Gravity Anomalies And Crustal Structure Of The Eastern Part Of The Verkhoyansk Fold-And-Thrust Belt, NE Russia: Evidence From The Junction Area Of The Adycha-Elga And Allakh-Yun Tectonic Zones

Abstract The results of geophysical studies of the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt located on the submerged eastern margin of the Siberian craton are presented. Three structural-mineral complexes are recognized: Archean-Paleoproterozoic, Mesoproterozoic-Middle Carboniferous, and Upper Carboniferous-Early Mesozoic. The Early Jurassic plume-related basaltic volcanism and suprasubduction Late Jurassic-Early Cretaceous granitoids, regional Brungadin and Suntar faults are identified. The goal of the research is to identify deep heterogeneities and clarify the structure of the Earth’s crust in the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt. The analysis of gravitational anomalies is carried out, their transformations are performed – distinguishing the medium and low-frequency components, the vertical derivative Vzz, and calculating the equivalent distribution of sources of density masses at depth. It is determined that the hidden granitoids of the Adycha-Elga tectonic zone are located mainly in linear zones of decompaction at a depth of about 3.5 km. In the Allakh-Yun zone, a large gravitational minimum has been identified, where it is assumed that there is a magma granitoid chamber occurring at a depth of about 9 km. The model of the deep structure of the territory is based on the analysis of materials on the reference seismic profile 3-DV with the use of gravimetric data and the regional structure of the territory. According to the results of the wave pattern interpretation, the thickness of the lithosphere varies from 41 to 44 km. The thickness of the Upper Carboniferous-Triassic terrigenous rocks is 8-12 km, Mesoproterozoic - Middle Carboniferous carbonate-terrigenous complex is up to 12 km. The Archean-Paleoproterozoic crystalline basement occurs at a depth of 19-21 km. The Conrad discontinuity is assumed at a depth of about 30 km. Intense deformations of the crystalline basement are recognized, and trans-crust faults are identified.

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Gravity anomalies of the United Arab Emirates: Implications for basement structures and infra-Cambrian salt distribution

GeoArabia ◽

10.2113/geoarabia1901143 ◽

2014 ◽

Vol 19 (1) ◽

pp. 143-158

Author(s):

Mohammed Y. Ali ◽

Anthony B. Watts ◽

Asam Farid

Keyword(s):

Gravity Anomaly ◽

United Arab Emirates ◽

Gravity Anomalies ◽

Abu Dhabi ◽

Fault System ◽

Bouguer Gravity ◽

Thrust Belt ◽

Bouguer Gravity Anomaly ◽

Fold And Thrust Belt ◽

Semail Ophiolite

ABSTRACT Gravity measurements onshore and offshore of the United Arab Emirates (UAE) have been used to construct a new Bouguer gravity anomaly map of the region. The gravity data, which has been gridded at 2,700 m × 2,700 m interval, has been used to constrain the tectonic elements, major lineation trends and structures of the Neoproterozoic basement of the Arabian Plate and the distribution of infra-Cambrian salt basins. Advanced transformation techniques (including first vertical derivative, total horizontal derivative, tilt derivative and Euler deconvolution) were applied to identify gravity source edges as an aid to structural interpretation and geological modelling of the study area. Three major structural provinces (fold-and-thrust belt, foreland and salt tectonic provinces) were identified based on the residual Bouguer gravity anomaly field. The eastern fold-and-thrust belt province is associated with short-wavelength positive gravity anomalies, which are attributed to the allochthonous series of the Semail Ophiolite and its related thrust sheets. The central foreland basin province is characterised by NNW-oriented negative gravity anomalies associated with deepening of the basement and thickening of Aruma and Pabdeh sediments in the foredeep basins and flexure of the top and base of the crust by the load of the Semail Ophiolite. The western salt tectonic province displays well-defined local gravity lows superimposed on a regional gravity high, which probably reflects the swelling of infra-Cambrian salt above a shallowing of the basement and thinning of the foredeep sediments. In addition, gravity modelling constrained by seismic and well data indicates the presence of substantial infra-Cambrian salt bodies in all basins of the UAE both onshore and offshore including the southern area of the Rub’ Al-Khali Basin. An extensive array of previously unmapped N-S, NW- and SW-trending lineaments affecting the basement and possibly overlying sediments are mapped in the UAE. The N-S Arabian trending lineament represents the effect of a major structure, along which many important oilfields are located (e.g. Bu Hasa). The SW trend has regular spacing and is dominant in the southern and central part of Abu Dhabi, east of the Falaha syncline. The NW-SE lineament is the most striking and includes two well-defined trends that cross Abu Dhabi Emirate, which in this paper are named as the Abu Dhabi Lineaments. These lineaments are associated with a linear gravity high extending from the southwestern border with Oman to the offshore close to Zakum oilfield. They are probably related to the Najd Fault System.

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Integrated multidisciplinary approach to constrain range fronts structure, a case study of the northern Tianshan piedmont (NW China)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.185.6.379 ◽

2014 ◽

Vol 185 (6) ◽

pp. 379-392 ◽

Cited By ~ 2

Author(s):

Ke Chen ◽

Charles Gumiaux ◽

Romain Augier ◽

Guillaume Martelet ◽

Yan Chen ◽

...

Keyword(s):

Data Analysis ◽

Cross Section ◽

Multidisciplinary Approach ◽

Deep Structure ◽

Thrust Belt ◽

Seismic Profiles ◽

Reflection Seismic ◽

Fold And Thrust Belt ◽

Northern Tianshan

Abstract Mountain fronts are key areas where to study the deformation mechanisms and the geodynamic evolution of orogenic belts. Different approaches based on either geological or geophysical data analysis have been proposed. However, in spite of recent theoretical and technical developments, these often remain within a single disciplinary framework and diverging views and models sometimes arise. The front of the northern Tianshan intracontinental collision range is thus quite exemplary for the variety of the tectonic models that have been proposed to explain its development. This paper introduces a multidisciplinary approach combining field geological/structural observations, reflection seismic profile interpretation, borehole results and a gravity study performed in the study area. This approach was conducted in the case study of a representative cross-section within the North Tianshan area, along the Jingou river. An extensive geological/structural survey across the fold and thrust belt was first carried out providing surface constraints on the shallowest parts of the section. Deep structure within the Junggar basin was constrained through processing and interpretation of reflection seismic data together with available borehole results. As it is often the case, the available seismic profiles do not extend to the frontal basement contact zone, or quality of the data was not good enough to allow interpretation. Consequently, a gravity survey and modelling finally allowed interpreting the deep structure of the cover/basement contact. By integrating all the data, the resulting regional-scale cross-section shows a new comprehensive image of the upper crustal structure in this area. In particular, results imply that the mountain basement thrust northwards onto the sedimentary layers with development of a second order fold. Besides, this study further suggests thick-skinned type deformations below the fold and thrust belt. From the example of the Jingou river section, this study illustrates the interest of incorporating gravity data analysis together with – more classical – seismic profiles interpretation and structural analyses for studying orogenic belt frontal areas.

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Thrust geometries and deep structure of the outer and lesser Himalaya, Kumaon and Garhwal (India): Implications for evolution of the Himalayan fold-and-thrust belt

Tectonics ◽

10.1029/93tc01130 ◽

1994 ◽

Vol 13 (1) ◽

pp. 89-109 ◽

Cited By ~ 283

Author(s):

Praveen Srivastava ◽

Gautam Mitra

Keyword(s):

Deep Structure ◽

Thrust Belt ◽

Lesser Himalaya ◽

Fold And Thrust Belt

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The April 9, 2013, Kaki Earthquake (Mw=6.3) in SW Iran Occurred along a Blind Backthrust in the Fars Geological Province of the Zagros Fold & Thrust Belt

Geological Society London Special Publications ◽

10.1144/sp501-2021-20 ◽

2021 ◽

pp. SP501-2021-20

Author(s):

Marzieh Khalili ◽

Yildirim Dilek

Keyword(s):

Surface Expression ◽

Fault System ◽

Thrust Belt ◽

Tectonic Zone ◽

Focal Mechanism Solutions ◽

Fluvial Terraces ◽

Fold And Thrust Belt ◽

Active Tectonic ◽

Sw Iran ◽

A Minor

AbstractThe Zagros Fold and Thrust Belt (ZFTB) in southern Iran is a seismically active tectonic zone, where SW-vergent thrust faults and NW-SE- and NE-SW-oriented strike-slip fault systems accommodate for crustal shortening, resulting from the active Arabia-Eurasia collision. The majority of earthquakes in Iran occur within the ZFTB, posing a major hazard for the society. The April 9th, 2013, Kaki Earthquake (Mw = 6.3) in the southern part of the ZFTB took place along a fault that was previously unknown, regarding its surface expression, geometry and kinematics. We have used surface-subsurface distributions and focal mechanism solutions of the Kaki Earthquake aftershocks to characterize the fault system responsible for the quake. Our results indicate that it was a NE-vergent thrust fault with a minor dextral component that slipped ∼7 to 17 km at depth, causing the Kaki Earthquake. There were no surface ruptures, although some surface fissures developed in fluvial terraces during the main shock. We interpret this fault as a blind backthrust, which likely represents a reactivated Mesozoic basement fault, emanating from the Zagros detachment surface. An upper shallow décollement zone within the Miocene Gachsaran Salt facilitated its upward propagation on the back-limb of an overturned syncline.

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Deep structure beneath Lake Ontario: crustal-scale Grenville subdivisions

Canadian Journal of Earth Sciences ◽

10.1139/e94-025 ◽

1994 ◽

Vol 31 (2) ◽

pp. 255-270 ◽

Cited By ~ 25

Author(s):

D. A. Forsyth ◽

B. Milkereit ◽

C. A. Zelt ◽

D. J. White ◽

R. M. Easton ◽

...

Keyword(s):

New York ◽

Shear Zone ◽

Deep Structure ◽

Gravity Anomalies ◽

Lake Ontario ◽

Shear Zones ◽

Tectonic Zone ◽

Prince Edward County ◽

Basement High ◽

Marine Seismic

Lake Ontario marine seismic data reveal major Grenville crustal subdivisions beneath central and southern Lake Ontario separated by interpreted shear zones that extend to the lower crust. A shear zone bounded transition between the Elzevir and Frontenac terranes exposed north of Lake Ontario is linked to a seismically defined shear zone beneath central Lake Ontario by prominent aeromagnetic and gravity anomalies, easterly dipping wide-angle reflections, and fractures in Paleozoic strata. We suggest the central Lake Ontario zone represents crustal-scale deformation along an Elzevir–Frontenac boundary zone that extends from outcrop to the south shore of Lake Ontario.Seismic images from Lake Ontario and the exposed western Central Metasedimentary Belt are dominated by crustal-scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east-dipping linear reflections. The images show that zones analogous to the interpreted Grenville Front Tectonic Zone are also present within the Central Metasedimentary Belt and support models of northwest-directed crustal shortening for Grenvillian deep crustal deformation beneath most of southeastern Ontario.A Precambrian basement high, the Iroquoian high, is defined by a thinning of generally horizontal Paleozoic strata over a crestal area above the basement shear zone beneath central Lake Ontario. The Iroquoian high helps explain the peninsular extension into Lake Ontario forming Prince Edward County, the occurrence of Precambrian inlier outcrops in Prince Edward County, and Paleozoic fractures forming the Clarendon–Linden structure in New York.

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