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Timescales and rates of magma ascent using 3D-CSD in lava flows of the Mangawhero Formation, Mount Ruapehu, New Zealand

Silvia Catalina Moreno Alfonso1 , Geoff Kilgour2, Georg F. Zellmer1, Satoshi Okumura3, Yoshiyuki Iizuka4, Masahiro Yasutake5, Kentaro Uesugi5, Stuart Mead1

  • Affiliations: 1Volcanic Risk Solutions, School of Agriculture and Environment, Massey University, Private Bag 11-222, Palmerston North 4442, Manawatu-Whanganui, New Zealand; 2Volcanology Department. Wairakei Research Centre. GNS Science. 114 Karetoto Road, RD4, Taupo 3384, New Zealand; 3Department of Earth science, Graduate school of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan; 4Institute of Earth Sciences, Academia Sinica, No.128, Section 2, Academia Road, Taipei 11529, Taiwan; 5SPring-8, JASRI, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 71

  • Programme No: 1.2.16

  • Theme 1 > Session 2

Abstract

Previous studies in the Tongariro Volcanic Centre tephra (<10 kyr) have yielded residence times between 2 to 4 days and ascent rates up to 9 cm/s. One of the volcanic centers generating tephras is Mount Ruapehu, an edifice built by massive lava flows over the last 250 kyr. Determination of the residence times and ascent rates of lava flows is therefore critical. The Mangawhero Formation is a lava flow unit of Mount Ruapehu composed mainly of andesites with plagioclase and two pyroxenes, emplaced between 50 and 15 kyr. Using pyroxenes from 9 lava samples of the Mangawhero formation, we determined the crystal size distributions (CSD) and subsequently the residence times using the slope of the CSDs and a known growth rate for orthopyroxene, obtaining residence times between 2 and 9 days. Further, plagioclase and pyroxene crystals were analyzed using EPMA to obtain their compositions and determine the P-T-H2O conditions using a combination of thermobarometry, hygrometry and MELTS modelling. We found that the magmas had water contents up to 3 wt.%, and resided at pressure up to 2.14 kbar and temperatures up to 1075°C. Lastly, using the maximum pressure obtained through melts modelling, we determined the maximum depth that in combination with the residence times provided information about the maximum ascent rates, ranging between 2 and 3 cm/s. This information will be crucial in determining the difference in the eruption style of the volcanic products.