Seismic imaging of the upper mantle beneath the Rocky Mountain foreland, southwestern Alberta

2000 ◽  
Vol 37 (11) ◽  
pp. 1493-1507 ◽  
Author(s):  
David W Eaton ◽  
Gerald M Ross ◽  
Frederick A Cook ◽  
A VanderVelden
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Rocky Mountain ◽  
Seismic Signal ◽  
Ductile Deformation ◽  
Crust And Upper Mantle ◽  
Western Canada Sedimentary Basin ◽  
Tectonic Belt ◽  
Canada Sedimentary Basin ◽  
Mafic Lower Crust

The Vibroseis Augmented Listen Time (VAuLT) experiment is a special seismic-reflection survey designed to image the fine-scale structure of the continental upper mantle of the Rocky Mountain foreland in southwestern Alberta to depths of 200 km or more. Two mutually perpendicular profiles were acquired across and within the Vulcan structure, a roughly east-west-trending tectonic belt in the crystalline basement beneath the Western Canada Sedimentary Basin that separates the Medicine Hat block from the Loverna block. Relative-amplitude-preserving processing procedures were developed to estimate the seismic-signal-penetration limit, which varies between 100 and 220 km depth. Amplitude-decay analysis and Q estimation show that a seismically unreflective zone within the Vulcan structure is not caused by inadequate signal penetration. This blank zone is interpreted as part of an intrusive complex that has overprinted the preexisting structural fabric. Unlike most other parts of Alberta, the reflection Moho is indistinct and the uppermost mantle (45–60 km depth) is reflective, particularly for source–receiver offsets >10 km. South-dipping reflectivity in the lower crust and upper mantle beneath the Loverna block and northern Vulcan structure gives way to subhorizontal reflectivity beneath the Medicine Hat block. We interpret this reflectivity as compositional layering and (or) zones of ductile deformation that were previously part of the mafic lower crust, but that have now undergone metamorphic transformation to eclogite. The deepest observed reflection is an isolated, gently north-dipping event at ~120 km depth.

Distributed deformation in the lower crust and upper mantle beneath a continental strike-slip fault zone: Marlborough fault system, South Island, New Zealand

Geology ◽  
2004 ◽  
Vol 32 (10) ◽  
pp. 837 ◽  
Author(s):  
Charles K. Wilson ◽  
Craig H. Jones ◽  
Peter Molnar ◽  
Anne F. Sheehan ◽  
Oliver S. Boyd
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Upper Mantle ◽  
Lower Crust ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Fault System ◽  
Crust And Upper Mantle

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>

An improved velocity model for the crust and upper mantle along the central mobile belt of the Newfoundland Appalachian orogen and its offshore extension

1998 ◽  
Vol 35 (11) ◽  
pp. 1238-1251 ◽  
Author(s):  
Deping Chian ◽  
François Marillier ◽  
Jeremy Hall ◽  
Garry Quinlan
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Velocity Structure ◽  
Sedimentary Basins ◽  
Velocity Model ◽  
Mobile Belt ◽  
Wide Angle ◽  
Crust And Upper Mantle ◽  
Angle Data ◽  
Appalachian Orogen

New modelling of wide-angle reflection-refraction data of the Canadian Lithoprobe East profile 91-1 along the central mobile belt of the Newfoundland Appalachian orogen reveals new features of the upper mantle, and establishes links in the crust and upper mantle between existing land and marine wide-angle data sets by combining onshore-offshore recordings. The revised model provides detailed velocity structure in the 30-34 km thick crust and the top 30 km of upper mantle. The lower crust is characterized by a velocity of 6.6-6.8 km/s onshore, increasing by 0.2 km/s to the northeast offshore beneath the sedimentary basins. This seaward increase in velocity may be caused by intrusion of about 4 km of basic rocks into the lower crust during the extension that formed the overlying Carboniferous basins. The Moho is found at 34 km depth onshore, rising to 30 km offshore to the northeast with a local minimum of 27 km. The data confirm the absence of deep crustal roots under the central mobile belt of Newfoundland. Our long-range (up to 450 km offset) wide-angle data define a bulk velocity of 8.1-8.3 km/s within the upper 20 km of mantle. The data also contain strong reflective phases that can be correlated with two prominent mantle reflectors. The upper reflector is found at 50 km depth under central Newfoundland, rising abruptly towards the northeast where it reaches a minimum depth of 36 km. This reflector is associated with a thin layer (1-2 km) unlikely to coincide with a discontinuity with a large cross-boundary change in velocity. The lower reflector at 55-65 km depths is much stronger, and may have similar origins to reflections observed below the Appalachians in the Canadian Maritimes which are associated with a velocity increase to 8.5 km/s. Our data are insufficient for discriminating among various interpretations for the origins of these mantle reflectors.

Measured and calculated elastic wave velocities for xenoliths from the lower crust and upper mantle

1990 ◽  
Vol 173 (1-4) ◽  
pp. 207-210 ◽  
Author(s):  
Ian Jackson ◽  
Roberta L. Rudnick ◽  
S.Y. O'Reilly ◽  
C. Bezant
Keyword(s):  
Elastic Wave ◽  
Upper Mantle ◽  
Lower Crust ◽  
Crust And Upper Mantle ◽  
Wave Velocities
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