Mid‐Cretaceous paleomagnetic reference field for North America: Restudy of 100 Ma intrusive rocks from Arkansas

Publisher Website
Google Scholar
Abstract
We have obtained new paleomagnetic data from three middle Cretaceous alkalic intrusive complexes in central Arkansas: Magnet Cove and Potash Sulfur Springs intrusions (about 100 Ma, 20 sites), and Granite Mountain stock (about 88 Ma, 6 sites). Out of 254 specimens measured, 147 from 20 sites were accepted. The remainders have scattered magnetization directions which experiments indicate were caused by lightning occurring during frequent electrical storms in this region. The geologic evidence indicates that the intrusions have not been tilted since emplacement. The directions of magnetization calculated with respect to present‐day horizontal yield a mean paleopole at 192.5°E, 74.1°N (N = 20, K = 34, A95 = 5.7°). This does not differ at 95% confidence from that determined previously by Scharon and Hsu, but the error is diminished by half. The angular dispersion (Sd) of site virtual geomagnetic poles (VGPs) is 13.6°, similar to the value of Sd (about 15°) predicted by current paleosecular variation models. The revised Arkansas paleopole is combined with four other cratonic North American paleopoles of mid‐Cretaceous age to yield a revised middle Cretaceous reference pole at 196°E, 71°N, A95 = 4.9°. The mean of nine paleopoles derived from overprints in rock units from the craton and craton margin, which range in age from Proterozoic to Jura‐Cretaceous, is 202°E, 68°N, A95 = 8.2°. This is not different from the reference paleopole, indicating that overprinting was very widespread across North America in mid‐Cretaceous time.