PALEOMAGNETIC CONSTRAINTS ON EXTENSION IN THE BASIN AND RANGE AND IN THE NORTH ATLANTIC AREA (SIERRA NEVADA, GREAT VALLEY SEQUENCE, CALIFORNIA, TECTONICS, COAST RANGE OPHIOLITE)

The chapters of this thesis describe four individual studies written to be published independently. Chapter one discusses paleomagnetic results from plutons in Yosemite National Park. A model that is consistent with this result and other geological and geophysical constraints from the Western United States associates the displacement of major crustal blocks with Basin and Range extension starting at about 35 Ma. Chapter two discusses paleomagnetic results from plutons in Kings Canyon National Park area. The pole position found in these studies is concordant with the pole of the first study. The mean pole of both studies limits the relative displacement between the Sierra Nevada and cratonal North American to 6 degrees of clockwise rotation and 6 degrees of poleward displacement. The 95 percent confidence limits are 8 and 6 degrees respectively. The amount of Basin and Range extension consistent with these results is about 220 and 260 km at latitudes 40 and 35 north respectively. The poleward displacement suggests right lateral shear of approximately 600 km within the Basin and Range, between 90 and 35 Ma.;In chapter four paleomagnetic results from the Coast Range ophiolite and the overlying Great Valley sequence are presented. All the magnetizations measured in this study are secondary. The origin of the remagnetizations is different in different localities. In southwest Oregon it is probably the result of tectonic events. In Wilbur Springs (California) it was caused by Plio-Pleistocene volcanic and hydrothermal activity. In Stonyford, Paskenta and Del Puerto (all in California) the loss of original magnetization might have occurred during long burial at about 7 km depth, followed by remagnetization during uplift in the Late Cretaceous or Tretiary.;In chapter three paleomagnetic data from Europe and North America are used to delineate the early rifting of these two continents. The relative positions of the two plates are reconstructed by fitting Late-Carboniferous - Early Triassic paleomagnetic pole paths of the two continents. The best fit reconstruction is in good agreement with extensional features in the North Sea, and suggests Alaska and Siberia were decoupled from the Late-Carboniferous through at least the Early Triassic.