Introduction

The reactivated Precambrian North China Craton (NCC) has been transformed from a region of thick (~200 km) cold continental lithosphere (Menzies et al. 1993; Griffin et al. 1998) into thin (80–120 km) hot lithosphere with oceanic characteristics (Chi 1988; Fan and Hooper 1989). This great transformation occurred in the Late Mesozoic and was accompanied by widespread magmatism (Zhai et al. 2004; Wu et al. 2005). However, the mechanism that removed Archean continental lithosphere and the geodynamic setting in which it took place are still not agreed, and although many models have been proposed, none have found general acceptance. The models include delamination of lower crust and mantle (Deng et al. 1996; Gao et al. 1998, 2004; Qian et al. 2003; Wu et al. 2005; Huang et al. 2007; Zhai et al. 2007; Yang and Li 2008), thermo-tectonic destruction of a lithospheric root (Menzies et al. 1993; Menzies and Xu 1998; Griffin et al. 1998; Xu 2001), hydrolytic weakening of subcontinental lithosphere (Niu 2005, 2006), and thinning associated with intracontinental rifting and continental marginal rifting (Ren et al. 2002). There are also many different proposals for tectonic forces that might have driven the thinning process: a global-scale mantle superplume (Jahn et al. 1999; Wilde et al. 2003), subduction of continental lithosphere at the southern boundary of the NCC during collision between South China and North China (Menzies and Xu 1998; Gao et al. 2002), subduction of continental lithosphere at the northern boundary of the NCC during collision between Siberia and the NCC (Meng 2003; Wang et al. 2006a; Guo et al. 2007), and a combination of northward and southward subduction and collision at both boundaries (Zhang et al. 2003; Zhai et al. 2007). None of these theories explain all the data (Wu et al. 2008).

Theories proposing Paleo-Pacific Plate subduction give a good explanation of the migration pattern of widespread Late Mesozoic granitoids and volcanic rocks in South China (Zhou and Li 2000; Zhou et al. 2006). After the NCC and South China craton had collided to form a single plate at the T3/J1 boundary (Lin and Fuller 1990), a continental margin must have been present to the east of the united East China block and become part of the East Asian continental arc (Şengör and Natal’in 1996). Late Mesozoic subduction of the Paleo-Pacific Plate from the east could have caused lithospheric thinning, tectonic erosion of the NCC and widespread magmatism (Zhao et al. 1994, 2004; Wu et al. 2003; Sun et al. 2007) as proposed in a recent overview by Wu et al. (2008). More data is needed to determine whether these processes occurred in a backarc setting (Watson et al. 1987; Zheng et al. 2006; Wang et al. 2006a; Xu et al. 2008) or at an active continental margin (Wu et al. 2008) or both, and what were the dominant tectonic regimes. The widespread Late Mesozoic volcanic rocks in the NCC and adjacent areas offer opportunities to obtain relevant tectonic information. Many geochronological and geochemical studies have been carried out on samples from several volcanic zones (Fig. 1) such as the Greater Xing’an Range (e.g. Zhang et al. 2008c), Songliao Basin (e.g. Wang et al. 2002), Yanji Zone (e.g. Li et al. 2007), Jibei-Liaoxi Zone (e.g. Zhang et al. 2008a; Yang and Li 2008), Xishan Zone (e.g. Yuan et al. 2006), and Ludong Zone (e.g. Qiu et al. 2002; Zhang et al. 2002), but there have so far been no studies of Mesozoic volcanic rocks in the Bohai Bay Basin.

Fig. 1
figure 1

Tectonic sketch map of North China, showing the positions of volcanic zones discussed in the text

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In this paper, we present zircon U–Pb dates and geochemical data that constrain the timing of volcanism and petrogenesis of Mesozoic volcanic rocks from the Huanghua depression in the Bohai Bay Basin, attempt to discover a spatio-temporal distribution pattern, and develop a tectonic model invoking subduction of the Paleo-Pacific Plate.

Geological setting and petrology

The NCC is bounded by the NE China Fold Belt to the north and Qinling–Dabie–Sulu Orogenic Belt to the south (Fig. 1) and comprises an eastern and a western Archean block separated by the north–south trending 1.8 Ga Proterozoic Central Orogenic Belt (Zhao et al. 2000), both containing cratonic nuclei of Archean to Paleoproterozoic crystalline basement (Liu et al. 1992; Zhao et al. 2001; Zhai and Liu 2003). The western part of the NCC lacks Mesozoic–Cenozoic volcanism, implying that it has been stable since the Mesozoic and we shall not discuss it further. By contrast, igneous rocks are widespread in the eastern part of the NCC (e.g., Wu et al. 2005). From northwest to southeast, the Mesozoic volcanic zones in the eastern NCC and NE China Fold Belt are the Greater Xing’an Range, the Jibei-Liaoxi zone of northern Hebei Province and western Liaoning Province, the Xishan zone of the Beijing Municipal Region, the Songliao Basin, the Yanji Zone, the Huanghua Zone of the Huanghua depression inside the Bohai Bay Basin, and the Ludong Zone of eastern Shandong Province (Fig. 1).

The Bohai Bay Basin in the eastern part of the NCC has the thinnest crust and highest geothermal gradient in eastern China (Liu 1987) and is considered to be an incompletely developed backarc basin because of the nature of Cenozoic volcanic rocks (Zhou and Armstrong 1982). Tertiary basaltic lavas occur all over the Basin (Liu et al. 1986; Gao and Zhang 1995; Zhang et al. 2009a), but Mesozoic volcanic rocks are mostly found in the Huanghua depression near the center. The Mesozoic volcanic rocks here are basic, intermediate and acid lavas and tuffs and breccias, often interbedded with terrigenous sediments. Figure 2 summarizes the temporal distribution of Mesozoic volcanic rocks from column sections obtained from representative boreholes through Mesozoic volcanic rocks. Acid volcanics are confined to the Fenghuadian district, while intermediate volcanics are more widely distributed along with basic components. Because of a lack of fossils in associated sediments and reliable isotopic dating of volcanic rocks, the timing and petrogenesis of Mesozoic volcanism has not so far been well constrained.

Fig. 2
figure 2

Isopach map of Mesozoic volcanic rocks in the Huanghua depression, Bohai Bay Basin based on column sections of principal boreholes shown (vertical scale top left). Note that acid volcanics only occur in the southwest near Fenghuadian Town, while intermediate and basic volcanics are interbedded in most sections. The distribution and depth are constrained by data from about 80 boreholes through Mesozoic volcanic rocks (PetroChina Dagang Oilfield Company, unpublished data). Because a great number of boreholes in the area do not go deeper than Cenozoic sediments, the actual distribution of Mesozoic volcanic strata might be wider than shown

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We have conducted zircon U–Pb dating on two samples, one of andesitic lava (sample K36-2) from borehole Kou36, and one of rhyolitic lava (sample F22) from borehole Feng22. Sample K36-2 has porphyritic texture and no lineation. The phenocrysts are amphibole and biotite and most have suffered secondary alteration giving rise to magnetite and fine-grained muscovite. Sample F22 is also porphyritic with K-feldspar and a few biotite phenocrysts and displays typical rhyolite flow lamination and lineation without secondary alteration. Basaltic lava (sample K12) from borehole Kou12 contains iddingsite phenocrysts almost entirely replacing the original olivine and abundant plagioclase microcrysts and is cut by numerous tiny calcite veins visible in thin section. The secondary alteration in samples K36-2 and K12 has had a significant influence on major element compositions but only a small influence on trace elements which will be discussed later.

Analytical methods

Zircons were separated and hand-picked from crushed rock samples for U–Pb dating and mounted in epoxy resin. Sections were ground down to about 1/3 thickness to expose grain centers, and cathodoluminescence (CL) imaging conducted to reveal the internal structure of zircon grains. Zircon U–Pb dating for sample F22 was performed using a sensitive high-resolution ion microprobe (SHRIMP II) at the Beijing SHRIMP Center, Chinese Academy of Geological Sciences, instrumental condition and analytical procedures given by Wan et al. (2005). Zircons from sample K36-2 were analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) Agilent 1700a coupled to a GeoLas 2005 DUV 193 nm UArF laser at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), instrumental conditions and analytical procedure described by Yuan et al. (2004). Analyses of major and trace element compositions were performed at the Analytical Institute of Hubei Bureau of Geology and Mineral Resources. Major element oxides were measured using a Regaku 3080E XRF spectrometer, and trace elements were measured with Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Relative standard deviation is <5% for major elements, <4% for REE and Y, and 5–10% for trace elements. Sr and Nd isotopic analyses were performed at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), using a Finnegan MAT-261 multicollector mass spectrometer. Analyses of NBS987 and La Jolla gave 87Sr/86Sr = 0.710289 ± 4 (2σ) and 143Nd/144Nd = 0.511845 ± 2 (2σ), respectively. Total procedural Sr and Nd blanks were <1 ng and <50 pg, respectively. Detailed analytical procedures for elemental and Sr–Nd isotopic measurements are given by Gao et al. (1999).

Results

Zircon U–Pb dating

Zircon U–Pb isotopic data for samples K36-2 and F22 are listed in Tables 1 and 2. The CL images showed that zircons from sample K36-2 were mostly prismatic with rhythmic oscillatory zoning and large length/width ratios, indicating magmatic crystallization. They were usually incomplete and might have crystallized in the volcanic conduit and subsequently been damaged during eruption (Fig. 3a). One oval zircon grain displayed weak rhythmic oscillatory zoning in the center surrounded by a homogenous high-luminescence rim, indicating overprinting by high temperature metamorphism on a magmatic core (Vavra et al. 1999). On a U–Pb concordia diagram (Fig. 4a), 16 analytical spots from 14 prismatic zircon grains formed a cluster close to the concordia curve yielding a weighted mean 206Pb/238U age of 118.8 ± 1.0 (1σ) Ma that probably represents the crystallization age of the lava. The analytical spot at the center of the oval zircon plotted on the concordia curve with a 206Pb/207Pb age of 2,424 ± 22 (1σ) Ma, indicating a Paleoproterozoic age of the magmatic protolith and showing that there could have been Archean–Palaeoproterozoic crystalline basement beneath the Bohai Bay Basin. The date is consistent with the peak of crystallization ages in NCC Archean and Palaeoproterozoic basement (Gao et al. 2004), indicating that the Bohai Bay Basin is indeed part of the NCC.

Table 1 LA-ICP-MS U–Pb data of zircons from sample K36-2
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Table 2 SHRIMP U–Pb data of zircons from sample F22
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Fig. 3
figure 3

Selected CL images of analyzed zircons from a K36-2 and b F22. Circles and the figures in them denote analytical spots and analysis numbers, while the figures under each circle denote Phanerozoic 206Pb/238U ages and one Precambrian 206Pb/207Pb age (Ma)

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Fig. 4
figure 4

Zircon U–Pb concordia diagrams for a K36-2 and b F22, obtained by LA-ICP-MS and SHRIMP, respectively

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Most zircon grains from sample F22 showed prismatic texture with rhythmic oscillatory zoning (Fig. 3b) indicating a magmatic origin. Because the radiogenic 207Pb of some analytic spots was below the detection limit, the U–Pb concordia diagram is presented as total 238U/206Pb versus total 207Pb/206Pb (Fig. 4b). The weighted mean 206Pb/238U age of nine spots on nine zircons was 71.5 ± 2.6 (1σ) Ma, representing the crystallization age of the lava. Analytical spot 3.1 in the outer zone of a zircon grain without clear oscillatory zoning had very low Th and U abundances and yielded a 206Pb/238U age of 47 ± 18 (1σ) Ma. We infer that it formed by zone-controlled or surface-controlled alteration that has reduced the Th and U abundances and removed the original zircon zoning (Vavra et al. 1999), and so we have excluded this result from the weighted mean age.

Geochemistry

Chemical compositions of representative volcanic rocks are listed in Table 3. In a TAS (Na2O + K2O versus SiO2) diagram (Fig. 5a), basic and intermediate volcanic rocks generally plot in a continuous series through the basanite, trachybasalt, basaltic trachyandesite, trachyandesite and trachydacite fields, mostly with alkaline affinity. On a K2O versus SiO2 binary diagram (Fig. 5b), the majority of the basic samples are classified as shoshonite but two samples belong to the high-K calc-alkaline series. The intermediate samples belong to both the shoshonite and high-K calc-alkaline series. Sample K12 has the lowest SiO2 content and plots as basanite but cannot represent the initial major elemental composition because the sample is cut by numerous calcite-forming veins that give rise abnormally to high CaO and CO2 contents. Sample K36-2 has an uncommonly high alkaline content especially of Na2O which could be result of input of alkaline liquid during later metasomatism. On the Nb/Y versus Zr/TiO2 diagram (Winchester and Floyd 1977, not shown) the basic and intermediate volcanic rocks plot as an alkali basalt and trachyandesite magma series. This implies that in most samples the contents of mobile elements such as K and Na and immobile high field strength elements (HFSE) such as Nb, Y and Zr have not been greatly affected by later metasomatism. The acid volcanic rocks straddle the alkaline-subalkaline boundary and plot as trachydacite, rhyolite and dacite. In diagrams of various oxides plotted versus MgO (Fig. 6), basic and intermediate volcanic rocks display consistent patterns, and acid volcanic rocks exhibit distinctive chemical variations, notably very low TiO2 and P2O5 contents. It is therefore unlikely that the acid lavas evolved from the basic or intermediate magmas; more likely they had a different origin.

Table 3 Elemental compositions of Mesozoic volcanic rocks in the Huanghua depression, Bohai Bay Basin
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Fig. 5
figure 5

Major element classification diagrams of volcanic rocks: a Na2O + K2O versus SiO2 after Le Bas et al. (1986) with dashed boundary between alkaline and subalkaline series after Irvine and Baragar (1971); b K2O versus SiO2 with field boundaries modified from Peccerillo and Taylor (1976). Data from Table 3 and Table S1 of supplementary material

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Fig. 6
figure 6

Diagrams of element abundances versus MgO for Mesozoic volcanic rocks in the Huanghua depression. FeOt (total FeO) = FeO + 0.9 × Fe2O3. The straight lines show significant trends for basic to intermediate rocks. Data from Table 3 and Table S1 of supplementary material

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Chondrite-normalized rare earth element (REE) and normal mid-ocean-ridge basalt (N-MORB) trace element patterns are shown in Fig. 7. All the Mesozoic basic, intermediate and acid volcanic rocks from the Huanghua depression have highly enriched light REE (LREE) contents and relatively depleted middle REE (MREE) and heavy REE (HREE), different from those of oceanic island basalt (OIB) and enriched mid-ocean-ridge basalt (E-MORB), and also from Cenozoic basalts of the Huanghua depression. The basic and intermediate samples have higher total REE abundance (321.39–660.26 ppm) and relatively stronger MREE/HREE fractionation ((Tb/Lu)N = 1.6–4.26) than the acid ones (∑REE = 192.16–320.58 ppm, (Tb/Lu)N = 1.47–1.99). The basic and intermediate samples generally show no evident Eu anomalies (Eu/Eu* = 0.75–0.97), while some of the acid ones show slight negative Eu anomalies (Eu/Eu* = 0.67–0.84). Strong enrichment in Rb, Ba and K, and marked depletion in Nb and Ta occur in all samples but Zr depletion occurs only in basic and intermediate samples, while depletions in Sr and Ti exist only in acid ones. These trace element features confirm that the acid series is not genetically related to the basic–intermediate series as revealed by U–Pb dating and major elements.

Fig. 7
figure 7

Chondrite-normalized REE patterns (a–c) and N-MORB normalized spidergrams (d–f) for Mesozoic volcanic rocks in the Huanghua depression, Bohai Bay Basin. Compositions of chondrite, N-MORB, E-MORB, and OIB from Sun and McDonough (1989). Tertiary basalts from the Huanghua depression from Zhang et al. (2009a); Tibetan Cenozoic post-collisional lavas from Turner et al. (1996); Late Cretaceous Fangcheng basalts from the Ludong volcanic zone from Zhang et al. (2002); and three common types of volcanic arc lavas, high-K (Java), medium-K (Rabaul), and low-K (Tonga) andesites, from Gill (1981) shown for comparison

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Sr and Nd isotopic compositions of representative volcanic rocks are listed in Table 4. The initial 87Sr/86Sr ratios and ε Nd(t) values were calculated in accordance with zircon U–Pb dates of 118 Ma for intermediate lava (K36-2) and 72 Ma for acid lava (F22). For basic lava (K12), an age of 118 Ma was used on the assumption that it formed synchronously with the intermediate lavas. All the volcanic rocks have homogeneous isotopic ratios with (87Sr/86Sr)i ranging from 0.7049 to 0.7066, (143Nd/144Nd)i ranging from 0.5115 to 0.5116, and ε Nd(t) ranging from −17.5 to −17.4. Their EMI-like isotopic character is similar to the enriched Late Mesozoic lithospheric mantle beneath the central NCC (Zhang et al. 2004) and distinct from Cenozoic asthenosphere-derived basalts (Zhang et al. 2002, 2009a).

Table 4 Sr and Nd isotopic composition of representative Late Mesozoic volcanic rocks from the Huanghua depression, Bohai Bay Basin
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Discussion

Spatio-temporal distribution of Mesozoic volcanic rocks

Magmatic zircons from sample K36-2 yielded a weighted mean 206Pb/238U age of 118.8 ± 1.0 Ma, indicating that intermediate volcanic lava was extruded in Early Cretaceous times. SHRIMP zircon dating of sample F22 obtains a result of 71.5 ± 2.6 Ma, which reveals that the acid lava formed much later in the Late Cretaceous. This zircon U–Pb age is similar to a K–Ar date of 75.8 ± 2.0 Ma for rhyolite lava obtained by Zhang 1989 (unpublished report, see Gao and Zhang 1995), but quite different from Early Cretaceous ages (128.2 ± 40.5 Ma) acquired from a Sm–Nd pseudo-isochron on several individual whole-rock samples (Gao and Zhang 1995). As shown in Fig. 2, the acid volcanic rocks only occur in a limited area near Fenghuadian Town and do not coexist with other types of volcanic rocks. In contrast, basic and intermediate volcanic rocks are widely distributed and often interbedded with each other, showing a close relationship. We conclude that the basic and intermediate lavas could have formed contemporaneously in the Early Cretaceous, and they might be evolved products from a common primary magma, supported by their similar geochemical features stated above. It is also possible that the Late Cretaceous acid volcanic rocks could represent another distinct episode of volcanic activity that only has an acid component, as evidenced by their distinctive ages, distribution and geochemical characteristics.

The major volcanic zones in North China and adjacent areas (Fig. 1) appear to be composed of similar types of volcanic rocks but erupted at different times over different durations (Fig. 8, references in caption) showing a younging trend from northwest to southeast. Volcanic activity began in the northwestern part of NE China Fold Belt and North China in the Early Jurassic (ca. 180–195 Ma) with eruption of basalt of the Tamulangou Formation in the Greater Xing’an Range, andesite and dacite of the Xinglonggou Formation in the Jibei-Liaoxi Zone, and basalt and andesite of the Nandaling Formation in the Xishan Zone. Mesozoic volcanism represented by basalt of the Yilikede Formation (ca. 106 Ma) in the Greater Xing’an Range, Jianguo alkaline basalt of the Fuxin Formation (ca. 106 Ma) in the Jibei-Liaoxi Zone and alkaline intermediate-acid lavas of the Donglanggou Formation (ca. 110 Ma) in the Xishan Zone ceased almost simultaneously in the three zones at the end of the Early Cretaceous. From Late Jurassic to Early Cretaceous (ca. 157–113 Ma), volcanism represented by intermediate-acid lavas occurred in the Songliao Basin. Much later, volcanic activity started in the Early Cretaceous (ca. 120 Ma) in the Huanghua Zone and in the Ludong Zone where it is represented by basaltic andesite and andesite. It ceased approximately at the same time in both zones near the end of the Late Cretaceous (ca. 71–73 Ma) with rhyolite of the Fenghuadian Formation and alkaline basalt of the Hongtuya Formation, respectively. There was Mesozoic volcanic activity with a limited duration in the Yanji Zone during the Early Cretaceous (ca. 106–117 Ma).

Fig. 8
figure 8

Column sections of principal Late Mesozoic strata (J1–K2) in several volcanic zones. Data sources: (1) Wang et al. (2006a, b, c), Zhang et al. (2008a, b, c); (2) Tan et al. (1989), Wang et al. (2002, 2009), Zhang et al. (2009b); (3) Li et al. (2007); (4) Davis et al. (2001), Li et al. (2001), Zhang et al. (2003), Niu et al. (2004), Yang et al. (2006), Yang and Li (2008), Zhang et al. (2008a, b); (5) Li et al. (2004b), Yuan et al. (2006); (6) this study; (7) Qiu et al. (2002), Yan et al. (2003), Ling et al. (2007), Zhang et al. (2002), Tang et al. (2008)

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Petrogenesis of Mesozoic volcanic rocks

The basic lavas from the Huanghua depression have low SiO2, but significant MgO and Ni contents (Fig. 6) implying that fractionation of olivine caused a major decrease of MgO and Ni but did not increase SiO2. Partial melts from mantle sources are normally basaltic (Wilson 1989), while partial melts from basaltic oceanic crust or lower continental crust are granitic or granodioritic (e.g., Rapp et al. 1991). High-degree partial dehydration melting of basaltic oceanic crust or lower continental crust under sufficiently high temperatures (ca. 1,100°C) can produce intermediate and even mafic melts (e.g., Rapp and Watson 1995) but these magmas are of much higher Na2O and lower MgO contents than mantle-derived basic lavas. This suggests that our basic lavas are unlikely to be products of partial melting of basaltic crust, but favor a mantle-derivation origin. As shown in the chondrite-normalized REE patterns and N-MORB normalized spidergrams (Fig. 7a, d), the basic lavas are strongly enriched in LREE and LILE such as Rb, Ba, K and Sr, but depleted in HFSE such as Nb, Ta, Zr and Ti. These trace elemental signatures are similar to subduction-related arc lavas which are generally formed by partial melting of a mantle wedge assisted by slab-derived aqueous fluids (Hofmann 1988; Wilson 1989).

Andesitic melt with high MgO and low alkalis could be produced by a small proportion of partial melting of hydrous mantle peridotite at ~30 km depth, as revealed by melting experiments (Green and Ringwood 1967), but this does not explain the large proportion of andesitic lavas from the Huanghua depression (Fig. 2) or their low MgO and high alkali contents (Fig. 6). Intermediate melts can also be generated by partial melting of a subducted oceanic slab with a garnet-bearing residue but little plagioclase in the source (Rapp and Watson 1995). Slab-originated lavas could have MORB-like Sr–Nd isotopic features (Martin 1999) and high MgO from interaction with peridotite during their ascent through the overlying mantle wedge (Rapp et al. 1999). The geochemistry of the Mesozoic intermediate volcanic rocks from the Huanghua depression is similar to slab-originated adakite in some aspects such as high Sr/Y and La/Yb ratios, but they have lower MgO and Mg#, and Sr–Nd isotopic compositions with an EMI affinity which effectively rule out a slab-melting origin. The intermediate volcanic rocks have higher SiO2, Na2O + K2O, Th and U, but lower MgO, FeOt, CaO, TiO2 and Ni contents than the basic rocks, agreeing well with fractionation of olivine, pyroxene and magnetite. The negative correlation between CaO/Al2O3 and MgO in the basalt–andesite series also indicates that the intermediate lavas could be residual melts derived from basic lavas via fractionation of olivine and clinopyroxene (Fig. 6). As REE are mainly contained in accessory phases such as monazite, zircon, apatite and allanite (Watt and Harley 1993; Bea 1996) and the partition coefficients of REE for olivine, pyroxene and magnetite are always less than 1 (Nielsen 2006), fractional crystallization of these mafic minerals would not cause notable variations in REE abundances, which is in accordance with the observed similarities of REE patterns of intermediate and basic volcanic rocks (Fig. 7a, b). Finally, possible crustal contamination during magma ascent is indicated by the inherited Precambrian zircon crystal. Thus, we suggest that the intermediate lavas evolved from basic lavas by fractionation of mainly olivine and pyroxene, and possibly slight crustal assimilation. This idea is supported by the close interbedded relationship between basic and intermediate lavas.

Compared with ordinary arc tholeiitic to calc-alkaline series, the basic and intermediate volcanic rocks from the Huanghua depression are characterized by strong enrichments in alkaline elements (Fig. 5), LREE (Fig. 8) and LILE (e.g., Rb and Ba), similar to Cenozoic post-collisional lavas of Tibet (Turner et al. 1996) and the Early Cretaceous Fangchen basalts from the Ludong volcanic zone (Zhang et al. 2002). Their highly enriched Nd isotope values (ε Nd(t) = ~−18, Table 4) have an EMI affinity, similar to Late Mesozoic gabbros in the Taihangshan region, central NCC (Zhang et al. 2004). This indicates that the source was unlikely to be depleted mantle, but probably ancient enriched lithospheric mantle which suffered metasomatism or influx of silicic melts. The silicic melts could have been high in LILE and low in HFSE and radiogenic Nd isotope because they were derived by partial melting of ancient lower crust (Zhang et al. 2004). This interaction between ancient lithospheric mantle and crust implies early subduction prior to the Late Mesozoic volcanism.

Rhyolite can be generated by two alternative mechanisms: partial melting of crust when heated by mantle-derived magma (e.g., Hochstein et al. 1993) or evolution of basaltic magma via fractional crystallization and/or crustal assimilation (e.g., McCulloch et al. 1994). The Late Cretaceous acid lavas from the Huanghua depression are characterized by high SiO2, but low MgO, FeOt, CaO, TiO2, Al2O3, P2O5 and Ni contents. Diagrams of element abundances plotted versus MgO (Fig. 6), especially for Al2O3, TiO2, FeOt and P2O5, usually show that the acid lavas occupy isolated compositional fields and show independent evolution trends from basic and intermediate lavas. The data field of Th/La versus Ta/La for acid lavas overlaps the field of lower continental crust (LCC), showing a genetic relationship (Fig. 9b). Low Al2O3 content (mostly <15%), negative Sr anomaly and a flat HREE pattern (Fig. 7) indicate that partial melting occurred in the presence of a plagioclase-rich but garnet-free residue, implying a low depth (<10 kbar) of melt generation (Rapp and Watson 1995). We therefore suggest that the Late Cretaceous acid lavas were generated by remelting of lower continental crust at a shallow level caused by heating of an unknown coeval mantle-derived magma, because of the relatively young isotopic ages and limited distribution of the acid volcanics.

Fig. 9
figure 9

Variations in trace element and ε Nd(t) values of representative Mesozoic–Cenozoic basalts in the NCC. a Nb/Y versus Rb/Y (inserted Nb/Zr versus Rb/Zr); b Th/La versus Ta/La; c La/Nb versus Zr/Nb; d Nb/Nb* versus ε Nd(t). Trends associated with fluid-related enrichment, melt-related enrichment and increasing degree of partial melting rom Kepezhinskas et al. (1996). Nb/Nb* indicating HFSE fractionation modified from Salters and Shimizu (1988) calculated as (Nb)N × 2/((U)N + (K)N). ε Nd(t) values calibrated for the formation ages of the respective rocks. N-MORB, E-MORB, and OIB from Sun and McDonough (1989). Lower and upper continental crust (LCC and UCC) from Rudnick and Gao (2003). Nandaling Formation basalt, Fangcheng basalt, Jianguo basalt, Daxinzhuang basalt, and Qujiatun basalt from Li et al. (2004a), Zhang et al. (2002, 2003), Yan et al. (2003) and Wang et al. (2006b). Tertiary alkaline basalts from the Huanghua depression after Zhang et al. (2009a)

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Migration of arc-related volcanism

The spatio-temporal distribution of Late Mesozoic volcanic rocks indicates migration of arc-related volcanism from northwest to southeast. In the Jibei-Liaoxi volcanic zone Mesozoic volcanism started at ca. 180 Ma as high-Mg adakitic andesite in the Xinglonggou Formation (Fig. 8), generated by partial melting of a subducted oceanic slab and subsequent interaction with mantle peridotite (Li 2006; Yang and Li 2008). In the Xishan volcanic zone, basalt and andesite of the Nandaling Formation represent the onset of volcanism in the Early Jurassic, with evidence of fluid-related enrichment of certain elements during partial melting (Fig. 9) that could be related to subduction (Li et al. 2004a). In the Greater Xing’an Range, subduction of the Paleo-Pacific Plate is the most likely geodynamic regime to explain Mesozoic volcanism, although geochemical evidence for partial melting of hydrated mantle wedge has not yet been obtained (Zhang et al. 2008c). In the Huanghua volcanic zone, basic–intermediate lavas were erupted in the Early Cretaceous (ca.120 Ma) and their metasomatic geochemical features support a volcanic arc origin (Fig. 9a). Although the Early Cretaceous Fangcheng basalt of the Qingshan Formation in the Ludong volcanic zone lacks obvious volcanic-arc affinity, it might have been generated by partial melting of enriched lithospheric mantle caused by extensive interaction with a crust-derived melt (Zhang et al. 2002). We suggest that northward subducted continental crust above northwestward subducted oceanic crust might have blocked fluid derived by dehydration of the subducted slab from entering the mantle wedge because of the location of the Ludong volcanic zone is close to the Sulu continental collision orogen.

Granitoids found in South Korea formed mainly in three episodes (Sagong et al. 2005): Triassic (248–210 Ma), Jurassic (197–158 Ma), and Cretaceous–Early Tertiary (110–50 Ma). The Cretaceous granites are volcanic–plutonic complexes with arc-related calc-alkaline affinities (Pouclet et al. 1994), indicating the presence of a volcanic arc. In Southwest Japan, volcanic arc-related magmatism started at ca. 100 Ma with the emplacement of Ryoke Granitoids (Kutsukake 2002) about 10 Ma later than similar arc-related magmatism in South Korea. Additionally, calc-alkaline mafic rocks from the Ryoke Belt (Southwest Japan) are in the age range of 71–86 Ma, which also show an eastward younging trend (Nakajima et al. 2005).

In a word, the spatio-temporal distribution of arc-related volcanism in East Asia shows a southeastward migration pattern which implies a progressive retreat of the subduction zone.

Migration of extension-related volcanism

The spatio-temporal distribution of extension-related volcanism displays southeastward migration in North China and the NE China Fold Belt. Alkaline basalts, basaltic andesite or rhyolite in the Jibei-Liaoxi and Xishan Zones and the Early Cretaceous Songliao Basin, the later Yanji, Huanghua and Ludong volcanic zones and the Liaodong peninsula related to lithospheric extension also exhibit an eastward migration pattern. The Jianguo alkaline basalt of the Fuxin Formation in the Jibei-Liaoxi Zone erupted at ca. 106 Ma and is derived from the asthenosphere, indicating that there was an extensional regime in greatly thinned lithosphere by the late Early Cretaceous (Zhang et al. 2003). The youngest volcanic rocks in the Xishan Zone, basaltic andesite and andesite of the Donglanggou Formation are high in alkalis indicating an extensional regime (Li et al. 2004b). In the Songliao Basin, Early Cretaceous intermediate lavas of the Yingcheng Formation are characterized by E-MORB-like Sr–Nd isotopic ratios and lack of depletion of HFSE (Wang et al. 2006b; Zhang et al. 2009b) similar to Cenozoic asthenosphere-derived basalts, also indicating an extensional regime and thinned lithosphere. The Late Cretaceous Daxizhuang alkaline basalt (Hongtuya Formation) in the Ludong Zone and the Qujiatun basalt in the Liaodong peninsula are also derived from an asthenospheric magma source (Yan et al. 2003; Wang et al. 2006c) indicating similar petrogenesis and tectonic regime to the Early Cretaceous Jianguo basalt in the Jibei-Liaoxi Zone (Fig. 9b–d), showing that the lithospheric thinning and extension were achieved later there. Even later in the southern part of Siberia, Korea, and Southwest Japan, intraplate alkaline basalts and continental rift tholeiites started to erupt from Late Cenozoic times (Pouclet et al. 1994; Choi et al. 2006; Chashchin et al. 2007). The migration of extension-related volcanic activity could be explained by delamination of a lithospheric root and post-subduction slab break-off, as discussed below.

Tectonic model

Many different models have been proposed to account for Late Mesozoic lithospheric thinning, destruction of the NCC and widespread magmatism as explained in the introduction. Triassic collision between South China and North China has been suggested as a likely trigger (Menzies et al. 1993; Xu 2001; Gao et al. 2002) but continental collision accompanied by northward subduction could not have formed the northeast-striking Mesozoic volcanic zones because they postdate the Triassic collision by at least 50 Ma. Early–Middle Jurassic continental collision between Siberia and Mongolia–North China is an alternative model (Meng 2003; Wang et al. 2006a) that does not explain the widely distributed Mesozoic volcanism far away from the collisional suture.

A tectonic model incorporating a slab window generated by subduction of the Kula/Pacific ridge in the Late Cretaceous (Kinoshita 2002) has been invoked to explain Cretaceous–Tertiary magmatism in Southwest Japan (Kinoshita 1995, 2002). Heat flux from the mantle through the window could have induced high-temperature (ca. 850°C) metamorphism at a shallow crustal depth (Brown 1998). Using a similar model, Kim et al. (2005) interpreted the Jurassic granitoids in South Korea as products of subduction of the Farallon/Izanagi ridge. Since the Farallon, Izanagi and Kula Plates continued to shift north or northeast (Maruyama 1997), slab window effects caused by subduction of oceanic ridges should have migrated northward or northeastward (Kinoshita 1995, 2002; Kim et al. 2005). Ling et al. (2009) employed a similar model to explain Cretaceous magmatism along the Lower Yangtze River fault zone in central East China. But this model does not agree with our observations in North China presented above that show southeastward migration of both arc- and extension-related volcanism, implying that ridge subduction had little effect on Late Mesozoic tectonomagmatic events. This discrepancy could be explained by transform plate shift nearly perpendicular to the subduction direction preventing the migration of the slab window inland, restricting it only to regions close to the continental margin. The opening of an oceanic ridge has been shown to spread from trench to inland as subduction continues (Thorkelson 1996) and if this is the case transform shift between the relevant oceanic plates along the boundary of the Eurasian Continent (Maruyama 1997) would migrate a slab window northeastward away from North China. On this view, it is reasonable to exclude slab window as the dominating tectonic model for North China.

Subduction of a Paleo-Pacific Plate is another candidate invoked to account for Late Mesozoic tectonomagmatic events in North China (Zhao et al. 1994; Wu et al. 2003; Zhao et al. 2004; Sun et al. 2007; Wu et al. 2008), but the models proposed are too general to be tested in detail. Instead, we advance a model involving subduction and retreat of a Paleo-Pacific Plate and post-subduction slab break-off to explain the southeastward migration of arc- and extension-related volcanism (Fig. 10a), preceding crustal compression (Davis et al. 2001) and later lithospheric extension (Zhai et al. 2004).

Fig. 10
figure 10

a Spatio-temporal distribution of Mesozoic volcanic rocks in East Asia. Zone I includes the Great Xing’an Range, Jibei-Liaoxi, and Xishan zones, Zone II includes the Yanji, Liaodong peninsula, Huanghua, and Ludong Zones. b–d Cartoons of tectonic scenarios describing oceanward migration of the generation of the main two types of volcanic rocks. See text for full explanation

Full size image

From Early to Late Jurassic times (ca. 180–150 Ma, Fig. 10b), northwestward subduction of Paleo-Pacific Plate caused the eruption of arc-related calc-alkaline volcanic rock series along the Greater Xing’an Range, Jibei-Liaoxi and Xishan Zone (Zone I in Fig. 10a). A flat subduction zone composed of moderately old oceanic crust (Gutscher et al. 2000) could explain the Xinglonggou high-Mg adakitic andesite derived from an oceanic slab (Li 2006; Yang and Li 2008). Extensive Jurassic accretionary complexes along the eastern margin of the East Asian continent indicate that subduction of Paleo-Pacific Plate has occurred since the Early Jurassic (Isozaki 1997; Maruyama 1997; Wu et al. 2007). A syn-subduction compressional regime could have been present (Davis et al. 2001; Zhang et al. 2007; Hu et al. 2009) as evidenced by pervasive NNE-NE oriented fault-fold systems (Zhao et al. 1994, 2004) as well as angular unconformities under the Xiahuayuan Formation in the Jibei-Liaoxi Zone and under the Jiulongshan Formation in the Xishan Zone (Fig. 8). It is generally believed that this crustal compression was accompanied by extensive thickening, which could have encouraged subsequent delamination of a lithospheric root in the Early Cretaceous (Wu et al. 2003, 2008; Meng 2003; Wang et al. 2006a).

In middle Early Cretaceous times (ca. 130–120 Ma, Fig. 10c), a deeply subducted oceanic slab broke off beneath Zone I, leading to local upwelling of asthenosphere similar to a backarc regime. Decompressional partial melting of uplifted asthenosphere could have generated OIB-type intracontinental basalts such as the Jianguo alkaline basalt of the Fuxin Formation (Zhang et al. 2003). At the same time, previously thickened crust was drastically thinned by lithospheric extension accompanied by gravitational delamination (Gao et al. 1998; Zhai et al. 2004) producing voluminous A-type granites and erosion of metamorphic core complexes (Wu et al. 2005). It is worthy of mention that abundant hydrous liquid derived by dehydration of oceanic slab appears to have been added to the lithospheric mantle. This would weaken the uppermost mantle by hydration and facilitate its delamination together with an overlying eclogitized crustal root (Sleep 2005). Heated by the upwelling asthenosphere, ancient lithospheric mantle was partially melted to produce basaltic melts (e.g., Chen et al. 2004) which made both a thermal and a material contribution to the simultaneous granitoids (e.g., Qian et al. 2003). At the same time, pervasive thermo-mechanical and chemical erosion at the lithosphere-asthenosphere interface transformed former cold refractory lithospheric mantle into hot fertile lithosphere (Menzies et al. 1993; Xu 2001). Slab rollback induced by slab break-off increased the subduction angle and caused the trench to retreat backward (Elsasser 1971) and consequently, the volcanic arc migrated southeastward along the Liaodong–Huanghua–Ludong zone (Zone II in Fig. 10c).

From late Early Cretaceous to Late Cretaceous (Fig. 10d), eastern North China and the NE China Fold Belt were dominated by crustal extension comparable with a backarc environment (Watson et al. 1987; Zheng et al. 2006; Wang et al. 2006a; Xu et al. 2008). Mantle-derived magmas were able to underplate continental crust and form new basaltic lower crust. Slab break-off gave rise to upwelling of asthenosphere and consequent generation of OIB-type basalts especially in Zone II, such as the Daxizhuang alkaline basalt in the Ludong Zone and the Qujiatun basalt in the Liaodong peninsula (Yan et al. 2003; Wang et al. 2006c). Continuing slab rollback moved the volcanic arc zone further southeastward into Korea and Southwest Japan (Zone III and IV in Fig. 10a) where abundant arc-related plutonic and volcanic igneous rocks were generated (Pouclet et al. 1994; Kutsukake 2002). It is worth pointing out that this Cretaceous subduction event must have been independent of the Triassic-Jurassic subduction along the East Asian margin (de Jong et al. 2009; Park et al. 2009) and could have been followed by Kula/Pacific ridge subduction in the Late Cretaceous (Kinoshita 2002).

This model includes a stagnant detached oceanic slab in the mantle transition zone that could still be a magma source, encouraging deep dehydration and convective circulation, and driving intraplate volcanism and continental rifting (Tatsumi et al. 1990). The presence of the slab is supported by seismic tomography across East Asia (Lei and Zhao 2005; Zhu and Zheng 2009) and geochemistry of Cenozoic intraplate Changbaishan basalts in northeastern China (Kuritani et al. 2009). Until the Tertiary alkaline basalts were quite widely erupted in eastern China (Zhou and Armstrong 1982; Basu et al. 1991) including the Bohai Bay Basin (Zhang et al. 2009a), indicating continuous enhanced lithospheric extension and asthenospheric upwelling.

Conclusions

Andesitic lava closely associated with basaltic lava and basic–intermediate volcanic rocks in the Huanghua depression of the Bohai Bay Basin were extruded in the Early Cretaceous, as indicated by LA-ICP-MS zircon U–Pb ages (118.8 ± 1.0 Ma). SHIRMP zircon U–Pb dating of acid lava that occurs only in a restricted part of the area has a Late Cretaceous extrusion date (71.5 ± 2.6 Ma). The Early Cretaceous basic–intermediate lavas are characterized by strong enrichment in LREE and LILE and depletion in HREE and HFSE, indicating a volcanic arc origin related to oceanic subduction. The intermediate lavas are interpreted as partial melts from the basic lavas that evolved by olivine and pyroxene fractionation possibly accompanied by crustal assimilation, evidenced by an inherited Paleoproterozoic zircon (core 2,424 ± 22 Ma). The Late Cretaceous acid lavas are probably products of crustal melting in an extensional regime.

Late Mesozoic arc-related volcanic events in the NCC and adjacent areas show a younging trend toward the Pacific Ocean that has also been found in asthenosphere-derived alkaline basalts and other lithospheric extension-related volcanic rocks. Southeastward retreat of northwestward subduction of the Paleo-Pacific Plate beneath East Asia could be the geodynamic mechanism responsible. As the subduction zone migrated, active continental margin and backarc tectonic regimes played successive roles in different parts of North China during the Late Mesozoic (J1–K2).