Rocky Mountain (56th Annual) and Cordilleran (100th Annual) Joint Meeting (May 3–5, 2004)

Paper No. 12
Presentation Time: 8:00 AM-5:00 PM


HOLLEY, Elizabeth A.1, CHENEY, Jack2 and ROSS, Tim1, (1)Geology, Pomona College, 609 N. College Avenue, Claremont, CA 91711, (2)Geology, Amherst College, Amherst, MA 01002,

The island of Syros is composed of stacked thrust sheets that form the structural mid-level of the Aegean Attic-Cycladic complex. The high-pressure, low-temperature metamorphism in the Cyclades results from the Cenozoic subduction between microplates and the Eurasian continent. Rocks formed in association with this event comprise the bulk of the Syros mafic suite. Their constituent mineral assemblages range from eclogite to epidote-blueschist facies. A second group of greenschist facies rocks also crops out on Syros. These are thought to result from Barrovian overprinting due to regional isothermal decompression at the Oligo-Miocence boundary. In general, high grade eclogite to epidote-blueschist rocks are found in the northern part of the island at the top of the north-dipping sequence. Greenschist rocks typically occur in the south at the base of the sequence. However, rocks of varying eclogitic composition can be found in outcrops throughout Syros. This distribution suggests that the metamorphic conditions to which the rocks responded may be more complex than previously interpreted. In this study, equilibrium parameters are determined for eclogites from six sample locations along the eastern half of Syros. These sites are distributed from the northern to the southern end of the island so that the relationship between metamorphic grade and structural level may be examined. Eclogitic samples of varying compositions were collected during fieldwork conducted through a Keck Geology Consortium project. Thirty of these rocks were analyzed in thin section for modal mineral composition. Mineral chemistry was determined through scanning electron microscopy and energy dispersive spectrometry analyses of equilibrium texture garnet, phengite and omphacite grains in the freshest thin section from each sampling location. From these data, metamorphic conditions are estimated using the thermodynamic program of Krough (1999). Results are compared to sample location to better characterize variation in metamorphic grade across the island. Additionally, garnet zoning is examined to constrain P-T-t paths for the samples.