Hf Model Research Articles

Crust periodic evolution: Evidence from the Taihua complex, southern North China Craton

The Taihua complex in the southern North China Craton (NCC), recording muti-episodes continental crust growth events, was divided into the lower and upper units. The lower unit were mainly composed of Neoarchean-Mesoarchean TTG gneisses and amphibolites. Here we report the whole-rock geochemistry, zircon U-Pb dating, trace element and Lu-Hf isotope compositions from the Wugang TTG within the lower unit of the Taihua complex LTC. They are characterized by high-SiO2 (62.2–70.73 wt%), high-Al2O3 (13.23–16.66 wt%), low-Mg# (31–53) and Cr contents (20–60 ppm), HREE and HFSE depletion with low to moderate Sr/Y (12.0–76.3) and (La/Yb)N (5.2–48.3, N denotes normalization by chondrite) in compositions. Magmatic zircons from representative samples, one granodioritic gneiss and one tonalitic gneiss (both are drilled samples), gave a consistent upper intercept ages at 2.85 Ga, reflecting the time of crystallization of the first time TTG pluton within LTC. They have positive zircon εHf(t) values (0.9–7.1) with the TDM1(Hf) model ages ranging from 2.85 Ga to 3.09 Ga with an average of 2.95 Ga, and TDM2(Hf) model ages ranging from 2.85 Ga to 3.23 Ga with an average of 3.01 Ga, their youngest Hf model ages (2.85 Ga) were close to the crystallized ages. In combination with data from Lushan Mesoarchean TTG rocks, they shared similar geochemical features, except for the depleted degree in HREE, indicating that they are generated from similar geologic dynamic setting but in different depths. These TTG rocks were principally derived from a depleted mantle sources, indicating a key juvenile crust accretion in the southern margin of the NCC at 2.85 Ga. They were most likely formed from occasional subduction and partial melting of oceanic plateaus, leaving a garnet-bearing amphibolitic residue at shallow depths (>25 km, Wugang TTG) and deep depths (>50 km, Lushan TTG) with different degree’s fractionation. In associated with previous study, we identified at least four stages of TTG formation, ∼2.85 Ga, ∼2.80 Ga, ∼2.76 Ga and ∼2.72 Ga, from the Southern NCC, which reconfirmed that the Archean continental evolution is episodic and periodic at least in the Taihua complex.

Early Silurian to Early Carboniferous ridge subduction in NW Junggar: Evidence from geochronological, geochemical, and Sr-Nd-Hf isotopic data on alkali granites and adakites

The Central Asian Orogenic Belt (CAOB) evolved through a long-lived orogeny involving multiple episodes of subduction and accretion marking a major phase of continental growth during the Paleozoic. The northern part of the Western Junggar region (NW Junggar) offers a window into these processes, particularly to constrain the timing of closure of the Paleo-Asian Ocean. Here we report geochemical, geochronological, and isotopic data from K-feldspar granites and adakitic rocks from the NW Junggar region. Zircon U-Pb ages suggest that the granites were emplaced during Early Silurian to the Early Carboniferous (434–328Ma). The granites show geochemical characteristics similar to those of A-type granites, with high SiO2 (71.13–76.72wt%), Na2O+K2O (8.00–9.59wt%), and Al2O3 (12.28–14.08wt%), but depleted Sr, Nb, Ta and Eu. They display moderate to high positive εNd(t) and εHf(t) values (4.26–8.21 and 7.69–14.60, respectively) and young Nd and Hf model ages (T2DM-Nd=489–740 Ma and T2DM-Hf=471–845 Ma), suggesting magma derivation through partial melting of lower crust in the Boshchekul-Chingiz and Zharma-Saur arcs. The adakites are characterized by high Sr content (406.5–751.6ppm), and low Y (13.8–16.4ppm) and Yb (1.5–1.8ppm) content, yielding relatively high Sr/Y ratios (25.38–49.41) similar to those of modern adakites. They have high positive εNd(t) and εHf(t) values (7.85–8.25 and 13.23–15.97, respectively) and young Nd and Hf model ages (T2DM-Nd=429–535Ma and T2DM-Hf=355–550Ma), indicating that their source magmas were likely derived from partial melting of the oceanic crust beneath the Boshchekul-Chingiz arc. The petrogenesis and distribution of the A-type granites and adakites, as well as the tectonic architecture of the region, suggest that a ridge subduction event might have occurred during the Early Silurian to Early Carboniferous. In combination with previous studies in the Chinese Altai, we suggest a two-sided ridge subduction model for the Junggar-Altai region.

In situ zircon U–Pb and Hf isotopes and tectonic implications of late Palaeoproterozoic host rocks from the Shuangfengling gold deposit, northern Tarim Block, NW China

The Tarim Block contains important information of the Precambrian crustal evolution of the Earth. In this paper, we present detailed petrographic and in situ zircon U–Pb and Hf isotopes data for the Palaeoproterozoic host rocks (gneiss and gneissic granite) of the Shuangfengling gold deposit in the Quruqtagh terrane in order to constrain their ages and magma sources and discuss their tectonic environments. Zircon laser ablation–inductively coupled plasma–mass spectrometry data indicated that the host rocks (gneiss and gneissic granite) of the Shuangfengling gold deposit were formed at 1948 ± 17 and 1944 ± 13 Ma, respectively, and all underwent a metamorphism immediately after magma emplacement. The Hf isotopic signatures, negative εHf(t) values and older Archean two‐stage Hf model ages, of the studied rocks suggested that the magmas of these rocks were derived by crustal reworking in a manner similar to the magmatism related to a collisional orogeny. This study further confirms the existence of this Palaeoproterozoic magmatic and metamorphic event in the Tarim Block. The Tarim Block was part of the Columbia supercontinent.

Ore genesis and geodynamic setting of the Lianhuashan porphyry tungsten deposit, eastern Guangdong Province, SE China: constraints from muscovite 40Ar−39Ar and zircon U–Pb dating and Hf isotopes

The Lianhuashan deposit has long been regarded as a typical tungsten porphyry deposit, located in the eastern Guangdong Province, in the Southeastern Coastal Metallogenic Belt (SCMB). LA–MC–ICP–MS zircon U–Pb dating of the quartz porphyry yielded a weighted mean 206Pb/238U age of 137.3 ± 2.0 Ma, which is interpreted as the emplacement age of the quartz porphyry. Hydrothermal muscovite yielded a plateau 40Ar/39Ar age of 133.2 ± 0.9 Ma, which is consistent with the zircon U–Pb age, suggesting that the tungsten mineralization is genetically related to the quartz porphyry. Combined with previous studies, we suggest that there is a 145–135 Ma episode linking the granitic magmas with W–Sn ore systems in the SCMB. Zircon eHf (t) values of the quartz porphyry are in range of − 3.8 to 0.9, and the two-stage Hf model ages (TDM2) are 1.1–1.4 Ga, which is younger than the basement rocks in the Cathaysia Block (1.8–2.2 Ga), signifying that the quartz porphyry was predominantly derived from melting of Mesoproterozoic crust containing variable amounts of mantle components. In combination with the newly recognized coeval alkaline/bimodal magmatism and A-type granites in eastern Guangdong, we suggest that the 145–135 Ma W–Sn metallogenic event of the SCMB is related to a geodynamic setting of large-scale lithospheric extension and thinning, which can be ascribed to melting of the crust caused by mantle upwelling, triggered by the oblique subduction of the Izanagi plate.

Generation of post-collisional normal calc-alkaline and adakitic granites in the Tongbai orogen, central China

Post-collisional granites are generally generated by partial melting of continental crust during orogenic extension. The occurrence of normal calc-alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension, which has been debated yet. In this paper, we present a comprehensive study of zircon U–Pb ages, Hf–O isotopes, as well as whole-rock major and trace elements and Sr–Nd isotopes, for Tongbai and Jigongshan post-collisional granitic plutons in the Tongbai orogen. Zircon U–Pb dating yields intrusion ages of ca. 140 and 135Ma for the Tongbai and Jigongshan plutons, respectively, suggesting they are post-collisional granites. These granites are high-K calc-alkaline series, metaluminous to weakly peraluminous with A/CNK ratios of 0.85–1.08. The Tongbai gneissic granites are normal calc-alkaline granite, having variable SiO2 (61.93–76.74wt%) and Sr/Y (2.9–38.9) and (La/Yb)N (1.7–30.1) ratios with variably negative Eu anomalies (0.41–0.92). They have relatively high initial Sr isotope ratios of 0.707571 to 0.710317, and low εNd(t) (−15.74 to −11.09) and εHf(t) (−17.6 to −16.9) values. Their Nd and Hf model ages range from 2.2 to 1.8Ga and 2.3 to 2.2Ga. On the contrary, the Jigongshan granites show higher SiO2 (66.56–72.11wt%) and Sr/Y (30.1–182.0) and (La/Yb)N (27.4–91.4) ratios with insignificant Eu anomalies (0.73–1.00), belonging to adakitic granite. They have Isr=0.707843–0.708366, εNd(t)=−19.83 to −17.59, and εHf(t)=−26.0 to −23.5. Their Nd and Hf model ages vary from ca. 2.5 to 2.4Ga and ca. 2.8 to 2.6Ga. The Tongbai and Jigongshan granites are characterized by mantle-like zircon δ18O values (5.17–5.46‰). These geochemical features suggest that the Tongbai and Jigongshan granites were derived from partial melting of Paleoproterozoic and Archean continental crust, respectively. Fractional crystallization affected the geochemical compositions of the Tongbai gneissic granites, while the compositions of the Jigongshan granites were mainly controlled by partial melting. The adakitic signatures of the Jigongshan granites were either inherited from their source or ascribed to more garnet in their residues. The voluminous post-collisional granites might form by the collapse of the thickened Tongbai orogenic root. The normal Tongbai gneissic granites occurred slightly earlier than the Jigongshan adakitic granites in the Tongbai orogen, suggesting that it is not a mandate to sign the tectonic transition from adakitic to normal calc-alkaline granites in post-collisional settings. Therefore, this study provides another example supporting the burst of voluminous post-collisional granites with different compositions as a consequence of the collapse of the thickened orogenic roots of collisional orogens.

New constraints on the Hadean to Proterozoic history of the Jack Hills belt, Western Australia

A 1010m traverse line on the eastern flank of Eranondoo Hill was mapped and sampled in detail, crossing the entire width of the Jack Hills supracrustal belt, Western Australia. The facies associations indicate a northward deepening of the sedimentary sequence and confirm a fan delta depositional environment. From a total of 157 samples processed for zircon extraction, precise MC-ICP-MS and SHRIMP zircon U-Pb isotope results from 51 of these yielded a total of 6308 dates that included 2819 concordant ages ranging from 4381±10Ma to 1618±22Ma (2σ). The rocks that yielded Proterozoic ages include schist, sandstone, quartzite and matrix-supported conglomerate and are widely distributed across the belt. However, there are similar lithologies that yield only Archean ages and so there is no relationship between rock-type and depositional age. Overall, rocks proven to contain Proterozoic zircon make up only ~12% of the belt, but confirm the presence of both Archean and Proterozoic successions at Jack Hills. A total of 1093 of the most concordant zircon grains from 46 samples were analysed for Lu-Hf, with negative εHf(t) values making up 94.3% of the population. For the Proterozoic zircons, the εHf(t) values ranged from −22.1 to 1.0, with an average εHf(t) value of −8.4 (n=10). For zircons with U-Pb ages from 2.5 to 3.0Ga, the εHf(t) values ranged from −14.7 to −1.6, with an average value of −7.9 (n=25). Zircons with U-Pb ages that ranged from 3.0Ga to 4.0Ga, have εHf(t) values from −17.6 to 5.6, with an average εHf(t) value of −6.3 (n=873). For Hadean zircons, the εHf(t) values ranged from −11.0 to 5.6, with an average εHf(t) value of −3.4 (n=185). Importantly, 92% of the Hadean zircon population recorded negative εHf(t) values, with Hf model ages indicating initial crustal generation at 4.4–4.5Ga. The Hf isotope data do not favour significant juvenile input into the parental Hadean magmas. Instead, the data support extensive reworking of long-lived, mafic, intermediate and felsic Hadean crust, which could only endure at or near the Earth's surface in the absence of subduction, thus mitigating against Hadean plate tectonics.

Tectonic evolution of Precambrian basement massifs and an adjoining fold-and-thrust belt (Gyeonggi Marginal Belt), Korea: An overview

This contribution provides an overview on geology, geochronology, and tectonics of Precambrian basement massifs and adjoining Gyeonggi Marginal Belt (GMB), Korea. The three massifs (Gyeonggi, Yeongnam, and Nangrim) record tectonothermal events represented by ∼2.0–1.85 Ga arc-related magmatism and collisional orogenesis, culminating at ∼1.88–1.85 Ga. The oldest (∼2.51 Ga) migmatitic gneisses limitedly occur in the Nangrim and Gyeonggi massifs, suggesting the North China Craton (NCC) affinity of both massifs. The Yeongnam Massif is characterized by the occurrence of ∼1.87–1.86 Ga anorthosite-mangerite-charnockite-granite suite. This anorthositic suite is a late-orogenic product linked to the amalgamation of ‘Paleoproterozoic Korean arc’ with the North China Craton, forming the Columbia/Nuna supercontinent. The majority of Hf and Nd model ages of basement gneisses are in the range of ∼3.5–2.5 Ga, attesting to the crustal evolution since the Paleoarchean. P-T paths of the Paleoproterozoic basement gneisses are apparently variable, and the Gyeonggi and Yeongnam massifs are characterized by the kyanite-sillimanite and andalusite-sillimanite facies types, respectively. The GMB comprises three fold-and-thrust sub-belts (Imjingang Belt, Taean–Hongseong Complex, and Ogcheon Metamorphic Belt) which are correlative with each other in terms of tectonostratigraphy and detrital zircon geochronology. Two (meta)sedimentary units are diagnostic of this belt: (1) the Neoproterozoic Sangwon Supergroup sharing the provenance with younger rocks in the Ogcheon Belt; and (2) the Devonian turbiditic sequences present in all the three sub-belts. The latter are most distinctive in their detrital zircon age distribution characterized by two major populations at ∼1000–950 Ma and 450–430 Ma. This age pattern as well as the turbiditic lithology is critical for the correlation between the GMB and the Qinling Belt. Taken together, we suggest that the South China Craton-like GMB units are built upon the NCC-like basement (Gyeonggi Massif); this feature is the key to the Qinling–Gyeonggi microcontinent model which accounts for the assembly of a variety of tectonic slivers in the GMB.

Geochemical, zircon U–Pb–Hf, and whole‐rock Sr–Nd isotopic study of Late Jurassic Sanming A‐type granite in the Wuyi area, Fujian province, Southeast China

The Sanming pluton is the only Late Jurassic A‐type granitic intrusion in the Wuyi area, west Fujian Province, Southeast China, and its formation has important implications for our understanding of the tectonic evolution of the region. The U–Pb ages of 157 ± 1 Ma and 159 ± 1.1 Ma were obtained for the pluton by zircon LA–ICP–MS analysis, which is interpreted to be the crystallization age of the Sanming pluton (i.e., Late Jurassic). The pluton has the geochemical characteristics of A‐type granite, such as high K2O+Na2O contents (average 7.703 wt%), FeOT/(FeOT + MgO) ratios (average 0.85), and high 10,000 Ga/Al values and Zr + Nb + Ce + Y (380–446.1 ppm, average 419.2 ppm) contents, but relatively low CaO, Sr, and Eu contents. Zircon saturation temperatures range from 875 °C to 890 °C, also similar to other A‐type granites. The (87Sr/86Sr)i ratios (0.707368–0.71102) and εNd(t) and εHf(t) values (−5.54 to −6.09, and −6.93 to −1.07, respectively), the 2‐stage Nd model ages of 1.50–1.55 Ga, and 2‐stage Hf model ages of 1.25–1.62 Ga, suggest the pluton was derived by extensive fractionation of melts containing both mantle materials and Mesoproterozoic crustal components. The Sanming A‐type granitic pluton is younger than adakitic rocks in the region (162 Ma), suggesting a localized transition from compressional to intraplate extensional tectonics at 162–159 Ma, with mantle‐derived material playing a crucial role in the formation of A‐type granites in the Wuyi Mountain area. This tectonic transition is explained by localized rollback of the subducting Pacific plate.

Lu-Hf ratios of crustal rocks and their bearing on zircon Hf isotope model ages: The effects of accessories

All other factors being equal, the calculation of zircon Hf two stage model ages (TDM Hf) depends on the particular Lu/Hf value assumed for the magmatic source, the effect being more pronounced as the age difference between zircon and magmatic source increases. It is generally considered that the Lu/Hf measured in the zircon-hosting rock does not represent the composition of the source because of potential garnet or zircon fractionation. Accordingly, most authors either assume a single fixed value for Lu/Hfsource, often Lu/Hf≈0.079 to 0.108, or use two alternative models, one for felsic sources, often Lu/Hf≈0.09, and the other for mafic sources, often Lu/Hf≈0.165. In contrast with these opinions, however, here we show that partial melting of peraluminous sources causes little decoupling of Lu from Hf because of similar solubilities of zircon and monazite. Furthermore, the effects of residual garnet are largely compensated by the numerous zircon inclusions that garnet and other residual minerals almost always contain. Partial melting of metaluminous sources may significantly decouple Lu from Hf if allanite and/or titanite are not present in the source, but the effect decreases as the melt fraction increases. Similarly, fractional crystallization of metaluminous magmas may decouple Lu from Hf if amphibole or clinopyroxene begin to crystallize before zircon saturation. The Lu/Hf distribution in 4784 rocks from different regions and ages is lognomal rather than normal, and the calculated medians, i.e. the maximum of the probability density function for the logarithmically transformed Lu/Hf, are Lu/Hfmafic rocks≈0.08, Lu/Hffelsic rocks≈0.05, i.e. notably lower than the above-mentioned felsic and mafic magmatic source averages. Magmatic sources may be remarkably heterogeneous with respect to Lu/Hf. Our calculations show that fixed Lu/Hfsource values translate the Lu/Hf heterogeneity of the source to the TDM Hf thus producing an artificial distribution of model ages that may be erroneously interpreted as different episodes of crustal growth. Therefore, we propose that the best strategy to calculate two stage Hf model ages of zircon is to use the analytically determined whole-rock Lu/Hf ratio as a proxy of the source. In the case of detrital or inherited zircons, for which no whole-rock information is available, it is advisable first to determine whether they come from a mafic or felsic rock by interpreting cathodoluminescence images, Th/U ratios and other chemical parameters, and then venture an estimate of the Lu/Hfsource from the SiO2 average.

Multi-stage modification of Paleoarchean crust beneath the Anabar tectonic province (Siberian craton)

According to present views, the crustal terranes of the Anabar province of the Siberian craton were initially independent blocks, separated from the convecting mantle at 3.1 (Daldyn terrane), 2.9 (Magan terrane) and 2.5 Ga (Markha terrane) (Rosen, 2003, 2004; Rosen et al., 1994, 2005, 2009). Previous studies of zircons in a suite of crustal xenoliths from kimberlite pipes of the Markha terrane concluded that the evolution of the crust of the Markha terrane is very similar to that of the Daldyn terrane. To test this conclusion we present results of U-Pb and Hf-isotope studies on zircons in crustal xenoliths from the Zapolyarnaya kimberlite pipe (Upper Muna kimberlite field), located within the Daldyn terrane, and the Botuobinskaya pipe (Nakyn kimberlite field) in the center of the Markha terrane.The data on xenoliths from the Botuobinskaya kimberlite pipe record tectonothermal events at 2.94, 2.8, 2.7 and 2 Ga. The event at 2 Ga caused Pb loss in zircons from a mafic granulite. U-Pb dating of zircons from the Zapolyarnaya pipe gives an age of 2.7 Ga. All zircons from the studied crustal xenoliths have Archean Hf model ages ranging from 3.65 to 3.11 Ga. This relatively narrow range suggests that reworking of the ancient crust beneath the Nakyn and Upper Muna kimberlite fields was minor, compared with the Daldyn and Alakit-Markha fields (Shatsky et al., 2016).This study, when combined with dating of detrital zircons, implies that tectonic-thermal events at 2.9–2.85, 2.75–2.7 and 2.0–1.95 Ga occurred everywhere on the Anabar tectonic province, and could reflect the upwelling of superplumes at 2.9, 2.7 and 2 Ga. The presence of the same tectonic-thermal events in the Daldyn and Markha terranes (Rosen et al., 2006a,b) supports the conclusion that the identification of the Markha terrane as a separate unit is not valid.

Multiple dating and tectonic setting of the Early Cretaceous Xianglushan W deposit, Jiangxi Province, South China

The Xianglushan W deposit in northwestern Jiangxi Province, South China, is one of numerous large-size W deposits along the northern margin of the Jiangnan Massif. The deposit comprises lenticular and stratiform-like orebodies, mainly along the contact between argillaceous limestone of the Cambrian Yangliugang Formation and a biotite granite pluton. The mineralization is zoned from proximal W greisen within the cupolas of the biotite granite, through W skarn and sulfide-scheelite bands near the pluton, to distal quartz-sulfide ± scheelite veins. The granitic pluton and an aplitic dyke in the mining area contain zircon grains with U–Pb ages of 123.8 ± 0.8 Ma and 117.3 ± 1.7 Ma, respectively. Six molybdenite samples collected from skarn ores yielded a Re–Os weighted mean age of 125.5 ± 0.7 Ma, and muscovite separates from greisen ores yielded a 40Ar/39Ar plateau age of 122.8 ± 0.78 Ma. The molybdenite Re–Os and muscovite Ar–Ar ages are consistent with the zircon U–Pb age of the hosting granite. The Xianglushan deposit is formed by an Early Cretaceous W–dominated polymetallic ore-forming event in the Jiangnan porphyry–skarn W belt. Zircon from biotite granites in the Xianglushan deposit has negative εHf(t) values, generally from − 5.7 to − 3.1, with corresponding two-stage Hf model ages of 1363–1218 Ma, reflecting derivation of magmas from a crustal source. Molybdenite has Re contents from 12.12 to 22.77 ppm, indicative of a mixed crustal-mantle source, but with a dominantly crustal component. A compilation of precise ages for magmatism and mineralization in the Jiangnan porphyry–skarn W belt shows that there are two stages of mineralization at 150–135 Ma and 130–120 Ma, respectively. Integrated with published data, our results suggest that the Xianglushan W deposit formed in an extensional tectonic setting during the Early Cretaceous.

Continental outbuilding along the margin of an Archean cratonic nucleus in the North China Craton

The history of crustal growth in the Early Earth, formation of cratonic nuclei and the building of large continents have important implications in understanding the secular evolution of our planet. The North China Craton (NCC) is envisaged in recent models as a collage of several Archean microblocks which were amalgamated along multiple zones of ocean closure during the late Neoarchean, and offers window to gain insights on the origin of cratonic nuclei and their subsequent outbuilding. Here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks, the Qianhuai Block. We present petrological, geochemical and zircon U–Pb geochronological and Lu-Hf isotopic data on a suite of rocks ranging from hornblendite through gabbro and dioritic gabbro to TTG (tonalite-trondhjemite-granodiorite) and granitoids exposed in the Miyun area, and representing the cross section of the lower to mid segments of a continental magmatic arc. Geochemically, the felsic units of the suite straddle from monzonite through granodiorite to granite with dominantly metaluminous affinity, magnesian composition and arc-related features. The metagranites and TTG gneisses are characterized by negative Nb-Ta anomalies and positive K and Pb anomalies. The diorite, gabbros and hornblendite display negative anomalies of Th-U, Nb-Ta and Zr-Hf and positive anomalies at Ba, Pb and Sm with negative Eu anomalies and minor positive Ce anomalies, attesting to arc-related origin. In the tectonic discrimination diagrams, the rocks plot in the volcanic arc field, indicating formation within a subduction-related setting.The oldest magmatic population with ages of ca. 2560 and 2529 Ma from the hornblendite and the TTG gneiss represent the magma emplacement ages with fractional crystallization of underplated basalts derived from slab melts, leaving hornblendite as the cumulate. Magmatic zircon grains from the metagranite and granodiorite show upper intercept ages of 2457 ± 21 Ma and 2475 ± 12 Ma whereas those from the TTG gneisses yield ages of 2529 ± 19 Ma and 2522 ± 38 Ma. Younger age groups of 2444.4 ± 8.3 Ma, 2418 ± 16 Ma and 2161 ± 31 Ma also occur in these rocks indicating multiple thermal events. The zircon grains from diorite and gabbros show 207Pb/206Pb weighted mean ages of 2411 ± 11 Ma–2486 ± 13 Ma with younger ages of 2.0–2.37 Ga. These rocks also carry older xenocrystic grains of ca. 2.51–2.65 Ga. The zircons in hornblendite show an upper intercept age of 2560 ± 33 Ma and a lower intercept age of 1947 ± 54 Ma. Young groups of ca. 2.2 Ga and 1.8 Ga are also found in this rock. The ca. 1.9 to 1.8 Ga ages correspond to the timing of metamorphism. The Hf isotopic data on zircons from the various rock types of the Miyun magmatic suite show both negative and positive εHf(t) values ranging from −9.64 to +7.04 with Hf model ages in the range of 2606–2844 Ma (TDM1) and 2635–3147 Ma (TDM2), suggesting crustal growth through both juvenile magmas from depleted mantle sources and reworked Meso- to Neoarchean crustal components. Our study reveals that the ca. 2.7–3.0 Ga core of the Qianhuai microcontinent represents one of the ancient cratonic nuclei in the NCC that underwent extensive continental outbuilding during late Neoarchean – early Paleoproterozoic through multiple magmatic events mostly related to convergent margin arc-type processes. It is possible that similar processes operated around the other Archean microcontinents in the NCC in the process of building the major crustal blocks which were finally amalgamated at the end of the Paleoproterozoic.

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages.The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

Origin of the Bashierxi monzogranite, Qiman Tagh, East Kunlun Orogen, NW China: A magmatic response to the evolution of the Proto-Tethys Ocean

The Qiman Tagh of the East Kunlun Orogen, NW China, lies within the Tethysides and hosts a large W–Sn belt associated with the Bashierxi monzogranite. To constrain the origin of the granitic magmatism and its relationship with W–Sn mineralization and the tectonic evolution of the East Kunlun Orogen and the Tethys, we present zircon U–Pb ages and Hf isotopic data, and whole-rock compositional and Sr–Nd–Pb isotopic data of the Bashierxi monzogranite. The granite comprises quartz, K-feldspar, plagioclase, and minor muscovite, tourmaline, biotite, and garnet. It contains high concentrations of SiO2, K2O, and Al2O3, and low concentrations of TiO2 and MgO, indicating a peraluminous high-K calc-alkaline affinity. The rocks are enriched in Rb, U, Pb, and light rare earth elements, and relatively depleted in Eu, Ba, Nb, Sr, P, and Ti, and are classified as S-type granites. Twenty zircon grains yield a weighted mean 238U/206Pb age of 432±2.6Ma (mean square weighted deviation=1.3), indicating the occurrence of a middle Silurian magmatic event in the region. Magmatic zircons yield εHf(t) values of −6.7 to 0.7 and corresponding two-stage Hf model ages of 1663–1250Ma, suggesting that the granite was derived from Mesoproterozoic crust, as also indicated by 207Pb/206Pb ages of 1621–1609Ma obtained from inherited zircon cores. The inherited zircon cores yield εHf(t) values of 8.3–9.6, which indicate the generation of juvenile crust in the late Paleoproterozoic. Samples of the Bashierxi granite yield high initial 87Sr/86Sr ratios and radiogenic Pb concentrations, and negative εNd(t) values. Isotopic data from the Bashierxi granite indicate that it was derived from partial melting of ancient (early Paleozoic to Mesoproterozoic) sediments, possibly representing recycled Proterozoic juvenile crust. Middle Silurian granitic magmatism resulted from continental collision following closure of the Proto-Tethys Ocean. The Qiman Tagh represents a Caledonian orogenic belt containing S-type granites and associated W–Sn deposits.

Magmatic evolution and source of a Proterozoic rapakivi granite complex in the North China Craton: New evidence from zircon U−Pb ages, mineral compositions, and geochemistry

Typical Proterozoic rapakivi granite of the Northern Hemisphere occur in Precambrian shield areas, and are commonly associated with anorthosites, mangerites, and charnockites, thus belonging to the AMCG (anorthosite–mangerite–charnockite–granite) suite. A similar suite is represented in the North China Craton (NCC) by the Shachang rapakivi granite and Damiao anorthosite complexes. The Shachang complex consists of amphibole–biotite rapakivi granite, porphyritic biotite granite, coarse-grained biotite granite, medium- to fine-grained biotite granite, and two-mica granite (listed from the earliest to the latest phases). New zircon U–Pb dating shows that the complex was formed over the period 1700–1682 Ma. The mafic minerals of the complex are calcic amphibole (ferroedenite–ferrohastingsite) and biotite (annite–siderophyllite), and the compositions of the amphibole suggest that the matrix of the amphibole–biotite rapakivi granite crystallized at a pressure of ∼4 kbar. The temperatures of crystallization, obtained from the compositions of amphibole, biotite, and zircon, decreased from ∼780 °C for the amphibole–biotite rapakivi granite to ∼660 °C for the two-mica granite. Our study of the Shachang complex indicates an evolution from early potassium-rich magmas to late silicon-rich magmas. The early amphibole–biotite rapakivi granite crystallized under relatively high temperatures (760–780 °C) and low fO2, while the later rocks formed under lower temperatures (760–660 °C) and high fO2. The Shachang rapakivi granite and Damiao anorthosite complexes contain different mafic minerals and show diverse trace element ratios and disparate geochemical evolutionary trends, suggesting different sources. Zircon Lu–Hf and whole-rock Sm–Nd isotopic data for the Shachang complex are relatively homogeneous, with εHf(t) and εNd(t) values varying from −9.8 to −3.3 and −6.4 to −3.4, respectively. Corresponding two-stage Hf model ages and Nd depleted mantle model ages vary from 2650 to 2850 Ma and from 2480 to 2840 Ma, respectively. These model ages are similar to the ages of Neoarchean lower crustal metamorphic rocks in the NCC (2500–2800 Ma). In addition, the compositions of the amphiboles and biotites in the granite in the Shachang complex indicate derivation from the crust. All the evidence points to the Shachang rapakivi granite complex having been formed from magmas derived from the lower crust of the NCC, rather than from the fractionation of mantle-derived mafic magmas with minor crustal contamination. This paper provides a detailed case study of the Shachang complex that will further our understanding of the sources of Proterozoic rapakivi granite in the Northern Hemisphere that belong to the AMCG suite of rocks.

Precambrian-Cambrian provenance of Matinde Formation, Karoo Supergroup, northwestern Mozambique, constrained from detrital zircon U-Pb age and Lu-Hf isotope data

The Permian-Triassic time interval was a period of high sedimentation rates in the intracontinental Karoo rift basin of northwestern Mozambique, reflecting high exhumation rates in the surrounding high ground Precambrian-Cambrian basement and juxtaposed nappes. U-Pb LA-MC-ICPMS dating and Lu-Hf isotopic analysis of detrital zircons from the Late Permian-Early Triassic Matinde Formation of the Karoo Supergroup is used as a reliable proxy to map denudation patterns of source regions. Data allow discrimination of U-Pb age populations of ca. 1250-900 Ma, a secondary population between ca. 900-700 and a major contribution of ages around ca. 700-490 Ma. Zircon grains of the Mesoproterozoic age population present Mesoproterozoic (1000–1500 Ma) to Paleoproterozoic (1800–2300 Ma) Hf TDM ages, with positive (0 to +11) and negative εHf values (−3 to −15), respectively. The younger U-Pb age population also presents two different groups of zircon grains according to Lu-Hf isotopes. The first group comprise Paleoproterozoic (1800–2300 Ma) ages, with highly negative εHf values, between −10 and −22, and the second group exhibits Mesoproterozoic ages (1200–1500 Ma), with increased juvenile εHf values (ca. 0 to −5). These Hf isotopes reinforce the presence of unexposed ancient crust in this region. The oldest U-Pb age population resembles the late stages of Grenville Orogeny and the Rodinia Supercontinent geotectonic activity mostly represented by magmatic rocks, which are widely present in the basement of northern Mozambique. The juvenile Hf-isotope signature with an older age component is associated to rocks generated from subduction processes with crust assimilation by continental arcs, which we correlate to rocks of the Nampula Complex, south and east of the Moatize-Minjova Basin. The U-Pb ages between 900 and 700 Ma were correlated to the calc-alkaline magmatism registered in the Guro Suite, related to the breakup phase of Rodinia, and mark the western limit of the Moatize-Minjova rift basin together with the Mungari Nappe and Chacocoma Granite, also probable sources. The εHf-isotopic signature (ca. −23 to 0) with Meso- and Paleoproterozoic Hf model ages of these zircons suggest assimilation of older crust by the Guro Suite continental arc. The Late Neoproterozoic - Cambrian U-Pb ages (ca. 700-490 Ma) comprise the wide interval of high-grade metamorphism, klippen and plutonism related to the Pan-African Orogeny. Hf-isotope pattern indicate high remelting of the older Mesoproterozoic and Paleoproterozoic crust. These ages correspond to magmatic and granulite metamorphic ages of the Monapo and Mugeba klippen, Nampula Complex and Guro Suite/Mungari Nappe/Chacocoma Granite rocks. The data suggests that these units were main source areas for the sediments of the Matinde Formation. The main Cambrian ages are related to the late stages of Pan-African Orogeny, marked by crustal delamination in NE Mozambique that was responsible for an extensive crustal partial melting associated to high-grade granulitic metamorphism and generation of large granitic plutons. The Nampula Complex was probably a large geotectonic entity in the Late Mesoproterozoic and reworked during the Pan-African Orogeny. This evidence, added to the N-NW paleoflow of the Proto-Zambezi river and provenance data, suggests that the Nampula Complex, Guro Suite and its juxtaposed nappes formed a high ground source area for fluvial sediments that fills the Moatize-Minjova Basin. Permian-Triassic rifting in northern Mozambique was induced by far-field stresses transferred from Gondwana margins. This stress disrupted the Nampula Complex reactivating Precambrian structures and fabrics, while the Jurassic-Cretaceous breakup of Gondwana and latter landscape evolution led to its actual morphology and configuration.

Age and nature of the Jurassic–Early Cretaceous mafic and ultramafic rocks from the Yilashan area, Bangong–Nujiang suture zone, central Tibet: implications for petrogenesis and tectonic Evolution

ABSTRACTThe Jurassic–Early Cretaceous Yilashan mafic–ultramafic complex is located in the middle part of the Bangong–Nujiang suture zone, central Tibet. It features a mantle sequence composed of peridotites and a crustal sequence composed of cumulate peridotites and gabbros that are intruded by diabases with some basalts. This article presents new whole-rock geochemical and geochronological data for peridotites, gabbros, diabases and basalts to revisit the petrogenesis and tectonic setting of the Yilashan mafic–ultramafic complex. Zircon laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) U–Pb ages of three diabase samples are 169.6 ± 3.3 Ma, 132.5 ± 2.5 Ma, and 133.6 ± 4.9 Ma, respectively. These ages together with previous studies indicate that the Yilashan mafic–ultramafic complex probably formed during the Jurassic–Early Cretaceous. The peridotites exhibit nearly U-shaped REE patterns and are distinct from abyssal peridotites. The diabase and basalt samples show arc features with selective enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILEs; e.g. Rb, U, and Sr) and depletion in high field strength elements (HFSEs; e.g. Nb, Ta, and Ti). The gabbro samples display cumulate features with selective enrichment in LILEs (e.g. Rb, Ba, and Sr) but depletion in LREEs and HFSEs (e.g. Nb, Zr, and Ti). Combing the positive εNd(t) values (+6.1 to +10.0) and negative zircon εHf(t) values (–16.5 to –11.7 and –13.6 to –0.4) with older Hf model ages for the mafic rocks, these signatures suggest that the Yilashan mafic and ultramafic rocks likely originated from an ancient lithospheric mantle source with the addition of asthenospheric mantle materials and subducted fluids coupled with limited crustal contamination in a continental arc setting as a result of the southward subduction of the Bangong–Nujiang Tethys Ocean beneath the Lhasa terrane during the Jurassic–Early Cretaceous.

Neoproterozoic tectonic evolution of the Jiuling terrane in the central Jiangnan orogenic belt (South China): Constraints from magmatic suites

The formation and tectonic evolution of the Jiangnan orogenic belt in South China have been debated in the context of plate subduction-collision versus mantle plume. Here we present new results from petrology, whole rock geochemistry, zircon U-Pb chronology and Hf isotopes, on three magmatic suites ranging in composition from felsic to mafic from the Jiuling terrane of the central Jiangnan orogenic belt in the southeastern margin of Yangtze Block. Suite 1 including meta-diorites and meta-basites are dated at 849.9±4.9, 848.8±4.5 and 846.3±3.5Ma. The meta-diorites and some of the meta-basites display enrichment of LREE, Rb and K and depletions of Nb, Ta and Ti anomalies, with distinctive geochemical features of continental arc setting. The εHf(t) values of zircons from meta-diorites range from 0.17 to 6.10. The other meta-basites have LREE depleted REE patterns, similar to N-MORB and intra-oceanic island arc settings, suggesting a fore-arc environment. Suite 2 consists of foliated granitoids dated at 816.8±4.2, 814.6±3.6, 812.5±3.5 and 810.3±3.5Ma, with the A/CNK values >1.1, and are classified as post-collisional granites in the Rb/(Y+Nb) diagram. Zircon grains from the granitoids show εHf(t) values in the range of −1.99 to 8.49 and Hf model ages of 1835–1041Ma. Suite 3 is composed of meta-diabase dated at 792.1±2.8Ma, with zircon εHf(t) values of 8.46–13.83. This suite shows E-MORB REE patterns, and plot within continental rift field. Their zircon Hf model ages mainly clustered at 1046–811Ma, indicating magma sourced through partial melting of early Neoproterozoic lithosphere mantle. These data suggest that the three Neoproterozoic Jiuling magmatic suites in the Jiuling terrane correlate with (1) the continental arc, fore-arc, (2) collision and (3) continental rift settings in the interval from 850Ma to 790Ma. These tectonic settings are consistent with a geodynamic process from the oceanic subduction beneath the Yangtze Block (850Ma), collision between Cathaysia and Yangtze Blocks (820Ma) and intracontinental rift (790Ma). This tectono-magmatic cycle in the Jiangnan orogenic belt is >200Ma later than the global Grenville orogeny in response to Rodinia supercontinent assembly, and challenges some of the existing models.

SHRIMP zircon U–Pb dating and Hf isotope analyses of the Muniushan Monzogranite, Guocheng, Jiaobei Terrane, China: Implications for the tectonic evolution of the Jiao–Liao–Ji Belt, North China Craton

The Paleoproterozoic granitoid rocks in the Jiaobei Terrane, which lies in the southern part of the Jiao–Liao–Ji Belt (JLJB) in China, provide valuable information on the tectonic and evolutionary history of the North China Craton (NCC). SHRIMP U–Pb dating of zircons from the Muniushan Monzogranite in the Guocheng gold deposit area, as well as in situ Hf isotope analyses of the zircons, were used to constrain the ages of emplacement and metamorphism, and to understand the petrogenesis of the granite. The geochronological data show emplacement ages of ca. 2.1Ga and metamorphic ages of ca. 1.85Ga. The magmatic cores of the zircons have εHf(t) values of −0.51 to 4.00 (average 1.98) and depleted mantle two-stage model ages (TDM2) of 2444–2703Ma (average 2563Ma). The rocks show the same trends of crustal evolution as ca. 2.5Ga tonalite–trondhjemite–granodiorite (TTG) rocks in the Jiaobei Terrane, indicating that they were formed by the remelting of those TTG rocks. The Muniushan Monzogranite is part of a linear belt of ca. 2.2–2.0Ga Paleoproterozoic granitoids within the JLJB. The granitoids are A-types, and are accompanied by coeval mafic intrusions and bimodal volcanic rocks, thus indicating widespread extension along the JLJB in the period 2.2–2.0Ga. The ca. 1.85Ga metamorphism was related to the collision of the Longgang and Nangrim blocks. The Paleoproterozoic evolution of the NCC constrains the crustal architecture and the source of Mesozoic granitoids in the Jiaobei–Sulu region. Inherited zircons of Paleoproterozoic age are widespread in the Mesozoic granitoids. In addition, Paleoproterozoic ages have been reported from lower crustal granulite xenoliths in the Sulu Orogen, and the southeastern margin of the NCC mirrors the evolution of the JLJB. It is probable, therefore, that NCC lower crust underlies the Sulu Orogen, and that the NCC was the main source for the Mesozoic granitoids in the Jiaobei–Sulu region. This view is consistent with the appearance of inherited zircons of Archean and Paleoproterozoic age on both sides of the orogen, normal δ18O values of magmatic zircons, and Paleoproterozoic to Archean two-stage Hf model ages for the granitoids.

Petrogenesis and thermal overprint of S-type granites in Helanshan region, North China Craton: Constraints on the 1.90 Ga khondalites decompression melting and 1.32 Ga tectono-thermal event

Widespread Paleoproterozoic S-type granites and khondalites (high-grade sillimanite-garnet gneisses) are exposed in the Khondalite Belt of the North China Craton (NCC). Porphyritic biotite granites in the Helanshan region from the western Khondalite Belt exhibit a gradual contact relationship with the neighboring khondalites. In order to constrain the petrogenesis of these granites and their genetic relationship with the khondalites, detailed geochronological data, as well as geochemical and whole-rock Sm-Nd and zircon Lu-Hf isotope compositions of these granites are reported. LA-ICP-MS zircon U-Pb dating on magmatic zircon cores yields an emplacement age of 1902±22Ma, whereas metamorphic rims define a metamorphic age of 1356±57Ma. The unpolished surfaces of zircon crystals selected based on the presence of rims visible in cathodoluminescence were further analyzed by SIMS depth profiling, which gave a more precise metamorphic age of 1317±18Ma. The Helanshan granites display typical S-type geochemical characteristics, e.g., high A/CNK (1.16–1.29) and K2O (5.09–5.86wt%) contents, but low FeOt/MgO (2.39–4.88) and P2O5 (0.15–0.23wt%) contents. Similar trace and rare earth element patterns, and consistent zircon Hf model ages (2366–2483Ma) and whole rock Nd model ages (2407–2499Ma) between the porphyritic biotite granites and the khondalites, suggest that they were derived from partial melting of khondalites. The geochemical character of the porphyritic biotite granites, including significant negative Eu anomalies, high Rb/Ba and Rb/Sr ratios, and variable HREE contents and (La/Yb)N ratios, suggest that they are probably related to the post-peak decompression stage that was characterized by biotite breakdown and the progressive replacement of garnet with the presence of K-feldspar and plagioclase in the residues. Homogeneous zircon εHf(t) values (mostly from −0.5 to +1.7), combined with low bulk-rock Fe2O3T content and CaO/Na2O ratios, preclude the contribution from mafic magma. Following the continental collision, the emplacement of the porphyritic biotite granites at ca.1.90Ga provides the latest limit on the timing of post-peak decompression metamorphism of the khondalites, and their formation supports a post-collisional mantle upwelling model to account for the 1.92–1.90Ga regional metamorphic/magmatic events. On the other hand, the metamorphic zircon rims indicate that S-type granites were overprinted by a 1.32Ga tectono-thermal event, which was probably related to the breakup of the Columbia supercontinent.