摘要:

The Canadian Arctic Islands Wenlock is represented by a diverse assemblage of graptolites from the Cape Phillips Formation. Cyrtograptids are continuously present throughout all but the uppermost Wenlock. Species ofCyrtograptusconstitute the main basis for biostratigraphic zonation, supported to a much lesser degree byMonograptus,Monoclimacis, andPristiograptusthrough most of the series. The uppermost Wenlock is dominated byPristiograptusin association with rareGothograptus.The following biostratigraphic zones and their correlations are proposed: (1)Cyrtograptus centrifugus–Cyrtograptus insectusZone (earliest Wenlock); (2)Cyrtograptusaff.rigidus–Monograptusaff.riccartonensisZone (late early Wenlock); (3)Cyrtograptus perneri–Monograptuscf.munchiZone, in whichCyrtograptus multiramisis a particularly common element (mid-Wenlock age); (4)Cyrtograptus lundgreni–Monograptus testisZone, divisible into a lowerMonograptus testisn.ssp. and an upperMonograptus testis testisSubzone (late Wenlock); and (5)Pristiograptus ludensisZone (latest Wenlock). The second and third zones are also possibly divisible into lower and upper subzones, but with less certainty.The degree of zonal subdivision in the Cape Phillips is lower than in Europe. It was observed locally that a number of the key species showed a high degree of overlap and some inconsistencies in their ranges from section to section.Paleoecologically, a few species, particularlyCyrtograptus preclarus,Cyrtograptuscf.malgusaricus, andPristiograptus meneghini, appear to have preferred basin-margin regions.

ISSN:0008-4077    

DOI:10.1139/e90-001

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Carbonates of the Table Head Group and associated strata were deposited along the western margin of a foreland basin during initial stages of the Taconian Orogeny and record collapse and cannibalization of a long-lived carbonate platform. The stratigraphy of Klappa, Opalinski, and James is here revised to reflect better understanding of lithologic units within this complex tectono-stratigraphic assemblage. The Table Head Group now contains only three formations: the Table Point and Table Cove formations, as originally defined, and the Cape Cormorant Formation, redefined and restricted to western Port au Port Peninsula. Black Cove Formation shales are removed from the Table Head. Distinctive conglomerates once placed in the Cape Cormorant are now recognized as separate units within the overlying flysch and called the Daniel's Harbour Member.The foreland basin developed in three stages: (1) fragmentation, uplift, and erosion of the platform and subsequent deposition of shallow-water limestones (Table Point) on a tectonically unstable shelf; (2) foundering of platform blocks and deposition of deep-water-slope carbonates (Table Cove), basinal black shales (Black Cove), or conglomerates of older shelf carbonates shed from submarine cliffs (Cape Cormorant); and (3) siliciclastic sedimentation interrupted by sediment gravity flows of Table Head clasts shed from submarine escarpments (Daniel's Harbour).

ISSN:0008-4077    

DOI:10.1139/e90-002

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Acton Vale limestone units of probable Early Ordovician age in the external nappe zone of the Appalachian foldbelt in southeastern Quebec host numerous occurrences of vein- and breccia-type copper deposits. Associated with these are two significant occurrences of barite: one at Upton consisting of a stratiform mass of probable economic potential; and the other at Lord Aylmer consisting of thin, tabular, karstic infillings of barite. Studies of the mineral occurrences at Acton Vale, Upton, and Lord Aylmer show that the mineralization is epigenetic and formed largely by open-space filling at shallow depths in parts of the limestones that had undergone ground preparation by brecciation and (or) karsting. Fluid-inclusion, sulphur-isotope, and strontium-isotope analyses show that mineral deposition occurred at temperatures ranging from 110° to 135 °C, that sea water formed the bulk of the mineralizing fluids, and that altered basaltic volcanic rocks associated with the Acton Vale limestones are. the most important source of metals and Ba.The mineral deposits seem to have formed during the evolution of the passive margin of Laurentia. The preferred model for their genesis is one involving deep circulation of water, which, on coming into contact with the volcanic rocks, leached metals and Ba and subsequently deposited them in favourable parts of Acton Vale limestones. Recurrent movements of faults of the Ottawa Graben, which is the failed arm of the Sutton Mountains triple junction, may have been a factor that facilitated deep circulation of fluids. In their present setting, the Acton Vale limestones and the associated volcanic rocks and shales probably represent slivers of the passive margin incorporated into the Cambrian shale – feldspathic sandstone assemblages of the Granby Nappe.

ISSN:0008-4077    

DOI:10.1139/e90-003

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Abundant carbonate is a characteristic feature of most Archean mesothermal Au–Ag vein deposits, but the source of the C is controversial. For Superior Province deposits collectively, the maximum variation of average δ13C values is from −9.0 ± 0.7‰ (1σ,n = 19; Darius) to −0.6 ± 1.6‰ (1σ,n = 7; Cochenour–Willians), and limiting δ13C values are−13.6 and + 1.3‰. At the deposit scale, Fe dolomites in nongraphitic lithologies are for the most part isotopically uniform, where δ13C = −3.4 ± 0.4 (1σ) (Hollinger), −3.2 ± 0.3 (McIntyre), −4.7 ± 1.7 (Dome), −2.8 ± 0.6 (Buffalo Ankerite), −3.6 ± 0.5 (Macassa), −3.2 ± 0.3 (Bousquet), −5.4 ± 0.9 (Lamaque), and −5.3 ± 0.5‰ (Hasaga): the restricted individual ranges of δ13C values imply a corresponding uniformity to the ambient temperature and δ13CΣCof the ore-forming fluids.Within individual deposits, small systematic variations of δ13C carbonate arise from (i) interaction of hydrothermal fluids with carbonaceous rocks, (ii) immiscible separation of CO2 + CH4, or (iii) Rayleigh fractionation effects. Positive shifts in δ13C result from buffering of the fluid to lower Eh by reaction with reduced C, whereas negative shifts reflect partial isotopic equilibration between13C-depleted C (δ13C ≈ −26‰) and aqueous hydrothermal C species. Transient immiscibility of CO2 + CH4acts to precipitate carbonates enriched relative to the main population of Fe dolomites. The δ13C values of carbonates in unmineralized alteration halos (−2.2 ± 1.1‰,n = 42) at the McIntyre deposit are enriched in13C relative to the main gold-bearing vein systems (δ13C = −3.2 ± 0.3‰): the enrichment is attributed to a Rayleigh fractionation accompanying progressive consumption of CO2as hydrothermal fluids infiltrate laterally from veins into wall rocks. Fe dolomite and calcite are variably enriched in18O with respect to equilibrium quartz-carbonate fractionations for ambient temperatures of 270–340 °C. Carbonate δ18O values diminish in an irregular manner with depth, converging on values of ~11‰ (Fe dolomite, 6800 ft (2073 m), McIntyre). Variable degrees of oxygen-isotope disequilibrium represent overprinting of carbonates by post-Archean brines in the Canadian Shield.Synvolcanic vesicle calcite in three groups of metabasalts (δ13C = −4.3 ± 2.1; −2.8 ± 1.5; −2.7 ± 1.3‰) and calcite in two groups of clastic sediments (−6.4 ± 1.8; −4.6 ± 2.5‰) remote from deposits are systematically depleted of13C relative to average Precambrian limestones (~0 ± 1‰), owing to the involvement of CO2derived from13C-depleted organic matter. Consequently, calcite in greenstone belt supracrustal rocks is not restricted to approximately 0‰. The total spread of average δ13CFe dolvalues (−9.0 ± 0.7 to −0.6 ± 0.6‰) in the Au deposits, which goes in hand with a geographical provinciality in O-, Sr-, and Pb-isotope compositions of the ore-forming fluids, is too large to be accounted for by mantle CO2(−6 ± 2‰) or magmatic CO2(−6 ± 2‰) alone but rather is interpreted as reflecting generation of hydrothermal fluids in crustal or subcreted rocks heterogeneous in terms of the distribution of13C-enriched (carbonate) and13C-depleted (reduced C) lithologie

ISSN:0008-4077    

DOI:10.1139/e90-004

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Little Elk Granite (2549 Ma) and granite at Bear Mountain (BMG) (~2.5 Ga) of the Black Hills formed as a result of a collisional event along the eastern margin of the Wyoming Province during the late Archean. Geochemical modelling and Nd isotopic data indicate that the Little Elk Granite was generated by the partial melting of a slightly enriched (ϵNd = −1.07 to −3.69) granodioritic source that had a crustal residence time of at least 190 Ma. The medium-grained to pegmatitic, peraluminous, leucocratic BMG was produced by melting a long-lived (>600 Ma), compositionally variable, enriched (ϵNd = −7.6 to −12.3) crustal source. This produced a volatile-rich, rare-earth-element-poor magma that experienced crystal–melt–volatile fractionation, which resulted in a lithologically complex granite.The production of volatile-rich granites, such as the BMG and the younger Harney Peak Granite (1715 Ma), is a function of the depositional and post-depositional tectonic environment of the sedimentary source rock. These environments control protolith composition and the occurrence of dehydration and melting reactions that are necessary for the generation of these volatile-rich leucocratic granites. These types of granites are commonly related to former continental–continental accretionary boundaries, and therefore their occurrence may be used as signatures of ancient continental suture zones.

ISSN:0008-4077    

DOI:10.1139/e90-005

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Mont Albert mafic–ultramafic complex of central Gaspé, Quebec, is generally regarded as a partial ophiolite with an underlying metamorphic sole. The metamorphic rocks include a number of mineralogical and textural varieties of amphibolite, including some migmatite, as well as minor metasedimentary and quartzo-feldspathic gneisses. The most intriguing rocks in the complex are mafic to ultramafic garnet- and clinopyroxene-bearing amphibolites that are restricted to the vicinity of the peridotite contact. These rocks have unusual Fe-rich, Si-poor bulk compositions and may represent tholeiites chemically modified by interaction with fluid or melt before or during metamorphism. These amphibolites are not retrograde eclogites, since andesine was present throughout the metamorphic history, and the clinopyroxene is not omphacitic. Coexisting mineral compositions and temperature estimates overlap for core, rim, and matrix grains of all the major phases in the garnet–clinopyroxene amphibolites, implying equilibration in the range 750–800 °C at 8–9 kbar (1 kbar = 100 MPa). Garnet amphibolites lacking clinopyroxene yielded somewhat lowerP–Testimates of 600–700 °C and 6–7 kbar. Owing to complex field relationships, it is not clear whether or not theseP–Tconditions resulted from evolution along a singleP–T–tpath.

ISSN:0008-4077    

DOI:10.1139/e90-006

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A tea-coloured cloudiness in groundmass feldspars characterizes dykes of two Early Proterozoic swarms (2.45 Ga Matachewan; 2.04 Ga Kapuskasing) that intrude amphibolite to granulite host rocks within the Kapuskasing Structural Zone (KSZ) of northern Ontario. Outside the KSZ the dykes occur in lower-grade terranes and contain unclouded feldspars. Matachewan dykes within the KSZ are also fresh, contain an aluminous, blue–green amphibole, have fewer plagioclase phenocrysts, and on average are thinner compared with their counterparts outside, which are more hydrously altered, contain a green, fibrous amphibole, and are locally abundant in felspar phenocrysts.Within the Matachewan swarm, magnetic polarity domains — areas of dominantly normal or reversed magnetization — have been identified; the boundaries of these domains correspond closely to major faults. Two of these faults form the boundaries of the KSZ and separate normal dykes within from dominantly reversed ones outside.The foregoing petrological and paleomagnetic observations are related to differential vertical crustal movements that have raised younger, normal-polarity Matachewan dykes (as exemplified by those within the KSZ) from a deeper crustal level and juxtaposed them against older, reversely magnetized dykes that were intruded at shallower crustal levels.Paleomagnetic baked-contact tests on Kapuskasing dykes suggest that they were intruded both before and after the main period of crustal uplift and tilting along the KSZ and that dykes within 4 km of the southeastern boundary fault were raised from depths where temperatures exceeded 580 °C, the Curie-point isotherm for magnetite.

ISSN:0008-4077    

DOI:10.1139/e90-007

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A seismic-reflection survey was carried out on Vancouver Island as part of Lithoprobe – Phase I to study the crustal structure and tectonics of this convergent margin. Four seismic profiles, which provided structural and velocity information using standard common-depth-point stacking, were shot. The lines were crooked; hence, this approach does not give one full confidence in the results obtained. However, because of the crookedness of the lines, the reflection points were located in three-dimensional space; therefore, it was possible to obtain the three-dimensional structure of the subsurface.Since the traveltime is a nonlinear function of model parameters, an iterative, damped least-squares technique is used to obtain three-dimensional structure and velocity with gradients. The ray tracing is performed for each shot–receiver pair by solving a system of nonlinear equations. In constant-velocity media the raypath is a straight line, whereas in media with velocity varying linearly with depth the raypath follows the arc of a circle. The interfaces are defined by polynomial surfaces where the raypaths satisfy Snell's law.The method was tested for a synthetic model: it was fast and effective. Then the method was applied to a small portion of line 1 to obtain velocity gradients and three-dimensional structures of the décollement and subduction zones. For reflector C on line 1 at an approximate depth of 15 km the velocity at the top of the horizon is found to be 6.8 km/s, with a gradient of 0.034 km/s per km. The dip and strike are 3 °and N18°E, respectively. For reflector E on line 1 at an approximate depth of 28 km the velocity at the top of the horizon is found to be 7.8 km/s. The dip and strike are 8.9 °and N65°E, respectively. To obtain more precise results, efforts should be made to record at wider angles of incidence.

ISSN:0008-4077    

DOI:10.1139/e90-008

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

U–Pb dating of zircon from the Guichon Creek batholith indicates an emplacement age of 210 ± 3 Ma. Comparison with previously published K–Ar (211–188 Ma) and Rb–Sr (205 and 196 Ma) dates reveals that intrusion, mineralization, cooling, and uplift of the batholith took some 20 Ma, spanning the Triassic–Jurassic boundary on the Decade of North American Geology (DNAG) time scale.The Mount Martley pluton and Tiffin Creek stock yield Late Jurassic dates of 155 ± 2 Ma (U–Pb, zircon) and 152 ± 5 Ma (K–Ar, hornblende), respectively, and provide a reliable minimum age (Kimmeridgian) for penetrative deformation in the Cache Creek terrane. K–Ar whole-rock dates from Cache Creek terrane and Ashcroft Formation argillites range from Early Permian (266 ± 8 Ma) and Early Jurassic (194 ± 6 Ma) to Late Jurassic, Kimmeridgian (154 ± 5 Ma). We interpret the younger dates as recording Middle–Late Jurassic tectonism and the older ones as possible relics from earlier deformation episodes.An Early Cretaceous K–Ar date (129 ± 5 Ma) for a lamprophyre dike that cuts the Nicola Group suggests that the Early Cretaceous magmatic arc of the Coast Plutonic Complex had an eastern alkalic fringe in the Intermontane Belt.

ISSN:0008-4077    

DOI:10.1139/e90-009

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Detailed paleomagnetic investigations have been completed on unconsolidated sediments from Duck Hawk Bluffs on Banks Island, in the Canadian Arctic Archipelago, that record some of the oldest late Cenozoic glacial and nonglacial events in Canada. The preglacial Worth Point Formation, the overlying Duck Hawk Bluffs Formation, including marine and glacial deposits laid down during the Banks Glaciation, and the lower part of the interglacial Morgan Bluffs Formation have magnetically reversed directions and therefore are of Matuyama age (>790 ka). Upper Morgan Bluffs Formation organic beds and deposits of the younger Thomsen Glaciation, Cape Collinson Interglaciation, and Amundsen Glaciation are normally magnetized and therefore of Brunhes age (<790 ka). The Brunhes–Matuyama boundary is recorded in the upper portion of the Morgan Bluffs Formation. Its precise position within the interglacial sequence can be identified, since the sediments document the gradual change from reversely inclined directions to normally inclined ones. These results confirm that the preglacial Worth Point Formation is at least Early Pleistocene in age and that the Banks Glaciation (the oldest and strongest continental glaciation recorded in the western Arctic) and a good part of the Morgan Bluffs Formation are of Early Pleistocene age. The study also documents a rare site in Canada where terrestrial sediments record the Brunhes–Matuyama transition and in doing so permits a precise correlation of part of the Banks Island stratigraphy with other key late Tertiary and Early to Middle Pleistocene arctic terrestrial and marine sequences.

ISSN:0008-4077    

DOI:10.1139/e90-010

出版商:NRC Research Press    

年代:1990

数据来源: NRC