A seismic refraction survey in the Kerguelen Isles, southern Indian Ocean

• Published in: Geophysical Journal International
• Main Authors: Recq, Maurice, Charvis, Philippe
• Format: Text
• Language: English
• Published: Oxford University Press 1986
• Subjects: Articles; Kerguelen; Indian; Broken Ridge; Pointe Suzanne; Mont Ross; Cap Ratmanoff; Val Studer; Antarc*; Antarctique*
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/84/3/529; https://doi.org/10.1111/j.1365-246X.1986.tb04370.x

Two 65 km long on-land refraction lines, with shot detonated at sea, were implemented in the Courbet Peninsula, eastern region of the Kerguelen archipelago (Terres Australes et Antarctiques Françaises, southern Indian Ocean). The first profile P1, oriented NE—SW, runs from Cap Ratmanoff toward Mont Ross, and the second one, P2, from Pointe Suzanne, SE of the Courbet Peninsula, through the Val Studer. Data from both profiles were supplemented by using the Bouguer gravity anomaly map not previously studied. The data combined standard travel-time interpretation, wide-angle reflected wave study, synthetic seismograms and S -wave analysis. The velocity—depth behaviour shows that the mean crustal thickness ranges from 14 to 17 km only, varying with the locality. The structure of the crust beneath Kerguelen resembles those observed beneath aseismic ridges (i.e. the Crozet Rise and the Madagascar Ridge). Average velocity of 5.5 km s−1 on both lines is in the range of those determined for oceanic layer 2, which is there 8–9 km thick. Average velocity of 6.6 km s−1 is in the range of velocities within oceanic layer 3. The transition to mantle velocity, 7.95 km s−1 is best modelled by a positive velocity gradient within the crust. This feature is similar to that observed on structures generated near spreading centres. These new data combined with geological and geochemical investigations in the archipelago support an oceanic origin for the Kerguelen—Heard Ridge, and also Broken Ridge. Both structures were joined 40 Myr ago, as shown by the magnetic anomaly pattern. Refraction studies invalidate the assumption that isostatic compensation is achieved by a 23 km deep crustal root, but substantiate the contribution of a low velocity mantle. Gravity data are consistent with refraction studies. No crustal root appears to be present beneath Mont Ross. The best match between gravity and refraction data in the Val Studer is obtained by assuming the presence of a shallow intrusive body, related to the fault and dyke system, and ...