HR: 0800h
AN: V41G-1543    [Abstracts]
TI: Pb Isotopic Compositions of Plagioclase From Fe-Ti Ore Deposits Related to the Saint-Urbain and Havre Saint-Pierre Anorthosites (Grenville Province, Canada)
AU: * Morisset, C
EM: cemorisset@eos.ubc.ca
AF: Pacific Centre for Isotopic and Geochemical Research, Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Scoates, J S
EM: jscoates@eos.ubc.ca
AF: Pacific Centre for Isotopic and Geochemical Research, Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Weis, D
EM: dweis@eos.ubc.ca
AF: Pacific Centre for Isotopic and Geochemical Research, Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: An important characteristic of many Proterozoic anorthosite massifs is the association of anorthosite with accumulations of massive Fe-Ti oxide minerals. The Fe-Ti oxides likely represent a component of the evolved Fe-enriched liquids that are complimentary to the cumulus plagioclase of the anorthosites. An important unresolved question is whether the anorthosites and Fe-Ti oxide ores from the same massif form from common parental magmas. In this study, we have determined the Pb isotopic compositions of leached plagioclase (An_42-49) by MC-ICP-MS of samples from two rutile-bearing hemo-ilmenite deposits in the Grenville Province of eastern Canada: (1) Bignell, Coulomb, General Electric, Séminaire and Furnace deposits from the small (~450 km²) Saint-Urbain anorthosite, and (2) Big Island deposit from the large (~11,000 km²) Havre Saint-Pierre anorthositic suite. For Big Island, the measured ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of leached plagioclase from the deposit and the hosting anorthosite form a tight cluster almost within error (17.006-17.036, 15.434-15.442 and 36.499-36.521), which is consistent with formation from the same parental magma. For Saint-Urbain, the leached plagioclase from the deposits forms two distinct groups. One group (17.131-17.164, 15.448-15.463 and 36.551-36.564) nearly overlaps the field of the enclosing anorthosites (17.021-17.085, 15.437-15.453, 36.479-36.608), while the second group (17.362-17.508, 15.483-15.493 and 36.618-36.740) is distinctly more radiogenic. These results indicate that the Saint-Urbain anorthosites and its associated hemo-ilmenite deposits were not formed directly from the same magmas. Contamination by the exposed country rocks in the area does not explain the observed variation. These two studied massifs from the central and eastern part of the Grenville Province have feldspar Pb isotopic compositions that are distinctly more radiogenic than other Grenvillian anorthosite massif feldspars (e.g. Atikonak, Mealy Mts), which may reflect more upper continental crustal contamination prior to emplacement in these massifs.
DE: 1020 Composition of the continental crust
DE: 1036 Magma chamber processes (3618)
DE: 1040 Radiogenic isotope geochemistry
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005