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(2020) Pulses of Aphyric Andesite Dykes Remobilising Micrometre-Sized Crystal Cargo at Tongariro, NZ

Lormand C, Zellmer GF, Sakamoto N, Kilgour G, Palmer AS, Yurimoto H, Nemeth K, Mead S, Ubide T, Iizuka Y & Moebis A


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05d: Room 2, Friday 26th June 06:03 - 06:06

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Lucy McGee on Wednesday 24th June 10:28
Really nice talk Charline! I just wondered what makes you say that the microphenocrysts are in fact antecrysts? See you at the Q&A :) Lucy

Submitted by Charline Lormand on Thursday 25th June 11:39
Thank you so much for listening to my talk Lucy! Unfortunately I didn't have time to elaborate more on the microphenocrysts but I will during my iPoster at the JpGU-AGU meeting next month (in case you are planning to attend). The argument of micro-antecrysts is based on both textural and chemical evidence. Texturally, several complex patterns (sometimes cryptic in BSE image) and zonations were observed in both plagioclase and pyroxene microphenocrysts, even within the same tephra unit. These include resorption and overgrowth, oscillatory zoning, sector zoning, sieve textures and fracturing events followed by overgrowth. Some of these textures were also described in previous studies for the phenocrystic cargos of TgVC, also attributed to an antecrystic origin. Chemically, the microphenocrysts of plagioclase and pyroxene have a large range of An contents and Mg#, and 10-40% of mineral-liquid pairs are in disequilibrium implying that the crystals cargo originated from different magma batches. This is why, we attributed the origin of the microphenocrysts to be antecrystic. I am happy to discuss more about it during the Q&A or via email :)

Submitted by Julie Roberge on Thursday 25th June 14:27
Hola Charline, I really enjoyed your talk, very interesting work you did. I have a little question. I did not get how you went from 0.4 wt% H2O at 5500 bars (16.5 km) in your results to 4 km depth in the cartoon. Looking forward to talk to you later today! Julie
Hola Julie! Thanks for watching my presentation and for your question. When running the hygrothermobarometry and the MELTS runs, I obtained ranges of water, temperature and pressure. MELTS runs produced valid results for up to mid-crustal depths (5500 bars) but when considering all the tephras, the average depth is about 4 km. In fact, this is the same for the water content: H2O ranges from 0 to 1.5 wt% but the average is 0.4 wt%. Sorry for the confusion, I should have written c. 4-16 km instead. I hope this makes more sense now.

Submitted by Emily Johnson on Friday 26th June 04:39
Hi Charline, thank you for the nice talk! Following Julie's question: so if the average depth is only 4 km, do you still think the microlites crystallized due to cooling? Or does ascent-driven crystallization make more sense at these more shallow levels? As a follow-up: do you see any textural evidence in the crystals for cooling-induced crystallization, rather than ascent-driven (rapid) crystallization? Thank you again!

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