scholarly journals Examining the tectono-stratigraphic architecture, structural geometry, and kinematic evolution of the Himalayan fold-thrust belt, Kumaun, northwest India

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 414-435 ◽  
Author(s):  
Subhadip Mandal ◽  
Delores M. Robinson ◽  
Matthew J. Kohn ◽  
Subodha Khanal ◽  
Oindrila Das
Keyword(s):  
Cross Section ◽  
Structural Model ◽  
Kinematic Model ◽  
Thrust Belt ◽  
Main Central Thrust ◽  
Thrust Sheet ◽  
Balanced Cross Section ◽  
Kinematic Evolution ◽  
Thrust Sheets ◽  
Northwest India

Abstract Existing structural models of the Himalayan fold-thrust belt in Kumaun, northwest India, are based on a tectono-stratigraphy that assigns different stratigraphy to the Ramgarh, Berinag, Askot, and Munsiari thrusts and treats the thrusts as separate structures. We reassess the tectono-stratigraphy of Kumaun, based on new and existing U-Pb zircon ages and whole-rock Nd isotopic values, and present a new structural model and deformation history through kinematic analysis using a balanced cross section. This study reveals that the rocks that currently crop out as the Ramgarh, Berinag, Askot, and Munsiari thrust sheets were part of the same, once laterally continuous stratigraphic unit, consisting of Lesser Himalayan Paleoproterozoic granitoids (ca. 1850 Ma) and metasedimentary rocks. These Paleoproterozoic rocks were shortened and duplexed into the Ramgarh-Munsiari thrust sheet and other Paleoproterozoic thrust sheets during Himalayan orogenesis. Our structural model contains a hinterland-dipping duplex that accommodates ∼541–575 km or 79%–80% of minimum shortening between the Main Frontal thrust and South Tibetan Detachment system. By adding in minimum shortening from the Tethyan Himalaya, we estimate a total minimum shortening of ∼674–751 km in the Himalayan fold-thrust belt. The Ramgarh-Munsiari thrust sheet and the Lesser Himalayan duplex are breached by erosion, separating the Paleoproterozoic Lesser Himalayan rocks of the Ramgarh-Munsiari thrust into the isolated, synclinal Almora, Askot, and Chiplakot klippen, where folding of the Ramgarh-Munsiari thrust sheet by the Lesser Himalayan duplex controls preservation of these klippen. The Ramgarh-Munsiari thrust carries the Paleoproterozoic Lesser Himalayan rocks ∼120 km southward from the footwall of the Main Central thrust and exposed them in the hanging wall of the Main Boundary thrust. Our kinematic model demonstrates that propagation of the thrust belt occurred from north to south with minor out-of-sequence thrusting and is consistent with a critical taper model for growth of the Himalayan thrust belt, following emplacement of midcrustal Greater Himalayan rocks. Our revised stratigraphy-based balanced cross section contains ∼120–200 km greater shortening than previously estimated through the Greater, Lesser, and Subhimalayan rocks.

scholarly journals Testing the effects of topography, geometry and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya

2017 ◽  
Author(s):  
Michelle E. Gilmore ◽  
Nadine McQuarrie ◽  
Paul Eizenhöfer ◽  
Todd A. Ehlers
Keyword(s):  
Cross Section ◽  
Kinematic Model ◽  
Main Central Thrust ◽  
Radiogenic Heat ◽  
Kinematic Evolution ◽  
Thrust Belts ◽  
Fault Kinematics ◽  
Erosional Unloading ◽  
Topographic Evolution ◽  
Geometry And Kinematics

Abstract. The temporal and kinematic evolution of fold-thrust belts is a critical component for evaluating the viability of proposed plate tectonic, geodynamic and even climatic processes in regions of convergence. Thermochronometer data have the potential to provide temporal constraints, but interpretations of these data are sensitive to both exhumational and deformational processes. In this study, reconstructions of a balanced geologic cross section in the Himalayan fold-thrust belt of eastern Bhutan are used in a flexural and thermal-kinematic model to understand the sensitivity of predicted cooling ages to changes in fault kinematics, geometry and topography. We sequentially deform the cross section with ~ 10 km deformation steps and apply flexural loading and erosional unloading at each step to develop a high-resolution evolution of deformation, erosion, and burial over time. Comparison of model-predicted cooling ages to published thermochronometer data reveals that cooling ages are most sensitive to (1) location and magnitude of fault ramps, (2) variable shortening rates between 68-6.4 mm/yr, and (3) timing and magnitude of out-of-sequence faulting. The predicted ages are less sensitive to (4) radiogenic heat production, and (5) estimates of topographic evolution. We propose a revised cross section geometry that separates one large ramp previously proposed for the modern decollement into two smaller ramps. The revised cross section results in an improved fit to observed ages, particularly young AFT ages (2–6 Ma) located north of the Main Central Thrust.

Thrust tectonics on Brøggerhalvøya and their relationship to the Tertiary West Spitsbergen Fold-and-Thrust Belt

2002 ◽  
Vol 139 (1) ◽  
pp. 47-72 ◽  
Author(s):  
K. SAALMANN ◽  
F. THIEDIG
Keyword(s):  
Middle Eocene ◽  
Kinematic Model ◽  
Thrust Belt ◽  
Fold Belt ◽  
Kinematic Evolution ◽  
Fold And Thrust Belt ◽  
Thrust Tectonics ◽  
Tectonic Transport ◽  
Thrust Sheets ◽  
West Spitsbergen

The Tertiary fold-and-thrust belt on Brøggerhalvøya is characterized by a NE-vergent pile of nine thrust sheets. The sole thrust of the pile is located in Precambrian phyllites and climbs up-section to the northeast. Four lower thrust sheets consisting predominantly of Upper Palaeozoic sediments are overlain by two thrust sheets in the central part of the stack which contain a kilometre-scale syncline and anticline. The fold is cut by juxtaposed thrusts giving rise to the formation of three structurally higher basement-dominated thrust sheets. A multiple-stage kinematic model is proposed including (1) in-sequence foreland-propagating formation of the lower thrust sheets in response to N–S subhorizontal bedding-parallel movements, (2) a change in tectonic transport to ENE and out-of-sequence thrusting and formation of the kilometre-scale fold-structure followed by (3) truncation of the kilometre-scale fold and stacking of the highest basement-dominated thrust sheets by hind-ward-propagating out-of-sequence thrusting. The strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheets, reflecting a temporal change to a more transpressive regime. Thrusting was followed by (4) N–S extension and (5) W–E extension. Comparison of the structural geometry and kinematic evolution of Brøggerhalvøya with the data reported for the fold belt further south allows us to assume a coeval evolution with the fold belt. A latest Paleocene/Early Eocene age for the main phase of thrusting is suggested for the West Spitsbergen Fold-and-Thrust Belt; the main phases therefore pre-date the separation of Svalbard and Greenland due to right-lateral movements along the Hornsund Fault Zone. The fold belt's temporal evolution followed by the formation of the Forlandsundet Graben can be linked with the plate-kinematic framework in the span between latest Paleocene and Middle Eocene times.

Structure, strain and AMS of the Uzunakhmat thrust sheet (Talas Range, Kyrgyz North Tian Shan)

2020 ◽  
Author(s):  
Anastasia Kushnareva ◽  
Artem Moskalenko ◽  
Alexander Pasenko
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Structural Evolution ◽  
Middle Part ◽  
Tien Shan ◽  
Initial Shape ◽  
Thrust Sheet ◽  
Structural Style ◽  
Thrust Sheets ◽  
Tian Shan

<p>The Talas Range forms the northwest part of the Caledonides of the Northern Tian Shan. Based on differences in the structural style, metamorphism and sedimentary successions, three thrust sheets have been identified – the Uzunakhmat, Talas, and Kumyshtag thrust sheets. The Talas and Kumyshtag thrust sheets consist of Neoproterozoic-Ordovician terrigenous and carbonate rock units, whereas the Uzunakhmat thrust sheet consists of Neoproterozoic terrigenous rocks metamorphosed up to greenschist facies. The Uzunakhmat thrust sheet is separated from the Talas and Kumyshtag thrust sheets by the southwest-dipping Central Talas thrust (CTT). The dextral strike-slip Talas-Fergana Fault bounds the Uzunakhmat thrust sheet in the southwest. The main deformation events occurred in the Middle-Late Ordovician.</p><p>Structural and strain studies were done along profiles normal to the strike of folds and faults and located in the northwest and southeast parts of the Uzunakhmat thrust sheet. We also incorporate in our study structural profile in the central part of the Uzunakhmat thrust sheet, documented by Khudoley (1993) and Voytenko & Khudoley (2012).</p><p>The main strain indicators were detrital quartz grains in sandstones. Rf/φ and Normalized Fry methods were used to identify the amount of strain. Oblate ellipsoids predominate with Rxz values varying mostly from 1,6 to 2,4. Long axes of strain ellipsoids are sub-horizontal with the southeast to east-southeast trend. Similar trends have long axes of the anisotropy magnetic susceptibility ellipsoid being parallel to fold axes, cleavage-bedding intersection and mineral lineation as well as the trend of the major thrusts, including CTT.</p><p>The modern shape of the Uzunakhmat thrust sheet is similar to an elongated triangle, pinching out northwest and expanding southeast. Cross-section balancing corrected for the amount of strain shows along-strike decreasing of shortening in the southeast direction. Total shortening varies from 35% to 55% between sections located about 15 km from each other. Such significant variation in shortening corresponds to variation in structural style with much more tight folds and more numerous thrusts for cross-sections with a higher amount of shortening. However, the restored length of all cross-sections is quite similar pointing to the approximately rectangular initial shape of the Uzunakhmat thrust sheet. Our interpretation is that during the Caledonian tectonic events, the Uzunakhmat thrust sheet was displaced in the northwest direction with accompanied thrusting and folding of rock units within the thrust sheet. These deformations formed the modern shape of the thrust sheet in accordance with the amount of shortening detected by cross-section balancing. This interpretation also implies that modern erosion did not significantly affect shape of the Uzunakhmat thrust sheet formed after the Caledonian deformation.</p><p>Khudoley, A.K., 1993. Structural and strain analyses of the middle part of the Talassian Alatau ridge (Middle Asia, Kirgiystan). J. Struct. Geol. 6, 693–706.</p><p>Voytenko N.V., Khudoley A.K. Structural evolution of metamorphic rocks in the Talas Alatau, Tien Shan, Central Asia: Implication for early stages of the Talas-Ferghana Fault. // C. R. Geoscience. 2012. V. 344. P. 138–148.</p>

scholarly journals The geological framework for Hvideklint, south-east Denmark, using glaciodynamic sequence stratigraphy

2021 ◽  
Vol 47 ◽  
Author(s):  
Stig A. Schack Pedersen ◽  
Peter Gravesen
Keyword(s):  
Sea Level ◽  
Sequence Stratigraphy ◽  
Cross Section ◽  
Cross Sections ◽  
Drill Hole ◽  
Balanced Cross Section ◽  
Geological Cross Section ◽  
Thrust Sheets ◽  
Practical Model ◽  
Complex Architecture

Glaciodynamic sequence stratigraphy provides a practical model for grouping and classifying complex geological data to aid interpretation of past climatic and environmental development in Quaternary successions. The principles of glaciodynamic sequence stratigraphy are applied here to summarise the complex glacial geological framework of Hvideklint on the island of Møn, south-east Denmark. The framework of the superimposed deformed Hvideklint is presented in a reconstructed geological cross-section of Hvideklint. For the construction of the architecture of the glaciotectonic complex, the interpretation of structures below sea level was based on a detailed new survey of the cliff section combined with construction of successive approximation balanced cross-sections. The new description is supported by drill hole data from the Jupiter database. Where chalk is not glaciotectonically deformed, the constructed depth to the top-chalk-surface is generally located about 30 m below sea level. In Hvideklint, thrust sheets with chalk are exposed 20 m above sea level, and the balanced cross-section constructions indicate that the décollement surface for a Hvideklint glaciotectonic complex is located about 80 m below sea level. Between the décollement level and the top of the complex, two or more thrust-fault flat-levels and connecting ramps add to the complex architecture of Hvideklint.

A structural analysis of a metamorphic fold–thrust belt, northeast Gagnon terrane, Grenville Province

1992 ◽  
Vol 29 (9) ◽  
pp. 1915-1927 ◽  
Author(s):  
Dennis Brown ◽  
Taoby Rivers ◽  
Tom Calon
Keyword(s):  
Deep Level ◽  
Greenschist Facies ◽  
Thrust Belt ◽  
Structural Elements ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Lake Formation ◽  
Transport Direction ◽  
Tectonic Transport ◽  
Thrust Sheets

Northeast Gagnon terrane is located within the Parautochthonous Belt of the Grenville Orogen, near the projected intersection of the front zones of the Grenville and New Quebec orogens. The area consists principally of supracrustal units of the Early Proterozoic Knob Lake Group, and a newly recognized unit, the Equus Lake formation. Both are intruded by the Middle Proterozoic Shabogamo gabbro. Structural elements in the rocks record evidence of a polyorogenic history that is attributed to both the ca. 1800 Ma Hudsonian and the ca. 1000 Ma Grenvillian orogenies. This paper is concerned with the latter.Grenvillian deformation resulted in the formation of a relatively deep-level fold–thrust belt. Three thrust sheets can be defined on the basis of basal thrusts, variations in morphology and orientation of structural elements, and internal thrust sheet geometry. The polydeformational style of the area, rotation of fold axes into subparallelism with the tectonic transport direction, and internal imbrication lead to a complex internal thrust sheet geometry. Thrusting has produced and inverted the metamorphic gradient, with lower greenschist facies in the basal thrust sheet and upper greenschist facies in the upper thrust sheet.Documentation of the northeastern margin of Gagnon terrane as a north- to northwest-directed metamorphic fold–thrust belt corroborates similar interpretations for Gagnon terrane from elsewhere along the Grenville Front and is in accord with the models of the Grenville Province as a collisional orogen. Furthermore, it is suggested that northeast Gagnon terrane is an exhumed, internal, ductile part of a fold–thrust belt.

scholarly journals Thrust tectonics in the Wetterstein and Mieming mountains, and a new tectonic subdivision of the Northern Calcareous Alps of Western Austria and Southern Germany

2021 ◽  
Author(s):  
Hugo Ortner ◽  
Sinah Kilian
Keyword(s):  
Eastern Alps ◽  
Northern Calcareous Alps ◽  
Main Body ◽  
Thrust Belt ◽  
Southeastern Part ◽  
Thrust Sheet ◽  
Northern Calcareous ◽  
Lateral Contact ◽  
Thrust Tectonics ◽  
Thrust Sheets

AbstractWe investigate the tectonic evolution of the Wetterstein and Mieming mountains in the western Northern Calcareous Alps (NCA) of the European Eastern Alps. In-sequence NW-directed stacking of thrust sheets in this thin-skinned foreland thrust belt lasted from the Hauterivian to the Cenomanian. In the more internal NCA major E-striking intracontinental transform faults dissected the thrust belt at the Albian–Cenomanian boundary that facilitated ascent of mantle melts feeding basanitic dykes and sills. Afterwards, the NCA basement was subducted, and the NCA were transported piggy-back across the tectonically deeper Penninic units. This process was accompanied by renewed Late Cretaceous NW-directed thrusting, and folding of thrusts. During Paleogene collision, N(NE)-directed out-of-sequence thrusts developed that offset the in-sequence thrust. We use this latter observation to revise the existing tectonic subdivision of the western NCA, in which these out-of-sequence thrusts had been used to delimit nappes, locally with young-on-old contacts at the base. We define new units that represent thrust sheets having exclusively old-on-young contacts at their base. Two large thrust sheets build the western NCA: (1) the tectonically deeper Tannheim thrust sheet and (2) the tectonically higher Karwendel thrust sheet. West of the Wetterstein and Mieming mountains, the Imst part of the Karwendel thrust sheet is stacked by an out-of-sequence thrust onto the main body of the Karwendel thrust sheet, which is, in its southeastern part, in lateral contact with the latter across a tear fault.

scholarly journals Influence of salt in the tectonic development of the frontal thrust belt of the eastern Cordillera (Guatiquía area, Colombian Andes)

2015 ◽  
Vol 3 (4) ◽  
pp. SAA17-SAA27 ◽  
Author(s):  
Vanessa Parravano ◽  
Antonio Teixell ◽  
Andrés Mora
Keyword(s):  
Structural Model ◽  
Salt Tectonics ◽  
Thrust Belt ◽  
Eastern Cordillera ◽  
Salt Migration ◽  
Colombian Andes ◽  
Kinematic Evolution ◽  
Geologic Maps ◽  
History Of ◽  
Tectonic Development

Geologic maps, seismic lines, and data from a dry exploration well were used to develop a new structural model for a segment of the eastern foothills of the Eastern Cordillera of Colombia, emphasizing the role of salt tectonics. Milestones in the deformation history of the Guatiquía foothills were studied by sequential section restoration to selected steps. Uncommon structural geometries and sparse salt occurrences were interpreted in terms of a kinematic evolution in which Cretaceous salt migration in extension produced a diapiric salt wall, which was subsequently welded during the main episodes of the Andean compression, when the salt wall was squeezed generating a large overturned flap. Salt-weld strain hardening resulted in breakthrough thrusting across the overturned flap in late deformation stages. We have evaluated a pattern of salt tectonics previously unrecognized in the foothills thrust belt, which may be significant in other parts of the external Colombian Andes.

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