with dextral transpression. A final tightening of the curved structures was possibly obtained by E‐W shortening during the late Permian to Triassic (265–230 Ma) Hunter‐Bowen orogeny. Key Points A strongly contorted orogen is recognized in the southern New England Orogen The curved geometry is outlined by the shape of Early Permian granitoids Oroclinal bending was possibly promoted by subduction rollback
The distribution of oceanic domains and continental blocks in Central Anatolia remains a challenge in understanding the Alpine geodynamic evolution of the Tethys realm. The consumption of a Neotethys oceanic branch at the Mesozoic‐Cenozoic boundary welded the Central Anatolian Crystalline Complex in central Turkey and the Anatolide‐Tauride Block in western Turkey, with the northerly Eurasian margin. Whether those two regions constituted a single or two distinct continental masses is still matter of debate. High‐pressure metamorphism has been locally evidenced in the Afyon Zone, which was, however, defined as a greenschist‐facies metamorphic zone of the Anatolide‐Tauride Block. Since the Afyon Zone composes a metamorphic equivalent of a continental margin exposed far south of the Izmir‐Ankara suture zone, this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central Turkey. Our investigations reveal that the high‐pressure minerals Fe‐Mg‐carpholite and glaucophane are present in the entire Afyon Zone, which we reconsider as a blueschist‐facies zone. We additionally present a tectonic reconstruction, stripping off the postcollisional tectonics. It reveals that today's bending of the high‐pressure belt is consistent with an Eocene collision of the Anatolide‐Tauride Block around the southern edge of the Central Anatolian Crystalline Complex. We argue that the Central Anatolian Crystalline Complex and the Anatolide‐Tauride Block were two distinct continental masses separated by a Neotethyan oceanic stripe, the closure of which engendered subduction‐related metamorphism in the latter and arc volcanism and high‐grade metamorphism in the former by late Cretaceous to early Cenozoic.
We report a sequence of crustal quakes that began after the Mw = 8.8 thrust‐subduction Maule earthquake that affected the Central Chile margin on 27 February 2010. This activity lasted by several months, having the most important events on 11 March 2010 (Mw = 6.9 and Mw = 7.0) with normal focal mechanisms. Seismicity shows a rupture oriented along a NW‐striking and SW‐dipping normal fault from the surface down to the interplate contact. Seismicity can be correlated with neotectonics extensional structures similarly oriented in the region, which have coexisted with NNE‐SSW reverse faults since the late Pliocene, even though both have older periods of activity since the Paleozoic. This crustal rupture would have been triggered by the high Coulomb stress change produced by the Maule earthquake, enhanced by likely fluid presence along weakened zones of the forearc crust as evidenced by high Vp/Vs ratio. The occurrence of relevant neotectonic activity in coincidence with short‐term deformation suggests a relationship with long‐term tectonic features of this region, which would have been acting as a barrier during the interseismic period, increasing the strain accumulation and triggering contractional faulting in the crust, as well as producing high slip patches during great subduction ruptures favoring triggering of crustal extensional faulting. Crustal faulting in Pichilemu suggests that this kind of events should be considered in seismic hazard analysis despite the absence of historical crustal seismic activity before the Maule earthquake. Key Points Normal faulting induced by the big Chilean earthquake Extensional tectonics during coseismic Compressional crustal tectonics during interseismic
Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco‐Paraná alluvial plain. Paleocene‐lower Eocene fluvial and lacustrine deposits are overlain by middle‐upper Eocene hypermature paleosols or an erosional disconformity representing 10–15 Myr. This ‘supersol/disconformity’ zone is traceable over a 200,000 km2 area in the Andean thrust belt, and is overlain by 2–6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene‐Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470–491, 522–544, 555–994, and 1024–1096 Ma. Proterozoic‐Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc‐derived zircons become prominent in Oligo‐Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ∼20 m/Myr during Paleocene‐Eocene time to 200–600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time. Key Points A Paleocene‐modern foreland basin system is present in NW Argentina The dominant mode of orogenic shortening was by simple shear Dynamic and post‐rift subsidence may have also accommodated distal foreland