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.

scholarly journals Crustal deformation and regional metamorphism across a terrane boundary, Coast Plutonic Complex, British Columbia

Tectonics ◽  
1987 ◽  
Vol 6 (3) ◽  
pp. 343-361 ◽  
Author(s):  
M. L. Crawford ◽  
L. S. Hollister ◽  
G. J. Woodsworth
Keyword(s):  
British Columbia ◽  
Crustal Deformation ◽  
Regional Metamorphism ◽  
Plutonic Complex ◽  
Coast Plutonic Complex

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.

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.

The southern Coast Mountains, British Columbia: New interpretations from geological, seismic reflection, and gravity data

2013 ◽  
Vol 50 (10) ◽  
pp. 1033-1050 ◽  
Author(s):  
Amanda M.M. Bustin ◽  
Ron M. Clowes ◽  
James W.H. Monger ◽  
J. Murray Journeay
Keyword(s):  
British Columbia ◽  
Early Cretaceous ◽  
Middle Jurassic ◽  
Gravity Data ◽  
Normal Faults ◽  
Southern Coast ◽  
Seismic Profiles ◽  
Coast Mountains ◽  
Clastic Rocks ◽  
Coast Plutonic Complex

The southern Coast Mountains of British Columbia are characterized by voluminous plutonic and gneissic rocks of mainly Middle Jurassic to Eocene age (the Coast Plutonic Complex), as well as metamorphic rocks, folds, and thrust and reverse faults that mostly diverge eastward and westward from an axis within the present mountains, and by more localized Eocene and younger normal faults. In the southeastern Coast Mountains, mid-Cretaceous and younger plutons intrude Bridge River, Cadwallader, and Methow terranes and overlap Middle Jurassic through Early Cretaceous marine clastic rocks of the Tyaughton–Methow basin. The combination of geological data with new or reanalyzed geophysical data originating from Lithoprobe and related studies enables revised structural interpretations to be made to 20 km depth. Five seismic profiles show very cut-up and chaotic reflectivity that probably represents slices and segments of different deformed and rearranged rock assemblages. Surface geology, seismic interpretations, physical properties, and gravity data are combined in two profiles across the Coast Mountains to generate two new 2-D density models that are interpreted in terms of the geological units. The western part of the southern Coast Mountains consists primarily of Jurassic to mid-Cretaceous plutons to depths of 20 km with slices of Wrangellia (in the west) and Early Cretaceous volcanic and sedimentary rocks (Gambier group) in the upper 10 km. The eastern part, east of the Owl Creek fault, consists of slices of Cadwallader and Bridge River terranes and Tyaughton–Methow basin strata with limited slices of plutonic rocks at depths less than 10 km. Below that, Eocene and Late Cretaceous plutons dominate for another 10 km.

Sign in / Sign up

Export Citation Format

Share Document