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Santunying is an important area for revealing nature of the late Neoarchean tectono-magmato-thermal events in the eastern Hebei part of the North China Craton. It is mainly composed of meta-intrusive rocks. Supracrustal rocks sporadically occur in the meta-intrusive rocks. The meta-intrusive rocks are subdivided into the Santunying tonalitic gneiss, Qiuhuayu tonalitic-trondhjemitic gneiss, Xiaoguanzhuang dioritic gneiss and Qingyangshu meta-gabbro. Respectively, SHRIMP U–Pb zircon dating on fourteen samples yielded weighted mean 207Pb/206Pb ages of 2525–2537, 2532–2546, 2530–2544 and ∼2531 Ma for magmatic zircons from them. Dioritic gneiss of the Xiaoguanzhuang gneiss contain abundant 2544–3487 Ma xenocrystic zircons. SHRIMP U–Pb dating on a garnet-biotite gneiss sample yielded a weighted mean 207Pb/206Pb age of 2537 Ma for detrital zircons. All rocks underwent strong metamorphism, deformation and anatexis, resulting in formation of leucosomes and residues, with some leucosomes concentrating to form large veins. They record a strong late Neoarchean event by metamorphic zircon ages of 2489–2519 Ma. Some rocks also record metamorphic zircon ages of 1772–1843 Ma. Magmatic zircons from the magmatic rocks show large variations in ε Hf (t) values ranging from −1.7 to +8.7. Combined with early studies, conclusions are: 1) Intrusive rocks with the involvement of mantle-derived materials have a narrow range of magmatic zircon ages from 2525 to 2546 Ma, and supracrustal rocks were formed during the same period. 2) Ancient crustal remnants (>2600 Ma) are present, consistent with the late Neoarchean arc magmatism involving older continental crust, similar to Phanerozoic Andean margins. 3) The Archean basement underwent a strong tectonothermal event at the end of the Neoarchean, with the metamorphic zircon ages being 10–30 million years younger than the timing of magmatism, a common feature of the North China Craton. 4) A late Paleoproterozoic tectonothermal event widely occurred in the western part of eastern Hebei, which is linked with regional ductile deformation. Unlabelled Image • Intrusive and supracrustal rocks have magmatic zircon ages of 2525–2546 Ma. • Ancient crustal remnants (>2600 Ma) are widely present in western Hebei. • The Archean basement underwent a strong tectono-thermal event at the late Neoarchean. • A late Paleoproterozoic tectonothermal event widely occurred in the study area. [ABSTRACT FROM AUTHOR]

Abundant late Neoarchean granitoids occur in southwestern Liaoning Province, part of the Eastern Ancient Terrane of the North China Craton. These rocks include intermediate gneiss, TTG gneisses and potassic granitoids, and we report on the geochemistry and zircon SHRIMP ages as well as Hf-in-zircon isotopes of these granitoids in order to determine their petrogenesis. Field relationships suggest that most of these granitoids experienced widespread metamorphism and deformation, associated with anatexis at some localities. The intermediate gneisses, TTG gneisses and potassic granitoids were all emplaced at the end of the Neoarchean (2.50–2.53 Ga), and CL images document widespread recrystallization in the zircons. The intermediate and TTG gneisses yielded similar Hf isotopic systematics (ε Hf(t) = −3.73 to +6.42) as the associated potassic granitoids (ε Hf(t) = −2.44 to +7.80), and both rock types yielded mean Hf crustal model ages of 2.8–2.9 Ga. Combined with the geochemistry, we propose that the formation of the intermediate and TTG gneisses was related to partial melting of mafic rocks at different depth, whereas the potassic granitoids have variable petrogenesis. The nearly coeval TTG gneisses and potassic granitoids and their widespread metamorphism, deformation and zircon recrystallization suggest that a large-scale heat source must have been present at or near the base of the crust in southwestern Liaoning Province at the end of the Neoarchean. We propose that collision and post-collisional extension is the most likely tectonic environment for generation of the above granitoids, and the formation of widespread potassic granitoids played an important role in the maturation of continental crust in the North China Craton. Unlabelled Image • TTG gneisses and potassic granitoids show indistinguishable formation ages and Hf isotopes. • Widespread zircon recrystallization occurred immediately after formation of these granitoids. • A long-lived heat source is necessary for the formation and metamorphism of these granitoids. • Post-collision extension is the most likely environment for these granitoids. [ABSTRACT FROM AUTHOR]

The North China Craton is an ideal place for studying the transition of the Earth's thermal structure and tectonics at the Archean–Proterozoic boundary due to its good preservation of the ~ 2.5 Ga tectono-thermal events. We report the discovery of a high-pressure mafic granulite from the Jiaodong Terrain in the North China Craton. The mafic granulite occurs as garnet–clinopyroxene–orthopyroxene–hornblende gneiss enclaves within a late-Archean trondhjemite–tonalite–granodiorite (TTG) gneiss. Typical high-pressure mineral assemblage of garnet–clinopyroxene–plagioclase–quartz ± rutile has been identified. Plagioclase + clinopyroxene ± orthopyroxene ± hornblende symplectite surrounding garnet (“white eye”) is also observed. Using the conventional geothermobarometry and the pseudosection modeling, a clockwise metamorphic P–T path with the peak conditions at ~ 17 kbar and ~ 880 °C was determined. Zircon U–Pb analyses (SHRIMP) on the overgrowth rim of zircon grains of two samples from the same outcrop yielded a metamorphic age of 2473 ± 6 Ma (MSWD = 0.8). The analyses on magmatic core gave a probable magmatic age of 2527 ± 12 Ma (MSWD = 1.9). The high-pressure granulite facies metamorphism corresponds to a collisional event between the ~ 2.5 Ga crust and ~ 2.9 Ga crust at the dawn of Paleoproterozoic in the North China Craton. It also represents a new but rare case of a subduction–collision tectonics at the Archean–Proterozoic transition and provides insight into the change of the Earth's thermal structure. [ABSTRACT FROM AUTHOR]

Abstract: The Upper Wulashan “Subgroup” at Daqingshan in the Khondalite Belt of the Western Block of the North China Craton contains an Early Paleoproterozoic (2.5–2.45Ga) supracrustal sequence, incorporating banded iron formations, which we refer to as the Daqingshan Supracrustal Rocks. They contain rounded to elliptical zircon grains that commonly show core–rim or core–mantle–rim structures and precise SHRIMP U–Pb dating of these domains allows the discrimination of a series of tectono-thermal events that straddle the Archean/Proterozoic boundary. Detrital zircon cores with oscillatory zoning have formation ages ranging from 2.55 to 2.50Ga, indicating derivation from Late Neoarchean magmatic rocks. As a result of exhumation and erosion, these became incorporated in earliest Paleoproterozoic sediments that were deposited between 2.50 and 2.45Ga and then underwent high-grade metamorphism at 2.45–2.40Ga. This event variously recrystallized the cores into two main domains: a dark inner domain and a gray outer domain, as imaged in cathodoluminescence. The gray domains commonly show sector zoning and have Th/U ratios of 0.1–0.5, a feature commonly noted in zircons recrystallized under high-grade metamorphic conditions. Metamorphic mantles are generally more homogeneous in structure and have lower Th/U ratios (commonly <0.1) than the recrystallized domains, although they show similar age distributions. However, they are difficult to distinguish when only two domains are present in the zircon and they represent a continuum of recrystallization. The rocks then underwent a second episode of high-grade metamorphism in the Late Paleoproterozoic, as revealed by thin overgrowth rims that are homogeneous or show only weak zoning, have low Th/U ratios (commonly <0.1), and record ages of 1.95–1.90Ga. This is the first time that two tectono-thermal events of Early and Late Paleoproterozoic age have been identified in single rock samples from the Western Block of the North China Craton. The conclusion that unequivocal earliest Paleoproterozoic sediments are present in the North China Craton is also supported by evidence that the Daqingshan Supracrustal Rocks are cut by anatectic garnet granite, previously dated at 2.39Ga. Combined with evidence obtained here and elsewhere in the North China Craton, we conclude that the 2.45–2.40Ga metamorphism was not an extension of the well-established, craton-wide Late Neoarchean tectono-thermal event, but a previously unrecognized episode that followed a short quiescent period that allowed sedimentation of the Daqingshan Supracrustal Rocks. [Copyright &y& Elsevier]

Abstract: A complex sequence of tectonothermal events shaped the Neoarchean–Paleoproterozoic crustal evolution in the North China Craton (NCC). Here we present a systematic SHRIMP zircon U–Pb investigation on a suite of metamorphic rocks from the Hademengou area of Daqingshan within the Khondalite Belt of the Inner Mongolia Suture Zone. We analyzed zircons from two meta-volcanic rocks of the Sanggan “Group” and four meta-igneous rocks of late Neoarchean to early Paleoproterozoic. Zircons from these rocks display typical core–rim or core–mantle–rim structures. The relict magmatic zircons record crystallization ages of ca. 2.5Ga followed by variable Pb loss, showing a range of ages in the concordia up to 2.1Ga. The recrystallized domains of zircons show sector zoning or are composed of inner dark domains, and outer lighter domains. The overgrowth mantles are homogeneous. The recrystallized zircons and overgrowth mantles show similar age data distribution along a concordia from ~2.5 to ~2.1Ga. The overgrowth rims are poorly developed but record ages (1.96–1.84Ga) similar to those displayed by metamorphic zircons in the late Paleoproterozoic “Upper Wulashan Subgroup” as well as the charnockites and UHT granulites reported in previous studies from this region. A meta-syenogranite intruding the Sanggan “Group” and Hypersthene dioritic gneiss contains 1.95Ga magmatic and 1.85Ga metamorphic zircons. Magmatic zircons of the late Neoarchean–early Paleoproterozoic metavolcanic rocks have εHf(t) of 1.2 to 7.0, tDM1(Hf) model ages of 2687 to 2532Ma and tDM2(CC)(Hf) model ages of 2837 to 2559Ma. The recrystallized zircons and mantle domains display Hf isotope composition similar to that of the magmatic domains. Our study is the first report from this region that identifies multiple tectonothermal events ranging from late Neoarchean through early to late Paleoproterozoic from zircons within single rock samples in the NCC. A strong overprint of late Paleoproterozoic metamorphism traced commonly in all the rock units indicates that these rocks were involved in the tectonothermal event associated with the final amalgamation of the NCC. [Copyright &y& Elsevier]

Abstract: We report SHRIMP zircon ages for felsic volcanic rocks of the early Archaean Nondweni greenstone belt (NGB) located in northern KwaZulu-Natal Province, South Africa. The NGB is part of a chain of greenstone belt remnants that occurs south of the well-known Barberton greenstone belt (BGB). Two samples of felsic volcanic rocks of the basal Toggekry Formation yielded zircon ages of ~3.53Ga, whereas significantly younger ages of ~3.41Ga were obtained for two samples of felsic rocks from near the top of the Witkop Formation. The latter date now constrains the age of stromatolite-like structures in cherts associated with the felsic rocks, which probably represent some of the oldest preserved evidence of life on Earth. The zircon ages also indicate that the NGB correlates well chronologically with the BGB and is one of the oldest volcano-sedimentary successions in the southeastern Kaapvaal Craton. Geochemical data for the felsic NGB rocks suggest formation by partial melting or crystal fractionation of a mafic source that was contaminated by older crust, possibly in a back-arc environment. Initial εNd values for NGB rocks range from −1.2 to +0.3 and suggest involvement of pre-greenstone continental crust that was possibly extensive in the southeastern part of the Kaapvaal Craton during Palaeoarchaean times. [Copyright &y& Elsevier]

The Singhbhum Craton of East India has a remarkably well-preserved Archaean geological record that rivals those of the Kaapvaal and Pilbara cratons. Based on a critical literature review, and aided by new field and geochronological data, a consistent framework of craton evolution during the Archaean is proposed that aims to put to rest some of the uncertainties on its geological history. The oldest rock assemblage so far identified in the Singhbhum Craton consists of ~3.5 to 3.3 Ga old greenstones of the Badampahar Group that are in tectonic contact with, or intruded by, broadly contemporaneous tonalite-trondhjemite-granodiorite of the Champua Suite, representing the precursor of grey gneisses of the Singhbhum Granitoid Complex. A reported Eoarchaean to Hadean detrital and xenocrystic zircon record suggests an even older onset of craton evolution, the details of which remain to be deciphered. Following >200 Ma of submarine volcanism and sedimentation, concomitant with granitoid emplacement of the Singhbhum Suite in the evolving craton, a regional event of deformation and metamorphism took place at ~3.3 Ga ago. It gave rise to syn -tectonic deposition of coarse siliciclastic successions of the Dhosrapahar Group, tight to isoclinal upright folding of the supracrustal rocks, and a greenschist to amphibolite facies metamorphic overprint. Starting at around 3.35 Ga, but overlapping with this regional event, was a broad change in the composition of felsic plutons towards more K-rich compositions, which culminated in the emplacement of granites of the Mayurbhanj Suite at 3.1 Ga that led to stabilization of the craton. Following tectonic uplift, erosion, and peneplanation, the intracontinental to continental margin volcano-sedimentary successions of the Koira Group and the correlative Simlipal Group were deposited on granitoid-greenstone basement between 3.0 and 2.75 Ga. Subsidence may have been related to extension of the craton that gave rise to the extrusion of largely subaerial basalts that may have been fed by a prominent mafic dyke swarm at ~2.80 Ga. At the same time, deformation and high-grade metamorphism affected the southwestern part of the craton. This event gave rise to widespread emplacement of granites that heralded the onset of tectonic reworking of the craton along its margins, which continued well into the Proterozoic. [ABSTRACT FROM AUTHOR]

The Central Zone of Limpopo Belt is a polymetamorphic and complexly deformed Precambrian terrane whose tectonic evolution is still uncertain because details on the timing of its evolution are not well established. We report zircon ages for newly discovered rocks in the Central Zone which document three distinct high-grade tectono-metamorphic events at 3.22, 2.62 and 2.02 Ga. The youngest of these has been well established, but the older two events were so far largely based only on rare zircon overgrowth rims. Most of our samples were collected from a large enclave in the 2.61 Ga Bulai pluton and constitute a strongly deformed, brecciated high-grade assemblage of supracrustal rocks, meta-anorthosite and granitoid gneisses, some of which are most likely equivalents of the pre-3.33 Ga Beit Bridge Complex. Magmatic zircon ages of 3.34–3.33 Ga for anorthositic and tonalitic gneisses in the enclave breccia support this correlation. Ca. 3.22 Ga metamorphic zircons, possibly reflecting the D 1 /M 1 event, were only found in one felsic granulite sample, and their regional significance remains uncertain. Abundant metamorphic zircons grew at ca. 2.62 Ga under granulite-facies conditions (D 2 /M 2 ), and some of these experienced variable degrees of recrystallization and/or Pb-loss during the third granulite-facies event at ca. 2.0 Ga (D 3 /M 3 ). Rocks outside the Bulai enclave contain abundant newly-formed ca. 2.02 Ga metamorphic zircons but only rarely preserve evidence for the ca. 2.62 Ga event since these late Archaean zircons show strong recrystallization and/or Pb-loss at ca. 2.0 Ga. We suggest that the Bulai pluton “protected” the rocks inside the enclave from severe overprinting at ca. 2.0 Ga because these rocks remained dry, whereas the assemblages outside the Bulai pluton experienced fluid-assisted metamorphic overprinting at ca. 2.0 Ga. Our new data sugggest that the tectonic evolution of the Central Zone was more complex than previously thought. We favour a scenario where collision involving the Limpopo Belt occurred in the Neoarchaean, whereas the high-grade Palaeoproterozoic event was most likely intracontinental and records far-field effects of plate movements elsewhere. The tectonic setting controlling the early Archaean D 1 /M 1 event remains unknown, largely because of insufficient data and extensive overprinting during later times. [ABSTRACT FROM AUTHOR]

Mafic granulite xenoliths are hosted by garnetiferous charnockites in the Archaean to Palaeoproterozoic Bumbuger Complex of northwestern Mongolia, one of the exotic basement terranes in the Central Asian Orogenic Belt. These rocks crystallized at ca. 1850 Ma under granulite-facies conditions (800 ± 27 °C, 6.8 ± 0.6 kbar) in the lower crust and were partly retrogressed to amphibolite-facies during ascent to higher crustal levels as a result of strong deformation resulting in northwest-trending isoclinal folds. The mafic xenoliths are likely derived from gabbroic protoliths, and geochemical, Hf-in-zircon and Nd whole-rock isotopic data suggest these rocks to have originated from parental melts of an enriched mantle source or from a depleted mantle with minor contamination by crustal material. The host garnetiferous charnockites crystallized from a strongly inhomogeneous melt predominantly derived from an Archaean to early Palaeoproterozoic lower crustal source, as also evidenced by partly recrystallized xenocrystic zircons, and minor contributions of mantle-derived material. The above data are compatible with a model whereby mantle-derived gabbroic melts under- and intraplate the lower crust, causing high-grade metamorphism, migmatization and anatexis, and the resulting ascending melts are mixtures of mantle and crustal sources. We speculate that the late Palaeoproterozoic events in the Baidarik Block may be the result of ca. 1.90–1.85 Ma accretion and collision processes that led to formation of the Columbia supercontinent. In the Neoproterozoic this block drifted toward Siberia and was incorporated into the Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two new paragneisses containing detrital zircons as old as 3.8Ga were reported. [•] Multi-phased crustal addition and recycling from 3.8 to 3.4Ga were identified. [•] A nearly complete Archean crustal evolution was recorded in eastern Hebei. [Copyright &y& Elsevier]

Abstract: Through detailed studies we have delineated a suite of banded TTG gneisses from the Zanhuang Complex. The protolith of the gneisses, predominantly tonalite, has undergone intensive metamorphism, deformation and anatexis and in a banded structure is intimately associated with melanocratic dioritic gneiss and leucocratic trondhjemitic veins. SHRIMP Zircon U–Pb data show that the tonalite was formed ca. 2692±12Ma ago. The tonalitic gneiss has the features of high SiO2 (67.76–73.31%), high Al2O3 (14.38–15.83%), rich in Na2O (4.48–5.07%) and poor in K2O (0.77–1.93%). The gneiss is strongly fractioned in REE ((La/Yb)N =12.02–24.65) and shows a weak positive Eu anomaly (Eu/Eu* =1.05–1.64). It has high contents of Ba (199–588ppm) and Sr (200–408ppm), low contents of Yb (0.32–1.00ppm) and Y (3.41–10.3ppm) with high Sr/Y ratios (21.77–96.77) and depletion in HFSE Nb, Ta and Ti. These characteristics are similar to those of the high-Si adakitic rocks. The melanocratic dioritic gneiss has low SiO2 (59.81%), high MgO (6.34%), high Al2O3 (14.02%) contents, rich in Na2O (3.7%) and poor in K2O (1.79%), with high Mg index (Mg# =67). REE and trace elements are on the whole similar to that of the tonalitic gneiss, but compatible element abundances V (116ppm), Cr (249ppm), Co (37ppm) and Ni (179ppm) are higher. The leucocratic felsic bands (approximating trondhjemite in composition) have major oxides similar to that of the TTG gneisses but the REE and compatible elements are extremely low, which are indicative of the products of anatexis. The tonalitic gneiss has positive ε Nd(t) (2.37–3.29) and low initial Sr (0.69719–0.70068) values with depleted mantle Nd model age of ca. 2.8Ga, suggesting its generation from partial melting of mantle-derived juvenile crust. The dioritic gneiss was also derived from subduction environment, but has undergone significant metasomatism of mantle wedge. The delineation of the ca. 2.7Ga TTG gneisses in the Zanhuang Complex further proves that the North China Craton experienced large-scale continental crustal accretion in early Neoarchean, and gives new constraints on the subdivision of the early blocks and greenstone belts of the craton. [Copyright &y& Elsevier]