Analysis and implications of the sequence of ridge jumps that eliminated the Surveyor Transform Fault

Shih, John Shai-Fu; Molnár, Péter

doi:10.1029/jb080i035p04815

Cited by 66 publications

(28 citation statements)

References 22 publications

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“…Ridgejumps of 50 to 100 km occur in response to energetically favourable re-orientations of spreading axes Shih & Molnar 1975;Lachenbruch, 1976;Hey et al 1980), and these new spreading centres originate in lithosphere less than a few Ma old assuming a spreading rate of 50 mm yr-a. New spreading centres formed in lithosphere about 10 Ma old, near the hypothetical age limit for such activity, in a rearrangement of the East Pacific spreading system at 5 to 10 Ma (Atwater 1970;Sclater et al 1971;Herron 1972), but such events are rare in the oceanic record.…”

Section: Oceanic Lithospherementioning

confidence: 99%

The tensile strength of the lithosphere and the localization of extension

Lynch

Morgan²

1987

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Continents appear to rift in preference to oceans. Furthermore, some areas of continents appear to be more susceptible to rifting than others. Experimental rock mechanics data are used to estimate lithospheric strength for lithospheres of different structure, thereby to investigate the possible causes of rift localization. Using optimum creep parameters for silicic, mafic and ultramafic rocks, we find that lithospheric strength is inversely related to both crustal thickness and heat flow. By virtue of its thinner crust, oceanic lithosphere is inherently stronger than continental lithosphere. We find that oceanic lithosphere older than about 10 Ma should be able to withstand the lithospheric forces exerted on it by gravity sliding and plate interactions. Rifting or ridge-jumps are therefore only likely to occur in very young oceanic lithosphere. Low heat flow continental shields should also be able to withstand likely lithospheric forces without significant deformation. As the heat flow increases, however, the lithosphere is weakened dramatically. A smaller amount of weakening is associated with crustal thickening. Thus, unless rifting is localized by a strongly heterogeneous stress field, it will be by anomalously weak lithosphere. This lithosphere is likely to have anomalously high heat flow and/or crustal thickness prior to extension.

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Section: Oceanic Lithospherementioning

confidence: 99%

The tensile strength of the lithosphere and the localization of extension

Lynch

Morgan²

1987

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“…These jumps ranged in distance from several hundred to a thousand kilometres. Shih and Molnar (1975) have postulated a series of lesser axis jumps, spanning 40 to 70 km, to account for the changing magnetic anomaly patterns in the northeast Pacific near the Surveyor Fracture Zone. The lengths of axis involved in those jumps, 100 to 200 km, are similar to those involved in the small on July 14, 2015 memoirs.gsapubs.org Downloaded from axis shifts along the Nazca-Pacific plate boundary, but longer than those involved with the small shifts along the Galapagos rift zone (Hey and Vogt, 1977).…”

Section: Origin Of Small Axial Offsetsmentioning

confidence: 99%

Tectonics of the Nazca-Pacific divergent plate boundary

Rea¹

1981

Geological Society of America Memoirs

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Five regions along the Nazca-Pacific plate boundary are the sites of detailed surveys completed during the Nazca Plate Project, four in relatively typical axial regions and one in the area of the tectonically complex Easter plate. Deep tow surveys have also been conducted on the spreading center and in a fracture zone. I n addition to the survey data, many tracklines of a reconnaissance nature cross the spreading center. Sea-floor spreading occurs at about 160 mm/ yr (whole rate) along this part of the East Pacific Rise. South of the Garret Fracture Zone at 13.5° S spreading is asymmetrical, being faster to the east than to the west. The lithosphere near fast-spreading rises is quite thin and therefore more susceptible to deformation than along slow-spreading ridges. The effects of a weak lithosphere take several forms: a long oblique ridge in the active portion of the Wilkes Fracture Zone at 9°S; twinned spreading centers surrounding the small Easter plate; and small, 10 to 15 km, offsets of the spreading center that can be formed or healed rapidly. These offsets are all formed within a time span of 0.5 m.y. or less and may involve segments of the rise axis up to 200 km long. Apparently they are the result of small, discrete axis jumps facilitated by the unusually thin lithosphere. Reconnaissance data between the 13.5°S and 4.5°S fracture zones are adequate to decipher the history of formation of the East Pacific Rise in this region. Spreading activity shifted 600 to 850 km westward from the old Galapagos Rise, now in the center of the Nazca plate, to its present location by three large jumps. Each of these jumps resulted in the formation of a fracture zone-bound section of the new rise; the jumping process covered about 2.5 m.y., from 8.2 to 5.7 m.y. ago. on July 14, 2015 memoirs.gsapubs.org Downloaded from on July 14, 2015 memoirs.gsapubs.org Downloaded from DIVERGENT BOUNDARY 31have provided the best bathymétrie maps of the Nazca plate and adjacent regions (Mammerickx and others, 1975;Mammerickx and Smith, 1978). DATA FROM THE RISE CREST 9° to 12° S RegionThe development of the EPR axis in the region between about 9° and 12°S is the simplest of the areas surveyed. Data in this region (Rea, 1976a) consist of a detailed survey area centered on the rise crest at about 10.5°S and several reconnaissance lines that cross the east flank and crest of the rise. A bathymetric contour map of the 10.5°S survey area (Fig. 2) depicts the typical features of the EPR crest. The precise axis of the EPR is a low ridge about 300 m high and 15 to 20 km wide (Figs. 2,3). The shallowest depth of this feature is 2,600 to 2,700 m, and the 3,000-m contour line (Fig. 2) generally defines its lateral extent. The axis is aligned along a trend of 018° in the northern two-thirds of the area, but changes trend at 11 ° S to 012° in the southern part of the survey area. Low ridges commonly occur along the flanks of the axial ridge and where well developed (Fig. 3, lines 4 and 5) divide the axial block into three peaks of subequal width; the ...

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We present a revised model of the tectonic evolution of the Juan de Fuca ridge by propagating rifting. This area, along with the adjacent Surveyor fracture zone area and the Galapagos area, also provided critical data for the development of the propagating rift theory [Shih and Molnar, 1975;Hey, 1977]. The rotation pole shifts at 8.5 and 5.0 Ma imply clockwise shifts in the direction of relative motion of 10 ø to 15 ø.

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mentioning

confidence: 99%

Propagation as a mechanism of reorientation of the Juan de Fuca Ridge

Wilson¹,

Hey

Nishimura³

1984

J. Geophys. Res.

128

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We present a revised model of the tectonic evolution of the Juan de Fuca ridge by propagating rifting. The new model has three different relative rotation poles, covering the time intervals 17.0–8.5 Ma, 8.5–5.0 Ma, and 5.0 Ma to the present. The rotation pole shifts at 8.5 and 5.0 Ma imply clockwise shifts in the direction of relative motion of 10° to 15°. At each of these shifts, the pattern of propagation reorganizes, and the new ridges formed by propagation are at an orientation closer to orthogonal to the new direction of motion than the orientation of the preexisting ridges. The model, containing a total of seven propagation sequences, shows excellent agreement with the isochrons inferred from the magnetic anomaly data, except in areas complicated by the separate Explorer and Gorda plates. The agreement between model and data near the Explorer plate breaks down abruptly at an age of about 5 Ma, indicating that the probable cause of the rotation pole shift at that time was the separation of the Explorer plate from the Juan de Fuca plate.

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Analysis and implications of the sequence of ridge jumps that eliminated the Surveyor Transform Fault

Cited by 66 publications

References 22 publications

The tensile strength of the lithosphere and the localization of extension

The tensile strength of the lithosphere and the localization of extension

Tectonics of the Nazca-Pacific divergent plate boundary

Propagation as a mechanism of reorientation of the Juan de Fuca Ridge

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