Tectonic Escape Research Articles

Escape tectonics and the extrusion of Alaska: Past, present, and future

The North Pacific Rim is a tectonically active plate boundary zone, parts of which may be characterized as a laterally moving orogenic stream. Crustal blocks are transported along large-magnitude strike-slip faults in western Canada and central Alaska toward the Aleutian–Bering Sea subduction zones. Throughout much of the Cenozoic, at and west of its Alaskan nexus, the North Pacific Rim orogenic Stream (NPRS) has undergone tectonic escape. During transport, relatively rigid blocks acquired paleomagnetic rotations and fault-juxtaposed boundaries while flowing differentially through the system, from their original point of accretion and entrainment toward the free face defined by the Aleutian–Bering Sea subduction zones. Built upon classical terrane tectonics, the NPRS model provides a new framework with which to view the mobilistic nature of the western North American plate boundary zone.

Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen into the Yangtze craton, central China

Cretaceous and Cenozoic reactivation of the Triassic Qinling‐Dabie orogen between the north China and Yangtze cratons resulted from the combined effects of Pacific subduction–back‐arc extension in east China and collisions in west China. We report new apatite fission track and apatite and zircon (U‐Th)/He data from east Qinling along a >400‐km‐long N‐S transect from Huashan through the Qinling orogen to Huangling. The ages show a general pattern of younging northward. Three major cooling phases are defined by modeling the multiple thermochronologic data sets. The first phase occurred locally in the North and South Qinling during the late Triassic to early Jurassic, following heating associated with the Triassic Yangtze subduction and exhumation of the Wudang metamorphic core complex on the cratonal edge. A second phase represents regional exhumation between 100 and 60 Ma, coeval with rifting marked by the Late Cretaceous–Eocene (K2–E) red bed deposition in eastern China and possibly indicating a link with Pacific subduction–back‐arc extension in eastern China; however, it may also have been superimposed by eastward tectonic escape resulting from the Lhasa–West Burma–Qiangtang‐Indochina collision. The third cooling phase was initiated at ∼45 Ma exclusively in the north Qinling and in the footwall of the graben‐bounding normal fault of the Weihe graben in the Lesser Qinling. We suggest the third phase was related to reactivation of the Qinling fault system as a result of eastward tectonic escape imposed by the India‐Asia collision at ∼50 Ma.

Variations in Late Cenozoic–Recent strike-slip and oblique-extensional geometries, within Indochina: The influence of pre-existing fabrics

From Yunnan to Northern Thailand, Late Cenozoic–Recent faults strike predominantly NNE–SSW, N–S to NNE–SSW and NE–SW to ENE–WSW. Associated sedimentary basins are aligned NE–SW to N–S. The regional fault patterns are commonly interpreted as strike-slip dominated deformation throughout the area. Releasing bend and en echelon stepping patterns on faults bounding sedimentary basins indicate sinistral displacement on NE–SW to ENE–WSW trending faults. Yet, in the escape tectonics model left lateral displacement on the NE–SW to ENE–WSW faults is thought to have occurred late in the Miocene, whilst earlier motion was dextral. However, in Yunnan the NE–SW Shmax direction required for dextral motion on the N–S Sagaing, Nanting and Gaoligong fault zones is consistent with sinistral motion on ENE–WSW striking faults, which is still their sense of motion today. In Northern Thailand the dextral–sinistral switch model during the Miocene is not tenable because the Fang basin is of Late Oligocene–Pliocene age, and requires similar age sinistral motion on the ENE–WSW Mae Chan fault in order to have opened. In an alternative model, Northern Thailand is interpreted to have evolved predominantly by oblique extension. The Golden Triangle area marks a transition from transtensional deformation in the north to oblique extension in the south. The activation of pre-existing fabrics strongly affects both strike-slip and extensional faults and has given rise to the similar extensional and strike-slip fault patterns. Multiple episodes of basin inversion in Northern Thailand during the Miocene require short-term changes in stress pattern. To produce the inferred changes in stress pattern it is suggested that stresses radiating out from the Himalayan syntaxis exert a strong influence, but were not the only important forces acting on the region.

The welding of Shan-Thai

The Shan-Thai Terrane is viewed as a remnant of paleo-Tethys in South East Asia. The more internal “Thai” elements of Shan-Thai, bordering with Indochina, are of Cathaysian type, while the more central part of the terrane is of transitional “Sibumasu” character: The external “Shan” elements of Shan-Thai that left Gondwana last have a clear cold-water imprint. Petrological and paleontological evidence corroborates the end Triassic—earliest Jurassic Late Indosinian orogeny, as the main Paleotethyan tectonic closure event. Its main axis consists of the Mae-Sariang Zone, which can be followed over Mae Sot to Kanchanaburi and Chanthaburi, from where it extends into southern Thailand and Peninsular Malaysia. Cenozoic Himalayan escape tectonics, alternating strike-slip movements and rotation severely compressed Shan-Thai, opened the Gulf of Thailand, disrupted the original alignment of the Mae Sariang zone and Gondwana-Tethys divide, and shaped the present tectonic configuration of SE Asia.

Spatial and temporal relationships between compression, strike-slip and extension in the Central Venezuelan Andes: Clues for Plio-Quaternary tectonic escape

The geometry of tectonic structures, attributed to the Neogene–Quaternary time interval, is described in the active setting of the Venezuelan Andes. Our methodology is based on the analysis of radar satellite and Digital Elevation Model imagery, complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale. Radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering, like the Venezuelan Andes. We focused our analysis in the Burbusay–Río Momboy and Boconó faults corner located in the central part of the belt. We have described three stages of deformation during the Neogene–Quaternary. The first one, Mio-Pliocene in age, is a NW–SE compression responsible for the uplift of the Venezuelan Andes. The second tectonic stage corresponds to a strike-slip regime of deformation marked by shearing along the Boconó, Burbusay and Valera faults, which separates two triangular wedges in the larger Trujillo block. This strike-slip faulting-dominated compressional-extensional tectonic regime allowed the Trujillo crustal block to move towards the NE. Wrenching has therefore started at some point between the Pliocene and the Quaternary. These two tectonic events are consistent with ongoing strain partitioning in the Venezuelan Andes. The third stage corresponds to extensional deformation limited to the Trujillo block and is still active today. Extension is associated with the motion of crustal blocks moving relative to each other, probably above the upper-lower crust boundary. Such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the NE. The combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process. The northeastward escape of the Trujillo block, which belongs to the larger North Andes block, occurs as a result of the combination of the NW–SE intracontinental convergence between the South-American plate and the Maracaibo block, and the presence to the north of the Caribbean oceanic plate considered as a free boundary. We have showed that the kinematics of the Caribbean plate offers not only a favorable environment, but may also be considered as the driving force of the tectonic escape of the North Andes block.

Cretaceous and Cenozoic cooling history across the ultrahigh pressure Tongbai–Dabie belt, central China, from apatite fission-track thermochronology

The crystalline terrane of the Tongbai–Dabie region, central China, comprising the Earth's largest ultrahigh-pressure (UHP) exposure was formed during Triassic collision between the Sino–Korean and Yangtze cratons. New apatite fission-track (AFT) data presented here from the UHP terrane, extends over a significantly greater area than reported in previous studies, and includes the (eastern) Dabie, the Hong'an (northwestern Dabie) and Tongbai regions. The new data yield ages ranging from 44 ± 3 to 142 ± 36 Ma and mean track lengths between ∼10 and 14.4 μm. Thermal history models based on the AFT data taken together with published 40Ar/ 39Ar, K–Ar, apatite and zircon (U–Th)/He and U–Pb data, exhibit a three-stage cooling pattern that is similar across the study region, commencing with an Early Cretaceous rapid cooling event, followed by a period of relative thermal stability during which rocks remained at temperatures within the AFT partial annealing zone (∼60–110 °C) and ending with a possible renewed phase of accelerated cooling during Pliocene to Recent time. The first cooling phase followed large-scale transtensional deformation between ∼140 and 110 Ma and is related to Early Cretaceous eastward tectonic escape and Pacific back arc extension. Between this phase and the subsequent slow cooling phase, a transition period from ∼120 to 80 Ma (to ∼70 to 45 Ma along the Tan–Lu fault) was characterised by a relatively low cooling rate (∼3–5 °C/Ma). This transition is likely related to a tectonic response associated with the mid-Cretaceous subduction of the Izanagi–Pacific plate as well as lithospheric extension and thinning in eastern Asia. The present regional AFT age pattern is therefore basically controlled by the Early Cretaceous rapid cooling event, but finally shaped through active Cenozoic faulting. Following the transition phase the subsequent slow cooling phase pattern implies a net reduction in horizontal compressional stress corresponding to increased extension rates along the continental margin due to the decrease in plate convergence. Modelling of the AFT data suggests a possible Pliocene–Recent cooling episode, which may be supported by increased rates of sedimentation observed in adjacent basins. This cooling phase may be interpreted as a response to the far-field effects of the frontal India–Eurasia collision to the west. Approximate estimates suggest that the total amount of post ∼120 Ma denudation across the UHP orogen ranged from ∼2.4 to 13.2 km for different tectonic blocks and ranged from ∼0.8 to 9.7 km during the Cretaceous to between ∼1.7 and 3.8 km during the Cenozoic.

Development of the Gulf of Guayaquil (Ecuador) during the Quaternary as an effect of the North Andean block tectonic escape

Interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the Gulf of Guayaquil (GG) area. These include two E‐W trending major detachments: the Posorja and the Jambelí detachment systems, which represent half grabens with oppositely dipping detachments, to the south and to the north, respectively. The NE‐SW trending Puná‐Santa Clara fault system developed as a transfer fault system between the Posorja and the Jambelí detachments. The Esperanza and the Jambelí basins exhibit 3–4 km of sediment that accumulated during the past 1.6–1.8 Myr. The Puná‐Santa Clara fault system bounds the Esperanza and the Jambelí basins, evidencing that the evolution of these basins is tightly controlled by the two detachments at depth. To the west, the N‐S trending Domito fault system bounding the Posorja detachment system and the Esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope. The Pliocene series show no significant variations in thickness throughout the Gulf of Guayaquil area suggesting that no important tectonic deformation occurred from 5.2 to 1.8–1.6 Ma. The major period of tectonic deformation in the Gulf of Guayaquil area occurred during the Pleistocene times. Three main tectonic steps are identified. From early Pleistocene to ∼180 ka, major subsidence occurred along the Esperanza and Jambelí basins. From ∼180 to ∼140 ka, most of the Gulf of Guayaquil area was above sea level during the isotope substage 6 low stand. From ∼140 ka to Present, tectonic activity is restricted along the normal faults bounding the Esperanza basin, the Tenguel fault, and the Puná‐Santa Clara and Domito fault systems. A N‐S trending tensional stress regime characterizes the Pleistocene times throughout. The northward drifting of the North Andean block is proposed to control the tectonic evolution and associated subsidence of the Gulf of Guayaquil area. It is also accepted that the collision of the Carnegie ridge with the trench axis has to play a major role in controlling the North Andean block northward drift. Because the Carnegie ridge subduction is possibly an ongoing process, which began prior to the Pliocene, we postulate the along‐strike morphology of the ridge at the origin of interplate coupling variations. The subduction of an along‐strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the GG area occurring at ∼1.8–1.6 Ma.

Structural evolution of the footwall of the Indus Suture in Malakand (N Pakistan) during the Himalayan collision

We report new data on the geometry and kinematics of structures in the rocks of the Indian Plate below the Indus Suture in the area of Malakand (N Pakistan). The study area forms part of the exposed northwestern promontory of the Indian Plate indenting Eurasia to form the Himalayan orogenic belt. Earlier widespread structures (i.e. regional foliation and lineation) are consistent with an approximate N–S convergence direction, in coincidence with the movement direction of the Indian Plate. Younger structures, such as NNE trending open folds that laterally become syntaxes (i.e. Besham or Nanga-Parbat), and relatively minor E–W dextral strike-slip shear zones, are related to a regional tectonic shortening direction subparallel to the trend of the suture. These folds are radial to the northwestern corner of the Indian Plate and contemporaneous with the general bulk N–S convergence. It is only very recently in the structural record that the irregular outline of the Indian Plate played a role in determining the orientation of new structures during its indentation. The structural pattern presents similarities to arcuate megastructures in ancient collisional orogens, such as the Ibero-Armorican arc of the Variscan belt in Europe, where indentation tectonics, as well as post-orogenic oroclinal folding, are invoked to explain the present curvature.

Surface Deformation Associated with the Mw 6.4, 24 February 2004 Al Hoceima, Morocco, Earthquake Deduced from InSAR: Implications for the Active Tectonics along North Africa

We study the surface deformation associated with the 24 February 2004 Al Hoceima earthquake (Mw 6.4) that recently affected the Rif Mountains of Mo- rocco. The coseismic displacement field is mapped using synthetic aperture radar interferometry (InSAR) with the Envisat (ESA) satellite data acquired in the ascend- ing and descending modes. Our analysis and modeling of InSAR data suggest that the earthquake is associated with a northwest-southeast-trending right-lateral, ap- parently blind strike-slip fault with a seismic moment reaching 6.8 10 18 N m. This result is in contrast with the north-northeast-south-southwest left-lateral fault mech- anism inferred from the modeling of seismic waves. Thrust-and-fold structures of the Rif Mountains developed during the Tertiary period, but the recent significant seismic events and late-Quaternary deformation indicate east-west extension accom- modated by north-south-trending normal and northwest-southeast- and northeast- southwest-trending conjugate strike-slip faults. The active deformation illustrates the fragmentation of the Rif Mountain range due to the Africa-Iberia collision and west- southwestward escape tectonics.

Eastern Mediterranean basin systems

Abstract The basins in the Eastern Mediterranean can be divided into those that were formed mainly in post-Miocene time and those that were formed during the rifting episodes that led to the formation of the Neotethys. The younger basins can be further divided into those that were formed mainly in post-Miocene time and those that were formed in post-Pliocene time. The separation is not only one of convenience but also corresponds to major adjustments in the plate tectonic situation in the Eastern Mediterranean. The late Miocene deposition of thick evaporites throughout the Mediterranean region, or, where evaporites are missing, the creation of an important erosional unconformity during the extreme lowstand of the Mediterranean, makes the Miocene-Pliocene boundary relatively easy to identify, especially on seismic reflection records. At about the same time, following the collision of the Arabian plate with Eurasia, the Anatolian and Aegean microplates came into existence between the convergent African and Eurasian plates to accommodate tectonic escape between them. The general configuration of the Eastern Mediterranean basins reflects the tectonic and structural gradients between the collisional domain of southeastern Turkey and Iran, and the continuing but increasingly limited subduction along the Calabrian and Hellenic arcs, with the Cyprus and Levantine zones between them. Several distinct zones can be identified in the Eastern Mediterranean. The Dead Sea Fault system marks the edge between the collisional and pre-collisional zones to the east and west, respectively. The meridian through the Anaximander Mountains (30©E) forms a rough boundary between the zone of incipient collision to the east and the zone of continuing but late-stage subduction to the west. The Malta Escarpment forms the Eastern boundary of the Eastern Mediterranean basins. The series of basins along the northern margin of the Eastern Mediterranean and the Aegean Sea share this progressive evolution, with those containing Messinian evaporites to the east and those without to the west. The Sicily Channel with its associated basins is an extensional zone between the Eastern and Western Mediterranean. The basins discussed in this paper are divided into two groups, the larger and older basins and the smaller and younger basins. In the first group are the Ionian Basin and the Levantine Basin, and in the second group the Cilicia Basin, Antalya Basin, Finike Basin, Rhodes Basin, Aegean basins, Sicily Channel basins, Latakia Basin and Larnaca Basin. The Eastern Mediterranean represents the last stage in the evolution of an ocean basin. Given the current motion between Africa and Eurasia, the Eastern Mediterranean will cease to exist in about 6-8 Ma from now. As a result, the larger and older basins are shrinking, whereas the younger and smaller basins are growing. Eventually the smaller basins will also disappear.

Tectonic and sedimentary evolution of the Cenozoic Hatay Graben, Southern Turkey: a two-phase model for graben formation

Abstract New structural and sedimentary studies form the basis of a new interpretation for the Neogene Hatay Graben. Fault analysis reveals three contemporaneous trends of fault orientation (000°–180°, 045°–225° and 150°–350°) suggesting that the graben is transtensional in nature. Sedimentary studies show that, following shallow-marine deposition from the Late Cretaceous to the Eocene, a hiatus ensued until Early Miocene fluvial sedimentation. After a Mid-Miocene marine transgression, water depths increased until the Messinian salinity crisis, followed by a regression from the Pliocene to the present day. The basin initially developed as the distal margin of a foreland basin of the Tauride allochthon to the north, developing a classic sedimentary sequence during Mid-Late Miocene. Stresses caused by loading of the crust created a flexural forebulge to the south that supplied sediment mainly northwards. During the Plio-Quaternary, transtensional graben development took place, primarily influenced by the westward tectonic escape of Anatolia along the East Anatolia Fault Zone and left-lateral offset along the northward extension of the Dead Sea Transform Fault. This area is, thus, an excellent example of a foreland basin reactivated in a strike-slip setting. Our new two-phase model: foreland basin, then transtensional basin for the Hatay Graben, is in contrast to previous models, in which it was generally assumed that the Plio-Quaternary Hatay Graben represents a direct extension of the Dead Sea Fault Zone or the East Anatolian Fault Zone.

West‐east variation in crustal thickness in northern Lhasa block, central Tibet, from deep seismic sounding data

A 500‐km‐long west‐east wide‐angle seismic profile from Selin Tso to Yaanduo in the northernmost Lhasa block of Tibet, acquired by the Sino‐French joint seismic program in 1982, has been reinterpreted. We model the P and S wave velocity structure of the whole crust, while recognizing that in many places, uncertainties are large. A surprising but robust conclusion, consistent with previous interpretations of both this data set and other newer data from Tibet, is that Moho depth is about 60–65 km at 90°E but 75–80 km depth at 92.5°E. Our detailed interpretation uses multiple wide‐angle P and S wave reflections from the crystalline basement and the Moho; but no Moho refractions are recognized. Along most of the profile, the crust may be crudely divided into an upper crust (∼5–30 km depth, 5.0 < Vp < 6.4 km/s), a middle crust (∼33–45 km depth, 6.5 < Vp < 6.8 km/s) and a lower crust (depths below ∼48 km, 7.0 < Vp < 7.4 km/s). The west‐to‐east increase in crustal thickness is accomplished by a ∼50% thickening of the middle and lower crust. Larger vertical velocity gradients separate these three layers and bound them above (surficial and sedimentary rocks) and below (Moho transition zone). The most notable low‐velocity zone in the crust lies at the base of the upper crustal layer. S wave velocity structure is less well constrained but parallels the P wave structure except that Vp/Vs ratios may decrease from west to east in the lower crust. Our data suggest considerable variation in structure along‐strike of the Tibetan Plateau and show that interpretations of Tibet as a purely two‐dimensional orogen are overly simplistic. The west‐east increase in crustal thickness may occur across the Karakorum‐Jiali fault system and be an indicator of lateral tectonic escape of the Qiangtang terrane.

How Sensitive Are Fault-Slip Rates in the Los Angeles Basin to Tectonic Boundary Conditions?

Geodetic studies have produced different interpretations of the relative vertical thickening versus escape tectonics occurring within the Los Angeles basin based on calculated horizontal strain rates ranging from 56 10 9 /yr contraction at N36 Et o 85 10 9 /yr north-south contraction and 60 10 9 /yr east-west extension. Three-dimensional forward mechanical models of faults in the Los An- geles basin are used to compare modeled slip rates and slip styles, represented as the rakes of average net slip vectors, under four representative horizontal strain condi- tions with geologically determined late-Quaternary slip rates and observed slip styles. The comparisons strive to identify the most mechanically viable tectonic boundary conditions for the Los Angeles basin. The three-dimensional fault surfaces used within the mechanical models have been defined by Southern California Earthquake Center (SCEC) workers based on surface geology and subsurface data. The model results suggest that northeast-southwest principal contraction is inappropriate for the Los Angeles basin because this tectonic boundary condition produces left-lateral slip along the Whittier and San Gabriel faults in contrast with abundant geologic evidence of right-lateral slip. Of the four tectonic boundary conditions evaluated, north-south contraction accompanied by either zero or slow east-west contraction gives the low- est mismatch of modeled and observed fault slip style. These results suggest that vertical thickening may be more predominant than escape tectonics in this region.

Block models of crustal motion in southern California constrained by GPS measurements

We estimate slip rates on major active faults in southern California using a block model constrained by Global Positioning System measurements of interseismic deformation. The block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle. Our estimates of the right‐lateral strike‐slip rate on the San Andreas fault vary by at least a factor of 5, from a high of 35.9 ± 0.5 mm/yr in the Carrizo Plain to a low of 5.1 ± 1.5 mm/yr through the San Bernadino segment. Shortening across the Puente Hills Thrust and left‐lateral slip on the Raymond Hill fault are consistent with both thickening and escape tectonics in the Los Angeles Basin. Discrepancies between geodetic and geologic slip rate estimates along the San Andreas and San Jacinto faults, as well as in the Eastern California Shear Zone, may be explained by a temporal change in fault system behavior. We find no substantial evidence for long‐term postseismic relaxation and infer that the viscosity of the lower crust/upper mantle may be relatively high (η > 1019 Pa s).

Deformation of the northeastern Venezuelan Andes. Relationships with the Caribbean overthrusts

The Merida Andes (Venezuela) formed in the middle Miocene due to oblique convergence between the South American plate and the Maracaibo block [Audemard et al., 2002] (figs. 1A and 1B). The study area corresponds to the so-called "Barbacoas platform" [Renz, 1960], which constitutes the northeastern termination of the belt, NE of Valera (fig. 2). It is located in the northeastern part of Trujillo block [Hervouet et al., 2001], considered as an independent block separated from the main Maracaibo block along the Valera fault. According to Stephan [1982], the N170°E-trending Caribbean compression developed in this area from late Cretaceous to Eocene. It was followed by a N105°E-trending compression older than middle Miocene, and finally by the NW-SE Andean compressional stage that lasted till now in most of the chain. However, east of El Empedrado fault, a NNE-SSW compression presently occurs that is oblique to the classical Andean stage. The tectonic evolution of the Andean stage is not well understood. The Merida Andes are mainly composed of Precambrian and Paleozoic rocks. The northern part of the belt only comprises a complete and continuous Jurassic to Paleogene cover. This lithologic pattern is probably a consequence of the tectonic escape of the Maracaibo block, and more particularly of the smaller Trujillo block. The Merida and Carribean belts being close to each other, the influence of the Andean deformation on the Caribbean allochthonous must be taken into account. In order to make a structural analysis at regional scale, we privileged the use of remote sensing data (Landsat, Spot and Radar images) and aerial photographs. This was complemented by structural data obtained in the field, allowing the study of geometric and chronological relationships between the tectonic structures.

Sedimentation of the Neogene–Recent Alaşehir (Gediz) continental graben system used to test alternative tectonic models for western (Aegean) Turkey

The Alaşehir (Gediz) Graben exemplifies clastic sedimentation in a long-lived continental half-graben in a semi-arid setting, developed within relatively incompetent metamorphic rocks. Early Miocene to Recent rift-related sediments are exhumed on both flanks of the graben, allowing detailed three-dimensional study. During the Early Miocene, small fan-delta lobes were shed northwards from the rugged Menderes Metamorphic Massif into a bordering lacustrine basin. During Early to Mid-Miocene time, large alluvial fans prograded northwards into this basin. Through-drainage to the Aegean Sea was established as the basin widened and filled. Discrete lobes of coarse alluvial fan sediments of latest Miocene(?)–Pliocene age, also shedding northwards, are likely to have been climatically influenced. Quaternary alluvium party infills the modern Alaşehır rift basin. The sedimentary information can be used to test two alternative tectonic models for the Alaşehır Graben. In the first model, an E–W graben bounded by high-angle faults was active during latest Miocene(?)–Recent time, whereas earlier Miocene sedimentation was controlled by N–S faulting related to a N–S compressional stress regime. In the second hypothesis, the Alaşehır Graben was initiated much earlier, in the Early Miocene and was then either continuously or episodically active until Recent. Our results, especially facies and palaeocurrent data from alluvial sediments, indicate that clastic sedimentation was controlled by mainly E–W faulting in a N–S stress regime. Assuming the Early Miocene clastic sediments are correctly dated, this supports the second (long-lived extension) model. However, rather than steady-state extension for ca. 15 Ma, the sedimentary evidence and regional context are consistent with a pulsed extension model, whereby initial Early to Mid-Miocene extension and related clastic sedimentation was followed by a second phase of extension in latest Miocene(?)–Pliocene time. The driving force of initial, Early Miocene extension was probably gravity spreading towards a south-Aegean subduction zone, whereas the inferred second extension pulse is seen as being triggered by westward “tectonic escape” of Anatolia towards the extending Aegean back-arc region.

Slab pull and indentation tectonics: insights from 3D laboratory experiments

We investigate, using 3D laboratory experiments, how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions. Lithospheric plates are modelled by sand–silicone plates floating on glucose syrup, and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced. Analogue experiments model the convergence between two lithospheric plates, a small continent indenting a large continental plate. We show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone. Slab break-off following the subduction of the small continent favours the indentation process, because it results in an increasing compression in front of the indenter, and extension above the neighbouring oceanic subduction, both of them being responsible for the appearance of the indenter-like geometry of the plate boundary. When the slab does not deform significantly at depth, in contrast, the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction, during which the tectonic regime within the wide continent remains quite homogeneous. Comparing the presented analogue experiments with the subductions both part of the Arabian indenter within Eurasia, our results suggest that the different tectonic regime on both sides of the Arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern Anatolia.

A pulsed extension model for the Neogene–Recent E–W-trending Alaşehir Graben and the NE–SW-trending Selendi and Gördes Basins, western Turkey

We have developed a significant body of new field-based evidence relating to the history of crustal extension in western Turkey. We establish that two of the NE–SW-trending basins in this region, the Gördes and Selendi Basins, whose sedimentary successions begin in the early Miocene, are unlikely to relate to late-stage Alpine compressional orogeny or to E–W extension of Tibetan-type grabens as previously suggested. We argue instead that these basins are the result of earlier (?) late Oligocene, low-angle normal faulting that created approximately N–S “scoop-shaped” depressions in which clastic to lacustine and later tuffaceous sediments accumulated during early–mid-Miocene time, separated by elongate structural highs. These basins were later cut by E–W-trending (?) Plio–Quaternary normal faults that post-date accumulation of the Neogene deposits. In addition, we interpret the Alaşehir (Gediz) Graben in terms of two phases of extension, an early phase lasting from the early Miocene to the (?) late Miocene and a young Plio–Quaternary phase that is still active. Taking into account our inferred earlier phase of regional extension, we thus propose a new three-phase “pulsed extension” model for western Turkey. We relate the first two phases to “roll-back” of the south Aegean subduction zone and the third phase to the westward “tectonic escape” of Anatolia.

Nested strike-slip duplexes, and other evidence for Late Cretaceous–Palaeogene transpressional tectonics before and during India–Eurasia collision, in Thailand, Myanmar and Malaysia

The Late Cretaceous–Palaeogene structural and tectonic events in the northern region of Sundaland represent a poorly known, but potentially important orogenic development in SE Asia. Extensive Late Cretaceous S-type granites extending from Malaysia through Thailand to Myanmar have long been used to infer an episode of crustal thickening, an inference supported by the presence of late Cretaceous–Eocene ophiolites in Myanmar. However, structural evidence for a well-developed associated fold and thrust belt has been lacking. Apatite and zircon fission-track studies of Thailand indicate a broad regional uplift from about 80 Ma to 40 Ma, suggesting an episode of crustal thickening, but the uplift amount is modest, and not that expected for a major fold and thrust belt. Left lateral motion on major NW–SE-trending strike-slip fault zones (Mae Ping and Three Pagodas faults) in Myanmar and Thailand has been attributed to Himalayan–Tibetan escape tectonics. This paper demonstrates that the fault zones are considerably more complicated than just NW–SE trends. They are a network of branching faults with important north–south trends as well as NW–SE trends, they form large-scale, nested strike-slip duplex structures and affect a region over 1000 km long and up to 250 km wide. This diffuse, branching network of strike-slip fault trends may represent a substantial Late Cretaceous–Palaeogene transpressional belt. Himalayan escape tectonics represent later increments of deformation with both Oligocene sinistral and late Oligocene–Recent dextral reactivation.

Neotectonic deformation in the transition zone between the Dead Sea Transform and the East Anatolian Fault Zone, Southern Turkey: a palaeomagnetic study of the Karasu Rift Volcanism

In southern Turkey ongoing differential impingement of Arabia into the weak Anatolian collisional collage resulting from subduction of the Neotethyan Ocean has produced one of the most complex crustal interactions along the Alpine–Himalayan Orogen. Several major transforms with disputed motions, including the northward extension of the Dead Sea Fault Zone (DSFZ), meet in this region. To evaluate neotectonic motion on the Amanos and East Hatay fault zones considered to be northward extensions of the DSFZ, the palaeomagnetism of volcanic fields in the Karasu Rift between these faults has been studied. Remanence carriers are low-Ti magnetites and all except 5 of 51 basalt lavas have normal polarity. Morphological, polarity and K–Ar evidence show that rift formation occurred largely during the Brunhes chron with volcanism concentrated at 0.66–0.35 Ma and a subsidiary episode at ∼0.25–0.05. Forty-four units of normal polarity yield a mean of D/ I=8.8°/54.7° with inclination identical to the present-day field and declination rotated clockwise by 8.8±4.0°. Within the ∼15-km-wide Hassa sector of the Karasu Rift, the volcanic activity is concentrated between the Amanos and East Hatay faults, both with left lateral motions, which have rotated blocks bounded by NW–SE cross faults in a clockwise sense as the Arabian Block has moved northwestwards. An average lava age of ∼0.5 Ma yields a minimum cumulative slip rate on the system bounding faults of 0.46 cm/year according with the rate deduced from the Africa–Arabia Euler vector and reduced rates of slip on the southern extension of the DSFZ during Plio-Quaternary times. Estimates deduced from offsets of dated lavas flows and morphological features on the Amanos Fault Zone [Tectonophysics 344 (2002) 207] are lower (0.09–0.18 cm/year) probably because they are limited to surface fault breaks and do not embrace the seismogenic crust. Results of this study suggest that most strike slip on the DSFZ is taken up by the Amanos–East Hatay–Afrin fault array in southern Turkey. Comparable estimates of Quaternary slip rate are identified on other faults meeting at an unstable FFF junction (DSFZ, East Anatolian Fault Zone, Karatas Fault Zone). A deceleration in slip rate across the DSFZ and its northward continuation during Plio-Quaternary times correlates with reorganization of the tectonic regime during the last 1–3 Ma including tectonic escape within Anatolia, establishment of the North and East Anatolian Fault Zones bounding the Anatolian collage in mid–late Pliocene times, a contemporaneous transition from transpression to transtension and concentration of all basaltic magmatism in this region within the last 1 Ma.