JURASSIC-CRETACEOUS HISTORY OF THE OMOLON MASSIF, NORTHEASTERN RUSSIA: GEOLOGIC AND PALEOMAGNETIC EVIDENCE

Abstract

Geologic and paleomagnetic research in the western part of the Omolon massif and in the Sugoi folded zone, northeastern Russia, suggests significant lateral displacements of these units relative to one another and with respect to the Siberian continent in late Mesozoic time. In the northern part of the Sugoi folded zone folds and thrust faults exhibit vergence in various directions, which may be related to a history of transpression. Lower Jurassic fine-grained terrigenous and calcareous deposits were studied, yielding two ancient paleomagnetic directions: (1) a postfolding one with declination (dec) = 30°, inclination (inc) = 83°, precision parameter (K) = 117, and confidence limit (α95) = 4° and (2) a probable prefolding one with dec = 229°, inc = 58°, K = 43, and α95 = 9.4°. Fault offsets (to a few hundreds of kilometers) occur mainly on sinistral strike-slip faults in the Sugoi zone, and were formed as the Omolon terrane and separate tectonic blocks in the Sugoi zone rotated 30°-70° counterclockwise relative to Siberia. In Early Jurassic time, the Omolon massif was located at lat 60°N, and in Early Cretaceous time, at lat 76°N.