The Central Asian Orogenic Belt (c. 1000-250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic- Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian-Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with formation of the Solonker suture. We evaluate contrasting tectonic models for the evolution of the orogenic belt. Current information provides little support for the main tenets of the one- or three-arc Kipchak model; current data suggest that an archipelago-type (Indonesian) model is more viable. Some diagnostic features of ridge-trench interaction are present in the Central Asian orogen (e.g. granites, adakites, boninites, near-trench magmatism, Alaskan-type mafic-ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, rhyolitic ash-fall tuffs). They offer a promising perspective for future investigations.
We argue that the production of mantle-derived or juvenile continental crust during the accretionary history of the Central Asian Orogenic Belt (CAOB) has been grossly overestimated. This is because previous assessments only considered the Palaeozoic evolution of the belt, whereas its accretionary history already began in the latest Mesoproterozoic. Furthermore, much of the juvenile growth in Central Asia occurred in late Permian and Mesozoic times, after completion of CAOB evolution, and perhaps related to major plume activity. We demonstrate from zircon ages and Nd-Hf isotopic systematics from selected terranes within the CAOB that many Neoproterozoic to Palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous Precambrian crust or through mixing of old continental crust with juvenile or short-lived material, most likely in continental arc settings. At the same time, juvenile growth in the CAOB occurred during the latest Neoproterozoic to Palaeozoic in oceanic island arc settings and during accretion of oceanic, island arc, and Precambrian terranes. However, taking together, our data do not support unusually high crust-production rates during evolution of the CAOB. Significant variations in zircon epsilon(Hf) values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources. We reiterate that the chemical characteristics of crustally-derived granitoids are inherited from their source(s) and cannot be used to reconstruct tectonic settings, and thus many tectonic models solely based on chemical data may need re-evaluation. Crustal evolution in the CAOB involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history, and we see many similarities with the evolution of the SW Pacific and the Tasmanides of eastern Australia. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
The architecture of accretionary orogens is a key to understand continental growth. Here we present an overview of the orogenic components and their amalgamation in the western Central Asian Orogenic Belt (CAOB). The CAOB records the convergence and interactions among various types of orogenic components including the Japan-type, Mariana-type, and Alaska-Aleutian-type arc systems, as well as the active marginal sequences of the Siberia Craton, which incorporated wide accretionary complexes and accreted arcs and terranes. During construction of the CAOB, the Kazakhstan arc chain was characterized by multiple subduction, whereas the northern fringe of the Tarim Craton remained mostly as a passive margin. The multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late Paleozoic and even in the early Triassic, involving parallel amalgamation, circum-microcontinent amalgamation and oroclinal bending. The preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units. The orogenesis in the CAOB was long-lived, lasting for more than 800 m.y., involving multiple-subduction and long, continuous accretion, and featuring the complexity of accretionary orogenesis and continent growth. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
The Central Asian Orogenic Belt (CAOB) is the largest accretionary orogen in theworld, which is responsible for considerable Phanerozoic juvenile crustal growth. The NE China and its adjacent areas compose the eastern segment of the CAOB, which is a key area for providing important evidence of the CAOB evolution and understanding the NE Asian tectonics. The eastern segment of the CAOB is composed tectonically of four micro-blocks and four sutures, i.e. Erguna block (EB), Xing'an block (XB), Songliao-Xilinhot block (SXB), Jiamusi block (JB), Xinlin-Xiguitu suture (XXS), Heihe-Hegenshan suture (HHS), Mudanjiang-Yilan suture (MYS) and Solonker-Xar Moron-Changchun-Yanji suture (SXCYS). The EB and XB were amalgamated by westward subduction, oceanic island accretions and final collision in ca. 500 Ma. The XB and SXB were amalgamated by subduction-related Early Paleozoic marginal arc, Late Paleozoic marginal arc and final collision in the late Early Carboniferous to early Late Carboniferous. The JB probably had been attached to the SXB in the Early Paleozoic, but broken apart from the SXB in the Triassic and collided back in the Jurassic. The closure of Paleo-Asian Ocean had experienced a long continue/episodic subduction-accretion processes onmargins of the NCC to the south and the SXB to the north from the Early to Late Paleozoic. The final closure happened along the SXCYS, from west Solonker, Sonid Youqi, Kedanshan (Keshenketengqi), Xar Moron River through Songliao Basin via Kailu, Tongliao, Horqin Zuoyizhongqi, Changchun, to the east Panshi, Huadian, Dunhua, Yanji, with a scissors style closure in time from the Late Permian-Early Triassic in the west to the Late Permian-Middle Triassic in the east. The amalgamated blocks should compose a unitedmicro-continent, named as Jiamusi-Mongolia Block (JMB) after Early Carboniferous, which bounded by Mongo-Okhotsk suture to the northwest, Solonker-Xar Moron-Changchun suture to the south and the eastern margin of JB to the east. (C) 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
The Central Asian Orogenic Belt (CAOB) evolved through complex closure of the Paleo-Asian Ocean from the Neoproterozoic to the late Phanerozoic. This caused the Chinese cratons to collide with Eurasia and led to the formation of the world's largest Phanerozoic orogenic belt. Ocean closure commenced in the west and was completed in the east near Changchun. Closure of the Paleo-Asian Ocean in NE China was along the Solonker-Xar Moron-Changchun-Yanji suture and this was likely completed in the Late Permian, although associated activity continued into the Triassic. There was an overlap in the latest Permian-Early Triassic between terminal activity associated with Paleo-Asian Ocean closure and the onset of tectonism associated with subduction of the Paleo-Pacific plate. This switch in geodynamic setting occurred at similar to 260-250 Ma, and is reflected by a relaxing of north-south directed compression and the onset of east-west directed processes related to Paleo-Pacific subduction. By the Early Jurassic, events associated with the westward advance of the Paleo-Pacific plate dominated, leading to extensive development of I-type granites as far inland as the Great Xing'an Range. From similar to 140 Ma, the Paleo-Pacific plate retreated eastward, resulting in an extensional setting in the Early Cretaceous, the effects of which were enhanced by regional thinning of the lithosphere, commonly attributed to delamination. Throughout this period, the eastern Asian margin was tectonically complex. The north-south oriented Jiamusi-Khanka(-Bureya) block was rifted away from the eastern margin of the CAOB in the Late Triassic, but was then re-united in the Jurassic by westward-advancing subduction that affected both the western and eastern margins of the block. Accretionary complexes continued to evolve in the Cretaceous along the whole eastern margin of Asia, with final accretion of the Nadanhada Terrane (part of the Sikhote-Alin accretionary terrane) with the CAOB at similar to 130 Ma, followed by the emplacement of S-type granites. (C) 2015 Elsevier B.V. All rights reserved.
The basement rocks in parts of NE China constitute a khondalitic sequence of sillimanite- and garnet-bearing gneisses, hornblende-plagioclase gneiss and various felsic paragneisses. Zircon U-Pb dating of garnet-sillimanite gneiss samples from the Erguna, Xing'an, Jiamusi and Khanka blocks indicates that high-grade metamorphism occurred at similar to 500 Ma. Evidence from detrital zircons in Paleozoic sediments from the Songliao Block also indicates the former presence of a similar to 500 Ma component. This uniformity of U-Pb ages across all crustal blocks in NE China establishes a >1300 km long Late Pan-African Khondalite belt which we have named the 'NE China Khondalite Belt'. This indicates the blocks of NE China were amalgamated prior to similar to 500 Ma, contrary to current belief. One scenario is that this amalgamated terrane had a tectonic affinity to the Siberia Craton, once forming part of the Late Pan-African (similar to 500 Ma) Sayang-Baikal orogenic belt extensively developed around the southern margin of the Siberia Craton. This belt was the result of collision between currently unidentified terranes with the Southeastern Angara-Anabar Province at about 500 Ma, where the rocks were deformed and metamorphosed to granulite fades. It appears likely that at sometime after similar to 450 Ma, the combined NE China blocks rifted away from Siberia and moved southward to form what is now NE China. The combined block collided with the North China Craton along the Solonker-Xar Moron-Changchun suture zone at similar to 230 Ma rather than in the end-Permian as previously thought. Local rifting at the eastern extremity of the developing Central Asian Orogenic Belt (CAOB) resulted in the splitting away of the Jiamusi/Khanka(/Bureya) blocks. However, this was only transient and sometime between 210 and 180 Ma, these were re-united with the CAOB by the onset of Pacific plate subduction, which has dominated the tectonic evolution of the region since that time. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
Based mainly on field geological observation and geochronologic data, six tectonic units have been recognized in western Inner Mongolia (China), including, from south to north: North China Craton (NCC), Southern Orogenic Belt (SOB), Hunshandake Block (HB), Northern Orogenic Belt (NOB), South Mongolia microcontinent (SMM), and Southern margin of Ergun Block (SME), suggesting that the tectonic framework of the CAOB in western Inner Mongolia is characterized by an accretion of different blocks and orogenic belts. The SOB includes, from north to south, fold belt, melange, arc-pluton belt, and retroarc foreland basin, representing a southern subduction-collision system between the NCC and HB blocks during 500-440 Ma. The NOB consists also of four units: arc-pluton belt, melange, foreland molasse basin, and fold belt, from north to south, representing a northern subduction-collision system between the HB and SMM blocks during 500-380 Ma. From the early Paleozoic, the Paleo-Asian oceanic domains subducted to the north and the south, resulting in the forming of the SOB and the NOB in 410 Ma and 380 Ma, respectively. This convergent orogenic system, therefore, constrained the consumption process of the Paleo-Asian Ocean in western Inner Mongolia. A double subduction-collision accretionary process is the dominant geodynamic feature for the eastern part of the CAOB during the early to middle Paleozoic. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
The Tianshan and Junggar orogenic collage occupies the southwestern part of the Central Asian Orogenic Belt and was assembled by collision/accretion of several continental blocks and island arcs during late Paleozoic-early Mesozoic time, following the consumption of the Junggar and South Tianshan oceanic basins in the western segment of the Paleo-Asian Ocean. Considerable and continuing controversy has surrounded when, where, and how this orogenic collage was eventually amalgamated, which plays a crucial role in understanding the formation of the Central Asian Orogenic Belt. This review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains. A comprehensive data compilation indicates that the formation of ophiolites along major sutures in the Tianshan and Junggar region lasted to the early Carboniferous for the Kalamaili suture zone, to the mid-Carboniferous for the West Junggar region and the North Tianshan suture zone, and to the late Carboniferous for the South Tianshan suture zone. Ca. 325-310 Ma (ultra-)high pressure metamorphism along the western part of the South Tianshan suture occurred nearly synchronously with the collision between the Tarim Craton and the Central Tianshan-Yili Block. The oceanic closure and collision events were sequentially followed by widespread and intensive A-type granitic and bimodal magmatism, which commenced in the mid-Carboniferous along the Kalamaili belt and in the latest Carboniferous to earliest Permian in other regions. Contemporaneously, large-scale strike-slip shearing took place along major faults subparallel to main sutures, with a dominant dextral sense and deformation time since the Carboniferous-Permian transition. Available data and geological evidence support an eastward propagating, scissor-like closure of the western segment of the Paleo-Asian Ocean along the South Tianshan and North Tianshan suture zones over a period from the mid- to end Carboniferous, with the South Tianshan belt representing the final suturing site. In the early Permian, the Tarim mantle plume likely merely affected the southwestern part of the assembled Tarim and Tianshan region, as indicated by regional discrepancy in type and geochemistry of early Permian A-type granitoids. The amalgamation of the Tianshan and Junggar orogenic collage was associated with the tectonic bending of the Kazakhstan orocline, leaving a piece of trapped oceanic crust in its middle part, beneath the present Junggar Basin.
The identification of a fossil arc-trench system from the ophiolite-decorated Solonker suture zone in the southernmost Central Asian Orogenic Belt (CAOB) enables us to constrain the timing of pre-subduction extension (ca. 299-290 Ma), subduction initiation (ca. 294-280 Ma), ridge-trench collision (ca. 281-273 Ma) and slab break-off (ca. 255-248 Ma) in the Permian. A fraction of proto-arc crust (ca. 45 km long, up to 8 km wide) is preserved as a volcanic-plutonic sequence and is juxtaposed against a wide (ca. 30-80 km) forearc melange. This proto-arc crust comprises two distinct magma series, island arc tholeiite (IAT) and mid-ocean ridge basalt (MORB), both of which have strong supra-subduction zone (SSZ) geochemical signatures. Zircons from a gabbro and a plagiogranite yielded weighted mean (206)pb/U-238 ages of 284.0 +/- 4.0 and 288.0 +/- 6.0 Ma. The forearc melange consists of numerous ophiolite fragments and continental margin-derived olistoliths/blocks that predate the ophiolite. The olistoliths are best represented by a gabbroic block (291.8 +/- 2.3 Ma) that contains granite xenoliths (312.6 +/- 1.8 and 313.6 +/- 3.1 Ma). Other dated blocks include a trondhjemite (323.9 +/- 2.7 Ma), a gabbro (296.6 +/- 1.7 Ma) and a tonalite (294.9 +/- 2.4 Ma). Small bodies of diabase, andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures. We dated zircons from an N-MORB-like diabase (274.4 +/- 2.5 Ma), an E-MORB-like diabase (252.5 +/- 2.3 Ma), a transitional sanukitoid/adakite (andesite, 250.2 +/- 2.4 Ma), a sanukitoid (high-Mg diorite; 251.8 +/- 1.1 Ma) and an anorthosite (252.2 +/- 1.7 Ma). The N-MORB-like diabase contains ca. 301-394 Ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench. The other dated rocks simultaneously formed near the Permian/Triassic boundary and captured abundant zircon xenocrysts (ca. 269-295 Ma; ca. 301-495 Ma; and ca. 923-2501 Ma). Our new formation ages constrain a magmatic episode in response to slab break-off beneath a fossil forearc in a young post-collisional setting, and the youngest xenocryst ages (ca. 269-273 Ma) may define the maximum depositional age of trench sediments. (C) 2010 Elsevier B.V. All rights reserved.
We present a detailed, new time scale for an orogenic cycle (oceanic accretion-subduction-collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical are-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497-477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473-470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461-450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451-434 Ma) and by ridge collision with the ophiolite (ca. 428-423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: are volcanism (ca. 488-444 Ma); adakite plutonism (ca. 448-438 Ma) and collision (ca. 419-415 Ma) of the are with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498-461 Ma) and juvenile arc crust (ca. 484-469 Ma), to ridge subduction (ca. 440-434 Ma), microcontinent accretion (ca. 430-420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500-438 Ma), ridge subduction (ca. 451-434 Ma) to microcontinent accretion/ collision (ca. 430-415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian-early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth. (c) 2007 Elsevier B.V. All rights reserved.