We consider the structure, composition, and age of Early Paleozoic intrusive associations of the Bumbat-Hairhan area located in the central part of the island-arc system of the Lake Zone, western Mongolia. There are large polychronous plutons (Bumbat-Hairhan and Gundguzin) and small intrusions in this area. We have established that they are composed of granitoid and gabbroid associations of different lithology, ages, and geodynamic nature. The results of U-Pb dating show that granitoid and basic magmatism took place within 551–465 Ma. Two main stages of intrusive magmatism are recognized, which reflect two stages of the geodynamic evolution of the region: island-arc (551–524 Ma) and accretion–collision (511–465 Ma). At all stages, predominant rocks in the region were diorite–tonalite–plagiogranite and plagiogranite associations of calc-alkaline series.

The paper presents 39Ar/40Ar 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 Ꞓ1-2, ~510 Ma (Üüreg Nuur association, Hayrhan intrusion), intraplate D1, 410–390 Ma (Tsagaan Shuvuut Range, Mor’t Uula intrusion), intraplate D3–C1, 345–360 Ma (Altan Gadas, Tavtyn Hundiyn, and Hu Tsan Bulak intrusions), island-arc C2, 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 Hanhöhiy 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).

The paper discusses geological, mineralogical, petrographic, and geochemical data on the Ureg Nuur volcanoplutonic association of high-Mg volcanic and subvolcanic rocks located 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 geological 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.

A new Wenlockian zircon U–Pb age (~426 Ma) of the Overmaraat-Gol nepheline syenite (foyaite, juvite) pluton in the SW Lake Hovsgol area (Northern Mongolia) prompts a long history of alkaline magmatism in the western Central Asian Orogenic Belt, exceeding the duration of the Devonian and Permian–Triassic events. The LILE and HFSE patterns of pluton samples analyzed by X-ray fluorescence (XRF) and inductively coupled plasma (ICP-MS) methods indicate intrusion in a complex tectonic setting during interaction of a mantle plume with accretionary-collisional complexes that previously formed on the active continental margin. As a result, the parent magma had a heterogeneous source with mixed mantle (PREMA and EM) and crustal components. This source composition is consistent with Nd–Sr isotope ratios of the Overmaraat-Gol alkaline rocks, from −0.1 to −1.2 ε_Nd(t) and from ~0.706 to 0.707 ⁸⁷Sr/⁸⁶Sr(t).

A Neanderthal Refugium in the Eastern Adriatic