Age of picrite and picrodolerite magmatism in western Mongolia

摘要

The paper presents ~(39)Ar/~(40)Ar and UPb (SHRIMP zircon method) geochronological data on minor picrodolerite intrusions from western Mongolia. Picrodolerite magmatism in western Mongolia took place within different age intervals and in different geodynamic settings: accretionary-collisional j{cyrillic, ukrainian} _(1-2), ~510 Ma (üüreg Nuur association, Hayrhan intrusion), intraplate D1, 410-390 Ma (Tsagaan Shuvuut Range, Mor't Uula intrusion), intraplate D_(3-)C_1, 345-360 Ma (Altan Gadas, Tavtyn Hundiyn, and Hu Tsan Bulak intrusions), island-arc C_2, 315-335 Ma (Dzahuy, Yaryn Had, and Javhlant intrusions), and intraplate P1, ~270 Ma (Dzaraa Uula intrusion).Petrographic, mineralogical, and geochemical data permit distinguishing derivates of picrobasaltic (12-14 wt.% MgO) (üüreg Nuur association, Tsagaan Shuvuut, Javhlant, Yaryn Had) and melabasaltic melts (7-10 wt.% MgO) (Mor't Uula, Altan Gadas, Dzahuy, 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 intrusion can be assigned to mafic magmatism in the Devonian large igneous province (LIP) in the North Mongolian megablock. The 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 Hanh?hiy Ridge (Dzagday Nuur, Hara Teg), and in the Argalantu trough (Tegshiyn Gol, Muhur Shurgah, and Deed Shurgah massifs) may be related to the Tarim LIP, where they are part of an Early Permian volcanoplutonic association. Carboniferous picrodolerite intrusions in the South Mongolian megablock and the Trans-Altai Gobi formed in subduction-related settings (Dzahuy, Yaryn Had, Javhlant).