期刊
EARTH AND PLANETARY SCIENCE LETTERS
卷 413, 期 -, 页码 111-122出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2014.12.024
关键词
garnet; subduction; dehydration; Sifnos; Sm-Nd
资金
- NSF [EAR-0547999, EAR-1250497, EAR-1250470, EAR-0949390]
- [NSF-0521266]
- Directorate For Geosciences
- Division Of Earth Sciences [1250470, 1258878] Funding Source: National Science Foundation
We use coupled zoned geochronology and thermodynamic modeling of garnet to elucidate the nature and scale of metamorphic dehydration during Eocene subduction of a quartzofeldspathic lithology from Sifnos, Greece. Two large garnet porphyroblasts were microdrilled to sample concentric growth zones, and these were dated using Sm-Nd geochronology. To put results in a geodynamic context and reveal the causes and consequences of garnet growth, we constructed thermodynamic forward models for a series of prescribed pressure-temperature (P-T) paths. Our data reveal three distinct phases of garnet growth: initial growth at 53.4 +/- 2.6 Ma (similar to 0.8 GPa and similar to 300 degrees C), followed by a period of very limited growth until a second phase, at 47.22 +/- 0.36 Ma, and then a major pulse of growth, responsible for the majority of the final garnet volume, at 44.96 +/- 0.53 Ma (2.06-2.19 GPa and 490-550 degrees C). This suggests a >2 order of magnitude acceleration in volumetric growth rate from crystal core to rim, with the final growth pulse occurring rapidly (<0.8 My), during a period of nearly isobaric heating at >75 degrees C/My. This final pulse was accompanied by net bulk rock dehydration of similar to 0.5 wt.%. Rapid heating during early stages of exhumation in the subduction channel, or by sharp thermal gradients related to slab-mantle coupling could be causes for this pulsed metamorphism and dehydration. The garnet data thus record a concentrated pulse of dehydration and heating during the otherwise slow and continuous process of subduction. (C) 2014 Elsevier B.V. All rights reserved.
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