High Remanent Magnetization Measured in Hydrothermally Altered Lavas

Abstract

Magnetic surveys are used to identify and monitor hydrothermally altered regions on volcanoes. Commonly such magnetic data are interpreted on the premise that hydrothermal alteration consumes Fe‐Ti oxides in the host rocks, reducing their total magnetization. Here, we report a contrasting observation from Whakaari (White Island) volcano in New Zealand. We study the magnetic properties of 42 conduit‐filling and surficial lithologies that have undergone varying degrees of acid‐sulfate alteration. We find that while the induced magnetization of lavas decreases with hydrothermal alteration, some altered lavas have an order of magnitude higher remanent magnetization than fresh lavas. We discuss plausible mechanisms by which altered lavas can retain high remanent magnetization including the importance of magnetic mineralogy and grain size. Our results urge caution in correlating reduced magnetization with hydrothermally altered regions. Furthermore, they highlight the importance of measuring both the induced and remanent magnetization of samples used to interpret field‐scale data.

The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)

“…However, a complete transformation of the initial minerals removes the magnetic minerals and reduces magnetic susceptibility about two orders of magnitude (0.09•10 -3 SI for advanced altered andesitic lavas). Likewise, Kanakiya et al (2021) reported high remnant magnetization in altered lavas of the Whakaari geothermal field. This phenomenon can also be observed to some extent in our data (Fig.…”

“…The reservoir samples can be grouped into (1) altered samples that still contain ferromagnetic minerals (10 -3 -10 -2 SI); (2) altered samples exhibiting magnetic susceptibilities reduced by about one to two orders of magnitude compared to group 1 (10 -3 -10 -4 SI); and (3) marbles, silicified lavas, and skarns showing a diamagnetic to paramagnetic behavior with magnetic susceptibilities that are up to three orders of magnitude smaller compared to group 1 (10 -4 -10 -6 SI). The loss of magnetic signals in the hydrothermally altered rocks could be used to identify and map the hydrothermal aureoles and thus, prospective fluid pathways in the reservoir using geophysics (e.g., borehole logs, airborne magnetic surveys; Kanakiya et al 2021).…”

Gathering insights into volcanic risk from Auckland to the Andes, Antilles, and Arabia: an unexpected journey to professorship in volcanology

“…Since my doctoral work in the Andes, my research has diversified to encompass a wide range of projects in numerous volcanic settings in the broad area of applied volcanology. For example, in the context of large, intermediate to silicic systems my recent PhD students have worked on exploring how the characteristics and distribution of tephra deposits can constrain numerical tephra hazard models (Constantinescu et al, 2021;Constantinescu et al, 2022), how hydrothermal alteration of rocks affects shallow plumbing systems and edifice stability (Kanakiya et al, 2021a;Kanakiya et al, 2021b;Kanakiya et al, 2022), and how pasture can be rehabilitated following large tephra falls (Sivarajan et al, 2020). A current student, Annahlise Hall, is exploring the explosive eruption history and hazards of the Tongan Volcanic Arc.…”

Suseptibilitas Magnetik Sistem Panasbumi Non Vulkanik Desa Terak Menggunakan Metode Geomagnetik

“…Daerah sekitar manifestasi panasbumi biasanya mengalami proses demagnetisasi akibat adanya alterasi pada sistem hidrotermal (Kanakiya et al, 2021). Nilai.…”