New geophysical study northwestern Antarctic Peninsula. Geodinamic implicances

VILAS, J. F.; TASSONE, A.; LIPPAI, H.L.

Acapulco.

Otro; American Geophysical Union. Joint Assembly; 2007

AGU

The current tectonic arrangement of Tierra del Fuego and Antarctica is the product of an extensive and complex evolution that involved the most southern part in South America (SA) from the Early Mesozoic when a subduction area settles down along the Pacific border of Gondwana (GDW) including the then continuous SA and Antarctic Peninsula (AP) (Dalziel and Elliot, 1973; Dalziel, 1982). The paleogeographic position of the AP immediately before the separation of the GDW has been a topic of controversy. The presently available information for the beginning of GDW fragmentation is contradictory. In the last years a new accretion model has been proposed for the Mesozoic development of the AP. This model requires of more data to sustain the extension of the old magmatic arc and GDW paleomargin. A geophysical campaign has been developed along Danco Coast - between Py Point to the south, and Vivot Cape to the north- with the aim of acquire new data to define the geometry, lateral relationships and tectonic development of the geologic units of the Mesozoic magmatic arc exposed in the western border of the AP. Rock outcrops mostly belong to plutonic bodies of granitic through tonalitic composition, and rhyolites, andesites and basaltic rocks. The geologic survey included the lithologic and structural sampling, a total of 216 rock cores were obtained for AMS and paleomagnetic studies. The acquired data have been GPS referred. The magnetic survey was carried out with two magnetometers of proton free- precession: a Scintrex ENVI GRAD (used as permanent base) and a Geometrics G856 magnetometer employed for sampling stations (which measured the intensity of the total magnetic field and worked synchronized with the base magnetometer in order to make the corresponding corrections). A total of 1670 registrations were acquired in the 334 GPS fixed onland stations. A Zodiac MK5 was employed for the offshore magnetic survey. 5162 stations constitute the magnetic grid in offshore areas, organized along orthogonal sections with a total length of around 380 km. The magnetic anomaly map produced with the acquired data shows five N-S-oriented belts of maximums up to 3000 nT separated by minimum of -500nT. The preliminary interpretation of the data might allow to infer the offshore prolongation of volcanic levels such as those observed in onland areas. Results of the magnetic survey along with the paleomagnetic and petrologic information presently in process will provide new insights of the western border of AP and its geodynamic relation with other segments of the old GDW margin.