bluuebunny/crossref_metadata_2025 huggingface dataset:
CIRCULAR PAPER CHROMATOGRAPHIC METHOD FOR DETERMINING TRACE AMOUNTS OF COBALT, COPPER, NICKEL, AND ZINC IN ROCKS AND SOILS
Authors: Mah D. C. , Mah S. , Tupper W. M.
Published: April 2011

Ascending, descending, and horizontal (circular) methods of paper chromatography were explored and compared. Circular chromatography was found to be the most suitable; it requires shorter development time, has more definite Rf values, less tailing, higher sensitivity, and better precision than ascending or descending methods.A methyl ethyl ketone: hydrochloric acid solution (93:7 v/v) is used as a developing solvent for cobalt, copper, and nickel, and a 1-butanol: 1 N hydro–chloric acid solution (7:3 v/v) is used as a solvent for zinc. Good separations were obtained with these solvents and no critical interferences were noted. Benzidine – rubeanic acid is used as a color indicator for cobalt, copper, and nickel; and dithizone (0.01%) for zinc. This method has an absolute sensitivity of 0.005 μg for zinc, and 0.02 μg for cobalt, copper, and nickel. Precision is estimated at ± 10%.Methods have also been developed for determining bismuth, silver, and tin.The separation of elements from complex mixtures by paper chromatography and by quantitative determination of the amounts present by emission spectrography have been investigated. This rarely considered process offers promise, because the sensitivity of several elements is higher in emission spectrography than in colorimetry.
OXYGEN ISOTOPIC STUDIES OF AMPHIBOLITES
Authors: Schwarcz H. P. , Clayton R. N.
Published: April 2011

The whole-rock oxygen isotope ratios of amphibolites from a variety of localities have been studied in an attempt to distinguish para-amphibolites from ortho-amphibolites. If para-amphibolites were derived from a pelite–carbonate mixture or any carbonate-bearing sedimentary rock, they should be enriched in18O relative to basaltic parents. Exchange with an external oxygen reservoir acting as an isotopic buffer during metamorphism would, however, tend to obliterate initial differences between basaltic and metasedimentary parent rocks. It is found that, except for feather amphibolites from the Grenville subprovince of Ontario, rocks from a given area which are geologically distinguishable as para- or ortho-amphibolites do not display the predicted differences in18O/16O ratios. Large differences in isotopic composition between localities are attributed in part to difference in grade of metamorphism and consequent differences in temperature of exchange with an external oxygen isotopic buffer. All samples appear to have exchanged to some extent.
NATIVE METALS IN THE MUSKOX INTRUSION
Authors: Chamberlain J. A. , McLeod C. R. , Traill R. J. , Lachance G. R.
Published: April 2011

The following native metals have been identified in the Muskox intrusion: native iron, native nickel–iron (awaruite), native cobalt–iron (wairauite), and native copper. Mineral distributions and textures indicate that the native metals formed more or less contemporaneously, during the period of serpentinization of the host dunites and related rocks.Conditions during serpentinization must have been more reducing in the central and lower parts of the layered series than in the margins and upper parts of the intrusion. This is indicated by the fact that most native metals are abundant in the central regions and are essentially lacking elsewhere, even in strongly serpentinized zones. This zoning suggests that reducing conditions may have been generated internally, possibly as a result of the serpentinization process itself. The composition of the primary olivine of forsterite80–88together with the presence of abundant secondary magnetite in equivalent serpentinites indicates that a redox reaction, olivine + water = serpentine + magnetite + hydrogen, contributed to the development of a progressively more reducing, or hydrogen-rich, fluid phase.Natural phase relations indicate that each native metal formed primarily in situ as a result of the decomposition of specific earlier formed minerals that had become unstable in the reducing environment. Native iron appears to have been formed by the reduction of magnetite; awaruite by the reduction of pentlandite; wairauite by the reduction of an unknown phase, possibly cobalt pentlandite or cobaltian pyrite; and native copper by the reduction of chalcopyrite. The feasibility of most of these reactions was confirmed by experimental studies carried out in systems open to moist hydrogen.
UPPER TRIASSIC AMMONOID ZONES OF THE PEACE RIVER FOOTHILLS, BRITISH COLUMBIA, AND THEIR BEARING ON THE CLASSIFICATION OF THE NORIAN STAGE
Authors: Tozer E. T.
Published: April 2011

The Triassic section at Pardonet Hill, Peace River, British Columbia, has been studied in detail, resulting in a new interpretation of the structure and of the rock and faunal sequence. This work necessitates revision of the sequence of Upper Triassic ammonoid zones and some changes in the age assignments. The following sequence of Upper Triassic ammonoid beds and zones is now recognized in the Peace River Valley: (1) Discotropites; (2) Anatropites; (3) Mojsisovicsites kerri; (4) Malayites dawsoni; (5) Juvavites magnus; (6) Drepanites rutherfordi; (7) Himavatites columbianus; (8) Monotis subcircularis (Bivalve Zone); (9) Rhabdoceras suessi. Faunas 1 and 2 are Upper Karnian; 3 and 4 are classed as Lower Norian; 5, 6, and 7 as Middle Norian; 8 and 9 as Upper Norian. The Peace River succession suggests that the generally accepted standard for the Norian Stage, established in Austria, may be incorrect. In particular, the Austrian zones of Cladiscites ruber and Sagenites giebeli are probably younger than the Cyrtopleurites bicrenatus Zone, not older, as formerly believed.
CHEMICAL PROPERTIES OF CHAMPLAIN SEA SEDIMENTS
Authors: Venture R. S. La , Warkentin B. P.
Published: April 2011

Measurements of soluble components, and characterization of the charge on the mineral surfaces, are reported for five samples of the Champlain Sea sediments. Large amounts of magnesium, beyond the amount of dolomite present, were slowly released in solution from the broken surfaces of the minerals. Amorphous aluminosilicates made up less than 6% of the sample weight, and their removal did not improve the X-ray diffraction patterns or alter significantly the chemical properties of the sediments. Of the cation exchange capacity of 20 to 30 meq/100 g at pH 7, from 50 to 75% was found to be due to pH-dependent charge, which leads to preferential adsorption of monovalent ions. In equilibrium with artificial seawater, the samples had from 50 to 25% exchangeable sodium.
TELLURIC FIELD AND APPARENT RESISTIVITY OVER AN INCLINED NORMAL FAULT
Authors: Naidu P. S.
Published: April 2011

The telluric field and apparent resistivity anomalies caused by an inclined normal fault are calculated along a profile perpendicular to the strike of the fault. The method of conformai mapping is used to obtain an analytic solution of the boundary value problem. Numerical results are presented in the form of a series of graphs. It is concluded that the angle of inclination for a basement fault can be determined quantitatively for a large throw or qualitatively for a moderate throw.The effect of anisotropic strata on the anomaly curves is discussed.
ARCHAEAN SEDIMENTARY ROCKS OF NORTH SPIRIT LAKE AREA, NORTHWESTERN ONTARIO
Authors: Donaldson J. A. , Jackson G. D.
Published: April 2011

Archaean sedimentary rocks of the North Spirit Lake area show little evidence of having been derived predominantly from associated Archaean volcanic rocks. Instead, compositions of the sediments reflect significant sedimentary and (or) granitoid provenance. A remarkably high content of clastic quartz in thick units of sandstone and conglomerate suggests either reworking of older quartzose sediments, or reduction of the labile constituents in quartz-rich granitoid rocks through prolonged weathering and rigorous transport. Observations for other sedimentary sequences in the region between Red Lake and Lansdowne House suggest that the North Spirit sediments are not unique in the Superior Province. Quartzose sandstones commonly are regarded as atypical of the Archaean, but such rocks arc abundant in northwestern Ontario. Frameworks of many Archaean greywackes actually are richer in quartz than typical greywackes from numerous Proterozoic and Phanerozoic sequences.The concept of rapidly rising volcanic arcs as the sole source of Archaean sedimentary detritus is rejected for the North Spirit area. The volcanies, rather than representing relicts of protocontinents, probably record events removed from initial volcanism in the history of the earth by one or more orogenic cycles. Major unconformities may therefore exist not only between sedimentary and volcanic units, but also between these units and older granitoid rocks.
SEISMIC STUDIES ON THE EASTERN SEABOARD OF CANADA: THE APPALACHIAN SYSTEM. I
Authors: Ewing G. N. , Dainty A. M. , Blanchard J. E. , Keen M. J.
Published: April 2011

The results of seismic refraction profiles in the Gulf of St. Lawrence and on the northwest and northeast coasts of Newfoundland are presented. The thickness of the crust is about 45 km in the region of the Gulf of St. Lawrence southwest of the Cabot Strait Trough, and off the northeast coast of Newfoundland east of the Long Range Mountains. One interpretation of the data suggests that the compressional wave velocities through the underlying mantle are 8.50 and 8.69 km s−1 respectively. An "intermediate" layer about 20 km thick is identified with compressional wave velocities of 7.35 and 7.52 km s−1 beneath these areas. A thinner crust, 33 km thick approximately, underlies the west coast of Newfoundland, and a crustal thickness of 35 km is postulated near Anticosti Island. The compressional wave velocity in the upper part of the mantle beneath this thinner crust is close to 8 km s−1. The intermediate layer thins and, possibly, pinches out in the vicinity of Anticosti Island and northwest Newfoundland. The results lead to the suggestion that we see within the crust and upper mantle the subsurface expression of the two-sided nature of the Appalachian system. The system shows no sign of quietly dying away beneath the northeastern coast of Newfoundland.
THE CONVERTED-WAVE METHOD OF SEISMIC REFRACTION INTERPRETATION FOR INTERFACES WITH SEVERE DIP AND CURVATURE
Authors: Hall Donald H.
Published: April 2011

In the converted-wave method of seismic refraction interpretation, travel times for compressional, converted, and transverse head waves are used in combination to obtain velocities and layer thicknesses. The applicability of the method over interfaces with high dip and curvature is investigated, treating the two- and three-layer cases for layers of uniform velocity, with upper-layer velocity known, where the problem is to calculate velocities at depth and delineate the interfaces. It is shown that although dip and curvature affect the calculation, procedures can be devised to obtain solutions in the presence of these factors. Examples of application of the method in the two-layer case to a plane interface dipping at 30°, and to a curved interface with dip changing linearly from 0° to 27° are given.Depth calculation using intervals between the travel times of converted waves are shown to be independent of dip for a plane interface, but sensitive to curvature for a curved interface. It is shown that in these cases, a satisfactory depth calculation is possible.Ratios of these time intervals are shown to produce depth ratios that are either independent of velocity or with low dependence upon this parameter.A number of capabilities peculiar to the converted-wave method are noted.
SYNTHESIS OF ALBITE AT 210–240 °C
Authors: Chagnon Jean-Yves , Saull V. A.
Published: April 2011

High temperature albite was synthesized at 210 and 240 °C from a mixture of kaolinite, NaCl, and Na2CO3, each run lasting about 63 days. Identification was made by X-ray diffraction, supplemented by electron microscopy.
HURONIAN STRATIGRAPHY OF THE McGREGOR BAY AREA, ONTARIO: RELEVANCE TO THE PALEOGEOGRAPHY OF THE LAKE SUPERIOR REGION
Authors: Young Grant M.
Published: April 2011

Mapping in the McGregor Bay area of Ontario has shown the presence of a sequence of formations which closely resembles that of the original Huronian of the Bruce Mines–Blind River area. Iron-rich siltstones and argillites above the Lorrain formation are correlated with the lower part of the Animikie iron-formations of the Port Arthur region of Lake Superior and the north central United States. The oldest Proterozoic rocks of the region south of Lake Superior are considered to be correlatives of the Cobalt group of the north shore of Lake Huron.
AN EMPIRICAL–STATISTICAL STUDY OF THREE-DIMENSIONAL FABRIC DIAGRAMS AS USED IN STRUCTURAL ANALYSIS
Authors: Stauffer Mel R.
Published: April 2011

A random arrangement of points on a sphere does not result in an isotropic distribution (unless a very large number of points is present), and different samples taken from an infinite number of points arranged into point-maximum or great-circle girdle patterns vary considerably, depending on the concentration strength and the number of points in the sample.Existing statistical tests are of limited use only, and visual determinations of symmetry and cell grouping are presently the best way to determine the nature of 'preferred-orientations', provided that the effects of sample size are given full consideration. It is unwise to consider as significant any feature of a natural fabric that could reasonably have occurred as a natural sampling variation.
EXPLORATION IN THE CANADIAN ROCKIES AND FOOTHILLS
Authors: Keating L. F.
Published: April 2011

The Canadian Rockies form the most easterly ranges of the Cordilleran system for a distance of more than 1 050 miles, from the Yukon border south into central Montana. They are bounded on the east by the Interior Plains and to the west by the Rocky Mountain Trench. The main deformation occurred during the Eocene, resulting in a system of stacked thrust plates which are restricted to the sedimentary section and do not involve the crystalline basement rocks. More than 100 miles of shortening in the sediments occurred as a result of this deformation.Exploration in this structural belt has resulted in an important oil- and gas- producing province, with the major reserves located in the southern Foothills. The vast amount of information that has been accumulated in the course of this exploration through surface mapping, drilling, and geophysical work has provided excellent structural detail over a large part of the area.Prospective structures are difficult to locate, and they require careful integration of all available geological and geophysical control. Reflection and refraction seismic methods have had considerable success in locating many of the presently producing fields and have provided information that is fundamental to our understanding of this complex structural belt.
MAPPING THE ANTARCTIC ICE SHEET BY SATELLITE ALTIMETRY
Authors: de Q. Robin G.
Published: April 2011

It is proposed that a radio altimeter be installed in a satellite to measure its height above the surface. It should work at a frequency of the order of 104 Mc/s and measure heights to an accuracy as close as practicable to ± 5 m. Heights above the ocean would be extrapolated to calculate satellite heights above sea level while over the Antarctic continent, and the difference between this calculated height and the measured height would give the surface elevation. Geometrical sounding errors and systematic errors may cause errors up to 50 m on relatively flat ice sheets, but incremental errors over 10 km should be of the order of 10 m. The systematic coverage of the Antarctic continent by a few weeks' observations from a satellite should make a detailed contour map practicable. The system would not be satisfactory for the peripheral areas where many slopes exceed 1:200 and are less regular than elsewhere, but these areas are being surveyed by conventional methods.
DEEP CRUSTAL STRUCTURE UNDER THE PLAINS AND ROCKY MOUNTAINS
Authors: Kanasewich E. R.
Published: April 2011

The Airy hypothesis of isostatic compensation is very useful in accounting for structural differences between oceans and the continental margins. However, within the continents the compensation mechanism becomes more complicated. The thickness of the crust under much of the plains in the United States and Canada is between 40 and 55 kilometers. Determinations of crustal thickness under the Rocky Mountains gives results between 30 and 50 kilometers. Although local mountain ranges may have small roots, the Cordilleran region does not have a crustal root when compared to the plains. It follows that a modified form of Pratt's hypothesis of isostasy must be applied to continental regions. The density of the upper mantle is then different under the plains from what it is under the Rocky Mountains. In the plains it appears that there is a broad conformity of the Precambrian basement surface and the Mohorovicic discontinuity. Therefore the cause of epeirogenesis must lie within the upper mantle, possibly at the level of Gutenberg's low-velocity layer. The crustal studies in the plains and mountains indicate that more consideration should be given to gravitational gliding tectonics in the development of the Rocky Mountain system, since it is possible that there was substantial vertical motion of large crustal blocks.
TECTONIC EVOLUTION OF THE NORTHERN CANADIAN CORDILLERA
Authors: Gabrielse H.
Published: April 2011

A tectonic framework that was established in the northern and eastern parts of the northern Canadian Cordillera in the late Proterozoic persisted generally until mid-Devonian time. Late Palaeozoic deposition was strongly influenced by a late Devonian and (or) early Mississippian orogeny, which produced coarse clastic sediments in the northern and western parts of the region, and by a late Pennsylvanian (?) orogeny evident in northern Yukon. The Cassiar and Coast geanticlines were established at least by late Triassic time and controlled the distribution and character of Mesozoic strata southwest of Tintina and Rocky Mountain Trenches.Metamorphism and granitic intrusion were concentrated along Cassiar and Coast Geanticlines. During the Mesozoic and early Tertiary, plutonic activity appears to have occurred at intervals of about 30 million years and was accompanied generally by deformation and development of regional unconformities. Crustal shortening has been much less in Mackenzie Mountains than in southern Rocky Mountains; a marked change in structural style of the eastern Cordillera occurs near Liard River. Many phases of deformation and intrusion have affected rocks in the southwestern part of the region; their differentiation is as yet incomplete.
SUBMERGED CORAL REEFS, WEST COAST OF BARBADOS, WEST INDIES
Authors: Macintyre I. G.
Published: April 2011

Seven sonar profiles of the sea floor were made at 3–mile intervals approximately perpendicular to the west coast of Barbados, W.I. Evidence from these profiles, first-hand observations, and deep-sea camera photographs indicate that two submerged barrier reefs parallel the coast at approximate depths of 70 and 230 ft. A trench is present in a deeper part of the sloping sea floor behind a small ridge at an average depth of 619 ft.The positions of the submerged barrier reefs probably were controlled by pauses in the post-Pleistocene eustatic rise in sea level. The First Ridge was established on an erosional terrace that could have been cut during a stillstand between 12 500 and 11 500 years B.P. The Second Ridge may have been established on a narrow ledge eroded during a stillstand between 16 500 and 15 000 years B.P. The trench appears to have resulted from faulting or submarine outcropping of Tertiary sedimentary rocks.
GEOCHRONOLOGY OF THE CANADIAN SHIELD IN NORTHEASTERN ALBERTA: I. ANDREW LAKE AREA
Authors: Baadsgaard H. , Godfrey John D.
Published: April 2011

Field work and petrographic investigation in the Precambrian of northeastern Alberta near Andrew Lake indicate a complex geologic history involving at least three major diastrophic periods. U–Pb, Rb–Sr, K–Ar, and several model lead dates determined on amenable phases of representative samples of the major rock units may be placed in three groups, roughly corresponding to the major diastrophic periods. All mica K–Ar dates are close to ~1 800 m.y., while the zircon, uraninite, and allanite U–Pb dates fall into two groups at ~1 900 m.y. and ~2 250 m.y, A whole-rock Rb–Sr isochron plot of selected basement gneiss samples also yields two groups of dates at ~1 900 m.y. and ~2 250 m.y. When the geologic history of seven selected representative rock samples is judged by petrographic examination of the dated minerals, the petrographically estimated response of the minerals to sequential geologic events is reflected with good correlation by the various dates determined on the minerals. Some discrepancies in this latter correlation are noted and include such things as a relatively 'old' zircon in a young intrusive plug, the apparent absence of primary intrusive rocks at the time of the oldest (zircon dates) and the youngest (K–Ar mica dates) diastrophic periods.
THE AGES OF CARBONATITE COMPLEXES IN EASTERN CANADA
Authors: Gittins J. , Macintyre R. M. , York D.
Published: April 2011

There are four chronological groups of carbonatite complexes in Ontario and Quebec. These are about 125 m.y., 565 m.y., 1075 m.y., and 1700 m.y., with a possible fifth at 1560 m.y. The recently proposed St. Lawrence Rift System is not considered to be a very likely control of carbonatite emplacement unless it includes a widespread system of branch faults. The coincidence of carbonatite complexes with the "Kapuskasing High" is striking and probably puts a minimum age of 1750 m.y, on the feature. Niobium is found in carbonatites of each age group.
COLLAPSE STRUCTURES NEAR SASKATOON, SASKATCHEWAN, CANADA
Authors: Christiansen E. A.
Published: April 2011

A structural depression herein called the "Saskatoon. Low" is apparent on structural maps drawn on the top of the Lea Park Formation–Upper Colorado Group, on the bedrock surface, and on the uppermost till surface. The structure was probably formed by collapse as a result of the removal of salt from the Elk Point Group. The structure presumably comprises numerous individual fault blocks, which are bounded by high-angle step faults. The structure may have started to form during deposition of the Bearpaw Formation. It was well developed, however, at the time of the advent of Pleistocene glaciation and continued to develop until late Pleistocene time. The final collapse is radiocarbon dated at about 12 000 years ago.
GEOLOGY OF PART OF THE NORTHERN CASCADES IN SOUTHERN BRITISH COLUMBIA
Authors: McTaggart K. C. , Thompson R. M.
Published: April 2011

The late Paleozoic(?) Hozameen Group consists of four divisions composed of various proportions of ribbon chert, basic lavas (now greenstones), limestone, and argillite, totalling at least 20 000 ft in thickness. In late Paleozoic or Triassic time, these rocks were metamorphosed to form the Custer Gneiss, a high-grade migmatitic complex of layered gneiss and schist. A second episode of high-grade regional metamorphism in Late Cretaceous time is associated with the emplacement of the Spuzzum Intrusions. This was followed by the Yale Intrusions (mainly foliated granodiorite), deposition of Eocene conglomerate and sandstone, and intrusion of Chilliwack batholithic rocks (mainly tonalite), which are partly of Miocene age. Several periods of deformation, some associated with the orogenies mentioned above, produced fold axes trending northwest, northeast, and northerly. The area contains three main fault zones. One separates the Custer Gneiss from its overlying cover of Hozameen rocks. A second, the Hozameen fault, separates the Hozameen beds from Mesozoic formations to the east and contains the 'serpentine belt'. The third, the Fraser River fault zone, is represented by the Hope and Yale faults.
Isotopic ages from the Appalachians and their tectonic significance
Authors: Harper C. T.
Published: April 2011

Geological field relationships and previously reported isotopic age determinations throughout the Appalachians provided evidence for a pattern of Lower Paleozoic tectogenesis. The regional isotopic age pattern indicates that intrusion of ultramafic and mafic igneous materials and major episodes of metamorphic recrystallization throughout the Appalachians were completed before the end of the Silurian Period.New K–Ar ages of metamorphic rocks from Vermont and adjacent regions in the Northern Appalachians are reported and confirm this pattern. Whole-rock ages of slates from the Taconic Klippe (460–445 m.y.) indicate that metamorphism and initial formation of slaty cleavage occurred during Middle to Late Ordovician times. Mica ages of Paleozoic schists exposed along the Green Mountain Anticlinorium (425–375 m.y.) are indicative of prolonged post-metamorphic uplift and cooling of this structure during the Silurian Period and Early Devonian Epoch. Local recrystallization and consequent loss of argon from the Taconic slates also occurred during this time. Ages obtained from a variety of metamorphic rocks from eastern Vermont fall in a narrow range (345 ± 7 m.y), indicating that renewed uplift and rapid cooling of this area, east of a line of ultramafic intrusions, occurred during Late Devonian time.Comparison of isotopic age data from the Appalachian and British Caledonian fold belts indicates that a broadly synchronous sequence of Lower Paleozoic tectonic and magmatic activity, lasting approximately 100 m.y., occurred in both regions.
Three measurements of heat flow in Eastern Canada
Authors: Jessop Alan M.
Published: April 2011

Heat flow measurements, with appropriate corrections for the effects of Wisconsin glaciation, from three widely separated locations in eastern Canada are reported. One value in the Grenville rocks of Ontario agrees with earlier published values, but, when corrected for the effects of glaciation, becomes close to the world average value. The heat flow found in the New Quebec part of the Superior Province is significantly lower than is found in the Grenville Province. This can be explained by a hypothesis based on geochemical analysis of the surface rocks.
Discussion: Stratigraphy and sedimentary environments of some Wilderness (Ordovician) limestones, Ottawa Valley, Ontario, by C. R. Barnes
Authors: Kay Marshall
Published: April 2011

Lowvillian, Chaumontian, and Rocklandian limestones have lithic facies within each stage. Conodont faunules listed from Rockland and Packenham quarries in the Ottawa Valley are from misidentified stratigraphic levels in Chaumontian and lower Rocklandian limestones.
Seaward extension of the Canadian Appalachians
Authors: Sheridan Robert E. , Drake Charles L.
Published: April 2011

The subsurface geology of the Gulf of St. Lawrence and of the continental shelf off Nova Scotia and Newfoundland is interpreted primarily from the results of 37 seismic-refraction profiles. The Gulf of St. Lawrence is underlain by more than 7 km of Carboniferous sediments deposited in an east–west-trending trough. Another important Carboniferous section about 5 km thick is observed northeast of Cape Breton Island in the Laurentian Channel. The Carboniferous trough north of Cape Breton Island swings irregularly east and south around a basement ridge and may hook into the deep east–west-trending Carboniferous trough extending out of Chedabucto Bay. The Gulf sedimentary basin is separated from the trough north of Cape Breton Island by a sharp rise in basement across Cabot Strait.Northeast of Newfoundland the pre-Upper Pennsylvanian basement plunges to deeper than 6 km in the area of the continental slope. A northeast–southwest-trending seaward-opening sediment-filled trough more than 5 km deep is revealed by the configuration of this basement northeast of the Avalon Peninsula.Seismic-refraction profiles across the Gulf of St. Lawrence between western Newfoundland and Quebec show no indication of rifting or the rotation of Newfoundland away from Quebec. Refraction profiles across the northeast rim of the Laurentian Channel indicate that the rim is erosional in origin and that the basement horizons pass continuously beneath.The seaward extension of the zone affected by the Acadian orogeny is characterized by highly metamorphosed basement with higher seismic velocities, 6.0–6.6 km/s, than the surrounding areas. Limited data northeast of Newfoundland indicate that these high velocities decrease gradually and suggest that the influence of the Acadian orogeny dies away about half way across the shelf.The seaward extension of the Taconic orogenic zone is characterized by an intermediate crustal layer, 6.6–7.6 km/s, at depths of 3–12 km. This intermediate layer continues intact all the way to the continental slope northeast of Newfoundland. It was not observed on the Labrador shelf, suggesting that the Appalachians continued straight rather than remaining marginal to North America.It is postulated that the Devonian (Acadian) orogenic belt was not continuous with a corresponding European orogen, but that the Ordovician (Taconic) orogeny may have persisted across into Europe. If this is correct, it implies the existence of a major rift at the Newfoundland slope during middle and late Paleozoic times.
A geochronological study of the White Creek batholith, southeastern British Columbia
Authors: Wanless R. K. , Loveridge W. D. , Mursky G.
Published: April 2011

Rb–Sr and K–Ar age measurements for whole-rock and mineral samples representing the various rock units of the White Creek batholith and the adjacent Precambrian country rocks are reported. Four geological events have been identified: (1) emplacement and (or) consolidation of the marginal zones of the batholith at, or subsequent to, 126 m.y.; (2) final consolidation of the leucocratic quartz monzonite core rocks at 111 ± 5 m.y.; (3) a period of thermal activity affecting all batholithic rocks at 85 m.y.; and finally (4) a second thermal event affecting all batholithic rocks and resulting in partial, localized redistribution of radiogenic argon and strontium at 65 m.y.The leucocratic quartz monzonite core rocks are characterized by a high initial 87Sr/86Sr ratio of 0.7250 in marked contrast to the lower average value of 0.7077 determined for the boundary rock units of the batholith.Chemical and mineralogical data for the whole-rock samples exhibit gradational trends between all rock units of the batholith, indicating they have developed as a consequence of the differentiation of a homogeneous source magma. However, evidence provided by isotopic and trace-element studies suggests that the leucocratic quartz monzonite core rocks were derived from a separate source, and were emplaced during an unique intrusive event late in the cycle of plutonic activity.
Massive sulfide–late diabase relationships, Home mine, Quebec: Genetic and chronological Implications
Authors: Mookherjee Asoke , Suffel G. G.
Published: April 2011

At the Home mine, Noranda, Quebec, evidence of penetration and apparent replacement of the 'Late Diabase' dikes by massive sulfides formerly led several workers to believe that these dikes were older than the orebodies. However, a glassy selvage of the diabase against a sulfide wall, in contrast with a microcrystalline one against adjoining rhyolite, demonstrates a different rate of cooling against materials of different thermal diffusivity. Also, dissociation of pyrite to magnetite, increase in the monoclinicity of pyrrhotite, copious development of chalcopyrite blebs in sphalerite, and some interesting sulfide-sulfide and sulfide-silicate reactions in the contact zone record unmistakable imprints of thermal metamorphism of the sulfide wall.Microscopic evidence indicates that, an early stage of dissociation of Fe-sulfides to magnetite was followed by pyritization of pyrrhotite and ferromagnesian silicates, and migration of chalcopyrite along and into the contact zone. These suggest a persistent pressure gradient towards the 'hot-wall' side of the reaction zone, created presumably by the fracturing of the chilled edge and by early dissociation of pyrite.Uninterrupted extensions of tabular, 'vein-like', chalcopyrite bodies from the massive sulfides protrude well into the diabase. Absence of chilling of the diabase along the walls and terminations of these protuberances, and the deformed and recrystallized fabric of these bodies point to their late emplacement by plastic flowage along post-intrusion shear planes. A similar mode of origin is proposed for the very small sulfide veins in 'D' dikelets because the two types of veins are similar.Sulfide patches within the diabase wall, with intensive but localized wall-rock alteration, retain evidence of more thorough dissociation of iron sulfides and other high-temperature mineralogical reconstitution. These masses are therefore inferred to represent clusters of detached or semi-detached portions of the sulfide wall that lost their identity due to the action of deuteric fluid. The fluid, enriched in sulfur, accounted for pyritization and other replacement and alteration features in the surrounding diabase that impart the deceptive appearance of an encroaching sulfide front.Galena-marcasite veinlets on either side of the contact in places indicate a much later solution activity along a potentially weak zone.
Phase relations in cordierite-bearing gneisses from the Gananoque area, Ontario
Authors: Reinhardt E. W.
Published: April 2011

Phase relations among sillimanite, cordierite, garnet, biotite, and hypersthene from regionally metamorphosed pelitic gneisses were determined from petrographic studies and the chemical compositions of 46 ferromagnesian minerals and 18 bulk rocks. The compatible mineral associations including quartz, feldspar, and opaque oxides are cordierite-sillimanite, cordierite-garnet-sillimanite, cordierite-garnet-biotite, cordierite-garnet-hypersthene, cordierite-biotite-hypersthene, cordierite-biotite, garnet-biotite, garnet-biotite-hypersthene, and biotite-hypersthene. The assemblages were graphically analyzed using A–F–M diagrams derived from compatibility tetrahedra by successive projections through the common phases quartz, alkali feldspar, plagioclase, magnetite, and ilmenite; this results in the subtraction of excess components such that A = Al2O3 − K2O − Na2O − CaO, F = FeO − Fe2O3 − TiO2, and M = MgO. Variations in the positions of the three-phase triangles defined by cordierite, garnet, and biotite in the A–F–M system are due to systematic variations of F: M ratios for these minerals and reveal that the external conditions of metamorphism were variable over the rock sequence studied. Partitioning of elements among coexisting minerals and field evidence indicate that equilibrium was reached at constant temperature in the gneisses around Gananoque Lake; possible variations in load pressure were inadequate to cause the observed variations in F/M. A correlation between the Fe+2/(Fe+2 + Mg) of coexisting ferromagnesian silicates and the oxidation ratios (2Fe2O3/(2Fe2O3 + FeO)) of respective rocks suggests that the mineralogical variations in F/M are a function of oxygen partial pressure. Increased oxygen pressures would give rise to magnetite at the expense of the ferromagnesian silicates, which would consequently become enriched in the magnesium end-members. It is further proposed that the equilibrium partial pressures of oxygen and water were interdependent in any small volume of pelitic gneiss during metamorphism, and that [Formula: see text] was the independent variable.
Biological events and the Precambrian time scale
Authors: Glaessner M. F.
Published: April 2011

For stratigraphic purposes, time scales are constructed on the basis of either geophysical and geochemical, or biological processes and events. Biological evolutionary processes provide the main markers linking the Phanerozoic time scale with fossiliferous rock sequences. Progress in the study of Precambrian fossils makes it necessary to assess present and future possibilities of their use as time markers and correlation indicators for the Precambrian. The low grade of diversification attained by organisms during the first one-half or two-thirds of Precambrian time may reduce the possibilities of biostratigraphic dating of early and middle Precambrian sediments to insignificance, but enough is known about late Precambrian plants and animals to suggest that careful investigation of their stratigraphic distribution and potential use as time markers will repay the effort.
Studies on the Rb–Sr and K–Ar dating of minerals from the Precambrian of India
Authors: Venkatasubramanian V. S. , Gopalan K. , Iyer S. S. , Pal S. , Krishnan R. S.
Published: April 2011

Mica samples from pegmatites and mica separates from associated rocks, belonging to the Dharwar formations of Kolar and the vicinity of Bangalore have been dated by Rb–Sr and K–Ar methods. The results by both methods show good concordance and support the concept of a plutonic-metamorphic event in this region in the interval 2050–2300 m.y. Muscovites of Nellore (Eastern Ghats cycle) and lepidolites from Hazaribagh (Satpura cycle) have also been analyzed to yield ages of 1500 m.y. and 900 m.y. respectively.
Pre-Katangan geochronology of Zambia and adjacent parts of Central Africa
Authors: Vail J. R. , Snelling N. J. , Rex D. C.
Published: April 2011

The significance of new age determinations on pre-Katangan (Late Precambrian) rocks and minerals from Zambia and adjacent parts of Tanzania and Rhodesia is discussed. In northwestern Rhodesia, the Lomagundi-Piriwiri sediments were deposited between 2500 and 2000 m.y. ago and were folded along meridional trends at circa 1940 m.y. A later episode of folding and metamorphism along similar trends occurred about 1700 m.y. ago, but only affected the western part of the sedimentary sequence (the Piriwiri Series). This latter date is comparable to that which appears to characterize the Tumbide trend, a N- to NE-trending fold system, in Zambia.In Zambia the Tumbide trend is the oldest tectonic episode preserved in the basement and is found only in isolated blocks and cores into which later tectonisms have not penetrated. The dominant pre-Katangan tectonism is represented by the NE to ENE Irumide trend. Such tectonic trends are particularly well developed in the Irumide Orogenic Belt of northern Zambia and adjacent Tanzania. Age determinations set a younger limit of circa 900 m.y. to this trend and the existence of an Irumide Cycle between about 1600 and 900 m.y. is suggested. The possibility that the relatively unmetamorphosed sediments of the Upper Plateau Series and Abercorn Sandstones at the southern end of Lake Tanganyika, the Mafingi Series of northern Malawi, and the Konse Series of Tanzania, represent near-contemporaneous platform deposition associated with the Irumide belt is considered.From this and other recent studies the distribution of orogenic belts in central and eastern Africa can be revised and a number of features of their pattern and inter-relationships noted.
The geochronology of some Precambrian rocks of southern West Africa
Authors: Tougarinov A. I. , Knorre K. G. , Shanin L. L. , Prokofieva L. N.
Published: April 2011

Age determinations completed during the last two years indicate a structural complexity previously undetected in the southern part of West Africa. Holmes and Cahen identified very ancient metamorphic rocks in Sierra Leone, in the western part of the Nigerian Shield. Their date of 2900 m.y. for monazite by the U–Pb method is comparable to a date of 2540 m.y. for biotite, recently determined by the K–Ar method.A Lower Proterozoic geosyncline, developed on the Archean basement, was deformed and metamorphosed 1800 to 2000 m.y. ago. The metamorphic complexes of the Ivory Coast and Ghana belong mainly to this period. The dominant trend of foliation is north to northeast.On the north slope of the Guinean crystalline complex younger granites are dated at 980 m.y. Associated extrusive rhyolites give an age of 1000 m.y.In eastern Ghana and Togo a thick sequency of conglomerates, sandstones, and pelitic sedimentary rocks contain glauconites dated at 620 m.y. These sedimentary rocks are the miogeosynclinal portion of an Upper Proterozoic geosyncline. The eugeosynclinal portion of this geosyncline was metamorphosed about 600 m.y. ago to form the Nigerian gneissic complex. The younger granites in Nigeria were intruded 170 m.y. ago.
Geochronology of the Aldan Shield, southeastern Siberia
Authors: Tougarinov A. I.
Published: April 2011

Crystalline Precambrian rocks exposed in the basins of the Olekma and Aldan Rivers represent the southeastern part of the Siberian Platform. To the north and east the basement is covered by Paleozoic and Upper Proterozoic formations. To the south and west lie younger deformed belts.The Aldan Shield can be divided into four regions. The Tcharskaja massif, in the west, is the most ancient block. Pb–U dates on allanite and zircon show a good concordance at 2950 m.y. The prevalent rock type is gneiss and migmatite.In the Aldan River basin three thick series of Lower Proterozoic rocks were deposited during the time interval 2000 to 2700 m.y. Granulite facies metamorphism of these rocks occurred 1800 to 2100 m.y. ago. The time of deposition of the lowest formations (Iengra Series) is given approximately by measurement of the isotopic composition of lead in different syngenetic mineral phases. Using muscovite and magnetite, the 207Pb/204Pb:206Pb/204Pb isochron yields a value of 2550 ± 300 m.y.In the east the crystalline basement of the Aldan complex is covered by thick Proterozoic sedimentary formations. These formations are intruded by alkaline rocks, dated at 1100 m.y. and small ring structures with associated carbonatites, dated at 600 to 650 m.y. The magmatic cycles, combined with glauconite age determinations, indicate a nearly complete, Middle and Upper Proterozoic stratigraphic section. The base of the Middle Proterozoic is established at 1900 ± 50 m.y.The Aldan complex, and the Stanovoi complex to the south are separated by a wide belt of tectonic fault zones. The prevailing metamorphic grade of the Stanovoi complex is amphibolite facies, with only local areas of granulite facies rocks. Pb–U ages from monazites, zircons, and allanites from pegmatites cutting the complex date the amphibolite facies metamorphism at 1900 m.y. Available data suggest an Archean age for the granulite facies rocks. The Stanovoi complex has been affected by at least two subsequent magmatic periods; the first were syenitic intrusions at 1100 m.y., and the second Jurassic granites at 150 m.y. The last magmatic cycle, found in many parts of the Aldan Shield, is an excellent demonstration of the recurrent rejuvenation of Precambrian terrains.
Potassium-argon age studies in West Greenland
Authors: Larsen Ole , Møller Jørgen
Published: April 2011

Geochronological units have been established in West Greenland partly on the basis of 34 new K–Ar age determinations, of which 32 were made on biotites.The central part of West Greenland belongs to a single basement gneiss unit more than 2700 m.y. old. Blocks of basement rocks are traversed by rectilinear shear zones tens of kilometers long and several kilometers wide. In these tectonic belts relic slices of supracrustal rocks occur within reworked basement gneisses. The latter give K–Ar ages of 2500–2700 m.y. Ages close to 1800 m.y. are found locally. North and south of the central region of old basement younger orogenic rocks are found: the Nagssutôqidian fold belt in northern West Greenland dated at approximately 1700 to 1750 m.y. and the Ketilidian fold belt in South Greenland of which the late- to post-kinematic granites are about 1500 to 1600 m.y. old. The Gardar non-orogenic igneous activity, 1000 to 1300 m.y., is found only in South Greenland.
Chronology of Precambrian events in the Front Range, Colorado
Authors: Peterman Zell E. , Hedge Carl E.
Published: April 2011

The Precambrian rocks of the Front Range have undergone a long and complex history involving multiple periods of metamorphism, deformation, and intrusive activity. Before 1750 m.y. ago sedimentation and volcanism resulted in the accumulation of many thousands of feet of sandstone and shale, and lesser amounts of calcareous and volcanic rocks on a basement terrane that has not yet been recognized.Regional and dynamic metamorphism at 1700 to 1750 m.y. ago converted the sedimentary-volcanic pile to a metamorphic terrane of dominantly medium- to high-grade gneisses and schists. Plutonic rocks typified by Boulder Creek Granite were emplaced during this event. After this orogeny, there is a time span of 250 to 350 m.y. for which there is no obvious geologic record. The interval 1390 to 1450 m.y. was a period of major igneous activity during which the extensive Silver Plume Granite, Sherman Granite, granitic and mafic dikes, and pegmatites were emplaced. Regional heating attendant with this plutonism was effective in resetting most K-Ar and Rb-Sr mineral ages of the older rocks. Tectonic activity along the great shear zone that trends northeast through Idaho Springs probably began during this orogeny and may have continued intermittently until about 1200 m.y. ago.The Pikes Peak batholith and smaller related granites were emplaced at 1040 m.y. ago. This event was not accompanied by regional metamorphism. There is no recognized sedimentary record between the earlier orogeny and this igneous activity. The Pikes Peak igneous activity is the youngest recognized Precambrian event, but it appears to be limited to the Pikes Peak batholith and satellite plutons.
The fabric of the granulites of Mont Tremblant Park, Quebec
Authors: Katz Michael
Published: April 2011

The fabric of the highly deformed and recrystallized gneisses formed under granulite facies conditions of metamorphism are described from Mont Tremblant Park, Quebec, Canada. These gneisses are termed granulites and are classified into quartzofeldspathic and hypersthene varieties.The term 'cataclastic-gneissose' fabrics is used to imply varying degrees of deformation and recrystallization without micro-brecciation or cataclasis 'sensu stricto' and a classification of these various fabrics is presented. The modifications in these granulites are progressive and are assumed to have the following sequence:[Formula: see text]During the evolution from mortar to granoblastic types, the minerals become flattened and increasingly elongated, while the individual recrystallized grains increase in size. The same deformation produced flaser and granoblastic gneisses in the quartzofeldspathic granulites and mortar and augen gneisses in the hypersthene granulites.The mineral relicts (porphyroclasts) in the mortar and augen gneisses are highly deformed and display evidence of strain, such as undulatory extinction, deformation bands, polygonization, mechanical twins, and bent cleavages. These mortar and augen gneisses display a poor preferred orientation of quartz c axis.In the recrystallized rocks the grains form a clear, fresh, unstrained polygonal mosaic and in the case of quartz, long leaf-like uniform plates are produced. In the flaser and especially the granoblastic gneisses no signs of strain remain and the recrystallized fabric consists of quartz plates alternating on a micro-scale with bands of polygonal fresh feldspar and granular streaks of dark minerals. A petrofabric diagram from a granoblastic gneiss shows a marked preferred orientation of quartz c axis.A review of the relevant literature on the natural and experimental investigations strongly supports the hypothesis that the fabrics of the granulites are produced as a result of the progressive deformation and recrystallization of the mineral constituents.