Picrodolerite intrusions of Western Mongolia: stages and geochemical features

In this paperauthors investigate 11 objects (massifs and areas), which are results of picrodoleritic magmatism of Western Mongolia. The authorsreceived new isotopic and geochemical data which allowed estimating stages and geochemical features of this magmatism. In the earlymiddleCambrian stage the formation of Uureg Nuur picrite-basaltic volcano-plutonic association (512 Ma, Ar-Ar in biotite) in theHarhiraa 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 of391,6±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-Huheiridge. Late Devonian-Early Carboniferous age was obtained for the picrodolerites of Altan-Gadas massif (355,9±4,8 Ma, SHRIMP-II) inthe northern part of Baruun-Hurai depression and small Tavyn-Hundijn massif (359,2±3,2 Ma, Ar-Ar in biotite) in the south of MongolianAltai 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 atypical island arc chamber, which was located in structures of Carboniferous island arc (Transalay terrane), accreted from the south toearlier structures (Tseel and Gobi-Altai terrains). Dzhavhlant massif (332,1 ± 4,1 Ma SHRIMP-II) is located in the rear part of the activecontinental margin that existed at that time. And Yaryn-Hud massif (316,2 ± 3,2 Ma, SHRIMP-II) associated with higher monzodioritegraniteseries corresponds to the beginning stages of generation of Late Carboniferous granitoids that are widely developed on thesouthern face of Mongolian Altai ridge, which captures the transition to an active continental margin of the Andean type. For Han-Huheiarea, located in the southern spur of ridge Han-Huhei south of Lake Uvs Nuur, Carboniferous ages (342-319 Ma) were obtained by theauthors on the complex dike of mica peridotite, including picrites and picrodolerites in district Hu-Tsan-Bulag and teschenite sill BominHara-Ula. With a manifestation of the Permian Tarim plume the results of our research in Western Mongolia, can connect basic magmatismof the southern Hangai uplift and Khan Tayshiri ridge. The Early Permian Age obtained for montsogabbro from Dzarа-Ula massif(269,2 ± 4,1 Ma, SHRIMP-II), is located in the left bank of the Dzabhan River.

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