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It was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip. Plain Language Summary: The Tethyan slab subduction and following collision of India and Asia produced two magmatic belts in the Lhasa‐Tengchong terrane. How did the magmatic flare‐ups or high‐flux episodes and sources spatiotemporally vary? We combine the new U‐Pb and Lu‐Hf isotopic data of captured zircons (xenocrystic zircons caught by volcanics from country rocks) and a comprehensive data set to show that the peak ages of early Cretaceous flare‐up of the northern magmatic belt are ca.10 Ma younger in central and northern Lhasa than in eastern Tengchong, possibly related to the diachronous closure of the Meso‐Tethys and flat subduction of the Neo‐Tethys. The southern magmatic belt in Tengchong and western southern Lhasa exhibit 75–45 Ma flare‐ups featured by the reworking of ancient crust, different from the eastern southern Lhasa with the flare‐ups at 100–85 Ma and 65–45 Ma which are dominated by the juvenile crustal growth. Such flare‐up variations may be related to changes of the Neo‐Tethyan slab dip. Key Points: The Neo‐Tethyan arc has asynchronous magmatic flare‐ups and diverse magmatic sourcesThe spatiotemporal changes of slab dip triggered the asynchronous flare‐ups of the Neo‐Tethyan arc [ABSTRACT FROM AUTHOR]

Trans‐plate crustal overthrust and underthrust are two unusual crustal architectures in nature, the mechanisms of which remain debated. Here, we construct a series of 2D numerical models to investigate the dynamics of trans‐plate crustal overthrust and underthrust. Model results indicate that the favourable conditions of crustal overthrust include low convergence rate, plastically strong crust, rheologically strong upper crust and hot subducting plate, which meanwhile contribute to the formation of 'crocodile' crustal structure. In contrast, a combination of a strong and buoyant subducting plate with a hot overriding plate facilitates crustal underthrust. The development of crustal overthrust shows no correlation with the subduction mode of lithospheric mantle, whereas crustal underthrust normally occurs in an advancing subduction system. Development conditions and crustal structures of the modelled overthrust and underthrust are consistent, on the first order, with the natural Dinarides orogen and the southern Tibetan plateau respectively. [ABSTRACT FROM AUTHOR]

The role of subducted sediments in arc magmatism has been widely documented. However, identifying the sedimentary provenance (e.g., pelagic vs. terrigenous) input in subduction systems is difficult because of the wide compositional range of sedimentary components and the complex magmatic evolution of arcs. Here we report zircon U‐Pb‐Hf‐O isotopes and whole‐rock elemental and Sr‐Nd‐Hf isotopic compositions of four Early Jurassic subduction‐related mafic intrusions from the Yanbian area, NE China. These rocks show typical trace element and isotopic features of arc magmas. In combination with the published data, we discover two distinct elemental‐isotopic arrays of the Early Jurassic mafic rocks across the arc magmatic belt. Such geochemical variations are mainly attributed to variable subducted sediment input into the mantle wedge instead of crustal contamination or assimilation during magmatic evolution. The mantle source for the southern Yanbian mafic rocks was enriched by addition of a crustal component dominated by terrigenous sediments, whereas that for the northern Lesser Hinggan‐Zhangguangcai Range, mafic rocks was modified by another crustal component comprising mainly pelagic sediments. The results can be best interpreted if the southern part was a continental arc as opposed to an oceanic arc in the north, which is analogous to the modern Kamchatka‐Honshu‐Izu‐Bonin‐Mariana arc systems in the western Pacific. Our reconstructed architecture, based mainly on the geochemical data, further suggests that the Khanka‐Jiamusi‐Buleya Massif was probably sinistrally and northwardly displaced to the present position after Mesozoic subduction of the Paleo‐Pacific Ocean. Plain Language Summary: Subducted sediments play an important role in generation of arc magmatism. However, the identification of the source (pelagic vs. terrigenous) of the sediments in subduction systems is difficult because of the wide compositional range of sedimentary components and the complex magmatic evolution of arcs. Here we carry out an integrated analysis of Sr‐Nd‐Hf‐O isotopic and elemental compositions of subduction‐related mafic intrusions across the Early Jurassic Paleo‐Pacific subduction zone in NE China. The combined geochemical data from our and previous studies suggest that the southern Yanbian mafic rocks were generated by melting of a depleted mantle with input of a terrigenous sediment component, whereas the mafic rocks from the northern Lesser Hinggan‐Zhangguangcai Range were derived from a depleted mantle modified by a pelagic sediment component. We thus propose that the Mesozoic subduction zone in NE China consisted of an intraoceanic arc in the northern segment and a continental arc in the southern part, as observed from the modern Kamchatka‐Honshu‐Izu‐Bonin‐Mariana arc systems in the western Pacific. Our study therefore provides a potential method to identify the provenance of the subducted sediments added into the subarc mantle, which may allow to reconstruct the architecture of paleo‐subduction zones. Key Points: Early Jurassic subduction‐related mafic intrusions in NE China show distinct geochemical compositionsBoth terrigenous and pelagic sediments contributed to mantle enrichments across the subduction zoneThe Paleo‐Pacific subduction zone in NE China contained both oceanic and continental arcs [ABSTRACT FROM AUTHOR]

Numerical experiments are used in this study to systematically investigate the effects of convergence rate, crustal rheological strength, and lithospheric thermal structure on the dynamics of continental collision. The study focuses on the types, conditions and processes of unstable continental subduction. Modelling results suggest that the development of unstable continental subduction can be promoted by conditions that tend to decrease rheological strength of the lithosphere, such as low crustal rheological strength, 'hot' thermal structure of the lithosphere, or low convergence rate. Unstable subduction mode can be further categorized into three types: (1) multi-stage slab breakoff, (2) continuously 'flowing' of fluid-like slab into the upper mantle, and (3) large-scale detachment of the thickened orogenic root. These three types of unstable continental subduction are respectively associated with (1) a low convergence rate, (2) 'hot' thermal structure of the lithosphere with a high convergence rate, and (3) moderate-high crustal rheological strength with a low convergence rate. It is also revealed that the evolution of crustal melting is dominated by the deformation pattern of continental collision, which is mainly controlled by crustal rheological strength. The modelling results have important implications for understanding of continental subduction mode selection under specific geodynamic conditions. [ABSTRACT FROM AUTHOR]

2D thermo-mechanical models are constructed to investigate the effects of oceanic and continental crustal eclogitization on plate dynamics at three successive stages of oceanic subduction, slab breakoff, and continental subduction. Crustal eclogitization directly increases the average slab density and accordingly the slab pull force, which makes the slab subduct deeply and steeply. Numerical results demonstrate that the duration time from initial continental collision to slab breakoff largely depends on the slab pull force. Specifically, eclogitization of subducted crust can greatly decrease the duration time, but increase the breakoff depth. The detachment of oceanic slab from the pro-continental lithosphere is accompanied with obvious exhumation of the subducted continental crust and a sharp uplift of the collision zone in response to the disappearance of downward drag force and the induced asthenospheric upwelling, especially under the condition of no or incomplete crustal eclogitization. During continental subduction, the slab dip angle is strongly correlated with eclogitization of subducted continental lower crust, which regulates the slab buoyancy nature. Our model results can provide several important implications for the Himalayan-Tibetan collision zone. For example, it is possible that the lateral variations in the degree of eclogitization of the subducted Indian crust might to some extent contribute to the lateral variations of subduction angle along the Himalayan orogenic belt. Moreover, the accumulation of highly radiogenic sediments and upper continental crustal materials at the active margin in combination with the strong shear heating due to continuous continental subduction together cause rising of isotherms in the accretionary wedge, which facilitate the development of crustal partial melting and metamorphism. [ABSTRACT FROM AUTHOR]

The subduction of the Paleotethyan Ocean and subsequent continental collision along the Lancang tectonic belt of the southeastern Paleotethyan belt is a major tectonic event in Southwest China, but the event of the subduction preceding the final collision is still not well-constrained. The mafic blueschists exposed in the Lancang accretionary complex provide crucial records of the Paleotethyan subduction process. In this paper, we present a set of new petrologic, geochronological and geochemical data for the Suyi mafic blueschists in the Lancang metamorphic zone. The mineral assemblage of these blueschists consists of zoned sodic amphibole (25–30%), albite (15–20%), epidote (25–30%), phengite (5–10%), chlorite (~ 5–10%), and minor amounts of actinolite, apatite, sphene, zircon, ilmenite, quartz and secondary limonite. This suggests a prograde metamorphism from ~ 0.5 to ~ 0.9 GPa and retrograde metamorphic overprinting (back to ~ 0.6 GPa) within the temperature range of 300–450 °C. The Suyi blueschists give a zircon U–Pb age of 260 ± 4 Ma and glaucophane minerals formed during prograde metamorphism yield a 40 Ar/ 39 Ar plateau age of 242 ± 5 Ma (MSWD = 0.77; P = 0.54). The blueschists have geochemical compositions of subalkaline basalt and show typical OIB-type REE and multi-elemental patterns and ε Nd (t) values ranging from + 3.35 to + 4.85. Based on available data, it is inferred that the protolith formed at 260 Ma and originated from a basaltic seamount. The basaltic rocks subducted down to 30–35 km depths beneath the Lincang arc to form the epidote blueschists at ~ 242 Ma. The blueschists were subsequently transported to shallower crustal levels in response to the continuous underthrust of the subducted slab and the continent–continent collision in the middle–late Triassic. These results provide a systematic constraint on the tectonic evolution and temporal framework of the southeastern Paleotethyan belt in Southwest China. [ABSTRACT FROM AUTHOR]

Adakites may form by partial melting of either the subducting oceanic lithosphere or the lower part of the continental crust. These two magma types can be discriminated geochemically using a combination of La/Yb, Sr/Y ratios, MgO and Na2O contents, and Sr-Nd isotopes. Given that the basaltic crust has Cu concentrations more than two times higher than the lower continental crust and the mantle wedge, 'primitive' adakites produced by oceanic slab melting should contain significantly higher Cu contents than adakites derived from the continental crust, as well as normal arc andesites. A globally compiled dataset shows that Cu concentrations in adakites are generally lower than that in normal arc rocks. We attribute this low copper content to loss of magmatic fluids as a result of sulphate reduction during adakitic magma differentiation, in turn induced by the crystallization of Fe-Ti oxides, essential to mineralization. Therefore, the underflow of oceanic-slab-derived adakites that can release larger amounts of Cu (presumably Au as well) by crystal fractionation leads to higher potential for Cu-Au mineralization along convergent margins, usually associated with ridge subduction. Such basaltic slab melts initially have considerably higher Cu contents and thus play a crucial role particularly in the relatively closed magma system responsible for generating porphyry Cu deposits. [ABSTRACT FROM AUTHOR]

Abstract Two distinct styles of continental collision are observed in nature, i.e. lithospheric-scale subduction versus crustal-scale underthrusting. The former refers to a collision scenario where the lower plate subducts below the lithospheric mantle of the overriding plate, whereas the latter is characterized by the underthrusting of the subducting plate beneath the crust of the overriding plate. Systematic numerical models were constructed to study the dynamics of these two different collision modes. The model results indicate that low convergence rate and cold overriding plate contribute to the lithospheric-scale subduction, which incorporates limited shortening of the overriding lithosphere during collision. In contrast, the crustal-scale underthrusting requires relatively high convergence rate and hot/weak overriding plate, in which the thickened lithospheric mantle of the overriding plate is progressively delaminated from the overlying crust and is replaced by the sub-horizontally underthrusted plate. The model results were systematically compared with four ongoing collisional orogens along the Alpine–Himalayan belt, i.e. the central-western Alps, the East Anatolian plateau, the Zagros–Iranian plateau, and the southern Tibetan plateau. It indicates that the lithospheric-scale subduction is widely observed and generally consistent with the natural orogens, for example, the Alps, Anatolia, and Zagros. On the other hand, the crustal-scale underthrusting is reconciled with the India–Asia collision zone, with respect to the geodynamic conditions, crustal-lithospheric structure, as well as the uplift history. Highlights • Continental lithospheric-scale subduction versus crustal-scale underthrusting • Density and thermo-rheological properties of the upper plate control mode selection • Plate convergence rate also affects the continental collision mode. • Models applied to four ongoing collisional orogens along the Alpine–Himalayan belt. [ABSTRACT FROM AUTHOR]

Eastern China is characterized by widespread Mesozoic magmatism that was closely related to subduction of the Paleo-Pacific Plate, but the genetic relationship between magmatism and subduction is not always clear. The Jiangnan Orogenic Belt (JOB) is a Neoproterozoic collisional belt between the Yangtze and Cathaysian blocks. Early Cretaceous felsic magmas from the Tianmushan basin in the eastern JOB form a > 3000 m thick volcanic sequence erupted within an extremely short period of time (132–130 Ma). These rocks are potassic (K 2 O = 3.86–6.05%) and peraluminous (A/CNK = 1.0–1.23), and are compositionally similar to experimental melts derived from predominantly clay-poor and K-rich metasediments or granodiorites at crustal conditions. They are LILE- and LREE-enriched ((La/Yb) CN = 9.0–14.6) and display variable Eu anomalies and Nb–Ta depletion. The weakly variable and negative whole-rock ε Nd (t) (− 5.4 to − 2.5) and heterogeneous zircon ε Hf (t) values (− 6.7 to + 3.5) of these rocks are similar to those of basement rocks beneath the JOB, suggesting a genetic relationship with basement. No magmas with clear subduction-related composition occurred at this time in the area and the compositions of the potassic rocks more closely resemble high-temperature melts of extensively thinned crust in continental rift environments. Our data favors a model that the Early Cretaceous potassic magmas formed as subduction of the Pacific–Izanagi ridge resulted in upwelling asthenosphere, providing the high temperatures required to extensively melt the lower-middle crust in the eastern JOB. [ABSTRACT FROM AUTHOR]

Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear when this subduction began. Here we report an Early Jurassic (~ 187 Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb–Ta depletion). It also had Sr–Nd–Hf isotopic compositions ( 87 Sr/ 86 Sr(i) = 0.7042 to 0.7044, ε Nd (t) = + 2.5 to + 3.5 and ε Hf (t) = + 8.4 to + 10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3–4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N–S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Siliceous high-Mg basalt (SHMB) is a rare rock type that occurs mainly at or near the Archean–Proterozoic boundary. It shares some geochemical similarities with Phanerozoic boninites, but there is a clear distinction. Whether the petrogenesis of SHMB resembles that of Phanerozoic boninites or is related to the komatiitic magmatism is controversial. Neoarchean SHMBs are identified for the first time from the Taishan granite–greenstone terrane within the Eastern Block of the North China Craton (NCC). Zircon U–Pb dating indicates that they were emplaced at ∼2.54Ga, contemporaneous with the generation of sanukitoids and adakitic rocks, but later than the eruption of the Late Archean (2.71Ga) komatiites and komatiitic basalts in the area. The high MgO (>8%), high SiO2 (>52%), and Al2O3/TiO2 ratio (12.4–45.0), together with low TiO2 (<0.5%) and HFSE contents and strong enrichment in LREE and LILE in the Taishan SHMBs are comparable with typical Phanerozoic boninites, except for distinct HREE depletion, lack of U-shaped REE patterns and conspicuous positive Zr anomalies. In conjunction with their more depleted Nd isotopic characteristics (ɛ Nd(t =2.54Ga)=+4.42 to +1.05) relative to Late Archean komatiites in the region, it suggests that these SHMBs were derived from partial melting of refractory depleted mantle which experienced earlier basalt extraction and was subsequently enriched in LILE and LREE by subduction-related metasomatization, rather than the products of assimilation–fractional crystallization (AFC) of komatiitic magma. A slab-derived adakitic melt was likely the metasomatizing agent, along with minor aqueous fluids released from the subducting oceanic slab. In combination with regional studies, the generation of these magmas was probably related to slab rollback, which is ascribed to the arrival of an oceanic plateau and/or residual thickened lithospheric keel at the subduction zone at that time. This mechanism might have played a crucial role in the formation of Archean granite–greenstone belts and was an important factor in continental crustal growth, particularly during the Late Archean. [Copyright &y& Elsevier]

The Neoproterozoic tectonic pattern of the South China Block (SCB) is considered to be a key element in the Rodinia reconstruction and subsequent Gondwana assembly. Numerous studies have been done on the Neoproterozoic igneous rocks along the SE and NW Yangtze Block of the SCB, but the contemporaneous igneous rocks in the SW Yangtze Block has poorly been known so far. This paper documents a comprehensive set of U–Pb geochronological, elemental and Sr–Nd–Hf isotopic data for the granitic gneiss and migmatite from the Ailaoshan tectonic zone of the SW Yangtze Block on the basis of field investigations. These granitic rocks are mainly granodiorite, monzogranite and quartz diorite and spatially associated with the synchronous mafic and dioritic rocks. On the basis of the A/CNK values and CIPW-normative corundum contents, these samples are subdivided into Group 1 with A/CNK > 1.1 and corundum of 1.5–6.5 vol.% and Group 2 with A/CNK = 0.87–1.09 and corundum = 0–1.5 vol.%, generally similar to the S- and I-type granitic rocks, respectively. The representative samples from Group 1 and 2 give the weighted mean ages of 810–785 Ma and 790–764 Ma, respectively, interpreted as the crystallization ages. They show strong Nb–Ta and P–Ti negative anomalies and variable Eu/Eu ∗ (0.10–0.92). The ε Nd (t) and ε Hf (t) values are in the ranges of −6.5 ∼ −4.2 and −3.8 ∼ +3.1 for Group 1 and of −6.2 ∼ +1.8 and −6.3 ∼ +5.7 for Group 2, respectively. These Neoproterozoic granitic rocks might originate from a hybridization source of metagreywacke with proportionally “ancient” mafic component for Group 1 but with abundant juvenile mafic-derived rocks for Group 2. Our data, along with the available geological observations, demonstrate the extensive occurrence of the Neoproterozoic (761–833 Ma) igneous rocks in the Ailaoshan tectonic zone. The previously-mapped Ailaoshan and Yaoshan groups might be the Complexes including the Neoproterozoic, Triassic and Cenozoic igneous rocks. A persistent and long-lived Neoproterozoic (∼830–760 Ma) subduction zone along the southwestern and northwestern margins of the Yangtze Block from Ailaoshan to Panxi and then to Hannan is proposed. The Yangtze Block might locate at the periphery of Rodinia during the early Neoproterozoic. [ABSTRACT FROM AUTHOR]

Abstract: Elemental, Sr–Nd–Pb isotopic and geochronological data are presented for the Taishan high-mg dioritic rocks (western Shandong) from the Eastern Block of the North China Craton in order to better understand the Archean tectonic evolution and crustal growth of the Craton. The rocks gave the zircon U–Pb age of 2536–2540Ma. They show low SiO2 and Al2O3 contents, high MgO, mg-number, Cr, Ni, Y, Yb, Sr and Ba, enriched LILEs and LREEs, depleted HFSEs and HREEs with (Nb/La)N of 0.07–0.12. They exhibit ɛ Nd(t) values of 1.53–3.30, (206Pb/204Pb)i of 11.20–15.30, (207Pb/204Pb)i of 14.14–14.83 and (208Pb/204Pb)I of 31.10–33.93. Such geochemical features with an affinity to both a mantle- and crust-like source for the Taishan dioritic rocks are similar to those of the typical Archean sanukitoids, suggesting an origination from a sub-arc mantle wedge variably metasomatized by the slab-derived dehydration fluids and melts before ∼50–100Ma of the emplacement of the Taishan sanukitoid plutons. It is proposed that the Taishan sanukitoids resulted from the sudden change of the downgoing slab from a flat subduction to subsequently steeper subduction in an active continental margin regime during Neoarchean time. [Copyright &y& Elsevier]