SM/ND GARNET GEOCHRONOLOGY AND PRESSURE-TEMPERATURE PATHS OF ECLOGITES FROM SYROS, GREECE: IMPLICATIONS FOR SUBDUCTION ZONE PROCESSES AND WATER LOSS FROM THE SUBDUCTING SLAB

Samarium/Neodymium (Sm-Nd) garnet geochronology of eclogites from Syros, Greece provides constraints on timing of peak metamorphism while thermodynamic modeling of the same samples allows a comparison of pressure-temperature (P-T) paths. Sm-Nd geochronology of four eclogite samples from the Katergaki area (southeastern part of the island) give ages of 48.8 ± 3.2 Ma (high ¹⁴⁷Sm/¹⁴⁴Nd = 0.49, n = 6, MSWD = 0.67), 48.1 ± 2.3 Ma (high ¹⁴⁷Sm/¹⁴⁴Nd = 1.22, n = 4, MSWD = 2.4), 44.7 ± 1.0 Ma (high ¹⁴⁷Sm/¹⁴⁴Nd = 3.9, n = 6, MSWD = 1.4), and 43.6 ± 1.6 Ma (high ¹⁴⁷Sm/¹⁴⁴Nd = 1.39, n = 6,MSWD = 2). These garnet growth ages span several million years and are younger than the only other published garnet eclogite ages from the island which use Lutetium/ Hafnium (Lu-Hf) garnet geochronology to place peak metamorphism at ~52 Ma (Lagos et al., 2007). Another eclogite sample from the Kini area (west side of the island) yields a less reliable age of 57.7 ± 6.3 Ma (high ¹⁴⁷Sm/¹⁴⁴Nd = 0.40, n = 10, MSWD = 1.9), significantly older than the other garnets dated in this study, but similar to the Lagos et al., 2007 result. The garnet ages from eclogites show that high pressure metamorphism, and related garnet growth and slab dehydration, on Syros spanned ~9 myr, similar to what has been reported for nearby Sifnos Island (Dragovic et al., 2015). Thermodynamic modeling of three samples reveals similar prograde P-T paths reaching peak pressures of up to 2.4 GPa despite differences in tectonic setting and chemistry between samples. Calculated maximum water loss from mineral breakdown during the span of subduction zone garnet growth varies between samples from 1.1 to 5.1 weight percent but is greatest for the most ultramafic sample due to chlorite stability permitting greater capacity for water to be carried to depth.