Download Evaluating the provenance of metasedimentary rocks of the

Evaluating the provenance of metasedimentary rocks of the
Jiangxian Group from the Zhongtiao Mountain using whole-rock
geochemistry and detrital zircon Hf isotope
LI Qiugen1,2, CHEN Xu1, LIU Shuwen1, WANG Zongqi2, ZHOU Yingkui3, ZHANG Jiang4 ,
WANG Tao2
1. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education,
School of Earth and Space Sciences, Peking University, Beijing 100871, China; Email:
[email protected] and [email protected]
2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
3. Jinzhuang Production and Construction Coal Mine of Zaozhuang City, Tengzhou 277522,
China
4. Department of Earth Sciences, University of Waterloo, 200 University Avenue West,
Waterloo, Ontario, N2L 3G1, Canada
Abstract
In this study, whole-rock geochemical and Nd isotopic data, as well as detrital zircon Hf isotopes of
Palaeoproterozoic metasedimentary rocks from the Jiangxian Group are presented to evaluate the characteristics of
their provenance and the tectonic history. The major and trace element compositions are comparable to PA-UCC
but with slight enrichment in the LILE with exception of Cs and Sr, and slight depletion in ferromagnesian
elements, HFS elements such as Nb and Ta, and some major elements such as CaO and Na 2O. The geochemical
data reveal that the collected metasedimentary rocks have experienced intermediate source weathering with CIA
values ranging from 72 to 78, varying degrees of K-metasomatism and post-depositional loss of Na as well as
negligible sorting, and are derived from weathering of mostly felsic and not mafic rocks. The selected Lu-Hf
isotopic analysis on detrital zircon supply additional clues pointing to both Trans-North China Orogen and Eastern
Block of the North China Craton as the most likely sources for the metasedimentary rocks of the Jiangxian Group.
However, a contribution of detritus from the Western Block of the North Chian Craton can be ruled out. The
sediments were probably deposited in back-arc basin within an active continental margin setting.
Key words: Palaeoproterozoic metasediments, Geochemistry, Provenance, Tectonic setting, Jiangxian Group,
North China Craton
1. Introduction
Clastic rocks not only record the compositional characteristics of the exposed continental crust at
the time of their deposition (Taylor and McLennan, 1985; Condie, 1993; McLennan, 2001; Rudnick
and Gao, 2003) but also preserve the geochemical signatures of tectono-magmatic events, which reflect
those of their source materials (Dickinson et al., 1983; Bhatia et al., 1986; McLennan et al., 1993, 2003;
Armstrong-Altrin et al., 2004; Li et al., 2005a,b, 2008a). The geochemical composition of clastic
sedimentary rocks is a complex function of several variables such as source material, weathering,
transportation, physical sorting, and diagenesis (Johnsson, 1993; McLennan et al., 1993, 2003; Fralick
and Kronberg, 1997; Fralick, 2003; Li et al. 2008a; Barovich and Hand, 2008; Manikyamba et al.,
2008). These variables other than source material have the potential to obscure information about the
source area. However, recent studies showed that a combination of chemical and radiogenic isotopic
compositions of terrigenous sedimentary rocks and their mineralogical components can be very
effective in evaluating important question of sedimentary processes, provenance, tectonic setting and
paleoclimates and crustal evolution (McLennan et al., 2003; Li et al., 2008a).
The Zhongtiao Mountain, one of the important Cu deposit regions in China, is located in the
central-south end of the Trans-North China Orogen of the North China Craton (Zhao et al., 1999, 2001).
It is the cradle of the nomenclature named the “Zhongtiao Movement” (Sun and Hu, 1993). Recently,
there is considerable disagreement concerning the nature of the “Zhongtiao Movement” or “Lüliang
Movement” (Li et al., 2000; Zhao et al., 1998, 2000, 2001, 2002, 2005; Kusky and Li, 2003; Zhai and
Liu, 2003). Some authors believed that the “Lüliang Movement” represents an intra-continental rifting
event in the craton (Li et al., 2000; Kusky and Li, 2003), whereas others argued that it was an
amalgamation event involved in the discrete Western and Eastern Blocks to form the North China
Craton (Zhao et al., 2000, 2003, 2005, 2008, Kröner et al., 2005, 2006). Particular controversy is the
issue regarding the tectonic attribution of the Zhongtiao Mountain during the early Precambrian era
(Zhao et al., 1998, 1999, 2000, 2003, 2005; Kusky and Li, 2003, Kusky et al., 2007), which is
attributable to the lag researches on the Precambrian geology of the Zhongtiao Mountain with respect
to others in the North China Craton. Such a debate has further promoted argument about both
subdivision of tectonic unit and basement architecture of the North China Craton, which are very
important for researchers to understand the tectonic evolution and processes for amalgamation of the
North China Craton (Wu and Zhong, 1998; Zhao et al., 1998, 1999, 2000, 2001, 2005, 2008; Wilde et
al., 2002, 2005; Kusky and Li, 2003; Zhai and Li, 2003; Liu et al., 2002, 2004, 2006; Kröner et al.,
2005, 2006; Polat et al., 2005, Zhai et al., 2005; Yu et al., 2006; Faure et al., 2007, Kusky et al., 2007;
Li and Kusky, 2007; Trap et al., 2007; Zhang et al., 2007).
In this contribution, we present herein new whole-rock geochemical and Nd isotopic data, coupled
with detrital zircon Hf isotopes, from metasedimentary rocks of the Jiangxian Group in the Zhongtiao
Mountain and integrate them with previous available geochemical data to evaluate their provenance
and tectonic setting, and trace their sedimentary processes. These results will provide some insights for
further discussing the tectonic attribution of the Zhongtiao Mountain in the early Precambrian time.
2. Geological Setting
The NNE-SSW-trending Zhongtiao Mountain is an important component of the Trans-North China
Orogen of the North China Craton, and is broadly limited in the region bounded by 110º15'~112º10'
longitude and 34º40'~35º30' latitude (Fig. 1). The Precambrian lithologies of the Zhongtiao Mountain
are subdivided into five tectonic-stratigraphic units separated by unconformities and tectonic or
intrusive contacts (Sun and Hu, 1993; Bai et al., 1997). These five units are in turn (Ⅰ) Sushi Complex,
(Ⅱ) Jiangxian, (Ⅲ) Zhongtiao, (Ⅳ) Danshanshi Groups, and (Ⅴ) Xiyanghe and Ruyang Groups (Fig. 1).
Its general Precambrian geology has been discussed in detail by Bai et al. (1997) and recently
summarized by Li et al. (2008b).
Two irregular outcrop zones of the Jiangxian Group occur to the east of the Sushi Complex. This
group, the focus of this study, extends in a north-east direction in the north segment of the Zhongtiao
Mountain. Major rock types include quartzites, quartz schists, biotite schists, garnet-muscovite schists,
garnet-staurolite schists, and metamorphic volcanic rocks, with minor metamorphic conglomerates and
marbles, metamorphosed to lower greenschist to lower amphibolite facies (Sun and Hu, 1993; Mei,
1994; Bai et al., 1997). Based on the lithologies, two subgroups have been distinguished, termed the
Henglingguan and Tongkuanyu subgroups. The Henglinguan subgroup, which exhibits tectonic contact
with the Sushui Complex (Xu et al., 1994), forms the basal unit of the Jiangxian Group and is
characterized by clastic sediments (Bai et al., 1997). The Tongkuangyu subgroup, which is dominated
by volcanic and volcaniclastic rocks, overlies the Henglinguan subgroup and is covered by the
Jiepailiang Formation of the Zhongtiao Group, the latter consisting of quartzites and conglomerates
(Sun and Hu, 1993). Sun and Hu (1993) reported a U-Pb TIMS upper-intercept age of 2166 ± 1 Ma and
a weighted mean SHRIMP 207Pb/206Pb age of 2115 ± 1 Ma. These two ages were obtained from the
analysis of euhedral zircon grains from two independent metamorphic tuffs in Tongkuangyu subgroup
and were interpreted as recording the age of volcanism. Sun and Ge (1990) also obtained a U-Pb TIMs
upper-intercept age of 2185 ± 1 Ma for a metamorphic tuff from the Tongkuangyu subgroup. On
structural grounds, Bai et al. (1997) suggested that the Jiangxian Group suffered at least two-phase of
deformation with the first-phase characterized by recumbent folding. Recently, according to the study
of detrital zircon ages, Li et al. (2008b) preliminarily concluded that the sediments of the Jiangxian
Group were derived predominately from both Trans-North China Orogen and Eastern Block of the
North China Craton.
3. Sampling and Analytical Methods
The samples for analyses were collected from Henglingguan and Shangyupo regions in the
Zhongtiao Mountain (Fig. 1). Rock types include various muscovite schist, quartz schist and biotite
schist. Their petrological characteristics were listed in Li et al. (2008b).
Major elements were acquired through the analysis of fused glass discs using a scanning wavelength
dispersion X-ray fluorescence (XRF) spectrometer (THERMO ARL ADVANT XP+) at the key
Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space
Sciences, Peking University. Analytical details were after Li et al. (2007) with analytical uncertainties
better than 1%. Loss on ignition (LOI) was determined gravimetrically after heating the samples at
980 °C for 30 minutes. Trace elements, including rare earth element (REE), were analyzed by a Perkin
Elmer Sciex Elan 6100DRC inductively coupled plasma-mass spectrometry (ICP-MS) in National Key
Laboratory of Continental Dynamics, Department of Geology, Northwest University. Analytical
process is described in Wu et al. (2005a), and the standards BHVO-2, AGV-1, BCR-2 and G-2, which
reference values are after Govindaraju (1994), were used. Analytical uncertainties for most elements
are better than 5%.
The Nd isotopic compositions were determined using an analytical protocol similar to that described
by Li et al. (2005, 2007). The chemical separation of Sm and Nd were performed at the Key Laboratory
of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences,
Peking University, and Isotopic analyses were made at Analyzing Center of Beijing Institute of Nuclear
Engineering using a multi-collector Isoprobe-T thermal ionization mass spectrometer (TIMS). The
whole procedural blank for Sm and Nd were < 50 pg. Nd isotopes were normalized to 146Nd/144Nd =
0.7219. The average 143Nd/144Nd ratio of the USGS rock standard BCR-2 was 0.512628 ± 10 (2σ, n=5)
during the period of data acquisition.
In situ Hf isotopic analyses were performed after LA-ICP-MS geochronology using a Neptune
MC-ICP-MS, equipped with a 193 nm laser, at the Institute of Geology and Geophysics, Chinese
Academy of Science. Analyses generally were carried out on the site of the geochronology-generated
pit in order to match Hf results with the corresponding age data. Instrumental conditions and analytical
procedures follow the method outlined in Xu et al. (2004) and Wu et al. (2006). The external
reproducibility for the analytical procedure was evaluated by repeated analysis of the international
reference zircons of 91500 and TEMORA during the analytical session yielding average 176Hf/177Hf
values of 0.282308 ± 44 (2σ, n = 10) and 0.282683 ± 32 (2σ, n = 3), respectively. These values are
identical, within error, in the recently published 176Hf/177Hf values of 0.282307 ± 31 (2σ, n = 44) and
0.282680 ± 31 (2σ, n = 15) for 91500 and TEMORA, respectively (Wu et al., 2006).
4. Result
4.1 Geochemistry
Major and trace element data of this study, together with three previous samples from Sun and Hu
(1993), are listed in Table 1. Their compositional variations of SiO2, TiO2, Al2O3, Fe2O3* and K2O are
63.2~80.3 wt%, 0.27~0.81 wt%, 12.0~20.5 wt%, 1.59~8.66 wt% and 2.95~5.50 wt %, respectively.
Using the geochemical classification diagram of Herron (1988), these samples are classified as shale,
wacke and litharenite (Fig. 2). Compared with Post-Archean upper continental crust (PA-UCC,
McLennan; 2001), the abundances of SiO2, TiO2 and Al2O3 in most samples are generally similar to the
PA-UCC, with negative troughs at CaO and Na2O suggestive of weathering in the provenance (Fig. 3a;
Nesbitt and Young, 1982; Fedo et al, 1995). The trace element contents are comparable to PA-UCC
with slight enrichments in the LILE, apart from Cs and Sr, and slight depletions in HFS elements (Nb
and Ta) and the ferromagnesian trace elements (Cr, Co, Ni, Sc and V; Fig. 3b). The REE abundances
and patterns of these samples are characterized by an enrichment of LREE, significant negative Eu
anomalies (0.55~0.78), and slight depletion of HREE (Fig. 3c). These samples display patterns similar
to PA-UCC (McLennan, 2001), however, the quartz-rich sample, ZH171-J, has lower abundance due to
dilution effect by quartz (Fig. 3c). Also, the relatively high (La/Yb)n (7.0~19.6) and ΣLREEs/HREEs
(8.0~12.3) values (Table 1) appear to be caused by a slight depletion of the HREES, indicating that
these sediments has not been accompanied by an enrichment of zircon (McLennan et al., 1993, Li et al.,
2005,2008a).
Three samples were selected for analysis of Sm-Nd isotopic compositions, and the results are
given in Table 2. These samples have 147Sm/144Nd values varying from 0.1036 to 0.1118 (Table 2). This
range is typical for fine-grained sedimentary rocks, indicating slight differentiation of Sm/Nd during
sedimentation and/or source magmatic process, and little fractionation of REE during exogenic
processes (Jahn and Condie, 1995; Barovich and Hand, 2008). Based on the U-Pb zircon ages of
2115-2182 Ma obtained for the tuffs of the Jiangxian Group(Sun and Ge, 1990; Sun and Hu, 1993),
initial isotopic compositions for the individual sample are presented in the form of εNd (t) calculated at
2.1 Ga. These metasedimentary rocks yield εNd (t) values between -6.0 and -2.8 (Table 2) with TDM
mean crustal residence ages between 2722 and 2893 Ma (Table 2), which is slightly older than the peak
ages of detrital zircons from the Jiangxian Group (Li et al., 2008b).
4.2 Detrital Zircon Hf Isotope
Detrital zircon 207Pb/206Pb ages and Hf isotopic data are given in Table 3, and are presented
graphically in Figure 4. All analytical zircon grains yield 176Lu/177Hf values less than 0.025, suggesting
that after formation of them, there is a little radiogenic Hf accumulation.
Thirty-two of the forty-five analyzed zircon grains from sample 05ZR02-1 gave concordant ages
and the remaining thirteen discordant grains contain seven grains which are less than 2.5 Ga (Li et al.,
2008b). The 207Pb/206Pb age spectrum (Fig. 4a) has a prominent peak at about 2667 Ma, with four
subsidiary peaks at 2290 Ma, 2503 Ma, 2849 Ma and 2903 Ma. Seven of these zircons measured for Hf
isotopes have 176Lu/177Hf values from 0.28083 to 0.281406 (Table 3). Of them, five grains display
positive εHf (t) values in the range from +2.8 to +5.9 (Table 3). Three grains (05, 06 and 07) with
different 207Pb/206Pb ages (2845, 2549 and 2669 Ma) predominantly yield εHf (t) values of greater than
+5.0, which plot near the evolution trend of the depleted mantle (Fig. 4b) and correspond to TCDM
continental model ages between 2685 and 2918 Ma. There are two exceptions; grains 01 and 02 give
εHf (t) values of -0.1 and -0.4, respectively, marked by the TCDM continental model ages of ca. 3200 Ma
(Table 3).
The forty analyzed zircon grains with concordant ages of 2160 Ma to 2814 Ma were identified in
sample 05YQ12-1(Table 3). On the detrital zircon age distribution and probability plot (Fig. 4c),
exhibit a typical Archean signature, with a striking peak at 2537 Ma, a shoulder at 2592 Ma and a
minor peak at 2731Ma. Thirty-four of them were analyzed for Hf isotopes, which have 176Lu/177Hf
values from 0.281126 to 0.281408 (Table 3). All Hf isotopic analyses fall between CHUR and depleted
mantle evolution lines or above the depleted mantle evolution line (Fig. 4d), with εHf (t) values ranging
from 0.7 to 9.0 (Table 3). The TCDM continental model ages vary between 2524 and 3084 Ma, with an
average of 2834 Ma.
5．Discussion
5.1 Weathering and sorting
Weathering intensity is commonly measured by employing the chemical index of alteration (CIA)
proposed by Nesbitt and Young (1982). This index can be calculated using molecular proportions: CIA
= [Al2O3/(Al2O3 + CaO* + Na2O + K2O)]×100, where CaO* is the amount of CaO incorporated in the
silicate fraction of the rock. The values for the Jianxian Group sediments, taking CaO only in silicate
minerals, range from 72~78 with a mean of 75(Table 1). Generally, in average shales (Taylor and
McLennan, 1985), the CIA values vary from 70 to 75, also reflecting values of muscovite, illite and
smectite, thus the existence of large proportions of clay minerals. Therefore, these sediments suffered
moderate chemical weathering at the source area. The data for the metasedimentary rocks investigated
are plotted in the Al2O3-(CaO*+Na2O)-K2O (A-CN-K; Nesbitt and Young 1984, 1989) in Figure 5a.
This A-CN-K system is useful for evaluating fresh rock compositions and examining their weathering
trends and diagenetic K-metasomatism (Fedo et al., 1995). For these metasedimentary rocks, these data
define an ideal trend sub-parallel to the A-CN axis scattering toward the area between illite and
muscovite in A-K line, and projecting onto the feldspar join for a probable source with a granodioritic
or PA-UCC composition (Fedo et al., 1995). Following this, the ideal trend does not terminate at the
CN-K line of the A-CN-K diagram where natural groundwater compositions lie (Fig. 5a), possibly as a
result of varying degrees of K-metasomatism during diagenesis, which has been identified in many
Precambrian clastic sedimentary rocks (Fedo et al., 1995; Li et al., 2005, 2008b; Manikyamba et al.,
2008). In a CIA-(Al/Na) diagram (Selvaraj and Chen, 2006), all sample not only fall into the
intermediate weathering but also form a characteristics of the increase of Al/Na ratios at nearly constant
CIA values (Fig. 5b), signifying post-depositional loss of Na (Nesbitt and Young, 1982).
Sedimentary sorting can lead to variation of specific elements such that they may no longer reflect
the sedimentary provenance (McLennan et al., 1993, 2003; Li et al. 2008a). Zircon addition by mineral
sorting and /or recycling can be responsible for the increase in Zr/Sc ratios (McLennan et al., 1993,
2003). On the Zr/Sc-Th/Sc plot (Fig. 6a), first order sediments show a simple positive correlation
between Th/Sc and Zr/Sc, whereas recycled sediments usually display Zr/Sc increasing more rapidly
than Th/Sc. These metasedimentary rocks from the Jiangxian Group cluster in the field sub-parallel to
the “compositional variation” not “zircon addition” trend, suggesting minimal influence of heavy
mineral sorting. Furthermore, in Al-Ti-Zr triangular diagram (Fig. 6b), data show a narrow range of Zr
and TiO2 variation, and deviation from the Zr-TiO2 line, precluding fractionation of Zr from Ti and Al
(Garcia et al., 1994; Li et al., 2005). As stated above, the sub-parallel REE and multielment patterns
(Fig. 3) also indicate that sorting exerts a negligible influence on the geochemical signature of the
metaedimentary rocks from the Jiangxian Group.
5.2 Provenance
Certain major/trace elements and REEs are most suitable for the determination of sediment
provenance (Taylor and McLennan, 1985; McLennan et al., 1993, 2003; Fralick, 2003). As mentioned
above, the depletion in Cr, Ni, Co, Sc, and V with respect to PA-UCC (Fig. 3b) suggests minor
contributions from mafic and ultramafic sources. Also, low Zr contents and intermediate SiO 2/Al2O3
ratios can reflect the absence of significant reworking of the terrigenous constituents (McLennan et al.,
1993; Li et al., 2008a). In the Ni versus TiO2 diagram (Floyd et al., 1990), these metasedimentary rocks
nearly follow the typical magmatic trend and plot in and around the field of felsic igneous rock rather
than in those of mafic igneous or sedimentary origins, suggesting a dominance of igneous sources
marked by highly felsic composition (Fig. 7a), in accord with the relationship of Th/Sc vs. Zr/Sc (Fig.
6a). Acidic precursors of magmatic origin are also demonstrated by the less mobile element ratios
Hf/Yb and La/Th (Patočka and Štorch, 2004; Fig. 7b).
The combination of La-ICP-MS U/Pb and Hf isotopic determinations for individual zircon grains
offers not only the age but also the nature and source of the host magma, whether juvenile mantle or
crustal materials, as well as model age of the provenance. In sample 05ZR02-1, three grains have εHf (t)
values of more than +5.0, which are close to the depleted mantle value and suggest juvenile crustal
additions. In sample 05YQ12-1, all investigated grains exhibit the characteristics of positive εHf (t)
value, indicating juvenile materials are significantly involved in the magma activity at their
crystallization. Also, the Hf isotopic composition of these Archean zircons is similar to the examined
composition of juvenile Archean basement (Wu et al., 2005b). However, the generally greater than 2.6
Ga TCDM continental model ages from the Jiangxian Group, comparable to 2.6 Ga as the best estimate
of the timing of major mantle extraction for the Western Block (Xia et al., 2006, 2008), preclude the
Western Block as the important source for the analyzed zircons. Moreover, the Nd model ages from the
Jiangxian Group ranging from 2722 to 2893 Ma are in agreement with those of both Trans-North China
Orogen and Eastern Block of the North China Craton, which is also consistent with this interpretation
(Wu et al., 2005b). In addition, for sample 05ZR02-1, the two negative εHf (t) value grains have TCDM
continental model ages of ca. 3200 Ma, suggesting their derivation from ancient continental crust
materials and the possible existence of up to 3.0 Ga continental crust in the North China Craton (Liu et
al., 1992, 2008; Song et al., 1996). Hence, it is little doubt that the Jiangxian Group has an affinity to
both Trans-North China Orogen and Eastern Block of the North China Craton rather than the Western
Block.
5.3 Tectonic setting
Chemically immobile elements can be applied as indicators of tectonic setting (Bhatia & Crook,
1986; McLennan et al., 1993, 2003; Schandle et al., 2000; Patočka & Štorch, 2004; Li et al., 2005,
2008a). For the investigated samples, the high and variable Th/Sc, La/Sc and Hf/Sc as well as low
La/Th and Eu/Eu* values (Table 1), reflect the dissection of a complex continental arc/active
continental margin source area composed chiefly of intermediate to acid (meta)igneous rocks
(McLennan et al., 1993, 2003; Patočka and Štorch, 2004). A relatively pronounced negative Nb-Ta
anomaly relative to PA-UCC becomes evident in all samples (Fig. 3b), also indicating the influence of
a volcanic arc in the source area (Hofmann, 1988). In the Th/Yb-Tb/Yb plot proposed by Schandle et al.
(2000), all of the metasedimentary rocks fall into the field of active continental margin (Fig. 8).
Furthermore, recent studies (Faure et al., 2007; Zhao et al., 2008) show that the most widespread
arc-related magmatic activity took place at ~2.1 Ga in the Lüliang region. This probably indicates a
continental magmatic arc developed to the northwest of the Zhongtiao Mountains (Zhao et al., 2008).
The Palaeoproterozoic ages of the source area are also suggested by the LA-ICP-MS U-Pb dating on
detrital zircons of the Jiangxian Group sediments (Li et al., 2008b). Again, Li et al. (2008b) considered
both Trans-North China Orogen and Eastern Block of the North China Craton as possible source
regions for the Jiangxian Group. Thus, it is possible that the Palaeoproterozoic Jiangxian Group is
interpreted to have deposited on a back-arc basin with respect to the Lüliang arc to the northwest and
the East Block to the east (present-day positions).
6. Conclusions
On the basis of the whole-rock geochemical and Nd isotopic data, combined with detrital zircon Hf
isotopes, from the Jiangxian Group, the following conclusions are yielded:
Chemical characteristics are mainly controlled by source composition, although they have
experienced intermediate source weathering, varying degrees of K-metasomatism and post-depositional
loss of Na. The provenance of metasedimentary rocks from the Jiangxian Group is dominantly felsic,
analogous in composition to PA-UCC or granodiorite. The selected Lu-Hf isotopic analysis on detrital
zircon supply additional clues pointing to both Trans-North China Orogen and Eastern Block of the
North China Craton as the most likely sources for the metasedimentary rocks of the Jiangxian Group.
However, a contribution of detritus from the Western Block of the North Chian Craton can be ruled out.
The sediments were probably deposited in back-arc basin within an active continental margin setting.
Acknowledgements
This study was done while the first author, QG Li, was a postdoctoral fellow at Institute of
Geology, Chinese Academy of Geological Sciences, financially supported by a NSFC project (Grant
No. 40602022), a China Postdoctoral Science Foundation Grant, a NSFC Major International Joint
Research Project (Grant No. 40420120135) and the Ministry of Science and Technology of People’s
Republic of China (Grant No. 2006BAB01A11 and 2002CB412608). Assistance in laboratories,
particularly the efforts of W. Tain and W.P. Zhu on the TIMS, Y. Liu on the ICP-MS, B. Yang with XRF,
and YH Yang on the LA-ICP-MS, is expressed our great gratitude.
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About the first author
Li Qiugen
Male; born in 1973; Lecture of the School of Earth and Space Sciences. He, upon attaining in 1998 a
bachelor’s degree of engineering from Shandong Institute of Mine and Technology, joined the Judicial Bureau of
Zaozhuang City of Shandong Province as a police-officer, and obtained a Ph.D at Peking University in 2005 and a
postdoctoral visitor to Chinese Academy of Geological Sciences from 2005 to 2007. Currently, main research
interest focuses on the geochemistry for tectonics, Precambrian Geology, tectonics of sedimentary basin, and in
particular sedimentary geochemistry and monazite geochronology.
Figure Captions
Fig.1. Geological map of the Zhongtiao Mountain (after Bai et al., 1997; Li et al., 2008b)
Fig.2. The Herron classification diagram of the terrigenous sandstones and shales (after Herron, 1988). Symbols: diamond and triangle
represent samples for this study and that of Sun and Hu (1993), respectively.
Fig.3. Multielement diagrams, (a) major elements and (b) trace elements normalized to Post-Archean upper continental crust (PA-UCC),
as well as (c) REE patterns normalized to chondrite. Chrondrite-normalizing values and PA-UCC are from Taylor and McLennan
(1985) and McLennan (2001), respectively.
Fig.4. Detrital zircon age frequency and probability plots (a and b; after Li et al., 2008b), and corresponding age-εHf (t) diagrams (c and d )
for the Jiangxian Group metasedimentary rocks.
Fig.5. Major element characteristics of metasedimentary rocks of the Jiangxian Group shown in (a) Al2O3-(Na2O+CaO*)-K2O molecular
proportion triangular (Nesbitt and Young, 1982) and (b) Al/Na ratios vs. Chemical Index of Alteration (CIA; Selvaraj and Chen, 2006)
diagrams. Idealized mineral abbreviations are after Kretz (1983). PAAS, Post-Archean Australian Shales, and AAUC, composition of
average Archean upper crust, are after Taylor and McLennan (1985), as well as PA-UUC, composition of average upper crust is after
McLennan (2001). Trends are shown for idealized weathering of AAUC (a), granodiorites or PA-UCC (b) and granites (c). Symbols
are same as in Fig. 2.
Fig.6. Plots showing the effects of heavy-mineral accumulation on selected elements and element ratios. (a) Zr/Sc-Th/Sc diagram. Stars
mark the average compositions for the proterozoic rocks, such as granite, TTG, felsic volcanic rock, andesite, and basalt and Archean
komatiite from Condie (1993). Shaded squares represent the average composition of Post-Archean upper continental crust (PA-UCC;
McLennan, 2001) and N-MORB (Hofmann, 1988), respectively. (b) Al-Ti-Zr triangular diagram. The solid contour encloses the
compositions observed in clastic sediments. CAS represents the field of calc-alkaline suites and SPG represents the field of strongly
peraluminous granites (Garcia et al. 1994). Symbols are same as in Fig. 2.
Fig.7. Rock classification diagrams for samples from the Jiangxian Group: (a) Ni-TiO2 (Floyd et al., 1990); (b) Hf/Yb-La/Th (Patočka
and Štorch, 2004). Symbols are same as in Fig. 2.
Fig.8. Ta/Yb-Th/Yb diagram of the metasedimentary rocks from the Jiangxian Group to discriminate tectonic setting (Schandl et al.,
2000). Symbols are same as in Fig. 2.
运用全岩地球化学和碎屑锆石 Hf 同位素方法确定中条山古元古代绛县群变质沉
积岩的源区性质
李秋根 1,2，陈旭 1，刘树文 1，王宗起 2，周英奎 3，张健 4，王涛 2
1. 造山带与地壳演化教育部重点实验室，北京大学地球与空间科学学院，北京 100871，
中国；电子邮箱：[email protected] 和 [email protected]
2. 中国地质科学院地质研究所，北京 100037，中国
3. 枣庄市金庄生建煤矿，滕州 277522，中国
4. 滑铁卢大学地球科学系，大学路西 200 号，滑铁卢，渥太华，N2L 3G1，加拿大
摘要：本文通过对中条山地区古元古代绛县群变质沉积岩进行全岩地球化学和 Nd 同位素以及碎
屑锆石 Hf 同位素分析，确定其源区特征和构造背景。样品的常量元素和微量元素特征表明，
它们的 LILE 元素除 Cs 和 Sr 外表现出富集，而镁铁质元素，高场强元素 Nb 和 Ta，一些常
量元素如 CaO 和 Na2O 则呈现出亏损；其他元素与 PA-UCC 相似。地球化学数据揭示这些变
质沉积岩主要源于长英质岩石的源区；其源区遭受中等程度的化学风化，风化指数为 72-78，
在沉积过程中经历了不同程度的钾交代，沉积期后的 Na 丢失，但其分选作用的影响可以忽
略。碎屑锆石 Hf 同位素特征进一步指出这些变质沉积岩最可能是源于华北克拉通的中部带
和东部陆块，而不是西部陆块。地球化学特征也表明这些变质沉积岩可能沉积在活动大陆边
缘的弧后盆地。