Pressure, Temperature, and Structural Evolution of the Orfordville Belt, West-Central New Hampshire |
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| Authors: | SPEAR FRANK S; RUMBLE DOUGLAS III |
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| Institution: | 1Department of Geology, Rensselaer Polytechnic Institute, Troy New York 12181
2Geophysical Laboratory, Carnegie Institution of Washington, 2801 Upton Street, N.W. Washington, D.C. 20008 |
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| Abstract: | Metamorphic P-T paths have been derived for staurolite-kyanitegrade and garnet grade rocks from the Orfordville Belt, west-centralNew Hampshire. P-T paths calculated from garnet zoning are consistentwith parageneses observed in amphibolites as determined froma petrogenetic grid derived for amphibolites. The P-T pathsfrom the staurolite-kyanite zone show a pressure maximum at6.5 to 7.5 kb and {small tilde} 500?C followed by heating anddecompression to approximately 5 kb, 580?C, and a final phaseof near isobaric cooling. The path from the garnet zone is similar,but does not show the final phase of isobaric cooling. Both nappe-stage and dome-stage folds are observed in the OrfordvilleBelt. Comparison of mesoscale structures with mineral growthindicates that the nappe stage deformation occurred near orbefore the pressure maximum and dome stage deformation tookplace along the decompression-heating path. The last phase ofnear isobaric cooling may have resulted from rapid verticalreadjustment of the Orfordville Belt. |
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