HR: 1340h
AN: T33A-0519    [Abstracts]
TI: Hydrothermal alteration and bulk rock chemistry of basaltic rocks in the eastern flank of Juan de Fuca Ridge, IODP Expedition 301
AU: * Sakaguchi, M
EM: masumi-s@cc.kochi-u.ac.jp
AF: Graduate School of Science, Kochi University, Akebono-cho 2-5-1, Kochi, 7808520 Japan
AU: Kiyokawa, S
EM: kiyokawa@geo.kyushu-u.ac.jp
AF: Earth and Planetary Science, Kyushu University, Hakozaki Higashiku 6-10-1, Fukuoka, 8128581 Japan
AU: Ishizuka, H
EM: ishizuka@cc.kochi-u.ac.jp
AF: Department of Geology, Kochi University, Akebono-cho 2-5-1, Kochi, 7808520 Japan
AB: IODP Expedition 301 cruise was planned to evaluate the formation-scale hydrogeologic properties within oceanic crust (e.g. linkages between fluid circulation, alteration, and microbiological processes). In this presentation, we will report the hydrothermal alteration feature of basaltic basement in the eastern flank of Juan de Fuca ridge from the result of alteration mineralogy and bulk rock chemistry. Site 1301 is located in the eastern flank of Juan de Fuca ridge, and water depth, temperature at the surface basement and age are 2680m, 63C° and 3.5Ma, resepectivelly. The basement was cored from 351.2 to 582.8 mbsf (86 to 317.6 m subbasement) in the Hole 1301B, and they consist of aphyric to phyric pillow basalts, massive basalt and basalt-hyaloclastite breccia. Many hydrothermal vein swarms, which is oriented steep angles (55-65, 80-90 degrees), identified with many hydrothermal alteration hallow in these basalt. The hydrothermal alteration in the upper oceanic rocks is characterized as alteration halos adjacent vein expressed the various color (e.g. gray, brown, black). The alteration types are divided, on the basis of alteration mineral associations, into the 3 types that are (1) saponite, saponite + carbonate and saponite + pyrite in the gray halo, (2) saponite + FeO(O,OH)x, saponite + celadonite and saponite + celadonite + Fe(O,OH)x in the black, brown and red halo, and (3) saponite + zeolite, saponite + pyrite and saponite + zeolite + carbonate in the matrix of hyaloclastite breccia and interstitial glass. The occurrences of alteration minerals dose not change with depth. These alteration features are similar to ODP drilling hole, for instance, Hole 504B (Alt et al., 1986), 896A (Teagle et al., 1996 and Laverne et al., 1996) and 801C (Alt and Teagle, 2003). The alteration temperature in the Hole 1301B is estimated to be lower than 100C§ by the alteration mineralogy and previous study (e.g. Laverne et al., 1996). Because thick carbonate vein is not recognized in the Hole 1301B, upwelling of a hydrothermal circulation cell may not be not so influential. The bulk rock chemistry is examined to evaluate the effect of the hydrothermal alteration between gray (type 1) halo and black or brown halos (type 2). The gray halo are scarce in Fe2O3, K2O and Rb and rich in SiO2_CAl2O3_CMgO_CCaO_CSc_CCo_CNi_CZn, Sr than the black and brown halo. Some of these elements fluctuate with increasing and decreasing Mg# or LOI. The basaltic rocks in the Hole 1301B are suffered the oxidized (type 2) and non-oxidized (type 1 and 3) alterations, and these alteration features seem to be caused by difference of fluid circulation style and composition.
DE: 1039 Alteration and weathering processes (3617)
DE: 3036 Ocean drilling
DE: 3617 Alteration and weathering processes (1039)
DE: 3653 Fluid flow
SC: Tectonophysics [T]
MN: Fall Meeting 2005