AGE OF PICRITE AND PICRODOLERITE MAGMATISM IN WESTERN MONGOLIA
A.E. Izokha,b, A.V. Vishnevskiia,b, G.V. Polyakova, and R.A. Shelepaeva,b
a V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Picrites, picrodolerites, geochronology, large igneous provinces, western Mongolia
Pages: 7-23
Abstract
The paper presents 39Ar-40Ar and U-Pb (SHRIMP zircon method) geochronological data on minor picrodolerite intrusions fr om western Mongolia. Picrodolerite magmatism in western Mongolia took place within different age intervals and in different geodynamic settings: accretionary-collisional Є1-2, ~510 Ma (Ььreg Nuur association, Hayrhan massif), intraplate D1, 410-390 Ma (Tsagaan Shuvuut Range, Mor't Uula massif), intraplate D3-C1, 345-360 Ma (Altan Gadas, Tavtyn Hundiyn, and Hu Tsan Bulak massifs), island-arc C2, 315-335 Ma (Dzahuy, Yaryn Had, and Javhlant massifs), and intraplate P1, ~270 Ma (Dzaraa Uula massif).
Petrographic, mineralogical, and geochemical data permit distinguishing derivates of picrobasaltic (12-14 wt.% MgO) (Ььreg Nuur association, Tsagaan Shuvuut Ridge, Javhlant and Yaryn Had massifs) and melabasaltic melts (7-10 wt.% MgO) (Mor't Uula, Altan Gadas, Dzahuy, and Dzaraa Uula) among picrodolerite magmatism in western Mongolia. Picritoids in these associations resulted from early olivine fractionation.
The Early Devonian picrites and picrodolerites of the Tsagaan Shuvuut Range and the olivine dolerites of the Mor't Uula massif can be assigned mafic magmatism in the Devonian large igneous province (LIP) (North Mongolian megablock). Late Devonian-Early Carboniferous picrodolerite intrusions in the Baruun Huuray zone (Altan Gadas) and Mongolian Altay (Tavtyn Hundiyn) are related to the Tien Shan LIP. Bimodal volcanism on the southern margin of the Hangayn Mts. (Dzaraa Uula), in the eastern segment of the Hanhuhiy Range (Dzagday Nuur, Hara Teg), and in the Argalantu trough (Tegshiyn Gol, Muhur Shurgah, and Deed Shurgah massifs) might be related to the Tarim LIP, wh ere they are part of an Early Permian volcanoplutonic association. Carboniferous picrodolerite massifs in the South Mongolian megablock and the Trans-Altai Gobi formed in subduction-related settings (Dzahuy, Yaryn Had, Javhlant).
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