58:: plates are rigid. This paradox is solved by the fact that the overlapping spreading centers are non-steady-state and propagate along the ridge; as one segment lengthens, the neighboring segment shortens. Which segment lengthens, is arbitrary; evidence shows that at times the spreading center tips have alternated migrating directions. The discovery of overlapping spreading centers revealed the time-varying behavior of mid-ocean ridge segments, with implications for magmatism, volcanism and patterns of
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between the hands. This 3:1 overlap to offset ratio (observed at a wide range of scales, from hundreds of meters to tens of km) holds the key to their mechanism of formation. In fracture mechanics, when two cracks propagate toward each other, they tend to deflect away from each other, propagate past each other, and then stall out when the ratio is 3:1 because at this point the crack propagation force drops to zero.
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that appears to offset each center. At an overlapping spreading center the adjacent centers overlap and are not connected by a transform fault. In plan view, overlapping spreading centers look like two people about to shake hands but over-reaching by a distance that is three times the distance
386:
Macdonald, K., Sempere, J.C. and Fox, P.J. (1984). "East
Pacific Rise from Siqueiros to Orozco fracture zones: Along‐strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers".
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Macdonald, K. C.; Sempere, J.-C.; Fox, P. J.; Tyce, R. (1987-11-01). "Tectonic evolution of ridge-axis discontinuities by the meeting, linking, or self-decapitation of neighboring ridge segments".
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Sempere, J.-C. and K.C. Macdonald (1986). "Overlapping spreading centers: Implications from crack growth simulation by the displacement discontinuity method".
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between the plates are higher than in other ocean basins. They occur on all fast-spreading rate centers (>90 mm/yr) including the
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Macdonald, K. C. (1982). "Mid-Ocean Ridges: Fine Scale
Tectonic, Volcanic and Hydrothermal Processes Within the Plate Boundary Zone".
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What results are two spreading centers overlapping, apparently pushing against each other, which would violate one of the rules of
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Schematic of oceanic overlapping spreading centers. Plates A and B are spreading apart. Black regions denote spreading centers.
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Macdonald, Ken C.; Fox, P. J. (1983). "Overlapping spreading centres: new accretion geometry on the East
Pacific Rise".
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Lonsdale, P. (1983). "Overlapping rift zones at the 5.5°S offset of the East
Pacific Rise".
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Overlapping spreading centers are found mostly on mid-ocean ridge spreading centers in the
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Macdonald, Ken C. (2019), "Mid-Ocean Ridge
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Macdonald, Kenneth C.; Fox, Paul J. (1990). "The Mid-Ocean Ridge".
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389:Journal of Geophysical Research: Solid Earth
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391:. 89(B7) (B7): 6049–6069.
450:1994E&PSL.121..195P
405:10.1029/JB089iB07p06049
263:10.1029/TC005i001p00151
228:10.1029/JB088iB11p09393
88:Pacific-Antarctic Ridge
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397:1984JGR....89.6049M
333:1982AREPS..10..155M
290:1987Geo....15..993M
255:1986Tecto...5..151S
220:1983JGR....88.9393L
177:1990SciAm.262f..72M
165:Scientific American
121:1983Natur.302...55M
76:rates of separation
72:Pacific Ocean basin
214:(B11): 2156–2202.
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42:Appearance
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