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2022 Vol. 33, No. 1

2022, 33(1): 0.
2022, 33(1): .
Special Issue on Isotope Geochronology and Isotope Geochemistry
Advances in Isotope Geochronology and Isotope Geochemistry: A Preface
Xiangkun Zhu, Zaicong Wang, Huayong Chen
2022, 33(1): 1-4. doi: 10.1007/s12583-021-1605-x
Zircon Xenocrysts from the Shaka Ridge Record Ancient Continental Crust: New U-Pb Geochronological and Oxygen Isotopic Data
Sergey G. Skublov, Natalia A. Rumyantseva, Qiuli Li, Boris G. Vanshtein, Dmitriy I. Rezvukhin, Xianhua Li
2022, 33(1): 5-16. doi: 10.1007/s12583-021-1422-2
Over the past two decades, a significant number of discoveries of ancient zircon xenocrysts in ocean-floor magmatic rocks have been reported. These findings provide compelling evidence for the presence of ancient continental crust within young oceanic lithosphere. Almost all finds of ancient zircon xenocrysts within oceanic crust are from the Mid-Atlantic Ridge. For other localities, however, similar data are very limited. This report presents the first age determinations (U-Pb, SHRIMP-II) and isotope-geochemical data (oxygen, trace and rare earth elements) for zircon xenocrysts from gabbro-diorites of the Shaka Ridge, in the vicinity of the Shaka fracture zone, near the western end of the Southwest Indian Ridge. The work is based on a study of bottom rock material dredged during expeditionary research on the R/V "Akademik Fedorov" (Russia) in 2016. The U-Pb isotope system of the zircon xenocrysts recorded a crystallization age of ~2.8 Ga at an upper discordia intercept and an age of ~600 Ma interpreted as the timing of a superimposed thermal event at a lower discordia intercept. The zircon xenocrysts show geochemical signatures of magmatic origin, i.e., fractionated REE distribution spectra with an increase in chondrite-normalized values from light to heavy REE, positive Ce anomalies and negative Eu anomalies, and high Th/U ratios (0.59-7.77). In discrimination diagrams based on a series of inter-element relationships, zircon compositions fall into the fields of zircons from rocks of continental crust, mostly granitoids. The Li content of the zircons is high (1.8 ppm-50 ppm), adding further evidence to their derivation from rocks of continental crust. During their residence within young oceanic crust, the zircon xenocrysts experienced alterations under the influence of submarine high-temperature hydrothermal fluids, which selectively affected the distribution of trace elements in the zircons and reduced the δ18O values to 1.75‰-3.15‰. The presence of obviously older zircons in Shaka gabbro-diorites clearly demonstrates the presence of ancient continental fragments and their recycling into the mantle at the western end of the Southwest Indian Ridge.
Long-Term Reproducibility of SIMS Zircon U-Pb Geochronology
Wenhao Zhao, Qiuli Li, Yu Liu, Guoqiang Tang, Xiaoxiao Ling, Jiao Li, Xianhua Li
2022, 33(1): 17-24. doi: 10.1007/s12583-021-1549-1
Secondary ion mass spectrometry (SIMS) zircon U-Pb dating has been widely used to confine the absolute ages of the magmatic or metamorphic events and to distinguish multiple events. Here, a data set consisting of the zircon standards dating data (~15 000 Plešovice and ~8 000 Qinghu items) accumulated for more than 8 years using the CAMECA IMS 1280HR of the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) is compiled to evaluate the long-term external reproducibility. With Plešovice zircon as the calibration standard and Qinghu zircon as an unknown sample, the analytical uncertainties for single-spot (n=7 723) and session analyses (n=691, with more than 7 single spot analyses in one session) are 2.6% and 0.9% (2RSD, relative standard deviation), respectively. It means that single-spot U-Pb dating for a standard-level zircon sample could vary 5.2% at 95% confidence level, while the average value (n>7) for each session may vary 1.8%. Thus, these values should be considered as the minimum uncertainty when comparing single spot and individual session analysis results for multiple dating works on a certain geological event.
Re-Os Geochronology of the Liuchapo Formation across the Ediacaran-Cambrian Boundary of the Yangtze Block (South China)
Yong Fu, Fuliang Wang, Chuan Guo, Chao Li, Peng Xia
2022, 33(1): 25-35. doi: 10.1007/s12583-021-1473-4
The Ediacaran-Cambrian (E-C) succession in South China records remarkable oceanic, biological and geochemical variations, but it was not well defined geochronologically, which hinders the interpretation of the spatio-temporal seawater chemical architecture during the time E-C interval. This study presents two Re-Os isochron ages of 520.2±6.1 and 561.7±8.5 Ma for the barite-rich black shales from the top Liuchapo and Doushantuo formations respectively in Tianzhu County, Guizhou Province. In combination with existing age data, the two new Re-Os isochron ages suggest that the Liuchapo Formation was deposited between 550 and 520 Ma. Moreover, like the polymetallic Ni-Mo-PGE layers of shelf margin (or platform) facies and V-rich horizons of transitional (or shelf slope) to deep-water facies, the barite deposits were likely formed due to differential mineralization. The timing offset likely resulted from differential elemental concentration related to certain local factors (i.e., hydrothermal fluids, seawater redox and biological activity). The isochron-derived initial 187Os/188Os ratios of the top Liuchapo Formation (0.902±0.048) and the Doushantuo Formation (0.740±0.042) fall within the range of continental weathering flux (1.54) and oceanic crust (0.126), implying the involvement of marine hydrothermal fluids. Moreover, their difference of initial 187Os/188Os ratios may reflect variations of continental weathering intensity and uplift magnitude.
Late Mesozoic Tectono-Thermal History in the South Margin of Great Xing'an Range, NE China: Insights from Zircon and Apatite (U-Th)/He Ages
Wen Zhang, Shuangfeng Zhao, Jingbo Sun, Ze Shen, Wen Chen
2022, 33(1): 36-44. doi: 10.1007/s12583-021-1537-5
The Late Mesozoic tectono-thermal evolution and geodynamic setting of the Great Xing'an Range (GXR), particularly in the south margin, are still ambiguous. In this study, we present original low-temperature thermochronological data of six granitoid samples collected from Maanzi pluton in the south margin of the GXR. The apatite and zircon (U-Th)/He ages vary of 70.8±4.3-119.0±7.0 Ma and 120.0±7.1-146.7±8.7 Ma, respectively. Further numerical inverse modeling results reveal that the granitoid plutons experienced a rapid cooling and exhumation stage during Early Cretaceous with a rate of ~5.0-6.0 ℃/Ma and ~0.14-0.17 mm/yr, respectively, including the western minor pluton emplaced during Early Permian and the major pluton crystallized in latest Jurassic, corresponding to the extensional tectonics in NE China. The rapid exhumation processes in the south margin of the GXR during the Early Cretaceous could be related to both the rollback of Paleo-Pacific oceanic plate and the collapse of thickened crust in the Mongol-Okhotsk Orogen.
Thermal Annealing Characteristics of Detrital Zircon Fission Track Obtained from Natural Borehole Samples
Chang'e Cai, Nansheng Qiu, Jian Chang, Cleber Jose Soares, Hong Chen
2022, 33(1): 45-56. doi: 10.1007/s12583-021-1512-1

Previous studies proposed thermal simulation experiment to investigate the annealing characteristics of fission tracks in igneous zircon samples. However, basic research about detrital zircon fission track was relatively weak. This study discussed the initial track length, annealing temperature and annealing model of zircon fission track by using the measured track lengths obtained from natural borehole samples in the sedimentary basins with different thermal background. The results show that the initial track length of zircon fission track is 12.97 μm. The total annealing temperature (Ttotal) of zircon fission track derived from the evolutionary curve of the mean track lengths is approximately 400 ℃. The temperature ranges of 120-230 ℃ corresponds to the partial annealing zone (PAZ), and is lower than the range obtained through thermal annealing experiments. The annealing model is modified based on the measured track lengths. In addition, a functional formula about the mean track length, annealing temperature, and geological time is proposed, and the fitted values of track lengths consist with the measured track lengths in this study. By properly understanding the initial track length and annealing behavior of zircon fission track can provide a significant guidance for the study of hydrocarbon accumulation in sedimentary basins.

Limited Contribution of Preferential Dissolution to Radiogenic Uranium Isotope Disequilibrium Observed in Weathered Moraines
Laifeng Li, Laura F. Robinson, Tianyu Chen, Zhewen Xu, Jun Chen, Gaojun Li
2022, 33(1): 57-66. doi: 10.1007/s12583-021-1523-y
Radiogenic uranium isotope disequilibrium (234U/238U) has been used to trace a variety of Earth surface processes, and is usually attributed to direct recoil of 234Th and preferential dissolution of radioactively damaged lattices at the mineral surface. However, the relative contribution of these two mechanisms in the natural environment remains unresolved, making it hard to use the extent of disequilibrium to quantify processes such as weathering. This study tests the contribution of preferential dissolution using well-characterized weathered moraines and river sediments from the southeastern Tibetan Plateau. The observations show that weathering of recent moraines where the contribution from direct recoil is negligible and is not associated with depletion of 234U at the mineral surface. It suggests a limited role for preferential dissolution in this setting. We attribute this lack of preferential dissolution to a near-to-equilibrium dissolution at the weathering interfaces, with little development of etch pits associated with radioactively damaged energetic sites.
Accurate Determination of Zr Isotopic Ratio in Zircons by Femtosecond Laser Ablation MC-ICP-MS with "Wet" Plasma Technique
Wen Zhang, Zhaochu Hu, Lanping Feng, Zaicong Wang, Yongsheng Liu, Yantong Feng, Hong Liu
2022, 33(1): 67-75. doi: 10.1007/s12583-021-1535-7
This work evaluates the use of femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS) for Zr isotopic analysis in zircons. The mass fractionation caused by instrumental mass discrimination was corrected by a combination of internal correction using Sr as an internal standard (coming from a NIST SRM 987 standard solution) and external correction using a matrix-matched standard. Several important instrument parameters were investigated, such as the effect of the addition of N2 and "wet" plasma condition, the mass fractionation behaviors between Zr isotopes and Sr isotopes, the position effect in laser ablation cell and the effect of laser ablation parameters (laser spot size and energy density). The Zr isotope compositions of seven zircons (GJ-1, 91500, Plešovice, Rak-17, Paki, Aus and Mala) were determined by the developed fs-LA-MC-ICP-MS and thermal ionization mass spectrometry (TIMS). Our fs-LA-MC-ICP-MS results for Zr isotope compositions agreed with TIMS analyses within analytical uncertainties, indicating the presented method is a suitable tool to resolve isotopic zoning in natural zircons. The results also suggest that GJ-1, 91500, Plešovice, Paki, Aus and Mala had the homogenous Zr isotope composition and could be considered as the potential candidates for the Zr isotope analysis in zircons, except Rak-17 which presented the large Zr isotope variation.
Assessment of Different Digestion Procedures for Mo Isotope Measurements of Black and Grey Shales Using the Double Spike Technique
Jin Li, Xiangkun Zhu, Suohan Tang
2022, 33(1): 76-81. doi: 10.1007/s12583-021-1520-1
This study investigates the behavior of Mo and Mo isotopes (δ98Mo) in shales following leaching with HCl and HNO3 with the aim of simplifying the shale dissolution procedure. Up to 6% of the Mo was lost and the Mo isotopes were unaffected when shales were leached using 9 M HCl after ashing. Bulk sample digestion or leaching by 4 M or more concentrated HCl after ashing were all found to be acceptable and reliable approaches to the analysis of Mo isotopes in shales. After black shale (CAGS-BS) was leached with 2 M HCl, 1 M HCl, and 9 M HNO3, the Mo concentration ([Mo]) in the leachate was lower and δ98Mo was heavier than that obtained from bulk digestion. A Mo isotope mass-balance model showed that the δ98Mo in the residues was lighter than the δ98Mo from the bulk digestion of CAGS-BS and of crustal igneous rocks. No more Mo was lost, nor did Mo isotope fractionation, if the double spike was added before rather than after ashing and followed by bulk digestion or leaching with 9 M HCl. For efficiency, leaching using 4 M or more concentrated HCl after ashing is preferred for Mo isotope measurements.
Copper Isotope Fractionation during Basalt Leaching at 25℃ and pH=0.3, 2
Dandan Li, Sheng-Ao Liu
2022, 33(1): 82-91. doi: 10.1007/s12583-021-1499-7
The geochemical cycling of copper in the hydrosphere and soil environments primarily involves the transport of Cu from rocks to rivers via weathering. Understanding the factors controlling Cu isotope fractionation during weathering is crucial for the purpose of using Cu isotopes as a tracer of geochemical cycling. Here, we performed acid-leaching experiments on natural basalts (BHVO-2 and GBW07105) and chalcopyrite in Erlenmeyer flasks at T=25 ℃ and different pH values (0.3 and 2). Our results reveal substantial Cu isotope fractionations (Δ65Cusolution-initial) between leachates (Cusolution) and starting materials (Cuinitial). The leachates released from GBW07105 and chalcopyrite are consistently enriched in heavier Cu isotopes relative to the starting materials at pH=2. However, the δ65Cusolution values decrease to about -0.6‰ first, then increase to >0 for BHVO-2 at pH=2 and GBW07105 at pH=0.3. Our results indicate that leaching of natural rocks by acidic liquids can produce both positive and negative Cu isotope fractionation, depending on pH values and the types of minerals in starting materials. X-ray power diffraction analysis (XRD) patterns reveal similar mineral assemblages between starting basalts and residues after each reaction round. The most likely mechanisms responsible for such Cu isotope fractionation are the relative rates of Cu oxidation at the surface and Cu release into solution, and the sequence of mineral dissolution. Our study represents an important step for future studies to use Cu isotopes to explain Cu isotopic variations in natural rocks and waters.
Cu and Zn Isotopic Evidence for the Magnitude of Organic Burial in the Mesoproterozoic Ocean
Yiwen Lü, Sheng-Ao Liu
2022, 33(1): 92-99. doi: 10.1007/s12583-021-1561-5
The rate of net primary production in the Proterozoic ocean was suggested to be no more than 10% of its modern value (Laakso and Schrag, 2019), however, in the Mesoproterozoic Xiamaling Formation, the export production values could reach 20%-150% of the present-day Equatorial Atlantic average values (Zhang et al., 2016). Here, we report Zn and Cu isotope data for black shales from the Xiamaling Formation to illustrate the biogeochemical cycling of Zn and Cu in the Mesoproterozoic ocean. The 65Cu-enriched signature in the authigenic fraction is similar to that in bioauthigenic Cu of the modern marine sediments. The Zn isotope ratios of sediments deposited in euxinic conditions are commonly higher than those of clastic sediments, indicating light Zn sinks in the coeval ocean. Combined with previously reported Mo isotope data, the proportion of organic carbon to total carbon burial in the Mesoproterozoic was about as half as that at present, which is larger than the previous estimation-a quarter of today's value (e.g., Ozaki et al., 2019) and is evidenced by a wide distribution of black shales. The organic burial may be ascribed to the increasing phosphorus inputs from large igneous provinces and consequently high primary productivity, which has spurred the hypothesized atmosphere-ocean oxygenation at ~1.4 Ga.
A Preliminary Study on Silver Isotopic Composition in Polymetallic Ore Deposits in Eastern China
Ge Dong, Hai-Zhen Wei, Yuanfeng Zhu, Xi Liu, Qi Guo, Wei Pu, Yibo Lin, Junlin Wang
2022, 33(1): 100-108. doi: 10.1007/s12583-021-1490-3
A preliminary survey of silver isotopic composition in four polymetallic ores in eastern China shows a larger variation in δ109Ag from -0.014‰ to +0.983‰, which is within the total ranges for the entire respective ore deposit types worldwide. The diversity of silver isotopic compositions in ore-deposits reported here and previous studies seemed to preclude simple isotopic links to particular sources, but reflected the silver isotope fractionation in transport- and deposit-related processes instead. The δ109Ag values in supergene samples from the Qixiashan Pb-Zn-Ag polymetallic deposit are more positive, in consistent with the statistical δ109Ag distribution from -0.4‰ to +2.2‰ in 36 pieces of supergene ore samples around the World, which reflects the diverse controls on silver isotope fractionation from the first-order thermodynamic effect, reduction-mediated reaction, remobilization of silver with surficial low-temperature weathering processes. The hypogene samples in Dazhuangzi orogenic Au-Ag ore deposit, have δ109Ag values close to 0, which implies that equilibrium partitioning associated with metal sources at the high-temperature does not result in a resolvable difference in silver isotopic compositions. By contrast, the hypogene samples which are dominated by pyrite without visible silver minerals (i.e., skarn iron ore deposit in Edongnan) have shown the largest variation range of δ109Ag, followed by that from the porphyry copper ore in Zijinshan. It could be concluded that the surface adsorption and/or lattice substitution are important factors to control Ag isotope fractionation in ore-forming processes, especially for skarn deposits with only pyrite. The perspective of silver isotope shows great potentials to understand the processes that lead to the concentrations of metals to economic levels and to constrain the physicochemical conditions during ore-mineralization in metallic ore-deposits.
Crustal Contaminations Responsible for the Petrogenesis of Basalts from the Emeishan Large Igneous Province, NW China: New Evidence from Ba Isotopes
Dong Yi, Jing Zhao, Chunhui Li, Xiuhong Peng
2022, 33(1): 109-120. doi: 10.1007/s12583-021-1513-0
Emeishan large igneous province (ELIP), one of the largest continental volcanic provinces worldwide (e.g., Karoo), is extensively distributed along the western margin of the Yangtze Block. Even though the consensus that the ELIP is of a plume-related origin has been reached for decades, the role of crustal contamination in the petrogenesis of these basalts is still debatable so far. This paper firstly reports the Ba isotopic compositions of the continental flood basalts from the Lijiang, Miyi and Emeishan regions to discuss the genesis of basalts from the ELIP. According to their TiO2 contents and Ti/Y ratios, these basalts are divided into two groups, the low-Ti basalts from Lijiang and the high-Ti basalts from Miyi and Emeishan. The Ba isotopic compositions show that the low-Ti basalts have the δ138/134Ba values from -0.33‰ to +0.23‰ with an average of -0.02‰±0.40‰, and the high-Ti basalts from -0.38‰ to +0.38‰ with an average of 0.038‰±0.36‰, all of which show a wider range of Ba isotopes relative to that of the primitive mantle (PM). This is unlikely to be explained by partial melting, fractional crystallization or even chemical weathering owing to little Ba isotopic fractionation during these processes. In contrast, variable extents of crustal contamination into the basaltic magmas more likely resulted in such isotopic diversity. The ratios of incompatible elements (e.g., Nb/U, La/Nb, and Nb/Y) further suggest that the low-Ti basalts experienced higher degrees of crustal contaminations than those high-Ti basalts, which is well consistent with their spatial distributions. In general, the basaltic magmas in the ELIP were probably contaminated by different degrees of crustal materials during their upwelling to the surface.
Carbonated Big Mantle Wedge Extending to the NE Edge of the Stagnant Pacific Slab: Constraints from Late Mesozoic-Cenozoic Basalts from Far Eastern Russia
Ronghua Cai, Shan Xu, Dmitri A. Ionov, Jian Huang, Sheng-Ao Liu, Shuguang Li, Jingao Liu
2022, 33(1): 121-132. doi: 10.1007/s12583-021-1516-x
It has been suggested that the carbonated mantle reflected by Mg-Zn isotopic anomalies of Cenozoic intraplate basalts from East Asia coincides with the stagnant West Pacific slab in the mantle transition zone. However, the northern boundary of such carbonated domain beneath East Asia is uncertain. Late Mesozoic-Cenozoic intraplate basalts are widespread in far eastern Russia and thus provide an opportunity to examine this issue. Here we report major-trace element contents and Sr-Nd-Mg-Zn isotopic compositions for 9 Late Mesozoic-Cenozoic basaltic samples from the Khanka Block and Sikhote-Alin accretionary complex. They are characterized by large variations in SiO2 contents (41 wt.% to 50 wt.%) and CaO/Al2O3(0.50 to 0.97), enrichments of large-ion lithophile elements (LILE), positive Nb-Ta anomalies and strongly negative K, Pb, Zr, Hf, Ti, Y anomalies in primitive mantle-normalized trace element spider diagram. Furthermore, the rocks show good correlations of Ti/Ti* with Hf/Hf*, La/Yb, Fe/Mn and trace element contents (e.g., Nb). In addition, they have lighter Mg and heavier Zn isotope compositions than the BSE estimates, coupled with depleted Sr-Nd isotope compositions. These elemental and isotopic characteristics cannot be explained by alteration, magma differentiation or diffusion, but are consistent with the partial melting of carbonated peridotite. By and large, the Late Mesozoic-Cenozoic basalts from far eastern Russia bear very similar geochemical characteristics as those Na-series Cenozoic basalts from eastern China. The extended region of Mg-Zn isotopic anomalies is roughly coincident with the stagnant West Pacific slab beneath East Asia, and all of these alkali basalts can be generated from mantle sources hybridized by recycled Mg-carbonates from the Pacific slab stagnant in the mantle transition zone. We infer that (1) the carbonated big mantle wedge extends to the NE edge of the West Pacific slab and may have also appeared in the Late Mesozoic due to the effect of the Paleo-Pacific slab beneath this region, and (2) decarbonation of stagnant slabs in the mantle transition zone is a key mechanism for carbon outgassing from deep mantle to surface via intraplate alkali melts.
Mantle Source Components and Magmatic Evolution for the Comei Large Igneous Province: Evidence from the Early Cretaceous Niangzhong Mafic Magmatism in Tethyan Himalaya
Yaying Wang, Lingsen Zeng, Kejun Hou, Li'e Gao, Qian Wang, Linghao Zhao, Jiahao Gao, Guangxu Li
2022, 33(1): 133-149. doi: 10.1007/s12583-021-1464-5
The Niangzhong diabase dikes, dated at 138.1±0.4 Ma, are located within the outcrop area of the Comei large igneous province (LIP). These diabase samples can be divided into two groups: samples in Group 1 show varying MgO (1.50 wt.%-10.25 wt.%) and TiO2(0.85 wt.%-4.63 wt.%) contents, and enriched initial isotope compositions (87Sr/86Sr(t)=0.705 6-0.711 2, εNd(t)=-0.3- +3.8), with OIB-like REEs and trace elements patterns, resulting from low degree melting of garnet-bearing lherzolite mantle sources; in contrast, samples in Group 2 show limited MgO (4.14 wt.%-7.75 wt.%) and TiO2(0.98 wt.%-1.69 wt.%) contents, and depleted initial isotope compositions (87Sr/86Sr(t)=0.707 5-0.711 2, εNd(t)=+5.5- +6.2), with N-MORB-like REEs and trace elements patterns, resulting from relatively high degree melting of spinel-bearing lherzolite mantle source. Combined with the published representative data about Comei LIP, we summarize that the source components for Comei LIP products include OIB end-member, enriched OIB end-member, and N-MORB end-member, respectively. Melts modeling suggests that magmas in the Comei LIP evolve in a relatively high oxygen fugacity condition, which influenced their fractionation sequences and led to systematic changes of TiO2 contents, Ti/Y and Ti/Ti* ratios. From the spatial and temporal distribution of above three end-member samples, deep process of Kerguelen plume during the Comei LIP formation can be interpreted as the interaction among the Kerguelen plume, the overlying lithospheric mantle, and the upwelling asthenosphere. The magmatism of Comei LIP began at ~140 Ma and then lasted and peaked at ~132 Ma with the progressively lithospheric thinning of eastern Gondwana upon the impact of Kerguelen plume.
Geochronology and Geochemistry of Late Devonian I- and A-Type Granites from the Xing'an Block, NE China: Implications for Slab Break-off during Subduction of the Hegenshan-Heihe Ocean
Zheng Ji, Wenchun Ge, Hao Yang, Yanlong Zhang, Yu Dong, Junhui Bi, Xiwen Liu
2022, 33(1): 150-160. doi: 10.1007/s12583-021-1497-9
We present detailed geochronological, geochemical, and zircon Hf isotopic data for Late Paleozoic granitic rocks from Handagai and Zhonghe plutons in the Xing'an Block, NE China, aiming to provide constraints on their origin and tectonic implications. New zircon U-Pb ages indicate they were formed in the Late Devonian (ca. 379 Ma) immediately after a striking 50 Ma magmatic lull (ca. 430-380 Ma) in the Xing'an Block. Petrological and geochemical features suggest that the Handagai monzogranites and Zhonghe alkali-feldspar granites are I- and A-type granites, respectively, although both of them have high-K calc-alkaline features and positive zircon εHf(t) values (+3.47 to +10.77). We infer that the Handagai monzogranites were produced by partial melting of juvenile basaltic crustal materials under a pressure of < 8-10 kbar, whereas the Zhonghe alkali-feldspar granites were generated by partial melting of juvenile felsic crustal materials at shallower depths (P ≤ 4 kbar). Our results, together with published regional data, indicate their generation involves a subduction-related extensional setting. Slab break-off of the Hegenshan-Heihe oceanic plate may account for the subduction-related extensional setting, as well as the transformation of arc magmatism from the Early-Middle Devonian lull to the Late Devonian-Early Carboniferous flare-up in the Xing'an Block.
Magma Generation of Magnetite-Rich Intermediate-Mafic Rocks and Its Mantle Processes in the Southwestern Alxa Block, NW China
Lu Tao, Hongfei Zhang, Jing Wu, Xiaochun Zhou, Liqi Zhang
2022, 33(1): 161-176. doi: 10.1007/s12583-021-1539-3
Many studies focus on mineralization of huge magnetite ore deposits and petrogenesis of their large-volume host rocks. However, magma generation of those small-scale intrusions with enrichment of magnetite is poorly reported and paid attention to. We here carry out an integrated study of magnetite chemistry, U-Pb zircon dating, geochemistry, and Sr-Nd-Hf isotopes for the magnetite-rich intermediate-mafic rocks from the Helishan pluton in the southwestern Alxa Block, Northwest China. This, together with several previously reported magnetite/iron-rich intrusions nearby, is capable of providing some constraints on magma generation of magnetite/iron-rich intrusive rocks. The Helishan pluton, dated at ca. 290 Ma, consists of hornblende gabbro, diorite, and quartz monzodiorite with ~3%-5% magnetite in all the lithologies. Study on magnetite chemistry manifests a magmatic origin for them. All the lithologies display high TFeO/MgO ratio (1.71-1.89), weakly fractionated REE patterns ((La/Yb)N=1.82-10.17), enrichment of Rb, Sr, and Pb, and depletion of high field strength elements. They have (87Sr/86Sr)i values of 0.705 2 to 0.705 8, εNd(t) values of +0.03 to +0.64, and zircon εHf(t) values of +6.5 to +12.0. We propose that they were derived from partial melting of iron-rich metasomatized lithospheric mantle. The systematic variations of Sr/Y ratios and Nd-Hf isotopic compositions with time for the Paleozoic igneous rocks at the southwestern Alxa Block indicate ever existence of thinning and rebirth of lithospheric mantle. This geodynamic process could be the potential mechanism to give rise to the iron-rich signature of the reborn mantle sources of the Helishan pluton. For intermediate-mafic intrusions at subduction zones, they are unlikely to form considerable magnetite ore deposits since their modest magmatic flux and early fractional crystallization of magnetite at a high oxygen fugacity and H2O condition.
Geology, Mineralogy, and Isotopic Characteristics of the Zhonghe Ag-Pb-Zn Deposit, Western Henan Province, Central China
Jiannan Xu, Changqian Ma, Shuo Yin, Yunzhen Chang, Huimin Jia, Zhongjie Wang, Liangliang Shi
2022, 33(1): 177-192. doi: 10.1007/s12583-021-1544-6
Located in Luoning County, western Henan Province, Central China, the Zhonghe Ag-Pb-Zn ore field, is a newly discovered deposit in the Xiaoshan District. Ore bodies controlled by NNW Faults occur as veins within the Paleoproterozoic Xiong'er Group or the Early Cretaceous porphyritic granite. Given that the Zhonghe deposit has been covered by thick Quaternary sediments, the paragenetic mineral assemblage was determined mainly by microscopic observations, including the quartz-siderite-pyrite alteration (Stage Ⅰ), polymetallic sulfide precipitation (Stage Ⅱ), silver mineralization (Stage Ⅲ), and quartz-carbonate stage (Stage Ⅳ). The host minerals for silver are diverse, such as freibergite, pyrargyrite, polybasite, argyrodite, canfieldite, argentite, and native silver, whereas those for Pb and Zn are galena and sphalerite, respectively. In order to constrain the ore-forming components of the Zhonghe deposit, a combined in-situ analysis was conducted on represented sulfides from Stage Ⅱ and Stage Ⅲ. In-situ δ34S values of the analyzed sulfides, including the pyrite, chalcopyrite, sphalerite, and galena, display a relatively narrow range (0.90‰-5.0‰), which is close to magmatic sulfur source. The 206Pb/204Pb and 207Pb/204Pb ratios show a narrow range (17.140-17.360 and 15.385-15.490), whereas the 208Pb/204Pb ratios exhibit a broad variation (36.601-37.943), indicating a contamination of the Xiong'er Group. Synthesis of geochronological and geochemical data from the Xiaoshan District, we contend that the ore-forming materials of the Zhonghe Ag-Pb-Zn deposit are originated from the lower crust, which has presumably been influenced by the large-scale lithospheric delamination of the eastern North China Craton during the Early Cretaceous. In consideration of the geological setting, mineralogy, and geochemical compositions, we suggest that the Zhonghe Ag-Pb-Zn deposit is characterized as intermediate sulfidation type epithermal deposit, and may be a potential exploration target for porphyry Mo-Cu deposits.
Multiple-Stage Mineralization in the Huayangchuan U-REE-Mo-Cu-Fe Ore Belt of the Qinling Orogen, Central China: Geological and Re-Os Geochronological Constraints
Hongjun Jiang, Chunsi Yang, Dequan Wang, Hui Zheng, Jie Li, Huayong Chen
2022, 33(1): 193-204. doi: 10.1007/s12583-021-1557-1
The Huayangchuan ore belt is located in the western segment of Xiaoqinling Orogen in the southern margin of the North China Craton (NCC), and hosts voluminous magmatism and significant U-REE-Mo-Cu-Fe polymetallic mineralization. However, geochronological framework of the various mineralization phases in this region is poorly understood. Here, we present new Re-Os isochron ages on magnetite from the Caotan Fe deposit (2 675±410 Ma, MSWD=0.55), and on pyrite from the Jialu REE deposit (2 127±280 Ma, MSWD=1.9) and Yuejiawa Cu deposit (418±23 Ma, MSWD=11.5), and Re-Os weighted average model age on pyrite from the Taoyuan Mo-U deposit (235±14 Ma, MSWD=0.17). These ages, combined with regional geology and mineralization ages from other deposits, suggest that mineralization in the Huayangchuan ore belt lasted from the Neoarchean to the Late Mesozoic. The mineralization corresponds to regional tectono-magmatic events, including the Neoarchean alkali magmatism (REE mineralization), Paleoproterozoic plagioclase-amphibolite emplacement (Fe mineralization), Paleoproterozoic pegmatite magmatism (U mineralization), Paleozoic Shangdan oceanic slab subduction-related arc magmatism (Cu mineralization), Early Mesozoic Paleo-Tethys Ocean subduction-related arc magmatism (Mo-U mineralization), and Late Mesozoic Paleo-Pacific oceanic plate subduction direction change-related Mo(-Pb) mineralization. We proposed that the Huayangchuan ore belt has undergone prolonged metallogenic evolution, and the magmatism and associated mineralization were controlled by regional geodynamic events.
Detrital-Zircon Evidence for the Origin of the Late Quaternary Loess in Qingzhou, Shandong Province and Its Implications for the Evolution of the Yellow River
Yanfei Shen, Meiyan Liang, Jianxun Wu, Shuzhen Peng, Guoqiao Xiao
2022, 33(1): 205-214. doi: 10.1007/s12583-021-1489-9
The loess depositions in Shandong Province are important parts of loess records in eastern China, but their origin and genetic linkage between the Yellow River and the Chinese Loess Plateau are still unclear. This paper presents the detrital-zircon evidence for the origin and provenance evolution of the Qingzhou loess in Shandong Province. The results show that: (1) the Qingzhou loess was sourced from the sandy lands within the North China Plain that were fed by the silty materials from the Chinese Loess Plateau, the mountainous region in central Shandong Province, and the Yanshan and Taihang Mountains; (2) the Qingzhou loess was mainly sourced from the loess materials transported by the Yellow River, and the basal age of the Qingzhou loess indicates the timing of intensified aridification of the North China Plain and integration of the Yellow River was not later than 0.5 Ma; and (3) the provenance and grain-size of the Qingzhou loess underwent a significant transition at ~0.22 Ma, which was related to the expansion of the sandy land within the North China Plain. Our results indicate that the origin of the loess on the North China Plain are obviously different from the loess on the Chinese Loess Plateau, and the increase of grain-size and accumulation rate in the loess records on the North China Plain at ~0.22 Ma was due to the environmental deterioration of the eastern China.
Origin, Distribution and Geochemical Significance of Isopropyltoluene Isomers in Crude Oil
Bingkun Meng, Daofu Song, Yuan Chen, Shengbao Shi, Shixin Zhou
2022, 33(1): 215-228. doi: 10.1007/s12583-020-1348-0
With comprehensive two-dimensional gas chromatography linked to time-of-flight mass spectrometry (GC×GC-TOFMS), ten light hydrocarbon (LH) compounds were qualitatively and quantitatively studied in light hydrocarbons (LHs) components of crude oils. For significant differences in the concentrations of 3-isoproyltoluene (3-iPT), 4-isoproyltoluene (4-iPT) and 2-isoproyltoluene (2-iPT) in crude oils, and the 2-iPT probably derived mainly from similar skeleton monocyclic terpenoids via dehydrogenation and aromatization, the ratios of (3+4)-/2-iPT (iPTr), 3-/2-iPT (iPTr1) and 4-/2-iPT (iPTr2) are proposed to distinguish the organic matter origin of crude oils. Relatively higher iPTr (> 8.0), iPTr1 (> 7.0) and iPTr2 (> 4.0) values indicate that crude oils are sourced from the co-contribution of lower aquatic organisms, bacteria, algae, and terrestrial higher plants, whereas lower iPTr (< 5.0), iPTr1 (< 3.0), iPTr2 (< 2.0) values suggest that crude oils originated from terrestrial higher plants. The iPTr, iPTr1, and iPTr2 values show notable distinction which is mainly controlled by 2-iPT concentrations, while the concentrations of 3-iPT and 4-iPT have similar distribution range in all studied oils. The 2-iPT depleted in marine oils from the Tarim Basin and lacustrine oils from the Beibuwan Basin is less than 0.30 mg/g LHs, whereas 2-iPT enriched in swamp oils from the Tarim Basin is greater than 0.50 mg/g LHs. The iPTr, iPTr1, and iPTr2 ratios and 2-iPT concentrations can be used to distinguish the organic matter origin of crude oils, especially for light oils and condensates with low concentrations of biomarkers.