Petrogenesis of Mesozoic Magmatic Suites in the Jiaodong Peninsula: Implications for Crust-Mantle Interactions and Decratonization

A craton is generally stable and lacks magmatism and deformation, since the underlying lithospheric mantle is more rigid and buoyant (led by extensive melt extraction) than the surrounding asthenosphere mantle [1]. The NCC has been stabilized after the Paleoproterozoic assembly (~1.85 Ga) of the eastern and western blocks along the Trans-North China Orogen [2]. Both the eastern and western blocks are dominated by Archean basements with a supracrustal cover. Early studies suggest that the NCC lithosphere mantle in the Early Paleozoic is thick (~200 km), as revealed by diamond inclusions in the Mengyin and Fuxian kimberlite, whereas it is relatively thin (80–120 km) in the Cenozoic, as constrained by the mantle xenoliths entrained in basalt [3]. The lithospheric mantle thinning, notably in the eastern NCC, was accompanied by asthenospheric upwelling and Archean lower crustal reworking [4, 5]. The latter is indicated by widespread crustal melting and the development of extensional structures, including metamorphic core complexes and pull-apart basins. This is collectively referred to as the NCC decratonization [4, 6, 7]. However, there are still debates on the decratonization mechanism of the NCC (i.e., mechanical delamination vs. chemical erosion).

The NCC decratonization reached its peak during the Early Cretaceous [4, 8], when the eastern NCC underwent extensive crust-mantle interactions. Some authors argued that the NCC decratonization occurred via mechanic delamination of the eclogitic lower crust and lithospheric mantle, during which adakite-like magmatic rocks were formed by partial melting of the descending eclogitic lower crust [9–12]. For the delamination model, the accreted lithospheric mantle was likely juvenile (Phanerozoic) and fertile and decoupled from the overlying Archean lower crust. Some other authors argued that the lithospheric thinning occurred via thermal erosion, i.e., replacement of old refractory lithospheric mantle by a juvenile fertile one, accompanied by the ascent of the lithosphere-asthenosphere boundary [6, 13]. Moreover, melt-peridotite reactions could also weaken the cold refractory lithosphere and refertilize it [14, 15]. The difference between delamination, thermal erosion, and refertilization is that the former occurs from top to bottom, while the latter two operate from bottom to top.

Lower crust-derived granitic magmas provide a window to examine the NCC decratonization mechanism and processes. The Mesozoic magmatic rocks in the Jiaodong Peninsula include the Jurassic Linglong biotite granite, Early Cretaceous Guojialing granodiorite, and Aishan granite porphyry (Figure 1). Extensive studies have been conducted to investigate their petrogenesis and to constrain the NCC decratonization [11, 16–19]. The Linglong granite is suggested to be derived from the melting of thickened Archean lower crust [17, 19] with no significant mantle contribution [20], while the genesis of the Early Cretaceous Guojialing granodiorite is still disputed [17, 19]. Yang et al. [21] suggested that the Guojialing granodiorite was originated from dehydration melting of the mafic low crust with garnet residue. Hou et al. [11] proposed that the Guojialing granodiorite magma was produced by partial melting of the delaminated eclogitic crust and then reacted with the asthenospheric mantle. The delamination model is supported by the higher Sr/Y and La/Yb ratios and lower $εNdt$ and $εHft$ values of the Guojialing granodiorite than the Linglong granite. However, Jiang et al. [22] and Koua et al. [23] invoked that the Guojialing granodiorite was formed by multistage magma mixing between the Archean lower crust-derived felsic magma and mafic lower crust-derived dioritic magma (during asthenosphere upwelling). Thus, it is still unclear whether melting of the delaminated lower crust is necessary for generating the Guojialing granodiorite. The Aishan granodiorite was emplaced several million years after the Guojialing granodiorite and is considered to have formed by partial melting of the middle/lower crust [16, 17].

Additionally, although the Linglong and Guojialing magmatic rocks share some common adakite-like features, e.g., high Sr/Y and La/Yb ratios [25], they could also be sourced from the continental lower crust with moderate Sr/Y and K₂O/Na₂O ratios [26, 27]. Source composition also exerts strong controls on the compositional variations of related magma [27, 28]. Geochemical modeling by Ma et al. [26] indicates that the adakite-like signature does not only necessarily require partial melting of the delaminated lower crust but also can be inherited from trace element-enriched lower crust. This would mean that the generation of adakite-like features does not necessarily require high-pressure melting. Here, we modeled partial melting of the lower crust to reveal whether it could generate the trace element patterns of these Mesozoic magmatic rocks in the Jiaodong Peninsula. We presented new whole-rock geochemical and zircon age, elemental, and Hf isotope data from these Mesozoic magmatic suites, mafic dykes, and MMEs in the Guojialing granodiorite to discuss the petrogenesis of the magmatic suite in Jiaodong and further put constraints on the decratonization of the NCC.

The NCC is one of the world’s oldest cratons and contains rocks of >3800 Ma [29]. The NCC was amalgamated by two main blocks (eastern block and western block) in the Paleoproterozoic (1.85 Ga) along Trans-North China Orogen (Figure 1) [2, 30]. The western block was formed by the 2.0–1.9 Ga collision between the Yinshan and Ordos blocks along the E–W-trending Khondalite belt [31]. Meanwhile, the eastern block underwent rifting and subsequent collision before 1.9 Ga, forming the Jiao-Liao-Ji metamorphic belt [32, 33]. Tonalite-trondhjemite-granodiorite (TTG) gneiss, along with greenschist- to granulite-facies meta-volcanic-sedimentary rocks, constitutes the Late Archean basement for both the eastern and western blocks [30]. Following the final stabilization of the NCC, the region had undergone prolonged sedimentation, forming widespread and thick sedimentary units [34].

The NCC is currently bounded by the Central Asian Orogenic Belt (CAOB) to the north, the South China Block (SCB) to the south, and the Pacific Ocean to the east (Figure 1). The Paleo-Asian Ocean was subducted beneath the northern NCC margin in the Paleozoic, and it was closed along the Solonker suture in the end Permian to Early Triassic [35]. To the south of the NCC, the subduction and continent-continent collision events were recorded by many high-/ultra-high-pressure blueschist and eclogite units (with clockwise P-T-t metamorphic paths) in the Qinling-Dabie-Sulu orogen [36, 37]. Syn-collisional sinistral shear along the NNE-trending Tanlu fault zone may have displaced the Qingling-Dabie orogen from the Sulu orogen. The fault zone may have reactivated several times during the west-dipping Paleo-Pacific subduction [38, 39]. Extensive magmatism, intracontinental extension, and syn-extensional sedimentation were developed in the Mesozoic, reflecting strong crust-mantle interaction and NCC decratonization [7, 40].

The Jiaodong Peninsula is located at the southeastern NCC margin and east of the Tanlu fault zone (Figure 1). The Jiaobei terrane, an integral part of the NCC, is separated from the Sulu orogen by the Wulian-Qingdao-Yantai fault. Precambrian basement rocks and Jurassic-Early Cretaceous granitoids are the main lithologies in Jiaodong. The Sulu orogen is featured by Triassic K-rich intrusions in the easternmost part, which were emplaced shortly after the ultra-high-pressure metamorphism [41]. There are no such intrusions reported in the Jiaobei terrane, which is the main distinction between these two tectonic units. The metamorphic basement rock series of Jiaobei terrane consists of Mesoproterozoic granite greenstone belts, which are composed of Qixia and Jiaodong Group gneiss suites. Main lithologies for these two suites include biotite granulite, plagioclase amphibolite, amphibolite, and TTG gneiss. Proterozoic metasedimentary rocks are also an integral part of the Jiaobei terrane. The Jingshan and Fengzishan Groups are composed of marble, granulite, gneiss, and schist with amphibolite-granulite facies metamorphic conditions. Jurassic granitoids include the Linglong, Biguo, and Luanjiahe plutons (called collectively as the Linglong suite hereafter) in the Jiaobei terrane and the Kunyushan pluton in the Sulu orogen. The Jurassic Linglong granite is the most widely exposed intrusive rock in the Jiaobei terrane, which is aligned parallel to the regional faults. Gold deposits in Jiaodong are mainly hosted in these faults [42, 43]. Early Cretaceous porphyritic granodiorite in the Jiaobei terrane includes (from east to west) the Guojialing, Congjia, Beijie, and Shangzhuang plutons (called collectively as the Guojialing suite hereafter). These granodiorites are exposed at the northern margin of the Jiaobei terrane and intrude into the Precambrian basement in the east and intrude into the Linglong granite in the west. Early Cretaceous porphyritic granite (slightly younger than granodiorite) includes the Aishan, Gushan, and Dazeshan plutons (called collectively as the Aishan suite hereafter) in the Jiaobei terrane. The Aishan suite emplaced within the Guojialing granodiorite and the Precambrian rocks, while the Gushan and Dazeshan porphyritic granite intruded within the Linglong granite in its southern part. The Sanfoshan, Weideshan, and Longxudao plutons in the Sulu orogen are plutonic rocks with almost identical ages to the Aishan suite. The Jiaolai basin contains Lower Cretaceous-Paleocene volcanic-sedimentary sequences [44].

Our samples were collected from the Jiaobei terrane (Figure 1), covering most outcropping Mesozoic magmatic rock units. These include the Linglong suite (Linglong $granite=3$ and Luanjiahe $granite=2$⁠), Guojialing suite (Beijie $pluton=3$⁠, Shangzhuang $pluton=3$⁠, and Guojialing $pluton=2$⁠, including one MME), Aishan suite (Aishan $pluton=3$ and Nansu $pluton=6$⁠), and mafic dykes in the Linglong goldfield (⁠$n=6$⁠). A summary of collected samples and conducted geochemical analyses is shown in Table 1.

The pluton is composed of medium-grained equigranular biotite granite, comprising mainly plagioclase, K-feldspar, and quartz (Figures 2(a) and 3(a)). Lineated biotite is less abundant, and accessory minerals include magnetite, zircon, apatite, and rare titanite. Most magnetite grains are euhedral and represent the early crystallization phase. Apatite is enclosed by zircon or quartz. Plagioclase crystallized before biotite, while the biotite is enclosed by K-feldspar. The Linglong granite contains no hornblende or large K-feldspar phenocryst, which distinguishes it from the Early Cretaceous granite.

The Guojialing and Beijie plutons are overall slightly more mafic than the Linglong granite, as they host varying proportions of amphibole (expect for the Shangzhuang pluton). The most salient feature is the prevalent coarse-grained K-feldspar phenocrysts in all the Guojialing suite plutons (Figures 2(b)–2(d)). Mafic minerals include mainly amphibole and biotite for the Guojialing and Beijie plutons (Figures 3(b)–3(d)). Major mineral phases are similar in these plutons, including plagioclase, K-feldspar, and quartz (Figures 3(b)–3(d)). Accessory minerals include titanite, apatite, zircon, and magnetite. The groundmass comprises biotite, amphibole, plagioclase, and K-feldspar. Most hornblende grains in the Guojialing pluton are euhedral, and some have biotite inclusions. MMEs are present in the Guojialing pluton (Figure 2(b)) but are rare in the Beijie pluton. The MMEs are several to tens of centimeters in size and comprise amphibole, plagioclase, biotite, and minor magnetite.

These rocks have a highly similar texture and mineral assemblage to the Guojialing suite (Figures 2(e), 2(f), 3(e), and 3(f)). Amphibole and biotite are relatively euhedral, and plagioclase is zoned. Amphibole, biotite, plagioclase, quartz, and magnetite are enclosed by K-feldspar phenocrysts (Figure 3(e)). The Aishan pluton has no MMEs, while the Gushan pluton has some subrounded MMEs. Some K-feldspar fragments were incorporated into the MMEs and are rounded. Biotite and trace magnetite occur along the amphibole cleavages (Figure 3(f)).

Mafic dykes in the Jiaobei terrane are several centimeters to tens of meters wide and steeply dipped. The dykes intruded the Linglong granite, and our samples were collected underground in the Linglong orefield. Clinopyroxene and plagioclase phenocrysts are <1 mm in size and variably altered, but the groundmass remains relatively fresh.

Analytical procedures for geochemical and isotopic analyses and modeling method are presented in Supplementary text.

The data were first back-calculated to 100% to eliminate the effect of LOI (loss on ignition). All the granitoid samples have relatively high silica contents, and there is little variation across the three magmatic suites, although the Linglong has higher SiO₂ content (73–76 wt.%) than the Guojialing (68–75 wt.%) and Aishan (70–73 wt.%) suites. The three granitic suites have high alkaline contents and belong to the high-K calc-alkaline series (Figure 4) (except for one very high-K and one very low-K sample from the Guojialing and Linglong suites, respectively). In the Harker-type plots of SiO₂ vs. CaO, TFe₂O₃, Al₂O₃, MgO, TiO₂, and P₂O₅, differentiation trends can be clearly identified (Figure 5), particularly when plotted together with published data [17, 19, 20], which indicate fractionation of rock-forming minerals. The Linglong and Aishan suites have on average lower CaO, TFe₂O₃, MgO, and TiO₂ contents than the Guojialing suite. Between the Linglong and Aishan suites, the former has lower concentrations of TFe₂O₃, MgO, TiO₂, and P₂O₅ at a given SiO₂.

All the samples are enriched in large ion lithophile elements (LILE), light rare earth elements (LREE), and Pb, but depleted in Ti, P, Nb, Ta, and heavy REEs (HREE) in the primitive mantle-normalized spider diagrams (Figure 6). No apparent negative Eu anomalies are present in both the Linglong and Guojialing suites (Figure 6), whereas some published data of the Aishan suite rocks have negative Eu anomalies [17]. In addition, the samples with negative Eu anomalies also exhibit listric-shaped patterns in the primitive mantle-normalized REE diagram (Figure 6). Yttrium and Yb concentrations are low in our samples (⁠$avg.<10$ ppm and 1.2 ppm, respectively), leading to high Sr/Y and La/Yb ratios. Barium and Sr concentrations are elevated and highly variable in the Linglong and Guojialing suites, but low in the Aishan suite (⁠$Ba<2000$ ppm; $Sr<800$ ppm) (Table S1). The positive Ba vs. Sr correlation may indicate K-feldspar fractionation.

EPMA data for amphibole from the Guojailing pluton and its enclaves are presented in Table S2. Amphibole grains analyzed in this study are Mg-hornblendite, according to the classification of Leake et al. [47]. Chemical compositions and textures of amphiboles from the Guojailing pluton and its MMEs are generally similar. Amphibole compositions were used to calculate the P–T conditions and water contents of the magmatic rocks, following the equation by Ridolfi et al. [48]. Oxidation states were also estimated with these data. The calculated crystallization pressure for the Guojialing pluton is ca. 150–210 MPa, while that of the MMEs is similar (ca. 135–210 MPa) (Figure 7(a)). The estimated temperature of the amphibole crystallization is 820–856°C and 806–852°C for the Guojialing pluton and MME, respectively (Figure 7(b)). Their oxidation state broadly overlaps and is slightly higher than that of the NNO (Ni–NiO) buffer (Figure 7(b)).

Analytical spots of zircon U-Pb dating and trace elements are selected based on CL images (Figure 8). The results are presented in Table S3–4 and illustrated in Figure 9. Zircons from the Lujiahe pluton (Linglong suite) yielded a weighted mean ²⁰⁶Pb/²³⁸U age of $157.8±1.6$ Ma (⁠$N=19$⁠, $MSWD=2.4$⁠). Unlike the Linglong pluton, no Archean-Paleoproterozoic inherited zircons were found in the Luanjiahe sample in this study. The Shangzhuang pluton (Guojialing suite) yielded a weighted mean ²⁰⁶Pb/²³⁸U age of $128.8±1.0$ Ma (⁠$N=22$⁠, $MSWD=0.37$⁠), while the Aishan suite is 118–116 Ma (NS-5A: $116.8±0.4$ Ma, $N=26$⁠, $MSWD=0.8$⁠; NS-16: $117.2±0.4$ Ma, $N=17$⁠, $MSWD=0.8$⁠; and AS-1: $116.2±0.6$ Ma, $N=27$⁠, $MSWD=0.8$⁠).

Zircons from MME (DCW-2A) display relatively simple inner texture and display oscillatory zoning (Figure 8). Zircon xenocrysts are rare in this sample. Twenty-nine zircons gave a concordia age of $129.7±0.5$ Ma and weighted mean ²³⁸U/²⁰⁶Pb age of $129.6±0.5$ Ma (⁠$MSWD=1.1$⁠) (Figure 9), similar to its host rock (Guojialing pluton sample DCW-1: $127.8±0.5$ Ma) and other Guojialing suite rocks within error. Zircons from the MME sample have mostly 100–400 ppm U and 20–250 ppm Th, with $Th/U=0.21$–0.69 (Table S4).

The Linglong granite has $176Hf/177Hf=0.281962$–0.282269 (Table S5) and corresponding $εHft=–25.4$ to –14.5 (Figure 10) for the Jurassic zircons and $εHft=–19.1$ to –1.9 for the Late Triassic zircons and 2.3 to –3.2 for the Proterozoic-Late Archean zircons. These results are the same as the published data [17, 19]. The Guojialing granodiorite (DCW-1) has $εHft=–10.4$ to –13.9 for the Cretaceous zircons (Figure 10) and +5.9 to +6.4 for the Neoarchean inherited zircons, whereas zircons from the MME sample (DCW-2A) have $εHft=–13.0$ to –8.9. Zircon $εHft$ values from the Aishan pluton are narrowly confined to be around –16. In contrast, zircon $εHft$ values of the two Gushan pluton samples are more scattered (–23.1 to –11.9, $N=15$⁠) (Table S5).

Zircons from the mafic dyke sample are smaller than those from the other suites. There are several Precambrian zircon xenocrysts in the mafic dyke, but they are not overgrown by Cretaceous zircon rims. The Cretaceous zircons have much more negative $εHft$ values (avg. –19.5) than those from the granodiorite (Figure 10(b)).

It is well recognized from numerous geochemical studies that the Mesozoic granitoid rocks of the Jiaodong Peninsula are generated by partial melting of the Archean-Paleoproterozoic lower crust [16, 19, 20]. Meanwhile, Sr-Nd isotopes are too variable and point to a heterogenous source region for the three granitic magma suites (Figure S1). Ma et al. [20] proposed that the Linglong granite was generated by the melting of the thickened lower crust from both North China and South China, possibly with contributions from collision-related alkaline rocks and UHP metamorphic rocks. Genesis of the Guojialing suite magma is more complex, although both the Linglong and Guojialing suites show some adakite-like geochemical features (e.g., high Sr/Y and La/Yb ratios). Growing evidence shows that continental lower crust with moderate Sr/Y and K₂O/Na₂O ratios may produce melts with adakite-like trace element patterns [26, 27]. To investigate the source control on these Mesozoic magmatic rocks, we modeled various degrees of partial melting of the lower crust under four sets of experimental conditions: (1) low P-T (#2: 10 kbar, 900°C), (2) medium P and low T (#5: 12.5 kbar, 900°C), (3) high P and low T (#9: 15.0 kbar, 900°C), and (4) high P-T (#12: 15.0 kbar, 1050°C) ([50]; methodology in Supplementary Text). The compiled geochemical data and those obtained in this study for the Linglong, Guojialing, and Aishan magmatic suites are regarded as a whole dataset and would be used for comparison with modeled results. The Linglong and Guojialing suites underwent no obvious crystal fractionation, as indicated in Figure S1 and previous studies [19, 20]. So, we compared the modeled results with the average compositions of these two suites. As discussed in Li et al. [42], the Aishan suite has undergone amphibole fractionation is also supported by decreasing Dy/Yb values with rising SiO₂ contents (Figure S1). Therefore, the trace element pattern of the lowest-Si sample was selected to represent the melt before amphibole fractionation.

Modeled melts under low P-T conditions have comparable Rb, Ba, Th, Nb, and Ta concentrations with the average values of the dataset (Figure 11(a)), despite the degree of melting. However, the REEs and HFSEs are more enriched in the modeled melts than in the measured compositions. REE (La to Yb, except Sr) concentrations are above the maximum values of the dataset (Figure 11(a)). Under higher pressure with residue garnet (18%) and rutile (1%) (#5; Figure 11(b)), trace element concentrations in the melts are more similar to the average values of the Linglong suite, particularly for HREE and Y. However, the LREE and Zr, Hf, and Tb contents are slightly higher in the melt, reaching the maximum values of the dataset at a high degree of partial melting (40%). Contents of trace elements (e.g., Sm, Eu, and Ti) are overestimated under such conditions. If the pressure increases to 15 kbar (garnet stability field), the HREE and Y concentrations are closer to those of the average Linglong suite, but the Sr content is high and falls out of the dataset (Figure 11(c)). At 15 kbar and 1050°C, experiment results indicate that the residue phase comprises mostly orthopyroxene and clinopyroxene [50]. The modeled result under this condition shows overall higher values than the maximum abundance of the dataset (Figure 11(d)). In summary, only the garnet-present melting could give rise to low HREE contents that match the average data for the Linglong suite. Almost all the modeled concentrations for elements from La to Ti in Figure 11 are inconsistent with the dataset under the various melting conditions. This implies that the relative proportions of residue phases (which can incorporate these elements, e.g., apatite and amphibole) are underestimated (Figure 11).

The element concentrations range widely, and the LREE contents are higher than those of the Linglong suite (Figure 12). Generally, the modeled Rb, Ba, and Th contents are mostly compatible with the dataset (regardless of the melt fraction or residue phase). Under low P-T conditions (plagioclase stability field), the modeled melts have lower Sr contents than the average data (Figure 12(a)). Meanwhile, the Zr, Hf, Tb, Y, and Yb concentrations in the modeled melt are slightly higher than the average compositions of the Guojialing suite. At 12.5 kbar and 900°C, the proportion of plagioclase decreases (16%) while that of garnet increases (18%) in the residue. This makes the modeled melts well fitted with the average compositions of the Guojialing suite (Figure 12(b)). Under higher pressure (50% garnet, no plagioclase), the HREE and Nb-Ta contents are slightly lower than the average Guojialing suite (Figure 12(c)), although the Sr and Zr-Hf contents become more similar. The high P-T condition (Figure 12(d)) produces melts that are compositionally very different from the average data. Overall, melting under medium-high pressure (garnet stability field) seems to produce the best match results with the average Guojialing suite (Figures 12(b) and 12(c)).

The average compositions of the dataset are lower than the sample with the lowest SiO₂ content (Figure 13). The low-Si sample has notably higher trace element abundance than the average measured data. The lowest-Si sample fit well the modeled melt in this study, particularly the low P-T one (Figures 13(a) and 13(b); 10.0–12.5 kbar, 900°C). However, the Nb-Ta contents do not match the measured data well under any of the four P-T conditions, and the Nb-Ta contents of the NCC granulite (which acts as the source rock in our modeling) are even lower than the minimum Nb-Ta contents of the Aishan suite. To obtain high Nb-Ta contents, no ilmenite or rutile (which hosts these two elements) could be left in the residues. Nevertheless, the first two P-T scenarios provide the best match for producing the Aishan suite.

We have also compared the Sr/Y and La/Yb ratios of the three magmatic suites with the modeling results (Figure 14). The Linglong and Guojialing suites have $Sr/Y=50$–200, while some Guojialing suite rocks are very high (up to 400). Sr/Y ratios for the Aishan suite are <100. Overall, the Guojialing suite has higher Y content than the Linglong and Aishan suites. In our modeling results, only high-P but low-T (15.0 kbar, 900°C) can produce the highest Sr/Y ratios required for both the Linglong and Guojialing suites (Figure 14(a)). In addition to the Sr/Y ratio, the La/Yb ratios for both the Linglong and Guojialing suites also require moderate- to high-P but low-T conditions (Figure 14(b)). Thus, we concluded that to obtain the trace element patterns and Sr/Y and La/Yb ratios of the Late Jurassic Linglong and Early Cretaceous Guojialing suites, the partial melting likely occurred in the garnet stability field (i.e., high-pressure) [51, 52].

The NCC was tectonically stable since its assembly at ~1.85 Ga [30]. The widespread Mesozoic granitic magmatism likely reflected the reactivation of this ancient craton [4, 40]. There are two major ways to generate granitic melts: dehydration melting and water-fluxed melting [53–56]. There are still arguments on which mechanism dominates in the deep crust [57, 58]. These two kinds of melting processes commonly occur under different geological environments. Dehydration melting requires dewatering of hydrous minerals like muscovite, biotite, or amphibole, whereas the water-fluxed melting requires external fluid input, mostly accompanied by recharge of mafic magma (e.g., [59, 60]). Several geochemical fingerprints, like the chemical compositions of the granitic melts or minerals, would help to determine whether the melting occurred with external fluid input [56, 61].

Partial melting experimental results from [62, 63], and references therein have shown that water-fluxed melting would generate Fe-rich melts with a lower Na/K ratio than those sourced from mica-dehydration melting from the same protolith (Figure 15(a)), since higher water activity enables granitic magmas to incorporate more MgO and FeO and destabilize the plagioclase in the source [64, 65]. Most data from the three magmatic suites fall outside both the dehydration and water-fluxed melting fields but show elevated total Fe content. However, in the Rb/Sr vs. Ba and Sr diagrams (Figures 15(b) and 15(c)), these magmatic suites display distinct patterns.

Modeling by Inger and Harris [61] shows that some trace elements (e.g., Rb, Sr, and Ba) behave differently when it comes to various melting reactions: Rb is enriched in mica due to its substitution with K, while Sr is mainly incorporated in plagioclase. Mica-dehydration melting would thus produce high-Rb/Sr but low-Sr melts. Meanwhile, biotite-dehydration melting would make the melt considerably higher-Rb/Sr but have little effect on either Sr or Ba content. On the contrary, water-fluxed melting would yield low-Rb/Sr but high-Sr melt. Most of the Ba is contained in K-feldspar; thus, Ba would be depleted when K-feldspar remains as restite [66]. There is currently no effective way to reveal amphibole-dehydration melting using geochemical data. However, it may be a common process considering that amphibole cumulates contribute to the large volume in the middle to lower crust (e.g., [67, 68]).

Therefore, we conclude that the Linglong and Aishan suites were primarily derived by amphibole-dehydration melting, while the Guojialing suite is produced by water-fluxed melting. This conclusion is also supported by the Ti-in-zircon content (Figure 15(d)). It is suggested that zircons would incorporate more Ti under high temperatures (e.g., [69]). The granitic magmas generated under different conditions have significantly different temperatures, with lower temperatures associated with water-fluxed melting [57, 58, 70, 71]. Overall, the Ti-in-zircon contents from the Guojialing suite and MMEs are lower than that of the Linglong and Aishan suites (Figure 15(d)), suggesting a lower formation temperature for the former.

The Linglong suite has a wide $εHft$ range and a two-stage model age of 1.9 to 3.0 Ga. The Aishan suite is characterized by narrow ranges of $εHft$ values and two-stage model ages. There is a slight difference in terms of Hf isotope data for the Early Cretaceous Guojialing suite, mafic dykes, and MMEs. Zircon $εHft$ values (ca. –10 to –15) in the Beijie and Guojialing plutons from the Guojialing suite are relatively high, which plot above the 1.9 Ga crustal evolution line (Figure 10). This is distinct from the zircon $εHft$ values obtained from the Linglong suite (mostly <–20) and Aishan suite (ca. –15 to –20), though there is overlap when the published data are included [17, 19, 20, 45]. These Hf isotope data suggest that the Guojialing suite contains relatively juvenile and depleted material, in contrast to Linglong and Aishan suites. Meanwhile, the whole-rock $εNdt$ values of the Guojialing suite are –10 to –27, while those of the Linglong and Aishan suites are –16 to –22 (Figure S1). The Guojialing suite has also higher MgO, TiO₂, Cr, and Ni contents than the Linglong and Aishan suites (e.g., [17]), suggesting that mantle input may have been important.

Two mantle-derived melt endmembers (i.e., lithosphere and asthenosphere) may be present. Zircon $εHft$ values from the 126 Ma mafic dyke (–17 to –23, avg. –19.5) are clearly higher than those of the low-Ti lamprophyres (–25 to –30) in Jiaodong Peninsula, which was interpreted to be derived from the ancient enriched lithospheric mantle [45]. These zircon $εHft$ values from the mafic dyke are lower than those of the Guojialing suite. Therefore, mixing between the lithosphere-derived mafic magma and the lower crustal-derived melt could not produce the isotopic features of the Guojialing suite. Mixing with asthenosphere-derived magma can be a plausible explanation [11].

The delamination model proposes that the eclogitic lower crust is partially melted when it sinks into the asthenospheric mantle, and this model is widely accepted (e.g., [9, 11]). However, the NCC lower crust had undergone extensive partial melting in the Jurassic and was likely very dry and depleted and hard to remelt. We modeled the remelting of the residue eclogitic lower crust (with orthopyroxene and garnet; [50]) that underwent 30% partial melting under 15 kbar and 900°C (Figure 16). The modeling result shows that trace element patterns of the modeled melt could not perfectly fit the compositions of the Guojialing suite. In the Sr/Y vs. Y and La/Yb vs. Yb plots (Figure 16), features of these elements by melting of the residue eclogitic lower crust deviate far from the Guojialing suite (regardless of the melt fractions). Both trace element patterns and ratios are inconsistent with the delamination model.

We prefer the model that the asthenosphere-derived magma had risen and ponded in the lower crust. The hot magma may have induced partial melting of the lower crust and mixed with the newly formed felsic magma. MMEs in the Guojialing granodiorite were interpreted to be products of magma mingling rather than restites [8, 72] because (1) zircons from the Guojialing pluton and the MMEs have the same U-Pb age but different Hf isotope compositions (Figures 9 and 10), which points toward different magma reservoirs, and (2) restite minerals are more likely to be anhydrous (e.g., orthopyroxene, plagioclase, and garnet; [73]), which is inconsistent with our MME samples (containing amphibole+plagioclase). Calculated P-T conditions by amphibole compositions (Figure 7(a)) and the calculated oxygen fugacity (Figure 7(b)) in the MME and Guojialing pluton are largely the same. We therefore deduced that these MMEs are the products of magma mixing/mingling. The Aishan suite has lower Sr/Y and La/Yb values than those of the Linglong and Guojialing suites (Figure 14). Our modeling results suggest that crustal melting under moderate P-T conditions (#5; 12.5 kbar, 900°C) can generate the trace element patterns akin to the Aishan suite. Thus, we believe that the Aishan suite was derived from shallow-level crustal melting (with minor garnet residue). The melting was induced by heating from the asthenosphere.

In summary, the NCC crust was thick during the Jurassic and underwent dehydration melting with large portions of garnet residue. During 130–120 Ma, the thick eclogitic lower crust at eastern NCC was chemically eroded by the convective asthenosphere and large volumes of lithosphere- and asthenosphere-derived mafic magma underplated beneath the lower crust. This mafic melt released fluid into the crust and induced the melting of the lower crust. After ca. 120 Ma, the crust was thinner than before. Crustal melting occurred at shallow levels of the crust with minor garnet remaining stable (Figure 17).

Based on geochemical analysis and trace element modeling on the Mesozoic magmatic suites from the Jiaodong Peninsula, we have found the following:

• (i)

  The Jurassic Linglong magmatic suite may have been generated by dehydration melting of the thickened Archean lower crust (>15 kbar) with substantial garnet residue phase

• (ii)

  The Early Cretaceous Guojialing suite may have derived from water-fluxed melting of the lower crust, rather than the descending eclogitic crust. The water and heat that caused the melting were possibly provided by the asthenosphere mantle-derived mafic magma. MMEs (carried by the Guojialing suite) may represent the mixing product between the asthenospheric mantle-derived magma and the lower crustal melts

• (iii)

  Magma differentiation may have been critical in forming the Aishan suite. Amphibole-dominated fractionation may have driven the magma toward lower Dy/Yb ratios. Modeling results reveal that melting under moderate P-T conditions (12.5 kbar, 900°C) can generate the trace element features akin to the most mafic whole-rock compositional data

The data are provided in supplementary files.

The authors declare that they have no conflicts of interest.

We would like to express our sincere thanks to Yu Chao and Zhou Limin for helping with the LA-(MC)-ICPMS zircon U-Pb dating and Hf isotope analyses and to Liu Yanhong and Liu Wei for helping with the whole-rock major element analyses. This study was financially supported by the National Natural Science Foundation of China-Shandong Joint Fund Program (U2006201), Fundamental Research Funds for the Central Universities (FRF-TP-20-042A1), and National Key Research and Development Program of China (2016YFC0600305).