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Subduction of oceanic lithosphere is a diagnostic characteristic of plate tectonics. However, the geodynamic processes from initiation to termination of subduction zones remain enigmatic mainly due to the scarcity of appropriate rock records. We report the first discovery of early Paleozoic boninitic blueschists and associated greenschists from the eastern Proto-Tethyan North Qilian orogenic belt, northeastern Tibet, which have geochemical affinities that are typical of forearc boninites and island arc basalts, respectively. The boninitic protoliths of the blueschists record intra-oceanic subduction initiation at ca. 492–488 Ma in the eastern North Qilian arc/forearc–backarc system, whereas peak blueschist facies metamorphism reflects subsequent subduction of the arc/forearc complex to high pressure at ca. 455 Ma. These relations therefore record the life circle of an intra-oceanic subduction zone within the northeastern Proto-Tethys Ocean. The geodynamic evolution provides an early Paleozoic analogue of the early development of the Izu–Bonin–Mariana arc and its later subduction beneath the extant Japanese arc margin. This finding highlights the important role of subduction of former upper plate island arc/forearcs in reducing the likelihood of preservation of initial subduction-related rock records in ancient orogenic belts.

The southern Altaids is of critical significance for a better understanding of the orogenic architecture and continental growth in Central Asia. The tectonic setting of the South Tianshan, a typical Paleozoic accretionary orogen within the southern Altaids, is controversial. This study reports new structural relations, geochemistry, and geochronology of previously assigned Late Silurian–Early Devonian strata in the Karaghol area of the South Tianshan. The constituent rocks are pillow basalts, ribbon cherts, limestones, siliceous mudstones, and turbiditic sandstones. Field relations show that these rocks are characterized by fault-bound tectonic slices and melanges with typical block-in-matrix structures. The pillow basalts show N-MORB, E-MORB, and OIB geochemical fingerprints, and our new LA-ICP-MS zircon U–Pb dates indicate that the maximum eruption age of the OIB-type basalts was ca. 386 Ma, whereas the Maximum Depositional Ages (MDAs) of the turbiditic sandstones were ca. 369 Ma and 355 Ma. The age spectra of the detrital zircons, which define prominent peaks at ca. 370 Ma, ca. 420 Ma, ca. 770 Ma, ca. 960 Ma with subordinate Proterozoic ages, are a good match with the igneous ages of intermediate to felsic magmatism in the Yili–Central Tianshan arc. We conclude that the previously assigned Late Silurian–Early Devonian strata in the Karaghol area are mostly dismembered structural components and melanges that belonged to an accretionary complex of Late Devonian to Early Carboniferous age, into which fragments of a Late Devonian seamount along with South Tianshan oceanic crustal rocks were likely emplaced during north-dipping subduction in the Early Carboniferous. This well-documented accretionary orogen in the Chinese South Tianshan is a key constraint on the accretionary orogenesis of the southern Altaids.

In this contribution we review the possibility of establishing the depositional age and tectonic settings of metamorphosed carbonate rocks from continental collision zones in the East African-Antarctic Orogen. The geochemical characteristics of regionally distributed meta-carbonate rocks from the Highland Complex (HC) in Sri Lanka are considered in detail and compared with similar occurrences in East Antarctica, India, Madagascar and Africa. The variations seen in the Highland Complex of Sri Lanka imply that carbonate deposition was younging from west to east, spanning apparent ages from Mesoproterozoic to Neoproterozoic. In the case of East Antarctica, such variations are within the Neoproterozoic, whereas in southern India, Madagascar and Mozambique they have a broader age range possibly from the Paleoproterozoic to Mesoproterozoic. There is also clear evidence that some carbonates were deposited in an open ocean surrounding volcanic islands in the Mesoproterozoic. Shale-normalized REE patterns have typical signatures of open ocean deposition in a passive continental margin with variable continental input in platforms nearby to island arcs. In comparison to Phanerozoic equivalents, the absence of a Ce anomaly is most significant, whereas other parameters such as (Pr/Yb)SN, (Pr/Tb)SN, and (Tb/Yb)SN were used to evaluate relative enrichments of the LREE, MREE and HREE fractions that are characteristic of ambient seawater. Pronounced La, and Y anomalies with minor Eu and Gd anomalies and correlations of REE parameters and anomalies with carbon and oxygen isotopes, 87Sr/86Sr initial ratios and eNd values are evaluated for meta-carbonate rocks in the Proterozoic collision zone. The eNd values and Sr initial ratios suggest that basins in the western Mozambique Ocean that separated the East Gondwana from West Gondwana received contributions from Archean continental crust and ambient seawater, whereas the eastern Mozambique Ocean had REE contributions from specific cratonic continents in passive margins or from continental/volcanic island arcs in active margins.

Knowledge of the Late Paleozoic accretionary processes responsible for the Altaids (or southern Central Asian Orogenic Belt) is critical for a better understanding of continental growth in Central Asia. Here, we systematic study the Late Carboniferous mafic-ultramafic-felsic complexes in eastern Central Tianshan to understand the tectonic evolution of the southern Altaids. Two gabbros yield zircon crystallization ages of 301.5 ± 2.3 Ma and 300.7 ± 2.6 Ma and one granite is dated as 301.6 ± 1.5 Ma. The gabbros are tholeiitic and characterized by typical subduction-related geochemical signatures with low TiO2 contents, enrichments in Rb, Ba, U, K, Pb and Sr, negative Nb and Ta anomalies, and negative to positive Eu and Ti anomalies. The granites are the A2-type granites with high contents of SiO2, K2O + Na2O, Ga, Zr, Nb, Y, HFSE, REE, and high ratios of Fe/Mg and Y/Nb (>1.2). The gabbros and granites have high eNd (t) values of +1.64 to +5.03, zircon eHf (t) values of −2.8 to +9.1, and low (87Sr/86Sr)i (0.704007–0.705437) values. These geochemical characters demonstrate that the rocks in the complexes are fractionation genesis and that the A-type granitic rocks are the highest fractionation facies of tholeiitic mafic rocks. These results suggest that they were originated from the asthenospheric garnet-free mantle in a supra-subduction zone. Combined with regional data, we suggest that the oblique subduction with slab break-off of the Southern Tianshan oceanic plate plausibly induced asthenospheric upwelling to form the tholeiitic magma, and which intrude along the strike-faults the Central Tianshan-Yamansu arc. Accordingly, these results reveal the Paleo-Asian Ocean continued to subduct at the southern Altaids in the Late Carboniferous.

The mechanics of crustal growth in the Altaids during the Phanerozoic is still not well understood. This paper reports new geochronological, geochemical, and isotopic data from Paleozoic adakitic intrusions in the Dananhu arc in the Chinese Eastern Tianshan with the aim of better understanding the specific mechanisms of crustal growth. Our new LA-ICPMS U–Pb zircon age data show that four phases of adakitic intrusions formed at 410–413 Ma, 385–387 Ma, 335 Ma, and 313–311 Ma. Combined with previous data of ours and from the literature, there were seven phases of adakitic intrusions from the Silurian to early Permian. All these adakitic intrusions have distinctive geochemical-isotopic signatures with high Na and Al, high Sr, low Yb and Y, high Sr/Y and (La/Yb)N values, relatively high MgO contents and Mg numbers (Mg# = 41–70), high abundances of compatible elements (Cr = 1.66–46.30 ppm, Ni = 2.40–26.96 ppm), and positive high eHf (t) (+ 7.1 to + 15.6) and a TDM (Ma) range from 325 to 670 Ma. These adakitic intrusions were associated with essential Cu polymetallic mineralization in the Dananhu arc. The above chemical data and relations indicate that the processes of oceanic slab melting generated these adakitic rocks. Our new geochronological, geochemical and isotopic data, integrated with the geology of the Dananhu intra-oceanic arc, lead us to conclude that multiphase of hot/young oceanic crust subduction and melting generated the massive crustal growth in the Silurian–early Permian. Our results indicate that the magmas were derived by slab melting of hot/young oceanic crust, which was one of the most critical mechanisms of continental crustal growth in the Paleozoic accretionary orogen of the Altaids.

The orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336–326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303–289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1–E3) separately occurred during D1–D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

The Central Asian Orogenic Belt has long been considered the largest Phanerozoic accretionary orogen in the world; it developed through the subduction and final closure of the Paleo–Asian Ocean. However, the architecture and duration of the accretionary orogenesis of the Central Asian Orogenic Belt are still controversial despite decades of investigation. In this study, we present field, compositional, and stratigraphically controlled detrital zircon geochronological data for late Paleozoic sedimentary rocks from the Alxa Tectonic Belt to constrain their provenance, tectonic setting, and the overall tectonic configuration of the southern Central Asian Orogenic Belt. A Devonian sample yields a unimodal age peak (ca. 424 Ma) and broad late Mesoproterozoic ages. A Carboniferous sample has Early Silurian (ca. 438 Ma) and Late Devonian (ca. 382 Ma) peaks along with Neoproterozoic to Archean ages. The Permian samples are dominated by Ordovician–Devonian and Carboniferous–Permian ages. They yield maximum depositional ages ranging from ca. 291 Ma to 248 Ma and contain abundant zircon ages that are close to their depositional ages. These data reveal Ordovician–Silurian and Carboniferous–Permian magmatic flare-ups separated by a Devonian magmatic lull in the southern Central Asian Orogenic Belt. The arc terranes in southern Mongolia, central Beishan, and northern Alxa provided major detritus for the late Paleozoic sediments. An abrupt shift of zircon εHf(t) values at ca. 400 Ma reveals significant late Paleozoic crustal growth and excludes southern Alxa as a source. Oceanic basins prevented detritus from southern Alxa from reaching northern Alxa during Permian–Early Triassic time. A geological and provenance comparison of Permian basins in the southern Central Asian Orogenic Belt reveals the existence of two separate forearcs ascribed to bipolar subduction of the Paleo–Asian Ocean. Combined with recent paleomagnetic data, this leads us to advocate for an archipelago-style accretionary process induced by subduction retreat for the late Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt, which continued into Late Permian–Early Triassic.

Recognition of accretionary tectonics in ancient orogenic collages is important for reconstructing the long-term subduction, accretion, and erosional history of fossil convergent margins, and for understanding crustal growth and supercontinent assembly. The North Qilian orogenic belt (NQOB), located between the Alxa block and the Central Qilian–Qaidam block in northeastern Tibet, is a typical Phanerozoic accretionary-to-collisional orogenic belt that represents the termination of the northern branch of the Proto-Tethys Ocean. It contains two subparallel ophiolitic belts, arcs, and subduction complexes; the ophiolitic rocks in the northern belt have generally been considered to have formed in a back-arc setting. However, the subduction-accretion-collision history, subduction polarity, and timing of closure of the back-arc ocean remain equivocal. To address these problems, we conducted detailed field, structural, and geochronological investigations of the Laohushan ophiolite–accretionary complex and related sedimentary rocks in the eastern NQOB. The Laohushan Complex is divisible into (1) a northern sedimentary forearc, and a supra-subduction zone-type ultramafic-mafic forearc (ca. 450 Ma) composed of serpentinized harzburgite, gabbro, basalt, and plagiogranite; and (2) a southern accretionary complex, which consists of relatively coherent basalt-chert-mudstone ocean plate stratigraphy that is structurally repeated many times, trench-fill turbidites, mélanges, and widespread thrust imbricates and duplexes, block-in-matrix and asymmetric structures. Kinematic analysis indicates that the accretionary complex underwent southward thrusting and shearing; coupled with the spatial architecture of the different tectonic units, which suggests northward subduction beneath the northern forearc on the southern margin of the Alxa block. Detrital zircon ages of forearc clastic sandstones, pelagic mudstones, trench-fill turbidites, and the matrix of mélanges, together with the zircon ages of igneous ophiolitic rocks and post-accretionary intrusions, indicate that the terminal accretion and tectonic stacking of the Laohushan subduction complex was between ca. 447 and 430 Ma. We propose a geodynamic model involving back-arc basin opening (ca. 517–449 Ma), intra-oceanic subduction-accretion (ca. 449–430 Ma), and final obduction of the northern forearc to account for the evolutionary processes of the North Qilian back-arc basin. The anatomy of the forearc ophiolite and structurally lower accretionary complex indicates the complicated origins and mechanism of emplacement of the ophiolitic rocks. Field-based reconstruction of accretionary complexes and upper plate ophiolites, together with provenance analysis of related sedimentary sequences, provide crucial constraints on the prolonged evolution of paleo-ocean basins and accretionary-to-collisional orogens.

As one of the largest Phanerozoic orogens in the world, the Central Asian Orogenic Belt (CAOB) is a natural laboratory for studies of continental dynamics and metallogenesis. This paper summarizes the research progresses of the accretionary processes and metallogenesis of the CAOB since the People’s Republic of China was founded, and puts forward the prospect for future research. During the early period (1950s–1970s), several geological theories were applied to explain the geological evolution of Central Asia. In the early period of China’s reform and opening-up, the plate tectonics theory was applied to explain the evolution of the northern Xinjiang and Xingmeng regions, and the opinion of subduction-collision between Siberian, Kazakhstan, and China-North Korea-Tarim plates was proposed. The idea of the Solonker-Yanbian suture zone was established. In the 1990s, the study of the CAOB entered a period of rapid development. One school of scholars including geologists from the former Soviet Union proposed a multi-block collision model for the assemblage of the CAOB. In contrast, another school of scholars, led by a Turkish geologist, Celal Sengor, proposed that the Altaids was formed through the growth and strike-slip duplicates of a single island arc, and pointed out that the Altaids is a special type of collisional orogen. During this period, Chinese geologists carried out a lot of pioneering researches on ophiolites and high-pressure metamorphic rocks in northern China, and confirmed the main suture zones accordingly. In 1999, the concept of “Central Asian metallogenic domain” was proposed, and it became one of the three major metallogenic domains in the world. Since the 21st century, given the importance for understanding continental accretion and metallogenic mechanism, the CAOB has become the international academic forefront. China has laid out a series of scientific research projects in Central Asia. A large number of important scientific research achievements have been spawned, including the tectonic attribution of micro-continents, timing and tectonic settings of ophiolites, magmatic arcs, identification and anatomy of accretionary wedges, regional metamorphism-deformation, (ultra)high-pressure metamorphism, ridge subduction, plume-plate interaction, archipelagic paleogeography and spatio-temporal framework of multiple accretionary orogeny, continental growth, accretionary metallogenesis, structural superposition and transformation, etc. These achievements have made important international influences. There still exist the following aspects that need further study: (1) Early evolution history and subduction initiation of the Paleo-Asian Ocean; (2) The accretionary mechanism of the extroversion Paleo-Asian Ocean; (3) The properties of the mantle of the Paleo-Asian Ocean and their spatio-temporal distribution; (4) The interaction between the Paleo-Asian Ocean and the Tethys Ocean; (5) Phanerozoic continental growth mechanism and its global comparison; (6) Accretionary metallogenic mechanism of the Central Asian metallogenic domain; and (7) Continental transformation mechanism.

The interaction of the Palaeo-Pacific and Palaeo-Asian Oceans is an enigmatic issue as their temporal and spatial features are controversial. To address this issue, we present a systematic study of large volumes of early Permian volcanic rocks and intrusions developed in the East Tianshan. The represented samples of basaltic andesites and rhyolites yield zircon crystallization ages of 285.1 ± 5.9 Ma and 275.3 ± 1.8 Ma, respectively. The basalts have normal mid-ocean ridge basalt (N-MORB) and arc-related geochemical signatures with high TiO2 contents, negative Rb, Th, U, Nb and Ta anomalies and positive Eu anomalies. Basaltic andesites and andesites have arc-related geochemical characteristics with moderate TiO2 contents and relatively negative Nb, Ta and Ti anomalies, together with slightly negative to positive Eu anomalies. The rhyolites show an affinity with A2-type granite with high SiO2, K2O + Na2O, Fe/Mg, Ga, Zr, Nb, Y, HFSE, REE and Y/Nb levels (>1.2). These geochemical data suggest that the rocks formed in a supra-subduction zone. The presence of high ϵNd(t) values of +4.6 to +8.2 and low (87Sr/86Sr)i (0.70342–0.70591) values indicates that the volcanic rocks originated from a depleted mantle. We propose that oblique subduction with slabs breaking off gave rise to transtension and to the emplacement of large volumes of mantle-derived melts in the early Permian in the East Tianshan, serving as an important record of the subduction zone of the Palaeo-Pacific Ocean.

To reconstruct the early tectonic history of the Himalayan orogen before final India-Asia collision, we carried out geochemical and geochronological studies on the Early Cretaceous Aulis Trachyte of the Lesser Himalaya. The trace-element geochemistry of the trachytic lava flows suggests formation in a rift setting, and zircon U-Pb ages indicate that volcanism occurred in Early Cretaceous time. The felsic volcanics show enrichment of more incompatible elements and rare earth elements, a pattern that is identical to the trachyte from the East African Rift (Kenya rift), with conspicuous negative anomalies of Nb, P, and Ti. Although much of the zircon age data are discordant, they strongly suggest an Early Cretaceous eruption age, which is in agreement with the fossil age of intravolcanic siltstones. The Aulis Trachyte provides the first corroboration of Cretaceous rifting in the Lesser Himalaya as suggested by paleomagnetic data associated with the concept that the northern margin of India separated as a microcontinent and drifted north in the Neo-Tethys before terminal collision of India with Asia.

The time of final closure of the Paleotethys Ocean is still hotly debated in particular regarding the Jinsha Ocean in northern Tibet. This study reports new geochronologic, geochemical and zircon Hf isotopic data of six granodiorites-diorites, which intrude the Mid-Late Triassic Songpan-Ganzi complex (SGC). LA-ICP-MS zircon U-Pb analyses of three quartz diorites (214.9 ± 2.2, 211.0 ± 1.3, 205.8 ± 1.4 Ma) and three granodiorites (210.8 ± 2.7, 206.7 ± 3.3, 205.9 ± 3.5 Ma) gave a Late Triassic age range (214.9–205.8 Ma). These granodiorite-diorite rocks have relatively high MgO (up to 9.1%) and Mg# (up to 70.2), Al2O3, Cr, Ni, but low TiO2, and high magnesium andesite/diorite (HMA) chemical signatures with low Sr and Y content, and slight-moderate negative Eu anomaly. Also, the dioritic enclaves and Late Triassic detrital zircons (as young as 208 Ma) were captured by studied rocks. Hf isotope data show overall slight to moderate negative zircon eHf(t) values (−1.97 to −5.76, −4.12 to −6.72) and heterogeneous TDMC ages (1.38−1.61Ga, 1.51−1.68Ga) for quartz diorites and granodiorites respectively, together with other published Hf isotopic data in SGC, are in highly concert with those around ~240 and ~440Ma magmas (as potential sources for SGC turbidites) in east Kunlun orogenic belt. Taken together, the HMA magmas were probably derived from a reaction between subducted marine sedimentary siliceous melts and peridotites from a mantle wedge. The linear distribution of Late Triassic HMAs and their eastward-younging trend (from northern Qiangtang to southern SGC), in combination with the contrasting distribution of volcanic rocks in the northern Qiangtang terrane, lead us to suggest that a slab window opened in the downgoing oceanic crust with two diverse slab angles during oblique subduction. Accordingly, the final closure of the Paleotethys Ocean was later than 205 Ma, and most likely in the end of the Late Triassic to Early Jurassic.

Plate tectonics describes the horizontal motion of rigid lithospheric plates away from midoceanic ridges and parallel to transforms, towards deep-sea trenches, where the oceanic lithosphere is subducted into the mantle. This process is the surface expression of modern-day heat loss from Earth. One of the biggest questions in Geosciences today is “when did plate tectonics begin on Earth” with a wide range of theories based on an equally diverse set of constraints from geology, geochemistry, numerical modeling, or pure speculation. In this contribution, we turn the coin over and ask “when was the last appearance in the geological record for which there is proof that plate tectonics did not operate on the planet as it does today”. We apply the laws of uniformitarianism to the rock record to ask how far back in time is the geologic record consistent with presently-operating kinematics of plate motion, before which some other mechanisms of planetary heat loss may have been in operation. Some have suggested that evidence shows that there was no plate tectonics before 800 Ma ago, others sometime before 1.8–2.7 Ga, or before 2.7 Ga. Still others recognize evidence for plate tectonics as early as 3.0 Ga, 3.3–3.5 Ga, the age of the oldest rocks, or in the Hadean before 4.3 Ga. A key undiscussed question is: why is there such a diversity of opinion about the age at which plate tectonics can be shown to not have operated, and what criteria are the different research groups using to define plate tectonics, and to recognize evidence of plate tectonics in very old rocks? Here, we present and evaluate data from the rock record, constrained by relevant geochemical-isotopic data, and conclude that the evidence shows indubitably that plate tectonics has been operating at least since the formation of the oldest rocks, albeit with some differences in processes, compositions, and products in earlier times of higher heat generation and mantle temperature, weaker oceanic lithosphere, hotter subduction zones caused by more slab-melt generation, and under different biological and atmospheric conditions.

Tracing the closure of oceans with irregular margins and the formation of an orocline are crucial for understanding plate reconstruction and continental assembly. The eastern Central Asian Orogenic Belt, where the Mongol-Okhotsk orocline is situated, is one of the world's largest magmatic provinces. Using a large data set of U-Pb zircon ages, we updated the timing of many published igneous rocks, which allowed us to recognize tightly ‘folded’ linear Carboniferous-Jurassic magmatic belts that wrap around the Mongol-Okhotsk suture and their migrations both sutureward and suture-parallel. The new successive magmatic belts reveal a rollback, scissor-like (or zipper-like) closure of the Mongol-Okhotsk Ocean that was fundamentally controlled by coeval subduction rollback and rotation of the Siberian and Mongolian-Erguna blocks. This study also demonstrates the complex mechanisms and processes of the closure of an ocean with irregular margins and the formation of a consequent orocline.