LATE CRETACEOUS TO EARLY PALEOGENE PALEOMAGNETIC RESULTS FROM SIKHOTE ALIN, FAR EASTERN RUSSIA: IMPLICATIONS FOR DEFORMATION OF EAST ASIA

Abstract

Welded tuffs in the Bogopol and Sijanov groups were sampled at 27 sites from 12 caldera formations in the Sikhote Alin mountain range around Kavalerovo (44.3°N, 135.0°E) for chronological and paleomagnetic studies. KAr age dates show that the welded tuffs erupted between 66 Ma and 46 Ma. All sites yield reliable paleomagnetic directions, with unblocking temperatures higher than 560°C. The high-temperature component at 12 sites and the medium-temperature component at 3 sites in the Bogopol Group show reversed polarity (D = 193.7°, I = −57.6°,α95 = 8.1°). The high-temperature component at 11 sites in the Sijanov Group showed both reversed and normal polarities and its mean direction reveals no detectable deflection from north (D = −2.9°, I = 59.6°,α95 = 11.2°). The combined paleomagnetic direction of the two groups yields a paleomagnetic pole of 250.5°E, 84.1°N (A95 = 8.8°), which falls near Cretaceous paleomagnetic poles from Outer Mongolia, Inner Mongolia, the North China Block and the South China Block. The Sikhote Alin area appears not to have been subjected to detectable motion with respect to East Asia since about 50 Ma. This implies that the Sikhote Alin area behaved as an integral part of East Asia during the opening of the Japan Sea at about 15 Ma. However, significant separation between the paleomagnetic poles of East Asia and Europe during the Jurassic-Paleogene implies a major relative movement between these two blocks since the Paleogene.