Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 1024, doi:10.1029/2002GC000364.
Description:
The Mid-Atlantic Ridge around the Fifteen-Twenty Fracture Zone is unique in that outcrops of lower crust and mantle rocks are extensive on both flanks of the axial valley walls over an unusually long distance along-axis, indicating a high ratio of tectonic to magmatic extension. On the basis of newly collected multibeam bathymetry, magnetic, and gravity data, we investigate crustal evolution of this unique section of the Mid-Atlantic Ridge over the last 5 Ma. The northern and southern edges of the study area, away from the fracture zone, contain long abyssal hills with small spacing and fault throw, well lineated and high-amplitude magnetic signals, and residual mantle Bouguer anomaly (RMBA) lows, all of which suggest relatively robust magmatic extension. In contrast, crust in two ridge segments immediately north of the fracture zone and two immediately to the south is characterized by rugged and blocky topography, by low-amplitude and discontinuous magnetization stripes, and by RMBA highs that imply thin crust throughout the last 5 Ma. Over these segments, morphology is typically asymmetric across the spreading axis, indicating significant tectonic thinning of crust caused by faults that have persistently dipped in only one direction. North of the fracture zone, however, megamullions are that thought to have formed by slip on long-lived normal faults are found on both ridge flanks at different ages and within the same spreading segment. This unusual partitioning of megamullions can be explained either by a ridge jump or by polarity reversal of the detachment fault following formation of the first megamullion.
Description:
This work was completed while T. Fujiwara was
a Guest Investigator at Woods Hole Oceanographic Institution
with funding from Japan Marine Science and Technology
Center (JAMSTEC), National Science Foundation, and the
JAMSTEC Research Overseas Program. J. Lin’s contributions
to this research were supported by NSF Grant OCE-9811924.
B. E. Tucholke’s contributions were supported by NSF Grant
OCE-9503561 and by the Andrew W. Mellon Endowment
Fund for Innovative Research and the Henry Bryant Bigelow
Chair at Woods Hole Oceanographic Institution.
Keywords:
Fifteen-twenty fracture zone
;
Morphology
;
Magnetic anomaly
;
Gravity anomaly
;
Megamullion
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
Format:
text/plain
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