New paleomagnetic data for the Triassic Guichon batholith of south-central British Columbia and their bearing on Terrane I tectonics

1983 ◽  
Vol 20 (8) ◽  
pp. 1340-1344 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Vertical Axis ◽  
Pole Position ◽  
Primary Component ◽  
Paleomagnetic Data ◽  
Clockwise Rotation ◽  
North American Cordillera ◽  
Thermal Demagnetization ◽  
South Central

The 198 Ma Guichon batholith outcrops in the southern end of the Intermontane Belt or composite Terrane I of the western North American Cordillera. Thermal demagnetization of specimens from 19 sites at 200, 450, and 560 °C isolates a stable primary component at 560 °C in 13 sites, giving a pole position of 347°W, 52°N (δp = 5°, δm = 9°). These data support earlier results obtained by the author that indicate the batholith has undergone a clockwise rotation about a vertical axis of ~43 ± 7°. They also show that the batholith has undergone northward motion of 13 ± 6°, which supports recent arguments that the terrane underwent 14 ± 2° of northward translation between Late Cretaceous and pre-Miocene time.

Paleomagnetism of the Triassic Guichon Batholith and Rotation in the Interior Plateau, British Columbia

1971 ◽  
Vol 8 (11) ◽  
pp. 1388-1396 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
British Columbia ◽  
Pole Position ◽  
Upper Triassic ◽  
Late Triassic ◽  
Ratio Analysis ◽  
Tectonic Block ◽  
Clockwise Rotation ◽  
The North ◽  
South Central ◽  
Intrusive Rocks

The Guichon Batholith, located near the south end of the Interior Plateau in south–central British Columbia, is composed of unmetamorphosed massive felsic intrusive rocks in several distinct phases (Northcote 1969). Stratigraphic and radiometric evidence indicate that the batholith was emplaced during the Late Triassic (198 ± 8 m.y.) and unroofed by Early Jurassic. Analysis of the remanence of 92 cores (184 specimens) from 19 representative sites led to the isolation of a stable primary remanent magnetism at 15 sites after alternating-field demagnetization. Variance ratio analysis of the remanence directions indicates that the phases cannot be distinguished by the paleomagnetic method. This supports the evidence from contact relationships and K–Ar isotopic dating of biotites that the phases cooled nearly contemporaneously. The pole position determined for the Guichon Batholith (12.9° E, 65.6° N) is discordant with other Upper Triassic pole positions determined for North American formations. The discordance may be explained by a clockwise rotation 40° ± 10° of the batholith and surrounding rocks in the southern end of the Interior Plateau, with most of the Plateau to the north acting as a stable non-rotated tectonic block. Other evidence is cited which is consistent with this hypothesis.

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.

Paleomagnetism of the 1180 Ma Grenvillian Umfraville gabbro, Ontario

1978 ◽  
Vol 15 (6) ◽  
pp. 956-962 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Paleomagnetic Data ◽  
Grenville Province ◽  
Thermal Demagnetization ◽  
Before And After ◽  
Primary Origin

The 1180 ± 20 Ma Umfraville gabbro is a slightly metamorphosed stock in the Grenville Province. It was sampled at 17 sites (183 specimens). After alternating field and thermal demagnetization the gabbro retains the same very stable remanent magnetization of primary origin both before and after screening. The screened AF direction from 10 sites (96 specimens) gives a pole position of 166°E, 11°S (δp = 7°, δm = 10°). This position is ≈ 13° southeast of that originally reported for the gabbro by Hood. This pole position either does not fit or necessitates modifications to the four hypotheses that have been invoked to explain Grenville paleomagnetic data.

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.

Timing of magnetization and vertical-axis rotations of the Cotiella massif (Late Cretaceous, South Central Pyrenees)

2015 ◽  
Vol 425 (1) ◽  
pp. 213-232 ◽  
Author(s):  
Miguel Garcés ◽  
Jesús García-Senz ◽  
Josep Antón Muñoz ◽  
Berta López-Mir ◽  
Elisabet Beamud
Keyword(s):  
Late Cretaceous ◽  
Vertical Axis ◽  
South Central ◽  
Central Pyrenees

The conglomerate of Churn Creek: Late Cretaceous basin evolution along the Insular–Intermontane superterrane boundary, southern British Columbia

2001 ◽  
Vol 38 (1) ◽  
pp. 59-73
Author(s):  
J W Riesterer ◽  
J Brian Mahoney ◽  
Paul Karl Link
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Clastic Rocks ◽  
South Central ◽  
Lower Member ◽  
Volcanic Source ◽  
Braided Stream ◽  
Bridge Group

Upper Cretaceous coarse clastic rocks exposed in the canyon of Churn Creek, south-central British Columbia, record active basin tectonism and coeval volcanism adjacent to the boundary between the Intermontane and Insular superterranes. Mid to late Albian (~104 Ma U–Pb), calc-alkaline andesite and basaltic andesite flows, with minor conglomerate and reworked epiclastic deposits and tuffs correlative with the Spences Bridge Group of the Intermontane superterrane are exposed in the canyon. In depositional contact above the volcanic rocks is the conglomerate of Churn Creek, which contains a thick (>1 km) sequence of complexly intertonguing conglomerate and sandstone that is divided into two members composed of four lithofacies. The lower member was deposited unconformably on the underlying Albian volcanic unit and contains late Albian–Cenomanian chert-pebble (>50% chert) conglomerate and interbedded chert- and volcanic-lithic sandstone. It is interpreted to have been deposited in a braided stream system flowing from southeast to northwest. The source for the chert was most likely the Bridge River terrane, a Mississippian to Jurassic ocean floor assemblage located to the southwest of Churn Creek, south of the Yalakom fault. Gradationally overlying the lower member throughout much of the basin is a mixed chert, plutonic, and volcaniclastic lithofacies of the upper member. Plutonic debris was provided to the mixed and plutonic lithofacies of the upper member by the Little Basin pluton, which was uplifted along the northeast-directed Little Basin thrust fault on the southwest margin of the basin. The upper member also contains a volcanic-rich lithofacies composed of chaotic volcanic conglomerate and local lithic tuff derived from a coeval proximal volcanic source. The conglomerate of Churn Creek records active northeast-vergent compressional tectonism and development of piggyback basins along the boundary between the Insular and Intermontane superterranes during Albian–Santonian time. The conglomerate of Churn Creek has been correlated to the Silverquick – Powell Creek succession of the Methow terrane, based on age, stratigraphic, lithologic, structural, geochemical, and paleomagnetic similarities, and may, therefore, represent an overlap assemblage linking the superterranes in the Late Cretaceous.

Paleomagnetism of the Middle Proterozoic Mount Nelson Formation: evidence for a regional remagnetization event in the Late Precambrian of the Cordillera

1983 ◽  
Vol 20 (4) ◽  
pp. 561-567 ◽  
Author(s):  
W. A. Morris ◽  
M. E. McMechan
Keyword(s):  
British Columbia ◽  
National Park ◽  
Acid Leaching ◽  
Pole Position ◽  
Glacier National Park ◽  
Geological Process ◽  
Thermal Demagnetization ◽  
Fine Grained ◽  
Late Precambrian ◽  
Middle Proterozoic

Chemical and thermal demagnetization of 92 specimens from the Mount Nelson Formation (uppermost Purcell Supergroup) in the Purcell Mountains of southeastern British Columbia yields two distinct directional groups. MN-A, found by thermal and chemical demagnetization, has a mean direction of D = 274°, I = 19° (α95 = 10°, tilt corrected), which corresponds to a pole position at 156 °E, 10 °N, MN-A resides in fine-grained hematite and is similar to other overprint directions reported from middle and upper Belt–Purcell strata in the Glacier National Park – Clark Range area. Genesis of this overprint is related to some regional geological process, most probably the Goat River Orogeny [Formula: see text]. Direction MN-B, which is found after acid leaching of more than 250 h, has a mean direction of D = 331°, I = 47°(α95 = +4°, tilt corrected), corresponding to a pole at 119 °E, 59 °N. The MN-B pole is significantly different from all poles previously reported from the Belt–Purcell Supergroup (ca. 210 °E, 20 °S). As the age of the MN-B pole is unconstrained the significance of this marked discrepancy is at present uncertain.

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