Seismic reflection profiles across deep continental crust exposed in the Kapuskasing uplift structure

Percival, John A.; Green, A. G.; Milkereit, B.; Cook, Frederick A.; Geis, Wayne T.; West, G. F.

doi:10.1038/342416a0

Cited by 71 publications

(27 citation statements)

References 12 publications

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“…Therefore the properties that increase the conductivity at mid-to-lower crustal depths are lost upon being thrust to the surface. However, the 1987-88 seismic reflection results (Percival et al 1989) suggest that the KU is a much thinner feature than inferred from earlier gravity modelling. The deepest exhumed metamorphic assemblages equilibrated at 25 to 30km and since our models (Figs 12 and 13) suggest that the resistivity is only beginning to decrease significantly at depths of 20 to 30 km, perhaps it should not be surprising that the rocks exhumed from the greatest depths west of the ILCZ are not notably more conductive.…”

Section: Discussioncontrasting

confidence: 59%

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

Kurtz

Craven

Niblett

et al. 1993

Geophysical Journal International

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S U M M A R YThe Kapuskasing Uplift has been interpreted as an oblique cross-section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid-to lower-crustal material. A magnetotelluric (MT) survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity. The only shallow conductive anomaly is related to the Ivanhoe Lake Cataclastic Zone but its electrical signature does not appear to extend more than one kilometer in depth.A regional apparent resistivity curve was determined from MT data and confirmed by subsequent controlled source electromagnetic surveys. Regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions. The data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world.There is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a N65"E and N25"W coordinate frame. Two different models are proposed to explain the data. The first consists of a conducting 2-D slab of approximately 50 km width in the lower crust and striking N65"E. The strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it. The second model invokes either micro or macro electrical anisotropy in the upper mantle. There is considerable evidence for seismic anisotropy in the region. The electrical anisotropy could be the result of preferential conduction along the c-axis of olivine crystals, hydrogen dissolved in the olivine lattice with preferential conduction along the a-axis, or possible alignment of dykes, joints and faults in the upper mantle. If the anisotropy is related to strain induced orientations of crystals or fabric, it will provide evidence for the motions of the mantle associated with plate tectonics.

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Section: Discussioncontrasting

confidence: 59%

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

Kurtz

Craven

Niblett

et al. 1993

Geophysical Journal International

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“…On the east and southeast, the belt is bordered by the Grenville Province. To the west, the Abitibi belt is separated from the Quetico and Wawa subprovinces by the high-grade metamorphic rocks of the Kapuskasing structural zone (Percival et al 1989). …”

Section: The Abitibi Subprovincementioning

confidence: 99%

Crustal velocity structure of the Superior and Grenville provinces of the southeastern Canadian Shield

Winardhi¹,

Mereu²

1997

Can. J. Earth Sci.

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The 1992 Lithoprobe Abitibi–Grenville Seismic Refraction Experiment was conducted using four profiles across the Grenville and Superior provinces of the southeastern Canadian Shield. Delay-time analysis and tomographic inversion of the data set demonstrate significant lateral and vertical variations in crustal velocities from one terrane to another, with the largest velocity values occurring underneath the Central Gneiss and the Central Metasedimentary belts south of the Grenville Front. The Grenville Front Tectonic Zone is imaged as a southeast-dipping region of anomalous velocity gradients extending to the Moho. The velocity-anomaly maps suggest an Archean crust may extend, horizontally, 140 km beneath the northern Grenville Province. Near-surface velocity anomalies correlate well with the known geology. The most prominent of these is the Sudbury Structure, which is well mapped as a low-velocity basinal structure. The tomography images also suggest underthrusting of the Pontiac and Quetico subprovinces beneath the Abitibi Greenstone Belt. Wide-angle PmP signals, indicate that the Moho varies from a sharp discontinuity south of the Grenville Front to a rather diffuse and flat boundary under the Abitibi Greenstone Belt north of the Grenville Front. A significant crustal thinning near the Grenville Front may indicate post-Grenvillian rebound and (or) the extensional structure of the Ottawa–Bonnechere graben. Crustal thickening resulting from continental collision may explain the tomographic images showing the Moho is 4–5 km deeper south of the Grenville Front.

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“…Lithoprobe seismic reflection data collected from the southern Kapuskasing uplift reveal a complex zone of low-angle reflections and high velocities that merges with the surface trace of the Ivanhoe Lake fault to the east and extends to normal depths of 15-20 km beneath the greenstone belts to the west. This zone, which dips about 20" northwest , is viewed as the detachment surface of the thrust along which 55-70 km of horizontal shortening was accommodated to produce the 20 km of inferred differential uplift between the Kapuskasing and Abitibi rocks (Boland et al 1988;Percival et al 1989;Geis et al 1990). As an intracratonic overthrust of crustal dimensions, the Kapuskasing uplift is comparable to the Laramide basement uplifts of the northeastern United States Cordillera (Percival and McGrath 1986).…”

Section: Regional Geology and Conceptual Modelsmentioning

confidence: 99%

“…The first set, comprising six crustal-scale profiles ( -50 km deep) and one high-resolution profile, was recorded over the Chapleau block in the southern part of the uplift (Percival et al 1989;Geis et al 1990; and supports the thrust interpretation. Here we focus on the recently reprocessed seismic data from the second set of three short profiles (lines 8, 9, and 10; totalling about 52 km) that traverse the Groundhog River block and eastern Val Rita block of the central Kapuskasing uplift (Fig.…”

Section: Seismic Reflection Data Location Of Seismic Projilesmentioning

confidence: 99%

“…Lithoprobe seismic reflection and refraction data preted to represent an oblique cross section through 20 km of recorded Over the segment the up1ift image a subthe upper and middle Archean crust that was uplifted along surface geometry that is generally the overthrust model (Cook 1985;Boland et al 1988;Percival et al 1989; lGeological survey of canada contribution 39992; ~i~h~~~~b~ Geis et al 1990;Mereu 1990, 1992). It is unclear how Card and Ciesielski 1986;Percival and McGrath 1986).…”

Section: Introductionmentioning

confidence: 99%

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Seismic reflection profiles across the central Kapuskasing uplift

Leclair¹,

Percival²,

Green³

et al. 1994

Can. J. Earth Sci.

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The central Superior Province is transected by the intracratonic Kapuskasing uplift, which contains rocks exhumed from 30 to 35 km paleodepth. As part of the Lithoprobe Kapuskasing transect, approximately 52 km of 16 s seismic reflection data were collected in the central segment of the uplift along three profiles that traverse the northern Groundhog River block, the bounding Saganash Lake fault, and the eastern Val Rita block. The seismic sections have the following characteristics in common: (i) a complexly reflective uppermost portion (< 1 s) limiting correlation of reflective zones and surface features; (ii) numerous subhorizontal, east- and west-dipping reflection zones; and (iii) a significant reduction in reflectivity beyond the refraction-defined Moho (~ 14 s). Beneath the Groundhog River block a series of straight, west-dipping (~ 20°) reflection zones between 2 and 10 s is underlain by subhorizontal reflections in the lower crust. Across the Saganash Lake fault, the Val Rita block is characterized by a maze of discontinuous, curvilinear reflections with general easterly dip down to 8 – 10 s, below which west-dipping events are prominent. A north–south cross profile reveals a highly reflective crust with dominantly horizontal reflection geometry below the Saganash Lake metavolcanic belt, and a steep truncation of reflection zones down to at least 7 s, which correlates with the surface trace of the Nansen Creek fault. This fault resembles well-known strike-slip faults in intraplate settings. The Saganash Lake fault, variably interpreted as a west-side-down normal fault with up to 15 km of throw or a major strike-slip zone, may be visible as a west-dipping, weakly reflective zone steeply truncating east-dipping reflections and becoming listric at depth. This interpretation accords with surface geological observations and gravity models for the structural geometry of the region in which the Groundhog River block is a thin thrust sheet of granulite perched on Abitibi belt rocks and truncated on the west by the crustal-scale Saganash Lake fault. Alternatively, the fault could be a seismically unresolved major transcurrent structure juxtaposing blocks with disparate reflection patterns in the upper 8 s. Limited amounts of late strike-slip motion have been inferred from various geophysical studies.

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Seismic reflection profiles across deep continental crust exposed in the Kapuskasing uplift structure

Cited by 71 publications

References 12 publications

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

Crustal velocity structure of the Superior and Grenville provinces of the southeastern Canadian Shield

Seismic reflection profiles across the central Kapuskasing uplift

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