The Age of the South Atlantic

Ladd, John W.; Dickson, G. O.; PitmanIII, Walter C.

doi:10.1007/978-1-4684-3030-1_14

Cited by 30 publications

(19 citation statements)

References 35 publications

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“…Spreading started about 125 Ma ago, and the series of poles and rates of opening based on magnetic anomalies Ladd, Dickson & Pitman 1973;Larson & Ladd I973 ;Ladd 1976) are reasonably consistent with the classic pre-drift reconstruction of Bullard,Everett & Smith (1 965). In the southernmost South Atlantic, however, fewer data are available and both the detailed history of South Atlantic spreading and its southward extent are uncertain.…”

Section: Introductionsupporting

confidence: 66%

The history of ridge-crest offset at the Falkland--Agulhas Fracture Zone from a small-circle geophysical profile

Barker

1979

Geophysical Journal International

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Summary. The magnetic and bathymetric profiles are described along a single ship track following a small circle of South Atlantic opening about 100 km south of the Falkland‐Agulhas Fracture Zone (FAFZ). The magnetic anomalies reveal a 700 km westward jump of the crest of the Mid‐Atlantic Ridge at about 61–64 Ma ago and suggest a second 100 km westward jump 58–60 Ma ago. The destinations of both jumps are now occupied by narrow rough‐topped ridges standing about 2 km above the adjacent ocean floor. It is suggested that these were formed at the times of the jumps, by volcanic and intrusive igneous activity associated with the rupture of older oceanic crust. The original offset of the ridge crest at the FAFZ was 1400 km, the length of the continental Falkland Plateau; of this only about 200 km remains. 800km of offset was eliminated by the two ridge jumps already detected, leaving 400 km unaccounted for. Under reasonable assumptions, a further westward ridge jump of 380 km at about 98 Ma is proposed, the destination of which is marked by the only other similarly anomalous elevations on the bathymetric profile, one of which is the Agulhas Plateau. Existing sediment samples from the Agulhas Plateau are consistent with this interpretation of its origin. Magnetic anomalies directly east of the Falkland Plateau are identical to those in the eastern Cape Basin, which suggests strongly that the South Atlantic spreading system extended some distance south of the FAFZ from its inception. The anomalous elevations extend about 600 km south of the FAFZ indicating the southward extent of the ridge jumps and perhaps therefore of the spreading system at 98 and 60 Ma. In many ways the elevations resemble others commonly identified as hotspot phenomena, some of which may also have formed initially at ridge jump destinations. The correspondence between the observed magnetic profile and a synthetic profile generated from the LaBrecque time scale is particularly good for the past 40 Ma. This allows a detailed comparison; using the enhanced sensitivity of a reduced distance plot, which reveals several departures from linearity. Some revision of the LaBrecque time scale may be required. The reduced distance plot also shows details of the asymmetric spreading which, being of the same degree and in the same sense on both sides of the FAFZ, did not change the offset significantly. The asymmetry resembles that found south of Australia in being without discernible ridge jumps but displaying abrupt changes in degree, and in that the more slowly accreting (African) plate is the more elevated.

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Section: Introductionsupporting

confidence: 66%

The history of ridge-crest offset at the Falkland--Agulhas Fracture Zone from a small-circle geophysical profile

Barker

1979

Geophysical Journal International

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“…The age of the Argentine Basin north of the Falkland Plateau has been well determined from magnetic anomalies (Ladd et al, 1973;Rabinowitz and LaBrecque, 1979). North of the plateau, the age varies from about 80 Ma in the east to 130 Ma in the west.…”

Section: Discussionmentioning

confidence: 99%

A Heat Flow Measurement on the Falkland Plateau

Langseth¹,

Ludwig²

1983

Initial Reports of the Deep Sea Drilling Project

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At Hole 511, on the margin of Maurice Ewing Bank, eastern Falkland Plateau, successful bottom hole temperature measurements were made at 52.5 and 113 meters below the seafloor. The results show a regular increase of temperature with depth of 0.074°C m"1 . Conductivity measurements on core samples, made on board ship and at the Lamont-Doherty repository, gave a mean value of 0.842 W "C^m~1. The heat flow indicated by these observations is 62.3 mWm~2 (1.49 HFU), a value that is compatible with the geological evolution of the plateau. EXPERIMENTAL TECHNIQUETemperature measurements are made in sediments at the bottom of the hole using the Tokyo/DSDP T-probe (Yokota et al., 1979). The instrument is lowered to the bottom of the drill string on the sand line during a pause in drilling. The electronic recorder, enclosed in a special core barrel that serves as a pressure-proof vessel, records temperature while the probe is being lowered down the pipe and during hoisting. When the core barrel is latched into the bottom of the drill string, the probe, carrying a thermistor in its tip, projects about one meter below the bottom of the bit.Temperature in the sediments is measured by driving the probe into the sediments at the bottom of the hole. The probe is left undisturbed in the sediments for a period of 15 to 20 minutes, which allows sufficient time for the probe to equilibrate with the surrounding sediments.While hoisting the probe back to the surface, a stop of several minutes is made just above the seafloor to allow the thermistor to equilibrate with the bottom water. This measurement provides a valuable data point, seafloor temperature, and an in situ check of instrument calibration, since the bottom water is usually known from nearby hydrographic data.For measurements in Hole 511, temperatures were recorded every minute, and up to 128 temperatures were recorded per lowering.HOLE 511 MEASUREMENTS Two successful temperature measurements were carried out at Hole 511. The heave compensator was used during the drilling and produced a stable bottom hole assembly in the unconsolidated sediments penetrated by the thermistor probe. The temperature records during lowering, penetration, a 20-min. wait on bottom, and hoisting back up the pipe are shown in Figure 1. In Figure 2 we show the temperature profile at a nearby hydrographic station INDOMED Leg XIII (SIO Data Report). Notice that the T-probe recorded the temperature minimum at 200-400 meters and a bottom water temperature of 0.7°C, both in excellent agreement with the hydrographic results. For some reason the recorder stopped functioning during hoisting, for both measurements. For the measurement at 52.5 meters (Measure- - - / r /. /

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“…We addressed this objective by targeting Site 361 above Anomaly M-4, and Site 363 on a projection of Anomaly M-O into the Walvis Ridge. We considered the dating of Cape Basin lineations (Larson and Ladd, 1973;Emery et al, 1975a;Mascle and Phillips, 1972) to be of great importance in determining the timing of the opening of the South Atlantic (Valencio and Vilas, 1969;Cox, 1970;Dietz and Holden, 1970;Dingle and Klinger, 1971;Le Pichon and Hayes, 1971;Francheteau and Le Pichon, 1972;Ladd et al, 1973) and the commencement of active ocean floor accretion at an axial spreading center.…”

Section: Specific Scientific Objectivesmentioning

confidence: 99%