Cretaceous Coast Belt paleomagnetic data from the Spetch Creek pluton, British Columbia: evidence for the "tilt and moderate displacement" model

1993 ◽  
Vol 30 (5) ◽  
pp. 1037-1048 ◽  
Author(s):  
T. A. Vandall
Keyword(s):  
British Columbia ◽  
North American Plate ◽  
East Side ◽  
Clockwise Rotation ◽  
Normal Polarity ◽  
The Difference ◽  
Differential Uplift ◽  
Displacement Model ◽  
Local Block ◽  
Tilt Model

Well-grouped stable magnetizations have been isolated at 14 of 20 sites sampled from the Spetch Creek pluton. The single-polarity primary magnetization directed at D = 026.2°, I = 73.5° (α95 = 4.4°, paleolatitude 59 ± 7°N, paleopole 73°N, 078°W, A95 = 7°) was acquired around 88 Ma during the Cretaceous normal polarity superchron (118–84 Ma). This direction is discordant from the expected mid-Cretaceous direction (D = 332.5°, I = 75.1°) for North America. The difference could be caused by one of two end member models: the all-tilt model requires a 15° east-side-up tilt about a horizontal axis striking 353°, and the displacement–rotation model requires 330 ± 770 km of northward displacement combined with 54 ± 14° of clockwise rotation. Regardless, this result provides a negative test of the Baja British Columbia model, which requires ~ 2400 km of northward displacement.A review of previously observed mid-Cretaceous magnetizations from the Coast Belt, which are also discordant, indicates that they exhibit common characteristics, although their discordance is not uniform. Assuming that present horizontal approximates paleohorizontal, post-mid-Cretaceous latitudinal displacements inferred from individual results vary between 330 and 3500 km northwards. Relative rotations about vertical axes vary between 17 and 57° clockwise. Such variation cannot be accounted for by the displacement and rotation of a superterrane as a whole. Recent studies emphasize that many of the intrusions have probably been locally tilted. Consistent with known geology, these discordant poles are best explained by the "tilt and moderate displacement" model. This model invokes moderate (500–1000 km) post-mid-Cretaceous northward displacement of the amalgamated Insular, Coast, and Intermontane terranes west of the major dextral Canadian Cordilleran fault systems, combined with variable local block tilting east- and northeast-side-up. Northward displacement was driven by Kula and (or) Farallon – North American plate interactions from 90 to 56 Ma. Tilting is most likely due to a combination of northeast–southwest compression, differential uplift, and extension.

scholarly journals Annual Spread Rate of Tomentosus Root Disease

Plant Disease ◽  
1997 ◽  
Vol 81 (9) ◽  
pp. 1053-1056 ◽  
Author(s):  
R. S. Hunt ◽  
F. G. Peet
Keyword(s):  
British Columbia ◽  
Tree Ring ◽  
Root Disease ◽  
Uninfected Control ◽  
Radial Increment ◽  
Spread Rate ◽  
Annual Increment ◽  
Temporal Differences ◽  
The Difference ◽  
A New Technique

The spread rate of tomentosus root disease, caused by Inonotus tomentosus, was investigated by a new technique employing temporal differences in the initiation of the reduced annual radial increment between pairs of diseased trees. Pairs of infected trees (stumps) located on the periphery of disease centers were selected in each of six widely separated spruce (Picea spp.) stands in British Columbia. Distances between 12 pairs of stumps were measured, and disks were collected from each stump. Similarly, disks from four additional pairs were collected from trees in a younger stand. Uninfected control disks were collected for all sites. Tree-ring measurements were determined for all disk samples and the year in which the reduction of the annual increment attributable to I. tomentosus began was determined for infected trees. The difference between initiation years for pairs of infected trees divided into the distance between them produced an average annual spread rate of 20 cm/yr. This rate will be used in developing a model for the disease.

History of the Larch Sawfly, with Notes on Origin and Biology,

1955 ◽  
Vol 87 (3) ◽  
pp. 103-111 ◽  
Author(s):  
H. C. Coppel ◽  
K. Leius
Keyword(s):  
British Columbia ◽  
North America ◽  
Native Species ◽  
Insect Pest ◽  
Forest Insect ◽  
Larch Sawfly ◽  
History Of ◽  
Biological Characters ◽  
The Difference ◽  
Forest Biology

The larch sawfly, Pristiphora erichronii (Htg.), is currently considered a major forest insect pest in Canada. At the present time within Canada, the sawfly reacts to parasitism by Mesoleius tenthredinis Morley in two ways. In Manitoba and Saslratchewan the sawfly encapsulates approximately 100 per cent of the parasite eggs deposited, whereas in British Columbia encapsulation rarely exceeds four per cent (Muldrew, 1953). The reasons for the difference in degree of encapsulation are apparently unknown; however, since the origin of the sawfly itself is obscure, the possibility exists that a native species, an introduced species, Or a combination of both may he present, or that geographical or ecological units may have arisen. Studies now under way by officers of the Forest Biology and Entomology divisions are attacking the problem of identity and origin following the pattern established for the European spruce sawfly, Diprion hercyniae (Htg.). In this instance, as with the larch sawfly, parasites were introduced on the assumption that the pest had been introduced from Europe. Critical investigations by Reeks (1941) and Balch, Reeks, and Smith (1941), involving morphological, cytological, and other biological characters, showed that the species occurring in North America was one of two species common in Europe, and previously referred to there as Gilpinia polytoma (Htg.). Balch et al. (1941) showed that D. hercyniae had been introduced into North America.

Diversity and abundance of arthropod by-catch in semiochemical-baited traps targeting apple clearwing moth (Lepidoptera: Sesiidae) in organic and conventional apple orchards in British Columbia, Canada

2014 ◽  
Vol 147 (2) ◽  
pp. 227-243 ◽  
Author(s):  
V. Marius Aurelian ◽  
Maya L. Evenden ◽  
Gary J.R. Judd
Keyword(s):  
British Columbia ◽  
Grape Juice ◽  
Tree Density ◽  
Mass Trapping ◽  
Apple Orchards ◽  
Apple Industry ◽  
Baited Traps ◽  
Clearwing Moth ◽  
The Difference ◽  
By Catch

AbstractApple clearwing moth (ACM),Synanthedon myopaeformis(Borkhausen) (Lepidoptera: Sesiidae), is an invasive species and destructive pest of commercial apple trees in British Columbia (BC), Canada. Mass trapping with Concord grape juice and sex pheromone is being developed as an organic pest management tactic. We quantified the diversity and abundance of arthropod by-catch in these traps during the 2009 flight (13 June–31 July) of ACM. Paired traps were deployed in organic and conventionally managed apple orchards planted using different tree densities representing the extremes of the current BC apple industry. Using seasonal by-catch and community-level statistical analyses we determined that family communities of arthropods caught in juice-baited and pheromone-baited traps differed significantly. Yellow juice-baited traps caught a greater variety of arthropod families in greater abundance than pheromone-baited yellow Unitraps®. We show that for each trap type, family communities caught in organic versus conventional orchards were significantly different. Organic orchard management affected abundance of some beneficial taxa, but the sign of the difference depended on the taxon examined (e.g., ladybeetles increased versus lacewings declined). Tree density had no effect on by-catch. Managing ACM by mass trapping may be detrimental to ecosystem services because many nontarget beneficial species are caught. A balanced risk-to-benefit approach should be taken before this technology is widely implemented against ACM.

Visions of the tenement: Jews, photography, and modernity on the lower east side

Images ◽  
2010 ◽  
Vol 4 (1) ◽  
pp. 57-81
Author(s):  
Sara Blair
Keyword(s):  
Social Experience ◽  
Specific Site ◽  
Lower East Side ◽  
East Side ◽  
The Difference

AbstractScholars have recently begun to focus on the problem of explaining a signal phenomenon: the preponderance of Jews (the so-called “people of the book”) in the development of modern photography. Against identitarian readings, this essay stresses the embeddedness of photography’s developing interests in a specific site in which both Jewishness and modernity were being made and remade: the variably iconic Lower East Side. Long imagined as a world apart, that space embodied the most profound and urgent paradoxes of historicity; it became a proving-ground for the powers of the camera to document new urgencies of social experience, and the experience of historicity itself. In particular, the built landscape and the iconography of its distinctive form, the tenements, became a resource for photographers of various affiliations for new stylistics and registers of response. Focusing on the difference the Lower East made to photographic practice, this essay aims to bring into view the importance of that site to the emergence of postwar photography, and to account more richly for the complex relations between Jewishness and visual practices.

scholarly journals ESTIMATING EULER POLE PARAMETERS FOR EASTERN CANADA USING GPS VELOCITIES

2015 ◽  
Vol 41 (4) ◽  
pp. 162-173
Author(s):  
Mohammad Ali Goudarzi ◽  
Marc Cocard ◽  
Rock Santerre
Keyword(s):  
North American Plate ◽  
Eastern Canada ◽  
Intraplate Earthquakes ◽  
Seismic Region ◽  
Ottawa River ◽  
The North ◽  
Euler Pole ◽  
Saint Lawrence River ◽  
The Difference ◽  
Gps Velocities

Eastern Canada is characterized by many intraplate earthquakes mostly concentrated along the Saint Lawrence River and Ottawa River valleys. After the rigid plate rotation of North America, the glacial isostatic adjustment (GIA) is by far the largest source of geophysical signal in eastern Canada. We estimate a set of Euler pole parameters for this area using a velocity field of 19 continuously operating GPS stations out of 112, and show that they are different from the overall rotation of the North American plate. This difference potentially reflects local stresses in this seismic region, and the difference in intraplate velocities between the two flanks of the Saint Lawrence River valley accumulate stress along the river.

Geochronometry of the Eagle Plutonic Complex and the Coquihalla area, southwestern British Columbia

1992 ◽  
Vol 29 (4) ◽  
pp. 812-829 ◽  
Author(s):  
C. J. Greig ◽  
R. L. Armstrong ◽  
J. E. Harakal ◽  
D. Runkle ◽  
P. van der Heyden
Keyword(s):  
British Columbia ◽  
Late Jurassic ◽  
Middle Eocene ◽  
Timing Constraints ◽  
Early Eocene ◽  
East Side ◽  
Eastern Margin ◽  
Plutonic Complex ◽  
Southwestern Margin

New U–Pb, K–Ar, and Rb–Sr dates from the Eagle Plutonic Complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the Intermontane Belt. U–Pb zircon minimum dates for Eagle tonalite and gneiss (148 ± 6, 156 ± 4, and 157 ± 4 Ma) document previously unrecognized Middle to Late Jurassic magmatism and syn-intrusive deformation along the eastern margin of the Eagle Plutonic Complex and the southwestern margin of the Intermontane terrane. Widespread mid-Cretaceous (Albian–Cenomanian) resetting of K–Ar and Rb–Sr isotopic systematics in Jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the Fallslake Plutonic Suite (110.5 ± 2 Ma, U–Pb) which crosscut Jurassic plutons and structures but were themselves ductilely deformed along the Pasayten fault during sinistral, east-side-up, reverse displacement. K–Ar and Rb–Sr cooling dates for the Fallslake Suite of ca. 100 Ma, including dates from mylonites along the Pasayten fault, suggest that uplift, cooling, and unroofing of the Eagle Plutonic Complex occurred in mid-Cretaceous time along the Pasayten fault. Regional geologic evidence suggests that this thermal and unroofing event affected much of the southwest margin of the Intermontane Belt. Initial 87Sr/86Sr ratios and U–Pb geochronometry for the Fallslake Plutonic Suite suggest that it was derived, in part, from preexisting and relatively nonradiogenic Paleozoic to Mesozoic crust. K–Ar dating of several stocks demonstrates widespread Early Eocene plutonism in the Coquihalla area, and dating of the Needle Peak pluton indicates plutonism continued into Middle Eocene time.

Stratigraphy and paleomagnetism of Brunhes and Matuyama (>790 ka) Quaternary deposits at Merritt, British Columbia

1992 ◽  
Vol 29 (1) ◽  
pp. 76-92 ◽  
Author(s):  
R. J. Fulton ◽  
E. Irving ◽  
P. M. Wheadon
Keyword(s):  
British Columbia ◽  
Quaternary Deposits ◽  
Lacustrine Deposits ◽  
South Central ◽  
Last Glaciation ◽  
Normal Polarity ◽  
Reversed Polarity

A succession of Quaternary deposits in the Merritt basin of south-central British Columbia contains evidence for four glaciations and two interglaciations. Paleomagnetic signatures in these sediments are of three types: normal polarity, proposed to have been acquired during the Brunhes Normal Polarity Chron; reversed polarity, proposed to have been acquired during the Matuyama Reversed Polarity Chron; and reversed polarity (Matuyama age) all but obscured by a normally magnetized overprint (Brunhes age).Reversely magnetized deposits at the base of the succession include glacial lacustrine deposits, interpreted as representing two different glaciations, and a paleosol and a succession of nonglacial sediments, which are evidence of two interglaciations. As the reversed polarity of these deposits is proposed to have been acquired during the Matuyama Reversed Polarity Chron, they are older than 790 ka.Normally magnetized deposits, which make up the rest of the succession, contain evidence for only two glaciations, but traces of other glaciations may have been removed during the erosion interval encompassed by a major unconformity that underlies deposits of the last glaciation. All are referred to the Brunhes Normal Polarity Zone. In addition to these glacial and interglacial deposits, a series of normally magnetized Quaternary basalt flows forms a bench 90 m above the floor of the basin. These basalts were extruded after 790 ka but before the penultimate glaciation.

scholarly journals Last Interglacial Muir Point Formation, Vancouver Island, British Columbia

2007 ◽  
Vol 44 (3) ◽  
pp. 337-340 ◽  
Author(s):  
Stephen R. Hicock
Keyword(s):  
British Columbia ◽  
Alluvial Fan ◽  
Last Interglacial ◽  
Modern Pollen ◽  
Pollen Rain ◽  
Stratigraphic Position ◽  
Normal Polarity ◽  
Tidal Stream ◽  
Exposed Part ◽  
Study Sites

ABSTRACT The Muir Point Formation probably represents the last interglacial and climatic maximum of the Late Pleistocene in southwest British Columbia. It comprises estuarine, floodplain, fluvial, alluvial fan, and debris flow lithofacies. The lower exposed part of the formation is normally magnetized and probably formed during the Brunhes Normal Polarity Chron (<790 ka BP). On the basis of similar polarity, palynology, lithologies, and stratigraphic position, the Muir Point Formation is correlated with the Whidbey Formation of northwest Washington State. It probably also correlates with the Highbury Formation under the Fraser Lowland of mainland British Columbia.These formations may be remnants of shallow marine or subaerial sediment shelves which once rimmed ancestral Strait of Georgia and Puget basins over 100 ka, but were mostly removed by later glaciations. During this time sea level may have been 10 m higher than today. The middle floodplain unit contains five pollen zones whose differences can be explained mainly by shifts in a meandering tidal stream. Throughout most of this record Douglas fir pollen is more abundant than in modern pollen rain around the study sites which indicates that paleoclimate was at least as warm and dry as present.

Paleomagnetic and 40Ar/39Ar geochronologic data bearing on the structural evolution of the Silver Peak extensional complex, west-central Nevada

2002 ◽  
Vol 114 (9) ◽  
pp. 1108-1130 ◽  
Author(s):  
Michael S. Petronis ◽  
John W. Geissman ◽  
John S. Oldow ◽  
William C. McIntosh
Keyword(s):  
Sedimentary Rocks ◽  
Vertical Axis ◽  
Lower Plate ◽  
Transfer System ◽  
Clockwise Rotation ◽  
Rapid Cooling ◽  
Walker Lane ◽  
Normal Polarity ◽  
Axis Rotation

Abstract The Silver Peak extensional complex, located in the Silver Peak Range of west- central Nevada, is a displacement-transfer system linking the Furnace Creek–Fish Lake Valley fault system and transcurrent faults of the central Walker Lane. Late Neogene, northwest-directed motion of an upper plate, composed of lower Paleozoic sedimentary rocks and late Tertiary volcanic and volcaniclastic strata, exhumed a lower-plate assemblage of metamorphic tectonites with Proterozoic and Mesozoic protoliths. Paleomagnetic investigation of Miocene–Pliocene pyroclastic and sedimentary rocks of the upper plate and Miocene mafic dikes in the lower plate reveals modest horizontal- axis tilting (northwest-side-up) and vertical-axis rotation (clockwise) within the extensional complex. Eight to ten samples from each of 123 sites were demagnetized; 95 sites yielded interpretable results. Dual- polarity results from one population of mafic dikes in the lower-plate assemblage indicate moderate, northwest-side-up tilting (declination D = 329°, inclination I = 37°, α95 = 4.3°, number N = 30 sites; in situ) (α95 = the confidence limit for the calculated mean direction expressed as an angular radius from the calculated mean direction). Some dikes yield exclusively normal-polarity results that are interpreted to indicate modest clockwise vertical-axis rotation (D = 021°, I = 57°, α95 = 4.3°, N = 19 sites; in situ) concurrent with uplift of the lower-plate rocks, and nine sites yield magnetization directions that are north-directed with positive inclinations of moderate steepness, similar to an expected Miocene field. Late Miocene pyroclastic rocks in the upper plate yield normal-polarity magnetizations suggestive of moderate, clockwise, vertical-axis rotation (D = 032°, I = 53°, α95 = 8.8°, N = 10 sites). The apparent clockwise rotation is unlikely to result from incomplete sampling of the geomagnetic field, because the overall dispersion of the VGP (virtual geomagnetic pole) positions is high for the latitude of the site location. Middle Miocene sedimentary rocks probably were remagnetized shortly after deposition. Of eight 40Ar/39Ar determinations from mafic dikes in the lower plate, five groundmass concentrates yield saddle-shaped age spectra, and one separate provided a plateau date of low confidence. Isochron analysis reveals that all six groundmass concentrates contain excess Ar. If rapid cooling and Ar retention below ∼250 °C are assumed, the preferred age estimate for mafic intrusions is provided by isochron dates and suggests emplacement between 12 and 10.5 Ma. The 40Ar/39Ar age-spectrum data are consistent with existing fission-track cooling and K-Ar isotopic age information from lower-plate granitic rocks and indicate rapid cooling of the lower-plate assemblage from well above 300 °C to 100 °C between 13 and 5 Ma. Rapid cooling may explain the overall distribution of paleomagnetic results from lower-plate intrusions such that the earliest acquired magnetizations reflect both northwest-side-up tilt and clockwise rotation and the younger magnetizations reflect northwest-side-up tilt. Overall, the paleomagnetic data from the Silver Peak extensional complex are interpreted to suggest that vertical-axis rotation of crustal-scale blocks, associated with displacement transfer in the central Walker Lane, may play an integral part in accommodating strain within a continental displacement-transfer system.

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