Kinematic reconstruction of the Early Caledonian accretion in the southwest of the Siberian paleocontinent based on paleomagnetic results

The kinematics of the Early Caledonian accretion process in the southwest (in modern coordinate) of the Siberian paleocontinent, and the structure of its active continental margin are debatable subjects. This paper contains a generalization of paleomagnetic data on island-arc terranes of the territories of the Altai–Sayan and Baikal–Vitim folded areas for the Late Vendian/Cambrian–Early Ordovician time interval, obtained mostly with the author’s participation during the last two decades. The large accumulated database finally allows one to find unambiguously interpretable patterns in the distribution of paleomagnetic poles for the analyzed terrane system and to justify numerically the kinematics of the Early Caledonian accretion. In particular, the analysis of paleomagnetic data proves our idea stating that the transformation of the active continental margin in the Cambrian consisted in its breakup and segmentation as well as in the detachment of fragments of the initially whole island arc along a system of sinistral strike-slips during the clockwise rotation of the craton and conform drift of the continental and oceanic lithospheric plates. It also validates the mostly oblique conditions of the subduction and subsequent accretion, which means a subduction-transform mode on the ocean–continent margin. We propose a complemented version of the paleotectonic reconstruction for the Cambrian evolution of the Siberian continent western margin, based on the kinematic scheme constructed from paleomagnetic data.     

Fragments of oceanic islands in accretion–collision areas of Gorny Altai and Salair, southern Siberia, Russia: early stages of continental crustal growth of the Siberian continent in Vendian–Early Cambrian time

The Altai-Salair area in southern Siberia is a Caledonian folded area containing fragments of Vendian–Early Cambrian island arcs. In the Vendian–Early Cambrian, an extended system of island arcs existed near the Paleo-Asian Ocean/Siberian continent boundary and was located in an open ocean realm. In the present-day structural pattern of southern Siberia, the fragments of Vendian–Early Cambrian ophiolites, island arcs and paleo-oceanic islands occur in the accretion–collision zones. We recognized that the accretion–collision zones were mainly composed of the rock units, which were formed within an island-arc system or were incorporated in it during the subduction of the Paleo-Asian Ocean under the island arc or the Siberian continent. This system consists of accretionary wedge, fore-arc basin, primitive island arc and normal island arc. The accretionary wedges contain the oceanic island fragments which consist of OIB basalts and siliceous—carbonate cover including top and slope facies sediments. Oceanic islands submerged into the subduction zone and, later were incorporated into an accretionary wedge. Collision of oceanic islands and island arcs in subduction zones resulted in reverse currents in the accretionary wedge and exhumation of high-pressure rocks. Our studies of the Gorny Altai and Salair accretionary wedges showed that the remnants of oceanic crust are mainly oceanic islands and ophiolites. Therefore, it is important to recognize paleo-islands in folded areas. The study of paleo- islands is important for understanding the evolution of accretionary wedges and exhumation of subducted high-pressure rocks.     

中亚大陆古生代构造形成及演化

西伯利亚、塔里木及哈萨克斯坦诸古板块中的微陆和地体构造了中亚十分复杂的拼贴构造图案。古生代时，南天巴准洋－阿萨伊锡弧沟弧系和额尔齐斯洋－成田弧沟弧系构成了哈萨克斯坦板块的原型，塔里木板块陆壳块体在泥盆纪相对于阿萨伊锡岛弧的左行低角度斜俯冲和碰撞，造成此弧的解体、走滑堆叠和山弯构造。与此同时，成田岛弧南北两侧分别受到南天巴准洋和额尔齐斯洋的俯冲。在晚古生代晚期这两个沟弧系演变为哈萨克斯坦板块的基本构     

Cambrian arc-continent collision in the Paleozoides of Kazakhstan

A model of the Cambrian evolution of the Paleozoides in Kazakhstan is presented on the basis of consideration of Cambrian rock complexes. The Middle Cambrian collision of an island arc and a passive continental margin was the main event of this evolution. Three stages of the Paleozoides evolution are recognized in the Cambrian. The first, precollision stage embraces a time span from the Early Cambrian to the first half of the Amgian Age of the Middle Cambrian in which the following elements of the continent-ocean transitional zone may be reconstructed: passive continental margin-backarc basin with oceanic crust-island arc-oceanic basin. At the second, collision stage (the second half of the Amgian Age), the backarc basin was closed and the continental margin and island arc collided, forming a suture zone. At the third, postcollision stage (the Mayan Age of the Middle Cambrian-Early Ordovician), the structure of the convergent margin was complicated. The volcanic belt started to develop on the accreted continental margin. A system of ensimatic island arcs originated at the same time and migrated toward the outer basin. The active rifting was typical of the inner part of the continental margin.     

Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area

Packages of Late Paleozoic tectonic nappes and associated major NE-trending strike-slip faults are widely developed in the Altai–Sayan folded area. Fragments of early deformational phases are preserved within the Late Paleozoic allochthons and autochthons. Caledonian fold-nappe and strike-slip structures, as well as accompanying metamorphism and granitization in the region, are typical of the EW-trending suture-shear zone separating the composite Kazakhstan–Baikal continent and Siberia. In the Gorny Altai region, the Late Paleozoic nappes envelop the autochthon, which contains a fragment of the Vendian–Cambrian Kuznetsk–Altai island arc with accretionary wedges of the Biya–Katun’ and Kurai zones. The fold-nappe deformations within the latter zones occurred during the Late Cambrian (Salairian) and can thus be considered Salairian orogenic phases. The Salairian fold-nappe structure is stratigraphically overlain by a thick (up to 15 km) well-stratified rock unit of the Anyui–Chuya zone, which is composed of Middle Cambrian–Early Ordovician fore-arc basin rocks unconformably overlain by Ordovician–Early Devonian carbonate-terrigenous passive-margin sequences. These rocks are crosscut by intrusions and overlain by a volcanosedimentary unit of the Devonian active margin. The top of the section is marked by Famennian–Visean molasse deposits onlapping onto Devonian rocks. The molasse deposits accumulated above a major unconformity reflects a major Late Paleozoic phase of folding, which is most pronounced in deformations at the edges of the autochthon, nearby the Kaim, Charysh–Terekta, and Teletskoe–Kurai fault nappe zones. Upper Carboniferous coal-bearing molasse deposits are preserved as tectonic wedges within the Charysh–Terekta and Teletskoe–Kurai fault nappe zones.Detrital zircon ages from Middle Cambrian–Early Ordovician rocks of the Anyui–Chuya fore-arc zone indicate that they were primarily derived from Upper Neoproterozoic–Cambrian igneous rocks of the Kuznetsk–Altai island arc or, to a lesser extent, from an Ordovician–Early Devonian passive margin. A minor age population is represented by Paleoproterozoic grains, which was probably sourced from the Siberian craton. Zircons from the Late Carboniferous molasse deposits have much wider age spectra, ranging from Middle Devonian–Early Carboniferous to Late Ordovician–Early Silurian, Cambrian–Early Ordovician, Mesoproterozoic, Early–Middle Proterozoic, and early Paleoproterozoic. These ages are consistent with the ages of igneous and metamorphic rocks of the composite Kazakhstan–Baikal continent, which includes the Tuva-Mongolian island arc with accreted Gondwanan blocks, and a Caledonian suture-shear zone in the north. Our results suggest that the Altai–Sayan region is represented by a complex aggregate of units of different geodynamic affinity. On the one hand, these are continental margin rocks of western Siberia, containing only remnants of oceanic crust embedded in accretionary structures. On the other hand, they are represented by the Kazakhstan–Baikal continent composed of fragments of Gondwanan continental blocks. In the Early–Middle Paleozoic, they were separated by the Ob’–Zaisan oceanic basin, whose fragments are preserved in the Caledonian suture-shear zone. The movements during the Late Paleozoic occurred along older, reactivated structures and produced the large intracontinental Central Asian orogen, which is interpreted to be a far-field effect of the colliding East European, Siberian, and Kazakhstan–Baikal continents.     

关于古亚洲洋构造演化研究的几点思考

古亚洲洋不是西伯利亚陆台和华北地台间的一个简单洋盆,而是在不同时间、不同地区打开和封闭的多个大小不一的洋盆复杂活动(包括远距离运移)的综合体.其北部洋盆起始于新元古代末-寒武纪初(573~522Ma)冈瓦纳古陆裂解形成的寒武纪洋盆.寒武纪末-奥陶纪初(510~480Ma),冈瓦纳古陆裂解的碎块、寒武纪洋壳碎块和陆缘过渡壳碎块相互碰撞、联合形成原中亚-蒙古古陆.奥陶纪时,原中亚-蒙古古陆南边形成活动陆缘,志留纪形成稳定大陆.泥盆纪初原中亚-蒙古古陆裂解,裂解的碎块在新形成的泥盆纪洋内沿左旋断裂向北运动,于晚泥盆世末到达西伯利亚陆台南缘,重新联合形成现在的中亚-蒙古古陆.晚古生代时,在现在的中亚-蒙古古陆内发生晚石炭世(318~316Ma)和早二叠世(295~285Ma)裂谷岩浆活动,形成双峰式火山岩和碱性花岗岩类.蒙古-鄂霍次克带是西伯利亚古陆和中亚-蒙古古陆之间的泥盆纪洋盆,向东与古太平洋连通,洋盆发展到中晚侏罗世,与古太平洋同时结束,其洋壳移动到西伯利亚陆台边缘受阻而向陆台下俯冲,在陆台南缘形成广泛的陆缘岩浆岩带,从中泥盆世到晚侏罗世都非常活跃.古亚洲洋的南部洋盆始于晚寒武世.此时,华北古陆从冈瓦纳古陆裂解出来,在其北缘形成晚寒武世-早奥陶世的被动陆缘和中奥陶世-早志留世的沟弧盆系.志留纪腕足类生物群的分布表明,华北地台北缘洋盆与塔里木地台北缘、以及川西、云南、东澳大利亚有联系,而与上述的古亚洲洋北部洋盆没有关连,两洋盆之间有松嫩-图兰地块间隔.晚志留世-早泥盆世,华北地台北部发生弧-陆碰撞运动,泥盆纪时,在松嫩地块南缘形成陆缘火山岩带,晚二叠世-早三叠世华北地台与松嫩地块碰撞,至此古亚洲洋盆封闭.古亚洲洋的南、北洋盆最后的褶皱构造,以及与塔里木地台之间发生的直接关系,很可能是后期的构造运动所造成的.     

Mesozoic syncollision siliciclastic sediments of the Bols’shoi Lyakhov Island (New Siberian Islands)

Graywackes and shales of the Bols’shoi Lyakhov Island originally attributed to the Mesozoic were subsequently considered based on microfossils as the Late Proterozoic in age. At present, these sediments in the greater part of the island are dated back to the Permian based on palynological assemblages. In the examined area of the island, this siliciclastic complex is intensely deformed and tectonically juxtaposed with blocks of oceanic and island-arc rocks exhumed along the South Anyui suture. The complex is largely composed of turbidites with members displaying hummocky cross-stratification. The studied mineral and geochemical characteristics of the rocks defined three provenances of clastic material: volcanic island arc, sedimentary cover and/or basement of the ancient platform, and exotic blocks of oceanic and island-arc rocks such as serpentinites and amphibolites. All the rock associations represent elements of an orogenic structure that originated by collision of the New Siberian continental block with the Anyui-Svyatoi Nos island arc. Flyschoid sediments accumulated in a foredeep in front of the latter structure in the course of collision. The Late Jurassic volcanics belonging to the Anyui-Svyatoi Nos island arc determine the lower age limit of syncollision siliciclastic rocks. Presence of Late Jurassic zircons in sandstones of the flyschoid sequence in Bols’shoi Lyakhov Island is confirmed by the fission-track dating. The upper age limit is determined by the Aptian-Albian postcollision granites and diorites intruding the siliciclastic complex. Consequently, the flyschoid sequence is within stratigraphic range from the terminal Late Jurassic to Neocomian. It appears that Permian age of sediments suggested earlier is based on redeposited organic remains. The same Late Jurassic-Neocomian age and lithology are characteristic of fossiliferous siliciclastic sequences of the Stolbovoi and Malyi Lyakhov islands, the New Siberian Archipelago, and of graywackes in the South Anyui area in Chukchi Peninsula. All these sediments accumulated in a spacious foredeep that formed in the course the late Cimmerian orogeny along the southern margin of the Arctic continental block.     

Dzhida island-arc system in the Paleoasian Ocean: structure and main stages of Vendian-Paleozoic geodynamic evolution

We propose a model of the geodynamic evolution of the Dzhida island-arc system of the Paleoasian Ocean margin which records transformation of an oceanic basin into an accretion-collision orogenic belt. The system includes several Vendian-Paleozoic complexes that represent a mature oceanic island arc with an accretionary prism, oceanic islands, marginal and remnant seas, and Early Ordovician collisional granitoids. We have revealed a number of subunits (sedimentary sequences and igneous complexes) in the complexes and reconstructed their geodynamic settings. The tectonic evolution of the Dzhida island-arc system comprises five stages: (1) ocean opening (Late Riphean); (2) subduction and initiation of an island arc (Vendian-Early Cambrian); (3) subduction and development of a mature island arc (Middle-Late Cambrian); (4) accretion and formation of local collision zones and remnant basins (Early Ordovician-Devonian); and (5) postcollisional strike-slip faulting (Carboniferous-Permian).     

Arc–continent collision and orogenesis in western Tasmanides: Insights from reactivated basement structures and formation of an ocean–continent transform boundary off western Tasmania

Crustal architecture in formerly contiguous basement terranes in SE Australia, Tasmania and northern Victoria Land is a legacy of late Neoproterozoic–Cambrian subduction-related processes, culminating in formation of the Delamerian–Ross orogen. Structures of Delamerian–Ross age were subsequently reactivated during late Mesozoic–Cenozoic Gondwana breakup, strongly influencing the geometry of continental rifting and providing clues about the origins and configuration of the pre-existing basement structures. An ocean–continent transform boundary developed off western Tasmania follows the trace of an older Paleozoic strike-slip structure (Avoca–Sorell fault system) optimally oriented for reactivation during the final separation of Australia from Antarctica. This boundary cuts across rocks preserving an earlier record of arc–continent collision during the course of which continental crust was subducted to mantle depths and Cambrian mafic–ultramafic island arc rocks were thrust westwards over late Neoproterozoic–Cambrian passive margin sequences. Collision was accompanied by development of a foreland basin into which 520–600 Ma arc-derived detrital zircons were shed. Following a reversal in subduction polarity, and change to transcurrent motion along the Gondwana margin, Tasmania migrated northward along the proto-Avoca fault system before entering a subduction zone located along the Heathcote–Governor fault system, precipitating a second collision, south-vergent thrusting, and tectonic reworking of the already accreted Cambrian arc–forearc assemblages and underlying passive margin sequences.     

Geological Evolution of Northeastern Anatolia

The paleogeography of the Eastern Pontides was defined by the Paleotethys ocean to the north and a continental assemblage to the south, prior to Carboniferous time. The S-dipping subduction of Paleotethys beneath Gondwana caused the development of arc magmatism, mostly active in the Early Carboniferous. Cessation of magmatism during Late Carboniferous-Early Permian time was accompanied by the deposition of platform carbonates, which were rifted to open a back-arc oceanic basin (Karakaya ocean) during the Triassic.

Accompanying closure of this Triassic basin, the Ladinian-Late Triassic products of Neotethys, opening in the south, transgressively overlay the basement in the Keban continent to the south. However, transgression reached the northern region (Pontide continent) during Liassic time, because of a topographic high created by southward subduction of the Paleotethys ocean as well as closure of the Karakaya ocean.

During the late Cenomanian/Turonian to Eocene, an island arc evolved as a result of N-dipping subduction of Neotethys. The ophiolite-melange association was obducted onto the Pontide continent as a retrocharriage process in the Turonian-Maastrichtian, Paleocene, and the end of the early Eocene, and onto the Keban continent in Campanian-Maastrichtian and pre-late Lutetian time.

A continental-lacustrine environment developed, and partial melting of the thickened crust initiated the development of volcanic units in the Miocene. The region was affected by right-lateral strike-slip faulting (the North Anatolian fault) and a NE-SW-trending left-lateral strike-slip fault system (the Northeast Anatolian fault).     

Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.     

中国东南大陆边缘若干问题的认识

中国东南大陆边缘自元古宙以来就以沟-弧-盆形式向洋增生扩张。浙闽变质带属于震旦纪至早古生代岛弧。华南地槽区是在这一时期由扩张作用形成的弧后盆地。这一沟弧盆系统在加里东期褶皱变质,与大陆拼贴。在晚古生代,沿海地区有新的扩张带形成。周期性的扩张和挤压是中国东南大陆边缘地壳演化的特征。     

中朝陆台北侧褶皱带构造发展的几个问题

中朝与西伯利亚陆台之间的乌拉尔—蒙古—鄂霍茨克褶皱系是古亚洲洋演化的结果。其发展分为两个大的阶段:早期阶段从中元古代起在北部形成蒙古—鄂霍茨克洋,到寒武纪初封闭,形成兴凯褶皱带;晚期阶段从震旦—寒武纪初起在南部形成乌拉尔—蒙古洋,到泥盆纪大洋封闭,形成早及中古生代褶皱带。这就是中朝与西伯利亚陆台边缘褶皱带发育不对称的原因。 乌拉尔—蒙古洋最后封闭的缝合带在内蒙古中部形成中古生代褶皱带。它包括贺根山蛇绿岩带,二道井—查干诺尔混杂体带和它们之间的锡林浩特花岗岩—变质岩带。后者是造山碰撞的中心,上泥盆统法门阶的磨拉石堆积主要沿此带分布。 石炭—二叠纪时,本区广泛兴起裂谷活动。这些裂谷发育在不同的基底之上,多数发生于不同时期构造带的界线上。它们在新增生的年青陆壳上形成,其特征不同于红海或东非型裂谷;其岩浆活动和变形、变质作用使年青陆壳增厚并更加稳固。     

Age and sources of the Paleoproterozoic premetamorphic granitoids of the Goloustnaya block of the Siberian craton: Geodynamic applications

This paper reports the results of geological, geochronological, and isotope geochemical investigations of two premetamorphic granite massifs of the Goloustnaya block of the Baikal salient of the basement of the Siberian craton and granite gneisses from the migmatite–gneiss sequence of this block. The U–Pb zircon age of the granites of the Khomut massif is 2153 ± 11 Ma. The age of the Elovka massif was previously determined by us as 2018 ± 28 Ma. The Khomut and Elovka granites underwent structural and metamorphic transformations accompanied by migmatization. An age of 1.98–1.97 Ga was obtained for the structural and metamorphic processes in the Goloustnaya block from the analysis of margins of zircon grains from the Khomut granites and zircon from the granite gneisses. The biotite granites of the Khomut massif show transitional I–S-type geochemical characteristics, which allowed us to suggest that they were derived by melting of a crustal source of intermediate–acid composition. The Khomut granites show positive ε_Nd(T) values from +2.0 to +2.2 and a Nd model age of 2.4 Ga, which may indicate their formation owing to the reworking of the Paleoproterozoic juvenile continental crust. The combined isotope geochemical data are consistent with collision of island arcs as a possible environment for the formation of the Khomut granites. The formation of these granites was not related to the development of the structure of the Siberian craton, similar to a few other anorogenic magmatic complexes of the margin of the Chara–Olekma terrane of the Aldan shield with ages of ~2.2–2.1 Ga, including the granites of the Katugin complex. The biotite–amphibole granites of the Elovka massif with an age of ~2.02 Ga are geochemically similar to I-type granites. The geochemical characteristics of these granites, including elevated Sr and Ba and low Nb and Ta contents, were inherited from a subduction-related source. Negative ε_Nd(T) values from–0.9 to–1.8 and rather high contents of K₂O and Th allow us to suppose a metamagmatic crustal source for the granites of the Elovka massif. The combined isotope geochemical characteristics of the Elovka granites suggest that a mature island arc or an active continental margin is the most probable environment of their formation. The estimates of the age of structural and metamorphic processes affecting the Goloustnaya block (1.98–1.97 Ga) coinciding with the time of similar transformations in the central part of the Aldan shield and eastern Anabar shield (1.99–1.96 Ga) indicate wide occurrence of collisional events of similar age in the Siberian craton and allow us to consider this age interval as an early large-scale stage of the formaiton of the structure of the Siberian craton.     

http://www.sciencedirect.com/science/article/pii/S1674987113001606

The paper reviews previous and recently obtained geological, stratigraphic and geochronological data on the Russian-Kazakh Altai orogen, which is located in the western Central Asian Orogenic Belt （CAOB）, between the Kazakhstan and Siberian continental blocks. The Russian-Kazakh Altai is a typical Pacific-type orogen, which represents a collage of oceanic, accretionary, fore-arc, island-arc and continental margin terranes of different ages separated by strike-slip faults and thrusts. Evidence for this comes from key indicative rock associations, such as boninite- and turbidite （graywacke）-bearing volcanogenic-sedimentary units, accreted pelagic chert, oceanic islands and plateaus, MORB-OIB-protolith blueschists. The three major tectonic domains of the Russian-Kazakh Altai are： （1） Altai-Mongolian terrane （AMT）; （2） subduction-accretionary （Rudny Altai, Gorny Altai） and collisional （Kalba-Narym） terranes; （3） Kurai, Charysh-Terekta, North-East, Irtysh and Char suture-shear zones （SSZ）. The evolution of this orogen proceeded in five major stages： （i） late Neoproterozoic-early Paleozoic subduction-accretion in the Paleo-Asian Ocean; （ii） Ordovician-Silurian passive margin; （iii） Devonian-Carboniferous active margin and collision of AMT with the Siberian conti- nent; （iv） late Paleozoic closure of the PAO and coeval collisional magmatism; （v） Mesozoic post-collisional deformation and anarogenic magmatism, which created the modern structural collage of the Russian- Kazakh Altai orogen. The major still unsolved problem of Altai geology is origin of the Altai-Mongolian terrane （continental versus active margin）, age of Altai basement, proportion of juvenile and recycled crust and origin of the middle Paleozoic units of the Gorny Altai and Rudny Altai terranes.     

内蒙古海勒斯台俯冲增生混杂岩地质特征及发现的意义

采用"造山带混杂岩区"新理论,首次在贺根山-黑河缝合带中段发现海勒斯台俯冲增生混杂岩,建立由"基质"+"岩块"组成的俯冲增生杂岩体系,其构造样式为整体左行逆冲剪切.基质主要有糜棱岩、千糜岩、超糜棱岩及少量的沉凝灰岩、粉砂岩、细砂岩,构造环境为弧前盆地,时代主要为中寒武世;岩块有洋岛海山岩块、弧后洋盆洋壳残片、火山弧岩块、裂离陆块,岩块的年龄区间主要在中寒武世-中奥陶世,裂离陆块时代为新太古代.结合俯冲增生杂岩基质年龄、岩块的年龄、侵入混杂岩的TTG年龄（449 Ma）和变形程度、接触关系等,将海勒斯台俯冲增生杂岩的形成时代厘定为中晚奥陶世.认为研究区俯冲作用在早寒武世就已经开始,在大陆边缘形成火山岛弧;奥陶纪初期弧后发育弧后盆地,至中奥陶世弧后盆地出现洋壳;此时中寒武世的基质经俯冲下切后在中奥陶世时期折返上升;晚奥陶世时期由于区域的持续汇聚挤压,该弧后洋盆很快夭折;弧陆开始碰撞,导致双向俯冲.在弧陆碰撞过程中,晚期形成的弧后盆地洋壳等新岩块混入早期形成的基质中.海勒斯台俯冲增生混杂岩带的发现填补了贺根山-黑河缝合岩带中段的空白,对区域构造格架厘定具有非常重要的意义,为研究古亚洲构造域演化提供了新的证据.      

Geodynamics of the northwestern sector of the pacific mobile belt in the Late Cretaceous-Early Paleogene

In the Late Cretaceous starting from the early Coniacian, three parallel suprasubduction structural units have developed contemporaneously in the northwestern Paleopacific framework: (1) the Okhotsk-Chukchi arc at the Asian continental margin, (2) the West Kamchatka and Essoveem ensialic arcs at the northwestern margins of the Kamchatka and Central Koryak continental blocks, and (3) the Achaivayam-Valagin ensimatic arc that extended to the southwest as the Lesser Kuril ensialic arc at the southern margin of the Sea of Okhotsk continental block. In this setting, the geodynamics of the Paleopacific plates exerted an effect only on the evolution of the outer (relative to the continent) ensimatic island arc, whereas the vast inner region between this arc and the continent evolved independently. As is seen from the character of the gravity field and seismic refractor velocity, the Kamchatka and Sea of Okhotsk continental blocks differ in the structure of the consolidated crust. These blocks collided with each other and the Asian continent in the middle Campanian (77 Ma ago). The extensive pre-Paleogene land that existed on the place of the present-day Sea of Okhotsk probably supplied the terrigenous material deposited since the late Campanian on the oceanic crust of the backarc basin to the south of the rise of inner continental blocks as the Khozgon, Lesnaya, and Ukelayat flysch complexes. The accretion of the Olyutor (Achaivayam) and Valagin segments of the ensimatic arc had different consequences due to the difference in thickness of the Earth’s crust. The Valagin segment was formed on an older basement and had a much greater thickness of the crust than the Olyutor segment. As follows from computations and the results of physical modeling, the island arcs having crust more than 25 km in thickness collide with the continental margin and are thrust over the latter. In the case under consideration, the thrusting of the Valagin segment led to metamorphism of the underlying rocks. The crust of the Olyutor segment was much thinner. The contact of this segment with the continental margin resulted only in surficial accretion, which did not bring about metamorphism, and the underlying lithospheric plate continued to plunge into the subduction zone.     

Cambrian to Lower Ordovician complexes of the Kokchetav Massif and its fringing (Northern Kazakhstan): Structure,age, and tectonic settings

A comprehensive study of the Lower Palaeozoic complexes of the Kokchetav Massif and its fringing has been carried out. It has allowed for the first time to discover and investigate in detail the stratified and intrusive complexes of the Cambrian–Early Ordovician. Fossil findings and isotope geochronology permitted the determination of their ages. The tectonic position and internal structures of those complexes have also been defined and their chemical features have been analyzed as well. The obtained data allowed us to put forward a model of the geodynamic evolution of Northern Kazakhstan in the Late Ediacaran–Earliest Ordovician. The accumulation of the oldest Ediacaran to Earliest Cambrian siliciclastics and carbonates confined to the Kokchetav Massif and its fringing occurred in a shallow shelf environment prior to its collision with the Neoproterozoic Daut island arc: complexes of the latter have been found in the northeast of the studied area. The Early Cambrian subduction of the Kokchetav Massif under the Daut island arc, their following collision and exhumation of HP complexes led to the formation of rugged ground topography, promoting deposition of siliceous–clastic and coarse clastic units during the Middle to early Late Cambrian. Those sediments were mainly sourced from eroded metamorphic complexes of the Kokchetav Massif basement. At the end of the Late Cambrian to the Early Ordovician within the boundaries of the massif with the Precambrian crust, volcanogenic and volcano-sedimentary units along with gabbros and granites with intraplate affinities were formed. Simultaneously in the surrounding zones, which represent relics of basins with oceanic crust, N-MORB- and E-MORB-type ophiolites were developed. These complexes originated under extensional settings occurred in the majority of the Caledonides of Kazakhstan and Northern Tian Shan. In the Early Floian Stage (Early Ordovician) older heterogeneous complexes were overlain by relatively monotonous siliceous–clastic units, that were being deposited until the Middle Darrivilian Stage (Middle Ordovician).     

西北太平洋岛弧系列成因的探讨

西北太平洋岛弧系列中的各岛弧(除马里亚纳岛弧为洋壳型弧外)均由陆壳型弧和洋壳型弧组成,并且左端与大陆相连,右端被后形成的岛弧所截。整个岛弧系列,从中生代末期开始发育至今,由北向南依次发展,规律明显。     

Geology and tectonics of Japanese islands: A review – The key to understanding the geology of Asia

The age of the major geological units in Japan ranges from Cambrian to Quaternary. Precambrian basement is, however, expected, as the provenance of by detrital clasts of conglomerate, detrital zircons of metamorphic and sedimentary rocks, and as metamorphic rocks intruded by 500 Ma granites. Although rocks of Paleozoic age are not widely distributed, rocks and formations of late Mesozoic to Cenozoic can be found easily throughout Japan. Rocks of Jurassic age occur mainly in the Jurassic accretionary complexes, which comprise the backbone of the Japanese archipelago. The western part of Japan is composed mainly of Cretaceous to Paleogene felsic volcanic and plutonic rocks and accretionary complexes. The eastern part of the country is covered extensively by Neogene sedimentary and volcanic rocks. During the Quaternary, volcanoes erupted in various parts of Japan, and alluvial plains were formed along the coastlines of the Japanese Islands. These geological units are divided by age and origin: i.e. Paleozoic continental margin; Paleozoic island arc; Paleozoic accretionary complexes; Mesozoic to Paleogene accretionary complexes and Cenozoic island arcs. These are further subdivided into the following tectonic units, e.g. Hida; Oki; Unazuki; Hida Gaien; Higo; Hitachi; Kurosegawa; South Kitakami; Nagato-Renge; Nedamo; Akiyoshi; Ultra-Tamba; Suo; Maizuru; Mino-Tamba; Chichibu; Chizu; Ryoke; Sanbagawa and Shimanto belts.The geological history of Japan commenced with the breakup of the Rodinia super continent, at about 750 Ma. At about 500 Ma, the Paleo-Pacific oceanic plate began to be subducted beneath the continental margin of the South China Block. Since then, Proto-Japan has been located on the convergent margin of East Asia for about 500 Ma. In this tectonic setting, the most significant tectonic events recorded in the geology of Japan are subduction–accretion, paired metamorphism, arc volcanism, back-arc spreading and arc–arc collision. The major accretionary complexes in the Japanese Islands are of Permian, Jurassic and Cretaceous–Paleogene age. These accretionary complexes became altered locally to low-temperature and high-pressure metamorphic, or high-temperature and low-pressure metamorphic rocks. Medium-pressure metamorphic rocks are limited to the Unazuki and Higo belts. Major plutonism occurred in Paleozoic, Mesozoic and Cenozoic time. Early Paleozoic Cambrian igneous activity is recorded as granites in the South Kitakami Belt. Late Paleozoic igneous activity is recognized in the Hida Belt. During Cretaceous to Paleogene time, extensive igneous activity occurred in Japan. The youngest granite in Japan is the Takidani Granite intruded at about 1–2 Ma. During Cenozoic time, the most important geologic events are back-arc opening and arc–arc collision. The major back-arc basins are the Sea of Japan and the Shikoku and Chishima basins. Arc–arc collision occurred between the Honshu and Izu-Bonin arcs, and the Honshu and Chishima arcs.