摘要:

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 intrusive granite, dikes, and sills of known radiogenic age, define the Epworth and Goulburn Groups as of Aphebian age.

ISSN:0008-4077    

DOI:10.1139/e69-001

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Metamorphosed and metasomatized basalts, and unmetamorphosed equivalents, were recovered from the steep slopes of Bald Mountain, a north–south elongated seamount lying 60 km west of the Median Rift Valley at 45° N. Block faulting and uplift of the seamount, together with the removal by submarine erosion of extrusive rocks capping the seamount, have resulted in the exposure of the more deep-seated metamorphosed horizons along the fault scarps.The block-faulted nature of Bald Mountain, indicative of brittle fracturing of the upper crustal layers of the Mid-Atlantic Ridge, may be a result of the low ocean floor spreading rates implied from age determinations and magnetic anomaly patterns at 45 °N.

ISSN:0008-4077    

DOI:10.1139/e69-002

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The Pharusian belt of west-central Ahaggar belongs to the 'basement complex' underlying the Paleozoic and later sediments of the Sahara. This paper reports and discusses the Rb–Sr ages obtained on total rocks and minerals from two granitic stocks of the belt: the Tioueiine and Iskel intrusions.Both plutons gave good whole-rock isochrons, which show that the systems were closed 560 ± 40 m.y. ago with respect to Rb and Sr. This is, most probably, the age of crystallization. Three of the four values obtained on biotites are somewhat lower and scattered in the range 502–526 m.y. The discrepancies are probably due to deuteric reactions or incipient weathering. They can be ascribed neither to the loss of87Sr during the cooling down of the granites, nor to rejuvenation by some later thermal or tectonic event.These studies confirm previous results of random sampling in Ahaggar and prove that large-scale igneous activity took place during the Early Cambrian Epoch. Knowing from field data that the Tioueiine and Iskel are late orogenic granites, it must be concluded that the Pharusian orogeny came to an end at that time.Such a result contradicts early assumptions, made in the field, of a middle Precambrian age for the Pharusian orogeny. It gives further weight to modern ideas concerning the 700–500 m.y. events in Africa, and it leaves time for erosion to create the Saharian platform before the deposition of the first Paleozoic sandstones.

ISSN:0008-4077    

DOI:10.1139/e69-003

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Mistastin Lake, Labrador, latitude 55°53′ N, longitude 63°18′ W, is a roughly circular lake with a large central island lying in a marked depression. A meteorite impact origin is indicated by shock metamorphism features and fracturing of anorthosite and adamellite on the central island and of inclusions in flat-lying igneous rocks on the western shore. The crater had an original diameter of about 20 km and an age, by whole-rock K–Ar determination, of 202 ± 25 m.y.

ISSN:0008-4077    

DOI:10.1139/e69-004

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Excess AlCl3was reacted with Mg(OH)2and Ca(OH)2in suspensions of Wyoming bentonite and the nature of the reaction products formed and their effect on the cation-exchange capacity (CEC) of the clay was determined. Reaction of Mg(OH)2and AlCl3with the clay produced marked decreases of the CEC in the bentonite, whereas much smaller decreases were observed in the Ca–Al–clay preparations. The decreases in the CEC were attributed to the formation of mixed Mg–Al and Ca–Al hydroxide clay complexes. The greater stability of the mixed Mg–Al hydroxide complexes with the clay appeared to account for the marked reduction of CEC in these systems.

ISSN:0008-4077    

DOI:10.1139/e69-005

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

New petrographic and chemical data for pseudoleucite from Spotted Fawn Creek and two new nearby localities in central Yukon Territory are presented and discussed in the light of recent experimental evidence on the origin of pseudoleucite. The petrologic, chemical, and experimental data suggest that natural pseudoleucite results from subsolidus breakdown of leucite under water pressure and that the space provided by this breakdown results in influx of the fluid phase that accomplishes partial removal of potash, enrichment in soda, and addition of water.

ISSN:0008-4077    

DOI:10.1139/e69-006

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

The numerous saline estuaries situated throughout Prince Edward Island permit high tides to carry salt water a long way inland and to penetrate the bedrock aquifer. Very little groundwater consumption occurs around the banks of the Eliot River estuary, yet salt water has moved into the bedrock and created a large zone of diffusion. This salty water extends as far as 1200 ft inland and has penetrated to a depth of 185 ft. Beneath this salty water is fresh groundwater, which extends down to about 600 ft where it is underlain by salty water.The salty water in the upper 185 ft of the aquifer is not separated from the fresh groundwater by a confining stratum, but is kept in this position by the higher head of the fresh groundwater. This head maintains a dynamic equilibrium with the heavier salty water. The effect of density in maintaining the position of a fresh and salt water front is not as important as has been previously thought.

ISSN:0008-4077    

DOI:10.1139/e69-007

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

A new technique for analyzing natural data is used on chemical data from the Dundonald sill. It is shown thereby that, with certain exceptions, the conclusions reached by Naldrett and Mason (1968) regarding the differentiation of the sill could have been expressed with greater certainty. The natural chemical data may be used as an independant check on rival hypothetical differentiation processes. The use of conventional graphical techniques has resulted in critical information remaining unused in tables of chemical analyses.

ISSN:0008-4077    

DOI:10.1139/e69-008

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

Deep seismic sounding of the earth's crust has been carried out between latitudes 49°30′ N and 51°30′ N, from longitude 93 °W to longitude 96 °W, by means of a refraction survey, using energy from underwater explosions. A two-layer crust was found, with velocities uniform both laterally and vertically within the layers. Velocities found were:Pg = 6.05 ± 0.05 km/s;Sg = 3.46 ± 0.05 km/s;P* = 6.85 ± 0.05 km/s;S* = 4.00 ± 0.05 km/s;Pn = 7.92 km/s;Sn = 4.60 ± 0.08 km/s. The discontinuity separating the crustal layers (called the Intermediate discontinuity) is believed to be similar to the Conrad discontinuity. Contour maps of depths to this discontinuity and the Mohorovicic discontinuity were produced. Average depths (below surface) are: Intermediate = 18.25 km; Mohorovicic = 34.28 km. Average surface elevation is 0.33 km. Velocity averaged vertically through the crust has a mean value over the area of 6.36 km/s. Structures on the discontinuities are related to at least one major surface geological feature. A form of the time-term method called thestation-pair methodwas designed during the survey and is recommended for the interpretation of seismic crustal refraction surveys.

ISSN:0008-4077    

DOI:10.1139/e69-009

出版商:NRC Research Press    

年代:1969

数据来源: NRC

摘要:

A regional aeromagnetic map, portraying the regional magnetic anomaly system in Northwestern Ontario west of longitude 92 °W and south of latitude 55 °N and extending westward into Manitoba to longitude 97 °W (with an additional block bounded by latitudes 54° N and 56 °N and longitudes 97° W and 102 °W) is presented. The map was prepared by multiple application of a two-dimensional smoothing operator applied to data digitized at 3 km intervals from the 1-inch-to-1-mile aeromagnetic map series published by the Geological Survey of Canada. Comparison was made with previous maps overlapping on portions of the area, which had been made by various techniques, including Fourier analysis, fitting of 6th-order polynomials, and photographic reduction. The general features of the anomaly system were found to be similar for all of these techniques. The regional anomaly system is found to be related in some cases to the thickness of the upper crustal layer (defined as lying above the Intermediate seismic discontinuity) and to structure within it, but not to the lower crustal layer or to the upper mantle.

ISSN:0008-4077    

DOI:10.1139/e69-010

出版商:NRC Research Press    

年代:1969

数据来源: NRC