One-dimensional thermal models of metamorphism resulting from the Coast Plutonic Complex sill, northern Coast Mountains, southeastern Alaska

2000 ◽  
Author(s):  
Harold H. Stowell ◽  
Michelle A. Pike
Keyword(s):  
Northern Coast ◽  
Thermal Models ◽  
Coast Mountains ◽  
One Dimensional ◽  
Plutonic Complex ◽  
Coast Plutonic Complex

Distribution and tectonic significance of Upper Triassic terranes in the eastern Coast Mountains and adjacent Intermontane Belt, British Columbia

1991 ◽  
Vol 28 (4) ◽  
pp. 532-541 ◽  
Author(s):  
Margaret E. Rusmore ◽  
G. J. Woodsworth
Keyword(s):  
Upper Triassic ◽  
Eastern Coast ◽  
Coast Mountains ◽  
Early Mesozoic ◽  
Tectonic Significance ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Basalt Geochemistry ◽  
Volcaniclastic Rocks ◽  
Final Closure

New data on Upper Triassic rocks in the eastern Coast Mountains show that it is Stikinia, not Wrangellia, that lies along the eastern margin of the Coast Plutonic Complex, at least as far south as latitude 51°N. These rocks constitute the upper Carnian–lower Norian Mt. Moore formation and the upper Norian Mosley formation. Clinopyroxene-phyric basaltic to andesitic breccia with lesser volcanic sandstone and rare carbonate compose the Mt. Moore formation. The Mosley formation comprises mafic volcaniclastic rocks and limestone. Correlation of these formations with Stikinia is based on similarities in age, stratigraphy, lithology, basalt geochemistry, and inferred tectonic setting.Recognition of Upper Triassic arc-related rocks of the Cadwallader terrane east of its previously known extent indicates that the Cadwallader terrane, rather than Stikinia, underlies much of the southern Intermontane Belt. The revised terrane distribution shows that Stikinia lay west of both the Cadwallader and Bridge River terranes prior to Cretaceous and Tertiary faulting. This configuration supports the idea that the Cadwallader and Stikine terranes represent fragments of a single early Mesozoic arc that was accreted during final closure of the Cache Creek – Bridge River ocean in Middle Jurassic time.

Magnetic anomalies and rock magnetizations in the southern Coast Mountains, British Columbia: possible relation to subduction

1977 ◽  
Vol 14 (8) ◽  
pp. 1753-1770 ◽  
Author(s):  
R. L. Coles ◽  
R. G. Currie
Keyword(s):  
Magnetic Material ◽  
British Columbia ◽  
Magnetic Anomaly ◽  
Western Coast ◽  
Coast Mountains ◽  
Deep Crust ◽  
High Oxygen Pressure ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Trend Variation

A qualitative correlation is observed between the northwesterly trending Coast Mountains Magnetic Anomaly, British Columbia, and a systematic, cross-trend variation of measured magnetizations within the more mafic rocks from the Coast Plutonic Complex between 50° and 51° N. This variation partly determines the form of the anomaly. A similar variation of magnetizations in more acidic rocks is not found. Quantitative modelling, however, indicates the presence of deeper, intense magnetizations below the high anomaly in the west. A magnetic crust as much as 40 km thick is consistent with geothermal studies in this region. The deep crust of Vancouver Island is less magnetic than that under the western Coast Plutonic Complex. The concentration of magnetic material may be a consequence of a subduction process, whereby water released by dehydration of the downgoing slab promotes partial melting, with subsequent uprising of heat and melt within a hydrous environment. The water tends to maintain a relatively high oxygen pressure, at least locally, and magnetite forms in the crystallization sequence. As subduction proceeds, this region cools and the magnetic material may then produce a high magnetic anomaly.

Magmatic evolution of the eastern Coast Plutonic Complex, Bella Coola region, west-central British Columbia

2009 ◽  
Vol 121 (9-10) ◽  
pp. 1362-1380 ◽  
Author(s):  
J. Brian Mahoney ◽  
Sarah M. Gordee ◽  
James W. Haggart ◽  
Richard M. Friedman ◽  
Larry J. Diakow ◽  
...  
Keyword(s):  
British Columbia ◽  
Eastern Coast ◽  
Magmatic Evolution ◽  
West Central ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Bella Coola

Obducted nappe sequence in the San Juan Islands – northwest Cascades thrust system, Washington and British Columbia

2012 ◽  
Vol 49 (7) ◽  
pp. 796-817 ◽  
Author(s):  
E.H. Brown
Keyword(s):  
British Columbia ◽  
Detrital Zircons ◽  
San Juan ◽  
San Juan Islands ◽  
Tectonic History ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
History Of ◽  
Accreted Terranes ◽  
Thrust System

The San Juan Islands – northwest Cascades thrust system in Washington and British Columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of Wrangellia and the Coast Plutonic Complex. Emplacement ages of the nappe sequence are interpreted from zircon ages, field relations, and lithlogies, to young upward. The basal nappe was emplaced prior to early Turonian time (∼93 Ma), indicated by the occurrence of age-distinctive zircons from this nappe in the Sidney Island Formation of the Nanaimo Group. The emplacement age of the highest nappe in the thrust system postdates 87 Ma detrital zircons within the nappe. The nappes bear high-pressure – low-temperature (HP–LT) mineral assemblages indicative of deep burial in a thrust wedge; however, several features indicate that metamorphism occurred prior to nappe assembly: metamorphic discontinuities at nappe boundaries, absence of HP–LT assemblages in the footwall to the nappe pile, and absence of significant unroofing detritus in the Nanaimo Group. A synorogenic relationship of the thrust system to the Nanaimo Group is evident from mutually overlapping ages and by conglomerates of Nanaimo affinity that lie within the nappe pile. From the foregoing relations, and broader Cordilleran geology, the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction-zone metamorphism south of the present locality, uplift and exhumation, orogen-parallel northward transport of the nappes as part of a forearc sliver, and finally obduction at the present site over the truncated south end of Wrangellia and the Coast Plutonic Complex.

The western margin of the Coast Plutonic Complex on Hardwicke and West Thurlow Islands, British Columbia

1979 ◽  
Vol 16 (6) ◽  
pp. 1166-1175 ◽  
Author(s):  
Jo Anne Nelson
Keyword(s):  
Quartz Diorite ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Western Margin ◽  
Late Mesozoic ◽  
The North ◽  
Early Mesozoic ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Maximum Contact

The western margin of the Coast Plutonic Complex, one of the major tectonic boundaries of the Canadian Cordillera, has been variously interpreted as an intrusive contact, a shear zone, and a suture zone joining the Early Mesozoic Insular Belt to the North American continent. A representative section of this boundary, exposed on islands in Johnstone Strait, is an intrusive contact along which a quartz diorite with peripheral mafic phases truncates Early Mesozoic sediments and volcanics of the Insular Belt. Concordant hornblende–biotite pairs and two whole rock biotite isochrons date the intrusion as Late Jurassic (151 Ma). Prior to intrusion the stratified units underwent prehnite–pumpellyite facies metamorphism and west-northwest block faulting.The contact aureole of the quartz diorite and its associated mafic phases involves greenschist and hornblende–hornfels facies assemblages. Total pressure in the upper Karmutsen Formation during contact metamorphism was less than 2.5 × 105 kPa. The maximum contact temperature was between 670 and 700 °C. Forcible emplacement of the intrusion caused penetrative deformation of wall rocks in the inner aureole. The maximum contact temperatures indicate that the plutonic bodies were at near-liquidus temperatures when emplaced.The contact on Hardwicke and West Thurlow Islands appears representative of most of the tectonic boundary between the southern Coast Plutonic Complex and the Insular Belt. The western margin of the Coast Plutonic Complex is thus a Late Mesozoic magmatic front, the western limit of the intense magmatism that generated the Coast Plutonic Complex. The formation of Georgia Depression over the province boundary was a later event, coeval with major uplift of the Coast Plutonic Complex.

Seismic investigation of the Coast Plutonic Complex – Insular Belt boundary beneath the Strait of Georgia

1984 ◽  
Vol 21 (9) ◽  
pp. 1033-1049 ◽  
Author(s):  
Donald J. White ◽  
Ron M. Clowes
Keyword(s):  
Crustal Structure ◽  
Seismic Refraction ◽  
Unconsolidated Sediments ◽  
The West ◽  
Strait Of Georgia ◽  
Seismic Properties ◽  
Air Gun ◽  
Plutonic Complex ◽  
Major Fault ◽  
Coast Plutonic Complex

The Strait of Georgia, a topographic depression between Vancouver Island and the mainland of British Columbia, is considered to be the boundary between two tectonic provinces: the Coast Plutonic Complex on the east and the Insular Belt to the west. The allochthonous nature of the Insular Belt has been established, mainly on the basis of paleomagnetic measurements. Various tectonic models to explain the geological differences between the two provinces have been proposed. One of these suggests that the boundary is an old transform fault zone and is represented currently by a thrust fault along the eastern side of the Strait of Georgia. Other models propose that the Coast Plutonic Complex is a feature superimposed by tectonic and metamorphic events after the accretion of the Insular Belt. Such models do not require a major crustal discontinuity along the Strait of Georgia.In May 1982, a seismic refraction survey using a 32 L air gun and a radio telemetering sonobuoy system was carried out in the Strait of Georgia with the objective of investigating the nature of this boundary and determining the upper crustal structure. Three reversed profiles across the strait were shot; these are supplemented by several high-resolution reflection profiles from previous experiments. Two-dimensional models of the crustal structure across the strait have been constructed using a forward modelling ray trace and synthetic seismogram algorithm to match the travel times and amplitude characteristics of the data.Three basic layers or strata form the models, for which the maximum depth of reliability is 3 km. The first layer consists of unconsolidated sediments and Pleistocene glacial deposits, and the second represents Late Cretaceous – early Tertiary basin fill sediments that form the Nanaimo Group, the Burrard–Kitsilano formations, and the Chuckanut Formation. The third layer is likely the extension of the Coast Plutonic Complex beneath the strait, but the westerly limit of this unit is undetermined because of seismic properties similar to those of the Insular Belt volcanics. A local fault is located ~15 km northeast of Galiano Island on the west side of the strait. However, our study shows no evidence for a major fault along the strait. Thus those aspects of tectonic models that require the existence of a major transform or transcurrent fault boundary along the Strait of Georgia. may have to be revised.

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