Evaluation of Nd isotope data for the Grenville Province of the Laurentian shield using a geographic information system

Abstract

The Grenville Province of eastern North America contains a record of continental growth on the southeast margin of Laurentia through much of the Proterozoic Eon, and this growth history can be charted using Nd model age mapping. This paper describes the first use of a geographic information system (GIS) to evaluate such data. The Grenville Province of Ontario and western Quebec, Canada, was chosen for study because there is a lack of agreement on the location of major geological boundaries, whereas the high density of Nd isotope sampling allows precise solutions to be proposed. Two different contouring algorithms, triangulated irregular networks (TIN) and inverse distance weighting (IDW), were first evaluated to select the best geospatial analysis method and parameters for visualizing and evaluating Nd model age distributions. The method chosen (IDW at a power of 6), was then used to test the location of two major boundaries that separate rocks of different crustal formation age, the Grenville-age Allochthon Boundary thrust and the pre-Grenvillian Archean-Proterozoic boundary. GIS analysis was initially performed using published data, after which further sampling was performed to improve coverage of problem areas. The GIS analysis was then repeated, incorporating Nd data for over 80 new localities. The result is a more reliable and accurate map of terrane boundaries in the southwest Grenville Province, which is a critical step in reconstructing the Proterozoic evolution of the southeast margin of Laurentia.