Szitkar, Florent, Tivey, Maurice A., Kelley, Deborah S., Karson, Jeffrey A., Früh-Green, Gretchen L. and Denny, Alden R. (2017) Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR). Earth and Planetary Science Letters, 461 . pp. 40-45. DOI 10.1016/j.epsl.2016.12.033.

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Abstract

Highlights

• First magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site.
• New inversion method resolves high-resolution magnetic anomaly in a steep environment.
• Lost City bears a positive magnetization resulting from specific chemical processes.

A 2003 high-resolution magnetic survey conducted by the Autonomous Underwater Vehicle ABEover the low-temperature, ultramafic-hosted hydrothermal field Lost City reveals a weak positive magnetic anomaly. This observation is in direct contrast to recent observations of strong positive magnetic anomalies documented over the high-temperature ultramafic-hosted hydrothermal vents fields Rainbow and Ashadze, which indicates that temperature may control the production of magnetization at these sites. The Lost City survey provides a unique opportunity to study a field that is, to date, one of a kind, and is an end member of ultramafic-hosted hydrothermal systems. Our results highlight the key contribution of temperature on magnetite production resulting from serpentinization reactions. Whereas high temperature promotes significant production and partitioning of iron into magnetite, low temperature favors iron partitioning into various alteration phases, resulting in a magnetite-poor rock. Moreover, the distribution of magnetic anomalies confirms results of a previous geological survey indicating the progressive migration of hydrothermal activity upslope. These discoveries contribute to the results of 25yrs of magnetic exploration of a wide range of hydrothermal sites, from low-to high-temperature and from basalt-to ultramafic-hosted, and thereby validate using high-resolution magnetics as a crucial parameter for locating and characterizing hydrothermal sites hosting unique chemosynthetic-based ecosystems and potentially mineral-rich deposits.

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