scholarly journals Basement Structure and Styles of Active Tectonic Deformation in Central Interior Alaska

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 127
Author(s):  
Nilesh C. Dixit ◽  
Catherine Hanks
Keyword(s):  
Crustal Structure ◽  
Foreland Basin ◽  
Active Regions ◽  
Structural Features ◽  
Tectonic Deformation ◽  
Block Rotation ◽  
High Concentration ◽  
Intraplate Earthquakes ◽  
Interior Alaska ◽  
Nenana Basin

Central Interior Alaska is one of the most seismically active regions in North America, exhibiting a high concentration of intraplate earthquakes approximately 700 km away from the southern Alaska subduction zone. Seismological evidence suggests that intraplate seismicity in the region is not uniformly distributed, but concentrated in several discrete seismic zones, including the Nenana basin and the adjacent Tanana basin. Although the location and magnitude of the seismic activity in both basins are well defined by a network of seismic stations in the region, the tectonic controls on these intraplate earthquakes and the heterogeneous nature of Alaska’s continental interior remain poorly understood. We investigated the crustal structure of the Nenana and Tanana basins using available seismic reflection, aeromagnetic and gravity anomaly data, supplemented by geophysical well logs and outcrop data. We developed nine new two-dimensional forward models to delineate internal geometries and the crustal structure of Alaska’s interior. The results of our study demonstrates a strong crustal heterogeneity beneath both basins. The Tanana basin is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the Central Alaska Range. Northeast-trending left lateral strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. The Nenana basin has a fundamentally different geometry. It is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Fault. This study identifies two distinct modes of current tectonic deformation in Central Interior Alaska and provides a basis for modeling the interplay between intraplate stress fields and major structural features that potentially influence the generation of intraplate earthquakes in the region.

scholarly journals Structural Features and Evolution of the Northwestern Sichuan Basin: Insights From Discrete Numerical Simulations

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenqiao Xu ◽  
Hongwei Yin ◽  
Dong Jia ◽  
Changsheng Li ◽  
Wei Wang ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Sichuan Basin ◽  
Lower Layer ◽  
Foreland Basin ◽  
Middle Layer ◽  
Lower Triassic ◽  
Structural Features ◽  
Tectonic Deformation ◽  
Thrust Front ◽  
Rapid Uplift

The northwestern Sichuan Basin has experienced Meso-Cenozoic intracontinental compressional tectonic processes and formed multi-detachment stratigraphic distribution of foreland basins and fold-thrust belts, which have caused complicated structural deformations in the deep buried layers. Rapid uplift with accelerated erosion and two sets of detachments in the Lower Triassic and Lower Cambrian controlled the multilevel deformation structure. We conducted discrete numerical simulations with double weak detachments and erosion under extrusion conditions in order to examine the mechanics and kinematics of the frontalpiedmont zones of the NW Sichuan Basin. The following findings were made. (1) With continuous compression, the weak detachments promoted the decoupled and ladder-like deformation of the thrust belt, where the deformation above the slip layer extended further than it did below it. Rapid uplift and erosion at the thrust front contributed to the formation of a passive roof fault and a monocline in the upper layer, a series of forward and backward thin-skinned thrust-buried structures in the middle layer sandwiched between two weak detachments and stacking structures in the lower layer. (2) Erosion effectively prevents the deformation from propagating above the upper detachment, but can advance a horizontal transition in the deformation style generated within the middle brittle layer: from oblique and tight fault propagation folds to symmetrical, wide, and gentle detachment folds. (3) The model results consistent with tectonic deformation in the NW Sichuan Basin indicate a possible evolutionary mechanism under compression. There is hierarchical deformation of uncoordinated contraction controlled by the Lower Triassic and Early Cambrian weak layers, with the characteristics of the shallow monocline, the middle thin-skinned thrusts, and the deeper basement-involved folds. Continuous compression contributed a sequential pattern of steps as a whole, from the frontalpiedmont zones to the foreland basin, autochthonous stacking thrusts, and the huge buried structure in the NW Sichuan Basin. During the Himalayan period, syntectonic erosion along with the uplifted thrust front maintained the development of a passive-roof duplex and a huge forward buried structure.

Seismic Reflection Expression of Reactivated Structures in the New Madrid Rift Complex

1988 ◽  
Vol 59 (4) ◽  
pp. 141-150 ◽  
Author(s):  
John. L. Sexton
Keyword(s):  
Seismic Reflection ◽  
Structural Features ◽  
Normal Faults ◽  
Earthquake Activity ◽  
Seismic Zone ◽  
Reflection Method ◽  
Intraplate Earthquakes ◽  
Reflection Data ◽  
Seismic Reflection Method ◽  
New Madrid

Abstract An important aspect of seismogenesis concerns the role of preexisting faults and other structural features as preferred zones of weakness in determining the pattern of strain accumulation and seismicity. Reactivation of zones of weakness by present day stress fields may be the cause of many intraplate earthquakes. To understand the relation between reactivated structures and seismicity, it is necessary to identify structures which are properly oriented with respect to the present-day stress field so that reactivation can occur. The seismic reflection method is very useful for identifying and delineating structures, particularly in areas where the structures are buried as in the New Madrid seismic zone. Application of the seismic reflection method in widely separated locations within the New Madrid rift complex has resulted in successful detection and delineation of reactivated rift-related structures which are believed to be associated with earthquake activity. The purpose of this paper is to discuss results from seismic reflection profiling in the New Madrid rift complex. Reflection data from several surveys including USGS Vibroseis* surveys in the Reelfoot rift area reveal reactivated faults and other deep rift-related structures which appear to be associated with seismicity. High-resolution explosive and Mini-Sosie** reflection surveys on Reelfoot scarp and through the town of Cottonwood Grove, Tennessee, clearly show reverse faults in Paleozoic and younger rocks which have been reactivated to offset younger rocks. A Vibroseis survey in the Wabash Valley area of the New Madrid rift complex provides direct evidence for a few hundred feet of post-Pennsylvanian age reactivation of large-offset normal faults in Precambrian-age basement rocks. Several earthquake epicenters have been located in the vicinity of these structures. In the Rough Creek graben, Vibroseis reflection data provide clear evidence for reactivation of basement faults. The success of these reflection surveys shows that well-planned seismic reflection surveys must be included in any program seeking to determine the relationship between preexisting zones of weakness and seismicity of an area.

scholarly journals Structural features in the Miocene sediments of the Pécs-Danitzpuszta sand pit (SW Hungary)

2021 ◽  
Vol 151 (4) ◽  
pp. 411-422
Author(s):  
Krisztina Sebe
Keyword(s):  
Late Miocene ◽  
Structural Evolution ◽  
Bedding Plane ◽  
Structural Features ◽  
Normal Faults ◽  
Time Interval ◽  
Block Rotation ◽  
Lake Pannon ◽  
Basin Inversion ◽  
Upper Miocene

The Pécs-Danitzpuszta sand pit in southern Hungary exposes middle and upper Miocene (Badenian to Pannonian/Langhian to Tortonian) sediments along the mountain front fault zone of the Mecsek Mts and preserves an essential record of tectonic events during and after the early late Miocene, which are not exposed elsewhere in the region. In this paper we present structural observations recorded over 20 years of work, date the deformation events with mollusk biostratigraphy and make inferences on the structural evolution of the area. At the beginning of the time interval between 10.2–10.0 Ma, NNW–SSE (to NW–SE) extension created normal faults and negative flower structures. These show that extension-related fault activity lasted here up to the late Miocene. Shortly thereafter, still in the early part of the time interval between 10.2–10.0 Ma, N–S to NNW–SSE compression ensued and dominated the area ever since. Deformations under this stress field included reverse faulting in the Pannonian marls and sands, folding of the whole succession, with bedding-plane slip and shearingelated block rotation in the already deposited middle and upper Miocene marl layers and continuously changing bedding dips and southward thickening layers in the Pannonian sands. Lake level changes of Lake Pannon must have played a role in the formation of an angular unconformity within the sands besides compression. The compressional event can be explained by the Africa (Adria) – Europe convergence, but cannot be correlated regionally; it pre-dates basin inversion-related events reported from the region so far.

KINEMATICAL MODEL FOR FORMING THE SIMEAN LOW OF THE URALIAN FORELAND BASIN

2018 ◽  
pp. 23-32
Author(s):  
Al. V. Tevelev ◽  
I. A. Prudnikov ◽  
Ark. V. Tevelev ◽  
A. O. Khotylev ◽  
E. A. Volodina
Keyword(s):  
Foreland Basin ◽  
Shear Zones ◽  
Structural Features ◽  
The North ◽  
Lateral Extrusion ◽  
Kinematical Model

In this work we reported the structural features and mechanism of the formation of the Simskaya low of the Uralian foreland basin, besides the Karatau-Suleyman block as a whole. This block has the shape of a wedge, so with a general latitudinal compression, it experienced lateral extrusion to the north along the conjugated shear zones. This factor determined the local situation of meridional compression and latitudinal tension. In the central part of the block, the latitudinal stretching was compensated for by gradual deflection, which led to the formation of the Simskaya low.

Feedbacks between internal fluvial drainage and high-plateau tectonic growth. A mechanistic perspective.

2020 ◽  
Author(s):  
Daniel Garcia-Castellanos ◽  
Weiming Liu ◽  
Zhongping Lai ◽  
Ivone Jiménez-Munt ◽  
Lucía Struth ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Numerical Models ◽  
Plate Boundary ◽  
Active Regions ◽  
Sedimentary Basins ◽  
Tectonic Deformation ◽  
The Tibetan Plateau ◽  
Internal Drainage ◽  
High Plateau ◽  
River Incision

<p>High-plateaus are relatively flat areas at high elevations. The stream-power river-incision law predicts that surface water incises the landscape proportionally to local river slope, and therefore the margins of high-plateaus are prone to a river erosion that should terminate the low relief of the highlands that characterizes the plateau. This means that long-lived high-plateaus need an additional mechanism to compete with river incision.</p><p>In absence of tectonic deformation, river networks propagate into the plateau via a retrogressive wave of river incision. A well-constrained non-tectonic scenario is provided by the Neogene Duero and Ebro sedimentary basins in N Iberia, where ongoing incision rates presently range from .02 (Duero) to .5 m/kyr (Ebro) and have propagated upstream at similar rates of up to 0.2 km/kyr, based on cosmogenic dating studies combined with numerical modeling. These rates started with the transition from internal (endorheic) to external (exorheic) drainage of both basins sometime between 8 and 12 million years ago. Interestingly, while the pre-exorheic Ebro Basin sedimentary plateau has been mostly obliterated by erosion, the Duero Basin still preserves large areas of low relief, in spite of the very similar geological setting. The causes will be discussed using landscape evolution numerical modeling.</p><p>In contrast, tectonically active regions can counteract river incision and preserve high plateaus by longer time periods. Recent studies based on sedimentary stratigraphy of endorheic basins suggest that large areas of the Tibetan high plateau remain internally drained since ca 35 Ma. In the Altiplano/Puna plateau region internal drainage dates to ~15 Ma and the majority of the topographic uplift has taken place after 10 Ma. Computer models have shown that tectonic deformation is sensitive to internal drainage, because endorheism implies a nearly perfect sediment trap that effectively reduces the output of orogenic erosion to zero. The cancellation of orogen-scale erosion can severely modify tectonic deformation patterns, increase topography and propagate deformation further into the undeformed forelands of the orogenic system. Symmetrically, internal drainage is also promoted by the orographic rain shadow due to the growth of topography in the early stages of tectonism.</p><p>Numerical models coupling the aforementioned mechanisms have shown that, as sediment transport and accumulation within the endorheic region progresses, the propagation of deformation to areas more distal to the tectonic plate boundary can lead to a lower‐relief landscape. A recent reassessment of the ages of the Tibetan plateau sedimentary record in the Lunpola Basin seems consistent with an early onset of low relief and internal drainage. Finally, as topography and crustal thickness increase, lower crust flow is facilitated by the lower viscosity implied by higher pressure, favoring a further reduction of local relief within the highlands.</p>

scholarly journals Cenozoic tectonic and thermal history of the Nenana basin, central interior Alaska: new constraints from seismic reflection data, fracture history, and apatite fission-track analyses

2017 ◽  
Vol 54 (7) ◽  
pp. 766-784 ◽  
Author(s):  
Nilesh Dixit ◽  
Catherine Hanks ◽  
Alec Rizzo ◽  
Paul McCarthy ◽  
Bernard Coakley
Keyword(s):  
Seismic Reflection ◽  
Fission Track ◽  
Strike Slip ◽  
Apatite Fission Track ◽  
Plate Convergence ◽  
South Central ◽  
Interior Alaska ◽  
Late Paleocene ◽  
Half Graben ◽  
Nenana Basin

The Nenana basin of interior Alaska forms a segment of the diffuse plate boundary between the Bering and North American plates and is located within a complex zone of crustal-scale strike-slip deformation that accommodates compressional stresses in response to oblique plate convergence to the south. The basin is currently the focus of new oil and gas exploration. Integration of seismic reflection and well data, fracture data, and apatite fission-track analyses with regional data improves our understanding of the tectonic development of this continental strike-slip basin. The Nenana basin formed during the Late Paleocene as a 13 km wide half-graben, affected by regional intraplate magmatism and localized crustal thinning across the Minto Fault in south-central Alaska. The basin was uplifted and exhumed along this faulted margin in the Early Eocene through to Late Oligocene in response to oblique subduction along the southern Alaska margin. This event resulted in the removal of up to 1.5 km of Late Paleocene strata from the basin. Renewed rifting and subsidence during the Early Miocene widened the basin to the west resulting in deposition of Miocene non-marine clastic rocks in reactivated and newly formed extensional half-grabens. In the Middle to Late Miocene, left lateral strike-slip faulting was superimposed on this half-graben system, with rapid subsidence beginning in the Pliocene and continuing to the present day. At present, the Nenana basin is in a zone of transtensional deformation that accommodates compressional stresses in response to oblique plate convergence and allows tectonic subsidence by oblique extension along major basin-bounding strike-slip faults.

The crustal structure of the Himalaya: A synthesis

2019 ◽  
Vol 483 (1) ◽  
pp. 483-516 ◽  
Author(s):  
Keith Priestley ◽  
Tak Ho ◽  
Supriyo Mitra
Keyword(s):  
Crustal Structure ◽  
Body Wave ◽  
Foreland Basin ◽  
Indian Plate ◽  
Mountain Range ◽  
Northeastern India ◽  
Himalayan Mountain ◽  
Southern Side ◽  
Tethys Himalaya ◽  
The Himalaya

AbstractThis chapter examines the along-arc variation in the crustal structure of the Himalayan Mountain Range. Using results from published seismological studies, plus large teleseismic body-wave and surface-wave datasets which we analyse, we illustrate the along-arc variation by comparing the crustal properties beneath four representative areas of the Himalayan Mountain Range: the Western Syntaxis, the Garhwal–Kumaon, the Eastern Nepal–Sikkim, and the Bhutan–Northeastern India regions. The Western Syntaxis and the Bhutan–Northeastern India regions have a complicated structure extending far out in front of the main Range, whereas the Central Himalaya appear to have a much simpler structure. The deformation is more distributed beneath the western and eastern ends of the Range, but in general, the crust gradually thickens from c. 40 km on the southern side of the Foreland Basin to c. 80 km beneath the Tethys Himalaya. While the gross crustal structure of much of the Himalaya is becoming better known, our understanding of the internal structure of the Himalaya is still sketchy. The detailed geometry of the Main Himalayan Thrust and the role of the secondary structures on the underthrusting Indian Plate are yet to be characterized satisfactorily.

scholarly journals Changing of the guard: How the Lyme disease spirochete subverts the host immune response

2019 ◽  
Vol 295 (2) ◽  
pp. 301-313 ◽  
Author(s):  
George Chaconas ◽  
Mildred Castellanos ◽  
Theodore B. Verhey
Keyword(s):  
Immune Response ◽  
Lyme Disease ◽  
Antigenic Variation ◽  
Genetic Manipulation ◽  
Transmitted Disease ◽  
Structural Features ◽  
High Concentration ◽  
Evolutionarily Conserved ◽  
One Step ◽  
The Many

Lyme disease, also known as Lyme borreliosis, is the most common tick-transmitted disease in the Northern Hemisphere. The disease is caused by the bacterial spirochete Borrelia burgdorferi and other related Borrelia species. One of the many fascinating features of this unique pathogen is an elaborate system for antigenic variation, whereby the sequence of the surface-bound lipoprotein VlsE is continually modified through segmental gene conversion events. This perpetual changing of the guard allows the pathogen to remain one step ahead of the acquired immune response, enabling persistent infection. Accordingly, the vls locus is the most evolutionarily diverse genetic element in Lyme disease–causing borreliae. Small stretches of information are transferred from a series of silent cassettes in the vls locus to generate an expressed mosaic vlsE gene version that contains genetic information from several different silent cassettes, resulting in ∼1040 possible vlsE sequences. Yet, despite its extreme evolutionary flexibility, the locus has rigidly conserved structural features. These include a telomeric location of the vlsE gene, an inverse orientation of vlsE and the silent cassettes, the presence of nearly perfect inverted repeats of ∼100 bp near the 5′ end of vlsE, and an exceedingly high concentration of G runs in vlsE and the silent cassettes. We discuss the possible roles of these evolutionarily conserved features, highlight recent findings from several studies that have used next-generation DNA sequencing to unravel the switching process, and review advances in the development of a mini-vls system for genetic manipulation of the locus.

Lithospheric buckling dominates the Cenozoic subsidence of the Qaidam Basin, NE Tibetan Plateau

2021 ◽  
Author(s):  
Hu Xiaoyi ◽  
Wu Lei
Keyword(s):  
Tibetan Plateau ◽  
Qaidam Basin ◽  
Foreland Basin ◽  
Structural Features ◽  
Tectonic Subsidence ◽  
The Tibetan Plateau ◽  
Basin Formation ◽  
Orogenic Belts ◽  
The Impact ◽  
First Time

<p>Flexural basins are the common geological feature in convergent settings, and usually regarded as the result of flexural subsidence of the margins of under-thrusting cratons in response to the gravitational load of over-riding orogens. This process usually causes the fastest tectonic subsidence and thickest orogenic-related deposits in the basin margins adjacent to the orogens, such as India Foreland Basin in front of the Himalaya. The Qaidam Basin, which is the largest sedimentary basin within the Tibetan Plateau interior, was once interpreted to belong to this type and form by flexural subsidence on its south and north margins in response to loading of the Qiman Tagh and the South Qilian Shan orogenic belts, respectively. However, the latest studies present sedimentary and structural features that contrast to a typical foreland basin. These features include (1) depocenters being located along the central axis, rather than the margins, with thickest sediments up to 15 km, and (2) development of many high-angle reverse faults, rather than thin-skinned thrusts, to generate upper-crustal shortening as low as 10-15% (20 – 30 km), indicating that the widths of the orogenic belts juxtaposed atop the basin margins are limited. These features cannot be explained by the flexural subsidence of basin margins and/or sediment load. Herein, we investigate the impact of lithospheric buckling, which has been ignored in most studies of basin formation in compressional settings, on the tectonic subsidence of the Qaidam Basin through numerical simulation based on finite elastic plate model. We first use the flexural backstripping method to calculate the tectonic subsidence of the Cenozoic basement across the Qaidam Basin. And then, we simulate the tectonic subsidence caused by (1) gravitational load of orogenic belts alone, and (2) combined gravitational load and lithosphere buckling. The result shows that the simulated tectonic subsidence curve fits well with the real one only when considering the effect of lithospheric buckling that accounts for >90% tectonic subsidence. Our finding indicates for the first time that lithospheric buckling is also an important mechanism for the subsidence of intramountain basins like the Qaidam Basin, and should not be ignored when studying lithospheric-scale deformation across large orogenic belts.</p>

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