USING OCEAN BOTTOM SEISMOMETERS TO STUDY THE DEEP CRUSTAL STRUCTURE OF BRANSFIELD STRAIT, WEST ANTARCTICA: A MODERN ANALOG OF THE PRE-ANDES

IN APRIL 2000, UTIG investigators will use the icebreaker Nathaniel B. Palmer to study the deep structure of a small piece of a big crustal jigsaw puzzle: Bransfield Strait, West Antarctica.

Geographic location of the Bransfield Strait

GEOLOGIC SETTING. The Strait is an actively extending "marginal" basin in the far southeast Pacific, between the Antarctic Peninsula and the South Shetland Islands, an inactive volcanic arc. Widespread crustal extension, accompanied by recent volcanism along the Strait's axis, appears to be associated with slow underthrusting of oceanic crust at the South Shetland Trench. Similar back-arc" extension occurred along the entire Pacific margin (now western South America/West Antarctica) of the supercontinent known as Gondwanaland some 130-200 million years ago. Approximately 100 million years ago, deformation of these basins initiated uplift of the Andes. By studying the deep structure and evolution of Bransfield Strait, UTIG scientists hope to evaluate the crustal precursor to the Andes, and thereby understand more fully the early evolution of this globally important mountain chain and the break-up of the supercontinent that accompanied it.

Crustal extension and recent volcanism along the Strait's axis are associated with underthrusting of oceanic crust at the S. Shetland Trench.

Multichannel seismic data collected in 1991 by investigators from UTIG and Lamont-Doherty Earth Observatory aboard the research vessel Maurice Ewing have been used to illustrate basinwide characteristics of Bransfield Strait. These data show widespread faulting associated with extension, the associated rise of crustal diapirs or domes leading to volcanic eruptions at the sea floor, and a complicated system of fault-bounded segments characteristic of rift basins all over the world. The axial rift of Bransfield Strait appears to lie near a critical transition from intracontinental rifting to seafloor spreading. These basinwide features make Bransfield Strait a wonderful "natural laboratory" for studying the diverse processes involved in forming continental edges.