Gobi Altai Research Articles

A new terrane subdivision for Mongolia: implications for the Phanerozoic crustal growth of Central Asia

We present a new terrane synthesis for Mongolia that incorporates geological, geochemical and geochronological data from more than 60 years of Mongolian, Russian and joint international studies. Forty-four terranes are distinguished and classified into cratonal, metamorphic, passive margin, island arc, forearc/backarc, accretionary complex, or ophiolitic types. New detailed stratigraphic columns for all terranes are presented which summarize the geological evolution of each terrane. Our analysis reveals that small Precambrian cratonic blocks in the Hangay region acted as a central nucleus around which Paleozoic arcs, backarc/forearc basin assemblages, associated subduction complexes and continental slivers were accreted. The temporal and spatial order of accretion and amalgamation was complex and probably not simply from north to south with time. The timing of terrane accretion is partly constrained by sedimentary overlap assemblages and post-amalgamation intrusive complexes. The main stages of amalgamation occurred during the Neoproterozoic, Cambrian–Ordovician, Devonian, Pennsylvanian–Permian and Triassic. The arcuate trends of terranes around the central Hangay region provide the first-order structural grain for Mongolia. This crustal anisotropy has played a major role in controlling the geometry and kinematics of all subsequent Phanerozoic deformation and reactivation of structures in the region, including the Cenozoic development of the Altai and Gobi Altai. Our results provide the most detailed synthesis to date of the basement geology of Mongolia which should provide an important crustal framework for interpreting the Phanerozoic tectonic evolution of a large part of Central Asia. In addition, our synthesis allows the economic resources of Mongolia to be placed in a modern tectonic context.

Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia

We conducted a preliminary study of paleoshoreline features associated with Böön Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.

Timing of formation of forebergs in the northeastern Gobi Altai, Mongolia: implications for estimating mountain uplift rates and earthquake recurrence intervals

Bedrock and Quaternary alluvial fans in the forelands of the northern Gobi Altai have been faulted and warped by foreland-propagating thrust faults to form elongate hills known as forebergs. Forebergs near Bogd town, north of Arsta Bogd, and at Ih Hetsüü, north of Baga Bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates of c. 0.05 m ka − 1 , and between c. 1.6 and 4.1 m ka − 1 , respectively. Comparisons between vertical surface rupture during the 1957 Gobi Altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288 ± 382 to 497 ± 120 years for the average recurrence interval of great earthquakes in the Baga Bogd region. These localized uplifts rates support the view that the Gobi Altai Mountains probably took between 50 and 25 million years to form and were, therefore, coeval with the uplift of the Himalayas and the Tibetan Plateau.

Lithospheric controls on late Cenozoic construction of the Mongolian Altai

The Altai is one of the great Cenozoic intracontinental and intraplate mountain ranges of central Asia, but it is one of the less studied mountain belts on Earth from a modern structural geology standpoint, and few western scientists are familiar with its tectonic evolution. The range is located dominantly in Mongolia with important sectors in Russia, China, and Kazakhstan and structurally links with the Chinese Tien Shan and Russian Sayan ranges. The Altai is tectonically active and is best understood as two kinematically distinct mountain belts that intersect at 46°N, 96°E: the right‐lateral transpressive western Altai and the left‐lateral transpressive Gobi Altai. Transpressional deformation dominates the late Cenozoic deformation of the Altai and is manifested by throughgoing strike‐slip faults, restraining bends, thrust fault‐bounded ranges linked by strike‐slip faults, and possibly inverted Mesozoic graben. Regionally, there is strong correlation between Cenozoic fault trends and older basement strike trends. Cenozoic deformation regimes appear to be dictated by the angular relationship between preexisting basement structural trends and the prevailing NE directed maximum compressive stress. The Altai is constructed on Paleozoic terranes dominantly consisting of arc and subduction complex assemblages and passive margin sedimentary rocks juxtaposed to the west, southwest and south of the Precambrian block that underlies the Hangay Dome area of central Mongolia. Because the Hangay Dome is characterized by diffuse extension and not transpression, regionally upwarped topography, late Cenozoic volcanism, and elevated heat flow, it is kinematically separate from the Altai region and has previously been interpreted to overlie a mantle plume or asthenospheric diapir. It is proposed that anomalously hot mantle beneath the Hangay Dome coupled with the regionally domed surface topography creates a radial horizontal stress field that acts against the regional NE directed maximum horizontal stress within the Altai. These conditions may deflect postulated NE flowing lithospheric mantle/lower crust that is believed to be driving the shallow upper crustal deformation in the Altai.

Geometry and style of partitioned deformation within a late Cenozoic transpressional zone in the eastern Gobi Altai Mountains, Mongolia

The Gobi Altai is the easternmost extension of the Mongolian Altai and consists of topographically discontinuous E-W-trending ranges with peaks averaging 2000–3000 m in elevation. The region is seismically active and characterized by prominent E-W left-lateral strike-slip faults that localize transpressional deformation and uplift along their lengths and at stepover zones. This report summarizes structural field investigations made in the easternmost Gobi Altai to document the structural geometry and style of late Cenozoic transpressional deformation in the region in order to better understand processes of intracontinental mountain building and the distant intracontinental strain response to the Indo-Eurasian collision. The Artsa Bogd range marks the northeastern terminus of the Gobi Altai and is topographically asymmetric with a high northern margin marked by N-vergent thrust faults and left-lateral oblique-slip faults. The northern side of the range is also bounded by a foreland basin that contains N-vergent thrust faults and folds that deform Quaternary sediments. The southern margin of Artsa Bogd appears tectonically inactive but contains S-vergent thrust faults and left-lateral wrench zones. The range appears to have a flower structure cross-sectional geometry that may reflect transpressional inversion of a Mesozoic basin. The isolated, high and narrow Tsost Uul range south of Artsa Bogd occupies a restraining bend position along the left-lateral Tsost Uul strike-slip fault system. Major faults within the range define a half-flower structure cross-sectional geometry. To the south of the Tsost Uul range, the Gobi Bulag left-lateral strike-slip fault system is marked by small push-up ridges and one major restraining bend mountain where the fault steps to the right near its western end. Throughout the region, Late Cretaceous-Tertiary basalts and Tertiary and Quaternary sediments are deformed by the major fault systems indicating late Cenozoic fault activity. These fault systems and the ranges formed along them occur at fairly regular intervals (approximately 20 km) between the North Gobi Altai fault system and the Gobi Tien Shan fault system, two major left-lateral strike-slip faults that cut across southern Mongolia. Together the faults define a parallel array of discrete linear belts of Cenozoic E-W left-lateral transpressional deformation south of the Hangay Dome. The regular spacing of the fault systems may suggest more uniform distributed left-lateral flow at depth. Eastward-directed lower crustal and lithospheric mantle flow is suggested by existing seismic anisotropy data for the eastern Gobi Altai and is believed to be the driving force for the upper crustal deformation.

Quaternary alluvial fans in the Gobi of southern Mongolia: evidence for neotectonics and climate change

Alluvial fans in southern Monglia occur along a group of narrow discontinuous mountain ranges which formed as transpressional uplifts along a series of strike-slip faults. They provide information on the nature of neotectonic activity in the eastern Gobi Altai range and on palaeoclimate change. Alluvial fan formation was dominated by various geomorphological processes largely controlled by climatic changes related to an increase in aridity throughout late Quaternary times. Their sedimentology shows that initially they experienced humid conditions, when the sedimentary environments were dominated by perennial streams, followed by a period of increasing aridity, during which coarse fanglomerates were deposited in alluvial fans by ephemerial streams and active-layer structures were produced by permafrost within the alluvial fan sediments. With climatic amelioration during early Holocene times, the permafrost degraded and fan incision and entrenchment dominated. Sedimentation was then confined to the upper reaches of the fans, adjacent to steep mountain slopes, and within the entrenched channels. The alluvial fans have been neotectonically deformed, faulted and their surface warped by small thrust faults that propagate from the mountain fronts into their forelands. Localised uplift rates are in the order of 0.1 to 1 m Ka -1 . © 1997 John Wiley & Sons, Ltd. alluvial fans; neotectonics; Gobi; Mongolia; cryoturbation.

Late Cenozoic transpression in southwestern Mongolia and the Gobi Altai-Tien Shan connection

The Gobi Altai region of southwestern Mongolia is a natural laboratory for studying processes of active, transpressional, intracontinental mountain building at different stages of development. The region is structurally dominated by several major E—W left-lateral strike-slip fault systems. The North Gobi Altai fault system is a seismically active, right-stepping, left-lateral, strike-slip fault system that can be traced along the surface for over 350 km. The eastern two-thirds of the fault system ruptured during a major earthquake (M = 8.3) in 1957, whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the Quaternary. The highest mountains in the Gobi Altai are restraining bend uplifts along the length of the fault system. Detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross-sectional geometries, with thrust faults rooting into oblique-slip and strike-slip master faults. Continued NE-directed convergence across the fault system, coupled with left-lateral strike-slip displacements, will lead to growth and coalescence of the restraining bends into a continuous sublinear range, possibly obscuring the original strike-slip fault system; this may be a common mountain building process.The largely unknown Gobi-Tien Shan fault system is a major left-lateral strike-slip fault system (1200 km + long) that links the southern ranges of the Gobi Altai with the Barkol Tagh and Bogda Shan of the easternmost Tien Shan in China. Active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section, indicating Quaternary activity. The total displacement is unknown, but small parallel splays have apparent offsets of 20 + km, suggesting that the main fault zone has experienced significantly more displacement. Field investigations conducted at two locations in southwestern Mongolia indicate that late Cenozoic transpressional uplift is still active along the fault system. The spatial relationship between topography and active faults in the Barkol Tagh and Bogda Shan strongly suggests that these ranges are large, coalescing, restraining bends that have accommodated the fault's left-lateral motion by thrusting, oblique-slip displacement and uplift. Thus, from a Mongolian perspective, the easternmost Tien Shan formed where it is because it lies at the western termination zone of the Gobi-Tien Shan fault system. The Gobi-Tien Shan fault system is one of the longest fault systems in central Asia and, together with the North Gobi Altai and other, smaller, subparallel fault systems, is accommodating the eastward translation of south Mongolia relative to the Hangay Dome and Siberia. These displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low, E–W trending corridor between the northern edge of the Tibetan Plateau and the Hangay Dome, presumably in response to the Indo-Eurasian collision 2500 km to the south.

New Species of Thysanoptera from Gobi Altai Mountains

New Species of Thysanoptera from Gobi Altai Mountains

New Species of Thysanoptera from Gobi Altai Mountains

AbstractTwo new species of Thysanoptera, Oxythrips altaicus sp. n. and Taeniothrips (Similothrips) vackari sp.n., collected in Gobi Altai Mountains, southern Mongolia are described and figured in detail.

New and Rare Bryophytes in the Flora of Mongolia

The known bryophyte flora of Mongolia consists of 269 moss species in 109 genera, and 40 liverworts in 25 genera. The present study is based on the examination of bryological collections of two Polish Scientific Expeditions and three botanists to Mongolia in 1977 and 1978. More than 25% of the species occur primarily in Central Asia and Southern Siberia, 47% in the Northern Hemisphere and 28% are widely distributed or cosmopolitan in the world. Only rare bryophytes and those new to Mongolia are included in the present paper. The investigated bryophytes were collected mainly during two Scientific Expeditions of the Polish Academy of Sciences to the Mongolian People's Republic. The first Expe- dition (I) was organized for the Selenga River basin and Asaraltu range (Central Aimak, northwestern Khentei Mountains), 1977. The second (II) was planned for the Kerulen River basin, Dumda Bajdalag-gol basin, southeastern Khentei Mountains, in the pro- gramme of Expedition Transmongolia 78, Khentei II, June-July, 1978. The above ex- peditions and their exploration programmes were organized and directed by Dr. K. Pqkala from the Maria Curie-Sklodowska University, Lublin. In addition, this paper includes two collections of bryophytes made in the Gobi Altai Mountains by Prof. D. Fijalkowski and C. Sandagijn, student of biology, who collected mosses in their native region in the Ta- myrin-gol (River) valley, Khangai Mountains. The bryoflora of Mongolia has been very poorly investigated. The first papers on this poorly investigated territory of Central Asia, mainly concerning areas neighbouring Central Siberia and China were published by Dixon (1928), Kaalaas (1918), as well as by Brotherus and Savich (1931). The paper of the latter authors contains a list of the species collected as early as 1902 by A. A. Elenkin, a Russian botanist, during his journey in the Sayan Mountains and northern Mongolia. However, fundamental studies on the bryophyte flora began with the publishing of a paper by A. L. Abramova and I. I. Abramov (1956). Their later papers were published with C. Cegmed (1977a,b, 1979). Data from herbaria have made it possible to correct the distribution of the acrocarpous mosses given in the first volume of the Handbook of the Mosses of the U.S.S.R. (Savich-Ljubitzkaya & Smirnova 1970). Single articles on Mongolian bryophytes were published also by Duda (1968), Boros (1970), Stefureac (1974) and Schubert et al. (1977). However, of major importance are the publications of Bardunov (1965, 1969) on mosses of the Eastern Sayan Mountains and Central Siberia. As a result of determinations of the collections of Expeditions I and II to the Khentei Mountains and of two private Mongolian collections (over 3600 specimens), 179 species of mosses, 5 species of peat mosses and 13 species of hepatics have been identified. In this paper, only more sparsely distributed taxa are listed. The main members of the moss flora are represented by common forest and epilithic species of the taiga associated with Larix sibirica-Pinus sibirica-Betula spp. Among the rich collections from Mongolia, there 007-2745/81/339-343$0.65/0

Outer Mongolia, 1957-1960

M CAJOR, BUT UNCONNECTED, EVENTS of the past three years in Mongolia' include a significant governmental purge in November I958 and March i959; the holding of the First International Congress of Mongolists in Ulan Bator, September i-8, i959; and a tremendous earthquake on December 4, I957. Chinese influence in the country continued to be important, activities of East Europeans in Mongolia increased, and the rate of collectivization of livestock herds was accelerated. Greater opportunities for Westerners to visit the country, more complete Soviet statistical information, and new studies by East Europeans and by the Mongols themselves, have combined to add significantly to our knowledge of the Mongolian People's Republic.2 The i958-i959 governmental and Party purge constituted an extensive shake-up, but Premier Tsedenbal has survived and apparently eliminated his major rival, Damba. The I959 First International Congress of Mongolists included 28 foreign representatives from I4 countries, with three American delegates, five Chinese and five Russian, and others from Eastern Europe, Western Europe, and Asia.3 The I957 earthquake occurred in the southwestern part of Outer Mongolia, in the Gobi Altai, and moved mountains and