Jurassic–Cretaceous rock units along the southern edge of the Wrangellia terrane on Vancouver Island

1985 ◽  
Vol 22 (8) ◽  
pp. 1223-1232 ◽  
Author(s):  
Margaret E. Rusmore ◽  
Darrel S. Cowan
Keyword(s):  
High Pressure ◽  
Upper Jurassic ◽  
Vancouver Island ◽  
Late Eocene ◽  
San Juan ◽  
Tectonic Event ◽  
Cretaceous Rock ◽  
Early Oligocene ◽  
Southern Margin ◽  
Wrangellia Terrane

Rocks formerly mapped as Leech River Formation can be subdivided into two partly coeval rock units with completely different histories. The Upper Jurassic – Lower(?) Cretaceous Pandora Peak unit, which comprises black mudstone, terrigenous greywacke, radiolarian ribbon chert, green tuff, metabasaltic greenstone, minor pebbly mudstone, and a few blocks of limestone, was probably deposited in small basins on a continental margin. Local stratal disruption occurred before sediments were lithified. A static, high-pressure, low-temperature metamorphism produced lawsonite-bearing assemblages in metaclastic rocks. The Pandora Peak unit was originally coextensive with the Pacific Rim complex on western Vancouver Island and the Constitution formation in the San Juan Islands of Washington. The Leech River complex consists of foliated metasandstone, phyllite, and minor metabasalt of probable Jurassic–Cretaceous age. Multiple folding, transposition, and synkinematic greenschist- to amphibolite-facies metamorphism culminated about 40 Ma.The Pandora Peak unit is separated from crystalline rocks of the Wrangellia terrane by major faults. In southeast Victoria, partly retrograded amphibolites of the Wark–Colquitz complex overlie locally cataclastic lawsonite-bearing Pandora Peak rocks along the newly discovered Trial Islands thrust. A similar thrust separates the two units in Finlayson Arm, but near Port Renfrew the Pandora Peak terrane and crystalline West Coast complex are juxtaposed along the high-angle San Juan Fault. In each of these areas, emplacement of the Pandora Peak unit postdated the high-pressure (lawsonite-grade) metamorphism, which occurred between late Albian – early Cenomanian and Santonian–Campanian time (approximately 99–83 Ma). The Pandora Peak terrane was emplaced during a major Late Cretaceous or early Tertiary tectonic event that modified and probably truncated the southern margin of the Wrangellia terrane. Following this event the Leech River complex was faulted against the southern margin of the Pandora Peak terrane near Port Renfrew and in Goldstream Park in the Late Eocene or Early Oligocene.

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

1987 ◽  
Vol 24 (1) ◽  
pp. 31-51 ◽  
Author(s):  
R. M. Clowes ◽  
M. T. Brandon ◽  
A. G. Green ◽  
C. J. Yorath ◽  
A. Sutherland Brown ◽  
...  
Keyword(s):  
Large Scale ◽  
Sedimentary Rocks ◽  
Indirect Evidence ◽  
Vancouver Island ◽  
Late Eocene ◽  
San Juan ◽  
Juan De Fuca Plate ◽  
Reflective Layer ◽  
Juan De Fuca ◽  
Accreted Terranes

The LITHOPROBE seismic reflection project on Vancouver Island was designed to study the large-scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting Juan de Fuca plate. In this paper, we interpret two LITHOPROBE profiles from southernmost Vancouver Island that were shot across three important terrane-bounding faults—Leech River, San Juan, and Survey Mountain—to determine their subsurface geometry and relationship to deeper structures associated with modem subduction.The structure beneath the island can be divided into an upper crustal region, consisting of several accreted terranes, and a deeper region that represents a landward extension of the modern offshore subduction complex. In the upper region, the Survey Mountain and Leech River faults are imaged as northeast-dipping thrusts that separate Wrangellia, a large Mesozoic–Paleozoic terrane, from two smaller accreted terranes: the Leech River schist, Mesozoic rocks that were metamorphosed in the Late Eocene; and the Metchosin Formation, a Lower Eocene basalt and gabbro unit. The Leech River fault, which was clearly imaged on both profiles, dips 35–45 °northeast and extends to about 10 km depth. The Survey Mountain fault lies parallel to and above the Leech River fault and extends to similar depths. The San Juan fault, the western continuation of the Survey Mountain fault, was not imaged, although indirect evidence suggests that it also is a thrust fault. These faults accommodated the Late Eocene amalgamation of the Leech River and Metchosin terranes along the southern perimeter of Wrangellia. Thereafter, these terranes acted as a relatively coherent lid for a younger subduction complex that has formed during the modem (40 Ma to present) convergent regime.Within this subduction complex, the LITHOPROBE profiles show three prominent bands of differing reflectivity that dip gently northeast. These bands represent regionally extensive layers lying beneath the lid of older accreted terranes. We interpret them as having formed by underplating of oceanic materials beneath the leading edge of an overriding continental place. The upper reflective layer can be projected updip to the south, where it is exposed in the Olympic Mountains as the Core rocks, an uplifted Cenozoic subduction complex composed dominantly of accreted marine sedimentary rocks. A middle zone of low reflectivity is not exposed at the surface, but results from an adjacent refraction survey indicate it is probably composed of relatively high velocity materials (~ 7.7 km/s). We consider two possibilities for the origin of this zone: (1) a detached slab of oceanic lithosphere accreted during an episodic tectonic event or (2) an imbricated package of mafic rocks derived by continuous accretion from the top of the subducting oceanic crust. The lower reflective layer is similar in reflection character to the upper layer and, therefore, is also interpreted as consisting dominantly of accreted marine sedimentary rocks. It represents the active zone of decoupling between the overriding and underthrusting plates and, thus, delimits present accretionary processes occurring directly above the descending Juan de Fuca plate. These results provide the first direct evidence for the process of subduction underplating or subcretion and illustrate a process that is probably important in the evolution and growth of continents.

Alpine high-pressure metamorphism at the Almyropotamos window (southern Evia, Greece)

2000 ◽  
Vol 137 (4) ◽  
pp. 367-380 ◽  
Author(s):  
YONATHAN SHAKED ◽  
DOV AVIGAD ◽  
ZVI GARFUNKEL
Keyword(s):  
High Pressure ◽  
Large Scale ◽  
Structural Data ◽  
Late Eocene ◽  
Crustal Thickening ◽  
Lower Grade ◽  
The South ◽  
Northern Greece ◽  
High Pressure Metamorphism ◽  
Early Oligocene

The Alpine orogenic belt of the Hellenides has been strongly reworked by ductile and brittle extensional tectonics. Extensional structures have affected the central Aegean region and obliterated much of the original orogenic architecture since at least early Miocene times. In the area of Almyropotamos (on the island of Evia, flanking the western part of the Aegean) a unique remnant compressional nappe stack involving Tertiary metamorphic rocks has been preserved. This nappe sequence comprises a high-pressure rock unit on top of a lower grade unit. The upper unit (South Evia Blueschist Belt) is thought to be the westward continuation of the Cycladic blueschist belt metamorphosed at high-pressure conditions during Late Cretaceous–Eocene times. The underlying unit (the Almyropotamos Unit) is a continental margin sequence covered by a flysch and containing Lutetian nummulites, indicating that this unit accumulated sediments until at least late Eocene times.In the present study we analyse the petrology of the Almyropotamos nappe stack and define the P–T conditions of each of the different rock units exposed there. The presence of glaucophane, lawsonite rimmed by epidote, and jadeite (70 mol.%) suggest that peak P–T conditions in the South Evia Blueschist Belt reached approximately 10–12 kbar and 350–450 °C. Unlike previous studies, which estimated that the underlying Almyropotamos Unit reached only greenschist-facies conditions, glaucophane relics and Si-rich phengites were found by us in this unit. These indicate that high-pressure metamorphism and crustal thickening in this part of the Aegean lasted until at least the late Eocene or early Oligocene. We note that in this respect the architecture of southern Evia resembles that of northern Greece (Olympos, Ossa). Our structural data indicate that rock units in the Almyropotamos area record different folding phases, with the South Evia Blueschist Belt having a more complex fold history than the underlying Almyropotamos Unit. The entire nappe stack shares large-scale folds which are E–W trending, and locally overturned-to-the-south, and which may represent (at present coordinates) N–S contraction and nappe transport.

Evolution of the Pacific Margin, Vancouver Island, and adjacent regions

1977 ◽  
Vol 14 (9) ◽  
pp. 2062-2085 ◽  
Author(s):  
J. E. Muller
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Upper Jurassic ◽  
Vancouver Island ◽  
Late Eocene ◽  
Volcanic Arc ◽  
Late Mesozoic ◽  
Clastic Sediments ◽  
The Pacific ◽  
Uplift And Erosion

The tectonic–stratigraphic evolution of Vancouver Island, a part of the Insular Belt, is reviewed as it relates to the other major tectonic belts recognized in the western Cordillera of Canada and the adjacent United States. The Pacific Belt, recognized south of the international border, is also identified in the west and south of the island. Oldest rocks of the Insular Belt are a late Paleozoic volcanic arc terrane and a crystalline 'basement' that is probably pre-Devonian. A thick Upper Triassic succession of tholeiitic pillow lavas and flows, overlain by carbonate–clastic sediments, rests in part on the Paleozoic. Elsewhere the tholeiite may represent oceanic floor, perhaps formed when the Insular Belt was fragmented and rifted off the continental margin far to the south. Above it the Early Jurassic volcanic arc with related batholiths may have been aligned with a similar terrane in the Intermontane Belt before the two belts assumed parallel positions in late Mesozoic time. An Upper Jurassic – Lower Cretaceous westward thickening clastic wedge indicates uplift and erosion of the volcanic arc in late Mesozoic time. Further west the 'inner Pacific Belt' of Jura-Cretaceous elastics and chert represent slope and trench deposits that have been deformed to mélange or converted to schist. They are coeval and homologous to Franciscan and Chugach Terranes and probably mark the late Mesozoic trench and subduction zone along the continental margin. The Coast Plutonic Belt represents the related volcanic arc, and pre-Cretaceous Insular Belt rocks, unconformably overlain by Cretaceous clastic sediments, represent the arc–trench gap and fore-arc basin. Until Late Cretaceous time convergence of the Insular and Pacific Belts occurred along San Juan Fault. In early Tertiary time Eocene oceanic basalt (Outer Pacific Belt) and Jura-Cretaceous metasediments (Inner Pacific Belt) converged by under-thrusting and (or) strike–slip faulting along Leech River Fault. In Late Eocene time the trench and subduction zone shifted westward to the present core zone of the Olympic Mountains and shifted again in Miocene time to its present position.

scholarly journals Kinematic analysis and tertiary evolution of the Lesvos ophiolites and metamorphic sole (Aegean sea, Greece)

2001 ◽  
Vol 34 (1) ◽  
pp. 267 ◽  
Author(s):  
D. MOUNTRAKIS ◽  
E. THOMAIDOU ◽  
N. ZOUROS ◽  
A. KILIAS
Keyword(s):  
Continental Margin ◽  
Aegean Sea ◽  
Late Eocene ◽  
Early Miocene ◽  
Tectonic Event ◽  
Detachment Faults ◽  
Early Oligocene ◽  
Tectonic Events ◽  
Extensional Tectonic ◽  
Thrust Sheets

In Lesvos Island, the ophiolites and the metamorphic sole are emplaced onto the Permo-Triassic continental margin rocks. New field data on the Tertiary kinematics distinguished three successive tectonic events that affected the Lesvos ophiolites and sole. The Dl compressional event took place in Late Eocene - Early Oligocene and produced several thrust sheets and their stacking over the continental margin. The thickening of the crust after the Dl event, was followed by an important extensional tectonic event (D2) in semi-ductile conditions in Oligocene-Early Miocene times, which produced the uplift process of the orogen and the lateral rejection of the tectonic nappes through large extensional semi-ductile faults of low angle (detachment faults) and caused the exhumation of the underlying continental margin rocks in the form of a tectonic window. This extensional tectonic event led to the thinning of the crust in the wider area of Lesvos and probably caused the Early Miocene volcanic activity. The last D3 extensional tectonic event, took place in brittle conditions and represents the neotectonic regime in Late Miocene-Recent times.

Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

1998 ◽  
Vol 11 (6) ◽  
pp. 711 ◽  
Author(s):  
Robert S. Hill ◽  
Leonie J. Scriven
Keyword(s):  
Leaf Morphology ◽  
Middle Eocene ◽  
Late Eocene ◽  
South Eastern ◽  
Early Oligocene ◽  
Extant Species ◽  
Eastern Australia ◽  
South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

Integrated geophysical modelling of terranes and other structural features along the western Canadian margin

1992 ◽  
Vol 29 (7) ◽  
pp. 1492-1508 ◽  
Author(s):  
S. A. Dehler ◽  
R. M. Clowes
Keyword(s):  
Seismic Refraction ◽  
Vancouver Island ◽  
Structural Features ◽  
Pacific Rim ◽  
Data Set ◽  
Reflection Seismic ◽  
Barkley Sound ◽  
The Pacific ◽  
Wrangellia Terrane ◽  
Lower Crustal

An integrated geophysical data set has been used to develop structural models across the continental margin west of Vancouver Island, Canada. A modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous Crescent and Pacific Rim terranes. These terranes in turn abut against the pre-Tertiary Wrangellia terrane that constitutes most of the island. Gravity and magnetic anomaly data, constrained by seismic reflection, seismic refraction, and other data, were interpreted to determine the offshore positions of these terranes and related features. Iterative 2.5-dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features. An average model was then developed to represent this part of the margin. The Pacific Rim terrane appears to be continuous and close to the coastline along the length of Vancouver Island, consistent with emplacement by strike-slip motion along the margin. The Westcoast fault, the boundary between the Pacific Rim and Wrangellia terranes, is interpreted to be 15 km farther seaward than in previous interpretations in the region of Barkley Sound. The Crescent terrane forms a thin landward-dipping slab along the southern half of the Vancouver Island margin, and cannot be confirmed along the northern part. Model results suggest the slab has buckled into an anticline beneath southern Vancouver Island and Juan de Fuca Strait, uplifting high-density lower crustal or upper mantle material close to the surface to produce the observed intense positive gravity anomaly. This geometry is consistent with emplacement of the Crescent terrane by oblique subduction.

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