Continental Massif Research Articles

Present-Day Kinematics of the Northern Margin of the Argun Continental Massif (Eastern Part of the Central Asian Belt)

This paper reports the first data on present-day movements in the northern margin of the Argun Continental Massif, obtained on the basis of GPS measurements. The processed GPS data have been obtained to calculate the vector field of displacement velocities in the geodynamic survey site of the Upper Amur Region. The estimated displacement parameters (direction and magnitude) are indicative of the uniform velocity vector field of the points in the northern margin of the Argun Massif and the absence of considerable motions within its range (differences in the vector components do not exceed a few millimeters per year). A conclusion is made on the present-day kinematic integrity of the northern margin of the Argun Massif.

Two stages of Neoproterozoic magmatism in the evolution of the Bureya continental massif of the Central Asian Fold Belt

U-Pb geochronological studies have shown at least two stages of Neoproterozoic magmatism, 940-933 and 804-789 Ma, throughout the geologic evolution of the Bureya continental massif in the east of the Central Asian Fold Belt. The first stage (940-933 Ma) was marked by the formation of the protoliths of metagabbroids and amphibole-biotite gneiss-granites of the Bureya River basin. The geochemical features of these rocks suggest that they formed, most probably, in an island-arc setting on the continental basement or on an active continental margin. The second stage (804-789 Ma) of magmatism was manifested as the formation of biotite leucogranites and hastingsite-lepidomelane granites (A-type granites) in the Chepkan River basin. The latter rocks are similar in geochemical features to within-plate granitoids. The established stages of magmatism are the most ancient for the continental massifs in the east of the Central Asian Fold Belt. It is not ruled out that these magmatism stages were related to the stages of formation and breakup of the Rodinia supercontinent.

Neoproterozoic magmatic complexes of the Songino block (Mongolia): A problem of formation and correlation of Precambrian terranes in the Central-Asian Orogenic Belt

An important role of the early Neoproterozoic juvenile crustal growth in the formation of the Khangai group of Precambrian terranes in the Central Asian Orogenic Belt was demonstrated by the example of the Holbo Nur Zone of the Songin Block. Magmatic complexes of this zone correspond to different settings of the Early Neoproterozoic ocean: oceanic islands, mid-ocean ridges, intraoceanic island arcs, and turbidite basins. Obtained data on volcanic rocks and associated granitoids constrain a timing of the island-arc magmatic complexes, at least within the interval of 888–859 Ma. The comparison of structures of the Songino and Tarbagatai blocks of the Khangai group of terranes showed that they share many common features in their geology and evolution and may be united into the single Songino–Tarbagatai terrane. This terrane was formed owing to the Early Neoproterozoic (~800 Ma) accretion of the ocean island, spreading, island-arc, and turbidite complexes of the oceanic plate to a stable continental massif represented by the Early Neoproterozoic Ider Complex of the Tarbagatai Block. The involvement of the Dzabkhan terrane into a Khangai collage of terranes is constrained between the formation of the volcanic rocks of the Dzabkhan Formation (~770–755 Ma), which are unknown in the Songino–Tarbagatai terrane, and the Tsagaan-Olom carbonate cover (~630 Ma), overlying both the Dzabkhan and Songino–Tarbagatai terranes. It was proposed that the formation of the Precambrian terranes of the Central Asian Orogenic Belt began from the Early Neoproterozoic accretion to the Rodinia supercontinent. The fragmentation of the latter above a mantle superplume at the end of the Early Neoproterozoic spanned also the newly formed fold area. This led to the formation of terranes, which included both fragments of the Paleoproterozoic craton and Early Neoproterozoic structures. Subsequent amalgamation of these Precambrian crustal fragments into composite terranes possibly occurred at the end of the early Baikalian tectonic phase.

Age, geochemistry, and sources of clastic materials and accumulation settings of the Glubokin Formation (Eastern Transbaikalia)

We report the results of geochemical, Sm–Nd isotope–geochemical, and U–Pb detrital zircon geochronological studies of metaterrigenous rocks of the Glubokin Formation assigned provisionally to the Upper Riphean. This formation is developed where the Mongol–Okhotsk belt is almost completely squeezed by the surrounding continental structures and, hence, bears important information on its evolution. The obtained results suggest the following conclusions: (1) the Glubokin Formation is Early Pennsylvanian or post-Early Pennsylvanian in age, not Riphean as previously suggested; (2) the Glubokin Formation belongs to the Mongol–Okhotsk Fold Belt rather than to the Argun continental massif, as suggested in the existing schemes of structural zoning; (3) the volcanogenic-terrigenous deposits of the Glubokin Formation were precipitated in a back-arc basin setting above the subduction zone subsiding beneath the southeastern margin of the North Asian Craton; and (4) the main sources of clastic material for the Glubokin Formation were igneous and metamorphic complexes of different ages from the southeastern margin of the North Asian Craton.

Early Mesozoic age of protolites of metasedimentary rocks from the Tukuringra terrane in the Mongolian–Okhotsk fold belt: Results of LA–ICP–MS U–Pb geochronological studies

This report presents the results of U–Pb geochronological LA–ICP–MS studies of detrital zircons from metasedimentary rocks of the western part of the Tukuringra terrane. The obtained data show that the Algainskaya, Garmakanskaya, and Teploklyuchevskaya series in the western part of the Tukuringra terrane are not of Middle Paleozoic but of Early Mesozoic age. It is shown that the main sources of clastic matter for these formations were Late Precambrian, Paleozoic, and Late Triassic–Early Jurassic complexes of continental massifs of the Amur superterrane.

Geochemical features and sources of clastic material in Paleozoic terrigenous deposits of the northeastern flank of the South Mongolia–Khingan orogenic belt

The results of geological and geochemical studies of terrigenous rocks of the main stratigraphic subdivisions in the northeastern flank of the South Mongolia–Khingan orogenic belt and also the results of U-Pb (LА-ICP-MS) geochronological studies of detrital zircons from these deposits are presented. It is demonstrated that the studied rocks differ significantly in the nature of distribution of detrital zircon ages and, consequently, they cannot be members of a single sedimentary sequence. The data obtained confirm the standpoint according to which the northeastern flank of the South Mongolia–Khingan orogenic belt represents a “joint” zone separating the Argun and the Bureya-Jiamusi Superterranes. This joint zone was formed as the result of closure of the oceanic basin separating the specified continental massifs in the Paleozoic era. The geochemical features of the studied rocks indicate their formation in the conditions of the island arc or the active continental margin. Lack of zircon generations younger than Ordovician age in the studied samples allows assuming that the sedimentary sequences identified within the northeastern flank of the studied belt as the Necla, Dagmara, siltstone-sandstone, and Gramatukha sequences that formed from the end of the Vendian (?) to the Devonian correspond to the youngest stages of belt formation. These sediments in the current structural plan evidently represent fragments of accretion complexes cropping out in fragments among the Cenozoic sequences of the Amur-Zeya Depression.

Middle Triassic age of metarhyolite of the Bondikha Formation, Argun Continental Massif, Central Asian Fold Belt

Research works carried out for the first time made it possible to determine the age of one of the key geological complexes in the Argun Continental Massif (Central Asian Fold Belt). It has been found that the metarhyolite of the Bondikha Formation is not Middle–Late Riphean, as previously thought, but is of Middle Triassic age (242 ± 6 Ma). Based upon the geochemical characteristics of the volcanics and regional geology of the Bondikha Formation, it can be assumed that they formed during one of the stages of subduction processes in the history of the Mongol–Okhotsk Fold Belt.

The Cambrian–Ordovician diorite–granodiorite–granite association of the Mamyn Terrane (Central Asian Fold Belt): U–Pb geochronological and geochemical data

New results of U–Pb geochronological and geochemical studies of rocks that form two structurally different massifs in the Mamyn Terrane are presented here. It has been found that the age of amphibole–biotite granites in the Kosmataya Massif, Oktyabrskii Complex is 488 ± 5 Ma. The same age has been defined for gneissose diorite 488 ± 8 and granodiorite 488 ± 5 Ma of the Ust–Inkan Massif. The results indicate that all the studied rocks have an identical Late Cambrian–Early Ordovician age of about 488 Ma. Considering that they were formed within a single tectonic structure (Mamyn Terrane), spatially close to each other and have similar geochemical characteristics, they may be considered as a single diorite–granodiorite–granite association. The results obtained indicate that a stage of intensive felsic magmatism occurred in the Mamyn Terrane in the eastern part of the Central Asian Fold Belt. This stage of magmatic activity is also clearly expressed in other continental massifs in the eastern part of this belt, which may indicate their common geodynamic history.

DETRITAL ZIRCON AGES AND SOURCES OF MATERIAL FOR THE LOWER CAMBRIAN DEPOSITS OF THE MEL'GIN TROUGH OF THE BUREYA CONTINENTAL MASSIF

Bureya continental massif is one of the largest continental massifs in the eastern part of the Central Asian orogenic belt (CAOB) (Fig. 1), and knowledge of its geological structure is of fundamental importance in understanding the history of its formation.

An Early Neoproterozoic gabbro–granite association in the Bureya Continental Massif (Central Asian fold belt): First geochemical and geochronological data

The fact that gneissose granites and gabbros of the Nyatygran Complex in the Bureya Continental Massif are not Palaeoproterozoic in age, as previously thought, but Neoproterozoic, ~933 Ma is proved. New data with the first direct evidence of Early Neoproterozoic magmatism in continental massifs composing the Bureya–Jiamusi Superterrane are given. At the moment, the obtained age estimates are the oldest for the magmatic rocks of this superterrane.

Areas and sources of metasedimentary rocks in the Tukuringra terrane of the Mongolian–Okhotsk mobile belt: Results of Sm–Nd isotope study

The results of Sm–Nd studies of metasedimentary rocks from the Tukuringra terrane, one of the largest units in the structure of the eastern part of the Mongolian–Okhotsk mobile belt, are reported. Metasedimentary rocks of the Algainskaya, Garmakanskaya, and Teploklyuchevskaya formations are characterized by similar model ages t Nd(DM) = 1.5–1.1 Ga. This shows that the major protoliths of metasedimentary rocks of the terrane are characterized by Mesoproterozoic estimates of the Nd model ages. The results obtained allow us to assume that introduction of terrigenous material into the sedimentary basin mostly occurred from the continental massifs united into the Amur superterrane, since their magmatic and sedimentary complexes are characterized by identical values of the Nd model ages.

Early Mesozoic granitoid and rhyolite magmatism of the Bureya Terrane of the Central Asian Orogenic Belt: Age and geodynamic setting

Early Mesozoic granitoids and volcanic rocks are widespread throughout the structures of all of the continental massifs in the eastern part of the Central Asian Orogenic Belt, although its tectonic setting is not yet clear. Generally, they are associated with subduction and plume processes or rifting. Such uncertainty is mostly explained by the unequal investigation of Early Mesozoic magmatism. This paper presents the results of geochemical, Sm-Nd isotope, and U–Pb geochronologic (ID-TIMS) studies of “key-type” Early Mesozoic magmatic rock complexes of the Bureya Terrane. This is one of the largest continental massifs in the eastern Central Asian Orogenic Belt and knowledge of its geological structure is of fundamental importance in understanding the history of its formation. It has been established that the leucogranites of the Altakhtinsky Complex and the trachyrhyolites of the Talovsky Complex are practically coeval (~209–208Ma). The subalkaline leucogranites of the Kharinsky Complex have a slightly younger age of ~199Ma. These data correspond to the general stage of Early Mesozoic magmatic and metamorphic events (236–180Ma) in most continental massifs in the eastern Central Asian Orogenic Belt. We believe that large-scale Early Mesozoic events were related to the amalgamation of the continental massifs of the eastern Central Asian Orogenic Belt into a single continental structure (the Amur superterrane or microcontinent Amuria) and collision with the North Asian Craton. It should be noted that the collision processes were followed by crustal thickening, thus creating the conditions for metamorphism and formation of magmatic rock complexes of various geochemical types.

First evidence of Ediacaran magmatism in the geological history of the Mamyn Terrane of the Central Asian fold belt

U–Pb geochronological studies reveal that the gabbro of the Mikitkin Massif and quartz diorite of the Ust’-Garin Massif of the Mamyn Terrane, which were provisionally assigned to the Early Proterozoic Garin Complex, have ages of 583 ± 6 Ma and 607 ± 8 Ma, i.e. Upper Riphean–Lower Vendian. The geochemical features of the magmatic rocks of the studied massifs indicate their suprasubduction origin. The parental melts of the magmatic rocks of the Garin Complex were formed in an active continental margin or ensialic island-arc setting due to melting of the subduction-modified depleted mantle source and the occurrence of contamination and fractional crystallization. These massifs were developed during the Ediacaran Stage of the geological evolution of the Mamyn Terrane and presumably reflect Neoproterozoic convergent geodynamic processes. These processes likely caused the ultimate formation of the Precambrian continental massifs in the eastern Central Asian fold belt, which were subsequently amalgamated into the structure of the epi-Paleozoic Amur microcontinent.

Black shales and other sediments with high organic matter contents in Phanerozoic climatic cycles: Communication 1. Black shales at the Gondwanan stage of biosphere evolution

The terminal Neoproterozoic was marked by the formation of a supercontinent, which was located during a long period at high latitudes of the Southern Hemisphere. The supercontinent named Gondwana united present-day Africa, Australia, Antarctica, South America, Arabia, Hindustan, and several other small continental blocks. It was separated from other, smaller continental blocks by ocean basins with the thinned continental and oceanic crust with the Panthalassa Ocean being largest among them. The Gondwanan stage, which comprised the Vendian and significant part of the Paleozoic, was one of the longest stages defined in the Neoproterozoic and Phanerozoic geological history lasting over 300–330 Ma. During this stage, the continental sector of the Earth’s crust included the Laurentia, Baltica, Siberia, Kazakhstan, and North China (Tarim) blocks, in addition to Gondwana, which were largely located at low latitudes of the Northern Hemisphere. In the Early Paleozoic, main tectonic events were related to the breakup in peripheral parts of Gondwana with the separation of small continental massifs, which moved in the northerly direction. Their collision with other continents was accompanied by the folding and formation of mountainous structures with corresponding foredeeps. For example, the Taconian phase of fold—thrust deformations resulted from the convergence of Laurentia with the Avalon block, which was separated from the northern margin of Gondwana in the Late Cambrian or Early Ordovician. The movement of Gondwana toward the equator and its amalgamation with other continents and smaller continental blocks in the terminal Cambrian resulted in the formation of the Pangea supercontinent, whose location near the equator for more than 150 Ma up to its disintegration at the terminal Jurassic—initial Cretaceous transition was responsible for significant global changes in the floral and faunal communities. Paleozoic epochs of the relatively stable warm climate alternated with shorter periods, which were characterized by global cooling due to expansion of the ice sheet in Gondwana. These periods are reflected in frequent migrations of climatic belts and rapid sea level oscillations, which were accompanied by changes in boundaries of facies zones and extinctions of biotic communities. Distribution patterns of black shales and other organic-rich sediments in sections imply cyclic climatic variations during the entire Paleozoic. Duration of individual cycles, which included a long phase of the dominant warm or even hot climate and shorter cooling phase crowning the cycle, was as long as 47 Ma. Two such cycles terminated with glaciations; others, with a less significant growth of the Gondwanan ice sheet.

Tectonic evolution of Kazakhstan and Tien Shan in Neoproterozoic and Early-Middle Paleozoic

Geological information on Kazakhstan and the Tien Shan obtained up to the present time has been considered and integrated in order to demonstrate the main features of continental massifs, basins with oceanic crust, island arcs, marginal volcanic-plutonic belts, and transform fault zones differing in type and age. We ascertained the character and probable causes of their evolution and transformations resulting in the origination and development of mosaic structural assembly at margin of the Paleoasian ocean that existed from Neoproterozoic. The main stages of the geodynamic history of Paleozoides in Kazakhstan and Tien Shan are characterized, and a model of the probable course of regional tectonic events has been proposed. This model is illustrated by published paleomagnetic data and a series of paleotectonic reconstructions for time intervals 950–900, 850–800, 750–700, 650–630, 570–550, 530–515, 500–470, 460–440, and 390–380 Ma.

Neoproterozoic tectonic evolution of the Taimyr Peninsula (Arctic Asia): An example of a Late Precambrian thrust-fold belt

Structural relationships between the Neoproterozoic rock complexes of a continental massif, island arc and back-arc basin geodynamic affinities are described and considered in this work based on field observations within the northeastern segment of the Central Taimyr tectonic zone distinguished in the late Hercynian fold-thrust belt of the Taimyr Peninsula. As is established for the first time, rock complexes of the continental massif with the early Late Riphean (Tonian-Cryogenian) volcanogenicsedimentary cover occur in the study region as the allochthonous syn- and post-sedimentary thrust sheets buried in, or thrust over, deposits of a back-arc basin, which accumulated in the terminal Late Riphean (Cryogenian)-initial Vendian (Ediacaran). These and other results of the large-scale structural observations elucidate important details of the tectonic development in the Late Precambrian, when two lateral ensembles of the Neoproterozoic structures originated in the region. In the first half of the Neoproterozoic, the regional tectonic ensemble included the oceanic plate abutting on the continental massif with a volcano-plutonic belt. The subsequent system of an island arc and marginal back-arc basin originated in the second half of the Neoproterozoic and existed approximately till the mid- Vendian (Ediacaran) phase of the intense formation of thrust sheets and folds (Baikalian orogeny).

The Rayner tectonic Province of East Antarctica: Compositional features and geodynamic setting

Geochemical and new isotopic (U-Pb, Sm-Nd) data on the Mesoproterozoic metaigneous complexes of the Rayner Province in central East Antarctica (Enderby Land-Kemp Land and the northern Prince Charles Mountains) are presented. These territories are mainly composed of amphibolite-to-granulite-facies orthogneisses, many of which are Y-depleted tonalite gneisses and mafic schists. The igneous complexes of their protolith are largely products of anatexis of the lower crust; mantle-derived and upper crustal rocks are less abundant. The geochemical features of the mafic rocks indicate that they crystallized from high-temperature plume-related mantle melts and low-temperature lithospheric melts. As follows from the published and new Nd model ages, the Rayner Province formed and evolved over the Paleo-to-Mesoproterozoic in the regime of accretionary and collisional tectonics with predominance of accretion of the juvenile Paleoproterozoic crust between 1500–2400 Ma. New data show that in the northern Prince Charles Mountains, granite-gneiss protoliths were emplaced ca. 1040 and 930 Ma ago. The Rayner Province is considered to be a long-living mobile belt formed as a result of collision of Paleoproterozoic island-arc terranes and Archean blocks amalgamating into a continental massif 1050–1000 Ma ago in the course of the growth of the Rodinia supercontinent. In the northern Prince Charles Mountains, thermal processes related to magmatic underplating at the base of the crust were probably important.

Ore belts of the Greater Altai and their ore resource potential

The results of comprehensive geological and metallogenic studies of the Greater Altai are presented. This project has been carried out since 1997 under the guidance of Academician G.N. Shcherba. The importance of these investigations is determined by the need to enhance and further develop mineral resources of nonferrous, noble, rare, and other metals for operating mining and metallurgical enterprises of Kazakhstan. The great body of information on the geology, geophysics, and metallogeny of the region obtained over many years has been integrated on the basis of new global tectonics. The Greater Altai embraces the Hercynides of the Rudny Altai, Qalba-Narym, West Qalba, Zharma-Saur, and the adjacent territories of Russia and China. The present-day tectonic units are considered to be detached blocks of ancient continental massifs that drifted in the Paleoasian ocean and then amalgamated into the structure of the Greater Altai during the Hercynian collision. The tectonic and metallogenic demarcation of the studied territory made possible the recognition of the Rudny Altai, Qalba-Narym, West Qalba, and Zharma-Saur ore belts, different in geology, geodynamic evolution, and metallogeny. The formation conditions and localization of volcanic-hosted massive sulfide, gold, and rare-metal deposits pertaining to certain ore-bearing geochronological levels were specified, and the potential of the region for various mineral resources was estimated.

Age of oceanic basalts of Bol’shoi Lyakhov Island (New Siberian Islands): Implication for the western boundary of the South Anyui ocean in the Jurassic

Serpentinites and pillow basalts exposed in the southeastern part of Bol’shoi Lyakhov Island are considered the northwestern continuation of the South Anyui suture of Chukotka [1, 2]. However, some researchers doubt that these rocks represent the lithosphere of the Mesozoic South Anyui oceanic basin. According to the rotation hypothesis of the opening of the Amerasian basin, it should be confined to Chukotka structures and not extend to the west [3]. Previous data on the inferred Paleozoic age of the oceanic pillow basalts exposed on the island [4] suggest that the northwestern continuation of the suture is the Paleozoic collisional zone, which lacks a direct relation to the Mesozoic tectonic events in the East Arctic. We present new data on the Middle‐Late Jurassic age of the oceanic basalts of Bol’shoi Lyakhov Island. Consequently, they formed precisely in the South Anyui oceanic basin. These data are of great importance for reconstructing the Mesozoic tectonic evolution of the East Arctic region and for discrediting the validity of the popular rotation hypothesis of the opening of the Amerasian oceanic basin. The southeastern part of Bol’shoi Lyakhov Island comprises diverse complexes of oceanic and island-arc (basic and ultrabasic) rocks [4, 5]. These complexes make up a series of allochthonous slices thrust onto the southeastern margin of the New Siberian continental block. The outcrops of the aforementioned rocks are considered to mark the northwestern continuation of the South Anyui suture—one of the most important tectonic sutures in the East Arctic region (Fig. 1) [1, 6, 7]. The South Anyui suture is a trace of the eponymous oceanic basin, which closed in the Neocomian simultaneously with opening of the Amerasian oceanic basin [1, 6, 8]. A composite collage of island-arc and continental terranes is located south of the suture [6], while the East Arctic continental massif is located north of the suture. Some geologists (for instance, [3]) believe that the eastern part of this massif (Chukotka microcontinent according to [6]) was a fragment of the North American Platform, while its western part was a continuation of the Siberian structures. These two blocks were separated by a hypothetical transform fault, which was formed during opening of the Amerasian basin

Late Carboniferous plutonism within the pre-Alpine basement of the External Hellenides (Kithira, Greece): evidence from U–Pb zircon dating

In memory of Theodor Doutsos, for his invaluable contribution to the understanding of geology of Greece. U–Pb zircon dating of three granitic orthogneisses, sampled from Kithira island, SW Greece, provide the first reliable evidence for Carboniferous plutonism within the pre-Alpine basement of the External Hellenides. Concordant zircons from two samples yielded ages at 324 ± 2 Ma and 323 ±3 Ma, whereas the third sample yielded a lower intercept age at 320 ± 1.2 Ma. The concordant ages are interpreted to date the emplacement of the igneous protolith. Ages of inherited zircons of two orthogneisses range from 2.5 to 2.4 Ga, indicating Late Archaean–Early Proterozoic crustal components. In combination with published ages for other Aegean metagranitoids, the new U–Pb ages provide additional evidence of a temporally restricted period of plutonism in the pre-Alpine Aegean region from 325 to 300 Ma. Comparing the post-Neoproterozoic evolution of the investigated basement with that of the Cycladic and Pelagonian basements and of the continental massifs of NE Greece and Turkey, we argue that all these crustal blocks were part of the Gondwana-derived Cimmerian terrane. Based on the spatial and temporal distribution of Late Carboniferous Aegean plutonism, we suggest that this period of magmatic events results from the southward subduction of Palaeotethys beneath the marginal fragments of northern Gondwana.