EVIDENCE FOR THE VOLCANOCLASTIC GENESIS OF THE CARNIAN DIAMONDIFEROUS BED IN THE UST'-OLENEK AREA ( from petrographic and geochemical data )
V.F. Proskurnin, N.P. Vinogradova, A.V. Gavrysh, and M.V. Naumov
A.P. Karpinsky Russian Geological Research Institute (VSEGEI), Srednii pr. 74, St. Petersburg, 199106, Russia
Keywords: Triassic, Diamonds, volcanoclastic deposits, phreatomagmatic eruption, Siberian Platform
Pages: 535-545
Subsection: PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
Abstract
A detailed petrographic study of a 0.4-1.2 m thick Carnian diamondiferous bed of the Angardam-Tasa Ridge (Ust'-Olenek area, northern Siberia) was performed. It showed that the bed earlier referred to as a terrigenous deposit might be interpreted as an intensely altered volcanoclastic lapilli tuff of basic and, probably, ultrabasic composition. The tuff occurs within a 100 m thick Ladinian-Carnian volcanosedimentary sequence. It consists mainly of resurgent material: altered lithoclasts (nodules of basic-ultrabasic lithology?), devitrified volcanic glass, fragments of autolithic breccia, etc. The thin volcanoclastic sheet is supposed to have formed within a sedimentation basin as a result of phreatomagmatic eruptions of kimberlite volcanoes. The substantiation of the volcanogenic origin of the Carnian diamondiferous bed might be a new approach to elucidate the primary source of widespread placer diamonds in Arctic Siberia.
|
