HR: 0830h
AN: ED41C-1175    [PDF]
TI: The Dutchess County, New York, Barrovian Sequence as a Teaching Tool for Metamorphic Petrology
AU: * Whitney, D L
EM: dwhitney@umn.edu
AF: University of Minnesota, Dept. of Geology and Geophysics, Minneapolis, MN 55455 United States
AU: Peck, W H
EM: wpeck@mail.colgate.edu
AF: Colgate University, Department of Geology, Hamilton, NY 13346 United States
AB: Sequences of regionally metamorphosed shales or mudstones (Barrovian sequences) are a classic teaching tool for demonstrating the effect of temperature and lithostatic pressure on mineral assemblages during progressive metamorphism. One of the most complete Barrovian sequences in the world is in Dutchess County, NY, in which the Paleozoic Taconic event of the Appalachian orogeny buried and heated a Cambro-Ordovician continental margin. In the western part of the sequence, near Poughkeepsie, NY, rocks have a faint metamorphic fabric but preserve many characteristics of the sedimentary protoliths: bedding, sedimentary structures, and detrital minerals. Over a map distance of 40 km, the metamorphic index minerals chlorite, biotite, garnet, staurolite, kyanite, sillimanite (fibrolite), and K-feldspar progressively appear in metapelitic rocks. Outcrop is abundant enough that changes within metamorphic zones can also be observed; for example, the staurolite zone can be tracked from the incipient growth of staurolite from chloritoid to the upper staurolite zone in which chloritoid was no longer stable. The effect of bulk composition can also be observed within the metamorphic zones; e.g., the appearance of chloritoid vs. biotite in different bulk compositions of the garnet zone. Although a database of mineral compositions, metamorphic reactions, P-T conditions, oxygen isotope values, and some geochronology results from metamorphic minerals exists, more work needs to be done integrating structural geology with metamorphic assemblages, and interesting questions remain about the assemblages in mafic and carbonate rocks interleaved with the pelitic rocks. These features make the Dutchess County sequence an excellent site for teaching fundamental concepts of metamorphic petrology.
DE: 3660 Metamorphic petrology
DE: 8102 Continental contractional orogenic belts
DE: 9350 North America
SC: Education and Human Resources [ED]
MN: 2003 Fall Meeting