LATE CRETACEOUS PALEOMAGNETIC DATA FROM THE MEDIAN RANGE OF KAMCHATKA, RUSSIA: TECTONIC IMPLICATIONS

Abstract

A Late Cretaceous island arc complex was sampled for paleomagnetic study in the northern part of the Median Range of Kamchatka. In most samples, thermal demagnetization in 12-18 steps revealed either a reversed characteristic remanent magnetization (ChRM) or a remagnetization circle. Combining these yielded a positive fold test (Ks/Kg=5.8) and we interpreted the ChRM to be primary. The tilt corrected overall mean direction of dec. = 105.5°, inc. = -67.0°, alpha95=4.1° for these rocks corresponds to a paleolatitude of 49.7° +/- 5.6°N. This value is 20° to 22° lower than the Late Cretaceous North American reference values, and northward transport of the subject tectonostratigraphic terrane and island arc to which it had originally belonged, is strongly indicated. The observed paleolatitudes are approximately similar for all Late Cretaceous island arc complexes in Kamchatka and the southern part of the Koryak Highlands. We conclude that these complexes were originally part of the same island arc which originated 20° to 25° south of the continental margin in the Campanian, and then was transported northward until its emplacement in the Paleocene. Northward drift of the island arc coincided with its activity, and the related subduction zone also had to drift with a rapidly moving oceanic plate, most probably the Kula plate. This relationship implies that the subduction zone dipped southward and was consuming oceanic lithosphere, presumably the oceanic periphery of the North American plate.