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Komatiites are presented as direct evidence for higher mantle temperatures during the Archean. In the North China Craton, komatiites with spinifex structure have been identified only at one locality, i.e. the Sujiagou area, western Shandong. They were considered as formed during the early Neoarchean mainly based on their association with supracrustal rocks considered to be that age. This study carried out SHRIMP U‐Pb zircon dating on metamorphosed trondhjemitic and monzogranitic dykes intruding the Sujiagou komatiites, and they have magmatic zircon ages of 2592 ± 12 Ma and 2586 ± 13 Ma respectively. This provides direct evidence that the komatiites formed during the early Neoarchean. [ABSTRACT FROM AUTHOR]

There are different viewpoints on metamorphic and anatectic zircons recording ages of 2.45–2.48 Ga or even younger in some areas of the North China Craton where both late Neoarchean and late Paleoproterozoic tectono-thermal events are well developed. These are: 1) partial resetting of the U-Pb isotopic system in the late Neoarchean zircons, 2) metamorphism lasting from the late Neoarchean to the earliest Paleoproterozoic, and 3) earliest Paleoproterozoic metamorphism as separate different event. Western Shandong Province is an area where the late Neoarchean tectono-thermal event is widely developed but the late Paleoproterozoic event has not been identified. This provides an opportunity to understand the geological processes around the Archean-Proterozoic boundary. Based on a field study, we carried out SHRIMP U-Pb zircon dating on seventeen samples of ∼2.5 Ga old metamorphic and anatectic rocks, including tonalite, trondhjemite, granodiorite, gabbro, quartz diorite, granite and paragneiss with primary emplacement or depositional ages of 2.52–2.68 Ga. Anatectic zircons show some textural and compositional features: a) Homogenous or blurred oscillatory zoning, b) high U contents and low in Th/U ratios (commonly <0.3), c) rare idiomorphic morphologies, and d) commonly containing inherited (xenocrystic) cores. We conclude that the strong late Neoarchean event is widespread in western Shandong and is limited between ∼2.50 and 2.54 Ga. In contrast, apparent 2.45–2.48 Ga metamorphic zircon ages in some other areas of the North China Craton may be the result of overprinting and partial recrystallization of Neoarchean metamorphic zircons during the late Paleoproterozoic event. The Archaean rocks of western Shandong can be divided into three belts, namely Belts A, B and C from the northeast to the southwest. The difference between Belts A and B in ∼2.5 Ga metamorphic and anatectic intensity may indicate that the former was elevated to a higher crustal level compared with the latter at the end of the Neoarchean. [ABSTRACT FROM AUTHOR]

Western Shandong Province is a typical area of the North China Craton (NCC) where Neoarchean plutonic and supracrustal rocks are widely distributed. Early studies documented that ∼2.7 Ga and ∼2.5 Ga magmato-tectono-thermal events are well developed in the area. Here we report SHRIMP U–Pb ages and Hf-in-zircon isotopic data from ten samples of different magmatic rock types including hornblendite, gneissic tonalite, gneissic trondhjemite and gneissic granite. Magmatic zircon grains have 207 Pb/ 206 Pb ages ranging from 2667 to 2598 Ma. Some rocks contain ∼2.5 Ga metamorphic rims and ∼2.7 Ga zircon cores. The magmatic zircon grains have ɛ Hf ( t ) values and Hf crustal model ages of −1.1 to +11.3 and 3.02–2.4 Ga, respectively. Combined with an earlier study, our main conclusions are that the middle Neoarchean rocks mainly occur together with early Neoarchean rocks in the northeastern portion of the central belt. Juvenile additions to continental crust and crustal recycling played important roles in the middle Neoarchean of western Shandong Province, and the entire Neoarchean tectonic evolution can be divided into middle to early Neoarchean (2.75–2.6 Ga) and late Neoarchean (2.6–2.5 Ga) events. [ABSTRACT FROM AUTHOR]

Abstract: At the end of the Neoarchean continental evolution, voluminous syenogranites were emplaced in the North China Craton, together with other magmatic rocks (trondhjemite–tonalite–granodiorite (TTG), monzogranite, diorite, gabbro). Syenogranites are widely distributed in Anshan-Benxi, Qinhuangdao and western Shandong, and also occur in southern Jilin, northern Liaoning, northwestern Hebei and central Henan. Based on geological relationships, degree of metamorphism, deformation and magmatic zircon ages, two phases of syenogranite magmatism are recognized. Rocks produced during the first phase show a gneissic texture and were formed between 2.53 and 2.52Ga and locally comprise abundant TTG. Rocks of the second phase cut late Neoarchean TTG and supracrustal rocks, display a massive structure, and mainly formed between 2.52 and 2.50Ga. All syenogranites share the same features in major element compositions, being high in SiO2 and low in CaO, total FeO, MgO, TiO2 and P2O5. However, they are different in trace and REE compositions and can be subdivided into three types. (1) Type 1 shows a large variation in total REE contents, low (La/Yb) n ratios, strong negative Eu*/Eu anomalies and Ba depletion; (2) Type 2 is similar to Type 1 but has higher (La/Yb) n ratios. (3) Type 3 shows a large variation in total REE and (La/Yb) n ratios and significantly do not show strongly negative Eu*/Eu anomalies and Ba depletion. Whole-rock Sm–Nd isotopic compositions show large variations in ɛ Nd(t) values and t DM(Nd) modal ages, ranging from −9.49 to −4.72 and 3.70 to 3.25Ga (Type 1), 0.55–1.03 and 2.77–2.71Ga (Type 2) and −2.35 to 1.23 and 2.93–2.66Ga (Type 3), respectively. Hf isotopic compositions of zircons from three samples have ɛ Hf(t) values and t DM1(Hf) ages of 0.7–7.2 and 2.84–2.56Ga (Type 1), 2.6–7.4 and 2.74–2.56Ga (Type 2) and 2.1–6.3 and 2.76–2.60Ga (Type 3). It is concluded that syenogranites were generated by melting of continental crust with different mean crustal residence ages, and most of them were emplaced during the second phase (2.52–2.50Ga) in an extensional tectonic regime. The formation of these voluminous syenogranites marks a tectono-magmatic event resulting in stabilization of the North China Craton at the end of the Neoarchean. [Copyright &y& Elsevier]

Western Shandong is the only area in the North China Craton where abundant supracrustal rocks of the early and late Neoarchean are developed. This study presents an integrated geological investigations, whole-rock geochemistry and SHRIMP U Pb zircon dating investigation of the supracrustal rocks at Yanlingguang, one of the most typical areas of Neoarchean supracrustal rocks in western Shandong. The original Yanlingguan 'formation' is now subdivided into three belts: the Northeastern, Central and Southwestern belts, which are all in tectonic contact. The Northeastern and Southwestern belts are mainly composed of meta-komatiitic and basaltic rocks. Four granitic dykes intruding these belts have magmatic zircon ages of 2731–2530 Ma, supporting the conclusion that the supracrustal rocks were formed in the early Neoarchean. Meta-basalt with pillow structures has been identified in several locations, with the largest being ~35 m in thickness. The meta-komatiitic rocks are Al-undepleted komatiites and have ∑REE and (La/Yb) n of 2.30–26.21 ppm and 0.29–2.35, respectively, whereas the meta-basaltic rocks have ∑REE and (La/Yb) n of 16.45–53.26 ppm and 0.67–1.78, respectively, and ε Nd (t) values of 3.36–4.76, being similar to N-MORB. Eleven samples of meta-sedimentary rocks (including meta-sandstones-siltstones and meta-conglomerates) from the Central Belt have zircon U Pb ages extending from 2760 to 2520 Ma, providing evidence for the first time that they were deposited during the late Neoarchean, rather than the early Neoarchean as previously thought. The meta-sandstones-siltstones show large variations in major element contents, but have low ∑REE (49.17–102.30 ppm) and (La/Yb) n (1.53–7.00) ratios, with negligible to weakly negative or positive Eu anomalies (Eu/Eu* = 0.60–1.17), and record ε Nd (t) values of 0.96–3.21. Combined with regional geological investigations, we conclude that the early Neoarchean supracrustal rocks were formed in an oceanic environment. It is also suggested that the sandstones-siltstones of the late Neoarchean were derived from the early Neoarchean basement, and that the conglomerates were derived from two separate source regions; one of early, and the other of late Neoarchean age. The identification of basal conglomerates is consistent with the arc model established in early studies. We suggest that the criteria employed in this study can be used for determining whether or not an Archean greenstone belt is of oceanic affinity. • Yanlingguang in western Shandong contains three greenstone belts that differ in age. • The Northwestern and Southwestern belts are early Neoarchean. • The Central belt is late Neoarchean. • Early Neoarchean ultramafic and mafic rocks formed at 2.75 Ga in an oceanic setting. • Late Neoarchean metasedimentary rocks formed at 2.52 Ga in an island arc setting. [ABSTRACT FROM AUTHOR]

Voluminous Neoarchean plutonic and supracrustal rocks are well developed in the Western Shandong Province of the North China Craton, which has been divided into a late Neoarchean crustally-derived granite belt, a middle to early Neoarchean ancient rock belt and a late Neoarchean juvenile rock belt. Earlier studies provided reconnaissance evidence for ∼2.60 Ga metamorphism in some areas. This study presents SHRIMP zircon U–Pb dating and O isotope analysis on nine metamorphosed igneous rock samples (gneissic tonalite, gneissic trondhjemite, gneissic quartz diorite and meta-gabbro) from the ancient rock belt. Magmatic zircons vary in age from 2.74 Ga to 2.60 Ga, whereas metamorphic and anatectic zircons vary in age from 2.63 Ga to 2.59 Ga, with an age peak of 2.61 Ga. In this study, we identified 2.69–2.67 Ga metamorphic zircons for the first time. Most of zircons, whether magmatic or metamorphic, have δ 18 O values of +4.5‰ to +6.5‰ (V-SMOW). However, the oldest tonalite sample with a protolith age of 2735 Ma has zircons showing low δ 18 O (V-SMOW) values, particularly in recrystallized domains and overgrowths. This suggests at least in local crustal extension and influx of meteoric water during the evolution of the rocks. Combined with data from earlier studies, we draw the conclusion that the Western Shandong Province experienced a regional tectono-thermal event at ∼2.60 Ga, as a result of high heat flow and crustal extension, perhaps caused by a mantle plume or mantle overturn activity. Therefore we conclude that 2.60 Ga can be regarded the break between early and late Neoarchean crustal accretion. The O isotope study indicates that in some cases, trondhjemitic leucosome was not derived from nearby gneissic tonalite, although they show a close relationship in outcrop. [ABSTRACT FROM AUTHOR]

Highlights: [•] ∼2.7 Ga rocks have been identified in eight areas of the North China Craton. [•] They are mainly tonalitic in composition and frequently underwent late alteration. [•] Their formation was a result of juvenile additions to the continental crust. [•] The North China Craton is similar in main period of crustal growth to other cratons. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of the North China Craton (NCC) is well known for a marked 2.55–2.50Ga tectonothermal event. However, supracrustal and intrusive rocks of 2.75–2.70Ga are in fact widely distributed in the western Shandong Province, the most important area of Archaean basement in the eastern part of the NCC. This paper reports SHRIMP U–Pb dating and LA-ICPMS Hf isotopic composition of zircons from 2.75–2.70Ga supracrustal and trondhjemite–tonalite–granodiorite (TTG) rocks in that area. Three fine-grained (hornblende) biotite gneiss samples (known locally as leptynite, with meta-volcanic or volcanosedimentary rock protoliths) and five TTG samples have SHRIMP zircon U–Pb ages varying from 2.75 to 2.70Ga and 2.74 to 2.71Ga, respectively. Zircons from most of the samples have high positive ɛ Hf(t) values (+4.7 to +10.0) and t DM(Hf) ages (2.85–2.60Ga) similar to their zircon U–Pb ages. This indicates that the rocks represent largely juvenile crustal additions derived from depleted mantle only a short time before. However, some granitoids show ɛ Hf(t) zircon values of −13.6 to +5.1 and t DM(Hf) of 3.51–2.80Ga. Therefore, the strong 2.75–2.70Ga tectonothermal event in the western Shandong Province involved not only juvenile addition to the continental crust but also intracrustal recycling of older components. Combined with craton-wide data, it is shown that the NCC is similar to many other cratons around the world where tectonothermal events of ∼2.7Ga are well developed. However, the main difference is that in the NCC, superimposed ∼2.5Ga tectonothermal events were much stronger than in most other cratons. [Copyright &y& Elsevier]