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The petrogenesis of biotite granites, which may be metaluminous or peraluminous in composition, is a subject of debate. In this study, we present new zircon U-Pb geochronology and O-Hf isotopic, and whole-rock major and trace element, and Sr-Nd isotopic data for biotite granites in the Langla–Laqinpu area of northern Lhasa Terrane, central Tibet. The rocks are distributed along the eastern segment of the Bangong–Nujiang Tethys Ocean suture, and were emplaced during the late Early Cretaceous (ca.119 Ma). The biotite granites are peraluminous, and have high SiO2 (67.5–72.4 wt%) and low MgO (0.57–1.20 wt%) and CaO (2.36–4.38 wt%) contents with variable K2O/Na2O ratios (0.77–1.32), and show geochemical affinity with the upper-continental crust, e.g., enrichment of Rb, Th, U, K and Pb, depletion of Nb, Ta, Ti, P, Eu, and Sr. They are characterized by relatively high initial 87Sr/86Sr ratios ((87Sr/86Sr)i = 0.7098–0.7137) and low eNd(t) values (−8.4 to −10.3), and high zircon δ18O values (8.29–13.47‰) and variable eHf(t) values (−0.02 to −21.36), indicating they were derived through partial melting of a crustal source consisting of metagreywackes with or without minor metaigneous rocks. Taking into account all available regional geological data, we suggest that the Bangong–Nujiang Tethys Ocean may undergo diachronous closure–although the eastern segment may have been closed by the late Early Cretaceous, its western and western–middle segments may still have been at least partially open and active at that time. The Langla–Laqinpu biotite granites were probably generated in post-collisional setting, following slab break-off after closure of the Bangong–Nujiang Tethys Ocean.

Collisional zones are commonly considered as important regions for crustal reworking, but the reworking mechanism remains debated. The well-known Himalayan-southern Tibetan orogen, built by India-Asia collision and convergence, has the thickest continental crust on Earth and is therefore an ideal region for studying crustal reworking during collisional orogenesis. Here we revisit the Miocene high-silica potassic rocks (trachytes) in the Konglong area of the central Lhasa block, southern Tibet. Integrated studies of geochronology, mineral compositions, bulk-rock major- and trace-element geochemistry, and Sr-Nd-Pb-Hf-O isotopes unequivocally indicate that the Konglong trachytes formed by mixing between enriched mantle-derived ultrapotassic and thickened ancient crust-derived magmas. Combined with post-collisional magma mixing recently identified in the southern Lhasa block, we suggest that magma underplating and subsequent mantle-crust interaction (i.e., the matter and energy transfer from the mantle to the crust) has been a common and important crustal reworking process in southern Tibet during Indian continental subduction. This process may be related to Indian plate flat subduction and subsequent foundering during the post-collisional stage. In combination with the nature of Cenozoic magmatism in the Himalaya block, we suggest that in addition to partial melting of the subducted continental crust, magma underplating and subsequent crust-mantle mixing beneath the obducted continent has also played an important role in crustal reworking of the collisional zone.

In this work, we report the geochemical, whole-rock Sr-, Nd-, and Hf-isotopes, and zircon U–Pb age and Hf–O isotopic compositions for six granitic intrusions in northeastern Fujian, coastal region of southeastern China, to elucidate the petrogenesis of aluminous and peralkaline A-type granites in this region. Zircon U–Pb dating of these rocks (including porphyritic syenites, porphyritic granites, alkali-feldspar granites, and arfvedsonite granites) yielded Late Cretaceous ages of 94–98 Ma. Mineral assemblage and geochemical features suggested that the arfvedsonite granites were peralkaline A-type but the porphyritic syenites, porphyritic granites, and alkali-feldspar granites were aluminous A-type. Geochemical data, whole-rock Nd–Hf isotopes (eNd(t) = −5.5 to −4.0, eHf(t) = −3.6 to 0), and the zircon Hf–O isotopes (eHf(t) = −3.0 to +1.4, δ18O = 5.4‰–6.0‰) indicated that the porphyritic syenites were produced by partial melting of crustal rocks in the lower crust. The porphyritic granites and alkali-feldspar granites had similar geochemical features and zircon Hf–O isotopic composition with the porphyritic syenites, suggesting that they were formed by feldspar-dominant crystal fractionation of deep crust derived syenitic magma under shallow crustal level. Compared with the aluminous A-type granites, the peralkaline A-type granites had lower abundance of Al2O3, MgO, CaO, Ba, and Sr, higher abundance of SiO2 and HFSE, as well as higher ratio of total FeO/MgO, Ga/Al, and Rb/Sr. However, the whole-rock Nd-, Hf- and zircon Hf–O isotopic compositions of the peralkaline and aluminous A-type granites were similar. It could be inferred that the peralkaline A-type granites were formed by crystal fractionation of aluminous A-type granitic magmas. Since the studied A-type granitic intrusions were coeval with the bimodal volcanic rocks and the extensional basins in the coastal region of southeastern China, they were likely produced in an extensional setting, possibly during lithospheric thinning that resulted from the subduction of the paleo-Pacific plate beneath southeastern China.

Amphibole is thought to be a key control on the differentiation of arc magmas but the fractionation of this mineral remains enigmatic because it is rarely present in erupted lavas. This study presents detailed petrological, mineralogical, and geochronological data for newly identified Late Triassic (217–215 Ma) mafic intrusive rocks from the Gangdese arc of southern Tibet. These gabbros host an amphibole-rich cumulate enclave and clinopyroxene crystal clots, including two mineral assemblages in chemical disequilibrium: (1) amphibole and Type-1 clinopyroxene within the enclave and clots; and (2) small crystals of Type-2 clinopyroxene, plagioclase, and biotite within the host. Textural and geochemical evidence indicate that the enclave and clots represent captured fragments of amphibole- and clinopyroxene-dominated lower crustal crystal mushes, respectively, whereas small host crystals formed by the shallow crystallization of evolved melts extracted from these crystal mushes. The compositional variations between the two types of clinopyroxene also reveal this melt segregation process. Amphibole with similar rare earth element patterns to associated Type-1 clinopyroxene inclusions suggest that the former formed through peritectic reactions consuming clinopyroxene. Enhanced amphibole fractionation may also have occurred as a result of the presence of high-density clinopyroxene inclusions. This indicates that the fractionation of amphibole together with precursory clinopyroxene inclusions within the deep crust controls the early chemical evolution of mafic arc magmas, a process that is consistent with the geochemical variations in lavas from three other active arc volcanoes. The associated cumulates can efficiently delaminate back into the mantle, ultimately leading to the generation of SiO2-rich continental crustal material.

Alkaline rocks contain essential information on post-collisional/intraplate extensional magmatic processes within the continental lithosphere. The Erhulai syenitic pluton in the Liaodong Peninsula, North China Craton, consists of quartz syenite, mafic enclaves, and porphyritic K-feldspar granite. Field observations and zircon U–Pb dating reveal that the quartz syenite and the hosted mafic enclaves were coeval (with identical emplacement ages of 129–126 Ma), and slightly older than the porphyritic K-feldspar granite (ca. 123 Ma). The mafic enclaves have relatively low SiO2 and high MgO contents (up to 3.0%), and lack Ba or Eu anomalies. Whole-rock analyses of the mafic enclaves and accessory minerals in the enclaves show relatively low initial 87Sr/86Sr ratios (0.7056 to 0.7078) and variable eNd(t) (−11.2 to −2.0) and eHf(t) (−15.8 to −5.5) values. Large proportion of zircons from the mafic enclaves possess mantle-like δ18O values. These geochemical features suggest an enriched mantle source, with the addition of crustal material. The quartz syenites have relatively high SiO2 and low CaO and MgO contents, as well as significantly positive K, Ba, and Eu anomalies. All the quartz syenites show variable (87Sr/86Sr)i ratios (0.7073 to 0.7081) and eNd(t) values (−10.4 to −8.6) for the whole-rocks and apatites, eHf(t) values of −12.4 to −3.6 for the zircons, and zircon δ18O values of +4.4‰ to +7.0‰ (mainly greater than +5.3‰). All these features can be isotopically produced by the partial melting of ancient crustal material, with the involvement of mantle-derived magma. Crystal fractionation process, such as K-feldspar crystallization and accumulation, played an important role in the formation of the quartz syenite. The porphyritic K-feldspar granites possess relatively evolved geochemical compositions with high silica contents (SiO2 > 69 wt%) and remarkable negative Ba and Eu anomalies, which are chemically complementary to the quartz syenite. A crystal mush model was employed to establish the genetic link between the porphyritic K-feldspar granite and the quartz syenite, with the granite representing the interstitial melt extracted from the crystal mush and the quartz syenite representing the residual accumulation of crystals. The variable isotopic compositions of the quartz syenite and the porphyritic granite were mainly the result of extensive interaction of isotopes between mantle- and crust-derived magmas during magma mixing. In situ analyses of the Sr, Nd, Hf, and O isotopes of accessory minerals, coupled with field observations and whole-rock geochemical data for the Erhulai syenitic pluton, indicate a complex multi-stage magmatic process involving magma mixing, crystal–melt segregation, and wall-rock assimilation. Our study also shows that in situ isotopic analyses of accessory minerals provide unique information on, and are powerful geochemical tracers of, mantle–crust interactions and magmatic processes.

High-silica granites that occur as isolated plutons are widely distributed in collisional orogenic belts and are considered a hallmark of continental collision processes. The late Mesozoic collision between the Lhasa and Qiangtang Terranes along the Bangong–Nujiang Suture Zone was key event in the evolution of the Tibetan Plateau; however, the timing of this collision remains debated. Here, we report the ages and geochemical characteristics of granites from the Gajin area in the north-central Lhasa Terrane, central Tibet. Zircon U Pb dating reveals that the Gajin granites formed at ~100 Ma. These granites exhibit uniformly high SiO2 contents (74.9–78.4 wt%), are weakly peraluminous compositions, and have high K2O, moderate Na2O and Al2O3, and low Fe2O3T, MgO, and CaO contents. They are characterized by enrichments in Rb, Cs, and U, and by depletions in Zr, Hf, Nb, and Ti. These characteristics, in combination with high Rb/Sr ratios and pronounced negative Eu anomalies, indicate that the Gajin granites are highly fractionated rocks. The granites have enriched whole-rock Nd (eNd[t] = −4.3 to −2.9) and relatively depleted and slightly variable zircon Hf (eHf[t] = −1.0 to +5.5) isotope compositions. The Gajin granites were probably generated by high degrees of crystal fractionations of magma produced by partial melting of mature crustal sources. The Cretaceous magmatic rocks in the north-central Lhasa Terrane record a magmatic lull between ~100 and 85 Ma, which corresponds to a transition in both geochemical composition (e.g., Hf Nd isotopes) and rock association at ~100 Ma. Combining the above characteristics with the development of a regional angular unconformity around the time of the formation of the granites, we suggest that the initial continental collision between the Lhasa and Qiangtang Terranes probably occurred between 110 and 90 Ma. Therefore, the ~100 Ma high-silica granites in the Gajin area were formed during the continuing continental convergence that followed the initial collision between the Lhasa and Qiangtang Terranes. The generation of discrete and monotonous high silica granites may constitute evidence for a significant tectonothermal transition in evolution of the continental crust.

Voluminous Mesozoic felsic volcanic rocks and granites in southeastern China provide a unique opportunity for studying the role of crustal magmatism in the evolution and modification of the crust in the eastern Cathaysia Block. The high-silica rhyolites of the upper volcanic sequence in eastern Zhejiang Province were investigated, focusing on their genesis and their relationship with contemporaneous granites. Rhyolites in the Tiantai, Yongkang and Liucheng basins were dated as late Early Cretaceous (from 111 Ma to 106 Ma in age). These rocks contain a large proportion of inherited zircons of ca. 130 Ma, corresponding to the age of the lower volcanic sequence in the area. However, the zircons of different ages have similar ranges of oxygen and Hf isotopes, implying similarities in the magmas from which they were generated. The rhyolites of the upper sequence also resemble those of the lower sequence in terms of their geochemistry. It is concluded that the former were derived by reworking of magma mush formed during the earlier magmatic episode via fractionation of feldspars and accessory minerals, e.g., zircon. Fractionation took place within the magma crystal mush by extraction of interstitial melts and accumulation of residual mineral phases, aided by the emplacement of contemporaneous basaltic magmas at the base of the crust. Overall, the geochemical features of the volcanic rocks in southeastern China indicate that episodic magmatism and reworking of crystal mush were essential mechanisms that drove the evolution of the igneous rocks and the hence crustal architecture in this area.

The Cretaceous granitoids in eastern Zhejiang were examined to establish a model for the construction of the highly silicic upper crust in southeastern China. The studied rocks include quartz monzodiorite, quartz monzonite, alkali feldspar granite, and their microgranular enclaves (ME). Zircon U Pb dating suggests that the granitic rocks and MEs were emplaced at approximately 102–114 Ma. Geochemical features and isotopic compositions of the quartz monzodiorite, quartz monzonite, and alkali feldspar granite indicate that they are mainly produced by the partial melting of Neoproterozoic to Mesoproterozoic crustal rocks. The quartz monzodiorites, quartz monzonites, and alkali feldspar granite appeared to derive from a similar silicic magma reservoir because they have comparable crystallization age, zircon trace element variation trend, Sr-, Nd-, and Hf-isotopic compositions, and complementary geochemical compositions. The studied quartz monzodiorites, quartz monzonites, and low silica alkali feldspar granites (SiO2 75 wt%) resemble frozen remnants of high silica melts segregated from a crystal mush because they are highly enriched in SiO2 and depleted in Ba, Sr, and Eu. The MEs hosted in the quartz monzodiorites and quartz monzonites have low SiO2 and high MgO contents, high initial 87Sr/86Sr ratio and negative eNd(t) and eHf(t) values, and variable zircon δ18O and eHf(t) values. Petrographic observations and geochemical features suggest that they are formed from solidified mafic magmas and generated by the crystal fractionation of mantle-derived hydrous mafic magma with subsequent crustal contamination. Compared with these mafic MEs, the MEs hosted by the alkali feldspar granites have relatively high SiO2 and low K2O contents, indicating that the felsic MEs are generated by crystal fractionation of the parental magma of the mafic MEs. Since abundant MEs occurred in the quartz monzodiorites, quartz monzonites, and alkali feldspar granites, magma recharge may have promoted the extraction and upward percolation of high silicic melts from the compacting crystal-rich mush in the shallow crust. Thus, the chemical and lithological diversity of the granitic plutons in eastern Zhejiang is generated in the upper crust via crystal-melt segregation. Specifically, the quartz monzonites and quartz monzodiorites are formed as residual cumulate, whereas the high silica alkali feldspar granites are generated as frozen remnants of high silicic melts segregated from a compacting crystal mush. More widely, our work suggests that the formation of the highly silicic upper crust in southeastern China is controlled by crystal-melt segregation processes in the shallow crust.

High-silica granites are common in collisional orogenic belts. However, the petrogenesis of such granites and the geodynamic processes associated with their emplacement are debated. In this study, we present zircon U–Pb ages and Hf isotopes, and whole-rock geochemical and Sr–Nd isotopic compositions for biotite granites from the Jiang Co area, in the Bangong–Nujiang suture zone, central Tibet. Zircon U–Pb dating reveals that the Jiang Co granites were emplaced during the late Early Cretaceous (ca.114 Ma). These granites are characterized by high and variable SiO2 (69.7–78.2 wt%) and K2O (4.7–8.4 wt%), and low MgO (0.09–1.25 wt%) and P2O5 (

We present new whole rock major and trace element and, Sr–Nd–Hf isotope data for Mesozoic basalts and andesites from the Siziwangqi area, northwestern China, in order to constrain their petrogenesis and regional tectonic implications. The basalts belong to the shoshonitic series and can be subdivided into olivine (Ol-) and plagioclase (Pl-)basalts. The Ol-basalts have moderate MgO contents (5.1–5.5 wt%) and Mg# values (48.7–50.3), and trace element patterns similar to typical ocean island basalts with positive Nb–Ta and negative Pb anomalies. We interpret the Ol-basalts as mantle-derived rocks. The Pl-basalts and andesites are more differentiated than the Ol-basalts, and have low MgO contents (3.9–4.5 and 0.55–3.4 wt%, respectively) and Mg# values (40.3–43.3 and 26.9–47.4; respectively). Trace element (e.g., low Nb/U and Ce/Pb ratios) and Sr–Nd–Hf isotope data for the Pl-basalts and andesites indicate an origin by fractionation and mixing between the mantle-derived magma parental to the Ol-basalts and a crust-derived silicic magma. Crustal melting was induced by the underplating of the mafic parental magmas of the Ol-basalts. Geochemical features of the Ol-basalts, including high SiO2, Nb, Ta, Na2O/K2O, and Fe/Mn and low Rb/Sr and Dy/Yb, are best explained by the vein-plus-wall rock melting of a metasomatized mantle source consisting of amphibole–clinopyroxene-rich veins and surrounding peridotites. The Ol-basalts have enriched Sr–Nd isotopic compositions ((87Sr/86Sr)i = 0.70585–0.70597; eNd(t) = −2.8 to −2.6) and decoupled Hf–Nd isotopes with positive ∆eHf(t) (+4.5 to +5.0) that are consistent with recent enrichment of the lithosphere by subduction components from the Paleo-Asian oceanic slab. We propose that the Siziwangqi magmatism was related to intra-continental extension of the North China Craton.

Microanalysis of accessory minerals was carried out to elucidate the controversial origin of the classical, ~430 Ma (Silurian) S-type granites and related lithic inclusions from the eastern Lachlan Orogen, southeastern Australia. Inclusions were separated into igneous-derived, mafic microgranular enclaves (MME) and metasedimentary inclusions. Apatite ɛNd(t), and monazite ɛNd(t) isotopic values for granite host and inclusions cover a similar range (~ −4 to −13), but their ɛNd(t) peaks are distinct. Whereas similar unimodal peaks exist for both minerals in the granites, suggesting widespread equilibration during hybridisation of two magmatic components in the host S-type magma, skewed or bimodal peaks characterize the MME and metasedimentary inclusions, indicating their different petrogenetic histories. The isotopic data suggests two endmembers: a mature metasedimentary source with ɛNd(t) of −12, represented by ubiquitous Ordovician quartzose turbidites, and a more radiogenic component represented by a − 5 ɛNd(t) peak in the MME. Zircon ɛ(Hf) values from −3 to −10, and δ18O values from 7.5‰ to 10.5‰, reflect variable incorporation (40–80%) of metasedimentary material with a mantle-like endmember. Temperature estimates for magmatic equilibration are 750-800 °C, though evidence exists for transient higher temperatures in some inclusions. Phase equilibria modelling using the average composition of the Ordovician turbidites as a potential source-rock suggests that melt compositions were uniform, silicic (75–76 wt% SiO2) and peraluminous (ASI = 1.13–1.22), for a wide range of temperatures and water contents. However, neither the modelled residual rock (restite) compositions, nor the analysed metasedimentary inclusions, lie along the Lachlan S-type compositional array. Rather, the compositional array projects to a mafic endmember defined by the MME, suggesting widespread, efficient hybridization with weakly peraluminous, andesitic magmas. Source mixing models (without significant mantle-derived magma input) are rejected on petrological and geological criteria. The andesitic MME-type magmas were hybridized in the lower crust, probably during mafic magma underplating, before incorporation into large, cool, midcrustal S-type magma reservoirs, and the observed MME represent the final mingled stage of that interaction during emplacement at shallow crustal levels. Using a modern example from the Andes, a model is presented of 2-stage hybridization, initially near the Moho, then in the midcrust as hot, hybrid andesitic magmas repeatedly infused a resident, giant, low-T, S-type magma body. Late-stage injection of the MME generated localized inclusion swarms, as at Cowra and Deddick, and promoted eruption of vast S-type ignimbrite sheets during a major magmatic flare-up in the Lachlan orogen.

Whole rock geochemistry and Sr-Nd-Hf isotope, zircon U Pb and Hf O isotope data are reported for the early Jurassic gabbro-syenite-alkali-feldspar granite in the inland of South China, in order to investigate their sources, petrogenesis and tectonic implication, and to further trace the rejuvenation of continental crust of South China. The zircon U Pb dating constrains the crystallization ages of 198–195 Ma for syenites, and of about 190 Ma for alkali-feldspar granites and gabbros, respectively. The early Jurassic gabbros have low SiO2 contents and high MgO, TiO2, Cr, V and Ni concentrations, with weak negative Nb and Ta anomalies, variable whole rock initial 87Sr/86Sr ratios (0.7064–0.7117), eNd(t) values (−1.5 to +0.6), eHf(t) values (−1.6 to +5.7) and zircon eHf(t) values (+3.4 to +6.4) and mantle-like δ18O values (+4.9 to +6.2‰). They are inferred to be derived from partial melting of a fertile lithospheric mantle that had been metasomatized by subduction-related fluids/melts, with subsequent limited crustal assimilation and fractional crystallization. The early Jurassic syenites are high-K to shoshonitic rocks with weakly negative Nb and Ta anomalies, strongly negative Sr, P and Ti anomalies, unradiogenic Sr and radiogenic Nd and Hf isotopic compositions (eNd(t) up to +5.3 and eHf(t) up to +11.5), indicating that they were generated by low-percentage partial melting of an amphibole-bearing lithospheric mantle, with subsequent crustal assimilation and extensive crystal fractionation and/or accumulation. The geochemical features of the early Jurassic K-feldspar granites suggest that they were mainly generated by mixing between mantle-derived mafic magma and crustal-derived felsic magma with extensive feldspar-dominant fractional crystallization. The early Jurassic magmatism was possibly triggered by asthenospheric upwelling following delamination of the flat-subducted Paleo-Pacific plate beneath South China, which provided heat to partial melting of above lithospheric mantle and continental crust. The underplating of depleted mantle-derived magmas changed the ancient crustal structures and modified the components of continental crust, indicating lithospheric rejuvenation during early Jurassic in South China.

Whole-rock geochemical and in situ zircon U Pb and Hf O isotope compositions have been measured for the Jurassic granitoids in the Liaodong Peninsula, in order to investigate their genesis and reveal the Jurassic crustal evolution of the eastern North China Craton. Our new data, combined with field and petrological observations, indicate multi-stage Jurassic magmatism, now represented by Early to Middle Jurassic biotite granites and monzogranites, and Late Jurassic two-mica monzogranites. The Early to Middle Jurassic granitoids have relatively low SiO2 contents (64.4–69.6 wt%) and K2O/Na2O ratios (0.4–1.0), adakitic characteristics with enriched LREE and depleted HREE contents, high Sr/Y ratios (52–189), positive Eu and Ba anomalies, and negative Nb and Ta anomalies. Together with their highly negative zircon ɛHf(t) (−26.6 to −16.1) and mantle-like δ18O (4.6‰ to 6.3‰) values, partial melting of a basaltic lower crust, which formed at ca. 2.5 Ga, can be proposed for the magma source of the Early to Middle Jurassic granitoids. These source rocks have not experienced significant water–rock alteration after formation. In contrary, the Late Jurassic two-mica granitoids exhibit relatively differentiated geochemical characteristics, with high SiO2 contents (>72 wt%) and K2O/Na2O ratios and variable Eu anomalies. Their parental magma was also enriched in LREEs and depleted in HREEs, with high Sr/Y (49.8–134) and (La/Yb)N (22.6–38.0) ratios. The magmatic zircons have extremely negative ɛHf(t) (−37.5 to −19.6) and relatively high δ18O (6.9‰ to 9.6‰) values, indicating the involvement of an ancient crustal component with high δ18O values, such as metasedimentary rocks. We propose, therefore, that the Late Jurassic two-mica monzogranites originated from partial melting of reworked ancient crustal materials at the depth of lower crust, and with the magma subsequently evolving as a result of plagioclase-dominated fractional crystallization. During Early to Middle Jurassic, westward subduction of the Paleo-Pacific plate, resulted in the partial melting of the mafic lower crust and the burial of ancient crustal materials in to deep crust, while crustal stretching in Late Jurassic might account for the decompression melting of the ancient crustal source. Thus, multi-stage Jurassic magmatism in the Liaodong Peninsula recorded a complex crustal evolution history, which closely related to the westward subduction of the Paleo-Pacific plate.

The character of the lithospheric mantle of the northern Siberian craton is not well established; nearly all published data are for mantle xenoliths from a single kimberlite in the center of the craton (Udachnaya). We report major elements of the whole rock, trace elements data of clinopyroxene and Re-Os isotope and PGE concentration of mantle xenoliths from the Obnazhennaya kimberlite pipe (160 Ma) in the northern part of Siberian craton. The Obnazhennaya mantle xenoliths include spinel harzburgites, spinel dunites, spinel lherzolites and spinel-garnet lherzolite. The spinel harzburgites and dunites have refractory compositions, with 0.23–1.35 wt% Al2O3, 0.41–3.11 wt% CaO and 0.00–0.09 wt% TiO2, whereas the lherzolites (both spinel- and spinel-garnet-) have more fertile compositions, containing 2.16–6.55 wt% Al2O3, 2.91–7.55 wt% CaO and 0.04–0.15 wt% TiO2. The trace element compositions and mineralogical textures of the Obnazhennaya xenoliths indicate the occurrence of metasomatic enrichments, including carbonatite melts, basaltic melts from Siberian Trap and kimberlitic melts. The spinel harzburgites and dunites have 187Os/188Os of 0.11227–0.11637, giving a TRD age of 1.6–2.2 Ga. This suggests that old cratonic mantle still existed beneath the Obnazhennaya. In contrast, both spinel and spinel-garnet lherzolites have more radiogenic 187Os/188Os ratios (0.11931–0.17627), enriched P-PGEs. But the higher Al2O3 and Os character of these lherzolites suggest that they were not juvenile mantle but the refertilized ancient mantle. Therefore, our results suggest that the cratonic mantle beneath the northern part of Siberian craton contain both ancient and reworked lithospheric mantle, and the metasomatism may not be effective at overprinting/eroding the pre-existing lithosphere.

The destruction of the North China Craton (NCC) culminated during the Early Cretaceous, inducing widespread magmatism and related mineralization in the eastern China. The Shizhuzi magmatic complex (SMC) from the Liaodong Peninsula is typical products of this event, thus could provide important insights on the destruction process. Here, we present petrological, geochronological, and elemental and isotopic geochemical data for the SMC rocks in order to reveal their magma sources, petrogenesis and the possible geodynamic process. The complex comprises quartz diorite, granodiorite, and granite, accompanied with Au, Cu and Mo mineral deposits. Zircon U Pb dating shows that the different rocks were coeval with the formation ages of 129–126 Ma, coincident with the associated mineralization. However, field relations, whole-rock major and trace element contents and isotopic compositions indicate different origin for the quartz diorites and the coeval granodiorites and granites. The quartz diorites are calc-alkaline rocks with high MgO, Mg# and low SiO2. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs) with significant negative Nb, Ta and Ti anomalies. These geochemical data and the highly enriched zircon Hf isotopes suggest that they were derived from partial melting of enriched subcontinental lithospheric mantle. The granodiorites and granites from the SMC have high SiO2 and low MgO contents, suggesting that they were derived from crustal sources. These rocks are I-type rocks with high-K calc-alkaline features. Their primary magma originated from the partial melting of basaltic lower crust and experienced fractional crystallization. The ascending mantle-derived magma provided heat for the melting of the crustal rocks. Based on regional geology, the SMC was generated in the extensional setting related to the roll-back of the subducted Paleo-Pacific plate. The concurrent mantle and crustal melting in the formation of the SMC revealed the loss of stability of the cratonic lithosphere, related to the destruction of the NCC during Early Cretaceous. Besides, the emplacement of SMC might also contribute to the formation of contemporaneous Au, Mo, and Cu deposits.

Continental subduction is an important but poorly known means of transporting the Earth's crust into the mantle. Continental subduction has also been proposed to responsible for the formation of the Cenozoic intracontinental potassic rocks widespread in Tibet and uplift of the Tibetan Plateau. However, such ancient continental subduction only occasionally been identified and is controversial. In this contribution, we explore the use of boron and its isotopes, to provide new constraints on the origin of newly identified Eocene potassium-rich volcanic rocks in northern Tibet and potential subduction of continental crust. Our results indicate that the latest Eocene (ca. 34 Ma) potassium-rich volcanic rocks are characterised by moderate silica, adakite-like trace elements, enriched Sr-Nd-Pb and light boron isotope (δ11B = −20.12‰ to −7.95‰) signatures. This isotopically light signature of boron suggests a melange source composed of mantle wedge peridotite and recycled dehydrated continental crust. The Eocene potassium-rich magmas were likely derived from low-degree partial melting of diapir melange at high-pressure and medium temperature within subduction channel. Our work indicates potential obduction of the Tibetan plate over the Asian plate thus triggering intracontinental subduction before the end of Eocene. This continental obduction may have accommodated a huge amount of crustal material during Cenozoic rapid convergence between India and Asia. We conclude that during this process an isotopically light component is likely to have been transported into the mantle to form a distinct source region. B isotopes therefore have the potential to trace the continental crust recycling in large collisional orogens.

Ascertaining the petrogenesis of granitoid rocks in subduction zones holds the key for understanding the processes of how continental crust is produced. The synchronous Taoyuan and Huanggang plutons occur in two different geological units of the Paleozoic Tongbai orogen of central China. They provide an optimal opportunity for a study to address the role of the crustal basement in generating voluminous granitoid magmatism in subduction zones. The Taoyuan and Huanggang plutons have identical U–Pb zircon crystallization ages of 440–444 Ma, which are temporally related to northward subduction of the Paleotethyan Ocean. The Taoyuan samples show high SiO 2 (73.36–79.16%) and low Al 2 O 3 (12.00–13.45%) contents, Mg numbers (20.6–38.2), and Sr/Y (2.04–10.1) and (La/Yb) N (2.34–7.32) ratios with negative Eu anomalies (Eu/Eu* = 0.33–0.93). They yielded positive e Nd (t) (+ 3.0 to + 6.7) and e Hf (t) (+ 11.8 to + 13.2) values, elevated initial Sr isotopic ratios (0.7040–0.7057) and relatively low zircon δ 18 O values of 4.62–5.39‰. These suggest that they were produced through partial melting of hydrothermally altered lower crust of the accreted Erlangping oceanic arc. In contrast, the Huanggang samples exhibit variable whole-rock geochemical and isotopic compositions with SiO 2 contents of 57.01–64.42 wt.%, initial Sr isotopic ratios of 0.7065–0.7078, and e Nd (t) values of − 5.7 to − 9.4. Additionally, they have high zircon δ 18 O values of 7.57–8.45‰ and strongly negative zircon e Hf (t) values of − 14.4 to − 10.5. They were suggested to have been mainly derived from ancient continental crust of the Kuanping crustal unit with the addition of 20–40% juvenile, mantle-derived material. Accordingly, the granitoids in both oceanic and continental arcs are likely to be mainly derived from intracrustal melting of their crustal basement. It is revealed by the Huanggang pluton that little net continental crust growth occurs in continental arcs, and addition of new volume of continental crust may be balanced by the loss of old mafic lower continental crust. Continental growth was likely achieved through the accretion and subsequent differentiation of oceanic arcs, as manifested by the Taoyuan pluton.

The Nanling Range (NLR) is the largest tungsten metallogenic province in China and perhaps in the world. The tungsten mineralization is believed to be related to Jurassic granitic magmatism. However, the petrogenesis of these granites and their relation to the tungsten mineralization are still debated. Whole-rock geochemical and Sr–Nd–Hf isotopic data and zircon in situ U–Pb ages and Hf–O isotopes are reported for W-bearing granitic intrusions from the southern Jiangxi Province in the NLR, in order to constrain their magmatic sources and petrogenesis. The NLR granites include biotite granites, two-mica granites and garnet muscovite granites. SIMS and LA-ICPMS U–Pb dating of zircons and monazites give emplacement ages of 161–154 Ma for these rocks. The granites are metaluminous to strongly peraluminous with high SiO 2 (> 72.3 wt.%) and high K 2 O (> 3.7 wt.%). Petrographic and geochemical features show that they are highly fractionated I-type granites. The biotite granites are enriched in light rare earth elements (LREEs) relative to heavy REEs, have weakly negative Eu anomalies and are depleted in Nb, Ba, P and Ti. In contrast, the two-mica and garnet-bearing muscovite granites have tetrad-type REE patterns with strongly negative Eu anomalies and are extremely depleted in Ba, Nb, Sr, P and Ti. Magmatic garnets are mainly almandine and spessartine, and have low-Mn cores and high-Mn rims. Their (Y + HREE) contents are high and generally decrease from core (1.2 wt.%) to rim (average = 4955 ppm). All of these granites are characterized by variable whole-rock initial 87 Sr/ 86 Sr (0.7053–0.8000), e Nd (t) (− 12.6 to − 9.4) and e Hf (t) (− 12.3 to − 8.5), as well as variable zircon e Hf (t) and δ 18 O, with values of − 16.3 to − 7.4 and 7.6 to 10.0‰, respectively. They contain abundant zircon xenocrysts and xenoliths of micaceous schist. All of these features are consistent with a process of crystal fractionation of crustally-derived magmas coupled with strong assimilation of sedimentary rocks. The assimilation of meta-sedimentary materials increased the concentrations of tungsten, alumina and manganese in the magmas, whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks. The W-enriched magmatic fluids formed the tungsten-bearing quartz veins, revealing the genetic relationship between tungsten mineralization and emplacement of garnet-bearing two-mica or muscovite granites in the NLR.

Late Carboniferous–middle Permian magmatism in the Jiamusi Massif of northeast China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), provides critical evidence regarding the tectonic history and geodynamic processes in the region. The gabbro–diorites of the Longtouqiao pluton and two groups of coeval granite in the study area comprise a bimodal magmatic suite. Precise LA-ICP-MS U–Pb zircon ages indicate that the granitoids and gabbro–diorites were emplaced in the late Carboniferous–middle Permian (302–267 Ma). Group I granites have high SiO2 (70.75–77.04 wt.%) and K2O (3.65–5.89 wt.%) contents, are enriched in LILEs (e.g., Rb, Th, and U) relative to HFSEs and LREEs, and have negative Nb, Ta, P, and Ti anomalies, which collectively indicate affinities with subduction-related magmas. Group II granites are weakly peraluminous (A/CNK = 1.03–1.07) and are characterized by enrichment in alkalis (Na2O + K2O = 8.22–8.90 wt.%), low MgO (0.04–0.09 wt.%) and P2O5 (0.01–0.04 wt.%) contents, high Zr and Nb contents, high 10,000 × Ga/Al ratios, and they are geochemically similar to aluminous A-type granites. All the magmatic zircons in these granitoids have great variations of eHf(t) (+ 7.89 to − 5.60) and two-stage Hf model ages (TDM2) of 0.8–1.7 Ga, which suggest that the precursor magmas originated from a heterogeneous source that involved juvenile components derived from a depleted mantle source during magma generation. The aluminous A-type granite magmas were probably derived by high-temperature partial melting of a felsic crustal source, whereas the other granite magmas probably resulted from partial melting of a mafic lower crust. The gabbro–diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for large positive anomalies in Ba, K, and Pb. These features reflect a limited degree of crustal contamination associated with the subduction-related magmatic processes. These data, together with previously reported data and the nature of various rock types along the eastern part of the Jiamusi Massif, suggest that the intrusive rocks were formed in a geodynamic regime that changed from compression to extension during the westwards subduction of the Paleo-Pacific oceanic lithosphere, probably as a result of slab break-off of the subducting plate.

We present eudialyte and zircon U–Pb ages, whole-rock geochemical, and Sr–Nd–Hf and zircon Hf–O isotope data for the Xiangshuigou silicic alkaline igneous complex from the northern margin of the North China Craton (NCC). We use these data to investigate the source and petrogenesis of these alkaline igneous rocks and the lithospheric mantle evolution of the NCC. The Xiangshuigou complex consists of nepheline and porphyritic syenites without associated mafic or intermediate rocks. Zircon and eudialyte U–Pb dating yielded consistent ages of 227–219 Ma for these rocks. All the alkaline igneous rocks from the Xiangshuigou complex have high Na2O, Al2O3, Rb, Th, and Zr, and low MgO, CaO, P2O5, and Ba contents, and are enriched in large-ion lithophile and light rare earth elements. These rocks are not depleted in high-field-strength elements. Whole-rock Nd–Hf isotopic compositions are slightly enriched, with eNd(t) = −3.7 to −3.0 and eHf(t) = −3.1 to +0.6. Zircon Hf–O isotope analyses yielded eHf(t) and δ18O values of −0.6 to −6.0 and +5.1‰ to +6.0‰, respectively. These geochemical and isotopic features suggest that the silicic alkaline igneous rocks were derived by partial melting of an enriched lithospheric mantle source before experiencing protracted two-stage fractional crystallization. The lithospheric mantle source of the Xiangshuigou complex was distinct from the Paleozoic cratonic lithospheric mantle and experienced mantle metasomatism by depleted mantle-derived carbonate-bearing materials prior to the alkaline magmatism. This indicates that, in addition to subducted crustal melts/fluids, asthenosphere-derived materials were also involved in modifying the lithospheric mantle of the northern NCC. As such, our work not only approves the effectivity of using whole-rock geochemistry and Sr–Nd–Hf–O isotopic data to reveal origin of the silicic alkaline igneous rocks, but also argues for a multiple modification for the northern NCC during the late Paleozoic to early Mesozoic.

Whether the formation of early Paleozoic granites in the South China Block was related to intracontinental orogenic processes or oceanic subduction continues to be debated. Here, we present whole-rock major element, trace element, and Sr Nd isotopic data, as well as secondary ion mass spectrometry and laser ablation–inductively coupled plasma–mass spectrometry zircon U Pb geochronological and Hf O isotopic data, from biotite, two-mica, and muscovite granites in the Baiyunshan and Maofengshan areas of Guangzhou City, South China. Zircon U Pb ages reveal that these rocks were formed during the early Paleozoic (446–438 Ma). These muscovite- and biotite-bearing granites have high SiO2 (69.0–80.4 wt%) and K2O (3.19–5.32 wt%) contents, and low MgO (0.46–1.17 wt%) contents. The granites are enriched in Rb, Th, U, and Pb, and depleted in Ba, Sr, Nb, and Ti. The Baiyunshan muscovite granites and Maofengshan biotite granites are slightly to moderately enriched in light rare-earth elements [LREEs; (La/Yb)CN = 2.27–15.1] with slight to pronounced negative Eu anomalies (Eu/Eu* = 0.27–0.72), whereas the Baiyunshan two-mica granites are significantly enriched in LREEs [(La/Yb)CN = 19.6–32.1] with moderate negative Eu anomalies (Eu/Eu* = 0.42–0.58). These muscovite- and biotite-bearing granites have enriched whole-rock Nd and zircon Hf isotopic compositions (eNd(t) = −12.1 to −7.6; eHf(t) = −11.4 to −0.8), and high zircon δ18O values (8.5‰–10.0‰). We suggest that the Baiyunshan granites were formed by partial melting of metasedimentary rocks, as they contain primary muscovite and have high zircon δ18O values. The Maofengshan granites were formed by partial melting of a hybridized crustal source containing metasedimentary rocks with subordinate amphibolites, as they have high zircon δ18O values, variable whole-rock SiO2 contents, and biotite compositions similar to those crystallized in I- and S-type magmas. These granites, along with the widespread early Paleozoic S-type granites in the Wuyi–Yunkai orogen, are distributed across a broad area rather than in a narrow belt. In addition, early Paleozoic S-type granites in the South China Block generally do not show younging trends from east to west or south to north. Moreover, the Baiyunshan–Maofengshan granites show geochemical characteristics similar to syn- or post-collisional granites and different from volcanic arc granites. We therefore propose that these muscovite- and biotite-bearing granites were formed in an intracontinental orogenic setting.

The Triassic Saima alkaline complex on the Liaodong Peninsula, northeastern China, consists mainly of potassic phonolite, nepheline syenite, and sodic lujavrite. The lujavrite shows significant Zr-REE mineralization, which is present in the form of early magmatic, Zr-REE-enriched clinopyroxene (30%–40%), titanite (5%), and loparite-(Ce), and late magmatic to hydrothermal wadeite, widespread eudialyte group minerals (5%–10%), and catapleiite. Ultimately, the fractionation of the alkaline magma leads to the crystallization of mosandrite and hezuolinite. Textural relations and compositional variation among the characteristic Zr-REE-bearing minerals record that both Zr and REEs were strongly incompatible in the sodic melt, but that Zr mineralization preceded REE mineralization. The main Zr-REE mineralization in the Saima lujavrite resulted from the high peralkalinity, Na/K ratio and HFSE content, low oxygen fugacity, and the intensive activity of water and volatiles of its evolving magma. The discontinuous and abrupt changes in melt composition and mineral assemblage from the potassic nepheline syenite of the complex to the sodic lujavrite suggest that their magma was derived from different episodes of magmatic activity with different physico-chemical characteristics, rather than from the continuous evolution of a single magmatic event.

Phanerozoic growth of continental crust has widely been considered as an important geological phenomenon and mainly occurs in an arc setting. However, the crustal growth models (mantle-derived basalt underplating or accretion of island or intra-oceanic arc complexes or oceanic plateau) have been disputed. Here we present new zircon LA–ICPMS U–Pb age, whole-rock major and trace element, Sr–Nd and zircon Hf isotopic data for Late Mesozoic intermediate–felsic intrusive rocks in the Rena Co area in southern Qiangtang, central Tibet. LA–ICP–MS zircon U–Pb dating for two granodiorite and three diorite samples and one granodiorite porphyry sample gives ages of ca. 150 Ma, ca. 112 Ma, respectively, indicating they were generated in the Late Jurassic–Early Cretaceous. All rocks are sub-alkaline in composition and belong to the high-K cal-alkaline series. The ~ 150 Ma diorites (SiO2 = 57.9–61.2 wt.%) exhibit relatively high MgO (3.13–3.88 wt.%) and Cr (52.4–282 ppm) contents and Mg# (47–51) values, similar to magnesian diorites. They are geochemically characterized by uniformly low eNd(t) (− 5.5 to − 5.2), high (87Sr/86Sr)i (0.7071 to 0.7078) and Th/La (0.22–0.32), and variable zircon eHf(t) (− 8.7 to + 4.8) values. They were probably generated by melting of oceanic sediment diapirs, followed by interaction with the surrounding mantle during the northward subduction of Bangong–Nujiang Oceanic lithosphere. The ~ 150 Ma granodiorites and ~ 112 Ma granodiorite porphyries are characterized by low MgO ( 15% wt.%) and Sr (> 400 ppm) and low Y (

Arc magmas are generated by complex geological processes in subduction settings. Due to the complexity of source materials and geological processes, the genesis of arc magmatic rocks can be difficult to disentangle. Here, we report on diorites from the Kenama area of the middle-eastern part of the Bangong–Nujiang suture zone in central Tibet. New SIMS and LA–ICP–MS zircon U Pb dating for three diorite samples indicates that they crystallized during the early Late Jurassic (ca. 161 Ma). The diorites can be divided into two groups based on whole-rock major element compositions and mineralogical characteristics: Group I diorites with relatively low SiO2 (47.6–53.4 wt%), and high MgO (4.97–9.10 wt%) and amphibole contents (50–54 vol%); and Group II diorites with slightly higher SiO2 (56.9–59.5 wt%), and low MgO (2.9–3.8 wt%) and amphibole contents (25–30 vol%). The Group I diorites exhibit relative enrichment in light rare earth element (LREE) ((La/Yb)N = 5.7–10.5) with slightly negative Eu anomalies, and are characterized by enrichment of large ion lithophile elements (LILEs; K, Rb, Ba, Th, and U), the depletion of high field strength elements (HFSEs; Nb, Ta, Zr, Hf, and Ti). The Group I diorites have relatively high initial 87Sr/86Sr ratios (0.7073–0.7094), variably negative eNd(t) values(−10.3 to −5.9), negative zircon eHf(t) values (−14.8 to–4.4), and slightly elevated δ18O values (6.5‰–7.3‰). The Group II diorites show similar trace element characteristics to Group I. They also have high initial 87Sr/86Sr ratios (0.7083–0.7087), uniformly negative eNd(t) values (−9.5 to −9.0), negative zircon eHf(t) values (−10.3 to −4.2), and elevated δ18O values (6.6‰–7.5‰). Amphiboles from Group I and Group II diorites have low Al2O3 contents (3.6–9.9 wt% and 5.6–8.5 wt%, respectively), and formed at similar P–T conditions (751–871 °C and 69–226 MPa and 745–832 °C and 77–162 MPa, respectively). On primitive mantle-normalized spider diagrams, these low-Al amphibole grains have slightly convex upward REE patterns with distinctly negative anomalies in Pb, Sr, Eu, Zr, Hf, and Ti, suggesting that amphiboles from both groups crystallized from the similar arc magmas after plagioclase and magnetite crystallization. These mineralogical, geochemical and isotopic characteristics suggest that both groups of Kenama diorites probably originated from an enriched lithospheric mantle metasomatized by subducted oceanic sediment-derived melts. Their parental magmas may have similar geochemical characteristics and underwent varying degrees of accumulation and fractional crystallization. The Group I diorites were likely generated by accumulation of amphibole and fractional crystallization of olivine, clinopyroxene, and plagioclase from mafic magmas, and the Group II diorites were formed by the fractional crystallization of clinopyroxene and plagioclase from mafic magmas that were geochemically similar to the Group I diorites. In combination with regional geology, in particular adjacent ophiolites, high-magnesian andesitic rocks and Cretaceous sedimentary rocks, we conclude that all of the Kenama diorites were probably generated in an early Late Jurassic arc setting related to the subduction of the Bangong–Nujiang Tethys oceanic lithosphere.

Whole rock major and trace elements and Sr-Nd-Hf isotopes and zircon in situ U Pb ages and Hf O isotopes have been determined for the Kalaqin granitic batholith and Heilihe Intrusive Complex (HIC) on the northern margin of the North China Craton (NCC), to investigate their magmatic sources and petrogenesis and further to reveal the lithospheric evolution of the craton. Zircon U Pb dating, combined with the field observations and petrographic features, shows that at least 5 episodes of granites can be identified in the Kalaqin Batholith, i.e., 246 Ma monzogranite in the north, 234–227 Ma medium-grained monzogranite in the southwest, 224–221 Ma syenogranites in the north, 211 Ma granites in the south-central part and 206 Ma coarse-grained to megacrystic monzogranites intruding into the early batholith, and 238–231 Ma for the HIC ultramafic to mafic rocks. The 246 Ma granites have high SiO2 contents, negative whole rock eNd(t) and eHf(t) values, and negative zircon eHf(t) values and high δ18O values (up to 6.55‰), with ancient Nd and Hf model ages, indicating that they were derived from an ancient continental crustal source. However, the 234–221 Ma granites have positive whole rock eNd(t) and eHf(t) values and zircon eHf(t) values, indicating that they were derived from a relatively young crustal source. The granites of later episodes own some transitional isotopic feature and are suggested to be derived from a mixed source. The 238–231 Ma HIC rocks have high MgO contents, primitive mantle-like whole rock eNd(t) and eHf(t) values and zircon eHf(t) values and slightly higher zircon δ18O values than mantle. Zircon Hf O isotopic constraints have further pointed to a mixed origin by depleted mantle and enriched lithospheric mantle for the HIC rocks. Calculation of the two-pyroxene thermobarometer yields crystallizing conditions of gabbronorites at around 1080 °C and 5 kbar, suggesting the emplacement of hot mantle-derived magmas into mid-crustal depth. All of the observations show that the lower continental crust beneath the northern margin of the NCC had been modified from ancient to relatively young by mantle-derived magma underplating during 246–221 Ma, although no solid evidences supporting the direct magmatic linkage were found between the batholith and the HIC. It is suggested that the lithosphere of the northern NCC had been modified and became weakened during 246–221 Ma, which makes the NCC easy to be destructed during late Mesozoic.

Syenogranite and related dioritic rocks (dioritic microgranular enclaves and quartz diorite) from the Early Cretaceous Shihuzhen–Jiudaogou pluton, NE China, were studied to investigate the formation and evolution of the granitic magma driven by the mantle-derived magma. All selected rocks were formed contemporaneously, with zircon U Pb ages of 125–121 Ma. Field and petrographic observations show that magma mixing happened between mafic and felsic magmas represented by dioritic enclaves and syenogranite. The dioritic enclaves with quenching textures have low SiO2 and high MgO contents, variable zircon eHf(t) compositions (−8.7 to +2.4), coupled with low initial 87Sr/86Sr ratios (0.70647–0.70772) and variable eNd(t) values (−8.8 to −3.9) for apatite, suggesting they were derived from an enriched mantle source with contamination of crustal materials. The syenogranites have relatively high 87Rb/86Sr ratios (2.92–22.0), variable zircon eHf(t) compositions (from −11.1 to −3.6), coupled with low initial 87Sr/86Sr ratios (0.70727 to 0.70791) and variable eNd(t) values (from −9.9 to −7.3) for apatite, requiring a juvenile crust origin with participation of mantle-derived magma. They were characterized by high SiO2 (> 74.0 wt.%) and low MgO, P2O5 contents, with conspicuous negative Ba, Sr, and Eu anomalies, implying a late fractionation phase. The quartz diorites have relatively high initial 87Sr/86Sr ratios (0.70781–0.70928) for apatite, with negative zircon eHf(t) values (−11.6 to −7.8) and apatite eNd(t) values (−10.5 to −8.9), which are identical to those of the felsic parental magma of syenogranite. They show complementary geochemical compositions with the syenogranite, including low SiO2 ( 744 ppm) contents, with obvious positive Ba and Sr anomalies and weakly positive Eu anomalies. Coupled with petrological observations (e.g., cumulate texture), we argue the crystal-melting segregation model account for the genetic link between the quartz diorite and syenogranite, representing residual crystal accumulations and segregated interstitial melt from a crystal-rich magma chamber. The partial melting of juvenile lower crust and the subsequent crystallization differentiation of intermediate-acid magma developed a crystal-rich magma chamber. The mantle-derived magma then drove the rejuvenation of pre-exist magma chamber, promoted the crystal-melt segregation process and mixed with the felsic magma, and then formed quartz diorite and syenogranite in the Shihuzhen-Jiudaogou pluton. Mantle-derived magma played an important role in the formation of the granitic rocks, providing heat for partial melting, materials, and the driving force for their compositional evolution.

Multiple petrogenesis models have been proposed for granitic rocks and the mafic microgranular enclaves (MMEs) hosted in them. The mantle and crust-derived magma mixing/mingling process was widely suggested for the formation of MMEs or the host granitoids. However, whether the mixing between magmas derived from different crustal sources may also form microgranular enclaves (MEs, not restricted to mafic) or the host granites remain unclear. Here, we report petrological, geochemical, and zircon in situ Hf-O isotopic data for MEs and their host granites in the northern Nyima area, southern Qiangtang terrane (SQT), central Tibet. The host granitic rocks consist of amphibole-bearing biotite granites and syenogranite, minor granodiorite and aplite veins, and MEs comprising diorite and granodiorite. Host rocks and MEs are contemporaneous and were generated in the Early Cretaceous (∼120 Ma). Host granitoid samples are high-K calc-alkaline rocks and have high SiO2 (66–78 wt%) and low MgO ( 5 wt%, high Zr >500 ppm with Zr/Hf ratios >45, and high Ba >400 ppm), implying biotite and zircon concentrations. Combining this information with embayed feldspars, curved biotites, and closely spaced feldspar grains, we suggest that liquid loss resulted from crystal compaction or filter pressing. Both the fine-grained syenogranites and aplite veins exhibit high SiO2 and Rb/Sr ratios in addition to low Zr/Hf ratios and Zr and Ba concentrations with remarkably negative Eu anomalies, indicating that they are highly differentiated melts extracted from felsic crystal mush. Such a crystal mush is possibly represented by the biotite granites. Gradual contact relationships between variable granitic phases indicate that melt extraction and crystal concentration were coeval. Residual melt extraction from the crystal mush was facilitated by mush remobilization resulting from magma replenishment. We suggest that for the host rocks, the biotite granites were mainly derived by partial melting of ancient crust, and the granodiorites most likely resulted from the magma mixing/mingling that might be accompanied with the loss of melts, the fine-grained syenogranites and aplites represent highly evolved residual melts. MEs are geochemically characterized by intermediate to felsic compositions (SiO2 = 56.3–67.8 wt%), with low MgO (

The Triassic Saima alkaline complex in the Liaodong Peninsula of northeastern China covers an area of about 20 km 2 and is dominated by nepheline syenite, with phonolite at its center, and a concealed body of eudialyte-bearing nepheline syenite in the northwest of the complex. The phonolite has similar features to miaskite, while the nepheline syenites are classified in the agpaitic group according to their mineral assemblage, and the alkalinity and aluminum saturation indexes. Zircon is the dominant Zr-bearing mineral in the phonolite, whereas wadeite occurs as the only primary Zr-bearing mineral in the nepheline syenites. The transitional crystallization from zircon to wadeite reveals an increase in alkalis and a high K/Na ratio as the magmas evolved from the volcanic to the intrusive stage. The primary wadeite grains underwent varying degrees of hydrothermal alteration. Overall, the areas of weak, medium, and strong alteration are characterized by the following respective associations: (1) wadeite + secondary catapleiite/gaidonnayite, (2) wadeite + secondary catapleiite/gaidonnayite + zircon, and (3) pseudomorphs after wadeite. The pseudomorphs are widespread and mainly consist of residual wadeite, secondary zircon, catapleiite/gaidonnayite, K-feldspar, calcite, and some Zr-bearing titanite and vesuvianite. All of the secondary zircon grains in the three associations are typically enriched in Ca and Al compared with the primary Ca-free zircons of the phonolite. The progressive alteration of wadeite suggests that the Saima complex underwent multiple episodes of fluid activity during a hydrothermal stage, including an initial Na-metasomatism via alkaline fluids, then stages most likely involving progressively CO 2 -rich fluids, and an intensive episode involving a mixture of these fluids with externally derived Ca-rich fluids.

Cenozoic adakitic rocks in the Lhasa block (southern Tibet) have been widely used to trace the lateral extent of crustal thickening. However, their petrogenesis remains controversial. Here, we report geochronological and geochemical data for the Napuri intrusive rocks in the core area of the Quxu batholith, southern Lhasa. Zircon U–Pb dating suggests that they were generated at approximately 48 Ma. The studied samples show significant geochemical variations, manifested by the coexistence of three types of igneous rocks. Groups I and II rocks exhibit variable and high SiO 2 (66.4–73.9 wt.%), high Al 2 O 3 (14.0–17.4 wt.%), K 2 O (3.9–5.3 wt.%), Sr (273–718 ppm) and Sr/Y (18.3 to 81.3) values, and low Y (3.6 to 16 ppm), heavy rare earth element (REE) (e.g., Yb = 0.48 to 1.8 ppm), MgO (0.4–1.0 wt.%), Cr (2.9–7.4 ppm) and Ni (1.6–4.5 ppm) contents, which are similar to those of thickened lower crust-derived adakitic rocks. The Group I rocks show higher Sr/Y (77.5–81.3) ratios and lower total REE (55.5–63.2 ppm) contents with clearly positive Eu and Sr anomalies, whereas the Group II rocks have relatively lower Sr/Y (18.3–65.7) ratios and higher total REE (115–375 ppm) contents with negligible or slightly negative Eu and Sr anomalies. Group III rocks have the highest SiO 2 (74.5–76.0 wt.%), Y (17.0–23.7 ppm) and Yb (2.91–3.30 ppm) contents, and the lowest Al 2 O 3 (12.5–13.2 wt.%), Sr (81.3–141 ppm) and Sr/Y (4.8–5.9) values with distinctly negative Eu and Sr anomalies. Compared with the Jurassic–Cretaceous granitoids in southern Lhasa, the relative enrichment in Sr–Nd–Hf isotopic compositions (( 87 Sr/ 86 Sr) i = 0.7049–0.7055, e Nd (t) = − 0.3 ± 0.7 and e Hf (t) zircon = + 3.6 ± 11.4) for the Napuri intrusive rocks indicates that they likely contained Indian continental components. The Group I and Group II rocks most probably originated from thickened mafic lower crust (amphibolite eclogites or garnet amphibolites) with garnet + rutile ± plagioclase as residual minerals in the source at > 1.5 GPa, corresponding to depths of > 50 km, and Group III rocks were probably generated by fractional crystallization of plagioclase from the adakitic magmas. Taking into account the narrow linear nature of the Eocene magmatic belt and reported synchronous asthenosphere-derived basaltic rocks in southern Lhasa, we suggest that upwelling asthenosphere triggered by the break-off of subducted Neo-Tethyan slab probably provided the required thermal conditions for lower crustal melting. The identification of Indian continental components in the Napuri intrusive rocks probably indicates that the Asia–India collision had taken place prior to their emplacement. The dramatic changes in the (La/Yb) N ratios and e Nd (t) and e Hf (t) values of magmatic rocks in the Gangdese area at ca. 51–46 Ma indicate that the Cenozoic crustal thickening associated with the indentation of the Indian continent began in the Early Eocene (ca. 51–46 Ma) at the latest.

Zircon U–Pb ages and in-situ trace elements and Hf–O isotope compositions, together with whole rock geochemical and Sr–Nd–Hf isotopic data, are presented for Cretaceous granitoids in southeastern (SE) China in order to establish their origin and the evolution of the underlying lithosphere during the Late Mesozoic. Two stages of Cretaceous magmatism, with contrasting geochemical features, have been identified: an earlier adakite-like biotite granite as represented by the Shangying pluton and a later enclave-bearing monzogranite as represented by the Zaoshan pluton. The Shangying biotite granites have a zircon U–Pb age of 99 ± 1 Ma. They have relatively low Y and Yb contents, with high La/Yb and Sr/Y ratios, showing geochemical features of adakite. Their Sr–Nd–Hf isotope compositions are similar to those of Early Cretaceous mafic rocks in the same area, indicating that they were generated by partial melting of juvenile granulitic crust at a depth of about 40 km. The source was formed by underplating of enriched lithosphere mantle-derived magmas. In contrast, the Zaoshan calc-alkaline monzogranites, their enclaves and associated dolerite dykes from the Zaoshan pluton have an emplacement age of ~ 88 ± 1 Ma. The dolerites have high MgO contents, relatively low SiO 2 concentrations and low La/Yb ratios, and depleted Hf isotope compositions. All these geochemical features suggest that they were derived from a depleted spinel Iherzolite mantle source. The enclaves have high SiO 2 contents, indicating that they were derived from a crustal source. They have variable zircon Hf and O isotope compositions, suggesting that two components, i.e., a high e Hf (t) and a low δ 18 O component and a low e Hf (t) and high δ 18 O component, were involved in their origin. The high zircon e Hf (t) values and low δ 18 O values are similar to those of the dolerites, indicating a common source. Thus, we suggest that the enclaves were generated by partial melting of newly underplated depleted mantle-derived materials. The monzogranites have distinctly different zircon Hf and O isotope compositions from the enclaves, indicating that the parental magmas were mainly derived from ancient crust that interacted with underplated depleted mantle-derived magmas. The monzogranites have relatively high HREE contents, suggesting a garnet-free source (

Little is known about the detailed processes associated with the transition from oceanic to continental lithosphere subduction in the Gangdese Belt of southern Tibet (GBST). Here, we report zircon U-Pb age, major and trace element and Sr-Nd-Hf isotopic data for Late Cretaceous-Early Oligocene (similar to 91-30 Ma) intermediate-acid intrusive rocks in the Chanang-Zedong area immediately north of the Yarlung-Tsangpo suture zone. These rocks represent five magmatic episodes at similar to 91, similar to 77, similar to 62, similar to 48, and similar to 30 Ma, respectively. The 91-48 Ma rocks have slightly lower initial Sr-87/Sr-86 (0.7037 to 0.7047), and higher epsilon(Nd)(t) (+1.8 to +4.3) and epsilon(Hf)(t) (+3.5 to +14.7) values in comparison with those (0.7057 to 0.7062, -3.3 to -2.5 and +2.2 to +6.6) of the similar to 30 Ma intrusive rocks. The similar to 91, similar to 62 and similar to 30 Ma rocks are geochemically similar to slab-derived adakites. The similar to 91 Ma Somka adakitic granodiorites were likely derived by partial melting of the subducting Neo-Tethyan oceanic crust with minor oceanic sediments, and the similar to 91 Ma Somka dioritic rocks with a geochemical affinity of adakitic magnesian andesites likely resulted from interactions between adakitic magmas and overlying mantle wedge peridotite. The similar to 77 Ma Luomu diorites were probably generated by partial melting of juvenile basaltic lower crust. The similar to 62 Ma Naika and Zedong adaldtic diorites and granodiorites were likely generated mainly by partial melting of thickened juvenile mafic lower crust but the source region of the Zedong adakitic rocks also contained enriched components corresponding to Indian continental crust. The similar to 48 Ma Lamda granites were possibly generated by melting of a juvenile basaltic crust. The younger (similar to 30 Ma) Chongmuda adakitic quartz monzonites and minor granodiorites were most probably derived by partial melting of Early Oligocene north-ward-subducted Indian lower crust beneath the southern Lhasa Block. Taking into account the regional tectonic and magmatic data, we suggest that the Gangdese Belt of southern Tibet (GBST) underwent a tectonodynamic transition from oceanic subduction to continental subduction between 100 and 30 Ma. It evolved through four stages: 100-65 Ma roll-back of subducted Neo-Tethyan oceanic lithosphere; 65-60 Ma initial collision between Indian and Asian continents; 60-40 Ma breakoff of subducted Neo-Tethyan oceanic lithosphere; and similar to 30 Ma northward subduction of the Indian continent (C) 2014 Elsevier B.V. All rights reserved.

At more than 500 km in length, the mainly Jurassic–Early Eocene Gangdese batholith is one of the most important constituents of the southern Lhasa sub-block and provides an ideal site for study of Tibetan orogenesis. Recent studies on Gangdese intermediate-felsic intrusive rocks, mainly granites, demonstrate that remarkable crustal growth as well as an early Late Cretaceous (ca. 100–80 Ma) magmatic “flare-up” event occurred in southern Tibet. However, the mechanism that drove this magmatic event and its relationship to crustal growth event are not yet clear. Here, we report detailed petrological, geochronological, geochemical and Sr–Nd–Hf isotopic data for recently identified norites and hypersthene-bearing hornblendites in the Milin area, southern Lhasa sub-block. These mafic rocks are dated at early Late Cretaceous (ca. 93 Ma), and are characterized by relatively uniform Sr–Nd–Hf isotopic compositions ((87Sr/86Sr)i = 0.7042 to 0.7047, eNd(t) = + 2.9 to + 3.6 and eHf(t)zircon = + 10.9 to + 17.0), suggesting that they evolved from similar parental magmas. The Milin norites and hornblendites are likely to be the products of mineral fractionation and accumulation from a common parental magma during the early and late stages of the magma evolution, respectively. Thermometric calculations indicate that pyroxenes from the Milin norites have high crystallization temperatures (1240–1349 °C). The parental magmatic compositions calculated from pyroxene trace element compositions in the Milin norites show slightly flat to enriched light rare earth element (LREE) patterns ([La/Yb]N = 2.9–3.4; [La/Gd]N = 2.1–2.9) with variable negative Nb anomalies ([Nb/La]N = 0.18–0.81), indicating their dual or hybrid geochemical characteristics. We suggest that their parental magmas may have been generated by the interaction of upwelling asthenospheric and metasomatized lithospheric mantle. Taking into account the spatial and temporal distribution of the Mesozoic magmatic rocks and regional paleomagnetic data, we further suggest that the early-Late Cretaceous magmatic “flare-up” in the southern Lhasa sub-block was also triggered by the asthenospheric upwelling, which resulted from roll-back of subducted Tethyan oceanic slab.

Understanding the processes responsible for the intra-plate early Paleozoic Wuyi–Yunkai orogeny (> 460 Ma to 420–415 Ma) in the South China Block (SCB) is important for deducing the interactions of this block with other continents at that time, as well as the tectonic evolution of East Asia. One salient feature of the orogen is that despite the wide occurrence of syn- to late-orogenic (440 Ma to 420–415 Ma) granites in the orogen, neither syn- to late-orogenic volcanic rocks nor mafic rocks of any type have been reported. Such mafic rocks could shed clues about any mantle–crust interaction during such a major orogeny, thus help to understand the dynamics of the orogenic event. We present here, for the first time, geochronological, isotopic and geochemical data for a mafic-intermediate volcanic succession in northern Guangdong, near the edge of the metamorphic core of the orogen. The volcanic rocks unconformably overlie strongly deformed Cambro-Ordovician strata, but are in low-angle unconformable contact with overlying post-orogenic mid-Devonian strata. LA-ICP-MS and SHRIMP U–Pb dating of zircons from two andesitic and dacitic samples gives a consistent crystallization age of ca. 435 Ma, younger than the 460–445 Ma peak metamorphism of the orogeny but synchronous with the widespread late-orogenic (ca. 440–415 Ma) granitic intrusions. Nine least crustally-contaminated basaltic samples are characterized by high MgO (12.3–19.2 wt.%), Ni (214–715 ppm) and Cr (724–1107 ppm), but low TiO2 (0.6–0.8 wt.%), Al2O3 (10.2–12.8 wt.%) and Fe2O3T (total Fe as Fe2O3) (8.7–11.4 wt.%) contents. The basalts also exhibit low Nb/La ratios (0.4–0.8) and constant eNd(t) values (− 8.0 to − 8.4) with variable SiO2 (44.8–51.5 wt.%) contents, suggesting a likely sub-continental lithospheric mantle origin. These high-magnesian basalts have chemical compositions similar to their primary magma, which was estimated using geochemical modeling at SiO2 ≈ 50 wt.%, MgO ≈ 14 wt.% and FeOT ≈ 9 wt.%. The estimated potential temperature for the melts is > 1300 °C, much higher than that of a normal sub-continental lithosphere. This implies that the magma was likely generated from partial melting of lithospheric peridotite heated by hot upwelling asthenosphere. The high-magnesian andesites are interpreted as the products of differentiation and AFC processes from the same basaltic magma source, as supported by their negative zircon eHf(t) values (− 21.7 to − 6.3) and high zircon δ18O values (7.3–9.0‰). Overall, we interpret that this post-kinematic basalts, plus andesites and dacites as differentiates, resulted from a late-orogenic lithospheric delamination which led to an orogenic collapse, melting of the SCLM, and widespread late-orogenic granitic intrusions in the orogen.

The Mesozoic geology of southeastern (SE) China was characterized by emplacement of voluminous felsic magmas. We present zircon U–Pb–Hf isotopic compositions and whole-rock major and trace elemental compositions of a series of felsic volcanic rocks from the eastern Guangdong and Fujian provinces. The volcanic rocks have been divided into three formations (the Douling, Nanyuan and Shimaoshan Fms.). Zircon U–Pb dating defines three eruption cycles: 168–145 Ma for the Douling Fm., 143–130 Ma for the Nanyuan Fm., and 104–95 Ma for the Shimaoshan Fm. In situ Hf isotope analyses on dated zircon yield an eHf(t) range of − 13.8 to + 6.9 and a TDM(Hf) range from 1400 to 486 Ma with a peak at ca. 930 Ma. The majority of the Mesozoic felsic lavas have more radiogenic Hf than that of metamorphic basement rocks and related igneous rocks, requiring the involvement of a juvenile component in their origin. The Mesozoic felsic magmas are predominantly dacites and rhyolites – with only minor basalt and andesite – and show relatively homogeneous Hf isotopic compositions of zircon in single sample. Combined these data indicated that neither differentiation of a mantle-derived magma, nor mixing of magmas from different sources, was a dominant petrogenetic process. Both the eHf(t) of zircon and the magma temperature increase from the Douling and Nanyuan Fms. to the Shimaoshan Fm. All these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle-derived magmas, as both a heat source inducing crustal melting and as a source of material (melt) that variably mixed with the local crustal melts. The felsic crustal melt component was generated at amphibolite-facies conditions with a residual assemblage of plagioclase +/− hornblende +/− garnet +/− zircon. Our results suggest a progressive role of crust–mantle interaction in generating the episodic felsic volcanic eruption during the Mesozoic.

The North China Craton (NCC) is the typical example of destruction of an ancient craton. However, the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction, which is the key to understanding the destruction processes. Based on temporal and spatial distributions of the igneous rocks, and their sources and tectonic settings, it is recognized that six stages of tectono-magmatism occurred in the NCC during the Phanerozoic, i.e., Carboniferous to Early Permian, Late Permian to Middle Triassic, Late Triassic, Jurassic, Early Cretaceous and Cenozoic. Among them, Cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern NCC. The first four stages of magmatism and tectonism, related to the southward subduction of the Paleo-Asian plate and the assembly of Sino-Korean and Yangtze cratons, are locally distributed in limited parts of the NCC, reflecting a multiple stage modification of the NCC from the Late Carboniferous to Jurassic. However, the intensive development of Early Cretaceous magmatism, extensional deformation and associated gold mineralization, with significant continental crustal growth, indicate that the eastern NCC was destroyed during this time period. This destruction was the result of Paleo-Pacific subduction beneath the eastern Asian continent, with lithospheric removal and/or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere.

In situ U–Pb age and Sr-, Nd-, Hf- and O- isotope analysis of accessory minerals (zircon, apatite and titanite) have been obtained for mafic microgranular enclaves and their host granites from the Early Cretaceous Fangshan pluton in the North China Craton, in order to constrain their sources and petrogenesis. The Fangshan pluton is composed of quartz monzodiorite at the margins, and granodiorite, with abundant mafic microgranular enclaves, in the core. Zircons from the marginal quartz monzodiorite record U–Pb ages of 130 to 133 Ma, identical to those of granodiorite in the core. The enclaves have zircon U–Pb ages of 133 to 134 Ma, identical within error to those of the host granodiorite, establishing that the mafic and felsic magmas were coeval. Furthermore, apatite and titanite from the enclaves and host granodiorite have the same U–Pb ages as the zircons, indicating rapid cooling of the Fangshan pluton. The granodiorites have relatively high SiO 2 and low MgO concentrations. They have variable negative e Hf (t) values of −25.1 to −18.2 and δ 18 O values for zircon of 6.2‰ to 8.3‰. The negative e Nd (t) values of −19.7 to −14.0 for titanite and apatite, with initial 87 Sr/ 86 Sr ratios of 0.7052–0.7058 for apatite, indicate that they were derived from an ancient lower crustal source with addition of materials with higher e Hf (t) and e Nd (t) values and low δ 18 O values. The enclaves have relatively high MgO contents (up to 15.5 wt.%) at intermediate silica concentrations, indicating that their parental magmas were derived from a mantle source. Their zircons have strongly negative Hf isotopic compositions (e Hf (t) = −22.9 to −14.9). The Nd isotopic composition of titanite and apatite is also strongly negative (e Nd (t) = −17.6 to −12.1). All these features, combined with the δ 18 O zircon values of 4.8‰–8.2‰ for zircons and relatively low initial Sr isotopic compositions of apatite (initial 87 Sr/ 86 Sr = 0.7051–0.7058), indicate that they were derived from an enriched and/or depleted mantle source, but with involvement of crustal materials. The marginal quartz monzodiorites have transitional geochemical features between those of the enclaves and host granodiorites. In situ Sr, Nd, Hf, and O isotopic data of accessory minerals, coupled with field observations and whole rock geochemical data, rule-out simple crystal–liquid fractionation or wall-rock contamination as the major genetic link between the enclaves and host rocks. Instead, mixing of mantle-derived mafic magmas with crustal-derived felsic magmas, coupled with assimilation of wall rocks, is compatible with the data. Our study shows that in situ Hf, O, Nd and Sr isotopic analyses of accessory minerals are powerful geochemical tracers that provide unique petrogenetic information regarding the origin of granitoids.

Most Cretaceous granitoids in the Jiaodong Terrane of Shandong Province, North China Craton, were intruded between ~ 130 and 122 Ma. However, four granitoid batholiths are significantly younger with an average zircon U–Pb SHRIMP emplacement age of 116 ± 2 Ma, these are: the Sanfoshan Batholith — 118 ± 1 Ma, the Aishan Batholith — 116 ± 1 Ma, the Yashan Pluton — 113 ± 2 Ma and the Laoshan Batholith — 115 ± 2 Ma. These granitoids post-date proposed delamination that occurred prior to ~ 125 Ma in the eastern NCC and their geochemistry thus provides information about the nature of the continental crust at this time. The rocks are mostly monzogranites and syenogranites of I-type affinity, with local alkali-feldspar granite of A-type affinity. In addition, a monzogranite sample from the Aishan Batholith records an age of 125 ± 3 Ma, indicating a direct association with the slightly older granitoids in the area. Indeed, they all contain inherited zircons with ages of ~ 125–120 Ma, indicating interaction with these earlier granitoids. Most samples are metaluminous, enriched in light rare earth elements and depleted in high-field strength elements. Paleo- to Neoarchean TDM2 model ages (ranging from 3900 Ma to 2491 Ma) and negative eHf(t) values imply the involvement of Archean basement and older recycled continental crustal material in the magma source region. They were likely derived from partial melting of the lower or middle crust due to mafic magma underplating followed by various degrees of interaction between mantle-derived mafic magma and felsic crustal magma, accompanied by fractional crystallization. We propose that lithospheric thinning and extension in the Early Cretaceous, due to roll-back of the Pacific Plate beneath the eastern North China Craton, led to asthenospheric upwelling and basaltic magmatism. This underplating in turn led to crustal melting and evolution of the granitic intrusions described here.

Determination of the emplacement ages and initial isotopic composition of kimberlite by conventional isotopic methods using bulk rock samples is unreliable as these rocks usually contain diverse clasts of crustal- and mantle-derived materials and can be subject to post-intrusion sub-aerial alteration. In this study, 8 samples from 5 kimberlites in southern Africa and twelve samples from 7 kimberlites from Somerset Island, Canada have been selected for in situ perovskite U–Pb isotopic age determination and Nd isotopic analysis by laser ablation using thin sections and mineral separates. These fresh perovskites occur as primary groundmass minerals with grain-sizes of 10–100 μm. They were formed during the early stage of magmatic crystallization, and record data for the least contaminated or contamination-free kimberlitic magma. U–Pb isotopic data indicate that the majority of the southern Africa kimberlites investigated were emplaced during the Cretaceous with ages of 88 ± 3 to 97 ± 6 Ma, although one sample yielded an Early Paleozoic age of 515 ± 6 Ma. Twelve samples from Somerset Island yielded ages ranging from 93 ± 4 Ma to 108 ± 5 Ma and are contemporaneous with other Cretaceous kimberlite magmatism in central Canada (103–94 Ma). Although whole-rock compositions of the kimberlites from southern Africa have a large range of eNd(t) values (− 0.5 to + 5.1), the analysed perovskites show a more limited range of + 1.2 to + 3.1. Perovskites from Somerset Island have eNd(t) values of − 0.2 to + 1.4. These values are lower than that of depleted asthenospheric mantle, suggesting that kimberlites might be derived from the lower mantle. This study shows that in situ U–Pb and Nd isotopic analysis of perovskite by laser ablation is both rapid and economic, and serves as a powerful tool for the determination of the emplacement age and potential source of kimberlite magmas.

The Great Xing'an Range in northeastern China is characterized by large-scale Mesozoic magmatism, and forms a key part of the NE-trending Mesozoic magmatic belt in East China. However, only limited precise age data for the volcanic rocks in this belt were previously available, which significantly hampers understanding of the petrogenesis and geodynamic setting of these rocks. Systematic dating of volcanic rocks in the Great Xing'an Range was undertaken in order to rectify this situation. The Mesozoic volcanic rocks in the area have been sub-divided into the Tamulangou, Shangkuli and Yilieke formations. The Tamulangou and Yiliekede formations are composed of basalt and basaltic andesite, whereas the Shangkuli Formation consists of rhyolite and dacite. Zircon U–Pb and whole rock 40 Ar/ 39 Ar dating, combined with published data, indicate that the Tamulangou Formation was formed over a large time interval from the Early Jurassic to Early Cretaceous; it should therefore not be regarded as a single stratigraphic unit. In contrast, volcanic rocks of the Shangkuli and Yiliekede formations were erupted in the Early Cretaceous, between 125–115 Ma. Overall, most Mesozoic volcanic rocks in the Great Xing'an Range were erupted during the Early Cretaceous with an age peak at ∼ 125 Ma, coeval with the time of lithospheric thinning in the eastern part of the North China Craton. Therefore, the Great Xing'an Range constitutes an important area that records a significant Early Cretaceous giant igneous event in eastern China. It is possible that this activity was related to subduction of the Pacific plate during the Late Mesozoic, as has been suggested to explain crustal thinning of the North China Craton.

Major and trace element, whole rock Sr and Nd isotope and zircon Hf isotope data are reported for a suite of A-type granites and mafic microgranular enclaves from the Early Cretaceous (126 ± 2 Ma) Qianshan pluton, Liaodong Peninsula, northeast China, with the aim of investigating the sources and petrogenesis of A-type granites. The Qianshan pluton includes hornblende alkali-feldspar granite, graphic biotite granite and mafic microgranular enclaves. The hornblende alkali-feldspar granites have high SiO 2 , Fe 2 O 3T / MgO, K 2 O + Na 2 O, Rb, Zr and LREE contents and low Ba and Sr concentrations with strongly negative Eu anomalies. Their high Rb / Sr ( 87 Rb / 86 Sr = 16.76–24.15) and initial 87 Sr / 86 Sr ratios (0.7215 to 0.7283), negative e Nd ( t ) values (− 14.1 to − 16.5) and zircon e Hf ( t ) values (− 18.9 to − 11.5) indicate they were mainly derived from a crustal source, but with involvement of high e Nd ( t ) and e Hf ( t ) materials. Graphic biotite granites have similar geochemical features and Sr–Nd–Hf isotopic compositions to enclaves, indicating they were the result of crystal fractionation of evolved mafic magmas, but with involvement of low e Nd ( t ) and e Hf ( t ) materials. The mafic enclaves have an igneous texture and contain acicular apatite, suggesting quenching of mafic magmas that have co-mingled with the host granites. They have low initial 87 Sr / 86 Sr ratios (0.7097–0.7148), negative e Nd ( t ) (− 14.5 to − 11.9) and zircon e Hf ( t ) (− 17.1 to − 6.9) values, and are enriched in LILEs and LREEs and depleted in HFSEs. When coupled with the high MgO (Mg# up to 54), this indicates derivation from an enriched lithospheric mantle source, but contaminated by crustal materials. Geochemical and Sr-, Nd- and zircon Hf-isotopic compositions rule out simple crystal–liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, magma mixing of mantle-derived mafic and crustal-derived magmas, coupled with crystal fractionation, is compatible with the data. This example shows that at least some A-type granites formed through a complex process involving mantle- and crustal-derived magma mixing, crystal fractionation and infracrustal melting.

Major and trace elements and Sr–Nd–Pb isotope data are reported for Cretaceous mafic dikes from the Jiaodong Peninsula, eastern China. These dikes range from medium-K and high-K calc-alkaline to shoshonitic or ultrapotassic rocks, which are characterized by high MgO (Mg#=71–53) and Cr (177–1012 ppm) and low TiO2 (0.55–0.90 wt.%), total Fe2O3 (5.12–9.48 wt.%) and CaO (4.99–9.94 wt.%). Overall, they are enriched in the large ion lithophile elements (LILE, e.g., Rb, Ba, Sr) and light rare earth elements (LREE), depleted in the high field strength elements (HFSE, e.g., Nb, Ti, P), and possess uniform initial 87Sr/86Sr (0.7094–0.7114) but relatively wide ranges of Nd [eNd (T)=−10.1–−17.0] and Pb (206Pb/204Pb=16.75–18.03) isotopic ratios, implying a magma origin from enriched but heterogeneous mantle sources. These geochemical and isotopic characteristics can be explained by the vein-plus-peridotite melting model, with amphibole- or phlogopite-bearing pyroxenite veins that reside in refractory lithospheric mantle beneath the North China Block. Such a vein-enriched mantle source formed by multiple metasomatic events, which we infer to have resulted from subduction-related processes that may have occurred in the Late Archean and Mesoproterozoic. The mafic dikes constitute a member of the widespread Mesozoic magmas emplaced in the North China Block as a result of regional lithospheric extension.

Rapid Mesozoic–Early Cenozoic crustal growth in the Gangdese area, southern Tibet, has commonly been attributed to pre-collisional and syn-collisional underplating of mantle-derived magmas. Here, we report on adakitic magnesian charnockites (i.e., hypersthene-bearing diorites and granodiorites) near Milin, in eastern Gangdese, that provide new insights into the crustal growth process of the region. Zircon U–Pb analyses of seven charnockite samples indicate that they were generated in the Late Cretaceous (100–89 Ma). They exhibit variable SiO2 (53.9 to 65.7 wt.%) contents, high Na2O/K2O (1.6 to 14.4) and Sr/Y (27.2 to 138.7) ratios, low Y (6.5 to 18.5 ppm), heavy rare earth element (e.g., Yb = 0.6 to 1.6 ppm) and Th (0.20–2.39 ppm) contents and Th/La (0.02–0.23) ratios, with relatively high Mg# (46 to 56) and MgO (2.0 to 4.5 wt.%) values. They are characterized isotopically by high and slightly variable eNd(t) (+ 2.4 to + 4.0) and eHf(t) (+ 10.1 to + 15.8) values with relatively low and consistent (87Sr/86Sr)i (0.7042 to 0.7043) ratios. Their pyroxenes have high crystallization temperatures (876 to 949 °C). The Milin charnockites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust that was followed by adakitic melt–mantle interaction, minor crustal assimilation and fractional crystallization of amphibole + plagioclase. The upwelling asthenosphere, triggered by the roll-back of subducted Neo-Tethyan oceanic lithosphere, provided the heat for slab melting. Therefore, we suggest that, in addition to pre-collisional and syn-collisional underplating of mantle-derived magmas, the recycling of subducted oceanic crust has also played an important role in continental crustal growth in southern Tibet.