CHANGING PLATE BOUNDARIES IN AND AROUND THE SOUTH GEORGIA MICROCONTINENT

Seismic reflection profiles collected during the NBP1408 cruise revealed some dramatic and recent bathymetry, and structural displacements to the southeast of South Georgia Island. It is believed that the plate boundary between South Georgia and the South American plate was to the north of South Georgia while it was being displaced from its original position off Tierra del Fuego as described by Dalziel et al. (1975). The North Scotia Ridge extends from Burdwood Bank to South Georgia microcontinent and was produced by the subduction of the South American plate beneath the Scotia Plate. The South Georgia microcontinent moved eastward relative to the South American Plate as the West Scotia Sea opened since 30 Ma until spreading ceased at ~6 Ma. Our new seismic reflection data indicate that the South Georgia microcontinent’s eastward motion was impeded and eventually stopped by collision with the Northwest and Northeast Georgia rises, LIPs on the South American plate. The collision, thought to have occurred around 10 Ma, caused seafloor spreading to start in the East Scotia Sea and to eventually cease in the West Scotia Sea.

Southeast of the South Georgia microcontinent, seafloor ridges appear to result from collisional shortening with very young seamounts orthogonal to the ridges. The seamounts may have resulted from complimentary extensional forces. The few available teleseismic fault plane solutions suggest that the South America – Scotia plate boundary is developing to the south of the South Georgia microcontinent replacing the earlier one to the North. It is ironic that the compressional seafloor features found on the RVIB N.B. Palmer cruise in 2014 closely resemble the onland South Georgia compressional features shown in Figure 3 of Dalziel et al., 1975.

Dalziel, I.W.D., Dott, R.H., Jr., Winn, R.D., Jr., and Bruhn, R.L., 1975, 3. Geological Society of America Bulletin 86, 1034–1040, doi:10.1130/0016-7606 (1975)86<1034:TROSGI>2.0.CO;2.