Zircon Lu-Hf Isotope Research Articles

Diverse magmatism along the northern margin of Tarim during the Ediacaran: Transition from Rodinian dispersing to Gondwana assemblage

The Ediacaran igneous rocks and sedimentary sequences play a key role for our understanding the transition from dispersing of the Rodinian continents to the assemblage of the Gondwana. On the other hand, some continental massifs at the marginal area of the Rodinia and Gondwana could preserve solid evidences for deciphering the geodynamic background from the break-up of Rodinia to the assemblage of Gondwana. In this contribution, we report field observations, petrography, ages and systematic geochemistry of the diverse Ediacaran igneous activities in the northern margin of the Tarim Block, which was favored as a marginal continental massif in the Rodinia configuration by most geologists. The Ediacaran igneous rocks along the northern margin of Tarim include the Baicheng and Yangxia granites, Tiemenguan syenite, Kurle mafic dykes and the basalt layers in the Zamoketi Formation (northeastern Tarim) and the Sugetbrak Formation (northwestern Tarim). Precise zircon UPb dating revealed that these distinct rocks were broadly coeval with crystallization/eruption ages of 630–600 Ma. Bulk-rock elemental and SrNd isotope compositions as well as zircon LuHf isotope compositions demonstrate that the Baicheng and Yangxia granites were derived from Neoarchean mafic lower crust and underwent intensive fractionation before their emplacements. The Tiemenguan syenites have potassic andesitic compositions, in combination with their pronounced enriched NdHf isotopes and extremely high Zr saturation temperatures (∼900 °C), we argue that their possible shoshonitic primary magmas were derived from previously metasomatized subcontinental lithospheric mantle source (amphibole-bearing) and then, coupling with assimilation and fractional crystallization (AFC) effects in magma chamber and/or en route to the emplacement space. This can account for their intriguing geochemical features. The ca. 615 Ma Zamoketi and Sugetbrak basalts and the slightly younger porphyrite dykes (ca. 580 Ma) cutting the Zamoketi basalt layer, show typical OIB-like geochemical signatures, they were most likely derived from a depleted asthenospheric mantle source with variable fractionation of olivine and pyroxene and negligible crustal contamination before eruption. On the whole, the geochemistry of the diverse Ediacaran igneous rocks unambiguously demonstrates that they were genetically related to an extensional environment. In combination with the significant passive continental features of the Ediacaran-Cambrian sedimentary sequences, we consider that these Ediacaran igneous rocks were the latest phase of igneous activity related to the dispersing of the Tarim at the margin of the Rodinia supercontinent.The dispersing of the Rodinian supra-continent was diachronic with the assemblage of the Gondwana. Late Tonian to Ediacaran dispersing of the Tarim from northern margin of Australia induced the opening of the Proto-Tethys Ocean. Then the initiation of the southward subduction of the Proto-Tethys Ocean at ca. 530 Ma (Fortunian) led to the Tarim assemblage to Gondwana at ca. 440 Ma.

Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting: A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China

The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

Archaean multi-stage magmatic underplating drove formation of continental nuclei in the North China Craton

The geodynamic processes that formed Earth’s earliest continents are intensely debated. Particularly, the transformation from ancient crustal nuclei into mature Archaean cratons is unclear, primarily owing to the paucity of well-preserved Eoarchaean–Palaeoarchaean ‘protocrust’. Here, we report a newly identified Palaeoarchaean continental fragment—the Baishanhu nucleus—in northeastern North China Craton. U–Pb geochronology shows that this nucleus preserves five major magmatic events during 3.6–2.5 Ga. Geochemistry and zircon Lu–Hf isotopes reveal ancient 4.2–3.8 Ga mantle extraction ages, as well as later intraplate crustal reworking. Crustal architecture and zircon Hf–O isotopes indicate that proto-North China first formed in a stagnant/squishy lid geodynamic regime characterised by plume-related magmatic underplating. Such cratonic growth and maturation were prerequisites for the emergence of plate tectonics. Finally, these data suggest that North China was part of the Sclavia supercraton and that the Archaean onset of subduction occurred asynchronously worldwide.

Early Jurassic A-type granite and monzodiorite from the Baoji batholith: Implication for tectonic transition from post-collision to post-orogenic extension in the Qinling Orogenic Belt, China

Introduction: The early Jurassic granitoids in the Qinling Orogenic Belt (QOB) play a crucial role in understanding the tectonic implications for the geological evolution of China. To elucidate the early Jurassic tectonic setting of QOB, we performed a comprehensive analysis of zircon U-Pb ages, whole-rock geochemistry, and in situ zircon Lu-Hf isotopes from early Jurassic monzodiorite and Kfeldspar granite within the Baoji batholith in western QOB.Geochronology Method and Results: The intrusions yielded zircon U-Pb ages of 186 ± 2 Ma and 188 ± 2 Ma, respectively.Geochemistry Results: The monzodiorites are characterized by relatively high MgO, Rb, Th, U, and LREE contents, as well as low P, Ti, and HREE contents. They also exhibit high Nb/Ta ratios (20.6–23.4). The zircon εHf(t) values for the monzodiorite sample range from −4.36 to 6.47, indicating significant contributions from a fertile continental lithospheric mantle with the involvement of crustal components. The K-feldspar granites are enriched in K2O+ Na2O, Rb, Zr, Hf, and Nb, and lower Ba, Sr, Ti, and P. They exhibit high Nb/Ta and Ga/Al ratios but low Y/Nb and Yb/Ta ratios. Their geochemical characteristics reveal an A-type granite affinity with elevated zircon saturation temperatures (848°C–900 °C). Additionally, the K-feldspar granite exhibits REE and trace element patterns similar to those observed in the monzodiorite. However, a wide range of zircon εHf(t) values (−4.72 to 3.98), differing from those of the monzodiorite, indicate that the parental magma of the K-feldspar granite experienced magma mixing between a monzodioritic magma and a crustal-derived felsic magma.Discussion: These findings suggest that both A-type K-feldspar granite and monzodiorite likely formed during post-orogenic processes. Additionally, the QOB commenced its postorogenic evolution as an extensional tectonic environment during the early Jurassic period.

Testing the TTG–Metabasite Connection in the Southern Superior Province: an Integrated Geochemical, Isotopic, and Petrogenetic Modelling Approach

Abstract Archean cratons are dominated by tonalite–trondhjemite–granodiorite (TTG) suites, the products of crustal differentiation that formed early continental crust. These rocks may have been primarily generated by partial melting of hydrated basaltic crust in a variety of settings including subduction zones or the deep lithosphere. Sources are mainly inferred from examination of TTGs alone, as potential source rocks are rarely exposed. In the southern Superior Province, Canada, the Kapuskasing Uplift exposes an important crustal cross-section with upper- to middle-crustal TTGs and lower-crustal metabasites, which show evidence of having produced trondhjemitic anatectic melt. Here, we test the hypothesis that these metabasites were the source of the Mesoarchean to Neoarchean TTGs in the Kapuskasing Uplift by combining phase equilibrium and melt trace element modelling with whole-rock and zircon Lu–Hf isotope analysis and geochronology (garnet Lu–Hf and zircon U–Pb) of metabasic samples. By comparison of the results with existing data from TTGs in the Kapuskasing Uplift, we determined that the metabasites are plausible source rocks for the TTGs. The Lu–Hf systematics of the metabasites and TTGs are the most robust evidence of a genetic connection. Modelling results support an increase in TTG source depth over time. New geochronological data constrain partial melting of metabasite and crystallization of anatectic melt between ca. 2685 Ma and ca. 2600 Ma, coeval with crystallization of only the youngest TTGs. Overall, these results indicate a complex history of intracrustal differentiation in the Kapuskasing Uplift, with partial melting of two isotopically distinct lower-crustal metabasic sources at different times and depths.

Geochemical and petrological diversity of a transcrustal magmatic system driven by mushy magma mixing: Insights from the Triassic dike swarms in East Kunlun orogen, northern Tibetan Plateau

Geochemical and petrological diversity within transcrustal magmatic systems usually reflects the magma properties and magmatic processes and thus is critical to understanding the origin of magmatic complexes and the evolution of continental crust. Herein, we present an integrated study on the petrology, mineralogy, geochronology, geochemistry, and Sr-Nd-Hf isotopes of Triassic mafic-felsic dikes in the East Kunlun orogenic belt, northern Tibetan Plateau, to elucidate the nature and evolution of the transcrustal magmatic system. The studied dikes intruding into the granodiorite pluton (ca. 235−233 Ma) comprise coeval ca. 220−218 Ma gabbroic diorite porphyry, diorite porphyry, granodiorite porphyry, and alkali-feldspar granite, resembling composite dike swarms. The macrocrysts in these dikes show various zoning patterns, indicating episodic magma recharge and crystal resorption. The compositional gap between the intermediate-mafic dikes (SiO2 = 52.9−67.8 wt%) and the granitic dikes (SiO2 >75 wt%), as well as their homogeneous whole-rock Sr-Nd isotopes, with (87Sr/86Sr)i = 0.708387−0.710995 and εNd(t) = −5.83 to −4.34, but variable zircon Lu-Hf isotopes, i.e., εHf(t) = −7.67 to −0.36, demonstrates that magma mixing rather than cogenetic fractional crystallization accounts for their origin. In combination with thermobarometric insights, these results suggest that the mafic and felsic parental magmas originating from an enriched lithospheric mantle and ancient continental crust, respectively, were ultimately emplaced and stagnated at varying crustal depths (∼22−30 km and 8−17 km). Subsequently, the felsic magma mush was replenished and rejuvenated by the underplated mafic magma, leading to varying degrees of crystal-melt and/or melt-melt mixing. This mush-facilitated crust-mantle magma mixing is an important mechanism accounting for the compositional diversity of the transcrustal magmatic system.

Genesis of the Devonian Habaqin ultramafic arc complex and associated low-grade Fe–Ti oxide mineralization in the northern North China Craton

In the northern North China Craton (NCC), abundant non-layered ultramafic complexes and associated low-grade Fe–Ti oxide ores (over 1000 million tons) were uncovered. However, their petrogenesis and metallogeny have remained unclear. The Habaqin complex is one of the larger intrusions of the region and hosts the largest low-grade magnetite occurrence. Here we present petrography, zircon U–Pb geochronology, mineral and whole-rock major and trace element compositions, and whole-rock Sr–Nd and zircon Lu–Hf isotopes of the complex to constrain its genesis. The complex includes early pyroxenite (∼75% clinopyroxene, ∼15% amphibole, ∼10% magnetite) and late hornblendite (∼80% amphibole, 15–20% magnetite, 0–5% apatite). Zircon grains from the hornblendite yielded a weighted mean 206Pb/238U age of 395 ± 2 Ma. The increasing whole-rock FeOtot and TiO2 contents from pyroxenite (FeOtot = 18.9 wt%, TiO2 = 1.31 wt%) to hornblendite (FeOtot = 19.1–30.4 wt%, TiO2 = 2.63–3.12 wt%) correlate with higher modal proportions of amphibole and magnetite. The pyroxenite and hornblendite display similar arc-like trace element characteristics of enrichment in LILEs and LREEs, and depletion in HFSEs. The complex formed by fractional crystallization of clinopyroxene, amphibole, magnetite, and apatite from a hydrous parent magma. Early removal of clinopyroxene caused H2O enrichment in evolved residual magmas and crystallization of magnetite and amphibole, forming low-grade mineralization with Ti-V-poor magnetite in hornblendite. The complex displays high initial 87Sr/86Sr ratios of 0.706413–0.707341, negative εNd(t) values of −16.0 to −14.2 and negative εHf(t) value of −30.6 to −12.0, suggesting a parent magma derived from an enriched lithospheric mantle, with possible existence of amphibole-bearing pyroxenite veins within the source. During the Early Devonian, the retreat of the subducted Paleo-Asian oceanic slab as well as arc-continental collision along the northern NCC induced partial melting of the veins and eventually formation of the complex.

Petrological and mineralogical constraints on the formation of Neoproterozoic calc-alkaline continental crust: The example of the Luding Intrusive complex, western Yangtze Block, South China

Decoding the trans-crustal magmatic evolution processes from exposed paleo-depth that are otherwise inaccessible above continental arc zone is instructive to understand the geochemical fractionation of arc magmatism and geochemical stratification of continental crust. To unravel trans-crustal magmatic processes leading to the formation of Neoproterozoic continental arc, we combined a comprehensive dataset of petrography, zircon UPb geochronology, whole-rock major and trace elements, and SrNd isotopes as well as zircon LuHf isotopes for the Neoproterozoic calc-alkaline Luding Intrusive Complex (LIC) in the western Yangtze Block, South China. The LIC is composed of monzodiorites, gabbro-diorites, diorites, and granodiorites that formed at ca. 783–779 Ma. The LIC lithologies are calc-alkaline with highly variable Mg# values (40.8–70.6) and subduction-related trace elemental patterns. In combination with predominantly depleted and comparable whole-rock SrNd (initial 87Sr/86Sr = 0.703244–0.704248 and εNd(t) = +2.35 ∼ +5.10) and zircon Hf isotopes (εHf(t) = +4.47 ∼ +9.99), the LIC originated from a common subduction fluids-metasomatized mantle source. The hornblende geothermobarometry and whole-rock normative mineral trajectories as well as previously experimental results collectively suggest that the crystallization of LIC occurred within the middle crustal level (11.4–20.9 km) at various temperatures (776–875 °C) and pressures (2.50–5.50 kbar), and underwent different degrees of fractional crystallization of predominant hornblende and plagioclase phases during the assemblage and solidification of cogenetic and multiple batches magmatic pluming. The diorites-granodiorites result from fractionation of early olivine + clinopyroxene phases followed by subsequent amphibole + plagioclase phases, and the monzodiorites mainly represent accumulation residues of dominant hornblende + plagioclase phases from more fractionated melts, while the gabbro-diorites underwent the fractionation from an isotopically homogeneous mantle source, but differ in their elemental compositions. The LIC from Neoproterozoic continental arc suggests that the cogenetic fractional crystallization of mantle-derived melts in intra-crustal magmatic system can account for the petrochemical diversities of arc magmatic rocks during the construction of the Neoproterozoic continental arc crust in the western Yangzte Block, South China.

Geochemical Characteristics, Zircon U-Pb Ages and Lu-Hf Isotopes of Pan-African Pegmatites from the Larsemann Hills, Prydz Bay, East Antarctica and Their Tectonic Implications

Prydz Bay is an important part of the Pan-African high-grade tectonic mobile belt. The focus of this investigation, by applying zircon LA-ICP-MS U-Pb geochronology, zircon Lu-Hf isotope systematics, and whole-rock geochemistry, is on Pan-African pegmatites in the Larsemann Hills of Prydz Bay, East Antarctica, their association with country rocks, and the formation conditions. Based on the obtained results, it is concluded that the pegmatites exhibit elevated levels of silica and alkali and possess peraluminous features. These pegmatites originated during the late Neoproterozoic–Early Cambrian (Pan-African) event, specifically in the D2–D4 stages. The D2 stage occurred between 546 and 562 Ma, followed by D3-stage pegmatites around 534 Ma. The pegmatites from the D2–D3 stages are considered to originate from Paleoproterozoic crustal materials, while there are at least two phases of pegmatites in the D4 stage (~517 Ma and ~521 Ma). The D4-1 pegmatite (~521 Ma) suggested both Paleo–Mesoproterozoic crustal origin, perhaps connected to extension. The D4-2 pegmatite (~517 Ma) originated from the crust layers. In the Larsemann Hills, Pan-African pegmatites formed in a recurring regime of tension. Therefore, the obtained data elucidate that a Pan-African stretching process might have occurred in Prydz Bay.

Petrogenesis and Tectonic Implications of the Qulihai Pluton in the Northern Margin of the Yili Block, NW China

Abstract Despite extensive research work that has been done, whether the northern margin of the Yili Block (YB) is still an active continental margin during the early Carboniferous period is still in debate. Herein, we conducted zircon U–Pb geochronology, geochemistry, and zircon Lu–Hf isotope studies on the Qulihai pluton in the northern margin of the YB to constrain the petrogenesis and dynamic process. The Qulihai pluton is a granitoid complex that is composed of quartz diorite, quartz monzonite, and syenogranite. The zircon U–Pb dating results revealed that the pluton was formed and emplaced between 346 and 342 Ma. The three different Qulihai pluton rock types had comparable εHf(t) values, ranging from +3 to +8. The corresponding two-stage model ages of 817–1182 Ma indicated their potential derivation from the Meso-Neoproterozoic juvenile crust. The Qulihai pluton typically features medium-to-high SiO2, K2O, and Al2O3 contents and low MgO and Fe2O3T contents. The quartz diorite and quartz monzonite samples had Mg# values of 43–47, indicating the input of mantle-derived melts in the source area. In contrast, the source region of syenogranite was purely crustal material. The Qulihai pluton is mainly characterized as strong metaluminous moderate-to-high-K cal-alkaline rocks of the I-type granite series, which are enriched in large-ion lithophile elements and depleted in high field strength elements while exhibiting active continental margin island arc magmatism. Our findings, combined with the comprehensive analysis of previous studies, suggest that the Qulihai pluton formation resulted from the subduction of the North Tianshan oceanic crust beneath the YB during the early Carboniferous period, contemporary with the tectonic regime transition from subduction advance to subduction retreat.

Late Magmatic Activity in the Tarim Large Igneous Province: Evidence from the Puchang Granites.

The magmatic evolution sequence and tectonic activity background of the Permian Tarim large igneous province were discussed based on the research of petrogeochemistry, chronology, and zircon Lu-Hf isotope of two types of granite distributed in the Puchang V-Ti-magnetite deposit in the northwestern margin of Tarim. The results show that the two types are characterized by high silica, alkali, and potassium content. Both types of granites are enriched with light rare earth elements, including porphyritic granites with a negative anomaly of Eu and biotite monzogranites with a weak positive anomaly of Eu. The trace elements generally show that the large-ion lithophile elements are enriched relative to the high-field-strength elements, P and Ti are obviously depleted, and Rb, U, and K are relatively enriched. The zircon U-Pb age of porphyritic granites is 275.7 ± 1.0 Ma, the εHf(t) value ranges from -6.6 to -3.3, and the tDM2 ranges from 1469 to 1684 Ma. The zircon U-Pb age of biotite monzogranites is 268.9 ± 1.4 Ma. The εHf(t) value ranges from -1.2 to 0.5, and the tDM2 ranges from 1232 to 1340 Ma. The two types of granite were formed in a postcollisional extensional environment at the end of the early Permian, which is related to the Permian Tarim mantle activity and asthenosphere upwelling. The porphyritic granite was derived from an enriched lithospheric mantle; the biotite monzogranite was formed by the melting of mantle with crust contamination; and basalt and intrusive complexes in the research area were formed in an extensional intraplate rift environment.

Petrogenesis of early Paleozoic granitoids in the North Qinling Orogen, Central China: Implications for crustal evolution in an accretionary orogen

Accretionary orogens are sites of extensive continental crustal growth and modification. The mechanism by which mafic crust is transformed into silicic melts (i.e., maturation of continental crust) is important for understanding the formation of the continental crust. The North Qinling Orogen (NQO) is a composite orogenic belt and contains an early Paleozoic accretion-dominated orogenic system, which is ideal for investigating continental crustal maturation. We obtained zircon and monazite U–Pb age and O isotope data, zircon Lu–Hf isotope data, and whole-rock major- and trace-element and Sr–Nd isotope data for early Paleozoic granitoids of the NQO. The granitoids are divided into three groups. Group 1 includes the Taiping tonalite (445 ± 3 Ma), the Manziying syenogranite (445 ± 2 Ma), and the Huoshenmiao granodiorite (436 ± 2 Ma). The Taiping and Huoshenmiao plutons have relatively high SiO2 contents (68.64–71.67 wt.%) and Na2O/K2O ratios (1.15–4.19), with enrichments in Rb, Ba, Th, and U and depletions in Nb, Ta, P, and Ti, and they are geochemically similar to sodic arc magmas. The Manziying syenogranite is a peraluminous potassic granite with high K2O contents (4.59–5.27 wt.%). Grantioids from Group 1 have similarly depleted Sr–Nd–Hf–O isotopic features (εHf[t] = +5.9 to +8.8; δ18O = 3.98‰–5.41‰), indicative of derivation via partial melting of oceanic arc crust, which suggests that partial melting of oceanic arc crust in a subduction system contributes to the generation of continental crust and causes its maturation. Group 2 consists of the Wuduoshan monzogranite (418 ± 2 Ma) and the Sikeshu granodiorite (423 ± 3 Ma). These plutons have relatively high SiO2 (65.59–72.06 wt.%), K2O (3.26–4.79 wt.%), and Al2O3 (14.65–16.12 wt.%) contents and Sr/Y (33–87) and (La/Yb)N (23–48) ratios. The Wuduoshan monzogranite has positive zircon εHf(t) (+0.4 to +3.1) and uniform δ18O (6.38‰–8.07‰) values, but the Sikeshu granodiorite has more variable isotopic compositions (εHf[t] = −1.9 to +5.0; δ18O = 6.37‰–10.60‰). The Wuduoshan monzogranite and Sikeshu granodiorite have similar whole-rock Sr–Nd isotopic compositions to basement rocks of the NQO. These features indicate that the two plutons formed by partial melting of basement rocks (i.e., subducted into the lower crust) of the North Qinling unit, along with juvenile crustal material. Group 3 is represented by the Xiaguan monzogranite, which formed at 434–430 Ma, and can be subdivided into heavy rare earth element (REE)-depleted and -enriched units. The former has high Sr/Y (56–98) and (La/Yb)N (34–73) ratios and low MgO (0.13–0.24 wt.%), Cr (0.37–1.69 ppm), and Ni (0.32–1.09 ppm) contents, similar to adakites derived from metabasaltic sources. The heavy REE-enriched nature of the Xiaguan monzogranite may reflect modification of its source by melt or fluid. Our results show that partial melting of enriched oceanic arc crust contributed to crustal maturation in an accretionary orogen. The addition of evolved crustal material also facilitated this process; therefore, the basement rocks and crustal thickness should be considered when assessing crustal dynamics in an accretionary orogen.

A synthesis of available detrital zircon data from the Qilian‐Qaidam‐Kunlun collage, northern Tibet

AbstractIn this article, we present a brief introduction to the procedure, methods and results of the collection and summarization of an updated detrital zircon U–Pb geochronology database for the Qilian‐Qaidam‐Kunlun collage in northern Tibet. A total of 620 samples with 59,830 raw data were compiled from 121 published papers, including 70 samples with in‐situ detrital zircon Lu–Hf isotopes. Samples from seven different geologic subunits are categorized. For sediments with different ages of deposition, we highlight the characteristics of age spans, probability density distributions, major peaks and εHf(t) values. Further syntheses of this metadata collection, the detailed raw data of which will be periodically accessible in the Deep‐Time Digital Earth repository, would be effectively applied to a variety of scientific attempts concerning the geologic history of the Qilian‐Qaidam‐Kunlun collage, in particular, provenance analyses, crustal evolution studies and supercontinent reconstructions.

A synthesis of available detrital zircon data from Turkey, Cyprus and Greek peninsula

AbstractThis paper describes the assembly of an updated dataset of detrital zircon geochronology and Lu–Hf isotopes for Turkey, Cyprus and Greek peninsula. This first version of the dataset documented 286 samples with detrital zircon U–Pb data and 70 samples with zircon Lu–Hf isotopes from 42 published articles. These samples are mainly distributed in seven geologic‐tectonic units in the Eastern Mediterranean Tethyan region. The compilation of dataset will be periodically accessed in the Deep‐Time Digital Earth repository, containing more updated raw data of (un)published scientific research. We believe that the construction of such a dataset is fundamental to studies of clastic strata and also to understanding of crustal evolution in the Eastern Mediterranean region.

Miocene lamprophyre and felsic volcanics in the outer zone of SW Japan: arc building through multiple sources in an active convergent margin

ABSTRACT Subduction-related magmatism is a significant contributor to arc building and continental growth. In the active convergent margin of the SW Japan arc, voluminous volcanic rocks and mafic dykes formed through subduction and back-arc rifting during Miocene. In this study, we investigate a suite of felsic volcanic rocks (rhyolite and dacite) and lamprophyres from central Shikoku Island, which occur in the north-central part of the Chichibu belt and Sanbagawa belt in the Outer zone of the SW Japan arc. Whole-rock geochemistry results show that the rhyolite and dacite samples are peraluminous, belong to the high-K calc-alkaline series, show LREE and LILE enrichment, HREE and HFSE depletion that suggest arc volcanic affinity. The lamprophyre samples belong to alkali lamprophyre, show LREE and HFSE enrichments, and display OIB (oceanic island basalt)-like geochemical features. The 206Pb/238U weighted mean ages of the zircons from the rhyolite and dacite samples range from 14.39 ± 0.21 Ma to 13.92 ± 0.30 Ma, whereas the lamprophyre shows 206Pb/238U weighted mean age of 12.21 ± 0.35 Ma. Zircon Lu-Hf isotope data suggest that the rhyolite and dacite were derived from the remelting of the arc crustal rocks and that the lamprophyre was derived from depleted mantle sources and was contaminated by crustal materials. The felsic volcanic rocks (rhyolite and dacite) can be correlated to Miocene (15.5 Ma to 13.5 Ma) magmatism in the Outer Zone of the SW Japan arc. The formation of lamprophyre dykes in the SW Japan arc may be related to the subhorizontal mantle flows beneath the SW Japan arc associated with the opening of the Japan Sea back-arc basin or asthenosphere upwelling through the slab-tear of the Philippine Sea Plate beneath the SW Japan arc. Our study shows that the SW Japan Arc was built by multiple magmatism from diverse sources in an active convergent margin.

Petrogenesis and Geodynamic Significance of the Early Triassic Nanpo Adakitic Pluton of the Luang Prabang-Loei Tectonic Belt (Northwestern Laos) in the East Tethys Domain: Constraints from Zircon U-Pb-Hf Isotope Analyses and Whole-Rock Geochemistry

Adakites are magmatic rocks with specific geochemical characteristics and specific dynamics that provide important clues to understanding the magmatic-tectonic evolution of orogenic belts. We studied the Early Triassic Nanpo adakitic pluton of the Luang Prabang-Loei tectonic belt in the Eastern Tethys domain (Laos Sarakan) using detailed petrological, zircon U-Pb chronological, whole-rock geochemical, and zircon Lu-Hf isotope studies to constrain their petrogenesis. The rocks are predominantly diorites and granodiorites with Early Triassic zircon U-Pb emplacement ages ranging from 247.9 ± 1.0 to 249.0 ± 2.4 Ma. Moderate SiO2 (56.26–65.95 wt%) and Na2O (3.24–5.00 wt%) contents, with Na2O/K2O values between 1.76 and 2.51 and A/CNK values between 0.81 and 0.94, indicate that the rocks belong to the metaluminous calc-alkaline rock series. The high Sr content (590–918 ppm), low Y (6.30–11.89 ppm) and Yb (1.99–3.44 ppm) contents, intermediate Mg# (42–50) values, and high Sr/Y and (La/Yb) N ratios (Sr/Y = 24–41, (La/Yb) N = 6.84–13.8) are typical for adakites. Zircon Hf isotope analysis shows a significant variation in the εHf(t) values (6.7–12.0), with a mean value of 9.4 and a TDM2 of 512–845 Ma. Geochemical evidence indicates that the Nanpo adakitic rock was formed by the partial melting of the thickened lower crust in the plate-breaking environment and has an important contribution to the underplated mantle-derived magma. We propose that the Early Triassic adakites in the Luang Prabang-Loei tectonic belt formed during the transition from subduction to a continental collision, and the mixing of crust- and mantle-derived magmas is the main mechanism for the growth of continental crust in the Paleo-Tethys orogenic belt of southeastern Asia.

Neoproterozoic tectonic transition from subduction to back-arc extension along the western Yangtze Block, South China: Petrological evidence of Nb-enriched basalts and arc-type intrusive rocks

Identifying the tectonic transition process from persistent slab subduction to back-arc extension is vital for the systematical study of arc magmatic evolution in a temporal perspective. Although Neoproterozoic subduction setting along the western Yangtze Block has been widely documented, the detailed tectonic transition from subduction to back-arc extension was not systematically constrained. The coexistence of Nb-enriched rocks and normal arc-type rocks can generally provide unique insights into back-arc extension background under subduction setting. Herein we therefore present combined data of petrology, mineralogy, zircon U-Pb geochronology, whole-rock major and trace elements, and Sr-Nd isotopes as well as zircon Lu-Hf isotopes for the Neoproterozoic Nb-enriched basalts and arc-type intrusive rocks (i.e., gabbros and diorites) from the Luding area along the western Yangtze Block (South China), to characterize back-arc extension setting of Neoproterozoic continental magmatic arc. Zircon U-Pb ages suggest that the Nb-enriched basalts and arc-type gabbros-diorites formed coevally at ca. 780 Ma. The Nb-enriched basalts have much clinopyroxene phases and display higher TiO2, P2O5, Nb, Nb/La, and Nb/U values than normal arc volcanics. They are weakly enriched in Rb and Ba, and slightly depleted in Nb, Ta, Zr, and Hf, and show decoupled Nd-Hf isotopes with highly positive whole-rocks εNd(t) (+5.79 ∼ +7.39) and relatively low zircon εHf(t) (+1.09 ∼ +9.05) values, indicating an origination of subduction slab melts-metasomatized mantle wedge source, resembling with the genesis of those typical Nb-enriched mafic rocks in a back-arc setting. Compared with Nb-enriched basalts, the arc-type gabbros and diorites contain more hornblende minerals, and are characterized by variably high MgO (3.10–5.71 wt%) contents and Mg# values (51.5–57.2), and enriched LREEs and LILEs (e.g., Rb, Ba, Sr, and K) as well as depleted Nb, Ta, and Ti. Considering their relatively depleted and coupled Nd-Hf isotopes, these arc-type gabbros and diorites were formed by partial melting of hydrous mantle wedge modified by subduction fluids. The co-occurrence of Nb-enriched basalts and arc-type gabbros-diorites studied here therefore reveal Neoproterozoic back-arc extension background under the subduction setting. Combined with ca. 810–780 Ma mafic rocks showing Nb-enriched signatures and ca. 860–740 Ma normal arc-type mafic-intermediate rocks in the western Yangtze Block, we support that Neoproterozoic geodynamic transition from continuing subduction to back-arc extension initially occurred at ca. 820–810 Ma. The Neoproterozoic back-arc extension is thus significant for geochemical changes of subduction-related metasomatized agents and arc magmatic types.

Geochemistry, Detrital Zircon U-Pb Geochronology, and Lu-Hf Isotopes of the Metasedimentary Rocks (Xinghongpu Formation, Late Devonian) in the Central South Qinling Orogenic Belt: Implications for Provenance and Tectonics

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems.

Petrogenesis of the Granitic Dykes in the Yangshan Gold Belt: Insights from Zircon U-Pb Chronology, Petrography, and In-Situ Hf Isotope Analysis

The Yangshan gold belt is renowned for its igneous rock formations, particularly dykes that form in tectonically weak zones. Some of these rock formations exhibit a close spatial relationship with gold mineralization, and a tiny portion of the granitic dykes serve as gold ore bodies by themselves. In order to investigate the nature of granitic dykes and their association with gold mineralization, we conducted a comprehensive study consisting of zircon U-Pb chronology, petrography, and in situ Hf isotope analysis of 25 granitic dyke samples collected from east to west across the belt. According to LA-ICP-MS zircon U-Pb dating results, the granitic dykes inherited zircon ages that are concentrated between 745.0 and 802.0 Ma, and magmatic intrusion ages that mainly fall between 201.0 and 213 Ma. Moreover, the granitic dykes display a calc-alkaline to high-K calc-alkaline peraluminous series, which is relatively enriched in light over heavy REE, with moderate Eu anomalies. These dykes are rich in large-ion lithophile elements and poor in high-field-strength elements. The zircon Lu-Hf isotope data range from εHf(t) values of −1.5 to 0.1, mantle model (TDM1) ages range from 859 to 937 Ma, and crustal model (TDM2) ages range from 1111 to 1218 Ma. The granitic dykes found in the Yangshan gold belt were formed between 200 and 213 Ma ago, during a period of intracontinental extension following the late collision between the Yangtze plate and Qinling microplates. These dykes originated from the volcanic basement of the Mesoproterozoic Bikou Group, which was formed by the melting of the upper crust under the crustal thickening caused by the subduction and collision of the Qinling microplate. Subsequently, the dykes were transported along a tectonically weak zone, assimilating surrounding rocks and undergoing a transformation from “I”-type to “S”-type granite before finally evolving into granite with specific “A”-type characteristics. Our study provides new insights into the petrogenesis of granitic dykes in the Yangshan gold belt, as well as the relationship between gold mineralization and magmatic activity, which has significant implications for mineral exploration and the geological understanding of gold mineralization in this region.

Petrogenesis of Early Triassic Felsic Volcanic Rocks in the East Kunlun Orogen, Northern Tibet: Implications for the Paleo-Tethyan Tectonic and Crustal Evolution

The felsic volcanic rocks in orogenic belts are vital probes to understand the tectonic evolution and continental crust growth. Here, we present a comprehensive study on the zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopes of Early felsic volcanic rocks from the Hongshuichuan Formation, East Kunlun Orogen, Northern Tibet, aiming to explore their petrogenesis and implications for the Paleo-Tethyan orogeny and crustal evolution. The studied felsic volcanics comprise rhyolite porphyry and rhyolite, exhibiting coeval zircon U–Pb ages of ca. 247–251 Ma. Rhyolite porphyries show metaluminous to peraluminous nature (A/CNK = 0.88–1.24) with high SiO2 contents (72.1–78.9 wt%) and moderate Mg# values (22–40), and they display enrichment of LREE with (La/Yb)N ratios of 6.02–17.9 and depletion of high field strength elements. In comparison, the rhyolites are strongly peraluminous (A/CNK = 1.09–1.74) with high SiO2 contents (71.7–74.3 wt%) and high Mg# values (43–52) and are also enriched in LREE ((La/Yb)N of 6.65–18.4) and depleted in HFSE (e.g., Nb, Ta, Ti). Combining with their different zircon Lu-Hf isotopes, i.e., enriched isotopes for the rhyolite porphyries (εHf(t) = −7.3 to −3.8) and depleted Hf isotopes for the rhyolites (ɛHf = −0.6 to +3.0), we interpret that the studied rhyolite porphyries and rhyolites were derived by partial melting of Mesoproterozoic metagreywacke sources followed by plagioclase-dominated fractional crystallization, but the latter shows the significant contribution of crust–mantle magma mixing. The mixed mantle-derived magma comes from an enriched lithospheric mantle source that had been metasomatized by subduction-related fluids. Combining with other geological evidence, we propose that the studied Early Triassic felsic volcanic rocks were formed in a subduction arc setting, and the reworking of ancient continental crust with crust–mantle magma mixing is the major mechanism of crustal evolution in the East Kunlun Paleo-Tethyan orogenic belt.