Results of paleomagnetic studies of Mesozoic-Early cenozoic rocks of Western Antarctica (the Argentinean islands archipelago)
© V.G. Bakhmutov, A.N. Tretiak
The new paleomagnetic data of Mesozoic and Early Cenozoic rocks in the region of the archipelago of Argentinean islands (west Antarctic) do not agree with the earlier paleomagnetic results. The age of volcanic and igneous complexes (the latter belong to the Andean series) varies from 55 to 93 Ma (the other data suggest it to be to 117 Ma). Two components of remanent magnetization - low temperature A-component (to 250-300°Ñ) and high temperature B-component (to 500-525°Ñ) were identified. The paleomagnetic results of different groups of islands have shown a good agreement both for containing rocks and for dykes. The direction of the B-components is reverse and is D=151°, I=81° for containing rocks and D=151°, I=82° for the cutting dykes. The directions of the low temperature A-component for the enclosing rocks and dykes are D=356°, I=-70° and D=1°, I=-80°, respectively. According to previous results of paleomagnetic investigation of the same rocks on the neighboring territory of Antarctic peninsula, only one reverse component with another direction (A.M. Grunow) has been obtained. The virtual geomagnetic poles positions differ from the average virtual geomagnetic poles positions calculated by different authors for the block of Antarctic peninsula earlier. On the basis of paleomagnetic data by different authors the palaeotectonic reconstruction of the block of Antarctic peninsula for the last 175 Ma are given. The Antarctic peninsula block is a key fragment in the history of Gondvana breakup and shaping of the present surface of the southern hemisphere. The disagreement of new paleomagnetic results with generally scheme could be explained by two reasons: 1) the luck of actual data or the methodical errors due, for example, to remagnetisation of rocks after secondary heating; 2) essential difference in geological history of Argentinean islands block and western part of Antarctic peninsula.