Seeing through metamorphic overprints in Archean granulites: Combined high-resolution thermometry and phase equilibrium modeling of the Lewisian Complex, Scotland
| العنوان: | Seeing through metamorphic overprints in Archean granulites: Combined high-resolution thermometry and phase equilibrium modeling of the Lewisian Complex, Scotland |
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| المؤلفون: | Phillip Gopon, Jacob B. Forshaw, Jon Wade, David J. Waters, Christine Gopon |
| المصدر: | American Mineralogist. 107:1487-1500 |
| بيانات النشر: | Mineralogical Society of America, 2022. |
| سنة النشر: | 2022 |
| مصطلحات موضوعية: | Geophysics, Geochemistry and Petrology |
| الوصف: | The Lewisian Complex in northwest Scotland presents a record of the transition from the Neo-Archean to the Paleoproterozoic. However, this record is complicated by a long and varied history after peak metamorphism that has erased and/or partially reset much of the early history of the rocks. Such overprinting is a common feature of Archean granulites and poses a substantial problem when trying to understand the tectonic processes that were active prior to the onset of modern plate tectonics. By combining careful petrography with phase diagram modeling and a range of exchange thermometers we obtain the peak and retrograde temperature history of the Lewisian Complex from a single, well-preserved, representative sample of garnet-bearing mafic granulite. We present the application of high-resolution electron probe microanalysis (HR-EPMA) to characterize sub-micrometer orthopyroxene exsolution lamellae in clinopyroxene. We discuss ways to mitigate issues associated with HR-EPMA including surface contamination, beam drift, standards, and the need to correct for secondary fluorescence effects. The resulting compositions from our HR-EPMA analyses provide an independent measure of the retrograde temperature conditions and can also be used to back-calculate the compositions of clinopyroxene in the peak assemblage. We obtain peak metamorphic conditions for the Lewisian of >11 kbar and >1025 °C, and constrain subsequent metamorphic overprints to 850 °C (Grt-Cpx), 590 °C (Opx-Cpx), and 460 °C (Mag-Ilm). These peak and retrograde temperatures span the range of those found in the literature. Whereas recent phase equilibrium studies assume equilibrium among all preserved high-T minerals, this study considers microstructural and mineral-chemical evidence for corona formation that reflects post-peak decompression with partial equilibration at ~850 °C, as recognized in some earlier studies. |
| تدمد: | 1945-3027 0003-004X |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_________::8ff38035320f2905404df552431cbbd7 https://doi.org/10.2138/am-2022-8214ccby |
| حقوق: | OPEN |
| رقم الأكسشن: | edsair.doi...........8ff38035320f2905404df552431cbbd7 |
| قاعدة البيانات: | OpenAIRE |
| تدمد: | 19453027 0003004X |
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