Primary and secondary mineral phases from Holes 1268A (11 samples), 1272A (9 samples), and 1274A (12 samples) were analyzed by electron microprobe in Bonn and Cologne (Germany) (Table T1). Bulk rock powders of these samples were also analyzed geochemically, including major and trace elements (Paulick et al., 2006).
Ocean Drilling Program (ODP) Leg 209 Holes 1268A, 1272A, and 1274A differ remarkably in alteration intensity and mineralogy, and details regarding their lithologic characteristics are presented in Bach et al. (2004) and Shipboard Scientific Party (2004).
Hole 1274A contains the least altered peridotite drilled during Leg 209; however, the abundance of serpentine-brucite-magnetite assemblages increases from 60 to >95 vol% downhole. In Hole 1272A, completely serpentinized harzburgite consists of serpentine-magnetite ± brucite ± iowaite assemblages. Iowaite (Mg4[OH]8Fe3+OCl·1–4[H2O]) has been described previously from submarine mud volcanoes (Heling and Schwarz, 1992) and serpentinites at the Iberian margin (Gibson et al., 1996). Hole 1272A represents the first documented occurrence of this mineral as a replacive phase in a mid-ocean-ridge setting (Shipboard Scientific Party, 2004), although iowaite has been reported as vein mineral in serpentinite from Hess Deep (Früh-Green et al., 2004).
Hole 1268A contains serpentinized and talc-altered harzburgite and dunite, and serpentinites contain as much as 3 vol% pyrite and other sulfide minerals, which are otherwise rare in the altered peridotite drilled during Leg 209. Talc alteration of serpentinites under static conditions is interpreted to be the result of Si metasomatism (Bach et al., 2004; Shipboard Scientific Party, 2004).
Because of the least altered character of peridotite in Hole 1274A, abundant clinopyroxene, orthopyroxene, olivine, and spinel were analyzed at this site. In Hole 1272A, primary silicates are rare and analyses were restricted to some samples that contain traces of olivine and orthopyroxene. Because of the intensity of alteration, Hole 1268A is devoid of primary phases except spinel. Commonly, alteration is pseudomorphic and serpentinization of olivine and orthopyroxene can be distinguished. Accordingly, compositional variations of the alteration minerals with regard to the precursor minerals are one of the issues investigated in this data report.
1Moll, M., Paulick, H., Suhr, G., and Bach, W., 2007. Data report: microprobe analyses of primary phases (olivine, pyroxene, and spinel) and alteration products (serpentine, iowaite, talc, magnetite, and sulfides) in Holes 1268A, 1272A, and 1274A. In Kelemen, P.B., Kikawa, E., and Miller, D.J. (Eds.), Proc. ODP, Sci. Results, 209: College Station, TX (Ocean Drilling Program), 1–13. doi:10.2973/odp.proc.sr.209.003.2007
2Mineralogisch-Petrologisches Institut, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany. Correspondence author: Holger.Paulick@uni-bonn.de
3Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Strasse 49b, 50674 Köln, Germany.
4Universität Bremen, Fachbereich 5-Geowissenschaften, Postfach 330 440, 28334 Bremen, Germany.
Initial receipt: 20 June 2006
Acceptance: 27 April 2007
Web publication: 13 July 2007
Ms 209SR-003