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Geological indexes of hydrothermal venting

Edward T. Baker

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington

Journal of Geophysical Research, 101(B6), 13,741–13,753 (1996)
Not subject to U.S. copyright. Published in 1996 by the American Geophysical Union.

Study Areas

The Juan de Fuca Ridge in the northeast Pacific extends from the Blanco transform fault at 44°30N to the Sovanco transform fault at 48°45N (Figure 1a). The full spreading rate is 55 mm yr­1 [Elvers et al., 1973; DeMets et al., 1994]. The ridge consists of six tectonic segments that vary considerably in morphology and are bounded by first- or second-order discontinuities. I consider here only Cleft, Vance, Cobb, and Endeavour; the Axial Volcano, West Valley, and Middle Valley segments are tectonically complex and largely unexplored for hydrothermal activity. Along-axis seismic data are scarce on the JDFR. Morton et al. [1987] ran three MCS lines over Cleft and Vance in 1981, and McDonald et al. [1994] used seismic refraction to examine the shallow extrusive layer in the same area. Rohr et al. [1988] ran a single MCS line across the bathymetric high of Endeavour. Site-specific seismic refraction experiments have been conducted by McClain and Lewis [1982] and Christeson et al. [1993] on Cobb, and by Cudrak and Clowes [1993] on Endeavour. Karsten et al. [1990], Rhodes et al. [1990], and Smith et al. [1994] reported chemistry of axial lavas. Baker and Hammond [1992] summarized the distribution of hydrothermal plumes.

Figure 1. Location maps of tectonic segments studied along the (a) Juan de Fuca Ridge, (b) northern East Pacific Rise (EPR), and (c) southern EPR. Segments Clipperton­Orozco2 and CO3 lie immediately north of segment CO1 on the northern EPR; H, G2, and G1 lie immediately south of I on the southern EPR. Segment labeling on the southern EPR from Sinton et al. [1991].

The northern EPR between 9° and 11°50N includes three segments bounded by first-, second-, or third-order discontinuities [Macdonald et al., 1992] (Figure 1b). Full-rate spreading increases from 95 mm yr­1 at 11°50N to 104 mm yr­1 at 9°N [DeMets et al., 1990, 1994]. Scheirer and Macdonald [1993] calculated axial cross sections for this area, and Detrick et al. [1987] reported an MCS survey of the area. Petrological sampling has been dense, particularly between 9° and 10°N [Thompson et al., 1985; Langmuir et al., 1986; Batiza and Niu, 1992; Perfit et al., 1994; Batiza et al., 1996]. Baker et al. [1994] mapped the hydrothermal plume distribution.

The southern EPR between 13°50 and 18°40S includes seven segments bounded by first-, second-, third-, and fourth-order discontinuities (Figure 1c). This ridge section is segmented by overlapping spreading centers (OSCs) noted by Lonsdale [1989] and Scheirer et al. [1996], plus large devals at 15°S and 17°05S. These OSCs and devals also correspond to petrologic boundaries [Sinton et al., 1991]. Full-rate spreading is ~145 mm yr­1 [DeMets et al., 1990, 1994]. Scheirer and Macdonald [1993] calculated axial cross sections for this area, Detrick et al. [1993] obtained MCS profiles from along and across axis, and Sinton et al. [1991] sampled axial lavas. Urabe et al. [1995] and Baker and Urabe [1996] have reported the distribution of along-axis hydrothermal plumes.


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