Two-stage Model Ages Research Articles

An Early Cretaceous Ag-Pb-Zn mineralization at Halasheng in the South Erguna Block, NE China: Constraints from U-Pb and Rb-Sr geochronology, geochemistry and Sr-Nd-Hf isotopes

The Halasheng deposit, located in the southern Erguna Block, is a vein-type Ag-Pb-Zn deposit in the Derbugan metallogenic belt. The orebodies, hosted in Middle-Late Jurassic volcanic rocks, show a close spatial and temporal relationship with Early Cretaceous granites. Zircon U-Pb dating suggests that the granites were emplaced at 134–128 Ma. Rb-Sr dating of ore-related sphalerite gives an imprecise age of 122 ± 18 Ma, indicating that the Halasheng deposit formed in the Early Cretaceous. Whole-rock major and trace element analyses show that the Cretaceous granites belong to the metaluminous to peraluminous, shoshonite to high-K calc-alkaline series, and can be classified as A-type granites. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field-strength elements (HFSE) and heavy rare earth elements (HREE). The quartz monzonite, which has a spatial relationship with mineralization, has low initial 87Sr/86Sr (0.7058–0.7069), and positive εNd (t) (0.42–0.61) and εHf (t) (3.47–6.45), with Nd and Hf two-stage model ages of 0.81–0.85 Ga and 0.69–0.86 Ga, respectively. These geochemical features are similar to those of major Mesozoic granite intrusions in the Erguna Block. We propose that these graintes originated from partial melting of juvenile crust in an intraplate extensional setting. Taken together, the Halasheng Ag-Pb-Zn deposit formed in the Early Cretaceous after the orogeny related to closure of the Mongol-Okhotsk Ocean. The relatively low-temperature of Ag-Pb-Zn ore and alteration mineralogy suggest that there is only a distal relationship, if any, to nearby potentially-causative granite intrusions.

Petrogenesis of the Early Cretaceous Aolunhua Adakitic Monzogranite Porphyries, Southern Great Xing’an Range, NE China: Implication for Geodynamic Setting of Mo Mineralization

This paper reports on whole-rock major- and trace-elemental and Sr–Nd isotopic compositions of the Aolunhua adakitic monzogranite porphyries from the Xilamulun district in the southern Great Xing’an Range, Northeast (NE) China. The high-K calc-alkaline Aolunhua monzogranite porphyries are characterized by high Sr/Y ratios (34.59–91.02), Sr (362–809 ppm), and low Y contents (7.66–10.5 ppm), respectively. These rocks also show slightly enriched Sr and Nd isotopes ((87Sr/86Sr)i = 0.7051–0.7058; εNd(t) = −2.98–0.92), with young two-stage model ages (T2DM = 0.84–1.16 Ga). Such a signature indicates that these rocks were most likely formed by partial melting of juvenile mafic lower crust. Based on equilibrium melting and batch-melting equations, we performed incompatible trace elements modeling. Low FeOT/(FeOT + MgO) values indirectly reflect these adakitic rocks were derived from an oxidizing source related to magnesian granitoids. The decreasing content of TiO2, Fe2O3, Nb/Ta ratio, and moderately negative Eu anomalies suggest that minimal fractionation of Fe–Ti oxides and plagioclase may have occurred in their evolutionary history. The result shows that the Aolunhua adakitic porphyries and coeval adakitic intrusive rocks in this area had not experienced extensive fractional crystallization and were derived from 20%–40% partial melting of lower continental crust, which was composed of ~25%–40% and 5%–20% garnet-bearing amphibolite, respectively. Integrating with rock assemblages and regional tectonic evolutionary history in this regime, high (Sm/Yb)SN (SN—source normalized data, normalized to mafic lower continental crust with Yb = 1.5 ppm and Sm/Yb = 1.87 for continental adakite) and low YbSN ratios suggest that these rocks were generated in an extensional environment related to lithospheric delamination without crustal thickening. The collision between North China and Siberian cratons around 160 Ma blocked the westward movement of the lithosphere as a result of the subduction of Pacific plate, which then led to lithospheric delamination induced by asthenospheric upwelling and underplating. Subsequently, partial melting of mafic lower crust caused by mantle upwelling resulted in the Early Cretaceous magmatic activities of adakitic rocks and associated Mo mineralization in the southern Great Xing’an Range.

Metallogeny of the continental collision-related Jiagang W-Mo deposit, Tibet: Evidence from geochronology and petrogenesis

The Jiagang W-Mo deposit is the first greisen-type tungsten deposit recognized in the Lhasa terrane, and thus it has important genetic implications for understanding the regional tungsten mineralization potential. Greisen-type orebodies dominate in the deposit. Ores characterized by veinlets and dissemination are located in intensively altered monzogranite and contact zones between the monzogranites and sedimentary rocks. The minor quartz vein-type orebodies occuring as large quartz veins mainly precipitated in the sedimentary rocks. Intrusions associated with the Jiagang deposit are monzogranites, which can be subdivided into medium-grained monzogranite (MMG), porphyritic monzogranite (PMG), and fine-grained monzogranite (FMG). The zircon U-Pb ages of the PMG and MMG are 18.2 ± 0.2 Ma and 18.6 ± 0.1 Ma, respectively. These ages are consistent with the muscovite 40Ar-39Ar plateau ages (18.7 ± 0.2 Ma, 18.5 ± 0.2 Ma) and the molybdenite Re-Os isochron age (19.0 ± 0.3 Ma) within errors, indicating that the Jiagang W-Mo mineralization took place during the post-collisional stage of the Indo-Asian continental collision. The mineralization is temporally, spatially and genetically associated with the monzogranitic intrusions. The FMGs have the lowest SiO2 contents (70.8–71.5 wt%), lowest differentiation index (DI = 85.7–86.3) and least obviously negative Eu anomalies (Eu/Eu* = 0.22–0.42). The PMGs and MMGs have higher SiO2 contents (72.6–76.3 wt%), higher differentiation index (DI = 89.3–92.7) and more negative Eu anomalies (Eu/Eu* = 0.11–0.24). Almost all of the rocks are strongly peraluminous (A/CNK = 1.02–1.29), enriched in LILEs and depleted in HFSEs. Concentrations of K2O, CaO, FeOT and TiO2 of the three types of monzogranites show negative correlations with SiO2, while P2O5 exhibits the opposite trend. Values of Nb/Ta decrease with SiO2 contents, and those of (La/Yb)N increase with La contents. Whole rock εNd(t) of the FMGs range from −11.3 to −11.1 with two-stage Nd isotopic model ages (TDM2) of 1741–1797 Ma, which are similar to those of the PMGs and MMGs (εNd(t) = −10.9– −10.6; TDM2 = 1709–1816 Ma). Zircon εHf(t) values of the PMG and MMG range from −13.8 to −5.3 with two-stage Hf isotopic model ages of 1439–1979 Ma. These data suggest that the ore-forming monzogranites are strongly peraluminous S-type granites, which should be derived from anatexis of the Proterozoic metagreywackes underneath the central Lhasa subterrane. The PMG and MMG are highly fractionated through various degrees of fractional crystallization of plagioclase, K-feldspar, biotite, monazite and allanite from the parental melts represented by the FMG. Zircon trace elements suggest that oxygen fugacity of the ore-forming magmas is relatively low and decreased as the magmas evolved, which is favorable to remove substantial tungsten from melts into the tungsten-mineralizing hydrothermal fluids. A high degree of fractional crystallization of the crustally-derived magmas with relatively low magmatic oxidation state are the critical factors determining the generation of the tungsten mineralization in the Jiagang deposit. Combined with the existing breakthroughs in prospecting exploration, we propose that the central Lhasa subterrane has great metallogenic potential in W-(Mo) mineralization associated with the Indo-Asian continental collision.

The genesis of felsic magmatism during the closure of the Northeastern Paleo-Tethys Ocean: Evidence from the Heri batholith in West Qinling, China

To better understand the origin of voluminous silicic rocks in a convergent continental margin, we conducted an integrated study in which we have obtained geochronological, mineralogical, and isotopic (including whole-rock Sr–Nd–Pb, in-situ zircon Hf) data of the Heri batholith in West Qinling on the NE Tibetan Plateau. The batholith is composed of metaluminous to weakly peraluminous granodiorites (235–233 Ma) and porphyritic granodiorites (230–223 Ma) with an I-type affinity. Both lithologies share similar major, trace elemental and SrNd isotopic compositions. Detailed elemental data demonstrate that these granodioritic rocks underwent fractional crystallization of hornblende and apatite, with plagioclase (i.e. sieve-textured plagioclase cores) accumulation to some extent. Except for porphyritic granodiorites, the Pb isotopes for other analyzed samples are characterized by high radiogenicity and uniformity ((206Pb/204Pb)t: 17.263–18.472, (206Pb/204Pb)t: 15.571–15.591, and (206Pb/204Pb)t: 38.032–38.304), together with limited variations in initial Sr ((87Sr/86Sr)t: 0.707251–0.708103) and Nd (εNd(t) = −7.1 to −6.3) isotopes with two-stage model ages (TDM2) of 1.58–1.52 Ga. These factors collectively point to a derivation from the Mesoproterozoic basement rocks at the lower crustal level, or a comprehensive mixing of different-age components that generated an average crustal residence age. The SrNd isotopic compositions of the porphyritic granodiorites are strikingly similar to those of granodiorites. Compared with the experimental melt compositions of amphibolites, the Heri granitoids are probably derived from an amphibolitic source under fluid-absent conditions due to the incongruent breakdown of amphibole and biotite. Based on the temporal–spatial distribution of granitic intrusions in West Qinling and the regional tectonic evolution, our interpretation is that the Heri batholith was formed during the initial collision between the North China Craton (NCC) and the South China Craton (SCC), which was accompanied by the closure of the Paleotethyan Ocean. Considering both previously published data and our new data, we propose that the Heri granitoids were mainly generated by the partial melting of lower crustal amphibolites, with minor mantle-derived melts.

Provenance and Tectonic Implications of Sedimentary Rocks of the Paleozoic Chiron Basin, Eastern Transbaikalia, Russia, Based on Whole-Rock Geochemistry and Detrital Zircon U–Pb Age and Hf Isotopic Data

The Chiron Basin extends along the southern periphery of the Siberian Craton and the western margin of the Mongol–Okhotsk Belt. Here, we present whole-rock geochemical data (major and trace elements and Sm–Nd isotopes) along with zircon U–Pb geochronology and Lu–Hf isotopic data from Paleozoic sedimentary rocks within the Chiron Basin to investigate their provenance and tectonic history. εNd(t) values of the siliciclastics rocks of the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations vary from −17.8 to −6.6, with corresponding two-stage Nd model ages (tNd(C)) ranging from 2.56 to 1.65 Ga. Detrital zircon grains from these rocks are predominantly Archean, Paleoproterozoic, and Carboniferous–Devonian in age. The data suggest that the southern flank of the Siberian Craton is the only viable source area for Archean and Paleoproterozoic zircon grains with Hf model ages (tHf(C)) of >2.20 Ga. The majority of zircon grains from sandstones from the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations are Devonian–Carboniferous in age. With respect to their Hf model ages, the zircon grains can be subdivided into two groups. The first group of Devonian–Carboniferous zircon grains is characterized by relatively old (mainly Paleoproterozoic) tHf(C) model ages of 2.25–1.70 Ga and the source was the southern margin of the Siberian Craton. The second group of Devonian–Carboniferous zircon grains is characterized by significantly younger (mainly Neoproterozoic) tHf(C) model ages of 1.35–0.36 Ga, which are consistent with a juvenile source, most likely eroded island arcs. Our data, show that sedimentary rocks of the Chiron Basin likely formed in a back-arc basin on the southern periphery of the Siberian Craton facing the Paleozoic Mongol–Okhotsk Ocean.

Timing of formation of the Western Jinshajiang and Ganzê–Litang sutures: evidence from the Duocai Granite in the Zhiduo region, West China

The timing of the closure of the Paleo-Tethys Ocean in West China remains debated. To investigate this problem, we examined the geochemical characteristics, zircon U–Pb chronology, and Hf isotopes of monzogranites and quartz diorites from the Duocai granite in the Zhiduo region, at the intersection of the Jinshajiang and Ganze–Litangsutures. The monzogranites have the chemical characteristics of calc-alkaline I-type granites and yield a weighted mean zircon U–Pb age of 234.6 ± 0.9 Ma [mean square weighted deviation (MSWD) = 0.36]. Initial eHf(t) values are high and positive, ranging from + 7.9 to + 13.6 with a mean of + 10.7, corresponding to two-stage Hf isotope model ages (TDM2) of 762–395 Ma. Geochemical and isotopic data indicate that the source magma of the monzogranites formed from mantle-derived magmas mixed with the overlying crustal materials. The quartz diorites, which also have compositional characteristics of calc-alkaline I-type granites, yield a weighted mean zircon U–Pb age of 209.1 ± 0.7 Ma (MSWD = 0.29). Initial eHf(t) values range from − 2.5 to + 0.6 with a mean of − 1.5, with the corresponding TDM2 of 1402–1210 Ma. Geochemical and isotopic data indicate that the primary magma of the quartz diorites was derived mainly from partial melting of the mafic lower crust and small amount mantle-derived magma involved. Combining these results with regional data, the studied granites are inferred to have formed as a result of continuous subduction of plates underlying the Western Jinshajiang Ocean–Ganze–Litang Ocean from 234 to 209 Ma, and were unrelated to subduction of the South Jinshajiang oceanic plate. We suggest that the Western Jinshajiang Ocean–Ganze–Litang Ocean closed by the end of Late Triassic.

Sr-Nd-Pb isotope systematics of Australasian tektites: Implications for the nature and composition of target materials and possible volatile loss of Pb

The Australasian tektite (AAT) strewn field is the largest strewn field on the Earth with about ∼10–30% coverage, both land and ocean, but a clearly identified source impact crater is absent despite the young age of AAT of ca. 790 ka. A genetic link between the Australasian tektites and their unequivocal parental materials is therefore largely impossible to establish. Nevertheless, the nature of the parental materials and the extent of volatilization can be constrained using the splash form tektites, carrying the chemical signatures of high-temperature processes, and the layered (so-called Muong Nong-type) tektites, which are less chemically homogenized and exceptionally abundant in the AAT field. New high-precision Sr, Nd and Pb isotopic measurements were obtained for a chemically and petrographically well-characterized suite of AAT, which included the Muong Nong-type (MN-AAT) with precisely known field locations in Laos and splash forms (SF-AAT) from different parts of the strewn field. In addition, optically dark and light zones of the MN-AAT were also separately analyzed. Homogeneous εNd values from −11.8 to −11.2, combined with a narrow range of two-stage Nd model ages from 1.67 to 1.72 Ga for the entire AAT suite, point to a well-mixed source, in terms of REE, of the crustal segment from which the sedimentary material for tektites was ultimately derived. The Sr isotopic data largely overlap for SF-AAT and MN-AAT (87Sr/86Sr = 0.71636–0.72021) and indicate Paleozoic to Mesozoic sedimentary parentage. However, late Neogene to early Quaternary re-deposition and formation of a thick silt-sized sedimentary section with vertical stratification is required to comply with 10Be data. Lead isotope systematics documents at least three different components which can perhaps be represented by different mineral phases, such as feldspar, zircon, organic matter adsorbed on young sediments etc., sorted during fluvial transport and final deposition. In addition, the SF-AAT have systematically lower Pb contents than the MN-AAT, and generally show isotopically heavier Pb isotopic ratios. This is theoretically consistent with a preferential volatilization of lighter Pb isotopes during evaporation and considerably larger Pb loss from SF-AAT when compared to MN-AAT. Nevertheless, further experimental work would be necessary to unambiguously distinguish kinetic fractionation from source mixing.

Geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Late Permian–Early Triassic granitoids in Eastern Kunlun Orogen, Northwest China: petrogenesis and implications for geodynamic setting

ABSTRACT The Eastern Kunlun Orogenic Belt (EKOB) in Northwest China, is an ideal area for understanding the tectonic evolution of the Palaeo-Tethys Ocean. The EKOB is marked by widespread Palaeozoic to Early Mesozoic magmatism. However, the Late Permian–Early Mesozoic tectonic evolution of the Palaeo-Tethys Ocean tectonic regime is poorly understood. Here, we report new zircon LA-ICP-MS U–Pb dating and geochemical analyses of Late Permian–Early Triassic intrusive rocks in the Xiangyanggouxi and Dageledong areas in the EKOB, Northwest China, to discuss their petrogenesis and geodynamic setting and reconstruct the tectonic evolution of Palaeo-Tethys oceanic tectonic regime. Zircon U-Pb dating results indicate that these granitoids crystallized during ca. 256–248 Ma, i.e. the Late Permian to Early Triassic. These granitoids are mainly comprised of granodiorites and monzonitic granites that possess high concentrations of SiO2 (66.81–75.98 wt.%), K2O+Na2O (6.21–7.92 wt.%), and low contents of MgO, CaO, Cr, Ni, and Mg# (<0.44). They are classified as medium- to high-K calc-alkaline and metaluminous I-type granitoids. These granitoids are rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. In addition, combined with the εHf(t) values of −2.4 to +2.4 with two-stage model ages ranging from 1409 Ma to 1027 Ma, and the εNd(t) values from −3.73 to −2.95, it is suggested that the primary magma of these granitoids was derived from the partial melting of the Late Meso–Proterozoic mafic lower crust. These findings, combined with spatio-temporal distributions of regional magmatism, reveal that the Late Permian and Early Triassic granitoids formed in a continental magmatic arc setting related to the northward subduction of the Palaeo-Tethys Ocean plate beneath the EKOB-Qaidam terrane.

Geochemistry, geochronology and Hf isotope of granitoids in the northern Alxa region: Implications for the Late Paleozoic tectonic evolution of the Central Asian Orogenic Belt

The tectonic setting of the northern Alxa region during the Late Paleozoic is highly controversial. The key to resolve this controversy is to recognize the Late Paleozoic magmatic processes in the northern Alxa. In this paper, we present new zircon U–Pb ages, Hf-isotopic compositions and whole-rock geochemical data of four granitoids along the Zhusileng-Hangwula Tectonic Belt in the northern Alxa region that could provide critical information about the tectonic evolution of this region. The zircon U–Pb data could be grouped as two phases: Late Devonian granite and diorite (ca. 373–360 ​Ma), and Late Carboniferous granodiorite (ca. 318 Ma). The Late Devonian granites and diorites are metaluminous to slightly peraluminous, with A/CNK and A/NK ratios of 0.90–1.11 and 0.95–2.19, respectively. The Late Devonian diorites are characterized by high MgO, Cr and Ni contents and MgO# values, together with variable εHf(t) values from –1.0 to +1.3 and old TDM2 ages varied from 1283 ​Ma to 1426 ​Ma, indicating the primary magma was potentially derived from magma mixing of depleted mantle with Mesoproterozoic continental crust. Even though the Late Devonian granites yielded most positive and minor negative εHf(t) values between –1.1 to +5.7 (three grains are negative) with two-stage model ages (TDM2) of 1003–1438 Ma, they display low MgO, Cr and Ni contents and MgO# values, suggesting that they were mainly derived from juvenile crustal materials, mixed with a small amount of ancient crust. The Late Carboniferous granitoids are metaluminous and medium-K calc-alkaline series, with A/CNK and A/NK ratios ranging from 0.88 to 0.95 and 1.75 to 1.90, respectively. These rocks were potentially derived from juvenile crustal materials mixed with depleted mantle, as evidenced by their high εHf(t) values (+11.6 to +14.1) and young TDM2 ages (427 ​Ma to 586 ​Ma), as well as high Mg# values, and MgO, Ni and Cr contents. Our data, along with available sedimentary evidence and previous researches, indicate that the Late Devonian and Late Carboniferous rocks are arc-related granitoids under the subduction setting. The identification of arc-related granitoids in the northern Alxa region not only reveals the Late Paleozoic magmatic process in response to the subduction of Paleo Asian Ocean, but also provide significant constrains to the tectonic evolution of the Central Asian Orogenic Belt.

Petrogenesis of paleoproterozoic (2.02–1.96 Ga) metagranitoids in the southwestern Yeongnam Massif, Korean Peninsula, and their significance for the tectonic history of northeast Asia: Insights from zircon U–Pb–Hf isotope and whole-rock geochemical compositions

The Jangsu-Gokseong area is located in the southwestern part of the Yeongnam Massif and mainly consists of Precambrian metagranitoids (metagranite, metaleucogranite and metagranodiorite) with minor migmatite and marble. Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb dating shows that the metagranitoids emplaced during ca. 2.02–1.96 Ga and metamorphosed at ca. 1.89–1.87 Ga. The metagranitoids show calc-alkaline trends, enrichment in large lithophile elements and negative Nb and Ta anomalies with low Sr/Y (<12), Nb/Th (<1) and Nb/Zr (<0.1) ratios. The metagranitoids have negative εHf(t) values (−1.63 to −6.41) with a Paleoarchean two-stage model age (TDM2 = 3.25 Ga). These data suggest that the protoliths of the metagranitoids were derived from ancient crustal materials with metagraywacke or metatonalitic compositions and formed in a subduction-related setting. The intrusion ages and geochemical composition of the metagranitoids in the study area match well with those of Paleoproterozoic metagranitoids distributed along the northern margin of the central to northeastern Yeongnam Massif. These metagranitoids show that Paleoproterozoic (ca. 2.02–1.96 Ga) subduction-related magmatism occurred widely along the northern margin of the Yeongnam Massif, which has not been reported from the Gyeonggi and Nangrim massifs on the Korean Peninsula and the Jiao-Liao-Ji belt in the eastern North China Craton. Therefore, the Yeongnam Massif might have existed as a separate crustal unit at least during the Paleoproterozoic.

Late Cretaceous–Eocene magmatism induced by slab rollback and breakoff in the Tengchong terrane, SW China

ABSTRACT Late Cretaceous–Eocene granites are widespread in the Tengchong terrane and related to subduction and closure of the Neo–Tethyan Ocean. However, the reason of their compositional and spatial variations is still under explored. This study reports zircon U–Pb geochronological, whole–rock and Nd isotopic data for Guyong, Houqiao and Menglong granites in the Tengchong terrane. Our data show that the three plutons crystallized at 70.4 ± 0.3Ma, 64.4 ± 0.3Ma and 47.6 ± 0.2Ma. Guyong monzogranites show an I–type affinity and may have experienced fractional crystallization of plagioclase, biotite and sphene. Negative εNd(t) values (−9.19 to −11.01) with two-stage model ages (T2DM = 1.59–1.78 Ga) indicate that Guyong monzogranites are derived from a predominantly Paleoproterozoic crustal source with little involvement of mantle–derived materials in an extensional setting. Lower εNd(t) (−9.33 to −11.63) and negative correlations of HREE, LREE, Th, and Y vs. SiO2 indicate that Houqiao plutons are S–type granites derived from a pure crustal source during crustal thickening. Low Zr/Hf and Nb/Ta ratios, zircon saturation temperature (TZr = 750°C–786°C) and negative δEu (0.11–0.40) of Menglong biotite granites indicate that they have experienced fractional crystallization of plagioclase, biotite and sphene. Relatively high εNd(t) (−6.81 to −7.07) values indicate that they are products of felsic magma mixed with mafic magma, which is also supported by numerous coeval mafic–intermediate rocks (Eocene) such as metagabbros, diorites and MMEs (mafic microgranular enclaves) in the western Tengchong terrane. A process of slab rollback and slab breakoff may have triggered the late Cretaceous–Eocene magmatism and the compositional variation of associated granitoids in the Tengchong terrane.

Petrogenesis and Tectonic Setting of Ore-Associated Intrusive Rocks in the Baiyinnuoer Zn–Pb Deposit, Southern Great Xing’an Range (NE China): Constraints from Zircon U–Pb Dating, Geochemistry, and Sr–Nd–Pb Isotopes

The Baiyinnuoer skarn Zn–Pb deposit, located in the Southern Great Xing’an Range, Northeast China, is the largest Zn–Pb deposit of the northern China, with a total reserve of 32.74 Mt at average grades of 5.44% Zn and 2.02% Pb. The Zn–Pb ore bodies are hosted in the Lower Permian Huanggangliang Formation. The results of zircon U–Pb geochronology show that the ore-associated granodiorite porphyry, granodiorite, and diorite were emplaced at 248 ± 1.3, 251 ± 1.8, and 249 ± 1.4 Ma, respectively. The granodiorites and granodiorite porphyry have low P2O5 (0.13–0.23 wt %) and A/CNK (0.79–1.05) values, and their SiO2 and P2O5 contents are negatively correlated, indicating I-type affinity. The positive εNd(t) values (+1.3 to +1.8) and young two-stage model ages (TDM2) (880–916 Ma) of the Baiyinnuoer intrusive rocks suggest that they might have formed by the mixing of both mantle and crustal materials. The variations in the major elements, Rb, Sr, and Ba, and the negative Nb–Ta–Ti anomalies indicate that fractional crystallization might have occurred during magma ascent. In combination with the regional geology, the new geochronological, geochemical, and isotopic data reveal that the ore-associated intrusive rocks at Baiyinnuoer were formed in a post-collision setting in the Late Permian.

U–Pb dating and geochemistry of granite porphyry dykes in the Xicha gold–(silver) deposit, southern Jilin Province, China, and their metallogenic significance

We report U–Pb dating of zircon, as well as geochemical and Hf isotope data, in order to constrain the formation time, magma source, and tectonic setting of granite porphyry dykes in the Xicha gold–(silver) district in southern Jilin Province, Northeast China. The zircon grains are euhedral–subhedral, display oscillatory growth zoning and have Th/U ratios varying between 0.11 and 0.78, which together imply a magmatic origin. The dating results indicate the porphyry formed in the Early Cretaceous (122 ± 1 Ma), and it contains SiO2 = 70.64–72.31 wt%, Al2O3 = 13.99–14.64 wt%, K2O + Na2O = 6.96–7.81 wt%, K2O/Na2O = 1.24–2.10, and A/CNK = 1.11–1.41. Chemically, the porphyry belongs to a high-K calc-alkaline S-type granite. Chondrite-normalized rare earth elements (REE) patterns show LREE enrichment, light rare earth elements (LREE)/heavy rare earth elements (HREE) = 9.93–11.97, (La/Yb)N = 11.08–15.16, and δEu = 0.69–0.95. On the trace element spider diagram, large ion lithophile elements such as Rb, Ba, K, Th, and U are enriched, whereas the high field strength elements Ti and P are depleted. The eHf(t) values of zircon from the granite porphyry vary between − 17.1 and − 13.2, and their Hf two-stage model ages vary from 2.01 to 2.26 Ga, implying that the magma was derived from partial melting of old lower crust. The granite porphyry dykes and many A-type granites in the region formed at the same time, suggesting an extensional environment. The combination of the occurrence of strong magmatism, large-scale mineralization, and extensional tectonics throughout much of Eastern China indicate that the Early Cretaceous was a period of significant lithospheric thinning. The southern Jilin Province, therefore, experienced lithospheric thinning during the Early Cretaceous.

Geochronology and source of the rare-metal pegmatite in the Mufushan area of the Jiangnan orogenic belt: A case study of the giant Renli Nb–Ta deposit in Hunan, China

The Jiangnan orogenic belt hosts many rare-metal deposits that exhibit close ore-forming ages and similar geological backgrounds and is an important Li–Be–Nb–Ta concentration belt located in eastern China. However, the metallogenic mechanism and regularity of these rare-metal deposits have not yet been reported in detail because of the lack of accurate geochronological data and systematic studies on the sources of metallogenic materials. The giant Renli rare-metal deposit, located at the south margin of the Mufushan batholith in the central Jiangnan orogenic belt, is one of the few high-grade granitic-pegmatite-type Nb–Ta deposits in China. Columbite–tantalite U–Pb dating has been developed as a more robust method when compared with the traditional dating methods to constrain the timing of rare-metal mineralization. Six columbite grains, obtained from the microcline–albite pegmatite of the Renli deposit, exhibit a concordant laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb age of 133.0 ± 2.6 Ma, which denotes the Nb–Ta mineralization age. The zircon grains from the columbite-bearing microcline–albite pegmatite subjected to different degrees of alteration by the hydrothermal fluids yield a concordant LA–ICP–MS U–Pb age of 131.2 ± 2.4 Ma, which can be considered to be the age of newly magmatic–hydrothermal growth and recrystallization under the transitional magmatic–hydrothermal conditions observed in case of the Renli deposit. Furthermore, the zircon grains from the host biotite monzogranite yield concordant LA–ICP–MS U–Pb ages of 140.7 ± 0.7 and 140.3 ± 0.7 Ma, whereas the zircon grains from the host two-mica monzogranite yield a concordant LA–ICP–MS U–Pb age of 138.3 ± 0.3 Ma, denoting the intrusion timing of two types of host Mufushan granites of the pegmatite dykes. Finally, the zircon grains from two schist samples of the Lengjiaxi Group yield concordant LA–ICP–MS U–Pb ages of 825.9 ± 5.6 and 834.4 ± 5.3 Ma, constraining the maximum age for the termination of deposition. These ages constitute a clear intrusion-cooling-hydrothermal time series with respect to the Renli deposit.Zircon can retain the original magmatic isotopic composition and is extensively used to trace the petrogenetic processes because it is quickly crystallized from magma. The Mufushan granite and rare-metal pegmatite exhibit consistent negative eHf(t) values (mean eHf(t) values of −7.2 and −7.3, respectively), and their two-stage model ages exhibit similar distribution patterns when compared with that exhibited by the Lengjiaxi Group. Furthermore, the Mufushan granite shows the typical geochemical characteristics of the crustal-derived granite. Thus, the rare-metal pegmatite and host granite of the Renli deposit were concluded to be sourced from the partial melting of the Lengjiaxi Group metasedimentary strata.The compressive torsional nature of the Gajiang fault zone, widespread occurrence of the S-type granite, and absence of basaltic rocks suggest that the central-to-eastern part of the Jiangnan orogenic belt was in a subduction setting during the Early Cretaceous. Thus, this economically important Early Cretaceous (ca. 133–129 Ma) rare-metal metallogenic belt was formed owing to the development of the Jiangnan orogenic belt, and the thick Lengjiaxi Group metasedimentary strata provided the metallogenic material source.

Paleoproterozoic tectonic evolution of the Yangtze Block: New evidence from ca. 2.36 to 2.22 Ga magmatism and 1.96 Ga metamorphism in the Cuoke complex, SW China

The infrequent early Paleoproterozoic rocks are essential for investigating the early evolution of the Yangtze Block and its reconstruction in the global supercontinent. Here, we carried out an integrated study of petrology, whole-rock geochemistry, as well as zircon U-Pb-Hf isotope compositions for granitoids from the recently discovered Cuoke complex in the southwestern Yangtze Block. SHRIMP zircon U-Pb dating yields magmatic crystallization ages of ca. 2.22 and 2.35 Ga for two monzogranites, ca. 2.36 Ga for a granodiorite, and ca. 2.34 Ga for a granitic gneiss. The granitic gneiss also contains metamorphic zircons that give an age of ca. 1.96 Ga. These results, compiled with published geochronological data, suggest that the western part of the Yangtze Block (WYB) features extensive magmatism with ages of ca. 2.5–2.2 Ga and multiple regional metamorphism with peaks ca. 2.50, 2.36, 1.96 and 1.85 Ga. This characteristic is significantly different from the eastern part of the Yangtze Block (EYB), which is dominated by the ca. 2.15–1.95 Ga subduction- and collision-related metamorphism and magmatism with a peak ~2.0 Ga. Our studied granitoids show negative zircon εHf(t) values from −14.0 to −1.9, with corresponding two-stage model ages of ca. 3.50–2.93 Ga, indicative of their derivation by reworking of ancient crustal materials. Geochemically, the ca. 2.22 Ga monzogranites have high HFSEs (Zr + Nb + Ce + Y = 777–1136 ppm) and 10,000*Ga/Al ratios (3.73–4.56) with dramatically negative Eu, Ba, Sr and Ti anomalies. Together with high Y/Nb (2.75–3.15) and Yb/Ta (2.11–2.94) ratios, they are classified as A2-type granites. The ca. 2.36–2.35 Ga granitoids have high CIPW-normative corundum contents of 4.92–6.06 vol% and are strongly peraluminous with A/CNK values of 1.46–1.64, similar to S-type granites. They are enriched in LREEs ((La/Yb)N = 14.55–25.33) with moderately negative Eu anomalies (Eu/Eu* = 0.56–0.66), but depleted in Nb, Sr and Ti. The ca. 2.34 Ga granitic gneisses show intermediate geochemical signatures between S-type and I-type granites. They are featured by no discernible negative Eu and Sr anomalies and relatively steep HREE patterns with (Gd/Yb)N ratios between 1.94 and 2.50. In combination with available observations, our new geochronological and geochemical dataset indicates that these ca. 2.36–2.34 Ga granitoids represent the post-collisional magmatism immediately following a possible collision event in the WYB, while the 2.22 Ga A2-type monzogranites were likely formed in a back-arc extensional setting. In addition, we further suggest that the Yangtze Block and NW Laurentia share a common succession of major Paleoproterozoic tectonothermal events, favoring their tight spatial linkage in the global Columbia supercontinent.

Generation of late Mesozoic felsic volcanic rocks in the Hailar Basin, northeastern China in response to overprinting of multiple tectonic regimes

We performed zircon U–Pb age dating and geochemical analyses of late Mesozoic felsic volcanic rocks in the Hailar Basin, NE China, with the aim of eclucidating their emplacement ages, origin and geodynamic significance. The volcanic rocks consist of dacites, rhyolites and rhyolitic tuffs. Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating results suggest that the rocks were erupted during the Late Jurassic–Early Cretaceous (161–117 Ma). They belong to the high-K calc-alkaline series and can be divided into two groups. Group I rocks are metaluminous to weakly peraluminous, contain low concentrations of heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and have low zircon saturation temperatures (average 786 °C), all of which indicate an I-type affinity. In contrast, Group II rocks have higher HREE and HFSE concentrations and zircon saturation temperatures (average 918 °C), suggesting an A-type affinity. All the felsic volcanic rocks have positive εHf(t) values of 1.43–12.32 with two-stage model ages of 1110–401 Ma. Our data indicate that the I-type felsic volcanic rocks formed from magmas generated by partial melting of a dominantly juvenile mica-bearing K-rich basaltic lower crust, whereas the A-type felsic volcanic rocks originated from the partial melting of a dry mafic–intermediate middle–lower crust that was dehydrated but not melt depleted. Based on the present results and previous research, we propose that the Late Jurassic I- and A-type felsic volcanic rocks in the Hailar Basin were formed in a post-collisional environment related to break-off of the subducted oceanic slab of the Mongol–Okhotsk Ocean and the subsequent gravitational collapse of the orogenically-thickened crust after closure of the ocean. In contrast, the Early Cretaceous I- and A-type felsic volcanic rocks were erupted in an extensional setting related to rollback of the subducted Paleo-Pacific Plate.

Zircon U-Pb-Hf isotopes and geochemistry of Jurassic igneous rocks from the southern Zhangguangcai Range, NE China: constraints on magmatism, petrogenesis and tectonic implications

ABSTRACT In this study, we present new zircon U-Pb and Hf isotope data and geochemical analyses for Jurassic igneous rocks from the southern Zhangguangcai Range, NE China. In the context of our new U/Pb data together with other published data (n = 165), we recognize three major magmatic pulses in the eastern Songnen Block during the Jurassic: earliest Jurassic (200–195 Ma), late Early Jurassic (183–175 Ma) and early Late Jurassic (ca. 163 Ma). According to the petrological classification scheme, rocks are divided into two categories of andesite and I-type granitoids. Generally, Early Jurassic monzogranites have more evolved compositions with SiO2, Al2O3, and K2O+Na2O concentrations of 67–74 wt.%, 13.28–17.04 wt.% and 7.25–9.31 wt.%, respectively than Late Jurassic granodiorite. Early Jurassic andesite has SiO2, Al2O3, Na2O+K2O contents of 54.64–56 wt.%, 17.27–17.44 wt.% and 3.47–4.06 wt.%, respectively with low Mg# values of 0.18–0.26. In addition, all samples show enrichment in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depletion in high strength field elements (HSFEs, such as Nb, Ta, P and Ti) and low Sr/Y and (La/Yb)N ratios, all of which are characteristic of arc-type magmatic signatures. In view of the Hf isotope signatures, these rocks show high initial 176Hf/177Hf ratios (0.282711–0.283069) corresponding to positive εHf(t) values (+0.39 to +13.66) and Neoproterozoic two-stage model ages (1154–550 Ma). In summary, the geochemical results suggest that the primary magmas of Jurassic granitoids were derived from variable degrees of partial melting of juvenile lower crust, whereas Early Jurassic andesite was derived from the partial melting of mantle wedge peridotite metasomatized by hydrous melts from subducting sediments and/or oceanic crust. The Jurassic arc-type magmatism in the eastern Songnen Block indicates that the Mudanjiang oceanic plate was still subducting in the Jurassic.

Zircon U–Pb chronology, geochemistry, and petrogenesis of the high Nb–Ta alkaline rhyolites at the Tuohe Tree Farm, northern Volcanic Belt, Great Xing’an Range, China

We studied newly found high Nb–Ta alkaline rhyolites in the northern volcanic belt of the Great Xing’an Range, China. The LA–ICP–MS U–Pb weighted mean age is 114.07 ± 0.55 Ma, indicating that the rocks formed during the late Early Cretaceous and were the product of the late eruption of a Mesozoic volcano. The major element contents are characterized by high Si, rich K, low Fe, and poor Ca and Mg. In the total alkaline–silicon diagram, the sample points are in the alkaline rhyolite region. Meanwhile, rare earth elements show obvious Ce/Ce* positive anomalies and Eu/Eu* negative anomalies. In addition, trace elements are characterized by high Nb, Ta, and Yb, and low Sr. The two-stage Nd isotopic model age T2DM of the depleted mantle is between 799–813 Ma, indicating that the diagenetic material originated from the depleted mantle or partial melting of newly formed young crustal materials. The source rocks melted at a relative shallow depth (&lt;30 km), under lower pressure (&lt;0.5 Gpa) and high oxygen fugacity; moreover, the residues in the source region were Ca-rich mafic plagioclase + amphibole + orthopyroxene. In the Nb–Y–3Ga and Nb–Y–Ce diagrams, the sample points are in the A1 type region. It can be concluded that the mantle-derived basaltic magma underplated and supplied the heat sources for partial melting of the metamorphic crustal rocks in an intraplate extensional tectonic environment related to a rift, mantle plume, and hot spot.

New insights into Paleoproterozoic tectonics of the Yangtze Block in the context of early Nuna assembly: Possible collisional granitic magmatism in the Zhongxiang Complex, South China

The newly discovered Zhongxiang Complex preserving extensive Paleoproterozoic granitoids plays a pivotal role in understanding the early tectonic processes of the Yangtze Block, South China, in the context of the Nuna supercontinent cycle. New zircon U-Pb age and Hf-isotope coupled with whole-rock chemical and Nd-isotope results from three granitic intrusions in the southern Zhongxiang Complex document a magmatic record of significant late Paleoproterozoic tectonic convergence in the region. Geochronological data show that granites from these intrusions were emplaced in a relatively long period at 2.0–1.93 Ga. The granites have variably high SiO2 contents of 74.01–77.19 wt%, and are weakly to strongly peraluminous with high ASI (alumina saturation index) values (>1.05). They are generally magnesian, showing fractionated S-type granite affinities. They have negative zircon εHf(t) of −9.69 to −17.11 and negative whole-rock εNd(t) of −7.43 to −11.69, corresponding to two-stage Hf model ages of 3.24–3.67 Ga and two-stage Nd model ages of 3.0–3.37 Ga, respectively, indicating a derivation of their parental magmas from remelting of ancient crustal components (i.e., the Yangpo “Group” paragneisses). The moderate to strong LREE/HREE fractionation ((La/Yb)N > 22, average 73.15) and the relatively low Sr/Y and negative Eu anomalies of the least felsic samples further imply a residual assemblage probably involving both garnet and plagioclase, corresponding to middle-lower crustal levels. This magmatic event most likely occurred at a convergent continental margin related to continental collision, which, in conjunction with broadly coeval metamorphism and the succeeding A-type granitic magmatism in the region, delineates a possible late Paleoproterozoic tectonic transition from compression to extension, signifying a cycle from collision (2.0–1.93 Ga) to post-collision (1.85 Ga) in the Zhongxiang Complex. Such a collisional orogenesis was potentially linked to the Paleoproterozoic internal assembly of the eastern part of the Yangtze Block, presumably as part of the early assembly of the Nuna supercontinent.

Genesis and tectonic setting of Shenshan Fe–Cu deposit in Inner Mongolia, Northeast China: Constraints from geochemistry, U–Pb and Re–Os geochronology, and Hf isotopes

The newly-discovered Shenshan Fe–Cu skarn deposit is located in the southern Great Xing’an Range of northeastern China. The mineralization occurs mainly in the exoskarn or marble wallrocks of the Permian Zhesi Formation, which were intruded by the Shenshan granodiorite and granite porphyry dykes. Molybdenite Re–Os dating yielded a weighted mean age of 160.2 ± 2.4 Ma (MSWD = 0.38), consistent with the LA–ICP–MS zircon U–Pb age of the granodiorite (161.6 ± 2.2 Ma; MSWD = 0.75), but significantly older than the granite porphyry dykes (132.8 ± 1.9 Ma; MSWD = 0.87). This suggests a coeval and causative relationship between the granodiorite and Fe–Cu mineralization. The Shenshan granodiorite has an adakite-like geochemical signature with high Sr contents (704–871 ppm), and high Sr/Y (46.79–80.21) and (La/Yb)N (17.54–31.13) ratios, but low Y (9.7–13.1 ppm) and Yb (0.70–1.18 ppm) contents. The granodiorite has relatively low contents of Mg (1.71–1.94 wt%), Cr (18–23 ppm), and Ni (4.1–9.0 ppm), and positive εHf(t) (−0.3 to 3.0, average 1.51), yielding two-stage model ages (TDM2) of 1.38–1.68 Ga (average 1.51 Ga). The results indicate that the parental magmas of the granodiorite were derived from partial melting of juvenile thickened lower crust with minor mantle-derived input. Meanwhile, the Shenshan granite porphyry dykes are high-K calc-alkalic and weakly peraluminous, with low MgO (0.21–0.24 wt%) and Mg# (19–21). The dykes exhibit HFSE (e.g., Nb, Ta) depletions and LILEs (e.g., Rb, K) enrichments, and strong to moderate negative Eu anomalies, indicating major continental crust-derived input in the magma source. Geochemical and Hf isotopic data compilation for granitoids across the Great Xing’an Range indicate that the mineralization at Shenshan was influenced by the south-dipping subduction of the Mongol–Okhotsk oceanic plate. The discovery of adakite-like rocks in the Shenshan Fe–Cu deposit, and the voluminous adakite-like rocks in the region, suggest that the Mesozoic Great Xing’an Range has considerable prospecting potential for Cu–Au–Mo deposits.