Table of Content

20 April 2022, Volume 28 Issue 2

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LA-ICP-MS Zircon U-Pb Dating and Hf Isotopic Composition of Dacite in Hezhou, Northeastern Guangxi

WANG Yongqiang, SHI Yu, LI Xiang, LIU Xijun, TANG Yuanlan, SUN Yirong

2022, 28(2):  141-152.  DOI: 10.16108/j.issn1006-7493.2021027

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The study area is located at the junction of Hunan and Guangxi in the western part of Nanling metallogenic belt, where Mesozoic magmatic activity is frequent and the diagenesis and mineralization are remarkable, especially during Yanshanian. In order to determine the formation age of kongzimiao dacite in Kaishan Town, Hezhou, northeastern Guangxi, and to discuss its source property, LA-ICP-MS zircon U-Pb dating and Lu-Hf isotope are obtained. zircon U-Pb age of 157.1±0.9 Ma displayed the formation age of the dacite. Zircons grains have a wide range of isotopic composition (εHf(t) values rang from -5.68 to -0.97), with corresponding two-stage Hf isotope model age (TDM2) varying from 1.26~1.54 Ga, suggesting that the protolith was predominantly derived from the crystalline basement crust in Mesoproterozoic, and may be accompanied by a small amount of mantle-derived materials. Combined with the previous studies on the Yanshanian diagenesis and mineralization in South China, it is considered that the dacite in the study area and the early Yanshanian rocks and deposits in Northeast Guangxi are the products of the first large-scale magmatic activity in the Yanshanian in South China, and the formation of dacite may be related to the intraplate extension thinning of the Yanshanian lithosphere in South China.

Petrogenesis of Xinmengshan Dacite Porthyry in Changning, Hunan Province: Implications for Relationship of Magmatism and Mineralization

ZHAO Zengxia, FENG Zuohai, LIU Lei, XIAO Yang

2022, 28(2):  153-164.  DOI: 10.16108/j.issn1006-7493.2021029

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Based on detailed geological investigation, this paper investigated the whole-rock element geochemistry, zircon U-Pb dating and chlorite mineral chemistry of Xinmegnshan dacite porphyry in Changning City, Hunan Province. With reference to previous research, we discussed petrochemical characteristics, magmatic age, magma sources, as well as relationship with mineralization in Shuikoushan orefield. LA-ICP-MS zircon U-Pb isotopic analyses showed that Xinmegnshan dacite porphyry erupted during the Late Jurassic, with a weighted mean 206Pb/238U age of 152.9±1.2 Ma (MSWD=0.27, 2σ, N=17). Xinmegnshan dacite porphyry was rich in Light Rare Earth Elements (LREEs) and Rb, Th, U, La, Pb, Nd, Zr, Hf, while depleted in Heavy Rare Earth Elements (HREEs) and Nb, Ta, Ba, Sr, P, showing crust-derived affinities, and might be contaminated by mantle material. Chlorite was mainly clinochlore with alteration temperature of 280℃ , which was similar to that of the Cu-Mo mineralization in this orefield. During Late Jurassic, the tectonic extension and thinning of the continental lithosphere in the study area induced partial melting of the crust, and produced granitic magma, which might mix with a small amount of mantle material. The magma then invaded along deep faults and formed Xinmegnshan dacite porphyry. At the late stage of magma crystallization, as Cu-Mo precipitation, the hydrothermal fluid replaced the dacite porphyry continuously and resulted in widespread chloritization.

Petrogenesis and Significance of the Guiling Pluton and Its Mafic Microgranular Enclaves

YANG Jinbao, FENG Zuohai, KANG Zhiqiang, BAI Yanping, WU Jie, ZHANG Chenglong, FENG Meng

2022, 28(2):  165-176.  DOI: 10.16108/j.issn1006-7493.2021028

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This paper reports petrological and geochemical studies of the Guiling pluton and its mafic microgranular enclaves (MMEs) and discusses the early Paleozoic crust-mantle interaction and tectonic setting in the western Nanling Mountains. The results show that the Guiling pluton is mainly composed of the biotite monzonitic granite, with silica content of 70.24%- 75.13% and total alkali content of 7.95%-8.44%. Chondrite-normalised rare-earth element (REE) of the granite shows light REE enrichment (with (La/Yb)_N=5.0-8.4) and significant negative europium anomalies (with δEu=0.37-0.58). The A/CNK index of the granite shows metaluminous-weak peraluminous characteristics. K₂O content, (⁸⁷Sr/⁸⁶Sr)i values and high Rb/Sr values indicate that it is highly fractionated S-type granite of high potassium calc-alkaline series. The MMEs have lower SiO₂ content (48.38%- 51.95%) and higher contents of Mg and Fe oxides than the host granite, with Mg# values of 59-67 and total alkali content of 3.81%-5.05%, indicating that they are gabbro and gabbroic diorite of medium potassium calc-alkaline series. The light and heavy REEs of the MMEs have significant fractionation (with (La/Yb)_N=11.74-12.12) and only slight negative europium anomalies (with δEu=0.92-0.94). On the characteristics of Sr-Nd isotopic composition, the host granite has lower εNd(t) values (-13.6--5.0) than the MMEs (3.4-3.6), and the crustal model age (1.6-2.3 Ga) of the granite is older than that (0.88-0.89 Ga) of the MMEs which show slight variation (0.706-0.708) of (87Sr/86Sr)i values. The geochemical obtained data in this study suggest that the MMEs were derived from mafic material that was likely associated with the Neoproterozoic lithospheric mantle underplating. Highly partial melting of the material caused by post-collisional extension during the Early Paleozoic time generated mafic magmas. Ascent and emplacement of the mafic magmas triggered partial melting of the Mesoproterozoic metagreywacke at the middle and lower crust levels, producing voluminous granitic magmas that were emplaced to form the Guiling pluton. During ascent and emplacement of the granitic magmas, the mafic magmas were intensively mingled and moderately chemically mixed with the host granitic magmas forming MMEs throughout the pluton.

Geochronology, Geochemistry and Tectonic Significance of Metamorphic Intermediate-Basic Igneous Rocks in Nuodong-Anping Area, Southeastern Guangxi

PANG Chaowei, SHI Yu, TANG Yuanlan, LIANG Renxin, LIU Xijun

2022, 28(2):  177-198.  DOI: 10.16108/j.issn1006-7493.2021120

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Zircon U-Pb dating and geochemical data are reported for actinolitization amphibolites (metamorphic basic rocks) and intermediate-basic volcanic breccias of Nuodong-Anping plutons, southeastern Guangxi. The data show that the formation age of the Nuodong pluton is later than 123 Ma, and the Anping pluton record two important magmatic activities. One was in Yanshanian period (or later) with the youngest age of ~138 Ma, and the other was in Early Paleozoic (452-450 Ma). A large number of captured zircons ranging from Middle Archean-Paleoproterozoic (3076-1806 Ma), Mesoproterozoic-Neoproterozoic to Early Paleozoic in both plutons indicate the existence of the Middle Archean-Paleoproterozoic basement materials and the Mesoproterozoic, Neoproterozoic and Early Paleozoic magmatism. Geochemical data exhibit that the Nuodong pluton is characterized by a flat or slightly loss rare earth elements (REEs) distribution model, with relatively enriched in large-ion lithophile elements (LILEs) (Th, U and Pb) and depleted in high-field-strength elements (HFSEs) (Nb, Ta, Zr, Hf and Ti). The Anping pluton is also enriched in LILEs (Rb, Ba, Th, U and Pb) and depleted in HFSEs (Nb, Ta, P and Ti), but they show enrichment in light REEs and depletion in heavy REEs contents. The geochemical characteristics are similar to the Caledonian (metamorphic) basic rocks in the study area, indicating that the geochemical characteristics of rocks have limitations and multiple solutions in determining the tectonic setting.

Petrogenesis of the Jurassic Representative Volcanic Rocks in Eastern Guangdong: Response to the Early Stage of the Paleo-Pacific Subduction

YUE Xiaohan, LIU Lei, ZHANG Zhiguo, ZHAO Zengxia, SUN Jie, ZHAO Yang

2022, 28(2):  199-210.  DOI: 10.16108/j.issn1006-7493.2021022

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It is widely accepted that the widespread Cretaceous volcanic rocks in SE China were formed at the late stage of the paleo-Pacific subduction. On the contrary, the geological response of the early stage of the subduction remains unclear. This study focuses on the representative Jurassic volcanic sections in eastern Guangdong, which are the most widespread in SE China. Zircon U-Pb dating results reveal that the Jurassic volcanic rocks were formed intermittently at 192-183 Ma (Songling Fm.), 177- 163 Ma (Jilingwan Fm.) and 162-156 Ma (Gaojiping Gp.). Thus, a younging trend along eastern Guangdong to eastern Fujian to southeastern Zhejiang could be identified for the entire Late Mesozoic volcanic rocks in SE China. Zircon Lu-Hf isotopic analyses show that the Jurassic volcanic rocks were mainly derived by remelting of the Paleoproterozoic crustal basement, with decreasing involvement of juvenile components in their origin over time from Early to Late Jurassic. The petrogenesis of the Jurassic volcanic rocks in eastern Guangdong suggests decreasing crustal extension, corresponding to the forward subduction of the paleo-Pacific slab. Thus, the Jurassic volcanic rocks in eastern Guangdong record the early stage of the paleo-Pacific subduction, and further suggest that the subduction started at around Early Jurassic.

The Deformation Age of Sanjiang Fault Zone and Discovery of Pan-African Tectonic Thermal Events in Adjacent Areas of Hunan and Guangxi

QIN Ya, FENG Zuohai, XING Quanli, WU Jie, XUE Yunfeng

2022, 28(2):  211-224.  DOI: 10.16108/j.issn1006-7493.2021025

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The chronology of the Changjie altered olivine pyroxenite of Tongdao area of western of Hunan province in Sanjiang fault is researched in this paper to discuss the emplacement age of rock, the deformation time of the fault and the response to the Pan-African event. Changjie altered olivine pyroxenite intruded into the Hetong formation of Danzhou group, which suffered intense chloritization, serpentinization and tremolite alteration. Microscopically, the late chlorite veinlets cut through the early altered minerals, showing the characteristics of multi-stage alteration and suggesting that they were affected by at least two tectonic thermal events after diagenesis. Zircon U-Pb dating results are concentrated at 441.0±11.0 Ma、546.5±8.5 Ma、774.3±3.9 Ma and 820-1000 Ma. 774.3±3.9 Ma is the youngest magmatic zircon age, which represents the formation age of the Changjie altered olivine pyroxenite. 820-1000 Ma is the age of captured zircons during magmatic emplacement. The hydrothermal zircon age of 441.0±11.0 Ma is consistent with the formation age of the regional NNE trending fault, which represents the active age of the Sanjiang fault. The age of 546.5±8.5 Ma is also hydrothermal zircon age, which is consistent with the age of Pan-African tectonothermal event, indicating that the research area was influenced by Pan-African tectonic thermal event.

LA-ICP-MS Zircon U-Pb Dating, Geochemical Characteristics and Tectonic Significance of Jundong Granites in Northeastern Guangxi

GAO Aiyang, SHI Yu, LIU Xijun, ZHAO Zengxia, LIU Minghui, HUANG Chunwen,

2022, 28(2):  225-239.  DOI: 10.16108/j.issn1006-7493.2021021

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The Jundong granitic pluton is located in the southwest of the Qin-Hang belt, with the rock combination of dioritetonalite-granodiorite. In this study, we present LA-ICP-MS zircon U-Pb ages of granitic rocks from the Jundong pluton, the crystallization age of the Jundong rock body is 423-430 Ma, belonging to the Caledonian period. The rocks have lower SiO₂ contents of 55.47-62.95 wt%. One of the samples belongs to the shoshonite series and the others are high-K calc-alkaline series. The A/CNK values are 0.70-1.18, showing as quasi-aluminous or peraluminous rocks. The rocks are enriched in large ion lithophile elements (LILE, e.g., Rb, Ba, Th and U) and relatively depleted in high field strength elements (HFSE, e.g., Nb, Ta, Sr, P and Ti) relative to primitive mantle. The Jundong granitic pluton are mixing products of different original rock sources and formed in the intracontinental collisional orogenic tectonic environment.


Chronological Records of Sedimentary Transformation between Danzhou Period and Nanhua Glacial Period in Northern Guangxi

WANG Baohua, QIN Ya, FENG Zuohai, HUANG Jingang, WU Jie, WAN Lei, XING Quanli, XUE Yunfeng

2022, 28(2):  240-261.  DOI: 10.16108/j.issn1006-7493.2021026

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U-Pb dating and Hf isotope analysis of detrital zircons from Hetong formation and Gongdong formation of Danzhou group and Chang’ an formation of Nanhuan system were carried out by LA-ICP-MS to reveal the chronological records of sedimentary transformation between Danzhou period and Nanhuan glacial period in northern Guangxi. The analytical results show that the Hetong formation and Gongdong formation of Danzhou group have similar detrital zircon age pedigrees, and the U-Pb ages are concentrated in 720-1000 Ma, 1700-2300 Ma and 2400-2700 Ma. The detrital zircon ages of Chang’ an formation of Nanhuan system are concentrated in 650-720 Ma and 720-1000 Ma, which are obviously different from Danzhou group. Hetong formation and Gongdong formation of Danzhou group have similar Hf isotopic characteristics, with negative εHf(t) and the TDM2 values of most zircons are greater than 2400 Ma. However, the zircon Hf isotopic characteristics of Chang’ an formation of Nanhua system are different from Danzhou group, with mainly positive εHf(t) values and TDM2 values concentrated in 1000-1300 Ma and 1400-2200 Ma. The differences of U-Pb age spectrum and Hf isotope of detrital zircon, combined with the difference of zircon CL image and provenance, show that there is obvious sedimentary transformation between Nanhua system and Danzhou sedimentary strata.

Study on Geochemical Characteristics of Mid-Low Temperature Geothermal Fluid in Representative Area of Subei Basin

ZOU Pengfei, QIU Yang, FAN Difu

2022, 28(2):  262-273.  DOI: 10.16108/j.issn1006-7493.2020099

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The Subei Basin was enriched with medium-low temperature geothermal resources. This paper selected one representative area of the Subei Basin where one proven middle-temperature geothermal well and a hot-dry-rock verification hole were found as the study area. We employed the geochemical information carried by the geothermal fluid to have knowledge of the basic characteristics of deep geothermal reservoirs and the formation of geothermal resources at different depths. Results showed that the dominant cation in the geothermal fluid in the study area was Na+, however, the anion was of composite ion type, mainly Cl-. There was a good positive correlation beween Na+, TDS and Cl-. The calculation results of geothermal reservoir temperature were 73.8-145.1℃ estimated by the cations and silica geothermometer. In addition, the deep circulation depth of geothermal fluids in the Huangdang geothermal field was estimated to be 2.1 km. Through quantitative calculation, the elevation of recharge area for the geothermal fluids has been estimated from 203.5 m to 418.5 m. The 14C age of the geothermal fluid corrected by Bayesian algorithm showed an increasing trend from west to east, which was related to the direction of runoff of the geothermal fluid. The recharge area might be located in Zhangbaling Hilly area along the Xuyi Laozi Mountain, Mingguang city as well as Chuzhou city on the southwest side of the study area. The hydrogen and oxygen isotopic composition of the atmospheric precipitation in the recharge area was relatively consistent with that of the geothermal fluids, which further demonstrated the rationality of the inference of recharge elevation. According to the circulation depth of geothermal fluids, circulation period（or revised age of the Huangdang geothermal field）, recharge elevation, geothermal reservior temperature, and logging results, the mineralization model of the Huangdang geothermal field in Baoying county was established for the first time.

Analysis and Implication of the Geological Big Data Management in Developed Countries: Take USA, UK, Australia and Canada as Example

LIU Wei

2022, 28(2):  274-286.  DOI: 10.16108/j.issn1006-7493.2020103

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The scientific data is an important national strategic resource, and data sharing is one of the means of effective exploitation and utilization on this resource. It is also an important basis for the transformation of current scientific research paradigm to data intensive. With the deep integration of modern information technology and exploration methods, geological exploration and geoscience research are being pushed into the era of Big Data, and it is urgent to conduct scientific management from the macro level. The developed countries in Europe and the United States have promoted the effective implementation of their own geological big data management by issuing policies and laying data infrastructure. In this paper, it investigates the data management work of the Geological Survey in the United States, Britain, Australia and Canada, and introduces and analyzes the status quo of the data management scope which including data policies, strategic plans, important databases and main data tools. Some Suggestions on data management in geological survey industry in China are put forward as follows: (1) Data management policy should adopt top-down design and implement bottom-up. (2) Open sharing and integrated communication of data is the development trend of global data research institutions in the future. (3) We will vigorously promote the construction of GeoCloud, and implement big data governance in the trinity of big data, artificial intelligence and cloud computing. (4) The construction of data sharing infrastructure should be promoted, and more discourse power should be gained through participating in inter- national governance.