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The Indian Ocean Triple Junction

The Indian Ocean Triple Junction,10.1029/JB085iB09p04723,Journal of Geophysical Research,Christopher R. Tapscott,Philippe Patriat,Robert L. Fisher,Joh

The Indian Ocean Triple Junction   (Citations: 41)
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The boundaries of three major plates (Africa, India, and Antarctica) meet in a triple junction in the Indian Ocean near 25°S, 70°E. Using observed bathymetry and magnetic anomalies, we locate the junction to within 5 km and show that it is a ridge-ridge-ridge type. Relative plate motion is N60°E at 50 mm/yr (full rate) across the Central Indian Ridge, N47°E at 60 mm/yr across the Southeast Indian Ridge, and N3°W at 15 mm/yr across te Southwest Indian Ridge; the observed velocity triangle is closed. Poles of instantaneous relative plate motion are determined for all plate pairs. The data in the South Atlantic and Indian oceans are consistent with a rigid African plate without significant internal deformation. Two of the ridges at the triple junction are normal midocean spreading centers with well-defined median valleys. The Southwest Indian Ridge, however, has a peculiar morphology near the triple junction, that of an elongate triangular deep, with the triple junction at its apex. The floor of the deep represents crust formed at the Southwest Indian Ridge, and the morphology is a consequence of the evolution of the triple junction and is similar to that at the Galapagos Triple Junction. Though one cannot determine with precision the stability conditions at the triple junction, the development of the junction over the last 10 m.y. can be mapped, and the topographic expressions of the triple junction traces may be detected on the three plates.
Journal: Journal of Geophysical Research , vol. 85, no. B9, pp. 4723-4739, 1980
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    • ...The SEIRand CIRare nearly collinear, and are intersected quasi-orthogonally by the SWIR [10]...
    • ...The RTJ has been stable for at least the last 5^10 Myr, and perhaps for as long as 40 Myr [10,12]...
    • ...For the last V80 Myr, the RTJ has been propagating eastward [13] ; since 10 Ma, the SWIRand CIRhave lengthened by an average of 2.7 and 1.3 cm/yr, respectively [10]...
    • ...The half-spreading rate for each spreading branch is indicated, and ridge abbreviations are given in Fig. 1. Arrows show plate motion with respect to the triple junction, modi¢ed from [10] for (a), [2] for (b), and [3] for (c)...
    • ...We ¢x the location of the triple junction in the center of Model 1, and prescribe the motions of the three plates with respect to the triple junction according to the RTJ velocity triangle calculated by [10]...

    Jennifer E. Georgenet al. Three-dimensional passive £ow and temperature structure beneath oceani...

    • ...The identified magnetic anomalies along the Central Indian Ridge indicate that the current half-spreading rate varies from 1.6 to 2.5 cm/yr between the northern and southern ends of the ridge (Fisher et al., 1971; Tapscott et al., 1980; DeMets et al., 1990)...

    M. Radha Krishna. Isostatic response of the Central Indian Ridge (Western Indian Ocean) ...

    • ... 1981 Goodlad et al., 1982 Guennoc et al., 1988 Karasik et al., 1986 LaBrecque and Hayes, 1979 Larson et al., 1978 Liu et al., 1982 Markl, 1974 Markl, 1978 McKenzie and Sclater, 1971 Mohr and Zannettin, 1988 Norton and Sclater, 1979 Patriat, 1987 Patriat, 1987 Rabinowitz and LaBrecque, 1979 Royer et al., 1988 Royer and Sandwell, 1989 Schlich, 1982 Schlich et al., 1987 Sclater et al., 1976 Segoufin, 1981 Segoufin and Patriat, 1981 Tapscott et ...

    J.-Y. Royeret al. A global isochron chart

    • ...The axial valleys and fracture zones of the CIR and SEIR, were approximately located by Tapscott et al. (1980) using conventional echo-sounder and magnetic data, mostly from two cruises of the R/V Atlantis II. More recent studies of Sea Beam and magnetic data over a 100 x 100 km area about the triple junction have been undertaken by Munschy (1987) and Munschy and Schlich (1989)...
    • ...This and a CIR spreading asymmetry between anomaly 2 and the Jaramillo will be shown to explain the formation of the small 5-kin-offset of the CIR and SEIR median valleys at the triple junction that was originally proposed by Tapscott et al. (1980) and later mapped by Munschy and Schlich (1989) with Sea Beam...
    • ...Their velocity diagram and a more recent analysis of Tapscott et al. (1980) differ only slightly from Figure l(b) of this study, which includes local plate velocities constructed from the rotation poles of DeMets et al. (1988)...
    • ...orthogonal trends of the SEIR magnetic anomalies (Munschy and Schlich, 1989; Tapscott et al., 1980)...
    • ...Tapscott et al. (1980) suggested that the CIR spreading segment immediately north of the triple junction may have been spreading obliquely but their observations were too coarse to resolve the details of the CIR valley...
    • ...There are, however, no obvious candidates in the GLORIA images for the persistent left-lateral ridge offsets suggested by Tapscott et al. (1980) and Munschy and Schlich (1989) on the basis of magnetic anomaly data, except to the southeast of the area at F trending 050 ~ which is also the site of recent seismic activity (Figure 9)...
    • ...Magnetic anomalies over the SWIR have very low amplitudes east of 68o30 , E; the Brunhes anomaly is not recognizable until farther west at 68~ ' E (Tapscott et al., 1980)...
    • ...Within this area, no clear evidence was found for asymmetric spreading over the SEIR, in accord with Tapscott et al. (1980)...
    • ...Tapscott et al. (1980) located fracture zone 3 but they had too few magnetic anomalies to resolve separate fracture zones 1 and 2. A further map of magnetic isochrons by Munschy and Schlich (1989) did not include the alongaxis movements of fracture zone !, and, although they showed its decay, the initiation of offset 2 at anomaly 2A.3 was not recognized, presumably because the coverage of anomaly data was insufficient (the anomaly picks ...
    • ...The second possible mechanism is that these fracture zones may form by small offsets of the CIR and SEIR segments at the triple junction, perhaps in a manner similar to that proposed by Tapscott et al. (1980) and Munschy and Schlich (1989)...

    N. C. Mitchell. An evolving ridge system around the Indian Ocean triple junction

    • ...The half spreading rate and ridge trend close to the RTJ are known to be 3.0cma -~ and N137 ~ respectively (Tapscott et al., 1980) and to progressively change to 3.7 cm a -~ and N094 ~ at the Macquarie Ridge Complex (Weissel and Hayes, 1972)...
    • ...The half spreading rate and ridge trend progressively change between the RTJ and the equator from 2.5cma -L and N149 ~ (Tapscott et al., 1980) to 1.8cma -~ and N142 ~ (Fisher et al., 1971)...
    • ...The Southwest Indian Ridge (SWIR), the boundary between the African and Antarctic plates, extends between the RTJ and the Bouvet Triple Junction (55~ and 01 ~ W); the ridge axis trends N090 ~ at the RTJ (Tapscott et al., 1980) and changes to N135 ~ at the Bouvet Triple Junction (Sclater et al., 1976)...
    • ...Tapscott et al. (1980) have analysed the data collected by the R/V Atlantis II, cruise 93 legs 5 and 6 (1976), within a 2...
    • ...The RTJ is a RRR junction for the last 80 Ma (Schlich, 1982) and appears to be stable in the sense of McKenzie and Morgan (1969), as discussed by Tapscott et al. (1980)...
    • ...Along the SEIR segment covered by the survey, no transform fault is visible, but Tapscott et aL (1980) have suggested that, close to the RTJ, the SEIR is spreading symmetrically in a direction normal to its strike...
    • ...Thus, a stable RRR model as proposed by Tapscott et al. (1980) on the basis of their study of the magnetic lineations and spreading directions of the three ridges since 10 Ma, is not consistent with the more detailed directions observed on the new bathymetric chart of the RTJ...
    • ...The RRF configuration was rejected by Tapscott et al. (1980)...
    • ...This is surprising because the RTJ has remained RRR regionally since the Late Cretaceous (Tapscott et aL, 1980; Schlich, 1982; Patriat, 1983)...

    M. Munschyet al. The Rodriguez Triple Junction (Indian Ocean): Structure and evolution ...

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