27 Igneous and Metamorphic Geology

Friday, 28 March 2008
1:00 PM - 4:20 PM

REGIONAL METAMORPHIC HISTORY AND EXHUMATION OF THE SOUTHERN CONNECTICUT VALLEY SYNCLINORIUM, SOUTHWESTERN CONNECTICUT

Paper number: 27-5
Program: Technical Sessions
Time: 2:20 PM – 2:40 PM

Authors

Abstract

Geothermobarometry, available 40Ar/39Ar cooling ages, and microstructural analysis, together with one-dimensional thermal modeling offer insight into the complex metamorphic and exhumation history of the southern Connecticut Valley synclinorium (CVS) in southwestern Connecticut. This study focuses on the metamorphic geology of a broad region ranging from Cameron's Line east to the Hartford basin, and from Roxbury south to the Long Island Sound. Field observations and available map data indicate that metamorphic grade increases from kyanite grade in the northwest to sillimanite grade in the southeast; kyanite and sillimanite found together in the same thin section from the southernmost edge of the study area offer insight into the peak metamorphic conditions and rate of exhumation. The metamorphic history of the CVS, however, is complicated by several observable foliations attributed to overprinting orogenic events.

Amphibole and biotite from the southernmost CVS yield 40Ar/39Ar cooling ages that can be correlated with the Alleghenian orogeny. The conventional interpretation of the regional geology, however, attributes the metamorphism in the CVS to the Taconic and Acadian orogenies. Geothermometry on rocks containing kyanite suggests that the southern CVS experienced temperatures in excess of 590 ± 25 °C, and preliminary EDX element maps reveal unzoned garnet profiles. When considered on the scale of this study, these data can offer insight into the extent of the Alleghenian orogeny on the southern CVS.