T306 Subduction, Fluids, Accessory Minerals, and Trace Elements: A Celebration of Sorena Sorensen's Career (Posters)

Wednesday, 4 November 2015
9:00 AM - 6:30 PM
Exhibit Hall

SAMARIUM/NEODYMIUM GARNET GEOCHRONOLOGY OF ECLOGITES FROM SYROS, GREECE

Paper number: T306-16
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Samarium/Neodymium (Sm/Nd) garnet geochronology of high pressure, low temperature metamorphic rocks from Syros, Greece provides constraints on timing of peak metamorphism with implications for regional subduction zone processes. Mafic eclogite appears predominantly as boudins in abundant host blueschist in the island’s Cycladic Blueschist Unit (CBU). Partial dissolution of heavily included garnets in eclogite facies samples yields Sm/Nd ratios of 0.9 to 3.9. Sm/Nd geochronology of these samples gives ages of 44.8 ±1.3 Ma (n=3, MSWD: 0.109, Sm/Nd: 3.9), 44.7 ±2.0 Ma (n=3, MSWD: 1.8, Sm/Nd: 1.1) and 48.9 ±3.0 Ma (n=2, Sm/Nd: 0.98).

With an average of ~46 Ma, these ages are younger than the only other published garnet eclogite age from the island, which uses Lutetium/Hafnium (Lu/Hf) garnet geochronology to place peak metamorphism at ~52 Ma (Lagos et al., 2007). The garnet ages from eclogites presented here agree with the 46.49 ±0.53 Ma Sm/Nd garnet age for a blueschist from nearby Sifnos, Greece also in the CBU (Dragovic et al., 2012). Discrepancy between the published Lu/Hf garnet eclogite ages (~52 Ma) and those reported here using Sm/Nd in garnet (~45 Ma) may result from possible zoning of Sm in garnet, such that Sm/Nd ages record the growth of the rim of the garnet rather than the entire garnet. Alternatively, age differences could be related to different tectonic histories for the two sample populations; the older garnet eclogite ages are from the northern mélange portion of the CBU while the younger ages reported here all come from the southern tip of the island (south of Vari) in a non-mélange portion of the CBU. Both interpretations require Syros to have experienced a prolonged period of metamorphism as seen in the portion of the CBU exposed on nearby Sifnos Island (Dragovic et al., 2015). Thermodynamic modeling of these dated eclogite samples will help to resolve the pressure-temperature history of subduction zone metamorphism on Syros.