Diking, young volcanism and diffuse hydrothermal activity on the southern Mid-Atlantic Ridge: The Lilliput field at 9°33'S

Haase, K. M., Koschinsky, A., Petersen, Sven, Devey, Colin W., German, C., Lackschewitz, Klas, Melchert, Bernd, Seifert, R., Borowski, C., Giere, O. and Paulick, H. and M64 1 Scientific Party, M68 1 Scientific Party, M78 2 Scientific Party (2009) Diking, young volcanism and diffuse hydrothermal activity on the southern Mid-Atlantic Ridge: The Lilliput field at 9°33'S Marine Geology, 266 (1-4). pp. 52-64. DOI 10.1016/j.margeo.2009.07.012.

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Detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed, at 9 degrees 33'S, the presence of the southernmost active hydrothermal field known so far on the Mid-Atlantic Ridge. The size of the hydrothermal field, which we have named "Lilliput", is about 1000 m x 250 m. It lies in a water depth of 1500 m on a ridge segment (Segment A3) with considerably thickened crust of 11 km. Four relatively small diffuse vent sites occur on a large young (estimated <100 years old) lava flow, partly covering the flow with hydrothermal Fe-oxide/hydroxide sediments. Based on homogeneous major element compositions of ca. 25 lava samples, this flow covers an area of at least 5 km x 0.6 km. The lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds. The volcanic ridge probably represents the surface expression of an underlying dike which fed the flow. Several drained lava pond structures were observed within the flow but only one shows hydrothermal activity. The hydrothermal venting and precipitation of abundant Fe-oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the Lilliput field lie along and almost equidistant from the eastern flank of the supposed dike. Although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years (2005 and 2006), no high-temperature venting associated with Lilliput has been found. in agreement with findings at other ridges with thick crust such as Reykjanes. High magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow-spreading segments with thick crust whereas diffuse venting is abundant. Interestingly, the fauna at the Lilliput vents largely consists of small and apparently juvenile mussels (Bathymodiolus sp.) and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity.

Document Type: Article
Keywords: South Atlantic spreading centre, vent fauna, basalt, De-Fuca Ridge, carbonate dissolution rates, East Pacific rise, ascension island, vent communities, midocean ridges, Galapagos rift, cleft segment, lava flows, eruption, RV Meteor, M64/1, M68/1, M78/2, ROV Kiel, AUV
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1016/j.margeo.2009.07.012
ISSN: 0025-3227
Projects: SPP 1144 "From Mantle to Ocean", Future Ocean
Date Deposited: 11 Feb 2011 12:15
Last Modified: 04 Aug 2017 12:16
URI: http://eprints.uni-kiel.de/id/eprint/9420

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