Heat flow structure in the Paleozoides of the Central Asian Fold Belt

Heat generation produced by radioactive decay of long-lived isotopes in the Earth’s crust (radiogenic heat flow) within the Paleozoic provinces of the Central Asian Fold Belt is considered. Heat flow from the mantle is calculated as the difference between the observed heat flow and the radiogenic flow. The major cause of this heat flow is the transition of potential energy of gravity differentiation into heat; in this respect, mantle heat flow is called gravigenic. Calculation shows that the fractions of radiogenic and gravigenic heat flows in the Paleozoides studied are nearly equal.     

Paleomagnetism of the Central Part of the Central Asian Fold Belt (Tuva,Mongolia)

Doklady Earth Sciences - Summarized paleomagnetic data for Tuva and Mongolia showed that the curves of latitudinal displacement of Siberia, Tuva, and northern Mongolia differ insignificantly and...     

West Pacific-type convergent boundaries and their role in the formation of the Central Asian Fold Belt

The type of convergent boundaries forming in the area of mantle plumes is considered. These convergent boundaries (West Pacific type) are characteristic of the western margin of the Pacific. West Pacific-type boundaries are a regular succession of structures from ocean to continent: island arcs, marginal basins, rift basins, and associated OIB-type volcanics at the continental edge. The convergence zones are up to a thousand kilometers wide.Studies of the history of the part of the Central Asian Fold Belt forming the folded periphery of the Siberian continent have shown that the continent drifted above the African plume or corresponding low-velocity mantle province for most of the Phanerozoic (up to the Early Mesozoic inclusive). This fact determined the West Pacific type of convergent boundaries for the accretionary structures of the Central Asian Fold Belt. The drift of Siberia from African to Pacific province in the Late Cenozoic determined the structure and development of the convergent boundary in the western Pacific, including extensive intraplate magmatism in continental Asia in the Late Mesozoic and Cenozoic.     

Tectonics and geodynamics of the western Central Asian Fold Belt (Kazakhstan Paleozoides)

On the basis of stratigraphical and geological data, paleogeographical and palinspastic reconstructions of the Kazakhstan Paleozoides were done; their multistage geodynamic evolution was considered; their tectonic zoning was proposed. The main stages are described: the initiation of the Cambrian and Ordovician island arcs; the development of the Kazakhstan accretionary–collisional composite continent in the Late Ordovician as a result of continental subduction and the amalgamation of Gondwana blocks with the island arcs (a long granitoid collisional belt also formed in this period); the development of the Devonian and Carboniferous–Permian active margins of the composite continent and its tectonic destruction in the Late Paleozoic.In the Late Ordovician, compensated terrigenous and volcanosedimentary complexes formed within Kazakhstania and developed in the Silurian. The Sakmarian, Tagil, Eastern Urals, and Stepnyak volcanic arcs formed at the boundaries with the Ural, Turkestan, and Junggar–Balkhash Oceans. In the late Silurian, Kazakhstania collided with the island arcs of the Turkestan and Ob'–Zaisan Oceans, with the formation of molasse and granite belts in the northern Tien Shan and Chingiz. This was followed by the development of the Devonian and Carboniferous–Permian active margins of the composite continent and the inland formation of the Early Devonian rift-related volcanosedimentary rocks, Middle–Late Devonian volcanic molasse, Late Devonian–Early Carboniferous rift-related volcanosedimentary rocks, terrigenous–carbonate shelf sediments, and carbonaceous lake–bog sediments, and the Middle–Late Carboniferous clastic rocks of closed basins. In the Permian, plume magmatism took place on the southern margin of the Kazakhstan composite continent. It was simultaneous with the formation of red-colored molasse and the tectonic destruction of the Kazakhstan Paleozoides as a result of a collision between the East European and Kazakhstan–Baikal continents.     

High-pressure complexes of Central Asian Fold Belt: geologic setting,geochemistry, and geodynamic implications

Blueschists are constituents of subduction-accretion complexes, where they occur either as separate tectonic slabs, slices, and lenses, or as exotic blocks in a melange. Often associated with ophiolites, blueschists are commonly metamorphosed members of ophiolite sections. Along with ophiolite, a typical component of high-pressure belts is alkaline ocean-island basalt comprehensively studied in the Uimon zone of Gorny Altai and Chara zone of Eastern Kazakhstan. This suggests active plume magmatism in the Early Paleozoic evolution of the Paleoasian Ocean. As inferred from sutures with high-pressure rocks, different parts of Paleoasian Ocean were closing successively.     

Paleozoic granitoid magmatism of the eastern part of the Central Asian Fold Belt and formation of large ore deposits

Evidence on the Paleozoic granitoids of the eastern part of the Central Asian Fold Belt (CAFB) was analyzed. A tectonic chart of orogenic belts was compiled. Sketch maps were constructed for the geodynamic settings of the formation of Paleozoic granitoids and the extensiveness of their occurrence. Two types of deep controlling structures were distinguished: zones of lithospheric faults and plumes, including the newly recognized Jiamusi-Bureya plume. It was sown that the distribution of large and superlarge Paleozoic ore deposits is related to these structures, primarily to plumes. Sites promising for large and superlarge deposits related to the Paleozoic granitoid magmatism were determined in the Russian Far East.     

青藏高原区域重磁异常的东西向分区及其构造地质特征

自从大陆整合以来作为一个整体的青藏高原继续受着印度板块向北俯冲的影响,也必定不断地改造着原各地体的结构构造,形成了高原整体意义上东西向的差异。这种差异与原本各地体的组成、结构和东西向延伸不一致。这不仅表现在南北向断裂构造跨各单个地体范围的出现,而且,逐步形成了东西的分区。这种分区突出地表现在区域重力与磁场的特征上,这不仅是局部的岩石磁性与密度变化的结果,而且是由于印度板块向北俯冲过程中,在其前缘的不同部位上经受的压力不同,以及地块的隆升与扩张作用的差异造成了高原东西各区段的地壳组分与厚度的变化。青藏高原的南北向断裂构造并非地壳上层的局部断裂,它具有深层的原因。由于印度板块向北推进的过程中不是均匀地齐头并进,而是在帕米尔高原以东的青藏高原范围内存在着推进速度和俯冲深度的差异,随着高原隆升的加剧高原本身出现断裂,自中新生代以来就存在着一定差异,所以南北向的断裂构造比目前地表见到的多些,而且具有较大的深度,Moho面的深度和地壳厚度都受南北向断裂的控制,并形成了区域重磁场的变化。同时,高原的东西向拉张作用也使南北断裂带发育加剧。     

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 junction of the eastern Central Asian Fold Belt and the Siberian Platform: deep structure and Mesozoic tectonics and geodynamics

The tectonic structure of the junction of the eastern Central Asian Fold Belt and the Siberian Platform, along with the deep structure of the Earth's crust and lithosphere in this region, has been described on the basis of new geological and geophysical data (seismic, geoelectric, and space-structural studies as well as new-generation geological maps), combined with new interpretation techniques (processing of the previous data by special software). The data suggest the existence of oblique collision during the convergence of the tectonic plates and, correspondingly, tectonic units composing these plates, when the Mongol–Okhotsk paleobasin closed. Such a scenario within the Aldan–Stanovoi Shield is evidenced by areas of syn- and postcollisional magmatism, with their deep-level and geochemical characteristics, and by the presence of a Late Mesozoic fold–thrust zone. Deep “traces” of these tectonomagmatic events, detected in the course of geological and geophysical modeling, are manifested in inclined deep boundaries between the crustal and lithospheric blocks. On the Earth's surface, they correspond to large fault systems: the Dzheltulak, North and South Tukuringra, Gulyui, and Stanovoi. It has been found that the influence of collision decreases northward with distance from the junction of the eastern Central Asian Fold Belt and the Siberian Platform (Dzheltulak and North Tukuringra transcrustal faults).     

The age and tectonic setting of the Lukinda dunite-gabbro-anorthosite massif in the east of the Selenga-Stanovoi superterrane,Central Asian Fold Belt

Results of integrated ⁴⁰Ar/³⁹Ar, Rb-Sr, and Sm-Nd geochronological studies of the Lukinda dunite-troctolite-gabbro-anorthosite massif in the northeast of the Selenga-Stanovoi superterrane, Central Asian Fold Belt, are presented. It is shown that this massif is much younger than formerly thought: 249 ± 14 to 251 ± 15 Ma vs. Paleoproterozoic. This date of magmatism corresponds to one of the stages of the formation of the Selenga-Vitim belt, which ranks among the largest Phanerozoic volcanoplutonic belts in Central Asia.     

Geochemical features,depositional settings,and provenances of Lower Paleozoic rocks in the Mamyn terrane,Central Asian Fold Belt

New data on geochemical features of the Lower Paleozoic terrigenous rocks in the Mamyn terrane (eastern Central Asian Fold Belt) and U–Pb geochronological studies of the detrital zircon from these rocks are presented. The obtained results suggest the following conclusions. 1. At present, the Kosmataya sequence includes different age Lower Cambrian terrigenous–carbonate and Lower Ordovician terrigenous rocks or represents Lower Ordovician olistostromes including limestone blocks with the Lower Cambrian fauna. Lower Ordovician terrigenous rocks were formed in an island arc or active continental margin, mainly, owing to the erosion of Cambrian–Early Ordovician plutons and volcanics that are widespread in structures of the Mamyn terrane and weakly reworked by the chemical weathering. 2. The Silurian Mamyn Formation was developed at a passive continental margin. The main sources of clastic material for this formation were the same Cambrian–Early Ordovician igneous rocks as for the Cambrian sequence, with the participation of Early Silurian and Vendian igneous complexes. The obtained data significantly refine concepts about the geological structure of the Mamyn terrane, which is a member of the Argun Superterrane, one of the largest tectonic structures in the eastern Central Asian Fold Belt.     

中亚造山带东段古生代山弯构造

中亚造山带东段位于西伯利亚和华北克拉通之间，经历了多构造体系叠加和多旋回洋陆转换的复杂演化过程，目前大量研究均以构造带为核心来限定区域构造格局，但一直争议较大。本文以构造单元的构造属性及其形成过程为主线，结合区域构造带演化，重新厘定了中国东北地区基本构造格局，建立了中国东北山弯构造演化模型。研究表明，古生代时期中国东北地区的主要构造单元由两个具前寒武纪基底的古老地块——额尔古纳地块和佳木斯地块及其张广才岭陆缘弧与两个古生代增生地体——兴安增生地体和松辽增生地体组成，其间由古亚洲洋分支新林- 喜桂图洋、贺根山- 嫩江洋、龙凤山洋和索伦洋分割。早古生代，西部额尔古纳地块东南部为西太平洋型活动陆缘，发育有嘎仙- 吉峰- 环宇洋内弧和头道桥等洋岛，~500 Ma随着新林- 喜桂图洋的关闭，这些洋内弧和洋岛拼贴增生至额尔古纳地块东南缘。随后贺根山- 嫩江洋的俯冲和后撤形成了一系列沟- 弧- 盆体系，持续的俯冲导致弧陆碰撞和陆缘增生，形成兴安增生地体的主体。同时，东部佳木斯地块西侧发育有龙凤山洋的安第斯型俯冲活动陆缘，形成了张广才岭陆缘弧。伴随着各大洋的俯冲和陆缘增生，额尔古纳地块和佳木斯地块以及它们的陆缘增生带构成了一个早古生代近东西向展布的地块链。南部以锡林浩特- 龙江微地块为核心发生陆缘俯冲，形成松辽增生地体雏形。索伦洋发生双向俯冲，并通过弧陆碰撞产生陆缘增生。晚古生代，伴随着古亚洲洋的北向俯冲和后撤，早期形成的地块链逐渐发生向南弯曲。二叠纪末期—中三叠世古亚洲洋俯冲消减闭合以及西北部蒙古- 鄂霍茨克洋和东部泛大洋的俯冲挤压，导致地块链进一步弯曲，同时，早期的古老地块、增生地体、弧岩浆岩、沉积建造等发生汇聚，最终形成一个以额尔古纳地块和兴安增生地体为西翼，佳木斯地块和张广才岭陆缘弧为东翼，松辽增生地体为核心的大规模山弯构造——中国东北山弯构造。     

Structures of degassing and fluid transport within the modern zones of the lithosphere destruction in the eastern margin of the Central Asian Fold Belt

The modern geodynamic transformations of the Amur geoblock are related to the activation of pull-apart–strike-slip and simple strike-slip movements. These movements resulted in the formation of destruction zones along ancient transregional fault systems (Nenjiang–Selemdzha, Lermontovka–Belogorsk, West Turan, Khingan, Tan Lu, and others) and young NW- and WE-trending fractures with distinctly expressed shearing displacements. These processes are fixed by earthquakes, focal magmatism, pulsed degassing of the Earth’s interior, and fluid discharge. High-permeability structures confined to the juncture of the destruction zones and young fractures served as the deep degassing drainage systems. These structures are traced by decompaction fields and anomalies of He and other gases. The most contrasting Varvarovka anomaly is located in the northeastern flank of the Yerkovtsy brown coal deposit. The paleogene coal-bearing rocks studied in the Yuzhny quarry within this deposit are characterized by high contents of noble, rare metals, and rare-earth elements, which frequently exceed their average abundances by ten orders of magnitude. Based on assay analysis, the Au content in the coals varies from trace amounts to 4.6 ppm.     

The First Evidence of Cambrian Granitoid Magmatism during the Formation History of the Bureya Continental Massif of the Central Asian Fold Belt

Doklady Earth Sciences - The results of U–Pb geochronological studies of Early Paleozoic granitoids from the northern part of the Bureya continental massif are presented. It has been...     

鲁西金刚石原生矿床区域重磁异常特征及深部地质构造背景

鲁西金刚石原生矿床成矿背景复杂,由于缺乏地壳结构、岩浆侵入体位置、断裂规模等信息作为参考依据,深部构造特征及其在成矿过程中的作用尚不明确。本文基于重磁数据和地震剖面资料,采用Parker-Oldenburg界面法、功率谱法和2.5D重磁震联合反演等方法,获得了鲁西地区地壳结构、断裂规模、岩浆侵入体位置等信息,在此基础上,探讨了金刚石原生矿床的深部构造背景。结果表明:鲁西金刚石原生矿床分布于区域布格重力异常低值区、磁异常中-低值区,布格重力异常平均值低于-100×10^-5 m/s²,磁异常变化范围较大,介于-160～60 nT之间;矿床位于莫霍面、居里面等值线密集的梯度带,即稳定区域与活化区域的过渡带,莫霍面深度约为31.2～32.2 km,居里面深度约27.5～30 km;矿床分布区NW向断裂构造切割深度均超过20 km,其中蒙山断裂切割深度为35 km,深达上地幔,新泰-垛庄断裂切割深度为28.5 km,深达居里面,泰山-铜冶店断裂切割深度为20.5 km;金伯利岩于古生代形成后,受中生代伸展构造影响,被NW向断裂逐级抬升、剥蚀,直至出露地...     

Intraplate geodynamics and magmatism in the evolution of the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) was produced as a consequence of the successive closure of the Paleoasian Ocean and the accretion of structures formed within it (island arcs, oceanic islands, and backarc basins) to the Siberian continent. The belt started developing in the latest Late Neoproterozoic, and this process terminated in the latest Permian in response to the collision of the Siberian and North China continents that resulted in closure of the Paleoasian ocean (Metcalfe, 2006; Li et al., 2014; Liu et al., 2009; Xiao et al., 2010; Didenko et al., 2010). Throughout the whole evolutionary history of this Orogenic Belt, a leading role in its evolution was played by convergent processes. Along with these processes, an important contribution to the evolution of the composition and structure of the crust in the belt was made by deep geodynamic processes related to the activity of mantle plumes.Indicator complexes of the activity of mantle plumes are identified, and their major distribution patterns in CAOB structures are determined. A number of epochs and areas of intraplate magmatism are distinguished, including the Neoproterozoic one (Rodinia breakup and the origin of alkaline rock belt in the marginal part of the Siberian craton); Neoproterozoic–Early Cambrian (origin of oceanic islands in the Paleoasian Ocean); Late Cambrian–Early Ordovician (origin of LIP within the region of Early Caledonian structures in CAOB); Middle Paleozoic (origin of LIP in the Altai–Sayan rift system); Late Paleozoic–Early Mesozoic (origin of the Tarim flood-basalt province, Central Asian rift system, and a number of related zonal magmatic areas); Late Mesozoic–Cenozoic (origin of continental volcanic areas in Central Asia).Geochemical and isotopic characteristics are determined for magmatic complexes that are indicator complexes for areas of intraplate magmatism of various age, and their major evolutionary trends are discussed. Available data indicate that mantle plumes practically did not cease to affect crustal growth and transformations in CAOB in relation to the migration of the Siberian continent throughout the whole time span when the belt was formed above a cluster of hotspots, which is compared with the African superplume.