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Thrusting Events (thrusting + event)
Selected AbstractsThe processes of underthrusting and underplating in the geologic record: structural diversity between the Franciscan Complex (California), the Kodiak Complex (Alaska) and the Internal Ligurian Units (Italy)GEOLOGICAL JOURNAL, Issue 2 2009F. Meneghini Abstract Existing studies on active subduction margins have documented the wide diversity in structural style between accretionary prisms, both in space and time. Together with physical boundary conditions of the margins, the thickness of sedimentary successions carried by the lower plate seems to play a key role in controlling the deformation and fluid flow during accretion. We have tested the influence of the subducting sedimentary section by comparing the structural style and fluid-related structures of four units from three fossil accretionary complexes characterized by similar physical conditions but different subducting sediment thicknesses: (1) the Franciscan Complex of California, (2) the Internal Ligurian Units of Italy and (3) the Kodiak Complex, Alaska. Subducting plates bearing a thick sedimentary cover generally result in coherent accretion through polyphase deformation represented by folding and thin thrusting events, while underplating of sediment-starved oceanic sections results in diffuse deformation and mélange formation. These two structural styles can alternate through time in a single complex with a long record of accretion such as Kodiak. The parallel analysis of the selected analogues show that although the volume of sediments carried by the lower plate determines different structural styles, deformation is strongly controlled by injection of overpressured fluids during underthrusting and accretion. Transient hydrofracturing occurs through the development of a system of dilatant fractures grossly parallel to the décollement zone. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ground penetrating radar survey and stratigraphic interpretation of the Plan du Lac rock glaciers, Vanoise Massif, northern French AlpsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2008Sébastien Monnier Abstract Internal boundaries of the Plan du Lac rock glaciers in the northern French Alps were investigated using ground-penetrating radar (GPR) and were correlated with the surface morphology. Data collected using 50,MHz antennae along three profiles were processed in a novel manner by applying modulated automatic gain control to discriminate reflection events according to coherence and continuity patterns. Based on the GPR and morphological analyses, the stratigraphy appears complex, with prominent internal boundaries dividing the features into several depositional units, interpreted as sequential creeping or thrusting events. Copyright © 2008 John Wiley & Sons, Ltd. [source] Linkage of Sevier thrusting episodes and Late Cretaceous foreland basin megasequences across southern Wyoming (USA)BASIN RESEARCH, Issue 4 2005Shao-Feng Liu ABSTRACT Deposition and subsidence analysis, coupled with previous structural studies of the Sevier thrust belt, provide a means of reconstructing the detailed kinematic history of depositional response to episodic thrusting in the Cordilleran foreland basin of southern Wyoming, western interior USA. The Upper Cretaceous basin fill is divided into five megasequences bounded by unconformities. The Sevier thrust belt in northern Utah and southwestern Wyoming deformed in an eastward progression of episodic thrusting. Three major episodes of displacement on the Willard-Meade, Crawford and ,early' Absaroka thrusts occurred from Aptian to early Campanian, and the thrust wedge gradually became supercritically tapered. The Frontier Formation conglomerate, Echo Canyon and Weber Canyon Conglomerates and Little Muddy Creek Conglomerate were deposited in response to these major thrusting events. Corresponding to these proximal conglomerates within the thrust belt, Megasequences 1, 2 and 3 were developed in the distal foreland of southern Wyoming. Two-dimensional (2-D) subsidence analyses show that the basin was divided into foredeep, forebulge and backbulge depozones. Foredeep subsidence in Megasequences 1, 2 and 3, resulting from Willard-Meade, Crawford and ,early' Absaroka thrust loading, were confined to a narrow zone in the western part of the basin. Subsidence in the broad region east of the forebulge was dominantly controlled by sediment loading and inferred dynamic subsidence. Individual subsidence curves are characterized by three stages from rapid to slow. Controlled by relationships between accommodation and sediment supply, the basin was filled with retrogradational shales during periods of rapid subsidence, followed by progradational coarse clastic wedges during periods of slow subsidence. During middle Campanian time (ca. 78.5,73.4 Ma), the thrust wedge was stalled because of wedge-top erosion and became subcritical, and the foredeep zone eroded and rebounded because of isostasy. The eroded sediments were transported far from the thrust belt, and constitute Megasequence 4 that was mostly composed of fluvial and coastal plain depositional systems. Subsidence rates were very slow, because of post-thrusting rebound, and the resulting 2-D subsidence was lenticular in an east,west direction. During late Campanian to early Maastrichtian time, widespread deposits of coarse sediment (the Hams Fork Conglomerate) aggraded the top of the thrust wedge after it stalled, prior to initiation of ,late' Absaroka thrusting. Meanwhile Megasequence 5 was deposited in the Wyoming foreland under the influence of both the intraforeland Wind River basement uplift and the Sevier thrust belt. [source] Thrusting and Exhumation Processes of a Bounding Mountain Belt: Constraints from Sediment Provenance Analysis of the Hefei BasinACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2001LIU Shaofeng Abstract Lithic (or gravel) composition analyses of the Jurassic Sanjianpu Formation and Fenghuangtai Formation in the Hefei basin show that the sediment provenance consists mainly of four kinds of rock units: the basement metamorphic complex, granitic rocks, medium- and low-grade metamorphic rocks, and sandy and muddy sedimentary rocks, which are distributed along the bounding thrust belt. The whole stratigraphic section can be divided into 2 lithic sequences and 7 subsequences. The regular distribution and changes of lithic fragments and gravels in lithic (or gravel) sequences reflect that the bounding thrust belt of basin has undergone 2 thrusting cycles and 7 thrusting events. Lithic (or gravel) composition analyses of the basin fully reveal that the northern Dabie basement metamorphic complex was exhumed on the earth's surface in the Middle and Late Jurassic, and extensive intermediate and acid intrusive rocks were developed in the southern North Huaiyang or northern Dabie Mountains during the basin's syndepositional stage. [source] | ||||||||||