Paper No. 162-4
Presentation Time: 1:30 PM-5:30 PM
KIMBERLITES FROM THE CENTRAL NEW YORK: MINERALOGY, GEOCHEMISTRY, XENOLITHS AND CONTACT PHENOMENA
LUPULESCU, Marian V., Research and Collections, New York State Museum, Cultural Education Building , 3140, Madison Avenue, Albany, NY 12230, mlupules@mail.nysed.gov, SHAW, George H., Geology Department, Union College, Schenectady, NY 12308, and BAILEY, David G., Hamilton College, 198 College Hill Rd, Clinton, NY 13323

Our study focuses on the mineralogy and geochemistry of the micaceous kimberlites from Central New York, their xenoliths and contact phenomena. The centimeters to meters width dikes intrude the Cambrian dolomites and Devonian shales and limestones, in places showing multiple intrusions and fluidal texture at the contact with the host rocks. Olivine megacrysts, kink banded or rounded phlogopite, pink and yellow garnet with a fibrous amphibole and phlogopite kelyphite rim, spinel, perovskite, green Cr-rich diopside in a matrix of calcite, in places with dendritic texture, serpentine and phlogopite (type II micas) define the porphyry texture of the rocks. The opaque minerals point out the oxidized character of the kimberlite (magnetite partially replaced by hematite), megacrysts (ilmenite), sulfurization assemblages (pyrite, pyrrhotite, millerite), and polysulfide globules (pentlandite, pyrrhotite, chalcopyrite). The electron microprobe data for the pink garnet show a composition between chrome-pyrope and low calcium chrome-pyrope, which characterizes the garnet lherzolites. The data for the yellow garnet reveal a grossular composition. Phlogopite megacrysts, as samples from a metasomatized mantle display chemical differences comparing with the groundmass phlogopite, formed as a groundmass liquidus phase. The low Ca (0.05%) olivine (Fo85) megacrysts are completely or partially replaced by serpentine or calcite and serpentine. The crustal xenoliths are pyroxene gneisses, hornblende-pyroxene syenite with strings perthitic feldspars, grossular (anisotropic) skarns, sandstones and shales. A very narrow, amphibole-rich contact reaction zone rims the pyroxene gneisses. Both, the pyroxene gneisses and hornblende-pyroxene syenite display evidences of feldspar melting and hornblende resorbtion. Sandstones and shales do not show any contact phenomena at microscopic scale. The geological features of the type II kimberlites from the Central New York point out that kimberlite magma moved in pulses and the rapid rise through the crust disaggregated the metasomatized mantle derived xenoliths. Their mineralogical, chemical and petrographical study unable us to reconstruct a stratigraphical column from the upper mantle to the upper crust under the Appalachian Basin in the Lower Cretaceous.

2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 162--Booth# 116
Petrology, Igneous and Experimental (Posters)
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Tuesday, October 29, 2002
 

© Copyright 2002 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.