摘要:

The Labrador Trough is a Proterozoic orogenic belt bordering the eastern margin of the Archean Superior Province. The volcano-sedimentary sequences of the trough were deformed and metamorphosed during the Hudsonian Orogeny (ca. 1800 Ma). The eastern basement, present as domal inliers, was remobilized during this orogeny, whereas the western basement remained unaffected.In this study we present U–Pb ages of the western and eastern basement of the Proterozoic Labrador Trough orogen between Leaf River and Koksoak River and of the northernmost extension of the DePas batholithic complex farther east. From the western basement, the Leaf Bay granodiorite has an age of 2721 ± 3 Ma (zircon). From the gneiss domes of the eastern basement the ages are as follows: Lac Moyer—2883 ± 6 Ma (zircon), 1793 ± 5 Ma (monazite), and 1746 Ma (minimum age, rutile); Lac Boulder—an upper-intercept age of 2868 ± 8 Ma and a lower-intercept age of 1783 ± 11 Ma (zircon–titanite regression) and an age of 1740 ± 5 Ma (rutile); Lac Olmstead Lake—2721 ± 4 Ma (zircon) and 1774 ± 5 Ma (titanite); Leaf Strait—2719 ± 7 Ma (zircon) and 1783 ± 2 Ma (monazite). The DePas Batholith contains four generations of zircon: the minimum ages of the three oldest are 2688, 2779, and 2922 Ma; we also obtained a monazite age of 1808 ± 2 Ma.These results lead us to the following conclusions: (i) The age of the Leaf Bay granodiorite, 2721 ± 3 Ma, is a minimum age of the gneisses of the Minto Subprovince, (ii) The westernmost gneiss domes of the eastern basement (Lac Moyer and Lac Boulder), bounded by two major faults, contain zircon formed during metamorphic events dated at 2868 ± 8 and 2883 ± 6 Ma and may be part of an allochthon. (iii) The Lac Olmstead and Leaf Strait domes contain metamorphic zircon dated at 2719–2721 Ma. (iv) The minimum age of migmatization of the DePas complex is 2688 Ma. (v) The monazite ages date the latest phase of metamorphism in the area, (vi) The titanite ages probably represent post-deformational cooling, whereas the rutile ages could represent late-metamorphic hydrothermal activity, (vi) The available data suggest the presence of continuous Archean basement—remobilized during the Hudsonian Orogeny—between the Labrador Trough and the DePas Batholith, which could represent a collision zone. The final stages of this collision could be slightly older (1808 Ma) than the equivalent activity in the Labrador Trough. These speculations raise the possibility that the evolution of the Labrador Trough is closely related in time and space to events occurring in its "hinterland".

ISSN:0008-4077    

DOI:10.1139/e89-001

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Lateral impressions of ammonites are described from three levels in shales of the Ribbon Creek Member (Fernie Formation) at Adanac Pass, southern Alberta. The occurrence ofKeppleritescf.costidensus(Imlay) andKepplerites subitus(Imlay) with East Pacific forms belonging toXenocephalitesandLilloettiaindicates correlation with the upper Bathonian of the Boreal sequence.

ISSN:0008-4077    

DOI:10.1139/e89-002

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The Archean Rice Lake greenstone belt in southeastern Manitoba is made up of mafic to felsic volcanic rocks and associated intrusive and metasedimentary rocks. The belt is flanked to the north by the Wanipigow River granitic complex and to the south by the Manigotagan gneissic belt. The Ross River quartz diorite pluton is intrusive into the centre of the greenstone belt. U–Pb zircon ages indicate a major volcanic and plutonic event in the area at 2730 Ma. Ages for two volcanic units of the Rice Lake Group are 2731 ± 3 and 2729 ± 3 Ma. The Ross River pluton yields an age of 2728 ± 8 Ma and the Gunnar porphyry gives an age of 2731 ± 13 Ma; both intrude rocks of the Rice Lake Group. Granitic rocks of the Wanipigow River granitic complex give ages of 2731 ± 10 and 2880 ± 9 Ma, while a post-tectonic granite in the Manigotagan gneissic belt has an age of 2663 ± 7 Ma.

ISSN:0008-4077    

DOI:10.1139/e89-003

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The data archive of the Water Survey of Canada, supplemented by data of the British Columbia Hydro and Power Authority, is used to investigate the areal pattern of fluvial sediment yield in British Columbia. The data represent suspended-sediment loads at 63 stations derived from observations within the period 1966–1985. In most of the province there is a single annual peak in sediment transport in spring, corresponding to the dominant snowmelt freshet. However, on the coast winter rainfall induces the sediment peak, and in the Coast and Cascade mountains there is a transitional regime with two peaks. From 65 to 90% of annual sediment yield occurs in the spring three months. Sediment yield per unit area (specific sediment yield) increases with drainage area at all scales from 10 up to 30 000 km2. The pattern persists seasonally throughout the year. This contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from erosion of the land surface. In British Columbia much of the sediment derives from erosion of Quaternary materials along stream banks and valley sides. Rivers draining glaciers and lakes behave distinctively. The observed pattern of sediment yield complicates prediction of drainage-basin sediment yield.

ISSN:0008-4077    

DOI:10.1139/e89-004

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Numerous gold occurrences, including the Lupin mine, exist in Archean iron formation within the Contwoyto Lake – Point Lake region of the Slave Province. Early studies suggested that gold was a syngenetic component of the iron formation; however, the present study suggests that the gold and sulphides are epigenetic.At both the Lupin mine and small-scale gold occurrences gold is associated with quartz veins and concentrations of pyrrhotite or pyrite and of arsenides (arsenopyrite ± loellingite) in iron formation. The quartz veins contain 0.03–1.00 ppm Au and comprise sulphide-poor quartz. A zoned sequence of hydrothermal alteration is present in iron formation adjacent to quartz veins. Immediately adjacent to the veins a calc-silicate lithology (0.03–1.00 ppm Au) is sometimes developed that comprises hedenbergite + quartz ± epidote ± scheelite ± grossular. Next is an arsenide-rich zone (5–30 ppm Au) comprising hornblende + quartz ± hedenbergite ± epidote ± actinolite. The next zone is an iron-sulphide zone (5–30 ppm Au), lacking abundant arsenides but containing pyrrhotite or pyrite and hornblende + quartz ± hedenbergite ± epidote ± actinolite. Farther from the veins, iron formation is unmineralized (≤0.03 ppm Au), lacks sulphides, and comprises grunerite + quartz ± magnetite. In the transition zone, hornblende replaces grunerite, and iron sulphides replace amphiboles and magnetite. The scale of the sequence of zones varies from millimetres to metres about individual veins. In well-mineralized portions of the Lupin mine, where quartz veins are closely spaced, unmineralized iron formation is absent between the veins.The symmetrical zonal pattern in the mineralogy and gold values about the veins at Lupin and at the small-scale occurrences indicates that mineralization at both scales of gold occurrence formed by an epigenetic process. Mineralization occurred by selective sulphidation of iron formation after most of the Archean deformation and was coincident, or nearly coincident, with peak thermal conditions. Gold was probably transported as an aqueous gold–sulphide complex and deposited as a result of sulphidation reactions.

ISSN:0008-4077    

DOI:10.1139/e89-005

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

On the basis of magnetotelluric two-dimensional models along three traverses, the regional electrical structure within the Senegal–Mauritania basin sediments has been studied. Correlation of the computed models with the wells drilled in the region shows that the main gross lithologic units were detected. The models can be generalized into three resistivity layers: (i) post-Turonian; (ii) pre-Senonian; and (iii) basement. In the southern part of the basin, there are relatively conductive formations below the Mesozoic that are interpreted as sediments of the Paleozoic Bove basin sequence. By combining the information that has been provided by the geoelectric cross sections and the lithologic and electric log data, a schematic model for the generalized sedimentary structure of Senegal has been generated. The interpretation that emerges shows that the basin is a westward-sloping, open homocline in which the structure is controlled by north–south-trending basement faulting that portrays a staircase structural style.

ISSN:0008-4077    

DOI:10.1139/e89-006

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Ten samples from a 160 m section through the lower Whittaker Formation yielded Red River Province conodonts as well as a shelly macrofossil assemblage representing the "Arctic Ordovician fauna." Both the microfossils and macrofossils have strong affinities with taxa represented in strata of Cincinnatian age in the western Midcontinent Province of North America.Conodont-based graphic correlation of section W-1 with a Composite Standard Section developed for midcontinental United States indicates that the lower Whittaker Formation on the east flank of the Redstone Arch represents nearly the entire Cincinnatian Series. Trilobites of theCeraurus mackenziensisZone occur in strata correlative with the upper Edenian and those of theWhittakerites planatusZone first appear at or just below the projected base of the Maysvillian Stage. The age of theCeraurinella necraZone is still uncertain but is likely to be early Edenian.Thaerodonta recedens(Sardeson) and other elements of theBighornia–Thaerodontafauna also debut in uppermost Edenian or lowermost Maysvillian strata. The morphology ofSowerbyella redstonensisn.sp. andThaerodonta recedensfrom the lower Whittaker Formation indicates that the common ancestor of earlyThaerodontaspecies may have arisen during latest Edenian time. The first appearance ofThaerodontamay constitute a useful biostratigraphic datum throughout the Red River Province. The stronglyThaerodonta-like species,Sowerbyella redstonensisn.sp., is described from silicified material of mid-Edenian age.

ISSN:0008-4077    

DOI:10.1139/e89-007

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The Main Contact Tuff, in the vicinity of Millenbach mine, Noranda, Quebec, is an extensive, although discontinuous, ore-related volcanic exhalative metalliferous sediment, or "tuffaceous exhalite," of Archean age. It was formed by the variable contribution of two constituents: (1) exhalite (chemical) composed mainly of pyrite, quartz, sphalerite, pyrrhotite, and chalcopyrite and (2) tuff (clastic) composed of quartz, chlorite, and sericite.Tuffaceous exhalites such as the Main Contact Tuff and the similar tetsusekiei of the Japanese Kuroko deposits (Miocene age) indicate a fossil hydrothermal system that may or may not have produced economic concentrations of metallic sulfides. The Main Contact Tuff displays cryptic variations, which provide exploration guides at different scales: (1) the Fe/[Fe + Mg] ratios of chlorite decrease from 0.63 to 0.32 over a distance of 0.3 km approaching ore from the north, and from 0.72 to 0.32 over 1.5 km from the south; (2) the FeO/[FeO + MgO] (sulfide-free) ratios of whole-rock specimens decrease from about 0.8 to 0.3 approaching the ore; (3) ilmenite is replaced in the ore zone by rutile and (or) sphene; and (4) the most manganiferous ilmenite is found close to ore. On the other hand, trace elements of exhalative origin (e.g., Ag, Co) in the Main Contact Tuff appear not to provide useful vectors towards ore. They are concentrated relative to normal pelagic rocks, but their distributions with respect to ore are complicated by multiple input sources and postexhalative redistributions of elements.

ISSN:0008-4077    

DOI:10.1139/e89-008

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Archean metasedimentary rocks in the eastern Point Lake area of the Slave Structural Province preserve a sequence of Archean structures consisting of two generations of folds (F1and F2) with little associated penetrative cleavage and two subsequent generations of cleavage (S3and S4) with little associated folding. Gneissic layering in the high-grade margin of the belt is composed of transposed bedding and the S3cleavage. Folding occurred prior to the thermal peak of metamorphism, whereas the develoment of subsequent cleavages spanned the thermal peak. The regional orientation of the folds and cleavages appears to be independent of the emplacement of granitoid intrusions, although their orientation is modified adjacent to syn- to late tectonic plutons. The supracrustal belt is interpreted as being part of a pre- to early metamorphic, west-verging fold (thrust?) belt whose strain pattern has been modified by post-folding, synmetamorphic shortening, and syn- to post-tectonic plutons. This deformation sequence is similar to those described in other supracrustal belts of the Slave Province and supports the concept that the Slave Province has undergone regional, horizontally directed compression before and during intrusion of large amounts of granitoids.

ISSN:0008-4077    

DOI:10.1139/e89-009

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The Middle Precambrian diabase dikes of the Highland Range in southwestern Montana are moderate- to high-TiO2continental tholeiites and are related along a differentiation trend involving strong iron enrichment. Postmagmatic metamorphism and K, Rb, and Sr metasomatism have altered the chemical composition of the igneous rocks of some of the samples. The metamorphic assemblage in the diabase dikes belongs to the low-pressure calcic plagioclase – actinolite hornfels facies, and we suggest that thermal effects associated with the intrusion of the Boulder Batholith are responsible for the metamorphic overprints in these rocks.Combined chemical data from the diabase dikes in the Highland Range, the Ruby Range, and the Tobacco Root Mountains produce smooth differentiation trends for most major oxides and trace elements, and we conclude that one magma was responsible for the dikes in the three ranges. Discrepancies in Rb–Sr age dates obtained for the dikes in the Tobacco Root Mountains can be explained if a Rb, Sr, and K metasomatic event like the one observed in the Highland Range had occurred in the Tobacco Root Mountains as well.Structurally, the diabase dikes in the Highland Range intruded into both east–west- and northwest-trending fractures at the same time. All dikes dip steeply to the north or northeast and are believed to have intruded into tensionally opened fractures related to the opening of the Belt Basin.

ISSN:0008-4077    

DOI:10.1139/e89-010

出版商:NRC Research Press    

年代:1989

数据来源: NRC