Showing papers on "Archean published in 1969"

Correlation of radiometric ages of Nipissing diabase and Huronian metasediments with Proterozoic orogenic events in Ontario

Abstract: Field evidence shows that the Huronian section of metasediments in Ontario is younger than the Archean and older than the Nipissing diabase. Previous radiometric investigations show the age of the latest Archean granitic intrusions to be about 2500 m.y. and the Nipissing diabase to be 2155 ± 80 m.y. In this paper we present whole-rock Rb–Sr data which (1) confirm the age of the diabase in a single sill at Gowganda (2162 ± 27 m.y.), and (2) show the age of the Gowganda Formation (which the sill intruded) to be 2288 ± 87 m.y. In marked contrast metasediments and metavolcanics in the Huronian section southwest of Sudbury show younger ages ranging between 1800 and 2200 m.y. This is interpreted in terms of known orogenic disturbance of the Huronian rocks south and west of Sudbury and its absence in the Cobalt–Gowganda area to the northeast. Both minerals and whole rocks have responded by showing low and discordant ages in the disturbed area. The higher and accordant ages in the undisturbed environment agree wi...

The geology and geochronology of the Makkovik Bay area, Labrador

Abstract: The sedimentary and volcanic formations of the Aillik series in the Makkovik Bay area of the Labrador coast are about 25 000 ft (~7620 m) in thickness. They have been folded into a series of northerly-trending folds and are intruded by gabbro, diorite, syenite, and abundant granite. Potassium–argon age determinations range from 1730 to 1830 million years for two gneisses, and from 1500 to 1600 million years for the metamorphosed sedimentary and volcanic rocks and intrusive granite-gneiss and granite. The structural features of the area indicate a single cycle of orogenic deformation for the sedimentary and volcanic rocks, in which the emplacement of synkinematic granite gneiss as domes and other bodies played an important role. One of the gneisses is considered a part of the migmatized Archean basement on which the Aillik series was laid down, and was subsequently involved in the Hudsonian orogenic cycle about 1600 million years ago. The area lies to the northwest of the Grenville Front, and has been intr...

Correlation of Proterozoic strata in the northwestern Canadian Shield

Abstract: The Epworth and Goulburn Groups comprise the lowermost sequences of the Proterozoic strata exposed near the northern margins of the Slave (structural) Province of the Canadian Shield. Each group is at least 4600 m thick and underlies a distinct and separate area of not less than 13 000 sq. km.The many features common to the two groups indicate that they are correlative: (1) each lies unconformably on an Archean basement; (2) each is overlain unconformably and successively by kaolinitic sandstone, by dolomite, and by Coppermine River Group basalt and sediments; (3) each has argillite and quartzite near the base, interbedded argillite and limestone in the upper parts, and sandstone at the top; (4) each exhibits features characteristic of deposition in shallow water; (5) both occupy similar structural basins and show the same style of folding and faulting; (6) both are traversed by gabbro dikes and sills of similar age.Field relationships among the Proterozoic strata and the relation these strata bear to int...

Polyphase Deformation in the Archean Basement Complex, Beartooth Mountains, Montana and Wyoming

Abstract: Minor tectonic structures and related metamorphic mineral growths in the Archean crystalline rocks (circa 2.7 b.y.) of the Beartooth Mountains indicate the effects of at least four successive phases of deformation. The most intense metamorphic recrystallization was associated with the formation of intrafolial passive flow folds in the earliest recognized phase. Flexural-flow folds, which are probably parasitic on the major structures of the region, and an associated secondary foliation, were developed subsequently. At least two successive sets of flexural folds, with related axial-planar structures, were formed in later deformational phases. The common granitic rocks of the region, the quartzo-feldspathic gneisses, are of early development. Cross-cutting pegmatitic veins were emplaced after the formation of the structures of the second phase while xenolith-bearing granite is of late formation. The tectonic, metamorphic, and igneous events recognized are considered to have been developed during a major erogenic episode which is named the Beartooth orogeny.

Diamonds and lithospheric mantle properties in the Neo - proterozoic igneous province of southern West Greenland

Abstract: The search for diamonds in Greenland has resulted in the discovery of many new dykes of kimberlite and ultramafic lamprophyre and, most importantly, in the acquisition of a wealth of chemical data on rocks and minerals representing mantle material entrained by the dyke magmas. The discovery of a diamondiferous sheet at Garnet Lake in southern West Greenland stimulated the research (Hutchison 2005). Over the past five to ten years, the Geological Survey of Denmark and Greenland together with the Bureau of Minerals and Petroleum in Greenland and international research groups have acquired, processed and interpreted data with the objective of identifying diamond-favourable regimes within the lithospheric mantle below the Archaean craton in West Greenland. Here we present mineral data from drift samples that allow us to identify where mantle conditions in terms of lithology and depth may be favourable for the occurrence of diamonds.

Configuration et nature du mode tectonique en bordure ouest de la partie centrale de la fosse du Labrador

Abstract: This paper deals with the use of geophysical methods to look for magnetic taconites in central part of the Labrador Trough and to study the tectonic style of the western margin of the Labrador Trough. The tectonic model that fits the best the geophysical informations obtained is a dkollement which took place between the Proterozoic sediments and the stable crystalline Archean complex.

Genhse des roches ii cordikrite-anthophyllite des gisements cupro-zincifhres de la r6gion de Rouyn-Noranda, QuCbec, Canada

Abstract: Cordierite-anthophyllite-bearing rocks are found in alteration pipes below some of the copper-zinc deposits of the Rouyn-Noranda area that occur in Archean volcanics. The cordierite and anthophyllite have been developed around the contact of the Dufault granodiorite, by isochemical metamorphism of ripidolite of ancient alteration pipes of volcanic origin.