Lithoprobe-Phase 1: southern Vancouver Island: preliminary analyses of reflection seismic profiles and surface geological studies

Yorath, C J; Clowes, Ron M.; Green, A G; Sutherland-Brown, A; Brandon, M. T.; Massey, N. W. D.; Spencer, Carl; Kanasewich, E. R.; Hyndman, R. D.

doi:10.4095/120150

Cited by 8 publications

(3 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 ). The Leec h River fault is believed to have been ac tive during the late Eocene (Brandon, 1984(Brandon, , 1985. This wedge of volcanics is an important accreted element in the architecture of the con tinental margin and is further illustrated in re flection profiles on southern Vancouver Island (R. M. Clowes et al, in prep.…”

Section: Swmentioning

confidence: 99%

Lithoprobe, southern Vancouver Island: Seismic reflection sees through Wrangellia to the Juan de Fuca plate

Yorath

Green²,

Clowes

et al. 1985

Geol

View full text Add to dashboard Cite

Multichannel seismic reftection profdes obtained on Vancouver Island show that above a zone of decoupling between the North American and Juan de Fuca plates, Wrangellia is underplated by two accreted terranes of probable oceanic origin. Both the zone of decoupling and Wrangellia are disrupted by easterly dipping faults, some of which are thrusts. The crustal structure of Wrangellia comprises Paleozoic and Mesozoic volcanic and sedimentary rocks disposed as roof pendants upon, and large irregular masse s within, a ubiquitous Jurassic plutonic and metamorphic complex.

show abstract

Section: Swmentioning

confidence: 99%

Lithoprobe, southern Vancouver Island: Seismic reflection sees through Wrangellia to the Juan de Fuca plate

Yorath

Green²,

Clowes

et al. 1985

Geol

View full text Add to dashboard Cite

show abstract

“…6. In this area, the C = Dl horizon (top of decollement zone of Yorath et al 1985aYorath et al , 1985b) is a major thrust that underlies Mesozoic and Paleozoic rocks of the Wrangellia terrane as well as an accreted slice of Eocene basalt (correlative with the Metchosin basalts in lines 2 and 4). The underplated region lies beneath this horizon and represents a land· ward continuation of the modern accretionary wedge that underlies the Vancouver Island margin.…”

Section: Data Acquisition and Processingmentioning

confidence: 99%

“…El marks the top of a layer, approximately 5 km thick, of quasi-continuous, closely spaced, high-amplitude reflections. Yorath et al (1985a) and Clowes et al (1984) interpreted El as the modem subduction thrust and the reflective zone below it as interbedded sediments and volcanics of the presently sub ducting Juan de Fuca plate. Another alternative is that the El -E2 layer represents another imbricated sequence within the underplated zone, similar to Dl -D2.…”

Section: Lower Structural Regionmentioning

confidence: 99%

LITHOPROBE—southern Vancouver Island: Cenozoic subduction complex imaged by deep seismic reflections: Reply

Clowes¹,

Brandon²,

Green³

et al. 1988

Can. J. Earth Sci.

View full text Add to dashboard Cite

CAN. J. EARTH SCL VOL. 24, 1987 determiner leur geometric en subsurface et leurs relations avec !es structures profondes dans la zone actuellement en voie de subduction.La structure sous-jacente a l'ile peut etre divisee en une region crustale superieure formee de plusieurs terranes d'accretion et en une region plus profonde qui represente une extension vers le continent d'un complexe oceanique de subduction contempo raine. Dans la region superieure, Jes failles Survey Mountain et Leech River apparaissent sur image sismique comme des chevauchements de pendage nord-est qui separent le vaste terrane mesozolque-paleozoi'que Wrangellia de deux terranes d'accretion plus petits: le schiste de Leech River, forme de roches mesozo!ques metamorphisees durant !'Eocene superieur; et la formation de Metchosin, une unite de basalte et gabbro d'age de !'Eocene inferieur. La faille Leech River clairement reflechie dans le profil sismique presente un pendage nord-est de 35-45°, et elle se prolonge jusqu 'a environ 10 km de profon deur. La faille Survey Mountain apparait au-dessus de la faille Leech River et se prolonge parallele a cette demiere jusqu'a la meme profondeur. La faille San Juan, Ia continuite accidentale de la faille Survey Mountain, n'apparait pas dans le profil, cependant d'autres indices revelent qu'elle est aussi une faille de chevauchement. Ces failles ont largement facilite !'amalga mation a l'Eocene des terranes Leech River et Metchosin sur le perimetre sud de la Wrangellia. Par la suite, ces terranes se comporterent comme un couvercle relativement solidaire en un complexe de suduction plus recent forme durant le regime con vergent de subduction (40 Ma a present) contemporaine.Les profils sismiques LITHOPROBE dans le complexe de subduction revelent trois bandes dominantes de retlectivite diffe rente avec foible pendage nord-est. Ces bandes representent des couches d'extension regionale sous-jacentes au couvercle forme des terranes accoles plus anciens. Nous croyons que Jes bandent sont dues a une penetration sous-plaque de materiaux oceaniques au-dessous du front de la plaque continentale chevauchante. La Couche superieure de reflexion peut etre extrapolee vers le sud en montant le pendange en un lieu d'affleurement dans !es monts Olympiques represente par !es roches de Core, un complexe cenozolque de subduction souleve et compose principalement de terrains marins sedimentaires accoles. La zone centrale de faible retlectivite n 'est pas expo see en surface, ma is Jes resultats obtenus par un !eve adjacent de sismique reflexion indiquent qu'elle est formee principalement de materiaux de vitesse relativement rapide ( -7,7 km/s). Cette zone peut etre expliquee de deux fa�ons: (1) une dalle detachee de la lithosphere oceanique s'est acealee durant un incident tectonique, ou (2) un paquetage imbrique de roches mafiques derivees par un accretion continue de la partie sommitale de la croute oceanique subductante. La couche inferieure de reflexion presente un profil sismique analogue a celui de la couche superieure...

show abstract

Comparison of deep structure along three transects of the western North American Continental Margin

Fuis¹,

Clowes²

1993

Tectonics

View full text Add to dashboard Cite

Similarities in geology and potential field data that have in the past been noted among the regions of southern Alaska, southern Vancouver Island, and central California are now seen to be accompanied by similarities in deep crustal structure. A number of tectonic elements have been identified in the deep structure along transects in these three regions, although not all elements are present along each transect. These elements are (A) an actively subducting oceanic plate and (B) an overriding continental plate that consists of (1) a Cenozoic accretionary prism, (2) a Mesozoic accretionary prism, (3) a backstop to the Mesozoic prism, (4) a tectonically underplated body of oceanic rocks, and (5) a crustal root. The Mesozoic prism is in some cases an underthrust body (type 2a) but in other cases forms the principal component of a landward verging tectonic wedge (type 2b). The technically underplated body of oceanic rocks extends landward from the fault contact between the Cenozoic and Mesozoic prisms to a point beneath the backstop. The crustal root lies beneath the backstop and landward of the underplated body. All of these elements are interpreted to be present along the Alaskan and Vancouver Island transects. In Alaska the underplated body is interpreted to be fragments of the Kula plate; the same may be true at Vancouver Island. These two transects appear to differ in that, in Alaska, the Mesozoic prism, in one interpretation, is the principal component of a tectonic wedge (type 2b), whereas at Vancouver Island, it is an underthrust body (type 2a). Along the central California transect, active subduction is no longer taking place, and the San Andreas fault has removed the Cenozoic prism from this region of the North American plate. On the North American plate (i.e., east of the San Andreas fault), the Mesozoic prism, interpreted as the main component of a tectonic wedge (type 2b), and the backstop to the Mesozoic prism are present. There is, however, no clear evidence of tectonically underplated oceanic rocks, and the crust is thin (no root). In both Alaska and Vancouver Island, the Mesozoic prisms above the underplated bodies experienced low‐pressure/high‐temperature metamorphism at about the time of tectonic underplating; no such metamorphism is currently exposed in California. The metamorphism may have been caused by the underplating of young, hot oceanic crust, or, alternatively, by subduction of an oceanic ridge. The presence of a tectonic wedge (type 2b) in Alaska and California and the absence of such a wedge at Vancouver Island could arise either from the fact that in the former two locations the Mesozoic prisms were more voluminous, owing to either more rapid trench sedimentation or more rapid convergence, or to the possibility that at the latter location the Mesozoic prism was juxtaposed with the backstop primarily by strike‐slip faulting.

show abstract

Lithoprobe-Phase 1: southern Vancouver Island: preliminary analyses of reflection seismic profiles and surface geological studies

Cited by 8 publications

References 11 publications

Lithoprobe, southern Vancouver Island: Seismic reflection sees through Wrangellia to the Juan de Fuca plate

Lithoprobe, southern Vancouver Island: Seismic reflection sees through Wrangellia to the Juan de Fuca plate

LITHOPROBE—southern Vancouver Island: Cenozoic subduction complex imaged by deep seismic reflections: Reply

Comparison of deep structure along three transects of the western North American Continental Margin

Contact Info

Product

Resources

About