Evolution of the Southern Kerguelen Plateau Deduced from Seismic Stratigraphic Studies and Drilling at Sites 748 and 750

Abstract

The evolution of the Raggatt Basin in the Southern Kerguelen Plateau, since the Late Cretaceous, was deduced from seismic stratigraphic interpretations of the multichannel seismic data and Ocean Drilling Program results at Sites 748 and 750. Synthetic seismograms were built using in situ and corrected core velocity values. Corrections were based on Wyllie's law, and exponential variations of porosity were calculated from logging data at Site 750. The synthetic seismograms in conjunction with the seismic sections allowed us to correlate the lithologic units and the seismic sequences.After the emplacement of oceanic basaltic basement at 110 Ma, the Late Cretaceous history of the Raggatt Basin was controlled by two rifting episodes at 88 Ma to the east and at 66 Ma to the west. The first rifting episode, with an axis of extension striking northwest-southeast, formed the eastern flank of the Southern Kerguelen Plateau. The second rifting episode, along a north-south axis, formed the 77°E Graben. At 45-42 Ma, the separation by seafloor spreading of the Kerguelen Plateau-Labuan Basin and Broken Ridge-Diamantina Zone marks a third rifting episode, which was recorded on the Southern Kerguelen Plateau by erosion.

Structure and tectonic history of the Southern Kerguelen Plateau (Indian Ocean) deduced from seismic reflection data

“…The present volcanic activity in the Kerguelen and Heard archipelagos suggest a continuing heat source in the region since the plateau was emplaced at about 114 Ma. The observation that Banzare Bank stayed at shallow water depths [Fritsch et al, 1992] until the tectonism also suggests that residual heat was present in the area at that time. This excessive heat source is likely to have weakened the crust, making the area more susceptible than the surrounding ocean basins to extension and rifting.…”

Alternative global Cretaceous paleogeography

“…Thermal rejuvenation of the northern part of the plateau has occurred during the time of formation of Broken Ridge about 88 Ma (Duncan, 1991), during the separation of Broken Ridge from Kerguelen Plateau about 43 Ma , and since 39 Ma (Giret and Lameyre, 1983). Stretching has occurred in the Ragatt Basin of the southern part of the plateau at 88 Ma in the east and at 66 Ma in the west (Fritsch et al, 1992). Stretching of large areas of the plateau may have occurred during separation of Kerguelen Plateau-Labuan Basin from the Broken Ridge-Diamantina Zone by sea-floor spreading at 45-42 Ma (Fritsch et al, 1992).…”

“…Stretching has occurred in the Ragatt Basin of the southern part of the plateau at 88 Ma in the east and at 66 Ma in the west (Fritsch et al, 1992). Stretching of large areas of the plateau may have occurred during separation of Kerguelen Plateau-Labuan Basin from the Broken Ridge-Diamantina Zone by sea-floor spreading at 45-42 Ma (Fritsch et al, 1992). Clearly, with all of these complications to its history, Kerguelen Plateau cannot have subsided as rapidly as Coffin suggested, and must have been a large land area even longer than he proposed in Alternative global Cretaceous paleogeography spite of the higher sea levels of the Late Cretaceous.…”

The Kerguelen plateau: Records from a long-living/composite microcontinent

“…Despite its remote location and inhospitable climate, the region has been the locus of several scientific surveys. Seismic surveys have been shot for both reflection and refraction data (Houtz et al, 1977;Coffin et al, 1990Coffin et al, , 2000Coffin et al, , 1997Collwell et al, 1988;Fritsch et al, 1992;Kö nnecke et al, 1998;Munschy and Schlich, 1987, Munschy et al, 1992a,b, 1993. Refraction (OBS) seismic surveys have been undertaken to understand the nature of the basement in various places in the region (Bradley and Frey, 1988;Recq et al, 1990, Charvis andOperto, 1999;Charvis et al, 1993Charvis et al, , 1995Charvis et al, , 1997Charvis, 1995, 1996;Rotstein et al, 1990Schlich and Schaming, 1999;Gladczenko and Coffin, 2001).…”