The Denali fault system and Alaska Range of Alaska: Evidence for underplated Mesozoic flysch from magnetotelluric surveys

Stanley, William D.; Labson, Victor F.; Nokleberg, Warren J.; Csejtey, Béla; Fisher, Michael A.

doi:10.1130/0016-7606(1990)102<0160:tdfsaa>2.3.co;2

Cited by 73 publications

(49 citation statements)

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“…Previous interpretations of MT data collected along five transects near and across the Alaska Range (Stanley, 1986(Stanley, , 1989Stanley et al, 1990) indicate a different distribution of rock resistivities from what we show here. In these early studies, a near-surface rock layer north of the Denali fault was found to vary in thickness from 4 to 7 km and to be characterized by a wide range of resistivity values (170-9900 X•m) that was identified as the amphibolite-facies schist of the YTT.…”

Section: Magnetotelluric Datacontrasting

confidence: 53%

“…The most likely source of the lowresistivity body was inferred to be carbon-rich Jurassic and Cretaceous flysch like that making up the Kahiltna terrane. One difference between the earlier impedance model (Stanley, 1986(Stanley, , 1989Stanley et al, 1990) and the one presented here (Fig. 9) is that the temporal recording range used to obtain the earlier data was about an order of magnitude higher than that used for data shown here.…”

Section: Magnetotelluric Datamentioning

confidence: 62%

“…At low metamorphic grades, carbon particles in these rocks can be smeared into films that are electrically conductive. Below the Alaska Range, carbon-rich rocks, like the Upper Jurassic and Lower Cretaceous flysch within the Kahiltna and related terranes, could have been buried during mountain building (Stanley, 1989;Stanley et al, 1990). Although intense heating and deformation can destroy carbon films, high-grade metamorphic rocks in the YTT do contain such films (Mathez et al, 1995).…”

Section: Discussion Causes For Variation In Crustal Resistivitymentioning

confidence: 99%

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Geophysical Data Reveal the Crustal Structure of the Alaska Range Orogen within the Aftershock Zone of the Mw 7.9 Denali Fault Earthquake

Fisher

Ratchkovski

Nokleberg

et al. 2004

Bulletin of the Seismological Society of America

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Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 M w 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25Њ north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (Ͼ10 X•m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the aftershock zone.

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Section: Magnetotelluric Datacontrasting

confidence: 53%

Section: Magnetotelluric Datamentioning

confidence: 62%

Section: Discussion Causes For Variation In Crustal Resistivitymentioning

confidence: 99%

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Geophysical Data Reveal the Crustal Structure of the Alaska Range Orogen within the Aftershock Zone of the Mw 7.9 Denali Fault Earthquake

Fisher

Ratchkovski

Nokleberg

et al. 2004

Bulletin of the Seismological Society of America

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“…The results therefore suggest that the same or a very similar body is being imaged on corridors 2 and 3. Ledo et al (2004) provide an interpretation of this dipping structure and compare it with a lower crustal conductor observed to the north in Alaska (Stanley et al 1990). The northeast-dipping conductor on the SNORCLE transect lies above, and parallel to, a suite of reflectors located at mantle depths that were interpreted by Cook et al (2001Cook et al ( , 2004 to be associated with convergent subduction of the Kula plate in the Paleocene (Engebretson et al 1984).…”

Section: Comparison Between Corridors 2 Andmentioning

confidence: 89%

“…The coincidence of the geometry of the conductor and the inferred position of the subducting slab provides a strong indication that the decreased resistivity is related to the Paleocene Kula plate subduction. The original explanation of the Alaskan Range conductor was that it was due to metasedimentary rocks emplaced into the deeper crust by the underthrusting of carbonaceous flysch during mid-Cretaceous convergence (Stanley et al 1990). Ledo et al (2004) suggest that the crustal part of the conductor observed on corridors 2 and 3 may also be metasedimentary rocks imbricated during Kula plate subduction.…”

Section: Comparison Between Corridors 2 Andmentioning

confidence: 99%

The electrical resistivity structure of Archean to Tertiary lithosphere along 3200 km of SNORCLE profiles, northwestern Canada

et al. 2005

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Magnetotelluric (MT) measurements to image the three-dimensional resistivity structure of the North American continent from an Archean core to a region of Tertiary assembly were recorded at almost 300 sites along 3200 km of profiles on the Lithoprobe Slave -Northern Cordillera Lithospheric Evolution (SNORCLE) transect in northwestern Canada. At the largest scale, the MT results indicate significant lithospheric thickness variation, from 260 km at the southwest margin of the Slave craton to significantly < 100 km at the southwestern end of the SNORCLE transect in the Cordillera. At intermediate scale, the resistivity results allow broad terrane subdivisions to be made. Several anomalously conductive zones along the SNORCLE transect, in rocks ranging in age from Archean to Tertiary, are attributed to the introduction of either water or carbon into the crust and mantle during subduction processes. At the local scale, the MT data image two major faults crossing the study area, the Great Slave Lake shear zone and the Tintina Fault. The resistivity images show that both the Tintina Fault and Great Slave Lake shear zone form crustal-scale features, and that the Tintina Fault has a remarkably uniform resistivity signature over a 400 km strike length in the study area. Arguably the most controversial conclusion reached is that the MT data do not support the western extension of North American autochthonous basement suggested from interpretation of the seismic reflection data. 1275Résumé : Afin d'obtenir une image de la structure de résistivité en trois dimensions du continent nord-américain, d'un noyau archéen à une région d'assemblage tertiaire, des mesures magnétotelluriques (MT) ont été enregistrées à près de 300 sites le long de 3200 km de profils de la géotraverse SNORCLE du projet Lithoprobe dans le nord-ouest du Canada. À la plus grande échelle, les résultats magnétotelluriques indiquent des variations importantes d'épaisseur de la lithosphère, de 260 km à la bordure sud-ouest du craton des Esclaves à passablement moins de 100 km à l'extrémité sud-ouest de la géotraverse SNORCLE, dans la Cordillère. À une échelle intermédiaire, les résultats des données de résistivité permettent de subdiviser le terrain en de larges terranes. Plusieurs anomalies de zones conductrices le long de la géo-traverse SNORCLE, dans des roches datant de l'Archéen au Tertiaire, sont attribuées à l'introduction de carbone ou d'eau dans la croûte et le manteau durant les processus de subduction. À une échelle locale, deux failles majeures traversent la région à l'étude, la zone de cisaillement du Grand lac des Esclaves et la faille Tintina. Les images de résistivité montrent que la faille Tintina et la zone de cisaillement du Grand lac des Esclaves sont des éléments d'une échelle crustale et que la faille Tintina a une signature de résistivité remarquablement uniforme sur une longueur de 400 km, selon la direction, dans la région à l'étude. Tel que suggéré par l'interprétation des données de sismique réflexion, il est permis de croire que la c...

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Electromagnetic Induction Studies

Wannamaker

Hohmann

1991

Reviews of Geophysics

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The Denali fault system and Alaska Range of Alaska: Evidence for underplated Mesozoic flysch from magnetotelluric surveys

Cited by 73 publications

References 0 publications

Geophysical Data Reveal the Crustal Structure of the Alaska Range Orogen within the Aftershock Zone of the Mw 7.9 Denali Fault Earthquake

Geophysical Data Reveal the Crustal Structure of the Alaska Range Orogen within the Aftershock Zone of the Mw 7.9 Denali Fault Earthquake

The electrical resistivity structure of Archean to Tertiary lithosphere along 3200 km of SNORCLE profiles, northwestern Canada

Electromagnetic Induction Studies

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