Onshore/Offshore magnetometric survey in Punta Primvera, Danco coast. Antarctic Peninsula.

HORACIO LIPPAI; ALEJANDRO TASSONE; JUAN FRANCISCO VILAS

19-20 de noviembre. Santiago. Chile

Simposio; International Geological Congress on the Southern Hemisfere (Geosur 2).; 2007

GEOSUR

Within an area of around 119 km2 at Danco Coast (64°09´ SL; 60°57´ WL) a magnetometric onshore/offshore survey was carried out during the 2005-06 and 2006-07 Antarctic summers. The Upper Cretaceous to Tertiary volcanic rocks intruded by a granodioritic pluton which crop out in coastal areas belong to the Mesozoic magmatic arc. Leucocratic and melanocratic andesitic dykes hosted in granodiorite at Cierva creek bear sulphide mineralization. The main structures consist of two fault systems of WNW-ESE and NE-SW orientation which delineate the morphology of onland areas and the shoreline.The aim of the study has been to establish the offshore continuity of the onshore units and structures. 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 registrations were acquired in the 5803 GPS fixed onland stations within an area of 2.55 km2. A Zodiac MK3 was employed for the offshore magnetic survey. 11672 stations constitute the magnetic grid in offshore areas, organized along broadly orthogonal sections with a total length of around 548 km within an area of 116 km2. Magnetic susceptibility data (k) were also acquired on outcrops in order to introduce this parameter in the modeling of magnetic anomalies. A Fugro GMS-2 susceptibilimeter was employed at each of the 989 GPS fixed sites in onshore areas. Preliminary processing of acquired data allowed producing an onshore/offshore map of magnetic anomalies. The map shows maximums (up to 3000 nT) and minimums (of - 500 nT) organized in parallel NE-SW oriented belts; correlation of onland geology with the anomaly magnetic map suggests the offshore continuity of outcropping volcanic levels. The obtained map also indicates the probable extension of volcanic dykes with sulphide mineralization in the Cierva creek northwards along Danco Coast. The information gained from the magnetometric survey combined with ongoing paleomagnetic and petrological work will produce further insights on the geodynamic evolution of NW Antarctic Peninsula and its relation with other plates of old Gondwana protoPacific margin.