CGRG Bibliography of Canadian Geomorphology
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Author : Doornbos, C.; Heaman, L.; Doupé, J.; England, J.; and Coulthard, R.
Date : 2005.
Title : Provenance of glacial erratics: integration of petrology, geochemistry and in situ u-pb geochronology to constrain glacial flow direction.
Publication : 35th Annual International Arctic Workshop. March 9-12, 2005. Timms Centre for the Arts, University of Alberta, Edmonton, Alberta, Canada.
Issue :
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Abstract
Local glacial flow direction can be determined using many techniques available today. However, regional glacial flow direction is difficult to determine, as there has been a complicated history of glacial movement from one major glacial event to another. Erratics composed of crystalline rocks, apparently derived from the Canadian Sheild, were collected from Prince Patrick Island, Melville Island, N.W.T., and Meighen Island, Nunavut. These regional erratics are identified using petrology, geochemistry and in situ geochronology then grouped based on these constraints. The in situ U-Pb geochronology approach is a new method of dating individual mineral grains (in this case zircon) within a thin section using Laser Ablation ICP-MS. This technique allows for rapid dating of smaller samples and is ideal for evaluating the age provenance of a large erratic population. The purpose of this study is to fingerprint the source of these erratics from the Canadian Shield and to constrain regional glacial flow direction. Twenty-seven samples were collected for this project (17 granites, 7 metasediments, 2 mafics and 1 carbonatite). The major focus of this study has been evaluating the provenance of the granite samples based on petrology, geochemistry and geochronology. Petrologically, these samples are dominated by undeformed monzo- to syeno-granites, with several sample displaying a strong deformational fabric. Based on major and trace element contents the granites can be broadly subdivided into two groups based on their alkalinity, specifically their potassium content: 1) a high K2O group (K2O>4.5 wt%) and 2) a low K2O group (K2O< 3.5 wt%). The in situ U-Pb ages obtained for zircon from 6 granite samples indicates at least four ages of granite erratics are present: 1) 1.8-1.9 Ga, 2) 1.9-2.0 Ga, 3) 2.4-2.5 Ga and 4) 2.5-2.6 Ga. These are the best constraints on the provenance of the granite samples and narrow the possible source regions to: 1) the Wopmay or Trans Hudson Orogen, 2) the Taltson-Thelon Orogen, 3) Queen Maud Block, 4) Churchill Province and 5) Slave Craton. The most compelling constraint on regional ice flow direction is the 1.9-2.0 Ga granite erratics, which can only be derived from the 2.02-1.91 Ga Taltson-Thelon orogen; a narrow terrane (~50 km wide) due south of the sample area, Prince Patrick and Melville Islands.
Bibliography of Canadian Geomorphology