(ADK) Anorthosite-Charnockite and Metamorphic Suite --
Adirondack Mountains, New York

(ADK) Anorthosite-Charnockite and Metamorphic Suite --
Adirondack Mountains, New York

The Adirondack Mountains of northern New York State are underlain by approximately 20,000 square miles of complexly deformed, high grade metamorphic rocks which are believed to represent a southern outlier of the much larger Grenville Province.The Adirondacks can be divided into the "Lowlands" and the "Highlands" . The Lowlands comprise the northwestern quarter of the belt and are characterized by amphibolite facies metamorphism. The Highlands appear to consist entirely of granulite facies rocks. All rocks in this suite have been collected from the Highlands and predominantly from the southern quarter of the Adirondacks.

This suite of rocks is designed to be representative of the Highlands in general. Therefore it includes both metasedimentary and metaigneous rocks. The latter are very common throughout the Adirondacks and contain the often-discussed anorthosite-charnockite suite of rocks. Almost all rocks in the Adirondack Highlands are strongly foliated. This is the result of intense polyphase deformation that has affected this area.

1980

Western Minerals Inc.

This rock suite was collected from the Adirondack Mountains located in the northeastern part of New York State.

The Adirondack Mountains were formed approximately 1.1- 1.3 billion years ago during the Grenville Orogeny (Precambrian eon, Proterozic era).

Purchased from Western Minerals Inc.

Start here: 
McLelland, J., and Selleck, B.W.,2011, Megacrystic Gore Mountain-type garnets in the Adirondack Highlands; age, origin, and tectonic implications:Geosphere, v.7, no. 5, p.1194-1208, doi: 10.1130/GES00683.1.

• This article describes the formation of the megacrystic garnet amphibolites in the Gore Mountain section of the Adirondack Mountains. The authors conclude that three main factors influenced the garnet development: collapse of the Ottawan orogeny, intrusion of Lyon Mountain Granite, and fluid-related alteration at high temperature.

Additional resources:
McLelland, J.M., Bickford, M.E., Hill, B.M., Clechenko, C.C., Valley, J.W., and Hamilton, M.A., 2004, Direct dating of Adirondack Massif anorthosite by U-Pb SHRIMP analysis of igneous zircon; implications for AMCG complexes: Geological Society of America Bulletin, v.116, no. 11-12, p.1299-1317, doi: 10.1130/B25482.1.

• This article describes techniques used to more accurately date the Adirondack Massif anorthosite.The authors concluded that the massifs constitute a single, composite anorthosite-mangerite-charnockite-granite (AMCG) suite intruded at ca. 1155 Ma. Although the rock suite is considered to be coeval, the authors conclude the rocks are not comagmatic.

McLelland, J., Bickford, M.E., Spear, F., and Storm, L., 2002, Geology and geochronolgy of the eastern Adirondacks in New England Intercollegiate Geological Conference, 94th, New York State Geological Association 74th: guidebook for field trips in New York and Vermont : Lake George, New York

• This field trip guide provides for nine stops in the eastern Adirondacks. It also include some thin sections images and zircon images from sample rocks of the field trip stops.

McLelland, J., Daly, J.S., and McLelland, J.M., 1996, The Grenville orogenic cycle (ca. 1350-1000 Ma); an Adirondack perspective: Tectonophysics, v.265, issue 1-2, p.1-28, doi: 10.1016/S0040-1951(96)00144-8.

• This article provides a detailed geochronological account of the Grenville orogeny (ca. 1350-1000 Ma) with emphasis on the impact it had on the formation of the Adirondack Mountains.

McLelland, J., Lewis, A., and Moore, L., 1994, Composition and petrogenesis of oxide-, apatite-rich gabbronorites associated with Proterozoic anorthosite massifs: examples from the Adirondack Mountains, New York: Contributions to Mineralogy and Petrology, v.116, p.225-238, doi: 10.1007/BF00310702.

• This article investigates the occurence of oxide-, apatite-rich gabbronorites with anorthosite massifs of the Adirondacks. The authors describe a multilple-step process of plagioclase crystal fractionation that ultimately leads to high concentrations of P, Fe, and Ti.

New York State Geological Survey
http://www.nysm.nysed.gov/nysgs/nygeology/mineralogy/adirondacks/index.html

• The NYS Geological Survey is a division of the New York State Museum system. This web page provides some details about the Adirondack Highlands and pictures of various minerals found in this region.

Regan, S.P., Chiarenzelli, J.R., McLelland, J.M., and Cousens, B. L., 2011, Evidence for an enriched asthenospheric source for coronitic metagabbros in the Adirondack Highlands: Geosphere, v.7, issue 3, p. 694-709, doi: 10.1130/GES00629.1.

• This article describes the formation of coronitc metagabbros through tectonic processes involving the asthenosphere. Through geochemical and isotopic analyses, the authors provide a timeline of tectonic and petrologic events that supports an asthenospheric source for coronitic metagabbros.