Small non-overlapping offsets of the East Pacific Rise

Batiza, Rodey; Margolis, S. H.

doi:10.1038/320439a0

Cited by 49 publications

(17 citation statements)

References 17 publications

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“…In addition to the relatively simple plate boundary geometry characterized by extensional volcanic lineaments offset by rectilinear and orthogonally oriented zones of strike-slip faulting, studies, based on high resolution investigations at a regional scale (Macdonald et al, 1984(Macdonald et al, , 1988Lonsdale, 1983Lonsdale, , 1989Langmuir et al, 1986;Batiza and Margolis, 1986;Kong et al, 1988), have shown that the axes of accretion are segmented along a spectrum of structures with characteristics that contrast with the zones of strike-slip faulting (i.e. overlapping spreading centers, oblique shear zones, deviations in axial linearity, inter-volcano gaps).…”

Section: Introductionmentioning

confidence: 99%

The Mid-atlantic Ridge (31°S–34°30′S): Temporal and spatial variations of accretionary processes

1991

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The ridge located between 31 ~ S and 34~ is spreading at a rate of 35 mm yr-1, a transitional velocity between the very slow (-<20 mm yr -1) opening rates of the North Atlantic and Southwest Indian Oceans, and the intermediate rates (60 mm yr-~) of the northern limb of the East Pacific Rise, and the Galapagos and Juan de Fuca Ridges. A synthesis of multinarrow beam, magnetics and gravity data document that in this area the ridge represents a dynamically evolving system. Here the ridge is partitioned into an ensemble of six distinct segments of variable lengths (12 to 100 km) by two transform faults (first-order discontinuities) and three small offset ( < 30 km) discontinuities (second-order discontinuities) that behave non-rigidly creating complex and heterogeneous morphotectonic patterns that are not parallel to flow lines. The offset magnitudes of both the first and second-order discontinuities change in response to differential asymmetric spreading. In addition, along the fossil trace of second-order discontinuities, the lengths of abyssal hills located to either side of a discordant zone are observed to lengthen and shorten creating a saw-toothed pattern. Although the spreading rate remains the same along the length of the ridge studied, the morphology of the spreading segments varies from a deep median valley with characteristics analogous to the rift segments of the North Atlantic to a gently rifted axial bulge that is indistinguishable from the shape and relief of the intermediate rate spreading centers of the East Pacific Rise (i.e., 21 ~ N). Like other carefully surveyed ridge segments at slow and fast rates of accretion, the along-axis profiles of each ridge segment are distinctly convex upwards, and exhibit along-strike changes in relief of 500 m to 1500 between the shallowest portion of the segment (approximate center) and the segment ends. Such spatial variations create marked along-axis changes in the morphology and relief of each segment. A relatively low mantle Bouguer anomaly is known to be associated with the ridge segment characterized by a gently rifted axial bulge and is interpreted to indicate the presence of focused mantle upwelling (Kuo and Forsyth, 1988). Moreover, the terrain at the ends of each segment are known to be highly magnetized compared to the centers of each segment (Carbotte et al, 1990). Taken together, these data clearly establish that these profound Marine Geophysical Researches 13: 1-20, 1991. 9 1991 Kluwer Academic Publishers. Printed in the Netherlands. spatial variations in ridge segment properties between adjoining segments, and along and across each segment, indicate that the upper mantle processes responsible for the formation of this contrasting architecture are not solely related to passive upwelling of the asthenosphere beneath the ridge axis. Rather, there must be differences in the thermal and mechanical structure of the crust and upper mantle between and along the ridge segments to explain these spatial variations in axial topography, crustal structure and magn...

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Section: Introductionmentioning

confidence: 99%

The Mid-atlantic Ridge (31°S–34°30′S): Temporal and spatial variations of accretionary processes

1991

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“…Earlier investigations identified regions of high magnetization associated with the propagating limb of OSCs, which were ] to deviations from axial linearity (DEVALs ), and small nonoverlapping offsets (SNOOs [Batiza and Margolis, 1986] …”

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Three‐dimensional shallow crustal emplacement at the 9°03′N overlapping spreading center on the East Pacific Rise: Correlations between magnetization and tomographic images

Bazin¹,

Harding²,

Kent³

et al. 2001

J. Geophys. Res.

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[Bazin, 2000]. In this study, we investigate the regional geometry of layer 2A using velocity models obtained by the refraction/tomography experiment. The air gun/ocean bottom receiver technique provides detailed information on upper crustal velocities owing to the combination of high source repetition rate and broad coverage.Earlier investigations identified regions of high magnetization associated with the propagating limb of OSCs, which were 16,101

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“…Such fast spreading ridges typically display a periodic segmentation, with the segments being separated from one another by a variety of structural and magmatic discontinuities, including faults, overlapping spreading centers, and small nonoverlapping offsets [Batiza and Margolis, 1986; [1988a]). Also shown are the locations of Figure 2 and of the lbra area studied by Gregory and Taylor [1981] and PaUisler and .…”

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confidence: 99%

The Northern Samail Ophiolite: An Oxygen isotope, microprobe, and field study

Stakes¹,

Taylor²

1992

J. Geophys. Res.

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Divi.Jion ofGeologk:alllllll Plondoty Sdenca, California .bulilu# ofT~ PtlStlllma Geological, petrological, and axygcn isotopic data are pn:sentecl for 228 whole rock and mineral samples collected from a 100x20 km area of the nortbem Samail opbiolite in Oman. MOlt of these samples arc from three detailed profiles tluough the pillow IIIYBI, sbeetecl dikes, and .red pbbi'OI of this laterally heterogeneous fratpnent of Cretaceous oceanic crust, down to and 8C1'0I& the petroaop: Moho. The profiles encompass a l'llDF of petrologic and tectonic styles, and each profile cmibit& distinctive llloJ 1 6o variations compared to one another and to mid-ocean ridge basalt&, as a result of ~ seawater-h)'drothermal interaction that varied in intensity along strike in the ophiolite. In general, 1 Bo depletions arc observed in the layered gabbi'OI and 1llo enrichments in most of the sheeted dikes and pillow lavas, similar to results previously observed in the southem part of the ophiolite (Ibra area), where 1 Bo depletions within the gabbroic section arc quantitatively balanced by 1llo enrichments in the sballower parts of the oceanic crust. The Wadi Hilti profile, selected as an example of relatively intact crust, differs from lbra in having more uniform and slightly bigher6 1 Bo in the gabbi'OI ( + S.4 to +6.3), as well as in containing more h)'drous alteration minerals (amphibole, epidote, cblorite, and prcbnite ). The profiles in the Wadi Kanut-Shafan and Wadi Rajmi sections arc much more complex and reveal the impact of off-axis intrusions and deep crustal shearing. Plagiogranitewebrlite intrusions in the Sbafan-Kanut area superimposed a local h)'drothermal aureole on the ophiolite, evident in dikes highly depleted in 1 Bo, quartz-sulfide veins, abundant epidote, thullite, and cblorite in shallower rocks, and low-temperature h)'drous alteration of deeper gabbroic rocks; the latter produced an overall increase in wbole rock 6 1 Bo ( +6.2 to +6.9). Such late stage intrusions arc found throughout the northem half of the Samail ophiolite. The Wadi Rajmi area, which is a possible fossil transform or propagating rift, represent& the most complex of the three profiles; it also contains the most abundant highly deformed and h)'drothermally altered rocks, together with the deepest and largest zone of 1 Bo depletion yet found in any ophiolite (locally61llo < + 2.0). Conduits for large volumes of high-temperature h)'drothermal fluids were provided by fractures now occupied by low-1 Bo gabbro pegmatitcs and Iow-lllo dikes. Material balance estimates for the regional samples and from the various transects through the ophiolite give crustal bulk 6 1 Bo averages ( +S.9 to +6.3) that arc, within sampling error, almost identical to the average MORB basalt value of about + S.8, if both vertical and lateral crustal heterogeneities are integrated into a threedimensional model. This supports and amplifies the conclusion of earlier workers that the 6 1 Bo of seawater is buffered and controned by h)'drothermal interaction with oceanic crust, as lon...

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Small non-overlapping offsets of the East Pacific Rise

Cited by 49 publications

References 17 publications

The Mid-atlantic Ridge (31°S–34°30′S): Temporal and spatial variations of accretionary processes

The Mid-atlantic Ridge (31°S–34°30′S): Temporal and spatial variations of accretionary processes

Three‐dimensional shallow crustal emplacement at the 9°03′N overlapping spreading center on the East Pacific Rise: Correlations between magnetization and tomographic images

The Northern Samail Ophiolite: An Oxygen isotope, microprobe, and field study

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