In this paper authors investigate 11 objects (massifs and areas), which are results of picrodoleritic magmatism of Western Mongolia. The authors received new isotopic and geochemical data which allowed estimating stages and geochemical features of this magmatism. In the early-middle Cambrian stage the formation of Uureg Nuur picrite-basaltic volcano-plutonic association (512 Ma, Ar-Ar in biotite) in the Harhiraa terrane and Haijerhan troctolite-gabbronorete massif (511 +/- 12 Ma, SHRIMP-II) in Lakes Zone occurred. Early Devonian age (406,5 +/- 7,1 Ma, SHRIMP-II) was received for the picrodolerites of Tsagan-Shuvuut ridge, north from Uureg Nuur Lake. Also age of 391,6 +/- 3,5 Ma (Ar-Ar in biotite) corresponds to the formation of picritic rocks of Mor't-Ula massif in the south slope of Altan-Huhei ridge. Late Devonian-Early Carboniferous age was obtained for the picrodolerites of Altan-Gadas massif (355,9 +/- 4,8 Ma, SHRIMP-II) in the northern part of Baruun-Hurai depression and small Tavyn-Hundijn massif (359,2 +/- 3,2 Ma, Ar-Ar in biotite) in the south of Mongolian Altai ridge. Middle Carboniferous isotope ages were obtained for several massifs situated to the east of Baruun-Hurai depression in Gobi Altai and Transaltai Gobi, and also in Han-Huhei area of North Mongolia. The authors supposed that Dzahoi massif represents a typical island arc chamber, which was located in structures of Carboniferous island arc (Transalay terrane), accreted from the south to earlier structures (Tseel and Gobi-Altai terrains). Dzhavhlant massif (332,1 +/- 4,1 Ma SHRIMP-II) is located in the rear part of the active continental margin that existed at that time. And Yaryn-Hud massif (316,2 +/- 3,2 Ma, SHRIMP-II) associated with higher monzodiorite-granite series corresponds to the beginning stages of generation of Late Carboniferous granitoids that are widely developed on the southern face of Mongolian Altai ridge, which captures the transition to an active continental margin of the Andean type. For Han-Huhei area, located in the southern spur of ridge Han-Huhei south of Lake Uvs Nuur, Carboniferous ages (342-319 Ma) were obtained by the authors on the complex dike of mica peridotite, including picrites and picrodolerites in district Hu-Tsan-Bulag and teschenite sill Bomin Hara-Ula. With a manifestation of the Permian Tarim plume the results of our research in Western Mongolia, can connect basic magmatism of the southern Hangai uplift and Khan Tayshiri ridge. The Early Permian Age obtained for montsogabbro from Dzara-Ula massif (269,2 +/- 4,1 Ma, SHRIMP-II), is located in the left bank of the Dzabhan River.

The new petrochemical and isotope-geochronological characteristics for picritoid and associated alkali-basaltic complexes of the Northern Mongolian Belt (NMB) are given. They are composed in small intrusions, dykes, sills, and volcanic covers with rocks of a higher potassium and titanium content. The studied areas with these units belonged to the western part of the NMB, which stretches sublatitudinally from Uureg Nuur Lake in the west to the south of Trans-Hovsgol Region in the east. By the petrochemical parameters, the complex corresponds to subalkaline basites and lamprophyres, including micaceous plagioperidotites and picrodolerites. The obtained values of Ar-Ar age (342–319 Ma B.P.), together with the known data on other areas in this complex where these rocks are distributed, evidences for a relatively wide (Middle-Late Paleozoic) interval of its origination.