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

Cisneros, Miguel; Barnes, Jaime D.; Behr, Whitney M.; Kotowski, Alissa J.; Stockli, Daniel F.; Soukis, Konstantinos

Retrograde metamorphic rocks provide key insights into the pressure–temperature (inline-formulaPinline-formulaT) evolution of exhumed material, and resultant inline-formulaPinline-formulaT constraints have direct implications for the mechanical and thermal conditions of subduction interfaces. However, constraining inline-formulaPinline-formulaT conditions of retrograde metamorphic rocks has historically been challenging and has resulted in debate about the conditions experienced by these rocks. In this work, we combine elastic thermobarometry with oxygen isotope thermometry to quantify the inline-formulaPinline-formulaT 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 inline-formula∼1.4–1.7 GPa between 500–550 inline-formulaC, retrograde epidote growth at inline-formula∼1.3–1.5 GPa between 400–500 inline-formulaC, and a second stage of retrograde epidote growth at inline-formula∼1.0 GPa and 400 inline-formulaC. 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 inline-formulaPinline-formulaT 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 inline-formulaPinline-formulaT-deformation conditions of retrograde mineral growth in high-pressure–low-temperature (HP/LT) metamorphic terranes.



Cisneros, Miguel / Barnes, Jaime D. / Behr, Whitney M. / et al: Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece. 2021. Copernicus Publications.


12 Monate:

Grafik öffnen


Rechteinhaber: Miguel Cisneros et al.

Nutzung und Vervielfältigung: