Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 120 (2015): 2119–2142, doi:10.1002/2014JB011501.
Description:
We use high-resolution multibeam bathymetry, shipboard gravity, side-scan sonar images, and magnetic anomaly data collected on conjugate flanks of the Mid-Atlantic Ridge at 25°N–27°30′N and out to ~27 Ma crust to investigate the crustal evolution of the ridge. Substantial variations in crustal structure and thickness are observed both along and across isochrons. Along isochrons within spreading segments, there are distinct differences in seafloor morphology and gravity-derived crustal thickness between inside and outside corners. Inside corners are associated with shallow depths, thin crust, and enhanced normal faulting while outside corners have greater depths, thicker crust, and more limited faulting. Across-isochrons, systematic variations in crustal thickness are observed at two different timescales, one at ~2–3 Myr and another at 〉10 Myr, and these are attributed to temporal changes in melt supply at the ridge axis. The shorter-term variations mostly are in-phase between conjugate ridge flanks, although the actual crustal thickness can be significantly different on the two flanks at any given time. We observe no correlation between crustal thickness and spreading rate. Thus, during periods of low melt supply, tectonic extension must increase to accommodate the full plate separation rate. This extension commonly is concentrated in long-lived faults on only one side of the axial valley, resulting in strong across-axis asymmetries in crustal thickness and seafloor morphology. The thin-crust flank has few volcanic features and exhibits elevated, blocky topography with large-offset, often irregular faults, while the conjugate thicker-crust flank shows shorter-offset, regular faulting, and common volcanic features. The variations in melt supply at the ridge axis most likely are caused either by episodic convection in the subaxial mantle or by variable melting of chemically heterogeneous mantle.
Description:
This study was funded by Chinese Natural Science Foundation grant 41206034 and Chinese Postdoc Scholarship award 2012M511130 (T.W.), by Ministry of Science and Technology 973 Project award 2012CB417303, and by the WHOI Henry Bryant Bigelow Chair (J.L.). ARSRP and MAREAST data acquisition was funded by Office of Naval Research grant N00014-90-J-6121 and by U.S. National Science Foundation grant OCE-9503561, respectively.
Description:
2015-10-21
Keywords:
Crustal thickness
;
Seafloor morphology
;
Mid-Atlantic Ridge
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
Format:
application/msword
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