Crustal structure and surface zonation of the Canadian Appalachians: implications of deep seismic reflection data

1989 ◽  
Vol 26 (2) ◽  
pp. 305-321 ◽  
Author(s):  
François Marillier ◽  
Charlotte E. Keen ◽  
Glen S. Stockmal ◽  
Garry Quinlan ◽  
Harold Williams ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Surface Expression ◽  
Seismic Profiles ◽  
Crust And Upper Mantle ◽  
Seismic Reflection Data ◽  
Central Block ◽  
Reflection Data ◽  
Lower Crustal ◽  
Canadian Appalachians

In 1986, 1181 km of marine seismic reflection data was collected to 18–20 s of two-way traveltime in the Gulf of St. Lawrence area. The seismic profiles sample all major surface tectono-stratigraphic zones of the Canadian Appalachians. They complement the 1984 deep reflection survey northeast of Newfoundland. Together, the seismic profiles reveal the regional three-dimensional geometry of the orogen.Three lower crustal blocks are distinguished on the seismic data. They are referred to as the Grenville, Central, and Avalon blocks, from west to east. The Grenville block is wedge shaped in section, and its subsurface edge follows the form of the Appalachian structural front. The Grenville block abuts the Central block at mid-crustal to mantle depths. The Avalon block meets the Central block at a steep junction that penetrates the entire crust.Consistent differences in the seismic character of the Moho help identify boundaries of the deep crustal blocks. The Moho signature varies from uniform over extended distances to irregular with abrupt depth changes. In places the Moho is offset by steep reflections that cut the lower crust and upper mantle. In other places, the change in Moho elevation is gradual, with lower crustal reflections following its form. In all three blocks the crust is generally highly reflective, with no distinction between a transparent upper crust and reflective lower crust.In general, Carboniferous and Mesozoic basins crossed by the seismic profiles overlie thinner crust. However, a deep Moho is found at some places beneath the Carboniferous Magdalen Basin.The Grenville block belongs to the Grenville Craton; the Humber Zone is thrust over its dipping southwestern edge. The Dunnage Zone is allochthonous above the opposing Grenville and Central blocks. The Gander Zone may be the surface expression of the Central block or may be allochthonous itself. There is a spatial analogy between the Avalon block and the Avalon Zone. Our profile across the Meguma Zone is too short to seismically distinguish this zone from the Avalon Zone.

scholarly journals Can we relate the surface expression of dike-induced normal faults to subsurface dike geometry?

Geology ◽  
2020 ◽  
Author(s):  
Craig Magee ◽  
Christopher A.-L. Jackson
Keyword(s):  
Free Surface ◽  
Seismic Reflection ◽  
A Priori ◽  
Three Dimensional ◽  
Surface Expression ◽  
Normal Faults ◽  
Normal Faulting ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Surface Measurements

Many igneous dikes do not reach the surface, instead triggering normal faulting and graben formation in overlying rock. The surface expression of these dike-induced faults provides important records of active and ancient diking. For example, surface measurements of graben half-widths have been used to estimate dike upper-tip depths by projecting faults straight downdip, whereas extension measured at the surface across dike-induced fault pairs (i.e., their cumulative heave) is considered a proxy for dike thickness. We use three-dimensional seismic reflection data to test how the surface expression of two buried dike-induced faults relates to dike geometry. The dike-induced faults are nonplanar, suggesting fault dips should not be assumed constant when using graben half-widths to estimate dike depth. Multiple displacement maxima occur across the dike-induced faults, but rarely at their lower or upper tips, suggesting they formed through linkage of isolated faults that nucleated between the dike and free surface. Fault heave is greatest where these subsurface displacement maxima occur, meaning the cumulative heave of the dike-induced fault pair measured at the syn-faulting free surface underestimates their total extension and poorly reflects dike thickness. Our results imply that at-surface analyses of dike-induced fault geometry cannot be used to estimate key dike parameters without a priori knowledge of fault structure and kinematics or host rock lithological variations.

Crustal geometry of the Abitibi Subprovince, in light of three-dimensional seismic reflector orientations

1998 ◽  
Vol 35 (5) ◽  
pp. 569-582 ◽  
Author(s):  
G Bellefleur ◽  
A J Calvert ◽  
M C Chouteau
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Seismic Reflection Data ◽  
Volcanic Arc ◽  
The North ◽  
Reflection Data ◽  
Abitibi Subprovince ◽  
Seismic Reflection Profiles ◽  
Lower Crustal ◽  
Seismic Reflector

We provide precise estimates of reflector orientations beneath the Archean Abitibi Subprovince, using two distinct approaches based on Lithoprobe seismic reflection data. In the first, we use the dip of reflections observed on intersecting profiles to establish the three-dimensional orientation of reflective structures. In the second, the strikes and dips of reflectors are estimated in the crooked parts of seismic reflection profiles by calculating a measure of coherency along the traveltime trajectories defined by a particular azimuth, dip, depth, and medium velocity. Mid-crustal reflectors define two areas with distinctive geometry: reflectors beneath the southern Abitibi belt are oppositely dipping, and convergent at depth, providing a V-shape aspect to the greenstone rocks; other reflectors beneath the northern Abitibi belt are, in general, subparallel, dipping at an average of 30° toward the north. These north-dipping reflectors are partly disrupted by a low-reflectivity zone, which is attributed to rocks of the Opatica Subprovince, located underneath the northern Abitibi belt. Lower-crustal reflectors have a similar, shallowly north-dipping orientation throughout the Abitibi Subprovince. The geometry of the reflectors recovered is consistent with the different tectonic histories proposed for the southern and northern Abitibi assemblages, until common deformation during a north-south shortening event. Attitudes recovered in the northern Abitibi belt are consistent with tectonic scenarios involving underthrusting of Abitibi middle and lower crustal terranes beneath the Opatica belt, whereas the oppositely dipping reflectors recovered in the middle crust beneath the southern Abitibi belt could be representative of a rifted volcanic arc environment.

Plumbing and architecture of a crustal mineralizing system in the Archean Superior Province, Canada

2021 ◽  
Author(s):  
Eric Roots ◽  
Graham Hill ◽  
Ben M. Frieman ◽  
James A. Craven ◽  
Richard S. Smith ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Spatial Association ◽  
Three Dimensional ◽  
3D Models ◽  
Superior Province ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Abitibi Subprovince ◽  
Lower Crustal

<p>The role of melts and magmatic/metamorphic fluids in mineralization processes is well established. However, the role of crustal architecture in defining source and sink zones in the middle to lower crust remains enigmatic. Integration of three dimensional magnetotelluric (MT) modelling and seismic reflection data across the Archean Abitibi greenstone belt of the Superior Province, Canada, reveals a ‘whole-of-crust’ mineralizing system and highlights the controls by crustal architecture on metallogenetic processes. Electrically conductive conduits in an otherwise resistive upper crust are coincident with truncations and offsets of seismic reflections that are mostly interpreted as major brittle-ductile fault zones. The spatial association between these features and low resistivity zones imaged in the 3D models suggest that these zones acted as pathways through which fluids and melts ascended toward the surface. At mid-crustal levels, these ‘conduit’ zones connect to ~50 km long, north-south striking conductors, and are inferred to represent graphite and/or sulphide deposited from cooling fluids. At upper mantle to lower crustal depths, east-west trending conductive zones dominate and display shallow dips. The upper mantle features are broadly coincident with the surface traces of the major deformation zones with which a large proportion of the gold endowment is associated. We suggest that these deep conductors represent interconnected graphitic zones perhaps augmented by sulphides that are relicts from metamorphic fluid and melt emplacement associated primarily with the later stages of regional deformation.  Thus, from the combined MT and seismic data, we develop a crustal-scale architectural model that is consistent with existing geological and deformational models, providing constraints on the sources for and signatures of fluid and magma emplacement that resulted in widespread metallogenesis in the Abitibi Subprovince.</p>

scholarly journals Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

2018 ◽  
Vol 477 (1) ◽  
pp. 223-240 ◽  
Author(s):  
D. M. Hodgson ◽  
H. L. Brooks ◽  
A. Ortiz-Karpf ◽  
Y. Spychala ◽  
D. R. Lee ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Submarine Landslides ◽  
Seismic Reflection Data ◽  
Karoo Basin ◽  
Reflection Data ◽  
Seabed Topography ◽  
Flow Evolution ◽  
Basal Shear ◽  
Process Product

AbstractMany mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides.

The Sask Craton and Hearne Province margin: seismic reflection studies in the western Trans-Hudson Orogen

2005 ◽  
Vol 42 (4) ◽  
pp. 403-419 ◽  
Author(s):  
Z Hajnal ◽  
J Lewry ◽  
D White ◽  
K Ashton ◽  
R Clowes ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Regional Tectonic ◽  
Detachment Zone ◽  
Tectonic Development ◽  
Seismic Images ◽  
Basal Detachment

A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the Rae–Hearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the Rae–Hearne margin – Reindeer zone boundary is established. Several phases of tectonic development, including multistage subduction and continent–continent collision, are inferred for the western margin of the orogen. A bright, shallow (2–3.5 s two-way traveltime) band of reflectivity (Wollaston Lake reflector) imaged over ~150 000 km2 area is inferred to be a large post-orogenic mafic intrusion. A highly reflective, well-defined and structurally disturbed Moho discontinuity is mapped throughout the western Trans-Hudson Orogen. The present-day crustal architecture of the western Trans-Hudson Orogen is described in terms of the tectonic evolution within the region.

The southern Omineca Belt, British Columbia: new perspectives from the Lithoprobe Geoscience Program

1995 ◽  
Vol 32 (10) ◽  
pp. 1720-1739 ◽  
Author(s):  
Sharon D. Carr
Keyword(s):  
Late Cretaceous ◽  
Seismic Reflection ◽  
Shear Zones ◽  
Crustal Thickening ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Basement Rocks ◽  
Peraluminous Granites ◽  
Surface Geology ◽  
Lower Crustal

Geological, isotopic, and geochronology studies carried out by university and government researchers, concurrently with the Lithoprobe program, have greatly refined our understanding of the regional geology, crustal structure, and tectonics of the Omineca Belt. Sound correlations have been established between surface geology and seismic reflection data. Cretaceous–Eocene thrust faults that are imaged in the subsurface in the Shuswap complex may be part of a break-forward thrust system that feeds into the Purcell Anticlinorium and the Foreland Belt. The Monashee décollement is the western continuation of the sole thrust beneath the Foreland Belt and provides a means of linking shortening across the entire orogen. The thermal peak of metamorphism in the central and southern Shuswap complex is now known to have occurred in the Late Cretaceous–Paleogene in contrast with earlier held views. North American basement rocks are now known to extend beneath the eastern half of the Canadian Cordillera. Geochronology studies have revealed Early Proterozoic and Late Cretaceous–Eocene metamorphism in basement rocks of the Monashee complex, and suggest that these rocks were located to the east of the metamorphic front throughout the Jurassic and Early Cretaceous. Anatectic peraluminous granites were produced in the Shuswap complex between 135 and 52 Ma in response to pulses of crustal thickening and heating, and in some cases served to localize Eocene extensional shear zones and to transfer extensional displacement from one shear zone to another. A flat Moho and other seismic reflection data are consistent with interpretations of lower crustal flow to balance early Tertiary extension in the upper crust. Crustal-scale extension and the Slocan Lake fault zone provided the source and setting for Ag–Pb–Zn–Au mineralization in the Nelson–Silverton area.

Integrating high‐resolution refraction data into near‐surface seismic reflection data processing and interpretation

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1339-1347 ◽  
Author(s):  
Kate C. Miller ◽  
Steven H. Harder ◽  
Donald C. Adams ◽  
Terry O’Donnell
Keyword(s):  
Seismic Reflection ◽  
Velocity Model ◽  
Surface Velocity ◽  
Seismic Profiles ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Interval Velocity ◽  
Velocity Models ◽  
Reflection Data ◽  
Seismic Reflection Profiles

Shallow seismic reflection surveys commonly suffer from poor data quality in the upper 100 to 150 ms of the stacked seismic record because of shot‐associated noise, surface waves, and direct arrivals that obscure the reflected energy. Nevertheless, insight into lateral changes in shallow structure and stratigraphy can still be obtained from these data by using first‐arrival picks in a refraction analysis to derive a near‐surface velocity model. We have used turning‐ray tomography to model near‐surface velocities from seismic reflection profiles recorded in the Hueco Bolson of West Texas and southern New Mexico. The results of this analysis are interval‐velocity models for the upper 150 to 300 m of the seismic profiles which delineate geologic features that were not interpretable from the stacked records alone. In addition, the interval‐velocity models lead to improved time‐to‐depth conversion; when converted to stacking velocities, they may provide a better estimate of stacking velocities at early traveltimes than other methods.

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