Late Mesozoic Ore‐forming Events in the Ningwu Ore District,Middle‐Lower Yangtze River Polymetallic Ore Belt,East China: Evidence from Zircon U‐Pb Geochronology and Hf Isotopic Compositions of the Granodioritic Stocks

Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district (Cretaceous basin) of the middle–lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed: one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic (-granitic) rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization (typically for zircons) ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131–127 Ma. In situ zircon Hf compositions of εHf(t) of the granodiorite are mainly from ?3 to ?8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.     

Late Mesozoic magmatism in the Jiaodong Peninsula,East China:Implications for crust-mantle interactions and lithospheric thinning of the eastern North China Craton

A section from the Linglong gold deposit on the northwestern Jiaodong Peninsula,East China,containing Late Mesozoic magmatic rocks from mafic and intermediate dikes and felsic intrusions,was chosen to investigate the lithospheric evolution of the eastern North China Craton(NCC).Zircon U-Pb data showed that low-Mg adakitic monzogranites and granodiorite intrusions were emplaced during the Late Jurassic(～145 Ma) and late Early Cretaceous(112-107 Ma),respectively;high-Mg adakitic diorite and mafic dikes were also emplaced during the Early Cretaceous at～139 Ma and ～118 Ma,and 125-145 Ma and 115-120 Ma,respectively.The geochemical data,including whole-rock major and trace element compositions and Sr-Nd-Pb isotopes,imply that the mafic dikes originated from the partial melting of a lithospheric mantle metasomatised through hydrous fluids from a subducted oceanic slab.Low-Mg adakitic monzogranites and granodiorite intrusions originated from the partial melting of the thickened lower crust of the NCC,while high-Mg adakitic diorite dikes originated from the mixing of mafic and felsic melts.Late Mesozoic magmatism showed that lithosphere-derived melts showed a similar source depth and that crust-derived felsic melts originated from the continuously thickened lower crust of the Jiaodong Peninsula from the Late Jurassic to Early Cretaceous.We infer that the lower crust of the eastern NCC was thickened through compression and subduction of the Palaeo-Pacific plate beneath the NCC during the Middle Jurassic.Slab rollback of the plate from ～160 Ma resulted in lithospheric thinning and accompanied Late Mesozoic magmatism.     

Geochronology, Geochemistry, and Sr–Nd–Hf Isotopes of the Balazha Ore-Bearing Porphyries: Implications for Petrogenesis and Geodynamic Setting of Late Cretaceous Magmatic Rocks in the Northern Lhasa Block, Tibet

The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, whole-rock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore-bearing porphyries in the northern Lhasa block belong to high-Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore-bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium-acid rocks, including ore-bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.     

Geochronology and Geochemistry of Mafic Rocks in the Xuhe, Shaanxi, China: Implications for Petrogenesis and Mantle Dynamics

The Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase-porphyrite, gabbro–diabase, diabase, and pyroxene diorite. Primitive mantle-normalized multi-element patterns show that, the Xuhe mafic rocks are enriched in large ion lithophile elements(LITE), such as Ba and Pb, depleted in K and Sr for basic rocks, and are depleted in Sr, P and Ti for pyroxene diorite. Chondrite-normalized REE patterns display LREE enrichment(LaN/YbN = 9.34–13.99) and have normalized patterns for trace element and REE similar to that of typical OIB. Detailed SIMS zircon U–Pb dating yields emplacement ages of 438.4 ± 3.1 Ma for Xuhe mafic rocks. The relatively low Mg O(basic rock: 3.11–7.21 wt%; pyroxene diorite: 0.89–1.21 wt%) and Mg#(0.20–0.49) for Xuhe mafic rocks suggest that they were possibly originated from an extremely evolved magma. The rising parental mafic magmas underwent pyroxene and plagioclase fractionation. Crustal contamination of pyroxene diorite before emplacement occurred at a higher crustal level compared to other lithology in Xuhe mafic rocks. The degree of partial melt was low(5%–10%) and in garnetspinel transition facies. Sr-Nd isotope of pyroxene diorite and enrichment mantle characteristics for Xuhe mafic rocks suggest that mafic rocks in the North Daba Mountains were derived from a mixture of HIMU, EMII and small amount of EMI components. Furthermore, this study discusses mantle geodynamic significance of Xuhe mafic rocks in the Silurian, which indicates subduction and uplift of magma caused back-arc extension.     

Zircon U–Pb geochronology and Hf isotope geochemistry of magmatic and metamorphic rocks from the Hida Belt,southwest Japan

Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks from the Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic to intermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean ~(206)Pb/~(238)U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios( 0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the Yeongnam Massif in southern Korea.The arc magmatism along this system was commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positive εHf(t) values( +12) of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondritic εHf(t) values(+5 to-2) of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zircon εHf(t) values(+9) shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.     

Petrogenesis and tectonic implications of early Paleozoic granitoids in East Kunlun belt: Evidences from geochronology,geochemistry and isotopes

The East Kunlun Orogenic Belt(EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism.Here we report the petrology, bulk geochemistry, zircon Ue Pb dating and, Lue Hf and SreN d isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U-Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450 -430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their(~(87)Sr/~(86)Sr)ivalues range from 0.7059 to 0.7085, εNd(t) values from -1.6 to -6.0 and the zircon εHf(t) values show large variations from +9.1 to -8.6 with Hf model ages(T_(DM2)) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.     

Early Permian–Late Triassic Magmatism in the Tuotuohe Region of the Qinghai–Tibet Plateau: Constraints on the Tectonic evolution of the Western Segment of the Jinshajiang Suture

In this paper we present new zircon U–Pb ages, whole-rock major and trace element analyses, and zircon Hf isotopic data for magmatic rocks in the Tuotuohe region of the western segment of the Jinshajiang suture. Our aim is to constrain the Early Permian–Late Triassic tectonic evolution of the region. Zircons from the magmatic rocks of the Tuotuohe region are euhedral–subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios(0.4–4.6), indicating a magmatic origin. The zircon U–Pb ages obtained using LA–ICP–MS are 281 ± 1 Ma, 258 ± 1 Ma, 244 ± 1 Ma, and 216 ± 1 Ma, which indicate magmatism in the Early Permian–Late Triassic. A diorite from Bashihubei(BSHN) has SiO2 = 57.18–59.97 wt%, Al2O3 = 15.70–16.53 wt%, and total alkalis(Na2O + K2O) = 4.46–6.34 wt%, typical of calc-alkaline and metaluminous series. A gabbro from Bashibadaoban(BSBDB) belongs to the alkaline series, and is poor in SiO2(45.46–54.03 wt%) but rich in Al2O3(16.19–17.39 wt%) and total alkalis(Na2O + K2O = 5.48–6.26 wt%). The BSHN diorite and the BSBDB gabbro both display an enrichment of LREEs and LILEs and depletion of HFSEs, and they have no obvious Eu anomaly; they have relatively low MgO contents(2.54–4.93 wt%), Mg# values of 43 to 52, and low Cr and Ni contents(8.07–33.6 ppm and 4.41–14.2 ppm, respectively), indicating they differentiated from primitive mantle magmas. They have low Nb/U, Ta/U, and Ce/Pb ratios(1.3–9.6, 0.2–0.8, and 0.1–18.1, respectively), and their initial Hf isotopic ratios range from +9.6 to +16.9(BSHN diorite) and +6.5 to +12.6(BSBDB gabbro), suggesting their primary magmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized by subduction fluids. Taking all the new data together, we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian–Late Triassic: oceanic crust subduction before the Early Permian, continental collision during the Early–Middle Triassic, and post-collisional extension from the Late Triassic.     

Ages of the Laocheng Granitoids and Crustal Growth in the South Qinling Tectonic Domain, Central China: Zircon U-Pb and Lu-Hf Isotopic Constraints

The Laocheng granitoid pluton is located in the South Qinling tectonic domain of the Qinling orogenic belt,southern Shaanxi Province,and consists chiefly of quartz diorite,granodiorite and monzogranite.A LA-ICP-MS zircon U-Pb isotopic dating,in conjunction with cathodoluminescence images,reveals that the quartz diorite and granodiorite were emplaced from 220 Ma to 216 Ma,while the monzogranite was emplaced at～210 Ma.In-situ zircon Hf isotopic analyses show that theε_(Hf)(t) values of the quartz diorite a...     

Neoproterozoic–Early Paleozoic Tectonic Evolution of the South China Craton: New Insights from the Polyphase Deformation in the Southwestern Jiangnan Orogen

A >1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton (SCC) consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen (JO) and experienced at least two phases deformation. Combined with new (detrital) zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed <800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica 40Ar/30Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.     

Laser Ablation ICP‐MS U‐Pb Zircon Geochronology of Granitoids and Quartz Veins in the Shihu Gold Mine,Taihang Orogen,North China: Timing of Gold‐mineralization and Tectonic Implications

The Shihu gold deposit, situated in the Taihang Mesozoic orogen of the North China Craton (NCC), is hosted by ductile-brittle faults within Archean metamorphic core complex. The deposit is characterized by gold-bearing quartz-polymetallic sulfides veins. The Mapeng granitoids stock and intermediate-basic dikes intruded the metamorphic basement rocks, and are spatially related to gold mineralization. Detailed laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) U-Pb zircon ages of the granitic rocks, dykes and mineralized quartz veins in the studied area reveal its magmatic and mineralized history. The mineralized quartz veins contain inherited zircons with ages of about 2.55 Ga and 1.84 Ga, probably coming from the basement. These two Precambrian events are coeval with those in other parts of the NCC. The Mapeng granitoid stock, the largest intrusion in the area, was emplaced at ca. 130 Ma, and is coeval with magmatic zircon populations from diorites and quartz diorite pophyrites in the same region. The ca. 130 Ma magmatism and gold mineralization were most likely related to an underplating event that took place in the Taihang orogen at Late Mesozoic. The timing of gold mineralization with respect to felsic magmatism in the area is similar to those observed in other major gold-producing provinces in the NCC. This episode is simultaneous with those in the eastern margin of NCC, indicative of a widespread late Yanshanian metallogenic event that was a response to the Early Cretaceous lithosphere in the eastern NCC, in which the mesothermal gold deposits were formed from similar tectono-magmatic environments.     

U–Pb geochronology and Lu–Hf isotopes of zircons from newly identified Permian–Early Triassic plutons in western Liaoning province along the northern margin of the North China Craton: constraints on petrogenesis and tectonic setting

Mafic to felsic gneisses along the northern margin of the North China Craton (NMNCC), in western Liaoning province, China, were previously assumed to be part of Archean metamorphic basement but are here identified as younger (Permian–Early Triassic) intrusions. LA–ICP–MS zircon U–Pb isotopic dating reveals that the magmatic precursors of the mafic gneisses were emplaced from 295 ± 3 to 259 ± 2 Ma and that the magmatic precursors of the dioritic and monzogranitic gneisses were emplaced at 267 ± 1 and 251 ± 2 Ma, respectively, thus recording a continuum of Permian to Early Triassic magmatism. The mafic and dioritic rocks exhibit zircon ε_Hf(t) values from ?20.7 to ?3.3, suggesting they were mainly derived from a metasomatized lithospheric mantle source, possibly involving some crustal contamination. The monzogranitic rocks display their zircon ε_Hf(t) values of +0.9 to +4.7, indicating the acidic magma was derived from partial melting of juvenile crustal materials from the depleted mantle source. Crustal model ages (T _DM ^C ) obtained from zircon Hf isotopes of these monzogranitic rocks range from 976 to 1,215 Ma, with an average of 1,074 ± 32 Ma, possibly implying an episode of Grenvillian crustal growth in western Liaoning province. These new lines of evidence show that the NMNCC witnessed abundant magmatic activity and interaction of the crust and mantle during the Permian and Early Triassic and that the mafic magmatism was earlier than the monzogranitic activity. These findings indicate that the monzogranitic activity was the result of underplating of mafic magma with an enriched mantle source. In the context of regional Late Paleozoic to Early Mesozoic magmatic activity, the Permian magmatism occurred in an Andean-style continental margin setting when the Paleo-Asian oceanic plate was subducted beneath the NMNCC, and in this context, the Late Permian to Early Triassic magmatism may have been linked to post-collisional extension and asthenospheric upwelling, suggesting that the western Liaoning province in the NMNCC may be an eastward extension of the Late Paleozoic to Early Mesozoic active continental margin.     

Early to late Neoproterozoic magmatism and magma mixing–mingling in Sri Lanka: Implications for convergent margin processes during Gondwana assembly

The Sri Lankan fragment of Gondwana preserves the records of Neoproterozoic tectonothermal events associated with the final assembly of the supercontinent. Here we investigate a suite of magmatic rocks from the Wanni, Kadugannawa and Highland Complexes through geological, petrological, geochemical and zircon U–Pb and Lu–Hf isotopic techniques. The hornblende biotite gneiss, charnockites, metagabbro and metadiorites investigated in this study show geochemical features consistent with calc-alkaline affinity and subduction-related signature including LILE enrichment relative to HFSE coupled with distinct Nb–Ta depletion and weak negative Zr–Hf anomalies. The felsic suite falls in the volcanic arc granites (VAGs) field and the mafic suite shows island arc basalt affinity in tectonic discrimination plots, suggesting that the protoliths of the rocks were derived from arc-related magmas in a convergent margin setting. LA-ICPMS zircon U–Pb analyses show crystallization of charnockite and dioritic mafic magmatic enclave from the Highland Complex during ca. 565 and 576 Ma corresponding to bimodal magmatism. The diorite also contains metamorphic zircons of ca. 525 Ma. Hornblende–biotite gneiss from the Kadugannawa Complex shows protolith emplacement age at 973–980 Ma, followed by new zircon growth during repeated thermal events through late Neoproterozoic. The dioritic enclaves in these rocks are much younger, and form part of a deformed and metamorphosed dyke suite with emplacement ages of 559 Ma, broadly coeval with the bimodal magmatism in the Highland Complex at that time. The youngest group of zircons in this rock shows ages of 508 Ma, corresponding to the latest thermal event. A charnockite from this locality shows oldest group of zircons at 962 Ma, corresponding to emplacement age similar to that of the magmatic protolith of the hornblende biotite gneiss. This rock also shows zircon growth during repeated thermal events at 832 Ma, 780 Ma, 721 Ma and 661–605 Ma. The lower intercept age of 543 Ma marks the timing of collisional metamorphism. Charnockite from the Wanni Complex shows emplacement age at 1000 Ma, followed by thermal event at 570 Ma, the latter correlating with the bimodal magmatic event in the Highland Complex. The dioritic enclave within this charnockite shows an age of ca. 980 Ma, suggesting intrusion of mafic magma into the felsic magma chamber. Zircons in the diorite also record multiple zircon events during 950 to 750 Ma. Zircons in the Highland Complex charnockite possess negative εHf(t) values in the range − 6.7 to − 12.6 with T_DM^C of 2039–2306 Ma suggesting magma derivation through melting of Paleoproterozoic source. In contrast, the εHf(t) range of − 11.1 to 1.6 suggests a mixed source of both of older crustal and juvenile material. The εHf(t) values of − 4.5 to 4.5 and T_DM^C of 1546–1962 Ma for the hornblende biotite gneiss also shows magma derivation from mixed sources that included Paleoproterozoic components. The younger dioritic intrusive, however, has a more juvenile magma source as indicated by the mean εHf(t) value of 1.3. The associated charnockite shows a tight positive cluster of εHf(t) from 0.6 to 5.1, suggesting juvenile input. Charnockite from the Wanni Complex shows clearly positive εHf(t) values of up to 13.1, and T_DM^C in the range 937–1458 Ma suggesting much younger and depleted mantle source. The diorite enclave also has positive εHf(t) values with an average value of 8.5 and T_DM^C in the range of 709–1443 Ma clearly suggesting younger juvenile sources. The early and late Neoproterozoic bimodal suites are correlated to convergent margin magmatism associated with the assembly of Sri Lanka within the Gondwana supercontinent.     

Magma mixing origin for the post-collisional adakitic monzogranite of the Triassic Yangba pluton, Northwestern margin of the South China block: geochemistry, Sr–Nd isotopic, zircon U–Pb dating and Hf isotopic evidences

Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively. The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element and evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.707069–0.707138, and ε_Nd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive ε_Hf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90), suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.7041–0.7061, and ε_Nd(t) = −3.1 to −4.3] and high contents of K₂O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55), Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite show negative ε_Hf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive ε_Hf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains the Neoproterozoic juvenile crust that has the positive ε_Hf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks.     

Magma mixing revealed from in situ zircon U–Pb–Hf isotope analysis of the Muhuguan granitoid pluton, eastern Qinling Orogen, China: implications for late Mesozoic tectonic evolution

In this paper, we present zircon U–Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U–Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative ε _Hf(t) values (?7.9 to ?2.5) and T _DM1 ages of 0.9–1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon ε _Hf(t) values of ?19.5 to ?8.8 and T _DM2 ages of 2.4–1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U–Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon ε _Hf(t) values (?29.8 to ?24.8) and Archean T _DM2 ages (3.0–2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of ε _Hf(t) between ?29.1 and ?9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U–Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has ε _Hf(t) values (?17.9 to ?9.3) and T _DM2 ages (2.3–1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.     

Origin of the Yinshan epithermal-porphyry Cu–Au–Pb–Zn–Ag deposit,southeastern China: insights from geochemistry,Sr–Nd and zircon U–Pb–Hf–O isotopes

The Yinshan deposit is a large epithermal-porphyry polymetallic deposit, and the timing and petrogenesis of ore-hosting porphyries have been hotly debated. We present new results from geochemical, whole-rock Sr–Nd and zircon U–Pb–Hf–O isotopic investigations. Zircon U–Pb data demonstrate that the quartz porphyry, dacitic porphyry, and quartz dioritic porphyry formed at ?172.2 ± 0.4 Ma, ?171.7 ± 0.5 Ma, and ?170.9 ± 0.3 Ma, respectively. Inherited zircon cores show significant age spreads from ?730 to ?1390 Ma. Geochemically, they are high-K calc-alkaline or shoshonitic rocks with arc-like trace element patterns. They have similar whole-rock Nd and zircon Hf isotopic compositions, yet an increasing trend in ?_Nd(t) and ?_Hf(t) values typifies the suite. Older (inherited) zircons of the three porphyries display Hf compositions comparable to those of the Jiangnan Orogen basement rocks. In situ zircon oxygen isotopic analyses reveal that they have similar oxygen isotopic compositions, which are close to those of mantle zircons. Moreover, a decreasing trend of δ¹⁸O values is present. We propose that the ore-related porphyries of the Yinshan deposit were emplaced contemporaneously and derived from partial melting of Neoproterozoic arc-derived mafic (or ultra-mafic) rocks. Modelling suggests that the quartz porphyries, dacitic porphyries, and quartz dioritic porphyries experienced ?25%, ?10%, and ?10% crustal contaminations by Shuangqiaoshan rocks. Our study provides important constraints on mantle–crust interaction in the genesis of polymetallic mineralization associated with Mesozoic magmatism in southeastern China.     

Early Cretaceous Magma Mingling in Xiaocuo, Southeastern China Continental Margin: Implications for Subduction of Paleo-Pacific Plate

Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs) show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similar ε_(Hf)(t) values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.     

Petrology and geochemistry of Early Cretaceous A-type granitoids and late Mesozoic mafic dikes and their relationship to adakitic intrusions in the lower Yangtze River belt,Southeast China

The relationship among magmatism, large-scale metallogenesis of Southeast China, and subduction of the Pacific plate has long been debated. The lower Yangtze River belt (LYRB) in the northeastern edge of Southeast China is characterized by intense late Mesozoic magmatism and associated polymetallic mineralization such as copper, gold, iron, tungsten, molybdenum, etc. The copper-related adakitic rocks (148–130 Ma) in this belt are the oldest episode of magmatism and intruded as small intermediate-acid intrusive bodies. The Huayuangong granitoids (HYG), located in the southern part of this belt, however, are copper-barren. Three granitoid samples from this pluton give zircon U–Pb ages of 126.4 ± 1.6 Ma, 125.9 ± 1.9 Ma, and 126.2 ± 1.2 Ma, respectively. The HYG has A-type affinity with metaluminous to weakly peraluminous, high FeO_T/(FeO_T+MgO) ratios, and high Zr+Nb+Ce+Yb contents. Meanwhile, 10 late Mesozoic mafic samples from the LYRB exhibit similar trace element characteristics to those of ‘continental arc andesite’ (CAA) and suggest an enriched lithospheric mantle source with depletion in high field strength elements (e.g. Nb, Ta, Zr, Hf, and Ti) and enrichment of large ion lithophile elements (e.g. Rb, Th, U, and Pb). Although the HYG exhibits similar Sr–Nd isotope composition with the mafic dikes, distinct whole-rock Pb isotope ratios imply that the granitoids and mafic magmas originated from heterogeneous mantle sources. Compared with coeval Baijuhuajian A-type rocks that are exposed along the Jiang–Shao fault of Southeast China, the HYG shows enriched Hf isotope ratios of zircon with ε_Hf(t) values ranging from ?4.8 to ?11.1. In the Yb/Ta versus Y/Nb diagram, being different from the major asthenospheric mantle-origin Baijuhuajian pluton, a large range of and high Y/Nb ratios as well as high Zr contents of the HYG pluton suggest a magmatic source of mixing between the asthenospheric and enriched crustal component in the LYRB. Compared with early-stage copper-related adakitic rocks (148–130 Ma) with subduction-related affinities and high oxygen fugacity, the copper-barren HYG has with-plate A-type affinities and lower oxygen fugacity. Summarizing, the production of early-stage (i.e. subduction related) adakitic rocks followed by late-stage A-type granitoids in the LYRB is ascribed to the rollback of the Palaeo-Pacific plate beneath Southeast China and associated with asthenospheric upwelling and lithospheric thinning during the late Mesozoic era.     

Archaean crustal growth through successive partial melting events in an oceanic plateau‐like setting in the Tanzania Craton

The detrital zircon population in quartzitic conglomerates from the northern Tanzania Craton yield ages between 2640 Ma and 2790 Ma which includes most of the igneous history from this part of the craton. The igneous evolution is characterised by mafic volcanism with an oceanic plateau‐like geochemical signature at ~2800 Ma followed by diorite and tonalite–trondhjemite–granodiorite dominated magmatism between 2790 and 2700 Ma, which transitioned into more evolved high‐K magmatism between 2700 and 2620 Ma. The ε_Hf values of the detrital zircons range from +2.4 to ?1.4 and change with time from radiogenic Hf pre‐2700 Ma (98% positive ε_Hf) to unradiogenic Hf post‐2700 Ma (41% positive ε_Hf). The petrological progression from mafic to felsic crust is reflected in the detrital age distribution and Hf isotopes and is consistent with juvenile mafic crust slowly maturing into more evolved felsic crust through a series of successive partial melting events in an oceanic‐plateau‐like environment.