Variations in ridge morphology and depth‐age relationships on the Pacific‐Antarctic Ridge

Marks, K. M.; Stock, J. M.

doi:10.1029/93jb02760

Cited by 27 publications

(12 citation statements)

References 28 publications

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“…12). An AAD-like anomaly has been suggested along a western segment of the Pacific-Antarctic ridge at about 185°W [Marks and Stock, 1994]. This segment has an axial valley along the ridge, somewhat similar to that along the AAD, and there is a small slope to the depth versus age 1 1 2 relation suggesting lower temperatures within the mantle [Marks and Stock, 1994].…”

Section: Discussionmentioning

confidence: 99%

“…An AAD-like anomaly has been suggested along a western segment of the Pacific-Antarctic ridge at about 185°W [Marks and Stock, 1994]. This segment has an axial valley along the ridge, somewhat similar to that along the AAD, and there is a small slope to the depth versus age 1 1 2 relation suggesting lower temperatures within the mantle [Marks and Stock, 1994]. Although this ridge segment does not cross inferred Mesozoic subduction it does meander close to the early Cretaceous position (Figure 12) and overlaps the strong free-air gravity and geoid low of the Ross Sea which may be associated with the overall position of Mesozoic subduction [Chase and Sprowl, 1983].…”

Section: Discussionmentioning

confidence: 99%

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Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous

Gurnis

Moresi

Müller

2000

Geophysical Monograph Series

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We propose that the anomalous Cretaceous vertical motion of Australia and distinctive geochemistry and geophysics of the Australian-Antarctic Discordance (AAD) were caused by a subducted slab which migrated beneath the continent during the Cretaceous, stalled within the mantle transition zone, and is presently being drawn up by the Southeast Indian Ridge. During the Early Cretaceous the eastern interior of the Australian continent rapidly subsided, but must have later uplifted on a regional scale. Beneath the AAD the mantle is cooler than normal, as indicated by a variety of observations. Seismic tomography shows an oblong, slab-like structure orientated N-S in the transition zone and lower mantle, consistent with an old subducted slab. Using a three-dimensional model of mantle convection with imposed plate tectonics, we show that both of t hese well documented features are related. The models start with slabs dipping toward the restored eastern Australian margin. As Australia moves east in a hot spot reference frame from 130-90 Ma, a broad dynamic topography depression of decreasing amplitude migrates west across the continent causing the continent to subside and then uplift. Most of the slab descends into the deeper mantle, but the models show part of the cooler mantle becomes trapped within the transition zone. From 40 Ma to the present, wisps of this cool mantle are drawn up by the northwardly migrating ridge between Australia and Antarctica. This causes a circular dynamic topography depression and thinner crust to develop at the present position of the AAD. The AAD is unique within the ocean basins because it is the only place where a modern ridge has migrated over the position of long term Mesozoic subduction. Our study demonstrates the predictive power of mantle convection models when they incorporate plate tectonics.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous

Gurnis

Moresi

Müller

2000

Geophysical Monograph Series

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“…At the same time, plume is highly oblique to APM and parallel to the Pacific‐Antarctic ridge. Because the Louisville plume source is deep, I speculate that ridge‐parallel asthenospheric flow (proposed to occur there by Marks and Stock [1994]) could be responsible for the anomalous plume .…”

Section: Implications For Mantle Flowmentioning

confidence: 98%

Absolute plate motions constrained by shear wave splitting orientations with implications for hot spot motions and mantle flow

Kreemer

2009

J. Geophys. Res.

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[1] Here, I present a new absolute plate motion model of the Earth's surface, determined from the alignment of present-day surface motions with 474 published shear wave (i.e., SKS) splitting orientations. When limited to oceanic islands and cratons, splitting orientations are assumed to reflect anisotropy in the asthenosphere caused by the differential motion between lithosphere and mesosphere. The best fit model predicts a 0.2065°/Ma counterclockwise net rotation of the lithosphere as a whole, which revolves around a pole at 57.6°S and 63.2°E. This net rotation is particularly well constrained by data on cratons and/or in the Indo-Atlantic region. The average data misfit is 19°and 24°for oceanic and cratonic areas, respectively, but the normalized root-mean-square misfits are about equal at 5.4 and 5.2. Predicted plate motions are very consistent with recent hot spot track azimuths (<8°on many plates), except for the slowest moving plates (Antarctica, Africa, and Eurasia). The difference in hot spot propagation vectors and plate velocities describes the motion of hot spots (i.e., their underlying plumes). For most hot spots that move significantly, the motions are considerably smaller than and antiparallel to the absolute plate velocity. Only when the origin depth of the plume is considered can the hot spot motions be explained in terms of mantle flow. The results are largely consistent with independent evidence of subasthenospheric mantle flow and asthenospheric return flow near spreading ridges. The results suggest that, at least where hot spots are, the lithosphere is decoupled from the mesosphere, including in western North America.

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“…The transition from a rift valley (south of the PFZ) to an axial high (north of the PFZ) is inferred based on the observed change in the axial gravity signal. The portion of the PacificAntarctic Ridge associated with the rift valley is also characterized by an unusually small subsidence constant relative to global averages [Marks and Stock, 1994].…”

Section: Pacific-antarctic Ridge At 65øs ß Background Informationmentioning

confidence: 99%

Flow line variations in abyssal hill morphology for the Pacific‐Antarctic Ridge at 65°S

Macario¹,

Haxby²,

Goff³

et al. 1994

J. Geophys. Res.

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Abstract. We present the results of a statistical study on the morphological characteristics of abyssal hills recently mapped along two adjacent segments of the Pacific-Antarctic Ridge at 65øS. The studied area is a densely surveyed corridor (60 km wide by 600 km long) which is centered on the Pitman Fracture Zone (PFZ) and extends to 12 Ma crust on both sides of the ridge. Abyssal hill size parameters (RMS height H and characteristic width •) are estimated using Hydrosweep multibeam data. Variations in abyssal hill characteristics are compared with spreading rate history and crustal structure (as inferred from the mantle Bouguer gravity) in order to indirectly quantify the evolution of this ridge crest system. The magnetic data document an abrupt acceleration in spreading rate from -36 to -63 mm/yr (full rate) at Chron 3a (5.7-6.4 Ma). Our results indicate a statistically significant negative correlation between abyssal hill size parameters and full spreading rates. Abyssal hills formed during the slower spreading period (ages >8 Ma; full rates 36-44 mm/yr) are 31-86% taller and 21-> 100% wider than hills created during the faster spreading interval (ages <4 Ma; full rates 52-63 mm/yr). The well-resolved positive correlation between H and g is interpreted as an indication of temporal changes in the flexural rigidity of the lithosphere near the vicinity of the ridge crest and, by implication, axial thermal structure. However, we cannot rule out that such positive trend is due to constructional volcanism. The lack of correlation between crustal thickness and abyssal hill size parameters is likely to be caused by the small magnitude of crustal thickness variations along flow lines (4).4 km in contrast to -2 km reported in previous studies for the Mid-Atlantic Ridge). The most significant variations in crustal thickness are seen across the PFZ (thinning from north to south by 0.5-0.7 km), which coincide with a well-resolved increase in the averaged • estimate. The predictions of the detachment surface model in terms of morphological and structural inside/outside comer asymmetries are not supported by our observations. The main variations in H and • that cannot be explained in terms of either the spreading rate or crustal thickness effect include the following: (1) anomalously large abyssal hills north of the PFZ for 4-6 Ma age crust; (2) abyssal hill size estimates for crustal ages greater than 8 Ma show significant asymmetry for opposite ridge flanks north of the PFZ; and (3) toward the segment ends, H estimates are 27-68% larger, while • estimates either do not significantly change (to the north of the PFZ) or are up to 40% smaller (to the south of the PFZ). We suggest that the H and g changes seen toward the segment ends are related to either an increase in the amount of extension (without a corresponding increase in the strength of the lithosphere) or variations in the relative contribution of constractional volcanism to overall abyssal hill morphology.

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Variations in ridge morphology and depth‐age relationships on the Pacific‐Antarctic Ridge

Cited by 27 publications

References 28 publications

Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous

Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous

Absolute plate motions constrained by shear wave splitting orientations with implications for hot spot motions and mantle flow

Flow line variations in abyssal hill morphology for the Pacific‐Antarctic Ridge at 65°S

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