Petrogenesis of post-orogenic syenites in the Sulu
Orogenic Belt, East China: geochronological,
geochemical and Nd–Sr isotopic evidence
Jin-Hui Yang
a,*, Sun-Lin Chung
b, Simon A. Wilde
c, Fu-yuan Wu
a, Mei-Fei Chu
b,
Ching-Hua Lo
b, Hong-Rui Fan
aaInstitute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China b
Department of Geosciences, National Taiwan University, Taipei 106, Taiwan
c
Department of Applied Geology, Curtin University of Technology, Perth, Australia Received 25 February 2004; accepted 26 August 2004
Abstract
The Jiazishan alkaline complex in the eastern Sulu ultrahigh pressure (UHP) metamorphic orogenic belt of eastern China is composed of potassic to ultrapotassic pyroxene syenite, quartz syenite and associated mafic dikes. A SHRIMP zircon206Pb/238U age of 215F5 Ma was obtained for the quartz syenite and mineral40Ar/39Ar dating gave emplacement ages of 214.4F0.3 and 214.6F0.6 Ma for the pyroxene syenite and 200.6F0.2 Ma for the mafic dike. These dates establish that the Jiazishan Complex was emplaced shortly after the UHP metamorphic event at 240 to 220 Ma due to the continental collision between the North China and Yangtze cratons. The ultrapotassic mafic dikes, with K2Oc4.4–6.4 wt.% and K2O/Na2Oc3.5, have high MgO (8.06–12.44
wt.%), Ni (119–319 ppm) and Cr (477–873 ppm) and moderately low CaO/Al2O3(~0.76) and TiO2(~1.12 wt.%). They also have
high Sr (87Sr/86Sr~0.7073), low Nd (eNd=~ 16.5) isotopic ratios, enriched LILE (Ba/La=66–74), LREE [(La/Yb)N=28–33] and
depleted HFSE (La/Nb=4–6). It appears that the mafic dikes were derived from a refractory, re-enriched lithospheric mantle source. The syenites have Sr and Nd isotopic compositions similar to the mafic dikes, implying a common origin. Geochemical and isotopic modeling suggests that the pyroxene syenites may have been generated by early fractionation of clinopyroxene and olivine, coupled with minor amounts of crustal contamination, of a mafic magma that had a similar composition to the mafic dikes. Subsequent fractionation of feldspar-dominated assemblages, with minor or no contamination, would result in the quartz syenites. This post-orogenic magmatism, resulting most likely in an extensional setting, provides time constraints on the major geodynamic transition from convergence to extension at the eastern margin of the North China craton. The Jiazishan potassic magmatism and geodynamic transition from convergence to extension can be explained by convective removal of the lower lithospheric mantle. D 2004 Elsevier B.V. All rights reserved.
Keywords: Post-orogenic magmatism; Potassic to ultrapotassic magmatism; Sulu UHP belt; North China craton
0009-2541/$ - see front matterD 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2004.08.053
* Corresponding author. Tel.: +86 10 62007900; fax: +86 10 62010846. E-mail address: jinhui@mail.igcas.ac.cn (J.-H. Yang).
Chemical Geology 214 (2005) 99 – 125
1. Introduction
Syenites and alkaline felsic rocks are commonly intimately associated with alkaline mafic rocks, especially alkali to transitional basalts. The origin of the more evolved rocks, however, remains controversial. Models proposed for the generation of syenites may be divided into three groups. First, syenite magmas may originate by partial melting of crustal rocks resulting from an influx of volatiles (e.g., Lubala et al., 1994) or in a closed system at pressures typical of the base of over-thickened crust (Huang and Wyllie, 1981). Second, syenite magmas may be products of partial melting of metasomatized mantle (Sutcliffe et al., 1990; Lynch et al., 1993) or the residual melts formed by differentiation of alkali basalt magma (Parker, 1983; Brown and Becker, 1986; Thorpe and Tindle, 1992). Third, syenites may result by magma mixing processes, particularly mixing of basic and silicic melts with subsequent differentiation of the hybrid liquids (Barker et al., 1975; Sheppard, 1995; Zhao et al., 1995; Litvinovsky et al., 2002), or by mixing of mantle-derived, silica-undersaturated alkaline magmas with lower crustally derived granitic magmas (e.g., Dorais, 1990). This range of petrogenetic models also reflects the diversity of geological settings in which syenite magmas are generated. For example, it is generally assumed that these rocks characterize non-orogenic, within-plate environments. However, several alkaline associations, although not strictly non-orogenic, post-date orogenic episodes by a short interval of time, such as the Permian–Triassic Western Mediterranean province (Bonin et al., 1987), the Pan-African Arabian Shield (Harris, 1985), in Tibet (Turner et al., 1996; Miller et al., 1999; Williams et al., 2004) and other examples (Sylvester, 1989). In this context, it is important to undertake detailed studies on plutonic complexes where one particular mechanism of syenite magma production can be established with confidence.
The Jiazishan Complex, exposed in the Sulu ultrahigh pressure (UHP) orogenic belt of NE China and comprised of an intrusive association of basan-ite–pyroxene syenite–quartz syenite, is one such example. In this paper, we present petrographic, geochronological, geochemical and Sr–Nd isotopic data for these rocks and demonstrate that the syenite
magmas were mainly formed as a result of crystal fractionation from enriched lithospheric mantle-derived magmas, with little or no assimilation of crustal material. Interpretation of the data leads to an integrated model of syenite genesis in a post-orogenic extensional setting.
2. Geological setting and petrography 2.1. Regional context
The Dabie–Sulu orogenic belt in east-central China (Fig. 1a) contains the largest distribution of UHP metamorphic rocks in the world, marking the collision zone between North China and Yangtze cratons (Huang, 1978; Wang et al., 1995; Cong, 1996). The Sulu terrane was offset to the north by sinistral movement on the Tanlu Fault of about 500 km (Xu and Zhu, 1994). Metamorphic rocks of the Sulu UHP belt are mainly amphibolite facies granitic gneisses, with subordinate amounts of coesite-bearing eclogites (e.g.,Yang and Smith, 1989; Hirajima et al.,
1990, 1992; Enami and Zang, 1993) and other UHP
metamorphic rocks such as ultramafics (Yang et al., 1993; Zhang et al., 1994), marbles (Kato et al., 1997), pelitic schists (Zhang et al., 1995) and meta-gran-itoids (Hirajima et al., 1992). These UHP metamor-phic rocks occur as sporadic lenticular bodies in the regional granitic gneisses. The margins of most eclogite lenses are transformed to amphibolite and reveal a significant amphibolite facies overprint after UHP metamorphism (Yao et al., 2000). While deep subduction of the Yangtze continental crust to over 120 km is evident from the occurrence of micro-diamond in eclogites (Xu et al., 1992), exhumation of more deeper rocks from over 200 km was deduced from exsolution minerals in eclogitic garnet (Ye et al., 2000). Abundant Sm–Nd mineral isochron and U–Pb zircon ages have documented that the continental collision and UHP metamorphism took place in the Early–Middle Triassic at 240–220 Ma (e.g., Ames et al., 1993; Li et al., 1993a,b; Chavagnac and Jahn, 1996; Hacker et al., 1998; Zheng et al., 2002; Liu et al., 2004).
High-K calc-alkaline granitic rocks are widely distributed in the Sulu orogenic belt, but most of them formed in the Late Jurassic (160–150 Ma) and
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 100
Early Cretaceous (130–125 Ma) (Wang et al., 1998;
Zhang et al., 2003). Only one syenitic complex—
the Jiazishan Complex—has been reported to be of Late Triassic age (Lin et al., 1992; Chen et al., 2003).
2.2. Jiazishan syenites
The Jiazishan Complex, located in the Jiaodong Peninsula (East China) and intruded into the Sulu UHP metamorphic belt, is one of the easternmost outcrops in the Sulu UHP metamorphic belt (Fig. 1b). It covers an area of ~140 km2and comprises at
least two magmatic sequences (Lin et al., 1992). Field mapping and detailed description of the Jiazishan rocks reveal the following sequence of magmatic events: (1) intrusion of pyroxene syenite and quartz syenite; (2) intrusion of biotite granite into the syenite and (3) intrusion of mafic dikes into the syenite.
Five alkaline phases (Fig. 1c) are distinguished in the complex according to field and petrographic data. Phase 1 is a trachytoid biotite–pyroxene syenite. Samples (JZS-11 and JZS-12) from phase 1 are composed of 54–68% subhedral alkali feldspar, 16– 26% plagioclase (with composition An51–55), 2–11%
Fig. 1. Location maps showing position of the Jiazishan Complex in eastern China. (a) Relation to the Dabie–Sulu ultrahigh pressure metamorphic belt; (b) position within the Jiaodong Peninsula and (c) distribution of components in the Jiazishan Complex.
biotite, 5–12% amphibole and 2–8% pyroxene, with minor olivine, titanite and magnetite. The rocks are porphyritic and characterized by phenocrysts of pyroxene and perthitic alkali feldspar. Alkali feld-spar laths define a subparallel flow direction. Perthitic tectures are abundant including mesoper-thite intergrowth of alkali and plagioclase feldspar and microperthite exsolution intergrowth of sodium-and potassium-rich feldspars. Plagioclase is weakly sericitized.
Phase 2 is a porphyritic biotite–pyroxene syenite. Samples (JZS-7 to JZS-10 in Table 3) are from this phase. The rocks are medium- to coarse-grained and porphyritic, consisting of up to 35% phenocrysts of perthitic alkali feldspar in a microcrystalline ground-mass of 4–6% pyroxene, 3–9% biotite, 8–25% plagioclase and 40–50% alkali feldspar. Minor olivine (b1%) is found as inclusions in the pyrox-ene. Some pyroxenes are also altered to hornblende. Alkali-feldspar phenocrysts range from 2 to 7 cm long and some grains are concentrically zoned. Mafic enclaves (samples JZS-7-1 and JZS-8-1) are also common in this phase and have similar mineral assemblages to the syenites, but with more abundant mafic minerals including biotite, hornblende, olivine and pyroxene. Plagioclase is weakly sericitized.
Phase 3 is a coarse-grained biotite–pyroxene syenite. Samples (JZS-13 to 17 inTable 3) from this phase have similar mineralogy to the trachytoid biotite–pyroxene syenite.
Phase 4 is a quartz syenite. Samples (1 to JZS-6 inTable 3) from this phase have 70% alkali feldspar, 10% plagioclase (with composition An20–22) and 10%
quartz, with accessory amphibole, clinopyroxene, apatite, titanite and magnetite. Perthitic alkali feld-spars are observed as inclusions in non-perthitic varieties. Quartz occurs as inclusions in the alkali feldspar or as anhedral grains interstitial to other minerals.
Phase 5 is a mafic dike that intruded into the syenites. Samples JZS-D-2 to JZS-D-5 are from this phase and are characterized by local phenocrysts of pyroxene and minor biotite in a groundmass of 35% pyroxene, 35% alkali feldspar, 10% olivine, 5% plagioclase, 5% hornblende and 10% biotite. The rocks have a massive texture. Plagioclase is weakly sericitized and olivine is locally replaced by iddingsite.
Lin et al. (1992) determined the age of the
pyroxene syenite and intrusive biotite granite as 220–217 Ma, using whole rock and biotite Rb–Sr geochronology, but they did not relate the origin of the complex to the overall development of the UHP belt.
Guo et al., (2001b) and Chen et al. (2003) reported zircon U–Pb ages of 225–205 Ma for the pyroxene syenite, but no detailed geochemical data were presented.
3. Analytical methods
3.1. Zircon SHRIMP U–Pb dating
SHRIMP U–Pb zircon analyses were performed at Curtin University of Technology. Sample preparation and basic operating procedures are described by
Nelson (1997). An average mass resolution of 4800 was obtained during measurement of the Pb/Pb and Pb/U isotopic ratios and Pb/U ratios were normalized to those measured on the standard zircon [CZ3-(206Pb/238U=0.0914)], with the calibration error on the standards being 1.54%. The 206Pb/238U ages are considered the most reliable, since the zircons are concordant and the low count rates on207Pb result in large statistical uncertainties, making the 207Pb/206Pb and 207Pb/235U ratios less sensitive measures of age for younger zircons (Compston et al., 1992). The measured 204Pb on the zircons was similar to the standard, and therefore common lead corrections were made assuming an isotopic composition of Broken Hill lead, since common lead is considered to be mainly related to surface contamination (Nelson, 1997). Data reduction was performed using the Krill 007 program of P.D. Kinny applying the 208Pb correction, since there is no evidence of post-crystallization disturbance to the U–Pb–Th system. Errors on individual analyses are at the 1r level (Table 1) and errors on pooled analyses are quoted at 2r or 95% confidence.
3.2. 40Ar/39Ar dating
Hornblende, K-feldspar and whole rock samples from the Jiazishan Complex were dated by
40
Ar/39Ar step-heating and single-grain fusion meth-ods using furnace and laser heating techniques.
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 102
Table 1
SHRIMP zircon U/Pb isotopic data for quartz syenite (JZS-3) from Jiazishan Complex Spot U (ppm) Th (ppm) Th/ U Pb (ppm) 204Pb/ 206Pb f206% 207Pba/ 206Pba F1r 208Pba/ 206Pba F1r 206Pba/ 238U F1r 207Pba/ 235U F1r 208Pba/ 232Th F1r AgeF1r (Ma) 206 Pba/ 238 U 207 Pba/ 235 U 207 Pba/ 206 Pba 208 Pba/ 232 Th JZS-3-1 475 435 0.92 20 0.00118 1.893 0.04223 0.00412 0.2692 0.0100 0.0343 0.0007 0.20 0.02 0.0101 0.0004 217F4 185F17 0F43 203F8 JZS-3-2 662 633 0.96 26 0.00016 0.249 0.05056 0.00198 0.2992 0.0053 0.0335 0.0006 0.23 0.01 0.0105 0.0003 213F4 213F9 221F91 211F5 JZS-3-3 720 1404 1.95 35 0.00015 0.235 0.04842 0.00159 0.6082 0.0060 0.0341 0.0006 0.23 0.01 0.0106 0.0002 216F4 208F7 120F74 214F4 JZS-3-4 83 61 0.73 4 0.00392 6.269 0.06075 0.02282 0.3084 0.0534 0.0300 0.0010 0.25 0.10 0.0126 0.0022 190F6 227F78 630F652 253F44 JZS-3-5 429 605 1.41 16 0.00085 1.357 0.06113 0.00544 0.4803 0.0140 0.0264 0.0005 0.22 0.02 0.0090 0.0003 168F3 204F17 644F192 181F6 JZS-3-6 38 78 2.08 2 0.00474 7.579 0.02887 0.04208 0.6184 0.1033 0.0311 0.0017 0.12 0.18 0.0092 0.0016 198F10 119F152 0F107 186F33 JZS-3-7 186 623 3.35 11 0.00001 0.012 0.05443 0.00499 1.0196 0.0189 0.0333 0.0007 0.25 0.02 0.0101 0.0003 211F4 226F20 389F207 203F6 JZS-3-8 260 675 2.59 14 0.00120 1.914 0.04053 0.00514 0.7849 0.0162 0.0324 0.0007 0.18 0.02 0.0098 0.0003 205F4 169F20 0F61 197F6 JZS-3-9 274 656 2.40 15 0.00038 0.611 0.04963 0.00486 0.7399 0.0148 0.0343 0.0007 0.23 0.02 0.0106 0.0003 217F4 214F20 178F213 213F6 JZS-3-10 773 1693 2.19 39 0.00010 0.155 0.05145 0.00175 0.6587 0.0064 0.0339 0.0006 0.24 0.01 0.0102 0.0002 215F4 219F8 261F78 205F4 JZS-3-11 56 92 1.65 3 0.00188 3.015 0.04462 0.01722 0.4668 0.0429 0.0331 0.0011 0.20 0.08 0.0094 0.0009 210F7 188F67 0F107 188F18 JZS-3-12 1074 2763 2.57 62 0.00016 0.260 0.04816 0.00141 0.8097 0.0061 0.0357 0.0006 0.24 0.01 0.0112 0.0002 226F4 216F7 108F65 226F4 JZS-3-13 470 815 1.73 22 0.00000 0.000 0.05447 0.00112 0.5614 0.0060 0.0344 0.0006 0.26 0.01 0.0111 0.0002 218F4 233F6 391F46 224F5 JZS-3-14 118 233 1.98 6 0.00057 0.912 0.05243 0.00899 0.6095 0.0243 0.0344 0.0008 0.25 0.04 0.0106 0.0005 218F5 226F36 304F350 214F10 f206% denotes (common206Pb)/(total measured206Pb).
a Radiogenic lead. J.-H. Y ang et al. / Chemical Geology 214(200 5) 99–125 103
Table 2
40Ar/39Ar data for K-feldspar, hornblende and whole rocks for the pyroxene syenites and mafic dike from the Jiazishan Complex
JZS-13 amphibole
T (8C) Cum. 39 36Ar/39Ar 37Ar/39Ar 38Ar/39Ar 40Ar/39Ar 40Ar/36Ar Ca/K Date (Ma) 1r
650 0.019 8.59e 01 4.87e 01 5.02e 01 3.20e+02 3.72e+02 1.62 317.3 3.7 725 0.079 1.62e 01 6.12e 01 1.40e 01 8.88e+01 5.50e+02 2.04 204.2 4.5 800 0.103 4.42e 02 1.43e 04 1.43e 04 5.66e+01 1.28e+03 0.00 215.5 2.7 850 0.128 2.57e 02 7.80e 02 1.31e 04 5.09e+01 1.98e+03 0.26 214.6 5.4 900 0.154 2.07e 02 4.39e 01 1.29e 04 4.99e+01 2.42e+03 1.46 217.1 3.0 925 0.176 2.28e 02 8.85e 01 1.54e 04 5.03e+01 2.21e+03 2.95 215.9 4.2 950 0.214 3.63e 02 1.69e+00 1.97e 02 5.00e+01 1.38e+03 5.63 196.1 3.0 975 0.240 1.91e 02 4.46e+00 4.30e 02 5.08e+01 2.66e+03 14.88 225.1 2.8 1000 0.287 2.60e 02 6.66e+00 1.71e 01 5.13e+01 1.98e+03 22.28 219.4 2.1 1025 0.364 2.01e 02 7.16e+00 2.24e 01 4.94e+01 2.46e+03 23.94 218.8 1.0 1050 0.451 1.51e 02 6.85e+00 2.22e 01 4.70e+01 3.11e+03 22.90 214.1 1.2 1075 0.569 8.05e 03 6.83e+00 2.49e 01 4.54e+01 5.64e+03 22.82 216.2 1.1 1100 0.695 6.77e 03 6.41e+00 2.42e 01 4.46e+01 6.58e+03 21.44 214.1 1.4 1150 0.792 7.06e 03 6.05e+00 2.13e 01 4.43e+01 6.27e+03 20.20 212.3 0.7 1200 0.899 1.07e 02 6.83e+00 2.26e 01 4.50e+01 4.19e+03 22.83 210.8 1.1 1400 1.000 3.14e 02 1.16e+01 2.60e 01 5.15e+01 1.64e+03 38.84 215.0 1.2 Sample mass=402.3 mg; J-value=0.002917F0.000003; Integrated date=215.7F0.5 Ma (39Ar volume=0.1559e 11 ccSTP/g;40Ar* volume= 0.6787e 10 ccSTP/g); Plateau age=214.6F0.6 Ma (1000–1400 8C; 71.3%39Ar).
JZS-11 K-feldspar
T (8C) Cum. 39 36Ar/39Ar 37Ar/39Ar 38Ar/39Ar 40Ar/39Ar 40Ar/36Ar Date (Ma) 1r
600 0.008 8.09e 05 8.09e 05 8.09e 05 5.73e+01 7.08e+05 278.7 3.3
700 0.115 5.97e 06 6.30e 02 1.18e 02 4.05e+01 6.78e+06 201.2 0.3
800 0.230 5.59e 06 5.70e 02 3.66e 03 4.10e+01 7.34e+06 203.7 0.5
850 0.247 3.70e 05 3.70e 05 3.70e 05 3.90e+01 1.06e+06 194.3 1.0
900 0.299 1.23e 05 4.55e 02 1.23e 05 4.06e+01 3.31e+06 201.9 0.7
950 0.330 2.08e 05 3.42e 03 2.08e 05 4.03e+01 1.94e+06 200.3 0.7
1000 0.352 2.88e 05 2.88e 05 2.88e 05 4.07e+01 1.42e+06 202.4 0.9
1025 0.415 1.02e 05 1.69e 02 2.35e 03 4.22e+01 4.15e+06 209.2 0.5
1075 0.484 9.29e 06 1.84e 02 7.36e 03 4.31e+01 4.64e+06 213.5 0.4
1100 0.546 1.03e 05 1.69e 02 6.29e 03 4.31e+01 4.18e+06 213.5 0.4
1125 0.647 6.33e 06 2.16e 02 1.38e 02 4.35e+01 6.87e+06 215.3 0.4
1175 0.791 4.69e 06 1.39e 02 1.13e 02 4.33e+01 9.23e+06 214.4 0.6
1200 0.861 9.17e 06 3.22e 03 1.72e 03 4.34e+01 4.73e+06 214.7 0.3
1220 0.923 1.04e 05 3.41e 05 9.32e 04 4.35e+01 4.20e+06 215.3 0.3
1270 0.933 6.28e 05 6.28e 05 6.28e 05 4.21e+01 6.71e+05 208.9 1.0
1350 0.964 2.05e 05 2.05e 05 2.05e 05 4.41e+01 2.15e+06 218.1 0.6
1400 0.978 4.62e 05 4.62e 05 4.62e 05 4.47e+01 9.69e+05 221.0 1.3
1600 1.000 2.91e 05 2.91e 05 2.91e 05 4.90e+01 1.68e+06 240.9 1.3
Sample mass=305.6 mg; J-value=0.002917F0.000003; Integrated date=211.0F0.2 Ma (39Ar volume=0.1074e 10 ccSTP/g;40Ar* volume= 0.4568e 09 ccSTP/g); Plateau age=214.4F0.3 Ma (1075–1220 8C; 50.8%39Ar).
JZS-D-01 whole rock
T (8C) Cum. 39 36Ar/39Ar 37Ar/39Ar 38Ar/39Ar 40Ar/39Ar 40Ar/36Ar Ca/K Date (Ma) 1r
400 0.003 2.22e 04 2.22e 04 2.22e 04 2.99e+01 1.35e+05 0.00 150.6 2.4 450 0.005 3.33e 04 3.33e 04 3.33e 04 3.65e+01 1.10e+05 0.00 182.1 6.1 500 0.009 1.52e 04 1.52e 04 1.52e 04 3.41e+01 2.25e+05 0.00 170.7 7.2 600 0.029 7.32e 04 8.97e 02 3.29e 05 3.24e+01 4.42e+04 0.30 161.7 0.4 650 0.076 2.56e 04 1.63e 01 1.66e 02 3.60e+01 1.41e+05 0.54 179.7 0.3
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 104
Mineral separates (N99% pure) were prepared using conventional heavy liquid and magnetic separation techniques. After sieving, mineral grains in the range of 250–140 Am were ultrasonically cleaned in 0.5 N HCl, washed with distilled water and then dried and handpicked to remove any visible contamination.
The samples were irradiated in the VT-C position at the THOR Reactor in Taiwan for 30 h. In order to monitor the neutron flux in the reactor, two aliquots of the LP-6 Biotite standard were stacked along with the samples in each irradiation. Standards and samples were either incrementally heated or totally fused using a double-vacuum resistance furnace and/or a US LASER Nd-YAG laser operated in continuous mode, and the gas was measured by a VG-3600 mass spectrometer at the National Taiwan University. The J-values were calculated using argon compositions of the LP-6 biotite standard with an 40Ar/39Ar age of 128.4F0.2 Ma (Renne et al., 1998). Ages were calculated from Ar isotope ratios measured after corrections made for mass discrimination, interfering nuclear reactions, decay of radiometric isotopes, procedural blanks and atmospheric Ar contamination. Total gas ages were calculated from the sum total of the argon compositions of all the temperature steps. Plateau dates were calculated by the same approach, but utilizing only the adjacent temperature steps
yielding dates which are concordant with each other within 2r. The39ArK,
38
ArCland 37
ArCarelease data
potentially reflect the chemical compositions (K, Cl and Ca, respectively) of the samples. Ca/K and Cl/K ratios were calculated according to the relationships Ca/K=3.319(F0.17)37ArCa/39ArK and Cl/K=
0.22(F0.04)38ArCl/39ArK, obtained from the
analy-ses of irradiated salts. The analytical results are given inTable 2and the data are plotted graphically as age spectra in Fig. 3. All errors given in the tables and figures are at 1r.
3.3. Major and trace elements
After petrographic examination, 24 fresh rock samples were selected, crushed and powdered in an agate mill. Major elements were determined by X-ray fluorescence techniques on fused glass beads using RigakuR RIX-2000 spectrometers at the National Taiwan University. The analytical proce-dures were the same as those described by Lee et al. (1997) and Wang et al. (2004), yielding analytical uncertainties better than F5% (2r) for all major elements. The fused glass beads were powdered and dissolved using an HF/HNO3(1:1) mixture in
screw-top Teflon beakers for N2h at ~100 8C, followed by evaporation to dryness, then refluxing in 7N HNO3
for N12h at ~ 100 8C and, finally, diluting the sample
JZS-D-01 whole rock
T (8C) Cum. 39 36Ar/39Ar 37Ar/39Ar 38Ar/39Ar 40Ar/39Ar 40Ar/36Ar Ca/K Date (Ma) 1r 700 0.168 1.84e 03 1.16e 01 4.60e 02 3.97e+01 2.16e+04 0.38 195.1 0.4 760 0.234 9.84e 06 5.18e 02 4.52e 02 3.97e+01 4.03e+06 0.17 197.3 0.9 840 0.340 6.10e 06 1.20e 01 4.65e 02 3.93e+01 6.45e+06 0.40 195.6 0.5 900 0.376 1.82e 05 1.11e 01 6.97e 03 3.99e+01 2.20e+06 0.37 198.4 0.3 950 0.432 5.23e 04 2.25e 01 4.45e 02 4.08e+01 7.80e+04 0.75 202.1 0.3 1000 0.508 8.55e 06 3.29e 01 6.69e 02 4.07e+01 4.76e+06 1.09 202.3 0.4 1050 0.609 6.43e 06 2.77e 01 7.50e 02 4.05e+01 6.30e+06 0.92 201.3 0.5 1100 0.717 6.01e 06 2.63e 01 6.33e 02 4.01e+01 6.67e+06 0.88 199.5 0.3 1150 0.831 5.90e 04 4.65e 01 4.71e 02 4.03e+01 6.82e+04 1.55 199.6 0.3 1200 0.928 3.26e 04 1.48e+00 4.14e 02 4.02e+01 1.24e+05 1.94 200.2 0.3 1250 0.964 1.83e 05 4.35e+00 2.92e 02 4.11e+01 2.24e+06 14.5 204.5 0.6 1300 0.976 5.09e 05 1.20e+01 5.09e 05 4.20e+01 8.26e+05 40.2 210.0 2.7 1600 1.000 2.71e 05 1.19e+01 4.18e 02 4.36e+01 1.61e+06 40.0 217.2 0.8 Sample mass=563.2 mg; J-value=0.002917F0.000003; Integrated date=197.9F0.2 Ma (39Ar volume=0.5745e 11 ccSTP/g;40Ar* volume= 0.2283e 09 ccSTP/g); Plateau age=200.6F0.2 Ma (950–1200 8C; 55.2%39Ar).
Table 2 (continued)
solution by 2% HNO3. An internal standard solution of
5 ppb Rh and Bi was added and the spiked solution was diluted with 2% HNO3 to a sample/solution
weight ratio of 1:2000. An internal standard was used for monitoring the signal shift during inductively coupled plasma-mass spectrometry (ICP-MS) meas-urements using an Agilent 7500s spectrometer at the National Taiwan University; it shows a good stability range with ~10% variation. The precision was generally better than F5% (2r) for most trace elements, as shown by the statistics of duplicate analyses on five rock standards AGV-1, AGV-2, GSP-1, JB-1 and JG-1 (see Appendix Table A). 3.4. Sr and Nd isotopes
Samples for isotopic analysis were dissolved in Teflon bombs after being spiked with 84Sr, 87Rb,
150
Nd and147Sm tracers prior to HF+HNO3 (with a
ratio of 2:1) dissolution. Rubidium, Sr, Sm and Nd were separated using conventional ion exchange procedures and measured using a Finnigan MAT 262 multi-collector mass spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences, China. Procedural blanks were b100 pg for Sm and Nd and b500 pg for Rb and Sr.143Nd/144Nd were corrected for mass fractionation by normal-ization to 146Nd/144Nd=0.7219 and 87Sr/86Sr ratios normalized to 86Sr/88Sr=0.1194. Typical within-run precision (2r) for Sr and Nd was estimated to be F0.000015. The measured values for the La Jolla and BCR-1 Nd standards and the NBS-607 Sr standard were 143Nd/144Nd=0.511853F7 (2rn, n=3)
and 0.512604F7 (2rn, n =3) and 87Sr/86Sr=
1.20042F2 (2rn, n=12) during the period of data
acquisition.
4. Results
4.1. Geochronology
SHRIMP U–Pb dating of zircon from the quartz syenite (JZS-3) defines a weighted mean 206Pb/238U age of 215F5 Ma (Fig. 2). A K-feldspar sample from the trachytoid pyroxene syenite (sample JZS-11) was dated by the40Ar/39Ar method and yields a plateau age of 214.4F0.3 Ma at high temperature
(Fig. 3a). A hornblende sample from porphyritic pyroxene syenite sample JZS-13 gives a plateau age of 214.6F0.6 Ma, composed of the steps with indistinguishable Ca/K ratio (22.56F0.44, Fig. 3b). These ages are consistent with the earlier Rb–Sr results of 220F13 Ma (Lin et al., 1992) and zircon U–Pb TIMS ages of 225F2 Ma and 211F3 Ma for pyroxene and quartz syenite, respectively (Chen et
al., 2003), and 211.9F1.5 Ma and 205.4F3.9 Ma
for pyroxene syenites (Guo et al., 2001b). Our new data indicate that the emplacement age of the syenites ranges from 215 to 209 Ma. The whole rock sample of ultrapotassic mafic dike defines an
40
Ar/39Ar plateau age of 200.6F0.2 Ma (Fig. 3c), constraining the emplacement age of the mafic dike. All these ages post-date the orogenic and UHP metamorphic ages of coesite-bearing eclogites in the Dabie–Sulu orogeny (240–220 Ma; Ames et al., 1993; Li et al., 1993a,b; Chavagnac and Jahn, 1996; Hacker et al., 1998; Webb et al., 1999; Zheng et al., 2002; Liu et al., 2004).
4.2. Geochemical characteristics
The geochemical and isotopic data for the syenites and mafic dike from the Jiazishan Complex are listed inTables 3 and 4.
The Jiazishan syenites show a range in SiO2values
from 54.44 to 64.20 wt.%. Nepheline-normative pyroxene syenites, mafic enclaves and the mafic dike represent a silica-undersaturated suite of rocks,
Fig. 2. SHRIMP U–Pb zircon concordia diagram for quartz syenite (JZS-3) from the Jiazishan Complex.
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 106
whereas the quartz syenites have normative quartz and are silica-saturated.
All samples plot in the alkaline field on the total alkali-silica (TAS) diagram (Fig. 4a). Three samples of mafic dike plot in the potassic trachybasalt field with N10% normative olivine (Table 3), whereas the other sample plots in the shoshonite field with Na2O-2bK2O (Table 3). Pyroxene syenite samples
plot in the latite and trachyte fields and quartz syenite plots in the trachyte field. One mafic enclave sample plots in the phonotephrite field and the other sample plots in the latite field (Fig. 4a). In the Na2O vs. K2O plot (Fig. 4b), pyroxene
and quartz syenites belong to the shoshonitic series, whereas the mafic dike samples, having K2ON3
wt.%, K2O/Na2ON2, MgON3 wt.% and high Cr
(477–873 ppm), are ultrapotassic rocks as defined by Foley et al. (1987).
Fig. 4c shows the composition of the syenites and mafic dikes in terms of their molar ratios of Al2O3/
(CaO+Na2O+K2O) (A/CNK) and Al2O3/(Na2O+K2O)
(A/NK). Based on these ratios, the pyroxene syenite and mafic dikes are metaluminous, whereas the quartz syenites straddle the metaluminous–peraluminous boundary. All rocks of the Jiazishan Complex display regular trends of increasing Al2O3, SiO2, Na2O, K2O
and decreasing CaO, Fe2O3, TiO2, P2O5, V, Cr and Ni
with decreasing MgO (Figs. 5 and 6). Pyroxene syenites and mafic enclaves have high Sr, Ba and Rb, whereas quartz syenites have low Sr and Ba contents (Fig. 6d–f). The mafic dikes always have a separate trend (Figs. 5 and 6), indicating that they are not comagmatic with the syenites.
The more siliceous rocks of the Jiazishan Complex (quartz syenite, SiO2N60 wt.%) display characteristics of A-type magmas as defined by Eby (1990), exhibiting anhydrous, hypersolvus mineral-ogy and an alkaline chemical affinity with low CaO (1.15–1.43 wt.%) and Sr and Ba concentrations (Table 3) and high Ga concentrations (N20 ppm). High concentrations of Zr, Nb, Ce and Y distin-guish the Jiazishan quartz syenites from I- and S-type granites and classify them as an A-S-type granite on the 10000 Ga/Al vs. Zr and Na2O+K2O
discrimination diagrams (Fig. 7a and b) of Whalen et al. (1987).
The chondrite-normalized REE patterns of the pyroxene syenites (Fig. 8a) show LREE enrichment,
Fig. 3. 40Ar/39Ar age spectra of (a) K-feldspar from pyroxene
syenite sample JZS-11, (b) hornblende from pyroxene syenite sample JZS-13 and (c) whole rock mafic dike (JZS-D-01).
Table 3
Chemical compositions of rocks from the Jiazishan Complex
No. JZS-01 JZS0-02 JZS-03 JZS-04 JZS-05 JZS-06 JZS-07-1 JZS-07-2 JZS-08-1 JZS-08-2 JZS-09 JZS-10 JZS-11 JZS-12 JZS-13 JZS-14 JZS-15 JZS-16 JZS-17 JZS-D-2 JZS-D-3 JZS-D-4 JZS-D-5
Rock Quartz syenite Enclave Py syenite Enclave Pyroxene syenite Pyroxene syenite Pyroxene syenite Mafic dike
Longitude and latitude
E122824V10.7", N36854V22.6" E122821’33.3", N37800’33.1" E122826’16.9",
N37801’13.7"
E122827’06.4", N36858’05.5" E122827’06.4", N36858’05.5"
Major element (in wt.%)
SiO2 63.57 63.70 64.03 64.01 64.20 63.13 53.45 60.10 48.09 60.06 59.72 60.11 59.31 58.47 54.44 56.59 56.29 55.86 56.67 48.05 48.27 46.60 50.81 TiO2 0.32 0.34 0.33 0.33 0.30 0.39 0.84 0.52 1.20 0.52 0.52 0.52 0.53 0.70 1.00 0.64 0.69 0.80 0.80 1.16 1.16 1.12 1.32 Al2O3 18.45 18.49 18.53 18.56 18.72 18.23 17.00 18.29 16.82 17.80 18.13 18.13 18.09 17.79 15.22 16.98 17.15 16.36 17.67 12.44 11.51 11.10 12.43 Fe2O3 2.37 2.34 2.28 2.37 2.03 2.87 7.54 3.84 10.20 3.88 3.97 3.82 4.09 4.49 7.27 5.56 5.62 5.87 5.15 8.84 8.90 8.60 7.33 MnO 0.11 0.10 0.10 0.11 0.08 0.13 0.16 0.10 0.16 0.10 0.11 0.10 0.10 0.10 0.15 0.11 0.13 0.14 0.10 0.13 0.14 0.13 0.11 MgO 0.35 0.24 0.28 0.32 0.20 0.41 3.07 1.36 4.80 1.44 1.40 1.33 1.49 1.17 3.56 2.36 2.52 3.22 2.36 10.04 12.44 11.97 8.06 CaO 1.37 1.27 1.31 1.34 1.15 1.43 5.90 3.06 6.74 3.14 3.13 3.03 3.38 2.74 5.44 4.21 4.20 4.93 3.91 8.24 8.78 8.47 6.88 Na2O 5.23 5.23 5.23 5.31 5.33 5.14 4.02 4.27 3.19 3.65 4.22 4.30 4.29 3.84 3.49 3.93 3.96 3.69 3.83 1.56 1.37 1.42 1.85 K2O 6.82 6.94 6.94 6.75 7.05 6.97 4.59 7.04 4.23 7.57 6.89 6.99 6.76 7.88 6.04 6.53 6.64 6.40 6.83 5.39 4.41 4.98 6.40 P2O5 0.09 0.07 0.07 0.08 0.06 0.10 0.81 0.33 1.26 0.35 0.33 0.32 0.35 0.24 0.73 0.54 0.52 0.59 0.51 0.99 0.96 0.93 0.97 TOTAL 98.68 98.71 99.10 99.17 99.11 98.78 97.38 98.90 96.69 98.50 98.42 98.65 98.39 97.41 97.33 97.46 97.72 97.86 97.82 96.84 97.94 95.32 96.14 Mg# 22.40 16.83 19.33 21.08 16.16 21.90 44.68 41.21 48.23 42.35 41.14 40.84 41.86 34.14 49.24 45.70 47.08 52.07 47.64 69.22 73.46 73.40 68.53 A/CNK 1.00 1.00 1.00 1.01 1.01 0.98 0.76 0.91 0.76 0.89 0.90 0.90 0.88 0.90 0.69 0.80 0.80 0.74 0.85 0.53 0.50 0.48 0.55 A/NK 1.15 1.15 1.15 1.16 1.14 1.14 1.47 1.25 1.71 1.25 1.26 1.24 1.26 1.20 1.24 1.25 1.25 1.26 1.29 1.48 1.64 1.44 1.25
CIPW normative minerals (%)
Q 3.84 3.83 4.02 4.16 3.62 3.24 1.03 2.38 1.22 1.22 0.47
Ne 0.50 2.82 0.84 0.42 1.63 0.99 0.31 3.45 0.85 4.34 1.06
Trace elements (in ppm)
V 32.6 30.5 29.6 31.4 26.7 29.1 162 76.3 185 72.4 76.2 70.0 79.1 76.8 126 103 104 98.7 104 172 166 154 133 Cr 2.80 4.47 3.16 2.96 2.42 2.05 6.09 10.3 36.9 7.74 9.56 15.2 12.3 11.6 63.1 18.8 19.5 51.2 14.9 630 873 834 477 Co 1.41 1.28 1.31 1.48 1.16 1.40 22.9 8.17 28.8 7.31 8.75 8.32 9.25 8.60 20.4 14.0 15.9 19.1 14.8 39.7 45.1 42.2 30.5 J.-H. Y ang et al. / Chemic al Geology 214 (2005) 99–125 108
Ni 1.81 2.77 1.79 1.73 1.63 1.65 13.6 6.38 18.4 6.78 8.13 9.14 7.76 8.55 18.2 12.6 15.0 15.2 12.9 224 319 300 119 Cu 5.30 3.92 4.56 4.23 3.91 3.95 47.0 6.41 27.3 21.4 7.47 10.2 9.98 14.8 15.3 10.5 12.4 39.6 18.3 45.9 58.8 57.4 133 Zn 57.5 47.5 50.0 53.9 44.5 58.0 132 65.0 141 68.6 64.7 67.8 80.0 69.9 84.8 64.4 67.3 81.0 68.4 81.2 77.1 72.0 108 Ga 21.9 21.5 21.8 21.8 21.6 22.0 21.4 20.0 20.4 19.5 20.3 20.0 20.3 22.2 23.3 21.3 21.3 22.1 20.2 16.0 14.9 14.3 16.4 Rb 145 146 150 138 147 145 126 162 113 159 155 155 153 179 184 179 196 193 179 113 86.4 102 161 Sr 221 205 192 191 217 213 2352 1323 3832 1409 1319 1213 1411 1053 1411 1790 2002 1511 2064 1649 1484 1413 1644 Y 44.0 50.4 47.0 47.0 43.4 53.7 37.1 25.9 30.5 28.2 25.4 23.7 24.7 49.0 45.5 29.1 27.4 35.7 32.2 24.2 23.3 22.2 20.8 Zr 699 635 675 680 557 848 514 651 276 588 685 621 631 1422 973 654 613 543 123 458 526 498 622 Nb 28.5 31.9 30.5 30.5 27.2 34.7 32.2 9.62 9.75 17.6 10.7 10.2 9.6 50.4 64.4 30.0 24.6 43.9 37.5 12.8 14.6 13.9 16.6 Cs 1.35 1.43 1.43 0.96 1.16 1.14 2.55 2.12 3.85 2.88 1.94 1.93 2.23 1.85 9.34 4.73 5.70 6.37 4.86 2.55 2.29 3.19 2.42 Ba 469 597 462 425 437 508 103700 4142 102000 4287 3914 3814 3939 2769 3448 5031 5689 3863 56230 5167 4763 4628 4254 La 168.4 135.5 133.8 147.9 135.1 164.4 150.4 97.20 129.1 100.6 89.95 79.66 84.27 194.7 147.1 118.0 115.8 132.9 137.6 78.75 65.68 62.94 62.02 Ce 322.9 280.9 266.4 282.0 256.9 320.1 282.5 174.3 248.7 188.1 167.4 148.7 157.2 389.6 306.0 220.0 210.6 258.1 272.5 157.9 136.7 130.8 125.0 Pr 33.60 31.56 29.03 29.52 27.09 33.86 30.17 18.95 28.43 20.27 18.05 16.08 17.12 41.67 33.41 22.85 21.92 27.27 29.16 19.35 16.96 16.12 15.21 Nd 121.1 120.2 108.0 106.6 97.17 124.3 113.3 72.51 116.8 77.23 69.24 62.50 66.68 152.7 126.1 84.32 81.68 101.5 109.6 75.83 66.46 63.43 58.82 Sm 17.77 20.29 17.42 16.28 14.88 18.96 16.49 10.67 17.46 11.45 10.42 9.53 10.13 21.80 18.86 12.27 11.87 14.98 16.45 12.82 11.69 11.00 10.03 Eu 2.31 2.25 2.01 1.94 1.69 2.19 4.45 2.96 5.36 2.93 2.82 2.69 2.83 3.50 3.61 3.05 3.17 3.05 3.99 4.06 3.54 3.31 3.15 Gd 13.86 15.32 13.25 12.83 11.72 14.44 12.65 8.24 13.13 8.76 7.94 7.15 7.71 16.09 14.09 9.42 9.11 11.22 11.78 9.82 8.85 8.22 7.56 Tb 1.85 2.24 1.86 1.74 1.63 1.98 1.52 1.03 1.50 1.10 1.00 0.92 0.98 2.04 1.78 1.14 1.11 1.41 1.45 1.08 1.00 0.94 0.86 Dy 8.60 10.89 8.98 8.28 7.71 9.37 6.50 4.64 6.15 4.88 4.46 4.12 4.37 8.87 7.95 5.04 4.76 6.21 6.21 4.62 4.44 4.19 3.85 Ho 1.55 1.99 1.64 1.52 1.42 1.72 1.17 0.82 1.03 0.89 0.81 0.74 0.79 1.57 1.41 0.89 0.85 1.09 1.05 0.87 0.83 0.78 0.73 Er 4.59 5.71 4.69 4.48 4.09 5.05 3.38 2.43 2.75 2.57 2.35 2.17 2.28 4.67 4.10 2.63 2.45 3.17 2.98 2.24 2.15 2.02 1.92 Tm 0.69 0.84 0.71 0.66 0.61 0.74 0.50 0.35 0.36 0.39 0.34 0.32 0.33 0.70 0.63 0.40 0.36 0.49 0.43 0.27 0.26 0.25 0.24 Yb 4.31 5.07 4.41 4.07 3.58 4.72 3.21 2.22 2.18 2.47 2.22 2.04 2.12 4.47 4.05 2.63 2.33 3.12 2.64 1.70 1.71 1.58 1.54 Lu 0.63 0.72 0.62 0.58 0.51 0.68 0.49 0.34 0.32 0.38 0.34 0.32 0.33 0.69 0.62 0.41 0.35 0.47 0.37 0.25 0.24 0.23 0.22 Hf 18.4 19.8 18.1 16.8 14.5 20.0 12.6 14.8 6.3 13.1 14.9 13.5 13.6 31.4 23.0 15.1 13.7 13.2 4.03 10.1 11.5 10.9 14.8 Ta 2.42 3.05 2.58 2.42 2.17 2.66 2.14 0.62 0.61 1.44 0.64 0.62 0.56 5.54 5.33 1.64 1.58 3.13 2.71 0.61 0.70 0.66 0.74 Pb 54.4 54.6 164 59.3 81.6 64.5 113 81.1 78.2 80.9 71.0 298 99.1 219 79.2 68.1 58.0 73.6 74.1 28.8 30.4 31.1 26.4 Th 24.2 21.8 21.4 22.0 22.2 26.2 46.5 10.5 5.72 17.6 10.5 9.00 8.42 47.6 49.7 28.4 28.4 59.8 26.4 8.82 9.24 8.99 5.81 U 2.58 2.76 2.99 2.91 1.98 2.73 7.33 1.98 1.44 5.36 1.94 1.97 2.07 5.06 15.2 6.02 7.27 9.02 5.09 1.68 1.80 1.73 1.21 J.-H. Y ang et al. / Chemical Geology 214(200 5) 99–125 109
Table 4
Sr and Nd isotopic compositions of rocks from the Jiazishan Complex
Sample no. Rock type Rb (ppm) Sr (ppm) 87Rb/86Sr 87Sr/86Sr 2r Sm (ppm) Nd (ppm) 147Sm/144Nd 143Nd/144Nd 2r 87Sr/86Sri eNd(t) a TDM(Ma) b fSm/Nd JZS-01 Qz syenite 138 221 1.805 0.712435 11 17.7 122 0.0882 0.511688 11 0.70692 15.6 1771 0.55 JZS-02 Qz syenite 138 205 1.947 0.713034 8 18.6 112 0.1000 0.511702 5 0.70708 15.6 1934 0.49 JZS-03 Qz syenite 141 195 2.090 0.713454 11 17.8 113 0.0952 0.511665 12 0.70706 16.2 1904 0.52 JZS-04 Qz syenite 132 195 1.966 0.712971 16 17.9 120 0.0907 0.511680 9 0.70696 15.8 1817 0.54 JZS-07-1 Mafic enclave 120 2352 0.1480 0.706891 11 18.0 126 0.0862 0.511733 7 0.70644 14.6 1690 0.56 JZS-08-1 Mafic enclave 112 3814 0.0853 0.706844 7 20.2 137 0.0890 0.511730 7 0.70658 14.8 1732 0.55 JZS-09 Py syenite 153 1215 0.3634 0.707840 14 11.7 80.3 0.0882 0.511687 6 0.70673 15.6 1773 0.55 JZS-10 Py syenite 153 1213 0.3638 0.707799 11 11.0 73.6 0.0900 0.511684 10 0.70669 15.7 1801 0.54 JZS-11 Py syenite 145 1294 0.3245 0.707695 8 11.4 77.0 0.0898 0.511709 7 0.70670 15.2 1769 0.54 JZS-12 Py syenite 173 1053 0.4745 0.708044 12 25.1 179 0.0852 0.511689 8 0.70659 15.5 1728 0.57 JZS-13 Py syenite 184 1339 0.3981 0.708026 10 22.3 151 0.0892 0.511710 6 0.70681 15.2 1759 0.55 JZS-14 Py syenite 182 1705 0.3091 0.707743 9 14.2 99.5 0.0862 0.511703 5 0.70680 15.2 1726 0.56 JZS-15 Py syenite 186 1837 0.2930 0.707711 8 13.6 94.7 0.0867 0.511673 12 0.70682 15.8 1769 0.56 JZS-16 Py syenite 187 1409 0.3840 0.708038 7 17.5 121 0.0876 0.511692 10 0.70686 15.5 1758 0.55 JZS-D-2 Mafic dike 110 1668 0.1908 0.707801 13 13.2 81.3 0.0981 0.511656 9 0.70722 16.5 1963 0.50 JZS-D-3 Mafic dike 102 1529 0.1923 0.707872 8 12.0 72.3 0.1007 0.511660 4 0.70728 16.4 2003 0.49 JZS-D-4 Mafic dike 5.97 36.2 0.0999 0.511655 6 16.5 1996 0.49 a and b: The143Nd/144Nd and147Sm/144Nd of chondrite and depleted mantle at present day are 0.512638 and 0.1967, 0.51315 and 0.222, respectively.
87Sr/86Sr
iand eNd(t) were calculated at 215 Ma.
J.-H. Y ang et al. / Chemic al Geology 214 (2005) 99–125 11 0
with steep slopes (LaN/YbN=28–37) and small or no
negative Eu anomalies. The quartz syenites (Fig. 8b) are also enriched in LREE, with LaN/YbN
values of 19–28. The distinctive negative Eu anomalies (Fig. 8b) and low Ti, Ba and Sr contents suggest that quartz syenites are highly differentiated rocks, in contrast to the pyroxene syenites. The chondrite-normalized REE patterns of the mafic dikes (Fig. 8c) are also steeply inclined and show relative enrichment of LREE over HREE (LaN/
YbN=29–43) without Eu anomalies. They have
lower total REE contents than either the pyroxene or quartz syenites.
In the primitive mantle-normalized trace element diagrams, pyroxene syenites (Fig. 9a) have highly variable trace element contents, particularly for Ba, Th, U, Nb, Ta, Zr and REE. They are characterized by enrichment in LILEs (i.e., Rb, Ba, Sr, Th and U) relative to LREEs (i.e., La, Ce, Pr, Nd and Sm) and HFSEs (i.e., Nb, Ta, P and Ti) with Ba/La and La/Nb ratios of 14–79 and 2.3–13. Quartz syenites have different patterns from the pyroxene syenites (Fig. 9b), with negative Ba and Sr anomalies and strong depletion in P and Ti. Mafic dikes have similar trace element patterns to the pyroxene syenites, but with weak Ti and P anomalies (Fig. 9c).
4.3. Nd and Sr isotopes
Table 4 gives the results of 17 new Nd and Sr
isotopic analyses which cover the major rock types of the Jiazishan Complex. The data are shown in a plot (Fig. 10) of eNd(t) vs. initial87Sr/86Sr ratios and
are compared on that diagram with published compositional fields for Late Mesozoic volcanic rocks from the Jiaodong Peninsula (Fan et al., 2001; Guo et al., 2001a), granites and lamprophyres (Yang, 2000; Yang et al., 2004). Also shown are compositional trends from available data for compo-nents of the lower and upper crust in the Jiaodong Peninsula (Jahn et al., 1999). Data for the Early Cretaceous samples were recalculated to a common age of 125 Ma.
The pyroxene syenites and quartz syenites from the Jiazishan Complex have very similar Nd and Sr isotopic ratios despite their geochemical differences. They have strongly negative eNd(t) values of 15.2
to 16.2 and low radiogenic initial87Sr/86Sr ratios of
Fig. 4. Classification of the Jiazishan Complex on the basis of (a) the TAS diagram. All the major element data have been recalculated to 100% on a H2O- and CO2-free basis (afterMiddlemost, 1994; Le
Maitre, 2002); (b) K2O vs. Na2O diagram, showing the Jiazishan
Complex to be shoshonitic and ultrapotassic (afterMiddlemost, 1972); (c) A/NK vs. A/CNK plot. All samples except for quartz syenites fall in the metaluminous field.
0.70659–0.70708. The mafic dikes have similar eNd(t) values (~ 16.5) to the syenites but have more
radiogenic initial 87Sr/86Sr ratios (0.70722–0.70728)
than the syenites. The mafic enclaves have slightly higher eNd(t) values ( 14.6 to 14.8) and less
radiogenic initial 87Sr/86Sr ratios (0.70644–0.70658)
Fig. 5. Major element oxides vs. MgO plots for the Jiazishan Complex. (a) Al2O3; (b) SiO2; (c) Fe2O3; (d) TiO2; (e) Na2O; (f) CaO; (g) K2O and
(h) P2O5.
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 112
than either the syenites or the mafic dikes (Fig. 10). All these rocks plot near the field of Early Creta-ceous mafic volcanic rocks but far from those of
Late Jurassic to Early Cretaceous granites and mafic dikes, lower crust and upper crust (Fig. 10). The model age (TDM, depleted mantle age, Sm–Nd) of
Fig. 6. Selected trace element and elemental ratios vs MgO plots for the Jiazishan Complex. (a) V; (b) Cr; (c) Ni; (d) Rb; (e) Sr; (f) Ba; (g) Ce/Pb and (h) Nd/P2O5.
the Jiazishan samples is mainly in the range of 2.0– 1.7 Ga (Table 4).
5. Petrogenesis of the mafic dikes 5.1. Mantle source
The low silica contents (46.6–50.8 wt.%) and relatively high concentrations of MgO (8.1–12.4 wt.%), Cr (477–872 ppm) and Ni (119–318 ppm) suggest that the mafic dikes were derived from an ultramafic source. Crustal rocks can be ruled out as possible sources because experimental evidence shows that partial melting of any of the older, exposed crustal rocks (e.g.,Hirajima et al., 1990; Yang et al., 1993; Zhang et al., 1994, 1995; Kato et al., 1997) and lower crustal intermediate granulites (Gao et al.,
1998a,b) in the deep crust would produce high-Si, low-Mg liquids (i.e., granitoid liquids; Rapp et al., 2003), not the highly magnesian magmas present in the Jiazishan Complex.
The parental magmas to the Jiazishan ultra-potassic mafic dikes have undergone variable amounts of clinopyroxene and olivine fractionation inferred from the correlation between Cr, Ni and MgO (Fig. 6b and c). Plagioclase was not an important fractionated phase, given the absence of negative Eu anomalies (Fig. 8c) and the occurrence of plagioclase phenocrysts in these lavas. Clinopyr-oxene and olivine were the main fractionated phases (see below). However, mafic lavas (such as JZS-D-3
Fig. 7. (a) Na2O+K2O and (b) Zr vs. 10000Ga/Al discrimination
diagrams showing that the syenites are A-type granites. After
Whalen et al. (1987), I=I-type, S=S-type and M=M-type granitoids.
Fig. 8. Chondrite-normalized REE patterns for (a) pyroxene syenite, (b) quartz syenite and (c) mafic dike from Jiazishan Complex. Note that all the quartz syenites have negative Eu anomalies. The chondrite values are fromSun and McDonough (1989).
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 114
and 4) with high MgO contents and Mg#c73 are near-primary melts.
The parental magmas, represented by samples JZS-D-3 and 4, have 46.6–48.3 wt.% SiO2 and
12.0–12.4 wt.% MgO, as well as elevated Mg# (~73.5), Cr (834–873 ppm) and Ni (300–319 ppm), moderately low CaO/Al2O3 (~0.76) and low TiO2
(~1.12 wt.%). The composition of these mafic dikes is similar to that of experimental melts from depleted
peridotite (Falloon et al., 1988), indicating a domi-nantly refractory lithospheric mantle contribution to the magma. The mafic dikes also share high La/Sm (~6) and depleted heavy REE and HFSE signatures, along with low Ti/V and Ti/Zr ratios and enrichment in Zr relative to Sm (Table 3 and Fig. 9c). The trace element systematics of the mafic dikes signify derivation from a refractory peridotite more depleted than the residua from MORB generation (Hickey and
Frey, 1982), which has been overprinted by an
enriched component.
The high K2O content (N4 wt.%) of the mafic dikes
requires a potassic phase in the source region. Melts in equilibrium with phlogopite are expected to have significantly higher Rb/Sr and lower Ba/Rb values than those formed from amphibole-bearing sources (Furman and Graham, 1999). High Ba/Rb (N45) and relatively low Rb/Sr (b0.1) ratios strongly suggest that the parental magmas to the mafic dikes formed through partial melting of an amphibole-bearing source. Therefore, the mafic dikes were derived from partial melting of an amphibole-bearing, refractory lithospheric mantle source.
5.2. Lithospheric mantle beneath the Sulu region The incompatible element contents and negative eNd(t) values (~ 16.5) of these mafic dikes are more
typical of crust-derived melts. The possibility remains that these chemical signatures resulted from crustal contamination during transport through the continen-tal crust. However, the low silica and high MgO and the lack of correlation of isotopic compositions with MgO (Fig. 11) preclude significant crustal assimila-tion during magma ascent.
The Nb/U (7.6–13.7) and Ce/Pb (7.6–9.9) ratios for the Jiazishan mafic dike are significantly lower than in mid-ocean ridge basalt or ocean island basalt (47 and 27, Hofmann et al., 1986), indicating the involvement of crustal components in their source region. The depletion of HFSEs relative to LILEs and LREEs (Fig. 9c) is usually considered to be indicative of arc magmas or magmas derived from ancient crust. However, O and H isotopic evidence indicates that the process of continental subduction is characterized by the relative lack of fluids (Zheng et al., 2003). Therefore, no significant amount of slab-released fluids or melts metasomatized the overlying
Fig. 9. Primitive mantle (PM) normalized diagrams for (a) pyroxene syenite and enclave, (b) quartz syenite and (c) mafic dike. Elements are arranged in the order of decreasing incompatibility from left to right. The PM values are fromSun and McDonough (1989).
lithospheric mantle during the Triassic subduction. Instead, the Yangtze lithospheric mantle can be considered the candidate that is consistent with the enrichment in incompatible and mobile elements, such as K, Rb, Pb and the LREEs, and depletion in the HFSEs. Nevertheless, the enrichment of mobile elements like K and Rb may be caused by the introduction of metamorphic fluids that were derived from decompression exsolution from amphibole, phengite and clinopyroxene and thus their arrival triggered partial melting (Zheng et al., 2003). The slight enrichment of the mafic dike samples in Rb/Sr and Nd/Sm, combined with their high initial
87
Sr/86Sr ratios and negative eNd(t) values, is
consistent with derivation from such an enriched part of the lithosphere.
In summary, the ultrapotassic mafic dike origi-nated from mafic magma that was derived from partial melting of an enriched lithospheric mantle source that was metasomatized by a subducted crustal component prior to magma generation and experienced fractionation of clinopyroxene and oli-vine. Unlike the subduction of oceanic crust that
accompanied a significant release of aqueous fluid to result in arc magmatism, a continental subduction did not produce a sufficient amount of aqueous fluid to metasomatize the overlying lithospheric mantle
(Zheng et al., 2003). Therefore, we prefer the
subducted Yangtze lithospheric mantle as the source of mafic dike.
6. Petrogenesis of the syenites
Assimilation, crystal fractionation (AFC) or magma mixing are usually postulated to explain the occurrence of comagmatic mafic and felsic rocks (e.g., DePaolo, 1981; Devey and Cox, 1987; Marsh, 1989; Mingram et al., 2000). Crustal assimilation, coupled with fractional crystallization, would result in progressive decreases in Cr, Ni, Co and MgO (or Mg#s), with concomitant increase in initial 87Sr/86Sr ratios and decrease in eNd(t) values. Magma mixing
should generate mixing curves in the isotopic corre-lation diagrams and in plots between isotopic ratios and certain elements (e.g., MgO or SiO2). These
Fig. 10. Sr and Nd isotopic data from the Jiazishan Complex compared with those of various Late Mesozoic igneous rocks from the Jiaodong Peninsula (Yang, 2000; Fan et al., 2001; Guo et al., 2001a; Yang et al., 2004). Also plotted are trends to Lower and Upper Crust (afterJahn et al., 1999). Inset is enlargement of Jiazishan Complex data set. Initial Sr and Nd isotopic ratios were calculated at 215 Ma, whereas those of Late Mesozoic rocks were calculated at 125 Ma.
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 116
features are not observed in the Jiazishan Complex (Figs. 6a–c and 11). The variation in composition within the Jiazishan Complex is not associated with a significant shift in isotopic composition (Fig 11); thus, neither magma mixing nor crustal assimilation are feasible mechanisms.
A major obstacle in identifying petrogenetic lineage among the syenites is that most rocks probably do not represent liquid compositions. The close similarities in Sr and Nd isotopic composition between syenites (containing mafic enclaves) and mafic dikes suggest a common source region. The most obvious candidates for the parental magmas of the syenites are similar to those of the mafic dikes, which have low silica (46–48 wt.%) and relatively high MgO content (~12 wt.%; Mg#~73.5). Although the dikes have been intruded after the syenites, it is possible that they crystallized from liquids equivalent in composition to those from which the syenites evolved.
On various major and trace element plots (Figs. 5
and 6), the relationship between mafic dike and
syenite samples are in agreement with closed-system crystal fractionation of mafic magma. The CaO content decreases with decreasing MgO contents (Fig. 5a). The Fe2O3 vs. MgO is similar to that of
CaO vs. MgO in that it steepens with declining MgO content (Fig. 5c and f). Cr, on the other hand, shows a continual decline as MgO decreases down to MgO~3 wt.%, when the Cr content becomes zero (Fig. 6b). As extensive clinopyroxene and feldspar fractionation would strongly alter the Ca/Al ratio of the melt, these two observations are consistent with continuous fractionation of pyroxene and feldspar and the onset of magnetite fractionation from MgOb3 wt.%. This is supported on the Ni and V vs. Cr diagrams (Fig. 12a and b) in which the variations in the mafic dikes and pyroxene syenites are consistent
Fig. 11. Plot of (a) initial87Sr/86Sr ratio and (b) e
Nd(t) value vs.
MgO, indicating crystal fractionation. See text for detailed discussion.
Fig. 12. (a) Ni and (b) V vs. Cr diagrams showing olivine- and clinopyroxene-dominated fractionation in the evolution of parental magmas to the Jiazishan Complex. Partition coefficients are from
Rollinson (1993).
with fractionation of clinopyroxene and olivine. The quartz syenites have lower Cr, Ni, Co and MgO, perhaps the result of these magmas having passed the peritectic where clinopyroxene and olivine disappear and feldspar fractionates.
The plots of Al2O3and Sr vs. MgO are similar (Figs. 5a and 6e). The Al2O3 content increases as MgO
decreases from 13 to ~2 wt.% and shows a sudden decline for MgO less than ~2 wt.%. Sr shows a general increase as MgO decreases to about MgO=5 wt.%, then shows a steep decline as MgO decreases further. These plots are consistent with feldspar fractionation below MgO~5 wt.%, which may explain the lack of Eu anomalies in the pyroxene syenites and mafic dikes with MgON5 wt.% (Fig. 9a and c). Feldspar fractiona-tion is also supported by significant deplefractiona-tions in Sr, Ba and Eu shown in the mantle-normalized trace element patterns (Figs. 8b and 9b). Negative Eu anomalies, combined with decreases in Ba and Sr (Fig. 13a and b), indicate that alkali feldspar and plagioclase have been
removed during magma evolution. In the Rb/Sr and Ba vs. Sr diagrams (Fig. 13c and d), decrease in Ba contents and increase in Rb/Sr ratios with decreasing Sr concentrations are the result of fractionation of alkali feldspar and plagioclase with biotite.
In addition to major phases, accessory minerals would have controlled much of the REE variation. The decrease in REE with increasing SiO2 contents
(Table 3) suggests a separation of minerals with high partition coefficients (Kd), such as apatite, titanite,
zircon, allanite and monazite, all of which are important accessory minerals in these rocks. The sharp P2O5 decrease and Nd/P2O5 increase through
pyroxene syenites to quartz syenites (Figs. 5h and 6h) are consistent with progressive removal of apatite. Accessory allanite (increasing Ce/Sr, Fig. 6g) is probably involved. Limited Zr variation restricts the involvement of zircon.
On the basis of the geochemical and isotopic data, we can conclude that the Jiazishan syenites
Fig. 13. Eu/Eu* vs. (a) Sr and (b) Ba. (c) Rb/Sr and (d) Ba vs. Sr diagrams showing plagioclase-, K-feldspar- and biotite-dominated fractionation in the evolution of the syenitic magma. Partition coefficients are fromRollinson (1993).
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 118
were derived from an enriched mantle source, similar to that of the mafic dikes. Major and trace element trends can be explained by the switch from clinopyroxene- and olivine-dominated crystalliza-tion, controlling evolution of the mafic magmas to metaluminous pyroxene syenite, to biotite- and plagioclase-dominated crystallization, with minor hornblende and accessory mineral contribution, controlling the pyroxene syenite to quartz syenite trend, i.e., A-type granites.
7. Tectonic implications
Field relationships, petrological, geochronological and geochemical data emphasize that the syenites and mafic dike from the Jiazishan Complex in the Sulu Orogenic belt were derived by partial melting of a metasomatized, refractory lithospheric mantle source, displaying features similar to other alkaline rocks referred to in the literature as post-collisional (Sylvester, 1989) or post-orogenic/anorogenic syen-ites (Bonin, 1990). Bonin (1990) proposed that alkaline granitoids post-dating a major orogenic episode can be divided into two groups, i.e., post-orogenic (PO) and early anpost-orogenic (EA) granitoids. Post-orogenic magmas are characterized by Mg/Mn-rich mafic minerals, high Ba and Sr abundances and crustal Sr isotopic signatures, whereas the early anorogenic granitoids are characterized by Fe-rich mafic mineral assemblages, low Ba and Sr abundan-ces and low initial Sr isotopic ratios. The transition from PO to EA types takes place within a rather short time period (10 Ma long) and has been ascribed to a new mantle source replacing an old complex system of mixed oceanic–continental crust– mantle sources and producing alkaline melts (Bonin et al., 1998).
The Jiazishan intrusive suite belongs to the PO group of alkaline rocks. Ages of emplacement (215– 200 Ma) indicate the magmatism post-dates the UHP metamorphic event at 240 to 220 Ma and thus the continental collision between North China and Yang-tze cratons. Furthermore, the ultrapotassic basic magmas of the Jiazishan Complex were derived from an enriched lithsopheric mantle source without addi-tion of new mantle material (e.g., asthenospheric mantle). They are also distinguished geochemically
and by tectonic setting from the anorogenic Na-rich granitoid suites of alkaline ring complexes derived from OIB-type mantle sources (e.g., Bonin, 1990; Bonin et al., 1998).
Chen et al. (2003) suggested that these syenites were syn-orogenic granitoids, resulting from oceanic slab breakoff of the buoyant continental lithosphere during subduction (Davies and von Blanckenburg, 1995; Chen et al., 2003). However, zircon SHRIMP U–Pb data and inferred P–T paths of metamorphic rocks show that the ultrahigh pressure metamorphic event occurred at 240 to 230 Ma, with a late amphibolite facies retrogressive overprint at 220 to 200 Ma (Hacker et al., 1998; Webb et al., 1999; Zheng et al., 2002; Liu et al., 2004), indicating the protoliths of UHP metamorphic rocks were sub-ducted to mantle depths in the Early–Middle Triassic and exhumated to mid-crustal levels in the Late Triassic. Furthermore, the syenites and mafic dikes of the Jiazishan Complex have signifi-cant arc signatures such as enrichment in LILE and LREE and depletion in HFSE (Fig. 9). Geochem-ical and Sr and Nd isotopic data indicate that they were derived from an enriched lithospheric mantle and formed by closed-system fractionation of their parental magmas. Because small fractions of K-rich melt can be produced by fluid-absent phengite dehydration-melting of metabasalts (flush melting)
(Schmidt and Poli, 2003), Zheng et al. (2003)
advocated that this mechanism is responsible for the generation of the Late Triassic potassic–ultrapotas-sic rocks in the Dabie–Sulu orogenic belt and thus classified them as the product of syn-exhumation magmatism rather than syn-collisional magmatism. In this regard, partial melting of the subducted Yangtze lithospheric mantle and its overlying lower crust after the breakoff is principally capable of generating the observed geochemical and isotopic features for both mafic dike and syenites. They are distinguished geochemically and tectonically from those syn-collisional granites which are generally peraluminous granitoids (granodiorites and leucog-ranite) and K-rich calc-alkaline granitoids (monzog-ranites) (Barbarin, 1990). In addition, slab breakoff should induce a linear heat pulse along the subduction zone that produces a long linear belt of K calc-alkaline bodies associated with high-or low-grade regional metamhigh-orphism (Davies and
von Blanckenburg, 1995; Atherton and Ghani, 2002). These have not been found in the Dabie– Sulu UHP belt. In contrast, there is a large Triassic granitoid belt in southern Qinling (Sun et al., 2002), but no UHP metamorphic rocks were ever reported there.
An alternative possibility is lithospheric thinning and crustal extension induced by convective insta-bility of a thickened mantle boundary layer ( House-man et al., 1981). The change in potential energy in the remaining lithosphere would then lead to a sudden uplift of the Sulu orogen (e.g., England and
House-man, 1989; Houseman and England, 1993). This is
evidenced by the Sm–Nd and Rb–Sr isotopic chronology of UHP metamorphic rocks and their country rocks, which distinguish two stages of rapid cooling of the deep-subducted slab corresponding to two stages of fast uplift (Li et al., 2003): initial rapid uplifting and cooling subsequent to the peak UHP metamorphic event may be caused by slab breakoff, and later rapid cooling may be caused by partial delamination due to the convective removal of lithsopheric mantle and related extension. Davies
and von Blanckenburg (1995) suggested that slab
breakoff in the Dabie–Sulu orogenic belt occurred at great depth to allow the subduction of crustal rocks to presuures of 4 GPa (N130 km). Linear magmatism would occur with breakoff at such great depths, which is not observed in the Dabie–Sulu orogenic belt. Consequently, the Jiazishan syenites and ultrapotassic dike would result from the convective removal of the lower continental litho-spheric mantle, which triggers crustal extension and decompressional melting of subducted lithospheric mantle. These rocks were emplaced where there is transition from continental plate convergence to continental plate divergence and may be good indicators of major change in the geodynamic environment.
8. Concluding remarks
The zircon U–Pb and 40Ar/39Ar ages of the Jiazishan syenites and mafic dikes in the Sulu UHP belt indicate that they evolved between 215 and 201 Ma, post-dating the UHP metamorphism due to continental collision of the North China and
Yangtze cratons. The suite has the characteristics of post-orogenic alkaline sequences as defined by
Bonin, (1990, 1998), i.e., alkaline pyroxene syen-ite–quartz syenite–ultrapotassic mafic dike associa-tion, representing the last magmatic event of the Sulu orogenesis due to partial melting of the subducted Yangtze lithospheric mantle during exhumation. The Jiazishan syenites and mafic dike belong to the potassic to ultrapotassic series and are of alkaline affinity. Field relations, petrography, geochemistry and isotopic composition define an evolution of lithospheric mantle-derived magmas that have expe-rienced extensive fractionation and minor contami-nation by crustal material. The silica-saturated A-type magmatism was not an intracrustal differentia-tion process but involved redistribudifferentia-tion of mass vertically within the lithosphere. Partial melting occurred in a post-orogenic setting related to litho-spheric removal and crustal extension induced by convective instability of a thickened mantle boun-dary layer and was not directly related to subduction. Interpretation of the data leads to an integrated model of syenite genesis in a post-orogenic exten-sional setting.
Acknowledgements
The authors would like to thank G. Nelson Eby, Roberta Rudnick and an anonymous reviewer for their constructive reviews of this manuscript. Prof. Yong-Fei Zheng is acknowledged for his suggestions and revisions on the revised version of the manu-script. J.H. Yang benefited from a 1-year stay in the Department of Geosciences, National Taiwan Uni-versity. We thank Chao-Feng Li for helping analyze Sr and Nd isotopes and Jing-Zhang Shi for help with
40
Ar/39Ar dating. The SHRIMP Laboratory at Curtin University is supported by the Australian Research Council and is operated by a consortium composed of Curtin University of Technology, the University of Western Australia and the Geological Survey of Western Australia. This study was supported by the National Science Foundation of China (Grant nos. 40133020, 40203005, 40325006 and 40132020) and the Chinese Academy of Sciences (Grant no. KZCX1-07 and bFunds for Hundred Outstanding Talents PlanQ. [RR]
J.-H. Yang et al. / Chemical Geology 214 (2005) 99–125 120
AGV-1 AGV-1 AGV-1 AGV-1a BCR-2 BCR-2a BHVO-2 BHVO-2 BHVO-2a BIR-1 BIR-1 BIR-1a JB-1 JB-1 JB-1a JG-1 JG-1a V 109 118 115 120F11 408 416F14 283 320 317F3 315 316 310F11 195 195 211F20 26 25.2F3.7 RSD% 3.7 6.3 0.9 0.9 1.9 1.3 3.9 1.8 0.2 0.2 1.2 Cr 8.16 7.59 8.33 10F3 17.22 18F2 267 278 280F7 375 375 370F8 492 425 425F63 54.2 53F6.9 RSD% 3.4 5.2 0.7 4.4 1.6 0.8 3.9 0.8 1.5 0.3 1.2 Co 13.9 14.4 15.9 15F1.2 37.11 37F3 41.8 46.6 45F7 50.6 50.7 52F2 43.2 37.4 38.2F5.2 4.16 4.1F0.8 RSD% 1.2 4.7 0.4 2.5 2.8 2.5 1.4 1.1 0.8 0.2 1.4 Ni 14.0 14.6 16.2 16 12.71 113 123 119F6 164 164 170F6 155 132 133F17 7.6 7F2.6 RSD% 2.7 4.3 0.3 3.0 3.4 2.3 2.44 0.97 0.5 0.5 1.4 Cu 56.9 60.0 62.5 60F6 21.59 19F2 129 130 127F6 123 121 125F4 59.8 51.3 55F5.5 2.64 2.5F1.2 RSD% 3.1 3.9 0.5 2.6 3.4 0.5 1.2 0.7 0.4 0.4 1.4 Zn 82.2 85.3 84.6 88F9 131.38 127F9 104 110 103F6 68.0 67.3 70F9 92.9 82.9 85.2F9.9 45.4 41.1F5.6 RSD% 2.3 4.8 0.7 1.0 3.1 1.7 2.2 1.4 1.2 1.0 0.8 Ga 19.7 20.5 21.2 20F3 23.3 23F2 20.8 21.6 21.7F4.0 14.6 14.6 16 18.1 17.3 17.9F2.9 17.4 17.8F3.1 RSD% 0.2 5.0 1.1 0.6 1.8 0.1 2.2 0.4 0.7 0.8 0.8 Rb 68.1 69.6 67.7 67F1 50.18 48F2 9.73 9.63 9.8F1.0 0.21 0.14 1.0F0.9 41.4 41.0 41.3F5.1 182 182F9.1 RSD% 1.4 4.3 0.9 0.6 1.9 1.9 36.1 18.5 1.4 0.4 0.7 Sr 644 656 642 660F9 350.88 346F12 413 397 389F6 108 108 110F2 444 454 444F29 186.0 184F17 RSD% 1.5 6.4 1.3 2.7 2.2 0.8 3.9 2.3 1.5 0.4 0.6 Y 19.4 20.0 20.0 20F3 38.47 37F2 28.3 27.6 26F2 15.6 15.6 16F1 24.3 24.0 24.3F3.6 31.4 30.6F2.5 RSD% 1.4 5.5 0.6 0.5 1.2 1.4 4.9 1.4 1.1 0.4 0.6 Zr 220 226 227 227F18 190.57 188F16 177 176 172F6 13.6 13.5 18F1 138 133 141F22 118 111F27 RSD% 3.8 3.9 0.7 3.4 0.9 1.1 4.9 1.2 1.3 0.7 0.6 Nb 12.7 13.0 14.9 15 11.88 17.8 17.4 18F2 0.47 0.46 0.6 35.2 33.6 33.3F6.5 11.4 12.4F1.3 RSD% 1.7 4.8 0.5 2.3 2.6 1.3 4.1 1.9 0.9 0.8 0.5 Cs 1.23 1.26 1.15 1.3F0.1 1.22 1.1F0.1 0.10 0.10 0.45F0.1 1.17 1.41 1.23F0.2 9.00 10.1F1.1 RSD% 2.3 2.7 1.0 2.3 4.3 1.3 91 13 0.8 1.2 0.4 Ba 1172 1209 1188 1230F16 707.68 683F28 142 130 130F13 7.37 6.38 7 477 594 493F46 468 466F27 RSD% 0.8 2.6 0.7 1.7 3.2 2.2 17.8 2.5 0.5 0.5 0.4 La 38.32 39.46 38.79 38F2 26.72 25F1 15.97 15.68 15F1 0.65 0.56 0.63F0.1 42.89 35.01 38.6F4.3 22.82 22.4F2.7 RSD% 1.0 3.5 0.7 0.8 2.2 1.0 6.9 1.5 0.4 0.9 0.5 Ce 67.97 69.90 69.44 67F6 51.57 53F2 39.21 40.49 38F2 1.92 1.72 1.90F0.4 74.82 61.40 67.8F6.8 45.71 45.8F4.7 RSD% 2.2 3.3 1.0 1.3 1.9 0.6 3.8 2.5 0.3 0.7 0.8 Pr 7.85 8.07 8.33 7.6 6.89 6.8F0.3 5.30 5.41 0.35 0.34 0.5F0.4 7.44 6.29 7.01F0.8 4.87 4.83F1.0 RSD% 1.2 4.1 0.6 1.7 0.6 1.4 2.6 1.4 0.3 0.4 1.4 Nd 30.88 31.31 32.04 33F3 30.40 28F2 25.48 25.97 25.0F1.8 2.32 2.24 2.5F0.7 28.29 24.64 26.8F2.3 19.76 19.3F2.5 Appendix A Table A
Measured and recommended trace element data (ppm) for rock standards
(continued on next page)
J.-H. Y ang et al. / Chemical Geology 214(200 5) 99–125 121
AGV-1 AGV-1 AGV-1 AGV-1a BCR-2 BCR-2a BHVO-2 BHVO-2 BHVO-2a BIR-1 BIR-1 BIR-1a JB-1 JB-1 JB-1a JG-1 JG-1a RSD% 1.5 4.7 0.5 1.5 1.7 1.7 3.2 0.8 0.5 1.2 0.7 Sm 5.62 5.70 5.83 5.9F0.4 6.74 6.7F0.3 6.33 6.38 6.2F0.4 1.06 1.02 1.1 5.45 4.83 5.13F0.5 4.68 4.62F0.56 RSD% 1.9 4.9 0.9 0.9 2.4 1.1 2.8 0.9 1.8 1.0 2.1 Eu 1.58 1.61 1.84 1.6F0.1 1.96 2.0F0.1 2.01 2.03 0.46 0.44 0.55F0.05 1.50 1.31 1.49F0.15 0.78 0.73F0.95 RSD% 1.8 3.3 0.8 0.9 4.3 0.9 0.7 2.4 0.8 1.1 0.8 Gd 4.83 4.92 5.35 5F0.6 6.60 6.8F0.3 6.11 6.04 6.3F0.2 1.53 1.48 1.8F0.4 5.14 4.48 4.90F0.47 4.23 4.28F0.69 RSD% 2.5 3.2 1.0 3.2 2.3 1.4 1.3 2.0 0.7 1.3 1.7 Tb 0.66 0.68 0.73 0.7F0.1 1.11 1.07F0.04 1.00 1.02 0.9 0.35 0.33 0.41F0.10 0.84 0.76 0.82F0.2 0.81 0.78F0.31 RSD% 3.0 5.4 0.8 0.9 1.3 0.4 1.8 1.8 0.7 1.5 0.7 Dy 3.48 3.55 3.59 3.6F0.4 6.56 5.57 5.37 2.42 2.38 2.4F0.3 4.46 4.15 4.14F0.38 4.35 4.14F1.22 RSD% 0.6 4.9 0.8 1.1 2.8 2.2 0.9 1.4 1.0 1.8 0.7 Ho 0.65 0.67 0.70 1.32 1.33F0.06 1.05 0.99 1.04F0.04 0.54 0.53 0.5F0.1 0.84 0.79 0.79F0.098 0.87 0.81F0.23 RSD% 0.7 4.0 1.1 1.2 1.9 2.3 1.5 2.1 0.8 2.4 0.6 Er 1.78 1.82 1.92 1.7 3.74 2.73 2.54 1.57 1.57 1.8F0.3 2.36 2.24 2.27F0.19 2.32 2.16F0.65 RSD% 1.9 1.6 0.9 1.7 2.3 2.0 1.93 0.86 0.5 1.2 0.2 Tm 0.26 0.26 0.27 0.34 0.54 0.54 0.36 0.34 0.25 0.24 0.27F0.10 0.36 0.34 0.35F0.056 0.45 0.41F0.14 RSD% 1.5 3.1 1.6 2.2 3.5 0.7 2.4 0.8 2.5 1.3 1.9 Yb 1.63 1.64 1.67 1.72F0.2 3.46 3.5F0.2 2.17 2.09 2.0F0.2 1.56 1.53 1.7F0.2 2.20 2.11 2.13F0.26 2.46 2.47F0.73 RSD% 1.3 5.9 1.1 2.0 1.9 2.7 0.8 3.0 1.8 0.4 1.3 Lu 0.25 0.26 0.26 0.27F0.03 0.52 0.51F0.02 0.31 0.30 0.28F0.01 0.24 0.24 0.26 0.33 0.31 0.31F0.029 0.40 0.39F0.12 RSD% 1.4 4.4 1.2 4.8 3.4 4.5 2.8 0.9 0.6 1.4 1.0 Hf 4.97 4.97 5.09 5.1F0.4 4.82 4.8F0.2 4.77 4.38 4.1F0.3 0.54 0.53 0.6F0.08 3.51 3.40 3.31F0.56 3.53 3.56F1.03 RSD% 1.5 3.9 0.8 1.4 1.1 0.6 4.3 2.7 0.9 0.9 1.1 Ta 0.83 0.85 1.04 0.9F0.1 0.73 1.29 1.18 1.4 0.04 0.04 0.06F0.05 3.25 2.88 2.93F0.79 1.79 1.79F0.51 RSD% 1.6 4.8 5.7 3.0 1.8 1.2 7.7 1.6 1.1 0.8 1.1 Pb 37.0 37.3 38.1 36F5 11.10 11F2 1.70 1.58 3.19 3.06 3 10.1 10.1 10F4.1 25.1 25.4F3.1 RSD% 1.0 3.3 0.5 0.3 1.7 2.3 3.6 1.5 1.6 0.6 1.6 Th 6.43 6.56 6.49 6.5F0.5 6.27 6.2F0.7 1.39 1.28 1.2F0.3 0.24 0.13 0.89F0.7 8.85 9.52 9.3F0.7 13.46 13.2F1.6 RSD% 2.5 3.2 0.8 1.4 0.9 0.8 28.4 8.2 0.4 0.5 1.0 U 1.85 1.91 1.93 1.92F0.2 1.56 1.69F0.19 0.46 0.43 0.01 0.01 0.05 1.59 1.72 1.67F0.28 3.59 3.47F0.71 RSD% 2.0 3.7 0.5 0.5 3.8 1.1 29.9 4.3 1.3 1.5 0.6
Recommended data are from:
JB-1 And JG-1: Imai, N., Terashima, S., Itoh, S., Ando, A., 1995. 1994 Compilation of analytical data for minor and trace elements in seventeen GSJ geochemical reference samples. Igneous Rock Series, Geostandards Newsletter 19, 135–213.
BIR-1, BHVO-1 and AGV-1: Govindaraju, K., 1994. 1994 Compilation of Working Values and Descriptions for 383 Geostandards. Geostandards Newsletter 118, 1–158. BCR-2: Wilson, S.A., 1997. The collection, preparation, and testing of USGS reference material BCR-2, Columbia River, Basalt. U.S. Geological Survey Open-File Report 98-00x. Appendix A (continued) J.-H. Y ang et al. / Chemic al Geology 214 (2005) 99–125 122
References
Ames, L., Tilton, G.R., Zhou, G.Z., 1993. Timing of collision of the Sino-Korean and Yangtze cratons: U-Pb zircon dating of coesite-bearing eclogites. Geology 21, 339 – 342.
Atherton, M.P., Ghani, A.A., 2002. Slab breakoff: a model for Caledonian, late granite syn-collisional magmatism in the orthotectonic (metamorphic) zone of Scotland and Donegal, Ireland. Lithos 62, 65 – 85.
Barbarin, B., 1990. Granitoids: main petrogenetic classifications in relation to origin and tectonic setting. Geol. J. 25, 227 – 238. Barker, F., Wones, D.R., Sharp, W.N., Desborough, G.A., 1975. The
Pikes Peak batholith, Colorado Front Range, and a model for the origin of the gabbro-anorthosite-syenite-potassic granite suite. Precambrian Res. 2, 97 – 160.
Bonin, B., 1990. From orogenic to anorogenic settings: evolu-tion of granitoid suites after a major orogenesis. Geol. J. 25, 261 – 270.
Bonin, B., Platevoet, B., Vialette, Y., 1987. The geodynamic significance of alkaline magmatism in the Western Medi-terranean compared with West Africa. In: Bowden, P., Kinnaird, J. (Eds.), African Geology Reviews, Geol. J., vol. 22, pp. 361 – 387.
Bonin, B., Azzouni-Sekkal, A., Bussy, F., Ferrag, S., 1998. Alkali-calcic and alkaline post-orogenic (PO) granite magma-tism: petrologic constraints and geodynamic settings. Lithos 45, 45 – 70.
Brown, P.E., Becker, S.M., 1986. Fractionation, hybridisation and magma-mixing in the Kialineq centre East Greenland. Contrib. Mineral. Petrol. 92, 57 – 70.
Chavagnac, V., Jahn, B.-M., 1996. Coesite-bearing eclogites from the Bixiling complex, Dabie Mountains, China: Sm-Nd ages, geochemical characteristics and tectonics implications. Chem. Geol. 133, 29 – 51.
Chen, J.F., Xie, Z., Li, H.M., Zhang, X.D., Zhou, T.X., Park, Y.S., Ahn, K.S., Chen, D.G., Zhang, X., 2003. U-Pb zircon ages for a collision-related K-rich complex at Shidao in the Sulu ultrahigh pressure terrane, China. Geochem. J. 37, 35 – 46.
Compston, W., Williams, I.S., Kirschvink, J.L., Zhang, Z., Ma, G., 1992. Zircon U-Pb ages for the Early Cambrian time-scale. J. Geol. Soc. (Lond.) 149, 148 – 171.
Cong, B.-L., 1996. Ultrahigh-Pressure Metamorphic Rocks in the Dabieshan–Sulu Region of China. Science Press, Beijing. 224 pp.
Davies, J.H., von Blanckenburg, F., 1995. Slab breakoff: a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens. Earth Planet. Sci. Lett. 129, 85 – 102.
DePaolo, D.J., 1981. Trace element and isotopic effects of combined wallrock assimilation and fractionation crystalliza-tion. Earth Planet. Sci. Lett. 53, 189 – 202.
Devey, C.W., Cox, K.G., 1987. Relationships between crustal contamination and crystallization in continental flood basalt magmas with special reference to the Deccan Traps of the western Ghats, India. Earth Planet. Sci. Lett. 84, 59 – 68. Dorais, M.J., 1990. Compositional variations in pyroxenes and
amphiboles of the Belknap Mountain complex, New
Hamp-shire: evidence for origin of silica-saturated alkaline rocks. Am. Mineral. 75, 1092 – 1105.
Eby, G.N., 1990. The A-type granitoids; a review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26, 115 – 134.
Enami, M., Zang, Q., 1993. High-pressure eclogite from northern Jiangsu and southern Shandong province, eastern China. J. Metamorph. Geol. 11, 589 – 603.
England, P., Houseman, G., 1989. Extension during continental convergence, with application to the Tibetan Plateau. J. Geophys. Res. 94, 17561 – 17579.
Falloon, T.J., Green, D.H., Hatton, C.J., Harris, K.L., 1988. Anhydrous partial melting of a fertile and depleted peridotite from 2 to 30 kbar and application to basalt petrogenesis. J. Petrol. 29, 1257 – 1282.
Fan, W.M., Guo, F., Wang, Y.J., Lin, G., Zhang, M., 2001. Post-orogenic bimodal volcanism along the Sulu Post-orogenic belt in eastern China. Phys. Chem. Earth, Part A Solid Earth Geol. 26, 733 – 746.
Foley, S.F., Venturelli, G., Green, D.H., Toscani, L., 1987. The ultrapotassic rocks: characteristics, classification and constraints for petrogenetic models. Earth-Sci. Rev. 24, 81 – 134.
Furman, T., Graham, D., 1999. Erosion of lithospheric mantle beneath the East African Rift system: geochemical evidence from the Kivu volcanic province. Lithos 48, 237 – 262. Gao, S., Luo, T.-C., Zhang, B.-R., Zhang, H.-F., Han, Y.-W.,
Zhao, Z.-D., Hu, Y.-K., 1998a. Chemical composition of the continental crust as revealed by studies in East China. Geochim. Cosmochim. Acta 62, 1959 – 1975.
Gao, S., Zhang, B.-R., Jin, Z.-M., Kern, H., Luo, T.-C., Zhao, Z.-D., 1998b. How mafic is the lower continental crust? Earth Planet. Sci. Lett. 106, 101 – 117.
Guo, F., Fan, W.M., Wang, Y.J., Lin, G., 2001a. Late Mesozoic Mafic intrusive complexes in North China block: constraints on the nature of subcontinental lithospheric mantle. Phys. Chem. Earth, Part A Solid Earth Geol. 26, 159 – 771.
Guo, J.H., Chen, F.K., Zhang, X.M., Fan, H.R., Cong, B.L., 2001b. Origin of granitoid and post-collisional tectonic process of the Sulu UHP belt: zircon U-Pb geochronology and geochemistry. Abstract of Symposium on Continental Subduction, Delamina-tion and Timing of Lithospheric Thinning, Xi’an, pp. 99 – 102. in Chinese.
Hacker, B., Ratschbacher, L., Webb, L., Ireland, T., Walker, D., Dong, S., 1998. U/Pb zircon ages constrain the architecture of the ultrahigh-pressure Qinling-Dabie orogen, China. Earth Planet. Sci. Lett. 161, 215 – 230.
Harris, N.B.W., 1985. Alkaline complexes from the Arabian Shield. In: Black, R., Bowden, P. (Eds.), Alkaline Ring Complexes in Africa, J. Afr. Earth Sci. vol. 3, pp. 83 – 88.
Hickey, R., Frey, F.A., 1982. Geochemical characteristics of boninite series volcanics: implications for their source. Geo-chim. CosmoGeo-chim. Acta 49, 1797 – 1811.
Hirajima, T., Ishiwatari, A., Cong, B., Zhang, R., Banno, S., Nozaka, T., 1990. Coesite from Mengzhong eclogite at Donghai county, northern Jiangsu province, China. Mineral. Mag. 54, 579 – 583.
