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May 30, 2014 - function of spreading rate, and thus the magmatic budget [Baker and ..... (38 N-34 N): Ultramafic exposures and hosting of hydrothermal vents, ...
PUBLICATIONS Geochemistry, Geophysics, Geosystems RESEARCH ARTICLE 10.1002/2013GC005206 Key Points:  The most extensive examination of hydrothermal activity on a slow ridge  Hydrothermal plumes are most common along asymmetrical ridge sections  Magmatic heat appears the primary hydrothermal driver even on this slow ridge

Tectonic and magmatic control of hydrothermal activity along the slow-spreading Central Indian Ridge, 8 S–17 S Juwon Son1, Sang-Joon Pak1, Jonguk Kim1, Edward T. Baker2,3, Ok-Rye You1, Seung-Kyu Son1, and Jai-Woon Moon1 1 Deep-sea and Seabed Resources Research Division, Korea Institute of Ocean Science and Technology, Ansan, South Korea, 2NOAA Pacific Marine Environmental Laboratory, Seattle, Washington, USA, 3Now at Joint Institute for the Study of the Atmosphere and Ocean—PMEL, University of Washington, Seattle, Washington, USA

Abstract The complex geology and expansive axial valleys typical of slow-spreading ridges makes evaluSupporting Information:  Readme  fs01  ts01 Correspondence to: J. Kim, [email protected]

Citation: Son, J., S.-J. Pak, J. Kim, E. T. Baker, O.-R. You, S.-K. Son, and J.-W. Moon (2014), Tectonic and magmatic control of hydrothermal activity along the slow-spreading Central Indian Ridge, 8 S–17 S, Geochem. Geophys. Geosyst., 15, 2011–2020, doi:10.1002/ 2013GC005206.

ating their hydrothermal activity a challenge. This challenge has gone largely unmet, as the most undersampled MOR type for hydrothermal activity is slow spreading (20–55 mm/yr). Here we report the first systematic hydrothermal plume survey conducted on the Central Indian Ridge (CIR, 8 S–17 S), the most extensive such survey yet conducted on a slow-spreading ridge. Using a combined CTD/Miniature Autonomous Plume Recorder (MAPR) package, we used 118 vertical casts along seven segments of the CIR (700 km of ridge length) to estimate the frequency of hydrothermal activity. Evidence for hydrothermal activity (particle and methane plumes) was found on each of the seven spreading segments, with most plumes found between 3000 and 3500 m, generally 55 mm/yr (full rate)) MORs, heat sources have long been recognized as the primary control: focused venting is overwhelmingly found only above an axial magma chamber [Baker, 2009], and modeling suggests that high-temperature venting can be sustained only where melt accumulation exceeds the rate needed for steady state crustal production [Lowell et al., 2013]. Along slow-spreading ridges, however, a complex geology—broad, deep axial valleys; a variety of axial offset types; detachment faults exposing vast surfaces of mantle rock—makes vent locations a complex interaction between heat and permeability. For example, Gercia et al. [2000] noted a favored occurrence of hydrothermal sites at segment man and Parson [1998] and Gra end nontransform offsets (NTOs) and argued that venting along the Mid-Atlantic Ridge resulted from interplay of magmatic and tectonic controls. Except for detailed work along the Reykjanes Ridge (which features an axial high rather than a deep axial valley), however, neither of these papers reported results from systematic and high-resolution surveys. Continued work along the slow-spreading Mid-Atlantic Ridge has thus far identified vents on neovolcanic axial ridges (Snake Pit) [Gente et al., 1991], at the intersection of axial valley faults (TAG) [Rona et al., 1986], on valley walls (Logatchev [Bogdanov et al., 1995] and Moytirra [Wheeler et al., 2013]), at nontransform discontinuities (Rainbow) [Charlou et al., 2002], and entirely outside the axial valley (Lost City [Kelley et al., 2005] and Nibelungen [Melchert et al., 2008]). Summarizing the Mid-Atlantic hydrothermal work, Escartin et al. [2008] found that between 13 N and 35 N active sites are preferentially associated not with symmetrically spreading, magmatic segments, but with asymmetrically spreading segments where detachment faults

SON ET AL.

C 2014. American Geophysical Union. All Rights Reserved. V

2011

Geochemistry, Geophysics, Geosystems

10.1002/2013GC005206

are common. They envision the heat source to be deep-seated magma or hot crustal/mantle rock that accesses the seafloor through fluid flow along detachment faults. These observations challenge the hypothesis that the spatial frequency of hydrothermal venting is a linear function of spreading rate, and thus the magmatic budget [Baker and Hammond, 1992; Baker and German, 2004]. For example, Baker and German [2004] found that, for a given magma supply rate, ultraslow (