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Title: Fold-and-thrust belts and associated basins: a perspective on their structure, sedimentation, and dynamics
Fold-and-thrust belts are structural features that accommodate upper-crustal shortening by the growth of a series of thrust faults and folds. Recent studies show that a better understanding of the structure and sedimentation styles of fold-and-thrust belts and their associated basins can provide crucial insights for improved interpretations of the evolution of ancient and modern convergent margins and the mechanisms of intracontinental deformation. To achieve a more comprehensive understanding of the development of contractional orogenic belts, this thematic collection gathers contributions that explore different types of fold-and-thrust belts at various scales around the world, via different approaches including theory development, structural and stratigraphic observations from the field, geophysical analyses, and numerical modelling. Case studies include the northern margin of the Tibetan plateau and Pamir region, the Timanian and Caledonian orogenies in northern Norway, orogenic belts in western Laurentia, and the Andes of western South America. These studies reemphasize the importance of integrating broad datasets when documenting the distribution, geometry, and kinematics of structures in fold-and-thrust belts and their associated basins, including field-based structural observations, provenance, low-temperature thermochronologic, geomorphologic, and subsurface data, and analog and numerical models. This thematic collection aims to encourage further efforts for comparative studies of the fold-and-thrust belts around the world and proposes interdisciplinary research to address outstanding questions in the study of contractional orogens. Thematic collection: This article is part of the Fold-and-thrust belts collection available at:  more » « less
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Journal of the Geological Society
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National Science Foundation
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  1. Unconformities in foreland basins may be generated by tectonic processes that operate in the basin, the adjacent fold–thrust belt or the broader convergent margin. Foreland basin unconformities represent shifts from high accommodation to non-depositional or erosional conditions in which the interruption of subsidence precludes the net accumulation of sediment. This study explores the genesis of long-duration unconformities (>1–20 myr) and condensed stratigraphic sections by considering modern and ancient examples from the Andes of western South America. These case studies highlight the potential geodynamic mechanisms of accommodation reduction and hiatus development in Andean-type retroarc foreland settings, including: (1) shortening-induced uplift in the frontal thrust belt and proximal foreland; (2) the growth and advance of a broad, low-relief flexural forebulge; (3) the uplift of intraforeland basement blocks; (4) tectonic quiescence with regional isostatic rebound; (5) the end of thrust loading and flexural subsidence during oblique convergence; (6) diminished accommodation or sediment supply due to changes in sea-level, climate, erosion or transport; (7) basinwide uplift during flat-slab subduction; and (8) dynamic uplift associated with slab window formation, slab break-off, elevated intraplate (in-plane) stress, or related mantle process. These contrasting mechanisms can be distinguished on the basis of the spatial distribution, structural context, stratigraphic position, palaeoenvironmental conditions, and duration of unconformities and condensed sections. Thematic collection: This article is part of the Fold-and-thrust belts collection available at: 
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  2. null (Ed.)
    Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a −1 , which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent. Supplementary material: Luminescence dating procedures and protocols is available at Thematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: 
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  3. Abstract

    Mesozoic crustal shortening in the North American Cordillera’s hinterland was related to the construction of the Nevadaplano orogenic plateau. Petrologic and geochemical proxies in Cordilleran core complexes suggest substantial Late Cretaceous crustal thickening during plateau construction. In eastern Nevada, geobarometry from the Snake Range and Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains (REWP) core complexes suggests that the ~10–12 km thick Neoproterozoic-Triassic passive-margin sequence was buried to great depths (>30 km) during Mesozoic shortening and was later exhumed to the surface via high-magnitude Cenozoic extension. Deep regional burial is commonly reconciled with structural models involving cryptic thrust sheets, such as the hypothesized Windermere thrust in the REWP. We test the viability of deep thrust burial by examining the least-deformed part of the REWP in the Pequop Mountains. Observations include a compilation of new and published peak temperature estimates (n=60) spanning the Neoproterozoic-Triassic strata, documentation of critical field relationships that constrain deformation style and timing, and new 40Ar/39Ar ages. This evidence refutes models of deep regional thrust burial, including (1) recognition that most contractional structures in the Pequop Mountains formed in the Jurassic, not Cretaceous, and (2) peak temperature constraints and field relationships are inconsistent with deep burial. Jurassic deformation recorded here correlates with coeval structures spanning western Nevada to central Utah, which highlights that Middle-Late Jurassic shortening was significant in the Cordilleran hinterland. These observations challenge commonly held views for the Mesozoic-early Cenozoic evolution of the REWP and Cordilleran hinterland, including the timing of contractional strain, temporal evolution of plateau growth, and initial conditions for high-magnitude Cenozoic extension. The long-standing differences between peak-pressure estimates and field relationships in Nevadan core complexes may reflect tectonic overpressure.

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  4. Abstract

    Cenozoic sedimentary rocks of the intermontane Bagua Basin record the Andean orogenic history of northern Peru at ~4–7°S. The northern Peruvian Andes define the northern termination of the Central Andes and are comprised of a narrow, low‐elevation orogen relative to the rest of the Central Andes. New stratigraphic and sedimentologic field observations, subsidence analysis, and detrital zircon provenance analysis enable reconstruction of the regional tectonic history. Late Cretaceous to Paleocene detrital zircon U‐Pb age spectra from the Fundo El Triunfo and Rentema formations reveal active volcanism in the Western Cordillera as early as ~80 Ma and early exhumation of Mesozoic rocks in a nascent Marañon Fold‐Thrust Belt. Eocene fluvial deposits of the Cajaruro Formation record a progressive increase in shortening and volcanism in the Western Cordillera. The upper Eocene–middle Miocene fluvial succession of the Sambimera Formation records deposition in a proximal foredeep setting. Sambimera deposits contain syndepositional detrital zircon U‐Pb age populations that reveal a major Cenozoic magmatic source in the west. An erosive boundary separates the Sambimera from the overlying San Antonio Formation. The San Antonio Formation was deposited in an intermontane basin associated with uplift of the Eastern Cordillera at these latitudes. These results highlight a foreland progression of fold‐thrust deformation, with shortening concentrated in the Western Cordillera from latest Cretaceous to middle Miocene time. We suggest that the late Miocene transition to intermontane deposition in the Bagua Basin marks initial exhumation during shortening of the Eastern Cordillera in northern Peru.

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  5. Abstract

    Documenting the spatio‐temporal progression of deformation within fold‐thrust belts is critical for understanding orogen dynamics. In the North American Cordillera, the geometry, magnitude, and timing of contractional deformation across a broad region of Nevada known as the “Sevier hinterland” has been difficult to characterize due to minimal exposures of syn‐contractional sedimentary rocks and overprinting of Cenozoic extension. To address this, we present geologic mapping and U‐Pb zircon geochronology from three exposures of the Cretaceous Newark Canyon Formation (NCF) in central Nevada. In the Cortez Mountains, NCF deposition between ∼119 and 110 Ma is hypothesized to be related to generation of relief by thrusting/folding to the west. In the Fish Creek Range, NCF deposition between ∼130 and 100 Ma was related to motion on an east‐vergent thrust fault. In the Pancake Range, NCF deposition is bracketed between ∼129 and 66 Ma and post‐dated east‐vergent folding. We incorporate these timing constraints into a compilation of deformation timing in the Sevier hinterland. Late Jurassic (∼165 and 155 Ma) shortening, which is largely post‐dated shortening in the Luning‐Fencemaker thrust belt to the west and pre‐dated initial deformation in the Sevier fold‐thrust belt to the east, is interpreted to represent diffuse, low‐magnitude deformation that accompanied eastward propagation of the basal Cordilleran décollement. Cretaceous (∼130 and 75 Ma) hinterland shortening, which includes deformation associated with NCF deposition, was contemporaneous with shortening in the Sevier fold‐thrust belt. This is interpreted to represent long‐duration strain partitioning between the foreland and hinterland during continued coupling above the basal décollement and the progressive westward underthrusting of thick North American lower‐middle crust.

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