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The granite porphyry hidden in the Shuangjianzishan deposit, southern Great Xing’an Range, NE China: geochronology, isotope geochemistry and tectonic implications

Published online by Cambridge University Press:  08 October 2020

Wei Wei*
Affiliation:
Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China
Xin-Biao Lv*
Affiliation:
Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China
Xiang-Dong Wang
Affiliation:
Wuhan Center of Geological Survey (CGS), Wuhan 430205, China
*
Author for correspondence: Wei Wei, Emails: wwei@cug.edu.cn; luxb@cug.edu.cn
Author for correspondence: Wei Wei, Emails: wwei@cug.edu.cn; luxb@cug.edu.cn
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Abstract

The Shuangjianzishan vein-type Ag-Pb-Zn deposit in the southern Great Xing’an Range (GXR), NE China, is hosted in the slate of the Lower Permian Dashizhai Formation intruded by granite porphyry. In this paper, U–Pb zircon ages and bulk-rock and isotope (Sr, Nd, Pb and Hf) compositions are reported to investigate the derivation, evolution and geodynamic setting of this granite porphyry. It is closely associated with Pb-Zn-Ag mineralization in the southern GXR and contains important geological information relating to regional tectonic evolution. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) zircon U–Pb dating yields an emplacement age of 131 ± 1 Ma for the granite porphyry. Bulk-rock analyses show that the Shuangjianzishan granite porphyry is characterized by high Si, Na and K contents but low Mg and Fe contents, and that the enrichment of Zr, Y and Ga suggests an A-type granite affinity. Most of the studied samples have relatively low 87Sr/86Sr values (0.70549–0.70558), with positive ϵNd(t) (0.71–0.88) and ϵHf(t) (4.9–6.9) values. The Sr–Nd isotope modelling results, in combination with the young TDM2 ages of Nd and Hf (850–864 and 668–778 Ma, respectively), reveal that the Shuangjianzishan granite porphyry may be derived from the melting of mantle-derived juvenile component, with minor lower crustal components; this finding is also supported by Pb isotopic compositions. Considering the widespread presence of granitoids with coeval volcanic rocks and regional geology data, we propose that the Shuangjianzishan granite porphyry formed in a post-orogenic extensional environment related to the upwelling of asthenospheric mantle following the closure of the Mongol–Okhotsk Ocean.

Information

Type
Original Article
Copyright
© The Author(s), 2020. Published by Cambridge University Press
Figure 0

Fig. 1. (a) Location of the Central Asian Orogenic Belt (after Liu et al. 2016). (b) Tectonic sketch of NE China (after Wu et al. 2011). (c) Regional geological map of the southern Great Xing’an Range (GXR) (after Mei et al. 2014).

Figure 1

Fig. 2. (a) Geological map of the Shuangjianzishan Pb-Zn-Ag deposit (after Liu et al. 2016). (b) Large-scale geological map of the Shuangjianzishan mining area.

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Table 1. Ages of magmatism in Shuangjianzishan deposit, all determined by zircon U–Pb dating

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Fig. 3. Simplified drill columnar section and photographs of intrusive contact relation.

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Table 2. Sample collection in Shuangjianzishan deposit, all coarse-grained granite

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Fig. 4. Hand-specimen photograph, photomicrographs and back-scatter electron image for the Shuangjianzishan granite porphyry: (a) porphyritic texture; (b) quartz phenocryst and matrix quartz; (c) sericite and chlorite alteration; (d) plagioplase phenocryst; (e) K-feldspar phenocryst; and (f) biotite and accessory minerals. Pl – plagioclase; Bi – biotite; Qtz – quartz; Kfs – K-feldspar; Ser – sericite; Ab – albite; Chl – chlorite; Hb – hornblende; Ap – apatite; Zrn – zircon; Py – pyrite; Rt – rutile.

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Fig. 5. Representative cathodoluminescence (CL) images of zircons from the Shuangjianzishan granite porphyry. Numbers and ages on zircon grains are the analysed spots in Table 3.

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Table 3. LA-ICP-MS zircon U–Pb Shuangjianzishan granite porphyry data

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Fig. 6. Zircon U–Pb concordia diagrams for the Shuangjianzishan granite porphyry. The concordia age, mean age and mean square weighted deviation (MSWD) are shown in each figure.

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Table 4. Major- (wt%) and trace-element (ppm) contents of the Shuangjianzishan granite porphyry

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Fig. 7. (a) SiO2–K2O discriminant plot (after Peccerillo & Taylor, 1976) for the Shuangjianzishan (SJZS) granite porphyry; (b) A/CNK–A/NK diagram (after Maniar & Piccoli, 1989) for the discriminant of metaluminous, peraluminous and peralkaline rocks; (c) chondrite-normalized REE pattern; and (d) primitive-mantle-normalized trace-element patterns. Primitive mantle and chondrite data are from Sun & McDonough (1989). Haobugao data are from Wang et al. (2018), the data represented by the square are from the SJZS granite (Gu et al. 2017) and Yanshanian granites data describing the southern GXR are from Mei et al. (2014), Ruan et al. (2015), Wang et al. (2016a) and Liu et al. (2017).

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Table 5. Sr–Nd isotopic compositions of the Shuangjianzishan granite porphyry

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Table 6. Pb isotopic compositions of the Shuangjianzishan granite porphyry

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Table 7. Zircon Lu–Hf isotopic data of the Shuangjianzishan granite porphyry

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Fig. 8. Discrimination diagrams of (a) Nb versus 10 000×Ga/Al; (b) Na2O+K2O versus 10 000×Ga/Al; (c) FeO/MgO versus 10 000×Ga/Al; (d) Nb-Y-Ce (after Whalen et al.1987; Eby, 1992). Triangle points are from Wang et al. (2018) and the square from Gu et al. (2017). A1 – anorogenic setting; A2 – post-collisional setting.

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Fig. 9. (a) Mantle: plot of ϵHf(t) versus t (Ma) for the zircons from the Shuangjianzishan granite porphyry. CAOB – the Central Asian Orogenic Belt; YFTB – Yanshan Fold and Thrust Belt (Yang et al. 2006). (b) Orogene: ϵNd(t) versus (87Sr/86Sr)t isotopic ratio plot showing mixing proportions between two end-members (after Wu et al. 2003): (1) depleted mantle or juvenile components (DM – upper mantle peridotite; B – basalt) and (2) crustal components (LCC – lower continental crust; UCC – upper continental crust; both represented by the Mashan gneisses in the Jiamusi Block; Wu et al. 2000). The grey area represents Mesozoic granites from Wu et al. (2003). (c) Upper crust: 207Pb/204Pb versus 206Pb/204Pb diagram and (d) lower crust: 208Pb/204Pb versus 206Pb/204Pb diagram for distinguishing tectonic setting (after Zartman & Doe, 1981). Haobugao data Wang et al. (2018).

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Fig. 10. (a) (Rb/30)-Hf-3Ta discrimination diagram (after Harris et al. 1986); (b) Rb versus (Yb+Ta) discrimination diagram (after Pearce, 1996). VAG – volcanic-arc granite; ORG – ocean-ridge granite; WPG – within-plate granite; COLG – collision granite; POG – post-collision granite. Triangle points are from Wang et al. (2018), the square from Gu et al. (2017) and the grey-shaded squares from Mei et al. (2014), Ruan et al. (2015), Wang et al. (2016a) and Liu et al. (2017).