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Qixia is a typical area of early Precambrian basement in eastern Shandong Province, eastern North China Craton. Many TTG (tonalite-trondhjemite-granodiorite) assemblages were once considered to be supracrustal rocks (the Jiaodong Group), and the formation ages of the rocks have only been determined in a few outcrops as shown on the early geological map of the area. We carried out geological mapping, geochemical study and SHRIMP U-Pb zircon dating in order to determine the temporal and spatial distribution and origins of the TTG rocks. In the newly compiled geological map (1:50,000), the main rock types of the Archean basement are ∼2.9 Ga, ∼2.7 Ga and ∼2.5 Ga tonalitic gneisses with local occurrences of trondhjemitic gneisses, granodioritic gneisses, (quartz) dioritic gneisses and meta-gabbro showing the same age range. Supracrustal rocks with ages of ∼2.9 Ga and ∼2.5 Ga are locally identified. All rocks broadly extend in a NW-SE direction as a result of strong tectonothermal events of the late Neoarchean and late Paleoproterozoic. Although the late Paleoproterozoic tectonothermal event strongly influenced all 2.7 to 2.9 Ga rocks in the area, metamorphic zircon ages are not widely recorded in these rocks because the high-grade metamorphism at ca. 2.5 Ga caused the older 2.7 to 2.9 Ga rocks to become relatively dry systems. The three generations of TTG rocks are similar in major element composition, characterized by high Na2O and low K2O, except for the late Neoarchean granodioritic gneisses, which locally occur and are relatively high in K2O. All the TTG rocks of different ages commonly have zircon O isotopic compositions within the range determined by Valley and others (2005) for Archean magmatic zircon. The ∼2.9 Ga TTG rocks show large Sr/Y and La/Yb variations and depletion in whole-rock Nd and zircon Hf isotopic compositions. The ∼2.7 Ga TTG rocks are similar in Nd-Hf isotopic compositions to the ∼2.9 Ga TTG rocks but have low Sr/Y and La/Yb ratios. The ∼2.5 Ga TTG rocks are similar in trace element composition to the ∼2.9 Ga TTG rocks, showing large variations in Sr/Y and La/Yb ratios. They can be further subdivided into two types in terms of Nd-Hf isotopic compositions with the depleted type mainly including tonalitic gneisses [eNd(t) = +1.86 to +4.59, eHf(t) = +1.0 to +8.7] and the enriched type including trondhjemitic and granodioritic gneisses [eNd(t) = −2.38 to −0.06, eHf(t) = −1.6 to −2.9]. It is concluded that the ∼2.9 Ga TTG rocks were formed in an oceanic environment (oceanic plateau or intra-ocean subduction), and the 2.7 Ga TTG rocks were formed by mantle underplating that resulted in partial melting of lower crustal mafic rocks under relatively low pressure conditions. More ancient continental materials played a role in the ∼2.5 Ga magmatic process, but more work is required to determine the tectonic environment (underplating or arc magmatism).

Metatonalite and amphibolite from the Taishan region of the Western Shandong Province in the North China Craton record c. 2.60 Ga fluid-present partial melting via the breakdown of biotite, plagioclase and quartz to produce peritectic hornblende and anatectic melt. Eight paired leucosome–melanosome samples from metatonalite and three paired samples from amphibolite were investigated to evaluate the composition of the melt. Hornblende, biotite and plagioclase in the leucosomes and hornblende and plagioclase in melanosomes from both rock types have similar compositions. Two leucosome samples from the metatonalite were influenced by the removal of heavy rare earth element-rich hornblende and the accumulation of plagioclase. The other leucosomes are interpreted to represent near initial melt compositions with a minor component of peritectic hornblende and are enriched in Si, Na and Sr and depleted in K, Ca, Ba and Rb relative to melanosomes. The enrichment of Na in the melt is inconsistent with experimental results of fluid-present melting of tonalite, but is broadly consistent with the experimental results of fluid-fluxed melting of amphibolite. The absence of K-feldspar in both rock types is a critical control on the composition of anatectic melt and initial melt compositions were probably similar for both rock types. Leucosomes inherited rare earth element patterns from their sources, which suggests that some trace element diagrams used to infer tectonic settings and depths of melting are not appropriate for reworked components of Archean grey gneisses. Whole-rockδ18O suggest that the fluids responsible for inducing local melting were derived from the intrusion and crystallization of ~2.60 Ga tonalites and trondhjemites in the Taishan region. One amphibolite sample has a relatively low δ18O suggestive of interaction with meteoric water or seawater possibly related to crustal extension and asthenosphere upwelling at ~2.60 Ga. Fluid-present partial melting reworked 2.75–2.60 Ga tonalites and amphibolites, generating ~2.60 Ga sodium-rich components of grey gneisses in the Western Shandong Province.

Almost all evidence for the oldest traces of life on Earth rely on particles of graphitic carbon preserved in rocks of sedimentary protolith. Yet, the source of carbon in such ancient graphite is debated, as it could possibly be non-biological and/or non-indigenous in origin. Here we describe the co-occurrence of poorly crystalline and crystalline varieties of graphitic carbon with apatite in ten different and variably metamorphosed banded iron formations (BIF) ranging in age from 1,800 to >3,800 Myr. In Neoarchean to Palaeoproterozoic BIF subjected to low-grade metamorphism, C-13-depleted graphitic carbon occurs as inclusions in apatite, and carbonate and arguably represents the remineralisation of syngenetic biomass. In BIF subjected to high-grade metamorphism, C-13-depleted graphite co-occurs with poorly crystalline graphite (PCG), as well as apatite, carbonate, pyrite, amphibole and greenalite. Retrograde minerals such as greenalite, and veins cross-cutting magnetite layers contain PCG. Crystalline graphite can occur with apatite and orthopyroxene, and sometimes it has PCG coatings. Crystalline graphite is interpreted to represent the metamorphosed product of syngenetic organic carbon deposited in BIF, while poorly crystalline graphite was precipitated from C-O-H fluids partially sourced from the syngenetic carbon, along with fluid-deposited apatite and carbonate. The isotopic signature of the graphitic carbon and the distribution of fluid-deposited graphite in highly metamorphosed BIF is consistent with carbon in the fluids being derived from the thermal cracking of syngenetic biomass deposited in BIF, but, extraneous sources of carbon cannot be ruled out as a source for PCG. The results here show that apatite + graphite is a common mineral assemblage in metamorphosed BIF. The mode of formation of this assemblage is, however, variable, which has important implications for the timing of life's emergence on Earth. (C) 2019 Elsevier B.V. All rights reserved.

The Lomagundi-Jatuli Event (LJE) is one of the largest and earliest positive carbon isotope excursions preserving δ13Ccarb values between +5 and +16‰ in Paleoproterozoic carbonates worldwide. However, the duration, amplitude and patterns of these excursions remain poorly constrained. The 2.14–1.83 Ga Hutuo Group in the North China Craton is a >10 km thick volcano- sedimentary sequence, including >5 km thick well-preserved carbonates that were deposited in supra- tidal to sub-tidal environments. C-O isotopic and elemental analyses of 152 least altered samples of the carbonates revealed a three-stage δ13C evolution. It began with an exclusively positive δ13Ccarb (+1.3 to + 3.4‰) stage in the ~2.1 Ga carbonate in the Dashiling and Qingshicun Formations, followed by a transition from positive values to oscillating positive and negative values in ~3 000 m thick carbonates of the Wenshan, Hebiancun, Jianancun, and Daguandong Formations, and end with exclusively negative δ13Ccarb values preserved in > 500 m thick dolostones of the Huaiyincun and Beidaxing Formations. It appears that much of the LJE, particularly those extremely positive δ13Ccarb signals, was not recorded in the Hutuo carbonates. The exclusively positive δ13Ccarb values (+1.3 to + 3.4‰) preserved in the lower formations likely correspond to the end of the LJE, whereas the subsequent two stages reflect the aftermath of the LJE and the onset of Shunga-Francevillian event (SFE). The present data point to an increased influence of oxygen on the carbon cycle from the Doucun to the Dongye Subgroups and demonstrate that the termination of the LJE in the North China Craton is nearly simultaneous with those in Fennoscandia and South Africa.

The Northern Liaoning Complex in northeastern China constitutes an important component of the Eastern Block in the North China Craton. The major lithologies consist of Archean granitoid gneisses with minor supracrustal rocks occurring as tectonic lenses. This study presents zircon Lu–Hf isotopic data for the first time as well as new SHRIMP zircon U–Pb data of the major lithologies from the Northern Liaoning Complex, in order to elucidate the crustal evolution of the complex and provide new constraints on the Neoarchean crustal evolution of the Eastern Block in the North China Craton. Magmatic zircon U–Pb data from this study show that the protolith magmas of the supracrustal rocks and granitoid gneisses were generated during ∼2.55–2.50 Ga. Metamorphic zircons document consistent metamorphic ages at 2.49–2.48 Ga, suggesting a regional metamorphic event immediately after the magmatism at the end of the Neoarchean in the Northern Liaoning Complex. Inherited/detrital zircons of 2.79–2.60 Ga suggest possible existence of ancient crust in this region. Zircon Lu–Hf isotopic compositions show that the magmatic zircons have variable ɛHf(t) values from −4.0 to +9.0 with depleted mantle model ages of 3.6–2.5 Ga, of which most ɛHf(t) values are positive with a model age peak at 2.9–2.7 Ga. These zircon Hf signatures reveal major juvenile crustal growth with additions of older crustal materials during 2.9–2.7 Ga, and a crustal reworking event with minor juvenile additions at 2.6–2.5 Ga in the studied area. Integrated with previous data from other Neoarchean complexes in the Eastern Block, both the major juvenile crustal growth during 2.9–2.7 Ga and the strong crustal reworking at 2.6–2.5 Ga contribute to the extensive Neoarchean crust formation of the Eastern Block in the North China Craton. The North China Craton share similar Neoarchean continental crustal evolution to other cratons in the world, though it is distinctively featured by intensive tectonothermal overprinting at the end of the Neoarchean.

We present an integrated study of zircon U-Pb dating and O-Hf isotopic analyses combined with whole-rock geochemistry and Nd isotopic systematics on widespread late Neoarchean syenogranites (Qidashan Pluton) and other granitoids (granodiorite, quartz monzonite, monzogranite) in the Anshan-Benxi area, eastern North China Craton. All these rocks were emplaced at ca. 2.5 Ga according to SHRIMP zircon U-Pb dating and other indirect methods. The syenogranites are characterized by high SiO2 and K2O/Na2O and low CaO, FeOt, MgO, TiO2 and P2O5. However, they differ in trace element and REE compositions and can be roughly subdivided into two types. Type 1 syenogranite has strongly negative Eu anomalies and Ba depletion, with large variations of LREE to HREE differentiation; type 2 syenogranite has no negative Eu anomaly and Ba depletion. Other granitoids are also rich in K2O and show similar trace element and REE compositional features as the type 2 syenogranite. Most syenogranite samples have whole-rock eNd(t) values of –10.5 to –2.7 and tDM(Nd) ages of 2.96 to 3.90 Ga, whereas the other granitoids have eNd(t) values of –5.2 to –2.2 and tDM(Nd) ages of 2.95 to 3.19 Ga. Magmatic zircon from the syenogranites has eHf(t) values and Hf crustal model ages ranging mainly from –11.0 to +4.4 and 2.70 to 3.46 Ga, respectively; those from other granitoids have eHf(t) values and Hf crustal model ages of –16.0 to +2.4 and 2.81 to 3.72 Ga, respectively. All these rocks contain Meso- to Paleoarchean xenocrystic zircon grains with eHf(t) values and Hf crustal model ages ranging from –14.3 to +8.3 and 2.79 to 3.93 Ga, respectively. Decoupling of whole-rock Nd and Hf-in-zircon isotopes occurs in some samples. Most low-U magmatic zircon (U

Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (~3.4 Ga) tonalite-gneiss called the Older Metamorphic Tonalitic Gneiss (OMTG) from the Champua area of the Singhbhum Craton, India, reveal 4.24-4.03 Ga xenocrystic zircons, suggesting that the OMTG records the hitherto unknown oldest precursor of Hadean age reported in India. Hf isotopic analyses of the Hadean xenocrysts yield unradiogenic 176Hf/177Hfinitial compositions (0.27995 ± 0.0009 to 0.28001 ± 0.0007; ɛHf[t] = −2.5 to −5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ɛHf[t] compositional array of the Hadean xenocrysts indicates a mafic protolith with 176Lu/177Hf ratio of ∼0.019 that was reworked during ∼4.2-4.0 Ga. This also suggests that separation of such an enriched reservoir from chondritic mantle took place at 4.5 ± 0.19 Ga. However, more radiogenic yet subchondritic compositions of ∼3.67 Ga (average 176Hf/177Hfinitial 0.28024 ± 0.00007) and ~3.4 Ga zircons (average 176Hf/177Hfinitial = 0.28053 ± 0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at ~3.4 Ga and ~3.3 Ga (average 176Hf/177Hfinitial is 0.28057 ± 0.00008 and 0.28060 ± 0.00003), respectively, corroborate that the enriched Hadean reservoir subsequently underwent mixing with mantle-derived juvenile magma during the Eo-Paleoarchean.

Magmatic zircon in high-grade metamorphic rocks is often characterized by complex textures as revealed by cathodoluminenscence (CL) that result from multiple episodes of recrystallization, overgrowth, Pb-loss and modifications through fluid-induced disturbances of the crystal structure and the original U-Th-Pb isotopic systematics. Many of these features can be recognized in 2-dimensional CL images, and isotopic analysis of such domains using a high resolution ion-microprobe with only shallow penetration of the zircon surface may be able to reconstruct much of the magmatic and complex post-magmatic history of such grains. In particular it is generally possible to find original magmatic domains yielding concordant ages. In contrast, destructive techniques such as LA-ICP-MS consume a large volume, leave a deep crater in the target grain, and often sample heterogeneous domains that are not visible and thus often yield discordant results which are difficult to interpret. We provide examples of complex magmatic zircon from a southern Indian granulite terrane where SHRIMP II and LA-ICP-MS analyses are compared. The SHRIMP data are shown to be more precise and reliable, and we caution against the use of LA-ICP-MS in deciphering the chronology of complex zircons from high-grade terranes.

A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing (Cr-muscovite) siliceous rocks – known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880–3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a (mature) quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthogneisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz, with lesser biotite, apatite (7%) and alkali-feldspar, and most inclusions are morphologically simple. A Neoarchaean orthogneiss from near Huangbaiyu displays morphologically simple inclusions with much more apatite (73%), as is typical for fresh calc-alkaline granitoids elsewhere. Zircons were also examined from a mature conglomerate quartzite clast and an immature feldspathic sandstone of the overlying weakly metamorphosed Mesoproterozoic Changcheng System. These zircons have oscillatory zoning, showing they were sourced from igneous rocks. The quartzite clast zircons contain only rare apatite inclusions (

The Central Hebei Basin (CHB) is one of the largest sedimentary basins in the North China Craton, extending in a northeast–southwest direction with an area of >350 km 2 . We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedimentary rocks recovered from drill holes that penetrated into the basement of the CHB. Two samples of gneissic granodiorite (XG1-1) and gneissic quartz diorite (J48-1) have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41–2.51 and ∼2.5 Ga, respectively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher ΣREE contents and lower Eu/Eu* and (La/Yb) n values. Two metasedimentary samples (MG1, H5) mainly contain ∼2.5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have e Hf (2.5 Ga) values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2.9 Ga, respectively. Therefore, ∼2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.

The Ordos Block is a large but poorly exposed crustal segment in the western part of the North China Craton. Little is known about its Precambrian basement rocks and their evolution because of an extensive cover by younger sedimentary rocks. We report SHRIMP zircon ages and Hf-in-zircon isotopic compositions for five samples recovered from drill holes that penetrated into the Ordos basement. Based on these data, two age groups of rocks can be distinguished: an early Paleoproterozoic group that is represented by one sample from the northern margin of the Ordos Block and a late (or middle-late) Paleoproterozoic group consisting of the remaining four samples. The early Paleoproterozoic sample contains zircon cores and metamorphic rims with ages of >2.4 Ga and >2.28 Ga, respectively. The cores have eHf(t) values of −8.8 to 6.2 and Hf crustal model ages of 2606 to 3221 Ma. The remaining rocks of late (or middle-late) Paleoproterozoic age contain zircons that may also show a core-rim structure, but with the cores having ages of ∼2.08 Ga and the metamorphic rims recording ages of ∼1.9 Ga. The zircon cores have eHf(t) values of −9.1 to 10.1, and Hf crustal model ages of 2039 to 3068 Ma. Combined with data from earlier studies, we draw the conclusion that late Paleoproterozoic metasedimentary rocks are widespread in the Ordos basement. There is no evidence from our samples of an Archean component, and this calls into question the prevailing view that the Ordos basement is an Archean cratonic block. The fact that the Ordos basement was involved in a widespread late Paleoproterozoic tectono-thermal event indicates that most current models for the tectonic evolution of the western portion of the North China Craton need to be revised.

The Gantaohe Group is an important early Precambrian unit in the Trans-North China Orogen, North China Craton, and is mainly composed of greenschist-facies metabasalt, meta-sandstone and dolomitic marble. We report whole-rock geochemical compositions and SHRIMP zircon ages as well as LA-ICP-MS Hf-in-zircon isotopeic analyses for metabasalts from the Gantaohe Group. SHRIMP dating yielded a weighted mean 207Pb/206Pb age of 2087±16 Ma (MSWD=1.3) for magmatic zircons, but there are also abundant ca. 2.5 Ga inherited zircon xenocrysts. The magmatic zircons shows a large ɛ Hf(t) variation in ɛ Hf(t) from −7.17 to +0.45, suggesting an isotopically highly heterogeneous source for the metabasalt. Chemically all samples show no distinct Zr or Hf anomalies, and some samples show no Nd or Ta anomalies in a primitive mantle-normalized trace element variation diagram, and their whole-rock ɛ Nd(t) values range from 4.0 to −0.8. We suggest that the basalt is formed by partial melting of a depleted mantle source, followed by significant crustal contamination. Field observations, the presence of abundant inherited zircon, as well as isotope and trace elements geochemistry support formation of the Gantaohe Group on top of a continental basement. These data and the regional geology lead us to conclude that the Trans-North China Orogen constituted an intracontinental rift during the Paleoproterozoic that was connected to the Eastern Block since the end of the Archean.

This paper carried out a study on U–Th–Pb behavior of zircons in a “dry” rock system during high-grade metamorphism in the Archean basement of eastern Shandong. The studied sample has a mineral assemblage of plagioclase + K-feldspar + clinopyroxene + biotite + quartz and its protolith is considered to be diorite. The zircons are stubby, equant or irregular in shape and show fir-leaf, sectorial, banded or oscillatory zoning. They contain inclusions, including mineral assemblages of clinopyroxene + orthopyroxene + hornblende + quartz and plagioclase + K-feldspar + biotite + quartz. Fifty SHRIMP analyses were performed on 34 zircon grains, which commonly yielded high Th/U ratios (mostly >0.5). Most analyses are distributed along concordia from 2.54 to 2.25 Ga, with the youngest age being ∼1.95 Ga. Compositions and ages show large variations even in a same zircon grain. Combined with early studies, conclusions can be drawn as follows: 1) the diorite underwent two episodes of high-grade metamorphism, at the end of the Neoarchean and the Paleoproterozoic (∼2.50 Ga and ∼1.95 Ga or slightly later); 2) high-grade metamorphism in a “dry” rock system may partially reset the U–Th–Pb system of zircons and, in this case, the ages between the oldest and youngest are chronologically meaningless; and 3) high Th/U ratios may be common features of zircons formed during high-grade metamorphic conditions.

The Assegaai, De Kraalen and Witrivier greenstone belts in the southeast part of the Kaapvaal craton contain strongly deformed volcano-sedimentary successions affected by amphibolite- to granulite-facies metamorphism at ∼3.22 to 3.20 Ga. These greenstone belts consist predominantly of mafic-ultramafic volcanic successions intercalated with chert and BIF. Single zircon SHRIMP ages of 3222 ±8 and 3193±5 Ma for two granitoids intrusive into the Assegaai greenstone belt provide a minimum age for the succession. Calc-silicates and amphibolites of the De Kraalen and Witrivier greenstone belts record a high-pressure metamorphic event (M 1 ) at ∼12 to 15 kbar and ∼600 °C and 800 °C, respectively. This high-pressure event was overprinted by a medium-pressure (7-8 kbar) amphibolite-facies event (M 2A ) that was recorded in all three greenstone belts, suggesting that the De Kraalen and Witrivier supracrustal rocks were buried to a deeper crustal level than the Assegaai rocks during crustal thickening. Decompression of the rocks along clockwise P-T paths possibly occurred during subsequent crustal extension at ∼3.22 to 3.20 Ga. The low geothermal gradient of this area (15-20 °C/km) contrasts with higher geothermal gradients reported for other Archean terrains worldwide and may support the view that crustal thickening processes related to convergence in a setting similar to subduction zones were operating in Paleoarchean times.

Western Shangdong Province experienced major crustal growth as a result of 2.75 to 2.50 Ga tectonothermal events, different from other Archean areas in the North China Craton. Besides early Neoarchean tonalite-trondhjemite-granodiorite (TTG) and supracrustal assemblages, there are large volumes of late Neoarchean gabbroic, dioritic and granitic rocks in western Shandong. SHRIMP zircon dating of thirty-one samples of different rock types from late Neoarchean rocks yielded a narrow age range from 2560 to 2490 Ma. Based on these data and previously published results, the following conclusions can be drawn: 1) the Archean basement can be divided into three belts: a Late Neoarchean (2525-2490 Ma) crustally-derived granite belt in the northeast, an Early Neoarchean (2.75-2.60 Ga) rock belt in the center, and a Late Neoarchean (2550-2500 Ma) belt of juvenile rocks in the southwest; 2) the tectonic regime in western Shandong Province probably changed from compressional to extensional at around 2525 Ma (between 2530 and 2520 Ma); 3) crustal recycling with addition from the mantle occurred at the end of the Neoarchean; 4) the late Archean magmatic rocks were probably formed in an arc environment.

We report SHRIMP U‐Pb, rare earth element, Hf isotope, and laser Raman spectroscopic data on zircons from ultrahigh‐temperature (UHT) granulites from the Jining Complex of the Khondalite Belt in the Western Block of the North China Craton (NCC). These UHT rocks form part of an ultrahot orogen that formed along the collisional margin of the NCC associated with the tectonics of assembly of the Paleoproterozoic supercontinent Columbia. Despite the core‐rim textures displayed by some of the UHT zircons, their age values sharply converge within error, yielding weighted mean 207Pb/206Pb ages of ca. 1.92 Ga, indicating growth by recrystallization under extreme thermal conditions. In general, the zircons show moderate heavy rare earth element enrichment with sharp positive Ce and negative Eu anomalies. The Hf isotope data from the UHT zircons also display a fairly uniform character, with the majority of them characterized by positive eHf values, without any indication of mixing between reworked crust and...

Eoarchaean crust in West Greenland (the Itsaq Gneiss Complex, 3870-3600 Ma) is >80% by volume orthogneisses derived from plutonic tonalite-trondhjemite-granodiorite (TTG) suites, 3850, c. 3810 and c. 3710 Mahave some compositional similarities to modern island arc basalts (IAB), suggesting their origin by hydrous fluxing of a suprasubduction-zone upper mantle wedge. Most of the Eoarchaean tonalites match in composition highsilica, low-magnesian adakites, whose petrogenesis is dominated by partial melting of garnetiferous mafic rocks at high pressure. However, associated with the tonalites are volumetrically minor more magnesian quartz diorites, whose genesis probably involved melting of depleted mantle to which some slab-derived component had been added. This assemblage is evocative of suites of magmas produced at Phanerozoic convergent plate boundaries in the case where subducted crust is young and hot. Thus, Eoarchaean 'subduction' first gave rise to short-lived episodes of mantle wedge melting by hydrous fluxing, yielding IABlike basalts ± boninites. In the hotter Eoarchaean Earth, flux-dominated destructive plate boundary magma generation quickly switched to slab melting of ('subducted') oceanic crust. This latter process produced the voluminous tonalites that were intruded into the slightly older sequences consisting of tectonically imbricated assemblages of IAB-like pillow lavas + sedimentary rocks, gabbros and upper mantle peridotite slivers. Zircon datingshows that Eoarchaean TTG production in the Itsaq Gneiss Complex was episodic (3870, 3850-3840, 3820-3810, 3795, 3760-3740, 3710-3695 and 3660 Ma). In each case, emplacement of small volumes of magma was probably followed by 10-40 Maquiescence, which allowed the associated thermal pulse to dissipate. This explains why Greenland Eoarchaean crustal growth did not have granulite-facies metamorphismdirectly associated with it. Instead, 3660-3600 Ma granulite-facies metamorphism(s) in the Itsaq Gneiss Complex were consequential to collisional orogeny and underplating, upon termination of crustal growth. Similar Eoarchaean crustal history is recorded in the Anshan area of China, where a few wellpreserved rocks as old as 3800 Ma have been found including high-MgO quartz diorites. For 3800 Ma rocks, this is a rare, if not unique, situation outside of the Itsaq Gneiss Complex. The presence of volumetrically minor 3800 Mamantle-derived high-MgO quartz diorites in both the Itsaq Gneiss Complex and the Anshan area indicates either that Eoarchaean 'subduction' zones were overlain by a narrow mantlewedge or that the shallow subduction trapped slivers of upper mantle between the conserved and consumed plates. © The Geological Society of London 2009.

High-grade pelitic metasedimentary rocks (khondalites) are widely distributed in the northwestern part of the North China Craton and were named the ‘Khondalite Belt’. Prior to the application of zircon geochronology, a stratigraphic division of the supracrustal rocks into several groups was established using interpretative field geology. We report here SHRIMP U–Pb zircon ages and Hf-isotope data on metamorphosed sedimentary and magmatic rocks at Daqingshan, a typical area of the Khondalite Belt. The main conclusions are as follows: (1) The early Precambrian supracrustal rocks belong to three sequences: a 2.56–2.51 Ga supracrustal unit (the previous Sanggan ‘group’), a 2.51–2.45 Ga supracrustal unit (a portion of the previous upper Wulashan ‘group’) and a 2.0–1.95 Ga supracrustal unit (including the previous lower Wulashan ‘group’, a portion of original upper Wulashan ‘group’ and the original Meidaizhao ‘group’) the units thus do not represent a true stratigraphy; (2) Strong tectono-thermal events occurred during the late Neoarchaean to late Palaeoproterozoic, with four episodes recognized: 2.6–2.5, 2.45–2.37, 2.3–2.0 and 1.95–1.85 Ga, with the latest event being consistent with the assembly of the Palaeoproterozoic supercontinent Columbia; (3) During the late Neoarchaean to late Palaeoproterozoic (2.55–2.5, 2.37 and 2.06 Ga) juvenile, mantle-derived material was added to the crust.

Sensitive high resolution secondary ion mass spectrometry (SHRIMP II), laser ablation inductively coupled plasma mass spectrometry (ICP-MS) and laser Raman spectroscopy have been used to determine the ages in zircons from carbonatite dikes associated with the Bayan Obo giant REE-Nb-Fe deposit, Inner Mongolia, China. Analyses of small amounts of zircon extracted from large samples of three carbonatite dikes yield late Palaeoproterozoic 207Pb/206Pb ages of 1894 ± 27, 1944 ± 20 and 1956 ± 9 Ma. One sample also contained inherited grains with ages up to ∼2.55 Ga. Zircon grains, even from a single rock, have a wide range of REE patterns, suggesting that they are probably inherited zircons trapped during magma genesis, not zircons crystallized from a single magma. None of the zircon grains has the extremely high Th/U characteristic of the Bayan Obo ore deposit or of the associated carbonatites. Further, mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals (quartz and feldspars), consistent with crystallization of the zircon from silicate, not from carbonate, magmas. The Palaeoproterozoic zircons in the Bayan Obo carbonatite dikes did not crystallize from carbonatite magma at the time of dike emplacement, but were derived from wall rock contamination. The ages obtained from the zircons are consistent with ages measured on basement igneous rocks elsewhere in the Bayan Obo region.

The Anshan area in the northeastern part of the North China Craton contains the oldest known rocks in China. Rocks with ages of ∼3.8 Ga are present in three trondhjemite-dominated gneiss complexes, referred to as the Baijiafen, Dongshan and Shengoushi complexes. The oldest material identified in these complexes has weighted mean 207Pb/206Pb ages of 3800 ± 5 Ma, 3794 ± 4 Ma and 3777 ± 13 Ma, respectively. In addition, younger geological events at 3680 ± 19 Ma, 3620 ± 23 Ma, and 3573 ± 21 Ma have been identified, recording the emplacement of several generations of trondhjemite. A biotite schist of possible supracrustal origin contains a zircon population with a weighted mean 207Pb/206Pb age of 3723 ± 17 Ma and is cut by a 3620 Ma trondhjemite, implying formation prior to ∼3.62 Ga. TDM(Hf) model ages for the zircons range from 3256 to 4264 Ma, but are mostly ∼3.9 Ga, indicating that significantly older crust was not present in the source region of the trondhjemitic magmas.

Most carbonate-rich magmatic rocks are mantle-derived, namely carbonatite(s), with a minority of them being contaminated by crustal rocks. It is debated whether there are also carbonate-rich magmatic rocks derived solely from crustal sources. In this contribution, we report crustally derived carbonate-rich magmatic rocks, named here crustal carbonatite(s), in the Daqingshan area, Western Block of the North China Craton. The Daqingshan crustal carbonatites were previously considered to be metasedimentary marbles. However, they cut adjacent rocks and contain some enclaves that are irregular in shape and show unoriented distribution of lithologies that cannot be found in the local wall rocks. Zircons from the crustal carbonatites show clear oscillatory zoning, and contain calcite, quartz, feldspar, diopside and CO2 inclusions. The zircons have correlated U and Th abundances and give a U/Pb age of 1951 ± 5 Ma, being the same age as metamorphic zircon cores and rims from a diopsidite enclave (1954 ± 27 Ma of core and 1944 ± 40 Ma of rim). The zircon from the crustal carbonatite has tDM(Hf) and eHf(t) of 2353 to 2457 Ma and –3.2 to 0.7, whereas the tDM(Hf) and eHf(t) of the core and rim zircons from diopsidite range from 2228 to 2160 Ma and 3.0 to 4.8 and 2219 to 2057 Ma and 3.2 to 7.4, respectively. The δ18O (‰)Zircon-V-PDB of zircon from the crustal carbonatite ranges from –21.5 to –19.6, with O isotope equilibrium temperature being 555°C to 635 °C. The crustal carbonatite shows a large variation in chemical composition, with SiO2=10.2–37.3% and Total REE=48–267 ppm. The tDM(Nd) age and eNd(t) are ∼2.5 Ga and –2.9 to –2.4. The δ18O(‰)Rock-V-PDB and δ13C(‰) Rock-V -PDB vary from –19.5 to –15.2 and from –5.2 to –2.4, being distributed between primary carbonatite field and the field of dolomitic marble from the study area in δ18O(‰) vs. δ13C(‰) diagram. Combined with previous studies, we drew the conclusion that some of the carbonate-rich rocks in the study area are magmatic in origin, by anatexis of impure marble plus common contamination by calc-silicates and other materials. This is consistent with the high-P-T experiments of CaO-CO2-H2O system (Wyllie and Tuttle, 1960) and MgO-CaO-CO2-H2O system (Fanelli and others, 1986), which indicate that partial melting of limestone will happen when temperature is > 700°C and when water is also present.

The Jiaodong Terrane in eastern Shandong Province is an important part of the Eastern Block of the North China Craton (NCC). In order to better understand the Precambrian crustal evolution of the NCC, we conducted a study of zircon geochronology, bulk-rock elemental and Nd-isotope geochemistry on gneisses and granodiorites from the Jiaodong Terrane. Zircon U-Pb SHRIMP analyses on biotite leptites and TTG gneisses yielded two groups of ages, one at ca. 2.90 Ga, and the other at 2.71 to 2.73 Ga. The new age results establish the existence of Mesoarchean and Neoarchean continental crust in the Jiaodong Terrane. The association of leptites, interpreted as metadacitic rocks, and TTG gneisses at 2.9 Ga was likely generated in an island-arc system, hence implying that plate tectonics, similar to the modern regime, was operative during the Mesoarchean. On the other hand, the results also indicate that the period of 2.71 to 2.73 Ga represents the most significant crust-forming episode in the Jiaodong Terrane. This is in contrast to the general understanding that the most important period of crustal growth and related metamorphism/deformation in the NCC took place in the terminal Archean (∼2.5 Ga). The geochemical and age constraints of the Neoarchean TTG rocks suggest that their formation was not related to subduction of oceanic crust, but to underplating and subsequent partial melting of lower crustal mafic rocks. Nd isotope data indicate that the Mesoarchean and Neoarchean rocks were mainly derived from juvenile sources with a limited amount of old crustal component. Like in other parts of the NCC, these rocks represent a juvenile addition to the late Archean continental crust. Finally, the formation of supracrustal rocks and most TTG gneisses in the period of 2.9 to 2.7 Ga distinguishes the Jiaodong Terrane from other tectonic units of the North China Craton.

New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and eND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive eND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids. A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite. The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series” recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane.

Sericite phyllite from the Sinian Shisanlitai Formation, Dalian area, Liaodong Peninsula, NE China, contains an assemblage of newly-formed lower-greenschist facies minerals (sericite, chlorite, Fe minerals and Ti minerals) plus aggregates of fine-grained monazite. The texture of the monazite, its mineral inclusions, and its close association with Fe oxide minerals show that it is not detrital or diagenetic, but a product of the low-grade metamorphism. SHRIMP U-Th-Pb dating of the monazite at 217 ± 15 Ma shows that the metamorphism, and associated regional deformation and fluid flow, occurred in the Late Triassic, coeval with the waning stages of the Dabie-Sulu orogeny. The Dabie-Sulu tectonothermal event has produced both deformation and metamorphism in rocks of the eastern North China Block at least up to ∼200 km north of the main continent-continent collision zone.

The reported new U-Pb age by sensitive high-resolution ion microprobe (SHRIMP II) on zircon was obtained from a tuff sample at the basal Doushantuo Formation in the Jiuqunao section, which situated at the western limb of the Huangling anticline in the Yangtze Gorges in Zigui, Hubei, South China. Eighteen spots of zircons were analyzed and they form two clusters: one includes three spots, with an inherited age of 784±15 Ma (MSWD=0.05); the other consists of 15 spots and gives a weighted mean 206Pb/238U age of 628.3±5.8 Ma (MSWD=0.86). It is the first SHRIMP U-Pb zircon age obtained nearly the base of the Doushantuo Formation of Ediacaran and represents a maximum age of the Doushantuo Formation It also forms an age constraint on the upper limit age of the Nantuo (Marinoantype) glaciation.

We introduce and propose zircon M257 as a future reference material for the determination of zircon U-Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS-determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for 206pb/238U and 0.7392 ± 0.0003 for 207pb/235U. Its 206pb/238U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U-Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ∼ 840 μg g−1 U (Th/U ∼ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit-cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U-Pb age, and the calculated alpha fluence of 1.66 × 1018 g−1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc-silicate skarn. Nous presentons et proposons a la communaute le zircon M257 qui pourrait devenir un materiau de reference pour la determination des âges U-Pb sur zircon par spectrometrie de masse a ions secondaires (SIMS). Ce specimen scie d'une gemme brun clair, sans defauts, provenant du Sri Lanka, pese 5.14 g (25.7 carats). Les moyennes des rapports isotopiques (et les incertitudes associees 2s) mesurees par TIMS sur ce zircon M257 sont 0.09100 ± 0.00003 en 206pb/238U et 0.7392 ± 0.0003 en 207pb/235U. Son âge 206pb/238U est de 561.3 ± 0.3 Ma (moyenne non ponderee, incertitude: 95% intervalle de confiance); le systeme U-Pb y est concordant, aux erreurs sur les constantes de desintegration pres. Le zircon M257 contient ∼ 840 μg g−1 U (Th/U ∼ 0.27). Ce materiel montre de tres faibles heterogeneites, avec une quasi absence de textures internes, meme a I'examen par cathodoluminescence. Le degre de dommage lie aux radiations (estime par I'expansion des parametres de la cellule unitaire, I'elargissement des parametres des spectres Raman et la densite) est modere et uniforme. II se correle bien, (sur I'alignement “Sri Lanka”) avec les concentrations en actinides, I'âge U-Pb et la fluence calculee de 1.66 × 1018 g−1 Ceci, couplea son âge (U+Th)/He de 419 ± 9 Ma (2s), nous permet d'exclure I'existence d'evenement thermique passe, ou de traitement par la chaleur, qui aurait potentiellement pu affecter le processus de retention de Pb radiogenique. Le rapport isotopique de I'oxygene de ce zircon est 13.9%o VSMOW, suggerant une genese par metamorphisme, au sein d'un marbre ou d'un skarn calco-silicate.