Paleomagnetism and geochronology of sills of the Doherty Mountain area, southwestern Montana: Implications for the timing of fold-and-thrust belt deformation and vertical-axis rotations along the southern margin of the Helena salient

2008 ◽  
Vol 120 (9-10) ◽  
pp. 1091-1104 ◽  
Author(s):  
S. S. Harlan ◽  
J. Wm. Geissman ◽  
S. C. Whisner ◽  
C. J. Schmidt
Keyword(s):  
Vertical Axis ◽  
Thrust Belt ◽  
Mountain Area ◽  
Southwestern Montana ◽  
Southern Margin ◽  
Fold And Thrust Belt

Syn-folding remagnetization events in the French-Belgium Variscan thrust front as markers of the fold-and-thrust belt kinematics

2003 ◽  
Vol 174 (5) ◽  
pp. 511-523 ◽  
Author(s):  
Rafal Szaniawski ◽  
Marek Lewandowski ◽  
Jean-Louis Mansy ◽  
Olivier Averbuch ◽  
Frederic Lacquement
Keyword(s):  
Foreland Basin ◽  
Vertical Axis ◽  
Natural Remanent Magnetization ◽  
Thrust Belt ◽  
High Temperature Component ◽  
Set Constraints ◽  
Thrust Front ◽  
Fold And Thrust Belt ◽  
Temperature Component ◽  
Major Strike

Abstract New paleomagnetic studies have been carried out within the Ardennes segment of the N France - S Belgium Variscan fold-and-thrust belt to set constraints on the fold-thrust belt kinematics and reveal the casual relationships between vertical-axis rotations and major strike deviated zones localised along the general trend of the belt. Magnetite-bearing Devonian and Carboniferous limestones yielded two characteristic, secondary components of the natural remanent magnetization : a low temperature component recorded most probably during the late stages of folding and a high temperature component, acquired during incipient stages of deformation. Both post- and synfolding magnetizations were identified in the Lower Devonian hematite bearing sandstones. Ages of magnetization, inferred from the analysis of characteristic remanence inclinations compared to the reference curves for the stable parts of the Old Red Sandstones Continent (ORC), suggest the previous remagnetization event to be due to the burial of sedimentary rocks under the thick molassic foreland basin of Namurian-Westphalian age and the second to the final out-of-sequence activation of the thrust front in Stephanian times. Irrespective of the age of the magnetizations, orientations of paleomagnetic directions are dominantly governed by second-order structural trends. Clockwise rotations are observed in relatively narrow zones featuring deviated orientations of fold axes, other sites show paleomagnetic directions akin to those known from the ORC. We interpret this feature as a result of local transpressive deformations and related rotations, which occurred at lateral borders of propagating thrust-sheets. The latter deformation zones are suggested to be controlled by deep-seated discontinuities inherited from the Devonian Rheno-hercynian basin development. The Ardennes thrust belt was thus not rotated as a whole unit with respect to the ORC after the Namurian, preserving the initial orientation of the continental margin.

Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece)

2020 ◽  
Author(s):  
Bernhard Grasemann ◽  
David A. Schneider ◽  
Konstantinos Soukis ◽  
Vincent Roche
Keyword(s):  
Eastern Mediterranean ◽  
Hanging Wall ◽  
Finite Extension ◽  
Normal Fault ◽  
Vertical Axis ◽  
Normal Faults ◽  
Low Grade ◽  
Thrust Belt ◽  
Fold And Thrust Belt ◽  
Variscan Basement

<p><span lang="EN-US">Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed.</span></p> <p><span lang="EN-US">In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems.</span></p> <p><span lang="EN-US">New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.</span></p>

scholarly journals Timing and magnitude of vertical-axis rotations in the eastwards-flanking synorogenic sediments of the South-Pyrenean fold-and-thrust belt. Kinematics and origin of the salient curvature.

2020 ◽  
Author(s):  
Charlotte Peigney ◽  
Elisabet Beamud ◽  
Óscar Gratacós ◽  
Luis Valero ◽  
Ruth Soto ◽  
...  
Keyword(s):  
Foreland Basin ◽  
Structural Data ◽  
Vertical Axis ◽  
Central Unit ◽  
Thrust Belt ◽  
The South ◽  
The North ◽  
South Central ◽  
Fold And Thrust Belt ◽  
Thrust Sheets

<p>The South-Pyrenean fold-and-thrust belt consists of three major thin-skinned thrust sheets (Bóixols, Montsec and Serres Marginals) made up of uppermost Triassic to Oligocene cover rocks emplaced during Late Cretaceous-Oligocene times. In its central part, it forms a major salient (the Pyrenean South-Central Unit) whose geometry is controlled by the areal distribution of the pre-orogenic Upper Triassic and synorogenic Eocene salt décollement layers. Both westwards and eastwards, the salient is fringed by Paleogene synorogenic deposits that are deformed by detachment folds with orientations ranging from N-S to E-W. In the western edge of the salient, the varying trend of the folds is a result of synorogenic vertical axis rotations (VAR) which caused the clockwise rotation of the folds from an initial predominant E-W trend to the current NW-SE to NNW-SSE trend. The salient, at least on its western part, developed from a progressive curve originated from divergent thrust transport directions and distributed shortening.</p><p>The aim of our study is to get a better understanding of the whole salient, by studying the kinematics of the deformation on the most frontal part of its eastern edge. Here, some sparse anticlockwise rotations have been reported but their origin and their possible relationship with the distribution of the salt décollements has not yet been addressed. For this purpose, 78 paleomagnetic sites have been sampled on the synorogenic upper Eocene-Oligocene materials of the NE Ebro foreland Basin, in the Artesa de Segre area, focusing on the limbs of oblique salt-cored anticlines (Ponts, Vilanova de l’Aguda, Cardona) which are detached above the synorogenic Eocene-Oligocene evaporites of the Cardona and the Barbastro formations. VAR analyses principally show anticlockwise rotations similar to those previously identified to the North in the Oliana Anticline, although a small number of clockwise rotations were also detected.</p><p>In addition to the VAR analysis, a magnetostratigraphic study of the Eocene-Oligocene continental materials of the northern limb of the Sanaüja Anticline has been conducted in order to constrain the age of these rotations from stratigraphic correlations. The demagnetization of 104 samples from a ca. 1100 m thick magnetostratigraphic section shows Priabonian to Rupelian ages for this succession. The integration of our results on timing, direction and magnitude of foreland VAR with previous paleomagnetic and structural data from both the western and eastern boundaries of the frontal thrust of the Pyrenean South-Central Unit will allow the understanding of the kinematics of the thrust salient as a whole.</p>

scholarly journals Structural Evolution of the Kohat Fold and Thrust Belt in the Shakardarra Area (South Eastern Kohat, Pakistan)

Geosciences ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 311
Author(s):  
Hamid Hussain ◽  
Zhang Shuangxi
Keyword(s):  
Seismic Data ◽  
Structural Evolution ◽  
Vertical Axis ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Thrust Faults ◽  
Thrust Belt ◽  
Fold And Thrust Belt ◽  
Basal Detachment ◽  
Northern Segment

The Kohat fold and thrust belt, located in North-Western Pakistan, is a part of Lesser Himalaya developed due to the collision between the Indian and Eurasian plates. The structural evolution records of this area indicate that it consists of tight anticlines and broad syncline structures. Previous studies show that the structural pattern of this area has been produced due to multiple episodes of deformation. In the present research, 2D seismic data has been integrated with our field surveys to clarify the role of active strike-slip faulting in reshaping the surface structures of Shakardarra, Kohat. At the surface, doubly plunging anticlines and synclines are evolved on evaporites as detachment folds, truncated by thrust faults along their limbs. Seismic data show that the thrust faults originate from basal detachment located at the sedimentary-crystalline interface and either cut up section to the surface or lose their displacement to splay or back thrusts. At the surface, the Shakardarra Fault, the Tola Bangi Khel Fault, the Chorlaki Fault, and the axial trend of fold change their strike from EW to NS showing that the thrust and axial trend of folds are rotated along the vertical axis by the influence of the Kalabagh strike-slip fault. Strike-slip motion dominates the style of deformation at the northern segment. The current deformation is concentrated on the splay faults in the northern segment of the Kalabagh Fault. We propose that Shakardarra is sequentially evolved in three episodes of deformation. In the first phase, the detachment folds developed on Eocene evaporites, which are truncated by thrust faults originated from the basal detachment in the second phase. In the third phase, early formed folds and faults are rotated along the vertical axis by the influence of Kalabagh strike-slip fault.

Paleoseismology of a newly discovered scarp in the Yakima fold-and-thrust belt, Kittitas County, Washington

2013 ◽  
Author(s):  
Elizabeth A. Barnett ◽  
Brian L. Sherrod ◽  
Robert Norris ◽  
Douglas Gibbons
Keyword(s):  
Thrust Belt ◽  
Fold And Thrust Belt
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