BASITES OF THE VILYUI PALEORIFT: GEOCHEMISTRY AND SEQUENCE OF INTRUSIVE EVENTS
M.D. Tomshin1, A.G. Kopylova1, K.M. Konstantinov2,3, S.S. Gogoleva1
1Diamond and Precious Metals Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
2Research Geological Enterprise ALROSA, Chernyshevskoe Shosse 16, Mirnyi, 678174, Russia
3Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Средний палеозой, Ar/Ar геохронология
, палеомагнитные исследования, дайковые пояса, долериты, Middle Paleozoic, 40Ar/39Ar geochronology, paleomagnetic studies, dike swarms, dolerites
Abstract
We present results of study of the basites of the Vilyui paleorift. The 40Ar/39Ar isotopic ages were used to establish the sequence of their intrusion, which lasted ~18 Myr. Dolerite sills of the Kontai-Dzherba zone were the first crystallizing phase (378.0-380.7 Ma), which was followed by the intrusion of dikes of the Vilyui-Markha zone (372-373 Ma). Dikes of the Chara-Sinsk zone were the last crystalizing phase (362-364 Ma). The prolonged plume-lithosphere interaction resulted in the successive enrichment of basaltic melt with titanium, phosphorus, REE, HSFE, and LILE. Accumulation of the melt and formation of a magmatic lens at the crust-mantle boundary led to early crystallization of the melt at a depth of 35-40 km from the paleosurface under reducing conditions at a temperature of 1450-1470 °C. We assume that the inception and sequent opening of the Vilyui paleorift were associated with the relative rotation of 22° of the Angara-Anabar block with respect to the Aldan block in Early Famennian time. The Euler pole of rotation was located in the southern part of the paleorift, and a melting zone was directly beneath it.
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