Search

The Permo-Triassic adakitic magmatism in the southern Korean Peninsula preserves important tectonomagmatic records along the East Asian continental margin. In this study, we present SHRIMP/LA–MC–ICPMS U-Pb zircon ages and Hf isotope signature with whole-rock geochemical compositions of the Middle Permian to Middle Triassic granitoid gneiss-granitoid suites and the Middle to Late Triassic plutonic rocks in the southeastern Korean Peninsula. The former yields three age groups of ca. 272–263 Ma, ca. 258–251 Ma and ca. 243–240 Ma, respectively. The latter group yields ca. 237–216 Ma ages, indicating a long term magmatism that lasted from the Middle Permian to late Triassic. The granitoid gneiss-granitoid suites have chemical compositions similar to high silica adakitic rocks, showing high SiO2 (59.55–73.97 wt.%), Na2O (3.55–5.30 wt.%), Sr/Y (30–401), and La/YbN (11–173), and low MgO (0.18–1.82 wt.%), Y (2–14 ppm) and YbN (2–7). These rocks are peraluminous with high Ba and Sr, and show relatively high K2O contents and K2O/Na2O ratios (> 0.7), with positive correlation between La/YbN vs. Sr/Y ratios and high initial Sr ratios. These features reflect different contribution of the slab-derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the Middle Paleoproterozoic lower crustal basement of the Yeongnam Massif. On the contrary, the Triassic alkaline magmatism in the Yeongnam Massif is alternatively interpreted either by a tectonic switch to the extension-dominated arc system or by a delamination of an overthickened arc. The results from this study offer important evidence for a common subduction-accretion system existed between the North and South China Cratons and microcontinents between them along margins of the East Asian continental blocks, with different plate interaction in different locations generating distinct magmatic suites.

The eastern part of the North China Craton suffered significant lithospheric thinning since the Mesozoic, and petrogenesis of the Dagushan adakitic diorite porphyries provides an excellent opportunity to investigate the lithospheric thinning mechanism and geodynamic setting. The zircon LA-ICP-MS U–Pb geochronology reveals that the representative Dagushan adakitic porphyry was formed at 120.5 ± 0.5 Ma. The Dagushan diorite porphyries are characterized by the relatively high contents of SiO2 (64.25–65.70 wt%), Al2O3 (15.00–15.38 wt%), Sr (333–491 ppm), low contents of Y (6.50–10.3 ppm), and Yb (0.57–0.85 ppm), and resultant high Sr/Y (47–57) and La/Yb (37–55) ratios, exhibiting geochemical characteristics of typical adakites. Moreover, the relatively high MgO contents (MgO = 2.23–2.29 wt%) and Mg numbers (Mg# = 54–56) of the Dagushan adakitic rocks imply that the pristine adakitic magma interacted with mantle peridotite. However, the zircon Hf isotopic signatures (eHf(t) = − 19.0 to − 28.0; TDM2 = 2378–2944 Ma) suggest an ancient lower crustal source. Therefore, it is proposed that the Dagushan adakitic rock was probably generated by partial melting of delaminated lower crust which was triggered by the Tan-Lu Fault Zone, and the interaction of pristine adakitic magma with mantle peridotite during the ascent finally generated the Dagushan high Mg# adakitic rocks. It is suggested that delamination was an important mechanism for lithospheric thinning of the NCC.

The East Kunlun orogenic belt (EKOB) is located in the northeastern part of the Qinghai-Tibetan Plateau, China. Voluminous Silurian-Devonian granitoids were formed during the Proto-Tethys Ocean subduction and collision process. In this study, zircon U-Pb age dating, in-situ Hf isotope analyses, and whole rock major and trace element analyses have been carried out on granitoids from the central to eastern EKOB. The formation ages of granodiorite in the Bairiqili area, the granodiorite in the Wulonggou area are 410 ± 2 Ma and 396 ± 1 Ma, respectively, and the granodiorites show I-type features. The Wulonggou syenogranite with a formation age of 398 ± 2 Ma has a high differentiation index (D.I. = 89.59–92.43), and may belong to the high fractionated I-type granite. The Lalangmai tonalite with a formation age of 423 ± 2 Ma has high Sr (339–590 µg/g), eHf(t) (1.5–7.3), and low Y (3.45–6.33 µg/g), which are similar to modern adakites. The Lalangmai tonalite is the latest adakite record during the Proto-Tethys evolution in EKOB. Combined with previous studies, it is concluded that the granitoids from Cambrian to Devonian divided into four episodes. The first episode (515–436 Ma) mainly consists of I-type island arc granites and adakite, which are formed in a subduction environment. The second episode (436–427 Ma) is characterized by the S-type granites related to the collision. The third episode (427–420 Ma) is the transition period between the collision and the post-collision environment. In the fourth episodes (420–385 Ma), granitoids were formed in post-collision extensional environment, which is characterized by I-type and A-type granites. The upwelling of asthenosphere material is likely caused by the collapse of the orogenic belt. After 420 Ma, I-type and A-type granites formed at different depths but in the same environment.

The 60 km-long Pan-African Bape massif intruded in the Adamawa-Yade Archaean block is an excellent case for the study of subduction–collision-related magmatism, its origin by interaction among magmas from various sources, and its bearing on the evolution of the Pan-African orogenic belt in Cameroon. An integrated study including mapping, petrography and geochemistry was carried out on these Ba–Sr rich quartz monzonites, quartz monzodiorites, monzonites, granodiorites (adakites), syenites and micromonzogabbros. The rocks are dominated by plagioclase + alkali feldspars + amphibole + biotite + sphene + opaque minerals + apatite + zircon ± pyroxene ± quartz assemblage. They are I-type, ferroan, metaluminous and belong to high-K calc-alkaline, shoshonitic series. REE patterns form two sets of tight closed and of highly differentiated patterns. The spider diagrams display Th, U, Nb, Ta, Zr and Hf negative and Ba, K, Pb and Sr positive anomalies. High K2O, Ba–Sr and moderate SiO2 contents and the variation of canonical ratios such as Zr/Sm, Zr/Hf, La/Sm, and Sm/Yb, point to multiple origins for the Bape granitoids such as (i) melting of a dehydrated subducting crust (adakites) and/or the metasomatized heterogeneous mantle wedge (spinel– and phlogopite–amphibole–garnet lherzolite), or (ii) the mixing of these liquids (other granitoids). The U–Pb emplacement age (640–603 Ma), coeval with the subduction–collision between the West-African and the Congo cratons, the occurrence of adakites, combined with geophysical data, support that these granitoids are link to the southeast–northwest subduction of the hot Yaounde oceanic crust under the Adamawa-Yade craton, during the Neoproterozoic time.

Diverse origins have been proposed for continental adakites, with great emphasis on high-pressure melting of the lower crust. However, the source composition is usually ignored in interpret...

U–Pb zircon dating of felsic volcanic rocks from the Konachan Complex (Algan Mountains, northwestern Koryak Highland) confirmed their Late Miocene age (34.6 ± 0.5–38.8 ± 0.4 Ma, Priabonian). It is shown that these rocks are represented by moderate-potassium peraluminous (ASI = 1.23–1.30), moderate- and high-Mg varieties, frequently with high Cr and Ni contents. The Sr, Y, and Yb contents are similar to those of adakites. The high 143Nd/144Nd and low 87Sr/86Sr ratios in the rocks of the complex in combination with their trace and rare-earth distribution patterns suggest that metabasites weakly contaminated by sedimentary material were one source of silicic melt. The magmatic rocks of the Konachan Complex were formed during accretion of the terranes of the Olyutorka–Eastern Kamchatka island-arc system; the compression locked the upwelling front of continental asthenosphere, thus initiating crustal anatexis and silicic magmatism.

Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites. However, the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks. In this work, we performed partial melting experiments at 1.5 ​GPa and 800–950 ​°C on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area, northern margin of the North China Craton. The experimental melts range from granitic to granodioritic compositions, with SiO2 ​= ​56.4–72.6 ​wt.%, Al2O3 ​= ​16.1–19.3 ​wt.%, FeO∗ ​= ​2.4–9.6 ​wt.%, MgO ​= ​0.3–2.0 ​wt.%, CaO ​= ​0.6–3.8 ​wt.%, Na2O ​= ​4.7–5.3 ​wt.%, and K2O ​= ​2.6–3.9 ​wt.%, which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks, except for the higher Al2O3 contents and the data point at 1.5 ​GPa and 800 ​°C. Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr (849–1067 ​ppm) and light rare earth elements (LREEs) and poor in Y (

New petrological, whole-rock geochemical, zircon U–Pb geochronological, and zircon Lu–Hf isotopic data have been reported for Early Cretaceous intrusive rocks in the Wulong region of the Liaodong Peninsula on the North China Craton. The zircon U-Pb chronology shows that the crystallization age of six groups of intrusive rocks from this region is 129–123 Myr ago. These intrusive rocks can be categorized into A-type granite (granodiorite), K-rich adakite (porphyritic-like monzogranite), highly fractionated I-type granites (porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite), and gabbro. These granitoids are shown to have negative zircon eHf(t) values(-21.0 to -11.1) with old two-stage Hf model ages (TDM2(Hf)) (1.88–2.50 Ga), while gabbro has higher zircon eHf(t) values(-14.3 to -9.4) with younger TDM2(Hf) (1.77–2.08 Ga) model ages. According to our results, we believe that the porphyritic-like monzogranite was produced through partial melting of the thickened eclogitic lower crust, the gabbro was generated by partial melting of a source formed by the mixing of enriched lithospheric mantle and delaminated eclogitic lower crust, the granodiorite was formed by mixing crust materials and mafic melts, the porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite originated from the medium- to high-K basaltic lower crust. The bimodal intrusive rocks (gabbro, porphyritic-like monzogranite, and porphyritic-like biotite monzogranite) and A-type granites (granodiorite) were emplaced in an extensional setting associated with Paleo-Pacific Plate subduction. We also determined that the tectonic setting changed from extension to transpression during 125–120 Myr ago (porphyritic-like syenogranite and syenogranite). Moreover, we confirmed the hypothesis that the Early Cretaceous delamination is the result of Paleo-Pacific Plate subduction.

The tectonic setting of Jurassic magmatism in the Northeast China (NE China) is unclear. Here, we present new petrological, whole-rock geochemical, zircon U-Pb geochronological, and zircon Lu-Hf isotope data for Jurassic granitoids of the Wulong region, Liaodong Peninsula, NE China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb data indicate that these granitoids were emplaced at 165–156 Ma. The biotite monzogranite, two-mica monzogranite, monzogranite, granodiorite, biotite granodiorite, and syenogranite are strongly peraluminous (A/CNK=1.09–1.29), contain peraluminous minerals such as muscovite, have high normative corundum abundances (1.26 wt.%–3.28 wt.%), and have high K2O/Na2O ratios (0.76–1.48), all of which indicate an S-type granite affinity. However, the biotite granodiorite and syenogranite have high Sr (391 ppm–570 ppm) and low Y (3.06 ppm–5.94 ppm) contents, with high Sr/Y (65.8–185.9) ratios, and the two-mica monzogranite, monzogranite, and granodiorite have relatively high Sr (138 ppm–379 ppm) and low Y (3.38 ppm–8.71 ppm) contents, with high Sr/Y ratios (19.1–77.9). All of the analyzed samples have negative zircon eHf(t) values (−41.4 to −20.6) with old two-stage Hf model ages (TDM2(Hf)=2.50–3.76 Ga). Therefore, we infer that the biotite monzogranite is the typical feature of S-type granite that was derived by partial melting of metagraywacke. The monzogranite, two-mica monzogranite, granodiorite, biotite granodiorite, and syenogranite exhibit geochemical characteristics of S-type granite with K-rich adakitic features, and were possibly derived by mixing of melts from clastic crustal materials and adakitic magmas. There are voluminous Jurassic igneous rocks in the NE China. By combining our study with the previous researches, this paper infers that the Jurassic magmatism within the Erguna-Xing’an Massif was related to the southward subduction and closure of the Mongol-Okhotsk Ocean; the Early Jurassic magmatism to the east of the Songliao Basin and in the northern North China Craton (NCC) was related to the subduction of the Pacific Plate; however, the Middle-Late Jurassic igneous rocks to the west of the Songliao Basin were related to the closure of the Mongol-Okhotsk Ocean and, in the northern NCC, were related to closure of the Mongol-Okhotsk Ocean with an influence from flat-slab subduction of the Pacific Plate.

Mesozoic magmatic rocks are widely distributed in the North China Craton (NCC) and are crucial to understanding the timing, location, and geodynamic mechanisms of lithospheric thinning of the NCC. In this study, we report geochronological, petrogeochemical, and Lu–Hf isotopic data for adakitic granitoids from different parts of Xiuyan pluton in the Liaodong Peninsula, aiming to constrain their magma sources, petrogenesis, and tectonic implications. The adakites are metaluminous to weakly peraluminous and are classified as high-K calc-alkaline I-type granite with Early Cretaceous zircon U–Pb ages of 129–126 Ma. They exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y and no pronounced Eu anomalies. They are enriched in Rb, U, and light rare-earth elements and are depleted in Ta, Nb, P, and Ti. The adakites from the eastern part of the pluton have low εHf(t) values (–8.5 to –4.0) with old TDM2 ages (1.57–1.31 Ga), indicating they were derived from the lower crust containing juvenile mantle-derived materials. In contrast, adakites from the northern part of the pluton have lower εHf(t) values (–19.7 to –16.6) with older TDM2 ages (2.21–2.03 Ga), indicating that they were derived mainly from an ancient crust. Our results show that both adakitic magmas were derived from partial melting of delaminated lower crust. Their relatively high MgO and Ni contents and Mg# values indicate that the melts interacted with mantle peridotites. The lower crust delamination beneath the Liaodong Peninsula resulted from paleo-Pacific plate subduction during the Early Cretaceous, which resulted in thinning of Mesozoic crust in the Xiuyan area.

Testing of the geochemical compositions of the Late Cenozoic volcanites of Kamchatka on new discriminant diagrams confirmed the idea of the existence of different geodynamic regimes at this time. It is shown that the Late Miocene (~6 Ma)-Pliocene volcanites of Eastern Kamchatka and the Central Kamchatka Depression, as well as the Late Pliocene (~3.5 Ma)-Holocene alkaline, calcareous-alkaline, and adakite volcanites of the central part of the Middle Ridge are similar to the volcanites of the transform margins of the Pacific type. At the same time, the Miocene–Holocene volcanites of Southern Kamchatka, the Miocene-Early Pliocene volcanites of the Middle Ridge, and the Pleistocene–Holocene volcanites of Eastern Kamchatka are similar to the volcanites of the convergent margins. In the central part of Kamchatka (from the coast to the Middle Ridge), at the end of the Miocene-Pliocene, during the collision of the Kronotsky terrane of the island arc and the slip of the Pacific plate, magmatic complexes typical of the transform margin were formed in this area. The geochemistry of the transform margin volcanites is due to the upwelling of the subslab asthenosphere both into the collision zone and into the zone of the volcanic arc of the Middle Ridge, after the rupture and subsequent separation of the Komandor-Kronotsky microplate slab.

Adakitic rocks are intermediate-acid magmatic rocks characterized by enrichment in light rare-earth elements, depletion in heavy rare-earth elements, positive to negligible Eu and Sr anomalies, and high La/Yb and Sr/Y ratios. Cenozoic adakitic rocks generated by partial melting of subducted oceanic crust (slab) under eclogite-facies conditions (i.e., the original definition of “adakite”) occur mainly in Pacific Rim volcanic arcs (intra-oceanic, continental, and continental-margin island arcs), whereas those generated by partial melting of thickened lower crust occur mainly in Tethyan Tibetan collisional orogens. In volcanic arcs, adakitic melts derived from the melting of subducted oceanic crust metasomatize the mantle wedge to form a unique rock suite comprising adakite-adakite-type high-Mg andesite-Piip-type high-Mg andesite-Nb-rich basalt-boninite. This suite differs from the basalt-andesite-dacite-rhyolite suite formed from mantle wedge metasomatized by fluids derived from subducted oceanic crust. Previously published data indicate that partial melting of mafic rocks can generate adakitic magmas under pressure, temperature, and hydrous conditions of 1.2–3.0 GPa, 800–1000°C, and 1.5–6.0 wt.% H2O, respectively, leaving residual minerals of garnet and rutile with little or no plagioclase. Cenozoic Au and Cu deposits occur proximally to adakitic rocks, with host rocks of some deposits actually being adakitic rocks. Adakitic rocks thus have important implications for both deep-Earth dynamics and Cu-Au mineralization/exploration. Although studies of Cenozoic adakitic rocks have made many important advances, there remain weaknesses in some important areas such as their tectonic settings, petrogenesis, magma sources, melt-mantle interactions of pre-Cenozoic adakitic rocks, and their relationship with the onset of plate tectonics and crustal growth. Future research directions are likely to involve (1) the generation of adakitic magmas by experimental simulations of partial melting of different types of rock (including intermediate-acid rocks) and magma fractional crystallization at different temperatures and pressures, (2) the relationship between magma reservoir evolution and the formation of adakitic rocks, (3) the tectonic setting and petrogenesis of pre-Cenozoic adakitic rocks and related geodynamic processes, (4) interactions between slab melts and the mantle wedge, (5) the formation of Archean adakitic tonalite-trondhjemite-granodiorite and its link to the onset of plate tectonics and crustal growth, and (6) the relationship between the formation of adakitic rocks and metal mineralization in different tectonic settings.

It is still hotly debated whether the subduction of the Indus-Yarlung Zangbo Tethyan oceanic lithosphere led to Cretaceous magmatism in the north Lhasa terrane or not. Here, we provide new data on ...

Modern oceans contain large bathymetric highs (spreading oceanic ridges, aseismic ridges or oceanic plateaus and inactive arc ridges) that, in total, constitute more than 20–30% of the total area of the world’s ocean floor. These bathymetric highs may be subducted, and such processes are commonly referred to as ridge subduction. Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics, they also play an important role in the generation of arc magmatism, material recycling, the growth and evolution of continental crust, the deformation and modification of the overlying plates, and metallogenesis at convergent plate boundaries. Therefore, these events have attracted widespread attention. The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window, and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt (OIB) or a mid-oceanic ridge basalt (MORB)-type rock suite, and is closely associated with Au mineralization. Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct, to typically collide with arcs or continents or to induce flat subduction (low angle of less than 10°) due to the thickness of their underlying normal oceanic crust (> 6–7 km) and high topography. However, the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic. On the eastern side of the Pacific Ocean, aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents, which may cause a magmatic gap. But slab melting can occur and adakites, or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing. Cu-Au mineralization is commonly associated with such flat subduction events. On the western side of the Pacific Ocean, however, aseismic ridges and oceanic plateaus are subducted at relatively high angles (>30°). These subduction processes can generate large scale eruptions of basalts, basaltic andesites and andesites, which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge. In addition, some inactive arc ridges are subducted beneath Southwest Japan, and these subduction processes are commonly associated with the production of basalts, high-Mg andesites and adakites and Au mineralization. Besides magmatism and Cu-Au mineralization, ridge subduction may also trigger subduction erosion in subduction zones. Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events, clarifying the associated geodynamic mechanisms, quantifying subduction zone material recycling, establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization, establishing criteria to recognize pre-Cenozoic ridge subduction, the onset of modern-style plate tectonics and the growth mechanisms for Archean continental crust.

The Delamerian Orogen formed at the final stages of assembly of the Gondwana supercontinent. This system marks the initiation of subduction of the Pacific oceanic lithosphere along a prior rifted and extended passive margin. This paper explores the magmatic consequences following the early Cambrian initiation at the palaeo-Pacific margin in South Australia (SA) and western Victoria. Our data reveal a 50 Ma syn- to post-Delamerian tectono-magmatic history. Sampled from drill core from beneath the eastern Murray Basin cover in eastern SA, boninitic high Mg andesite from drill hole KTH12 and 516.1 ± 2 Ma quartz diorite suggest that first subduction established a volcanic arc within easternmost SA. Pacific-ward trench retreat then resulted in arc migration to reach the Mt Stavely Belt and Stawell Zones in western Victoria by ~510 Ma where boninitic arc magmatism continued until ~490 Ma. In the SA foreland of the Delamerian Orogen, early (522 ± 4 Ma) alkali basalt gave way to intrusion and extrusion of MORB-like tholeiites of back-arc basalt character. Through much of the middle and late Cambrian the SA Delamerian was in the back-arc and under extension but with periodic compression resulting from periodic Pacific-Australian plate coupling beneath the forearc in western Victoria. In SA syn-tectonic I- and S-type granites reflect interaction of MORB-like back-arc magmas and their transported heat with continental-derived sediment of the Kanmantoo Group. The termination of the Delamerian orogeny at ~490 Ma was accompanied by buoyancy-controlled, exhumation and erosion. This was driven by delamination of a mafic, crustal underplate, whose re-melting at 1.5 to 2 GPa and 1050 °C generated the unique 495 ± 1 Ma Kinchina/Monarto adakite. Delamination resulted in lithospheric mantle thinning and local convective overturn allowing upwelling of the asthenosphere to drive the post-kinematic magmatic phase of the Delamerian, yielding voluminous 490 Ma–470 Ma A-type granites.

This paper presents new data on rocks dredged from the Hahajima Seamount during the cruise KH03-3 of R/V Hakuho-Maru in 2003. It is shown that the seamount is a tectonically displaced block of the Earth’s crust composed of island-arc ophiolites. The basement of the ophiolite complex is made up of highly depleted mantle residue (dunites and harzburgites). Upward, they grade into cumulate lherzolites, various gabbroids, dolerites, and basalts. This complex marks the initial stages of island-arc evolution: formation of an oceanic crust of the marginal sea. Upward, the section is built up of the island-arc rock association consisting of tholeiites, boninites, and adakites. New data on mineralogy and geochemistry of the studied rocks are reported. The ophiolitic complex served as the basement for island-arc association and was affected by the powerful heat flow that resulted in repeated melting of mantle residue and metamorphism of the above rocks.

The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane (SLT) of the eastern North China Craton (NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt (Group#1), basaltic andesite (Group#2), dacite (Group#3) and rhyodacite (Group#4). LA-ICP-MS zircon U–Th–Pb dating reveals that they formed at ~2.53–2.51 ​Ga. Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element (REE) patterns with low (La/Yb)N ratios and a narrow range of (Hf/Sm)N ratios, and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids. Compared to Group#1 samples, Group#2 samples display strongly fractionated REE patterns with higher (La/Yb)N ratios and more scattered (Hf/Sm)N ratios, indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids. Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns, which resemble typical high-Si adakites, and the magmatic precursors were derived from partial melting of a subducted oceanic slab. Group#4 samples have the highest SiO2 and the lowest MgO and transition trace element contents, and were derived from partial melting of basaltic rocks at lower crust levels. Integrating these tholeiitic to calc-alkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses, the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin. Furthermore, the affinities in lithological assemblages, metamorphism and tectonic regime among SLT, eastern Hebei to western Liaoning Terrane (EH–WLT), northern Liaoning to southern Jilin Terrane (NL–SJT), Anshan-Benxi continental nucleus (ABN) and Yishui complex (YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC. Keywords: Late Neoarchean, Volcanic rocks, Subduction, Southern Liaoning Terrane, Eastern North China Craton

The Neoarchean crust-mantle interaction and crustal evolution of the North China craton are controversial and are instructive of the processes of continental crust growth and cratonic evolution. We present here a systematic study of the petrology, geochemistry, and geochronology of Neoarchean granitoids from the eastern North China craton to elucidate their petrogenesis and tectonic setting. The rocks were collected from the Jielingkou, Anziling, and Qinhuangdao plutons, and an amphibole-monzoporphyry dike in the Qinhuangdao pluton. Samples from the Jielingkou pluton, consisting dominantly of monzodiorite and diorite with minor monzonite and granodiorite, contain 52.2-64.4 wt% SiO2, 2.46-4.52 wt% MgO (Mg# = 0.41-0.54), 3.76-5.77 wt% Na2O, and K2O/Na2O ratios of 0.29-0.71. The Anziling pluton samples, comprising syenite and monzonite, display slightly higher SiO2 (60.9-66.7 wt%) and K2O/Na2O ratios (0.70-1.11), but lower MgO (1.54-2.33 wt%) and Mg# (0.40-0.47) values, compared to the Jielingkou rocks. The Qinhuangdao pluton samples, consisting mainly of granite and minor syenite and granodiorite, with some diorite and monzoporphyry dikes, are characterized by the highest SiO2 values (75.7-76.9 wt%) and K2O/Na2O ratios (0.73-1.41) and lowest MgO content (0.14-0.32 wt%) among the studied samples. The amphibole-monzoporphyry dike has intermediate SiO2 (56.3 wt%), high MgO (3.79 wt%), Na2O (5.55 wt%), and Mg# (0.45), and low K2O/Na2O ratio (0.66). Zircon U-Pb laser-ablation-inductively coupled plasma-mass spectrometry dating showed that all plutons have a ca. 2.5 Ga crystallization age. Zircon crystals have mildly positive εHf(t) values (+0.24 to +5.45) and a depleted mantle model age (TDM1) of ca. 2.7 Ga. We interpret the granitoid rocks as sanukitoid-related, Closepet-type granites, potassium-rich adakites, and potassium-rich granitoid rocks that crystallized in the late Neoarchean (2.5 Ga) and were derived from partial melting of mantle peridotite that was metasomatized with the addition of slab melt, thickened alkali-rich juvenile lower crust and juvenile metamorphosed tonalitic rocks. Mantle plume activity ca. 2.7 Ga is thought to have been responsible for the early Neoarchean tectono-thermal event in the eastern North China craton. This activity resulted in a major crustal accretion period in the craton, with subordinate crustal reworking at its margins. A steep subduction regime between ca. 2.55 Ga and ca. 2.48 Ga led to the remelting of older crustal material, with subordinate crustal accretion by magma upwelling from a depleted mantle source resulting in late Neoarchean underplating. This crustal reworking and underplating resulted in the widespread ca. 2.5 Ga plutons in the eastern North China craton. Continental crust growth in the North China craton thus occurred in multiple stages, in response to mantle plume activity, as well as protracted subduction-related granitoid magmatism during the Neoarchean.

Late Neoarchean metavolcanic rocks are widely distributed in the Western Shandong Terrane (WST). They are classified as ~2590–2580 Ma tholeiites (Group MB-1), ~2550–2530 Ma tholeiites (Group MB-2), calc-alkaline basalts (Group MB-3), high-Si adakites (Group MAD) and ~2520–2500 Ma tholeiites (Group MB-4) based on zircon U-Pb chronological and geochemical data. Their parental magmas have complex origins and were derived from a depleted mantle wedge enriched by slab-derived melts or fluids (Group MB-1); an unaltered depleted mantle (Group MB-2); the delaminated lower crustal materials (Group MAD); a strongly melt- and fluid-metasomatized depleted mantle (Group MB-3); and a fluid- and sediment-metasomatized asthenospheric mantle (Group MB-4). The late Neoarchean geodynamic evolution of the WST revealed by these multi-genetic volcanic rocks can be summarized as follows: (1) an ~2.62–2.53 Ga eastward subduction operated along the ancient continental margin, followed by delamination of unstable continental lithosphere in the back-arc region during ~2.60–2.53 Ga; and (2) delamination-derived mantle magmas ascended and caused the regional extension, further inducing the asthenosphere to passively rise and the back-arc basin to open during ~2.52–2.50 Ga. The above intense mantle magmatism and crust-mantle interactions have consumed abundant mantle energy and facilitated the continental stratification and final cratonization of the WST.

A study of the composition and the age (U–Th–Pb method for zircon, SIMS) of the Neoarchean volcanic rocks of the Khedozero-Bolshozero greenstone structure of Central Karelia was carried out. The volcanogenic sequence of this structure is composed primarily of dacites and andesite-dacites, and to a lesser extent of andesites and andesite basalts. The ultra-felsic volcanic rocks, previously attributed to the sequence, compose intersecting dikes and are represented by rhyolite porphyry. According to geochemical characteristics, the volcanic rocks of the sequence are similar to the basalt-andesite-dacite-rhyolite rock series of modern island arcs, their chemical composition being comparable with the high-silica and low-silica adakites. The age of andesibasalts and dacites of the Khedozero-Bolshozero structure is Neoarchean: 2705 ± 9 Ma for andesibasalts and from 2712 ± 6 to 2703 ± 7 Ma for dacites. The Nd isotopic composition shows that the sources of melts for volcanic rocks were mixed owing to the mantle–crust interaction. The ancient Sm–Nd model ages and low eNd values (0.4 and 0.3) of dacites indicate a significant part of the crustal source in the initial melt. The younger model age of meta-andesibasalts and the high value of eNd (2.8) indicate the predominantly mantle nature of lavas with a minor crustal contamination. According to the age of crystallization, dikes of rhyolite porphyry (2704 ± 12 Ma) are close to the volcanic rocks of the sequence, but they have geochemical differences and a more ancient crustal protolith (3.17 Ga). As compared to the rocks of the Kontok Group of the Kostomuksha greenstone belt, the Khedozero-Bolshozero volcanic rocks have a different composition, a younger age, and a higher position in the stratigraphic scale. It is possible that alternative geodynamic settings, such as an active continental margin, turning into collision, or the combined action of the mantle plume and plate tectonics, led to the formation of the rocks studied.

A model of the geological evolution of the Sea of Okhotsk is presented based on data from radioisotope age determinations and the mineral and isotope-geochemical composition of Late Mesozoic–Cenozoic volcanic rocks. We discuss the probable interrelationship between gas geochemical manifestations of gas fluxes with anomalous methane concentrations and the formation of gas hydrates, along with the occurrence of volcanic processes in the Sea of Okhotsk, fault zones, and different geological structures of basement and sedimentary deposits, landslides, and earthquakes. As a result of the studies, the nature of each volcanic stage has been determined. These include the Late Cretaceous continental-marginal belt stage (calc-alkaline), the Eocene transform-marginal (adakite) stage, and the Pliocene-Pleistocene island arc stage in the southern part of the Sea of Okhotsk. The sources of magma generation have been recognized, namely, the lithosphere subcontinental, asthenosphere oceanic, and plume-oceanic (OIB). The change in geodynamic regimens was traced back from the Late Cretaceous subduction regimen to the Maastrichtian–Datian transform-marginal, which continued as far as the Pliocene and ended at the resumption of the Pliocene–Pleistocene subduction of the Pacific Plate beneath the Eurasian continent. This involved the processes of destruction of the subduction plate, lithosphere and asthenosphere diapirism, and lower mantle plume upwelling. In the periods of geodynamic, seismotectonic and volcanic activities, gas migrated along the fault zones from the depth to the surface, together with different volcanic substrates ascending through the upper and lower mantle. Gas contained CO2, CH4, H2, He, N2, O2, and superheated steam (Н2О). Gas plays an important dynamic and physicochemical role in the evolution of the Sea of Okhotsk. At the present stage, gas fluxes migrating from the depth to the surface manifest as gas bubbles penetrating from the bottom sediments into the water column, with some portion of gas penetrating into the atmosphere. In the areas with gas fluxes, the fields containing anomalous concentrations of hydrocarbons, gas hydrate, carbon dioxide, hydrogen, and helium result in the formation of gas hydrates and associations of authigenic minerals and various geochemical elements.

Bangong-Nujiang Suture Zone (BNSZ) in central Tibet plays an important role in evaluating the formation and uplift mechanism of Tibetan Plateau. However, its Mesozoic tectonic evolution is ambiguous and intensely debated. In this study, Early Cretacesous adakites and sodium-rich arc rocks are identified in Western Qiangtang (WQ) and Northern Lhasa (NL) sub-terranes. Forty-four adakite samples from both WQ and NL have akin geochemical features, and are derived from partial melting of subducted oceanic crust with amphibole residual. Nineteen sodium-rich samples originated from a mixed source region between crustal sediment and enriched lithospheric mantle. These two parallel arc belts separated by the Bangong-Nujiang Suture Zone (BNSZ) represent the divergent double subduction of the Bangong-Nujiang Tethyan Ocean (BNTO). Combined with the previous studies, our new data suggest three significant magmatic flare-ups at ∼240–140 Ma, 135–105 Ma and 92–60 Ma in the WQ and BNSZ, and two at 135–105 Ma and 92–60 Ma in the NL. These asymmetrical magmatic activities indicate that the southern subduction may have commenced at about 135 Ma and experienced slab breakoff at the latest Early Cretaceous, and the northern subduction could trace back to L-Triassic (228 Ma) and experienced episodic low-angle subduction, slab rollback (190-140 Ma) and oceanic ridge subduction (135-100 Ma). The 100–92 Ma magmatic gap, 92–60 Ma magmatic flare-up and L-Cretaceous angular unconformities indicate that the double-sided subduction of the BNTO resulted in soft collision with oceanic lithosphere detachment.

The tracing of Triassic arc magmatism is much-debated for a long time along the Sakarya Composite Terrane in Turkey and the southern Black Sea region. The Dodurga Pluton is located in the Central Pontides (N Turkey), one of the most complicated regions around the Black Sea region, and represents the first documented middle Triassic continental arc in the region. This pluton comprises of dacite porphyry and granodiorite, and displays calc-alkaline signatures, which is in agreement with arc-related and I-type magmas. The PM-normalized multi element and CN-normalized REE patterns are akin to volcanic arc granites, and characterized by LILEs and LREEs enrichments relative to HFSEs and HREEs coupled with negative Nb anomalies, which confirm derivation in a subduction-related tectonic setting. Moreover, the major and trace element systematics of the samples including higher Sr/Y ratios (22.93–101.36) and lower Yb contents (0.31–1.30 ppm) are consistent with those from adakitic melts compared to classical arc magmas. Therefore, this pluton also represents the first middle Triassic adakite-like magmatic occurrence in Turkey. Overall petrographic and geochemical signatures reported here indicate that the Dodurga Pluton might have been derived from a heterogeneous source, mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin. Based on the Tethyan evolution in the Anatolian realm, three geodynamic scenarios are possible for its formation, and it could have been formed as a result of northward or southward-subduction of the Paleotethys Ocean or northward-subduction of the northern branch of Neotethys Ocean during the middle Triassic.

In the eastern North China Craton (NCC), Mesozoic tectonics was dominated by the Paleo-Pacific subduction rollback and the Tanlu crustal-scale fault movement. The regional transtension had generated extensive adakitic magmatism, some Cu-Au ore-forming but others not. To establish the geodynamic setting and any metallogenic link for the adakites from the southeastern NCC margin, we analyzed the ore-barren adakitic rocks from underground mines in the Huaibei-Linhuan coalfield (where surface igneous outcrops are scarce), and compared their ages and geochemistry with other mineralized and ore-barren adakites across Eastern China. Zircon U-Pb dating reveals two magmatic episodes in the Huaibei-Linhuan coalfield: 1) early-Early Cretaceous (ca. 130–129 Ma) (quartz-)diorite and granodiorite, and 2) late-Early Cretaceous (ca. 115.8 and 105.8 Ma) microgabbro and dolerite. Whole-rock geochemistry indicates that the (quartz-)diorite and granodiorite are high-Mg adakitic, featured by low K2O/Na2O (avg. 0.33), high Sr/La (avg. 44.3), and lack of correlation between SiO2 (fractionation index) and Sr/Y (avg. 56.55) and MREE/HREE (avg. 1.09), resembling typical adakites derived from oceanic-slab partial melting. Geochronological correlation with the regional tectonic events suggests that the slab-melting may have been caused by the Paleo-Pacific subduction rollback. Further extension and crustal thinning in the late-Early Cretaceous along the southern Tanlu fault may have formed the gabbro-dolerite in the coalfield. Geochemical comparison suggests that parental magma of the Huaibei-Linhuan adakites may have had similar water content [similar zircon 10,000*(Eu/Eu*)/Y and Eu/Eu* ratios] to typical porphyry Cu-Au ore-forming magmas, yet the former may have been considerably more reduced (lower zircon Ce/Nd and whole-rock V/Sc ratios). We considered that the assimilation of Carboniferous-Permian coal seams in the area may have further lowered the magma fO2 and thus its potential to form Cu-Au mineralization.

The results of petrological-geochemical and isotope-geochemical studies of the Late Pleistocene-Holocene lavas of the Kazbek Neovolcanic Center, one of the largest centers of youngest magmatism in the Greater Caucasus, are presented. It has been established that the volcanic rocks of the Kazbek center arise a continuous compositional series basaltic (trachy-)andesites(trachy-)andesitesdacites with a predominance of calc-alkaline intermediate and moderately-acid lavas. The obtained results indicate that the processes of fractional crystallization and mixing of melts had a leading role in the petrogenesis of the rocks. The crustal assimilation was of limited importance; its influence is noticeable only in the rocks of the earliest and late pulses of magmatic activity within the Kazbek center. The common crustal lithologies participated in the assimilation were presented by metamorphosed Jurassic sediments (mainly shales and sandstones), forming the foot of the Kazbek center, and Mesozoic mafic metamorphosed volcanites very rarely. The specific features of AFC processes during the development of the studied magmatic system (including the presence of noticeable amount of water in the melt, the leading role of Amp in the cumulus and the absence of Pl fractionation) led to the appearance of dacitic lavas with geochemical signs of adakites as an evolutional end-member. The volcanic rocks of the Kazbek center are derived from trachybasalt magmas, the source of which was presented by the mantle reservoir of OIB-type. Recent and previously published results of studies of the Neogene-Quaternary magmatism manifested within the Greater Caucasus show that the main petrological and geochemical characteristics of this regional mantle reservoir remained constant from the end of the Miocene to the present time.

An Ediacaran complex of dyke rocks has been identified for the first time in the Yenisei Ridge orogen. These igneous rocks are represented by basic, intermediate and acid variants and formed in the conditions of the transform active continental margin at the stages of its development before and during the interruption of subduction and slab breakoff: from dykes of the picrodolerite - ​dolerite-quartz diorite - leucogranite association with age in the range of 626-623 Ma (U-Th-U isotope data for zircons, SHRIMP-II method, this work) up to adakite - gabbro-anorthosite magmatism at the end of the Ediacaran.

The timing of major tectonic events and the driving mechanisms for magma generation during Late Cenozoic convergence and collision between Arabia and Eurasia still remain unknown. The Sakarya Zone (SZ) in northern Turkey is a critical member of this collisional assemblage. In the easternmost part of the SZ, we have recognized a Late Miocene volcanic suite termed the Cagirankaya volcanics which displays characteristic post-collisional geochemical features. Here, we report a new data set of zircon U-Pb ages, whole-rock major and trace element, as well as Sr-Nd isotope analyses for dacite and and esite samples from the cagirankaya volcanics. Zircon U-Pb ages for a selected dacitic sample average 5.16 +/- 0.11 Ma (mean square of weighted deviates. MSWD = 0.45, n = 35), confirming a late Miocene age of this volcanic episode. The high-K calc-alkaline andesites and dacites exhibit an adakite-like geochemical signature, and are characterized by high Sr (424 to 552 ppm), Sr/Y ratios (31-43), and low Mg# (42 to 46) values, along with low Y (12-14 ppm) and heavy rare earth element (HREE) concentrations, that resemble those in adakites formed by partial melting of hot oceanic slab during subduction. Isotopic compositions are near bulk Earth (Sr-87/Sr-86(t) = 0.70482 to 0.70489, epsilon(Nd)(t) = +1.08 to +133), which rules out a solely asthenospheric origin. Elevated Nb/Ta (14 to 17) and K2O/Na2O (0.6-1.0) imply a juvenile mafic lower crustal source composed of similar to 20% garnet-bearing amphibolite. Geochemical modeling suggests that adakite-like parental melts were generated in the absence of subduction and without large-scale delamination of lower continental crust. Instead, our findings suggest that Late Miocene adakite-like volcanic rocks in the SZ formed in a post-collisional intra-continental setting, which experienced far-field extension after the subducted slab of the southern Neotethyan branch became detached in the collision zone. Asthenospheric upwelling and underplating of basaltic magma provided the heat for partial melting of lower crustal amphibolite, forming minor amounts of adakite-like melts in the SZ. (C) 2019 Elsevier B.V. All rights reserved.

An algorithm for identifying derivatives of potentially ore-bearing magmas among Precambrian rocks of tonalite–trondhjemite–granodiorite associations (TTGAs) is elaborated and tested using current genetic models. The algorithm is a succession of geochemical criteria for identifying the genesis of source of matters and, as a result, the melt products of geochemical reservoirs enriched in Au and other ore elements. This algorithm (a set of geochemical criteria of the ore potential) can be used for metallogenic zoning of the territories composed of TTGA rocks within ancient cratons.

Sanukitic dikes, mainly consisting of pyroxene diorite porphyrite, diorite porphyry, quartz diorite porphyrite and quartz diorite, were widely distributed in the Bieluagaxi area, southern West Junggar. In this contribution, we present new LA-ICP-MS zircon U-Pb ages, major and trace elements, and Sr-Nd-Hf isotopes for these dioritic dikes. These rocks formed in the early Late Carboniferous (ca. 319–315 Ma), coeval with abundant magmatic rocks in the region, and exhibit high MgO, Cr and Ni concentrations and K/Na ratios, and also show strong enrichment in large ion lithophile elements relative to high field strength elements, with pronounced negative Nb, Ta, and Ti anomalies, analogues to those of Cenozoic sanukitoids of the Setouchi Volcanic Belt. Compositionally, the sanukitic dikes are divided into two groups. Group 1 have MgO contents greater than 6 wt% (6.18–9.34 wt%), with Mg# values ranging from 58.2 to 73.7. They also have relatively low SiO2 (51.7–55.7 wt%) and Sr (356 ppm in average) contents, and low Sr/Y (15.1–25.4) ratios, but high concentrations of Cr (6.2–490 ppm) and Ni (12.8–163 ppm). Compared to the Group 1, the Group 2 samples have slightly lower MgO (2.12–5.58 wt%; Mg# = 45.8–68.5), Cr (10.1–329 ppm) and Ni (2.84–136 ppm), but relatively higher SiO2 (58.6–65.7 wt%) and Sr (304–521 ppm) concentrations and Sr/Y (19.2–41.0) ratios, making them akin to adakitic rocks elsewhere. These dikes also exhibit depleted Sr-Nd-Hf isotopic signatures, with (87Sr/86Sr)i = 0.70353–0.70480, eNd(t) = +5.03 to +7.61, eHf(t) = +10.9 to +15.3. Geochemical and Sr-Nd-Hf isotopic data suggest that the Group 1 rocks are similar to the typical sanukitoids of the Setouchi Volcanic Belt, and were likely derived from partial melting of a depleted mantle source with subducted sediment melts. While the Group 2 rocks show a remarkable geochemical affinity with the Northwestern Karamay sanukitoids, and were derived from partial melting of a depleted mantle source metasomatized by slab-derived adakitic melts and fluids. Combined with the identified and reported subduction-related magmatism, i.e., adakites, sanukitoids, Nb-enriched basalts, lagged arc volcanic rocks, and I-type granitoids in the Western Junggar region and taking into consideration the previous achievements, therefore, we consider a multi-stage subduction-accretionary orogeny model may account for the difference of subduction duration between the northern segment and southern segment of Western Junggar.

The paper reports the isotope-geochronological and petrological-geochemical studies of the Pliocene moderately-acid volcanism of the Akhalkalaki Plateau in the central part of the Lesser Caucasus (Javakheti highland, Georgia). K-Ar dating showed that young dacitic lavas and pyroclastic rocks were formed in the mid-Pliocene (3.28 ± 0.10 Ma) in relation with the explosive–effusive eruptions of small composite volcanic cones and formation of minor extrusive domes confined mainly to the eastern margin of the region. Isotope-geochronological data in the combination with results of structural drilling indicate that the considered short-term pulse of the volcanic activity occurred during a short gap between two phases of the Pliocene–Early Pleistocene mafic magmatism widespread within the Akhalkalaki plateau. The studied Pliocene dacites were erupted at the post-collisional stage of the evolution of the Lesser Caucasus, but bear petrological-geochemical affinity of adakitic series. They are characterized by the steady presence of amphibole phenocrysts, the elevated contents of Sr, Ba, LILE and the lowered contents of Y, Nb, Ta, and HREE, and have depleted Sr isotopic composition (87Sr/86Sr < 0.7045). Analysis of petrogenetic models earlier proposed to explain the generation of adakite-like magmas in the modern collision zones showed that the origin of the Pliocene dacitic lavas of the Akhlkalaki plateau is best described by the crystallization differentiation of water-saturated calc-alkaline basaltic melts with removal of common mafic rock-forming minerals (first of all, amphibole and pyroxene) and accessory phases (apatite, titanite, Ti-magnetite) as cumulus minerals. Crustal assimilation of evolved magmas only insignificantly contributed to the petrogenesis of the dacites.

During the Miocene, the evolution of the Northern Andes was influenced by the subduction of the young Oceanic Nazca Plate and the final collision of the Panama-Choco Block (PCB) with the continental margin of Colombia. This work presents an integrated field, geochemical, Hf-Nd-Sr isotopic and geochronological study of volcanic arc front rocks of the Combia volcanic complex in the northern segment of the Cauca-Valley (North of 5°N) in order to reconstruct the petrologic and tectonic significance of a short life arc with a very heterogeneous geochemical signature. The Combia volcanic complex includes a series of basalts, andesites, pyroclastic rocks, porphyritic andesitic-dacitic domes, and dacitic to andesitic porphyries, with zircon U Pb crystallization ages between 8.5 and 5.2 Ma. Negative anomalies of Nb and Ti, enrichment in Light Rare Earth Elements (LREE) and depletion in Heavy Rare Earth Elements (HREE) are characteristic of magma origin in a convergent margin setting. This magmatism shows different tholeiitic, calc-alkaline, and adakite-like geochemical signatures, which may be related to an initial adiabatic-controlled dry melting, followed by wet melting conditions from the hydrated mantle wedge. Variations in crustal thickness between 17 and 45 km estimated by the Ce/Y, La/Yb, and Sr/Y ratios are related to local thinning of a previously thickened continental crust. Such pattern can be explained by strain partitioning in which crustal thinning may be a relatively local phenomenon. Arc magmatism in this segment of the margin apparently migrates eastward from the Western Cordillera to the Cauca-Valley between 11 and 9 Ma and was followed by a magmatic quiescence after ~5.2 Ma. This spatio-temporal history is consistent with continuous oblique convergence of the Nazca Plate and slab flattening beneath the continental margin until it achieves its modern tectonic configuration.

This paper reports geochronological, geochemical, zircon U–Pb and Hf–O isotopic data of the Late Triassic and Early Jurassic intrusive rocks in the northeastern North China Craton (NCC), with the aim of reconstructing the tectonic evolution and constraining the spatial–temporal extent of multiple tectonic regimes during the early Mesozoic. Zircon U–Pb ages indicate that the early Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Triassic (221–219 Ma) and Early Jurassic (180–177 Ma). Late Triassic magmatism produced mainly granodiorite and monzogranite, which occur as a NE–SW-trending belt parallel to the Sulu–Jingji Belt. Geochemically, they are classified as high-K calc-alkaline and metaluminous to weakly peraluminous granitoids, and are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating an affinity to adakite. Combined with their eHf(t) values (−17.9 to −3.2) and two-stage model ages (2387–1459 Ma), we conclude that the Late Triassic granitoid magma in the northeastern NCC was derived from partial melting of the thickened lower crust of the NCC and was related to deep subduction and collision between the NCC and the Yangtze Craton (YC). The Early Jurassic magmatism is composed mainly of monzogranites, which are classified as metaluminous, high-K calc-alkaline, and I-type granite. Their eHf(t) values and two-stage model ages are −16.7 to −4.2 and 2282–1491 Ma, respectively. Compared with the Late Triassic granitoids, the Early Jurassic granitoids have relatively high HREE contents, similar to calc-alkaline igneous rocks in an active continental margin setting. These Early Jurassic granitoids, together with the coeval calc-alkaline volcanic rocks and gabbro–diorite–granodiorite association in the northeastern (NE) Asian continental margin, comprise a NNE–SSW-trending belt parallel to the NE Asian continental margin, indicative of the onset of Paleo-Pacific Plate subduction beneath Eurasia.

Late Cretaceous magmatism in the southern Lhasa subterrane, Tibet, provides critical constraints on the subduction processes of the Neo-Tethyan oceanic plate. Here, we provide data on the whole-rock geochemistry, zircon U Pb ages, trace element contents, and Hf isotopes of early Late Cretaceous volcanic rocks from Sangri County to Sangye Temple (SS) along the southern Lhasa subterrane. The SS volcanic rocks include basalts, andesites, and dacites. SIMS and LA–ICP–MS zircon U Pb data indicate that the SS dacites were erupted at ca. 95 Ma, coeval with the early Late Cretaceous “flare-up” event in the southern Lhasa subterrane. The SS volcanic rocks belong to the calc-alkaline to high-K calc-alkaline series and have the geochemical features of subduction-related volcanic rocks with negative Nb, Ta, and Ti anomalies. The basalts have similar rare earth element (REE) patterns to E-MORB and are characterized by high Zr abundances (65–190 ppm) and Zr/Y ratios (3.3–6.5). They were possibly derived by high-degree partial melting of mantle peridotite that had been metasomatized by subduction-related fluids with an input of asthenospheric components. Positive whole-rock eNd(t) (+2.9 to +3.2) values for the andesites, and their variable Mg# values (35–61) and MgO (2.29–7.32 wt%), Cr (12–232 ppm), and Ni (10–127 ppm) contents can be attributed to medium-degree partial melting of mantle peridotite followed by fractional crystallization of clinopyroxene and olivine. The calc-alkaline SS dacites are similar to adakites with high Sr (663–1188 ppm) and low heavy rare earth element (HREE) and Y (10.7–11.5 ppm) contents. These adakitic dacites have positive whole-rock eNd(t) (+2.9 to +3.4) and zircon eHf(t) (+8.4 to +14.9) values with relatively high values of Mg# (36–57) and high contents of compatible elements, indicating that they were derived from the partial melting of subducted oceanic slab, and with the ascending magma interacting with mantle wedge peridotite. Our new data indicate a distinct rock association of coeval asthenosphere-component-involved basalts and slab-derived adakitic dacites. Such an association, together with the coeval high-temperature charnockites and high-temperature granulite-facies metamorphism of the charnockitic country rocks in the southern Lhasa subterrane, indicates an anomalous input of materials and heat during the early Late Cretaceous “flare-up” event. Such an event can probably be attributed to the northwards subduction of a Neo-Tethyan oceanic ridge that allowed for contributions from upwelling asthenosphere that differed from the typical results of normal-angle subduction or low-angle/flat subduction and subsequent slab rollback.

The Sheyda volcano study area, located in the Hamedan-Tabriz volcanic belt of western Iran, is composed of intermediate to acidic volcanic rocks of Miocene age and is partially covered by Plio-Quaternary sedimentary rocks. The igneous rocks have primarily microlithic, porphyrytic and glomeroporphytic textures and less frequently, trachytic texture involving phenocrysts of plagioclase feldspar and hornblende with minor alkali feldspar , quartz and biotite . The Sheyda high-potassium, calc-alkaline trachydacites and dacites have been called "adakites" on the basis of their high SiO 2 (67.5–51.7 wt %), Al2O3 (18–15.6 wt %), Sr/Y (67–49) and La/Yb (28–23), and low Mg# (average 41.5). Rare earth elements geochemistry data, demonstrate that these rocks do not originate as melts of subducted oceanic crust . Rare earth element abundance variations and the absence of a significant positive relationship between Sr/Y and La/Yb ratios and SiO 2 and MgO contents indicate that fractional crystallization or partial melting can played role in their genesis. The existence of the subducted oceanic slab beneath the studied area and the thin continental crust as well as thinning in the lithosphere suggested that these adakites originated from melting metasomatized continental lithosphere that could be garnet or clinopyroxene bearing amphibolite in composition.

Multistage igneous rocks identified in the newly discovered Fukeshan porphyry Cu Mo deposit, NE China give new insights into the late-stage southwards subduction of the Mongol-Okhotsk oceanic slab (MOOS) and Cu Mo mineralization during the late Mesozoic. The U Pb ages of zircons from medium-grained monzogranite, coarse-grained monzogranite, ore-related quartz diorite porphyry, quartz monzonite, ganodiorite porphyry, diorite porphyry and andesitic porphyry associated with the Fukeshan deposit are 192.7 ± 1.9, 192.2 ± 2.7, 148.7 ± 0.8, 148.8 ± 0.9, 144.1 ± 1.1, 144.9 ± 0.9, and 144.8 ± 1.3 Ma, respectively. The Early Jurassic coarse-grained monzogranite, Late Jurassic quartz monzonite and quartz diorite porphyry, and Early Cretaceous granodiorite porphyry are characterized by low Yb and Y contents, and high Sr/Y ratios, indicating adakite affinities. The whole-rock geochemistry, and Sr Nd and zircon Hf isotopic features of the coarse-grained monzogranite and granodiorite porphyry indicate they were derived from the partial melting of a thickened basaltic lower crust. On the other hand, the quartz monzonite and quartz diorite porphyry probably originated from the melting of oceanic crust together with assimilation of enriched mantle and continental crust. The medium-grained monzogranites were possibly derived from a basaltic lower crust at shallower depths, and the diorite porphyry and andesitic porphyry probably originated from a metasomatized mantle source. Considering the Early Jurassic–Early Cretaceous magmatism and regional tectonic evolution of the Erguna Block, we propose that the MOOS was subducted towards the south during the Early Jurassic (195–170 Ma), slab retreat occurred during the early Late Jurassic (165–155 Ma), oceanic ridge subduction took place during the Late Jurassic (150–147 Ma). The final closure of the Mongol-Okhotsk Ocean occurred during the Early Cretaceous (145–143 Ma). The southwards subduction of a ridge on the MOOS provided a favorable tectonic setting for Cu Mo mineralization, and this is accordance with the discovery of many Late Jurassic–Early Cretaceous porphyry Cu Mo deposits in the eastern part of the Erguna Block.

The continental lithosphere is not forever; some cratons have lost their original roots during the course of their evolution. Yet, it is not clear whether gravitational instability of dense lower crust is the primary driver of decratonization. This is addressed here with emphasis being placed on the North China Craton (NCC), because it represents one of the best examples of craton-root disruption in the world, and a place where models can be tested. If lower-crustal delamination was the trigger for decratonization, we would expect a clear contrast in crustal structure and composition between disturbed (rootless) and intact cratons. However, the eastern (disturbed) and western (intact) parts of the NCC show virtually identical physical structure and composition (a thin mafic lower crust and a predominantly intermediate composition overall) although the crust in the disturbed part is thinner than in the intact craton. This suggests that delamination of the lower crust was not a viable mechanism of craton-root disruption in the NCC case. Indeed, the crust beneath the NCC largely resembles those of stable Archean cratons worldwide. Therefore the delamination, if it occurred, may have taken place much earlier (Archean) than previously thought, rather than in the Mesozoic. Delamination may have been a common phenomenon in the early evolution of cratons, probably due to relatively higher mantle temperatures in the Archean Eon.

The timings of subduction of the Palaeo-Pacific Plate beneath the North China Craton and of associated mineralisation remain unresolved. We studied a granodiorite porphyry in the Banmiaozi gold mining area, located along the northeastern margin of North China Craton, to shed light on these timings. Using zircon U–Pb geochronology, major- and trace-element geochemistry, Sr–Nd isotopes, and biotite compositions, we show that the granodiorite porphyry formed during the early Middle Jurassic and has a composition similar to those of ‘C-type adakites’ from eastern China. The granodiorite rocks have initial Sr isotopic compositions of 0.713418–0.713694, eNd(t) values of −15.9 to −16.69, and depleted-mantle single-stage model ages of 2.70–2.49 Ga, implying that the parental magma originated via subduction of the Palaeo-Pacific Plate beneath the North China Craton and resulted also in the generation of basaltic magmas and partial melting of thickened lower crust. As the Archaean basement rocks were rich in Au and magnetite, the magma was characterized by high Au contents and oxygen fugacity (fO2 = 10−13 bar). Subsequent mixing with, or contamination by, partially melted Proterozoic marine strata, such as the marble-bearing Laoling Group, played an important role in mineralisation. These country rocks provided large quantities of Cl−, CO32−, and SO42− to the magma, which formed soluble complexes with ore-forming elements such as Au, allowing enrichment and migration of the metals. Our data show that the Banmiaozi gold deposit is an orogenic gold deposit associated with subduction-related adakitic magmatism.

International audience; doi: 10.7185/geochemlet.2006 Underexplored accessory minerals such as titanite and apatite have the potential to give insights into the nature and the petrogenesis of their host rock. Their trace element and REE-rich compositions carry a record of crystallisation history and chemical characteristics of their source. Moreover, titanite and, to a certain extent, apatite are resistant to erosion during sedimentary cycles which makes them ideal to reconstruct the history of long-eroded continental land-masses. Here we report new trace element data on apatite and titanite from granitoids of different Archean cratons and comparative granitoids from the Phanerozoic. Trace element signatures of both minerals reveal systematic chemical trends in Y, LREE and Sr contents related to the nature of their host magma, which are used to construct discrimination diagrams delineating Archean TTGs from sanukitoids, and modern adakites from S/I-type granites. By comparing Archean granitoids (TTG and sanukitoids) and their Phanerozoic counterparts (adakite and high Ba-Sr granites), we show that the robust nature of these phases makes them reliable recorders of petrogenetic information from Archean rocks, that usually have been affected by secondary processes (meta-morphism, deformation, hydrothermal activity). Applied to the rock record, both phases potentially provide detailed archives of magmatic evolution through time.

This study is financially supported by the National Natural Science Foundation of China (Grant Nos. 41530207, 41772188 and 41472165). Peter A. Cawood acknowledges support from Australian Research Council grant FL 160100168. The Neoarchean Western Liaoning basement terranes in the northern part of North China Craton chiefly consist of tholeiitic basalts in the north, TTG gneisses and metavolcanic rocks in the northwest, and K-rich granitoids in the southeast. In the southeastern zone, porphyritic monzodioritic-quartz monzodioritic-granodioritic-monzogranitic (MQGM) gneisses are the major lithological assemblage, and locally contain minor xenoliths of TTG gneisses. Based on the major mafic mineral phases, the porphyritic MQGM gneisses can be divided into amphibole-dominated and biotite-dominated groups. Zircon UPb isotopic dating indicates that the amphibole-dominated MQGM gneisses, biotite-dominated MQGM gneisses, and tonalitic gneiss xenolith were emplaced during 2546–2529 Ma, 2546–2531 Ma, and at 2563 Ma, respectively. The 2563 Ma tonalitic gneiss xenolith displays geochemical affinities to high-SiO2 adakites, and may be formed by the partial melting of descending oceanic slabs, with the melt contaminated by mantle peridotite. The amphibole-dominated MQGM gneisses are geochemically analogous to sanukitoids, and their magmatic precursors were formed by partial melting of lithospheric mantle, which was metasomatized by dehydration fluids and melts derived from subducted oceanic sediments and slabs. The magmatic precursors of the biotite-dominated MQGM gneisses were generated by the partial melting of medium-K to high-K mafic rocks at medium pressures. Integrated with previous studies on supracrustal sequences and granitoids in Western Liaoning Province, the Neoarchean lithological assemblages in the southeastern zone were most likely formed in an active continental margin setting. Postprint

Identification of arc magmatic rock associations in a subduction zone has important implications for specifically revealing the geodynamic evolution of the subduction system. The closure time of the Bangong-Nujiang Tethyan Ocean and the detailed subduction processes have been hotly debated, hindering our understanding of the tectonic evolution of central Tibet. Here, we investigated the ca. 110-104 Ma Gerze lavas (basalts, basaltic andesites, andesites, dacites, and rhyolites) in southern Qiangtang. Fusion of slab fluid-metasomatized mantle wedge could yield the basalts, and such basaltic magmas, if contaminated with ancient basement orthogneisses, could have formed the andesites. The basaltic andesites with high Nb and Nb/La are similar to the Nb-enriched arc basalts and probably originated from slab melt-metasomatized mantle. The dacites were generated by fractional crystallization of the subducted melange-derived intermediate magmas. The rhyolites have geochemical characteristics (high SiO2 and La/Yb; low MgO and Sr/Y) similar to those of Jamaican-type adakites and were possibly sourced from the subducted oceanic plateau at low pressures. The Gerze Jamaican-type adakites and Nb-enriched basalt association could imply intense slab-mantle interactions. The Gerze lava suites show clear arc affinities, indicating that oceanic subduction may have lasted until 100 Ma. Based on previous studies and a noticeable ca. 145-125 Ma magmatic lull in southern Qiangtang, we suggest that the Bangong-Nujiang oceanic subduction geodynamics involved normal subduction (170-145 Ma), flat subduction (145-125 Ma), and slab roll-back (125-101 Ma). Moreover, the flat subduction was most likely caused by subduction of the oceanic plateau. Therefore, we propose, for the first time, that Tethyan oceanic plateau subduction during the Early Cretaceous could explain the tectonic evolution of the Bangong-Nujiang Ocean and distinctive magmatism in southern Qiangtang, central Tibet.

The Honghai volcanogenic massive sulfide (VMS) deposit occurs in the Kalatage inlier of the Dananhu-Haerlik arc, Eastern Tianshan, in the southern Altaids. The deformed deposit, hosted in a suite of early Paleozoic basic to intermediate volcanic, volcaniclastic, and sedimentary rocks, consists of lenticular massive to semimassive, and sulfide-silicate stockwork orebodies. The orebodies are characterized by zoning of metallogenic elements and sulfide minerals outward from a central stockwork zone as follows: (Fe +/- Cu), (Fe + Cu + Zn + Au + Ag; Cu > Zn), (Fe + Zn + Cu + Au + Ag; Zn > Cu), and (Fe +/- [Cu/Zn]). A typical VMS hydrothermal alteration zone that formed around the foot of the massive orebodies is several times larger than the lenticular massive orebody. The hydrothermally altered rocks contain sericite, chlorite, and epidote zones from the core outward. Re-Os and argon dating of pyrite and sericite shows that the Honghai VMS deposit formed in the Early Silurian (436 +/- 2 Ma) and was deformed in the Early Devonian (410 +/- 4 Ma). This is the first documented early Paleozoic VMS deposit in the Eastern Tianshan. Our multidisciplinary data indicate that the Honghai Cu-Zn deposit formed in an immature/nascent island arc, where early tholeiitic lavas evolved into transitional basic-andesitic volcanic rocks and calc-alkaline intrusions with relatively high epsilon(Nd)(t) values (+6.2-+8.4) and low (Sr-87/Sr-86)(i) ratios (0.70412-0.70541). The Sr-Nd-Pb-S isotopic and geochemical data suggest that the ore-forming melts started in mantle-derived volcanic rocks and deep subvolcanic intrusions, and some alteration was influenced by seawater. The deposit formed in a high-level subvolcanic intrusion driven by sub-seafloor CO2-rich, NaCl-CaCl2-H2O hydrothermal fluids (temperatures: 99-377 degrees C, salinities: 6%-18% NaCl equivalent) circulating in active extensional faults in a submarine caldera. Extension of the immature (nascent) intra-oceanic arc was one of the important factors that controlled the development and preservation of the VMS deposit. Future work will benefit from this improved understanding of the VMS deposits formed in immature (nascent) intra-oceanic arcs, especially in early Paleozoic island arcs in the Eastern Tianshan in the southern Altaids.

The Khanui Group, the Permian volcanic rock series of northern Mongolia, is a key geologic unit in the understanding of the Permian subduction-related magmatism at the southern margin of the “Siberian continent” (Siberian craton and accreted geologic units). Several studies have been carried out in the Khanui Group, but fundamental questions on its detailed petrogenesis remain to be answered. In this paper, the lithology, stratigraphy, zircon U-Pb age, and geochemistry of the Khanui Group in the Bulgan area of Mongolia, are described, and the Permian magmatism of the southern margin of the Siberian continent is discussed. The Khanui Group in this area is composed of intermediate lava and pyroclastic rocks. The zircons from this lava give a U-Pb age of 256.9 ± 2.2 Ma, and are thus Late Permian. The lava is 53–61 wt.% SiO2, 17 wt.% Al2O3, low K2O/Na2O (avg. 0.4), high Sr/Y (avg. 97), high La/Yb (avg. 21), and comparatively high Mg# (avg. 43) which suggests that it is composed of adakites originating from subducted basaltic slab-melt. The lava is enriched in Cr and Ni compared with typical slab-melt, which likely to be the result of an interaction between the slab-melt and the overlying mantle peridotite. The Khanui rock thus confirms the existence of a basaltic slab beneath the Permian Siberian continent, and also the Late Paleozoic subduction of the Mongol-Okhotsk oceanic plate beneath the Siberian continent.

We describe a previously unidentified Proterozoic ophiolite complex situated in the Madura Province in southeastern Western Australia. The Madura Province is almost entirely covered by Mesozoic to Cenozoic basin rocks but new basement drillcores have revealed oceanic crustal assemblages that record continental marginal basin formation followed by oceanic subduction and basin closure. The Pinto Basalt has E-MORB/OIB chemical affinity and ɛNd (1600 Ma) from 2.54 to +3.3. It formed by mantle upwelling beneath extending crust in an ocean-continent transition zone and must be considerably older than c. 1389 Ma adakite that intrudes it. The Sleeper Camp Formation comprises mafic metavolcaniclastic schist intruded by metadolerite and plagiogranite veins. Zircon crystals from the metavolcaniclastic schist yield a dominant age component and maximum depositional age of 1536 ± 13 Ma. The metadolerite and plagiogranite veins have zircon crystallization ages of 1479 ± 8 Ma and 1471 ± 5 Ma, respectively. Interlayered basalt and sediments of the Malcolm Metamorphics have a maximum depositional age of c. 1470 Ma and were metamorphosed at 1315 ± 11 Ma. The mafic rocks from both units are tholeiitic, with MORB-like HFSE ratios that point to a depleted mantle source similar to N-MORB, but with trace element patterns that indicate subduction enrichment. V/Ti ratio trends suggest the Sleeper Camp Formation marks oceanic subduction initiation at c. 1479 Ma. The progression to oceanic arc formation is recorded by the Malcolm Metamorphics after c. 1470 Ma, and the Haig Cave Supersuite from 1415 to 1389 Ma. The majority of these rocks occur within the hanging wall of the Rodona Shear Zone and were structurally emplaced above the continental margin of the West Australian Craton between 1389 and 1330 Ma during oceanic arc–continent collision, forming the Arubiddy Ophiolite Complex. The occurrence of oceanic crustal assemblages behind the accreted ophiolite complex frozen by the emplacement of voluminous 1192–1125 Ma Moodini Supersuite ferrogabbros and granites demonstrates that continental collision did not occur between the West Australian and South Australian Cratons. The preservation of rocks of oceanic affinity behind ophiolites could be a hallmark of other Proterozoic terranes that have escaped full continent-continent collision.

The tectonic evolution of the Central Asian Orogenic Belt (CAOB) is related to the subduction and closure of the Paleo-Asian Ocean (PAO). Considerable controversy still surrounds whether, when and how the PAO subducted underneath the northern margin of the North China Craton (NCC). This study carries out whole rock geochemical and zircon U-Pb-Hf isotopic investigations on Paleozoic intrusive rocks in both the Bainaimiao arc and the northern margin of the NCC. Zircon U Pb dating of gabbroic diorite and diorite in the Bainaimiao arc and the granite and diorite at the northern margin of the NCC yielded crystallization ages of 458 ± 2 Ma, 428 ± 2 Ma, 326 ± 2 Ma, and 258 ± 2 Ma respectively. In the Bainaimiao arc, the middle Silurian diorite as the main body of the arc-related intrusive rocks there show geochemical characteristics of continental margin arc magma with negartive ƐHf(t) values and old Hf model ages. On the other hand, the middle Ordovician gabbroic diorite mainly shows typical calc-alkaline continental arc geochemical characteristics with positive ƐHf(t) values and relative young Hf model ages, indicative of the southward-propagating reworking and arc-accretion processes. Thus, we interpret these rocks as a consequence of southward subduction of the PAO beneath the Bainaimiao arc, here termed as Bainaimiao Arc terrane, BAT. The early Carboniferous granite and late Permian diorite at the northern margin of the NCC show geochemical characteristics similar to post-collisional adakites and typical continental arc rocks, respectively. Combined with previous work, the early Carboniferous post-collisional adakite shows limited distribution and corresponds to the subsequent effect of the amalgamation between the BAT and the NCC. Whereas most of the Carboniferous-Permian magmatic rocks (ca. 342–258 Ma) at the northern margin of the NCC are arc-related and resulted from the continued effect of the southward subduction of the PAO. Moreover, the southward subduction in the early Paleozoic was transformed from relative high angle subduction beneath the BAT to shallow subduction beneath the unity of the NCC and the BAT in the late Paleozoic, which lasted until the late Permian (ca. 258 Ma).

The Sahiya and Khashabi volcano-sedimentary successions are exposed near the southern tip of the Sinai Peninsula, the northernmost segment of the Arabian-Nubian Shield (ANS). These Neoproterozoic successions include a series of intermediate to acidic lavas and associated pyroclastic deposits. Field observations and geochemical data reveal two distinct eruptive phases. The lavas representing each phase are intercalated with volcaniclastic greywackes and siltstones. The first eruptive phase, well exposed at Wadi Sahiya, includes basaltic andesite, andesite and dacite with minor rhyolite. The rocks of this sequence are at most weakly deformed and slightly metamorphosed. The second eruptive phase, well exposed at Wadi Khashabi, includes only undeformed and unmetamorphosed dacite and rhyolite. The two volcano-sedimentary successions were separated and dismembered during intrusion of post-collisional calc-alkaline and alkaline granites. Geochemical compositions of the Sahiya and Khashabi volcanic rocks confirm the field data indicating discrete phases of magmatism, however all the compositions observed might plausibly be derived from a common source and be related to one another dominantly through fractional crystallization. The low and variable Mg# values (55–33) measured in the basaltic andesites and andesites preclude their equilibration with a mantle source. Rather, even the most primitive observed lavas are already the products of significant fractional crystallization, dominated by removal of amphibole and plagioclase. Continued fractionation eventually produced dacite and rhyolite marked by significant depletion in Y and HREE. The gradual appearance of negative Nb-Ta anomalies with increasing SiO_2 through both suites suggests at least some component of progressive crustal contamination. The medium- to high-K calc-alkaline character of the Sahiya and Khashabi volcanics could be explained either by their formation at an active continental margin or by a two-stage model that appeals to re-melting of arc material in a post-collisional setting. The Wadi Sahiya basaltic andesite and andesite samples exhibit the defining chemical characteristics of adakites: high Sr (>700 ppm), low Y ( 20) and low Yb (

Recent studies show that the Cretaceous intracontinental and arc tectonomagmatism in Northeast Asia resulted from the intracontinental mantle plume under the North China Craton and its channel-like flow that was dragged into the underneath of the ancient arc, respectively. Although the southwest-to-northeast migration of the channel-like flow in the mantle wedge might have occurred along the Cretaceous margin from southeast China to southwest Japan, adakites, implying partial melting of the subducted oceanic crust, were only observed along southwest Japan. To understand the localized adakite occurrences, a three-dimensional numerical subduction model which covers the margin from southeast China to southwest Japan through the present East China Sea was formulated by considering the southwest-to-northeast migration of the channel-like flow in the mantle wedge. Our model calculations show that increased slab-surface temperatures under southeast China by the channel-like flow were lower than the solidus of the hydrated oceanic crust; no adakites were generated in southeast China. In contrast to that in southeast China, younging subducting slab from the Early to Late Cretaceous along the eastern East China Sea and southwest Japan allowed the channel-like flow to increase the slab-surface temperatures over the solidus; adakites were generated in the eastern East China Sea and southwest Japan. Our model calculations are consistent with the adakite occurrences in southwest Japan and the occurrences in the eastern East China Sea can be verified via oceanic drilling.

The Paleo Asian Ocean underwent a protracted closure history during Late Paleozoic. Here we investigate the magmatic evolution during this process based on a detailed study in the Baiyinwula region along the Uliastai continental margin. The major rock types in this area are Late Carboniferous-Early Permian volcanic sequences and coeval intrusions. We identified four stages of magmatic evolution based on the diverse assemblages and their precise isotopic ages. The first stage is represented by andesites with a zircon 206Pb/238U age of ca. 326 ± 12 Ma. These rocks are metaluminous to weakly peraluminous, high-K calc-alkaline, and possess high Na2O/K2O ratios in the range of 1.23 to 2.45. They also display enrichment of large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE), with markedly positive zircon eHf (t) varying from 8.1 to 15.6.The geochemical features of these andesites are similar to those of typical arc volcanic rocks. The second stage includes granodiorites emplaced at 318.6 + 1.8 Ma. The rocks are high-K calc-alkaline with A/CNK values ranging from 0.95 to 1.06, and show enrichment in LILE and depletion in HFSE. They show geochemical affinities to adakites, with high Sr and low Y and Yb contents, indicating magma derivation from thickened lower crust. Zircon grains from these rocks display positive initial eHf (t) values ranging from 11.1 to 14.6 with corresponding two-stage Hf model ages (TDM2) of 394–622 Ma. The third stage consists of syenogranite together with a volcanic suite ranging in composition from rhyolite todacite, which formed during 303.4 ± 1.2 to 285.1 ± 2.2 Ma. They possess elevated silica and alkali contents, high FeOt/MgO and Ga/Al ratios, low Al2O3, MgO and CaO contents, and high Rb, Y, Nb, Ce, Zr, Y, and Ga contents, strong negative Ba, Sr and Eu anomalies, showing I- to A-type granitic affinities. Zircons in these rocks show elevated Hf isotopic compositions (eHf (t) = 9.9 to 14.6) with TDM2 varying from 324 to 673 Ma. The fourth magmatic pulse is represented by K-feldspar granite with zircon U-Pb ages from 283.2 ± 1.9 Ma to 280.0 ± 1.4 Ma, and typical alkalic A-type granite geochemistry. These rocks possess positive eHf (t) values in the range of 9.7 to15.2, and a restricted range of Hf model age from 327 to 684 Ma. The magmatic rocks from the four stages show comparable eHf (t) and T2DM, suggesting that the magmas were derived from the same evolving mantle-derived source. We propose a tectonic model linking the evolution of the magmatism with the closure of the Paleo Asian Ocean that involved the following stages. The andesites were formed during the initial oceanic subduction stage with magma sourced from the metasomatized lithospheric mantle. Stage 2 adakite-like rocks were derived from subduction-induced thickened crust. Subsequent slab rollback resulted in asthenospheric upwelling and melting of residual juvenile crust to generate the I- and A- type syenogranite, rhyolite and dacite suite, finally followed by the A-type K-feldspar granite.

This study presents new zircon U–Pb–Hf and whole-rock geochemical data for intrusive rocks in the Xing'an Massif of NE China, with the aim of furthering our understanding of the evolution and spatial influence of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that five stages of Mesozoic magmatism are recorded in the Xing'an Massif, namely during the Middle Triassic (~237 Ma), the Late Triassic (~225 Ma), the Early Jurassic (~178 Ma), the Middle Jurassic (~168 Ma), and the late Early Cretaceous (~130 Ma). The Middle Triassic–Early Jurassic intrusive rocks in the Xing'an Massif are dominantly granodiorites, monzogranites, and syenogranites that formed from magma generated by partial melting of newly accreted continental crust. Geochemistry of the Middle Triassic–Early Jurassic granitoid suites of the Xing'an Massif indicates their formation at an active continental margin setting, related to the southwards subduction of the Mongol–Okhotsk oceanic plate. The Middle Jurassic monzogranites in the Xing'an Massif are geochemically similar to adakites and have eHf(t) values (+3.8 to +5.8) and Hf two-stage model ages (TDM2; 979–850 Ma) that are indicative of derivation from magma generated by partial melting of thickened juvenile lower crust. The Middle Jurassic monzogranites formed in a compressional setting related to the closure of the Mongol–Okhotsk Ocean. The late Early Cretaceous intrusive rocks in the Xing'an Massif are dominated by A-type granitoids that are associated with bimodal volcanic rocks, suggesting their formation in an extensional environment related to either (i) delamination of a previously thickened region of the crust, associated with the Mongol–Okhotsk tectonic regime; (ii) the subduction of the Paleo-Pacific Plate; or (iii) the combined influence of these two tectonic regimes.