Paleomagnetism of the Late Cretaceous ignimbrite from the Okhotsk-Chukotka Volcanic Belt, Kolyma-Omolon Composite Terrane: Tectonic implications

Abstract

New Late Cretaceous paleomagnetic results from the Okhotsk-Chukotka Volcanic Belt in the Kolyma-Omolon Composite Terrane yield stable and consistent remanent directions. The Late Cretaceous (86–81Ma) ignimbrites from the Kholchan and Ola suites were sampled at 19 sites in the Magadan area (60.4°N, 151.0°E). We isolated the characteristic paleomagnetic directions from 16 sampled sites using an alternating field demagnetization procedure. The primary nature of these directions is ascertained by dual polarities and positive fold tests. A tilt-corrected mean direction (D=42.8°, I=84.7°, k=46.0, α95=10.0°) yields a paleomagnetic pole of 66.7°N, 168.5°E (A95=18.8°) which appears almost identical to the 90–67Ma pole reported from the Lake El’gygytgyn area of the Okhotsk-Chukotka Volcanic Belt (Chukotka Terrane). This consistency suggests that the Kolyma-Omolon Composite Terrane and Chukotka Terrane has acted as a single tectonic unit since 80Ma without any significant internal deformation. Accordingly, we calculate a combined 80Ma characteristic paleomagnetic pole (Long.=164.7°E, Lat.=68.0°, A95=10.9°, N=12) for the Kolyma-Omolon-Chukotka Block which falls 16.5–17.5° south of the same age poles from Europe and East Asia. We ascribe this discrepancy in pole positions to tectonic activity in the area and infer a southward displacement of 1640±1380km for the Kolyma-Omolon-Chukotka Block with respect to the North American and Eurasian blocks since 80Ma; more than 260km of it is attributed to tectonic displacement in the Arctic Ocean due to the opening of the Canadian Basin.