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David W Eaton - One of the best experts on this subject based on the ideXlab platform.
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how the crust meets the mantle Lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition
Canadian Journal of Earth Sciences, 2010Co-Authors: Frederick A Cook, David W Eaton, Alan G Jones, Jeremy Hall, D J White, R M ClowesAbstract:Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovicic discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics.
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How the crust meets the mantle: Lithoprobe perspectives on the Mohorovičić discontinuity and crust–mantle transition
Canadian Journal of Earth Sciences, 2010Co-Authors: Frederick A Cook, David W Eaton, Alan G Jones, Don White, Jeremy Hall, R M ClowesAbstract:Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovicic discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics.
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teleseismic studies of the canadian landmass Lithoprobe and its legacy
Canadian Journal of Earth Sciences, 2010Co-Authors: M G Bostock, David W Eaton, D B SnyderAbstract:National Research Council of Canada NRC Research Press http://www.nrc-cnrc.gc.ca/notices_e.html Copyright / Permission to Reproduce Materials on this Web site were produced and/or compiled by the National Research Council for the purpose of providing Canadians with direct access to information about the programs and services offered by the Government of Canada. The material on this site is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without written permission.
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multi genetic origin of the continental moho insights from Lithoprobe
Terra Nova, 2006Co-Authors: David W EatonAbstract:This paper reviews four hypotheses for the origin of the continental crust–mantle boundary and discusses seismic parameters with which these hypotheses might be tested. The relict Moho hypothesis posits that the oceanic Moho is preserved during continental assembly; the magmatic underplating hypothesis posits formation of a new Moho by episodic emplacement of sill-like intrusive bodies; the metamorphic (or metasomatic) front hypothesis posits that the Moho is overprinted by a phase transformation; and the regional decollement hypothesis posits that the Moho behaves as a structural detachment. These hypotheses are not mutually exclusive, and examples from the Canadian Lithoprobe program suggest that all four may be applicable in different regions of North America. Comparison of seismic images from a fossil subduction zone with modern subduction at Cascadia suggests that serpentinization of the forearc mantle, a previously unrecognized mechanism for overprinting and erasing the reflection Moho, may have occurred in the Proterozoic.
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Structural fabric of the Central Metasedimentary Belt of southern Ontario, Canada, from deep seismic profiling
Tectonophysics, 2004Co-Authors: C.r. O'dowd, David W Eaton, Donald W. Forsyth, H.w. AsmisAbstract:Abstract The Central Metasedimentary Belt boundary tectonic zone (CMBbtz) is a 10–20-km-wide zone of intense structural deformation within the 1.3–1.0 Ga Grenville orogen of southeastern Canada. The crustal structure of the exposed CMBbtz has been well studied, but its sub-Phanerozoic location and geometry beneath the urban development and nuclear stations of the Toronto region are not well known. A new 75-km Lithoprobe reflection profile acquired close to Toronto provides a clear image of the CMBbtz as a panel of southeast-dipping reflections that extends with moderate dip (
Ron M Clowes - One of the best experts on this subject based on the ideXlab platform.
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the Lithoprobe trans continental lithospheric cross sections imaging the internal structure of the north american continentthis article is one of a series of papers published in this special issue on the theme Lithoprobe parameters processes and the
Canadian Journal of Earth Sciences, 2010Co-Authors: Philip T C Hammer, Ron M Clowes, F A Cook, Arie J Van Der Veldena J Van Der Velden, Kris VasudevanAbstract:Three lithospheric cross sections provide a continental-scale synthesis of more than two decades of coordinated multidisciplinary research during the Canadian Lithoprobe project. The sections are based on seismic reflection and refraction data combined with a broad range of geological, geochemical, geochronological, and geophysical data. The dataset is derived from remnants of nearly every kind of tectonic regime, and the geologic history of the entrained rocks spans the Present to the Mesoarchean. The longest of the three cross sections is located within a 6000 km long Trans-Canada corridor traversing the North American continent at 45°N–55°N. From west to east, the profile crosses the Juan de Fuca ridge and active Cascadia subduction zone, the Cordilleran, Albertan, and Trans-Hudson orogens, the Superior Province, the Midcontinent rift, the Grenville and Appalachian orogens, and the Atlantic passive margin. The two northern cross sections include ( i ) a 2000 km long corridor in northwestern Canada (54°N–63°N) crossing the Cordilleran, Wopmay, and Slave orogens; and ( ii ) a 1600 km long corridor in northeastern Canada (52°N–61°N) crossing the New Quebec and Torngat orogens, the Nain craton, and the Makkovik and Grenville orogens. The unprecedented scale of the cross sections illuminates the assembly of the North American continent. Relationships between orogens are emphasized; plate collisions and accretions have sequentially stacked orogen upon orogen such that the older crust forms basement to the next younger. The large-scale perspective of these regional sections highlights the subhorizontal Moho that is indicative of either structural or thermal re-equilibration (or both), as few crustal roots beneath orogens are preserved. In contrast, heterogeneities in the lithospheric mantle suggest that, in certain situations, relict subducted or delaminated lithosphere can remain intact beneath and eventually within cratonic lithospheric mantle.
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mantle heterogeneities and their significance results from Lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme Lithoprobe parameters processe
Canadian Journal of Earth Sciences, 2010Co-Authors: Ron M Clowes, D J White, Zoltan HajnalAbstract:Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) reflection profiling and 12 refraction – wide-angle reflection (R/WAR) surveys were acquired. While the main results related to crustal structure, the data also indicated substantial heterogeneity in the lithospheric mantle. Images of fossilized subduction zones from the Eocene to the Neoarchean demonstrate that current plate tectonic processes have been active for more than 2.6 Ga. The Canadian Cordillera has a thin (50–60 km) lithosphere that is likely receiving some dynamic support from the asthenosphere below. Vestiges of the last stage of accretionary tectonic processes that formed the Archean Superior craton are indicated by an unusual anisotropic high velocity layer that may represent relic oceanic lithosphere. Within the Paleoproterozoic Trans-Hudson Orogen, a restricted region of upper mantle P-wave velocity anisotropy is identified with the continental collision between the bounding Hearne and Superior ...
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initiation development and benefits of Lithoprobe shaping the direction of earth science research in canada and beyondthis article is one of a series of papers published in this special issue on the theme Lithoprobe parameters processes and the evolu
Canadian Journal of Earth Sciences, 2010Co-Authors: Ron M ClowesAbstract:Lithoprobe is Canada’s national, collaborative, multidisciplinary, Earth science research project established to develop a comprehensive understanding of the evolution of northern North America. It is regarded internationally as one of the most successful national geoscience projects ever undertaken. Part of Lithoprobe’s success derives from its history and organizational structure. A one-year Phase I program (1984–1985) was highly successful. Phases II to V carried the project forward until 2005, when funding terminated. Lithoprobe was organized as a decentralized research network of multidisciplinary scientific studies and collaborating scientists. About 1500 scientific publications were generated. Lithoprobe’s legacy also includes economic and social benefits. New and improved understanding of Earth history provides petroleum and mining companies with an enhanced knowledge base. Lithoprobe demonstrated the applicability of high-resolution seismic reflection studies to mineral exploration. Development of a portable seismic refraction recorder and a long-period magnetotelluric system led to technology transfer to Canadian companies. Very high-resolution seismic reflection studies, applied first by Lithoprobe, are proving effective for exploration for uranium deposits in Saskatchewan. In the cratonic areas of Canada, Lithoprobe seismic and magnetotelluric studies have provided significant new information relevant to exploration for diamonds. On the west coast of Canada, Lithoprobe studies provided data and a framework for better understanding the mega-thrust earthquake hazard in the region. Lithoprobe established a highly effective public outreach strategy that involved the print and electronic media as well as material for educational purposes. Unequivocally, Lithoprobe has enhanced the already strong reputation of the Earth sciences in Canada.
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Initiation, development, and benefits of Lithoprobe — shaping the direction of Earth science research in Canada and beyondThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and t
Canadian Journal of Earth Sciences, 2010Co-Authors: Ron M ClowesAbstract:Lithoprobe is Canada’s national, collaborative, multidisciplinary, Earth science research project established to develop a comprehensive understanding of the evolution of northern North America. It is regarded internationally as one of the most successful national geoscience projects ever undertaken. Part of Lithoprobe’s success derives from its history and organizational structure. A one-year Phase I program (1984–1985) was highly successful. Phases II to V carried the project forward until 2005, when funding terminated. Lithoprobe was organized as a decentralized research network of multidisciplinary scientific studies and collaborating scientists. About 1500 scientific publications were generated. Lithoprobe’s legacy also includes economic and social benefits. New and improved understanding of Earth history provides petroleum and mining companies with an enhanced knowledge base. Lithoprobe demonstrated the applicability of high-resolution seismic reflection studies to mineral exploration. Development of a portable seismic refraction recorder and a long-period magnetotelluric system led to technology transfer to Canadian companies. Very high-resolution seismic reflection studies, applied first by Lithoprobe, are proving effective for exploration for uranium deposits in Saskatchewan. In the cratonic areas of Canada, Lithoprobe seismic and magnetotelluric studies have provided significant new information relevant to exploration for diamonds. On the west coast of Canada, Lithoprobe studies provided data and a framework for better understanding the mega-thrust earthquake hazard in the region. Lithoprobe established a highly effective public outreach strategy that involved the print and electronic media as well as material for educational purposes. Unequivocally, Lithoprobe has enhanced the already strong reputation of the Earth sciences in Canada.
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the Lithoprobe trans canada lithospheric cross sections a plate scale view of continental assembly
2010Co-Authors: Philip T C Hammer, Ron M ClowesAbstract:Introduction A continental-scale synthesis of more than two decades of coordinated multidisciplinary Earth science research has yielded a lithospheric-scale cross-section of the entire North American continent. The Lithoprobe Trans-Canada Profile and two additional profiles through northern Canada provide a unique perspective at a continental scale. The cross-sections were developed to be useful for teaching purposes and the non-specialist audience, as well as for the research community. The interpreted profiles illuminate the assembly of the North American continent and highlight the lithospheric structures generated as collision and accretion builds continents. For the more advanced audience, relationships between orogens are emphasized and the display permits visual comparisons to be made regarding structure and tectonic development.
Gerald M Ross - One of the best experts on this subject based on the ideXlab platform.
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introduction to special issue of canadian journal of earth sciences the alberta basement transect of Lithoprobe
Canadian Journal of Earth Sciences, 2000Co-Authors: Gerald M RossAbstract:From outcrops in northeastern Alberta to exposures within structural culminations in the Canadian Cordillera, the crystalline basement that lies buried beneath the Phanerozoic Alberta Basin of western Canada represents a significant part of the Canadian Shield, ca. 750 000 km2. The advent of modern high resolution aeromagnetic data and UPb geochronology have opened the doors for the next era of investigation of the crystalline basement of the Alberta Basin. Aeromagnetic data and geochronology provided important physical and temporal links to the exposed Canadian Shield, which allowed its structural framework to be extrapolated into the subsurface. The most recent chapter in this evolving story has been the Alberta Basement Transects of Lithoprobe, a 12-year program, which has used multi disciplinary geoscience studies to further elucidate the nature, history, and geometric characteristics of basement domains beneath the Alberta Basin. This special issue is the second in a three issue set of publications ...
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Lithoprobe seismic transect of the alberta basin compilation and overview
Bulletin of Canadian Petroleum Geology, 1999Co-Authors: Jacqueline Hope, David W Eaton, Gerald M RossAbstract:ABSTRACT Between 1992 and 1995, approximately 2000 km of seismic-reflection profiles were collected along three transects across the province of Alberta, as part of Canada's ongoing Lithoprobe geoscience project. Using these data, a 1450- km long structural seismic section has been assembled to image the stratigraphy of a large segment of the Western Canada Sedimentary Basin (WCSB) between Fort St. John, British Columbia and Pincher Creek, Alberta. The procedure for compiling this section from the individual profiles included application of static corrections using a floating datum and smoothly varying replacement velocity in order to resolve significant mis-ties between the lines. The large extent of the resulting composite section enables the interpretation of regional reflection characteristics spanning several basement tectonic domains, as well as interregional comparisons of key structural elements in the WCSB. As an alternative to mapping reflection geometries within the uppermost basement, which are largely obscured by multiple reverberations, we focus instead on seismic attributes (instantaneous frequency and amplitude) of the top of basement reflection in order to gain a better understanding of the nature of the crystalline basement and its contact with the overlying sedimentary strata. Seismic attribute analysis was also carried out for the Base of Fish Scales (BFS) reflector, an Upper Cretaceous seismic marker that serves here as a reference reflection. Within the Lacombe domain, a basement domain composed of weakly metamorphosed volcanic and sedimentary rocks, the top of basement reflection is characterized by anomalously high amplitude and frequency. Comparison of Carboniferous normal faulting in the Peace River Arch (PRA) region with Late Cretaceous (or younger?) faults in southern Alberta shows a number of common characteritics, including drape of sedimentary layers over deeper brittle detachments. These features in the Alberta Basin exhibit a strong similarity to previously published laboratory models of extensional forced folds. In structures of this type, brittle basement offset gives way upwards to a broader region of deformation within which extensive fracturing, mostly at a sub-seismic scale, is present. RESUME Entre 1992 et 1995, approximativement 2000 km de coupes sismiques ont ete acquises le long de trois transects traversant la province de l'Alberta, ces transects faisant partie du projet de geoscience Lithoprobe du Canada. En utilisant ces donnees, une coupe sismique structural de 1450 km de long a ete assemblee pour representer graphiquement la stratigraphie d'un grand segment du bassin sedimentaire de l'Ouest du Canada (BSOC) entre Fort St-John en Colombie-Britannique et Pincher Creek en Alberta. La procedure suivie pour compiler cette coupe a partir des coupes individuelles comprend l'application de corrections statiques utilisant un datum flottant et des velocites de remplacement variant doucement, de facon a resoudre les raccordements ambigus entre les lignes. La grande etendue de la coupe composite resultante, qui enjambe plusieurs domaines tectoniques du socle, permet l'interpretation de caracteristiques regionales de reflexion de meme que des comparaisons inter-regionales d'elements-cles situe dans le BSOC. Plutot que de cartographier les geometries de reflexion a l'interieur de la partie la plus haute du socle, qui est grandement obscurcie par de multiples reverberations, nous mettons l'accent surtout sur les attributs sismiques (frequence instantanee et amplitude) du sommet de la reflexion sismique de facon a obtenir une meilleure comprehension de la nature du socle cristallin et de son contact avec les strates sedimentaires sus-jacentes. L'analyse des attributs sismiques a aussi ete accomplie pour le reflecteur de la base du Fish Scales (BFS), un marqueur sismique du Cretace superieur qui sert ici de reflexion de reference. A l'interieur du domaine de Lacombe, un domaine de socle compose de roches volcaniques et sedimentaires faiblement metamorphisees, le sommet de la reflexion du socle est caracterise par des amplitudes et de frequences elevees, qui sont anomaliques. La comparaison des failles normales du Carbonifere de la region de l'arche de Peace River avec les failles du Cretace superieur (ou plus jeunes) dans le sud de l'Alberta montre un certain nombre End_Page 331------------------------ de caracteristiques communes, incluant le recouvrement de couches sedimentaires au-dessus de decollements fragiles situe plus profondement. Ces elements du bassin de l'Alberta montrent de fortes similarites avec des modeles de laboratoire publies precedemment, de plis forces par l'extension. Dans les structures de ce type, le rejet par faille du socle fragile laisse place vers le haut a une region plus large de deformation, a l'interieur de laquelle la fracturation intense, surtout d'echelle sous-sismique, est presente. Traduit par Lynn Gagnon
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Lithoprobe reflection studies of archean and proterozoic crust in canada
Tectonophysics, 1996Co-Authors: Ron M Clowes, David W Eaton, Jeremy Hall, Zoltan Hajnal, Andrew J Calvert, Gerald M RossAbstract:Abstract Lithoprobe, Canada's national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the North American continent, is a multidisciplinary program spearheaded by seismic reflection studies. Five recently recorded seismic lines, discussed in this paper, are located in Precambrian regions: the Mesoproterozoic Grenville Province, the Paleoproterozoic Trans-Hudson orogen (THO), the Paleoproterozoic/Archean basement of Alberta, and the Archean Superior Province. Data acquired across the Grenville orogen in eastern Quebec show strong reflectivity throughout the crust; upper crustal reflections can be correlated with exposed structural elements, including extensional shear zones and packages of deformed high-pressure rocks (eclogites). In a marine survey across the Grenville orogen off southeastern Labrador, seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly. Data acquired across central Alberta show crustal-scale thrust stacking and imbrication of the Archean Hearne craton. To the east across the Trans-Hudson orogen, images of similar collisional features are observed. Geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1.8 Ga, suggesting that collisional tectonic activity was coeval over a broad crustal region, ca. 1000 km across strike. In the Superior Province, seismic data across a collision zone involving the northern Abitibi greenstone belt and the arc-related Opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s (∼30 km) into the mantle. The latter feature is interpreted as representing a relict 2.69-Ga-old suture associated with subduction, providing the first direct evidence that plate tectonics was active in the late Archean. These five examples, supported by other Lithoprobe results, refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies, combined with other geoscience studies, can lead to a better understanding of Precambrian tectonics. Reflectivity persists throughout the crust; there is no general separation into a poorly reflective upper crust and a reflective lower crust. Crustal reflectivity in Archean and Proterozoic regions is as pervasive as that in areas of more recent tectonism. The Precambrian reflection Moho is generally well defined but shows a range of characteristics. Relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity.
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paleoproterozoic collisional orogen beneath the western canada sedimentary basin imaged by Lithoprobe crustal seismic reflection data
Geology, 1995Co-Authors: Gerald M Ross, David W Eaton, E R Kanasewich, Bernd Milkereit, D J White, Michael J A BurianykAbstract:Exceptionally clear images of crustal structure of the Canadian Shield that underlies the western Canada sedimentary basin beneath 3.5–2.2 km of Phanerozoic sedimentary strata have been obtained on a seismic-reflection profile acquired by Lithoprobe. The profile crosses tectonic domains of central Alberta and delineates a major buried orogenic belt of Paleoproterozoic (∼1.8 Ga) age associated with crustal scale thrust imbrication and deflections in the crust-mantle boundary. Available geochronologic data suggest that crustal imbrication observed in the Alberta basement was coeval with that documented in the Trans-Hudson orogen to the east (1.80–1.83 Ga) and implies that a large region of continental crust, extending >1000 km from the western Superior province to the Snowbird tectonic zone, underwent considerable shortening during assembly of this part of the Canadian Shield.
D J White - One of the best experts on this subject based on the ideXlab platform.
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mantle heterogeneities and their significance results from Lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme Lithoprobe parameters processe
Canadian Journal of Earth Sciences, 2010Co-Authors: Ron M Clowes, D J White, Zoltan HajnalAbstract:Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) reflection profiling and 12 refraction – wide-angle reflection (R/WAR) surveys were acquired. While the main results related to crustal structure, the data also indicated substantial heterogeneity in the lithospheric mantle. Images of fossilized subduction zones from the Eocene to the Neoarchean demonstrate that current plate tectonic processes have been active for more than 2.6 Ga. The Canadian Cordillera has a thin (50–60 km) lithosphere that is likely receiving some dynamic support from the asthenosphere below. Vestiges of the last stage of accretionary tectonic processes that formed the Archean Superior craton are indicated by an unusual anisotropic high velocity layer that may represent relic oceanic lithosphere. Within the Paleoproterozoic Trans-Hudson Orogen, a restricted region of upper mantle P-wave velocity anisotropy is identified with the continental collision between the bounding Hearne and Superior ...
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how the crust meets the mantle Lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition
Canadian Journal of Earth Sciences, 2010Co-Authors: Frederick A Cook, David W Eaton, Alan G Jones, Jeremy Hall, D J White, R M ClowesAbstract:Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovicic discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics.
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tectonic evolution of the western superior province from natmap and Lithoprobe studies
Canadian Journal of Earth Sciences, 2006Co-Authors: John A Percival, Herwart Helmstaedt, M Sanbornbarrie, T Skulski, Greg M Stott, D J WhiteAbstract:Five discrete accretionary events assembled fragments of continental and oceanic crust into a coherent Superior craton by 2.60 Ga. They exhibit similar sequences of events at 10 million year intervals: cessation of arc magmatism, early deformation, synorogenic sedimentation, sanukitoid magmatism, bulk shortening, regional metamorphism, late transpression, orogenic gold localization, emplacement of crust-derived granites, and postorogenic cooling. The Northern Superior superterrane recorded 3.7-2.75 Ga events prior to 2.72 Ga collision with the 3.0 Ga North Caribou superterrane. Following 2.98 Ga rifting, the Uchi margin of the North Caribou superterrane evolved in an upper plate setting before 2.72-2.70 Ga collision of the <3.4 Ga Winnipeg River terrane, which trapped synorogenic English River turbidites in the collision zone. The Winnipeg River terrane was reworked in 2.75-2.68 Ga magmatic and tectonic events, including the central Superior orogeny (2.71-2.70 Ga) that marks accretion of the juvenile western Wabigoon terrane. In the south, the Wawa-Abitibi terrane evolved in a mainly oceanic setting until Shebandowanian collision with the composite Superior superterrane at 2.695 Ga. Synorogenic Quetico turbidites were trapped in the collision zone. The final accretionary event involved addition of the Minnesota River Valley terrane (MRVT) from the south, and deposition and metamorphism of synorogenic turbidites of the Pontiac terrane during the 2.68 Ga Minnesotan orogeny. Seismic reflection and refraction images indicate north-dipping structures, interpreted as a stack of discrete 10-15 km thick terranes. A slab of high-velocity material, possibly representing subcreted oceanic lithosphere, as well as Moho offsets, support a model of progressive ac- cretion through plate-tectonic-like processes. Resume : Il y a 2,60 Ga, cinq evenements accretionnaires distincts ont rassemble des fragments de croute continentale et oceanique; le craton coherent du lac Superieur est le resultat de cette accretion. Ces fragments montrent des sequences d'evenements semblables, a des intervalles d'environ 10 Ma : la cessation du magmatisme d'arc, une deformation precoce, une sedimentation synorogenique, un magmatisme sanukitoide, un retrecissement en vrac, un metamorphisme regional, une transpression tardive, la localisation de l'or orogenique, la mise en place de granites derives de la croute et un refroi- dissement post-orogenique. Le superterrane du lac Superieur septentrional a enregistre des evenements de 3,7-2,75 Ga avant la collision a 2,72 Ga avec le superterrane de North Caribou de 3,0 Ga. A la suite de la distension il y a 2,98 Ga, la bordure de la sous-province d'Uchi du superterrane de North Caribou a evolue en un environnement de plaque supe- rieure avant la collision, 2,72-2,70 Ga, avec le terrane de Winnipeg River, <3,4 Ga, ce qui a piege les turbidites sy- norogeniques d'English River dans la zone de collision. Vers 2,75-2,68 Ga, le terrane de Winnipeg River a ete remaine lors d'evenements magmatiques et tectoniques, incluant l'orogene du centre de la Province du lac Superieur (2,71-2,70 Ga) qui marque l'accretion du terrane juvenile Wabigoon occidental. Vers le sud, le terrane de Wawa-Abitibi a evolue dans un environnement surtout oceanique jusqu'a sa collision au Shebandowanien avec le superterrane composite du lac Su- perieur a 2,695 Ga. Des turbidites synorogeniques de Quetico ont ete piegees dans la zone de collision. L'evenement accretionnaire final a implique l'ajout du terrane de Minnesota River Valley provenant du sud ainsi que la deposition et le metamorphisme de turbidites synorogeniques du terrane de Pontiac au cours de l'orogenese minnesotaine, 2,68 Ga. Les donnees de sismique reflexion et refraction indiquent des structures a pendage vers le nord qui sont interpretees comme un empilement de terranes distincts d'une epaisseur de 10-15 km. Une dalle de materiau a haute vitesse, repre- sentant possiblement une lithosphere oceanique accretee par le dessous, ainsi que des decalages du Moho, supportent un modele d'accretions progressives par des processus semblables a celui de la tectonique des plaques.
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teleseismic studies of the lithosphere below the abitibi grenville Lithoprobe transect
Canadian Journal of Earth Sciences, 2000Co-Authors: Stephane Rondenay, D J White, M G Bostock, Thomas M Hearn, Hua Wu, G Senechal, Shaocheng Ji, Marianne MareschalAbstract:In the past decade, the Abitibi-Grenville Lithoprobe transect has been the site of numerous geological and geophysical surveys oriented towards understanding the lithospheric evolution of the southeastern Superior and adjoin - ing Grenville provinces. Among the different geophysical methods that have been employed, earthquake seismology provides the widest range of information on the deep structures of the upper mantle. This paper presents a review of studies, both complete and ongoing, involving teleseismic datasets that were collected in 1994 and 1996 along the transect. A complete shear-wave splitting analysis has been performed on the 1994 dataset as part of a comparative study on electrical and seismic anisotropies. Results suggest a correlation between the two anisotropies (supported by xenolith data) and favour a lithospheric origin for the seismic anisotropy. The two anisotropies are believed to represent the fossilized remnants of Archean strain fields in the lithospheric roots of the Canadian Shield. Preliminary splitting results for the 1996 experiment suggest that the S-wave azimuthal anisotropy may be depth dependent and laterally varying. Ongoing receiver function analysis and traveltime inversion studies provide velocity models of the crust and upper mantle beneath the study area. Preliminary receiver function results reveal the presence of an S-velocity increase at ∼90-100 km depth which appears to be laterally continuous over 200 km. Traveltime inversion models indicate the presence of an elongate, low-velocity anomaly beneath the southern portion of the 1996 array which strikes obliquely to major geological structures at the surface (e.g., Grenville Front). Preliminary interpretation relates this anomaly to the same process (e.g., fixed mantle plume, continental rifting) responsible for the emplacement of the Monteregian Hills igneous province.
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paleoproterozoic collisional orogen beneath the western canada sedimentary basin imaged by Lithoprobe crustal seismic reflection data
Geology, 1995Co-Authors: Gerald M Ross, David W Eaton, E R Kanasewich, Bernd Milkereit, D J White, Michael J A BurianykAbstract:Exceptionally clear images of crustal structure of the Canadian Shield that underlies the western Canada sedimentary basin beneath 3.5–2.2 km of Phanerozoic sedimentary strata have been obtained on a seismic-reflection profile acquired by Lithoprobe. The profile crosses tectonic domains of central Alberta and delineates a major buried orogenic belt of Paleoproterozoic (∼1.8 Ga) age associated with crustal scale thrust imbrication and deflections in the crust-mantle boundary. Available geochronologic data suggest that crustal imbrication observed in the Alberta basement was coeval with that documented in the Trans-Hudson orogen to the east (1.80–1.83 Ga) and implies that a large region of continental crust, extending >1000 km from the western Superior province to the Snowbird tectonic zone, underwent considerable shortening during assembly of this part of the Canadian Shield.
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how the crust meets the mantle Lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition
Canadian Journal of Earth Sciences, 2010Co-Authors: Frederick A Cook, David W Eaton, Alan G Jones, Jeremy Hall, D J White, R M ClowesAbstract:Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovicic discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics.
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How the crust meets the mantle: Lithoprobe perspectives on the Mohorovičić discontinuity and crust–mantle transition
Canadian Journal of Earth Sciences, 2010Co-Authors: Frederick A Cook, David W Eaton, Alan G Jones, Don White, Jeremy Hall, R M ClowesAbstract:Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovicic discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics.
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an 1800 km cross section of the lithosphere through the northwestern north american plate lessons from 4 0 billion years of earth s history
Canadian Journal of Earth Sciences, 2005Co-Authors: Frederick A Cook, Philippe ErdmerAbstract:The Lithoprobe Slave Northern Cordillera Lithospheric Evolution (SNORCLE) study across northwestern North America, in combination with related crustal studies, has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high-resolution geophysical data (seismic reflection, refraction, electromagnetic, potential fields) and detailed bedrock geology. The cross section offers one of the longest "continuous" profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships. The primary conclusion of the study is that, during all major orogenic episodes recorded from Archean to present in that part of Earth's lithosphere, the crust, and perhaps much of the mantle, was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis. The observed subsurface geometries of relict subduction zones, accretion ...
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tectonic significance of potential field anomalies in western canada results from the Lithoprobe snorcle transect
Canadian Journal of Earth Sciences, 2005Co-Authors: Elissa C Lynn, Frederick A Cook, Kevin W HallAbstract:Potential-field anomalies within the Lithoprobe SNORCLE (Slave Northern Cordillera Lithospheric Evolution) transect area provide geometrical constraints for regional crustal and lithospheric structures, as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles. Areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections, and forward modelling provides tests of different interpretations of deep (crustal and upper mantle) density structures. In a key result from modelling, a Paleoproterozoic subduction zone beneath the Wopmay orogen probably consists of high-density rocks, such as eclogite, within the upper mantle. This result supports the concept of moderate- to low-angle intra-lithospheric sutures. On an even larger scale, applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus ...
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Skeletons and fractals — a statistical approach to deep crustal seismic data processing and interpretation
Tectonophysics, 1998Co-Authors: Kris Vasudevan, Frederick A CookAbstract:Abstract Coherent seismic reflection events are identified using seismic skeletonization, an automatic pattern recognition technique in which waveforms are parameterized such that the attributes of each event are identified and stored in a relational database, or ‘event file’. This new approach to seismic interpretation allows statistical analyses of the attributes including estimation of scaling laws for reflectivity observed on deep seismic data, and development of new filtering techniques based on characteristics such as dip and reflection event length. Applications of the technique to deep crustal reflection data sets from the Alberta Basement Transect of the Lithoprobe project assist interpretation in areas that lack surface outcrop or other means of relating reflections from the deep crust to the surface.