Crystal size distribution (CSD) in a lava sample from Ruapehu volcano, New Zealand: a case study comparing the use of semi-automatic tools in 2D versus 3D images.
Silvia Catalina Moreno-Alfonso1, Satoshi Okumura2, Georg F. Zellmer1, Stuart Mead1, Yoshiyuki Iizuka3, Masahiro Yasutake4, Kentaro Uesugi4 and Akira Miyake5.
Affiliations: 1 Volcanic Risk Solutions, School of Agriculture and Environment, Massey University, Private Bag 11-222, Palmerston North 4442, Manawatu-Whanganui, New Zealand. Phone: +64210505282. Fax +6463505632 E-mail: s.morenoalfonso@massey.ac.nz. (corresponding author). 2 Department of Earth science, Graduate school of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578 , Japan. 3 Institute of Earth Sciences, Academia Sinica, No.128, Section 2, Academia Road, Taipei 11529, Taiwan 4 SPring-8, JASRI, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan. 5 Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
Presentation type: Poster
Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall
Poster Board Number: 258
Programme No: 1.3.8
Abstract
The determination of crystal size distributions (CSD) is used for the determination of the magma residence times, using a well know crystal growth rate and the slope of the distribution. Furthermore, once the residence times are obtained these can be used together with the depth to calculate the ascent rates. Usually, the CSDs are determined using two-dimensional (2D) images in which crystals can be overlapped misrepresenting the natural tridimensionality of the particles. The use of three-dimensional (3D) images where crystals can be measured directly, is key in providing a more robust distribution, particularly for samples with a high density in crystals. For these samples the use of semi-automated tools facilitates the crystal outlining and measurement processes. We evaluated the comparability between 2D and 3D CSD plots, assessing the similarities and differences for different mineral shapes and axis plots in magnetite and pyroxene, obtained using semi-automatic tools in one lava sample from Mangawhero Formation. The sample was analyzed through back-scattered scanning electron microscopy (BS-SEM) and synchrotron radiation X-ray micro-computational tomography (SR-XCT). Our findings include similar patterns for 2D and 3D CSDs for all axes, including similar kinked features; closer results between 2D and 3D CSDs for non-equant tabular shapes, and a lesser influence of the aspect ratios over the 2D intermediate axis plots. Additionally, a better comparability in terms of shapes and slopes was observed between large axis plots irrespective of the crystal shapes and number of crystals.