Stage Model Ages Research Articles

Modern-style subduction during the late Neoarchean to early Paleoproterozoic? Geochemical evidence from ca. 2.45 Ga arc-type magmatism in the Feidong Complex, northeastern Yangtze Craton, South China

The late Neoarchean to early Paleoproterozoic tectonic evolution of the Yangtze Craton remains poorly constrained as a result of the poor exposure of contemporaneous basement rocks. This study presents new zircon U–Pb–Hf isotopic data and whole–rock geochemical and Sr–Nd isotopic data for orthogneisses from the Feidong Complex of the northeastern Yangtze Craton. Two orthogneiss samples yielded weighted mean ages of 2416 ± 21 and 2436 ± 21 Ma, respectively, indicating the timing of protolith formation. These samples contain relatively high concentrations of SiO2 (54.04–63.25 wt%), but low concentrations of Na2O (3.29–4.12 wt%) and K2O (1.87–2.84 wt%), indicating they are calc–alkaline intermediate rocks. They are enriched in the light ion lithophile elements (LILE) and the light rare earth elements (LREE) but are depleted in Nb–Ta, Ti, the heavy REE (HREE), and Y. They also plot within the arc affinity fields of (La/Yb)N vs. (Yb)N and Sr/Y vs. Y diagrams, consistent with their relatively high Th/Yb and Ta/Yb and low Ce/Pb and Nb/U values, all of which are indicative of rocks formed by arc–type magmatism. The two orthogneiss samples have zircon εHf(t) values that vary between –6.83 and +2.54 with two–stage model ages (TDM2) of 3.35–2.79 (peak at 3.2 Ga) and with similar Nd isotopic compositions. The high total REE contents and Nb–Ta depletions within the orthogneiss samples may reflect derivation from magmas sourced from regions containing fluids released from a subducting slab. These data indicate that the calc–alkaline protoliths of these orthogneisses formed from magmas generated by the partial melting of mantle wedge material driven by the addition of fluid released from a subducted slab. This process induced the partial melting of ca. 3.2 Ga lower crustal material in a manner similar to that associated with modern arc–type magmatism. Taken collectively, the regional magmatism recorded by the ca. 2.50–2.47 Ga tonalite–trondhjemite–granodiorite (TTG) gneisses of the Douling Complex, the ca. 2.45 Ga calc–alkaline arc-type magmatic rocks in the Feidong Complex, and contemporaneous metamorphism within the north margin of Yangtze Craton all provide evidence that modern–style subduction occurred within the northeastern Yangtze Craton between the late Neoarchean and the early Paleoproterozoic.

Mesoproterozoic (∼1.3 Ga) S–type granites in Shangdu area, Inner Mongolia of the North China Craton (NCC): Implications for breakup of the NCC from the Columbia supercontinent

Mesoproterozoic (∼1.3 Ga) magmatism in the North China Craton (NCC) was characterized by diabase sills, while contemporary granitic magmatism was relatively rare, limiting our understanding of the NCC’s evolution during this period. In this manuscript, we report newly identified ∼1.3 Ga S–type granitic plutons in the Shangdu area, the western part of the northern NCC. Based on the results of geochemical, geochronological and zircon in–situ Lu–Hf isotope analyses, we discussed the petrogenesis, tectonic setting of the granitic plutons and the regime that drove the break–up of the NCC from the Columbia supercontinent. The zircon laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results indicate that these granites were emplaced at some time between 1315 ± 21 Ma and 1307 ± 32 Ma. Moreover, the geochemical results show that they have high contents of SiO2 (75.34–76.97 wt%), Al2O3 (12.90–13.61 wt%) and Na2O + K2O (6.21–8.31 wt%), but low MgO (0.09–0.25 wt%) and Mg# (14–34). The A/CNK ratios varied between 1.10 and 1.28, indicating that the granites belong to the peraluminous series. Furthermore, the existence of Al–rich minerals (e.g., muscovite and garnet) suggests that they are the S–type granites. The ∼1.3 Ga zircon display negative to slightly positive εHf(t) values (−9.28–3.1) and old two–stage model ages (TDM2) (3.3–2.1 Ga). The ages of the inherited zircon and Lu–Hf isotope compositions of the ∼1.3 Ga zircon in the granite are consistent with those of the detrital zircon from Jining complex, the eastern part of the Khondalite Belt. Based on these facts, we infer that the granites in this study derived from the partial melting of the Jining complex. The coeval mafic dykes (in the Yanliao large igneous province) and the Shangdu granite in the north margin of the NCC strongly suggest an extensional setting, which was related to the break–up of the NCC from the Columbia supercontinent. A mantle plume was likely the dominant driver of the break–up and it should have provided heat for the partial melting of Jining complex.

Mesoproterozoic (∼1.4 Ga) magmatism in the Liaoyuan Accretionary Belt, NE China: New implications for tectonic affinity and crustal evolution of microcontinents along the southern Central Asian Orogenic Belt

The Mesoproterozoic granitic magmatism has been identified in the middle and western part of the southern margin of Central Asian Orogenic Belt (CAOB), but rarely reported from the eastern part. In this study, Mesoproterozoic granitic rocks were identified in the Liaoyuan Accretionary Belt (LAB), an area located in the northeast China, within the eastern part of the southern CAOB. Information obtained from these samples is likely to elucidate the current understanding of the Precambrian evolution in this area. The five granitic rocks yielded zircon U–Pb weighted mean ages between 1321 ± 43 Ma and 1388 ± 31 Ma. These samples are characterized by high SiO2 (69.30–77.51 wt%), MgO (1.96–2.34 wt%), Fe2O3 (3.48–3.82 wt%), and Cr (40–80 ppm) contents, moderate Al2O3 contents (11.23–15.80 wt%), and high Mg# values (45–56). Furthermore, they are rich in light rare earth elements (LREEs), Zr, and Hf, but depleted in heavy rare earth elements (HREEs), Nb, Ta, and Ti. Moreover, they also exhibit significant negative Eu anomalies (Eu/Eu* = 0.25–0.84). In addition, the samples have high Zr + Ce + Y + Nb contents (300–497 ppm) indicating A-type granite affinities. The zircons depicted positive εHf(t) values (3.31 to 11.1, average value of 7.5) with two stage model ages (TDM2) varying from 1480 Ma to 2128 Ma. Based on the above data, it was concluded that the Mesoproterozoic granitic rocks in this area were derived from partial melting of juvenile crust with addition of mantle-derived materials. The granites were emplaced in an extensional setting caused by roll back or break off of subducted oceanic slab. Juvenile ∼ 1.4 Ga granitic rocks, like these in the LAB, were also preserved in other microcontinents along the southern CAOB. Their geochemical characteristics are comparable to rocks derived from contemporaneous igneous activity in Laurentia and Baltica, but not those in the North China, Tarim or the Siberian Cratons. Based on the present and previous studies, the microcontinents that preserved the juvenile ∼ 1.4 Ga rocks might belong to a continental terrane in the periphery of the Columbia supercontinent and show tectonic affinity with the combined Laurentia–Baltica landmass.

Mineralization age, tectonic setting and ore genesis of the Wuxing Pt–Pd-rich magmatic Cu-Ni sulfide deposit, Northeast China

• Wuxing deposit with age of 516.7 Ma is reported. • Wuxing intrusive rocks experienced independent diagenetic processes. • The Wuxing deposit was formed in a post–collision extensional setting. The Wuxing deposit in Northeast China, tectonically located in the Jiamusi–Khanka Block, is a Pt–Pd-rich Cu-Ni sulfide deposit related to mafic–ultramafic rocks. The zircon U–Pb ages of pyroxenites , gabbros , porphyritic granites , and leucogranits in the mining area are 516.7 ± 2.6, 513.8 ± 2.0, 505.4 ± 2.3 and 499.5 ± 2.9 Ma, respectively, indicating that the diagenesis and metallogenesis of the Wuxing deposit occurred during the Cambrian. The ore-forming complex is cut by quartz diorite porphyritic and plagiogranite porphyry dikes. Zircon U–Pb ages of the quartz diorite porphyrite and plagiogranite porphyry are 206.6 ± 2.1 and 201.6 ± 1.3 Ma, respectively. The U–Pb ages indicate the metallogenic age constraint of 516.7 ± 2.6 Ma for the Wuxing deposit, rather than Cambrian and Triassic magmatic activities. The Hf isotopic composition ε Hf (t) of zircons in the pyroxenites and gabbros are −11.5 to −7.7 and −5.8 to −2.5, with the two–stage model ages (t DM2 ) of 2198–1958 and 1841–1633 Ma, respectively. Geochemically, the mafic–ultramafic complexes are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in high-field strength elements (HFSE), indicating these rocks originated from the enriched mantle. The porphyritic granites are high-K calc-alkaline rocks (Rittman index δ = 1.92–2.00), and the leucogranites are low-K alkaline rocks ( δ = 4.76–4.86) with ε Hf (t) and t DM2 of −9.2 to +0.8 and 2037–1411 Ma, respectively. The porphyritic granites and leucogranites are characterized by low A/CNK values (0.91–1.05), 10,000 Ga/Al values (1.76–2.36), and Zr saturation temperature (731–823 ℃) similar to those of I-type granites. Along with contemporaneous intrusions, the Wuxing deposit is inferred to have formed in a post-collisional extension environment. Consequently, the origin of the Wuxing deposit is likely related to the evolution of enriched mantle magma during the Cambrian post-collision extensional setting of the Jiamusi–Khanka Block.

Geochronology and geochemical characteristics of granitoids in the Bastielieke tungsten polymetallic deposit in the southern margin of Altay: Implications for tungsten mineralization

巴斯铁列克钨多金属矿床位于新疆阿尔泰造山带南缘，是近年来在区内发现的首例中型钨多金属矿床。矿体主要产于二叠纪花岗岩与上志留统-下泥盆统康布铁堡组火山-沉积岩接触带的矽卡岩中。钨矿化与矿区花岗质岩石有明显的空间关系。然而，与钨矿化有关的花岗质岩石成因尚不清楚。本文对矿区出露的与矿化关系密切的黑云母花岗岩、二长花岗岩和二云母花岗岩进行了锆石U-Pb 年代学和岩石地球化学研究。3个样品的LA-ICP-MS锆石U-Pb加权平均年龄分别为282.3±3.2Ma、284.3±2.2Ma和284.8±2.3Ma，属早二叠世岩浆活动的产物，与成矿年龄一致。所有岩石具有高硅（SiO₂=73.6%~78.3%）、富碱（K₂O+Na₂O=5.15%~9.62%）富钾（K₂O/Na₂O>1.1）、贫钙（CaO=0.19%~0.75%）和钛（TiO₂=0.04%~0.24%）、弱过铝-强过铝质（A/CNK=1.01~1.39）特征。这些岩石稀土元素总量（∑REE）变化较大（变化于20.3×10^-6~328×10^-6），但二云母花岗岩显示轻重稀土元素分异不明显（（La/Yb）_N=0.96~2.06）、Eu强烈负异常（δEu=0.07~0.41）的深V型稀土元素分布特征，黑云母花岗岩和二长花岗岩显示轻稀土略富集（（La/Yb）_N分别为2.8~5.5和4.8~7.4）且Eu负异常（δEu=0.33~0.39和0.34~0.63）明显的右倾型稀土元素分布特征。所有样品均显示相对富集Rb、Th、U、Pb元素和相对亏损Nb、Ti、P、Sr、Ba元素，但二云母花岗岩中W含量（4.6×10^-6~9.4×10^-6）相对低于黑云母花岗岩和二长花岗岩中W含量（分别为15.1×10^-6~168×10^-6和8.4×10^-6~16.0×10^-6）。所有样品的锆石具有正的高ε_Hf（t）值（+3.8~+11）和相对年轻的亏损地幔模式年龄（Hf的t_DM2为0.60~1.0Ga）。以上特征说明，这些岩石属高钾钙碱性分异I-A过渡型花岗岩。结合区域地质背景，认为这些岩体是二叠纪时期后碰撞伸展环境下两个独立岩浆事件的产物，母岩浆均来源于新生地壳熔体与幔源岩浆，经过高度分异演化后结晶形成矿区岩石。花岗质岩浆活动为巴斯铁列克钨矿床提供了成矿物质，岩浆演化过程（结晶分异与熔体-流体作用）对成矿元素有富集作用。;The medium-sized Bastielieke tungsten polymetallic deposit is a newly discovered deposit in the Kelan Basin at the southern margin of Altay Orogenic Belt. The skarn hosted the orebody which is at the outer contact zone between the granitoids and volcanic-sedimentary rocks of the Upper Silurian to Lower Devonian Kangbutiebao Formation. Two-mica granite, biotite granite and monzogranite outcrop in the Bastielieke ore district showing obvious spacial relation to the hosted ore deposits. The petrogenesis of these rocks associated with the tungsten mineralization is indefinitive. LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements and zircon Hf isotope are performed to discuss their petrogenesis. These granites show consistent weighted mean ²⁰⁶Pb/²³⁸U ages of 282.3±3.2Ma, 284.3±2.2Ma and 284.8±2.3Ma, respectively, which indicate that the Permian magmatic events at the southern margin of Altay is consistent to the ages of mineralization. These granitoids exhibit high SiO₂ concentration (73.6%~78.3%), high total alkali (Na₂O+K₂O) (5.15%~9.62%) concentration and low CaO (0.19%~0.75%) and TiO₂ (0.04%~0.24%) concentrations. In addition, they are enriched in potassium (K₂O/Na₂O=1.08~2.06) with high A/CNK values (1.01~1.39). The total REE contents of these granites vary from 20.3×10^-6 to 328×10^-6 with different chondrite-normalized REE patterns. The two-mica granite is characterized by low (La/Yb)_N ration (0.96~2.06) with pronounced negative Eu anomaly from 0.07 to 0.41, and showing a deep V-type pattern. The biotite granite and monzogranite display enrichment of LREE with (La/Yb)_N ration ranging from 2.8 to 5.5 and 4.8 to 7.4, and moderate negative Eu anomalies ranging from 0.33 to 0.39 and 0.34 to 0.63, respectively. All samples display noticeable negative anomalies of Nb, Ti, P, Sr, Ba and strong positive anomalies of Rb, Th, U and Pb. The two-mica granite has lower W concentrations varying from 4.6×10^-6 to 9.4×10^-6 than those in the biotite granite and monzogranite from 15.1×10^-6 to 168×10^-6 and 8.4×10^-6 to 16.0×10^-6, respectively. In addition, zircon ε_Hf(t) values range from +3.8 to +11, two stage model ages (t_DM2) ranging from 0.6Ga to 1.0Ga. The petrologic and geochemical data indicate that these rocks are high-K calc-alkaline and weak peraluminious to strongly peraluminous, which is similar to the geochemical behavior of the fractionated I-A type granitoids. Combined with regional geology, we suggest that they are derived from melting of the juvenile crust and mantle, and followed by subsequent crystallization fractionation in deeper magma chamber in a post-collision environment by two independent magmatic events. These granites provide key ore components for the formation of Bastielieke tungsten polymetallic deposit and preconcentrate tungsten by crystallization fractionation and melts-fluid exsolution.

Triassic granitoids in the East Kunlun Orogenic Belt, Northwestern China: magmatic source and implications for geodynamic evolution

ABSTRACT Granitoids, an important part of the continental crust, are the direct and indelible evidence of the accretion and reworking process of the continental crust in different tectonic settings. Therefore, these early geodynamic mechanisms can be roughly reconstructed by analysing the geochemical characteristics of granitoids. In this study, the Permian–Triassic Granitoids widely distributed in the East Kunlun Orogenic Belt (EKOB) are studied to determine their chronology and petrogenesis to restrict their source regions and establish the significance of their geodynamic and crustal growth. Zircon inductively coupled plasma mass spectrometry (ICP–MS) dating results show that the crystallization ages of these granitoids are between 252–240 Ma, during the early and middle Triassic. These granitoids have high SiO2 and medium Na2O + K2O contents, plotting into the granite region, and calc-alkaline to high-K calc-alkaline series on the SiO2–Na2O + K2O and SiO2–K2O diagrams, respectively. All the samples have aluminium saturation index (A/CNK) values from 1.00 to 1.25 showing peraluminous characteristics. In terms of trace and rare earth elements, the samples are depleted in high field strength elements (HFSEs) such as Nb, Ta, P, and Ti and are enriched in large ion lithophile elements (LILEs) such as Rb, K, Ba, and U. Moreover, all granitoids show right-inclined rare earth element (REE) distribution patterns with weak to moderate Eu anomalies (δEu = 0.50–0.93). In addition, the samples have low P2O5 contents, 10,000*Ga/Al ratios (1.65–2.39), and Zr + Nb + Ce + Y (212–262 ppm) displaying affinities to I-type granite. Combined with their εHf (t) values of −2.31 to 4.44, with 1.0–1.4 Ga two stage model ages (TDM2), they are considered to be the products of the reworking of the Mesoproterozoic lower crust; therefore, they are not related to the continental net growth in the EKOB. On the tectonic discrimination diagrams of granitoids, all the samples fall into the area of volcanic arc granite (VAG) and continental margin arc; this suggests that the Paleo-Tethys Ocean slab was still in the subduction stage during 252–240 Ma, and the continental collision had not yet started. Based on the plenty of magmatic rock dating results published previously, it appears there are two magmatic peak periods (260–240 Ma and 230–210 Ma) and one magmatic intermittence period (240–230 Ma) during the late Permian to Triassic of the EKOB, corresponding to three geodynamic evolution stages of subduction, post-collision extension, and syn-collision, respectively.

Geochronology, geochemistry and petrogenesis of the Dengfuxian lamprophyres: Implications for the early Cretaceous tectonic evolution of the South China Block

The middle–late Mesozoic tectonic evolution of the South China Block is not well constrained due to limited studies of synchronous mafic rocks in this area. The Dengfuxian area is located at the central to northern parts of the Nanling Range in the South China Block with many lamprophyre dikes seen cross-cutting the late Jurassic granites. This contribution is the first to report the whole-rock geochemistry, zircon U–Pb age and Sr–Nd–Hf isotope signature of these lamprophyres; provide a geochronological and petrogenetic studies that sheds new light on regional geodynamic evolution. The Dengfuxian lamprophyre dikes have variable contents of major oxides like SiO2 (58.45–65.19 %), Al2O3 (12.18–15.73 %), Fe2O3T (6.31–6.93 %), MgO (2.48–4.14 %), CaO (4.21–5.19 %), Na2O (1.08–3.02 %), K2O (2.78–4.00 %), TiO2 (0.59–1.00 %), MnO (0.15–0.33 %) and P2O5 (0.28–1.22 %). Identified as high-K calc-alkaline rock series, the lamprophyres are enriched in large ion lithophile elements (e.g., Rb, U, K and Pb) but depleted in Ba, Sr and high field strength elements (e.g., Nb, Ta, Zr and Hf). The HREEs are relative depleted compared to LREEs, with weak Ce anomalies (Ce/Ce* = 0.99–1.06) but marked negative Eu anomalies (Eu/Eu* = 0.61–0.79). A total of 30 magmatic zircon grains from the studied lamprophyre yields weighted mean U–Pb ages of 141–143 Ma, suggestive of an early Cretaceous emplacement. The Negative εNd(t) (–4.3 to –6.0) and εHf(t) (–4.1 to –10.9) values, old Nd depleted mantle model ages (TDM = 1231–1628 Ma) and Hf single stage model ages (TDM = 998–1243 Ma), with high initial 87Sr/86Sr (0.71057–0.71322) indicate that the parent magma was sourced from a subduction-modified enriched mantle. Together with integrated major and trace elements studies, it can be inferred that the parent magma of the Dengfuxian lamprophyres originated from low degree (1–3 %) partial melting of an enriched mantle source (garnet peridotite) that was altered by subduction sediments in a progressive intra-plate extension environment. The magma experienced significant fractional crystallization of olivine, clinopyroxene, plagioclase, Fe-Ti oxides and apatite with little crustal contamination. A two-stage geodynamic model is presented to constrain the tectonic evolution of the South China Block during the early Cretaceous.

Middle–late permian I-type granitoids from the Diaobingshan region in the northern margin of the North China Craton: insight into southward subduction of the Paleo–Asian Ocean

ABSTRACT An integrated study of the petrology, zircon U–Pb geochronology, whole–rock geochemistry, and in situ zircon Hf isotopic compositions of middle–late Permian granitoids from the Diaobingshan region in the northern margin of the North China Craton (NCC) has been implemented, with the aim of investigating their geochronological framework, petrogenesis, and tectonic significance. The studied granitoids are widely distributed on the southern side of the Changchun–Yanji suture zone and comprise mainly monzogranite and syenogranite, with minor quartz monzonite. New zircon U–Pb data measured by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) yield emplacement ages of 262–256 Ma, reflecting middle–late Permian magmatism. Geochemically, the rocks contain 60.53–73.33 wt.% SiO2, 12.60–18.35 wt.% Al2O3, 3.50–8.10 wt.% K2O, 0.18–0.91 wt.% TiO2, and 0.22–1.01 wt.% MgO, and exhibit weakly peraluminous (A/CNK = 0.86–1.01) and high-K calc–alkaline and shoshonitic characteristics, indicating I-type granite affinities. They are also characterized by low Sr and high Yb contents, reflecting low-pressure magma source conditions with residual plagioclase (i.e. amphibolite facies). These granitoids also exhibit geochemical characteristics typical of arc–type magmatic rocks, with enrichment in large ion lithophile elements (LILEs; e.g. Rb, Ba, and K) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs; e.g. Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating that they were formed in a subduction-related setting. Moreover, magmatic zircons from the studied rocks have relatively homogeneous Hf isotopic compositions (εHf(t) = – 1.4 to +15.1) and corresponding two–stage model (TDM2) ages of 1839–348 Ma, indicating that they were generated by partial melting of Paleoproterozoic–Phanerozoic accreted lower crust, with minor contributions of ancient crustal materials. Their geochemical characteristics and specific lithological assemblage, together with the temporal–spatial distribution of Permian granitic magmatism, indicate that the formation of middle–late Permian granitoids in the northern margin of the NCC was related to southward Paleo–Asian oceanic subduction. Data from this and previous studies lead us to favour a double-sided, early–late Permian subduction model, with the Paleo–Asian Ocean closing after the late Permian.

Anorthosites from an Archean continental arc in the Dharwar Craton, southern India: Implications for terrane assembly and cratonization

Anorthositic rocks have attracted attention in terms of their possible role as the primordial crust of our planet, and also as markers of Archean-Paleoproterozoic plate tectonic regimes. Here we investigate the Konkanhundi gabbro-anorthosite suite from Peninsular India, adjacent to the major collisional suture between the Western and Eastern Dharwar cratonic blocks. The anorthosites display high Al2O3 contents with negative correlation against MgO, high CaO and Sr contents, and positive Eu anomalies indicating plagioclase flotation in the magma chamber. The pyroxenite and gabbroic rocks of the suite show high Ni, Cr, Co contents and geochemical features typical of pyroxene cumulation. LA-ICPMS U-Pb analyses of magmatic zircon grains yield weighted mean 207Pb/206Pb ages of 2601 ± 12 Ma for pyroxenite, 2616 ± 12 Ma for gabbro, 2615 ± 13 Ma and 2627 ± 14 Ma for anorthositic gabbro, 2594 ± 16 Ma for anorthosite, and 2605 ± 27 Ma for microgabbro. The age data from the different rock types in the anorthosite suite are broadly consistent, marking the emplacement time as ca. 2.6 Ga, and providing insights on one of the oldest anorthosite complexes in Peninsular India. Zircon grains in the surrounding TTG gneisses into which the gabbro-anorthosite suite was emplaced show weighted mean 207Pb/206Pb age of 3321 ± 11 Ma suggesting Mesoarchean basement. The zircon grains display high Th/U values and REE patterns typical of magmatic crystallization with enriched HREE, positive Ce and Sm anomalies, and negative Pr, Nd, Eu anomalies. Zircon Lu-Hf analysis yield negative εHf(t) values of −4.9–−0.7 with TDMC (two stage model ages) of 3123–3376 Ma for pyroxenite, −4.5–−1.7 and 3192–3366 Ma for gabbro, −5.3–0.9 and 3034–3410 Ma for anorthositic gabbro, and −3.9–-2.4 and 3221–3311 Ma respectively, suggesting the incorporation of Mesoarchean components within the Neoarchean magmatic suite. However, zircon grains in the TTG gneiss possess more ‘juvenile’ εHf(t) values in the range of −0.2–1.3 with TDMC in the range of 3554–3646 Ma. The zircon Hf isotopes and trace element data, together with the whole rock geochemical features suggest that the parent magma of the Konkanhundi gabbro-anorthosite suite was derived from subduction-related depleted mantle source that also incorporated continental crustal components. The time of emplacement of the gabbro-anorthosite complex broadly correlates with widespread arc magmatism and crust production as well recycling in other domains of the Dharwar Craton. We envisage multiple convergence of microblocks during craton assembly at the end of Archean in Dharwar, with the greenstone belts marking zones of paleo-ocean closure.

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

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

Isotope geochronology, geochemistry, and mineral chemistry of the U-bearing and barren granites from the Zhuguangshan complex, South China: Implications for petrogenesis and uranium mineralization

The Zhuguangshan complex carries some of the most important granite-hosted uranium deposits in South China. Here we investigate the Changjiang and Jiufeng granites which represent typical U-bearing and barren granites in the complex, using zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data, and mineral chemistry, to constrain the petrogenesis and uranium mineralization. LA-ICP-MS zircon U-Pb dating shows that both the Changjiang and Jiufeng granites were emplaced ca. 160Ma. These rocks show high silica, weakly to strongly peraluminous compositions, enrichment in Rb, Th, and U, and depletion in Ba, Nb, Sr, P, and Ti. These features coupled with the high initial 87Sr/86Sr ratios, negative εNd(t) values and εHf(t) values, and the Paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to S-type granites, and the parental magmas of the two granites were derived from the Paleoproterozoic metasedimentary rocks. However, the granitoids show different mineralogical characteristics. The biotite in the Changjiang granite belongs to siderophyllite, marking higher degree of chloritization, whereas the biotite in the Jiufeng granite is ferribiotite, characterized by only slight chloritization. Compared with the Jiufeng granite, the biotite in the Changjiang granite has lower crystallization temperature and oxygen fugacity, but higher F content, and the uraninite has higher UO2 content but lower ThO2 content, and stronger corrosion. The chemical ages of uraninites from both granites are (within error) consistent with the zircon U-Pb ages and are considered to represent the emplacement ages of granites. Chemical ages of pitchblende in the Changjiang granite yield 118±8Ma, 87±4Ma, and 68±6Ma, representing multiple episodes of hydrothermal events that are responsible for the precipitation of U ores in the Changjiang uranium ore field. Our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic-hydrothermal system are the key factors that control the different U contents of these two granites. The mineralogical characteristics of uraninite and biotite can be used to distinguish between U-bearing and barren granites, and serve as a potential tool for prospecting granite-hosted uranium deposits.

Geochemistry and geochronology of ore-bearing and barren intrusions in the Luanchuan ore fields of East Qinling metallogenic belt, China: Diverse tectonic evolution and implications for mineral exploration

The Luanchuan ore fields form part of the East Qinling metallogenic belt in central China. In this study, we compare two ore-bearing intrusions, the Shibaogou granitic pluton (SBG) and the Zhongyuku granitic pluton (ZYK), with the ore-barren Laojunshan intrusion (LJS) from the Luanchuan ore field. Geochemically, all the three intrusions are characterized by high-Si, high-K, and alkalis, together with moderate-ASI, exhibiting I-type granite features. The rocks, especially the ore-related plutons also show enrichment in LREEs. Mineral chemistry of biotite from the intrusions exhibits similar features of high Si and Mg, and low Al and Fe. Zircon grains from the ZYK intrusion yielded a U-Pb age of 149.6±2.4Ma. The zircon grains show εHf (t) values and two stage model ages (TDM2) in the range of −16.8 to −19.7 and 1998–2156Ma respectively. The biotite composition and Hf isotopic data indicate that the magma was derived by re-melting of deep crustal material with minor input of mantle components. We evaluate the results to understand the physico-chemical conditions, petrogenesis, and tectonic setting, and their implications for mineral exploration. The ore-bearing plutons show wide ranges of temperature and oxygen fugacity, favoring Mo-W mineralization. In addition, estimates on pressure and depth of emplacement suggest that lower solidification pressure in a decompressional setting contributed to the evolution of magmatic hydrothermal deposits. Our data suggest that the ZYK has the highest potential for Mo-W mineralization. The ore-bearing plutons of ZYK and SBG were formed in a transitional tectonic setting from compression to extension, with the large-scale metallogeny triggered by slab melts at ca. 145Ma. However, the ore-barren LJS batholith formed in an extension-related geodynamic setting at ∼115Ma. Our study shows that different tectonic settings and consequent physico-chemical conditions dictated the ore potential of the intrusions in the Luanchuan ore district.

Zircon U-Pb ages and Lu-Hf isotope compositions from clastic rocks in the Hutuo Group: Further constraints on Paleoproterozoic tectonic evolution of the Trans-North China Orogen

The Hutuo Group, as one of the classic examples of Paleoproterozoic strata, plays an important role in establishing evolutionary processes in the Trans-North China Craton. In this contribution, we present petrologic, detrital zircon U-Pb ages and Lu-Hf isotopes from three subgroups of the Hutuo Group. Sandstones in the Doucun and Dongye Subgroups are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with minor lithic fragments, suggesting that the detrital components were mainly derived from both the continental block and recycled orogen. In contrast, clastic components in the Guojiazhai Subgroup are mainly Q and lithic fragments, indicating they were derived predominantly from the recycled orogen. The ages of detrital zircons from sandstones in the Doucun and Dongye Subgroups are mainly concentrated at ca. 2.5Ga and 2.2–2.1Ga with minor 2.7Ga zircons also present which indicates they were dominantly sourced from 2.5Ga Wutai, Fuping and Zanhuang Complexes, and Paleoproterozoic intrusives. The Guojiazhai Subgroup displays a different zircon age population of ca.2.4Ga, 2.2–2.1Ga and 2.0–1.9Ga, which indicates likely derivation from Paleoproterozoic intrusives in the Wutai, Lüliang and Hengshan areas. Based on the observation that sandstone clastic components in the Doucun and Dongye Subgroups are dominantly quartz, feldspar and sedimentary lithic fragments, but not volcanic lithics, we propose that they were deposited in a rift-related setting. Zircons from the lower sequence of the Hutuo Group yielded a young population of 2140Ma. Considering the volcanic rocks of 2140±14Ma at the base of the group and 2.2–2.0Ga magmatism along the TNCO, we propose that Doucun and Dongye Subgroups formed at 2.2–2.0Ga. The youngest, ca. 1.9Ga, zircons in the Guojiazhai Subgroup indicate this Group was deposited during closure of the rift at 1.9–1.8Ga. The two stage model ages of the detrital zircons mainly range from 2.6 to 2.9Ga with a minor ∼2.5Ga contribution. Therefore, we infer that 2.6–2.9Ga represents a period of intensive crustal growth in the Trans-North China Orogen, but that some degree of crustal growth continued to ∼2.5Ga.

The discovery of late Triassic mylonitic granite and geologic significance in the middle Gangdese batholiths, southern Tibet

The Gangdese magmatic belt, located in the southern margin of the Lhasa terrain and carrying significant copper poly-metallic mineralization, preserves important information related to the tectonics associated with the Neo-Tethys Ocean subduction, Indian-Asian collision and the crustal growth of southern Tibet. Here, we investigated the Namling batholiths in the central domain of the Gangdese magmatic belt and report for the first time the occurrence of late Triassic mylonitic granite, and present its petrologic, zircon U-Pb-Hf isotopes and the whole-rock chemistry dataset. Zircon LA-ICP-MS U-Pb dating from three mylonitic granitic samples yields crystallization ages of 209.4±1.1Ma, 206.7±1.1Ma and 212±1.1Ma, indicating a late Triassic magmatic event in the Gangdese magmatic belt. Geochemically, the mylonitic granite exhibits magnesian genesis and calcic and calc-alkalic features. The depletions of Nb, Ta and Ti and enrichments of LREEs together suggest that the magmas from which these rocks crystallized were generated in an active continental margin. Besides, all the analyzed samples also demonstrate highly positive εHf(t) values of 8.95–12.91 (mean value 10.84), corresponding to single stage model ages (tDM1) in the range of 326Ma–486Ma (mean 414Ma), attesting to crustal growth in southern Lhasa terrain. The mylonitic pluton are likely sourced from partial melting of the lower crustal components (amphibolite or basaltic stuff) that was heated and metasomatized by underplating basaltic magmas, and subsequently might undergo fractional crystallization and upper sediments contamination during parental magmas ascent. In light of the distribution of the early Mesozoic magmatic events and robust sedimentary evidence together suggest that the northward subduction of the Neo-Tethys oceanic crust beneath the Lhasa terrain should commence prior to late Triassic (∼210Ma).

Origin of the Badaguan porphyry Cu[sbnd]Mo deposit, Inner Mongolia, northeast China: Constraints from geology, isotope geochemistry and geochronology

The Badaguan porphyry CuMo deposit is located in the Derbugan metallogenic belt of northeastern Inner Mongolia, China. The host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230Ma and 238Ma, respectively. The granodioritic porphyry has (87Sr/86Sr)i values of 0.70535–0.70549, εNd(t) values of 0.41–1.17, εHf(t) values of 1.30–6.51, and two–stage model ages (TDM2) of 1131–848Ma. In contrast, the granitic porphyry is characterized by εHf(t) values from −0.75 to 7.28 that yield TDM2 model ages of 1355–816Ma. The geochemical and SrNdHf isotopic data for the magmatic rocks associated with the Badaguan porphyry CuMo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust. The δ18O values of ore fluids from different mineralizing stages are between −6.0‰ and +1.5‰, and the fluid δDwater values vary from −119.3‰ to −140.0‰, indicating a mixed fluid of magmatic and meteoric water, the SPb isotopes show that the metal was mostly derived from a deep-seated magma that involved some crustal materials, with a narrow δ34S range (−2.4‰ to +3.5‰). We infer that the Badaguan porphyry CuMo deposit formed during a period of southeast–directed subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Block.

Age and depositional setting of the Paleoproterozoic Gantaohe Group in Zanhuang Complex: Constraints from zircon U–Pb ages and Hf isotopes of sandstones and dacite

The Gantaohe Group, located in the Zanhuang area, contains typical North China Craton Paleoproterozoic strata, and is one of the best-preserved examples of these rocks. It is therefore a significant area for deciphering evolutionary process in the trans-North China Orogen. In this paper, we present petrologic, detrital and volcanic zircon U–Pb ages and Lu–Hf isotopes from three formations of the Gantaohe Group. The zircons from a conglomerate at the base of the Gantaohe Group yielded a young population of ca. 2.1Ga. Dacite from the upper section of the Nansizhang Formation yielded zircon 207Pb/206Pb ages of 2090±14Ma. Thus, the initial deposition of the Gantaohe Group occurred at ∼2.1Ga. The Group underwent greenschist to low amphibolite facies metamorphism, identical to regional 1.87–1.85Ga metamorphism in Zanhuang Complex. Therefore, we propose that the Gantaohe Group was deposited in the period between 2.1Ga and 1.9Ga. Sandstones in the Gantaohe Group are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with only minor lithic fragments, suggesting that detrital components were mainly derived from a cratonic source. Detrital zircons from sandstones exhibit a dominant population of 2.55–2.5Ga grains with minor contributions of ∼2.7Ga and ∼2.1Ga grains, which further indicate they were dominantly sourced from ∼2.5Ga TTG gneisses, late Archean Zanhuang and late Archean to Paleoproterozoic Guandu Groups, with subordinately input from ∼2.7Ga TTG gneisses and the Paleoproterozoic Xuting granite. Given that the sandstone clastic components chiefly comprise quartz and feldspar, there is a lack of volcanic lithics, and the major detrital zircons are 400Ma older than the initial deposition age, we propose that the Gantaohe Group was deposited in a rift-related setting far from any back-arc basin at ∼2.1Ga or 1880–1810Ma syn-collisional processes. A few 2.5–2.7Ga zircons have positive εHf(t) values identical with the contemporaneous depleted mantle and the 207Pb/206Pb ages are similar to their single stage model ages (TDM1), which suggests some degree of 2.5–2.7Ga crustal growth. Most ∼2.5 zircons, however, show 207Pb/206Pb ages that are much younger than the Hf single stage model ages, which indicates intensive crustal reworking in the late Neoarchean. The zircons collectively present two stage model ages ranging from 2.6 to 2.9Ga. Therefore, we suggest that the 2.6–2.9Ga periods represents a time of intensive crustal growth in the Zanhuang Complex.

Late Triassic crustal growth in southern Tibet: Evidence from the Gangdese magmatic belt

The Gangdese magmatic belt, located in the southern margin of the Lhasa terrane and carrying significant copper and polymetallic mineralization, preserves important information relating to the tectonics associated with Indian–Eurasian collision and the crustal growth of southern Tibet. Here we investigate the Quxu batholith in the central domain of the Gangdese magmatic belt and report the occurrence of hornblende gabbros for the first time. We present petrologic, zircon U–Pb–Hf isotopic and bulk-rock chemistry data on these rocks. The hornblende gabbros display sub-alkaline features, and correspond to tholeiite composition. They also show medium K calc-alkaline to low K affinity. The rocks show enrichment in LILEs and LREEs, but are depleted in HFSEs, indicating a subduction-related active continental margin setting for the magma genesis. Our computations show that the gabbroic pluton was emplaced in the middle-lower crustal depth of ca. 18km. Zircons from the hornblende gabbros yield crystallization age of ca. 210Ma, revealing a late Triassic magmatic event. Combined with available data from the Gangdese magmatic belt, our study suggests that the northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane might have been initiated not later than the Norian period of Triassic. Zircons from the hornblende gabbro show positive εHf(t) values of 9.56 to 14.75 (mean value 12.44), corresponding to single stage model ages (TDM1) in the range of 256Ma to 459Ma, attesting to crustal growth in the southern Lhasa terrane associated with the subduction of the Neo-Tethys oceanic crust.

Magma mingling and chemical diffusion in the Taojiang granitoids in the Hunan Province, China: evidences from petrography, geochronology and geochemistry

Petrographic study and zircon LA-ICP-MS U-Pb dating reveal that the Taojiang pluton is mainly composed of Late Indosinian biotite granodiorites (216 ± 2 Ma, 217 ± 1 Ma and 217 ± 1 Ma) with contemporaneous microgranular enclaves (219 ± 3 Ma). The host rocks belong to metaluminous to peraluminous and high-K calc-alkaline granodiorite with mean K2O/Na2O ratio less than 1, while the microgranular enclaves belong to metaluminous and shoshonitic monzodiorite and quartz monzonite, with average K2O/Na2O greater than 1. The enclaves contain back-veins and xenocrysts of quartz, biotite and plagioclase, and have contents of K, Rb and total REE higher than their host rocks, indicating mingling of two different magmas and elemental diffusion from the felsic magma to the mafic magma due to temperature gradient between them. The host granodiorites have initial 87Sr/86Sr of 0.71411 ~ 0.71508, e Nd(t) values of −6.05 ~ −7.39 and Nd isotope two stage model ages $$ \left( {\mathrm{T}_{\mathrm{NdDM}}^2} \right) $$ of 1.49 Ga to 1.60 Ga, while the enclaves have initial 87Sr/86Sr of 0.71438, e Nd(t) values of −6.92 and $$ \mathrm{T}_{\mathrm{NdDM}}^2 $$ of 1.56 Ga, showing similar features. The zircon e Hf(t) values of the enclaves (−4.21 ~ 0.54) are slightly higher than those of the host rocks (−6.77 ~ −2.18), and the zircon Hf isotopic two stage model ages $$ \left( {\mathrm{T}_{\mathrm{NfDM}}^2} \right) $$ of the enclaves (mainly 1.21 Ga ~ 1.45 Ga) are accordingly slightly younger compared with those of the host rocks (1.39 Ga to 1.75 Ga). These data suggest that the host rock magma was derived mainly from partial melting of Mesoproterozoic - Paleoproterozoic crustal rocks, while the enclave magma was originated from partial melting of basic/ultrabasic rocks intruding in the crust during Mesoproterozoic period. Three inherited zircon cores from the granodiorites are dated 1512 Ma, 2325 Ma and 2458 Ma, also giving evidence for involvement of Mesoproterozoic- Paleoproterozoic crust rocks in the magma formation. The more evident negative Eu anomaly of the enclaves than their host granodiorites may have resulted from more distinct fractional crystallization of plagioclase in the enclave magma before mingling with the felsic magma.

Emplacement Ages and Petrogenesis of the Molybdenum–bearing Granites in the Jinduicheng Area of East Qinling, China: Constraints from Zircon U–Pb Ages and Hf Isotopes

Abstract:The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from –10 to –16, and –20 to –24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from –18 to –20, –28 to –38, and –42 to –44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively), the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.

Growth and reworking of the early Precambrian continental crust in the North China Craton: Constraints from zircon Hf isotopes

We synthesize more than 2600 Hf isotope data on the Archean-Paleoproterozoic zircons from the North China Craton (NCC). Recalculation of the data based on single stage and two-stage Hf model ages of the Eastern Block of the NCC shows peak ages of 3902±13Ma and 3978±18Ma, respectively, and also small peaks at 3.5–4.0Ga. The majority of zircon εHf(t) values are positive, suggesting the possibility of the crust and the mantle differentiation at ca. 3.9–4.0Ga in the Eastern Block of the NCC. Most magmatic zircons from the whole of NCC have their Hf model age range of 2.4–2.9Ga, and the single stage model ages is cluster at 2698±4Ma, whereas the two-stage model ages concentrate at 2714±5Ma, implying that the protoliths were juvenile crustal rocks. The most prominent peak at 2.7Ga indicates that this period marks the most important stage of the crust-mantle differentiation and crust formation of the NCC. The widespread 2.5Ga rocks in the NCC and the absence of the 2.5Ga peaks in Hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2.5Ga. Furthermore, the 2.5–1.7Ga zircon Hf isotope features are also related to the reworking of the crustal rocks. Our results from the integration of a large database suggest that the Eastern Block and the Trans-North China Orogen have undergone similar crust-mantle differentiation and magmatism, leading to the conclusion that the essential cratonization of the North China took place at the end of Neoarchean.