scholarly journals Paleomagnetic Studies of Radiometrically Dated Igneous Rocks in the Cordillera, British Columbia

1971 ◽  
Author(s):  
D T A Symons
Keyword(s):  
British Columbia ◽  
Igneous Rocks

Bridge River tephra: revised distribution and significance for detecting old carbon errors in radiocarbon dates of limnic sediments in southern British Columbia

1980 ◽  
Vol 17 (11) ◽  
pp. 1454-1461 ◽  
Author(s):  
Rolf W. Mathewes ◽  
John A. Westgate
Keyword(s):  
British Columbia ◽  
Sedimentary Rocks ◽  
Lacustrine Sediments ◽  
Igneous Rocks ◽  
The South ◽  
Radiocarbon Dates ◽  
Carbon Contamination ◽  
Horseshoe Lake ◽  
Tephra Beds

Ash-grade Bridge River tephra, identified as such on the basis of shard habit, modal mineralogy, and composition of ilmenite, occurs in sedimentary cores from three lakes located to the south of the previously documented plume and necessitates a significant enlargement of the fallout area of that tephra in southwestern British Columbia.These new, more southerly occurrences are probably equivalent to the ~2350 year old Bridge River tephra, although it can be argued from the evidence at hand that the 14C dates and biotite-rich nature support relationship to a slightly earlier Bridge River event.Large differences exist in the 14C age of sediments immediately adjacent to the Bridge River tephra at these three lake sites; maximum ages of 3950 ± 170 years BP (GX-5549) and 3750 ± 210 years BP (I-10041) were obtained at Phair and Fishblue lakes, respectively, whereas the corresponding age at Horseshoe Lake is only 2685 ± 180 years BP (GX-5757). The two older dates are considered to be significantly affected by old carbon contamination for the bedrock locally consists of calcareous sedimentary rocks and the lacustrine sediments are very calcareous. The 14C date from Horseshoe Lake, which occurs in an area of igneous rocks, appears to be only slightly too old relative to the ~2350 year old Bridge River tephra.Well-dated tephra beds, therefore, can be very useful in assessing the magnitude of old carbon errors associated with radiocarbon dates based on limnic sediments. Calcareous gyttja deposits beneath Bridge River tephra within the study area exhibit old carbon errors of the order of 1350–1550 years.

Potassium–Argon Ages of Igneous Rocks from the Area near Hedley, Southern British Columbia

1972 ◽  
Vol 9 (12) ◽  
pp. 1632-1639 ◽  
Author(s):  
J. C. Roddick ◽  
E. Farrar ◽  
E. L. Procyshyn
Keyword(s):  
British Columbia ◽  
Igneous Rocks ◽  
Magmatic Activity ◽  
Radiometric Ages

K–Ar ages are reported for 19 samples collected from the Hedley, Okanagan, and Similkameen Complexes located in the vicinity of Hedley, British Columbia. Although the zoned nature of amphiboles collected from the Hedley Complex makes interpretation of their radiometric ages difficult, it is suggested that the Hedley Complex was intruded at least 165 m.y. ago and was a part of the same magmatic activity that gave rise to both the Okanagan and Similkameen batholithic complexes. These latter complexes yield ages ranging from 141 m.y. to 184 m.y.

scholarly journals Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 867
Author(s):  
Stefanie M. Brueckner ◽  
Gregory Johnson ◽  
Stephanie Wafforn ◽  
Harold Gibson ◽  
Ross Sherlock ◽  
...  
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Isotope Composition ◽  
Massive Sulfide ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Volcanogenic Massive Sulfide ◽  
North West ◽  
Group A ◽  
Group B

The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, x-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

Uranium series disequilibrium in young surficial uranium deposits in southern British Columbia

1984 ◽  
Vol 21 (5) ◽  
pp. 559-566 ◽  
Author(s):  
A. A. Levinson ◽  
C. J. Bland ◽  
J. R. Dean
Keyword(s):  
British Columbia ◽  
Uranium Content ◽  
Igneous Rocks ◽  
Uranium Deposits ◽  
Secular Equilibrium ◽  
Uranium Series ◽  
South Central ◽  
Activity Ratios ◽  
Different Sources

Disequilibrium studies involving the determination of total U and the activity ratios of 234U/238U and 234U/230Th or activities of 230Th, 226Ra, and 210Pb were carried out on samples from three surficial (generally within 5 m of the surface) uranium deposits in south-central British Columbia that give apparent 234U/230Th ages of 1000–20 000 years. As a result of the young ages, the deposits have not yet reached radioactive secular equilibrium and, therefore, yield very little gamma activity.The deposits formed from groundwaters that leached labile uranium from intermediate to felsic igneous rocks. Two accumulation mechanisms concentrate the uranium: evaporation, and adsorption onto organic matter.The uranium content and the activities of the various daughter nuclides are highly variable within and between the various deposits studied. Some of the variations can be explained in terms of the accumulation processes. In the evaporative process the highest value of uranium and daughter nuclides will be found at the surface, whereas in those deposits in which adsorption is the dominant mechanism these nuclides are found in association with buried organic matter. Under these circumstances, accumulations will be influenced by the flow of groundwater from different sources and also depend on whether daughter nuclides remain immobile or are leached after formation.

The influence of mantle plume in the genesis of the Cache Creek oceanic igneous rocks: implications for the geodynamic evolution of the inner accreted terranes of the Canadian Cordillera

2001 ◽  
Vol 38 (4) ◽  
pp. 515-534 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
L C Struik ◽  
D Bosch ◽  
P Brunet
Keyword(s):  
British Columbia ◽  
Rare Earth ◽  
Earth Element ◽  
Oceanic Island ◽  
Igneous Rocks ◽  
Fault System ◽  
Ultramafic Rocks ◽  
Type 3

West of Prince George, British Columbia, the Cache Creek Terrane is composed of mafic lavas interlayered with both mid-Permian pelagic limestones and Upper Triassic siliceous shales and greywackes. Gabbro, basalt, dolerites, and foliated clinopyroxene-rich ultramafic rocks are exposed within the Pinchi Fault system. The mid-Permian lavas show affinities of oceanic island tholeiites. Among the Triassic lavas, three types of rocks have been distinguished. Type 1 is geochemically similar to the mid-Permian volcanic rocks. Type 2 differs from type 1 by higher TiO2 abundances and convex rare earth element patterns. Type 3 has the highest Zr, Nb, and Ta abundances and the greatest light rare earth element enrichment. The mafic rocks within the Pinchi Fault system are similar to N-type mid-ocean-ridge basalt (N-MORB), and the foliated ultramafic rocks are characterized by very low trace element contents, similar to extremely depleted harzburgites. Permian lavas and Triassic type 1 and igneous rocks from the Pinchi Fault system have the highest εNd(i) ratios (+7.4 to +9.6) and those of type 3 alkali have the lowest ratios (+2.0 to +5.3). The εNd(i) values of type 2 are intermediate between those of type 1 (~+7) and type 3 (~+4.9). This suggests that the Triassic rocks generated from a heterogeneous plume source or the mixing between depleted N-MORB and enriched oceanic island basalt sources. If the mafic igneous rocks sampled in central British Columbia are representative of the preserved parts of an oceanic crust, within the Cache Creek Terrane, then that crust was dominated by oceanic plateau components, perhaps due to the difficulty of subducting thick crust.

Paleointensity study of late Miocene igneous rocks from British Columbia, Canada

1970 ◽  
Vol 7 (1) ◽  
pp. 176-181 ◽  
Author(s):  
D. T. A. Symons ◽  
E. J. Schwarz
Keyword(s):  
Magnetic Field ◽  
British Columbia ◽  
North America ◽  
Late Miocene ◽  
Igneous Rocks ◽  
Lava Flows ◽  
Basaltic Lava ◽  
Remanent Magnetism ◽  
South Central ◽  
Demagnetizing Fields

Sixty-nine specimens representing 49 late Miocene (10–15 m.y. ago) basaltic lava flows and 4 associated gabbroic intrusive plugs were studied in an attempt to estimate the paleointensity of the earth's magnetic field in south-central British Columbia. The paleointensity determination was based on the comparison of the decay of natural remanent magnetism intensity with that of an artificial thermoremanent magnetism (H = 0.35 Oe) in progressively higher alternating demagnetizing fields (peak: 800 Oe). Only 22 of the 69 specimens were considered to yield reliable paleointensity determinations which give an estimated average equatorial intensity for the late Miocene earth's field of 0.18 Oe ± 0.11. This result agrees reasonably well with those from contemporaneous rocks from North America, Japan, and Iceland. Several low determinations with consistent, normal, or reversed remanence directions suggest that the intensity of the non-dipole components of the late Miocene earth's field must have been very small in the sampled area.

U–Pb zircon and titanite ages of three Mesozoic igneous rocks south of the Thor–Odin – Pinnacles area, southern Omineca Belt, British Columbia

1991 ◽  
Vol 28 (11) ◽  
pp. 1877-1882 ◽  
Author(s):  
Sharon D. Carr
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Middle Jurassic ◽  
Igneous Rocks ◽  
Intrusive Rocks ◽  
Age Limit ◽  
Okanagan Valley

U–Pb zircon and titanite ages were obtained from three intrusive rocks near the Monashee Highway between the Valhalla complex and the Okanagan Valley in the southern Omineca Belt. Granitoid phases that have been previously grouped together and referred to as the Whatshan batholith have been subdivided on the basis of lithology and U–Pb geochronology into the Middle Jurassic Spruce Grove batholith and the Late Cretaceous Whatshan batholith. A 77 ± 0.5 Ma phase of the Whatshan places a maximum age limit on regional F3 folding in the Pinnacles area.

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