Eclogite resembling metamorphic disequilibrium assemblage formed through fluid-induced metasomatic reactions
Sanghoon Kwon1, Vinod O Samuel2, Yungoo Song1
1Department of Earth System Sciences, Yonsei University, Seoul, 03722, Republic of Korea.
Scientific Reports
|November 17, 2020
Summary
Disequilibrium garnet-omphacite assemblages in mafic rocks can form via fluid-induced reactions, not just deep-earth eclogite processes. Textural equilibrium is key to identifying true eclogite facies rocks.
Area of Science:
- Geology
- Metamorphic Petrology
- Geochemistry
Background:
- Eclogites, characterized by omphacite and garnet, are typically formed at great lithospheric depths.
- Understanding the conditions and processes of eclogite formation is crucial for deciphering Earth's deep crustal evolution.
Purpose of the Study:
- To investigate a unique natural occurrence of an eclogite-like assemblage formed under disequilibrium conditions.
- To elucidate the role of fluid-induced metasomatic reactions in generating such assemblages.
- To reassess the criteria for defining eclogite facies.
Main Methods:
- Petrographic analysis of mafic rocks with garnet-omphacite assemblages.
- Microstructural and mineralogical investigation of fluid-induced reactions.
- Thermodynamic analysis of metamorphic conditions (temperature and pressure).
Main Results:
- A garnet-amphibolite facies metamorphism occurred at ~500-700 °C and 0.8-1 GPa.
- Carbon dioxide (CO2) fluid-induced fracturing and dissolution-reprecipitation reactions took place at ~700 °C and 1 GPa.
- The formation of omphacite-albite assemblages replacing earlier symplectites indicates fluid-induced disequilibrium reactions.
Conclusions:
- Disequilibrium garnet-omphacite assemblages can originate from crustal reworking processes below granulite facies conditions.
- Textural equilibrium is a critical factor in the accurate classification of eclogite facies rocks.
- Fluid metasomatism plays a significant role in generating complex mineral assemblages previously attributed solely to high-pressure, deep-seated processes.
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