Two-stage Hf Model Ages Research Articles

Paleoproterozoic A1- and A2-type coexisting monzogranites in the Daqingshan Complex, Khondalite Belt, North China Craton and its tectonic implications

Paleoproterozoic granitoids, widely exposed in the Daqingshan Complex in the Khondalite Belt of North China Craton (NCC), are of great significance for understanding the magmatic evolution and tectonic setting of the blet. Zircon LA-ICP-MS U-Pb dating results of four monzogranite samples are 2385 ± 18 Ma, 2358 ± 24 Ma, 2437 ± 32 Ma, and 2338 ± 24 Ma. Zircon Lu-Hf isotopic analysis shows that the monzogranites have positive εHf(t) values of +0.5 to +4.5, with two-stage Hf model ages (TDMC) range from 2859 to 2617 Ma, indicating that these rocks were mainly produced from ancient crust through the process of assimilation-fractional crystallization. The Daqingshan monzogranites are high-K calc-alkaline to shoshonite series, metaluminous to peraluminous series, enriched in large-ion lithophile elements (LILEs, such as Rb, Ba, La, and Ce) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti. They have low Sr/Y (3.48–35.72) and (La/Yb)N (4.79–46.50) ratio and weakly Eu negative anomalies (δEu = 0.14–1.23), indicating that they were formed in the continental magmatic arc environment. In addition, the monzogranites have high alkaline (Na2O + K2O) and SiO2 components, and high Ga/Al and HFSE values, showing the coexistence of A1- and A2-type granitoids. Combined with previous studies, our new results provide that the Khondalite Belt underwent magmatic events from 2.44 to 2.34 Ga during a long-lived arc-continental accretion process along the southern margin of the Yinshan Block. However, the Daqingshan monzogranites do not preserve records of Paleoproterozoic collisional event at 1.95–1.85 Ga in the Khondalite Belt, indicating that they did not experience subduction-related metamorphism and subsequent collision. Thus, the Daqingshan monzogranites may represent the post-collisional to late orogenic granitoids during the transition from compressive to rift tectonics following collision between the Yinshan and Ordos blocks.

Reconstruction of Rodinia supercontinent: Evidence from the Erguna Block (NE China) and adjacent units in the eastern Central Asian orogenic Belt

The Central Asian Orogenic Belt is sandwiched between the Siberian, East European (Baltica), Tarim, and North China cratons, which contain several Precambrian micro-continental blocks, such as the Kazakhstan-Yili-Central Tianshan blocks, the Junggar Block and the Amuria Block. The tectonic nature and positions of these micro-continental blocks are unclear and disputed in many supercontinent reconstructions. In particular, the position of the Amuria Block in the eastern Central Asian Orogenic Belt, which is important for the reconstructions of the Precambrian Rodinia supercontinent, remains unknown because of the lack of late Palaeoproterozoic to Neoproterozoic geological and geochronological data. The Erguna Block, a part of the Amuria Block in NE China, has been considered as a constituent block of the Rodinia supercontinent. However, the late Palaeoproterozoic to Neoproterozoic tectonic evolution of the Erguna Block with respect to the assembly and break-up of Rodinia remains poorly understood. Here we present zircon U–Pb–Hf–O isotopic data and whole-rock elemental data of the newly discovered late Palaeoproterozoic and Neoproterozoic records in the northern Erguna Block. The gneissic granites have protolith and metamorphic ages of 1839 ± 24 and 497 ± 6 Ma, respectively, and relatively uniform two-stage Hf model ages (TDM1) of 2.67–1.26 Ga, indicating that the Erguna Block has a Palaeoproterozoic crystalline basement. The zircon U–Pb ages for the Neoproterozoic intrusive rocks define two stages of magmatism in early Neoproterozoic (Stage 1; i.e., ca. 946 Ma) and middle Neoproterozoic (Stage 2; i.e., 833–737 Ma), respectively, implying that the Erguna Block had switched to an intra-continental extensional setting (833–737 Ma) after the early Neoproterozoic (ca. 946 Ma) convergence–accretion. A comparison of data from the Erguna Block and its adjacent units reveals that the Erguna and Central Mongolia blocks were likely in a single crustal entity with the Tarim Craton associated with the Rodinia assembly at ca. 900 Ma. This composite block then detached from the Tarim Craton at ca. 800 Ma following the break-up of Rodinia, and drifted southwards to the vicinity of the Siberia Craton during the Cambrian.

Magmatism and related metamorphism as a response to mountain-root collapse of the Dabie orogen: Constraints from geochronology and petrogeochemistry of metadiorites

ABSTRACTPost-collisional mountain-root collapse and subsequent massive partial melting occurred in the high-temperature (HT) ultrahigh-pressure (UHP) metamorphic terrane of the North Dabie complex zone (NDZ), central China. The NDZ was deeply subducted in the Triassic, producing widespread migmatites and various magmatic intrusions in the Cretaceous. Post-collisional metadiorites with distinctive large K-feldspar augen porphyroblasts, locally reported but rarely exposed in the NDZ, underwent a complex evolutional history. In this contribution, integrated studies including field investigation, petrographic observation and mineral analysis, zircon U-Pb geochronological and Hf isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic analyses of the metadiorites were carried out. Our results provide new constraints on the mountain-root collapse in the Dabie orogen. The metadiorites are enriched in large ion lithophile elements and light rare earth elements, whereas they are depleted in high field strength elements and heavy rare earth elements with significant Ba positive anomalies, a composition consistent with the lower continental crust. All the studied samples have moderately enriched initial 87Sr/86Sr ratios (0.707582–0.708099), low εNd(t) values (−15.3 to −20.4), and low initial Pb isotopic ratios (16.0978–16.8452, 15.3167–15.4544, and 37.1778–37.8397 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively). However, they have highly negative εHf(t) values and Paleoproterozoic two-stage Hf model ages, which are only partially consistent with data from the associated UHP metamorphic rocks. Such features suggest the metadiorites resulted from a magma produced by mixing of Triassic UHP mafic lithologies and minor amounts of mantle-derived materials. Zircon morphological analysis and U-Pb sensitive high-resolution ion microprobe dating combined with conventional thermobarometry indicate that these upwelling melts crystallized at pressure-temperature (P-T) conditions of 5.4–5.7 kbar and 750–768 °C at ca. 130 Ma and subsequently suffered HT metamorphism at ca. 125 Ma. We conclude that the metadiorites’ precursors were derived from partial melting of the Triassic subducted Neoproterozoic mafic lower-crustal rocks, with addition of minor amounts of mantle-derived materials in the Early Cretaceous, in response to mountain-root collapse of the orogen. Based on petrographic textures and mineral compositions, it is moreover inferred that formation of the distinctive K-feldspar porphyroblasts is likely related to a two-stage process, i.e., crystallization derived from biotite breakdown after the formation of the metadiorite at T = 640–703 °C and P < 4.5 kbar and coarsening related to shear deformation.

The geochemistry and geochronology of Permian granitoids from central Inner Mongolia, NE China: Petrogenesis and tectonic implications

Permian granitoids have been identified in the Zhalageamu district, Inner Mongolia, NE China, which provide an excellent opportunity to constrain the tectonic evolution of the Central Asian Orogenic Belt (CAOB). In this study, we determined the zircon UPb ages of the quartz diorite, granodiorite porphyry, diorite porphyry and granite porphyry at Zhalageamu. These ages are 269.5 ± 1.8, 261.4 ± 1.9, 256.4 ± 2.0 and 255.2 ± 2.0 Ma, respectively. The granitoids have high contents of SiO2 (61.95–75.41 wt%) and Al2O3 (11.87–15.88 wt%), and their A/CNK ratios range from 0.91 to 1.44. Their Na2O + K2O contents range from 6.04 to 9.28 wt% and help classify them as having calc-alkaline to high-K calc-alkaline affinity. The low P2O5 contents of the quartz diorite, diorite porphyry and granite porphyry and their decrease with increasing SiO2, in combination with low 10,000*Ga/Al ratios (1.51–2.58) and Zr + Nb + Ce + Y contents (128–264 ppm) identify them as I-type granitoids, whereas the strongly peraluminous character of the granodiorite porphyry classifies it as an S-type granite. These I-type granitoids are characterized by an enrichment in large ion lithophile elements (LILE; e.g., Rb, Ba and Th) and a depletion in high field strength elements (HFSE; e.g., Nb, Ta and Ti). This, and their weakly negative Eu anomalies on chondrite-normalized REE diagrams, are features of typical arc magmatic rocks. The ɛNd(t) values and initial 87Sr/86Sr ratios range from 2.9 to 4.2 and 0.7010 to 0.7039, respectively, and both sets of values point to a mantle source. Hafnium isotopic analysis of quartz diorite yielded positive εHf(t) values of 8.5–12.3 and young two-stage Hf model ages (TDM2) of 0.51–0.72 Ga, suggesting a juvenile crustal source. These features are similar to those of locally occurring coeval volcanic arc rocks, indicating that the Zhalageamu granitoids mostly formed by partial melting of juvenile mantle-derived crust. Our geochemical and Sr-Nd-Hf isotopic data show that the Zhalageamu granitoids were generated in a subduction setting related to the northward subduction of the Paleo-Asian Ocean.

Geochronology, geochemistry and Sr-Nd-Hf isotopes of the Heihuashan granite porphyry, NE China, and implications for Cu-Mo mineralization

Heihuashan is a newly discovered porphyry Cu-Mo prospect in Heilongjiang Province, northeastern China, with considerable Cu and Mo mineralization. Until now the ages of the Cu-Mo ores and the causative granite porphyry, the magma origin and characteristics, as well as the mineralization potential at depth are still unclear. In this contribution, whole rock geochemical and Sr-Nd isotopic compositions, zircon U-Pb ages and Hf isotopes, and molybdenite Re-Os dating, are presented to constrain the timing of the magmatism and mineralization, and the petrogenesis of the causative intrusion. The results also provide an opportunity for evaluating the potential of the deep Cu-Mo mineralization.Zircon U-Pb dating using LA-ICP-MS yields a crystallization age of 146.4 ± 1.8 Ma for the Heihuashan granite porphyry, which is consistent with the molybdenite Re-Os isochron age of 143.7 ± 3.1 Ma. These results indicate that the porphyry Cu-Mo mineralization at Heihuashan occurred at late Jurassic to early Cretaceous. The whole rockgeochemicaldatasuggest that the ore-related intrusion is mildly peraluminous and belongs to the high-Kcalc-alkalineseries, I-type granitoids. The granite porphyry samples are enriched in Rb, Ba, Th, U, and Sr, but depleted in Nb and Ta, showing typical arc magma affinities. They also have initial 87Sr/86Sr ratios of 0.70546–0.70550 and εNd(t) values between +0.4 and +0.7. The zircon εHf(t) values for the granitic intrusion range from +3.5 to +9.2, with two-stage Hf model ages of 977–614 Ma. The geochemical and Sr-Nd-Hf isotopic compositions suggest that the parental magma was dominantly derived from the slab-metasomatized mantle, which could have mixed with some lower crust components.The Fe2O3/FeO ratios of the Heihuashan granite porphyry are relatively high, ranging from 0.52 to 1.17, indicating a high magmatic oxidation state. This is also supported by the high zircon Ce/Ce*, Eu/Eu* and Ce/Nd ratios (33–2433, 0.22–0.70 and 2.4–44.0, respectively) and the high magmatic ΔFMQ values (+0.1 to +3.5 with an average of +2.1) calculated using the zircon trace elements. The intrusion has relatively high Sr/Y ratios (40–94) and displays negligible Eu anomalies (Eu/Eu* = 0.68–1.07); the zircons from the intrusion have high (Eu/Eu*)/Y (mostly > 0.0001) and (Ce/Nd)/Y ratios (mostly > 0.01), but low Dy/Yb ratios (generally < 0.4). These suggest that the fractionation of hornblende rather than plagioclase is dominant during the magma crystallization, which reveals a high magmatic water content. The above results indicate that the ore-related magma at Heihuashan is oxidized and hydrous, both of which are critical for porphyry Cu-Mo mineralization. The Heihuashan granite porphyry is geochemically similar to other Cu-related intrusions in NE China and also comparable to many porphyry Cu (-Mo) systems worldwide, implying a high Cu-Mo mineralization potential. Considering the surface and shallow levels at Heihuashan are characterized dominantly by sericite alteration, we suggest exploration and drilling focusing on the deeper levels beneath the currently mineralized domains, where major potassic alteration zones, likely associated with more extensive Cu-Mo mineralization, could be discovered.

Magmatic controls on the mineralization potential of a porphyry Cu system: The case of Jurassic Tongshan skarn Cu deposit in the Qin–Hang Belt, South China

The Qin–Hang suture belt in South China formed during the Neoproterozoic amalgamation between the Cathaysia and Yangtze blocks. There are several Jurassic porphyry–skarn Cu deposits in this region, and the factors controlling the mineralization potential remain unclear. This study reports geochemical data for the Tongshan skarn deposit and zircon trace element data for five porphyry- or skarn-type Cu deposits in this region, in order to identify geochemical indexes for the mineralization potential of the ore-related intrusions. A garnet U–Pb age (170 Ma) for the Tongshan skarn indicates that Cu mineralization occurred in the Middle Jurassic, which is consistent with the zircon U–Pb ages (173 Ma–171 Ma) of the host granodiorite porphyries. Granodiorite porphyry samples from the Tongshan deposit have moderately high SiO2 contents (64.4–65.0 wt%), low MgO contents (1.39–1.47 wt%), and high (La/Yb)N ratios (14.7–16.8), typical of low-Mg adakitic rocks. The whole-rock geochemistry, bulk Earth-like εNd (t) values (–1.5 to –1.6) and positive zircon εHf(t) values (+2.7 to +6.0), corresponding to two-stage Hf model ages of 1014–832 Ma, suggest the porphyries were derived from thickened juvenile lower crust initially generated during Neoproterozoic amalgamation. In addition, the porphyry samples have arc-like geochemical characteristics (Nb–Ta–Ti depletion), low Th/Yb ratios (average = 4.7), high Ba/Th ratios (average = 346), zircon Eu/Eu* values (average = 0.71) and 10000×(Eu/Eu*)/Y values (average = 6.80), and moderate zircon Ce/Ce* values (average = 705) and Ce/Nd ratios (average = 17.1). These features demonstrate that the parental magmas of the porphyries were formed by melting of a mantle wedge.That had been metasomatized by moderately oxidized slab-derived fluid near a Neoproterozoic subduction zone. Previous studies suggest porphyries from large to giant deposit (e.g., Dexing and Yinshan) have similar two-stage Hf model ages and were derived from Neoproterozoic juvenile crust. But these porphyries have higher whole–rock Th/Yb ratios and zircon Ce/Ce* and Ce/Nd values than those of intrusions from medium-sized deposits (e.g., Tongshan, Chuankeng and Jiande). This indicates that the magma source of the former may have been distant from the trench in the Neoproterozoic, and formed by melting of a mantle wedge that had been metasomatized by highly oxidized slab-derived melt. Our results and previously published data indicate that the Neoproterozoic two-stage Hf model ages of the intrusions are positive indicators of Jurassic Cu mineralization, and granitoids with relatively high Th/Yb ratios and zircon Ce/Ce* and Ce/Nd values likely have more potential to form large to giant Cu deposits.

Zircon Hf[sbnd]O isotope and magma oxidation state evidence for the origin of Early Cretaceous granitoids and porphyry Mo mineralization in the Tongbai-Hong'an-Dabie orogens, Eastern China

The Tongbai-Hong'an-Dabie orogens constitute the east segment of the Qinling-Dabie orogenic belt, which host several large molybdenum deposits, with a proven reserve of over 8 million tons metal Mo. In this study, we present an integrated study of in situ zircon UPb dating and HfO isotopes, in combination with magma oxidation state estimation for the Early Cretaceous granitoids in the Tongbai-Hong'an-Dabie regions. These granitoids can be divided into three groups on the basis of zircon UPb ages, including early-stage ore-related granitoids from Mushan, Xiaofan and Wangwan deposits (143–136 Ma), ore-barren granites (136–130 Ma), and late-stage ore-related granitoids from Qian'echong, Bao'anzhai, Tangjiaping and Shapinggou deposits (130–110 Ma). Early-stage ore-barren granitoids have the lowest average εHf(t) and δ18O values of −27.1 ± 1.6 and 4.25 ± 0.63‰ as well as the oldest two-stage Hf model ages (TDM2) of ~2.8 Ga, which are roughly comparable with the inferred Dabie lower crust, indicating that they were mainly derived from the partial melting of the lower crust. Ore-forming granitoids in two stages show similar two-stage Hf model ages from 2.2 to 2.3 Ga which differ from any inferred layer of crusts, while they exhibit different zircon HfO isotope and oxygen fugacity evolutionary trends. Granitoids display decreasing average εHf(t) and δ18O values from −17.1 ± 1.9 to −27.1 ± 1.6, and 5.71 ± 0.50‰ to 4.25 ± 0.63‰, and increasing average logƒO2 values from −17.4 ± 4.5 to −6.7 ± 3.8 with a decrease in age from 143 to 130 Ma. In addition, relict zircon cores with Paleoproterozic and Archean ages were observed with εHf(t) and δ18O values analogous to those of the Kongling Complex. These characteristics suggest that the early-stage granitoids were possibly produced by the remelting of the subducted lower crust mixed with the Kongling Complex, with the involvement of reducing Mo-rich black shales in the Yangtze Block that seemingly account for the lower oxygen fugacity of ore-forming granitoids with younger two-stage Hf model ages and lead to the formation of those early-stage Mo deposits. As the increasing contributions of the lower crust in the magma source, the metallogenic gap developed from 136 to 130 Ma in the Tongbai-Hong'an-Dabie orogens. Zircon HfO isotopic compositions of ore-related granitoids increase simultaneously up to −14.2 ± 4.3 and 5.82 ± 0.33‰ respectively at a lower slope after 130 Ma. Part of zircon δ18O values is slightly higher than 6.5‰, implying the involvement of supercrustal materials. Meanwhile, magma oxygen fugacity exhibits an abrupt drop at ca. 130 Ma in the Qian'echong deposit with the lowest average logƒO2 value (−19.3 ± 4.5) and Ce4+/Ce3+ ratios (1–138), then rises quickly up to a maximum average logƒO2 value of −7.3 ± 2.3. As such, these granitoids were likely generated by mixing of a blended crustal magma, derived from the lower crust and supercrustal materials, and the mantle-derived component which also contributes to the late-stage Mo mineralization. We propose that not only the highly oxidized magma but also the continuous change of oxygen fugacity in the deep magma chamber may have positive effects on the formation of porphyry Mo deposits. Given the significant geochemical change at ca. 130 Ma instead of 125 Ma, we agree that the intensive magmatism and mineralization in the Tongbai-Hong'an-Dabie orogens are closely associated with the delamination of the thickened lower crust of the Yangtze Block, which caused the asthenosphere upwelling that provided the heat source and led to partial melting of overlaying lower crust.

Geochronological Constraint on the Evolution of the Aktyuz Terrane, Kyrgyz North Tianshan, and the Fate of the Taldybulak Levoberezhny Gold Deposit

The Aktyuz Terrane in Kyrgyz North Tianshan is of particular interest due to the occurrence of high and ultrahigh pressure (HP–UHP) rocks and it containing the third largest gold deposit in Kyrgyz North Tianshan, i.e., Taldybulak Levoberezhny (abbreviated to Taldybulak Lev.). To constrain the ages of the host Kemin Complex and its auriferous monzogranite porphyry, detailed zircon U–Pb dating [by laser ablation inductively coupled plasma-mass spectrometry (LA-ICPMS) and secondary ion mass spectroscopy (SIMS)] and Lu–Hf isotopic analyses were carried out. The intensively altered auriferous monzogranite porphyry yielded two weighted mean ages of 444 ± 3 Ma (n = 14, mean squared weighted deviation (MSWD) = 0.49, by LA-ICPMS) and 440 ± 5 Ma (n = 8, MSWD = 0.82, by SIMS) that are indistinguishable within error ranges. Such ages are consistent with a previously reported sulfide Re–Os isochron age of 434 ± 18 Ma, supporting a Silurian porphyry gold mineralization. The granitic gneiss yielded a protolith age of 773 ± 7 Ma (n = 7, MSWD = 0.04) and two metamorphic ages of 514 ± 4 Ma (n = 8, MSWD = 0.09) and 483 ± 3 Ma (n = 11, MSWD = 0.04). Detrital zircons from one fuchsite schist sample yielded highly variable ages from 729 ± 13 Ma to 2,463 ± 30 Ma, with 12 data points weighted at 740 ± 5 Ma (MSWD = 0.95). The metamorphic overgrowth yielded a weighted mean age of 460 ± 4 Ma (n = 4, MSWD = 0.15). Detrital zircons in the migmatitic amphibolite are aged from 788 ± 7 Ma to 3,447 ± 32 Ma, with two major concentrations at 941 ± 7 Ma (n = 13, MSWD = 0.95) and 794 ± 5 Ma (n = 8, MSWD = 0.19). The metamorphic overgrowth yielded an average age of 555 ± 4 Ma (n = 8, MSWD = 0.65). The detrital and xenocryst zircons, and evolved εHf(t) values (−20.9 to −7.8) and old two-stage Hf model ages (1,367–3,159 Ma), revealed the presence of a Precambrian basement that may be dated back to the Archean Eon. The two metamorphic ages may correlate with oceanic subduction and continental collision, respectively.

Geochronology, geochemistry, and isotope compositions of “Grenvillian” S-type granites in the North Qinling unit, central China: Petrogenesis and tectonic significance

An integrated study of whole-rock elements, Sr–Nd isotopes, and zircon U–Pb ages and Hf-O isotopes was carried out for the “Grenvillian” granites from the North Qinling unit, central China. The results not only place clear constraints on the petrogenesis of these granites, but also give insights into the geodynamic evolution of the Qinling orogen during the assemblage of supercontinent Rodinia. LA-ICPMS zircon U–Pb dating of three representative granites from the Dehe, Fangzhuang, and Zhaigen outcrops yielded formation ages of ca. 940–900 Ma. These muscovite-bearing granites have high silica contents (72–79 wt%) and are weak to strong peraluminous (ASI = 1.01–1.15). They exhibit arc-like trace element distribution patterns with enrichment of LREE and LILE (e.g., Rb, K, Pb) but depletion in HFSE (e.g., Nb, Ta, Ti). Besides, they show variable initial 87Sr/86Sr ratios of 0.704 to 0.729 and relatively low εNd(t) values of −3.2 to −6.1, as well as variable zircon εHf(t) and δ18O values (−8.1–+2.6, 7.9‰–12.0‰). These results suggest their derivation from partial melting of a heterogeneous source that dominated by supracrustal components. Furthermore, a few inherited grains give negative εHf(t) values of −9.4 to −18.4 with two-stage Hf model ages up to 2.9 Ga, suggesting the involvement of minor Archean crustal components. Along with their peraluminous features, high zircon δ18O values, and enriched Sr–Nd isotope compositions, these granites were unambiguously derived from partial melting of metasedimentary rocks and thus are of S-type affinity. Geothermometric and compositional approaches suggest these S-type granites were likely generated by dehydration melting of metagraywacke- and/or metapelite-dominated sources. They might be formed in an accretionary orogen associated with the Rodinia-assembly during the early Neoproterozoic, through which the outboard North Qinling terrane was eventually adjacent to the South China Block.

Age constraints on the genesis of the Changkeng tungsten deposit, Nanling region, South China

Abstract The Changkeng quartz vein tungsten deposit is located in the eastern part of the Helong ore field, Nanling region, South China. It has a proven WO3 reserves of 9680 tons WO3, and an average grade of 2.98%. It contains 28 ore-bearing quartz veins, and the mineralization stages are divided as follows: (I) quartz-wolframite-cassiterite-scheelite stage; (II) quartz-wolframite-scheelite-molybdenite-pyrite-sphalerite-galena-flourite stage; (III) quartz-calcite-flourite stage. The intrusion within the deposit is concealed, and comprising medium- and coarse-grained biotite monzogranite. Zircon grains from the Changkeng pluton have a U-Pb age of 156.7 ± 0.54 Ma (MSWD = 2.9). Cassiterite grains from stage I yield a weighted mean 206Pb/238U age of 156.1 ± 3.4 Ma (MSWD = 3.4). Molybdenite separates from stage II have a well-defined 187Re/187Os isochron age of 156.9 ± 2.0 Ma (MSWD = 0.77), with model ages ranging from 155.6 ± 2.5 to 157.5 ± 2.2 Ma. The zircon eHf(t) values range from −14.1 to −11.1, and the Hf two-stage model ages range from 1.87 to 2.06 Ga, indicating a primary reworking of the Paleoproterozoic crust. The low rhenium contents (0.3238 to 8.763 μg/g) in molybdenite suggest that the ore-forming materials was derived from a crustal source. The age consistence between the intrusion and mineralization, together with the Hf and Re isotope signature, all indicate a close genetic link between magmatism and mineralization. The Changkeng deposit is an example of a Jurassic regional-scale tungsten-tin ore-forming event between 160 and 150 Ma in the Nanling region, South China.

Metallogenic chronology and tectonic setting of the Erdaohe Pb–Zn–Ag deposit in Inner Mongolia, NE China: Constraints from sphalerite Rb–Sr dating, zircon U–Pb dating, and Hf isotope analysis

• The Erdaohe deposit is a large-scale Pb-Zn-Ag deposit in the Great Hinggan Range. • The granite porphyry and the sphalerite in the deposit formed at 133.6Ma and 130.5Ma. • The mineralization was affected by the Mongolia-Okhotsk and Paleo-Pacific Ocean. • The discovery of the Erdaohe deposit shows a good exploration prospect in the region. The Erdaohe deposit is a recently discovered large-scale Pb–Zn–Ag deposit in the northern section of the Great Hinggan Range, Inner Mongolia, China. The ore bodies are mainly located in the skarnized contact zone between the granite-porphyry and calcareous wall rock, and in the fissures of the wall rock of the outer contact zone. Several vein-type ore bodies are located in the fissures of the distal volcanic strata, with obvious magmatic–structural ore-control characteristics. In this study, seven sphalerite samples from ores in the quartz–sulfide metallogenic stage yielded an Rb–Sr isochron age of 130.5 ± 1.9 Ma (MSWD = 1.6), with initial 87 Sr/ 86 Sr ratios of 0.70967 to 0.70994. LA-ICP-MS zircon U–Pb dating of the granite-porphyry samples yielded a concordant age of 133.6 ± 0.46 Ma (MSWD = 1.2). Combined with the previous studies, dating results and the field relation between the granite-porphyry and the ore body, it is considered that the granite-porphyry is genetically related to the mineralization of the deposit. The zircon ε Hf (t) values of the granite-porphyry ranged from 6.8 to 8.5, and the two-stage Hf model age (t DM2 ) ranged from 575 to 668 Ma, revealing that the granite-porphyry originated from the partial melting of the juvenile crust accreted from the depleted mantle during the end of the Neoproterozoic. Extensive magmatism during the Early Cretaceous was caused by lithospheric delamination after the closure of the Mongolia–Okhotsk Ocean and the back-arc extension induced by the subduction of the Paleo-Pacific Plate towards Eurasia; thus, the Erdaohe deposit was formed under this favorable metallogenic structure and material system. By comparing the metallogenic age, tectonic setting, and ore-forming resources, we propose that the formation of Erdaohe Pb–Zn–Ag deposit belongs to the same regional metallogenic event as the Pb–Zn–Ag deposits in the southern segment of the Great Hinggan Range, potentially indicating further exploration prospects for Pb–Zn–Ag deposit in the middle segment of the Great Hinggan Range.

Mineralization of the Daolundaba Cu–Sn–W–Ag deposit in the southern Great Xing'an Range, China: Constraints from geochronology, geochemistry, and Hf isotope

Abstract The Daolundaba deposit, located in the southern Great Xing'an Range, is a medium-sized Cu–Sn–W–Ag deposit dominated by Cu. The intrusive rocks in the ore district mainly include the Early Permian Qianjinchang medium-grained biotite monzogranite and the Early Cretaceous Zhangjiayingzi fine-grained granite and porphyritic granite. Cassiterite U–Pb dating for two Cu–W–Sn ore samples yielded ages of 134.7 Ma and 136.8 Ma, respectively. Zircon U–Pb dating for fine-grained granite and porphyritic granite of the Zhangjiayingzi intrusion yielded ages of 134–136 Ma and 135 Ma, respectively. The Zhangjiayingzi intrusion is high-K calc-alkaline and featured by enrichment of Rb, Th, U, K, Nd, Zr, Hf, and Sm and steady depletion of Ba, Sr, P, Eu, and Ti, with extremely negative Eu anomalies and noticeable tetrad effect of rare earth elements, indicating the intrusion has a highly fractionated granite affinity. The Zhangjiayingzi intrusion has high zircon eHf(t) values (4.1–10.2) and relatively young zircon Hf two-stage model ages (541–929 Ma), suggesting that it dominated originated from the partial melting of a Neoproterozoic juvenile lower crust. The geochronology and geochemistry indicate that the mineralization of the Daolundaba deposit is closely related to Early Cretaceous highly fractionated granites. Fractional crystallization of granitic magmas is the important controlling factor for the formation of the Zhangjiayingzi highly fractionated granite and the Daolundaba Cu–W–Sn–Ag deposit.

Petrogenesis and tectonic implications of the late Paleoproterozoic A-type rhyolites at the southwestern North China Craton

The late Paleoproterozoic A-type granitoids are important for constraining of the lithotectonic and geodynamic processed involved in the creation of continental crust. The newly identified late Paleoproterozoic felsic extrusive rocks from the southwestern margin of the North China Craton (NCC) consist of rhyolites which show melting corrosion structure, autoclastic texture and fiber structure of mineral grains and have weighted mean SIMS zircon UPb ages of 1794.7 ± 3.6 Ma to 1780.3 ± 5.6 Ma. The rhyolite samples show high SiO2 (67.59–74.38 wt%) and K2O + Na2O (3.68–11.10 wt%), and low MgO (0.05–1.17 wt%), CaO (0.19–2.58 wt%) and P2O5 (0.08–0.16 wt%). They display aluminous A-type granite/rhyolite geochemical compositions, such as high A/CNK (0.78–1.23), FeOT/(FeOT + MgO) (0.81–0.99) and 10000Ga/Al (2.32–4.03) ratios, and high Zr + Nb + Ce + Y (824–1272 ppm) concentrations, as well as high zirconium saturation temperatures (TZr = 873–964 °C). These signatures, along with their low εHf(t) (−3.6 to −1.5) and εNd(t) values (−4.31 to −3.31) and old two-stage Hf model ages (TDMC = 2.70–2.57 Ga), indicate that the rhyolites were derived from partial melting of the Neoarchean felsic basement rocks. These volcanic rocks also have low zircon δ18O values ranging from 1.5‰ to 6.8‰, which were inherited from the Neoarchean 18O-depleted basement rocks that underwent high-T hydrothermal alteration, rather than resulted from contamination or later high-T water/rock interaction. The rhyolite rocks in this study, the earliest igneous rocks in the southwestern NCC after the Paleoproterozoic consolidation of the crystalline basement, were formed in a rift setting, marking the initial breakup of the Guyuan Rift in the southwestern NCC. The rhyolite rocks in combination with the Xiong'er volcanic rocks in the southern NCC mark the initial rifting of the NCC (Xiong'er Rift and Guyuan Rift) after cratonization (~1.85–1.8 Ga). The youngest retrograde metamorphism (1.80–1.79 Ga) in the NCC indicates that the transition from post-orogenic to intracontinental rift setting occurred at ca. 1.79 Ga.

Geochronology, geochemistry and oxidation state of the Dongyuan biotite granite in the Jiangnan tungsten ore belt: Implications for the I-type granite-related W mineralization

The Dongyuan deposit, located in the southern Anhui Province, China, is a large porphyry W–(Mo) deposit in the Jiangnan tungsten ore belt. Ore minerals are dominated by scheelite and molybdenite, which occur as disseminated or veined in biotite granite. Zircon U–Pb dating of biotite granite is 143.5 ± 0.7 Ma, which is consistent with formation age of regional tungsten mineralization. Chemical compositions of biotites from biotite granite plot near or below Ni–NiO buffer on a Fe3+–Fe2+–Mg2+diagram, suggesting that the Dongyuan biotite granite has a relatively low oxygen fugacity. The biotite granite samples are characterized by high SiO2 (68.78–70.98 wt%), Al2O3 (14.60–15.32 wt%), K2O (3.45–4.82 wt%) contents and K2O/Na2O ratios (0.98–1.59), with A/CNK ranging from 0.97 to 1.02, belonging to I-type granite. They show adakite-like geochemical features, with high Sr/Y (35.98–57.90) and (La/Yb)N (21.41–38.78) ratios but low Y (5.54–6.77 ppm) and Yb (0.44–0.55 ppm) contents, which have low MgO (0.60–0.77 wt%), Cr (15.39–28.52 ppm) and Ni (3.68–5.66 ppm) contents and Mg# (31–35) values. These samples have high initial 87Sr/86Sr ratios (0.7144–0.7160) and negative ƐNd(t) values (−9.1 to −5.5), with two-stage Nd model ages (TDM2) of 1379–1695 Ma, while the zircon ƐHf(t) values and two-stage Hf model ages (TC DM) are −6.4 to −0.7 and 1243 to 1601 Ma, respectively. These data suggest that the Dongyuan biotite granite was derived from partial melting of a thickened crustal source which had been previously produced by Neoproterozoic magmatic underplating. Combined with previously published data, we propose that the W mineralization of the Dongyuan deposit was controlled by metal-rich source region, fractional crystallization, low oxygen fugacity condition, and enrichment of fluorine volatiles, which also influenced other I-type granite-related W deposits in the Jiangnan tungsten ore belt. Furthermore, the W-related granitic rocks in this tungsten ore belt developed in a compression–extension transitional setting that was triggered by the subducted Paleo-Pacific slab roll-back.

Himalayan Miocene adakitic rocks, a case study of the Mayum pluton: Insights into geodynamic processes within the subducted Indian continental lithosphere and Himalayan mid-Miocene tectonic regime transition

AbstractThe Himalayan Orogen is a typical continental collision orogenic belt that formed during India-Asia collision. The orogeny involved a transition in tectonic regime, which led to E-W–trending extension during the middle Miocene. At the same time, widespread post-collisional adakitic magmatism occurred in southern Tibet, particularly in the Lhasa Terrane, and these rocks provide a valuable record of the collisional geodynamic processes within the lithosphere. Few studies have focused on the middle Miocene adakitic rocks of the Himalayan Orogen, so further research is required to constrain their origin and geodynamics. This study presents new geochronological and geochemical data, including the whole rock Sr-Nd and zircon Hf isotopic compositions from the Mayum pluton in the Mayum-Gong Tso area, Northern Himalaya. Zircon U-Pb ages show that the Mayum granodiorite porphyries crystallized at 16.67 ± 0.14 Ma (mean square weighted deviation [MSWD] = 0.82, n = 29) and 16.68 ± 0.16 Ma (MSWD = 1.13, n = 28), indicating that they formed during the middle Miocene. The major and trace element characteristics are as follows: SiO2 = 65.79–67.31 wt%, Al2O3 = 15.28–16.00 wt%, MgO = 1.77–1.89 wt%, Y = 12.0–13.5 ppm, Yb = 0.11–0.99 ppm, Sr = 719–822 ppm, (La/Yb)N = 21.89–27.02, Sr/Y = 56.1–65.5, and the rocks have weak negative Eu anomalies (Eu/Eu* = 0.76–0.85), indicating that they are adakitic rocks and show high Sr-Ba granite affinity. The Mayum granodiorite porphyries have high K2O contents (3.42–3.65 wt%), Na2O (3.76–4.04 wt%), and K2O/Na2O ratios of 0.91–0.95, indicating a high-K calc-alkaline affinity. All samples are enriched in large-ion lithophile elements and depleted in high field strength elements. The initial 87Sr/86Sr ratios are 0.709262–0.709327 and εNd(t) values are −6.36 to −7.07, which correspond to two-stage Nd model ages [TDM2(Nd)] of 1405–1348 Ma. In situ zircon Lu-Hf isotopic compositions are variable, with 176Hf/177Hf ratios of 0.2823845–0.282824, εHf(t) values of −13.37 to +2.17, and two-stage Hf model ages [TDM2(Hf)] of 1704–841 Ma. These geochemical and Sr-Nd-Hf isotopic characteristics indicate that the Mayum granodiorite porphyries may be derived from partial melting of the subducted Indian thickened ancient mafic lower crust (∼92%) mixed with depleted mid-ocean ridge basalt mantle material input (∼8%) slightly. Crust-mantle interaction was induced by asthenospheric upwelling followed by the underplating of the Himalayan lower crust beneath Southern Tibet during the middle Miocene in response to significant changes in the geodynamics of the India-Asia collisional orogen. These deep geodynamic processes reflect the break-off or rollback of the subducted Indian continental slab, which caused asthenospheric upwelling, the input of juvenile heat, and the addition of depleted mantle material. This study indicates that the middle Miocene Himalayan adakitic rocks, which include the Miocene Yardoi two-mica granite, Gyangzê granite porphyry dike, Bendui two-mica granite, Langkazi enclave, Kuday dacitic dike, Lasa pluton, and Mayum pluton, form a belt of adakitic rocks in the Northern Himalaya to the south of the Indus-Tsangpo Suture Zone. These adakitic rocks have similar temporal and spatial distributions, geochemical features, and Sr-Nd isotopic compositions, indicating that their petrogenesis and geodynamic settings were similar. At that time there was widespread initiation of N-S–trending rifting, exhumation of central Himalayan eclogites, and large changes in the compositions of Himalayan leucogranites in the Himalayan Orogen. These can be attributed to significant changes in the characteristics of the subducted Indian continental lithosphere during the middle Miocene. The middle Miocene Himalayan adakitic rocks provide valuable insights into this transition in the tectonic regime and deep geodynamic processes.

Early Cretaceous granitoids and gabbro in the Liaodong Peninsula: implications for delamination of the North China Craton and Paleo-Pacific Plate subduction

New petrological, whole-rock geochemical, zircon U–Pb geochronological, and zircon Lu–Hf isotopic data have been reported for Early Cretaceous intrusive rocks in the Wulong region of the Liaodong Peninsula on the North China Craton. The zircon U-Pb chronology shows that the crystallization age of six groups of intrusive rocks from this region is 129–123 Myr ago. These intrusive rocks can be categorized into A-type granite (granodiorite), K-rich adakite (porphyritic-like monzogranite), highly fractionated I-type granites (porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite), and gabbro. These granitoids are shown to have negative zircon eHf(t) values(-21.0 to -11.1) with old two-stage Hf model ages (TDM2(Hf)) (1.88–2.50 Ga), while gabbro has higher zircon eHf(t) values(-14.3 to -9.4) with younger TDM2(Hf) (1.77–2.08 Ga) model ages. According to our results, we believe that the porphyritic-like monzogranite was produced through partial melting of the thickened eclogitic lower crust, the gabbro was generated by partial melting of a source formed by the mixing of enriched lithospheric mantle and delaminated eclogitic lower crust, the granodiorite was formed by mixing crust materials and mafic melts, the porphyritic-like biotite monzogranite, porphyritic-like syenogranite, and syenogranite originated from the medium- to high-K basaltic lower crust. The bimodal intrusive rocks (gabbro, porphyritic-like monzogranite, and porphyritic-like biotite monzogranite) and A-type granites (granodiorite) were emplaced in an extensional setting associated with Paleo-Pacific Plate subduction. We also determined that the tectonic setting changed from extension to transpression during 125–120 Myr ago (porphyritic-like syenogranite and syenogranite). Moreover, we confirmed the hypothesis that the Early Cretaceous delamination is the result of Paleo-Pacific Plate subduction.

Origin and tectonic implications of the early Middle Triassic tuffs in the western Yangtze Craton: Insight into whole-rock geochemical and zircon U-Pb and Hf isotopic signatures

The tuff layer steadily distributed in the western Yangtze Craton is a regional marker for the Early–Middle Triassic (Olenekian–Anisian) boundary. Integrated studies of whole-rock geochemistry and zircon geochronology reveal that the parental magma of the tuff is of felsic composition, generated via volcanic eruptions in the continental arc setting along the southwestern margin of the Yangtze Craton at ~247 Ma. The syn-depositional zircons in the tuff layers and in the coeval igneous rocks exhibit uniform negative εHf(t) values of approximately −20 to −6, indicating the significant input of crustal materials. Massive crustal assimilation implies a large-scale remelting of the pre-existing continental crust, triggered by the intensive arc–continental collision during that time. This intensive collisional tectonomagmatic event is an important signal for the closing of the eastern Paleo-Tethys branch and points to the initial collision of the Indochina Block and the Yangtze Craton. Xenocrystic zircons in the Precambrian-age offer insight into the early evolution of the southwestern Yangtze Craton, which shows episodic crustal growth and reworking of ~2.9–2.2 Ga, crustal reworking of ~1.9–1.7 Ga, rifting-related tectonomagmatism of ~1.6–1.4 Ga, and crustal growth of ~1.1–0.8 Ga. The older crystallization ages (3.4–2.5 Ga), lower initial 176Hf/177Hf values (0.2805–0.2813), negative εHf(t) values (−15.7 to −1.6), and two-stage Hf model ages (3.9–2.8 Ga) of zircons further suggest that an unexposed Archean basement exists beneath the southwestern Yangtze Craton. Significant contributions of mantle-derived materials occur at ~1.3–1.0 Ga, implying that the southwestern Yangtze Craton may not be involved in the Grenvillian-aged continental–continental collision orogeny. Comparable age spectrums and Hf isotopic data suggest that the Paleoproterozoic igneous rocks are a non-negligible provenance for Proterozoic metasedimentary in the Kangdian region.

Petrogenesis of Jurassic Granitoids on Liaodong Peninsula, Northeast China: Constraints on the Evolution of the Mongol-Okhotsk and Pacific Tectonic Regimes

The tectonic setting of Jurassic magmatism in the Northeast China (NE China) is unclear. Here, we present new petrological, whole-rock geochemical, zircon U-Pb geochronological, and zircon Lu-Hf isotope data for Jurassic granitoids of the Wulong region, Liaodong Peninsula, NE China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb data indicate that these granitoids were emplaced at 165–156 Ma. The biotite monzogranite, two-mica monzogranite, monzogranite, granodiorite, biotite granodiorite, and syenogranite are strongly peraluminous (A/CNK=1.09–1.29), contain peraluminous minerals such as muscovite, have high normative corundum abundances (1.26 wt.%–3.28 wt.%), and have high K2O/Na2O ratios (0.76–1.48), all of which indicate an S-type granite affinity. However, the biotite granodiorite and syenogranite have high Sr (391 ppm–570 ppm) and low Y (3.06 ppm–5.94 ppm) contents, with high Sr/Y (65.8–185.9) ratios, and the two-mica monzogranite, monzogranite, and granodiorite have relatively high Sr (138 ppm–379 ppm) and low Y (3.38 ppm–8.71 ppm) contents, with high Sr/Y ratios (19.1–77.9). All of the analyzed samples have negative zircon eHf(t) values (−41.4 to −20.6) with old two-stage Hf model ages (TDM2(Hf)=2.50–3.76 Ga). Therefore, we infer that the biotite monzogranite is the typical feature of S-type granite that was derived by partial melting of metagraywacke. The monzogranite, two-mica monzogranite, granodiorite, biotite granodiorite, and syenogranite exhibit geochemical characteristics of S-type granite with K-rich adakitic features, and were possibly derived by mixing of melts from clastic crustal materials and adakitic magmas. There are voluminous Jurassic igneous rocks in the NE China. By combining our study with the previous researches, this paper infers that the Jurassic magmatism within the Erguna-Xing’an Massif was related to the southward subduction and closure of the Mongol-Okhotsk Ocean; the Early Jurassic magmatism to the east of the Songliao Basin and in the northern North China Craton (NCC) was related to the subduction of the Pacific Plate; however, the Middle-Late Jurassic igneous rocks to the west of the Songliao Basin were related to the closure of the Mongol-Okhotsk Ocean and, in the northern NCC, were related to closure of the Mongol-Okhotsk Ocean with an influence from flat-slab subduction of the Pacific Plate.

Geochronology and petrogenesis of the Late Triassic A-type granitoids in the Yeongnam Massif and its implication for Late Triassic geodynamics of northeast Asia

The Late Triassic A-type granitoids along the continental margins of East Asia are important for deciphering the crust-mantle interactions, transformation of tectonic regime, and termination of the Indosinian Orogeny (known as the Songrim Orogeny in South Korea). The newly identified Wangdong plutons are distributed in the southwestern part of Yeongnam Massif, South Korea. U–Pb dating of zircons from the Wangdong plutons has established its date of emplacement at ca. 226–221 Ma, similar to the emplacement ages of the Daegang and Ian alkali granites. Geochemical data have shown that the Wangdong granitoid samples are magnesian to ferroan in composition and can be further classified in the range from alkalic to calc-alkalic. They have a high zircon saturation temperature (~ 850 °C), K2O/Na2O and, Ga/Al ratios, and are enriched with high field strength elements (e.g., Zr and Y), indicating an A-type granite affinity. Their classification into A2-type granites based on the A-type subdivision diagrams suggest that they formed in an extension-related tectonic setting. Moreover, the Wangdong A-type granitoids have high (La/Nb)N and (Th/Nb)N ratios with peraluminous characteristics (value of aluminum saturation index >1.0). In addition, magmatic zircons from the Wangdong granitoids have negative ɛHf(t) values (−6.6 to −15.5) with a Paleoproterozoic to Mesoproterozoic two-stage Hf model ages (from 1.99 to 1.49 Ga). This suggests that the Wangdong granitoids were derived from ancient crustal materials with compositions similar to metagraywackes. Based on geochemical, isotopic, and geochronological studies, we concluded that the lithospheric mantle delamination induced by slab roll-back of the subducted Paleo-Pacific plate is the main trigger in the production of Late Triassic magmatism in Yeongnam Massif, South Korea.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.