scholarly journals The distribution and composition of high‐velocity lower crust across the continental U.S.: Comparison of seismic and xenolith data and implications for lithospheric dynamics and history

Tectonics ◽  
2017 ◽  
Vol 36 (8) ◽  
pp. 1455-1496 ◽  
Author(s):  
Vera Schulte‐Pelkum ◽  
Kevin H. Mahan ◽  
Weisen Shen ◽  
Josh C. Stachnik
Keyword(s):  
High Velocity ◽  
Lower Crust ◽  
Lithospheric Dynamics

Spatial distribution and origin of the high-velocity lower crust in the northeastern South China Sea

2021 ◽  
pp. 229086
Author(s):  
Jinhui Cheng ◽  
Jiazheng Zhang ◽  
Minghui Zhao ◽  
Feng Du ◽  
Chaoyan Fan ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
South China Sea ◽  
South China ◽  
High Velocity ◽  
Lower Crust ◽  
China Sea ◽  
Northeastern South China Sea

Crust-mantle velocity structure in Shanxi rift, Central North China Craton

2020 ◽  
Author(s):  
Yan Cai ◽  
Jianping Wu
Keyword(s):  
Upper Mantle ◽  
High Velocity ◽  
North China Craton ◽  
Lower Crust ◽  
North China ◽  
Velocity Structure ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
The North ◽  
Shanxi Rift

<p>North China Craton is the oldest craton in the world. It contains the eastern, central and western part. Shanxi rift and Taihang mountain contribute the central part. With strong tectonic deformation and intense seismic activity, its crust-mantle deformation and deep structure have always been highly concerned. In recent years, China Earthquake Administration has deployed a dense temporary seismic array in North China. With the permanent and temporary stations, we obtained the crust-mantle S-wave velocity structure in the central North China Craton by using the joint inversion of receiver function and surface wave dispersion. The results show that the crustal thickness is thick in the north of the Shanxi rift (42km) and thin in the south (35km). Datong basin, located in the north of the rift, exhibits large-scale low-velocity anomalies in the middle-lower crust and upper mantle; the Taiyuan basin and Linfen basin, located in the central part, have high velocities in the lower crust and upper mantle; the Yuncheng basin, in the southern part, has low velocities in the lower crust and upper mantle velocities, but has a high-velocity layer below 80 km. We speculate that an upwelling channel beneath the west of the Datong basin caused the low velocity anomalies there. In the central part of the Shanxi rift, magmatic bottom intrusion occurred before the tension rifting, so that the heated lithosphere has enough time to cool down to form high velocity. Its current lithosphere with high temperature may indicate the future deformation and damage. There may be a hot lithospheric uplift in the south of the Shanxi rift, heating the crust and the lithospheric mantle. The high-velocity layer in its upper mantle suggests that the bottom of the lithosphere after the intrusion of the magma began to cool down.</p>

Seismic investigation of the East Greenland volcanic rifted margin

1997 ◽  
pp. 50-54
Author(s):  
Trine Dahl-Jensen ◽  
W. Steven Holbrook ◽  
John R. Hopper ◽  
Peter B. Kelemen ◽  
Hans Christian Larsen ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
High Velocity ◽  
Lower Crust ◽  
The South ◽  
East Greenland ◽  
Seismic Investigation ◽  
Iceland Plume ◽  
Greenland Margin ◽  
Rifted Margin

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Dahl-Jensen, T., Holbrook, W. S., Hopper, J. R., Kelemen, P. B., Larsen, H. C., Detrick, R., Bernstein, S., & Kent, G. (1997). Seismic investigation of the East Greenland volcanic rifted margin. Geology of Greenland Survey Bulletin, 176, 50-54. https://doi.org/10.34194/ggub.v176.5061 _______________ The SIGMA project (Seismic Investigation of the Greenland MArgin) was designed to make accurate measurements of crustal thickness, velocity structure and seismic reflectivity along the hotspot-influenced volcanic rifted margin (VRM) off South-East Greenland (Fig. 1). SIGMA is a joint project between researchers at Woods Hole Oceanographic Institution (Woods Hole, Mass., USA) and the Danish Lithosphere Centre (DLC), and data was acquired on a cruise with R/V Maurice Ewing in August–October 1996. VRMs are characterised by a prism of igneous rocks that occupies the continent–ocean transition zone in an 80 to 150 km wide belt, several times thicker than normal oceanic crust, and which extends in some regions for more than 1500 km along strike. This thick igneous crust has two characteristics on seismic data: a seawarddipping reflector sequence (SDRS) interpreted as subaerially erupted basalt flows and intercalated volcanoclastics, and a high-velocity lower crust with P-wave velocities (7.2–7.6 km/s) suggestive of mafic to ultramafic intrusive rocks (Hinz, 1981; Mutter et al., 1982, 1984, 1988; Larsen & Jakobsdóttir, 1988; White & McKenzie, 1989; Holbrook & Kelemen, 1993). Several models for the thermal and mechanical processes involved in the formation of VRMs have been proposed, including: decompression melting during passive upwelling near a mantle plume (White & McKenzie, 1989); actively upwelling plume heads impinging on the base of the lithosphere (Richards et al., 1989; Duncan & Richards, 1991; Griffiths & Campbell, 1991); enhanced upper mantle convection driven by steep, cold lithospheric edges adjacent to the rift (Mutter et al., 1988) and hot upper mantle due to non-plume ‘hot cells’ or insulation by supercontinents (Gurnis, 1988). SIGMA consists of four transects systematically sampling the structure of the South-East Greenland margin and the continent–ocean transition at increasing distance from the Iceland hotspot track, in order to investigate the South-East Greenland VRM with respect to the following questions:1) What is the structure of the transition from continental to thick igneous crust, and thence to normal oceanic crust? Is the transition abrupt or gradual? To what extent does faulting play a role? Does the abruptness of the continent–ocean boundary change with distance from the Iceland plume? 2) What was the total volume of magmatism during continental breakup on the South-East Greenland margin and its conjugates, and how does it vary in space and time? How does this magmatism relate to distance from the Iceland plume and to its temporal magmatic budget? What is the proportion of plutonic to volcanic rocks, and how does this vary with distance from the hotspot track and with total crustal thickness? 3) Does high velocity lower crust exist beneath the margin, and if so, is there any evidence that its composition, thickness, and distribution change along strike? How might such changes relate to variations in melting conditions (temperature and degree of melting) with distance from the plume? 4) Is the structure of the South-East Greenland margin symmetrical with its conjugate margins on the Hatton–Rockall Bank and Iceland–Faeroes Ridge? What combinations of pure shear and simple shear processes might explain the conjugate structures?

A high‐velocity layer in the lower crust of the North German Basin

Terra Nova ◽  
1995 ◽  
Vol 7 (3) ◽  
pp. 327-337 ◽  
Author(s):  
W. Rabbel ◽  
K. Förste ◽  
A. Schulze ◽  
R. Bittner ◽  
J. Röhl ◽  
...  
Keyword(s):  
High Velocity ◽  
Lower Crust ◽  
North German Basin ◽  
The North ◽  
High Velocity Layer ◽  
Velocity Layer ◽  
German Basin

Crustal structure of the Grenville Province in southeastern Labrador from refraction seismic data: evidence for a high-velocity lower crustal wedge

2001 ◽  
Vol 38 (10) ◽  
pp. 1463-1478 ◽  
Author(s):  
Thomas Funck ◽  
Keith E Louden ◽  
Ian D Reid
Keyword(s):  
Crustal Structure ◽  
High Velocity ◽  
Lower Crust ◽  
Lower Layer ◽  
P Wave ◽  
Grenville Province ◽  
Middle Crust ◽  
Basaltic Magmatism ◽  
Refraction Seismic ◽  
Lower Crustal

The crustal structure of the eastern Grenville and Makkovik provinces was determined using two onshore–offshore refraction seismic lines of the Lithoprobe Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT). A gravity high in the Hawke River terrane correlates with increased P-wave velocities in the upper 30 km of the crust (6.2–6.7 km/s in the upper and middle crust and 6.9–7.1 km/s below) which we interpret as structure inherited from the Labradorian orogen. Velocities in the adjacent Groswater Bay terrane are 6.0–6.55 km/s in the upper and middle crust and 6.6–6.95 km/s in the lower crust. The entire Grenville crust is underlain by a 15–20 km thick high-velocity lower crustal (HVLC) wedge consisting of an upper layer (7.1–7.4 km/s) and a lower layer (7.6–7.8 km/s). The HVLC wedge is interpreted as an underplated layer formed during Iapetan rifting. This interpretation is based on the correlation with the 615 Ma Long Range dykes onshore and the eastward termination of the wedge at the Cartwright Arch. Similar HVLC layers are found offshore western Newfoundland, suggesting that the underplating may be a continuous feature along the passive Grenvillian margin. The Cartwright Arch is characterized by velocities of 6.4 km/s and 4 km thick sediment sequences (4.3–5.7 km/s) in the surrounding basin, interpreted as an extensional basin with basaltic magmatism within the arch. The Grenville front is clearly marked by a decrease of velocities in the Makkovik Province (5.8–6.4 km/s in the upper and middle crust, 6.65–6.85 km/s in the lower crust) and a gradual thickening of the crust (not including the HVLC layer) from 30 km in the Grenville Province to 35 km in the Makkovik Province.

scholarly journals Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental break-up

2014 ◽  
Vol 6 (1) ◽  
pp. 1335-1370 ◽  
Author(s):  
K. Becker ◽  
D. Franke ◽  
R. B. Trumbull ◽  
M. Schnabel ◽  
I. Heyde ◽  
...  
Keyword(s):  
High Velocity ◽  
Lower Crust ◽  
Small Body ◽  
Seismic Refraction ◽  
South Atlantic ◽  
The South ◽  
Cross Sectional ◽  
Velocity Models ◽  
Rifted Margins ◽  
Break Up

Abstract. High-velocity lower crust (HVLC) and seaward dipping reflector sequences (SDRs) are typical features of volcanic rifted margins. However, the nature and origin of HVLC is under discussion. Here we provide a comprehensive analysis of deep crustal structures in the southern segment of the South Atlantic and an assessment of HVLC along the margins. Two new seismic refraction lines off South America fill a gap in the data coverage and together with five existing velocity models allow a detailed investigation of the lower crustal properties on both margins. An important finding is the major asymmetry in volumes of HVLC on the conjugate margins. The seismic refraction lines across the South African margin reveal four times larger cross sectional areas of HVLC than at the South American margin, a finding that is in sharp contrast to the distribution of the flood basalts in the Paraná-Etendeka Large Igneous Provinces (LIP). Also, the position of the HVLC with respect to the seaward dipping reflector sequences varies consistently along both margins. Close to the Falkland-Agulhas Fracture Zone a small body of HVLC is not accompanied by seaward dipping reflectors. In the central portion of both margins, the HVLC is below the inner seaward dipping reflector wedges while in the northern area, closer to the Rio Grande Rise/Walvis Ridge, large volumes of HVLC extend far seawards of the inner seaward dipping reflectors. This challenges the concept of a simple extrusive/intrusive relationship between seaward dipping reflector sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and break-up process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple shear dominated extension.

scholarly journals Long-lived Paleoproterozoic eclogitic lower crust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sebastian Buntin ◽  
Irina M. Artemieva ◽  
Alireza Malehmir ◽  
Hans Thybo ◽  
Michal Malinowski ◽  
...  
Keyword(s):  
High Velocity ◽  
Lower Crust ◽  
Crustal Layer ◽  
Crustal Rocks ◽  
Long Term Stability ◽  
Eclogite Facies ◽  
Conventional Models ◽  
Lower Crustal

AbstractThe nature of the lower crust and the crust-mantle transition is fundamental to Earth sciences. Transformation of lower crustal rocks into eclogite facies is usually expected to result in lower crustal delamination. Here we provide compelling evidence for long-lasting presence of lower crustal eclogite below the seismic Moho. Our new wide-angle seismic data from the Paleoproterozoic Fennoscandian Shield identify a 6–8 km thick body with extremely high velocity (Vp ~ 8.5–8.6 km/s) and high density (>3.4 g/cm3) immediately beneath equally thinned high-velocity (Vp ~ 7.3–7.4 km/s) lowermost crust, which extends over >350 km distance. We relate this observed structure to partial (50–70%) transformation of part of the mafic lowermost crustal layer into eclogite facies during Paleoproterozoic orogeny without later delamination. Our findings challenge conventional models for the role of lower crustal eclogitization and delamination in lithosphere evolution and for the long-term stability of cratonic crust.

scholarly journals Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental breakup

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 1011-1026 ◽  
Author(s):  
K. Becker ◽  
D. Franke ◽  
R. Trumbull ◽  
M. Schnabel ◽  
I. Heyde ◽  
...  
Keyword(s):  
High Velocity ◽  
Lower Crust ◽  
Small Body ◽  
Seismic Refraction ◽  
South Atlantic ◽  
Large Igneous Province ◽  
Asymmetric Distribution ◽  
The South ◽  
Velocity Models ◽  
Rifted Margins

Abstract. High-velocity lower crust (HVLC) and seaward-dipping reflector (SDR) sequences are typical features of volcanic rifted margins. However, the nature and origin of HVLC is under discussion. Here we provide a comprehensive analysis of deep crustal structures in the southern segment of the South Atlantic and an assessment of HVLC along the margins. Two new seismic refraction lines off South America fill a gap in the data coverage and together with five existing velocity models allow for a detailed investigation of the lower crustal properties on both margins. An important finding is the major asymmetry in volumes of HVLC on the conjugate margins. The seismic refraction lines across the South African margin reveal cross-sectional areas of HVLC 4 times larger than at the South American margin, a finding that is opposite to the asymmetric distribution of the flood basalts in the Paraná–Etendeka Large Igneous Province. Also, the position of the HVLC with respect to the SDR sequences varies consistently along both margins. Close to the Falkland–Agulhas Fracture Zone in the south, a small body of HVLC is not accompanied by SDRs. In the central portion of both margins, the HVLC is below the inner SDR wedges while in the northern area, closer to the Rio Grande Rise-Walvis Ridge, large volumes of HVLC extend far seaward of the inner SDRs. This challenges the concept of a simple extrusive/intrusive relationship between SDR sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and breakup process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple-shear-dominated extension.

Regional lithospheric deformation beneath the East Qinling-Dabie orogenic belt based on ambient noise tomography

2021 ◽  
Author(s):  
Yu Wei ◽  
Shuangxi Zhang ◽  
Mengkui Li ◽  
Tengfei Wu ◽  
Yujin Hua ◽  
...  
Keyword(s):  
High Velocity ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
North China ◽  
3D Model ◽  
Orogenic Belt ◽  
Yangtze Block ◽  
North China Block ◽  
The North ◽  
Dabie Orogenic Belt

Summary The Qinling–Dabie orogenic belt, which contain the arc-shaped Dabbashan orocline and is the world's largest belt of HP/UHP metamorphic rocks, formed by a long-term complex amalgamation process between the North China Block and the Yangtze Block. To understand the collision processes and tectonic evolution, we constructed a three-dimensional (3D) S-wave velocity model from the surface to a depth of ∼120 km in the eastern Qinling-Dabie orogenic belt and its adjacent region by inverting 5–70 s phase velocity dispersion data of Rayleigh waves extracted from ambient noise data. Our 3D model reveals low velocities in the middle–lower crust and high velocities in the upper mantle beneath the orogenic belt, suggesting the delamination of the lower crust. Our results support a two-stage exhumation model for the HP/UHP rocks in the study area. First-stage exhumation was caused by the slab breaking away from the subducted Yangtze Block during the Early–Middle Triassic. Partial melting of the lithospheric mantle caused by slab breakoff–related asthenospheric upwelling weakened the lithospheric mantle beneath the orogenic belt, and continued convergence of the two continental blocks led to further thickening of the lower crust. Such processes promoted lower-crust delamination, which triggered the second-stage exhumation of the HP/UHP rocks. In the Dabbashan orocline, two deep-rooted high-velocity domes, that is, Hannan–Micang and Shennong–Huangling domes, acted as a pair of indenters during the formation stage. High-velocity lower crust was observed beneath the Dabbashan orocline. In addition, our 3D model reveals that high-velocity lithospheric mantle extends from the Sichuan Basin to the Dabbashan orocline, with a subhorizontal distribution, providing strong support for the high-velocity lower crust. We also observed the destruction of lithospheric mantle beneath the Yangtze Block; the destruction area is bounded by the North–South Gravity Lineament, suggesting that the destruction mechanism of the Yangtze Block may be similar to the North China Block.

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