Tectonic evolution of ridge-axis discontinuities by the meeting, linking, or self-decapitation of neighboring ridge segments

Abstract

Research Article| November 01, 1987 Tectonic evolution of ridge-axis discontinuities by the meeting, linking, or self-decapitation of neighboring ridge segments K. C. Macdonald; K. C. Macdonald 1Department of Geology and Marine Science Institute, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar J.-C. Sempere; J.-C. Sempere 2Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar P. J. Fox; P. J. Fox 3Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar R. Tyce R. Tyce 3Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Geology (1987) 15 (11): 993–997. https://doi.org/10.1130/0091-7613(1987)15<993:TEORDB>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation K. C. Macdonald, J.-C. Sempere, P. J. Fox, R. Tyce; Tectonic evolution of ridge-axis discontinuities by the meeting, linking, or self-decapitation of neighboring ridge segments. Geology 1987;; 15 (11): 993–997. doi: https://doi.org/10.1130/0091-7613(1987)15<993:TEORDB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Recent deep-tow, Sea Beam, and SeaMARC II studies indicate that ridge axis discontinuities along the East Pacific Rise evolve in several different ways. Where magmatic pulses along the spreading center happen to meet head-on, a low point or “saddle point” occurs along the axial depth profile of the spreading center. Where the magmatic pulses misalign, overlapping spreading centers develop and two distinct evolutionary paths are possible. One spreading center tip may cut through to and link with the adjacent en echelon ridge, chopping off the opposing ridge tip, as proposed by Macdonald and Fox (1983). In addition, either spreading center may cut inside or outside of itself, repeatedly decapitating its own ridge tip. Crack-propagation studies show that the crack-propagation force, G, drops significantly when the ratio of crack overlap to crack offset (L/W) exceeds 3. Applying this relation to spreading centers, we suggest that propagation of the individual spreading center tips may stall when L/W is greater than 3. If linkage has not yet occurred, then the next magmatic pulse that propagates along the ridge may be deflected away from the path of the existing ridge tip, decapitating the ridge tip in a process we call self-decapitation. Subsequent magmatic pulses may be deflected or “derailed” from the existing path of the ridge because freezing of the axial magma chamber near ridge-axis discontinuities creates a core of coherent, unfaulted gabbroic rock along the spreading axis which is strong relative to the intensely faulted lithosphere on either side of the frozen magma chamber. In addition, the local stress field rotates near the discontinuity so that subsequent magma pulses and associated cracking fronts will tend to deflect away from the preexisting path of the ridge. For propagating rifts, which represent first-order changes in plate-boundary geometry, L/W remains <1.5 so that G is maintained near its maximum value and episodes of continued propagation in the same direction are enhanced. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.