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Geochimica et Cosmochimica Acta 96 (2012) 193–214

Two tales of the continental lithospheric mantle priorto the destruction of the North China Craton: Insights

from Early Cretaceous mafic intrusions in westernShandong, East China

Xiao-Long Huang a,⇑, Jun-Wei Zhong a,b, Yi-Gang Xu a

a State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Chinab Graduate University of Chinese Academy of Sciences, Beijing 100049, China

Received 30 December 2011; accepted in revised form 9 August 2012; available online 3 September 2012

Abstract

Weakened lithospheric zones such as the Dabie-Sulu orogenic belt and Tan-Lu fault zone played important roles in thedestruction of the North China Craton (NCC) during the late Mesozoic. Early Cretaceous mafic intrusions in westernShandong, contemporary with extensive magmatism during the destruction of the NCC, delineate two spatially distinctmantle domains (EM1- and EM2-like) beneath the craton’s interior and weakened lithospheric zones, respectively. The Jinanand Zouping gabbros from the craton interior (�128 Ma) show fractionated LREE and nearly flat HREE patterns([La/Yb]N = 2.94–8.95; [Dy/Yb]N = 1.23–1.69) with notable negative Ta, Nb and Ti anomalies. They have strong negativeeNd(t) (�15.7 to �7.1), low initial 87Sr/86Sr (0.7039–0.7060) and negative zircon eHf(t) of �20.0 to �6.2. These “crustalfingerprints” cannot be explained by crustal contamination, but were likely derived from a hybrid mantle source. Crustaldelamination or detachment during the Early Paleoproterozoic might be responsible for the involvement of Early Precam-brian crustal materials in the Mesozoic mantle source beneath the southeastern NCC. In comparison, the Early Cretaceousmafic igneous rocks from regions (e.g., Yinan, Mengyin and Fangcheng) adjacent to the Dabie-Sulu orogenic belt and Tan-Lufault zone have higher 87Sr/86Sr ratios (0.7059–0.7119), suggesting modification of the lithospheric mantle by melts/fluidsderived from the Yangtze crust. The Mesozoic crustal delamination may have triggered the destruction of the lithosphericroot beneath the Dabie-Sulu orogenic belt, whereas the lithospheric thinning beneath the interior of the southeastern NCCis attributed to the thermo-mechanical erosion by lateral convective asthenosphere.� 2012 Elsevier Ltd. All rights reserved.

1. INTRODUCTION

It is widely accepted that the old, thick and refractorylithospheric keel beneath the eastern North China Craton(NCC) was replaced by young and fertile lithospheric man-tle during the Mesozoic and Cenozoic (e.g., Menzies et al.,1993; Griffin et al., 1998; Menzies and Xu, 1998; Fan et al.,2000; Xu, 2001; Gao et al., 2002). However, the mechanism

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⇑ Corresponding author. Tel.: +86 20 85290010; fax: +86 2085291510.

E-mail address: xlhuang@gig.ac.cn (X.-L. Huang).

of the Mesozoic lithospheric thinning beneath the NCC (ordestruction of the NCC) are still a subject of debate (e.g.,Xu, 2001, 2004, 2007; Xu et al., 2004a, 2009; Gao et al.,2004; Niu, 2005; Wu et al., 2006a, 2008; Deng et al.,2007; Menzies et al., 2007; Zhai et al., 2007).

The eastern NCC is surrounded by Phanerozoicorogens, and is cut by the NEE-trending Tan-Lu fault zone(Fig. 1a). These weakened zones may have played animportant role in the destruction of the NCC. Xu et al.(2009) suggested that the destruction of the craton was ini-tiated from these weakened lithospheric zones and thenexpanded towards the interior of the craton. There are

Fig. 1. (a) Simplified tectonic framework and distribution of two Ordovician diamondifeous kimberlite (Mengyin and Feixian) and threegranulite-xenolith locations (Nushan, Junan and Hannuoba) in eastern China; the North China Craton is cut by the Tan-Lu fault zone(TLFZ) to the east and the Daxinganling-Taihangshan Gravity Lineament (DTGL) to the west; (b) Distribution of the Mesozoic intrusiveand eruptive rocks in Shandong Province and the locations of the Jinan and Zouping gabbros (modified after the geological maps ofShandong Province in 1/1,500,000 scale from the Geological Atlas of China); Dashed line denotes the possible boundary that separates twospatially decoupled mantle domains (EM1- and EM2-like, respectively) modified after Xu et al. (2004b) and Yang et al. (2012); (c) Geologicsketch map of the Jinan gabbro (after Yang et al., 2005) and sample locations; (d) Geologic sketch map of Zouping area (modified after theZhangqiu geological map of 1/200,000 scale) and the sample locations.

194 X.-L. Huang et al. / Geochimica et Cosmochimica Acta 96 (2012) 193–214

two mantle domains (EM1- and EM2-like, respectively;Fig. 1b) beneath western Shandong Province (Xu et al.,2004b). If the EM1-type mantle domain represents the pro-to-lithospheric mantle beneath the NCC, and the EM2-typemantle domain represents the lithospheric mantle modifiedby the Yangtze crust and its derived melts/fluids (Zhanget al., 2002; Xu et al., 2004b), the spatial distribution ofthese two mantle domains may yield information on mech-anisms of the cratonic destruction. The generation of theYinan gabbro-diorite complex (Xu et al., 2004a,b, 2007b)was probably related to reactivation of weakened litho-spheric zones of the southeastern NCC along the Dabie-Sulu orogenic belt and Tan-Lu fault zone (Fig. 1a and b).

In contrast, the Jinan and Zouping gabbros, which are lo-cated far from the weakened zones (Fig. 1b), may captureinformation about the lithospheric mantle prior to thedestruction of the NCC. Previous studies focused on theage, geochemistry and petrogenesis of these rocks (e.g.,Guo et al., 2001, 2003; Yang et al., 2005; Li et al., 2007).However, source characteristics and their implications forthe evolution of the lithospheric mantle beneath thesoutheastern NCC remain uncertain. In this study, we pres-ent new whole-rock major and trace element data, Sr–Ndisotopic data, and in situ zircon U–Pb age and Hf isotopedata for the Jinan and Zouping gabbros with the aims ofcharacterizing magma sources and inferring the nature of

X.-L. Huang et al. / Geochimica et Cosmochimica Acta 96 (2012) 193–214 195

the lithospheric mantle beneath the southeastern NCC. Incombination with previous data, we outline the differencein lithospheric thinning beneath the interior of the cratonand beneath the weakened lithospheric zones.

2. GEOLOGICAL BACKGROUND AND SAMPLES

The North China Craton (Fig. 1a), bounded by the Qin-ling–Dabie–Sulu orogenic belt to the south and the CentralAsia orogenic belt to the north, is the largest cratonic blockin China with widespread Archean to Paleoproterozoicbasement (e.g., Zhao et al., 2005). The eastern NCC, eastof the Daxinganling-Taihangshan Gravity Lineament(DTGL), is considered to have encountered tectonothermalremobilization during Phanerozoic time, and was markedby considerable Mesozoic lithospheric thinning (Menzieset al., 1993; Menzies and Xu, 1998; Fan et al., 2000; Xu,2001, 2007). Shandong Province, located in the central partof the eastern NCC, is separated by the Tan-Lu fault zoneinto two parts (Fig. 1a and b). The western part, Luxi,where Ordovician diamondiferous kimberlites are situated,and the eastern part is the Jiaodong Peninsula, mostly con-sisting of the Sulu orogenic belt and the Jiaolai basin.Mesozoic igneous rocks in this province are composeddominantly of batholiths and plutons, with subordinatevolcanic rocks (Fig. 1b).

The studied Jinan-Zouping region is located to west ofthe Tan-Lu fault (Fig. 1a). The Jinan gabbro complex,intruding into the Ordovician and Carboniferous to Perm-ian sedimentary sequence, is mostly buried by the Quater-nary covers with minor outcrops distributed westward,such as at Queshan, Woniushan, Huashan, Biaoshan,Yaoshan and Kuangshan (Fig. 1c). Previous laserablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) U–Pb dating on zircons of several samplescollected from different outcrops yielded a weighted mean206Pb/238U age of 130.8 ± 1.5 Ma (2r), but those from a sin-gle sample gave a slightly younger age of 127 ± 2 Ma (Yanget al., 2005). The samples for this study were collected fromthe outcrops of the core and marginal parts of the complex.They are fresh, coarse-grained gabbros composed mainly ofolivine (Ol), clinopyroxene (Cpx) and plagioclase (Pl), withminor orthopyroxene (Opx) and biotite (Bi). Biotites usuallyoccur as surrounding rims on clinopyroxene. Ti-magnetite isa common accessory mineral.

The Zouping gabbroic complex intrudes into the LateJurassic sedimentary sequence and Early Cretaceous basal-tic volcanic rocks of the Qingshan Formation (Fig. 1d) thatwas formed at 128–130 Ma in the Luxi area (BGMRSP,1991; Ling et al., 2009). The Zouping gabbro complex ismainly composed of olivine gabbro and olivine-free two-pyroxene gabbros. Monzonite and syenite are located atthe northern part of the pluton. The samples for this studywere collected from the southern part of the pluton. Theyare coarse to medium-grained gabbros with or without oliv-ine. They are composed mainly of plagioclase, clinopyrox-ene and biotite with minor orthopyroxene. Accessoryminerals are apatite and Ti-magnetite. The content of bio-tite in the Zouping samples (2–5%) is higher than that inthe Jinan samples (<1%).

3. ANALYTICAL METHODS

Geochemical and Sr–Nd isotopic analyses were carriedout at the Guangzhou Institute of Geochemistry, ChineseAcademy of Sciences (GIG-CAS). Major element oxideswere analyzed using a Rigaku RIX 2000 X-ray fluorescencespectrometer (XRF), and analytical uncertainties aremostly between 1% and 5% (Li et al., 2006). Trace elementconcentrations were obtained by the inductively coupledplasma-mass spectrometry (ICP-MS), and detailed proce-dures are described by Li et al. (2006). Precision of REEand other incompatible trace elements is estimated to bebetter than 5% from the USGS Rock Reference BIR-1and the laboratory standard (ROA-1). Sr–Nd isotopic anal-yses were performed on a subset of whole rock samplesusing a Micromass Isoprobe multi-collector ICPMS at theGIG-CAS, using analytical procedures described by Liet al. (2006). REEs were separated using the cation ex-change columns, and Nd fractions were further separatedby HDEHP-coated Kef columns. Measured 143Nd/144Ndratios were normalized to 146Nd/144Nd = 0.7219. Referencestandards were analyzed along with samples, and gave87Sr/86Sr = 0.710243 ± 14 (2r) for NBS987 and143Nd/144Nd = 0.512124 ± 11 (2r) for Shin Etsu JNdi-1,which are comparable to the recommended values ofNBS987 (87Sr/86Sr = 0.710248; McArthur, 1994) and ShinEtsu JNdi-1 (143Nd/144Nd = 0.512115 ± 7; Tannaka et al.,2000).

Zircons were separated using conventional heavy liquidand magnetic techniques and purified by hand-picking un-der a binocular microscope. They were mounted togetherwith the standard zircons (TEMORA 2 and 91500) inepoxy resin. The mount was polished to expose the graincenters and then gold-coated. The internal structure ofthe zircons was examined using cathodoluminescence(CL) prior to U–Th–Pb isotopic analyses. Zircon U–Th–Pb analyses were performed on the CAMECA IMS 1280ion microprobe at the Institute of Geology and Geophysics,Chinese Academy of Sciences (IGG-CAS) in Beijing, Chi-na. Analytical procedures are similar to those describedby Li et al. (2009). The O2

� primary ion beam was acceler-ated at 13 kV, with an intensity of ca. 8 nA. The ellipsoidalspot is about 20 � 30 lm in size. Positive secondary ionswere extracted with a 10 kV potential. Calibration of Pb/U ratios is relative to the standard zircon TEMORA 2(417 Ma) based on an observed linear relationship betweenln(206Pb/238U) and ln(238U16O2/238U). U–Th–Pb isotopicratios and absolute abundances of unknowns were deter-mined relative to the standard zircon 91500 (Wiedenbecket al., 1995). Measured Pb isotopic compositions werecorrected for common Pb using the measured 204Pb. Anaverage of present-day crustal composition (Stacey andKramers, 1975) is used for the common Pb. Data reductionwas carried out using Isoplot (ver. 3.23) (Ludwig, 2003).

In-situ zircon Hf isotopic analyses were carried out onthe dated spots using a Neptune MC-ICPMS, equippedwith a 193 nm laser, at the IGG-CAS. Spot sizes of 40 lmwith a laser repetition rate of 8 Hz were used, whichobtained a signal intensity of �5 V at 180Hf mass with theenergy density of 15 J/cm2. The detailed analytical

Table 1Zircon U–Pb data obtained by ion probe for the Jinan and Zouping gabbros.

Spots U (ppm) Th (ppm) Th/U 206Pb/204Pb measured f206a (%) 207Pb/206Pbb (1r) 207Pb/235Ub (1r) 206Pb/238Ub (1r) 207Pb/206Pb

Age (Ma) (1r)

207Pb/235UAge (Ma) (1r)

206Pb/238UAge (Ma) (1r)

%ccc

JN-1

1.1 202 209 1.03 3.56E+03 0.53 0.0533 ± 22 0.1299 ± 77 0.0192 ± 3 124 ± 7 122 ± 2 1012.1 1751 1953 1.12 2.14E+04 0.09 0.0493 ± 6 0.1387 ± 28 0.0207 ± 3 132 ± 3 132 ± 2 1003.1 96 54 0.56 2.71E+02 6.91 0.0936 ± 32 0.1027 ± 412 0.0193 ± 4 99 ± 39 123 ± 3 804.1 1376 1004 0.73 2.22E+05 0.01 0.1354 ± 3 7.544 ± 115 0.4042 ± 61 2169 ± 4 2178 ± 14 2188 ± 28 1005.1 3612 2894 0.80 8.47E+04 0.02 0.1539 ± 2 8.304 ± 139 0.3917 ± 65 2388 ± 3 2265 ± 15 2131 ± 30 1066.1 2708 4282 1.58 4.30E+04 0.04 0.0486 ± 4 0.1374 ± 25 0.0206 ± 3 131 ± 2 132 ± 2 997.1 206 160 0.78 1.29E+04 0.15 0.0490 ± 16 0.1327 ± 49 0.0196 ± 3 127 ± 4 125 ± 2 1018.1 830 904 1.09 4.41E+03 0.42 0.0518 ± 8 0.1347 ± 44 0.0202 ± 4 128 ± 4 129 ± 2 1009.1 844 483 0.57 9.34E+04 0.02 0.1418 ± 5 7.698 ± 119 0.3941 ± 59 2248 ± 6 2196 ± 14 2142 ± 27 10310.1 875 911 1.04 2.48E+04 0.08 0.0493 ± 8 0.1377 ± 30 0.0203 ± 3 131 ± 3 129 ± 2 10111.1 289 518 1.80 5.44E+03 0.34 0.0486 ± 17 0.1303 ± 50 0.0195 ± 3 124 ± 5 124 ± 2 100

CYS-2

1.1 194 114 0.59 1.27E+03 1.47 0.0576 ± 22 0.1207 ± 93 0.0190 ± 3 116 ± 9 122 ± 2 952.1 994 1110 1.12 3.93E+03 0.48 0.0508 ± 10 0.1269 ± 38 0.0196 ± 3 121 ± 3 125 ± 2 973.1 465 476 1.03 2.33E+04 0.08 0.0491 ± 11 0.1382 ± 38 0.0204 ± 3 132 ± 3 130 ± 2 1014.1 2216 3360 1.52 3.05E+04 0.06 0.0490 ± 4 0.1353 ± 35 0.0202 ± 3 129 ± 2 129 ± 2 1005.1 2161 3836 1.78 5.81E+04 0.03 0.0486 ± 5 0.1362 ± 25 0.0204 ± 3 130 ± 2 131 ± 2 996.1 612 519 0.85 2.91E+04 0.06 0.0472 ± 11 0.1339 ± 37 0.0206 ± 3 128 ± 3 131 ± 2 977.1 769 817 1.06 9.07E+03 0.21 0.0500 ± 8 0.1326 ± 32 0.0199 ± 3 126 ± 3 127 ± 2 1008.1 1176 1520 1.29 1.64E+04 0.11 0.0492 ± 7 0.1363 ± 32 0.0205 ± 3 130 ± 3 131 ± 2 999.1 370 254 0.69 8.17E+03 0.23 0.0497 ± 13 0.1319 ± 46 0.0200 ± 3 126 ± 4 128 ± 2 9910.1 736 1211 1.65 1.28E+04 0.15 0.0488 ± 9 0.1328 ± 34 0.0202 ± 3 127 ± 3 129 ± 2 9811.1 222 184 0.83 8.49E+03 0.22 0.0482 ± 14 0.1339 ± 44 0.0201 ± 3 128 ± 4 129 ± 2 9912.1 525 463 0.88 1.33E+04 0.14 0.0482 ± 9 0.1280 ± 35 0.0197 ± 3 122 ± 3 126 ± 2 9713.1 594 599 1.01 1.55E+04 0.12 0.0493 ± 9 0.1360 ± 35 0.0204 ± 3 130 ± 3 130 ± 2 9914.1 1483 1817 1.23 4.75E+03 0.39 0.0519 ± 7 0.1359 ± 34 0.0202 ± 3 129 ± 3 129 ± 2 10015.1 1086 1786 1.65 1.88E+04 0.10 0.0489 ± 7 0.1348 ± 29 0.0203 ± 3 128 ± 3 130 ± 2 99

a f206 is the percentage of common 206Pb in total measured 206Pb.b All radiogenic lead corrected using 204Pb.c Percentage concordance (%cc) = 100 * [(207Pb/235U age)/(206Pb/238U age)].

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Fig. 2. Concordia diagrams for Cameca zircon U–Pb chronologyof the Jinan and Zouping gabbros. MSWD and Probability ofconcordance are at the 1r level. The scale bar of CL images is100 lm.

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technique and data correction procedures are described inWu et al. (2006b). The mean bYb (172Yb/173Yb) value ob-tained from zircon itself was applied for the interferencecorrection of 176Yb and 176Lu on 176Hf (Wu et al., 2006b;Xie et al., 2008). 176Yb/172Yb = 0.5886 and 176Lu/175Lu =0.02655 were used for the elemental fractionation correc-tion (Chu et al., 2002). Due to the extremely low176Lu/177Hf in zircon (normally < 0.003 in the studiedsamples), the isobaric interference of 176Lu on 176Hf is neg-ligible (Iizuka and Hirata, 2005). No relationship between176Yb/177Hf and 176Hf/177Hf ratios was observed in thestudied samples, indicating that the correction of 176Ybinterference on 176Hf is precise for obtaining accurate176Hf/177Hf values. During analysis of the samples, thezircon standard 91500 applied for the instrumental massfractionation gave 176Hf/177Hf = 0.282292 ± 14 (2r), whichis identical with the 176Hf/177Hf ratios of 0.282284 ± 22reported by Griffin et al. (2006). The uncertainties ofcalibrated isotope ratios include those from the sample,standards, and reference values, which are given at ±2rin Table 2.

4. ANALYTICAL RESULTS

4.1. Zircon U–Pb geochronology and Hf isotopes

4.1.1. Zircon U–Pb dating

The gabbroic samples JN-1 from Jinan and CYS-2 fromZouping were selected for zircon U–Pb dating. These zir-cons consisted entirely of fragments (inset in Fig. 2) dueto over-crushing. CL images of zircons show oscillatoryzoning (inset in Fig. 2), indicating a magmatic origin.

The zircons of sample JN-1 from Huashan (Fig 1c) inJinan City contain variable Th and U contents (54–4282and 96–3612 ppm, respectively) with relatively high Th/Uratios of 0.56–1.79 (Table 1). The analyses of spots 4, 5and 9 gave old ages (207Pb/206Pb ages from 2169 ± 4 Mato 2388 ± 3 Ma; Table 1), interpreted as dating inheritedancient zircons. One analysis (spot 3), with low Th and Ucontents, shows a very high proportion of common 206Pbin measured total 206Pb (Table 1), giving rise to large errorsin the apparent 207Pb/206Pb and 206Pb/238U ages. Sevenother analyses have similar apparent 207Pb/235U and206Pb/238U ages, and define a concordant age of 127.5 ±2.2 Ma (1r) (Fig. 2a), which is the same as given by a sam-ple from Kuangshan (127 ± 2 Ma) (Yang et al., 2005). Thisage is interpreted to be the crystallization age of the Jinangabbro.

Zircons of sample CYS-2 from Zouping have moderateto high Th and U contents (114–3830 and 194–2216 ppm,respectively) with high Th/U ratios of 0.65–1.78 (Table 1).The analysis of spot 1 gives the lowest Th and U contents,and shows a high proportion of common 206Pb in measuredtotal 206Pb, and large errors in 207Pb/235U and 207Pb/206Pbratios (Table 1), yielding a young apparent 206Pb/238U ageof 122 ± 2 Ma. Fourteen other analyses have very similarapparent 207Pb/235U and 206Pb/238U ages, and define aconcordant age of 128.7 ± 0.5 Ma (1r) (Fig. 2b), which isinterpreted as the crystallization age of the Zoupinggabbro.

4.1.2. LA-ICPMS Lu–Hf isotopes

All zircons selected for Lu–Hf isotopic analyses werepreviously dated using a CAMECA IMS-1280 on the samespots (Table 2). The initial Hf isotope ratios were calculatedat their crystallization ages (Table 2).

The three ancient zircons from sample JN-1 haverelatively low 176Hf/177Hf ratios of 0.281302–0.281541,and other zircons have variable 176Hf/177Hf ratios of0.282143–0.282537. The oldest inherited zircon shows apositive eHf(t) value (+8.43) when calculated at its apparent207Pb/206Pb age, plotting on the evolution curve of thedepleted mantle (Fig. 3). The Mesozoic zircons showvariable and negative eHf(t) value of �20.0 ± 1.3 to�6.2 ± 1.8 (calculated at 127.5 Ma) (Table 2).

Zircons from sample CYS-2 have low 176Hf/177Hf ratios(0.282154–0.282312) and negative eHf(t) values of �19.6 ±0.9 to �14.1 ± 0.9 (calculated at 128.7 Ma) (Table 2).

The inherited zircons of the Jinan gabbro have similarHf isotopic compositions as the Late Archean to EarlyPaleoproterozoic zircons in the Tongshi monzonite-monzo-diorites and Yinan gabbro-diorites (Xu et al., 2007b), whichdefine the Hf isotope evolution trend of the crustal end-member for the Mesozoic intrusions in western Shandong

Table 2Zircon Lu–Hf isotope data for the Jinan and Zouping gabbros.

Spots Dating site 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf (±2r) eHf(t)a (±2r) TDM1-Hf

b (Ma) (±2r) TDM2-Hfb (Ma) 206Pb/238U Age (Ma)

JN-1

J-01 1.1 0.00824 0.000299 0.282358 ± 30 �12.3 1.1 1240 42 1922 122 ± 2J-02 2.1 0.08463 0.002853 0.282300 ± 39 �14.6 1.4 1412 57 2061 132 ± 2J-03 3.1 0.01908 0.000682 0.282346 ± 32 �12.8 1.1 1269 45 1950 123 ± 3J-04 4.1 0.01534 0.000682 0.281339 ± 28 �3.1c 1.0 2647 38 2933 2169 ± 4d

J-05 5.1 0.03070 0.001113 0.281541 ± 29 8.4c 1.0 2401 39 2408 2388 ± 3d

J-06 6.1 0.09195 0.002854 0.282537 ± 52 �6.2 1.8 1063 76 1536 132 ± 2J-07 7.1 0.01478 0.000538 0.282399 ± 36 �10.9 1.3 1191 50 1833 1259 ± 2J-08 8.1 0.06067 0.001810 0.282143 ± 36 �20.0 1.3 1596 51 2402 129 ± 2J-09 9.1 0.02338 0.000837 0.281302 ± 31 �2.8c 1.1 2709 42 3011 2196 ± 14d

J-10 10.1 0.04820 0.001629 0.282268 ± 29 �15.6 1.0 1412 41 2127 129 ± 2J-11 11.1 0.01336 0.000446 0.282234 ± 23 �16.7 0.8 1415 32 2197 124 ± 2

CYS-2

C-01 1.1 0.06658 0.002078 0.282300 ± 25 �14.5 0.9 1383 37 2058 122 ± 2C-02 2.1 0.06488 0.001994 0.282189 ± 26 �18.4 0.9 1539 38 2302 125 ± 2C-03 3.1 0.04967 0.001544 0.282184 ± 21 �18.5 0.7 1527 29 2311 130 ± 2C-04 4.1 0.09050 0.002835 0.282312 ± 25 �14.1 0.9 1394 36 2035 129 ± 2C-05 5.1 0.09926 0.003032 0.282216 ± 27 �17.5 0.9 1543 39 2247 131 ± 2C-06 6.1 0.07953 0.002411 0.282228 ± 24 �17.1 0.8 1500 34 2219 131 ± 2C-07 7.1 0.03596 0.001137 0.282188 ± 33 �18.4 1.2 1505 46 2300 127 ± 2C-08 8.1 0.03196 0.000996 0.282229 ± 24 �16.9 0.9 1442 34 2209 131 ± 2C-09 9.1 0.03636 0.001218 0.282221 ± 23 �17.2 0.8 1461 32 2227 128 ± 2C-10 10.1 0.08873 0.002745 0.282200 ± 23 �18.1 0.8 1555 33 2282 129 ± 2C-11 11.1 0.03044 0.000898 0.282181 ± 21 �18.6 0.8 1505 30 2314 129 ± 2C-12 12.1 0.04479 0.001405 0.282154 ± 26 �19.6 0.9 1564 36 2376 126 ± 2C-13 13.1 0.01912 0.000655 0.282198 ± 23 �17.9 0.8 1472 32 2275 130 ± 2C-14 14.1 0.05204 0.001590 0.282229 ± 22 �16.9 0.8 1465 32 2212 129 ± 2C-15 15.1 0.08793 0.002697 0.282200 ± 27 �18.1 1.0 1553 39 2282 130 ± 2

a Initial Hf isotope values eHf(t) are calculated with reference to the chondritic reservoir at the time of magma crystallization; a decay constant for 176Lu of 1.867 � 10�11 yr�1 (Soderlund et al.,2004) and the chondritic ratios of 176Hf/177Hf (=0.282785) and 176Lu/177Hf (=0.0336) (Bouvier et al., 2008) are adopted. t = 127.5 Ma (JN-1) and 128.7 Ma (CYS-2).

b Single-stage model ages (TDM1-Hf) are calculated using the measured 176Lu/177Hf ratios, referenced to a depleted mantle model with a present-day 176Hf/177Hf ratio of 0.28325 and176Lu/177Hf = 0.0384 (Griffin et al., 2000). Two-stage model ages (TDM2-Hf) are calculated by assuming formation from average continental crust (176Lu/177Hf = 0.015) that originally was derivedfrom the depleted mantle (Griffin et al., 2004).

c Calculated using 207Pb/206Pb ages.d 207Pb/206Pb ages.

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Table 3Major (wt.%) and trace element (ppm) concentrations of the Jinan and Zouping gabbros.

Sample CYS-1 CYS-2 CYS-3 CYS-4 CYS 10-2 CYS 10-4 CYS 10-6 WS-1 WS-2 WS-3 WSH 10-5 WSH 10-6

SiO2 54.07 53.36 50.58 54.64 55.44 54.81 54.60 56.23 56.36 56.18 55.53 56.35TiO2 0.93 0.81 0.70 0.95 0.94 0.85 0.86 0.89 0.92 0.95 0.87 0.89Al2O3 15.55 14.59 11.39 15.38 15.09 15.32 16.30 16.24 16.35 16.32 15.94 16.24Fe2O3 10.20 10.33 10.21 9.83 9.25 9.60 9.48 8.86 8.94 9.12 8.56 7.18MgO 5.28 6.51 12.34 5.12 5.42 5.62 5.29 4.01 3.93 3.92 4.35 4.66MnO 0.14 0.15 0.15 0.14 0.14 0.14 0.14 0.12 0.14 0.13 0.15 0.13CaO 7.67 8.16 8.49 7.43 7.36 7.28 7.71 6.55 6.54 6.53 7.05 7.77Na2O 3.48 3.29 2.45 3.52 3.22 3.39 3.41 3.94 3.85 3.85 4.58 4.34K2O 2.06 2.07 1.71 2.23 2.43 2.44 1.76 2.49 2.25 2.33 1.46 1.20P2O5 0.36 0.35 0.28 0.36 0.37 0.38 0.35 0.38 0.35 0.37 0.37 0.39LOI -0.07 0.03 1.33 0.06 0.15 -0.03 -0.09 -0.02 0.05 -0.01 0.99 0.68Total 99.67 99.66 99.64 99.67 99.80 99.80 99.80 99.69 99.69 99.69 99.83 99.82Mg# 54.7 59.5 73.8 54.8 57.7 57.7 56.5 51.3 50.6 50.1 54.2 60.2Sc 27.1 28.4 28.7 23.1 23.0 23.2 23.1 20.7 19.8 20.4 21.5 20.2V 223 226 185 218 201 210 227 187 187 206 202 192Cr 80 187 966 78 155 156 110 33 26 24 91 109Co 34.6 39.2 53.1 34.1 26.8 29.6 27.1 31.3 33.6 29.3 18.1 14.9Ti 5752 4510 3513 5520 5310 4945 5033 4178 4813 5640 5211 4898Ni 18 45 263 19 32 40 27 11 8 7 27 31Cu 82.5 78.5 83.6 109.2 82.8 77.2 56.5 77.1 49.5 42.1 10.3 18.1Zn 92.8 90.4 85.0 88.3 87.2 130 88.5 88.4 87.5 96.7 64.2 54.0Ga 19.2 18.3 14.1 18.4 30.5 34.6 31.6 20.1 19.3 20.6 35.3 29.7Ge 1.42 1.44 1.30 1.25 1.27 1.33 1.28 1.36 1.19 1.51 1.26 1.10Rb 35.6 37.8 32.1 39.1 48.8 47.5 29.8 43.9 36.2 38.3 18.4 12.5Sr 771 755 566 699 631 745 813 782 733 728 815 872Y 16.3 15.0 13.1 15.6 15.5 14.5 13.1 16.4 15.9 16.3 13.7 14.4Zr 145 80.7 72.3 136 71.8 66.6 74.2 116 114 102 100 102Nb 4.81 3.84 3.38 5.37 7.07 4.61 3.46 5.55 6.41 6.73 5.12 5.25Ba 781 795 720 794 763 877 776 1013 920 936 911 710La 17.9 19.0 15.2 18.6 20.4 21.1 18.2 25.2 23.3 22.8 15.6 14.8Ce 39.1 41.0 33.0 41.1 42.3 43.8 37.9 54.2 49.5 48.8 34.0 32.6Pr 5.18 5.46 4.47 5.39 5.64 5.83 5.08 7.11 6.35 6.45 4.73 4.63Nd 21.9 22.9 19.1 22.5 23.7 24.8 21.5 29.6 25.8 26.7 20.9 20.7Sm 4.34 4.55 3.85 4.32 4.54 4.78 4.13 5.57 4.74 4.95 4.18 4.22Eu 1.29 1.32 1.13 1.26 1.35 1.51 1.41 1.59 1.35 1.37 1.33 1.25Gd 3.77 3.84 3.36 3.79 4.13 4.21 3.70 4.62 3.96 4.09 3.79 3.80Tb 0.56 0.55 0.51 0.55 0.59 0.58 0.53 0.66 0.57 0.61 0.53 0.54Dy 3.02 3.04 2.74 3.17 3.15 3.01 2.76 3.54 3.17 3.35 2.81 2.93Ho 0.60 0.58 0.52 0.61 0.61 0.58 0.52 0.68 0.61 0.65 0.54 0.55Er 1.54 1.50 1.36 1.66 1.59 1.52 1.38 1.78 1.60 1.74 1.44 1.47Tm 0.22 0.20 0.18 0.23 0.23 0.21 0.19 0.24 0.24 0.25 0.20 0.21Yb 1.47 1.33 1.19 1.44 1.44 1.38 1.27 1.55 1.52 1.53 1.27 1.33Lu 0.22 0.20 0.18 0.23 0.22 0.21 0.19 0.22 0.22 0.24 0.19 0.20

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Table 3 (continued)

Sample CYS-1 CYS-2 CYS-3 CYS-4 CYS 10-2 CYS 10-4 CYS 10-6 WS-1 WS-2 WS-3 WSH 10-5 WSH 10-6

Hf 2.87 1.84 1.65 2.90 2.13 1.97 2.01 2.54 2.58 2.43 2.63 2.63Ta 0.28 0.24 0.22 0.33 0.40 0.24 0.18 0.34 0.40 0.40 0.27 0.27Pb 6.17 6.72 5.94 7.46 8.49 9.37 7.74 9.22 8.16 8.14 9.93 7.01Th 1.49 1.57 1.63 1.86 2.25 1.77 1.27 2.23 1.93 1.84 1.73 1.96U 0.53 0.49 0.48 0.60 0.63 0.54 0.38 0.67 0.49 0.52 0.36 0.43Eu/Eu* 0.95 0.94 0.94 0.93 0.93 1.01 1.08 0.93 0.93 0.91 1.00 0.94[Nb/La]N 0.26 0.20 0.21 0.28 0.33 0.21 0.18 0.21 0.26 0.28 0.32 0.34Rb/Sr 0.046 0.050 0.057 0.056 0.077 0.064 0.037 0.056 0.049 0.053 0.023 0.014

WSH 10-7 WSH 10-9 ZP 10-1 ZP 10-2 ZP 10-3 ZP 10-4 JN-1 JN-2 JN-3 JN-5 JN-6 JN-7

SiO2 55.02 54.59 50.82 51.04 55.60 55.41 49.89 49.97 55.81 54.92 52.75 50.01TiO2 0.96 0.91 0.91 0.91 0.95 0.93 0.57 0.53 0.71 0.71 0.67 0.54Al2O3 15.12 14.75 12.14 12.75 15.45 15.41 13.26 13.28 15.95 15.75 14.40 13.63Fe2O3 6.18 8.85 10.21 10.16 9.17 9.28 10.58 10.40 8.12 8.31 9.80 10.43MgO 6.99 6.62 9.76 9.39 4.87 5.00 11.02 11.12 5.75 5.90 8.72 10.86MnO 0.11 0.12 0.22 0.21 0.13 0.14 0.17 0.16 0.13 0.13 0.15 0.16CaO 9.39 7.45 9.51 9.04 6.90 6.97 10.85 10.99 7.33 7.24 8.86 10.76Na2O 4.15 3.19 2.23 2.21 3.50 3.47 2.30 2.28 3.93 3.77 2.79 2.35K2O 0.53 2.23 2.35 2.17 2.67 2.64 0.89 0.86 1.58 2.37 1.38 0.83P2O5 0.45 0.44 0.31 0.32 0.50 0.50 0.13 0.12 0.23 0.23 0.17 0.12LOI 0.91 0.66 1.34 1.60 0.08 0.05 -0.03 -0.08 0.16 0.34 -0.03 -0.07Total 99.81 99.81 99.81 99.79 99.81 99.81 99.64 99.64 99.68 99.67 99.66 99.64Mg# 72.5 63.5 69.0 68.3 55.3 55.7 70.8 71.3 62.3 62.3 67.5 70.8Sc 23.9 23.7 32.5 30.6 22.0 21.4 38.3 37.6 23.1 23.7 31.6 36.0V 209 201 220 215 203 197 190 205 178 189 191 182Cr 256 272 396 352 124 130 669 684 219 231 395 666Co 18.6 30.2 35.8 28.1 25.8 25.6 55.2 51.2 34.1 32.2 49.8 51.1Ti 5614 5403 5411 5365 5565 5279 2861 2580 3301 3496 3240 2548Ni 79 94 81 76 28 29 109 104 63 66 89 114Cu 9.48 44.7 35.0 40.6 80.3 80.4 40.8 38.0 13.7 69.9 59.7 36.7Zn 34.2 55.3 54.9 48.7 91.2 85.7 81.9 72.7 63.1 69.3 85.1 73.5Ga 18.5 32.9 27.7 23.6 35.1 33.1 15.8 14.3 17.9 18.0 16.9 14.4Ge 1.12 1.26 1.31 1.35 1.32 1.35 1.49 1.51 1.41 1.34 1.47 1.33Rb 9.26 50.7 74.9 70.2 58.9 55.5 17.1 15.2 28.8 32.3 24.8 13.6Sr 768 656 430 431 737 721 657 647 632 644 504 609Y 17.7 16.5 16.8 17.0 16.7 16.2 12.4 11.6 15.2 15.6 14.4 10.7Zr 116 120 88.4 93.6 118 112 45.8 41.3 96.8 89.4 74.3 37.1Nb 6.42 5.95 5.82 5.93 5.56 5.63 2.28 2.01 4.15 4.18 3.21 1.83Ba 341 864 721 570 922 852 403 376 691 829 571 385La 15.0 23.5 14.8 15.2 25.3 25.3 8.99 7.98 19.3 19.1 13.8 7.69Ce 35.4 48.9 32.5 32.2 52.7 52.1 21.4 18.7 40.2 40.5 30.1 18.0Pr 5.28 6.45 4.49 4.55 7.03 6.98 3.05 2.66 5.04 4.98 3.96 2.58Nd 24.4 27.2 19.9 20.4 29.7 29.2 13.6 12.0 20.5 20.2 16.7 11.8Sm 5.19 5.08 4.21 4.28 5.48 5.49 3.13 2.81 3.88 3.86 3.45 2.75Eu 1.39 1.50 1.28 1.29 1.64 1.58 1.06 0.99 1.12 1.15 1.05 0.98Gd 4.58 4.56 4.13 4.11 4.66 4.80 2.88 2.66 3.37 3.26 3.06 2.55Tb 0.68 0.64 0.61 0.63 0.67 0.65 0.45 0.41 0.49 0.48 0.48 0.38

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Dy 3.60 3.30 3.43 3.47 3.48 3.43 2.47 2.33 2.86 2.80 2.81 2.26Ho 0.67 0.64 0.68 0.69 0.65 0.65 0.47 0.44 0.55 0.57 0.58 0.44Er 1.81 1.68 1.77 1.82 1.77 1.73 1.21 1.15 1.53 1.53 1.60 1.11Tm 0.26 0.24 0.26 0.25 0.25 0.25 0.17 0.16 0.22 0.22 0.24 0.16Yb 1.56 1.52 1.60 1.66 1.56 1.57 1.05 1.00 1.46 1.44 1.48 0.99Lu 0.23 0.23 0.24 0.26 0.24 0.23 0.17 0.14 0.24 0.22 0.22 0.16Hf 3.01 3.12 2.43 2.58 3.14 2.98 1.08 0.97 2.16 1.92 1.77 0.94Ta 0.32 0.31 0.34 0.37 0.29 0.30 0.16 0.14 0.25 0.24 0.22 0.13Pb 3.73 5.07 4.45 2.79 17.4 9.86 2.36 2.30 4.25 22.29 6.10 2.28Th 2.45 2.23 1.60 1.71 2.67 2.41 0.86 0.74 1.97 1.27 1.62 0.70U 0.41 0.68 0.52 0.69 0.79 0.74 0.26 0.22 0.52 0.40 0.46 0.21Eu/Eu* 0.85 0.93 0.93 0.93 0.97 0.92 1.06 1.09 0.92 0.96 0.97 1.11[Nb/La]N 0.41 0.24 0.38 0.38 0.21 0.21 0.24 0.24 0.21 0.21 0.22 0.23Rb/Sr 0.012 0.077 0.174 0.163 0.080 0.077 0.026 0.024 0.046 0.050 0.049 0.022

JN-8 JN-9 JNW 10-1 JNW 10-6 JNF 10-10 JNF 10-11 JNB 10-13 JNB 10-16 JNY 10-19 JNY10-22 JNK 10-23 JNK 10-26

SiO2 49.60 49.86 50.89 50.48 50.59 51.75 50.41 48.96 53.34 53.74 49.95 49.42TiO2 0.53 0.44 0.44 0.61 0.42 0.40 0.48 0.33 0.77 0.72 0.60 0.88Al2O3 13.27 12.74 13.51 12.92 16.23 16.26 16.45 11.22 14.06 14.51 14.06 17.56Fe2O3 10.80 10.34 9.74 10.30 9.22 8.57 9.45 11.46 9.77 9.28 11.78 10.56MgO 11.33 13.43 11.91 11.26 9.55 9.17 9.04 14.18 8.78 8.09 9.96 6.96MnO 0.16 0.16 0.16 0.17 0.15 0.15 0.15 0.20 0.16 0.15 0.18 0.13CaO 11.14 9.91 10.45 10.98 10.66 10.18 10.89 11.67 8.88 8.56 10.68 10.65Na2O 2.24 2.13 2.15 2.15 2.53 2.60 2.67 1.74 2.66 2.77 2.13 2.77K2O 0.64 0.56 0.57 0.88 0.41 0.61 0.29 0.22 1.14 1.59 0.54 0.38P2O5 0.09 0.08 0.09 0.14 0.06 0.07 0.03 0.03 0.22 0.17 0.07 0.41LOI -0.17 -0.02 -0.12 -0.10 -0.03 0.01 -0.08 -0.22 0.00 0.21 -0.16 0.06Total 99.63 99.64 99.78 99.78 99.78 99.79 99.78 99.78 99.80 99.80 99.78 99.78Mg# 71.0 75.2 74.0 71.8 70.7 71.4 69.0 74.3 67.7 67.0 66.3 60.6Sc 41.8 32.8 54.9 30.1 28.0 31.6 37.5 29.7 28.4 35.4 24.0V 199 160 296 153 139 221 149 227 208 308 376Cr 713 1021 1192 330 280 306 841 445 381 413 177Co 58.0 55.7 92.2 49.9 37.9 44.8 62.9 40.7 38.6 55.5 40.0Ti 2844 2143 4678 2508 2151 2896 1924 4551 4227 3491 5115Ni 113 290 278 68 51 65 187 95 88 103 40Cu 35.5 22.2 49.8 14.8 15.6 9.88 10.0 64.0 66.2 30.6 19.8Zn 87.9 73.4 130 70.7 67.6 65.1 89.6 84.1 82.5 110 79.8Ga 15.3 13.6 28.4 17.3 16.8 15.5 10.8 23.1 27.3 14.6 16.4Ge 1.59 1.27 2.34 1.31 1.20 1.31 1.38 1.39 1.29 1.37 1.30Rb 10.2 8.03 16.1 4.50 8.85 1.78 1.41 22.0 33.6 7.43 3.56Sr 679 538 1044 788 650 752 495 446 464 511 864Y 11.1 9.73 17.3 7.38 6.91 6.34 7.69 16.0 14.0 9.04 7.80Zr 34.7 31.6 49.2 17.2 22.1 9.6 10.1 50.0 55.3 26.6 13.0Nb 1.66 1.36 2.76 0.73 1.08 0.34 0.25 3.42 4.27 1.14 0.60Ba 356 304 563 302 314 256 182 514 667 254 260La 6.72 5.98 11.0 5.54 5.58 3.73 3.27 16.2 14.6 5.89 7.15Ce 15.7 13.8 24.1 11.3 11.5 7.52 8.20 33.2 29.7 12.4 15.4Pr 2.29 2.01 3.48 1.63 1.57 1.12 1.22 4.44 3.89 1.77 2.25

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Tab

le3

(co

nti

nu

ed)

JN-8

JN-9

JNW

10-1

JNW

10-6

JNF

10-1

0JN

F10

-11

JNB

10-1

3JN

B10

-16

JNY

10-1

9JN

Y10

-22

JNK

10-2

3JN

K10

-26

Nd

10.9

9.07

16.3

7.48

7.05

5.44

6.21

18.7

16.8

8.43

10.9

Sm

2.65

2.11

3.86

1.72

1.59

1.39

1.68

3.88

3.45

1.97

2.31

Eu

0.93

0.79

1.59

0.86

0.79

0.77

0.79

1.25

1.20

0.83

1.07

Gd

2.51

2.03

3.89

1.69

1.61

1.44

1.77

3.65

3.25

1.99

2.24

Tb

0.39

0.32

0.60

0.27

0.24

0.22

0.27

0.55

0.49

0.31

0.30

Dy

2.26

1.89

3.52

1.51

1.34

1.29

1.64

3.15

2.78

1.88

1.66

Ho

0.44

0.38

0.70

0.30

0.29

0.27

0.32

0.65

0.57

0.39

0.32

Er

1.12

1.01

1.87

0.80

0.76

0.68

0.84

1.69

1.50

1.00

0.80

Tm

0.16

0.14

0.27

0.12

0.11

0.10

0.12

0.26

0.22

0.15

0.11

Yb

1.02

0.90

1.68

0.74

0.71

0.61

0.75

1.61

1.41

0.91

0.64

Lu

0.16

0.14

0.26

0.11

0.11

0.10

0.12

0.25

0.21

0.14

0.09

Hf

0.92

0.76

1.41

0.53

0.62

0.34

0.38

1.53

1.74

0.81

0.42

Ta

0.13

0.10

0.18

0.05

0.06

0.03

0.02

0.25

0.26

0.08

0.04

Pb

3.03

2.01

4.64

3.03

4.20

2.35

5.19

8.54

9.12

3.41

2.81

Th

0.54

0.50

0.78

0.30

0.48

0.11

0.08

1.47

2.23

0.56

0.27

U0.

150.

140.

240.

080.

130.

030.

020.

400.

600.

160.

08E

u/E

u*

1.09

1.15

1.24

1.52

1.50

1.66

1.39

1.00

1.08

1.28

1.41

[Nb

/La]

N0.

240.

220.

240.

130.

190.

090.

070.

200.

280.

190.

08R

b/S

r0.

015

0.01

50.

015

0.00

60.

014

0.00

20.

003

0.04

90.

072

0.01

50.

004

Mg#

=M

g/(M

g+0.

85F

etot );

Eu

/Eu

*=

Eu

N/[

(Sm

N�

Gd

N)0

.5];

N–

Ch

on

dri

teN

orm

aliz

ed.

Fig. 3. Plot of zircon eHf(t) vs. age of the Jinan and Zoupinggabbros and some other Mesozoic intrusions (Tongshi, Yinan andLaiwu; Xu et al., 2007b) in western Shandong Province. Ages areapparent 206Pb/238U (Mesozoic) or 207Pb/206Pb (Precambrian) agesby U–Pb dating; the evolution of depleted mantle (DM) is drawnusing a present-day 176Hf/177Hf = 0.28325 and 176Lu/177Hf =0.0384 (Griffin et al., 2000). The field of the TTG in the southernNorth China Craton (SNCC) is compiled from the data in Huanget al. (2010a, 2012).

202 X.-L. Huang et al. / Geochimica et Cosmochimica Acta 96 (2012) 193–214

Province (Fig. 3). Overall, the Mesozoic zircons of the Jinanand Zouping gabbros have more negative eHf(t) values thanthose of the Yinan gabbro-diorites (Fig. 3).

4.2. Major and trace elements

Bulk rock analyses of 36 samples are presented in Table3 and plotted in Fig. 4. Eighteen samples from the Jinanarea have high MgO (5.75–14.18 wt.%), Fe2O3 (8.12–11.78 wt.%) and CaO (7.24–11.67 wt.%), but low SiO2

(48.96–55.81 wt.%), TiO2 (0.33–0.77 wt.%), P2O5 (0.03–0.23 wt.%), Na2O (1.74–3.93 wt.%) and K2O (0.22–1.59 wt.%). Eighteen samples from the Zouping area showconsiderable compositional overlap with the Jinan samples,but overall have higher SiO2 (51.04–56.36 wt.%), TiO2

(0.70–0.95 wt.%), P2O5 (0.28–0.50 wt.%), Na2O (2.21–4.58 wt.%) and K2O (0.53–2.67 wt.%), but lower MgO(3.92–12.34 wt.%), Fe2O3 (6.18–10.33 wt.%) and CaO(6.53–8.49 wt.%) than the Jinan samples.

The Jinan gabbros have extremely variable trace elementconcentrations. In chondrite-normalized REE plots(Fig. 5a), all the samples show fractionated LREE andnearly flat HREE patterns ([La/Yb]N = 2.94–8.95; [Dy/Yb]N = 1.23–1.69) with weak negative to moderate positiveEu anomalies (Eu/Eu* = 0.92–1.66; Table 3). On primitivemantle-normalized spidergrams (Fig. 5b), they are charac-terized by negative Nb–Ta–Ti anomalies and positive Pband Sr anomalies. The Zouping gabbro samples have over-all higher trace element concentrations than the Jinan sam-ples (Fig. 5). They show fractionated REE patterns withweak negative to positive Eu anomalies (Eu/Eu* = 0.85–1.08; Table 3) (Fig. 5b), and are characterized by pro-nounced negative Nb–Ta and Ti anomalies and positiveSr anomalies on the spidergrams (Fig. 5b).

Fig. 4. MgO variation diagrams of representative major element oxides and minor elements for the Jinan and Zouping gabbros and someother Mesozoic intrusions (Tongshi, Laiwu and Yinan; Xu et al., 2004a,b) in western Shandong province. Also shown for comparison are theMesozoic OIB-type basalts from Jianguo (Zhang et al., 2003) and the Cenozoic basalts from Shandong Province compiled by Xu et al.(2004b).

X.-L. Huang et al. / Geochimica et Cosmochimica Acta 96 (2012) 193–214 203

4.3. Whole rock Sr–Nd isotopes

The Jinan gabbros have low initial 87Sr/86Sr ratios(0.7039–0.7060) and variable negative eNd(t) (�13.4 to�7.1). The eNd(t) values of the Zouping gabbros (�15.7 to�10.2) are generally lower than those of the Jinan gabbros,whereas the initial 87Sr/86Sr ratios of the Zouping samples(0.7043–0.7048) are generally lower than the Jinan samples(Fig. 6). The depleted mantle Nd model ages (TDM) of theJinan gabbros vary from 1.76 to 2.24 Ga, with an averageof 1.99 Ga, and the Zouping samples have TDM varyingbetween 1.82 and 2.06 Ga, with an average of 1.99 Ga(Table 4). In combination with the previously published data

(Guo et al., 2001; Zhang et al., 2004; Li et al., 2007; Yang,2007), both the Jinan and Zouping gabbros show a very lim-ited range in 87Sr/86Sr, but a wide range in eNd(t) comparedto mafic rocks from Laiwu, Yinan, Fancheng and Mengyinthat show higher 87Sr/86Sr ratios (Fig. 6).

5. DISCUSSION

5.1. Petrogenesis of the Jinan and Zouping gabbros

5.1.1. Fractional crystallization and accumulation

The gabbroic magmatism in Jinan and Zouping areas arecoeval according to zircon U–Pb dating (Yang et al., 2005;

Fig. 5. Chondrite-normalized REE patterns and primitive mantle-normalized trace element spidergrams for the Jinan and Zouping gabbros.The Yinan gabbros (Xu et al., 2004b) are shown for comparison. Chondrite and PM normalization factors are from Taylor and McLennan(1985) and Sun and McDonough (1989), respectively.

Table 4Sr and Nd isotope data for the Jinan and Zouping gabbros.

Samples 87Rb/86Sra 87Sr/86Sr (2r) (87Sr/86Sr)ib 147Sm/144Nda 143Nd/144Nd (2r) (143Nd/144Nd)i

b TDMc (Ma) eNd(t)c

JN-1 0.075 0.704179 ± 6 0.704042 0.139 0.512217 ± 4 0.512101 1895 �7.3JN-3 0.132 0.706209 ± 18 0.705969 0.114 0.511852 ± 7 0.511756 1982 �14.0JN-5 0.145 0.706297 ± 20 0.706033 0.116 0.511866 ± 7 0.511769 1993 �13.7JN-6 0.142 0.705741 ± 20 0.705482 0.126 0.512119 ± 7 0.512015 1761 �8.9JN-7 0.064 0.704250 ± 15 0.704133 0.141 0.512227 ± 8 0.512109 1932 �7.1JN-8 0.043 0.704024 ± 14 0.703945 0.147 0.512166 ± 9 0.512043 2237 �8.4JN-9 0.043 0.704814 ± 17 0.704735 0.141 0.512145 ± 10 0.512027 2096 �8.7CYS-1 0.134 0.704657 ± 5 0.704412 0.120 0.511873 ± 4 0.511772 2063 �13.7CYS-2 0.145 0.705088 ± 14 0.704823 0.120 0.511884 ± 8 0.511782 2060 �13.5CYS-3 0.164 0.704891 ± 17 0.704590 0.122 0.512052 ± 9 0.511949 1819 �10.2CYS-4 0.162 0.704600 ± 21 0.704303 0.116 0.511915 ± 7 0.511817 1928 �12.8WS-1 0.162 0.704993 ± 18 0.704695 0.114 0.511815 ± 7 0.511719 2029 �14.7WS-2 0.143 0.704994 ± 5 0.704733 0.111 0.511764 ± 5 0.511670 2050 �15.7WS-3 0.152 0.705001 ± 18 0.704722 0.112 0.511806 ± 6 0.511711 2011 �14.8

a 87Rb/86Sr and 147Sm/144Nd are calculated using whole-rock Rb, Sr, Sm and Nd contents listed in Table 3.b (87Sr/86Sr)i = (87Sr/86Sr)s � (87Rb/86Sr)s � (ekt � 1); (143Nd/144Nd)i = (143Nd/144Nd)s � (147Sm/144Nd)s � (ekt � 1). Decay constants

(k) = 1.42 � 10�11 yr�1 (Rb–Sr) and 6.54 � 10�11 yr�1 (Sm–Nd).c TDM = ln{[(143Nd/144Nd)s � (143Nd/144Nd)DM]/[(143Sm/144Nd)s � (147Sm/144Nd)DM]}/k (DePaolo, 1981); eNd(t) = [(143Nd/144Nd)S/

(143Nd/144Nd)CHUR � 1] � 10000;. In the calculation, (143Nd/144Nd)CHUR = 0.512638 (Goldstein et al., 1984), (147Sm/144Nd)CHUR = 0.1967,(143Nd/144Nd)DM = 0.51315, (147Sm/144Nd)DM = 0.2137 (Peucat et al., 1988) and t = 128 Ma.

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this study). The wide variation in major and trace elementcompositions suggest that parental melts to the Jinan andZouping gabbros may have experienced varying degrees offractional crystallization and/or crystal accumulation.

The positive correlations between Cr–Ni–CaO and MgO(Fig. 4) point to fractional crystallization/accumulation ofolivine and clinopyroxene. Specifically, the high-Mg sam-ples (MgO > 10 wt.%) may have been subjected to olivine-dominated (with spinel and minor clinopyroxene) fraction-ation/accumulation, given their variable Ni and Cr, butnearly constant CaO contents. Clinopyroxene-dominatedfractionation/accumulation is inferred for the samples with<10 wt.% MgO, given the positive correlation between CaOand MgO (Fig. 4e).

The Jinan gabbro samples show a strong positive corre-lation between Eu/Eu* and Sr/Sr* (Sr/Sr* = 2 � SrPM/[SmPM + NdPM]) (Fig. 7a). The samples with high Eu/Eu*

have overall lower REE, Th and U abundances than the

samples with low Eu/Eu* (Figs. 5a and 7b and c). This indi-cates variable extents of plagioclase accumulation in therock (Fig. 7), because that mineral/melt distribution coeffi-cients for Sr and Eu in plagioclase are typically high,whereas distribution coefficients for Th, U and other REEsare low in plagioclase (McKay et al., 1994). Consequently,the positive correlation between Sr/Y and Eu/Eu* suggeststhat plagioclase accumulation elevates the Sr/Y ratios(Fig. 7d), a phenomenon also observed in TTGs (Huanget al., 2010a). When the effect of plagioclase accumulationin the Jinan samples is taken into account, the trace-elementcompositions of the Jinan gabbros are similar to those ofthe Zouping gabbros (Figs. 5 and 7). Plagioclase fraction-ation is responsible for negative Eu anomalies (Eu/Eu* aslow as 0.85) in some samples from Zouping and Jinan.The Zouping gabbros have overall higher REE, Th andU than the Jinan gabbros, which is attributed to clinopy-roxene-dominated fractionation (Fig. 7b and c).

Fig. 6. Initial eNd(t) vs. 87Sr/86Sr for the Jinan and Zouping gabbros. Large symbols are data of this study (Table 4); Small symbols are datafrom the literature: the Jinan gabbro (Guo et al., 2001; Zhang et al., 2004; Yang, 2007), the Zouping gabbro (Guo et al., 2001; Li et al., 2007),the Tongshi monzonite-monzodiorite and syenite (Xu et al., 2004a; Lan et al., 2012), the Laiwu diorite (Xu et al., 2004a) and andesite (Yinget al., 2006), the Mengyin volcanic rocks (Ying et al., 2006; Liu et al., 2008; Ling et al., 2009), the Yinan gabbro-diorite (Xu et al., 2004a,b), theFangcheng basalt (Zhang et al., 2002) and mantle xenoliths (Zhang et al., 2008), the Ordovician kimberlite-borne mantle xenoliths fromMengyin and Feixian (Zhang et al., 2008), the metamorphic and igneous rocks in the Dabie orogenic belt (Jahn et al., 1999; Zhang and Gao,2002; Fan et al., 2004; Wang et al., 2005), the granulite xenoliths within the Late Cretaceous mafic dyke at Junan (Ying et al., 2010) and theCenozoic alkali basalts at Hannuoba (Zhou et al., 2002) and Nushan (Huang et al., 2004). The field for the Jianguo Mesozoic basalts is afterZhang et al. (2003). Marine sediment data are after Ben Othman et al. (1989) and McLennan et al. (1990). The MORB and OIB data are basedon compilation of Stracke et al. (2003). DMM, EM1 and EM2 are based on Zindler and Hart (1986). Diagram also showing mixing modelsfor source (solid line) and melt assimilation (dotted line). The mixing parameters are assumed as follows:

(1) Sr-Nd isotopes: AS, AM – the Jianguo basalts (Zhang et al., 2003); LS, LM � the Mengyin garnet lherzolite xenolith (Zhang et al., 2008);LC � the Nushan granulite xenolith (Huang et al., 2004); UC � assumed. (2) Sr-Nd concentrations: LS � the Mengyin garnet lherzolitexenolith (Zhang et al., 2008); AS – the primitive mantle (Sun and McDonough, 1989); LM, AM – the Jianguo basalt (Zhang et al., 2003); LC� the Nushan granulite xenolith (Huang et al., 2004); UC � Upper crust (Rudnick and Gao, 2003).

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5.1.2. Crustal contamination

Crustal contamination is inevitable for mantle-derivedmelts during their ascent through continental crust or theirevolution within a crustal magma chamber. Contaminationof parental melts by upper crustal materials can be excludedby the distinctly low initial 87Sr/86Sr ratios in the Jinan andZouping samples. The low initial 87Sr/86Sr ratios, negativeeNd(t) values (Fig. 6) and significant depletion of Th andU (Fig. 5), however, indicate the possibility of lower crustalcontamination.

The Nushan granulite xenoliths are characterized byhigh Th/U, Zr/Hf, Nb/Ta (Fig. 8), strongly negative whole

rock eNd(t) and very low 87Sr/86Sr (Fig. 6). They show avery close affinity with the Archean basement of the NCC(Huang et al., 2004), and are compositionally comparablewith the average of granulite terrains of the NCC (Gaoet al., 1998; Huang et al., 2004). Therefore, the Nushangranulite xenoliths can be considered suitable candidatesfor the Mesozoic lower crust in the southeastern NCC.On the diagrams of Th/U vs. Nb/Ta and Th/U vs. Zr/Hf(Fig. 8), a few Zouping samples have elevated Th/U ratiosand show a weak trend consistent with lower crustal con-tamination (Fig. 8), whereas the Jinan gabbros deviate sig-nificantly from the contamination trend (Fig. 8). Therefore,

Fig. 7. Plots of Sr/Sr* (=2SrPM/[SmPM + NdPM]), RREE, Th + U and Sr/Y vs. Eu/Eu* for the Jinan and Zouping gabbros. RREE is the sumof all rare earth elements. The sample JN-1 is assumed as the initial melts of accumulation (plagioclase) and Rayleigh fractionation (20%olivine + 60% clinopyroxene + 20% plagioclase). The numbers of the curves denote degrees of accumulation and fractional crystallization inpercent, using the partition coefficients of McKenzie and O’Nions (1991) (Ol, Cpx) and Tepley et al. (2010) (Pl). The trace elementconcentrations of accumulated plagioclase are calculated from the assumed initial melts using the partition coefficients of Tepley et al. (2010).

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lower crustal contamination may have partially been in-volved in the Zouping gabbros, but was not significant inthe Jinan gabbros in spite of the occurrence of a few EarlyPaleoproterozoic inherited zircons (see discussions in fol-lowing sections).

5.1.3. Nb–Ta–Ti depletion and refertilized lithosphere mantle

source

The [Nb/La]N values of the Jinan gabbros (Table 3) aremostly lower than the mean value of the lower continentalcrust ([Nb/La]N = 0.6; Rudnick and Gao, 2003). This indi-cates that the depletions in Nb, Ta and Ti in the Jinan-Zou-ping gabbros (Fig. 5) could not have been caused by crustalcontamination or assimilation, which would have increasedthe [Nb/La]N of the Jinan gabbro. Besides crustal contam-ination, the origin of such geochemical features could be re-lated to recycled terrigenous sediments hybridizing themagma source (e.g., Hawkesworth et al., 1993), supra-sub-duction zone fluid metasomatism (e.g., Donnelly et al.,2004) or Ti-bearing minerals (such as rutile and Ti-bearingamphibole) crystallization or retention in the source region(e.g., Ionov and Hofmann, 1995).

The incorporation of recycled terrigenous sediment tothe mantle source region is not considered a major mecha-nism because the Jinan and Zouping gabbros have verylow initial 87Sr/86Sr. It is notable that the isotopic range ofoceanic sediments is not sufficient to explain the observedisotopic compositions of the Jinan and Zouping gabbros(Fig. 6). The positive correlation between [Nb/La]N andTi/Ti* (=2TiPM/[SmPM + TbPM]) is predicted if the crystal-

lization of Ti-bearing minerals (such as rutile and Ti-bearingamphibole) plays an important role in the petrogenesis(Huang et al., 2010b). However, this is not observed in theJinan and Zouping gabbros (Fig. 9), which rules out thefractionation of Ti-bearing minerals as a mechanism to gen-erate Ta–Nb–Ti depletion in the Jinan gabbros.

Here we propose that the geochemical and isotopiccharacteristics of the Jinan and Zouping gabbros primarilyreflect those of the magma source. The Jinan and Zoupinggabbros contain higher SiO2 and lower FeO and TiO2 thanthe Cenozoic basalts and the Late Cretaceous Jianguo OIB-type basalts at comparable MgO (Fig. 4a, c and d). Like theYinan gabbros (Xu et al., 2004b), this indicates an overallrefractory source. The presence of abundant biotites inthe Jinan and Zouping gabbros suggests a hydrous source.The presence of water may trigger the melting of refractoryperidotites, and expands the Ol primary phase field in thesystem forsterite-nepheline-silica such that Opx meltsincongruently to produce SiO2-rich melts (e.g., Kushiro,1972). High SiO2 in the Jinan and Zouping gabbros is con-sistent with a hydrated source that produced melts withhigher SiO2 and lower FeO and CaO than melts producedunder anhydrous conditions (Xu et al., 2004b). Further-more, the Jinan and Zouping gabbros have relatively lowerNi and higher Cr contents than the Cenozoic basalts at agiven MgO (Fig. 4g and h), which would imply a pyroxenitevein-plus-peridotite type mantle rather than a pure perido-titic source (Yang et al., 2004; Xu et al., 2004b). Therefore,a fertilized lithosphere mantle source is proposed for petro-genesis of the Jinan and Zouping gabbros.

Fig. 8. (a) Th/U versus Nb/Ta, and (b) Th/U versus Zr/Hf for theJinan and Zouping gabbros and some other Mesozoic intrusions(Tongshi, Yinan and Laiwu; Xu et al., 2004a,b; Lan et al., 2012) inwestern Shandong province. The dashed-line arrows mark thelower crustal contamination trend beneath the southeastern NCC.PM and OIB from Sun and McDonough (1989), mean compositionof the continental lower crust (LC) from Rudnick and Gao (2003),Lower crust of the North China Craton (NCLC) from Gao et al.(1998), and modeled composition of the Nushan lower crust(NSLC) from Huang et al. (2004).

Fig. 9. Plots of [Nb/La]N vs. Ti/Ti* (=2TiPM/[SmPM + TbPM]) forthe Jinan and Zouping gabbros.

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5.1.4. Formation of EM1-type source

The Jinan and Zouping gabbros have overall low initial87Sr/86Sr ratios and negative eNd(t) (Fig. 6), displaying acharacteristic similar to that of EM1-type basalts. Long-term isolation of a metasomatized mantle lithospheric do-main generally produces extremely enriched Sr–Nd–Pb iso-topic compositions (McKenzie, 1989; Menzies, 1990),which could not be responsible for the EM1-type Sr–Ndisotopes. Given the absence of significant crustal assimila-tion in the Jinan gabbros, we suggest that the mantle sourcecontains some ancient crustal materials characterized by ex-tremely low 87Sr/86Sr and 143Nd/144Nd ratios.

Because the lower crust of the southern North ChinaCraton (SNCC) has strongly negative eNd(t) and very low87Sr/86Sr (e.g., Huang et al., 2004; Ying et al., 2010)(Fig. 6), it represents a possible candidate for the putativehybridization of source of the magma. However, althoughlower crustal contamination may have partially been in-

volved in the Zouping gabbros (Fig. 8), lower crust is incon-sistent with their highly negative eNd(t). In order to changeeNd(t) of the Jinan-Zouping gabbros from �4 to �21, largevarying degrees of lower crustal assimilation (�20–70%)would be required (Fig. 6) even though the end memberlower crust, the Nushan granulite xenoliths, have strongnegative eNd(t) and high Nd concentrations (Huang et al.,2004). Involvement of large proportions of crustal materialis unlikely given the overall low Th/U of the Jinan and Zou-ping gabbros (Fig. 8). However, addition of a few percentof lower crustal component to the mantle source would suf-fice to account for the observed isotopic composition. Therequired proportion of a lower crustal component wouldbe less than 10% for the source mixing model even thoughthe mantle source is highly depleted (Fig. 6). Melting ofsuch a mantle source would yield a melt in which the majorelements are dominated by mantle components, while thetrace element and isotopic compositions are governed bythe crustal components. The key issue is how and whenthe crustal materials were recycled into the mantle source,which we will discuss below.

5.2. Recycling of crustal components in the lithosphere

mantle beneath the southeastern NCC

5.2.1. Lower crustal delamination

Delamination is a process by which a dense segment ofthe lower crust and lithospheric mantle sink into the con-vective asthenosphere as a result of their negative buoyancy(Rudnick and Fountain, 1995). To initiate the delamina-tion, the basaltic lower crust must have undergone a largedensity increase, which can occur due to the “eclogitic”

phase transitions (Kay and Kay, 1993; Lustrino, 2005).So it is important that the basaltic lower crust has beenthickened enough for partial melting with a restite of denseeclogite or garnet-clinopyroxenite (Kay and Kay, 1993),and that the partial melts have adakitic affinity (Lustrino,2005).

Late Mesozoic high-Mg adakitic rocks found in theNCC are all located close to the Dabie-Sulu orogenic belt

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at its southern margin (e.g., Xu et al., 2006; Wang et al.,2006, 2007a,b) or in the Yanshan orogenic belt at the north-ern margin (e.g., Gao et al., 2004; Deng et al., 2007). This isbecause the lithospheric delamination commonly takesplace at orogenic settings (Lustrino, 2005) due to colli-sion-induced crustal thickening. However, such a processoccurs rarely in the interior of a craton. In fact, so far noadakitic rocks are observed in the interior of the NCC (Zhaiet al., 2007), including the Jinan-Zouping area.

Nevertheless, the low initial 206Pb/204Pb (16.545–16.998), 207Pb/204Pb (15.242–15.350) and 208Pb/204Pb(36.488–36.944) of the Jinan gabbros are interpreted to beindicative of lower crust components (Li et al., 2007). Wespeculate that the recycling of crustal components intothe lithospheric mantle may have taken place in the EarlyPaleoproterozoic, given the following lines of evidence. (a)The inherited Late Neoarchean-Early Paleoproterozoic zir-cons in the Jinan gabbros and Yinan gabbro-diorites are allolder than the peak metamorphic age of �1.85 Ga in theNCC (Zhao et al., 2005) or 1.92 Ga in the southern NCC(Huang et al., 2004). This indicates that the crustal materi-als involved in the Jinan and Zouping gabbros formedmainly during the Late Archean to Early Paleoproterozoic.(b) The widely distributed Late Archean-Early Paleoprote-rozoic TTGs (�2.57–2.30 Ga) in the southern NCC consistof both juvenile and reworked materials, which are mostlyattributed to the accretionary orogen accompanied by thebasaltic underplating (Huang et al., 2012). The observationof dominantly juvenile lower crust in the southern NCCduring the Late Archean to Early Paleoproterozoic is con-sistent with positive eHf(t) values in most inherited zircons(Fig. 3). The “eclogitic” restites beneath the thickened lowercrust in Early Paleoproterozoic orogenic settings wouldprovide a driving force for the delamination. The orogeniccollapse in the southern NCC during 2.19–2.08 Ga (Huanget al., 2012) coincides with the delamination. Similar Paleo-proterozoic delamination had probably occurred in thenorthern portion of the central block of the NCC (Gaoet al., 2002; Liu et al., 2011). During the formation ofTTG, the restite eclogite/garnet-clinopyroxenite is charac-terized by low to very low Rb/Sr and U/Pb and relativelylow Sm/Nd ratios (Lustrino, 2005), which are compatiblewith the characteristics of Sr–Nd–Pb isotopes of the Jinangabbros. (c) The Nushan and Junan granulite xenoliths thatmostly formed during the Late Neoarchean to Early Paleo-proterozoic (Huang et al., 2004; Ying et al., 2010) provideimportant evidence for overall low time-integrated87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb (i.e., extremelylow Rb/Sr, Sm/Nd and U/Pb ratios) of the lower crust inthe southern NCC (Huang et al., 2004; Ying et al., 2010).

5.2.2. Two mantle domains in western Shandong

Isotopic data available for the Mesozoic mafic magmasreveal two distinct mantle domains beneath western Shan-dong Province (EM1-like and EM2-like), and the “litho-spheric boundary” between them is located west of theTan-Lu fault (�80 km) (Xu et al., 2004b). The gabbrosfrom Jinan-Zouping, which are located far away from theDabie-Sulu orogenic belt (�600 km) and the Tan-Lu faultzone (�150 km) (Fig. 1), delineate an EM1-like mantle

source with low 87Sr/86Sr and eNd(t) (Fig. 6). This EM1-likemantle domain therefore may represent the lithosphericmantle beneath the southeastern NCC, unmodified by thecontinental subduction of the Yangtze Block and/or sinis-tral shearing of the Tan-Lu fault. In contrast, the EarlyCretaceous mafic rocks from Yinan, Mengyin and Fangch-eng, which are adjacent to both the Dabie-Sulu orogenicbelt and the Tan-Lu fault zone, delineate an EM2-like man-tle source with high and variable initial 87Sr/86Sr ratios(Fig. 6). It has been suggested that addition of a few percentof upper crustal component to an enriched mantle sourcewould significantly increase 87Sr/86Sr ratios and lowereNd(t) values of the melts, therefore accounting for the var-iable Sr–Nd isotopes in the magmas from Yinan, Mengyinand Fangcheng (Fig. 6). The continental collision betweenthe NCC and South China Block (SCB) may have startedat the eastern ends of the NCC and SCB, followed by theclosure of a remanent sea temporally from east to west(Li, 1998). The process may have initiated the sinistralshearing of the lithospheric Tan-Lu fault and producedthe thrust system at western Shandong adjacent to the fault(Li, 1998). Thus, recycling of upper crust into the litho-spheric mantle beneath western Shandong adjacent to thesouthern part of the Tan-Lu fault zone or the Dabie oro-genic belt may have been facilitated by the continental sub-duction of the Yangtze Block during the Triassic SouthChina-North China collision (Yang et al., 2012).

The Early Cretaceous mafic rocks from two mantle do-mains show highly variable zircon Hf isotopes (Fig. 3).Their zircon Hf isotopes are overall more depleted thanthose of the Early Jurassic Tongshi monzodiorite (Fig. 3),probably indicating the role of the asthenosphere in theEarly Cretaceous magmatism. Specifically, the Jinan-Zou-ping gabbros have lower zircon eHf(t) values than the gab-bro-diorites from Yinan (Fig. 3), indicating a largercontribution of the asthenosphere in the magmatism adja-cent to the Tan-Lu fault zone. The great degree of astheno-sphere involvement in the magmatism close to the Tan-Lufault zone is probably because the fault is a trans-litho-spheric shear zone (Xu et al., 1987, 1993).

5.3. Roles of the weakened zone on lithospheric thinning

beneath the craton’s interior

The continental lithospheric mantle-derived magmatismwithin the NCC might have lasted for �100 Ma (MiddleJurassic to Early Cretaceous; Xu et al., 2009). The Meso-zoic destruction of the thick lithospheric keel beneath theNCC might have taken place via thermo-mechanical ero-sion by the convective asthenosphere over a relatively longperiod (Xu et al., 2004a), which may not be consistent witha delamination model (Xu et al., 2004a). However, theeclogitic/garnet clinopyroxenite xenoliths in the EarlyCretaceous high-Mg adakitic intrusions from the Xuzhou-Huaibei region along the southeastern margin of theNCC provide evidence of Mesozoic “eclogitic” lower crustand subsequent delamination (Xu et al., 2006, 2008). Also,the petrogenesis of some other Mesozoic high-Mg adakiticrocks from the regions close to the Tan-Lu fault zone or theDabie-Sulu orogenic belt (Fig. 10a) have been attributed to

Fig. 10. (a) Distribution of the Mesozoic adakitic rocks at or adjacent to the Dabie–Sulu orogenic belt and the part of southern Tan-Lu faultzone; (b) Histogram of zircon U–Pb ages of the Mesozoic adakitic rocks at or adjacent to the Dabie–Sulu orogenic belt and the southern partof Tan-Lu fault zone; (c) Geodynamic sequence and corresponding magmatic sequence in Western Shandong, the Dabie orogenic belt andsouthern part of Tan-Lu fault zone in the Early Cretaceous. Data sources from Xu et al. (2004c, 2007a), Wang et al. (2006, 2007a,b), Zi et al.(2008), Huang et al. (2008), Liu et al. (2009, 2010), Zhang et al. (2010, 2011) and He et al. (2011).

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lower crust delamination and interaction between adakiticmelts and peridotite (Wang et al., 2006, 2007a; Huanget al., 2008; Zhang et al., 2010). It is noteworthy that thereis an overlap in ages between the Mesozoic high- and low-Mg adakites at or adjacent to the Dabie-Sulu orogenic belt(Xu et al., 2007a; Wang et al., 2007b; He et al., 2011), with aportion of low-Mg adakitic rocks extending to older ages(Fig. 10b). The lower range in age of the high-Mg adakitesis consistent with the short duration of delaminationexpected for an “eclogitic” lower crust beneath an orogenicbelt.

The extensive adakitic magmatism in the southern partof the Tan-Lu fault zone or the Dabie-Sulu orogenic beltmainly occurred at �134–125 Ma (Fig. 10b), coincidentwith the large-scale mafic magmatism in western Shandong(132–125 Ma) (e.g., Xu et al., 2004a,b; Yang et al., 2005;Ling et al., 2009). This suggests that the crustal delamina-tion at the weakened lithospheric zones might have had astrong influence on lithospheric thinning beneath the inte-rior of the craton (Fig. 11). Furthermore, the earliest low-Mg (�157 Ma; Zhang et al., 2010) and high-Mg(�136 Ma; Wang et al., 2006) adakitic magmatism tookplace prior to the large-scale magmatism in westernShandong (132–125 Ma) (e.g., Xu et al., 2004a,b; Linget al., 2009). Such a magmatic sequence can be interpretedas the following dynamic sequence: crustal thickening-induced adakitic magmatism! crustal delamination fol-lowed by interaction of adakitic melts with surroundingmantle! upwelling asthenosphere which heated and

promoted melting of the overlying enriched lithosphericmantle (Fig. 10c). This geodynamic sequence suggests thatthe destruction of the NCC may have been initiated fromthe weakened lithospheric zones and from the cratonic mar-gins and then propagated towards the interiors (Xu et al.,2009). The continental collision between the SCB andNCC occurred in the Triassic to form the Dabie-Sulu oro-genic belt (e.g., Li, 1998). If the delamination occurred inthe Cretaceous, one question is why it was delayed foralmost 100 Ma after the collision. Reactivation of thetrans-lithospheric Tan-Lu fault in the early Cretaceous(Zhu et al., 2005) might trigger the earliest crustal delami-nation near the fault zone and subsequent partial meltingof over-thickened lithosphere in the Dabie-Sulu orogenicbelt (Huang et al., 2008). The delamination beneath theorogen and fault also offers an important channel ofupwelling of the asthenosphere because a space is createdby the detachment of the lithospheric keel beneath the oro-gen and fault. As a result of northwestward drifting of Pa-cific plate at �125–122 Ma (Sun et al., 2007), theasthenospheric mantle beneath the southeastern NCCwould have flowed southeastward because Western Pacificsubduction-induced corner-flow requires asthenosphericmaterial replenishment from the west (Niu, 2005). More-over, the lithosphere beneath the eastern NCC might havealready been partially thinned prior to the 120–130 Mapeak magmatism (Xu et al., 2009), which is overall thinnerthan that beneath the western NCC (Xu, 2007). The lateral(southeastward) and upwelling asthenosphere convection

Fig. 11. Cartoon showing the roles of Dabie-Sulu orogenic beltand Tan-Lu fault zone on lithospheric thinning beneath thecraton’s interior in the Early Cretaceous. (a) The partial meltingof overthickened crust from the collision beneath the Dabie-Suluorogenic belt produced the low-Mg adakite and eclogitic litho-spheric keel. Continental collision between the North China Craton(NCC) and South China Block (SCB) resulted in the orogenic beltand also modified the lithospheric mantle beneath western Shan-dong adjacent to the Dabie-Sulu orogenic belt and the southernpart of Tan-Lu fault zone. (b) The lateral convection of astheno-sphere induced intraplate thermo-mechanical erosion beneath thesoutheastern North China Craton. An “eclogitic” overthickenedlithospheric keel sinks into the asthenosphere beneath the Dabie-Sulu orogenic belt and the southern part of Tan-Lu fault zone, andthe delaminated lower crust undergoes partial melting producinghigh-Mg adakitic melts; when the asthenospheric mantle replacesthe interspace vacated by delaminated lithospheric mantle andlower crust beneath the orogenic belt and the fault zone, theextensive thermo-mechanical erosion took place because of theupwelling and southeastward displacement of asthenospherebeneath the southeastern NCC.

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may be responsible for the Early Cretaceous thermo-mechanical erosion of the intraplate lithosphere beneaththe southern NCC (Fig. 11).

This model is compatible with the spatially distinct man-tle domains beneath the southeastern NCC (Xu et al.,2004b). The genesis of low-87Sr/86Sr mafic rocks from theinterior of the NCC (i.e., Jinan and Zouping) is attributedto partial melting of dominant proto-lithospheric mantleand subordinate asthenosphere. In contrast, the magma-tism in the areas (i.e., Yinan, Mengyin and Fangcheng)adjacent to the weakened zones (Dabie-Sulu orogenic beltand the Tan-Lu fault zone) have high 87Sr/86Sr ratios andless negative eNd(t) values (Fig. 6) and overall more de-pleted zircon Hf isotopes (Fig. 3). The mantle source ofthese magmas contained a higher degree of contributionfrom the asthenosphere, and was significantly modified by

the subduction of the Yangtze Block (Yang et al., 2012).The diorites from Laiwu, which is geographically interme-diate between two mantle domains (Fig. 1b), show Sr–Nd–Hf isotopes that plot between the two domains (Figs.3 and 6).

6. CONCLUSIONS

The Jinan-Zouping gabbros formed in the Early Creta-ceous (�128 Ma), contemporary with extensive magmatismduring the destruction of the NCC. They have strong neg-ative whole rock eNd(t), low initial 87Sr/86Sr and negativezircon eHf(t), as well as notable negative Ta, Nb, and Tianomalies. These gabbroic magmas are attributed to partialmelting of intraplate lithosphere mantle of the southernNCC, which was hybridized by Precambrian crustal mate-rials as a result of crustal delamination or detachment inthe Early Paleoproterozoic.

Mesozoic crustal delamination may have taken place inthe Dabie-Sulu orogenic belt and in the region adjacent tothe Tan-Lu fault zone. This process facilitated upwelling ofthe asthenosphere replacing the vacancy previously occu-pied by the delaminated lithosphere, and flowing laterallytowards the region with thick lithosphere. The lateral con-vection of the asthenosphere promoted thermo-mechanicalerosion of the lithosphere, accelerating the destruction ofthe lithospheric keel beneath the southeastern NCC.

ACKNOWLEDGEMENTS

We gratefully acknowledge the careful and constructive com-ments of Richard J. Walker, Jingao Liu, Yaoling Niu and an anon-ymous reviewer, which considerably improved the manuscript. Weappreciate Yin Liu for major element analyses, Xianglin Tu for traceelement analyses, Xirong Liang for Sr–Nd isotope analyses, Qiuli Lifor zircon CAMECA U–Pb dating and Yueheng Yang for zirconLu–Hf isotope analyses. This research was supported by the Knowl-edge Innovation Projects of the Chinese Academy of Sciences(KZCX2-YW-QN106) and National Natural Science Foundationof China (NSFC Projects 40914001, 91014007, 41121002,40773015). This is contribution No. IS-1543 from GIG-CAS.

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Associate editor: Richard J. Walker