摘要:

The Duxbury massif, Eastmain District, Quebec, is a complex tonalitic intrusion that is internally divisible into a homogeneous border zone of granodiorite (Rb–Sr total-rock isochron age = 2500 ± 85 Ma; initial87Sr/86Sr = 0.7023 ± 0.0003) and a heterogeneous core zone of tonalite (Rb–Sr total-rock errorchron age = 3060 ± 180 Ma; initial87Sr/86Sr = 0.7014 ± 0.0003). The geologic, petrographic, and isotopic data are consistent with a model of remobilization of 3.1 Ga sialic basement during the Kenoran orogeny at 2.5 Ga. Evidence suggests that the source material was of tonalitic composition, that it was never more deeply buried than 15–20 km, and that it was remobilized in a plastic to brittle subsolidus state. Slab-sample studies of the tonalite indicate the 3.1 Ga age is a metamorphic one, and that the source material had a pre-history at that time. Sr-isotope constraints imply source region formation as juvenile material from the mantle at between 3.5 and 3.6 Ga. The Duxbury massif, hence, records a history of crustal development spanning at least 600 Ma and possibly more than 1 Ga. These results may be applicable on a larger scale to many of the regional tonalite massives found in the Superior Province of Canada and elsewhere.

ISSN:0008-4077    

DOI:10.1139/e80-001

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The history of Late Wisconsinan glaciation in southwestern Manitoba has been established by identifying and correlating ice-laid lithostratigraphic units in the subsurface. Five Late Wisconsinan tills are defined on the basis of their texture, mineralogic composition, and stratigraphic position. These new formations are, from youngest to oldest, Marchand, Whitemouth Lake, Roseau, Senkiw, and Whiteshell Formations.Late Wisconsinan ice first invaded southeastern Manitoba 22 000 to 24 000 years ago. This Laurentide glacier advanced from the northeast across the Precambrian Shield and deposited the sandy Whiteshell and Senkiw tills, which contain abundant Precambrian rock fragments and minerals and few Paleozoic carbonate grains. Shortly after this, Keewatin ice advanced from the northwest over Paleozoic carbonate rocks, depositing the loamy carbonate-rich Roseau Formation throughout most of the area. This ice remained over southeastern Manitoba until after 13 500 years ago, when it rapidly retreated northward with Lake Agassiz on its heels. Two brief glacial readvances occurred. The first overrode Lake Agassiz lacustrine sediment as far south as central North Dakota shortly after about 13 000 years ago. The clayey Whitemouth Lake till was deposited in southern Manitoba at this time. After a rapid retreat, the ice briefly pushed southward over southeastern Manitoba about 12 000 years ago to just south of the International Boundary. The sandy carbonate-rich Marchand Formation was deposited at this time as the ice overrode its own sandy outwash. By 11 000 years ago, ice had disappeared from southeastern Manitoba.

ISSN:0008-4077    

DOI:10.1139/e80-002

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Five 1 m diameter pods of very high-rank coal (meta-anthracite) have been discovered in a normally high-volatile coal seam on Eagle Mountain, Elk Valley Coalfield, British Columbia. Two zones of colour alteration occur on the surface of local siltstones in the immediate vicinity of this occurrence and a thin overlying seam is reduced to ash. A study of the mineralogy of low-temperature coal ash (LTA) and also of the petrography of these high-rank pods provides evidence of localized temperatures of around 800 °C together with extreme rank gradients of 0.07%and supports a hypothesis that one or more lightning strikes were responsible for this occurrence.

ISSN:0008-4077    

DOI:10.1139/e80-003

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Preliminary analysis of gravity anomalies across the Bonnet Plume Basin indicates that the gravity method can be used as a relatively inexpensive method of establishing basin structure and approximating formation thickness in coal basins with little to no subsurface control, providing that density contrast between the coal-bearing strata and underlying rocks is sufficiently high. In the Bonnet Plume Basin gravity measurements recorded along an east–west profile give Bouguer anomalies which vary from −42 to −82 mGal and place constraints on geological models which can be applied to the clastic fill of the Cretaceous–Tertiary basin. Within these constraints the Bonnet Plume Formation can be modelled as an eastward, gently dipping (1–9°) sequence of coal-bearing rocks which attains a maximum thickness of between 760 m and 4.7 km in a region 7 km west of Knorr Fault. The unconformity between the Bonnet Plume Formation and underlying Proterozoic rocks, east of this zone of maximum thickness, dips to the west at between l0and 44°. Accurate estimates of both the thickness and dip of the sequence cannot be made due to inadequate knowledge of the subsurface distribution of the upper (low density) and lower (high density) members of the formation. Application of a two-layer model for the Bonnet Plume Formation would indicate that the upper, lignite-bearing member of the formation may be more restricted than previously suspected and that the greater proportion of the basin to the south of the line of profile is underlain only by the lower member, containing subbituminous coals.

ISSN:0008-4077    

DOI:10.1139/e80-004

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The loess derived soils of the Hinton district provide a record of soil formation for the entire postglacial period. Loess originates from the shorelines of Brûlé Lake and from the sandbars and braided channels of the Athabasca River.The geochronology of the loess, as established through the study of paleosols and volcanic ash beds, indicates that loess deposition was continual but irregular. Soil formation occurred contemporaneously with loess deposition, and varying soil morphologies were attributed to differing local rates of loess accumulation. There was no evidence for marked climatic change during the Holocene in the study area, but increased loess supply after 4000 years BP may reflect gradual change.

ISSN:0008-4077    

DOI:10.1139/e80-005

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A tectonic model that attempts to explain common features of Archean geology is investigated. The model supposes the accumulation, by volcanic eruptions, of a thick basaltic pile on a granitoid crust. The thermal blanketing effect of this lava raises the temperature of the granitic crust and eventually softens it enough that gravitational slumping and downfolding of the lava follows.Numerical models of the thermal and mechanical evolution of a granitoid crust covered with a thick lava sequence indicate that such an evolution is possible when reasonable assumptions are made about the temperature dependence of the viscosity in crustal rocks. These models show the lava sinking in relatively narrow regions while wider granite diapirs appear in between. The convection produces strong horizontal temperature gradients that may cause lateral changes in metamoprhic facies. A one order of magnitude drop in accumulated strain occurs between the granite–basalt interface and the center of the granite diaper at a depth of 10–15 km.

ISSN:0008-4077    

DOI:10.1139/e80-006

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

In both physical and mathematical models of the Earth's core it has been difficult, so far, to discuss all the terms in the magneto-hydrodynamic energy equation under one unifying theory and to relate all the physical mechanisms involved in a specific model. The reason for this is mainly the uncertainty about the energy sources, or, when they could be accounted for, with uncertainty about their location. In the following article we deduce and examine a model of the Earth's core which can be regarded as a sequel to theories of the formation of a fluid core in the course of the Earth's thermal evolution.General cooling and pressure-freezing cause the formation of solid phases at the boundaries of the fluid core, leading to a solid inner core (IC) and a lower mantle shell (Bullen's D″ layer) from slow overgrowth at the mantle–core (MC) boundary. For simplicity, the core fluid is assumed to consist of two major phases, one conducive to solid metallic core formation, and the other to crystallization of a lower mantle phase from "solution" in a metal "solvent." The presence of a third, minor constituent, by selective partitioning between phases, acts as a solid phase growth regulator.On the basis of this model the energy available for fluid core motion and thereby for maintenance of the magnetic field, is related directly to the time rate of change of the growth of the solid phases at the IC and MC boundaries. Most of the available energy is gravitational and is associated with density and concentration currents which offset density inhomogeneities caused by selective acceptance and rejection of the fluid core constituents by the two solid phases.A very conservative estimate of the net gain per second in gravitational potential energy resulting from the mass redistribution via density currents and solid phase formation is 2.6 × 1013 W which may become available in different forms. The fraction which is converted into kinetic energy associated with differential circulatory motion around the rotation axis amounts to 3.4 × 1011 W, based on radial interchange with respect to the Earth's centre. The heat liberated as a result of IC solidification is 2.7 × 1011 W, assuming that the metallic phase is mainly iron. Since our ideas of other constituents of the core fluid are less definite we can draw only very general conclusions about the MC boundary. If silicates and oxides are likely candidates, it is possible that in the crystallization of the mantle phase from the core fluid, heat is being absorbed, thus creating a heat sink at the MC boundary. An estimate of the net strain energy associated with compression of IC material by about 1.4% and expansion of MC material by, on the average, 0.4% gives 1.5 × 1011 W.Magnetic polarity reversals might be explained as due to epochs during which the solid phase growth rate which dominates the fluid motion shifts from the IC to the MC boundary and vice versa. Intensity changes might be due to significant variations in the ratio of the radial and horizontal velocity components of the fluid motion.

ISSN:0008-4077    

DOI:10.1139/e80-007

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Water and suspended sediment samples were collected at 12 stations on the Yamaska and St. François Rivers, located in southeastern Quebec, and were analyzed for the trace metals Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. The suspended sediment samples were subjected to a sequential extraction procedure designed to partition the particulate trace metals into five fractions: (1) exchangeable; (2) bound to carbonates; (3) bound to Fe–Mn oxides; (4) bound to organic matter; and (5) residual.Although suspended sediment levels as well as total soluble and particulate trace metal concentrations were highly variable in time and space, speciation patterns for each metal proved reasonably constant. Very small proportions of all metals, except Cd and Mn, were found in the exchangeable fraction, whereas high levels of all metals were present in the residual fraction; Fe–Mn oxides and organic matter constituted important transport phases for most metals. Deviations from this general behaviour were occasioned by man-induced perturbations (e.g., inputs of municipal sewage or mine waste water). At stations influenced by such factors, total particulate metal concentrations increased and the relative contribution of the residual fraction decreased. The trace metal content of fraction 3 proved to be particularly sensitive to anthropogenic inputs; other phases acting as trace metal sinks included those liberated in fractions 1 (Cd, Cu, Ni, Zn), 2(Cu, Ni, Zn), and 4(Cu, Ni).

ISSN:0008-4077    

DOI:10.1139/e80-008

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Chitinozoan and acritarch assemblages from Caradocian and Ashgillian strata forming part of the White Head Formation of the Percé region, Gaspé Peninsula, Québec, contain species known from the central United States, eastern Canada, and northwestern Europe. One new species,Orthosphaeridium gaspesianum, is described.

ISSN:0008-4077    

DOI:10.1139/e80-009

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Shallow marine deposits of the Arisaig Group (Silurian–Devonian) of Nova Scotia consist of shaly sediments with varying proportions of coarser interbeds. Brachiopods, graptolites, crinoids, corals, and bivalves are present in parts of the group.One end-member lithology consists of black, fissile shale with few fossils. This grades into grayer, less fissile, more fossiliferous shale with coarse siltstone interbeds up to 5 cm thick. Higher in the group, nearer nonmarine beds, the background sediments consist of mottled, nonfissile silty mudstone with many largein situbrachiopods and lenses of coarse siltstone. The interbeds are composed of coarse siltstone or fine sandstone and, in some cases, have lenses of coquina within them. They range from 5–50 cm in thickness, but in places have amalgamated by scouring and locally comprise almost 100% of the section. Most of the coarse interbeds have sharp bases with horizontal or low angle laminations, but some thicker beds show sets of low angle, curving laminations which truncate other sets, termed “hummocky cross-stratification," The top surfaces of these beds are covered by interference ripples and burrows.The coarse interbeds were laid down rapidly by fractional seaward-flowing bottom currents during storms. Some of the coarse beds were later modified by bioturbation during fair weather periods when settling of sediment from suspension and faunal activity were the dominant processes. The Arisaig Group represents the deposits of a storm-dominated shelf and illustrates the range in variation which can occur in the sediments of this type of environment.

ISSN:0008-4077    

DOI:10.1139/e80-010

出版商:NRC Research Press    

年代:1980

数据来源: NRC