Magnetite in seafloor serpentinite--Some like it hot

Klein, Frieder; Bach, Wolfgang; Humphris, Susan E.; Kahl, Wolf‐Achim; Jöns, Niels; Moskowitz, Bruce M.; Berquó, Thelma S.

doi:10.1130/g35068.1

Cited by 209 publications

(196 citation statements)

References 18 publications

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“…Our optimum susceptibility ( k =0.02, Table ) translates to a magnetization of 0.9 A/m, rather lower than the 1.38 of Blakely et al () but again their average thickness may be smaller (their Figure D). Our values of k are also in line with measurements from serpentinized rock samples (Bonnemains et al, ; Klein et al, ), with the exception of Vanuatu where the optimum k value is likely to be spuriously high for reasons discussed in section .…”

Section: Discussionsupporting

confidence: 89%

“…There is good evidence that the temperature of serpentinization exerts a strong control on the magnetic properties of the resulting serpentinite. This has been observed in seafloor hydrothermal vents of different temperatures (Szitkar & Murton, ), Ocean Drilling Program samples of serpentinized peridotites (Klein et al, ), and ophiolites (Bonnemains et al, ). In all cases the critical temperature is 200 °C, below which Fe partitions into brucite rather than magnetite.…”

Section: Discussionmentioning

confidence: 76%

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Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

Williams

Gubbins

2019

JGR Solid Earth

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Most subduction zones have associated long‐wavelength anomalies in the lithospheric magnetic field observed at satellite altitude. We model the 13 subduction zones defined by seismicity and seismic tomography using vertically integrated magnetizations that are increasing, level, or decreasing away from the trench. These mimic end members of a magnetized mantle wedge, a uniform layer, and a magnetized dipping lithospheric slab. They are added to a global model of vertically integrated magnetization based on continental and oceanic geology. We find the dipping slab places the anomaly too close to the trench, while the other two fit the data equally well and use the level model in the main part of the study. Anomalies at the Sunda, Aleutians, Cascadia, Central American, and Kamchatka‐Japan zones are well modeled by uniform magnetization of differing susceptibilities and spatial extents. We show the South American anomaly is weak because the magnetization lies mainly in the null space that produces no external potential magnetic field. There is no anomaly associated with the Ryukyu system, possibly because the present subduction started too recently for magnetization to have formed. The magnetic anomaly stretching down the Baja California peninsula is not present in the prediction because there is no seismicity on which to base a slab geometry, but recent tomography suggests a fossil slab there and we propose historic subduction as the origin of the Baja magnetic anomaly. Finally, we discuss the mineralogical origins of the magnetization and favor serpentinization of the region above the subducted plate.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 76%

Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

Williams

Gubbins

2019

JGR Solid Earth

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“…The serpentine (± brucite) veins in magnetite‐poor dunite (DB11‐58) and harzburgite (DB11‐52) samples contain low SiO 2 contents of 34.4–42.4 wt % and low X Mg (Mg/(Mg+ΣFe)) of 0.89–0.93 (Table ). These results follow the evolution trend for Fe‐rich serpentine‐brucite minerals reported by Klein et al [], who documented that temperatures <~200°C lead to Fe‐rich brucite and relatively little magnetite in serpentinized mantle peridotites.…”

Section: Discussionmentioning

confidence: 99%

Magnetic properties of serpentinized peridotites from the Dongbo ophiolite, SW Tibet: Implications for suture‐zone magnetic anomalies

Zheng

Moskowitz

et al. 2017

JGR Solid Earth

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Magnetic properties of a suite of variably serpentinized peridotites from the Dongbo ophiolite, SW Tibet (China), have been investigated to determine the magnetic signatures of suture zones. The degree of serpentinization (S) for these peridotites is mainly in the range of S < 60%. Petrography, mineral chemistry, and thermomagnetic analyses reveal that magnetite occurring in the interior of various serpentine veins is the predominant magnetic phase. Magnetic hysteresis and first‐order reversal curve diagrams suggest that the magnetite is mixture of interacting single‐domain, and pseudo‐single‐domain and/or multidomain particles. Superparamagnetic magnetite occurs in the S = 40–60% serpentinized but weakly magnetic dunites. Overall, the magnetite content and magnetic susceptibility increase consistently from ~0 to 20% of serpentinization and then decrease from S = 30 to 60%. Peak magnetite abundance is at S~25% (density, ~3.1 ± 0.05 g cm–3) and may suggest localized enrichment of fluids. The low magnetite abundance in dunite results from low‐temperature serpentinization. Finally, strong intensities of magnetization (1–10 Am–1) reside in the S > 60% and S = 20–30% serpentinized peridotites, indicating that peridotites with such degrees of serpentinization contribute to the aeromagnetic anomalies within the Yarlung‐Zangbo suture zone in south Tibet.

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“…The 167 intensity of magnetite magnetization is subject to the strength of the magnetizing field (i.e. of the magnetic anomaly is therefore believed to mainly depend on the magnetite concentration 173 within the rocks, which, in turn, can be influenced by temperature, oxidation processes, 174 water/rock ratios, and/or Fe partitioning into brucite or other alteration phases (Früh-Green et al, 175 1996; Früh-Green et al, 2004; Andreani et al, 2013;Klein et al, 2014). 176…”

Section: ) Discussion 158mentioning

confidence: 99%

Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR)

Szitkar

Tivey

Kelley

et al. 2017

Earth and Planetary Science Letters

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25A 2003 high-resolution magnetic survey conducted by the Autonomous Underwater Vehicle ABE 26 over the low-temperature, ultramafic-hosted hydrothermal field Lost City reveals a weak positive 27 magnetic anomaly. This observation is in direct contrast to recent observations of strong positive 28 magnetic anomalies documented over the high-temperature ultramafic-hosted hydrothermal vents 29 fields Rainbow and Ashadze, which indicates that temperature may control the production of 30 magnetization at these sites. The Lost City survey provides a unique opportunity to study a field 31 that is, to date, one of a kind, and is an end member of ultramafic-hosted hydrothermal systems. 32Our results highlight the key contribution of temperature on magnetite production resulting from 33 serpentinization reactions. Whereas high temperature promotes significant production and 34 partitioning of iron into magnetite, low temperature favors iron partitioning into various alteration 35 phases, resulting in a magnetite-poor rock. Moreover, the distribution of magnetic anomalies 36 confirms results of a previous geological survey indicating the progressive migration of 37 hydrothermal activity upslope. These discoveries contribute to the results of 25 years of magnetic 38 exploration of a wide range of hydrothermal sites, from low-to high-temperature and from 39 basalt-to ultramafic-hosted, and thereby validate using high-resolution magnetics as a crucial 40 parameter for locating and characterizing hydrothermal sites hosting unique chemosynthetic-41 based ecosystems and potentially mineral-rich deposits. 42 43 1) Introduction 44The discovery of hydrothermal activity along the Galapagos Rift (Corliss et al., 1979) paved the 45 way for large-scale, deep-sea exploration of oceanic ridges, revealing a myriad of hydrothermal 46 vent fields primarily hosted on basaltic crust, with lesser gabbroic and ultramafic material (Kelley 47 and Shank, 2010). In contrast to intermediate-and fast-spreading systems where basaltic rocks 48 dominate, along slow-to ultraslow-spreading centers, the tectonically-dominated geology 49 (Karson and Elthon, 1987; Tucholke et al., 1998; Escartin et al., 2008) gives rise to a higher 50 abundance of hydrothermal systems hosted by variable amounts of ultramafic and gabbroic 51 material, such as the well-known Rainbow and Ashadze hydrothermal fields (Charlou et al., 52 2002; Charlou et al., 2010; Fouquet et al., 2008). These high-temperature venting systems 53 (>350°C) are characterized by sulfide chimneys emitting low pH fluids rich in carbon dioxide, 54 methane and hydrogen; chemical signatures that are hallmarks of fluid interaction with mafic and 55 ultramafic material in the subsurface (Charlou et al., 2002; Fouquet et al., 2010; Kelley and 56 Shank, 2010;Ohara et al., 2012). 57Although the magnetic signature of basalt-hosted hydrothermal sites is well constrained (Tivey et 58 al., 1993; Tivey and Johnson, 2002; Tivey and Dyment, 2010;Szitkar et al., 2014a; Szitkar et al., 59 2015),...

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Magnetite in seafloor serpentinite--Some like it hot

Cited by 209 publications

References 18 publications

Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

Magnetic properties of serpentinized peridotites from the Dongbo ophiolite, SW Tibet: Implications for suture‐zone magnetic anomalies

Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR)

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