A PaleomagneticTest of the Patagonian Orocline, Thirty Years Later: New data, new Insights, new Problems.

AUGUSTO RAPALINI; FRANCISCO HERVE; MAURICIO CALDERON; SILVIA SINGER; HORACIO LIPPAI; ALEJANDRO TASSONE; UMBERTO CORDANI

New Orleáns, Los Angéles. USA.

Otro; AGU Joint Assembly; 2005

AGU

Inst. Geociencias, Univ. Sao Paulo, SAo Paulo, BrazilThe Andean Chain undergoes a 90 degrees bend at around 52 S, from N-S to the north to E-W to the south. This feature is called the Patagonian orocline and its origin and evolution have been much debated. Since the first paleomagnetic test performed by Dalziel et al. in the early seventies that suggested a secondary bend, several paleomagnetic studies have been carried out in the region. However, density of studies is still very low compared to other oroclines. Despite numerous uncertainties, including in cases experimental reliability, ages of magnetization and paleohorizontal control, some preliminary conclusions can be drawn from the available distribution of paleomagnetic declinations along the curved orogen. A systematic pattern of ccw rotation is apparent along the orogen that in a broad sense is consistent with a secondary origin for the bend. Largest values of rotation, 90 or more degrees, on the ocean side of the inverted Rocas Verdes marginal basin, suggest that its closure was probably an important event in the development of the orocline. To the foreland, rotations aresmaller, with ca. 30 degrees in the Fueguian Andes (south of 52 S), which suggest either magnetization ages younger than most of the oroclinal bending or a complex development with local patterns of rotations. To the north, anomalous ccw rotations of ca. 50 degrees have been observed along the front of the Magallanes thrust and fold belt and an identical declination anomaly has been found along the whole Sarmiento ophiolite, although in the latter case an alternative explanation to crustal block rotation around a vertical axis is possible.