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.

Paleomagnetism of the Triassic Nikolai Greenstone, McCarthy Quadrangle, Alaska

1977 ◽  
Vol 14 (11) ◽  
pp. 2578-2592 ◽  
Author(s):  
J. W. Hillhouse
Keyword(s):  
British Columbia ◽  
High Temperature ◽  
North America ◽  
Vertical Axis ◽  
Upper Triassic ◽  
Present Position ◽  
Stable Component ◽  
South Central ◽  
Early Mesozoic ◽  
Lamellar Texture

Paleomagnetic evidence indicates that the extensive early Mesozoic basalt field near McCarthy, south-central Alaska, originated far south of its present position relative to North America. Results obtained from the Middle and (or) Upper Triassic Nikolai Greenstone suggest that those basalts originated within 15° of the paleoequator. This position is at least 27° (3000 km) south of the Upper Triassic latitude predicted for McCarthy on the basis of paleomagnetic data from continental North America. The Nikolai pole, as determined from 50 flows sampled at 5 sites, is at 2.2° N, 146.1° E (α95 = 4.8°). The polarity of the pole is ambiguous, because the corresponding magnetic direction has a low inclination and a westerly declination. Therefore, the Nikolai may have originated near 15° N latitude or, alternatively, as far south as 15° S latitude. In addition to being displaced northward, the Nikolai block has been rotated roughly 90° about the vertical axis. A measure of the reliability of this pole is provided by favorable results from the following tests: (1) Within one stratigraphic section, normal and reversed directions from consecutive flows are antipolar. (2) Consistent directions were obtained from sites 30 km apart. (3) Application of the fold test indicated the magnetization was acquired before the rocks were folded. (4) The magnetizations of several pilot specimens are thermally stable up to 550 °C. The stable component is probably carried by magnetite with lamellar texture, a primary feature commonly acquired by a basalt at high temperature during initial cooling of the magma. Geologic and paleomagnetic evidence indicates that the Nikolai is allochthonous to Alaska and that, together with associated formations in southern Alaska and British Columbia, it is part of a now disrupted equatorial terrane.

Late Pleistocene stratigraphy of south-central British Columbia

1978 ◽  
Vol 15 (6) ◽  
pp. 971-980 ◽  
Author(s):  
Robert J. Fulton ◽  
Geoffrey W. Smith
Keyword(s):  
British Columbia ◽  
North America ◽  
Great Lakes ◽  
Late Pleistocene ◽  
Pacific Coast ◽  
Coastal Regions ◽  
South Central ◽  
The Pacific ◽  
Valley Area ◽  
Coast Region

The late Pleistocene deposits of south-central British Columbia record two major glacial and two major nonglacial periods of deposition. The oldest recognized Pleistocene deposits, called Westwold Sediments, were deposited during a nonglacial interval more than 60 000 years ago. Little information is available on the climate of this period, but permafrost may have been present at one time during final stages of deposition of Westwold Sediments. The latter part of this nonglacial period is probably correlative with the early Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. However, deposition of the Westwold Sediments may have begun during the Sangamon Interglacial.Okanagan Centre Drift is the name applied to sediments deposited during the glaciation that followed deposition of Westwold Sediments. Okanagan Centre Drift is known to be older than 43 800 years BP and probably is older than 51 000. It is considered to correlate with an early Wisconsin glacial period.Bessette Sediments were deposited during the last major nonglacial period, which in south-central British Columbia persisted from at least 43 800 years BP (possibly more than 51 000) to about 19 000 years BP. This episode corresponds to Olympia Interglaciation of the Pacific Coast region and the mid-Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. During parts of Olympia Interglaciation the climate was probably as warm as the present-day climate in the interior of British Columbia. Information from coastal regions indicates that there may have been periods of cooler and moister climate.Kamloops Lake Drift was deposited during the last major glaciation of south-central British Columbia. Ice occupied lowland areas from approximately 19 000 to 10 000 years BP. This period corresponds approximately to the Fraser Glaciation of the Pacific Coast region and the late Wisconsin Substage of central and eastern parts of North America.

Paleointensity derived from igneous rocks of Kamchatka volcanoes of the Late Pleistocene-Holocene epoch

2020 ◽  
Author(s):  
Iuliia Sleptsova ◽  
Valeriy Maksimochkin
Keyword(s):  
Magnetic Field ◽  
Curie Temperature ◽  
Lava Flow ◽  
Geomagnetic Field ◽  
Single Domain ◽  
Igneous Rocks ◽  
Lava Flows ◽  
Virtual Geomagnetic Pole ◽  
Temperature Oxidation ◽  
Curie Temperature Tc

<p>This work is devoted to paleomagnetic studies of lava samples from three volcanoes of Kamchatka in order to define the age of lava flows and to obtain data of paleosecular variations of the geomagnetic field for the Kamchatka region. We studied 53 samples from 7 sites from lava flows of the Avachinsky, the Gorely and the Tolbachik volcanoes. The study of paleosecular variations recorded in the magnetization of the lava flows of volcanoes makes it possible to create a magnetochronological scale for epochs of the same polarity.</p><p>According to the data of electron microprobe and thermomagnetic analyzes, the magnetic properties of samples from the lava flows of the Avachinsky volcano are mainly determined by titanic magnetite with a Curie temperature Tc = (540-580) °С. The study of magnetic mineral grains using electron and magnetic force microscopy showed the presence of decay structures in grains, indicating the high-temperature oxidation of titanomagnetite. Ferrimagnetic grains of samples from the Gorely and Tolbachik volcanoes are represented by titanomagnetite with a Curie temperature Tc = (200–300) °C. According to the hysteresis characteristics, the magnetic structure of the grains corresponds to a single-domain and pseudo-single-domain state. Thermal and magnetic cleanings showed the predominance of one component in the NRM. The geomagnetic field intensity was determined by the Thellier method in the Coe modification.</p><p>It was found that the paleointensity value H<sub>anc</sub> = 55±3 μT, determined from the NRM of samples of the 2012 eruption from the Tolbachik volcano, differs from the modern magnetic field in the area of this volcano by the IGRF-12 model by only 4% (Н<sub>IGRF</sub> = 53 μT). This indicates the reliability of our methodology for determining paleointensity from the most stable part of the NRM of igneous rocks.</p><p>A comparison of the coordinates of the paleomagnetic pole (N 66º±4º, E 266º±5º) and the virtual dipole magnetic moment of the Earth (VDM = 8.3±0.9*10<sup>22</sup> A*m<sup>2</sup>) with data on variations of the geomagnetic field over the past 10,000 years [Burlatskaya, 2007; McElhinny, 1982] allows us to conclude that the investigated lava flow belongs to the historical eruptions of 1827. The coordinates of the virtual geomagnetic pole (N 83º±3º, E 254º±21º) and the value of VDM = 8.0±0.3*10<sup>22</sup> A*m<sup>2</sup> determined from the samples belonging to the second lava flow of the Avachinsky volcano indicate that rocks are formed in the result of the eruption, which occurred 5-5.5 thousand years ago.</p><p>It was revealed that the magnitude (H<sub>anc</sub> =65±5μT) and the direction of paleointensity determined by the NRM of the samples from Gorely volcano significantly differ from the characteristics of the modern magnetic field. The assumption is made that the studied samples belong to the outpouring of lava, which occurred about 2.7 thousand years ago, during the "Sterno-Etrussia" geomagnetic excursion.</p><p> </p><p>This work was supported by the Russian Foundation for Basic Research, project 20-05-00573.</p>

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.

Paleomagnetism of four late Miocene gabbroic plugs in south-central British Columbia

1969 ◽  
Vol 6 (4) ◽  
pp. 653-662 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
British Columbia ◽  
Statistical Analysis ◽  
Late Miocene ◽  
Pole Position ◽  
Olivine Gabbro ◽  
Geologic Time ◽  
South Central ◽  
Paleomagnetic Study ◽  
Geomagnetic Pole ◽  
Short Span

A paleomagnetic study was made of 101 cores from 20 sites representing about equally 4 small olivine gabbro plugs which intrude tectonically undisturbed olivine-rich plateau basalts of late Miocene age in the southern Cariboo region of south-central British Columbia. After alternating-field cleaning, statistical analysis of the stable remanence indicates that the site mean directions are significantly distinct within each plug so that even such small intrusive bodies (250–800 ft (78–248 m) in diameter) must be thoroughly sampled to derive a representative mean remanence direction. Both Tin Cup Mountain and Lone Butte plugs have normally polarized remanence, whereas Mount Begbie and Forestry Hill plugs have reversely polarized remanence. Statistical analysis indicates that these plugs were emplaced over a short span of geologic time of possibly less than 1 × 106 years and that at least three polarity intervals are represented. The geomagnetic pole position computed from the normalized site mean directions is 146.7 °W, 84.9 °N (δp = 4.8°, δm = 5.5°). This pole position is almost coincident with the pole position determined for the surrounding plateau basalts, and it is consistent with those obtained from other Miocene formations. These results support the hypothesis that the plugs represent the original volcanic vents from which the plateau basalts were extruded.

Chronostratigraphy of glaciations and permafrost episodes in the Cordillera of western North America

1994 ◽  
Vol 18 (3) ◽  
pp. 366-395 ◽  
Author(s):  
Stuart A. Harris
Keyword(s):  
North America ◽  
Climatic Change ◽  
Sierra Nevada ◽  
Late Miocene ◽  
Complete Sequence ◽  
Lava Flows ◽  
Radiometric Dating ◽  
Western North America ◽  
Quaternary Period ◽  
Cold Events

Glaciations in the Cordillera of western North America began during the Late Miocene in the St Elias Range and coastal ranges near Anchorage, Alaska. Radiometric dating of the tephra and lava flows intercalated in the succession of older tills, loesses and outwash deposits permits the reconstruction of the probable early glacial sequence along the Cordillera. No one site shows the complete sequence, but the available data suggest synchroneity of the major glacial events throughout the region. The first evidence for cold conditions at low elevations at midlatitudes is from 3.5 Ma BP. By 2.8 Ma, alpine glaciations may have occurred in the Sierra Nevada and ice wedges had formed in bedrock near Fairbanks, Alaska. Three more major glaciations complete with contemporary periglacial and permafrost landforms had occurred by 1.65 Ma, while at least six more major cold events can be recognized during the Quaternary period. Once again, expansion of permafrost conditions occurred during each event and forms an integral part of the evidence for climatic change.

Geochemistry of the Mamainse Point volcanics, Ontario, and implications for the Keweenawan paleomagnetic record

1990 ◽  
Vol 27 (9) ◽  
pp. 1194-1199 ◽  
Author(s):  
Kenneth W. Klewin ◽  
Jonathan H. Berg
Keyword(s):  
North America ◽  
Lake Superior ◽  
Lava Flows ◽  
Geochemical Data ◽  
Basaltic Lava ◽  
Trace Element Data ◽  
Eastern Shore ◽  
Midcontinent Rift ◽  
History Of ◽  
Entire Sequence

The Keweenawan (1100 Ma) Mamainse Point volcanics, located along the eastern shore of Lake Superior in Ontario, formed in the Midcontinent Rift of North America. They are a 5250 m thick sequence of over 350 predominantly basaltic lava flows. The Mamainse Point section is the most continuous Keweenawan volcanic sequence and spans nearly the entire igneous history of the rift. The lower part of the section consists of high-MgO picrites and basalts, but the upper part of the section is composed of olivine tholeiites intercalated with numerous conglomerate layers. Major- and trace-element data reveal that the section consists of numerous stratigraphically constrained, geochemically distinct groups of lava flows. The comprehensive geochemical data on the entire sequence indicate that the section has no repetition due to faulting, as has been suggested by other workers on the basis of paleomagnetic studies. Evidently, the three paleomagnetic reversals previously found in the Mamainse Point section are real, and therefore there were multiple paleomagnetic reversals during Keweenawan time.

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