Geochemical characterization of mid-Cretaceous granitoids of the Kootenay Arc in the southern Canadian Cordillera

1993 ◽  
Vol 30 (5) ◽  
pp. 1076-1090 ◽  
Author(s):  
Alan D. Brandon ◽  
Richard StJ. Lambert
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Crustal Thickening ◽  
Precambrian Basement ◽  
Crustal Anatexis ◽  
Volcanic Arcs ◽  
North American Continent ◽  
Isotopic Compositions ◽  
The North ◽  
Host Rocks

Within southeast British Columbia, mid-Cretaceous granitoid batholiths are exposed in the Omineca Belt, a north–south-trending metamorphic and plutonic orogenic belt. The Bugaboo, Horsethief Creek, and Fry Creek batholiths are post-kinematic with respect to regional metamorphism that affected their host rocks, and are composed of hornblende and biotite granodiorites and granites in all three batholiths, and two-mica granites in Fry Creek. The biotite granites are weakly peraluminous, have initial εSr ranging from + 36 to + 56 and initial εNd ranging from −4.8 to −7.5, and overlap the range of Nd–Sr isotopic compositions for Precambrian basement gneisses and Proterozoic metasediments found in southeast British Columbia. The initial 206Pb/204Pb versus 208Pb/204Pb and 207Pb/204Pb for these granitoids lie in bands between model lower and upper crustal Pb isotopic compositions above the Northern Hemisphere Reference Line for oceanic basalts. These granitoids have high Nb and Rb and low Ba abundances relative to granites found in volcanic arcs. The two-mica granites are strongly peraluminous and have εSr ranging from + 170 to + 470, εNd ranging from −10 to−21, and more radiogenic initial Pb-isotope ratios than the biotite granites. The two-mica granites have trace element compositions similar to those of granites found in within-plate and collisional tectonic settings.We favor a model for crustal anatexis of Precambrian basement gneisses and Proterozoic metapelites to produce the mid-Cretaceous biotite granites and two-mica granites, respectively. Crustal anatexis was likely in response to crustal thickening that occurred during the Mesozoic in southeast British Columbia as exotic terranes collided with and were accreted to the western edge of the North American continent.

Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part I: Jurassic to mid-Cretaceous

1983 ◽  
Vol 20 (12) ◽  
pp. 1891-1913 ◽  
Author(s):  
D. A. Archibald ◽  
J. K. Glover ◽  
R. A. Price ◽  
E. Farrar ◽  
D. M. Carmichael
Keyword(s):  
British Columbia ◽  
North America ◽  
Regional Metamorphism ◽  
Granitic Rocks ◽  
Early Paleozoic ◽  
Small Bodies ◽  
Western Margin ◽  
The North ◽  
Windermere Supergroup ◽  
Igneous Activity

K–Ar dates and U–Pb zircon dates define three periods of igneous activity in the southern Kootenay Arc: (1) emplacement of late-synkinematic to post-kinematic granodioritic plutons in mid-Jurassic time (170–165 Ma) accompanying amphibolite-facies regional metamorphism; (2) emplacement of post-kinematic granitic plutons in mid-Cretaceous time (~100 Ma); and (3) emplacement of small bodies of syenite in Eocene time (~50 Ma) in the western part of the area. Micas from mid-Jurassic plutons that yield the oldest K–Ar dates (158–166 Ma) also yield plateau-shaped 40Ar/39Ar age spectra. Age spectra for biotites younger than these but older than 125 Ma reflect thermal overprinting.In southeastern British Columbia, the Kootenay Arc marks the transition from the North American rocks of the Cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it.Deformation, metamorphism, and plutonism recorded in rocks of the southern Kootenay Arc commenced in mid-Jurassic time as a composite allochthonous terrane was accreted to and overlapped the western margin of North America. The geochronology and metamorphic geothermobarometry show that in less than 10 Ma between 166 and 156 Ma: (1) rocks as young as the late Proterozoic Windermere Supergroup and the early Paleozoic Lardeau Group were carried rapidly to depths of 20–24 km while being deformed and intruded by granitic rocks of a hornblende–biotite suite that were also being emplaced at a much shallower level in the overriding allochthonous terrane; and (2) the miogeoclinal rocks of the Windermere Supergroup in the southern Kootenay Arc were then uplifted by more than 7 km at an estimated rate of 2 mm/year, and thrust over the allochthonous terrane prior to being intruded by post-kinematic granitic rocks, many of which belong to the two-mica suite of mid-Cretaceous age..

U–Pb geochronometry in the Horseranch Range, northern Omineca Belt, British Columbia, Canada

1994 ◽  
Vol 31 (2) ◽  
pp. 341-350
Author(s):  
Heather E. Plint ◽  
Randall R. Parrish
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Granitic Rocks ◽  
Precambrian Basement ◽  
North Central ◽  
Magmatic Rocks ◽  
Granitic Magmatism ◽  
Common Observation ◽  
Western Side ◽  
Dextral Strike Slip

A U–Pb geochronometric study of granitic rocks in the Horseranch Range in the northern Omineca Belt, north-central British Columbia, was carried out to determine the age of deformation, metamorphism, and magmatism and to determine if Precambrian basement is exposed in the range.Our results document Eocene (48–54 Ma) and late Early Cretaceous (113 Ma) granitic magmatism, limit the regional schistosity development to 113 Ma and older, and constrain the peak of syn- to posttectonic regional metamorphism to about 113 Ma. There is no direct evidence for Jurassic metamorphism, although our data do not preclude it. Dextral, oblique-slip mylonitization along the western side of the range is, in part, of Eocene age and related to transtensional tectonics synchronous with movement along regional, dextral strike-slip faults. No Precambrian basement was identified. However, U–Pb data indicate Early Proterozoic inheritance in some of the granitic rocks, a common observation in magmatic rocks of the Omineca Belt.

Metamorphic rocks of the 1985 Tibet Geotraverse, Lhasa to Golmud

1988 ◽  
Vol 327 (1594) ◽  
pp. 203-213 ◽  
Keyword(s):  
Tibetan Plateau ◽  
Regional Metamorphism ◽  
Metamorphic Grade ◽  
Metamorphic Rocks ◽  
The Tibetan Plateau ◽  
Crustal Anatexis ◽  
Prograde Metamorphism ◽  
Lhasa Terrane ◽  
The North ◽  
Peak Metamorphism

Two examples of uplifted basement have been studied in the Lhasa Terrane of the Tibetan Plateau. The Nyainqentanglha orthogneisses are bounded by staurolite-garnet schists to the north which record prograde metamorphism at 5 .0 ± 1.3 kbar, 610 ± 70 °C. Garnet sillimanite xenoliths within the orthogneiss suggest that peak temperatures reached at least 700 ± 70 °C at 5.1 ± 2 .5 kbar. These P / T fields reflect high T /low P metamorphism during Eocene subduction, and indicate that the syntectonic Nyainqentanglha orthogneiss was emplaced at depths greater than 10 km. Sillimanite-bearing assemblages from the Amdo gneisses in the northern Lhasa Terrane provide evidence of crustal anatexis at temperatures > 680 °C. This event is poorly constrained in time but is probably Cambrian or earlier. Within the Kunlun Terrane, biotite and garnet isograds north of the Xidatan Fault indicate an increase in metamorphic grade from north to south, reaching peak metamorphism at 470 ± 30 °C, 4 .3 ± 1.5 kbar synchronous with the emplacement of the Triassic batholith. Regional metamorphism was followed by uplift of at least 2 km before emplacement of post-tectonic, early Jurassic granites.

scholarly journals Linking metamorphism, magma generation, and synorogenic sedimentation to crustal thickening during Southern Appalachian mountain building, USA

Lithosphere ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 722-749
Author(s):  
H.H. Stowell ◽  
J.J. Schwartz ◽  
S.B. Ingram ◽  
J. Madden ◽  
C. Jernigan ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Foreland Basin ◽  
Progressive Increase ◽  
Crustal Thickening ◽  
Garnet Growth ◽  
Metamorphic Rocks ◽  
Blue Ridge ◽  
Magma Generation ◽  
The North ◽  
North American Craton

Abstract The nature of metamorphism, magma compositions, the spatial distribution of plutons, and foreland sediments reflect, in part, the character and thickness of continental crust. We utilized metamorphic pressure-temperature-time (P-T-t) paths, garnet Sm-Nd ages, zircon U-Pb ages, and pluton compositions to estimate paleocrustal thickness and temporal changes in crustal magma sources in the Blue Ridge of the southernmost Appalachians. Garnet Sm-Nd ages for amphibolite-facies metamorphic rocks range from 331 ± 4 to 320 ± 3 Ma. Low- and high-Sr/Y plutons that intruded these metamorphic rocks have zircon U-Pb ages of 390 ± 1 to 365 ± 1 Ma and 349 ± 2 to 335 ± 1 Ma, respectively. Therefore, garnet growth began during regional metamorphism synchronous with or shortly after intrusion of the youngest high-Sr/Y trondhjemite plutons. Phase diagram sections and thermobarometry indicate that garnet growth initiated at ∼5.8 kbar and 540 °C and grew during temperature increases of 60–100 °C and pressure increases of 2–3 kbar. The older, low-Sr/Y magmas are inferred to have been sourced in the crust at depths <∼30 km, insufficient for garnet to be stable. However, the younger, high-Sr/Y magmas are inferred to have been sourced at >30 km depths where garnet was stable. Hafnium isotopic compositions for all the plutons, but one, exhibit a range from negative initial εHf(i) to weakly positive initial εHf(i), indicating incomplete mixing of dominantly crustal sources. Our data require minimum crustal thicknesses of ∼33 km at 331 Ma; however, Alleghanian crustal thicknesses must have locally reached 39 km, based on crustal reconstruction adding the Alleghanian thrust sheet beneath the eastern Blue Ridge. We infer the presence of hot, tectonically thickened crust during intrusion of the early Alleghanian high-Sr/Y plutons and conclude that garnet growth and plutonism reflect a progressive increase in crustal thickness and depth of magma generation. The crustal thickening was synchronous with deposition of Mississippian to early Pennsylvanian sediments in the foreland basin of the Appalachian orogen between 350 and 320 Ma. This crustal thickening may have preceded emplacement of the Alleghanian thrust sheets onto the North American craton.

scholarly journals Physiological resilience of pink salmon to naturally occurring ocean acidification

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Andrea Y Frommel ◽  
Justin Carless ◽  
Brian P V Hunt ◽  
Colin J Brauner
Keyword(s):  
British Columbia ◽  
Elevated Co2 ◽  
Condition Factor ◽  
Pacific Salmon ◽  
Pink Salmon ◽  
Hypoxia Tolerance ◽  
High Co2 ◽  
The North ◽  
Naturally Occurring ◽  
Co2 Levels

Abstract Pacific salmon stocks are in decline with climate change named as a contributing factor. The North Pacific coast of British Columbia is characterized by strong temporal and spatial heterogeneity in ocean conditions with upwelling events elevating CO2 levels up to 10-fold those of pre-industrial global averages. Early life stages of pink salmon have been shown to be affected by these CO2 levels, and juveniles naturally migrate through regions of high CO2 during the energetically costly phase of smoltification. To investigate the physiological response of out-migrating wild juvenile pink salmon to these naturally occurring elevated CO2 levels, we captured fish in Georgia Strait, British Columbia and transported them to a marine lab (Hakai Institute, Quadra Island) where fish were exposed to one of three CO2 levels (850, 1500 and 2000 μatm CO2) for 2 weeks. At ½, 1 and 2 weeks of exposure, we measured their weight and length to calculate condition factor (Fulton’s K), as well as haematocrit and plasma [Cl−]. At each of these times, two additional stressors were imposed (hypoxia and temperature) to provide further insight into their physiological condition. Juvenile pink salmon were largely robust to elevated CO2 concentrations up to 2000 μatm CO2, with no mortality or change in condition factor over the 2-week exposure duration. After 1 week of exposure, temperature and hypoxia tolerance were significantly reduced in high CO2, an effect that did not persist to 2 weeks of exposure. Haematocrit was increased by 20% after 2 weeks in the CO2 treatments relative to the initial measurements, while plasma [Cl−] was not significantly different. Taken together, these data indicate that juvenile pink salmon are quite resilient to naturally occurring high CO2 levels during their ocean outmigration.

scholarly journals Gitksan

2016 ◽  
Vol 46 (3) ◽  
pp. 367-378 ◽  
Author(s):  
Jason Brown ◽  
Henry Davis ◽  
Michael Schwan ◽  
Barbara Sennott
Keyword(s):  
British Columbia ◽  
The South ◽  
The West ◽  
The North

Gitksan (git) is an Interior Tsimshianic language spoken in northwestern British Columbia, Canada. It is closely related to Nisga'a, and more distantly related to Coast Tsimshian and Southern Tsimshian. The specific dialect of Gitksan presented here is what can be called Eastern Gitksan, spoken in the villages of Kispiox (Ansbayaxw), Glen Vowell (Sigit'ox), and Hazelton (Git-an'maaxs), which contrasts with the Western dialects, spoken in the villages of Kitwanga (Gitwingax), Gitanyow (Git-anyaaw), and Kitseguecla (Gijigyukwhla). The primary phonological differences between the dialects are a lexical shift in vowels and the presence of stop lenition in the Eastern dialects. While there exists a dialect continuum, the primary cultural and political distinction drawn is between Eastern and Western Gitksan. For reference, Gitksan is bordered on the west by Nisga'a, in the south by Coast Tsimshian and Witsuwit'en, in the east by Dakelh and Sekani, and in the north by Tahltan (the latter four of these being Athabaskan languages).

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