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Pb and Nd isotopic composition of granitoids from the Lake Zone, Mongolian and Gobi Altai was analyzed to decipher the continental crustal growth of heterogeneous terranes of the Central Asian orogenic belt. The granitoids were generated in the Late Neoproterozoic–Early Paleozoic juvenile crust of the Lake Zone during island-arc, accretion, and post-accretionary stages at 535–440 Ma. Their Pb and Nd isotopic characteristics are similar and illustrate the dominance of juvenile material in the source of granitoids of all three stages. An insignificant terrigenous contribution in their source provides dispersion of the Pb isotopic composition at a weak effect on the Nd isotopic composition. The Pb and Nd isotopic study of Middle Paleozoic (∼380–355 Ma) synkinematic and Late Paleozoic (∼350–270 Ma) post-kinematic granitoids in the Mongolian and Gobi Altai revealed a significant heterogeneity of their source, which is mainly inherited from terrigenous rocks of the Altai accretionary wedge variably metamorphosed under greenschist to granulite facies conditions. The main source of Altai terrigenous sediments was volcanic rocks from the Lake Zone juvenile crust with subordinate contribution of more mature rocks from the Tuva-Mongolian and Dzabkhan microcontinents, which supplied sediments with highly radiogenic Pb and Nd isotopic composition. The Pb isotopic compositions of the granitoids from the Lake Zone, Mongolian and Gobi Altai, and also the Trans-Altai Gobi (Savatenkov et al., 2016) show that their mantle source has an elevated Th/U ratio compared to the depleted mantle (Kramers and Tolstikhin, 1997). This is a hallmark of the depleted mantle source of the Paleo-Asian province. Juvenile continental crust terrains of the Central Asian orogenic belt (Lake Zone and Trans-Altai Gobi terranes) were formed in various tectonics settings. The island-arc complexes of the Lake Zone developed near the Precambrian Tuva-Mongolian and Dzabkhan microcontinents, which supplied terrigenous material with highly radiogenic Pb to granitoid sources. The Trans-Altai Gobi was a system of ensimatic island arcs separated from the Siberian paleocontinent by a continent-dipping subduction zone, which prevented the influx of ancient terrigenous material from the continent.

Tectonic sheets of various size along the southern slope of the Mongolian and Chinese Altai ranges and in eastern Kazakhstan include high-grade metamorphic rocks, which are collectively referred to as the Southern Altai Metamorphic Belt. Rocks of the sheets show traces of amphibolite-facies elevated-pressure metamorphism of the kyanite–sillimanite type M2. Some of the tectonic sheets display evidence of polymetamorphism: the rocks preserve textures and mineral assemblages of an earlier metamorphic episode (of elevated temperature and relatively low pressure) of the andalusite–sillimanite facies series M1. The earlier metamorphic episode occurred at 390–385 Ma, and the later one, at ~370–356 Ma. The protoliths of the high-grade metamorphic rocks were mostly Early Paleozoic terrigenous rocks and subordinate amounts of volcanic rocks analogous to the weakly metamorphosed or unmetamorphosed rocks in their northern surroundings. Typical rocks of the tectonic sheets are mafic dikes and massifs of the Gashun Nuur Complex, which were emplaced between metamorphic episodes M1 and M2. According to their geochemistry and Nd isotopic parameters, most of the metabasites are similar to enriched basalts of mid-oceanic ridges and oceans plateaus. The quantitatively subordinate group of the layered mafic bodies displays geochemical characteristics of subduction-related rocks. Correlations between the metamorphic events and magmatism in the continental (Mongolian and Chinese Altai) and paleoceanic (Trans-Altai Gobi and eastern Junggar) regions led us to suggest a geodynamic model for the development of the Southern Altai Metamorphic Belt. The volcano-terrigenous rocks, which were later metamorphosed, were accumulated mostly in the Early Paleozoic as an accretion wedge on an active continental margin. The earlier episode of high-temperature metamorphic M1 and coeval large-scale calc–alkaline magmatism occurred at the same active continental margin after the magmatic front shifted southward (in modern coordinates). The emplacement of the swarms of mafic bodies of the Gashun Nuur Complex and simultaneous rifting in the southern Chinese Altai were triggered by the subduction of an spreading ridge of an oceanic or backarc basin beneath the active margin. The second metamorphic episode (elevated-pressure metamorphism) M2 and overthrusting in the structures of the Altai are correlated with deformations at low angles and the transition from oceanic to continental volcanism in the Trans-Altai Gobi and Junggar. These tectonic processes were induced by the accretion of a system of mid-Paleozoic ensimatic island arcs of the Trans-Altai Gobi and Junggar to the Altai margin of the Siberian paleocontinent.

In the Late Paleozoic and Early Mesozoic, during about 100 m.y., the world’s three largest batholiths (Angara-Vitim, Khangai, and Khentei, each up to 1 000 000 km3 in volume) had formed within the limits of the Central Asian orogenic belt. Considering the case of the Khangai batholith, the problem of how, when, and why such an extensive granite formation took place is analyzed. The geochronological data for granitoids of the batholith by U–Pb (ID-TIMS) and 40Ar/39Ar dating methods are systematized to distinguish three age groups of rocks. These rock groups are correlated to the geological events occurred in the region. The earliest group includes granitoids formed in the interval of 302–283 Ma. They tend to the western and southern framings of the batholith and correspond to the fragments of two igneous belts that crossed the region, where the batholith formed later, and reached the areas far beyond. The youngest group of igneous rocks (230–200 Ma) is developed in the eastern periphery of the batholith and corresponds to the marginal part of the large Early Mesozoic Mongol-Transbaikalian igneous zone, with the main part being located far away to the east of there. Igneous complexes that formed in the interval of 273–238 Ma correspond to the batholith proper. They are concentrated within the zone of 350 × 400 km in size and are represented by rocks of two associations: granite-granodiorite (Khangai complex) and granite-leucogranite (Sharaus Gol complex). The coeval analogs of these rocks are reported only in the framing of the batholith. The comparison between the Khangai batholith and two other giant ones (Angara-Vitim and Khentei) revealed their similarity in terms of structure and evolution. They are all composed of similar rock associations and are of comparable sizes and age intervals of formation. For example, the Angara-Vitim and Khentei batholiths formed mainly in the intervals of 305–275 and 229–195 Ma, respectively. The obtained estimates of formation time of ~30 m.y. should seemingly be considered as the time necessary for chambers of anatectic magmas, which to certain degree formed giant (~1 000 000 km3 in volume) batholiths, to cool down in the Earth’s interior. The formation of giant batholiths is attributed to the effect of mantle plumes on the lithosphere of a young fold zone that appeared as a result of accretionary-collisional events in the marginal part of the Siberian paleocontinent.

Mongolia lies in the central part of the Central Asian Orogenic Belt [Mossakovsky et al., 1994; Zorin, 1999; Jahn, 2004; Khain et al., 2003; Badarch et al., 2002; Windley et al., 2007; Zhang et al, 2008], or Altaids [Şengör et al., 1993; Şengör, Natal’in, 1996; Wilhem et al., 2012], which is fringed by the Siberian craton in the north and by the Tarim and Sino-Korean Cratons in the south. According to the recent tectonic subdivision, the territory of Mongolia is subdivided into Northern and Southern domains which are separated by the so called Mid Mongolian Tectonic Line [Tomurtogoo, 2012]. The Herlen Massif is one of the important tectonic units of the South Mongolian domain in the Argun-Idermeg super terrane extending through the territories of Russia and China [Parfenov et al., 2009; Tomurtogoo, 2014b]. The Herlen massif, also known as Herlen superterrane [Tomurtogoo, 2012] or Idermeg terrane [Tomurtogoo, 2014a] is composed of Ereendavaa, Undur-Khaan, Idermeg and Gobian Altay-Baruun Urt terranes converged at the end of the Cambrianbeginning of the Ordovician [Badarch et al., 2002; Tomurtogoo, 2014b].

The paper reviews previously published and presents new data on the Darhad Basin, Mongolia, which is a key locality for reconstruction of Quaternary glaciation and environmental changes in northern Central Asia. The previously published data include those obtained in the 20th century by Soviet geological surveys and academic researches of the Darhad Basin, which are, as a rule, not accessible for an international reader, and those obtained by several international teams during the last decade. The new results include geomorphologic, sedimentological and geochronological data obtained prior to and within the International Darhad Drilling Project (DDP-2010). These data show that the Darhad sedimentary sequence has been formed since the Pliocene and represents a detailed archive of environmental changes due to a high content of lacustrine beds. Lakes formed several times in the Darhad Basin by basaltic, glacial and sedimentary dams, which blocked the water outlet of the basin. Of special interest in this paper are the late Pleistocene damming events, which are well-documented in the sediments and landforms, however, their chronology is still obscure. There have been two stages of deep lake. The first lake was dammed by a glacier during late MIS 5 ( Krivonogov et al., 2005 ) or, alternatively, during early to middle MIS 3 ( Gillespie et al., 2008a ). The second damming, glacial or sedimentary, formed another deep lake during MIS 4 or MIS 2. The level of the lake was greatly variable up to its complete disappearance. Our new data from the DDP10-3 and DN-1 boreholes and from the Hodon outcrop illustrate the Holocene history of the paleolake, which was dammed by the sediments and was kept at low levels. We propose a first sedimentation model for the Holocene part of the lacustrine sedimentary sequence. The lake was minimal or disappeared at ca 12–9.6 and after 4.5 ka cal. BP, relatively deep at 9.6–7.1 and 6.4–4.5 ka cal. BP and shallow at 7.1–6.4 ka cal. BP. Conclusively, we highlighted solved and unsolved geological problems of the Darhad Basin, the most important of which are our recognized stages of the paleolake development (solved) and the detailed chronology and environments of the lacustrine and glacial events (unsolved).

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.

Platinum group element (PGE) mineral assemblage has been discovered in the gold placers along the Burgastain Gol and Iljgen Gol (Western Mongolia). It includes isoferroplatinum (Pt3Fe) grains with inclusions of cooperite (PtS), laurite-erlichmanite (RuS2-OsS2), cuprorhodsite-malanite (CuRh2S4-CuPt2S4), irarsite-hollingworthite (IrAsS-RhAsS), and bowieite (Rh2S3). It has been established that the isoferroplatinum assemblage was generated from a volcanoplutonic picrite complex in the Ureg Nuur area, which is widespread in the central part of the Harhiraa accretionary terrane. According to composition, the PGE mineral–Cr-spinel assemblage was referred to as the Ural-Alaskan type.

A new experiment of the Hövsgöl Drilling Project was carried out in Lake Hövsgöl in 2004, as part of the international program of scientific drilling in the Baikal Rift. The reported data include a preliminary description of the recovered lake sediments (HDP-04 core), with their compositions and physical properties, and a tentative age-depth model based on the paleomagnetic polarity scale. This is the first evidence that the lithology of sediments deposited for the past ~1 Myr records periodic alternation of carbonate-free diatomaceous mud and carbonate-bearing silty clay. The diatom intervals in the record are interpreted as corresponding to interglacials by analogy with the periodicity known since the Last Glacial. The core bears signature of at least nine lithological change events. The sediment lithology records extremely low stand of Paleo-Hövsgöl (shallow-water facies produced by erosion of older sediments at the point where the today’s lake reaches a depth of 240 m). Correlation of the HDP-04 core data with reflection profiling evidence confirms the presence of quite a large gap in the Pleistocene sedimentary record from the Hövsgöl rift basin. The discovery of alternating carbonate-rich/carbonate-free cycles and evidence for sudden lake level changes impart special importance to the Hövsgöl archive: It can provide a deeper insight into the regional water budget and humidity history than it has been so far possible for the Middle and Late Pleistocene.

Since 2002, a new electronic database of patient information has been introduced in Mongolia.

We have developed the method to determine the specific radioactivity of Rn-222 in water using the HP-Ge gamma-spectrometer, solid state nuclear track detector and liquid scintillator. Using this methods, the absorbed dose from radon was calculated.

Two gravity cores (1.1 and 2.2 m long) of deep-water bottom sediments from Lake Khubsugul (Mongolia) were studied. The Holocene, biogenic silica and organic matter-rich part of the first core was subjected to AMS radiocarbon dating which placed the date of dramatic increase of pelagic diatoms (40 cm below sediment surface) at a calendar age of 11.5 cal ky BP. ICP-MS analysis of weak nitric acid extracts revealed that the upper Pleistocene, compared to the Holocene samples, were enriched in Ca, Cinorg, Sr, Mg and depleted of U, W, Sb, V and some other elements. Transition to the Holocene resulted in an increase of total diatoms from 0 to 108 g-1, of BiSi from 1% to 20%, of organic matter from 6%. The Bølling–Allerød–Younger Dryas–Holocene abrupt climate oscillations manifested themselves in oscillations of geochemical proxies. A remarkable oscillation also occurred at 22 cm (ca. 5.5 ky BP). The Pleistocene section of the second, longer core was enriched in carbonate CO2 (up to 10%) and water-extractable SO42- (up to 300 times greater than that in Holocene pore waters). All this evidence is in an accord with the earlier finding of drowned paleo-deltas at ca. 170 m below the modern lake surface of the lake [Dokl. Akad. Nauk 382 (2002) 261] and suggests that, due to low (ca. 110 mm) regional precipitation at the end of the Pleistocene, Lake Khubsugul was only 100 m deep, and that its volume was ca. 10 times less than today.