A New Late Middle Cambrian Paleomagnetic Pole for the Ellsworth Mountains, Antarctica

A paleomagnetic study of the late Middle to possibly early Late Cambrian Liberty Hills Formation in the Ellsworth Mountains, Antarctica, reveals a stable magnetization with positive fold and reversal tests. The paleopole is based on 16 sites from volcanic and sedimentary rocks and lies at lat 7.3 degrees N and long 326.3 degrees E (A95=6.0&j0;). The new paleomagnetic data support the view that the Ellsworth Mountains are part of a microplate-the Ellsworth-Whitmore Mountains crustal block-that rotated independently of the main Gondwana continental blocks during breakup. The Liberty Hills pole differs from both previous poles recovered from Cambrian rocks in the Ellsworth Mountains and from the available Gondwana reference pole data. Our pole indicates a more northerly prebreakup position for the Ellsworth Mountains than previously suggested, contradicting the overwhelming geologic evidence for a prebreakup position close to southern Africa. The reasons for this are uncertain, but we suggest that problems with the Gondwana apparent polar wander path may be important. More well constrained, early Paleozoic paleomagnetic data are required from the Ellsworth Mountains and the Gondwana continents if the data are to constrain further the Middle-Late Cambrian location of the Ellsworth-Whitmore Mountains block.