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Presentation Charline Lormand's viva
- 1. 1 PhD Oral Examination Charline Lormand
- 3. 3 Introduction McCanta et al. (2007) JVGR Microlites and micro-phenocrysts Phenocrysts
- 4. 4 Introduction Cassidy et al. (2018) Nature Com. McCanta et al. (2007) JVGR Microlites and micro-phenocrysts Phenocrysts
- 5. 5 Introduction Phenocrysts Conceptual model of the magmatic system beneath Ngauruhoe based on the textural variations of plagioclase phenocrysts (Coote et al., 2016, Lithos) Ngauruhoe magmatic plumbing system interpreted from phenocryst textures and isotope analyses Shane et al. (2019) CMP
- 6. 1. Develop an accessible and fast automated computing tool for classifying crystals from BSE images for CSD purposes (published in 2018 in Microscopy & Microanalysis) 6 Objectives
- 7. 1. Develop an accessible and fast automated computing tool for classifying crystals from BSE images for CSD purposes (published in 2018 in Microscopy & Microanalysis) 2. Define the origin of microlites and micro-phenocrysts through high resolution imaging (to be submitted in Frontiers in Petrology) 7 Objectives
- 8. 1. Develop an accessible and fast automated computing tool for classifying crystals from BSE images for CSD purposes (published in 2018 in Microscopy & Microanalysis) 2. Define the origin of microlites and micro-phenocrysts through high resolution imaging (under re-review in Contributions to Mineralogy and Petrology) 3. a) Use microlite CSDs to decipher magmatic processes and magma transfer through the volcanic conduit at the onset of eruptions b) Identification of the P-T-X(H2O) conditions during microlite crystallisation to understand the magmatic processes at work during magma ascent (under re-review in Journal of Petrology) 8 Objectives
- 10. 10 BSE image Classic manual outlining Trainable Weka Segmentation Semi-automatic outlining Paper 1:
- 11. 11 4-10 times faster! BSE image Classic manual outlining Trainable Weka Segmentation Semi-automatic outlining Paper 1:
- 12. 12 Paper 1: Similar shape factors and CSD slopes
- 13. 13 Paper 2: Blue and grey fields: H2O-saturated and dry experiments from basaltic to rhyolitic melts of Waters & Lange (2015)
- 14. 14 10-20% of microlites are in disequilibrium with their surrounding melt(s) Paper 2: Blue and grey fields: H2O-saturated and dry experiments from basaltic to rhyolitic melts of Waters & Lange (2015)
- 15. 15 Strontium zoning Resorption & Overgrowth Oscillatory zoning Single comp. jump Sieve textures Fracture Resorption & Overgrowth Aluminium zonation Mg core & Ca rim FractureCa-rich rims 1270 Ion Mobility Spectrometer equipped with a Stacked, Complementary Metal- Oxide Semiconductor Active Pixel Sensor @ IIL, Hokkaido University FE-SEM (JEOL JSM-7000F), @ Isotope Imaging Laboratory, Hokkaido University Paper 2:
- 16. 16 Strontium zoning Resorption & Overgrowth Oscillatory zoning Single comp. jump Sieve textures Fracture Resorption & Overgrowth Aluminium zonation Mg core & Ca rim FractureCa-rich rims 1270 Ion Mobility Spectrometer equipped with a Stacked, Complementary Metal- Oxide Semiconductor Active Pixel Sensor @ IIL, Hokkaido University FE-SEM (JEOL JSM-7000F), @ Isotope Imaging Laboratory, Hokkaido University Antecrystic origin of large microlites and micro-phenocrysts of plagioclase and pyroxene Paper 2:
- 17. 17 Paper 3: 60,000 microlites were outlined using Trainable Weka Segmentation (Lormand et al, 2018)
- 18. 18 Paper 3: 60,000 microlites were outlined using Trainable Weka Segmentation (Lormand et al, 2018)
- 19. 19 Paper 3: t = − 1 slope × G G = 1.8 (±0.6) × 10−11 m s−1 (2σ) Determined for Mangatawai opx (Zellmer et al., 2016, 2018) 60,000 microlites were outlined using Trainable Weka Segmentation (Lormand et al, 2018)
- 20. 20 Paper 3: t = − 1 slope × G G = 1.8 (±0.6) × 10−11 m s−1 (2σ) Determined for Mangatawai opx (Zellmer et al., 2016, 2018) Microlites have crystallised 2 – 4 days before eruption 60,000 microlites were outlined using Trainable Weka Segmentation (Lormand et al, 2018)
- 21. 21 Paper 3: Microlite crystallisation: ~4 km, up to 16.5 km Water-poor magmas Unusually hot magmas
- 22. 22 Paper 3: Microlite crystallisation: ~4 km, up to 16.5 km Water-poor magmas Unusually hot magmas Combining P and t Ascent rate of up to 9 cm s-1 Too slow to feed explosive eruptions even after water exsolution and volume expansion
- 23. 23 Paper 3:
- 24. 24 Key contributions: • Microlite rims are not necessarily in equilibrium with their surrounding melts and may be entrained and recycled upon ascent • No correlation between CSD slopes and eruption style • Style of explosive eruptions fed by water-poor magmas are controlled by shallow processes e.g. conduit geometry • Vertically oriented reservoirs may be more common than typically acknowledged • A new and fast method to classify crystals from BSE images
- 25. 25 THANK YOU! Where to contact me: Charline.Lormand@gmail.com charlinator_as
Editor's Notes
- Good morning and thank you all for being here this morning, physically or via Skype. Three and a half years ago I came to New Zealand to pursue my passion for learning and understanding volcanic processes using petrological and geochemical techniques. This PhD focused on tephras from explosive eruptions of the Tongariro Volcanic Centre, located in the Central North Island of New Zealand, and more specifically to understand the shallow magmatic processes and their timescales using microanalytical instruments.
- Magma is composed of 3 phases: liquid which is the melt, gas which are the volatiles, dissolved and then exsolved, and solid being the crystal. Phenocrysts are large crystals that form early in the system and which record essential information about the deep processes. Micro-phenocrysts and especially microlites form shallower. This CSD which stands for crystal size distributions, clearly shows the two populations of crystals associated with different nucleation and crystallization kinetics. Microlites, as shown on this sketch are commonly associated with decompression-induced degassing, and sometimes with cooling.
- Magma is composed of 3 phases: liquid which is the melt, gas which are the volatiles, dissolved and then exsolved, and solid being the crystal. Phenocrysts are large crystals that form early in the system and which record essential information about the deep processes. Micro-phenocrysts and especially microlites form shallower. This CSD which stands for crystal size distributions, clearly shows the two populations of crystals associated with different nucleation and crystallization kinetics. Microlites, as shown on this sketch are commonly associated with decompression-induced degassing, and sometimes with cooling.
- Magma is composed of 3 phases: liquid which is the melt, gas which are the volatiles, dissolved and then exsolved, and solid being the crystal. Phenocrysts are large crystals that form early in the system and which record essential information about the deep processes. Micro-phenocrysts and especially microlites form shallower. This CSD which stands for crystal size distributions, clearly shows the two populations of crystals associated with different nucleation and crystallization kinetics. Microlites, as shown on this sketch are commonly associated with decompression-induced degassing, and sometimes with cooling.
- At TgVC, several studies have focussed on phenocrysts which provided
- Concaved up CSDs due to nanolites and micro-phenocrysts. No correlation between CSD slopes and eruption style.
- Concaved up CSDs due to nanolites and micro-phenocrysts. No correlation between CSD slopes and eruption style.
- Concaved up CSDs due to nanolites and micro-phenocrysts. No correlation between CSD slopes and eruption style.
- Concaved up CSDs due to nanolites and micro-phenocrysts. No correlation between CSD slopes and eruption style.
- We now know that: Vertically oriented reservoirs, suggested here by the tectonic setting of the area and the polybaric crystallisation of microlites, may be more common that typically acknowledged