Paleomagnetism of Jurassic and Cretaceous rocks in central Patagonia:: a key to constrain the timing of rotations during the breakup of southwestern Gondwana?

A paleomagnetic study in Jurassic and Cretaceous rocks from the Canadon Asfalto basin, central Patagonia, indicates the occurrence of about 25-30 degrees clockwise rotation in Upper Jurassic-lowermost Cretaceous rocks, whereas the overlying mid-Cretaceous rocks do not show evidence of rotation. This constrains the tectonic rotation to be related to a major regional unconformity in Patagonia, which in turn seems to be close in time with the early opening of the South Atlantic Ocean. The sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern Gondwana, suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent. On the other hand, the mid-Cretaceous rocks in the region yield a paleopole located at Lat. 87 degrees South, Long. 159 degrees East, A95 = 3,8 degrees. This pole position is consistent with coeval high-quality paleopoles of other plates when transferred to South American coordinates, implying it is an accurate determination of the Aptian (circa 116 Ma) geomagnetic field in South America. (C) 2000 Elsevier Science B.V. All rights reserved.