scholarly journals Control of Permian and Triassic faults on Alpine basement deformation in the Argentera massif (external southern French Alps)

2003 ◽  
Vol 174 (5) ◽  
pp. 481-496 ◽  
Author(s):  
Jean Delteil ◽  
Jean-François Stephan ◽  
Mikaël Attal
Keyword(s):  
Sedimentary Cover ◽  
Lower Triassic ◽  
Structural Investigations ◽  
French Alps ◽  
Blind Thrust ◽  
Thrust System ◽  
Block Pattern ◽  
Heterogeneous Deformation ◽  
Basement Deformation ◽  
Compressional Strain

Abstract Structural investigations reveal intense and heterogeneous deformation of the sedimentary cover attached to the basement complex of the southern Argentera and Barrot massifs (southernmost External Basement Massifs of the French Alps). Permian and early Triassic syn-depositional extensional tectonics imparted a tilted block pattern to the massifs. An early Miocene first stage of Alpine compression caused pervasive cleavage. This cleavage was controlled by the former pre-existing faults but is nevertheless consistent with NNE contraction. Where regional shortening is orthogonal to the trend of pre-existing faults the pervasive deformation produced either irrotational compressional strain (where no fault inversion occurred), or rotational compressional strain involving syn-cleavage shearing (where faults with favorable paleo-dip were inverted). Where the shortening direction is oblique to the paleo-fault trends, a component of strike-slip movement may locally prevail. A 22 %, N020o directed horizontal shortening, of 11 km, has been calculated based on deformed sedimentary markers in the Permian series and parallel folds in Lower Triassic quartzite. A shallower deformation as brittle reverse faults postdates the cleavage at the southwestern tip of the Argentera Massif and accounts for 4 km of extra shortening. Both types of deformation are connected at depth to a crustal blind thrust system and the Argentera Massif is over-thrust to the south-southwest. The observed strain indicates the Argentera Massif area underwent, from earliest Miocene to Present, a NNE to N rotating compression at distance from the left-lateral southwestern boundary of the Adria block.

scholarly journals Hillslope denudation and morphologic response to a rock uplift gradient

2020 ◽  
Vol 8 (2) ◽  
pp. 221-243 ◽  
Author(s):  
Vincent Godard ◽  
Jean-Claude Hippolyte ◽  
Edward Cushing ◽  
Nicolas Espurt ◽  
Jules Fleury ◽  
...  
Keyword(s):  
High Resolution ◽  
Strong Dependence ◽  
Digital Terrain Model ◽  
Slip Rate ◽  
Joint Analysis ◽  
Deformation Model ◽  
Base Level ◽  
Denudation Rates ◽  
Blind Thrust ◽  
Thrust System

Abstract. Documenting the spatial variability of tectonic processes from topography is routinely undertaken through the analysis of river profiles, since a direct relationship between fluvial gradient and rock uplift has been identified by incision models. Similarly, theoretical formulations of hillslope profiles predict a strong dependence on their base-level lowering rate, which in most situations is set by channel incision. However, the reduced sensitivity of near-threshold hillslopes and the limited availability of high-resolution topographic data has often been a major limitation for their use to investigate tectonic gradients. Here we combined high-resolution analysis of hillslope morphology and cosmogenic-nuclide-derived denudation rates to unravel the distribution of rock uplift across a blind thrust system at the southwestern Alpine front in France. Our study is located in the Mio-Pliocene Valensole molassic basin, where a series of folds and thrusts has deformed a plateau surface. We focused on a series of catchments aligned perpendicular to the main structures. Using a 1 m lidar digital terrain model, we extracted hillslope topographic properties such as hilltop curvature CHT and nondimensional erosion rates E∗. We observed systematic variation of these metrics coincident with the location of a major underlying thrust system identified by seismic surveys. Using a simple deformation model, the inversion of the E∗ pattern allows us to propose a location and dip for a blind thrust, which are consistent with available geological and geophysical data. We also sampled clasts from eroding conglomerates at several hilltop locations for 10Be and 26Al concentration measurements. Calculated hilltop denudation rates range from 40 to 120 mm kyr−1. These denudation rates appear to be correlated with E∗ and CHT that were extracted from the morphological analysis, and these rates are used to derive absolute estimates for the fault slip rate. This high-resolution hillslope analysis allows us to resolve short-wavelength variations in rock uplift that would not be possible to unravel using commonly used channel-profile-based methods. Our joint analysis of topography and geochronological data supports the interpretation of active thrusting at the southwestern Alpine front, and such approaches may bring crucial complementary constraints to morphotectonic analysis for the study of slowly slipping faults.

Rift inheritance controls the switch from thin- to thick-skinned thrusting and basal décollement re-localization at the subduction-to-collision transition

2021 ◽  
Author(s):  
Stefano Tavani ◽  
Pablo Granado ◽  
Amerigo Corradetti ◽  
Giovanni Camanni ◽  
Gianluca Vignaroli ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Complete Removal ◽  
Lower Plate ◽  
Accretionary Wedge ◽  
Convergent Margins ◽  
Middle Crust ◽  
Rifted Margins ◽  
Thrust System ◽  
Structural Levels ◽  
Rifted Margin

In accretionary convergent margins, the subduction interface is formed by a lower plate décollement above which sediments are scraped off and incorporated into the accretionary wedge. During subduction, the basal décollement is typically located within or at the base of the sedimentary pile. However, the transition to collision implies the accretion of the lower plate continental crust and deformation of its inherited rifted margin architecture. During this stage, the basal décollement may remain confined to shallow structural levels as during subduction or re-localize into the lower plate middle-lower crust. Modes and timing of such re-localization are still poorly understood. We present cases from the Zagros, Apennines, Oman, and Taiwan belts, all of which involve a former rifted margin and point to a marked influence of inherited rift-related structures on the décollement re-localization. A deep décollement level occurs in the outer sectors of all of these belts, i.e., in the zone involving the proximal domain of pre-orogenic rift systems. Older—and shallower—décollement levels are preserved in the upper and inner zones of the tectonic pile, which include the base of the sedimentary cover of the distal portions of the former rifted margins. We propose that thinning of the ductile middle crust in the necking domains during rifting, and its complete removal in the hyperextended domains, hampered the development of deep-seated décollements during the inception of shortening. Progressive orogenic involvement of the proximal rift domains, where the ductile middle crust was preserved upon rifting, favors its reactivation as a décollement in the frontal portion of the thrust system. Such décollement eventually links to the main subduction interface, favoring underplating and the upward motion of internal metamorphic units, leading to their final emplacement onto the previously developed tectonic stack.

scholarly journals Co-Seismic Deformation and Fault Slip Model of the 2017 Mw 7.3 Darbandikhan, Iran–Iraq Earthquake Inferred from D-InSAR Measurements

2019 ◽  
Vol 11 (21) ◽  
pp. 2521 ◽  
Author(s):  
Zicheng Huang ◽  
Guohong Zhang ◽  
Xinjian Shan ◽  
Wenyu Gong ◽  
Yingfeng Zhang ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Sedimentary Cover ◽  
Historical Seismicity ◽  
Crystalline Basement ◽  
Geometrical Parameters ◽  
Seismic Zone ◽  
Seismogenic Fault ◽  
Long Distance ◽  
Blind Thrust ◽  
Seismic Deformation

The 12 November 2017 Darbandikhan earthquake (Mw 7.3) occurred along the converence zone. Despite the extensive research on this earthquake, none of this work explained whether this earthquake rupture was limited to the thick sedimentary cover or it extends to the underlying crystalline basement rock (or both). Besides, whether this region will generate devastating earthquakes again and whether there is a one-to-one correlation between these anticlines and blind-reverse faults need further investigation. In this study, we derived the co-seismic interferograms from the Sentinel-1A/B data and successfully described the surface deformation of the main seismic zone. The fringe patterns of both the ascending and descending interferograms show that the co-seismic deformation is dominated by horizontal movements. Then, using the along- and across-track deformation fields of different orbits, we retrieved the three-dimensional deformation field, which suggests that the Darbandikhan earthquake may be a blind thrust fault close to the north–south direction. Finally, we inverted the geometrical parameters of the seismogenic fault and the slip distribution of the fault plane. The results show that the source fault has an average strike of 355.5° and a northeast dip angle of −17.5°. In addition, the Darbandikhan earthquake has an average rake of 135.5°, with the maximum slip of 4.5 m at 14.5 km depth. On the basis of the derived depth and the aftershock information provided by the Iranian Seismological Center, we inferred that this event primarily ruptured within the crystalline basement and the seismogenic fault is the Zagros Mountain Front Fault (MFF). The seismogenic region has both relatively low historical seismicity and convergent strain rate, which suggests that the vicinity of the epicenter may have absorbed the majority of the energy released by the convergence between the Arabian and the Eurasian plates and may generate Mw > 7 earthquakes again. Moreover, the Zagros front fold between the Lurestan Arc and the Kirkuk Embayment may be generated by the long-distance slippage of the uppermost sedimentary cover in response to the sudden shortening of the MFF basement. We thus conclude that the master blind thrust may control the generation of the Zagros front folding.

Rediscovery of a major alpine thrust : the Helvetic Basal Decollement

2021 ◽  
Author(s):  
Antoine Mercier ◽  
Philippe Hervé Leloup ◽  
Gabriel Courrioux ◽  
Séverine Caritg ◽  
Simon Lopez ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Sedimentary Cover ◽  
Western Alps ◽  
European Alps ◽  
The North ◽  
Deformation Phase ◽  
Thrust Sheets ◽  
Thrust System ◽  
Lithosphere Deformation ◽  
Natural Laboratory

<p>Since two centuries the European Alps are a natural laboratory to study continental lithosphere deformation during mountain building. Since the early studies, a constant question has been to evaluate the importance of vertical versus horizontal displacements in the building of reliefs. Whilst the occurrence of large thrust sheets, as initially proposed from field observations, are now well explained in the frame of plate tectonics, controversies still arise on the precise geometry, amount, and timing of major thrusting during the orogeny.</p><p>We present a new detailed 3D structural study of the cover/basement relationships in the Chamonix synclinorium in between the Mont-Blanc (MB) and Aiguilles Rouges (AR) ranges. These massifs are two of the main external basement ranges of the western Alps.  The study allows deciphering the area structural history: the Mesozoic sedimentary cover has been thrust at least 10km NW above the Helvetic Basal Décollement (HBD) before to be offset by late steep thrusts during exhumation in the Miocene.</p><p>Such interpretation fundamentally diverges from the classical view of the sedimentary cover of the Chamonix synclinorium being expulsed from a former graben during a single deformation phase and implies that a major thrust phase lasting ~10 Ma has been overlooked. Our observations show that the HBD was a major thrust system active between ~30 and ~20 Ma, possibly until 15 Ma, with a shortening of more than 10km in the south to 20km in the north. It extends below most of the subalpine ranges and emerges in front of the Bauges and within the Chartreuse and Vercors massifs, and was rooted east of the External Cristalline Massifs (Mont-Blanc and Belledonne). During the Miocene, the HBD was cut by steep reverse faults and uplifted above the basement culmination of the External Cristalline Massifs obscuring its continuity and precluding its recognition as a major structure even if it was previously described at several localities.</p>

Basement-controlled Neogene polyphase cover thrusting and basin development along the Chianti Mountains ridge (Northern Apennines, Italy)

1999 ◽  
Vol 136 (2) ◽  
pp. 133-152 ◽  
Author(s):  
MARCO BONINI
Keyword(s):  
Sedimentary Cover ◽  
Normal Fault ◽  
Northern Apennines ◽  
Fault System ◽  
Time Interval ◽  
Tectonic Structures ◽  
Quaternary Period ◽  
Deformation Stages ◽  
Thrust System ◽  
Continental Basin

The Chianti Mountains is an important sector of an E-verging regional thrust-related fold (the so-called Tuscan Nappe) extending along the whole length of the Northern Apennines. This thrust system involves the Tuscan Sequence superposing the Macigno sandstones onto Cervarola-Falterona sandstones, both of which are sedimented in adjacent foredeep basins. Detailed field mapping and analysis of superposition relations among tectonic structures, as well as correlation between structures and syntectonic deposition, has allowed Chianti Mountain evolution to be interpreted in terms of three main stages of deformation.The D1 stage resulted in the NE-directed synsedimentary thrusting of the Macigno onto the Cervarola-Falterona sandstones, while large NE to ENE-vergent thrust-related folds developed during the two successive deformation stages (D2 and D3). Fault-propagation folds developed during the D2 stage, and were affected by the Main Chianti Mountains Thrust (MCMT) during the successive D3 stage. In particular, the D3 stage has been correlated to the development, during the Pliocene period, of the hinterland Upper Valdarno Basin, which was previously considered to be an extensional basin. In fact, this continental basin formed along the eastern margin of the Chianti Mountains, ahead of the MCMT that also produced a shortening of the basin fill. With the beginning of the Quaternary period, the tectonic regime switched to extensional, as manifested by the development of a normal fault system on the opposite basin margin.The data presented here allow us to infer that the Chianti Mountains thrust system (D2 and D3) developed during a time interval spanning from the Late Miocene (∼12 Ma) until the Late Pliocene (∼2 Ma) periods. In the Northern Apennines, polyphase thrusting recorded by cover rocks has been related to the activity of basement thrusts, which have been recently evidenced by geophysical data. In this context, the two latest stages of deformation recognised in the Chianti Mountains have been attributed to the activity of the Abetone–Cetona crustal thrust, the deformational effects of which propagated forward in the sedimentary cover.

Chemical and structural analysis of proposed ca. 3.7 Ga stromatolites from the Isua Supracrustal Belt (West Greenland) - a reappraisal

2020 ◽  
Author(s):  
Mike Zawaski ◽  
Nigel Kelly ◽  
Omero Felipe Orlandini ◽  
Claire Nichols ◽  
Abigail Allwood ◽  
...  
Keyword(s):  
Major Element ◽  
Structural Investigations ◽  
West Greenland ◽  
Microbial Structures ◽  
Supracrustal Belt ◽  
Primary Origin ◽  
Heterogeneous Deformation ◽  
Emergence Of Life ◽  
Electron Back Scattered Diffraction ◽  
Rapid Emergence

<p>The biogenicity of proposed stromatolites from deformed greenschist/amphibolite facies Eoarchean (ca. 3.71 Ga) rocks of the Isua Supracrustal Belt (ISB) in West Greenland, is debated  [1,2; cf. 3]. To assess their promise as primary sedimentary structures – as opposed to artefacts of strain localization in layered ductile rocks – we report new field mapping at the discovery site of Nutman et al. (2016) to guide micro- and macro-structural investigations and geochemical sampling. Discontinuous field relations preclude confident assignment of these outcrops as being structurally overturned as originally argued. The structures are not deformed conical stromatolites, but instead linear inverted ridges aligned with azimuths of local and regional fold axes, and parallel to linear structures. Combined major element (e.g., Ca, Mg, Si) scanning μXRF maps, and electron back-scattered diffraction (EBSD) patterns on fresh surfaces cut perpendicular and parallel to the ridges show that the structures lack any internal laminae. Seeming internal layering previously inferred for these features instead arises from variable weathering of outcrop surfaces that otherwise conceal structureless quartz ± dolomite granoblastic cores. These asymmetric boudins sit between semi-continuous competent layers of enveloping quartzite in a calc-silicate schist. Boudinage fabrics reflect viscosity contrasts of the different ductile layers during deformation, and are thus not of primary origin. Collectively, our results show that such structures were probably never stromatolites, but are instead the expected result of a tectonic fabric that preserves no fine-scale primary sedimentary structure.</p><p>[1] Nutman, A.P. et al. 2016, Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures: Nature, v. 537, p. 535–538; [2] Nutman, A.P. et al., 2019, Cross-examining Earth’s oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks: Precambrian Research, v. 331, p. 105347; [3] Allwood, A.C. et al. 2018, Reassessing evidence of life in 3,700-million-year-old rocks of Greenland: Nature, doi: 10.1038/s41586-018-0610-4.</p>

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