Test of Nature and Extent of Continental Drift as Provided by Study of Proterozoic Dike Swarms of Canadian Shield<xref ref-type="fn" rid="ch60fn1"><sup>1</sup></xref>

Flood basalts, dike swarms and sub-crustal flow

Canadian Journal of Earth Sciences ◽

10.1139/e68-010 ◽

1968 ◽

Vol 5 (1) ◽

pp. 93-96 ◽

Cited By ~ 4

Author(s):

Paul M. Clifford

Keyword(s):

Unsteady Motion ◽

Canadian Shield ◽

Published Data ◽

Flood Basalts ◽

Crustal Movements ◽

Geologic Time ◽

Dike Swarms ◽

Convective Cells

A review of published data on flood basalts and diabase dike swarms suggests that they are related in origin, typically being developed in zones of crustal tension induced by sub-crustal flow. Perhaps, therefore, these basaltic effusions may be used to map convective cells in the mantle for various periods during geologic time. The inferred pattern of sub-crustal movements, particularly for the southern continents, is seen to be complicated, both temporarily and spatially, and is strongly suggestive of unsteady motion. Dikes of the Canadian Shield permit inferences about the site of convective cells back to 2150 million years.

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Tuzo Wilson and the acceptance of pre-Mesozoic continental drift

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2013-0172 ◽

2014 ◽

Vol 51 (3) ◽

pp. 197-207 ◽

Cited By ~ 2

Author(s):

Paul F. Hoffman

Keyword(s):

Continental Drift ◽

Early Experience ◽

Canadian Shield ◽

Sea Floor ◽

Geologic Time ◽

Sea Floor Spreading ◽

Continental Accretion

Tuzo Wilson’s well-known pre-1961 opposition to continental drift stemmed from his early experience as a geologist in the Appalachians and the Canadian Shield, which convinced him that orogenesis did not change drastically over geologic time. Conversely, Taylor (in 1910) and Wegener (in 1912) hypothesized that continental drift began in Cenozoic or Mesozoic time. Between 1949 and 1960, Tuzo Wilson with Adrian Scheidegger developed a quasi-uniformitarian model of progressive continental accretion around fixed Archean nuclei. Tuzo abruptly jettisoned this model in 1961 when, under pressure from paleomagnetic evidence for continental drift and a nascent concept of sea-floor spreading, he finally entertained the possibility of pre-Mesozoic as well as younger continental drift. He immediately found it a superior fit to Appalachian and Shield geology, while his uniformitarian conviction remained intact. Tuzo had blinded himself to the evidence for continental drift so long as he confined it to Taylor or Wegener’s conception. In continental drift operating continuously over geologic time, he found a theory he could eagerly accept.

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The chemical evolution of the Canadian Shield

Canadian Journal of Earth Sciences ◽

10.1139/e68-122 ◽

1968 ◽

Vol 5 (5) ◽

pp. 1247-1252 ◽

Cited By ~ 43

Author(s):

W. F. Fahrig ◽

K. E. Eade

Keyword(s):

Chemical Evolution ◽

Sedimentary Basins ◽

Crystalline Rocks ◽

Canadian Shield ◽

Progressive Change ◽

Chemical Zoning ◽

Crystalline Crust ◽

Secondary Result ◽

Dike Swarms ◽

Proterozoic Age

Archean surface crystalline rocks of the Canadian Shield differ chemically from those of Proterozoic age. The younger rocks are higher in K2O, TiO2, U, and Th and lower in Na2O, Cr, Ni, and possibly MgO and CaO. This may be a secondary result of vertical chemical zoning of the crust as a result of metamorphism accompanied by anatectic melting. The erosion of a zoned crust would result in the enrichment of elements such as K, Na, Si, U, and Th in younger sedimentary basins. The crystalline crust subsequently evolved from the sediments of these basins would be enriched in these elements relative to older rocks exposed as a result of erosion. The secular chemical evolution of the shield may also reflect a progressive, though irregular, shift in the composition of new sial being added to the crust. Evidence for this progressive change is found in the increase in the abundance of potassium of successive dike swarms that were feeders of new sial to the upper part of the crust.

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