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Oxygen fugacity controls the behavior of multivalent elements and compositions of C-O-H fluids in Earth’s mantle, which further affects the cycling of materials between the deep interior and surfac...

We present mineralogical and geochemical compositions of mantle xenoliths from two Cenozoic basalt localities of the northeastern North China Craton. These xenoliths include lherzolite, harzburgite, and websterite. They are generally fertile in major elements and different from the typical cratonic lithosphere, which is consistent with previous hypotheses regarding craton destruction. The ratios of 87Sr/86Sr and (La/Yb)N of clinopyroxenes (Cpx) in one lherzolite are relatively low in the core but high in the rim. The center of the Cpx grain has a high U concentration. Changes in trace elements and Sr isotopes indicate that later stage high 87Sr/86Sr melt metasomatism superimposed on the early hydrous melt/fluid. The Cpxs in some xenoliths are low in Ti/Eu but high in Ca/Al and light rare earth elements, which indicates carbonate melt metasomatism. 87Sr/86Sr is increased in the core and decreased in the rim of most Cpx grains, which reflects the superposition of two-stage metasomatism. The early agent should be high in 87Sr/86Sr, and the recent agent should be low in 87Sr/86Sr. The Cpxs in olivine websterite are low in 87Sr/86Sr (0.70220–0.70320), which reflects the recent metasomatism of asthenosphere-derived melt. Collectively, these observations reflect a three-stage modification of the lithospheric mantle. First-stage hydrous melt/fluid could come from the dehydration of young subducted plates. Second-stage melt/fluid of high 87Sr/86Sr could derive from the partial melting of the subducted altered oceanic crust, and the recent melt/fluid of low 87Sr/86Sr should be from the asthenosphere.

The Archean mantle lithosphere beneath the North China Craton (NCC) was transformed in the Mesozoic, leading to the craton destruction. Despite the significant breakthroughs in the craton studies, lithospheric transformation mechanisms are yet to be fully understood. Compositional variations of mantle-derived rocks and xenoliths provide insights into the nature of the mantle lithosphere before and after the craton destruction. The Paleozoic lithosphere of the NCC is ∼200 km thick. It has a refractory mantle with an evolved isotopic signature. The Mesozoic mantle lithosphere was relatively fertile and highly heterogeneous. In the Cenozoic, the lithosphere in the eastern NCC is about 60–80 km thick. It has an oceanic-type mantle that is fertile in composition and depleted in the Sr-Nd isotopic signature. The Central Zone lithosphere is >100 km thick and has a double-layer mantle with an old upper layer and a new lower layer. The Western Block has a lithosphere of ∼200 km thick. The lithospheric mantle beneath the southern and northern margins and eastern part of the NCC has been transformed significantly by peridotite-melt reactions due to the multiple subductions of adjacent plates since the Paleozoic. Paleo-Pacific subduction and the associated dynamic processes significantly alter the lithosphere based on the distribution of craton destruction. The involved mechanisms include mechanical intrusion of subduction plates, melt fluid erosion, and local delamination. The lithospheric thinning of ∼120 km is relevant to the continental extension caused by subduction plate rollback and trench retreat.

To investigate the potential of using Barium (Ba) isotopes to trace recycled crustal materials, we report high-precision Ba isotopic compositions for 22 well-characterized samples of Cenozoic basalts from the Taihang Mountains, North China Craton. The basalts have δ138/134Ba [= (138Ba/134Basample/138Ba/134BaSRM3104a – 1) × 1000] of −0.06‰ to +0.03‰(±0.05‰，2SD), lower than the depleted upper mantle (+0.03‰ to +0.15‰). Because Ba isotope fractionation during basaltic magmatic differentiation is negligible, the light Ba isotopic compositions likely reflect the involvement of isotopically light crustal materials in the mantle source. The Ba isotopic variations, combined with the data of elements and Sr Nd isotopes of the basalts, indicate that the light Ba isotopic compositions mainly resulted from marine sediments rather than altered oceanic crust. The quantitative modeling using Sr-Nd-Ba isotopic compositions suggests that about 0.5% to 3% of marine sediments were involved in generating the continental basalts. Our study here highlights the potential of using Ba isotopes to trace recycled materials in the mantle.

Clinopyroxene megacrysts in volcanic rocks can provide substantial information on the evolution of the magmatic system at depth. Although considerable attention has been paid to these crystals, their origin is not yet completely resolved. The clinopyroxene megacrysts worldwide can be divided into two major types in general: the green Cr-diopside type and the black Al-augite type. There is a consensus view that the Cr-diopside megacrysts are mantle xenocrysts, whereas two contrasting opinions exist regarding the origin of the black Al-augite megacrysts. One favours a cognate origin, viewing them as crystallization products of the host magmas under high-pressure; while the other argues that they are xenocrysts crystallized from previous alkali basalts or fragments of mantle peridotites, pyroxenites or pegmatite veins. A review study on the clinopyroxene megacrysts in Meso-Cenozoic volcanic rocks from the North China Craton (NCC) and their comparison with those worldwide provides new constraints on their origin, namely, the Cr-diopside megacrysts, as previously thought, are all xenocrysts, representing disaggregated clinopyroxene crystals from clinopyroxene-rich mantle rocks. Contrary to the formerly proposed cognate origin, the Al-augite megacrysts are also xenocrysts, having no direct genetic link to their host rocks. They crystallized from melts that have formed earlier than the host magmas, and probably accumulated in a magma chamber or occurred as sheets or veins filling a fracture network surrounding a magma chamber in the upper mantle. During the subsequent eruption of the host lavas, these previously formed crystals were incorporated into the magma and were brought up to the surface.

This paper reports petrology, major and trace element abundances in bulk-rocks and minerals, and clinopyroxene Sr-Nd-Hf compositions from a suite of mantle xenoliths entrained in Cenozoic Sanyitang alkali basalts, Jining County in the Inner Mongolia Suture Zone. The aim is to constrain the nature and evolution of the lithospheric mantle beneath the western North China Craton. The Sanyitang mantle xenoliths are mainly anhydrous spinel lherzolites with subordinate websterites. Petrological and geochemical features of the spinel lherzolites suggest that they are refractory mantle residues formed by variable degrees of melt extraction (3–14%), followed by silicate and carbonatite metasomatism. The Sr-Nd-Hf isotopic compositions (87Sr/86Sr = 0.7031–0.7037, eNd = +5.2 − +11.2 and eHf = +8.4 − +29.3) of clinopyroxene separates from the majority of the spinel lherzolites lie on, or close to, the mantle array defined by the composition of ocean-island basalts and mid-ocean ridge basalts. On the other hand, clinopyroxene separates from a minority of spinel lherzolites (SYT09-01, SYT09-09, SYT11-01) have high 87Sr/86Sr (0.7040–0.7049), eNd (+12.4 − +21.9) and eHf (+58.2 − +67.8), above the mantle array, reflecting long-term depletion of the mantle. The websterites are characterized by lower MgO (18–22 wt%) and higher Al2O3 contents (4.5–5.6 wt%), and lower Mg# (86.2–87.3) than the spinel lherzolites (Mg# = 89.3–90.8; Al2O3 = 0.9–3.6 wt%). Their convex upward rare earth element patterns, along with lower Ni contents (334–389 ppm) indicate that they were cumulates fractionated from basaltic magmas circulating through the upper mantle. The trace element patterns of clinopyroxenes from three phlogopite-free websterites show enrichment in large ion lithophile and negative anomalies for the high field strength elements. In addition, the phlogopite-free websterite clinopyroxene Sr-Nd-Hf isotope ratios plot in the enriched lithospheric field (87Sr/86Sr = 0.7058–0.7061, eNd = −9.2 to −8.4 and eHf = −5.2 to −3.7 respectively), which implies the contribution of recycled lower crustal materials to their source. The presence of phlogopite in some Sanyitang websterites, coupled with strong enrichments in both light rare earth elements and large ion lithophile elements, as well as high 87Sr/86Sr (0.7065–0.7068) and negative eNd (−1.5 to −0.3) and eHf (−6.1 to −4.8) values of clinopyroxene, provide strong evidence for the existence of subduction-related hydrous fluids/melts metasomatism. This study demonstrates that the Sanyitang mantle xenoliths and their component minerals record the complex petrological history and local heterogeneity of the subcontinental mantle lithosphere under the western North China Craton.

We present detailed major-, trace-element and Sr-Nd-Mg isotopic geochemistry for a suite of pyroxenite xenoliths entrained in Oligocene basalts in Yangyuan county, North China Craton, to reveal their origins and to further constrain the evolution of the lithospheric mantle beneath this area. The Yangyuan pyroxenites exhibit a lithologic spectrum ranging from orthopyroxenite, through orthopyroxene-rich websterite and clinopyroxene-rich websterite to clinopyroxenite. Their equilibrium temperatures (874–975 °C), which are within the temperature range of the upper mantle and lower crust, suggest that they came from the crust-mantle transition zone. The Yangyuan pyroxenite xenoliths can be subdivided into three types based on the compositions of their constituent clinopyroxene. Clinopyroxenes in the type I pyroxenites are characterized by high Mg# (88.3–92.0; Mg# = Mg/(Mg + Fe2+)*100) and Cr2O3 contents (0.86–1.63 wt.%). Their resemblance to those from the peridotite xenoliths, together with their light rare earth element (LREE) enrichment, indicates that the type I pyroxenites should be produced by lithological heterogeneity in the mantle, which may have including metasomatism. Clinopyroxenes in the type II pyroxenites have intermediate Mg# (81.0–86.7) and Cr2O3 contents (0.53–0.73 wt.%), which are similar to those of strongly metasomatized mantle-derived Fe-lherzolite xenoliths. Their LREE-enriched compositions, as well as the high Ni contents of the orthopyroxenes and clinopyroxenes, suggest that the type II pyroxenites were produced by melt-peridotite interactions. Clinopyroxenes from type III pyroxenites have the lowest Mg# (65.2–76.5) and Cr2O3 contents (0.05–0.38 wt.%), which are comparable to those formed by fractional crystallization of primary basalts, suggesting that they are the products of fractional crystallization. The high Mg#, Ti/Eu ratios, the low (La/Yb)N and Ca/Al ratios, and Rb and Ba contents of the clinopyroxenes, as well as the depleted Sr-Nd isotopes of most of the Yangyuan pyroxenites, suggest that asthenosphere or juvenile lithospheric mantle-derived silicate melts were probably involved in their formation, whereas the enriched Sr-Nd isotopes of sample YY17-5 indicate that its source may have mixed with melts derived from recycled ancient lower crust. The light and variable Mg isotopic compositions (δ26Mg = −0.23 to −0.46‰) of the Yangyuan pyroxenites suggest contributions from a subducted oceanic slab. The diverse origins of these pyroxenite xenoliths provide evidence that the deep lithosphere beneath Yangyuan has been modified by multiple melt-rock interactions and magma underplating.

The nothern margin of the North China Craton (NCC) preseves the tectonic imprints of early Paleozoic to Triassic tectonic processes. Here we investigate the geochronology, geochemistry, zircon hafnium and whole rock Nd isotope data on a suite of magmatic rocks from the Ningcheng pyroxenite–gabbro–diorite complex and the Jiwangyingzi Formation in the Inner Mongolia region of the northern NCC. The zircon U–Pb dating identifies multiple stages of mafic to intermediate magmatism from Early Permian (298 ± 4 Ma) to Middle Triassic (219 ± 1 Ma) in this area and their hafnium isotopes display diverse mantle sources. An integration of field observations, geochronology and elemental and isotopic geochemistry indicates a complex petrogenetic history for the magmatic suite. The Ningcheng pyroxenite–gabbro–diorite complex is a product of multiple pulses of magmas with crystal fractionation, hybridization and assimilation, with the involvement of melts derived from lithospheric mantle and even the asthenosphere. Our data reveal an increasing involvement of mantle component from Late Permian to Triassic. The features of progressive mantle upwelling correlate with tectonic processes associated with the closure of Paleo-Asian Ocean and subsequent post collisional extension, resulting in active magmatism from Carboniferous to Triassic in this region.

The North China Craton (NCC) provides one of the classic examples of craton destruction, although the mechanisms and processes of its decratonization are yet to be fully understood. Here we integrate petrological, geochemical, geochronological and geophysical information from the NCC and conclude that the destruction of the craton involved multiple events of circum-craton subduction, which provided the driving force that destabilized mantle convection and tectonically eroded the lithospheric mantle beneath the craton. Furthermore, subducted-slab-derived fluids/melts weakened the subcontinental lithospheric mantle and facilitated thermo-mechanical and chemical erosion of the lithosphere. The more intense destruction beneath the eastern part of the NCC reflects the crucial contribution of Pacific plate subduction from the east that overprinted the mantle lithosphere modified during the early subduction processes. Our study further establishes the close relationship between lithospheric modification via peridotite–melt reactions induced by oceanic plate subduction and cratonic destruction.

article i nfo Studies of mantle xenoliths have confirmed that Archean subcontinental lithospheric mantle (SCLM) is highly depleted in basaltic components (such as Al, Ca and Na) due to high-degree extraction of mafic and ultramafic melts and thus is refractory and buoyant, which made it chronically stable as tectonically independent units. However, increasing studies show that ancient SCLM can be refertilized by episodic rejuvenation events like infiltration of upwelling fertile material. The North China Craton is one of the most typical cases for relatively complete destruction of its Archean keel since the eruption of Paleozoic kimberlites, as is evidenced by a dra- matic change in the compositions of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, reflecting significant lithospheric thinning and the change in the character of the SCLM. The compositional change has been interpreted as the result of refertilization of Archean SCLM via multiple-stage peridotite-melt reactions, suggested by linear correlations between MgO and indices of fertility, covariations of Al2O3 with CaO, La/Yb, 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, 187 Os/ 188 Os and Re-depletion ages (TRD), high Re abundances, scatter in Re-Os isotopic plot, variablein situTRDages of sulfides, andcorrelationbetween TRDagesand olivine Foof peridotite xenoliths in Paleozoic kimberlites and Cenozoic basalts on the craton. By integrating major and trace element, Sr, Nd and Os isotopic compositions of peridotite xenoliths and oro- genic massif peridotites from the continents of Europe, Asia, America, Africa and Australia, together with pre- vious studies of petrology andgeochemistry of global peridotites, we suggest that(1) refertilizationof cratonic and circum-cratonic lithospheric mantle is widespread; (2) Archean SCLM worldwide has experienced a multi-stage history of melt depletion and refertilization since segregation from the convecting mantle; (3) cratonic SCLM may be more susceptible to compositional change caused by refertilization than is generally assumed; (4) the original character of much Archean cratonic mantle has been partly overprinted, or even erased by varying degrees of refertilization, which may play a key role in the rejuvenation and erosion of the SCLM beneath the Archean cratons. Due to the refertilization of ancient SCLM, (1) many published whole-rock Re-depletion ages cannot repre- sent the formation ages of peridotites, but the mixtures of different generations of sulfides. Thus, the chro- nological significance of the Re-Os isotopic composition in individual peridotite should be cautiously interpreted; (2) many kimberlite- and intraplate basalt-borne lherzolite xenoliths, with major element compositions close to primitive mantle, may be the fragments of the ancient SCLM, strongly refertilized by infiltration of asthenosphere-derived melts, rather than newly-accreted SCLM. Consequently, new accre- tion of SCLM beneath ancient cratons such as the North China Craton may be less than was previously assumed.

A comprehensive synthesis of U–Pb geochronology and Hf isotopes of zircons from granulite/pyroxenite xenoliths entrained in Phanerozoic magmatic rocks and inherited xenocrysts from the associated lower crust rocks from various domains of the North China Craton (NCC) provides new insights into understanding the Phanerozoic evolution of the lower crust in this craton. Episodic widespread magma underplating into the ancient lower crust during Phanerozoic has been identified throughout the NCC from early Paleozoic to Cenozoic, broadly corresponding to the Caledonian, Hercynian, Indosinian, Yanshanian, and Himalayan orogenies on the circum-craton mobile belts. The early Paleozoic (410–490 Ma) ages come from xenoliths in the northern and southern margins as well as the central domain of the Eastern Block of the craton which mark the first phase of Phanerozoic magma underplating since the final cratonization of the NCC in the Paleoproterozoic. The magmatism coincided with the northward subduction of the Paleotethysian Ocean in the south and the southward subduction of the Paleoasian Ocean in the north. The subduction not only triggered magma underplating but also led to the emplacement of the diamondiferous kimberlites on the craton, marking the initiation of decratonization. The late Paleozoic event as represented by the 315 Ma garnet pyroxenite and/or lherzolite xenoliths in Hannuoba was restricted to the northern and southern margins of the craton, correlating with the arc magmatism continuous associated with the subduction of the Paleotethysian and Paleoasian Oceans and resulting in the interaction between the melts from subducted slabs and the lithospheric mantle/lower crust. The early Mesozoic event also dominantly occurred in the northern and southern margins and was related with the final closure of the Paleotethysian and Paleoasian Oceans as well as the collisional orogeny between the NCC and the Yangtze Craton. The late Mesozoic (ca. 120 Ma) was a major and widespread magmatic event which manifested throughout the NCC, associated with the geothermal overturn due to the giant south Pacific mantle plume. The Cenozoic magmatism, identified only in the dark clinopyroxenite xenoliths in the Hannuoba, was probably induced by the Himalayan movement in eastern Asia and might also have been influenced by the subduction of the Pacific Ocean to some extent. These widespread and episodic magma underplating or rejuvenation of the ancient lower crust beneath the NCC revealed by U–Pb and Hf isotope data resulted from the corresponding addition of juvenile materials from mantle to lower crust, with a mixing of the old crust with melts. The process inevitably resulted in the compositional modification of the ancient lower crust, similar to the compositional transformation from the refractory lithospheric mantle to a fertile one through the refractory peridotite — infiltrated melt reaction as revealed in the lithospheric mantle beneath the craton.

article i nfo High-Mg# peridotite xenoliths in the Cenozoic Hebi basalts from the North China Craton have refractory min

a b s t r a c t A comprehensive review of U-Pb geochronology and Hf isotopes of zircons separated from granulite xenoliths entrained in Phanerozoic magmatic rocks and inherited xenocrysts from the associated lower crust rocks from various domains of the North China Craton (NCC) provides new insights into under- standing the evolution of the lower crust in this part of the Precambrian nucleus of Asia. The oldest zircons recorded in granulite xenoliths show ages up to 3.6 Ga, slightly younger than the oldest zircons (3.8 Ga) from samples of the exposed Archean upper crust. However, the Hf isotope features indicate that the oldest lower crust might have been derived from a 4.0 to 4.1 Ga primordial crust as indicated by the data from an inherited zircon in the North Qinling Orogenic Belt at the southern part of the NCC. Our synthesis also suggests that ca. 2.5 Ga mark an important period for the evolution of the lower crust of the NCC and the cratonization of the Archean blocks in the NCC, at least for the Eastern Block, with a pos- sible link to mantle plume activity. The occasional presence of zircons with 2.6-3.1 Ga ages in the lower crustal granulite xenoliths suggests a continuous reworking of the Paleoarchean lower crust during the Archean. The comprehensive data also show that 1.8-2.0 Ga period was the first significant event for the evolution of the lower crust after the cratonization of the Archean blocks of the NCC, which affected the whole lower crust of the Eastern NCC. Episodic growth or rejuvenation of the Precambrian lower crust beneath the NCC is also revealed by U-Pb and Hf isotope data, resulting from the corresponding addition of juvenile materials from mantle to lower crust, with a mixing of the old crust with juvenile magma. This compositional modification of the lower crust resembles the compositional transformation from the refractory lithospheric mantle to a fertile one through the refractory peridotite - infiltrated melt reaction as revealed in the lithospheric mantle beneath the NCC.

In-situ lithium (Li) concentrations and δ7Li of olivine, orthopyroxene (opx) and clinopyroxene (cpx) in mantle xenoliths from the Quaternary Longgang maar provide insights into the nature and evolution of the lithospheric mantle beneath the easterly part of the North China Craton. SIMS analyses show Li partitioning of olivine > opx ≥ cpx and Li isotopic disequilibrium in each sample. Olivines in harzburgite are generally homogeneous, with Li abundances in the range of normal mantle, but their δ7Li (− 0.9 to − 4.0) are lower than normal mantle olivine δ7Li values of ~+4 ± 2. Olivines in cpx-rich lherzolite and pyroxenite have higher Li contents and normal mantle-like δ7Li values. The olivine δ7Li values in the harzburgite and cpx-poor lherzolites are much lower than those published for worldwide peridotites, showing the peculiarity of these peridotites. The Li abundances and δ7Li in the olivines show a positive correlation, indicating mixing between a low-δ7Li melt and normal mantle. Collectively, Li elemental and isotopic compositions of the xenoliths suggest that low δ7Li in olivines reflect a slab-derived Li isotopic signature in the lithospheric mantle. These observations, coupled with geochemical and geophysical evidence, suggest that the lithospheric mantle has been modified three times by (1) low-δ7Li melt likely derived from the subducted Pacific plate (leading to the low δ7Li of olivines), (2) high-degree partial melting (decreasing Li abundances of harzburgite and cpx-poor lherzolites close to the normal mantle), and (3) refertilization by melts mainly from the asthenosphere (producing the normal mantle-like δ7Li and high Li contents in cpx-rich lherzolite and pyroxenite). The melts/fluids derived from the subducted Pacific plate could play a crucial role in the destruction of the craton.

Mineral electron microprobe, bulk rock major, trace elements and Nd isotopes, and zircon U–Pb and Hf isotopic data are reported for granites and dioritic enclaves from the Guangtoushan granitic complex in the northern margin of the North China Craton. The zircon U–Pb dating identifies two stages of magmatism. The early stage enclave and host granite have identical ages (250 ± 2 Ma) and similar bulk rock Nd isotopes (eNd(t) = − 11.5 to − 12.2) as well as similar zircon Hf isotopes (eHf(t) = − 13.3 to − 17.4). However, although the late stage enclave (206 ± 2 Ma), host granite (208 ± 1 Ma) and leucogranite (207 ± 3 Ma) display comparable ages, but exhibit distinct isotopic features: the granite displays moderate bulk rock Nd isotopic value (eNd(t) = − 8.3) and zircon eHf(t) from − 2.6 to − 10.4; the enclave shows least negative bulk rock eNd(t) of − 3.9 and zircon eHf(t) from 0 to − 5.4; and the leucogranite possesses more pronounced negative bulk rock Nd (eNd(t) = − 17.2) and zircon Hf isotopic compositions (eHf(t) = − 6.2 to − 19.0). An integration of field observations, geochronology, geochemistry and zircon Hf isotopic data points to a complex petrogenetic history, where the early stage enclave–granite pair is a product of the early crystallization of felsic magmas that evolved from a mafic magma, whereas the late stage enclave and granite were derived by magma mixing. The late stage leucogranite is considered as a product of remelting of Phanerozoic igneous rocks within this region. The Guangtoushan granitic complex offers robust evidence for a gradual mantle upwelling during Triassic in the northern margin of the North China Craton.

We report U–Pb ages and Hf isotopes of zircons in granulites from two continental suture zones in the North China Craton (NCC)—from granulite xenoliths entrained in the Cenozoic Hannuoba basalts within the Trans-North China Orogen (TNCO) that amalgamates the Western and Eastern Blocks, and from a mafic granulite associated with ultrahigh-temperature (UHT) granulites within the Inner Mongolia Suture Zone (IMSZ) that welds the Yinshan and Ordos Blocks. The zircons in these rocks, together with the inherited zircons from Mesozoic subalkalic intrusives of these regions, show several distinct U–Pb age populations and provide constraints on the evolution of the lower crust beneath the NCC. Parts of the older zircons from the TNCO yield discordant data that project to ages of about 2.5 to 2.7 Ga. These old zircons show Hf TDM model ages of 2.6–2.9 Ga suggesting the existence of Archean lower crust beneath the TNCO, which is coupled with the Neoarchean metamorphic basement and greenstone belt. A major zircon population grew at 1.75–2.0 Ga, consistent with the timing of the Paleoproterozoic collision between the various crustal blocks within the NCC, suggesting that this event had a significant effect on the Archean lower crust. The older inherited zircons from the Western Block also yield discordant data that project to younger ages of about 1.8 to 1.9 Ga. This age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the UHT rocks in the khondalite belt within the IMSZ. These older zircons yield Hf TDM model ages of 2.0–2.5 Ga suggesting that the lower crust beneath the Western Block in the NCC to be dominantly Paleoproterozoic, and decoupled with the Archean metamorphic basement of the region. Yet another population of zircons from the Hannuoba banded granulite xenoliths, garnet-bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of Phanerozoic concordant ages ranging from 470 Ma to 40 Ma with peaks at 315 Ma, 220–230 Ma, 120 Ma and 46 Ma. The Late Paleozoic zircons predominantly occur in the garnet-bearing pyroxenite xenoliths and yield variable eHf(t) values of − 24 to + 18. Triassic–Cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable eHf(t) values, ranging from − 48 to + 16. The Tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted eHf(t) with a dominant range from 0 to + 18. These data suggest episodic magmatic underplating in the ancient lower crust of the NCC, lasting continuously throughout Phanerozoic, producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust. Our data clearly demonstrate the important events of Phanerozoic magmatic underplating beneath the Neoarchean–Paleoproterozoic crust of the NCC.

The Archean lithospheric root of the North China Craton (NCC) has been considerably eroded and modified by Phanerozoic magmatic processes. Here we investigate the decratonization of the NCC through U–Pb and Hf isotopic analyses of zircons from Cenozoic basalts in the Liaodong Peninsula using ion-probe and MC-ICPMS techniques. The U–Pb zircon geochronology identifies three zircon populations: Precambrian, Paleozoic and Mesozoic. The Precambrian zircons yield 207Pb/206Pb ages of 2275–2567 Ma with a peak at around 2.5 Ga. They define a U–Pb discordia with upper intercept ages of 2447 ± 50 Ma to 2556 ± 50 Ma and a wide range of Hf TDM ages with a mode at 2.7–2.8 Ga. Our results clearly demonstrate the presence of an Archean lower crust in the Liaodong region. The Paleozoic zircons from the Liaodong region lack the clear internal zoning and are subhedral to rounded in shape, and yield a narrow 206Pb/238U concordant ages of 419–487 Ma with a weighted mean age of 462 ± 16 Ma. The Mesozoic zircons predominantly show crystallization in the early Cretaceous and yield a relatively large range in 206Pb/238U ages from 100 to 138 Ma (n = 53) with a peak around 120 Ma. Three samples give indistinguishable weighted mean 206Pb/238U ages of 120 ± 5 Ma, 120 ± 4 Ma and 121 ± 2 Ma. These early Cretaceous zircons have enriched Hf isotope compositions with eHf(t) values from −26 to −16. Our results provide important constraints on episodic magmatism during the Phanerozoic in the Liaodong region, which led to substantial reactivation of the Archean basement of the North China Craton.

Elemental and Li-Sr-Nd isotopic data of minerals in spinel peridotites hosted by Cenozoic basalts allow us to refine the existing models for Li isotopic frac- tionation in mantle peridotites and constrain the melt/fluid- peridotite interaction in the lithospheric mantle beneath the North China Craton. Highly elevated Li concentrations in cpx (up to 24 ppm) relative to coexisting opx and olivine (\4 ppm) indicate that the peridotites experienced metasomatism by mafic silicate melts and/or fluids. The mineral d 7 Li vary greatly, with olivine (?0.7 to ?5.4%) being isotopically heavier than coexisting opx (-4.4 to -25.9%) and cpx (-3.3 to -21.4%) in most samples. The d 7 Li in pyroxenes are considerably lower than the normal mantle values and show negative correlation with their Li abundances, likely due to recent Li ingress attended by diffusive fractionation of Li isotopes. Two exceptional samples have olivine d 7 Li of -3.0 and -7.9%, indicating the existence of low d 7 Li domains in the mantle, which could be transient and gener- ated by meter-scale diffusion of Li during melt/fluid-peri- dotite interaction. The 143 Nd/ 144 Nd (0.5123-0.5139) and 87 Sr/ 86 Sr (0.7018-0.7062) in the pyroxenes also show a large variation, in which the cpx are apparently lower in 87 Sr/ 86 Sr and slightly higher in 143 Nd/ 144 Nd than coexisting opx, implying an intermineral Sr-Nd isotopic disequilib- rium. This is observed more apparently in peridotites having low 87 Sr/ 86 Sr and high 143 Nd/ 144 Nd ratios than in those with high 87 Sr/ 86 Sr and low 143 Nd/ 144 Nd, suggesting that a rela- tively recent interaction existed between an ancient me- tasomatized lithospheric mantle and asthenospheric melt, which transformed the refractory peridotites with highly radiogenic Sr and unradiogenic Nd isotopic compositions to the fertile lherzolites with unradiogenic Sr and radiogenic Nd isotopic compositions. Therefore, we argue that the litho- spheric mantle represented by the peridotites has been het- erogeneously refertilized by multistage melt/fluid-peridotite interactions.

A suite of peridotite xenoliths from Cenozoic Beiyan basalts within the Tancheng-Lujiang (Tan-Lu) wrench fault zone, eastern North China Craton (NCC), has been studied to provide constraints on the nature and evolution of the lithospheric mantle beneath this region. These xenoliths commonly have porphyroclastic, granuloblastic to resorption textures with the absence of coarse-grained texture. They can be subdivided into three types: lherzolite, clinopyroxene (cpx)-rich lherzolite and wehrlite. Lherzolites are characterized by low forsterite contents (Fo) (88–91) in olivines. Whole rock and cpx separates from lherzolites have convex-upward rare earth element (REE) patterns except for one sample which has the highest Fo in olivine and shows a spoon-shaped REE pattern. The Sr–Nd isotopic compositions of cpx separates are depleted, similar to those of mid-ocean ridge basalts (MORB). These geochemical characteristics indicate that the lherzolites represent fragments of newly accreted lithospheric mantle that makes up much of the Late Mesozoic–Cenozoic lithosphere beneath the Tan-Lu fault zone. Cpx-rich lherzolite and wehrlite reflect the interaction of the lithosphere with melt, as evidenced by relatively lower Fo (

Li contents and its isotopes of minerals in mantle peridotite xenoliths from late Cretaceous mafic dikes, analyzed in situ by Cameca IMS-1280, reveal the existence of melt/rock interaction in remains of refertilized Archean lithospheric mantle in Qingdao, Jiaodong Peninsula, North China Craton. Two groups of peridotites exist, i.e., low-Mg# lherzolite and high-Mg# harzburgites. The low-Mg# lherzolite has a relatively homogeneous Li concentration (ol: 2.01–2.11 ppm; opx: 1.77–1.88 ppm; cpx: 1.75–1.93 ppm) and Li isotopic composition (δ7Li in ol: 4.2–7.6‰; in opx: 6.0–8.3‰; in cpx: 5.3–8.4‰). The similarity in δ7Li value to the fresh MORB provides further evidence for the argument that the low-Mg# lherzolite could be the fragment of the newly accreted lithospheric mantle. The high-Mg# harzburgites have heterogeneous Li abundances (ol: 0.83–2.09 ppm; opx: 0.92–1.94 ppm; cpx: 1.12–4.89 ppm) and Li isotopic compositions (δ7Li in ol: −0.5 to +11.5‰; in opx: −6.2 to +11.1‰; in cpx: −34.3 to +10.1‰), showing strong disequilibrium in Li partitioning and Li isotope fractionation between samples. The cores of most minerals in these high-Mg# harzburgites have relatively homogeneous δ7Li values, which are higher than those of fresh MORB, but similar to those previously reported for arc lavas. These harzburgites have enriched trace elemental and Sr–Nd isotopic compositions. These observations indicate that in the early Mesozoic the lithospheric mantle beneath the southeastern North China Craton was similar to that in arc settings, which is metasomatized by subducted crustal materials. Extremely low δ7Li preserved in cpxs requires diffusive fractionation of Li isotopes from later-stage melt into the minerals. Thus, the Li data provide further evidence that the Archean refractory lithospheric mantle represented by the high-Mg# harzburgites was refertilized through melt/rock interaction and transformed to the Mesozoic less refractory and incompatible element and Sr–Nd isotopes enriched lithospheric mantle.

Zoned olivine grains are abundant in the late Mesozoic Shatuo gabbro (southern Taihang Mountains, central North China Craton). Olivine cores are rich in MgO and NiO, rims are rich in FeO and MnO, and both cores and rims have very low CaO contents. The cores invariably have a high Mg no. (92–94), similar to olivine xenocrysts from Palaeozoic kimberlites in eastern China. The compositional features of these olivines imply that they are xenocrysts rather than phenocrysts, namely, disaggregates of mantle peridotites at the time of intrusion. The compositional similarity of olivine cores to xenocrysts from Palaeozoic kimberlites suggests that the lithospheric mantle beneath the central North China Craton is ancient and refractory in nature, and quite different from eastern China, where the mantle is mainly composed of newly accreted materials resulting from large-scale lithospheric removal and replacement. The contrasting features of the lithospheric mantle beneath the eastern and central North China Craton imply that the large-scale lithospheric removal in Phanerozoic times was mainly confined to the eastern North China Craton.

A rare composite xenolith and abundant cumulative pyroxenites obtained from the Mesozoic Fangcheng basalts on the eastern North China Craton record a complex history of melt percolation and circulation in the subcontinental lithospheric mantle. The composite xenolith has a dunite core and an olivine clinopyroxenite rim. The dunite is of cumulative origin and has a granular recrystallized texture and extremely low Mg# [100 Mg/(Mg + Fe) = 81–82] contents in olivines. The olivine clinopyroxenite contains larger clinopyroxene and/or orthopyroxene with a few fine-grained olivine and tiny phlogopite, feldspar, and/or carbonate minerals interstitial to clinopyroxene. The clinopyroxene has low Mg# (83–85). Compositional similarity between dunitic olivine and pyroxenitic one indicates a sequential crystallization of dunite and pyroxenite from a precursor melt. Pyroxenite xenoliths include olivine websterites and clinopyroxenites, both are of cumulative origin. Estimation of the melt from major oxides in olivines and REE concentrations in clinopyroxenes in these composite and pyroxenite xenoliths suggests a derivation from subducted crustal materials, consistent with the highly enriched EMII-like Sr and Nd isotopic ratios observed in the pyroxenites. Occurrence of phlogopite, feldspar and carbonate minerals in some xenoliths requires the melt rich in alkalis (K, Na), silica and volatiles (water and CO2) at the latest stage as well, similar to highly silicic and potassic melts. Thus, the occurrence of these composite and pyroxenite xenoliths provides an evidence for voluminous injection of recycled crustal melts into the lithosphere beneath the southeastern North China Craton at the Late Mesozoic, a reason for the rapid lithospheric enrichment in both elemental and isotopic compositions.

The Mesozoic lithospheric mantle beneath the North China craton remains poorly constrained relative to its Palaeozoic and Cenozoic counterparts due to a lack of mantle xenoliths in volcanic rocks. Available data show that the Mesozoic lithospheric mantle was distinctive in terms of its major, trace element, and isotopic compositions. The recent discovery of mantle peridotitic xenoliths in Late Cretaceous mafic rocks in the Jiaodong region provides an opportunity to further quantify the nature and secular evolution of the Mesozoic lithospheric mantle beneath the region. These peridotitic xenoliths are all spinel-facies nodules and two groups, high-Mg# and low-Mg# types, can be distinguished based on textural and mineralogical features. High-Mg# peridotites have inequigranular textures, high Mg# (up to 92.2) in olivines, and high Cr# (up to 55) in spinels. Clinopyroxenes in the high-Mg# peridotites are generally LREE-enriched ((La/Yb)N>1) with variable REE concentrations, and have enriched Sr–Nd isotopic co...

The Cenozoic Haoti kamafugite field (23 Ma) is situated at the western Qinling Orogen, Gansu Province in China, which is a conjunction region of the North China Craton, the Yangtze Craton and the Tibetan Plateau. Fresh peridotitic xenoliths entrained in these volcanic rocks provide an opportunity to study the nature and processes of the lithospheric mantle beneath the western Qinling. These xenoliths can be divided into two groups based on the petrological features and mineral compositions, type 1 and type 2. Type 1 xenoliths with strongly deformed texture have higher Fo (90–92.5) contents in olivines, Mg# (91–94) and Cr# (15–35) of clinopyroxenes, and Cr# (36–67) of spinels than the weakly deformed type 2 xenoliths, which have the corresponding values of 89–90, 89–91.5, 10–15 and 5–15 in minerals, respectively. CaO contents in fine-grained olivines are slightly higher than 0.10 wt% compared with coarse-grained ones (less than 0.10 wt%). Fine-grained clinopyroxenes have low Al2O3 + CaO contents (generally 23 wt%). Fo contents in fine-grained olivines mainly in the melt pocket of the type 1 xenoliths are higher than those in coarse-grained ones, which is somewhat contrary to the type 2 xenoliths without melt pocket. Clinopyroxenes of the type 2 display higher Na2O contents (1.7–1.9 wt%) than those of the type 1 ( 10%), modal metasomatic and deformed characteristics, and may represent the old refractory lithospheric mantle. In contrast, the type 2 peridotites show fertile features with low degree of partial melting (

The occurrence of the Pishikou mafic dike in the Qingdao region, China provides important constraints on the origin of Late Cretaceous (86–78 Ma) mafic magmatism on the eastern North China craton. The Pishikou mafic dike is distributed in the Cretaceous Laoshan granitoid body, Qingdao region and contains peridotitic and granulitic xenoliths, xenocrysts, and megacrysts. Rocks from the Pishikou mafic dike are basanites and have low SiO2 ( 8 wt%), total alkalis (Na2O + K2O > 4.8 wt%, Na2O/K2O > 1), TiO2 (> 2.5 wt%), CaO (> 9 wt%) and P2O5 (> 1 wt%). In trace element abundances, they are highly enriched in large ion lithophile elements (LILEs) and light rare-earth elements (LREEs) (ΣREE = 339–403 ppm, (La/Yb)N = 39–42) without high field strength element (HFSE) depletion. These rocks have radiogenic Sr and Pb, and less radiogenic Nd isotopic compositions [(87Sr/86Sr)i > 0.7059, eNd ≈ 2.7–3.8 (206Pb/204Pb)i ≈ 18.0 ± 0.1]. The diagnostic elemental ratios, such as Nb/La, Nb/U, and Nb/Th, are compatible with those of mid-oceanic ridge basalts (MORBs) and oceanic island basalts (OIBs). Therefore, the Pishikou mafic dike has a geochemical feature completely different from those of the Early Cretaceous mafic dikes from the Qingdao region, but similar to those of back-arc basalts from the Japan Sea. This geochemical feature suggests that the Pishikou mafic dike was derived from an asthenosphere source, but contaminated by materials from the subducted Pacific slab. The discovery of this mafic dike thus provides a petrological evidence for the contribution of subducted Pacific slab to the Late Cretaceous magmatism in the Qingdao region of the eastern North China craton.

The petrology and geochemistry of peridotite xenoliths in the Cenozoic basalts from Fanshi, the central North China Craton (NCC), provide constraints on the evolution of sub-continental lithospheric mantle. These peridotite xenoliths are mainly spinel-facies lherzolites with minor harzburgites. The lherzolites are characterized by low forsterite contents in olivines (Fo 91), high-Cr# spinels and clinopyroxenes with low abundances of heavy REE (HREE). These features are similar to those from old refractory lithospheric mantle around the world, and thus interpreted to be relics of old lithospheric mantle. The old lithospheric mantle has been chemically modified by the influx of melts, as evidenced by the Sr–Nd isotopic compositions of clinopyroxenes and relatively lower Fo contents than typical Archean lithospheric mantle (Fo > 92.5). The Sr–Nd isotopic compositions of harzburgites are close to EM1-type mantle, and of the lherzolites are similar to bulk silicate earth. The latter could be the result of recent modification of old harzburgites by asthenospheric melt, which is strengthened by fertile compositions of minerals in the lherzolites. Therefore, the isotopic and chemical heterogeneities of the Fanshi peridotite xenoliths reflect the refertilization of ancient refractory lithospheric mantle by massive addition of asthenospheric melts. This may be an important mechanism for the lithospheric evolution beneath the Central NCC.

In situ zircon U–Pb ages and Hf isotopic compositions and whole rock geochemical and Sr–Nd–Pb isotopic data are presented for the Zijinshan alkaline intrusive complex from the Shanxi Province, western North China Craton. Salic rocks dominate the complex with the monzonite occurring in the outermost and pseudoleucite phonolitic breccia in the center. The intrusion took place 127 Ma ago with the earliest emplacement of monzonite and the termination of cryptoexplosive pseudoleucite phonolitic breccia. All rocks from this complex show LREE enrichment and HFSE depletion and exhibit enriched to depleted Sr–Nd isotopic features. The presence of inherited zircons and enriched Hf isotopic compositions in zircon rims, along with the enriched whole rock Sr–Nd isotopic compositions, indicate that the monzonite was formed through the mixing of lithospheric mantle-derived magma with lower crust-derived melts. The diopside syenite and nepheline-bearing diopside syenite are more depleted than the monzonite in terms of the Sr and Nd isotopes, together with their very high concentrations of LILE, we proposed that they originated from a mixed mantle source of enriched lithospheric mantle and depleted asthenosphere. The nepheline syenite has very low concentrations of MgO, Ni, Cr, suggesting that the magma underwent significant crystal fractionation. The most depleted Sr and Nd isotopic compositions ((87Sr/86Sr)i = 0.7036–0.7042, eNd(t) = − 0.2–0.3) among all rock types indicate a great contribution of asthenosphere to the nepheline syenite. The Zijinshan complex and its related crust-mantle interaction occurred in an extensional environment which resulted in continuously asthenospheric upwelling. Such an extensional environment might have been developed during the post-orogenic stage of the Late Paleozoic amalgamation of North China Craton with Mongolian continents and subsequent Mongol–Okhotsk ocean closure.

Li concentrations and isotopic compositions of coexisting minerals (ol, opx, and cpx) from peridotite xenoliths entrained in the Hannuoba Tertiary basalts, North China Craton, provide insight into Li isotopic fractionation between mantle minerals during melt–rock interaction in the considerably thinned lithospheric mantle. Bulk analyses of mineral separates show significant enrichment of Li in cpx (2.4–3.6 ppm) relative to olivine (1.2–1.8 ppm), indicating that these peridotites have been affected by mantle metasomatism with mafic silicate melts. Bulk olivine separates (d 7 Li � +3.3‰ to +6.4‰) are isotopically heavier than coexisting pyroxenes (d 7 Li �� 3.3‰ to � 8.2‰ in cpx, and � 4.0‰ to � 6.7‰ in opx). Such large variation suggests Li elemental and isotopic disequilibrium. This conclusion is supported by results from in situ SIMS analyses of mineral grains where significant Li elemental and isotopic zonations exist. The olivine and opx have lower Li concentrations and heavier Li isotopes in the rims than in the cores. This reverse correlation of d 7 Li with Li concentrations indicates diffusive fractionation of Li isotopes. However, the zoning patterns in coexisting cpx show isotopically heavier rims with higher Li abundances. This positive correlation between d 7 Li and Li concentrations suggests a melt mixing trend. We attribute Li concentration and isotope zonation in minerals to the effects of two-stage diffusive fractionation coupled with melt–rock interaction. The earliest melts may have been derived from the subducted oceanic slab with low d 7 Li values produced by isotopic fractionation during the dehydration of the seawater-altered slab. Melts at later stages were derived from the asthenosphere and interacted with the peridotites, producing the Li elemental and isotopic zoning in mineral grains. These data thus provide evidence for multiple-stage peridotite–melt interaction in the lithospheric mantle beneath the northern North China Craton.

A highly fertile mantle xenolith entrained in the Upper Cretaceous Daxizhuang basalt, Shandong Province, China provides petrological evidence for reaction between basaltic melt and refractory peridotite in Mesozoic lithospheric mantle beneath the eastern North China craton. The xenolith is zoned with a lherzolite core, a sheared wehrlite mantle, and a reactant rim. The lherzolite has a medium-grained granular texture and contains olivine, orthopyroxene, clinopyroxene, and spinel with low Mg# values (≤87). This is the lowest value observed globally in mantle xenoliths entrained in both kimberlites and basalts from old cratons, but is close to low-Mg# spinel lherzolites entrained in adjacent region of the eastern North China craton. The wehrlite mantle shows clear orientation and foliation of constituent olivine and clinopyroxene. The reactant rim displays a symplectite texture of fine-grained olivine, clinopyroxene, and spinel, and is characterized by LREE-enriched patterns. Orthopyroxene is lacking from t...

International audience; Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ7Li in Archean lithospheric mantle. The δ7Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from −27 to +21, in marked deviation from the δ7Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1–2 ppm). The Li abundances and δ7Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ7Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ7Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.

Compositions of Cenozoic basalts from the Fansi (26.3–24.3 Ma), Xiyang–Pingding (7.9–7.3 Ma) and Zuoquan (∼5.6 Ma) volcanic fields in the Taihang Mountains provide insight into the nature of their mantle sources and evidence for asthenosphere– lithospheric mantle interaction beneath the North China Craton. These basalts are mainly alkaline (SiO2=44–50 wt.%, Na2O+ K2O=3.9–6.0 wt.%) and have OIB-like characteristics, as shown in trace element distribution patterns, incompatible elemental (Ba/Nb=6–22, La/Nb=0.5–1.0, Ce/Pb=15–30, Nb/U=29–50) and isotopic ratios ( 87 Sr/ 86 Sr=0.7038–0.7054, 143 Nd/ 144 Nd=0.5124–0.5129). Based on TiO2 contents, the Fansi lavas can be classified into two groups: high-Ti and low-Ti. The Fansi high-Ti and Xiyang–Pingding basalts were dominantly derived from an asthenospheric source, while the Zuoquan and Fansi low-Ti basalts show isotopic imprints (higher 87 Sr/ 86 Sr and lower 143 Nd/ 144 Nd ratios) compatible with some contributions of subcontinental lithospheric mantle. The variation in geochemical compositions of these basalts resulted from the low degree partial melting of asthenosphere and the interaction of asthenosphere-derived magma with old heterogeneous lithospheric mantle in an extensional regime, possibly related to the far effect of the India–Eurasia collision.

Mantle xenoliths entrained in a newly discovered Late Cretaceous basaltic breccia at Junan, Shandong Province, China provide important constraints on the nature and evolution of the Late Mesozoic lithospheric mantle beneath the eastern North China Craton. The basaltic breccia erupted at 67 Ma contains abundant mantle and lower crustal xenoliths, including peridotites, pyroxenites, and granulites. The peridotitic xenoliths are all spinel-facies lherzolites and two types of lherzolites, high-Mg# and low-Mg#, occur. The low-Mg# lherzolites are dominant peridotitic xenoliths and have coarse-grained texture. These lherzolites are characterized by the occurrence of low Mg# (Fo

Major and trace element as well as Sr–Nd isotopic compositions of mid-Cretaceous lavas across western Shandong Province, China have been studied. These lavas can be generally divided into southern Shandong group (including Pingyi and Mengyin) and northern Shandong group (including Laiwu and Zouping) based on their geochemistry. The southern group lavas are characterized by extreme enrichment in LREE, large ion lithophile elements (LILE), and depletion in HFSE along with EMII-like Sr–Nd isotopic compositions, suggesting that the crustal involvements play a significant role in their petrogenesis. Comparing studies with Fangcheng basalts reveal that the Triassic continent–continent collision between the Yangtze craton (YC) and the North China craton (NCC), and subsequent extensive modification of the sub-continental lithospheric mantle (SCLM) beneath the south part of the NCC by silicic melts released from the subducted Yangtze lower crust, formed an enriched lithospheric mantle which was the source of the southern Shandong group lavas. In contrast, the northern Shandong group lavas are mildly enriched in LREE and LILE relative to those of the southern group lavas. The isotope compositions are also distinctive in that the Sr isotopic ratios are very low. Available geochemical evidence and comparing studies with spatially closed related mafic intrusions suggest that the SCLM feeding the northern group lavas seems to be linked to carbonatitic metasomatism and changed modal proportion of phlogopite and clinopyroxene in the mantle rather than subduction-related modifications. The contrasting geochemical characters of the mid-Cretaceous lavas across western Shangdong suggest that the SCLM of the NCC is spatially heterogeneous in Mesozoic.

Mesozoic alkaline intrusive complexes are widespread in the southern portion of the North China Craton and can provide some important constraints on the evolution of the Mesozoic lithosphere beneath the region. Three selected intrusive complexes (Tongshi, Hongshan, and Longbaoshan) are generally high in alkalis (K2O+Na2O=9∼13 wt.%) and Al2O3 (14∼21.6 wt.%) and low in CaO and TiO2 ( 0; (206Pb/204Pb)i>18). The Hongshan complex has low REE concentrations (∑REE=28.2∼118.7 ppm, (La/Yb)N=4.6∼14.7) and is moderately enriched as demonstrated by their Sr–Nd isotopic ratios ((87Sr/86Sr)i>0.706; eNd 0.7078; eNd

Major and trace element and Nd–Sr isotope data of the Mesozoic Laiwu–Zibo carbonatites (LZCs) from western Shandong Province, China, provide clues to the petrogenesis and the nature of their mantle source. The Laiwu–Zibo carbonatites can be petrologically classified as calcio-, magnesio- and ferro-carbonatites. All these carbonatites show a similarity in geochemistry. On the one hand, they are extremely enriched in Ba, Sr and LREE and markedly low in K, Rb and Ti, which are similar to those global carbonatites, on the other hand, they have extremely high initial 87Sr/86Sr (0.7095–0.7106) and very low eNd (−18.2 to −14.3), a character completely different from those global carbonatites. The small variations in Sr and Nd isotopic ratios suggest that crustal contamination can not modify the primary isotopic compositions of LZC magmas and those values are representatives of their mantle source. The Nd–Sr isotopic compositions of LZCs and their similarity to those of Mesozoic Fangcheng basalts imply that they derived from an enriched lithospheric mantle. The formation of such enriched lithospheric mantle is connected with the major collision between the North China Craton (NCC) and the Yangtze Craton. Crustal materials from the Yangtze Craton were subducted beneath the NCC and melts derived from the subducted crust of the Yangtze Craton produced an enriched Mesozoic mantle, which is the source for the LZCs and Fangcheng basalts. The absence of alkaline silicate rocks, which are usually associated with carbonatites suggest that the LZCs originated from the mantle by directly partial melting.

The old lithospheric mantle beneath the North China Craton (NCC, Fig. 1a) was extensively thinned during the Phanerozoic, especially in the Mesozoic and Cenozoic, resulting in the loss of more than 100 km of the rigid lithosphere (Menzies et al., 1993; Fan et al., 2000). This inference comes from the studies on the Ordovician diamondiferous kimberlites (Fig. 1b), Mesozoic lamprophyre-basalts and Cenozoic basalts, and their deep-seated xenoliths (e.g. Lu et al., 1995; Griffin et al., 1998; Menzies & Xu, 1998; Zhang et al., 2002). This remarkable evolution of the subcontinental lithosphere mantle, which has had profound effects on the tectonics and magmatism of this region, has attracted considerable attention (e.g. Guo et al., 2003; Deng et al., 2004; Gao et al., 2004; Rudnick et al., 2004; Xu et al., 2004; Ying et al., 2004; Zhang et al., 2004a, 2005, 2008; Wu et al., 2005; Tang et al., 2006, 2007, 2008, 2011; Zhao et al., 2010). However, the cause of such a dramatic change, from a Paleozoic cold and thick (up to 200 km) cratonic mantle (Griffin et al., 1992; Menzies et al., 1993) to a Cenozoic hot and thin (< 80 km) “oceanic-type” lithospheric mantle, is still controversial. Based on the Mesozoic basalt development, Menzies and Xu (1998) argued that thermal and chemical erosion of the lithosphere was perhaps triggered by circum-craton subduction and subsequent passive continental extension. This suggestion was first supported by the geochemical studies on the Mesozoic basalts and high-Mg# basaltic andesites on the NCC (Zhang et al., 2002, 2003). A partial replacement model was proposed, having a subcontinental lithospheric mantle in this region composed of old lithosphere in the uppermost part and newly created lithosphere in the lower part (Fan et al., 2000; Xu, 2001; Zheng et al., 2001). The clearly zoned mantle xenocrysts found in Mesozoic Fangcheng basalts (Zhang et al. 2004b) provide the evidence for such a replacement of lithospheric mantle from high-Mg peridotites to low-Mg peridotites through peridotite-melt reactions (Zhang, 2005). Another different model was also proposed that ancient lithospheric mantle was totally replaced by juvenile material in the Late Mesozoic (Gao et al., 2002; Wu et al., 2003). On the basis of Os isotopic evidence from mantle xenoliths enclosed in Cenozoic basalts, Gao et al. (2002) suggested that two times replacement existed in the NCC. They attributed the replacement of the old lithospheric mantle beneath the Hannuoba region to the collision of the Eastern

article i nfo In Central China, long-distance effects from collision between the North China and Yangtze cratons, uplift of the Tibetan Plateau and subduction of the Pacific Ocean are believed to converge in the Western Qinling. Mantle xenoliths from Baiguan and Haoti kamafugites in the Western Qinling were investigated to understand the lithospheric structure and mantle metasomatism beneath the orogenic belt. The Western Qinling lithosphere with depths of at least 120 km is geothermally hot and compositionally stratified, companied by a step-wise decrease in fertility with depth. The shallower portion of the lithospheric mantle is represented by type 2 xenoliths which lack alteration and deformation, and have fertile characteristics in compositions. The dominant rock type in the mantle section is the type 1 peridotites, which have had undergone relatively higher melt extraction and subsequent metasomatism. In-situ trace element data for minerals in the Baiguan and Haoti xenoliths are presented in this study. Baiguan clinopyroxenes have high LREE and show Ba, Th, U, Pb, Sr enrichment and negative Hf and Y anomalies, but the Haoti clinopyroxenes have large variations in trace elements and complicated distributions in LILE, and show negative Ti, Zr and Hf anomalies. Clinopyroxenes from both xenolith types have Ti/Eu and (La/Yb)N ratios in large ranges of 902-15,813 and 0-20, respectively. The petrological and geochemical characteristics suggest that the Western Qinling peridotites had been subjected to silicate and subsequent carbonatite metasomatism, and that carbonatite metasomatism was predominant in Baiguan but lesser in Haoti. Comparisons with the Western Qinling carbonatites and world-wide carbonatites indicate that carbonatite melts involved in the metasomatism originated from deep mantle and most likely related to carbonatite magma, with contributions from subducted oceanic crust. The type 2 peridotites, comprising clinopyroxene megacrysts and clinopyroxenite display similar trace element abundances and patterns, suggesting a close affinity in petrogenesis.

Mesozoic Fangcheng basalts from the North China Craton contain many clinopyroxene xenocrysts and pyroxenite xenoliths, which provide important information about melt circulation and crust-mantle interaction in the evolution of the sub-continental lithosphere beneath the region. All the xenocrysts show textural and chemical zoning. The zoning is mostly simple (simply-zoned), but some show complex patterns (complexly-zoned). In-situ major and trace element analyses suggest that all the simply-zoned xenocrysts may have been disaggregated from pyroxenite veins at mantle depth. The zoning is interpreted to result from chemical exchange with the host magma after their entrainment. The complexly-zoned xenocrysts record a complicated history of the lithospheric evolution: their cores could preserve information of high-temperature granulite-facies metamorphism in the lower crust and their intermediary zones might record metamorphic overgrowth in the mantle spinel-facies stability field. Therefore, the cores of the complexly-zoned xenocrysts have probably been derived from the Archean lower crust or newly-accreted lower crust and the intermediary zones could be formed through crust–mantle interaction. All the pyroxenite xenoliths are cumulates and were crystallized from the LREE enriched melts at mantle depth or crust–mantle transitional zone. Thus the clinopyroxene xenocrysts and pyroxenite xenoliths provide evidence for the existence of considerable crust–mantle interaction and melt circulation in the lithospheric mantle, which led to rapid lithospheric enrichment.

a b s t r a c t In order to understand the Precambrian crustal growth and reworking history of the North China Craton, in situ U-Pb and Lu-Hf isotope analyses were carried out on the detrital zircons from a well-preserved, nearly undeformed Proterozoic sedimentary section with time interval of 1.8–0.8 Ga. Totally, 806 zircons separated from 7 samples collected from each representative stratigraphic unit were measured for UPb and Lu-Hf isotopic compositions, of which 430 grains yielded concordant U-Pb ages. The concordant zircons show three prominent age groups of 1.6–1.8 Ga, 1.9–2.2 Ga and 2.3–2.6 Ga. Both positive and negative eHf(t) values were exhibited by zircons from all groups, suggesting both juvenile crust addition and crustal reworking for all age groups. The Hf crustal model ages of zircons reveal that the juvenile materials were continuously added to the crust between 4.0 and 2.0 Ga with a prominent peak at 2.7–3.0 Ga and a less significant peak at 3.1–3.4 Ga. The juvenile contributions to the newly formed crust decrease stepwise through time, and crustal reworking has dominated over juvenile inputs to the continental crust since 2.6 Ga. Compared with the detrital zircons from modern rivers running within the North China Craton, the sedimentary rocks contain more older zircons, implying the relatively poor preservation of Archean crustal rocks in modern river sand, and accordingly the weights of Archean crystallizations ages and crustal growth inferred from detrital zircons in modern river are significantly underestimated. The integrated studies of detrital zircons from both modern river sands and ancient sedimentary rocks are essential to decipher the early crustal growth history more faithfully.