COMPOSITION OF WHITEFACE MOUNTAIN ANORTHOSITES AND ITS BEARING ON ROCK FORMING PROCESSES

Within the High Peaks region in the Adirondack Park in upstate New York is one of the few places on Earth where one can find exposed formations of anorthosite rock, defined as rock with a composition comprised of >90% plagioclase feldspar. One of these locations, Whiteface Mountain, is located in the outskirts of the High Peaks Region in the northern part of the Adirondack park. The Mount Marcy and Whiteface Mountain facies comprise the two main formations of anorthositic rock in the Adirondack region. The Whiteface Mountain facies is Tonian in age but the orogenic event didn’t occur until 20 million years after the emplacement. This was the Rigolet Orogeny, the last orogeny of the Grenville Cycle where Baltica collided with Laurentia. A literature review was conducted on ‘the Problem of the Anorthosites,’ including N.L. Bowen’s landmark 1917 paper of the same name, as well as W.N. Lodochnikow’s 1925 discussion of the aforementioned paper and N. Arndt’s 2013 paper discussing the emplacement of massif anorthosites, among others. The essence of the so called ‘problem of the anorthosites’ is that normal models of crystal fractionation do not account for such a high proportion of plagioclase feldspar found in anorthosites. Our studies led us to Whiteface Mountain where we collected a suite of 12 rock samples in July 2016, along with GPS waypoints indicating where each of the rock samples were collected. We have also acquired three samples of metagabbro from a site close to the main sampling region. Thin sections have been made and petrographic analyses of plagioclase composition have been conducted. Small samples of each rock have been sent out to the Peter Hooper GeoAnalytical Lab at Washington State University for X-ray fluorescence spectroscopic geochemical analysis. The results from this analysis will be interpreted using IgPet software to model crystal fractionation. The final goal of the project is to use these methods to make a determination of whether the anorthosites arose from crystal fractionation of the same parent magma as the metagabbro collected nearby.