THE UREG NUUR PT-BEARING VOLCANOPLUTONIC PICRITE-BASALT ASSOCIATION IN THE MONGOLIAN ALTAY AS EVIDENCE FOR A CAMBRIAN-ORDOVICIAN LARGE IGNEOUS PROVINCE
A.E. Izokha, A.V. Vishnevskiia, G.V. Polyakova, V.M. Kalugina, T. Oyunchimegb, R.A. Shelepaeva and V.V. Egorovaa
aV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, prosp. Akad. Koptyuga 3, Novosibirsk, 630090, Russia
bInstitute of Geology and Mineral Resources, Mongolian Academy of Sciences, Peace Ave. 63, Ulaanbaatar, Mongolia
Keywords: Picrite, basalt, geochemistry, large igneous provinces, plume, Ural-Alaskan-type Pt -bearing intrusions, western Mongolia
Pages: 521-533
Abstract
The paper discusses geological, mineralogical, petrographic, and geochemical data on the Ureg Nuur volcanoplutonic association of high-Mg volcanic and subvolcanic rocks localized among Vendian-Cambrian accretionary structures in the Mongolian Altay. These rocks have a high potassium alkalinity (K2O/Na2O up to 1.2), are enriched in LILE and Sr, and have negative Zr-Hf and Nb anomalies in multielement spectra; this confirms the suprasubduction type of the source of melts. The geologic setting and established age (512.4±6.1 Ma, 39Ar-40Ar dating of biotite phenocrysts) evidence picritic magmatism at the accretionary stage of the development of the Altay fragment of the Paleoasian ocean. This indicates a large igneous province related to a mantle plume.
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