Tectonic Wedge Research Articles

Three‐Dimensional Model of the Lithospheric Structure Under the Eastern Tibetan Plateau: Implications for the Active Tectonics and Seismic Hazards

AbstractDetails of lithospheric structures in three‐dimensions (3‐D) are key to understanding the dynamics of crustal deformation and earthquakes in active orogenic systems. In this study, we develop a 3‐D model of the eastern Tibetan Plateau using the Skua‐Gocad software based on the latest Rayleigh wave tomography. We perform a quantitative modeling workflow to map the details of the Moho discontinuities and the high‐velocity anomalies. Then, we integrate the topography, major active faults, large earthquakes, and crustal Poisson's ratios to analyze the relationship between the shallow and deep structures of this region. Our study shows that the Moho is generally coupled with the topography. A steep Moho ramp exists under the plateau margin and its surface projection intersects the Longmen Shan (LMS) at a low oblique angle (~22°). Active deformation and large earthquakes are related to the steep Moho ramp under the plateau margin. Moreover, based on a 3‐D model of the Poisson's ratio perturbations, we find that deformation across the central LMS is characterized as a crocodile‐type wedge in the crust and lithospheric mantle, due to the resistance of the Yangtze craton and isostatic rebound. We suggest that a tectonic wedging model that contains both the upper‐crust thrusting and lower‐crustal thickening contribute to the LMS orogeny. Three‐dimensional visualization of the lithospheric structure is well suited to reveal the different levels of deformation and their relationships. Quantitative modeling methods provide effective constraints on the active blocks in the eastern Tibetan Plateau.

New Insights on the Role of the Strike-Slip Tectonics in the Late Miocene-Quaternary Evolution of Sicily

Understanding the influence of the Late Miocene-Quaternary opening of the Tyrrhenian Basin on the evolution of the external sectors of the Africa paleo-margin in Sicily, actually, represents a hard challenge, even though several, and contrasting, models have been proposed in the last decades. One open problem refers to localizing the main regional scale tectonic lineaments of Sicily that accommodated the hundreds of kilometers of lateral displacement, due to the Tyrrhenian Basin opening. In the present work, we present the results rising from a detailed field mapping carried out in relevant vast areas of central Sicily. These data enabled to reconstruct a Neogene-Quarternary kinematic evolutionary model of the collision belt of Sicily. We analyzed the northern tectonic margin of the Caltanissetta Through, which represents a structural depression hosting a thick allochthonous tectonic wedge, on which lay different unconformable thrust-top basin deposits. In more details, our study aims to reconstruct the tectono-sedimentary Late Tortonian-to-Quaternary evolution of this tectonic wedge, revealing that regional E-W-trending dextral shear zones deform and cut the NE-oriented, SE-verging, thrust-and-fold belt. The strike-slip tectonics thus controlled the deposition of different sedimentary cycles on the thrust-top basins and governed the tectonic inversion of the external sectors of the Africa paleo-margin.

Tectonic, eustatic and climatic controls on marginal‐marine sedimentation across a flexural depocentre: Paddy Member of Peace River Formation (Late Albian), Western Canada Foreland Basin

AbstractIn north‐central Alberta and adjacent British Columbia, clastic strata of the middle to late Albian Peace River and Shaftesbury formations were deposited in alluvial to shallow‐marine environments across the foredeep of the Western Canada Foreland Basin. A high‐resolution, log and core‐based allostratigraphic framework for the Paddy Member of the Peace River Formation established nine allomembers, PA to PI, bounded by flooding surfaces and apparently equivalent non‐marine surfaces. Within the estimated 2 Myr. duration of the Paddy, allomembers allow the evolving palaeogeography and changing relationship between accommodation and sedimentation rates to be analysed on time‐steps on the order of 105 years. Paddy strata fill an arcuate depocentre ca 300 km wide, across which the rocks thin eastward from 125 m to ca 5 to 10 m. The northern part of the basin is occupied by muddy, offshore marine deposits that pass abruptly southward into a linear, WSW‐ENE‐trending body of sandstone deposited in a wave‐dominated barrier‐strandplain, at least 350 km long. Extending >200 km to the south of the strandplain was a region of shallow brackish to freshwater lagoons and lakes that graded to the SW into alluvial facies. Within the lagoon region, few‐m thick, elongate and patchy sandstones represent river‐dominated deltas. In allomembers PA to PG, these sandstones are concentrated in the west and south, implying supply from the western Cordillera. In allomembers PH and PI, sandstones are mainly in the east and have a distinctive, quartz‐rich composition. They can be correlated eastward into the coeval Pelican Formation, and were sourced probably from the Canadian Shield on the opposite side of the basin. In the western foredeep, alluvial rocks comprise aggradational, unconfined floodplain deposits with ribbon sandstones, dissected, on at least nine separate levels, by palaeovalleys that are confined to the proximal foredeep. Valleys are 10 to 30 m deep, few km wide, and filled with multi‐storey channel‐bars of pebbly coarse sandstone or conglomerate. Valleys cut down from well‐developed interfluve palaeosols that record a falling and then rising water table. Alternating aggradation and degradation, and advance and retreat of the alluvial gravel front is attributed to cycles of varying rainfall intensity, rather than tectonism or eustasy. Apparently, coeval transgressive‐regressive successions in the lagoon and marine regions are attributed to few‐m scale eustatic changes. On the NE margin of the basin, tidal sandstone fills a northward‐opening estuary cut on the basal Paddy unconformity. This sandstone contains the first well‐documented specimens of Gnesioceramus comancheanus (Cragin), proving contemporaneity with at least part of the marine Joli Fou Formation to the east. Paddy allomembers change shape upward from short blunt wedges, through more acutely tapered wedges, to sheets. This change reflects initially rapid flexural subsidence, attributed to active thickening of the adjacent orogenic wedge. A waning rate of deformation permitted wider dispersal of sediment across the basin, driving broad isostatic subsidence beneath increasingly sheet‐like rock bodies. A major hiatal surface, VE3, records non‐deposition or subtle erosion attributed to erosional unloading and uplift of the adjacent orogen. A subsequent marine transgression is attributed to renewed thickening of the tectonic wedge that triggered deposition of marine mudstone that thickens westward from 0 to >110 m over 300 km. A postulated Milankovitch‐band climatic control on both local gravel supply (via fluctuating rainfall), and shoreline movement (via ?Antarctic glacio‐eustasy or groundwater storage), might account for cycles of alternating incision and aggradation in the alluvial realm. The same mechanism may also explain why shallow‐marine units such as the Cretaceous Viking and Cardium formations contain abundant conglomerate in lowstand shoreface deposits (higher river discharge), yet have highstand shorelines dominated by sandstone (lower river discharge).

Large-Scale Crustal-Block-Extrusion During Late Alpine Collision

The crustal-scale geometry of the European Alps has been explained by a classical subduction-scenario comprising thrust-and-fold-related compressional wedge tectonics and isostatic rebound. However, massive blocks of crystalline basement (External Crystalline Massifs) vertically disrupt the upper-crustal wedge. In the case of the Aar massif, top basement vertically rises for >12 km and peak metamorphic temperatures increase along an orogen-perpendicular direction from 250 °C–450 °C over horizontal distances of only <15 km (Innertkirchen-Grimselpass), suggesting exhumation of midcrustal rocks with increasing uplift component along steep vertical shear zones. Here we demonstrate that delamination of European lower crust during lithosphere mantle rollback migrates northward in time. Simultaneously, the Aar massif as giant upper crustal block extrudes by buoyancy forces, while substantial volumes of lower crust accumulate underneath. Buoyancy-driven deformation generates dense networks of steep reverse faults as major structures interconnected by secondary branches with normal fault component, dissecting the entire crust up to the surface. Owing to rollback fading, the component of vertical motion reduces and is replaced by a late stage of orogenic compression as manifest by north-directed thrusting. Buoyancy-driven vertical tectonics and modest late shortening, combined with surface erosion, result in typical topographic and metamorphic gradients, which might represent general indicators for final stages of continent-continent collisions.

Shortening and structural architecture of the Andean fold-thrust belt of southern Bolivia (21°S): Implications for kinematic development and crustal thickening of the central Andes

Reliable crustal shortening estimates for the central Andes (South America) are a critical component in validating models of Cordilleran processes. In southern Bolivia, insight into crustal shortening and the kinematic development of the Andean thrust belt are limited by the lack of a unified structural evaluation across the entire width of the retroarc region. To address these shortcomings, we (1) estimate crustal shortening by integrating new geologic mapping with published geophysical data to construct a balanced cross section across the Subandean zone (SAZ), Interandean zone (IAZ), and Eastern Cordillera (EC) at 21°S; (2) develop a kinematic model for the retroarc thrust belt; and (3) estimate crustal budgets and average crustal thicknesses over the region. We estimate 337 ± 69 km (36% ± 7%) of total shortening (SAZ, 82 km; IAZ, 70 km; EC, 120 km; Altiplano, 65 km). The thrust belt developed from late Eocene time to the present by tectonic wedging and eastward emplacement of two ∼10–12-km-thick basement thrust sheets that distribute slip into overlying sedimentary rocks. Our range of crustal shortening values can account for 90%–118% of the current retroarc crustal area. Assuming an initial crustal thickness of 35 km, the EC and Altiplano did not achieve modern crustal thicknesses (∼65 km) until the present. However, assuming a 40-km-thick initial crust, the EC and Altiplano attained the critical thickness for either eclogitic phase changes or lower crustal flow (>45–50 km) by ca. 27–25 Ma, modern thicknesses by ca. 10 Ma, and currently exceed geophysically observed thicknesses by ∼2.5–14.5 km; this suggests crustal losses significant enough to have affected hinterland surface elevation.

Basin inversion in tectonic wedges: Insights from analogue modelling and the Alpine-Carpathian fold-and-thrust belt

This work simulates the inversion and incorporation of sub-thrust segmented half-graben basins into tectonic wedges by means of sandbox analogue models. Segmented half-graben basins - striking at 90°, 45° and 15° to the extension direction - were created first, and then shortened using different angles for the basal detachment and topographic slope. A shallow viscous polymer layer located above the half-graben basin was included in one of the models. The experiments were analysed using time-lapse photography, topography laser scans and image-based 3D voxels. The results indicate a deformation sequence characterised by layer-parallel compaction, fault reactivation, thrust propagation and related folding. Fault reactivation was associated with the layer-parallel compaction accomplished by slip along the basal detachment, prior to and in between pulses of thrusting. Results reveal the fundamental control imposed by the vertical load of the tectonic wedge and its integrated strength profile in the inversion of sub-thrust basins. Results are compared to the Alpine-Carpathian fold-and-thrust belt.

Cenozoic history of topography in southeastern Gorny Altai: thermochronology and resistivity and gravity records

The Central Asian Orogen was reactivated in the Cenozoic, which gave rise to mountain systems and sedimentary basins, strike-slip and thrust faults, ramps, and rift basins under the far-field effect of the India-Eurasia collision. Pre-Cenozoic structures, as well as the superposed Cenozoic deformation, are traceable in the gravity pattern. Analysis and correlation of stratigraphic, tectonic, geomorphological, and geophysical (resistivity and gravity) data from Gorny Altai and tectonic modeling on the basis of apatite fission-track thermochronology show that vertical motions have been the most active for the past 5 Ma. The uplift and subsidence produced, respectively, the Chulyshman and Ukok Plateaus with high mountains around and the the Kurai-Chuya basin between them. Gravity data suggest the existence of Late Carboniferous, Jurassic, and Cretaceous rocks found in tectonic wedges around the basin at the base of its sedimentary fill.

The accretion of foreland basin sediments during early stages of continental collision in the European Alps and similarities to accretionary wedge tectonics

AbstractWe present structural observations from foreland basin sediments that were incorporated into the orogenic wedge of the central European Alps during early stages of continental collision. Our analysis focuses on the prograde evolution and considers the full history of the sediments ranging from their deposition in the basin to deep burial and metamorphism at temperatures of ~320°C. The tectonic evolution is matched with constraints on the diagenetic alteration of the sediments. For this purpose, we calculate the temperatures and depths of sediment compaction and illitization as well as the associated fluid liberation. The data set highlights that the tectonic incorporation of the sediments into the orogenic wedge was strongly controlled by their diagenetic state. Earliest deformation took place during imbrication and frontal accretion of unconsolidated and fluid‐saturated sediments. Ductile folding of the sediments occurred already at this stage and was assisted by particulate flow. With the progressive consolidation of the sediments the elastic strength increased, which resulted in an overall embrittlement. This rheological change is recorded by the onset of out‐of‐sequence thrusting, brittle faulting, and the formation of massive quartz‐calcite veins, which took place in the approximate temperature range of the seismogenic zone (i.e., ~150–350°C). Moreover, widespread pressure solution resulted in the formation of a penetrative cleavage and records slow but long‐lasting deformation at low background strain rates. In summary, the prograde tectonic evolution of the frontal Alpine wedge exhibits many similarities with the structural and mechanical evolution of accretionary wedges at active subduction zones.

Alpine tectonic wedging and crustal delamination in the Cantabrian Mountains (NW Spain)

Abstract. The Cantabrian Mountains have been interpreted as a Paleozoic basement block uplifted during an Alpine deformation event that led to the partial closure of the Bay of Biscay and the building of the Pyrenean range in the Cenozoic. A detailed interpretation of deep seismic reflection profile ESCIN-2 and the two-dimensional seismic modelling of the data allowed us to construct a N–S geological cross section along the southern border of the Cantabrian Mountains and the transition to the Duero Cenozoic foreland basin, highlighting the Alpine structure. The proposed geological cross section has been constrained by all geophysical data available, including a 2-D gravity model constructed for this study as well as refraction and magnetotelluric models from previous studies. A set of south-vergent thrusts dipping 30 to 36° to the north, cut the upper crust with a ramp geometry and sole in the boundary with the middle crust. These thrusts are responsible for the uplift and the main Alpine deformation in the Cantabrian Mountains. A conspicuous reflective Moho shows that the crust thickens northwards from the Duero basin, where subhorizontal Moho is 32 km deep, to 47 km in the northernmost end of ESCIN-2, where Moho dips to the north beneath the Cantabrian Mountains. Further north, out of the profile, Moho reaches a maximum depth of 55 km, according to wide-angle/refraction data. ESCIN-2 indicates the presence of a tectonic wedge of the crust of the Cantabrian margin beneath the Cantabrian Mountains, which is indented from north to south into the delaminated Iberian crust, forcing its northward subduction.

Crustal structure beneath the Blue Mountains terranes and cratonic North America, eastern Oregon, and Idaho, from teleseismic receiver functions

AbstractWe present new images of lithospheric structure obtained from P‐to‐S conversions defined by receiver functions at the 85 broadband seismic stations of the EarthScope IDaho‐ORegon experiment. We resolve the crustal thickness beneath the Blue Mountains province and the former western margin of cratonic North America, the geometry of the western Idaho shear zone (WISZ), and the boundary between the Grouse Creek and Farmington provinces. We calculated P‐to‐S receiver functions using the iterative time domain deconvolution method, and we used the H‐k grid search method and common conversion point stacking to image the lithospheric structure. Moho depths beneath the Blue Mountains terranes range from 24 to 34 km, whereas the crust is 32–40 km thick beneath the Idaho batholith and the regions of extended crust of east‐central Idaho. The Blue Mountains group Olds Ferry terrane is characterized by the thinnest crust in the study area, ~24 km thick. There is a clear break in the continuity of the Moho across the WISZ, with depths increasing from 28 km west of the shear zone to 36 km just east of its surface expression. The presence of a strong midcrustal converting interface at ~18 km depth beneath the Idaho batholith extending ~20 km east of the WISZ indicates tectonic wedging in this region. A north striking ~7 km offset in Moho depth, thinning to the east, is present beneath the Lost River Range and Pahsimeroi Valley; we identify this sharp offset as the boundary that juxtaposes the Archean Grouse Creek block with the Paleoproterozoic Farmington zone.

Seismic reflection patterns associated with continental convergent margins through time

The important role of tectonic wedging in accommodating horizontal shortening strain is increasingly recognized to occur at all scales within continental convergence zones. Wedge structures appear most common in accretionary orogens involving former passive margins with large-volume turbidite sedimentary fans or accretionary prisms. Relatively small-scale wedges can be recognized in outcrop, but crustal scale wedge geometries must be observed and analysed using seismic reflection methods. Reflection profiles now exist across a large number of accretionary orogen settings of diverse ages and continents. Similarities in seismic patterns within the major eras enable creation of a series of stylised continental margin transects for each major time period. Relatively low rock strength found in turbidite sediments rich in micas, especially when contrasted with strengths of igneous volcanic arc rocks, plays a major role because it localizes thrust faults within weaker horizons. Schematic cross sections across accretionary margins that span five geological eras summarize the principal features interpreted on numerous seismic reflection sections. Important details vary, such as the depths where tectonic wedging initiates, but tectonic wedges of diverse scales are observed in all cross sections. The percentage and degree of consolidation or metamorphism of turbiditic greywackes apparently controls the degree, depth and scale of the crustal wedging.

Sea–land geology of Marettimo (Egadi Islands, central Mediterranean sea)

ABSTRACTWe present a 1:10,000 scale geological map of Marettimo Island and its offshore (Egadi Archipelago, central Mediterranean Sea). The map was achieved by integrating a new geological survey with data from recent, marine, geological and geophysical surveys acquired along the adjacent continental shelf. The island is composed of a Mesozoic, mostly carbonate platform succession, which is overlain by continental to coastal marine Quaternary deposits. Extensional tectonics have affected the carbonate platform since the Late Triassic producing an initial increase of accommodation space that was filled by interbed breccias, marls and calcareous marls. During the Jurassic, a NE-SW-directed normal fault-bounded structural lows where thick beds of megabreccias accumulated followed upwards by cherty limestone and bedded cherts. During the building of the chain, the compressional tectonics generated a southeast-verging tectonic wedge, displaced by subsequent transpression. During the Quaternary, repeated sea-level changes shaped a rough erosional surface along the inner shelf and controlled the lateral facies variation of the continental and marine coastal deposits along the present day coastline.

Extrusion vs. duplexing models of Himalayan mountain building 2: The South Tibet detachment at the Dadeldhura klippe

Himalayan mountain building has been dominantly explained by two types of models: extrusion and duplexing. To elucidate possible roles of these mechanisms during emplacement of the Himalayan crystalline core, we investigate an area speculated to contain the southern leading edge of the crystalline core: the northeastern margin of the Dadeldhura klippe, western Nepal. We found an ~700m thick, primarily top-to-the-north shear zone within the klippe; we term this as the Tila shear zone. The shear zone occurs within a right-way-up metamorphic field gradient, and separates footwall gneiss from hanging wall schist. Similarly, deformation temperatures estimated from quartz and feldspar microstructures and quartz c-axis fabrics indicate a right-way-up thermal gradient of ~77–189°C/km. U–Pb zircon dating of post-kinematic leucogranite dikes suggests that ductile shearing along the Tila shear zone occurred prior to ~17–14Ma. We correlate the Tila shear zone to the South Tibet detachment (STD) on the basis of consistent structural fabrics (shear sense), lithologies, metamorphism, and deformation timing. This interpretation, in combination with regional constraints, indicates southwards-increasing proximity of the STD (Tila shear zone) and the Main Central thrust (MCT). These two shear zones are separated by ~3km of structural section in the northern portion of our study area, and become close to within ~1km of separation, in the southern portion. Interpolation suggests that the STD (Tila shear zone) and MCT merge 15±10km southwest of our study area. The increasing-to-south proximity and potential merger of the two shear zones suggest that the STD formed as a backthrust from the MCT. This interpretation contrasts with the long-standing normal fault interpretation of the STD. Because the STD and MCT bound the Himalayan crystalline core, these findings document crystalline core emplacement at depth via tectonic wedging. This kinematic evolution is consistent with duplexing, but not extrusion to the surface.

Crustal-scale tectonic wedging in the central Longmen Shan: Constraints on the uplift mechanism in the southeastern margin of the Tibetan Plateau

This study focuses on the upper–middle crust (UMC) deformation in the central Longmen Shan (LMS). The results of this study are constrained by the surface geology, typical seismic reflection profiles, previously available thermochronology, and deep geophysical data. Regional seismic profiles demonstrate a strata dip of about 2°, northwest trending, from the Sichuan Basin (SB) to LMS. The interpretation of shallow artificial seismic reflection data indicates that an unknown basement structure lead to the uplifting of the sedimentary cover by 3–4km. A long and wide-angle reflection seismic profile presents evidence that the middle crustal-scale structure is involved in the deformation. Geophysical data support that there is an upper detachment (D1) at the depth of ∼20km. The other lower detachment (D2) could be generated at approximately 30–40km depth in the low velocity zone. The ductile middle crust between the D1 and D2, has shortening and forming a wedge tip beneath the transition zone of the LMS and the SB. The deformation of the LMS frontal monocline belt is related to this crustal-scale wedging. Two different tectonic stages are distinguished in the Cenozoic through the axial surface analysis and chronological data. During the first stage, the crustal-scale tectonic wedge was developed between the upper and lower detachment, resulting in the uplift of the UMC. During the second stage, the middle crust could hardly be extruding and uplifting. The brittle upper crust was rapidly uplifted and shortened by the shallow major thrusts, which were developed on the D1. The D1 and D2 controlled the uplifting and shortening in the southeastern margin of the Tibetan Plateau. The lower crust (LC) may be decoupled from the D2 and subducted due to the resistance by the stable craton underlying the SB. The structural model manifests the importance of multi-detachments and the superimposed deformation in the LMS thrust belt. However, we emphasize that this crustal-scale tectonic wedging only discovered in the central LMS. The tectonic wedge is an important uplifting pattern that should be not neglected.

Fault strength in thin-skinned tectonic wedges across the smectite-illite transition: Constraints from friction experiments and critical tapers

The strength, shape, and ultimately seismic behavior of many thin-skinned fold and thrust belts, including marine accretionary wedges, are strongly controlled by large-scale faults that develop from weak, clay-rich sedimentary horizons (decollements). The increase of temperature with depth along clay-rich faults promotes the so-called smectite-illite transition, which may influence the fault strength, fluid distribution, and possibly the onset of seismicity. Here we report on the frictional properties of intact fault rocks retrieved from two large decollements, which were exhumed from depths above and below the smectite-illite transition. We find that all tested rocks are characterized by very low friction (μ = 0.17–0.26), velocity-strengthening behavior, and low rates of frictional healing, suggesting long-term fault weakness. Combining our experimental results with the critical taper theory, we computed the effective friction, F , of megathrusts beneath several accretionary wedges around the world; the result was extremely low (0.03 < F < 0.14), and in agreement with other independent estimates. Our analysis indicates a long-term weakness that can explain the shape of several tectonic wedges worldwide without invoking diffuse near-lithostatic fluid overpressures.

Subduction or delamination beneath the Apennines? Evidence from regional tomography

Abstract. In this study we present a new regional tomography model of the upper mantle beneath Italy and the surrounding area derived from the inversion of travel times of P and S waves from the updated International Seismological Centre (ISC) catalogue. Beneath Italy, we identify a high-velocity anomaly which has the appearance of a long, narrow "sausage" with a steeply dipping part down to a depth of 400 km and then expanding horizontally over approximately 400 km. Rather than to interpret it as a remnant of the former Tethyan oceanic slab, we consider that it is made up of the infra continental lithospheric mantle of Adria, which is progressively delaminated, whereas its overlying crust becomes progressively accreted into the Apenninic tectonic wedge.

On a new law of faulting along tectonic wedges: Cosserat explanation of the preferred (paleo)stress states in the Earth's crust

Cosserat extension of the Gauss stress-strain inversion method and multiple-slip method (MSM) are used to analyse 18 examples of natural wedge faulting observed in Slovenia. Based on additional numerical tests we show that kinematic incompatibility of slip along intersecting faults (wedges) has a significant effect on the state of stress in the Earth's crust. The slip direction along intersecting faults (wedges) can only be subparallel to the intersection direction between the faults. The normal stress on the wedges is then equal to the intermediate principal stress (eigenvalue) of the symmetric part of the stress tensor. This equality is very fundamental and could potentially be interpreted as a new law of faulting along tectonic wedges and non-planar faults. In the Cosserat theory of wedge faulting we also define two stress criteria, these are the weak and the strong stress conditions. The weak stress condition is related to the frictional reactivation of the wedges. It defines two limit values of the stress parameter and intermediate principal stress of the symmetric part of the stress tensor. The strong stress condition is related to the brittle faulting along tectonic wedges. It relates the angle of internal friction to the value of the stress parameter and the intermediate principal stress of the symmetric part of the stress tensor. For the value of the angle of internal friction larger than zero, the stress parameter is less than 0.5, which is in agreement with numerical and empirical observations described in this paper.

Early- to mid-Silurian extrusion wedge tectonics in the central Scandinavian Caledonides

Research Article| April 01, 2015 Early- to mid-Silurian extrusion wedge tectonics in the central Scandinavian Caledonides Jens C. Grimmer; Jens C. Grimmer 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Search for other works by this author on: GSW Google Scholar Johannes Glodny; Johannes Glodny 2Inorganic and Isotope Geochemistry Section, Chemistry of the Earth Department, GFZ German Research Centre for Geosciences, D-14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Kirsten Drüppel; Kirsten Drüppel 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Search for other works by this author on: GSW Google Scholar Reinhard O. Greiling; Reinhard O. Greiling 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Search for other works by this author on: GSW Google Scholar Agnes Kontny Agnes Kontny 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Jens C. Grimmer 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Johannes Glodny 2Inorganic and Isotope Geochemistry Section, Chemistry of the Earth Department, GFZ German Research Centre for Geosciences, D-14473 Potsdam, Germany Kirsten Drüppel 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Reinhard O. Greiling 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Agnes Kontny 1Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany Publisher: Geological Society of America Received: 09 Nov 2014 Revision Received: 23 Jan 2015 Accepted: 27 Jan 2015 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (4): 347–350. https://doi.org/10.1130/G36433.1 Article history Received: 09 Nov 2014 Revision Received: 23 Jan 2015 Accepted: 27 Jan 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jens C. Grimmer, Johannes Glodny, Kirsten Drüppel, Reinhard O. Greiling, Agnes Kontny; Early- to mid-Silurian extrusion wedge tectonics in the central Scandinavian Caledonides. Geology 2015;; 43 (4): 347–350. doi: https://doi.org/10.1130/G36433.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We present evidence for an extrusion wedge in the Scandian fold-thrust belt of the central Scandinavian Caledonides (Seve nappe complex). Rb-Sr multimineral geochronology in synkinematic assemblages indicates simultaneous movements at the normal-sense roof shear zone and at the reverse-sense floor shear zone between 434 Ma and 429 Ma. A Sm-Nd age of 462 Ma from a mylonitic garnet mica schist documents prograde garnet growth and possible incipient subduction. Pressure-temperature pseudosection calculations provide evidence for eclogite facies metamorphic conditions and nearly isothermal decompression at ∼670 ± 50 °C from 17.5 to 14.5 kbar in garnet-kyanite mica schists during reverse-sense shearing, and from 15 to 11 kbar in garnet mica schists during normal-sense shearing. These data and the presence of decompression-related pegmatites dated at 434 Ma and 429 Ma indicate that the Seve nappes form a large-scale extrusion wedge. This wedge extends along strike for at least 150 km and marks an early stage of ultrahigh-pressure metamorphism, exhumation, and orogenic wedge formation in this part of the Scandinavian Caledonides predating the major, post–415 Ma ultrahigh-pressure exhumation processes in southwestern Norway. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The role of fluid pressure in contractional systems: examples from the Southern Canadian Rocky Mountains

Abstract Fold and thrust belts are contractional systems created by tectonic plate collisions, creating stress conditions where the maximum principal stress is horizontal and the minimum principal stress is vertical. The stress orientation favours the development of low-angle reverse faults. The trigger mechanism for thrust activation as a recurring seismic event is related to fluctuations in fluid pressure. The fluctuating fluid pressure creates a temporal cycle of elevated and relaxed fluid pressure that shifts the system in and out of failure conditions. The generation of hydrocarbons from organic material is a source of fluids and a means of temporally fluctuating the fluid pressure. In the southern Canadian Rocky Mountains the major detachments follow organic-rich strata that have generated hydrocarbons. The nature of the fluids impacts the size and distributions of faults within the tectonic wedge. The critical taper of the wedge is modified by the presence of high fluid pressure.

Extrusion vs. duplexing models of Himalayan mountain building 3: duplexing dominates from the Oligocene to Present

The Himalaya is a natural laboratory for studying mountain-building processes. Concepts of extrusion and duplexing have been proposed to dominate most phases of Himalayan evolution. Here, we examine the importance of these mechanisms for the evolution of the Himalayan crystalline core via an integrated investigation across the northern Kathmandu Nappe. Results reveal that a primarily top-to-the-north shear zone, the Galchi shear zone, occurs structurally above and intersects at depth with the Main Central thrust (MCT) along the northern flank of the synformal Kathmandu Nappe. Quartz c-axis fabrics confirm top-to-the-north shearing in the Galchi shear zone and yield a right-way-up deformation temperature field gradient. U-Pb zircon dating of pre-to-syn- and post-kinematic leucogranites demonstrates that the Galchi shear zone was active between 23.1 and 18.8 Ma and ceased activity before 18.8–13.8 Ma. The Galchi shear zone is correlated to the South Tibet detachment (STD) via consistent structural fabrics, lithologies, metamorphism, and timing for four transects across the northern margin of the Kathmandu Nappe. These findings are synthesized with literature results to demonstrate (1) the broad horizontality of the STD during motion and (2) the presence of the MCT-STD branch line along the Himalayan arc. The branch line indicates that the crystalline core was emplaced at depth via tectonic wedging and/or channel tunnelling-type deformation. We proceed to consider implications for the internal development of the crystalline core, particularly in the light of discovered tectonic discontinuities therein. We demonstrate the possibility that the entire crystalline core may have been developed via duplexing without significant channel tunnelling, thereby providing a new end-member model. This concept is represented in a reconstruction showing Himalayan mountain-building via duplexing from the Oligocene to Present.