Constraints on rift propagation history at the cobb offset, juan de Fuca Ridge, from numerical modeling of tectonic fabric

Shoberg, Thomas G.; Stein, Seth; Karsten, Jill L.

doi:10.1016/0040-1951(91)90047-v

Cited by 18 publications

(17 citation statements)

References 35 publications

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“…Our inversion excludes PmP travel times for ridge crossing paths, which reduces the number of Moho reflections near the ridge axis, but synthetic inversions with the same ray geometry and travel times based on a uniform thickness crust beneath the plateau, show only a small decrease in apparent crustal thickness toward the ridge axis (Figure S8a) suggesting that the observed crustal thinning is not an artifact of uneven ray coverage. Carbotte et al [] suggest that renewed northward propagation of the Cobb OSC in the past 100,000 years as the Northern Symmetric Segment lengthens [ Johnson et al , ; Shoberg et al , ] is consistent with a waning influence of the Heckle melt anomaly. In addition, the chemistry of basalts along the Endeavour has been interpreted in terms of a failing rift that is underlain by diminishing mantle melting [ Karsten et al , ].…”

Section: Discussionmentioning

confidence: 99%

Near‐axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

Soule

Wilcock

Toomey

et al. 2016

Geophysical Research Letters

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A model of crustal thickness and lower crustal velocities is obtained for crustal ages of 0.1–1.2 Ma on the Endeavour Segment of the Juan de Fuca Ridge by inverting travel times of crustal paths and non‐ridge‐crossing wide‐angle Moho reflections obtained from a three‐dimensional tomographic experiment. The crust is thicker by 0.5–1 km beneath a 200 m high plateau that extends across the segment center. This feature is consistent with the influence of the proposed Heckle melt anomaly on the spreading center. The history of ridge propagation on the Cobb overlapping spreading center may also have influenced the formation of the plateau. The sharp boundaries of the plateau and crustal thickness anomaly suggest that melt transport is predominantly upward in the crust. Lower crustal velocities are lower at the ends of the segment, likely due to increased hydrothermal alteration in regions influenced by overlapping spreading centers, and possibly increased magmatic differentiation.

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Section: Discussionmentioning

confidence: 99%

Near‐axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

Soule

Wilcock

Toomey

et al. 2016

Geophysical Research Letters

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“…A conjugate partial ridge is present east of the current axis within the southern part of the segment indicating that the axis jump was confined within the axial rift of this region. Renewed northward propagation of Northern Symmetric segment has occurred in the past 100,000 years [ Shoberg et al , 1991], which may reflect a current waning in influence of the Heckle anomaly on melt production at Endeavour segment as this anomaly is transferred to the east flank of the ridge.…”

Section: Discussionmentioning

confidence: 99%

“…Northward propagation of the Cobb offset, which separates Endeavour and Northern Symmetric segments, initiated at ∼4.5 Ma [ Wilson , 1993]. The Cobb offset reached its maximum northward extent at ∼0.8 Ma, then retreated to approximately 47°35′N as Endeavour segment propagated southward (Figure 2a) [ Shoberg et al , 1991]. Propagation has reversed in the past 100,000 years, with the northern end of Northern Symmetric segment currently located at 47°46′N.…”

Section: Regional Setting and Recent Tectonic Historymentioning

confidence: 99%

Variable crustal structure along the Juan de Fuca Ridge: Influence of on‐axis hot spots and absolute plate motions

Carbotte

Nedimović

Canales

et al. 2008

Geochem Geophys Geosyst

117

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[1] Multichannel seismic and bathymetric data from the Juan de Fuca Ridge (JDFR) provide constraints on axial and ridge flank structure for the past 4-8 Ma within three spreading corridors crossing Cleft, Northern Symmetric, and Endeavour segments. Along-axis data reveal south-to-north gradients in seafloor relief and presence and depth of the crustal magma lens, which indicate a warmer axial regime to the south, both on a regional scale and within individual segments. For young crust, cross-axis lines reveal differences between segments in Moho two-way traveltimes of 200-300 ms which indicate 0.5-1 km thicker crust at Endeavour and Cleft compared to Northern Symmetric. Moho traveltime anomalies extend beyond the 5-15 km wide axial high and coincide with distinct plateaus, 32 and 40 km wide and 200-400 m high, found at both segments. On older crust, Moho traveltimes are similar for all three segments ($2100 ± 100 ms), indicating little difference in average crustal production prior to $0.6 and 0.7 Ma. The presence of broad axis-centered bathymetric plateau with thickened crust at Cleft and Endeavour segments is attributed to recent initiation of ridge axiscentered melt anomalies associated with the Cobb hot spot and the Heckle melt anomaly. Increased melt supply at Cleft segment upon initiation of Axial Volcano and southward propagation of Endeavour segment during the Brunhes point to rapid southward directed along-axis channeling of melt anomalies linked to these hot spots. Preferential southward flow of the Cobb and Heckle melt anomalies and the regional-scale south-to-north gradients in ridge structure along the JDFR may reflect influence of the northwesterly absolute motion of the ridge axis on subaxial melt distribution.

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“…To the south, the Cobb offset has undergone net northward propagation over the past few million years, punctuated by short episodes of reversed motion [ Johnson et al , 1983]. The latest episode of northward propagation commenced only 0.05 Myr ago [ Delaney et al , 1981], and current migration rate is 0.4–0.9 m yr −1 [ Shoberg et al , 1991]. Karsten et al [1990] have suggested that much, if not all, of the Endeavour rift is in the process of failing.…”

Section: Discussionmentioning

confidence: 99%

Microearthquakes on the Endeavour segment of the Juan de Fuca Ridge

2002

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[1] We report the results of a 55-day microearthquake experiment on the Endeavour segment of Juan de Fuca Ridge. The network covered a 5-km section of the ridge axis centered on the Main vent field and extended 15-km off axis on the west flank. The ridge axis and flanks were seismically active, and 1750 earthquakes were located with a minimum of five travel time picks including at least one S wave. Over half the earthquakes occurred in swarms, and a waveform cross-correlation technique was used to obtain relative locations. On the western flank, the hypocenters for four swarms at midcrustal depths are compatible with steeply dipping fault planes that strike at 035-050°N and oblique to the abyssal hills. Focal mechanisms determined from P wave first motions and P/S amplitude ratios are predominantly strike-slip with north-south compression and appear to be affected by the reorganization of the Explorer plate. Earthquakes beneath the ridge axis are concentrated in a band of intense seismicity at 1.5-3.5 km depth. To the north of High Rise vent field, the seismicity defines a plane striking parallel to the ridge axis and dipping east at 70°and the earthquakes appear to extend beneath an axial reflector previously imaged at 2.3 km depth. Farther south, the hypocenters are not compatible with a single fault plane. Focal mechanisms are characterized by subhorizontal tension axes oriented in all directions except parallel to the ridge and suggest a stress field that is about equally influenced by ridge spreading and hydrothermal cooling.

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Constraints on rift propagation history at the cobb offset, juan de Fuca Ridge, from numerical modeling of tectonic fabric

Cited by 18 publications

References 35 publications

Near‐axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

Near‐axis crustal structure and thickness of the Endeavour Segment, Juan de Fuca Ridge

Variable crustal structure along the Juan de Fuca Ridge: Influence of on‐axis hot spots and absolute plate motions

Microearthquakes on the Endeavour segment of the Juan de Fuca Ridge

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