Paleomagnetic analysis of the Patagonian Orocline: a review.

AUGUSTO RAPALINI; FRANCISCO HERVÉ; MAURICIO CALDERÓN; ALEJANDRO TASSONE; SILVIA SINGER; HORACIO LIPPAI

19-20 de noviembre. Santiago. Chile.

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

GEOSUR

The dramatic change in the structural trend of the Andean orogen in southernmost Patagonia has long been considered a possible example of a true orocline. Paleomagnetism has proved a powerful tool to determine whether a curved orogen acquired its shape as a secondary feature. Paleomagnetic data obtained so far in the southern Patagonian and Fuegian Andes are reviewed in order to test the origin of the Patagonian orocline. Systematic counterclockwise (ccw) rotations along the arc are suggested by widespread ccw deflections of paleomagnetic declinations, which may be compatible with some secondary curvature of the orogen. Larger values of declination anomalies in the outer arc are consistent with some oroclinal bending related to mid-Cretaceous closure of the Late Jurassic - Early Cretaceous Rocas Verdes marginal basin. However, a thorough paleomagnetic test of the origin of the Patagonian Orocline is hampered by several problems that affect most results. Main problems with the present database are: i) small amount of data considering the extent of the region under investigation; ii) unevenly distributed sites; iii) significant fraction of the data composed by low quality analytical results; iv) lack of paleohorizontal control in many cases; v) uncertain rock and magnetization ages and vi) reduced resolution of the paleomagnetic method at high latitudes. So far, these limitations preclude a reliable answer to whether the southern Patagonian - Fuegian Andes are a true orocline. Preliminary results from new paleomagnetic studies in progress in the region will also be presented and analyzed.