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R A Klassen - One of the best experts on this subject based on the ideXlab platform.
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the application of Glacial dispersal models to the interpretation of till geochemistry in labrador canada
Journal of Geochemical Exploration, 1999Co-Authors: R A KlassenAbstract:Abstract In western Labrador, Canada, bedrock composition and Glacial history are both reflected in till geochemistry. There, compositional contrasts between igneous and metamorphic bedrock of the Canadian Shield and comparatively unmetamorphosed bedrock of the Labrador Trough allow regional-scale (100s of km) definition of Glacial dispersal trends through lithological and geochemical analyses. Compared to till derived from shield terrane, Labrador Trough till is depleted in chromium, but enriched in zinc, iron, and manganese. Further, the study area is situated near one or more dispersal centers of the Laurentide Ice Sheet and has been subjected to a complex sequence of ice flow, defined by striations and indicator erratic distributions. Three Glacial events serve as the principal controls on drift composition, although their relative significance varies. Compositional profiles along the axis of two Glacial dispersal trends show systematic changes in indicator erratic concentrations with distance along the path of ice flow. In the profile having one prominent Glacial Transport direction, indicator concentrations decrease exponentially with increasing distance of Glacial Transport. From dispersal models, Renewal Distances representing the compositional `half-life' tend to increase with decrease in grain size, i.e. 15 to 25 km for pebbles, and 30 to 40 km, or more, in silt- and finer-sized fractions. The differences between geochemical and lithological profiles reflect differences in: (1) the intensity or duration of subGlacial process affecting the milling of indicator detritus to finer fractions; and (2) the physical and chemical properties of the rocks and minerals hosting the trace metals. Where regional Glacial dispersal trains extend across contrasting geological terranes, indicator properties can be used to resolve till composition into `local' and `Transported' components, providing a better approximation of bedrock composition for mineral exploration. The compositional expression of bedrock can be masked by Transported overburden, with the extent of masking dependent on the trace metal examined. Linear relations between metals (Cr, Zn) and lithophile elements (e.g. K, Mg) indicate that Mg-bearing minerals, likely phyllosilicates, have a strong mineralogical control on till geochemistry, and metal : lithophile element ratios can be used to distinguish bedrock provenance in Glacially Transported materials of western Labrador.
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Glacial history and ice flow dynamics applied to drift prospecting and geochemical exploration
1997Co-Authors: R A KlassenAbstract:Mineral exploration by drift prospecting has long relied on Glacial dispersal models to trace indicator erratics in Glacial deposits and locate their bedrock source. In the past decade, advances in the fields of glaciology and Glacial sedimentology have lead to more sophisticated interpretations of the Quaternary geological record in terms of Glacial process, Glacial sediment provenance, and Glacial history. At the same time, models of the Laurentide Ice Sheet, and its adjacent glacier complexes, have included geological and physical properties of the ice bed, thereby providing more accurate portrayals of spatial and temporal variations in regional ice flow dynamics. Those models show that ice divides were long-standing, dynamic features of the ice sheet, affecting drift composition over large areas of glaciated terrain, and have indicated that ice streams served as important agents of erosion, Transport, and deposition. Their accuracy has been refined by the empirical evidence of drift composition and ice flow history resulting from ongoing regional surveys of drift composition. Together, the empirical and theoretical models provide a regional framework for developing mineral exploration strategies in terms of Glacial process and its effects on drift composition. For example, an exponential decrease in indicator concentrations with distance of Glacial Transport reflects Glacial Transport and abrasion as part of the basal debris load, whereas linear to no decrease reflects enGlacial Transport with minimal to no deposition during Transport. Linear profiles may be characteristic of ice streams. The linkages among distance and direction of Glacial Transport, Glacial history, and ice sheet dynamics have thus enhanced the value of Glacial dispersal models as predictive tools for exploration.
Martin Roy - One of the best experts on this subject based on the ideXlab platform.
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ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec
Quaternary Science Reviews, 1999Co-Authors: Jean J Veillette, Arthur S Dyke, Martin RoyAbstract:Abstract Outcrops bearing stained, striated facets indicative of north–northeastward moving ice, truncated by unstained, striated facets indicative of various younger flows occur in the Caniapiscau area of north–central Quebec. This is the first report of differential staining of striated facets in the region. We propose that the staining occurred in an ice-free interval of probable interGlacial age. This early ice flow probably occurred during ice retreat toward the Quebec highlands. Ice flow and Glacial Transport data from the southern Hudson Bay and James Bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an Early Wisconsinan glacier in the Quebec highlands. The northern part of this flow was diverted northwestward through Hudson Bay, and the southern part southwestward across James Bay, following a progressive counterclockwise rotation of flow. A zone of intersection (ZI) of two major glacier bedform systems, often referred to as the horseshoe-shaped Labrador Ice Divide, represents the head of a large northward convergent ice-flow system that extended to Ungava Bay and beyond. The Ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of Caniaspiscau reservoir. We propose that this capture event correlates with the Gold Cove Advance in Ungava Bay and on Baffin Island at about 9900 14C yr BP. It is the largest advance of Quebec-Labrador ice yet proposed for the region. This correlation is based on the relative ice-flow chronology, accommodation of Glacial lakes Naskaupi and McLean in the deglaciation sequence, the constraints placed on Last Glacial Maximum (LGM) ice configuration by the postGlacial uplift pattern and events in the deep-sea record. Therefore, the Ungava ice-flow pattern is not a relict pre-Wisconsinan Glacial landscape as recently proposed.
Hannu Peltoniemi - One of the best experts on this subject based on the ideXlab platform.
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till lithology and Glacial Transport in kuhmo eastern finland
Boreas, 2008Co-Authors: Hannu PeltoniemiAbstract:Till lithology and Transport distance were studied along five transects running in the direction of ice flow and intersecting the N-S-oriented Kuhmo Greenstone Belt, which is some 5 km in width. A total of 531 stone counts were performed on three fractions (> 20 cm, 6–20 cm and 2–6 cm) in 162 pits dug with a mechanical excavator. An experimental model is developed for predicting the Transport distances of clasts in basal tills. It shows the traditional method of expressing Transport in terms of half-distance (i.e. the distance at which the proportion of a given rock type in the till has been halved from what it was at the distal contact of a given rock type in the bedrock) to be dependent upon the width of the source unit in the bedrock, varying in the present case from 0 km to 16 km as the width of the source belt increases from 0 km to infinity. The Kuhmo Greenstone Belt being 5 km broad, the mean half-distance for the Transport of stones and boulders in the till is 2 km, the boulders having been moved somewhat shorter distances and the pebbles longer distances. It is recommended that Transport distances for till material should be expressed in terms of the renewal distance (i.e. the distance over which the proportion of a new rock type increases from 0% to 50%). In the Kuhmo area this distance is 16 km.
S J Pehrsson - One of the best experts on this subject based on the ideXlab platform.
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till geochemistry in west central manitoba interpretation of provenance and mineralization based on Glacial history and multivariate data analysis
Economic Geology, 2016Co-Authors: I Mcmartin, L A Dredge, Eric C Grunsky, S J PehrssonAbstract:Till geochemical datasets from archived samples in west-central Manitoba are interpreted using multivariate data analytical techniques such as principal component analysis and pathfinder element index methods, combined with a spatial representation of the data in a geographic information system (GIS). Results show that carbonate till derived from Hudson Bay, as expressed by the (Ca + Mg)/Na ratio, is found predominantly east of Leaf Rapids and extends south into the Northeastern Kisseynew Domain. A 30- to 70-km-wide zone is documented beyond the limit of dissolvable carbonate dispersal that contains till of Labradorean provenance with low Ca-Mg-Mn-Te concentrations, noncalcareous till of Keewatin provenance, and silty calcareous till at depth. The variation in till provenance, together with the predominance of southwesterly ice-flow indicators, suggests that carbonate dispersal occurred prior to deglaciation, and that surface tills in the zone of confluence between Labradorean and Keewatin ice are likely the result of recycling of calcareous tills and/or carbonate-leached sandy tills, mainly by Keewatin ice. The newly defined limits of carbonate and Ca-rich till, typically used to assess provenance and Glacial Transport, provide a new framework for evaluating the significance of till geochemical patterns when drift prospecting over the Trans-Hudson orogen. Several regional- to local-scale dispersal trains from geochemically distinct bedrock sources are discussed in terms of elemental association, Glacial Transport characteristics, and potential bedrock sources. The multivariate statistical approach combined with GIS mapping also highlights new areas with small multi- or single-element enrichments that may be of further interest for volcanogenic massive sulfide exploration or for potentially more detailed drift sampling.
Jean J Veillette - One of the best experts on this subject based on the ideXlab platform.
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ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec
Quaternary Science Reviews, 1999Co-Authors: Jean J Veillette, Arthur S Dyke, Martin RoyAbstract:Abstract Outcrops bearing stained, striated facets indicative of north–northeastward moving ice, truncated by unstained, striated facets indicative of various younger flows occur in the Caniapiscau area of north–central Quebec. This is the first report of differential staining of striated facets in the region. We propose that the staining occurred in an ice-free interval of probable interGlacial age. This early ice flow probably occurred during ice retreat toward the Quebec highlands. Ice flow and Glacial Transport data from the southern Hudson Bay and James Bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an Early Wisconsinan glacier in the Quebec highlands. The northern part of this flow was diverted northwestward through Hudson Bay, and the southern part southwestward across James Bay, following a progressive counterclockwise rotation of flow. A zone of intersection (ZI) of two major glacier bedform systems, often referred to as the horseshoe-shaped Labrador Ice Divide, represents the head of a large northward convergent ice-flow system that extended to Ungava Bay and beyond. The Ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of Caniaspiscau reservoir. We propose that this capture event correlates with the Gold Cove Advance in Ungava Bay and on Baffin Island at about 9900 14C yr BP. It is the largest advance of Quebec-Labrador ice yet proposed for the region. This correlation is based on the relative ice-flow chronology, accommodation of Glacial lakes Naskaupi and McLean in the deglaciation sequence, the constraints placed on Last Glacial Maximum (LGM) ice configuration by the postGlacial uplift pattern and events in the deep-sea record. Therefore, the Ungava ice-flow pattern is not a relict pre-Wisconsinan Glacial landscape as recently proposed.