Extensive Sills in the Continental Basement from Deep Seismic Reflection Profiling

Crustal seismic reflection profiling has revealed the presence of extensive, coherent reflections with anomalously high amplitudes in the crystalline crust at a number of locations around the world. In areas of active tectonic activity, these seismic “bright spots” have often been interpreted as fluid magma at depth. The focus in this report is high-amplitude reflections that have been identified or inferred to mark interfaces between solid mafic intrusions and felsic to intermediate country rock. These “frozen sills” most commonly appear as thin, subhorizontal sheets at middle to upper crustal depths, several of which can be traced for tens to hundreds of kilometers. Their frequency among seismic profiles suggest that they may be more common than widely realized. These intrusions constrain crustal rheology at the time of their emplacement, represent a significant mode of transfer of mantle material and heat into the crust, and some may constitute fingerprints of distant mantle plumes. These sills may have played important roles in overlying basin evolution and ore deposition.

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Crustal domains in the Western Barents Sea

Geophysical Journal International ◽

10.1093/gji/ggaa112 ◽

2020 ◽

Vol 221 (3) ◽

pp. 2155-2169

Author(s):

Alexey Shulgin ◽

Jan Inge Faleide ◽

Rolf Mjelde ◽

Asbjørn Breivik ◽

Ritske Huismans

Keyword(s):

Seismic Reflection ◽

Barents Sea ◽

The Body ◽

Gravity Modelling ◽

Southern Boundary ◽

Mafic Intrusions ◽

Crustal Block ◽

The Barents Sea ◽

Crystalline Crust ◽

Regional Gravity

SUMMARY The crustal architecture of the Barents Sea is still enigmatic due to complex evolution during the Timanian and Caledonian orogeny events, further complicated by several rifting episodes. In this study we present the new results on the crustal structure of the Caledonian–Timanian transition zone in the western Barents. We extend the work of Aarseth et al. (2017), by utilizing the seismic tomography approach to model Vp, Vs and Vp/Vs ratio, combined with the reprocessed seismic reflection line, and further complemented with gravity modelling. Based on our models we document in 3-D the position of the Caledonian nappes in the western Barents Sea. We find that the Caledonian domain is characterized by high crustal reflectivity, caused by strong deformation and/or emplacement of mafic intrusions within the crystalline crust. The Timanian domain shows semi-transparent crust with little internal reflectivity, suggesting less deformation. We find, that the eastern branch of the earlier proposed Caledonian suture, cannot be associated with the Caledonian event, but can rather be a relict from the Timanian terrane assemblance, marking one of the crustal microblocks. This crustal block may have an E–W striking southern boundary, along which the Caledonian nappes were offset. A high-velocity/density crustal body, adjacent to the Caledonian–Timanian contact zone, is interpreted as a zone of metamorphosed rocks based on the comparison with global compilations. The orientation of this body correlates with regional gravity maxima zone. Two scenarios for the origin of the body are proposed: mafic emplacement during the Timanian assembly, or massive mafic intrusions associated with the Devonian extension.

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Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling

Science ◽

10.1126/science.274.5293.1688 ◽

1996 ◽

Vol 274 (5293) ◽

pp. 1688-1690 ◽

Cited By ~ 235

Author(s):

L. D. Brown ◽

W. Zhao ◽

K. D. Nelson ◽

M. Hauck ◽

D. Alsdorf ◽

...

Keyword(s):

Seismic Reflection ◽

Southern Tibet ◽

Bright Spots ◽

Seismic Reflection Profiling

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Cenozoic crustal deformation of the offshore Burgos basin region (NE Gulf of Mexico). A new interpretation of deep penetration multichannel seismic reflection lines

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.179.2.161 ◽

2008 ◽

Vol 179 (2) ◽

pp. 161-174 ◽

Cited By ~ 10

Author(s):

Charlotte Le Roy ◽

Claude Rangin

Keyword(s):

Gulf Of Mexico ◽

Fault Zone ◽

Coastal Plain ◽

Crustal Deformation ◽

Seismic Reflection ◽

Tectonic Activity ◽

Normal Faults ◽

Deep Penetration ◽

Reverse Fault ◽

Seismic Profiles

Abstract Along northeastern Mexico close to the Texas-Mexico border, the Burgos basin and its extension offshore was developed and deformed from the Paleocene up to Present time. This is a key triple junction between the sub meridian dextral transtensive coastal plain of the Gulf of Mexico extending far to the south in Mexico, the NE Corsair fault zone offshore and the sinistral Rio Bravo fault zone, a reactivated segment of the Texas lineament. Offshore NE Mexico, in the main study area covered by available seismic profiles, we have evidenced below the main well known gravitational décollement level (5 to 7 s twtt → 6 to 8 km) a Cenozoic deep-rooted deformation outlined by a N010° W trending deep-seated reverse fault zone and crustal folding down to the Moho (11 s twtt → ~ 20 km). Based on extensive offshore 2D industrial multi-channel seismic reflection surveys, deep exploration wells and gravimetric data, we focus our study on the deep crustal fabric and its effects on the gravitational tectonics in the upper sedimentary layers: submeridian crustal transtensional normal faults and open folding of the identified Mesozoic basement were interpreted as Cenozoic buckling of the crust during a major phase of oblique crustal extension. This deformation has probably enhanced gravity sliding along N030° growth-faults related to salt withdrawal and halokinesis in the offshore Burgos basin. We have tentatively made a link between this crustal deformation episode and the Neogene tectonic inversion of the Laramide foredeep basin of the Sierra Madre Oriental. The latter is still affected by crustal strike slip faulting associated with basaltic volcanism observed into the gulf coastal plain. This study favours a dominant crustal Cenozoic tectonic activity along the gulf margin without any clear evidence of Mesozoic tectonic reactivation. We propose that the large gravity collapse of the gulf margin was triggered by subsequent crustal deformation.

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Processed and interpreted U.S. Geological Survey seismic reflection profile and vertical seismic profiles, Niobrara County, Wyoming

10.3133/oc114 ◽

1981 ◽

Keyword(s):

Seismic Reflection ◽

Geological Survey ◽

Seismic Reflection Profile ◽

Seismic Profiles ◽

Vertical Seismic Profiles ◽

Reflection Profile

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The North American Midcontinent Rift beneath Lake Superior from Glimpce seismic reflection profiling

Tectonics ◽

10.1029/tc008i002p00305 ◽

1989 ◽

Vol 8 (2) ◽

pp. 305-332 ◽

Cited By ~ 122

Author(s):

W. F. Cannon ◽

Alan G. Green ◽

D. R. Hutchinson ◽

Myung Lee ◽

Bernd Milkereit ◽

...

Keyword(s):

North American ◽

Seismic Reflection ◽

Lake Superior ◽

Midcontinent Rift ◽

The North ◽

Seismic Reflection Profiling

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Incomplete AVO near salt structures

Geophysics ◽

10.1190/1.1443268 ◽

1992 ◽

Vol 57 (4) ◽

pp. 543-553 ◽

Cited By ~ 4

Author(s):

Christopher P. Ross

Keyword(s):

Seismic Profiles ◽

Spectral Modeling ◽

Signal Degradation ◽

Amplitude Versus Offset ◽

Bright Spots ◽

Close Proximity ◽

Pseudo Spectral ◽

Amplitude Versus ◽

Structure Class ◽

Made In

Amplitude versus offset (AVO) measurements for deep hydrocarbon‐bearing sands can be compromised when made in close proximity to a shallow salt piercement structure. Anomalous responses are observed, particularly on low acoustic impedance bright spots. CMP data from key seismic profiles traversing the bright spots do not show the expected Class 3 offset responses. On these CMPs, significant decrease of far trace energy is observed. CMP data from other seismic profiles off‐structure do exhibit the Class 3 offset responses, implying that structural complications may be interfering with the offset response. A synthetic AVO gather was generated using well log data, which supports the off‐structure Class 3 responses, further reinforcing the concept of structurally‐biased AVO responses. Acoustic, pseudo‐spectral modeling of the structure substantiates the misleading AVO response. Pseudo‐spectral modeling results suggest that signal degradation observed on the far offsets is caused by wavefield refraction—a shadow zone, where the known hydrocarbon‐bearing sands are not completely illuminated. Such shadow zones obscure the correct AVO response, which may have bearing on exploration and development.

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Results of a seismic reflection survey across the fault zone between the Thompson nickel belt and the Churchill Tectonic Province, northern Manitoba

Canadian Journal of Earth Sciences ◽

10.1139/e81-002 ◽

1981 ◽

Vol 18 (1) ◽

pp. 13-25 ◽

Cited By ~ 5

Author(s):

A. G. Green

Keyword(s):

Fault Zone ◽

Lower Crust ◽

Seismic Reflection ◽

High Amplitude ◽

Small Scale ◽

Upper Crust ◽

Travel Times ◽

Reflection Point ◽

Point Data ◽

Amplitude Reflection

Approximately 11 km of four-fold common reflection point data have been recorded across a region that spans the contact fault zone between the Thompson nickel belt and the Churchill Tectonic Province. From these data it is shown that the upper crust in this region and, to a lesser extent, the lower crust are characterized by numerous scattered events that originate from relatively small-scale features. Within the Thompson nickel belt two extensive and particularly high-amplitude reflection zones, at two-way travel times of t = 5.0–5.5 s and t = 6.0–6.5 s, are recorded with apparent northwesterly dips of 0–20 °C. These reflection zones, which have a laminated character, are truncated close to the faulted contact with the Churchill Province. Both the contact fault zone and the Churchill Province in this region have crustal sections that are relatively devoid of significant reflectors. The evidence presented here confirms that the crustal section of the Thompson nickel belt is fundamentally different from that of the Churchill Tectonic Province.

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