PRINCIPLES IN DIFFERENTIATING STRUCTURAL-TECTONIC ZONES IN ORE-PETROGRAPHIC PROVINCES AND ORE DISTRICTS

The Zeya-Bureya plain and its mountain fringe are components of the Mongolo-Okhotsk folded belt, a northern segment of the East Asia Hercynian structure located between the ancient Siberian and Chinese platforms. The basement is a complex combination of Proterozoic, Sinian-lower Paleozoic and middle Paleozoic folded structures. In the Tomesk synclinorial zone, what appear to be parageosynclinal middle to upper Paleozoic structures, rest directly on Proterozoic crystalline foundation, and are correlative with similar formations in the western slope of the ancient Bureya-Girin massif. Structural trends in the southern half are north-northeasterly and north of latitude 52°; the trend is sublatitudinal. Deep rifts have been particularly important in the tectonics of the region. Regional Mesozoic structure shows inherent features from earlier stages, expressed in Paleozoic structural trends and faults. The largest and deepest of the Mesozoic troughs are associated with Paleozoic synclinoria and uplifts; swells are associated with pre-Sinian basement highs and Paleozoic anticlinoria. Maps showing geophysical anomalies and fields and tectonic features are included.—C. E. Sears.