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.

中文翻译：

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从弹性热压法到挖掘希腊锡罗斯高压变质岩的见解

摘要。我们将弹性热压法与氧同位素测温法相结合，以量化基克拉迪岩单元（CBU）逆行变质岩的压力-温度（PT）演化，该基岩是暴露于希腊锡罗斯（Syros）的发掘俯冲复合体。我们采用石榴石石榴石法和榴莲石英石气压计分别限制俯冲条件和发掘期间石榴石和榴石的生长压力。boudin颈中的石英和方解石的氧同位素测温法可用于估算发掘期间的温度并完善压力估算值。三种不同的压力组与不同的变质事件和结构有关：500- 1550°C时高压石榴石生长在〜1.4–1.7 GPa，400–500°C时逆向枝晶生长在〜1.3–1.5 GPa，第二种逆向史密斯生长的大约1个阶段。0 GPa和400°C。这些结果与从野外观察和微观结构观察推断出的变形的不同阶段相一致，记录了俯冲俯冲到蓝片岩-榴辉岩相以及随后在蓝片岩-绿片岩相条件下的倒退。我们的新结果表明，CBU在达到最大高压/低温条件后，在减压期间经历了冷却。这些PT条件和结构观察结果与中新世岩心复合体形成之前，在靠近俯冲板的俯冲通道内的发掘和冷却相一致。这项研究还说明了将弹性热压法与结构和微结构约束结合使用的潜力，