High‐resolution magnetic signature of active hydrothermal systems in the back‐arc spreading region of the southern Mariana Trough

Abstract

High-resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back-arc spreading region of the southern Mariana Trough using Shinkai 6500, a deep-sea manned submersible. A new 3-D forward scheme was applied that exploits the surrounding bathymetry and varying altitudes of the submersible to estimate absolute crustal magnetization. The results revealed that magnetic-anomaly-derived absolute magnetizations show a reasonable correlation with natural remanent magnetizations of rock samples collected from the seafloor of the same region. The distribution of magnetic-anomaly-derived absolute magnetization suggests that all five andesite-hosted hydrothermal fields are associated with a lack of magnetization, as is generally observed at basalt-hosted hydrothermal sites. Furthermore, both the Pika and Urashima sites were found to have their own distinct low-magnetization zones, which could not be distinguished in magnetic anomaly data collected at higher altitudes by autonomous underwater vehicle due to their limited extension. The spatial extent of the resulting low magnetization is approximately 10 times wider at off-axis sites than at on-axis sites, possibly reflecting larger accumulations of nonmagnetic sulfides, stockwork zones, and/or alteration zones at the off-axis sites.

Heat Flow and Near‐Seafloor Magnetic Anomalies Highlight Hydrothermal Circulation at Brothers Volcano Caldera, Southern Kermadec Arc, New Zealand

“…Thus, to resolve magnetic anomalies at the scale and depth of the hydrothermal systems and to counteract the natural decay of the magnetic field with depth, near‐seafloor data collected by deep‐submergence vehicles such as autonomous underwater vehicles (AUVs) or remotely operated vehicles (ROVs) are required. Near‐seafloor high‐resolution magnetic surveys of basalt‐hosted hydrothermal vent sites at MORs or back‐arc basins (e.g., Caratori Tontini et al, ; Caratori Tontini et al, ; Fujii et al, ; Tivey et al, ; Tivey & Dyment, ; Tivey & Johnson, ) and at submarine arc volcanoes (Caratori Tontini, Davy, et al, ; Caratori Tontini et al, , Honsho et al, ; Szitkar et al, ) have revealed well‐defined magnetic “burnholes,” that is, discrete zones of reduced crustal magnetization in and around areas of active and extinct vent sites, inferred to represent hydrothermal upflow zones.…”

Origin of magnetic highs at ultramafic hosted hydrothermal systems: Insights from the Yokoniwa site of Central Indian Ridge

“…Zealand showed that hydrothermal alteration of magnetic minerals is the most important 68 mechanism for creating zones of weak magnetization rather than by thermal 69 demagnetization processes (Hochstein and Soengkono, 1997). In the seafloor realm, 70 weak magnetization zones were observed in both active and extinct vent areas, also 71 suggesting that differences in the thermal environment do not significantly affect 72 magnetic anomalies (Fujii et al, 2015;Tivey and Johnson, 2002). Another explanation 73 for zones of weak magnetic response is the accumulation of thick hydrothermal deposits, 74 which may result in an apparent magnetic low due to the increased distance between the 75 measurement point and the underlying magnetized basalt (Szitkar et al, 2014a).…”

“…The location and spatial extent of 46 hydrothermal activity are difficult to constrain; however, studies of near-seafloor 47 magnetic field can highlight these features because crustal magnetic minerals can be 48 destroyed or created by hydrothermal processes. Reduced magnetization associated with 49 hydrothermal deposits was widely observed in both the active and inactive lava-hosted 50 hydrothermal fields in varied tectonic settings, including: the hydrothermal site TAG 51 (Trans-Atlantic Geotraverse) and the 4°48′S fields of the Mid-Atlantic Ridge (MAR; 52 Tivey and Dyment., 2010;Tivey et al, 1993Tivey et al, , 1996Tivey et al, , 2003, the Main Endeavour Field and 53 Raven Field of the Juan de Fuca Ridge (JFR; Tivey and Johnson, 2002;Tivey et al, 2014), 54 a site on the Southwest Indian Ridge (Zhu et al, 2010), back-arc-type sites of the 55 Southern Mariana Trough (Fujii et al, 2015;Nakamura et al, 2013), the Hakurei Field 56 within a caldera of the Izu-Ogasawara arc-back-arc volcano (Honsho et al, 2013), and 57 the Brothers Field within a caldera of the Kermadec intraoceanic arc volcano 58 (Caratori- Tontini et al, 2012). 59…”

Crustal magnetization and the subseafloor structure of the ASHES vent field, Axial Seamount, Juan de Fuca Ridge: Implications for the investigation of hydrothermal sites

“…Near‐seafloor magnetic surveys provide a unique method for mapping hydrothermal alteration in the submarine environment [e.g., Tivey and Johnson , ; Tivey and Dyment , ; Tivey et al , ; Honsho et al , ; Fujii et al , ; Szitkar et al , , ]. Young oceanic crust is characterized by strong magnetization caused by magnetite and titanomagnetite minerals within the lavas.…”