Showing papers on "Tectonics published in 2002"

Hot orogens, tectonic switching, and creation of continental crust

Abstract: Many granulite terrains were too hot to have formed during continental collision. Rather, along with many high-grade metamorphic terrains that typify continental crust, most formed in accretionary orogens during tectonic switching, when prolonged lithospheric extension was interrupted by intermittent, transient contraction. Based on modern and ancient examples, tectonic switching occurs when slab retreat induces upper plate extension, causing arc splitting, formation of microcontinent slivers, and backarc basins; then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction (or slab flip) and crustal thickening. During slab retreat, basaltic magmas produced from decompressed asthenosphere advect into the extending orogen, causing granulite facies metamorphism and granite generation, but subsequent thickening during flat subduction cools the region. Thickening is focused in the thermally softened backarc region and, if sediment filled, a hot, short-lived (~10 m.y.), narrow (50– 100 km) orogenic belt forms. Such thickening is often misleadingly ascribed to arc or microcontinent collision. Once slab-retreat mode is reestablished, lithospheric extension recommences and a new arc-backarc system forms, generally outboard. Arrival of another plateau will reverse the procedure, and another short-lived, hot orogen will form within the orogenic system. Cycles of tectonic switching efficiently produce continental crust.

Active tectonics of the South Caspian Basin

Abstract: SUMMARY We use observations of surface faulting, well-constrained earthquake focal mechanisms and centroid depths, and velocity structure determined by surface wave propagation and teleseismic receiver functions to investigate the present-day deformation and kinematics in and around the South Caspian Basin. The lack of earthquakes within the basin itself indicates that it behaves as a rigid block, though its sedimentary cover is deformed by numerous folds that are decoupled from its rigid basement by overpressured mud. The basin contains a sedimentary sequence almost 20 km thick above a relatively highvelocity basement that is thinner within the basin than on its margins. The basement beneath the basin could be either unusually thick oceanic crust or thinned, but relatively high-velocity, continental crust. The South Caspian Basin is surrounded by active earthquake belts on all sides. No earthquakes deeper than 30 km can be confirmed in the Kopeh Dag, Alborz and Talesh, which bound the NE, S and W sides of the basin. In contrast, earthquakes occur to depths of at least 80 km on the Apsheron-Balkhan sill, which bounds the N side of the basin and where no earthquakes can be confirmed that are shallower than 30 km. We interpret these deeper earthquakes to indicate the onset of subduction of the South Caspian Basin beneath the central Caspian, a process that appears to occur aseismically at shallow levels. Although oblique shortening is partitioned into pure strike-slip and pure thrust in many areas, conjugate right-lateral and leftlateral components in the Kopeh Dag and eastern Alborz suggest that the South Caspian Basin has a westward component of motion relative to both Eurasia and Iran. This motion enhances westward underthrusting of the basin beneath the Talesh mountains of Iran and Azerbaijan. We estimate the present motions of the South Caspian Basin to be ~ 13-17 mm yr- to the SW relative to Iran (a maximum value) and ~ 8-10 mm yrto the NW or NNW relative to Eurasia. We suspect that these motions are all relatively recent, and may have begun only in the Pliocene (3-5 Ma). The South Caspian Basin will ultimately be destroyed by subduction or underthrusting and its present situation may represent an intermediate stage between that of the eastern Mediterranean and that of the seismically active slab beneath the Hindu Kush. ~~~1 I ~~~~~~~NTRODUCTIO ~N

Reconstruction of the tectonic evolution of the western Mediterranean since the Oligocene

Abstract: We present a tectonic synthesis and an animation of the tectonics of the western Mediterranean since the Oligocene. This work is based on data derived from different geological datasets, such as structural geology, the distribution of metamorphic rocks, magmatic activity, sedimentary patterns, palaeomagnetic data and geophysics. Reconstruction was performed using an interactive software package (PLATYPLUS), which enabled us to apply rotational motions to numerous microplates and continental terranes involved in the evolution of the western Mediterranean basins. Boundary conditions are provided by the relative motions of Africa and Iberia with respect to Europe, and the Adriatic plate is considered here as an African promontory. The reconstruction shows that during Alpine orogenesis, a very wide zone in the interface between Africa and Europe underwent extension. Extensional tectonics was governed by rollback of subduction zones triggered by gravitational instability of old and dense oceanic lithosphere. Back-arc extension occurred in the overriding plates as a result of slow convergence rates combined with rapid subduction rollback. This mechanism can account for the evolution of the majority of the post-Oligocene extensional systems in the western Mediterranean. Moreover, extension led to drifting and rotations of continental terranes towards the retreating slabs in excess of 100-800 km. These terranes - Corsica, Sardinia, the Balearic Islands, the Kabylies blocks, Calabria and the Rif-Betic - drifted as long as subduction rollback took place, and were eventually accreted to the adjacent continents. We conclude that large-scale horizontal motions associated with subduction rollback, back-arc extension and accretion of allochthonous terranes played a fundamental role during Alpine orogenesis.

Evidence for active subduction beneath Gibraltar

Abstract: We report on a marine seismic survey that images an active accretionary wedge west of Gibraltar. Ramp thrusts offset the seafloor and sole out to an east-dipping decollement, indicating ongoing westward-vergent tectonic shortening. New traveltime tomographic re- sults image a slab of oceanic lithosphere descending from the Atlantic domain of the Gulf of Cadiz, passing through intermediate-depth (60-120 km) seismicity beneath the west- ernmost Alboran Sea, and merging with a region of deep-focus earthquakes 600-660 km below Granada, Spain. Together, these new data provide compelling evidence for an active east-dipping subduction zone.

Active Tectonics and Alluvial Rivers

Abstract: Part I. Background: 1. Introduction 2. Deformation and river response Part II. Effects of Known Measurable Deformation: 3. Experimental studies 4. Measured active tectonics 5. Earthquake effects Part III. Effects of Unmeasured Deformation: 6. Response of channel morphology, sedimentology, hydrology, and hydraulics 7. Lateral response Part IV. Applications: 8. Tectonics and fluvial sedimentation 9. Identification of active and neotectonic structures 10. Applications References Index.

Asymmetric slip partitioning in the Sea of Marmara pull-apart: a clue to propagation processes of the North Anatolian Fault?

Abstract: Between 1939 and 1999 the North Anatolian fault (NAF) experienced a westward progression of eight large earthquakes over 800 km of its morphological trace. The 2000-km-long North Anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale (∼10 Myr). The Sea of Marmara is a large pull-apart that appears to have been a geometrical/mechanical obstacle encountered by the NAF during its propagation. The present paper focuses on new high-resolution data on the submarine fault system that forms a smaller pull-apart beneath the Northern Sea of Marmara, between two well-known strike-slip faults on land (Izmit and Ganos faults). The outstandingly clear submarine morphology reveals a segmented fault system including pull-apart features at a range of scales, which indicate a dominant transtensional tectonic regime. There is no evidence for a single, continuous, purely strike-slip fault. This result is critical to understanding of the seismic behaviour of this region of the NAF, close to Istanbul. Additionally, morphological and geological evidence is found for a stable kinematics consistent both with the long-term displacement field determined for the past 5 Myr and with present-day Anatolia/Eurasia motion determined with GPS. However, within the Sea of Marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull-apart. The loading associated with the westward propagation process of the NAF may have provided a favourable initial geometry for such a slip separation.

The Earthquake Potential of the New Madrid Seismic Zone

Abstract: The fault system responsible for New Madrid seismicity has generated temporally clustered very large earthquakes in A.D. 900 100 years and A.D. 1450 150 years as well as in 1811-1812. Given the uncertainties in dating liquefaction features, the time between the past three New Madrid events may be as short as 200 years and as long as 800 years, with an average of 500 years. This advance in understanding the Late Holocene history of the New Madrid seismic zone and thus, the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake-induced liquefaction features at more than 250 sites across the New Madrid region. We have found evidence that prehistoric sand blows, like those that formed during the 1811-1812 earthquakes, are probably com- pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences. From the spatial distribution and size of sand blows and their sedimentary units, we infer the source zones and estimate the magnitudes of earth- quakes within each sequence and thereby characterize the detailed behavior of the fault system. It appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the A.D. 900 and A.D. 1450 events as well as in 1811-1812. On the basis of a minimum recurrence rate of 200 years, we are now entering the period during which the next 1811-1812-type event could occur.

Offset on the Main Recent Fault of NW Iran and implications for the late Cenozoic tectonics of the Arabia-Eurasia collision zone

Abstract: SUMMARY We use drainage patterns, geological markers and geomorphological features to determine a right-lateral offset of ∼50 km, and possibly as much as ∼70 km, on the Main Recent Fault in NW Iran. This fault trends NW‐SE and forms the NE border of the Zagros mountains. It accommodates the strike-slip component of the N‐S convergence between Arabia and Eurasia, with the NE‐SW shortening component being accommodated in the Zagros Fold Belt. Its ∼50 km strike-slip offset implies a shortening of ∼50 km in the fold belt and ∼70 km total N‐S convergence accommodated in the NW Zagros. This is a substantial fraction of the 85‐ 140 km overall Arabia‐Eurasia convergence expected over the last 3‐5 Ma. If the Main Recent Fault initiated at that time, as seems likely from geological arguments, it has a horizontal slip rate of at least 10‐17 mm yr −1 and should be the source of frequent earthquakes of Ms 6‐7, as has been seen in the 20th century and the earlier historical record. The similarity of the offsets and probable ages of the North Anatolian and Main Recent Faults suggests that they have been active as an almost continuous zone of right-lateral shear on the north edge of the Arabian and Anatolian plates since the early Pliocene.

Interaction of metamorphism, deformation and exhumation in large convergent orogens

Abstract: Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr−1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m−3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m−3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen.

Along-Strike Variations of Morphotectonic Features in the Western Foothills of Taiwan : Tectonic Implications Based on Stream-Gradient and Hypsometric Analysis

Abstract: The Taiwan mountain belt provides a key example for analyzing the relation between morphology and tectonics in an active compressional environment. There is a striking geometrical relationship between the location of salients and reentrants of the mountain belt and the presence of major crustal inhomogeneities such as structural highs in the foreland basin. Major along-strike variations of structural styles occur in range-front rock units of the fold-thrust belt. Stream-gradient and hypsometric analysis has been carried out to highlight the along-strike variations of morphotectonic features and to illustrate the relative activities in different tectonic regimes of the Western Foothills. The normalized stream length-gradient index (SL index) and the Hack profile are two of the stream-gradient indices that effectively reflect the tectonic uplift in a region. De-trending and residual analysis of the hypsometric integral (HI) eliminates the spatial dependency of small drainage basins, and the residual hypsometric integral corresponds to differential uplift activity. Integration of stream-gradient indices and hypsometry provides more robust tectonic interpretation. Five morphotectonic provinces have been identified in the Western Foothills based on stream-gradient indices and hypsometry. Each province is bounded by a series of N140°E-trending transfer fault zones, either inherited from the Eurasian passive margin and/or newly formed in the sedimentary cover in response to the presence of basement highs within the foreland basin (the Peikang and Kuanyin highs). The morphotectonic features as well as deformation styles vary within each province. A high uplift but low shortening rate typifies the crustal deformation style in the transpressional regime north of the Peikang Basement High. On the contrary, a low uplift but high shortening rate characterizes the crustal deformation style in the transtensional regime south of the Peikang Basement High. The higher geomorphic indices suggest that greater tectonic activity occurs in central than in southwestern Taiwan. This inference is also supported by the coseismic deformation of the 1999 Chi-Chi earthquake.

Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea

Abstract: Non-volcanic continental margins may form up to 30% all present-day passive margins, and remnants of them are preserved in mountain belts. The papers in this volume demonstrate the benefits of integrating offshore and onshore studies, and illustrate the range of information obtained at different scales when comparing evidence from land and sea. Data sets collected across a range of spatial scales are evaluated: thin sections, cores, outcrops, seismic reflection profiles, and other geophysical data. The outcrop scale is crucial because it enables the spatial gulf to be bridged between DSDP and ODP cores and marine seismic data. There is also the problem that basins on land and beneath the sea inevitably have had different post-rift histories resulting in their contrasting present-day elevation. In mountain belts, portions of continental margins and oceanic crust are superbly exposed, but dismembered by subsequent compressional tectonics. Off present-day passive margins, extensional features have only been slightly deformed, if at all, by compressional movements, but are buried beneath significant thicknesses of post-rift sediments and so can only be sampled by ocean drilling at a small number of points. The first paper reviews the synergies that have occurred between investigations of the eastern North Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the Alps, and some later papers return to this theme. However, papers describing margins from other parts of the world show that it may be premature to use models based on the Atlantic and the Alps as the paradigm for all non-volcanic margins. The following 25 papers in the book are grouped under the following headings: (1) Margin overviews; (2) Exhumed crust and mantle; (3) Tectonics and stratigraphy; (4)Numerical models of extension and magmatism.

Arc parallel extension and localization of volcanic complexes in Guadeloupe, Lesser Antilles

Abstract: [1] Subduction of Atlantic seafloor under the Caribbean plate causes shallow earthquakes within the Lesser Antilles volcanic arc. Such earthquakes, above the subduction interface, show strike-slip or normal fault plane solutions, the latter with ∼E-W striking nodal planes. To better assess seismic hazard and the coupling between volcanism and tectonics, we investigated faulting related to overriding-plate deformation in the Guadeloupe archipelago. Using aerial photographs, satellite SPOT images, and topographic maps (1/25000 scale), we mapped active and middle to late Pleistocene fissures and normal fault systems that cut the uplifted coral platforms Grande-Terre and Marie-Galante and the volcanic rocks of Basse-Terre. The available marine geophysical data show that the faults extend offshore to bound submarine rifts. The E-W striking, 1500 m deep, V-shaped Marie-Galante rift separates the two islands of Marie-Galante and Grande-Terre. Normal faults in the north of Grande-Terre appear to mark the similarly V-shaped, western termination of the 5000 m deep, N°50E to N130°E striking Desirade graben. Three shallow, M ∼ 5.5 earthquakes (6 May 1851, 29 April 1897, 3 August 1992) appear to have ruptured segments of the Marie-Galante rift boundary faults. The young “La Grande Decouverte” volcanic complex of Basse-Terre, including the 1440 A.D. Soufriere dome, lies within the western termination of the Marie-Galante rift. The ancient volcanic shoulders of the rift buttress the active dome to the north and south, which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the Caribbean Sea, or southeastward into the Atlantic Ocean. The Marie-Galante rift is typical of other troughs transverse to the northeastern edge of the Caribbean plate. We interpret such troughs, which are roughly orthogonal to the arc, to result from slip-partitioning and extension perpendicular to plate convergence. That they disappear southward implies that they result from interaction between the Caribbean and North American plates.

Shaping the Australian crust over the last 300 million years: Insights from fission track thermotectonic imaging and denudation studies of key terranes

Abstract: Apatite fission track thermochronology is a well‐established tool for reconstructing the low‐temperature thermal and tectonic evolution of continental crust. The variation of fission track ages and distribution of fission track lengths are primarily controlled by cooling, which may be initiated by earth movements and consequent denudation at the Earth's surface and/or by changes in the thermal regime. Using numerical forward‐modelling procedures these parameters can be matched with time‐temperature paths that enable thermal and tectonic processes to be mapped out in considerable detail. This study describes extensive Australian regional fission track datasets that have been modelled sequentially and inverted into time‐temperature solutions for visualisation as a series of time‐slice images depicting the cooling history of present‐day surface rocks during their passage through the upper crust. The data have also been combined with other datasets, including digital elevation and heat flow, to image the denu...

Structural characteristics and petroliferous features of Tarim Basin

Abstract: Using the modern tectonic geology theories and methods such as the plate tectonic analysis, the paleo-structure analysis, the structural-lithofacies analysis, and the fault related fold and petroleum system, and combining with the seismic data, well drilling data and the circumferential field geology, study on the structural characteristics and petroleum prospect in the Tarim Basin has been carried out. Results show that the Tarim Basin is a large superimposition and combination basin with continental crustal basement, composed of a Paleozoic craton and Meso-Cenozoic foreland basins. The characteristics of the basin are: the kernel part of the basin is the marine facies Paleozoic craton, superimposed 4 continental facies foreland basins. Though the scale of the paleozoic craton of the Tarim Basin is relatively small, the structure is steady. The petroleum prospect of the Paleozoic craton is: multiphase pool-generation and accumulation controlled by ancient uplift. The Meso-Cenozoic foreland basins in the Tarim Basin, which are distributed on the cratonic circumference and are a long-term subsidence, turned into rejuvenated foreland basins after the Meso-Cenozoic period. The petroleum prospects are: coal-bed generating hydrocarbon, abundant natural gas, pool-generation in later and recent periods, the oil and gas distribution controlled by the foreland thrust belt. The structural characteristics of Tarim provide it with a superimposition and combination petroleum system of multiple resources, multiple reservoirs and multiphase pool-generation. The oil and gas exploration prospect covers two large fields: the Paleozoic craton and the Meso-Cenozoic foreland thrust belt.

Back arc extension, tectonic inheritance, and volcanism in the Ligurian Sea, Western Mediterranean

Abstract: [1] The Ligurian basin, western Mediterranean Sea, has opened from late Oligocene to early Miocene times, behind the Apulian subduction zone and partly within the western Alpine belt. We analyze the deep structures of the basin and its conjugate margins in order to describe the tectonic styles of opening and to investigate the possible contributions of forces responsible for the basin formation, especially the pulling force induced by the retreating subduction hinge and the gravitational body force from the Alpine wedge. To undertake this analysis, we combine new multichannel seismic reflection data (Malis cruise, 1995) with other geophysical data (previous multichannel and monochannel seismic sections, magnetic anomalies) and constrain them by geological sampling from two recent cruises (dredges from Marco cruise, 1995, and submersible dives from Cylice cruise, 1997). From an analysis of basement morphology and seismic facies, we refine the extent of the different domains in the Ligurian Sea: (1) the continental thinned margins, with strong changes in width and structure along strike and on both sides of the ocean; (2) the transitional domain to the basin; and (3) a narrow, atypical oceanic domain. Margin structures are characterized by few tilted blocks along the narrow margins, where inherited structures seem to control synrift sedimentation and margin segmentation. On the NW Corsican margin, extension is distributed over more than 120 km, including offshore Alpine Corsica, and several oceanward faults sole on a relatively flat reflector. We interpret them as previous Alpine thrusts reactivated during rifting as normal faults soling on a normal ductile shear zone. Using correlations between magnetic data, seismic facies, and sampling, we propose a new map of the distribution of magmatism. The oceanic domain depicts narrow, isolated magnetic anomalies and is interpreted as tholeitic volcanics settled within an unroofed upper mantle, whereas calcalkaline volcanism appears to be discontinuous but massive and has jumped in space and time, from the beginning of rifting on the Ligurian margin (� 30 Ma), toward the Corsican margin at the end of the Corsica-Sardinia block rotation (� 16 Ma). This space and time shift reveals the importance of the rollback of the Apulian slab and of the migration of the Alpine-Apennines belt front toward the E-SE for driving basin formation. We also state that initial rheological conditions and inherited crustal fabric induce important changes in the styles of deformation observed along margins and between conjugate margins. In the NE Ligurian basin the prerift Alpine crustal thickening together with slow rollback velocity likely contribute to distribute strain across the whole NW Corsican margin, whereas farther south the inherited Hercynian structural pattern combined with a faster rollback of the subducting plate tend to focus the extension at the foot of the margin, up to the Sardinian rift which ends within the SW Corsican margin. Therefore the mode of opening and the margin structures mainly depend on the balance between intrinsic, inherited crustal heterogeneity (fabric and rheological changes) and external conditions imposed by rollback of the subducting lithosphere. INDEX TERMS: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 3025 Marine Geology and Geophysics: Marine seismics (0935); 8109 Tectonophysics: Continental tectonics—extensional (0905); 8159 Tectonophysics: Rheology—crust and lithosphere;

Archaean tectonics: a review, with illustrations from the Slave craton

Abstract: Abstract The tectonic evolution of Archaean granite-greenstone terranes remains controversial. Here this subject is reviewed and illustrated with new data from the Slave craton. These data show that a thick, c. 2.7Ga, pillow basalt sequences extruded across extended sialic basement of the Slave craton at a scale comparable with that of modern large igneous provinces. The pillow basalts do not represent obducted oceanic allochthons. Basement-cover relationships argue for autochthonous to parautochthonous development of the basaltic greenstone belts of the west-central Slave craton, an interpretation that is further supported by geochemical and geochronological data. Similar data exist for several other cratons and granite-greenstone terrains, including the Abitibi greenstone belt of the Superior craton, where stratigraphic and subtle zircon inheritance data are equally incompatible with accretion of oceanic allochthons. Many classical granite-greenstone terrains, including most well-documented komatiite occurrences, thus appear to have formed in extensional environments within or on the margins of older continental crust. Closest modern analogues for such basalt-komatiite-rhyolite-dominated greenstone successions are rifts, marginal basins and volcanic rifted margins. Indeed, these environments have high preservation potential compared with fully oceanic settings. Collapse and structural telescoping of these highly extended volcano-sedimentary basins would allow for the complex structural development seen in granite-greenstone terrains while maintaining broadly autochthonous to parautochthonous tectonostratigraphic relationships. Seismic reflection profiles cannot discriminate between these telescoped autochthonous to parautochthonous settings and truly allochthonous accretionary complexes. Only carefully constructed structural-stratigraphic cross-sections, allowing some degree of palinspastic reconstruction, and underpinned by sufficient U-Pb zircon dating, can address the degree of allochthoneity of greenstone packages. Furthermore, seismic reflection profiles are essentially blind for the steep structures produced by multiple phases of upright folding and buoyant rise of mid- to lower-crustal, composite, granitoid and gneiss domes. Such structures are ubiquitous in granite-greenstone terrains and, indeed, most of these terrains appear to have experienced at least one phase of convective overturn to re-establish a stable density configuration, irrespective of the complexities of the pre-doming structural history. Buoyant rise of mid- to lower-crustal granitoid and gneiss domes can explain the typical size and spacing characteristics of such domes in granite-greenstone terranes, and the coeval deposition of late-kinematic, ‘Timiskaming-type’ conglomerate-sandstone successions in flanking basins. The extensional and subsequent contractional evolution of granite-greenstone terrains may have occurred in the overall context of a plate tectonic regime (e.g. volcanic rifted margins, back-arc basins) but highly extended, intraplate, rift-like settings seem equally plausible. Explaining the evolution of the latter in terms of Wilson cycles is misguided. Periods of intense rifting and flood volcanism (e.g. 2.73–2.70 Ga) may have been related to increased mantle plume activity or perhaps catastrophic mantle overturn events. Although there is evidence for plate-like lateral movement in late Archaean time (e.g. lateral heterogeneity of cratons, arc-like volcanism, cratonscale deformation patterns, strike-slip faults, etc.), the details of how these plate-like crustal blocks interacted and how they responded to rifting and collision appear to have differed significantly from those in Phanerozoic time. The most productive approach for Archaean research is probably to more fully understand and quantify these differences rather than the common emphasis on the superficial similarities with modern plate tectonics.

Basement-involved shortening and deep detachment tectonics in forelands of orogens: Insights from recent collision belts (Taiwan, Western Alps, Pyrenees)

Abstract: [1] New combined structural and seismotectonic analyses demonstrate basement-involved shortening in forelands of recent collisional orogens (Taiwan, Western Alps, Pyrenees) Basement thrusts documented by seismicity (eg, the 21 September 1999, Chi-Chi earthquake in Taiwan) and/or structural data are triggered and localized by preexisting basement faults which constitute crustal weakness zones available for reactivation under low stress levels Reactivation of basement faults may induce localization of folds and thrusts in the shallow thrust wedge, development of crystalline thrust sheets, out-of-sequence basement thrusting and late basement uplift, deformation/refolding of shallow thin-skinned nappes, and development of accommodation structures such as transfer faults leading to a kinematic segmentation of foreland thrust belts Reactivation of preexisting basement faults also occurs in the far foreland in response to the far-field transmission of orogenic stresses depending on the amount of the changing-through-time mechanical coupling between the orogen and its foreland Displacements related to basement shortening in forelands are accommodated at the scale of the upper crust, which requires that it is partially decoupled from the deeper lithospheric levels by a crustal detachment This detachment presumably occurs along the midcrustal, thermally weakened brittle-ductile transition It may either ramp toward the surface into a shallow, upper crustal detachment beneath the fold-thrust belt and/or extend beneath the foreland and accommodate basin inversion far away from the orogen Occurrence and relative timing of shallow and deep detachment tectonics in forelands seem to be dependent on mechanical boundary conditions such as the presence of ductile horizons within the cover sequence or of preexisting weakness zones in the underlying basement

Tectonic inversion in the Santa Barbara System of the central Andean foreland thrust belt, northwestern Argentina

Abstract: [1] The Santa Barbara System (SBS) of northern Argentina is a 400 km long segment of the Subandean foreland thrust belt. It is characterized by predominantly west verging, relatively high-angle thrust faults. Many of these faults are reactivated normal faults from one branch of a complex Cretaceous to Paleogene rift system. Heteroaxial folding in parts of the SBS is probably due to a slight component of range-parallel dextral strike-slip motion acting on preexisting faults striking north and NE during inversion. Regional balanced cross sections along two transects across the northern SBS indicate that the major faults flatten into a detachment in the basement at about 10 km depth. Neogene E-W contraction in the SBS is of the order of 21–26 km. Rift extension is not very well constrained but was probably less than 10 km. The structural style of the SBS differs from the thin-skinned Subandean thrust belt to the north and from the large-wavelength Sierras Pampeanas basement uplifts to the south. The changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland, suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style.

The Tectonic and Climatic Evolution of the Arabian Sea Region

Abstract: Over long periods of time the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate: (i) through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean; (ii) through the growth and erosion of orogenic belts, resulting in changes in oceanic chemistry and disruption of atmospheric circulation. The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet. The Tectonic and Climatic Evolution of the Arabian Sea Region brings together a collection of recent studies on the area from a wide group of international contributors. The paper range from high resolution, Holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic. Marine geophysics, stratigraphy, isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea. while much work remains to be done to understand fully the tectonic and climatic evolution of the Arabian Sea, a great deal has been achieved since the last major review, as detailed in the 26 contributions. This volume is essential reading for palaeoceanographers, sedimentologists and geophysicists. It will also be interest to structural geologists and those working in the petroleum industry.