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Foreland contraction and hinterland extension in the Southern Apennines orogen of Italy produced a complex spatial and temporal pattern of vertical and horizontal displacement. Remarkably, Late Miocene to mid-Pleistocene foreland migration of the contractional front at ∼16 mm yr−1 was not accompanied by uplift and the frontal thrust belt remained at or below sea level. Only following a mid-Pleistocene reduction in horizontal displacement did the frontal thrust belt and foreland begin uplift at ∼0.5 mm yr−1, a rate that increased to ∼1 mm yr−1 after 125 ka. Although the extensional hinterland experienced net subsidence during formation of the Tyrrhenian basin, an extensional transition zone adjacent to the frontal thrust belt records sustained uplift at ∼0.3 mm yr−1. The interaction of preexisting crustal structure and deep tectonic processes resulted in time-integrated displacement rates suggesting steady-state deformation for periods of 106 years. Displacement rate changes were abrupt and occurred over intervals of 105 years or less. 相似文献
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Boudins with long axes (BA) oriented subnormal to bedding and to associated fold axes are observed in folded rocks in a thrust sheet exposed near the base of a regionally extensive allochthon in west-central Nevada, USA. Formation of the boudins is related to development of a regional fold-set coeval with major thrusting. The axes of boudins lie at a high angle to bedding, and in some instances, boudins define tight to isoclinal folds which are geometrically associated with the regional deformation. Quartz c-axis fabrics from oriented thin-sections of the boudins indicate extension parallel to the boudin axes (BA).
These relations and other mesoscopic structural data indicate a complex deformational history for boudin development. The history involves thin layers (to become boudins) deformed in folds disharmonic to major structures within the thrust sheet followed by flattening and associated extension parallel to fold axes. During flattening, arcuation occurred within the deforming mass resulting in rotation of fold axes and boudin axes (BA) toward the axis of finite extension (X). Extension parallel to BA recorded in the petrofabrics of boudins records incremental strain axes oriented at a high angle (50°) to the finite X and is probably related to an early plane-strain state associated with disharmonic folding. The finite extension (X) is down-dip in axial planes of major folds formed during thrusting and indicates a northwest to southeast transport for the thrusts. 相似文献
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J.S. Oldow 《Journal of Structural Geology》1981,3(1):39-49
The northern Pilot Mountains of west-central Nevada, consist of a complexly deformed terrane of imbricate thrust nappes composed of rocks of Permian(?), Triassic through Jurassic, and possible Cretaceous ages. Three episodes of fold and thrust generation are recognized on the basis of folded thrusts and thrusted folds, and deformation and emplacement of the nappes is constrained as having occurred during the late Mesozoic. Folds are apparently coeval with thrust faults, and fold geometry is used in determining approximate directions of thrust displacement. The history of thrust displacement is complex and involves three directions of motion on a regionally extensive detachment surface, the Luning thrust. The first motion, from NW to SE, results in displacements of the order of several tens of kilometres and is the probable result of NW-SE regional compression. The final two episodes of motion are NE-SW followed by E-W; they result in small displacements and are possibly the product of gravity sliding of the thrust sheet into depressions in the autochthon. Sites of downwarp in the autochthon may have been formed either by load induced subsidence or regional compression. 相似文献
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The Southern Apennine fold and thrust belt differs from other parts of the peri-Tyrrhenian orogen. In most of the peri-Tyrrhenian belt, hinterland extension is oriented at a high-angle to the orogen axis and appears to be related to rifting and formation of oceanic crust within the Tyrrhenian basin. The Southern Apennines share the late-stage development of normal faults related to the opening of the Tyrrhenian Sea, but also experienced an episode of extension parallel to the strike of the tectonic belt. The orogen-parallel extension was apparently formed in response to the increase in length of the deformed belt during arcuation. Arcuation ostensibly was related to asymmetrical rifting in the hinterland, which was greater in the Southern Tyrrhenian Sea than in areas to the north, and proportionately greater shortening in the frontal parts of the southern belt as compared to regions in the north. During arcuation, extension was spatially concentrated within structural domains and was accomplished by displacement on low-angle detachment faults cutting through a previously imbricated thrust stack. During the Miocene-Pliocene, NNW-SSE extension in the interior of the Southern Appennine belt formed coveally with ENE-WSW shortening in the foreland. Longitudinal extension ceased in the Pleistocene, when younger high-angle normal faults formed in response to the easterly migration of Tyrrhenian Sea rifting and NE-SW extension associated with lithospheric stretching. 相似文献
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