Model of evolution of the Bella Coola – Ocean Falls Region, Coast Mountains, British Columbia

1968 ◽  
Vol 5 (6) ◽  
pp. 1429-1441 ◽  
Author(s):  
A. J. Baer
Keyword(s):  
British Columbia ◽  
Granitic Rocks ◽  
Coast Mountains ◽  
Early Tertiary ◽  
Upper Paleozoic ◽  
Late Tertiary ◽  
Bella Coola

Granitic rocks and metavolcanics underlie most of the Coast Mountains of British Columbia between the fifty-second and the fifty-third parallel, about half-way between Vancouver and Prince Rupert. The age of most rocks is unknown. The area has been involved in at least two orogenic cycles. The oldest known supracrustal rocks (Upper Paleozoic?) have been metamorphosed to gneisses, deformed along northeasterly trends, and intruded by granitic plutons, probably early in the Mesozoic Era. These rocks formed the basement of disconformable Mesozoic sediments and volcanics. The basement and its Mesozoic cover were metamorphosed and deformed along northwesterly trends in the early Tertiary. In the late Tertiary (Pliocene?) post-kinematic granites were emplaced and basalts were extruded for a period extending to postglacial times. The model is possibly applicable to all of the Coast Mountains in Canada.

Geology of the Chatham Sound region, southeast Alaska and coastal British Columbia

2001 ◽  
Vol 38 (11) ◽  
pp. 1579-1599 ◽  
Author(s):  
George E Gehrels
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Upper Jurassic ◽  
The West ◽  
Southeast Alaska ◽  
Coast Mountains ◽  
Early Tertiary ◽  
Metavolcanic Rocks ◽  
Upper Paleozoic ◽  
Coastal British Columbia

The Coast Mountains orogen is thought to have formed as a result of accretion of the Alexander and Wrangellia terranes against the western margin of the Stikine and Yukon–Tanana terranes, but the nature and age of accretion remain controversial. The Chatham Sound area, which is located along the west flank of the Coast Mountains near the Alaska – British Columbia border, displays a wide variety of relations that bear on the nature and age of the boundary between inboard and outboard terranes. Geologic and U–Pb geochronologic studies in this area reveal a coherent but deformed and metamorphosed sequence of rocks belonging to the Yukon–Tanana terrane, including pre-mid-Paleozoic marble, schist, and quartzite, mid-Paleozoic orthogneiss and metavolcanic rocks, and upper Paleozoic metaconglomerate and metavolcanic rocks. These rocks are overlain by Middle Jurassic volcanic rocks (Moffat volcanics) and Upper Jurassic – Lower Cretaceous strata of the Gravina basin, both of which also overlie Triassic and older rocks of the Alexander terrane. This overlap relationship demonstrates that the Alexander and Wrangellia terranes were initially accreted to the margin of inboard terranes during or prior to mid-Jurassic time. Accretion was apparently followed by Late Jurassic – Early Cretaceous extension–transtension to form the Gravina basin, left-slip along the inboard margin of Alexander–Wrangellia, mid-Cretaceous collapse of the Gravina basin and final structural accretion of the outboard terranes, and early Tertiary dip-slip motion on the Coast shear zone.

Early Tertiary Anaconda Metamorphic Core Complex, southwestern Montana

2004 ◽  
Vol 41 (1) ◽  
pp. 63-72 ◽  
Author(s):  
J Michael O'Neill ◽  
Jeff D Lonn ◽  
David R Lageson ◽  
Michael J Kunk
Keyword(s):  
Sedimentary Rocks ◽  
Shear Zones ◽  
Detachment Fault ◽  
Integrated System ◽  
Metamorphic Core Complex ◽  
Granitic Rocks ◽  
Core Complex ◽  
Early Tertiary ◽  
Late Tertiary ◽  
Metamorphic Core

A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts, overprinted by late Tertiary Basin and Range faulting.

Neoglacial history of the Coast Mountains near Bella Coola, British Columbia

1990 ◽  
Vol 27 (2) ◽  
pp. 281-290 ◽  
Author(s):  
J. R. Desloges ◽  
J. M. Ryder
Keyword(s):  
British Columbia ◽  
Tree Ring ◽  
Little Ice Age ◽  
Ice Age ◽  
Canadian Cordillera ◽  
Sampling Errors ◽  
Coast Mountains ◽  
History Of ◽  
Glacier Advance ◽  
Bella Coola

The maximum Holocene extent of glaciers in the study area is marked by late Neoglacial (Little Ice Age) terminal moraines. Moraine stratigraphy and 14C dates from a small number of sites suggest that glacier advance, almost as extensive as that of the late Neoglacial, occurred about 2500 14C years BP, and that late Neoglacial advance began well before 770 14C years BP (or the thirteenth century A.D.); glacier termini then stood close to the position of the climax moraines for several centuries. Dates of stabilization of end moraines at 16 glaciers were determined by dendrochronology, with tree-ring counts corrected for sampling errors and ecesis. Most terminal moraines date from 1860 to 1900. Many recessional moraines were formed between 1900 and 1940, coincident with a regionally documented phase of cooler and wetter climate. The proposed chronology is similar to results from elsewhere in the Canadian Cordillera.

Sign in / Sign up

Export Citation Format

Share Document