Two-stage Hf Model Ages Research Articles

Cambrian ultrapotassic rhyolites from the Lhasa terrane, south Tibet: Evidence for Andean-type magmatism along the northern active margin of Gondwana

The petrogenesis and tectonic significance of early Paleozoic magmatic rocks in south Tibet is debated. In this paper, we report Cambrian ultrapotassic felsic volcanics from the Lhasa terrane. Petrographic and whole-rock geochemical studies indicate that these rocks are rhyolite and rhyolitic ignimbrite, and have varying SiO2 (69.56–82.09wt.%), Al2O3 (9.52–16.61wt.%) and Fe2O3t (1.0–7.9wt.%). The rocks are ultrapotassic (high K2O 4.19–6.90wt.%, and very low Na2O 0.01–0.06wt.%) and peraluminous (A/CNK=1.41–2.22). They are enriched in Rb, Th, U, Pb, Zr and Y, and showed negative Ba, Sr, P, Nb, Ta and Ti anomalies, and slightly fractionated REE patterns with moderately negative Eu anomalies, typical of A-type granitoids. Zircons from six samples yielded crystallization ages of ca. 512Ma. These zircons show εHf(t) values in the range of −4.7 to +1.3, and two-stage Hf model ages of 1734–1392Ma. Combining with previous results, we propose that these ultrapotassic rhyolites were derived from the partial melting of middle Proterozoic crustal rocks in the lower crust under high-temperature and water-absent conditions in an extensional environment of active magmatic arc. Thus, this study provides new insights into early Paleozoic Andean-type orogeny along the northern margin of Gondwana supercontinent.

Early Permian–Late Triassic granitic magmatism in the Jiamusi–Khanka Massif, eastern segment of the Central Asian Orogenic Belt and its implications

Whole-rock major and trace elements, together with zircon U–Pb and Hf-isotope data, are reported for the granitic intrusions in the central part of the Jiamusi–Khanka Massif in the eastern segment of the Central Asian Orogenic Belt (CAOB), in order to investigate their precise geochronological framework, petrogenesis, sources and tectonic implications. LA-ICP-MS zircon U–Pb data, combined with previous ages, indicate that the Jiamusi–Khanka Massif is dominated by three stages of granitic magmatism, i.e., Cambrian (530–493Ma), Permian (299–254Ma) and Late Triassic (223–212Ma), with two possible subordinate magmatic events that occurred in the Silurian (434–416Ma) and Carboniferous (331–317Ma). The Permian diorite and granodiorite contain high Al2O3 (15.81–19.07wt.%), Na2O (K2O/Na2O=0.25–0.44) and Sr (748–949ppm) contents and low Y (4–18ppm) and Yb (0.37–1.94ppm) contents, with high Sr/Y ratios of 54–207, indicating that they probably originated from partial melting of a mafic lower crust at high-pressure conditions. However, the coeval monzogranite and granite porphyry have higher SiO2, Y, Yb and HREE contents and lower Al2O3, Na2O/K2O ratio and Sr contents, together with the features of LILE-enriched, HFSE-depleted and Nb–Ta–Ti troughs, reflecting that they were likely produced by partial melting of arc-type crustal materials at a relatively shallow crustal level. Meanwhile, the Late Triassic granites contain high SiO2 (75.90–77.40wt.%) and K2O (4.17–4.87wt.%), combined with low Sr and high Y and HREE, suggesting that they were possibly generated from crustal materials with involvement of slab-derived fluids at low pressure. All the granitoids have high 176Hf/177Hf ratios (0.282518–0.282842) with Hf two-stage model ages of 2005–809Ma, and most of the magmatic zircons have positive εHf(t) values, indicating that the primary magmas of these rocks were derived from partial melting of a dominantly “old” source with a possible significant addition of juvenile materials. Based on the geochemical data and the regional geological investigations, we propose that the Jiamusi–Khanka Massif was an exotic block probably derived from Gondwana, which might be located in a relatively southerly place compared with the current position and faced the Paleo-Pacific Ocean during the Early Permian–Late Triassic time. The Permian granitoids would form in an active continental margin setting, whereas the Late Triassic granites were most likely generated within a local extensional environment, both of which were closely related to the westward subduction of the Farallon plate of the Paleo-Pacific Ocean beneath the Jiamusi–Khanka Massif.

Mesozoic intraplate granitic magmatism in the Altai accretionary orogen, NW China: Implications for the orogenic architecture and crustal growth

The Central Asian Orogenic Belt (CAOB) is the world9s largest Phanerozoic accretionary orogen and is the most important site for juvenile crustal growth in the Phanerozoic. In this work, we employed U-Pb zircon geochronology to identify the early and middle Mesozoic intraplate granitic intrusive events in the Chinese Altai segment of the southern CAOB in order to better understand the crustal architecture of the CAOB. We also used whole-rock geochemical, Sr-Nd isotopic and zircon Hf isotopic data to constrain the generation for these granitic rocks and to evaluate the implications for vertical crustal growth in this region. The Early Mesozoic granitic intrusions were emplaced between 220 and 200 Ma in the central Altai “microcontinental terrane” (also widely referred to as Units 2 and 3). The granites have shoshonitic and high-K calc-alkaline affinities and show the characteristics of differentiated I-type granite. The whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7058-0.7128) and ε_Nd(210) values (−0.6 to −4.3), as well as the zircon ε_Hf(t) values (−4.0 to +5.0) and two-stage Hf model ages (0.94-1.52 Ga), suggest that the granitic magmas were produced from a mixed source with both mantle-derived and recycled crustal components. The middle Mesozoic granites were emplaced at ∼150 Ma in the southern Altai “accretionary terrane” (Units 4 and 5). They show A-type characteristics with the REE tetrad effect and have positive ε_Nd(151) whole-rock values of +1.0 to +5.2 and two-stage Nd model ages (T_DM2) of 0.6 to 1.0 Ga. Zircon Hf data show positive zircon ε_Hf(151) values of +1 to +8 and two-stage Hf model ages of 0.6 to 1.2 Ga. The Nd-Hf isotopic data suggest that the granitic magmas were derived from short-lived juvenile mantle-derived materials. Thus, the isotopic signatures of all the Mesozoic granites from the central (old terrane) and southern (young accretional terrane) Altai suggest that the basement of both terranes has retained its original nature. The data further imply that the Altai orogen has kept its original architecture of Paleozoic horizontal accretion during Mesozoic time, as commonly observed in accretionary orogens where horizontal tectonics are dominant. All the early Mesozoic intrusions in the Altai were emplaced in an intraplate anorogenic setting; hence are distinguished from the contemporaneous syn- or post-orogenic magmatism in the eastern CAOB. We conclude that the early Mesozoic granites in the CAOB were emplaced in a variety of tectonic settings.

Early Paleozoic depositional environment and intraplate tectono-magmatism in the Cathaysia Block (South China): Evidence from stratigraphic, structural, geochemical and geochronological investigations

The early Paleozoic geological evolution of the South China Craton composed of the Yangtze and Cathaysia Blocks has been the focus of long debate. The Cathaysia block has been central to the controversy regarding convergent margin versus intraplate environment in the early Paleozoic. In order to address the early Paleozoic evolution of Cathaysia, we undertook a systematic study of the stratigraphic sequences, deformational features and geochronology of magmatic event. Our results show that (1) during the early Paleozoic, the Jiangnan domain of the SE Yangtze block was characterized by a carbonate platform and the Cathaysia block by a graptolite-facies clastic rock assemblage, (2) in the Cathaysia block, a littoral-neritic depositional environment prevailed in Cambrian whereas a neritic-bathyal setting dominated during the early-middle Ordovician, and (3) the Late Ordovician depositional sequence in Cathaysia witnessed a period of transition from neritic-bathyal to littoral-land environment, marking the initial uplift process. Paleo-current measurements on the crossbeds revealed northwestward and westward transport directions, suggesting a source area to the east-southeast. All samples collected from the Cambrian-Ordovician strata show similar chemical characteristics; they have negative ε~Nd~(*t*) values (−9.7 to −13.7) and two-stage εNd(t) model ages at *ca.*2.04 to 2.36 Ga. This suggests that the early Paleozoic rocks were derived from the eroded Paleoproterozoic basement, and little or no mantle component was identified. During the Silurian, the Cathaysia block underwent strong folding, thrusting, weak metamorphism and large-scale anatexis accompanied by granitoid emplacement, building the South China Fold Belt. The maximum shortening is estimated at 67 percent. A kinematic analysis of the ductile sheared rocks revealed a fan-shape thrust pattern, with top-to-the southeast in the southeastern and top-to-the northwest in the northwestern Cathaysia block. Zircon U-Pb dating of four granitic plutons yielded ^206^Pb/^238^U ages of 435 ± 4 Ma, 424 ± 5 Ma, 428 ± 3 Ma and 427 ± 2 Ma. All the zircon εHf(t) values are negative (−6 to −9) and show a peak of two-stage Hf model ages around 1.9 Ga, indicating that the Silurian granitic magma was derived from the recycling of Paleoproterozoic basement. Major features of the early Paleozoic South China Fold Belt include the lack of early Paleozoic ophiolites and volcanic rocks, the absence of coeval HP-type blueschists, and the absence of mantle-derived juvenile magmatic rocks. Consequently, a subduction-collision-type orogeny is excluded. The magmatism most probably took place in an intraplate tectonic setting with little or no input of mantle components. We therefore conclude that the South China Fold Belt was an intraplate orogen, and is possibly related to the global early Paleozoic continental assembly.

Zircon U-Pb geochronological and Hf isotopic constraints on the Precambrian crustal evolution of the north-eastern Yeongnam Massif, Korea

In situ U-Pb dating and Hf isotopic analyses were conducted on zircons extracted from Paleoproterozoic metasedimentary rocks and peraluminous (meta)granitoids in the north-eastern Yeongnam Massif, Korea. Combined with previous results, analyses from detrital zircons from the metasedimentary rocks yield a predominant age population of ca. 2.5Ga with subordinate clusters at ca. 2.7, 2.3, and 2.1Ga, and minor points older than 2.8Ga. The detrital zircons frequently have textureless rims that were overgrown at ca. 2.03–1.85Ga, indicating post-depositional thermal overprints associated with the intrusion of neighbouring granitoids and metamorphism. The (meta)granitoids are divided into three lithologic groups of banded or augen biotite gneisses (group I: Pyeonghae and Buncheon gneiss), massive cordierite or two mica granitic gneisses (group II: Icheonri and Hongjesa granitic gneiss), and a garnet-bearing leucogranite (group III: Imwon leucogranite). The best estimates of the timing of the emplacement of the first two groups are indistinguishable within their error ranges; 1980±22Ma (Pyeonghae gneiss), 1966±15Ma (Buncheon gneiss), 1985±14Ma (Icheonri granitic gneiss), and 1975±16Ma (Hongjesa granitic gneiss). The upper intercept discordia ages of ca. 1.86Ga indicated by the metamorphic overgrowth rims of zircons from the Buncheon gneiss and the Icheonri granitic gneiss agree with the emplacement age of the Imwon leucogranite (1867±6Ma). A close genetic link between the (meta)granitoids and metasedimentary rocks is demonstrated by the comparable age pattern of inherited zircon cores in the former with that of detrital zircons in the latter. The lower intercept ages of zircons indicate repeated Pb loss events in the Neoproterozoic to Paleozoic, although their exact tectonic meaning is still unclear. Most zircons have negative ɛHf values corresponding to two-stage Hf model ages (T2DM) from 3.4 to 2.7Ga, demonstrating Neoarchaean to Paleoproterozoic reworking of the Paleo- to Neoarchaean crust. Zircons from group I metagranitoids display a narrow T2DM range (2.74±0.09Ga). The Neoarchaean Hf model ages are also reduced by high-ɛHf zircons from the metasedimentary rocks and group II metagranitoids (T2DM=ca. 2.75Ga), and most zircons from the Imwon leucogranite (T2DM=2.62±0.06Ga). The protoliths of group I metagranitoids are considered to be I-type granites that was derived by infracrustal melting at depth. In contrast, the scattered Hf model ages of zircons from group II metagranitoids are suggestive of crystallisation from heterogeneous S-type magmas derived from the partial melting of supracrustal rocks. It is concluded that the Neoarchaean Era (ca. 2.75–2.62Ga) marks the most important stage of crustal formation in the north-eastern Yeongnam Massif. The Paleoproterozoic (ca. 2.50–1.98Ga) magmas from which the zircons crystallised were principally a product of crustal reworking. These Hf isotopic features generally match those reported for zircons from the North China Craton and the eastern part of the Cathaysia Block in the South China Craton, but the zircon ages determined here do not allow an indisputable correlation of the north-eastern Yeongnam Massif with Paleoproterozoic terranes in eastern China.

Geochronology, petrogenesis and tectonic implications of Paleoproterozoic granitoid rocks in the Jiaobei Terrane, North China Craton

Paleoproterozoic granitoid rocks in the Jiaobei Terrane of the North China Craton mainly comprise deformed hornblende/biotite-bearing monzogranitic gneisses, undeformed biotite-bearing syenogranite, and tourmaline-bearing pegmatitic granite. In order to define the emplacement ages, sources, and petrogenesis of the granitoids, we have conducted a coupled LA-ICP-MS U–Pb dating, trace element and in situ Hf isotopic study of zircons from three representative Paleoproterozoic granitoid rocks in the Jiaobei Terrane. Our new zircon U–Pb data yield emplacement ages of 2181±12 and 1801±21Ma for deformed monzogranitic gneiss and undeformed syenogranite, respectively. The deformed hornblende/biotite-bearing monzogranitic gneisses in the Jiaobei Terrane, along with the Liaoji granitoids, define pre-tectonic granitoid events at ca. 2.2–2.0Ga, whereas the undeformed syenogranite corresponds to the post-tectonic or anorogenic granitoid event at ca. 1.8Ga. Zircons from the pre-tectonic hornblende-bearing monzogranitic gneiss have ɛHf(t) values varying from −2.13 to +6.18 (average=+1.2), two-stage Hf model ages (TDM2) of 2313–2780Ma and same trends of crustal evolution as ca. 2.5Ga TTG rocks, suggesting an origin by remelting of ca. 2.5Ga TTG rocks. Zircons from the pre-tectonic biotite-bearing monzogranitic gneiss have negative ɛHf(t) values of −7.36 to −2.85 (average=−5.26), two-stage Hf model ages (TDM2) of 2930–3206Ma and the same trends of crustal evolution as ca. 2.7 and/or ca. 2.9Ga TTG rocks, indicating derivation by partial melting of ca. 2.7 and/or ca. 2.9Ga TTG rocks. Zircons from the post-tectonic syenogranite display negative ɛHf(t) values ranging from–6.58 to −3.26 (average=−4.89), two-stage Hf model ages (TDM2) varying from 2663 to 2868Ma, and the same trends of crustal evolution as ca. 2.5Ga TTG rocks, indicating an origin by partial melting of ca. 2.5Ga TTG rocks. The linear belt of pre-tectonic, deformed A-type granitoid rocks with emplacement ages of 2.2–2.0Ga from the Liaoji area, Jiaobei Terrane, through to the Bengbu area of Anhui Province, together with the coeval mafic intrusions and bimodal volcanic assemblages, suggest that widespread extensions occurred along the Jiao-Liao-Ji Belt in the period of 2.2–2.0Ga. In contrast, the post-tectonic or anorogenic granitoid events may be linked to extensions following the amalgamation of the North China Craton.

Zircon U–Pb ages, major and trace elements, and Hf isotope characteristics of the Tiantangzhai granites in the North Dabie orogen, Central China: tectonic implications

AbstractCretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.

Petrogenesis and mineralization of the Fenghuangshan skarn Cu–Au deposit, Tongling ore cluster field, Lower Yangtze metallogenic belt

The Fenghuangshan copper–gold deposit, located in the Tongling ore cluster field along the Lower Yangtze metallogenic belt (LYRB) in eastern China, mainly consist of skarn ores hosted in granodiorite. U–Pb dating of magmatic zircons from Fenghuangshan granodiorite yields a weighted mean 206Pb/238U age of 143.1±1.6Ma. Five molybdenite samples collected in the Fenghuangshan deposit yield a Re–Os isochron age of 141.7±0.8Ma, demonstrating that the ore formation event is coeval with the Fenghuangshan granodiorite intrusion. The magmatic zircon ƐHf(T) values vary from −12.0 to −28.3, corresponding two-stage Hf model ages between 1.6Ga to 2.4Ga. Geochemical and isotopic signatures suggest that the Fenghuangshan granodiorite resembles adakite, which was derived from partial melting of the subducted oceanic crust towards LYRB during the early Cretaceous. The occurrence of inherited zircons shows the intrusive granodiorite was assimilated by old crustal materials during its emplacement. The biotite thermobarometry, zircon Ce(IV)/Ce(III) ratios and Eu anomalies coincidently demonstrate that the magma source of granodiorite was under high to moderate oxidized condition, conducive to Cu–Au mineralization. The sulfide ores in Fenghuangshan deposit are enriched in Pd and Pt, which could also be a consequence of the high oxidized magma source. The high Re abundance in molybdenite and platinum group element (PGE) contents of sulfide ores suggest that the ore-forming materials are characterized by mixed sources from the mantle and crust, and were slightly affected by hydrothermal alteration.

Geochronology and geochemistry of Mesoproterozoic granitoids in the Lhasa terrane, south Tibet: Implications for the early evolution of Lhasa terrane

The early history of the Lhasa terrane remains poorly constrained due to the poor exposure of the Proterozoic rocks. We report here U–Pb zircon ages, geochemical and Hf isotopic data for granite gneisses and biotite gneisses from the Bomi Complex in the eastern part of the Lhasa terrane, south Tibet. Petrological and geochemical data suggest that the protoliths of the granite gneisses and the biotite gneisses could be granites and tonalites, respectively. LA-ICPMS U–Pb zircon analyses yielded ages of 1343±27Ma (MSWD=0.3) and 1276±22Ma (MSWD=0.4) for two granite gneisses, and a consistent age of ca. 1250Ma for two biotite gneisses. These ages are interpreted as the magma crystallization time of both the gneisses protoliths, and thus the Bomi Complex represents the oldest rocks found in the Lhasa terrane. Our data indicate that the Mesoproterozoic detrital zircons from the Paleozoic metasedimentary rocks in the Lhasa terrane could be derived from the Lhasa terrane itself or the Tethyan Himalaya, rather than necessarily from the Albany-Fraser belt in the Australia. Geochemical characteristics show that the granite gneisses have an aluminous A-type granite affinity. The two granite gneisses dated in this study have zircon ɛHf(t) values between +4.0 and +1.8 and between +2.6 and +0.2, respectively. They have identical two-stage Hf model ages of ∼2.0Ga. We suggest that the protoliths of the granite gneisses were produced by protracted high temperature partial melting of a felsic intracrustal source in an extensional setting. In contrast, the biotite gneisses have similar geochemical characteristics to those of calc-alkaline granitoids that probably formed in a subduction-related environment. Zircons from the two dated biotite gneisses have relatively higher ɛHf(t) values of +8.1 to +3.6 and +10.5 to +5.7, respectively, indicating a juvenile mantle contribution to their magma source. Earlier magmatism at ∼1343–1276Ma may formed in a continental rift setting related to the final breakup of supercontinent Columbia, while subsequent magmatism of ∼1250Ma resulted from subduction of ocean slab during the assemblage of Rodinia. We thus infer that the Bomi Complex was related to the contact zone between the Eastern Ghats Belt and the Archean cratons in southeastern India during the Mesoproterozoic

Zircon U–Pb geochronology and elemental and Sr–Nd–Hf isotopic geochemistry of the Daocheng granitic pluton from the Yidun Arc, SW China

The Garze–Litang suture zone, located in the eastern part of the Tethyan tectonic domain, is notable for widespread Late Triassic granitic plutons, which are genetically associated with the evolution of the Paleo–Tethys Ocean. The Daocheng granitic pluton in the eastern Yidun Arc, SW China, is located in the middle of the Garze–Litang suture zone and has an outcrop area of ∼2800km2. In the present study, we report zircon U–Pb ages and elemental and Sr–Nd–Hf isotopic data for the Daocheng granitic intrusion. Secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry U–Pb analyses on zircons yield consistent ages of ca. 216Ma for three samples from the pluton. All the Daocheng granitic rocks are enriched in Si (SiO2=68.1–76.4%) and large-ion lithophile elements but depleted in high-field-strength elements (e.g., Nb, Ta, and Ti). Mineralogical and geochemical features indicate that these are high-K and calc-alkaline and I-type granites. They are characterized by relatively variable initial 87Sr/86Sr ratios (0.7059–0.7102), negative εNd(t) values (−5.7 to −7.8), wide-ranging εHf(t) values (−9.8 to +3.4), and two-stage Hf model ages of 1.04 to 1.88Ga. These isotopic signatures indicate that the source for the Daocheng granite was probably derived from partial melting of a Late Paleoproterozoic to Early Mesoproterozoic mafic–intermediate lower crust with a variably minor addition (<20%) of depleted mantle-derived magma. The parental magma thereafter underwent extensive fractional crystallization of ferromagnesian minerals, plagioclase, apatite, ilmenite, and rutile during emplacement, under temperatures from 785°C to 839°C. In combination with previous studies on synchronous magmatism in the Yidun Arc, we propose that the Daocheng granite was generated in a syncollisional tectonic setting. The westward subduction and closure of the Garze–Litang paleo-ocean triggered the underplating of large-scale mantle-derived magma and provided heat for the anatexis of the lower crust. Hybrid melts including minor depleted mantle-derived magma and lower crustal magma were then generated; these thereafter were continuously injected into a shallow-level chamber and gave rise to the Daocheng granite.

Zircon Hf isotope of Yingfeng Rapakivi granites from the Quanji Massif and ∼2.7 Ga crustal growth

The Quanji (全吉) Massif is located in the Northwest China, which is interpreted as a micro-continent that is composed of metamorphic basement and stable cover strata. There are some controversies of genetic relationship between the Quanji Massif and the major cratons in China. In this study, we obtained in situ zircon U-Pb and Hf isotopic compositions of the Yingfeng (鹰峰) rapakivi granites from the northwest Quanji Massif by application of LA-MC-ICP-MS technique. Twenty U-Pb age measurements points are concordant or near concordant, and their weighted mean 207Pb/206Pb age is 1 793.9±6.4 Ma (MSWD= 1.09), yields an upper intercept age of 1 800±17 Ma (MSWD=0.41); 19 Hf isotope measurements yield a two-stage Hf model ages (T DM2) of 2.63 to 2.81 Ga, with a weighted average age of about 2.70±0.02 Ga and ɛHf(t) values variate between -8.91 to -5.35. This indicates that magma source of the Yingfeng rapakivi granites were produced from partial melting of late stage of Neoarchean juvenile crust, and suggests a significant crustal growth event occurred in the Quanji Massif at that time. The Quanji Massif might be an ancient continental segment detached from the Tarim Craton based on the crustal growth history and other geological records. The Tarim Craton (including the Quanji Massif) and the North China Craton had a similar or homological early crustal evolution around ∼2.7 Ga, which implies that Tarim Craton might be one of the component parts of North China Craton.

Late Permian tectonic evolution at the southeastern margin of the Songnen–Zhangguangcai Range Massif, NE China: Constraints from geochronology and geochemistry of granitoids

This paper reports the LA-ICP-MS U–Pb zircon dating and geochemical data for the Huangqigou, Xiaobeihu and Lalagou granitic plutons at the southeastern margin of the Songnen–Zhangguangcai Range Massif, which will not only place important constraints on the rock-forming ages, source characteristics and tectonic setting of these granitic plutons, but will also provide insights into understanding the tectonic evolution of the eastern segment of the Central Asian Orogenic Belt. Zircons from three plutons have distinct oscillatory zoning structures in their cathodoluminescene (CL) images, which, combined with the Th/U ratios of 0.28–1.06, indicate their magmatic origins. Zircon U–Pb dating results for these granitic plutons indicate that the granitic magmatism occurred mainly in the late Permian (256–252Ma). The granites have SiO2 of 58.0–74.3%, Na2O of 2.74–3.76%, K2O of 2.75–3.95%, Na2O/K2O of 0.77–1.13, Mg# [100(Mg/(Mg+Fe2+)] of 21.8–39.9, and A/CNK of 0.88–1.08, with REE patterns characterized by LREE/HREE=7.75–12.82, (La/Yb)N=7.88–14.9 and δEu=0.56–0.87. The trace element spider diagrams indicate that these granites are enriched in large ion lithosphile elements (Rb, Ba, Th, U, etc.) and relatively depleted in high field-strength elements (Ti, Nb, Ta), with Sr and Pb ranging from 205 to 350ppm and from 2.02 to 3.60ppm, respectively. The in-situ Hf isotope analysis reveals that εHf(t) values range from −2.22 to +11.65, and the two-stage Hf model ages (TDM2) range between 641 and 1274Ma. These geochemical characteristics indicate that the late Permian granitic plutons at the SE margin of the Songnen–Zhangguangcai Range Massif can be assigned to metaluminous and weakly peraluminous high potassium calc-alkaline I-type granites with low-Sr and high-Yb features, and that the magmas to have formed these granites were originated from the partial melting of mafic igneous rocks in the lower crust. The source rocks are composed mainly of the juvenile crust with small contributions of ancient continental crust. Considering the existence of coeval mafic intrusive rocks and sedimentary basins, we propose that the Late Permian magmatism in the study area occurred in a post-collisional extensional setting following the collision of the Xingkai Block and the united Jiamusi and Songnen–Zhangguangcai Range Massifs.

Mid-Neoproterozoic crustal evolution of the northeastern Yangtze Block: Evidence from the felsic-gneiss xenoliths hosted in the Donghai Cenozoic basalts

Crustal xenoliths can provide new insights into the unexposed crust, and those from the northeastern Yangtze Block have rarely been studied. This paper reports U–Pb–Hf isotopes and trace-element compositions of zircons from six felsic xenoliths hosted by the Neogene alkali basalts in the Donghai region (i.e. Anfengshan and Pingmingshan) of the Sulu orogen in central eastern China. The xenoliths are mainly composed of orthoclase and quartz, or orthoclase and natrolite, with accessory minerals of Fe–Ti oxides and zircon. Most zircon grains show core-rim structures, with the cores and rims being magmatic and metamorphic in origin, respectively. The zircon cores mainly yield ages of ca. 827–794Ma, while the zircon rims give ages of ca. 232–212Ma. We interpret the zircon core ages as the time of an early Mid-Neoproterozoic magmatic event in the northeastern Yangtze Block and the zircon rim ages as the time of collision between the Yangtze and North China Blocks. Our data suggest that much more ca. 830–800Ma magmatic records are possibly preserved in the unexposed deep crust, and the early Mid-Neoproterozoic is an important era for the crust evolution of the northeastern Yangtze Block. The new zircon Hf isotopic analyses show that the Anfengshan sample (south of Donghai) has zircon εHf (820Ma) values ranging from −15.3 to −9.4, and two-stage Hf model ages of 2.66–2.30Ga; the Pingmingshan sample (southeast of Donghai) has zircon εHf (820Ma) values ranging from −1.4 to +3.8, and two-stage Hf model ages of 1.80–1.47Ga. These data suggest that ancient crust as old as Neoarchean to Mesoproterozoic was involved in the early Mid-Neoproterozoic magmatism. Combined with the previously reported zircon U–Pb–Hf results of the exposed rocks, it is highlighted that crustal recycling was dominant in the early Mid-Neoproterozoic (ca. 830–800Ma) magmatism, whereas both crustal recycling and addition of mantle-derived melts were significant in the late Mid-Neoproterozoic (ca. 800–720Ma) magmatism in the northeastern Yangtze Block.

The growth, reworking and metamorphism of early Precambrian crust in the Jiaobei terrane, the North China Craton: Constraints from U–Th–Pb and Lu–Hf isotopic systematics, and REE concentrations of zircon from Archean granitoid gneisses

Archean granitoid (tonalite–trondhjemite–granodiorite, TTG) gneisses are widely distributed in the early Precambrian metamorphic basement of the Jiaobei terrane, the North China Craton (NCC), and record the formation and evolution of the continental crust in the early Precambrian. In this study, zircon cathodoluminescence (CL) images have assisted in obtaining U–Th–Pb and Lu–Hf isotopic systematics, and rare earth element (REE) concentrations from distinct zircon domains of complex zircons, and the results have been integrated in order to unravel the growth, reworking and metamorphism of the early Precambrian crust in the Jiaobei terrane. Zircons from seven representative Archean granitoid samples, collected from the Jiaobei terrane, record three groups of magmatic ages of ∼2.9, ∼2.7 and ∼2.5Ga, and two groups of metamorphic ages of ∼2.5 and ∼1.86Ga. The ∼2.5Ga metamorphic event is thought to be linked to underplating of large amounts of mantle-derived magma, and the ∼1.86Ga metamorphic event to arc (or continent)–continent collision. Magmatic zircons have positive ɛHf(t) values (+0.7 to +12.58, average +5.5), and two-stage Hf model ages cluster at ∼2.7–2.8 and ∼2.9–3.0Ga. This indicates that the Archean granitoid rocks were derived from partial melting of juvenile crust that was formed mainly during ∼2.7–2.8 and ∼2.9–3.0Ga which represent two periods of growth of juvenile crust. The most significant period of crustal growth is ∼2.7–2.8Ga, whereas ∼2.5Ga represents a period of reworking of the ∼2.7–2.8Ga juvenile crust in the Jiaobei terrane, as well as other areas in the NCC.

Element geochemistry, mineralogy, geochronology and zircon Hf isotope of the Luxi and Xiazhuang granites in Guangdong province, China: Implications for U mineralization

The Luxi and Xiazhuang granitic plutons are parts of the Guidong granite belt in northern Guangdong Province, China. They occur next to each other and have similar crystallization ages. However, the Xiazhuang pluton hosts several important uranium (U) ore deposits, whereas the Luxi pluton does not. This study compares the two plutons using whole-rock geochemistry, biotite compositions, zircon U–Pb ages by LA-ICPMS, and in situ zircon Hf isotope data by LA-MC-ICPMS, to understand the fundamental controls. Results show that the two plutons have similar ages, 237Ma for the Luxi pluton and 234Ma for the Xiazhuang pluton. They also have similar geochemical features that are characteristic of S-type granites. Zircons from both plutons have negative εHf(t) values (−9 to −12) and a Paleoproterozoic two-stage Hf model age (TDM2=1838Ma to 2025Ma), suggesting that their parental magmas were all derived from Paleoproterozoic metasedimentary rocks. The geochemical and petrological data suggest that these two plutons crystallized from magmas derived from the same parent at different stages, the parental magma of the Xiazhuang pluton is more evolved than that of the Luxi pluton. This factor, plus different physical–chemical conditions (such as temperature, volatile components and oxidation state) resulted in higher U content and favorable U-bearing species in the Xiazhuang magmatic hydrothermal system. U occurs mainly as uraninite in the Xiazhuang pluton, which facilitates U transfer from granite into CO2-rich hydrothermal fluid to form U ore deposits. In contrast, U occurs mainly as REE-bearing minerals in the Luxi magmatic system, preventing U transfer to associated hydrothermal fluids. As a result, the Xiazhuang pluton hosts several important uranium ore deposits, whereas the Luxi pluton is ore-barren.

Petrogenesis of the Xihuashan granites in southeastern China: Constraints from geochemistry and in-situ analyses of zircon U[sbnd]Pb[sbnd]Hf[sbnd]O isotopes

The Xihuashan tungsten deposit, located in the Nanling tungstentin province, is renowned for being one of the largest and the earliest exploited deposits of tungsten worldwide. It is a vein‐type deposit genetically associated with the Xihuashan granite pluton. The granite was emplaced in four phases, and representative samples from each phase were analyzed using SIMS zircon UPb techniques, and the results indicate ages ranging from 161±3Ma to 158±2Ma (2σ). Whole rock analyses show the Xihuashan granitic rocks have high contents of SiO2 (74.5wt.%–78.1wt.%) and total alkali (7.68wt.%–8.86wt.%), and their aluminum saturation index (ASI) values have a narrow range of 1.01–1.16. The second and third phases of the Xihuashan granite are enriched in heavy rare earth elements and are depleted in Eu, Ba, Sr, P and Ti. P2O5 vs SiO2, zirconium saturation temperatures and zircon δ18O values indicate that the Xihuashan granites are highly evolved I–S transformation-type. Whole rock εNd(t), zircon εHf(t) and δ18O values fall into the ranges −11.3 to −10.4, –14.0 to −4.8, and 6.93‰–11.23‰ respectively, and the Nd and Hf two-stage model ages (TDM2) are 1.63–1.88Ga and 1.51–2.09Ga, respectively. The data indicate a primary reworking of Late Paleoproterozoic to Early Mesoproterozoic lower crust without any obvious participation of mantle material. The Xihuashan intrusion was emplaced at the same time as the widespread 165–150Ma I-type and A-type granites and syenites of the Nanling region, following the initiation in adjacent areas of intraplate basaltic activity, gabbros, bimodal volcanic rocks, and A-type granites from 190 to 165Ma. It can be inferred that the Nanling Range and neighboring regions were subjected to lithospheric extension during the Early Jurassic.

Geochronology and isotopic geochemistry of the A-type granites from the Huanggang Sn–Fe deposit, southern Great Hinggan Range, NE China: Implication for their origin and tectonic setting

The Huanggang Sn–Fe deposit, Inner Mongolia, is located in southern Great Hinggan Range metallogenic belt. LA-ICP-MS zircon U–Pb dating show that the K-feldspar granite and granite-porphyry in the Huanggang mine were formed at 136.7±1.1Ma and 136.8±0.57Ma, respectively. Sr–Nd–Pb isotope of the rocks and In situ zircon Hf isotopic systematics show that (87Sr/86Sr)i values range from 0.70211 to 0.70729, close to the (87Sr/86Sr)i of oceanic basalts and lower than those of continental crust. The εNd(t) values and Nd model ages (TDM) vary from −0.8 to 0.9 and 855 to 993Ma, respectively. The Pb isotopic compositions are also variable with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18.974–26.107, 15.554–15.914 and 38.894–39.890, respectively, suggesting that the lead is derived from a mixed source. The 176Hf/177Hf values range from 0.282744 to 0.282922, with corresponding εHf(t) values ranging from 1.9 to 18.3, and two-stage Hf model ages (TDM2) of between 561 and 888Ma. The isotope composition shows that Huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle, perhaps contaminated by small amounts of ancient continental crust. Younger Nd, Hf isotope model ages imply that an important crustal growth event took place in this area during the Neoproterozoic. Integrating our data with previously published results and the Late Mesozoic regional tectonic setting, we conclude that the Huanggang granites were generated in an intraplate tectonic–magmatic setting. Asthenospheric mantle upwelling due to lithospheric delamination and magma underplating, caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle. This resulted in remelting, differentiation and a continued evolution of the mafic juvenile crust, producing a large quantity of granitic magma. The tectonic setting for these processes may be linked to the NNW subduction of the Pacific plate (Izanagi) in the Mesozoic, which affected most of eastern China.

Geochronology, petrogenesis and tectonic implications of Triassic granitoids from Beishan, NW China

Five Triassic granitic plutons have been identified from the Beishan orogen by zircon U–Pb dating that defines two age groups: 240–238Ma and 225–217Ma. They belong to the high-K calc-alkaline and shoshonitic series and have alkalic and alkali-calcic characteristics, and are weakly peraluminous–metaluminous. These granitoids are mainly highly fractionated I-type granite and A-type granite. They have high Isr values (0.7049–0.7096) and negative εNd(t) values of −0.9 to −2.8, with Nd model ages of 0.89–1.13Ga, suggesting a crustal contribution. They also exhibit relatively high zircon εHf(t) values (−1.3 to +6.1) and two-stage Hf model ages of 1.34–0.87Ga, suggesting a mixture of mantle and various amounts of crustal components. The mantle component probably originated from underplated magmas produced by partial melting of lithospheric mantle metasomatized by fluids or melts, possibly derived from pre-existing subducted materials. The mid-Triassic (240–238Ma) pluton has relatively high Sr/Y (15.9–41.8) ratios and MgO (1.22–3.77%) contents, with negligibly to weakly negative Eu anomalies (δEu=0.57–0.80), indicating adakite-like features. This was likely the result of partial melting of crustal components in response to voluminous underplated mantle-derived magmas, probably linked to lithospheric delamination and asthenospheric upwelling. The Late Triassic (217–225Ma) granitic plutons show strong negative anomalies of Eu, Ba, Nb, Ta, Sr, P and Ti. These were likely the result of fractional crystallization and crustal contamination for the granitic magma emplaced in a post-orogenic setting.

Permian Tectonic Evolution in Southwestern Khanka Massif: Evidence from Zircon U‐Pb Chronology, Hf isotope and Geochemistry of Gabbro and Diorite

Abstract:Laser ablation‐inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral‐subhedral in shape and display fine‐scale oscillatory zoning as well as high Th/U ratios (0.26–1.22), implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian (282±2 Ma) and in the Late Permian (255±3 Ma), respectively. In addition, the captured zircons with the weighted mean age of 279±4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low‐K tholeiitic series, and are characterized by low rare earth element (REE) abundances, flat REE pattern, weak positive Eu anomalies (δEu), and depletion in high field strength elements (HFSEs, Nb, Ta, and Ti), similar to the high‐aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from +7.63 to +14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc‐alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs (Nb, Ta, and Ti), similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two‐stage model ages of zircons from the diorite range from +11.22 to +14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo‐Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent (Khanka Massif) happened in the late stage of the Late Paleozoic.

Syn-exhumation magmatism during continental collision: Evidence from alkaline intrusives of Triassic age in the Sulu orogen

A combined study of zircon U–Pb ages, Lu–Hf isotopes, mineral O isotopes, whole-rock elements and Sr–Nd isotopes was carried out for alkaline intrusive rocks (including gabbro, syenite and granite) in the Sulu orogen. The results provide insights into crust–mantle interaction in the continental subduction zone. SIMS and LA-ICPMS zircon U–Pb dating yield Late Triassic ages of 201±2 to 212±1Ma for their crystallization. These ages are younger than Middle Triassic ages for ultrahigh-pressure (UHP) metamorphism of country rocks, corresponding to syn-exhumation magmatism during continental collision. The alkaline rocks are characterized by the arc-like patterns of trace element distribution, with relative enrichment of LILE and LREE but relative depletion of HFSE. They have high initial 87Sr/86Sr ratios of 0.7064 to 0.7114 and highly negative εNd(t) values of −16.4 to −13.8 with two-stage Nd model ages of 2.11 to 2.33Ga for whole-rock. Zircon Lu–Hf isotope analyses also show highly negative εHf(t) values of −20.9±0.5 to −14.1±0.9, with two-stage Hf model ages of 2.10±0.06 to 2.56±0.03Ga. The zircon exhibits relatively consistent δ18O values of 5.6 to 6.2‰, slightly higher than normal mantle values. The enrichment of radiogenic Sr–Nd–Hf isotopes in the gabbro indicates its origination from an isotopically enriched mantle source, whereas the arc-like pattern of trace element distribution for it suggests a fertile mantle source with enrichment of LILE and LREE. Thus, it is part of the orogenic lithospheric mantle that would be generated by underplate reaction of the subcontinental lithospheric mantle with hydrous felsic melts derived from the subducted continental crust during the Triassic continental collision. On the other hand, there are general similarities in trace element and radiogenic isotope characteristics between the syenite–granite and UHP metaigneous rocks in the Dabie–Sulu orogenic belt, suggesting its genetic link to the subducted continental crust itself. Therefore, the alkaline rocks are derived from partial melting of the orogenic lithospheric mantle and the subducted continental crust in the stage of exhumation. They provide a petrological record of recycling the subducted continental crust into mantle depths with consequent crust−mantle interaction during the continental collision.