Rocks of two major sedimentary fades, shelf and eugeosynclinal, outcrop in the most northern part of Newfoundland. The area is similar in geological setting to the west coast of Newfoundland where the juxtaposition of two such fades of equivalent ages has been the subject of much discussion. Strata of the shelf fades occur in three units: (1) Lower and Middle Ordovician limestones, (St. George and Table Read Formations) forming the western half of the region; (2) Middle Ordovician shale and greywacke, (Goose Tickle Formation) lying to the east of the limestone; (3) clean white Cambrian sandstone restricted to islands off the east coast. Eugeosynclinal rocks lie to the east of the limestone. Black and green shale of the Lower Ordovician Northwest Arm Formation is contemporaneous with the nearby limestone but is surrounded Q faults. The remainder of the eugeosynclinal rocks lie further east in two thrust slices, one on top of the other. The lower slice consists of volcanic rocks, greywacke, and shale whereas the upper slice is composed of volcanic rocks intruded and metamorphosed by peridotite. Intensity of structural deformation increases from west to east but also varies with the lithologies involved. The massive limestones are gently folded whereas the volcanic and clastic rocks in the east are more tightly folded, and are overturned towards the west. In addition to the major thrust planes that underlie parts of the eugeosynclinal group several smaller thrusts cut the shelf rocks. Movement of the thrust slices was towards the northwest. The eugeosynclinal rocks are thought to have originated 60 km to the southeast and to have been moved to their present position by gravity sliding.

A suite of 13 late Archean subalkaline to alkaline intrusions were studied by major and trace element geochemistry and neodymium, hafnium and lead isotopic methods. The intrusions (2683 - 2678 Ma) are located in the Quetico metasedimentary belt, western Superior Province, and include pyroxene hornblendite, diorite, monzonite, syenite and carbonatite. The samples display arc-like trace element patterns with high Cs, Ba, Sr and light rare earth element abundances and low Zr, Hf, Nb, Ta and Ti. Neodymium and hafnium isotope data reflect derivation from a depleted mantle source with minor contribution from an enriched source. Lead isotope ratios from K-feldspar separates are dominated by a slab fluid or crustal component. Quantitative modeling of trace element and isotope ratios illustrates that a metasomatic event shortly before melting produced the main geochemical signatures, but a contribution from an older crustal source is also required to explain the range in data. Melting models based on rare earth element variations suggest that melting occurred over a range of pressures or took place in the garnet spinel transition zone. The intrusive complexes can be subdivided into two groups on the basis of high field strength element distribution, which appears to reflect mantle heterogeneities resulting from differences in metasomatic processes. The most abundant group exhibits super-chondritic Nb/Ta and excess Nb relative to magmas produced by melting of a fluid metasomatized mantle. These characteristics are in accord with metasomatism by silicic melts that have left rutile in the residue and the metasomatic agent is thought to be a mixture of slab-derived fluids and melts. The trace element chemistry of the remaining intrusions reflects a source affected by fluid metasomatism. Carbonatite constitutes a minor part of the Beaverhouse Lake intrusion. Qualitative major and trace element modeling suggests that the carbonatite formed by carbonate-silicate liquid immiscibility. The carbonatite is characterized by highly depleted hafnium isotopic signatures, which are interpreted to result from a previous episode of carbonate metasomatism. Modeling of Lu-Hf partitioning during silicate-carbonate liquid immiscibility suggests that anomalously high hafnium isotopic ratios should develop with time in the carbonate phase, which has potentially important implications for carbonate metasomatism.

Variolites are mafic to intermediate volcanic rocks containing centimetre-sized, spherical domains, termed varioles. Varioles are dominantly composed of plagioclase spherulites. Variolitic volcanic rocks host ore in many epigenetic Au deposits within Archean greenstone belts. The geochemistry and alteration of variolitic rocks were studied within the Archean Abitibi Greenstone Belt in Harker Township, Ontario and in the Dome Mine area, Timmins, Ontario. The study demonstrates that there is a connection between the anomalously high Fe/Mg ratio of the variolites and disseminated sulphide-Au mineralization. Variolites occur dominantly in the upper, more evolved parts of Fe tholeiitic volcanic sequences. They commonly have a more differentiated composition than typical Fe tholeiitic MORB rocks. They have elevated concentrations of incompatible elements, silica, iron, titanium and phosphorous, and lower than expected concentrations of compatible elements such as vanadium and magnesium. In addition, their Fe/Mg ratio is anomalously high, commonly greater than 3.0. Varioles tend to be more concentrated in intermediate-acidic flows, which are characterized by flow banding, extensive development of hyaloclastite, and brittle fracture. Disequilibrium crystal habits, including plagioclase spherulites, branching amphiboles (after pyroxene), and dendritic oxides, are common in variolites and are related to diffusion limited growth conditions. These conditions were likely caused, in part, by the relatively silica-rich nature of the lavas and undercooling. The differentiation of the variolitic suites is interpreted to be due to fractional crystallization. The compositional range of the suite is similar to other strongly differentiated Archean tholeiitic rocks, such as the Golden Mile Dolerite in Kalgoorlie, Australia. The variolitic suites are also similar to modern evolved, oceanic suites developed in areas of thicker oceanic crust. The variolitic suites are interpreted to result from injection of tholeiitic magma along faults to high levels in the crust where lower temperatures and pressures promoted rapid and extensive differentiation. Alteration studies of variolites associated with Au mineralization revealed that the alteration mineralogy is partly related to the host rock composition. The upper, more evolved flows of the variolitic suites tend to stabilize a complex mineral assemblage, including albite, Fe-Ti oxides, and pyrite whereas the lesser evolved flows stabilize a simpler assemblage, generally dominated by carbonate minerals. In both areas, mineralized zones have significant addition of CO2, S, and Au and depletion of H2O. Hydrothermal alteration in the Harker Lake area is characterized by oxidation of the host rock with addition of Na2O and Sr and depletion of Zn, MgO, MnO and, to a minor extent, HREE, whereas alteration at the Dome Mine is characterized by reduction of the host rock, addition of K2O, Ba, CaO, B, and LREE, and depletion of Na2O, Sr, and HREE. These results reflect differences between the two areas in the size and intensity of the mineralizing events, the influence of structural styles, and the local rock types. In variolites, Au is deposited by destabilization of the Au-bisulphide complex largely due to removal of sulphur from solution by reaction with iron in the host rock to form pyrite. Bohlke (1988) has demonstrated that the Fe/Mg ratio of the host rock plays a key role in determining whether Fe-Mg(-Ca) carbonates or pyrite will be formed in the alteration zone. Pyrite will tend to form in host rocks which have a high Fe/Mg ratio. This effect is enhanced when the auriferous hydrothermal fluids have previously equilibrated with high magnesian rocks. The anomalously high Fe/Mg ratio of variolitic rocks (> 2.0) makes them ideal chemical traps for sulphide-Au mineralization. Additionally, their tendency for brittle fracture enables the fluids to affect a greater volume of rock, enhancing the potential for mineralization. Variolites may be useful in the exploration for epigenetic Au deposits. As a consequence of their composition, variolites have excellent potential to host disseminated sulphide-Au mineralization in association with shear zones or faults, which have provided the pathways for auriferous fluids.

The Gracefield pluton is composed of two distinct syenite intrusions; both of which appear to have been intruded late in the Grenville tectonic and metamorphic history. They both exhibit a well developed concentric mineralogical zoning. They have shonkinitic cores which grade laterally into alkali syenite. The larger (earlier) intrusive is locally transitional to nepheline syenite along the south margin. The temperature of mineral equilibration of the nepheline-bearing syenite was determined to be 730°C. The temperature of the magma at the time of intrusion was somewhat higher. If the oxygen fugacity during the crystallization history of the early intrusive was close to that of the QFM buffer, the fugacity of water was between 302 and 1950 bars. The silica activity in the magma was low during crystallization. The two intrusives are mineralogically, chemically, and texturally similar. They also appear to have had similar crystallization histories. It is highly probable that the temperature of intrusion, oxygen and water fugacities, and silica activity in the later intrusive, were in the same range as those in the early intrusive. The mineralogical zoning in the intrusives is due to the operation of convection cells during the early parts of their crystallization histories. Shortly after emplacement of a largely liquid magma, salite, apatite, and minor amounts of magnetite and ilmenite started crystallizing along the walls of the magma chamber. These crystals were then concentrated in the lower part of the magma chamber by slow moving convection cells. This resulted in an alkalic magma in the upper part of the chamber, and a crystal mush in the lower part. After convection ceased, crystallization of the feldspars, barkevikite, biotite, most of the magnetite, and nepheline and calcite commenced in the larger intrusive.

Conodonts from the Stonehouse Formation of Arisaig, Nova Scotia, include species reported from the Silurian section of the Karnic Alps by Walliser. In particular, the costeinhornensis zone is represented and the faunal list includes the following: Ligonodina elegans Walliser, Lonchodina detorta Walliser, Lonchodina greilingi Walliser, Lonchodina sp. indet., Ozarkodina typica denckmanni Ziegler, Ozarkodina cf. jaegeri and Trichonodella inconstans Walliser. In addition, two new species of the genus Neoprioniodus are present together with some fish fragments.

The initiation and distribution of certain types of degradational processes together with resultant topographical changes on an ice cored moraine were studied in terms of the variation in micro climatic and glacial surge inputs operating on it. The study was conceived in terms of a process-response model. The study area was located on a large arcuate shaped ice cored end moraine, which rims the terminus of the Donjek Valley Glacier located in the Donjek Valley, St. Elias Mountains, Yukon Territory. The end moraine lies approximately 0.8 to 2.7 Km downvalley from the present position of the glacier and is detached from it. The regional climate of the area was determined from data collected from a nearby government operated meteorological station. Climatic inputs occurring on or near the moraine surface, from June 1 to July 25, 1972, were obtained from two micro meteorological stations located directly on its surface. All data was abstracted and shown on graphs as mean daily values. The number of days that one station exceeded the other either/or on a mean daily basis and over three hour intervals, was also noted over the study period.

Southeast of Bancroft, Ontario, Precambrian metasedimentary and metavolcanic rocks of the amphibolite facies lie tightly folded between a gneiss complex and granitic plutons underlying the Haliburton-Hastings highlands to the north, and the Weslemkoon granitic batholith to the southeast. The metamorphic rocks were subjected to at least three discontinuous phases of deformation, with resultant folds F1, F2 the dominant, and F3. F1 folds, which are only exposed in metasedimentary rocks at a few localities, are small-scale and isoclinal. The preservation within later garnet porphyroblasts of a fine-grained schistosity S1 that is axial-planar to micro F1 folds in relict layering suggests that F1 formed under conditions of relatively low-grade metamorphism. The orientation of S1 before overprinting by later folding and crystal growth is not clear, but in some areas the geometry of low-plunging F2 folds suggests that it was subhorizontal. F2 folds affect both bedding and S1 on all scales, vary in tightness, and are upright to overturned northwest. An axial-surface foliation S2, either a schistosity or gneissic layering, is regionally penetrative and extends into synkinematic or earlier plutons. Some sillimanite crystals are bent by F2 folds, but most lie within S2, and a few are crosscutting; thus high-grade metamorphism preceded, accompanied, and outlasted the folding. Hinge lines of minor F2 folds and axial lineations L 2 and irregular in detail, but commonly plunge at northeast or southwestward along the axial traces of large-scale F2 folds. As demonstrated by rake isogons and moving averages, towards the northern complex of gneiss and plutons L2 progressively changes direction and steepens until, as in the gneiss, it plunges southeast down the dip of S2. To the southeast near the large Weslemkoon pluton, F2 axes and L 2 also plunge steeply down-dip. Flattening of F2 folds, as calculated from systematic changes in thickness of calc-silicate layers in fold profile, varies locally, but in general increases with the axial steepening towards the plutons. Thus it appears that the presence or emplacement of relatively rigid plutons during folding imposed an element of constrictional strain that influenced the orientation and shape of adjacent F2 folds. F3 folds, only locally present, are open, recumbent structures bending S1 and S2 foliations; mineral grains disrupted in the axial regions indicate that folding was virtually post-metamorphic. Narrow mylonite zones occur within the gneiss complex near its southern border. Structures within the mylonites are of similar form and orientation to those associated with F1, F2, and F3. The similarity of the small-scale structures and related fabrics within the gneisses, mylonites, and metasedimentary-metavolcanic group of rocks indicates that the mylonite zones were initiated at an early stage in a common deformational history. K-Ar radiometric ages obtained from minerals forming S2 or L2 fabrics, nepheline from the gneiss complex, biotite and hornblende in the southern metasediments, and biotite from a foliated part of the Weslemkoon pluton, are compatible with a Grenvillian age (about 1000 m.y.) of deformation and metamorphism throughout the area.

Abstract not available.

Abstract not available.

A suite of 13 late Archean subalkaline to alkaline intrusions were studied by major and trace element geochemistry and neodymium, hafnium and lead isotopic methods. The intrusions (2683 - 2678 Ma) are located in the Quetico metasedimentary belt, western Superior Province, and include pyroxene hornblendite, diorite, monzonite, syenite and carbonatite. The samples display arc-like trace element patterns with high Cs, Ba, Sr and light rare earth element abundances and low Zr, Hf, Nb, Ta and Ti. Neodymium and hafnium isotope data reflect derivation from a depleted mantle source with minor contribution from an enriched source. Lead isotope ratios from K-feldspar separates are dominated by a slab fluid or crustal component. Quantitative modeling of trace element and isotope ratios illustrates that a metasomatic event shortly before melting produced the main geochemical signatures, but a contribution from an older crustal source is also required to explain the range in data. Melting models based on rare earth element variations suggest that melting occurred over a range of pressures or took place in the garnet spinel transition zone. The intrusive complexes can be subdivided into two groups on the basis of high field strength element distribution, which appears to reflect mantle heterogeneities resulting from differences in metasomatic processes. The most abundant group exhibits super-chondritic Nb/Ta and excess Nb relative to magmas produced by melting of a fluid metasomatized mantle. These characteristics are in accord with metasomatism by silicic melts that have left rutile in the residue and the metasomatic agent is thought to be a mixture of slab-derived fluids and melts. The trace element chemistry of the remaining intrusions reflects a source affected by fluid metasomatism. Carbonatite constitutes a minor part of the Beaverhouse Lake intrusion. Qualitative major and trace element modeling suggests that the carbonatite formed by carbonate-silicate liquid immiscibility. The carbonatite is characterized by highly depleted hafnium isotopic signatures, which are interpreted to result from a previous episode of carbonate metasomatism. Modeling of Lu-Hf partitioning during silicate-carbonate liquid immiscibility suggests that anomalously high hafnium isotopic ratios should develop with time in the carbonate phase, which has potentially important implications for carbonate metasomatism.