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[Display omitted] • Late Neoarchean migmatites and crustally-derived K-rich granites are widespread in Yishan, western Shandong. • Progressive changes in the features of zircons from paleosome, through migmatite, to granite. • The oscillatory zoning of newly-grown zircons becomes more pronounced with migmatite evolution. • The widespread granites in western Shandong did not form through further evolution of the diatexites. • These granites formed by higher-temperature melting of the source region. Sequential changes in the texture, composition and U-Pb age of zircon from the late Neoarchean migmatites and related rocks in the Yishan area of western Shandong, eastern North China Craton, record the evolution of melt and magma from paleosome to crustally-derived granite. Zircon grains from the paleosome and metatexite have features of recrystallization, with narrow rims; those from leucosome have inherited cores and wide homogenous rims; those from diatexite preserve evidence of a complex evolution involving dissolution and growth, with the euhedral morphology of the rims, and the cross-cutting relationship between cores and rims, consistent with a magmatic origin. With the increase in melt content toward granite, the newly-grown zircon has clearer magmatic zoning and higher Th/U ratios. The low whole-rock Zr saturation temperatures (684–728 ℃) indicate that the diatexites, with abundant residual zircon, might be the product of low-temperature melting. The contemporaneous, crustally-derived granites, however, contain no or much less xenocrystic zircon and have high zircon saturation temperatures (740–868 ℃). Only at the higher temperature was sufficient partial melt produced to start the migration of magma out of the source region to form the granites. Anatectic (magmatic) zircons in diatexite commonly contain xenocrystic (residual) zircons, no matter how the magmatic system evolves further, the xenocrystic zircons in the anatectic (magmatic) zircons will still be retained. On the other hand, the crustlly-derived granites widely distributed in the area contain few residual zircons. Therefore, the crustally-derived granites widely distributed in western Shandong cannot form by further evolution of the diatexites, but require a higher degree of partial melting under higher temperature conditions. SHRIMP U-Pb zircon dating, combined with CL imaging, reveals that zircon crystals from the diatexites mostly are characterized by inherited cores with thick magmatic overgrowths, recording a regional anatectic event at ∼2.51 Ga. Residual source rock enclaves and xenocrystic zircons in the diatexites mostly have ages of ∼2.70 Ga and ∼2.53 Ga, suggesting that the diatexites were derived from Neoarchean continental crust. [ABSTRACT FROM AUTHOR]

Abundant mafic‐ultramafic blocks and dikes occur in the area north of Zunhua City, eastern Hebei Province, and were previously suggested to be part of a late Archean ophiolitic assemblage. We employed SHRIMP zircon dating and a geochemical study on these mafic and surrounding rocks to test the ophiolite hypothesis. The SHRIMP data suggest that three metagabbro samples were metamorphosed at ∼1.8 Ga. Numerous ∼2.5 Ga zircons display strong oscillatory zoning, characteristic of zircons from granitoid rocks but not from gabbro, so we suggest that these are xenocrystic grains. The age of these xenocrystic zircons and their metamorphic rims suggests that these mafic blocks formed in Paleoproterozoic. The surrounding gneiss of intermediate composition also contains 2.5 Ga zircons with oscillatory zoning and 1.8 Ga metamorphic rims. Fractionated REE patterns and Nb, Ta, Zr, Hf negative anomalies to variable extent were observed in the mafic blocks and surrounding rocks, also supporting a significant difference in the chemistry of ophiolitic rocks. Our data suggest that many mafic blocks in northern Zunhua are not part of a late Archean ophiolite complex but part of a tectonically dismembered Paleoproterozoic intrusive gabbro complex. This study shows that late Paleoproterozoic metamorphism occurred in the western part of eastern Hebei Province. [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]

Eastern Shandong is one of the important early Precambrian areas in the North China Craton, where extensive 2.5, 2.7 and 2.9 Ga magmatic activities have been identified, followed by very strong late Neoarchean and Paleoproterozoic tectono-thermal events. We carried out SHRIMP zircon dating, Hf-in-zircon isotope analysis and a whole-rock geochemical study on ca. 2.9 Ga Mesoarchean magmatic rocks. These include gneissic diorite, gneissic quartz diorite, gneissic tonalite and gneissic high-Si trondhjemite and were identified in five new areas. All these rocks contain ca. 2.5 Ga metamorphic zircons. The dioritic and tonalitic rocks are enriched in large ion lithosphile (LIL) elements (K, Rb, Ba) and depleted in Nb and P with moderate to highly fractionated REE patterns, similar in chemical compositions to Archean TTG rocks worldwide. The high-Si trondhjemites are characterized by very high SiO 2 and very low FeOt + MgO. The magmatic zircon grains from all these rocks are similar in their Hf isotopic compositions and have ɛ Hf ( t ) values ranging from + 1.3 to +9.9. Combined with previous work, our main conclusions are: (1) eastern Shandong underwent a major magmatic event at ca. 2.9 Ga; (2) diorites and tonalites formed by melting of thickened lower crust or the root of an oceanic plateau, whereas the high-Si trondhjemites were derived from melting of intermediate to felsic rocks; (3) the Mesoarchean (ca. 2.9 Ga) was a major period of juvenile crustal addition from the depleted mantle, earlier than the major crustal growth period at 2.7–2.8 Ga in the North China Craton; (4) the 2.7–2.9 Ga rocks underwent strong metamorphism at ca. 2.5 Ga, probably as a result of magmatic underplating. [ABSTRACT FROM AUTHOR]

The western Shandong Province (WSP) is one of the typical Neoarchaean granite-greenstone belts in the Eastern Block of the North China Craton (NCC) and is an important region to investigate the early Precambrian evolutionary history of the NCC. The Taishan association, consisting of a ~2.7 Ga komatiite-tholeiite sequence and a ~2.5 Ga felsic volcano-sedimentary sequence, is the major lithological assemblage in the WSP. In the Qixingtai area, the felsic volcano-sedimentary sequence, partly subjected to anatexis, is composed of hornblende gneiss, voluminous fine-grained biotite gneiss and biotite plagioclase gneiss. SHRIMP zircon dating shows that the protolith of the biotite plagioclase gneiss formed after ca. 2.53 Ga. The tonalite intrusion into the volcanic protoliths of the fine-grained biotite gneiss and biotite plagioclase gneiss occurred at 2.52 Ga. Our age data constrain the time of formation of the felsic volcano-sedimentary sequence in the Taishan area as 2.53-2.52 Ga. The majority of zircons from the felsic volcano-sedimentary rocks have intermediate εHf(t) values (−1.2 to +2.1). The whole rock Nd isotopes of the Taishan felsic volcano-sedimentary rocks yield the εNd(t = 2522 Ma) values of +2.6 to −1.8 and TDM2 ages 3.03-2.68 Ga. These values indicate the pre-existing crust was reworked at the end of the Neoarchaean (~2.5 Ga). The Taishan felsic volcano-sedimentary rocks are rhyodacite-dacite and andesite in composition. These rocks and the tonalite display similar high SiO2 (65-72 wt.%) and low MgO (1-2 wt.%) content. In contrast, the minor andesites in the area have lower SiO2 (61-62 wt.%) and higher MgO (5.3-6.3 wt.%), suggesting more mantle contribution during their petrogenesis. However, the Mg-rich andesites have identical rare earth element and multi-element patterns with the rhyodacite-dacites and distinguish them from the Taishan sanukitoids. We suggest that the 2.53-2.52 Ga felsic volcanics of the Taishan association are the products of partial melting of a subducted oceanic crust. The andesites were produced by minor modification of the ascending tonalite-trondhjemite-granodiorite-type magma by the mantle wedge. Our study indicates that (1) the tectonic regime of the WSP greenstone belt was dominated by an arc-subduction system at ~2.52 Ga and (2) the 2.53-2.52 Ga felsic volcano-sedimentary rocks and intrusive tonalite are the products of crustal reworking. The felsic volcano-sedimentary sequence of the Taishan association and other ~2.5 Ga arc-like assemblages in the NCC provide important clues to understand the nature of the tectonothermal events at the end of the Neoarchaean. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Daqingshan area in the North China Craton (NCC) incorporates several suites of magmatic intrusives including gabbros, granodiorites, charnockites and syenogranites, which were overprinted by subsequent metamorphic events. In this study, we report detailed morphological and textural characteristics as well as sensitive high resolution ion microprobe (SHRIMP) U-Pb ages of zircons from ten representative samples of the magmatic suites including syenogranites, charnockites and granodiorites. The zircons in these rocks are characterized by typical magmatic crystallization features including elongate prismatic grains with angular to sub-angular faces which are overprinted by a variety of reworked textures indicating strong recrystallization. These structures are terminated by thin and variable metamorphic overgrowths. U-Pb analyses of the zircons reveal multiple tectono-thermal events including magmatic crystallization at 2.30-2.00, 1.96-1.94 and 1.85-1.82 Ga and metamorphic overprint at 1.97-1.94 and 1.87-1.82 Ga. The episodic magmatism and regional metamorphism recorded in our study show a complex sequence of tectonic processes during the early to late Palaeoproterozoic associated with the amalgamation of crustal blocks within the NCC, with the youngest episode of the syenogranites representing regional extension at the end of the final cratonization of the NCC. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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 North China Craton (NCC) is the largest craton on the Chinese Mainland, with 3.8–3.0 Ga rocks occurring mainly in three areas, namely: Anshan-Benxi (Anben), eastern Hebei, and Xinyang. In addition, 3.0 Ga and 3.1 Ga TTG (tonalite-trondhjemite-granodiorite) rocks have also been identified in north Liaoning and the Bohai Bay Basin, respectively. Detrital and xenocrystic zircons dated at 4.1–3.1 Ga occur more widely in the craton. In Anben, >3.3 Ga rocks are mainly distributed in six complexes, whereas in eastern Hebei, 3.8 Ga TTG rocks and 4.0–3.9 Ga detrital zircons have recently been discovered. Anben is similar to eastern Hebei in terms of the Archean zircon age records, but >3.3 Ga TTG rocks are different in both rock-type and composition. The recent identification of 3.8 Ga granitic xenoliths in young volcanic rock at Xinyang indicates the existence of Eoarchean rocks in the deep crust of the craton. Taking the NCC as a whole, the most significant zircon-forming magmatic events occurred at 3.8 Ga, 3.7–3.65 Ga, 3.45 Ga, 3.3 Ga and 3.1 Ga. The >3.0 Ga TTG rocks are mainly trondhjemite, with their low Sr/Y and La/Yb ratios indicating formation under low- to medium-pressure conditions. These are different from 3.0 to 2.5 Ga TTG rocks in the NCC and 3.8–3.0 Ga TTG rocks in southern West Greenland, which are dominated by tonalite, with some having high Sr/Y and La/Yb ratios. The >3.0 Ga rocks have large variations in whole-rock ε Nd (t) and in-situ zircon ε Hf (t), with many showing negative values. Zircons have δ18O values mainly between 5.0 and 7.0‰, consistent with Hadean and Archean magmatic zircon data worldwide. The diversity of Eoarchean granitoid magmatism across the craton indicates that continental evolution on Earth at that time already displayed complexity and maturity. It is further considered that the NCC may contain several different ancient continental nuclei with long-term formation and evolutionary histories back to the Hadean. [ABSTRACT FROM AUTHOR]

Mesoarchean and older potassic granites are important indicators of recycling of ancient continental crust early in Earth's history. This study of integrated whole rock and zircon geochemistry and geochronology reports the age and identification of the source materials of the > 200 km 2 Mesoarchean Tiejiashan-Gongchangling granite in the Anshan-Benxi area, North China Craton, the largest pre-Neoarchean granite domain in the craton. SHRIMP U-Pb zircon dating on 15 samples indicates the magmatic crystallization of the granites between 2.95 and 3.0 Ga and reveals a superimposed tectonothermal event at ~ 2.91 Ga. The granites are characterized by high SiO 2 and K 2 O, low CaO, FeOt, MgO and TiO 2 with peraluminuous features. They show large variations in (La/Yb) n and strong negative Eu and Ba anomalies and Nb, P and Ti depletions. Whole rock Nd and magmatic zircon Hf isotopic compositions show large variations, but with most having ε Nd (t) and ε Hf (t) values < 0, with t DM (Nd) and t DM (Hf) values varying from 3.3 to 3.9 Ga and 3.3 to 4.0 Ga, respectively. Magmatic zircons without very strong lead loss (discordance ≤ 20%) have δ 18 O values of + 3.14 to + 8.39. 3.3–3.7 Ga xenocrystic zircons occur in some samples. The granite formed as a result of recycling of Paleo- to Eoarchean continental material in an intracontinental environment, with little if any contribution from Mesoarchean mantle sources. The sources could be predominantly unaltered ancient gneisses, together with yet to be identified Paleo- to Eoarchean materials affected by early low temperature alteration (weathered rocks or clastic sediment). [ABSTRACT FROM AUTHOR]

We report zircon ages, Hf-in-zircon isotopes as well as whole-rock geochemistry and Hf–Nd isotopic systematics for Palaeoarchaean grey gneisses of the Ancient Gneiss Complex of Swaziland, the oldest components of the Kaapvaal craton, southern Africa. The Hf-in-zircon isotopic compositions in these compositionally heterogeneous, multicomponent, migmatitic gneisses are highly variable, even in the oldest zircons dating back to 3.66 Ga, suggesting growth of zircon from melts representing a mix of juvenile and anatectic material derived from differentiated continental crust of Eoarchean to late Hadean age. In contrast, the initial Nd and Hf whole-rock isotopic compositions are frequently not in agreement with the Hf-in-zircon data that mostly show approximately chondritic initial values for Nd and strongly radiogenic initial values for Hf. We consider it likely that both the Lu–Hf and Sm–Nd whole-rock isotopic systems were disturbed and partly reset during later episodes of partial melting and crustal reworking, most likely during a pervasive 3.2 Ga tectono-metamorphic event. Primitive mantle-normalized trace element patterns show the variable influence of residual plagioclase and garnet in the sources as well as high contents of strongly incompatible elements. In conjunction with the Hf-in-zircon isotopic data the trace element contents are best explained by the incorporation of older continental crustal material into the sources of the grey gneisses. Our data support evidence from other Palaeoarchean terranes that crustal recycling, as seen in even the oldest crustal components, played an important role in early continental evolution. Rocks previously classified as a subduction-related tonalite–trondhjemite–granodiorite suite are complex, and their chemistry alone cannot be used to reconstruct tectonic settings. [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]

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: We report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from Lushan in the far south of the Trans-North China Orogen of the North China Craton that reveal the oldest rocks yet dated from the orogen. A detailed investigation of the internal structures of zircons, combined with targeted SIMS U–Pb and oxygen isotope analyses and ICP-MS Hf zircon analyses, has resulted in the discovery of previously unknown geological events in the North China Craton. Magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829±18 Ma to 2832±11 Ma in the tonalites and from 2838±35 Ma to 2845±23 Ma in amphibolite. Hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination. Oxygen isotope ratios in zircons range from 5.1 to 7.3‰ VSMOW, with high δ18O results recorded only from metamorphic domains. The earliest stage of metamorphic zircon growth, present in all four samples analyzed in this study, occurred between 2772±17/22 in the tonalites and 2776±20 and 2792±12 Ma in the amphibolites. A younger metamorphic event at 2638±61 in the tonalite and between 2671±13 and 2651±13 Ma in the amphibolites is recognized in zircons from three of the four samples investigated. This is the first time that metamorphic events at either of these times have been recorded in the North China Craton. Importantly, there is no evidence for the 1.8 Ga high-grade metamorphic event that is manifest in the northern and central parts of the Trans-North China Orogen. [Copyright &y& Elsevier]