西北天山莱历斯高尔岩体年代学、地球化学及其成因

西北天山莱历斯高尔岩体主要由花岗闪长斑岩和二长花岗斑岩组成,二者具有相似的地球化学特征,可能为同源岩浆分异演化的产物。锆石SHRIMP U-Pb年龄显示岩体形成于晚泥盆世(374±4 Ma)。莱历斯高尔岩体具有较高的SiO2(67.75% ～74.71%)含量和K2O/Na2O(1.24～2.20)比值,属于高钾钙碱性系列。稀土元素配分曲线为轻稀土富集型(La/Yb)N(5.25～10.57),具有中等—弱的Eu负异常δEu(0.55～0.92)。微量元素特征显示富集大离子亲石元素(LILE),而亏损高场强元素(HFSE),具有较低的Sr(122×10-6～356×10-6)含量、较高的Y(17.19×10-6～21.82×10-6)和Yb(1.78×10-6～2.57×10-6)含量。岩体的Sr-Nd同位素特征为ISr=0.707 867～0.709 654,εNd(t)=-2.79～-1.46。铅同位素特征为206Pb/204 Pb=18.423～19.915,207 Pb/204Pb=15.576～15.685,208 Pb/204Pb=38.344～39.305。元素和同位素地球化学特征表明,莱历斯高尔岩体岩浆源区主要为中元古代下地壳的部分熔融,并有部分地幔物质的加入。岩体形成于晚泥盆世准噶尔洋向伊犁—中天山微板块陡角度俯冲的大陆弧构造环境。     

Morphologic expression of Quaternary deformation in the northwestern foothills of the Ysyk-Köl basin,Tien Shan

The Tien Shan is one of the most active intracontinental mountain belts exhibiting numerous examples of Quaternary fault-related folding. To provide insight into the deformation of the Quaternary intermontane basins, the territory of the northwestern Ysyk-Köl region, where the growing Ak-Teke Anticline divided the piedmont apron of alluvial fans, is studied. It is shown that the Ak-Teke Hills are a sharply asymmetric anticline, which formed as a result of tectonic uplift and erosion related to motions along the South Ak-Teke Thrust Fault. The tectonic uplift gave rise to the local deviation of the drainage network in front of the northern limb of the fold. Optical (luminescent) dating suggests that the tectonic uplifting of the young anticline and the antecedent downcutting started 157 ka ago. The last upthrow of the high floodplain of the Toru-Aygyr River took place 1300 years ago. The structure of the South Ak-Teke Fault is examined by means of seismologic trenching and shallow seismic profiling across the fault. A laser tachymeter is applied to determine the vertical deformation of alluvial terraces in the Toru-Aygyr River valley at its intersection with the South Ak-Teke Fault. The rates of vertical deformation and an inferred number of strong earthquakes, which resulted in the upthrow of Quaternary river terraces of different ages, are calculated. The study territory is an example of changes in fluvial systems on growing folds in piedmont regions. As a result of shortening of the Earth’s crust in the mountainous belt owing to thrusting, new territories of previous sedimentation are involved in emergence. The tectonic activity migrates with time from the framing ridges toward the axial parts of intramontane basins.     

Stenian granitoids of the west Kyrgyz Ridge (North Tien Shan): Position, structure, and age determination

In the structure of west Kyrgyz Ridge (North Tien Shan), a great role is played by complexly dislocated Upper Precambrian-Cambrian terrigenous-carbonate and shale strata, as well as by granitoids that comprise several coupled WNW-striking synforms and antiforms, the largest of which is the Makbal antiform. Southeast of the core of this antiform, granitoids comprise the large Kara Dzhilga massif and several massifs that are of lesser size and have tectonic correlations with the hosting terrigenous-carbonate strata. In the Kara Dzhilga massif, the rocks of three penetration phases are distinguished; contacts between rocks are often of tectonic character. The early phase is presented by monzonite and monzodiorite; the main one, by large-porphyric biotitic granites; and the additional one, by aplitic granites and pegmatites. By the chemical composition, granites of Kara Dzhilga massif of the main phase correspond to subalkaline granites of high-potassium calc-alkali series. The age of their crystallization (zircon-based U-Pb method) is 1131 ± 4 Ma (Stenian). The formation of Stenian granitoids in the North Tien Shan may be related to development of Grenville fold belts, whose fragments were identified in the units of the Central Asian Belt. Tectonic correlations between these granitoids and hosting terrigenous-carbonate strata appeared as a result of immersion to significant depths and subsequent exhumation into the upper crustal horizons in the Early Ordovician.     

Geodymanics of Tibet,Tarim, and the Tien Shan in the Late Cenozoic

The tectonic and geodynamic consequences of the collision between Hindustan and Eurasia are considered in the paper. The tectonic evolution and deformation of Tibet and the Tien Shan in the Late Cenozoic is described on the basis of geological, geophysical, and geodetic data. The factual data and their interpretation, which shed light on the kinematics of the tectonic processes in the lithosphere and the geodynamics of the interaction between the Tien Shan, Tarim, and Tibet are discussed. A geodynamic model of their interaction is proposed.     

Ground-water geochemistry of uranium and other elements, Monticello area, New York

About 500 well and spring waters were collected on an approximately 1-km spacing in an area centered on six small U and Cu-U occurrences near Monticello, N.Y., as an orientation survey in the NURE program. Rocks of the area belong to the Devonian Catskill Group and are predominantly red sandstones and shales of fluvial origin. The sediments dip 0–5° in the main part of the area, but steepen to 45° in the east. The ground waters were analyzed for 46 elements plus several other water properties.An R-mode factor analysis extracted 10 factors. The strongest factor, termed “Dissolved solids”, has heavy loadings on most major elements, plus U, B, Li, Sr, and Zn. This factor is attributed to varying degrees of interaction between original rainwater and rocks. Recognition of anomalies for elements loaded on this factor is aided by evaluation of ratios or plots against total dissolved solids or conductivity. Three weaker factors apparently represent admixtures with two types of deep brine and with waters of enhanced Fe-Mn resulting from reducing conditions. Other factors include an assemblage of insoluble trace metals and a Zn-Cu-P factor, both possibly related to contamination and/or analytical problems, a rare earth group, and an Se-As-Ag factor. The waters are clearly complex mixtures of effects.The geographic distribution of high U values shows some correlation with the distribution of U occurrences, but many equally high values occur outside the known mineralized area. When the data are projected to a vertical section normal to the strike, high U values define two gently dipping aquifers. The upper anomalous aquifer contains the known occurrences but extends downdip. Samples within this aquifer show patterns in U, dissolved O₂, and conductivity, apparently related to influx of fresh water from updip, along major rivers, and along possible fractured zones. High He values are also most numerous near the occurrences and define the deeper U-rich aquifer. The interpretation of the data is greatly clarified by separation of individual aquifers.Saturation indices are generally −3.4 to −5 and show patterns similar to dissolved U, except for values of −6 to −9 in a few samples with high phosphate. Predominant U species are usually UO₂(CO₃)₂²⁻, or less commonly UO₂CO₃⁰ or UO₂(HPO₄)₂²⁻.     

A geotraverse across two paleo-subduction zones in Tien Shan,Tajikistan

We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earliest Middle Devonian. Thereafter the northern side of the Turkestan Ocean remained a passive margin until the Early Carboniferous. (2) In the Early Carboniferous, subduction under the northern margin of the Turkestan Ocean resumed and the 315 to 305 Ma old Kara-Kiya, Muzbek, and Karamazar intrusions formed in a supra-subduction setting in the Mogol-Tau and Kurama ranges. (3) At the same time, in the Early Carboniferous, rifting of the southern passive margin of the Turkestan Ocean formed the short-lived Gissar Basin, separated from the Turkestan Ocean by the Gissar micro-continent. North-dipping subduction in the Gissar Basin is documented by the 315 Ma Kharangon plagiogranite and the voluminous ca. 321–312 Ma Andean-type supra-subduction Gissar batholith. The Kharangon and Khanaka gabbro-plagiogranite intrusions of the southern Gissar range have geochemical and Sr–Nd isotopic compositions (⁸⁷Sr/⁸⁶Sr(t) 0.7047–0.7056, εNd of + 1.5 to + 2.3) compatible with mantle-derived origin typical for plagiogranites associated with ophiolites. The supra-subduction rocks from the Gissar batholith and from the Mogol-Tau Kurama ranges have variably mixed Sr–Nd–Pb isotopic signatures (⁸⁷Sr/⁸⁶Sr(t) 0.7057–0.7064, εNd of − 2.1 to − 5.0) typical for continental arcs where mantle-derived magmas interact with continental crust. (4) In the latest Carboniferous, the Turkestan Ocean and the Gissar Basin were closed. The Early Permian Chinorsay (288 Ma) and Dara-i-pioz (267 Ma) post-collisional intrusions, emplaced in the northern part of the Gissar micro-continent after a long period of amagmatic evolution, have intraplate geochemical affinities and isotopic Sr–Nd–Pb isotopic compositions (⁸⁷Sr/⁸⁶Sr(t) 0.7074–0.7086, εNd of − 5.5 to − 7.4) indicating derivation from Precambrian continental crust which is supported by old Nd model ages (1.5 and 1.7 Ga), and by the presence of inherited zircon grains with ages 850–500 Ma in the Chinorsay granodiorite. The post-collisional intrusions in the southern Gissar and in the Mogol-Tau and Kurama ranges (297–286 Ma), emplaced directly after supra-subduction magmatic series, have geochemical and isotopic signatures of arc-related magmas. The distinct shoshonitic affinities of post-collisional intrusions in the Mogol-Tau and Kurama ranges are explained by the interaction of hot asthenospheric material with subduction-enriched wedge of lithospheric mantle due to slab break-off at post-collisional stage. Despite origination from different tectonic environments, all magmatic rocks have relatively old Nd model ages (1.7–1.0 Ga) indicating a significant proportion of Paleoproterozoic or older crustal material in their sources and their model ages are similar to those of post-collisional intrusions from the Alai and Kokshaal Segments of the South Tien Shan.     

Extremely large rockslides and rock avalanches in the Tien Shan Mountains, Kyrgyzstan

Most systematic research on large rock-slope failures is geographically biased towards reports from Europe, the Americas, the Himalayas and China. Although reports exist on large rockslides and rock avalanches in the territory of the former Soviet Union, they are not readily available, and few translations have been made. To begin closing this gap, we describe here preliminary data from field reconnaissance, remote sensing and geomorphometry of nine extremely large rock-slope failures in the Tien Shan Mountains of central Kyrgyzstan. Each of these catastrophic and prehistoric failures exceeds an estimated 1 km³ in volume, and two of them involve about 10 km³. Failure of rock slopes in wide valleys favoured the emplacement of hummocky long-runout deposits, often spreading out over >10 km², blocking major rivers. Most of these gigantic slope failures are located on or near active faults. Their spatial clustering and the high seismic activity in the Tien Shan support the hypothesis that strong seismic shaking caused or triggered most of these large-scale rock-slope failures. Nevertheless detailed field studies and laboratory analyses will be necessary to exclude hydroclimatic trigger mechanisms (precipitation, fluvial undercutting, permafrost degradation), and to determine their absolute ages, frequency and the large-landslide hazard of central Kyrgyzstan.     

Indications of late medieval earthquakes in the Talas-Fergana Fault Zone,Tien Shan

A paleoseismological study in the Talas-Fergana Fault Zone of the Tien Shan was accompanied by age determination of ancient seismic events. The calibrated radiocarbon datings of recent and buried soils allowed us to recognize the fault segments reactivated during strong earthquakes that occurred in the 14th- 16th centuries A.D. The magnitude of the paleoseismological event in the 16th century was no lower than 7.0 and no lower than IX in seismic intensity.     

Geomechanical conditions of the Tien Shan and Altai Orogeny

The results of numerical modelling of deformation of the Earth’s crust along the Tarim–Altai profile caused by the force of gravity and lateral compression using the approximate two-dimensional model of the elastoplastic transition are presented. The conditions of the formation of mountains and their roots were determined taking into account some geological and geophysical parameters.     

Rare earth and other rare elements in uranium ores of paleovalley deposits in the Vitim district: Distribution,occurrence, and applied implications

The degree of concentration and REE and Zr distribution and occurrence in uranium ore samples from paleovalley deposits are considered. Various types of REE distribution in ores with variable uranium content has been revealed: the negative type with predominance of LREE in ordinary ore and the V-shaped type with significant growth of Y, MREE, and HREE contents in high-grade ore. In addition, the relationship between U, on the one hand, and MREE, HREE, Y, and Zr, on the other hand, has been established. Predominant isomorphic incorporation of these elements into various uranium constituents is suggested. The conclusion was arrived at about the most probable gain of REE and Zr along with U on various geochemical barriers from postvolcanic thermal carbonated and sulfuric-acid aqueous solutions enriched in these chemical elements. The significant enrichment of uranium ore in REE confirms the real possibility of recovery of them as a by-product from working solutions in the process of in situ uranium leaching.     

Crustal Shortening on the Margins of the Tien Shan,Xinjiang, China

We present the results of mapping selected cross-sections across the margins of the Chinese Tien Shan, an intracontinental mountain belt that formed in response to the India-Eurasia collision. This belt contains significant lateral variation in topography, structure, and stratigraphy at all scales, and our estimated rates of shortening also reveal a distribution of shortening that varies laterally. At the largest scale, it consists of two major high mountain ranges in the west that merge eastward into a complex, single high mountain belt with several distinct ranges, then separates farther eastward into several low mountain ranges in the south and a single narrow high mountain range in the north. Active fold-and-thrust belts along parts of the north and south flanks of the Tien Shan involve only Mesozoic and Cenozoic sedimentary cover, which varies in both stratigraphy and structure from east to west. The southern fold-and-thrust belt decreases in width and complexity from west to east and ends before reaching Korla. The northern belt begins near the longitude where the southern belt ends, and increases in width and complexity from west to east. Within these two fold-and-thrust belts are both E-W and N-S variations in stratigraphy at the scale of the fold-and-thrust belts and across individual structures. All these variations make it very difficult to generalize either structure or stratigraphy within the Tien Shan or within local areas.

Four maps and cross-sections, two across each of the northern and southern fold-and-thrust belts, imply different magnitudes of shortening. In the eastern part of the northern belt, a cross-section along the southern part of the Hutubi River yields shortening of 6.2 km, and a section to the north across the Tugulu anticline yields shortening of 5.5 km. The two parts of the cross-section cannot be added because the Tugulu anticline lies 20 km west of the Hutubi River, and diminishes greatly in amplitude toward the Hutubi River. In the western part of the northern belt, cross-sections require 4.6 to 5.0 km of shortening at Tuositai and 2.12 to 2.35 km across the Dushanzi anticline. The Tuositai structure lies south of the Dushanzi anticline, but shortening in these two areas also cannot be summed, because they seem to be separated by a N-trending strike-slip fault. In the western part of the southern fold-and-thrust belt, an incomplete cross-section along the Kalasu River suggests shortening of 12.1 to 14.1 km. If the estimated shortening of 6 to 7 km in the Qiulitage anticline, which we did not map, is added, the total shortening in this cross-section would be ～18 to 21 km. To the east, a complete cross-section at Boston Tokar yielded shortening of 10.3 to 13.0 km.

Calculating long-term shortening rates from these four cross-sections is difficult, because the time of initiation of deformation is poorly known. In the Kalasu River area of the southern belt, there is evidence that limited shortening of 2 to 4 km occurred in the early Miocene, if major thickness changes in deposition of conglomerate unit 3b are interpreted to be growth strata. Geological evidence suggests that most of the shortening began in both belts after the beginning of the deposition of the thick conglomerate unit shown as lower Quaternary on Chinese geological maps. Strata within the middle part of these conglomerates were deposited during the growth of the folds. Presence of Equus near the base of similar conglomerates indicates a Quaternary age, but the fossil localities are far from most of our cross-sections, and the contemporaneity of the rocks remains in question. The beginning of conglomerate deposition may be controlled by climate change, and if so, the beginning of conglomerate deposition may be generally contemporaneous throughout the region at ～2.5 Ma. Deformation began at some time after the onset of conglomerate deposition, but this time is not well constrained. Thus we have calculated shortening rates for 2.5, 1.6, and 1.0 Ma that should bracket maximum and minimum slip rates. These calculations yield the following ranges in the northern fold-and-thrust belt: southern Hutubi River = 2.5 to 6.2 mm/yr; Tugulu anticline = 2.1 to 5.5 mm/yr; Tuositai anticline = 1.8–2.0 to 4.6–5.0 mm/yr; and Dushanzi anticline = 0.8 to 2.1–2.4 mm/yr; and in the southern fold-and-thrust belt: Kalasu River = 4.6–5.6 (including the Qiulitage anticline = 7.2–8.4) to 12.1–14.1 (including Qiulitage anticline = 18–21) mm/yr; and at Boston Tokar = 4.1–5.2 to 10.3–13.1 mm/yr. If 2 to 4 km of shortening occurred in the Kalasu River section during early Miocene time, the long-term rates for Quaternary time are 3.2–4.8 (including Qiulitage anticline = 5.6–7.6) to 8.1–12.1 (including Qiulitage anticline = 14–19) mm/yr.

Calculation of the shortening rate across the entire width of the Tien Shan is difficult because of the rapid lateral variations in structure and because of active deformation within the range, which we have not studied. The cross-sections at Boston Tokar in the south and Tuositai in the north lie along the same longitude. Adding the shortening rates in these areas would yield a minimum range (using 2.5 Ma as the initiation time) of 5.7 to 7.2 mm/yr. If deformation began at 1.6 or 1.0 Ma, the range of shortening rates would be 10–11.2 mm/yr to 14.9–18.1 mm/yr, respectively. Because the first indication of structural growth with the mapped areas occurs above the base of the conglomerates at the top of the stratigraphic succession, a minimum shortening rate greater than 5.7 to 7.2 mm/yr is more likely.

Both the marginal fold-and-thrust belts have a thin-skinned geometry with the drcollement at -6 to 10 km and within Mesozoic and Cenozoic sedimentary rocks. Toward the interior of the range the decollement must pass into the Paleozoic basement rocks and steepen beneath the flanks of the range. The structural style is similar to that in the Laramide Rocky Mountains and the California Transverse Ranges. The highest parts of the Tien Shan are adjacent to areas of active shortening. Such a relation might suggest that the major uplift of the Tien Shan is very young, mostly latest Cenozoic or Quaternary in age. The shortening across the Tien Shan is inhomogeneous and spatially distributed.     

Evidence of uranium biomineralization in sandstone-hosted roll-front uranium deposits, northwestern China

We show evidence that the primary uranium minerals, uraninite and coffinite, from high-grade ore samples (U₃O₈>0.3%) in the Wuyiyi, Wuyier, and Wuyisan sandstone-hosted roll-front uranium deposits, Xinjiang, northwestern China were biogenically precipitated and psuedomorphically replace fungi and bacteria. Uranium (VI), which was the sole electron acceptor, was likely to have been enzymically reduced. Post-mortem accumulation of uranium may have also occurred through physio-chemical interaction between uranium and negatively-charged cellular sites, and inorganic adsorption or precipitation reactions. These results suggest that microorganisms may have played a key role in formation of the sandstone- or roll-type uranium deposits, which are among the most economically significant uranium deposits in the world.     

Tien Shan,Pamir, and Tibet: History and geodynamics of phanerozoic oceanic basins

Geological and biogeographical data on the paleooceanic basins of the Tien Shan and High Asia are summarized. The oceanic crustal rocks in the Tien Shan, Pamir, and Tibet belong to the Tethian and Turkestan-Paleoasian systems of paleooceanic basins. The tectonic evolution of these systems in the Phanerozoic was not coeval and unidirectional. The sialic blocks of the future Tien Shan, Pamir, and Tibet were incorporated into the Eurasian continent during several stages. In the Late Ordovician and Silurian several microcontinents were preliminarily combined into the Kazakh-Kyrgyz continent as a composite aggregation. The territories of the Tien Shan and Tarim became a part of Eurasia after the closure of the Turkestan, Ural, and Paleotethian oceans in the Late Carboniferous and Early Permian. The territories of the Pamir, Karakorum, Kunlun, and most of Tibet attached to the Eurasian continent in the Triassic. The Lhasa and Kohistan blocks were incorporated into Eurasia in the Cretaceous, whereas Hindustan was docked to Eurasia in the Paleogene.     

Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan, central Asia

The Chinese Tien Shan range is a Palaeozoic orogenic belt which contains two collision zones. The older, southern collision accreted a north-facing passive continental margin on the north side of the Tarim Block to an active continental margin on the south side of an elongate continental tract, the Central Tien Shan. Collision occurred along the Qinbulak-Qawabulak Fault (Southern Tien Shan suture). The time of the collision is poorly constrained, but was probably in in the Late Devonian-Early Carboniferous. We propose this age because of a major disconformity at this time along the north side of the Tarim Block, and because the Youshugou ophiolite is imbricated with Middle Devonian sediments. A younger, probably Late Carboniferous-Early Permian collision along the North Tien Shan Fault (Northern Tien Shan suture) accreted the northern side of the Central Tien Shan to an island arc which lay to its north, the North Tien Shan arc. This collision is bracketed by the Middle Carboniferous termination of arc magmatism and the appearance of Late Carboniferous or Early Permian elastics in a foreland basin developed over the extinct arc. Thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin. Post-collisional, but Palaeozoic, dextral shear occurred along the northern suture zone, this was accompanied by the intrusion of basic and acidic magmas in the Central Tien Shan. Late Palaeozoic basic igneous rocks from all three lithospheric blocks represented in the Tien Shan possess chemical characteristics associated with generation in supra-subduction zone environments, even though many post-date one or both collisions. Rocks from each block also possess distinctive trace element chemistries, which supports the three-fold structural division of the orogenic belt. It is unclear whether the chemical differences represent different source characteristics, or are due to different episodes of magmatism being juxtaposed by later dextral strike-slip fault motions. Because the southern collision zone in the Tien Shan is the older of the two, the Tarim Block sensu stricto collided not with the Eurasian landmass, but with a continental block which was itself separated from Eurasia by at least one ocean. The destruction of this ocean in Late Carboniferous-Early Permian times represented the final elimination of all oceanic basins from this part of central Asia.     

Tectonic evolution of Early Paleozoic island-arc systems and continental crust formation in the Caledonides of Kazakhstan and the North Tien Shan

The extended Saryarka and Shyngyz-North Tien Shan volcanic belts that underwent secondary deformation are traced in the Caledonides of Kazakhstan and the North Tien Shan. These belts are composed of igneous rocks pertaining to Early Paleozoic island-arc systems of various types and the conjugated basins with oceanic crust. The Saryarka volcanic belt has a complex fold-nappe structure formed in the middle Arenigian-middle Llanvirnian as a result of the tectonic juxtaposition of Early-Middle Cambrian and Late Cambrian-Early Ordovician complexes of ensimatic island arcs and basins with oceanic crust. The Shyngyz-North Tien Shan volcanic belt is characterized by a rather simple fold structure and consists of Middle-Late Ordovician volcanic and plutonic associations of ensialic island arcs developing on heterogeneous basement, which is composed of complexes belonging to the Saryarka belt and Precambrian sialic massifs. The structure and isotopic composition of the Paleozoic igneous complexes provide evidence for the heterogeneous structure of the continental crust in various segments of the Kazakh Caledonides. The upper crust of the Shyngyz segment consists of Early Paleozoic island-arc complexes and basins with oceanic crust related to the Saryarka and Shyngyz-North Tien Shan volcanic belts in combination with Middle and Late Paleozoic continental igneous rocks. The deep crustal units of this segment are dominated by mafic rocks of Early Paleozoic suprasubduction complexes. The upper continental crust of the Stepnyak segment is composed of Middle-Late Ordovician island-arc complexes of the Shyngyz-North Tien Shan volcanic belt and Early Ordovician rift-related volcanics. The middle crustal units are composed of Riphean, Paleoproterozoic, and probably Archean sialic rocks, whereas the lower crustal units are composed of Neoproterozoic mafic rocks.     

Geodynamics of late Paleozoic magmatism in the Tien Shan and its framework

The Devonian-Permian history of magmatic activity in the Tien Shan and its framework has been considered using new isotopic datings. It has been shown that the intensity of magmatism and composition of igneous rocks are controlled by interaction of the local thermal upper mantle state (plumes) and dynamics of the lithosphere on a broader regional scale (plate motion). The Kazakhstan paleocontinent, which partly included the present-day Tien Shan and Kyzylkum, was formed in the Late Ordovician-Early Silurian as a result of amalgamation of ancient continental masses and island arcs. In the Early Devonian, heating of the mantle resulted in the within-plate basaltic volcanism in the southern framework of the Kazakhstan paleocontinent (Turkestan paleoocean) and development of suprasubduction magmatism over an extensive area at its margin. In the Middle-Late Devonian, the margins of the Turkestan paleoocean were passive; the area of within-plate oceanic magmatism shifted eastward, and the active margin was retained at the junction with the Balkhash-Junggar paleoocean. A new period of active magmatism was induced by an overall shortening of the region under the settings of plate convergence. The process started in the Early Carboniferous at the Junggar-Balkhash margin of the Kazakhstan paleocontinent and the southern (Paleotethian) margin of the Karakum-Tajik paleocontinent. In the Late Carboniferous, magmatism developed along the northern boundary of the Turkestan paleoocean, which was closing between them. The disappearance of deepwater oceanic basins by the end of the Carboniferous was accompanied by collisional granitic magmatism, which inherited the paleolocations of subduction zones. Postcollision magmatism fell in the Early Permian with a peak at 280 Ma ago. In contrast to Late Carboniferous granitic rocks, the localization of Early Permian granitoids is more independent of collision sutures. The magmatism of this time comprises: (1) continuation of the suprasubduction process (I-granites, etc.) with transition to the bimodal type in the Tien Shan segment of the Kazakhstan paleocontinent that formed; (2) superposition of A-granites on the outer Hercynides and foredeep at the margin of the Tarim paleocontinent (Kokshaal-Halyktau) and emplacement of various granitoids (I, S, and A types, up to alkali syenite) in the linear Kyzylkum-Alay Orogen; and (3) within-plate basalts and alkaline intrusions in the Tarim paleocontinent. Synchronism of the maximum manifestation and atypical combination of igneous rock associations with spreading of magmatism over the foreland can be readily explained by the effect of the Tarim plume on the lithosphere. Having reached maximum intensity by the Early Permian, this plume could have imparted a more distinct thermal expression to collision. The localization of granitoids in the upper crust was controlled by postcollision regional strike-slip faults and antiforms at the last stage of Paleozoic convergence.     

Interior linear uplifts in Alpine troughs of central Tien Shan

The sections, the map, and the geological analysis of the area show that the uplifts within the large area of the Paleogene-Neogene subsidence had arisen during Anthropogene time, in consequence of a certain tectonic reconstruction of the area. The uplifts appear to be anticlinal folds whose strike tends to follow and even coincide with the strike of the major structures of the Hercynian base. Similar uplifts in tectonically similar environments are found also in northern Tien Shan and elsewhere in central Asia. – IGR Staff.