Crustal velocity structure from SAREX, the Southern Alberta Refraction Experiment

2002 ◽  
Vol 39 (3) ◽  
pp. 351-373 ◽  
Author(s):  
Ron M Clowes ◽  
Michael JA Burianyk ◽  
Andrew R Gorman ◽  
Ernest R Kanasewich
Keyword(s):  
Velocity Structure ◽  
Data Interpretation ◽  
Crustal Thickening ◽  
Tectonic Zone ◽  
Crustal Layer ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Southern Alberta ◽  
Magmatic Underplating ◽  
Lower Crustal

Lithoprobe's Southern Alberta Refraction Experiment, SAREX, extends 800 km from east-central Alberta to central Montana. It was designed to investigate crustal velocity structure of the Archean domains underlying the Western Canada Sedimentary Basin. From north to south, SAREX crosses the Loverna domain of the Hearne Province, the Vulcan structure, the Medicine Hat block (previously considered part of the Hearne Province), the Great Falls tectonic zone, and the northern Wyoming Province. Ten shot points along the profile in Canada were recorded on 521 seismographs deployed at 1 km intervals. To extend the line, an additional 140 seismographs were deployed at intervals of 1.25–2.50 km in Montana. Data interpretation used an iterative application of damped least-squares inversion of traveltime picks and forward modeling. Results show different velocity structures for the major blocks (Loverna, Medicine Hat, and Wyoming), indicating that each is distinct. Wavy undulations in the velocity structure of the Loverna block may be associated with internal crustal deformation. The most prominent feature of the model is a thick (10–25 km) lower crustal layer with high velocities (7.5–7.9 km/s) underlying the Medicine Hat and Wyoming blocks. Based on data from lower crustal xenoliths in the region, this layer is interpreted to be the result of Paleoproterozoic magmatic underplating. Crustal thickness varies from 40 km in the north to almost 60 km in the south, where the high-velocity layer is thickest. Uppermost mantle velocities range from 8.05 to 8.2 km/s, with the higher values below the thicker crust. Results from SAREX and other recent studies are synthesized to develop a schematic representation of Archean to Paleoproterozoic tectonic development for the region encompassing the profile. Tectonic processes associated with this development include collisions of continental blocks, subduction, crustal thickening, and magmatic underplating.

Crustal velocity structure in the eastern Insular and southernmost Coast belts, Canadian Cordillera

1993 ◽  
Vol 30 (5) ◽  
pp. 1014-1027 ◽  
Author(s):  
B. C. Zelt ◽  
R. M. Ellis ◽  
R. M. Clowes
Keyword(s):  
High Velocity ◽  
Velocity Structure ◽  
Canadian Cordillera ◽  
Western Coast ◽  
Upper Crust ◽  
Crustal Layer ◽  
Near Surface ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Lower Crustal

Seismic refraction data recorded along a 330 km cross-strike profile through the eastern Insular and southernmost Coast belts of the Canadian Cordillera are interpreted using an iterative combination of traveltime inversion and amplitude forward modelling. The resultant model is characterized by large lateral variations in velocity. The most significant of these variations is a decrease in upper and middle crustal velocities to the east of the surface trace of the Harrison fault, which likely represents the transition from crust of the Insular superterrane to that of the Intermontane superterrane. This interpretation is consistent with some present geological models that place the possible (probable) location of the suture between the two superterranes less than 20 km east of the Harrison fault. Velocities at the base of the upper crust average 6.4 and 6.2 km/s west and east of the fault, respectively. Mid-crustal velocities average 6.6–6.9 km/s to the west and 6.35–6.45 km/s to the east of the fault. Lower crustal velocities also decrease slightly to the east. Other features of the velocity model include (i) a thin near-surface layer with velocities between 2.5 and 6.1 km/s; (ii) upper crustal thickness of 12.5 km, thinning to 8 km at the eastern boundary of the Western Coast Belt (WCB); (iii) high velocity (6.6–6.9 km/s) mid-crustal layer west of the Harrison fault extending to 21 km depth; (iv) high-velocity (6.75–7.1 km/s) lower crustal layer; (v) low-velocity gradient upper mantle with depth to Moho at 34–37 km beneath most of the Coast Belt, decreasing to 30 km beneath the eastern Insular Belt, a depth much less than previous estimates. The inferred crustal velocity structure beneath the WCB is consistent with the three-layer electrical conductivity structure for this area derived from magnetotelluric surveys. The association of high resistivities with the upper crust suggests that the upper 8–12 km represents the massive cover of plutonic rocks which characterizes the WCB. Middle and lower crustal velocities beneath the WCB are consistent with Wrangellian velocities found beneath Vancouver Island, suggesting Wrangellia may extend at depth eastward as far as the Harrison fault.

The seismic velocity structure of northern Appalachian crust around western Newfoundland

1992 ◽  
Vol 29 (3) ◽  
pp. 462-478 ◽  
Author(s):  
H. Karin Michel ◽  
K. E. Louden ◽  
F. Marillier ◽  
I. Reid
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Velocity Structure ◽  
The North ◽  
Crustal Block ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Sediment Layers ◽  
Lower Crustal ◽  
Broad Region

The crustal velocity structure beneath western Newfoundland is constrained by a reanalysis of older, regional refraction profiles together with an analysis of one new profile. Initial interpretation of the older data gave inconsistent and discontinuous structures that are difficult to reconcile with more recent deep reflection profiles. We also show that traveltimes predicted by the earlier models often do not yield acceptable fits to the original observations. Our reinterpretation reveals a simpler pattern, in which the crust is characterized by a persistent, high-velocity, lower crustal (HVLC) layer. This layer has velocities of 7.0–7.9 kmls and thicknesses of 5–23 km. It is thickest beneath the Grenville crustal block, east of the Appalachian structural front, and thins or is possibly absent within the Central block. Analysis of the new, much higher resolution profile off western Newfoundland confirms the existence of the HVLC layer with a velocity of 7.2 kmls and thicknesses of 11–19 km, increasing to the northeast. The upper crust has well-defined velocities of 6.2–6.4 kmls and is overlain by a complex sandwich of sediment layers with principal velocities of 3.9, 4.95, and 5.58 kmls and maximum total thicknesses of 8.5 km in the south to 5.5 km in the north. Total crustal thickness varies from 39 to 43 km from south to north. Comparison of the velocity–depth models with the pattern of deep crustal reflectivity revealed by deep multichannel profiles shows that the HVLC layer is coincident with a zone of flat-lying reflectors that terminate to the west at the base of the crust beneath the Appalachian structural front. The HVLC may continue eastward to cover a broad region of central Newfoundland as suggested by the older data, but its association with the reflectivity is not clear.

Crustal velocity structure across the Tornquist and Iapetus Suture Zones — a comparison based on MONA LISA and VARNET data

1999 ◽  
Vol 314 (1-3) ◽  
pp. 69-82 ◽  
Author(s):  
Tanni Abramovitz ◽  
Michael Landes ◽  
Hans Thybo ◽  
A.W.Brian Jacob ◽  
Claus Prodehl
Keyword(s):  
Velocity Structure ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Mona Lisa
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