Zircon U-Pb age and Hf isotopic characteristics of the Huangtuliang monzonitic granite, North Hebei Province, China

HU Huabin, NIU Shuyin, ZHANG Zhanyang, TIAN Ye, LIU Xiaoyu, CHEN Xicai, and CHEN Haijiao

1College of Resources, Shijiazhuang University of Economics, Shijiazhuang 050031, China

2Congli Zhijin Mining Industry Limited Liability Co., Hebei, Congli 076350, China

*Corresponding author, E-mail: huhb27@163.com

Zircon U-Pb age and Hf isotopic characteristics of the Huangtuliang monzonitic granite, North Hebei Province, China

HU Huabin1*, NIU Shuyin1, ZHANG Zhanyang2, TIAN Ye1, LIU Xiaoyu1, CHEN Xicai1, and CHEN Haijiao1

1College of Resources, Shijiazhuang University of Economics, Shijiazhuang 050031, China

2Congli Zhijin Mining Industry Limited Liability Co., Hebei, Congli 076350, China

*Corresponding author, E-mail: huhb27@163.com

Chin.J.Geochem.(2014)33:001-008

The Huangtuliang monzonitic granite outcrops on the northern side of the Huangtuliang gold mining district, Chicheng, North Hebei Province. Our predecessors only made isotopic age determination using the K-Ar method. Through LA-MC-ICP-MS zircon U-Pb dating and zircon Hf isotopic composition determination, this study acquired the age of 244.8±2.0 Ma (MSWD=0.57) on the basis of the weighed mean206Pb/238U ratio, indicating that the Huangtuliang monzonitic granite was formed during the Middle Triassic period, which is the product of Early Indosinian magmatic activities in the region of North Hebei. εHf(t) values vary relatively evenly, within the range of -10.65- -14.03, with an average of -12.14. The two-stage evolution model ages,tDM2, vary between 1943 and 2144 Ma, implying that the rock-forming materials of the Huangtiliang monzonitic granite mainly came from the Paleoproterozoic recirculated crustal materials, though a small quantity of enriched-mantle materials would have been involved.

Huangtuliang monzonitic granite; zircon U-Pb age; Hf isotope; Hebei landmass

The Huangtuliang gold deposit is located in the Zhaojiagou-Erbaozi ductile-brittle shear zone on the southern side of the Congli-Chicheng ductile-brittle shear zone and the orebodies are hosted in the eastern section of the Shuiquangou-Dananshan monzonite complex. In recent years important advances have been made in research on structurally controlled mineralization, metallogenic rules and ore-search orientation (Niu Shuyin et al., 2003; Fu Fangjian et al., 2006). Under the direction of the newly developed theory of metallogenesis an important breakthrough has been made in geological prospecting of this deposit (Niu Shuyin et al., 2008). However, deep-going research has not yet been conducted on the age and genesis of magmatic rocks in this mining district, for example, only a K-Ar age of 197.68±2.94 Ma has been reported for the monzonitic granite situated on the northern side of the mining district (Liu Haitian, 1999). Due to intense Paleozoic-Mesozoic magmatic activities in this region the K-Ar ages would be easily affected by thermal events after rock mass emplacement, and therefore, the reliability of ages is relatively poor. Through LA-MC-ICP-MS U-Pb dating and Hf isotopic composition determination of zircon, this study explored the formation age and genesis of the Huangtuliang monzonitic granite, as well as their geological significance.

1 Rockbody characteristics and brief sample introduction

The monzonitic granite outcrops on the northern side of the Chicheng-Huangtuliang gold mining district, North Hebei Province (Fig. 1). The southern part of the rockbody is in fault contact with the Devonian syenite and its northern part is in fault contact with the Jiangouhe Formation of the Congli Group. The sampling location is N40°56'32", E115°39'22". The rock-body is light flesh pink in color and exhibits granular texture and massive structure. The rocks are composed mainly of oligoclase, barbierite and quartz. The oligoclase is subhedral clintheriform-anhedral, with sericitization, muscovitization and kaolinization. Some crystals were contaminated by K-feldspar to form creep texture, with the content of about 40%. The barierite is mostly anhedral and irregular in crystal form but subordinately subhedral and clintheriform. It was metasomatized to form oligoclase with the content of 25%-30%. The quartz is euhdral and fills in the cracks, showing wavy extinction, with the content of 20%-25%. The accessory minerals include magnetite (1%), apatite (1%) and zircon (0.5%). Zircon grains sorted from the samples are mostly colorless or light yellowish-brown in color under transmission light and the grains are mostly long prismatic in form with the macro-axes varying between 150-200 μm and the ratios of major axis to minor axis varying between 1.5∶1-3∶1 (Fig. 2).

Fig. 1. Geological map of the Huangtuliang gold deposit. 1. Jurassic Xiahuayuan Formation; 2. Congli Group Jiangouhe Formation; 3. Paleoproterozoic porphyritic granite; 4. Triassic monzonitic granite; 5. Devonian syenite; 6.diorite-porphyrite; 7.fault; 8. gold orebody; 9. sampling site.

Fig. 2. Cathod luminescence (CL) images of the representative zircon crystals in the Huangtuliang monzonitic granite.

2 Analytical method

LA-MC-ICP-MS zircon U-Pb dating was accomplished at the Laboratory for Isotopic Research, Institute of Mineral Resources, Chinese Academy of Geological Sciences. The analytical instruments are the Finnigan Neptune-Type MC-ICP-MS and the assorted Newwave UP 213 Laser Denudation System. LA-MC-ICP-MS laser denudation sampling was conducted in the mode of single-point denudation. Before data analysis zircon GJ-1 was used for instrumental debugging. In zircon U-Pb dating zircon GJ-1 was used as the external standard and the U and Th contents were corrected by using zircon M127 (U 923×10-6, Th 439×10-6, Th/U 0.475) (Nasdala et al., 2008) as an external standard. In the process of isotopic measurement two zircon GJ-1 samples were repeatedly measured before and after 5 samples were analyzed to correct the measurement results of the samples. Meanwhile, one zircon Plesovice sample was measured. Under this circumstance the operation status of the instrument was carefully observed so as to guarantee the precision of the measurement. The ICPMADataCa 4.3 program was adopted for data processing (Liu Yongsheng et al., 2010). In the test process206Pb/204Pb＞1000 for the most majority of the analytical points, with no correction for common Pb.204Pb was tested by means of an ion counter. The analytical points with abnormally high contents of204Pb would have been affected by common Pb, for instance, from fluid inclusions, and those with abnormally high contents of204Pb should be rejected in calculation. Zircon age concordant plot was obtained using the Isoplot 3.0 program. The errors involved in the single points listed in the expression are all equal to 1σ, and the weighed mean ages have a 95% confidence coefficient. For the details of the experimental and test processes, please refer to Hou Kejun et al. (2009).

Zircon Hf isotopic measurement was conducted at the Laboratory for Metallogenesis and Resource Evaluation, Ministry of Land and Resources, Institute of Mineral Resources, Chinese Academy of Geological Sciences on the Neptune multi-reception LA-ICP-MS and Newwave UP 231 ultraviolet laser denudation system (LA-MC-ICP-MS). In the experimental process He was taken as denudation-material carrier gas. According to the size of zircon the denudation diameter was taken to be 55 or 40 μm. In the test process the international zircon standards GJ-1 and Plesovice were taken as the reference materials .The analytical points and those for U-Pb dating are located in the same site. For the operation conditions of the related instruments and the details of the analytical procedure, please refer to Hou Kejun et al. (2007). In the analytical process the weighed mean value of176Hf/177Hf was 0.282007±0.000007 (2σ,n=36), completely consistent with the values reported in the literature (Hou Kejun et al., 2007; Morel et al., 2006) within the limit of errors.

3 Results of zircon U-Pb dating and Hf isotopic composition

The U contents of the Huangtuliang monzonitic granite samples vary between 10.59×10-6-783.17× 10-6, their Th contents vary between 5.70×10-6-453.19 ×10-6, their Th/U ratios are 0.42-1.31 (Table 1), and their206Pb/238U apparent ages vary between 232.58 and 248.38 Ma. Twenty-one analysis points are concentrated on the concordant curve and its vicinities (Fig. 3) and the206Pb/238U weighed mean age is 244.8±2.0 Ma (MSWD=0.57), representing the intrusion age of the monzonitic granite.

Micro-areain-situanalysis of the Huangtuliang monzonitic granite sample HG-5 was made for zircon Hf isotopic composition, with a total of 18 points analyzed. The176Lu/177Hf ratios of the analyzed zircon vary over a small range, between 0.000233 and 0.000844; the176Hf/177Hf ratios of the sample vary over a relatively small range, between 0.282232 and 0.282320; the εHf(t) values also vary in a relatively small range, between -10.65 and -14.03, with an average of -12.14 and a standard deviation of 1.116; the two-stage evolution model ages (tDM2) vary between 1943 and 2144 Ma (Table 2), i.e., mainly concentrated within the range reported for the Paleoproterozoic period.

Fig. 3. LA-ICP-MS zircon U-Pb age concordia plot of the Huangtuliang monzonitic granite.

Table 2 Results of zircon Hf isotopic measurement for the Huangtuliang monzonitic granite

4 Discussion

4.1 Formation age and geological significance of the Huangtuliang monzonitic granite

Th/U ratios in zircons from the monzonitic granite studied in this paper are greater than 0.1, varying between 0.42 and 1.31, indicating that the zircons are of magmatic origin. Cathod luminescence research showed that zircons of this type keep a perfect long columnar crystal shape, the magmatic girdles are well developed, further indicating their magmatic origin. Therefore, the weighed mean age of 244.8±2.0 Ma (MSWD=0.57) obtained in this study represents the crystallization age of the monzonitic granite. The International Commission on Stratigraphy (ICS) (2008) prescribed a limit of 228.7-245.9 Ma to the Middle Triassic, indicating that the monozonitic granite in this region was formed during the Middle Triassic epoch.

Messozoic magmatic activities were intense in the Zhang-Xuan region, North Hebei Province, but, as for their time limit, they mostly occurred during the Jurassic-Cretaceous periods. Little report has been made on Triassic, especially Early Triassic magmatic activities. The relatively reliable zircon ages are those U-Pb TIMS ages for hornblende monzonite, coursegrained granite and light fresh-pink phenocrystbearing granite in the Beichagoumen region, North Hebei Province, which vary from 250±3.6 to 246.7±2.5 Ma (Mao Debao et al., 2003; Chen Zhihong et al., 2004). The Huangtuliang monzonitic granite and granitoid rocks in the Beichagoumen region, North Hebei, are the magmatic response to the Early Indosinian tectonic movement in the region of North Hebei. In the middle segment of the northern margin of the North China landmass the Middle-Late Triassic magmatic activities were relatively extensive. For example, the zircon LA-ICP-MS U-Pb age of the Honghualiang granite about 20 km west of the Huangtuliang monzonitic granite is 235±2 Ma (Jiang Neng et al., 2007); the zircon SHRIMP U-Pb age of the Guzuizi granite is 236±2 Ma (Miao Laicheng et al., 2002); the zircon SHRIMP U-Pb age of the Bingshanliang granodiorite at Chicheng is 228.0±3.1 Ma (Liu Kuangyin et al., 2010); the zircon SHRIMP U-Pb ages of the Dushan granite porphyry dykes in the Sanjia gold mining district on the eastern side are 223±2 and 222±4 Ma, respectively (Luo Zhenkuan et al., 2003); Wu Fuyuan et al. (2005) made use of zircon TIMS and LA-ICP-MS U-Pb dating methods and obtained the forming age of 233±1 Ma for the Saima rockbody and the forming age of 231±1 Ma for Bailinchuan rockbody. The Sr-Nd-Pb isotopic characteristics showed that all those rockbodies, more or less,possess the isotopic characteristics of the enriched mantle (Yan Guohan et al., 2000).

The destruction of the North China Craton has become a hot topic in the geological field both at home and abroad in recent ten years, which involves the time, space, mechanism and driving force of the North China Craton destruction (Wu Fuyuan et al., 2008). Some researchers considered that the destruction of the North China Craton started mainly in the Triassic period (Xu Wenliang et al., 2006; Yang Jinhui et al., 2009) and some other scholars held that it started in Late Mesozoic time (Gao Shan et al., 2004; Yang Jinhui et al., 2008). On the basis of their understanding of Triassic magmatism in the Chicheng region, North Hebei Province, Li Yin et al. (2010) suggested that the destruction of the North China Craton started in the Indosinian period. So, whether the Huangtuliang monzonitic granite in the Chicheng region of North Hebei is the product of North China Craton dectruction still needs to be further studied. Because the time at which the North China Craton collided and joined together with the Siberian Plate is 290-234 Ma, i.e., the paleo-Asian Ocean closed finally at 234 Ma (Zhang Shuanhong et al., 2009, Ma Xu et al., 2012), the Huangtuliang monzonitic granite is a constituent part of the Triassic alkaline rock belt which extends nearly as long as 1500 km in the eastern-western direction on the northern margin of the North China landmass, and its formation seems to be more closely related to the extension background of the North China Craton during the time period from late collision to post-orogenesis.

4.2 Magma source region

Zircon Hf isotopic micro-areain-situanalysis of 21 points of sample HG-5 of the Huangtuliang monzonitic granite was carried out and176Lu/177Hf ratios in the tested zircons vary over a relatively small range, between 0.000233 and 0.000844.176Lu/177Hf values for all the analytical points are less than 0.002, indicating that almost no radiogenic Hf accumulation occurred after the formation of zircons and the zircons were seldom affected by any later-stage magmothermal event. Therefore, the176Lu/177Hf values for the tested sample may basically represent the Hf isotopic values at the time of formation of the sample.176Hf/177Hf values vary in a relatively small range, between 0.282232 and 0.282320. εHf(t) values also vary over a small range, between -10.65 and -14.03, with an average of -12.14 and a standard deviation of 1.116. The Hf isotopic composition of the Huangtuliang monzonitic granite lies in the range recorded at the time of Paleoproterozoic crust evolution (Fig. 4), just overlapping the distribution range of εHf(t) values for the Yanshanian folded zone, and obviously differing from the distribution range of εHf(t) values for the eastern segment of the Xingmeng orogenic belt (Yang Jinhui et al., 2006). The two-stage model ages (tDM2) stand between 1943 and 2144 Ma, concentrated within the range recorded for the Paleoproterozoic period, implying that the residence time of the granomagmatic material source in the crust is Paleoproterzoic.

Fig. 4. The Hf isotopic evolution plot of the Huangtuliang monzonitic granite.

The positive εHf(t) values of granitic rocks are thought to be resultant from partial melting of crustal materials from the depleted mantle or of newly proliferative crustal materials derived from the depleted mantle, and the negative εHf(t) values are indicative of ancient crust origin (Wu Fuyuan et al., 2007). It was testified by further studies that εHf(t) may be around -9.0 for the enriched lithospheric mantle (EM) in North China (Yang Jinhui et al., 2006; Chen Bin et al., 2008). As viewed from the Hf isotopic composition, the ancient lower crust has a very low εHf(t) value (about -35) (Zheng Jianping et al., 2004; Chen Bin et al., 2008). The zircon Hf isotopic composition of the Huangtuliang monzonitic granite is slightly lower than the εHf(t) value of the enriched lithospheric mantle (EM), North China, but obviously higher than the Hf isotopic composition of the ancient lower crust, North China. At present, some important achievements have been made in the Hf isotopic study of Mesozoic magmatic rocks in the Zhang Xuan region in the middle segment of the northern margin of the North China landmass, and the obtained εHf(t) values are used to explore the nature of the magma source region. For example, the εHf(t) values of the Xiaozhangjiakou basic-ultrabasic rockbody dated at 220 Ma, corresponding to Late Triassic, vary between -2.9 and 1.66. This is thought to be the result of partial melting caused by interaction and mixing betweenmantle fluid/melt in the depleted asthenosphere and the enriched lithospherical mantle (Tian Wei et al., 2007); the εHf(t) values of the Middle Triassic (235 Ma) Honghuagang granite at Dongping vary between -9.9 and -23.3, the two-stage evolution model ages are mostly within the range of 1892-2321 Ma, and the granomagmatic source region was formed from the Paleoproterzoic lower crust materials (Jiang Neng et al., 2007); the Hf isotopic values of zircons in the Early Cretaceous Houcheng Formation dacite in the Zhangxuan region vary between -15.1 and -18.5; the former is thought to have come mainly from Late Archean crustal materials while the latter is considered to have been derived from the mixture of Archean crustal materials and mantle-source materials (Yang Jinhui et al., 2006). The εHf(t) values of zircons in the Huangtuliang monzonitic granite are obviously lower than those of zircons in the mantle-source Xiaozhangjiakou basic-ultrabasic rockbody, slightly higher than those of zircons in the Zhangjiakou Formation rhyolite , falling within the range of εHf(t) values for the Middel Triassic Honghuagang granite at Dongping. All this, in conjunction with the zircon two-stage evolution model ages, implies that the monzonitic granite in this region was formed mainly from the Paleoproterozoic recirculated crustal materials, while the involvement of a small amount of enriched mantle material should not be excluded.

5 Conclusions

(1) The weighed mean206Pb/238U age obtained from LA-MC-ICP-MS zircon U-Pb dating (244.8±2.0 Ma）represents the age of magmatic crystallization. The Huangtuliang monzonitic granite was formed during the Middle Triassic, and it was the product of Early Indosinian tectono-magmatic activities. Regionally, the Huangtuliang monzonitic granite is a part of the nearly EW-extending alkaline rock belt on the northern margin of the North China landmass, and its formation may be related to the extension from the late stage of collision to post orogenesis on the northern margin of the North China Craton.

(2) The εHf(t) values of samples from the Huangtuliang monzonitic granite vary over a relatively small range, between -10.65 and -14.03, with an average of -12.14, just overlapping the range of εHf(t) values for the Yanshanian fold belt. The two-stage evolution model ages (tDM2) stand between 1943 and 2144 Ma, concentrated within the Paleoproterozoic range, indicating that the crustal residence time of material source of granitic magma is Paleoproterozoic, the monzonitic granite was mainly derived from Paleoproterozoic recirculated crustal materials, though there would be involved a minor amount of enriched mantle material.

AcknowledgementsThe authors wish to cordially thank Engineer Shi Ping of the Huangtuliang Gold Mining Administration for his help with the field work and Doctor Hou Kejun of the Institute of Mineral Resources, Chinese Academy of Geological Sciences, for his instruction in isotopic measurement. This research project was financially supported jointly by the Geological Investigation Item sponsored by the China Geological Survey (No. 1212011220492), the Scientific Research Base of China’s Typical Metallic Ores (No. 200911007) and the National Natural Science Foundation of China (40872137).

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10.1007/s11631-014-0655-5

Received June 6, 2013; accepted August 5, 2013

© Science Press and Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg 2014