Tectonics
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The Ainsa Fold and thrust oblique zone of the central Pyrenees: Kinematics of a curved contractional system from paleomagnetic and structural data Abstract Integration of structural, stratigraphic, and paleomagnetic data from the N–S trending structures of the Ainsa Oblique Zone reveals the kinematics of the major thrust salient in the central Pyrenees. These structures experienced clockwise vertical axis rotations that vary from 70° in the east (Mediano anticline) to 55° in the west (Boltaña anticline). Clockwise vertical axis rotations of 60° to 45° occurred from early Lutetian to late Bartonian when the folds and thrusts of the Ainsa Oblique Zone developed. This vertical axis rotation stage resulted from a difference of about 50 km in the amount of displacement on the Gavarnie thrust and an accompanying change in structural style at crustal scale from the central to the western Pyrenees, related to the NE–SW trending pinch out of Triassic evaporites at its basal detachment. A second rotation event of at least 10° took place since Priabonian, as a result of a greater displacement of the Serres Marginals thrust sheet with respect to the Gavarnie thrust sheet above the Upper Eocene‐Oligocene salts. The deduced kinematics demonstrates that the orogenic curvature of the central Pyrenees is a progressive curvature resulting from divergent thrust transport direction. Layer parallel shortening mesostructures and kilometer‐scale folds also developed by a progressive curvature related to divergent shortening directions during vertical axis rotation. Rotation space problems were solved by along‐strike extension which triggered the formation of transverse extensional faults and diapirs at the outer arcs of structural bends.
Tectonics - Tập 32 Số 5 - Trang 1142-1175 - 2013
Thermochronology of high heat‐producing crust at Mount Painter, South Australia: Implications for tectonic reactivation of continental interiors The Mount Painter Region in the Northern Flinders Ranges, South Australia, contains a Mesoproterozoic gneissic complex characterized by extraordinary heat production (∼16 μW m−3 ), resulting in the development of elevated middle‐upper crustal thermal gradients through much of the Paleozoic. Early Paleozoic deformation and metamorphism attained amphibolite facies (>500°C) in the deepest parts of the metamorphic pile (∼10–12 km) during the ∼500 Ma Cambro‐Ordovician Delamerian orogeny. The subsequent thermal history of these rocks is assessed through new K/Ar and40 Ar/39 Ar age measurements on amphiboles and micas and multiple‐diffusion‐domain thermal modeling of K‐feldspar40 Ar/39 Ar data. The preferred interpretation of these data is that the deepest rocks were at ∼500°C until around 430 Ma, requiring average upper crustal thermal regimes of the order of 40°C km−1 for at least 70 million years. At around 430 Ma, and again at 400 Ma, the terrane underwent periods of moderately fast cooling, possibly separated by a period of isothermal residence. Following cooling at 400 Ma, the terrane entered a second period of relative tectonic quiescence remaining essentially isothermal until ∼330 Ma. This long residence near the closure temperature of biotite resulted in variable argon loss from biotites in the 400 Ma to 330 Ma interval. Tectonic and thermal stability was terminated by a further period of moderately fast cooling (∼4°–8°C Ma−1 ) in the interval between 330 and 320 Ma. The three cooling episodes at around 430 Ma, 400 Ma, and 330 Ma are interpreted to be the result of exhumation resulting in a combined minimum of 6–7 km of denudation. We attribute this exhumation to the Alice Springs orogeny, a major intraplate tectonothermal event known throughout central Australia but not previously recognized as a significant tectonic event in the Adelaide Fold Belt. These new data provide compelling evidence that thermally modulated variations in lithospheric strength control the distribution of intraplate deformation at the continental scale.
Tectonics - Tập 21 Số 4 - 2002
Neogene‐Recent Reactivation of Pre‐Existing Faults in South‐Central Vietnam, With Implications for the Extrusion of Indochina Abstract Vietnam contains complex faults coupled with a diffuse igneous province that has been active since the mid‐Miocene. However, existing fault maps demonstrate little consensus over the location of Neogene basalt flows and relative ages of mapped faults, which complicates interpretations of tectonic model for the evolution of Indochina. This paper identifies discrete tectonic blocks within Vietnam and aims to define the Neogene‐Recent tectonic setting and kinematics of south‐central Vietnam by analyzing the orientation, kinematics, and relative ages of faults across each block. Fault ages and relative timing are estimated using cross‐cutting relationships with dated basalt flows and between slickenside sets. Remote sensing results show distinct fault trends within individual blocks that are locally related to the orientations of the basement‐involved block‐bounding faults. Faults observed in the field indicate an early phase of dip‐slip motion and a later phase of strike‐slip motion, recording the rotation of blocks within a stress field. Faulting after the change in motion of the Red River Fault Zone at ∼16 Ma is inferred, as faults cross‐cut basalt flows as young as ∼0.6 Ma. Strike‐slip motion on block‐bounding faults is consistent with rotation and continuous extrusion of each block within south‐central Vietnam. The rotation of the blocks is attributed to the “continuum rubble” behavior of small crustal blocks influenced by upper mantle flow after the collision between India and Eurasia. We infer a robust lithospheric‐asthenospheric coupling in the extrusion model, which holds implications for other regions experiencing extrusion even in the absence of a free surface.
Tectonics - Tập 43 Số 4 - 2024
Negligible convergence and lithospheric tearing along the Caribbean–South American plate boundary at 64°W Prior studies of the Caribbean–South American plate boundary have suffered from poor constraint on the structure of the crust and uppermost mantle. We use a recent wide‐angle velocity model from the Broadband Ocean‐Land Investigation of Venezuela and the Antilles arc Region project to constrain new seismic reflection data and previously published line drawing interpretations of the Caribbean–South American plate boundary at 64°W. Though commonly characterized as obliquely convergent, we determine that convergence is negligible in our study area. Previous estimates of Miocene to present north‐south shortening onshore eastern Venezuela have commonly been 115 km or higher, but we constrain shortening to ∼35 km onshore, with an additional ∼30 km offshore. With such minor convergence, we conclude that uplift and basin subsidence in eastern Venezuela does not derive from typical collisional orogeny. Instead, the largely vertical tectonics likely result from mantle dynamics associated with an eastward propagating, near‐vertical tear in the lithosphere along the former passive margin.
Tectonics - Tập 27 Số 6 - 2008
Cenozoic collision of the Lesser Antilles Arc and continental South America and the origin of the El Pilar Fault It is proposed that the Cenozoic tectonic record of the southern Lesser Antilles arc and northeastern continental South America can be explained by ongoing right‐oblique collision between the arc and continent. The collision has proceeded by the transport of the leading edge of the arc across the slope and outer shelf of a former north facing passive margin of the South American continent. The overriding began in the study region near the Gulf of Cariaco in eastern Venezuela in late Eocene or Oligocene time and has migrated with a generally SE vector. Suturing has occurred between the arc and continent after the attainment of a critical distance of overlap; today's point of suturing lies in the Paria Peninsula. East of there, overriding continues. Major tectonic elements engaged in or created by the collision are the southern Lesser Antilles magmatic arc, forearc basin, the Araya‐Tobago terrane, a South American foreland thrust and fold belt, and a foreland basin. The Araya‐Tobago terrane is thought to consist of sediments of South American provenance that were accreted to the Lesser Antilles forearc during its transit of an ocean basin and the continental slope and outer shelf. The emplacement of the magmatic arc and the Araya‐Tobago terrane caused tectonic imbrication of shelf strata to propagate ahead of the arc front as a foreland thrust and fold belt. Tectonic loading of the shelf also caused subsidence of a major foreland basin on the continentward side of the thrust belt. It is proposed the El Pilar fault exists between the Gulf of Cariaco and the Paria Peninsula as an active right slip fault but not east of Paria. It is not a throughgoing transform fault between the South American and Caribbean plates. The El Pilar fault exists where the overlapping arc and the continent are sutured and takes up a suture‐parallel component of convergence between arc and continent. The eastern tip of the fault propagates east with the point of suturing. Reconstructions of the Cenozoic collision of the Lesser Antilles arc and the South American continent suggest that the arc lay somewhat north and west of its present position in the Eocene. This conclusion differs from that of plate reconstructions that assume that the arc was the leading edge of a Caribbean plate that has moved east from Pacific longitudes since the Eocene.
Tectonics - Tập 4 Số 1 - Trang 41-69 - 1985
Spectral analysis of gravity anomalies and the architecture of tectonic wedging, NE Venezuela and Trinidad We have analyzed the spectral content of free air gravity anomalies in the Caribbean‐South American plate boundary zone in order to determine better the near‐surface (0–120 km) distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region. The plate boundary zone in northeastern Venezuela and Trinidad is the site of the world's sea level continental minimum of Bouguer gravity anomalies, yet the region is also one of mild topography (mean value 43 m, maximum 1200 m). We find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone. We interpret interfaces at 30–35 km and 32 km beneath the Guyana Shield and the Aves Ridge, respectively, to be the Moho. Other shallow interfaces (5–14 km) are most likely sediment cover‐basement contacts in the Maturin foreland basin and southern Grenada Basin. Deeper interfaces (54–63 km) we associate with loaded and downwarped continental and oceanic South American lithosphere. The deepest boundaries, at depths of 89–120 km, may be related to detached or detaching oceanic lithosphere overridden by continental South America. We use our results to test the tectonic wedging model of the plate boundary zone recently published by Russo and Speed (1992). We find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner Guyana Shield crust.
Tectonics - Tập 13 Số 3 - Trang 613-622 - 1994
Southward extrusion of Tibetan crust and its effect on Himalayan tectonics The Tibetan Plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during India‐Asia collision, and the contrast in potential energy between the Plateau and its surroundings strongly influences the modern tectonics of south Asia. The distribution of potential energy anomalies across the region, derived from geopotential models, indicates that the Himalayan front is the optimal location for focused dissipation of excess energy stored in the Plateau. The modern pattern of deformation and erosion in the Himalaya provides an efficient mechanism for such dissipation, and a review of the Neogene geological evolution of southern Tibet and the Himalaya shows that this mechanism has been operational for at least the past 20 million years. This persistence of deformational and erosional style suggests to us that orogens, like other complex systems, can evolve toward “steady state” configurations maintained by the continuous flow of energy. The capacity of erogenic systems to self‐organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far‐field plate interactions.
Tectonics - Tập 20 Số 6 - Trang 799-809 - 2001
Structure and U/Pb geochronology of Central Hoggar (Algeria): A reappraisal of its Pan‐African evolution Discovery of large‐scale deep‐seated thrusts in Central Hoggar, with a plurifacial evolution ranging from lower amphibolite facies to upper greenschist facies conditions and linked to a regional refoliation, has led us to reconsider the Pan‐African tectonic and metamorphic history in that region. Two areas are described, and a review of other thrusts leads to an interpretative cross section of a large portion of reactivated continental crust. The age and kinematics of this structural reworking have been approached using U/Pb zircon dating in the Tamanrasset region. Despite the difficulty of estimating the age of the initiation of the assumed intracontinental A‐type subduction, the results provide a time span of 30–40 m.y. between the climax of granitoid emplacement and a late retrogressive offset along the thrust planes. Some key ages were determined: (1) 2075 ± 30 Ma is the age given by granulite facies remnants which escaped from the refoliation, the corresponding lower intercept at 530 ± 70 Ma confirms the Pan‐African imprint; (2) 615 ± 5 Ma reflecting the age of syntectonic to late‐tectonic granitoids emplaced in reworked gneisses and in preserved granulites; (3) 580 Ma, the concordant age of sphenes and monazites from the same granitoids, which is interpreted as corresponding to the end of medium‐grade conditions. No evidence has been found of a ∼1000 Ma age: a Kibaran event does not appear to exist in Central Hoggar. The age similarity between the observed deep intracontinental evolution of Central Hoggar and the collision‐related tectonics of Western Hoggar and Iforas suggests a common origin for both phenomena.
Tectonics - Tập 5 Số 7 - Trang 955-972 - 1986
Reconstruction of the Exhumed Mantle Across the North Iberian Margin by Crustal‐Scale 3‐D Gravity Inversion and Geological Cross Section Abstract Recent models support the view that the Pyrenees were formed after the inversion of a previously highly extended continental crust that included exhumed upper mantle rocks. Mantle rocks remain near to the surface after compression and mountain building, covered by the latest Cretaceous to Paleogene sequences. 3‐D lithospheric‐scale gravity inversion demands the presence of a high‐density mantle body placed within the crust in order to justify the observed anomalies. Exhumed mantle, having ~50 km of maximum width, continuously extends beneath the Basque‐Cantabrian Basin and along the northern side of the Pyrenees. The association of this body with rift, postrift, and inversion structural geometries is tested in a balanced cross section across the Basque‐Cantabrian Basin that incorporates a major south‐dipping ramp‐flat‐ramp extensional detachment active between Valanginian and early Cenomanian times. Results indicate that horizontal extension progressed ~48 km at variable strain rates that increased from 1 to ~4 mm/yr in middle Albian times. Low‐strength Triassic Keuper evaporites and mudstones above the basement favor the decoupling of the cover with formation of minibasins, expulsion rollovers, and diapirs. The inversion of the extensional system is accommodated by doubly verging basement thrusts due to the reactivation of the former basin bounding faults in Eocene‐Oligocene times. Total shortening is estimated in ~34 km and produced the partial subduction of the continental lithosphere beneath the two sides of the exhumed mantle. Obtained results help to pinpoint the original architecture of the North Iberian Margin and the evolution of the hyperextended aborted intracontinental basins.
Tectonics - Tập 36 Số 12 - Trang 3155-3177 - 2017
Tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean: Example of the western Pyrenees In this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western Pyrenees. The Labourd‐Mauléon area situated in the western Pyrenees, at the termination of the V‐shaped Bay of Biscay, is an ideal natural laboratory to study how such complex basins evolve in time and space. Because of a mild inversion of the basin during Pyrenean compression, the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field. The basin shows a complex polyphase evolution that starts with left‐lateral dominated transtension in latest Jurassic–early Aptian time. This event is overprinted by a late Aptian–early Albian extension that is related to the counterclockwise rotation of Iberia away from Europe leading to the opening of the Bay of Biscay. During this stage, the Late Triassic to Jurassic carbonate platform was stretched, salt migrated, and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor. The final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by N40° to N60° transfer faults. The sedimentary architecture is characterized by late Aptian synrift sediments (e.g., Urgonian limestones) that were deposited in fault‐bounded basins and are overlain by thick latest Aptian to Albo‐Cenomanian sediments (e.g., Flysch noir) that define a sag sequence. The complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic/thermal event that postdates mantle exhumation.
Tectonics - Tập 28 Số 4 - 2009
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