A one‐million‐year history of the 11°45′N East Pacific Rise discontinuity

Perram, Laura Jean; Macdonald, Ken C.

doi:10.1029/jb095ib13p21363

Cited by 46 publications

(37 citation statements)

References 53 publications

(23 reference statements)

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“…For example, ridge tip abandonment events at OSCs may occur in response to magmatic cycles in the adjoining ridge segments [45], and a recurrence interval of 50-100 ka has been estimated for the 9º03 0 N OSC [16]. A similar interval was estimated from the spacing of abandoned ridge tips associated with the 11º45 0 N OSC [46]. Structures along the northern boundary of the Siqueiros Fracture Zone have been interpreted to reflect a 300-500 ka episodicity in the volcanic and tectonic processes in this region [47].…”

Section: Origin Of Temporal Chemical Variationsmentioning

confidence: 99%

Variations in the geochemistry of magmatism on the East Pacific Rise at 10°30′N since 800 ka

Regelous

Niu

Wendt

et al. 1999

Earth and Planetary Science Letters

145

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Section: Origin Of Temporal Chemical Variationsmentioning

confidence: 99%

Variations in the geochemistry of magmatism on the East Pacific Rise at 10°30′N since 800 ka

Regelous

Niu

Wendt

et al. 1999

Earth and Planetary Science Letters

145

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“…Considering that the fit of WDCA/SQ1 to data from land-based geomagnetic observatories was only slightly better than 10 nT, the overall reduction of crossover error that we achieved appears to be quite remarkable. In magnetic surveys conducted at on the EPR at 1 1*45'N by Perram and Macdonald [1990], the rms crossover error was 28-29 nT, even after shifting the field values of individual track lines by a constant amount to minimize the overall crossover error in a least squares sense . also report an rms crossover error of 33 nT in their study of magnetic anomalies of the EPR at 8 0 -10 0 30'N.…”

Section: Reduction Of Magnetic Field Datamentioning

confidence: 99%

Tectonics of the East Pacific rise : studies of faulting characteristics and magnetic and gravity anomalies

Lee¹

1995

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The global mid-ocean ridge system is one of the most striking geological features on the surface of the Earth. In this system, the East Pacific Rise (EPR) is the fastest spreading ridge and is thus considered as the most active magmatically among the plate boundaries. In January and February of 1988, an extensive survey by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution was conducted along the EPR between 9*05' and 9 0 55'N to study the crustal structure of the axial region.This thesis, the result of that cruise, comprises four main topics: (1) characterization of normal faulting from Sea Beam bathymetric data, (2) application of mechanical models to explore the hypothesis that buoyancy arising from crustal magma chambers and gravitational spreading of the upper crust are the principal processes leading to the initiation and development of normal faults, (3) investigation of seafloor magnetization anomalies to constrain upper crustal structure, and (4) analysis of gravity anomalies to examine possible correlations between observed variations in seafloor manifestations of volcanism and deformation and underlying structure. Thus, each topic focuses on different levels of the mid-ocean ridge. Together with the results of seismic and other observations, the findings are woven into a better understanding of the tectonic processes and structure of fastspreading mid-ocean ridges.First, to understand the characteristics of normal faults at fast-spreading ridges, we utilized swaths of Sea Beam bathymetry and estimated the distribution and geometry of normal fault zones using the slope of the seafloor as the criterion for a faulted surface. In our survey area, normal fault activity begins 2-8 km off-axis and continues at least to 30-40 km from the axis, as indicated by an increase in the total and average throws of normal fault zones versus distance from the axis. There appears to be no significant difference in the plan-view area of inward-and outward-facing normal fault zones. The distance from the rise axis to the nearest large-offset fault zone (throw > 20 m) on either side of the axis is approximately symmetric to the north of 9*23'N, but the midpoint between nearest largeoffset fault zones is offset 2-3 km to the west of the bathymetric axis to the south of 9*23'N. The continued growth of normal fault zones suggests that significant extensional stress persists to greater distances from the axis than previously thought and that the rise axis possesses a finite strength. The argument that the rise axis has finite strength is consistent with recent evidence for solidified axial dikes along magmatically active portions of the EPR from near-bottom seismic refraction experiments, which suggests that, while eruption of magma at the rise axis weakens the axis, the persistence of such weak zones is short-lived and the emplacement zones at any given time are localized along the axis.We examined how the presence of a low-density, low-strength magma chamber within the crust and gra...

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“…Recent morphologic and magnetic studies suggest that there has been a gradual 3 ° to 7 ° counterclockwise change in the direction of relative plate motion along the Pacific-Cocos Plate Boundary in the past 1 to 2m.y. (Perram and Macdonald, 1990;Carbotte and Macdonald, 1992). However, the orientation of the Clipperton Fracture Zone has apparently changed very little in the past 3 m.y.…”

Section: Tectonic Setting Of the Clipperton Fracture Zonementioning

confidence: 93%

“…(Perram and Macdonald, 1990;Carbotte and Macdonald, 1992). Such a change must cause compression across the right-stepping Clipperton offset while causing extension across the other, left-stepping offsets along this boundary.…”

Section: Are Intersection Highs Propagating Ridge Tips?mentioning

confidence: 94%

The origin of bathymetric highs at ridge-transform intersections: A multi-disciplinary case study at the Clipperton Fracture Zone

1994

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Abstract. Bathmetric highs on the old crust proximal to ridge-transform intersections (RTIs), termed "intersection highs", are common but poorly understood features at offsets of fast to intermediate rate spreading centers. We have combined new reflection seismic, photographic, and geochemical data with previously published Seabeam, SeaMARC I, and SeaMARC II data to address the nature of the intersection highs at the Clipperton Fracture Zone. The Clipperton Intersection Highs are both topped by a carapace of young lavas at least 100 m thick. These lavas, which were erupted on the intersection highs, are chemically similar to their adjacent ridge segments and different from the surrounding older crust. At least some of the erupted magma traveled directly from the adjacent ridge at a shallow crustal level. Ridge-related magma covers and intrudes at least the upper 500 m of the transform tectonized crust at the RT1. We suspect that additional magma enters the intersection highs from directly below, without passing through the ridge. The young oceanic crust near the western Clipperton RTI is not thin by regional comparison. The 1.4 m.y. old crust near the eastern Clipperton RTI thickens approaching the transform offset. If the thermal effects of the proximal ridge were negligible, the eastern intersection high crust would appear to be in isostatic equilibrium. We believe that thermal effects are significant, and that the intersection high region stands anomalously shallow for its crustal thickness. This is attributable to increased temperature in the mantle below the ridge-proximal crust. Although ridge magma is injected into the proximal old crust, plate boundary reorganization is not taking place. Intersection high formation has been an ongoing process at both of the Clipperton RTIs for at least the past 1 m.y., during which time the plate boundary configuration has not changed appreciably. We envision a constant interplay between the intruding ridge magma and the disrupting transform fault motion. In addition, we envision a nearly constant input of magma from below the high, as an extension of the magma supply to the ridge * Now at Department of Geophysics, Stanford University, Stanford, CA, 94305-2215 U.S.A. from the mantle. Because the proximal ridge profoundly affects the juxtaposed crust at the RTI, sea floor fabric along the aseismic extensions of this fast-slipping transform fault is primarily a record of processes at work at the RT! rather than a record of transform tectonism.

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A one‐million‐year history of the 11°45′N East Pacific Rise discontinuity

Cited by 46 publications

References 53 publications

Variations in the geochemistry of magmatism on the East Pacific Rise at 10°30′N since 800 ka

Variations in the geochemistry of magmatism on the East Pacific Rise at 10°30′N since 800 ka

Tectonics of the East Pacific rise : studies of faulting characteristics and magnetic and gravity anomalies

The origin of bathymetric highs at ridge-transform intersections: A multi-disciplinary case study at the Clipperton Fracture Zone

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