Abstract

Paleomagnetic results from the investigation of 13 magnetically stable units (92 oriented rock samples) of Upper Cretaceous (“Andean”) plutons and dikes from the Orville Coast and eastern Ellsworth Land, Antarctica, define a mean direction of magnetization of I = −77°, D = 51° (α95 = 5.9°), with a paleomagnetic pole at 71°S, 165°W. The sampled units were emplaced after the Late Jurassic to Early Cretaceous intense folding associated with subduction along the western side of the Antarctic Peninsula. In addition, all sampled intrusive rocks are normally magnetized and are believed to have been emplaced during the Late Cretaceous period of predominantly normal polarity. There is no evidence of post-emplacement remagnetization. Unlike rocks from other Andean paleomagnetic collecting localities on the Antarctic Peninsula, whose mean declinations are oriented approximately north, the mean declination of samples from the Orville Coast and eastern Ellsworth Land is rotated 51° clockwise from north. Uncertainty in declination at the 95% confidence level (δ95) is ±27°. The data support the conclusion that the southern bend of the S-shaped Antarctic Peninsula was formed after Late Cretaceous time. Early Tertiary right-lateral transform faulting across the base of the Antarctic Peninsula may have produced this major oroclinal bend.

Data from four localities (21 samples; I = −79°, D = 30°, α95 = 4.3°) in Upper Jurassic(?) massive rhyodacite porphyry lava flows in the northern part of the area are similar to those of the Andean igneous rocks. Although the evidence is not conclusive, it seems most probable that the porphyry was magnetically reset by Late Cretaceous plutonism.

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