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Complex conductivity of volcanic rocks and the geophysical mapping of alteration in volcanoes
Ghorbani A.a, Revil A., Coperey A., Soueid Ahmed A., Roque S., Heap M.J., Grandis H.d, Viveiros F.e
a Department of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran
b Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, Grenoble, 38000, France
c Géophysique Expérimentale, Institut de Physique de Globe de Strasbourg, UMR 7516 CNRS, Université de Strasbourg/EOST, Strasbourg Cedex, France
d Applied and Exploration Geophysics Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung (ITB), Bandung, Indonesia
e Instituto de Investigação em Vulcanologia e Avaliação de Riscos, Universidade dos Açores, Ponta Delgada, Portugal
[vc_row][vc_column][vc_row_inner][vc_column_inner][vc_separator css=”.vc_custom_1624529070653{padding-top: 30px !important;padding-bottom: 30px !important;}”][/vc_column_inner][/vc_row_inner][vc_row_inner layout=”boxed”][vc_column_inner width=”3/4″ css=”.vc_custom_1624695412187{border-right-width: 1px !important;border-right-color: #dddddd !important;border-right-style: solid !important;border-radius: 1px !important;}”][vc_empty_space][megatron_heading title=”Abstract” size=”size-sm” text_align=”text-left”][vc_column_text]© 2018 Elsevier B.V.Induced polarization measurements can be used to image alteration at the scale of volcanic edifices to a depth of few kilometers. Such a goal cannot be achieved with electrical conductivity alone, because too many textural and environmental parameters influence the electrical conductivity of volcanic rocks. We investigate the spectral induced polarization measurements (complex conductivity) in the frequency band 10 mHz–45 kHz of 85 core samples from five volcanoes: Merapi and Papandayan in Indonesia (32 samples), Furnas in Portugal (5 samples), Yellowstone in the USA (26 samples), and Whakaari (White Island) in New Zealand (22 samples). This collection of samples covers not only different rock compositions (basaltic andesite, andesite, trachyte and rhyolite), but also various degrees of alteration. The specific surface area is found to be correlated to the cation exchange capacity (CEC) of the samples measured by the cobalthexamine method, both serving as rough proxies of the hydrothermal alteration experienced by these materials. The in-phase (real) conductivity of the samples is the sum of a bulk contribution associated with conduction in the pore network and a surface conductivity that increases with alteration. The quadrature conductivity and the normalized chargeability are two parameters related to the polarization of the electrical double layer coating the minerals of the volcanic rocks. Both parameters increase with the degree of alteration. The surface conductivity, the quadrature conductivity, and the normalized chargeability (defined as the difference between the in-phase conductivity at high and low frequencies) are linearly correlated to the CEC normalized by the bulk tortuosity of the pore space. The effects of temperature and pyrite-content are also investigated and can be understood in terms of a physics-based model. Finally, we performed a numerical study of the use of induced polarization to image the normalized chargeability of a volcanic edifice. Induced polarization tomography can be used to map alteration of volcanic edifices with applications to geohazard mapping.[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Author keywords” size=”size-sm” text_align=”text-left”][vc_column_text]Cation exchange capacities,Electrical conductivity,Electrical double layers,Environmental parameter,Hydrothermal alterations,Physics-based modeling,Quadrature conductivity,Spectral induced polarization[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Indexed keywords” size=”size-sm” text_align=”text-left”][vc_column_text][/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Funding details” size=”size-sm” text_align=”text-left”][vc_column_text]M. J. Heap thanks the Buttle family, Pee Jay Tours, GNS Science, and all those that helped collect the materials from Whakaari volcano (particularly B. Kennedy). We thank the USGS Core research Center in Denver, Colorado for allowing us to sample Yellowstone drill cores Y-2 and Y-8. The field samples at Yellowstone were collected under the research permit YELL-2016-SCI-7006. The research at Yellowstone was funded by Labex OSUG@2020 ( ANR10 LABX56 ) and CNRS-INSU program SYSTER . We thank François Beauducel, Mochammad Husni Rizal, and Shaul Hurwitz for fruitful discussions, and A. Bayu Adji, S. Sumarti, A. Riyan, B. Santoso and S. Widodo for the mineralogical analysis of the rock samples from Indonesia, H. Humaida for the core samples from Merapi, and M. Frichnel for her help with the measurements with the core samples from Merapi and Papadayan. We thank E. Zimmermann for the quality of his instrument. We thank the two referees and the Editor for their comments and professional handling of our manuscript.[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”DOI” size=”size-sm” text_align=”text-left”][vc_column_text]https://doi.org/10.1016/j.jvolgeores.2018.04.014[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/4″][vc_column_text]Widget Plumx[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][/vc_column][/vc_row]