14 Sep 2020

14 Sep 2020

Review status: a revised version of this preprint is currently under review for the journal SE.

Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece

Miguel Cisneros1,2, Jaime D. Barnes1, Whitney M. Behr1,2, Alissa J. Kotowski1,3, Daniel F. Stockli1, and Konstantinos Soukis4 Miguel Cisneros et al.
  • 1Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
  • 2Geological Institute, ETH Zürich, Zürich, Switzerland
  • 3Department of Earth and Planetary Sciences, McGill, Montreal, Canada
  • 4Faculty of Geology and Geoenvironment, NKUA, Athens, Greece

Abstract. We combine elastic thermobarometry with oxygen isotope thermometry to quantify the pressure-temperature (P-T) evolution of retrograde metamorphic rocks of the Cycladic Blueschist Unit (CBU), an exhumed subduction complex exposed on Syros, Greece. We employ quartz-in-garnet and quartz-in-epidote barometry to constrain pressures of garnet and epidote growth near peak subduction conditions and during exhumation, respectively. Oxygen isotope thermometry of quartz and calcite within boudin necks was used to estimate temperatures during exhumation and to refine pressure estimates. Three distinct pressure groups are related to different metamorphic events and fabrics: high-pressure garnet growth at ~1.4–1.7 GPa between 500–1550 °C, retrograde epidote growth at ~1.3–1.5 GPa between 400–500 °C, and a second stage of retrograde epidote growth at ~1.0 GPa and 400 °C. These results are consistent with different stages of deformation inferred from field and microstructural observations, recording prograde subduction to blueschist-eclogite facies and subsequent retrogression under blueschist-greenschist facies conditions. Our new results indicate that the CBU experienced cooling during decompression after reaching maximum high-pressure/low-temperature conditions. These P-T conditions and structural observations are consistent with exhumation and cooling within the subduction channel in proximity to the refrigerating subducting plate, prior to Miocene core-complex formation. This study also illustrates the potential of using elastic thermobarometry in combination with structural and microstructural constraints, to better understand the P-T-deformation conditions of retrograde mineral growth in HP/LT metamorphic terranes.

Miguel Cisneros et al.

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Miguel Cisneros et al.

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Solid Inclusion Calculator Miguel Cisneros and Kenneth Befus

Miguel Cisneros et al.


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Short summary
Constraining the conditions at which rocks form is crucial for understanding geologic processes. For years, the conditions under which rocks from Syros, Greece formed, have remained enigmatic; yet, these rocks are fundamental for understanding processes occurring at the interface between colliding tectonic plates (subduction zones). Here, we constrain conditions under which these rocks formed, and show they were transported to the surface adjacent to the down-going (subducting) tectonic plate.