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The 2022 Winter Olympics will be held in the Beijing-Zhangjiakou area, which is located in the eastern North China Craton (NCC) and contains a comprehensive geological record from the Archaean to Cenozoic. In this paper, we first review the geology of the Beijing-Zhangjiakou area, then, combined with data from the rest of the NCC, we discuss the geological evolution of the area in the context of the NCC. The geological and tectonic evolution of the Beijing-Zhangjiakou area can be regarded as a proxy or analogue for the geological history of the whole of the NCC. Six stages have been divided as follows: 1) Neoarchean massive continental crust growth; 2) Paleoproterozoic cratonization; 3) Meso-Neoproterozoic multi-stage rifting; 4) Palaeozoic marginal orogeny; 5) Mesozoic craton destruction; and 6) Cenozoic intra-plate extension. We hope this paper will be helpful to both geologists and non-geologists who will attend the 2022 Beijing-Zhangjiakou Winter Olympics and may be interested in rocks and geology around the Winter Olympic sites. [ABSTRACT FROM AUTHOR]

The recycling of supracrustal materials, and in particular hydrated rocks, has a profound impact on mantle composition and thus on the formation of continental crust, because water modifies the physical properties of lithological systems and the mechanisms of partial melting and fractional fractionation. On the modern Earth, plate tectonics offers an efficient mechanism for mass transport from the Earth's surface to its interior, but how far this mechanism dates back in the Earth's history is still uncertain. Here, we use zircon oxygen (O) isotopes to track recycling of supracrustal materials into the magma sources of early Archean igneous suites from the Kaapvaal Craton, southern Africa. The mean δ 18O values of zircon from TTG (tonalite–trondhjemite–granodiorite) rocks abruptly increase at the Paleo-Mesoarchean boundary (ca. 3230 million years ago; Ma), from mantle zircon values of 5‰–6‰ to approaching 7.1‰, and this increase occurs in ≤3230 Ma rocks with elevated Dy/Yb ratios. The 18O enrichment is a unique signature of low-temperature water–rock interaction on the Earth's surface. Because the later phase was emplaced into the same crustal level as the older one and TTG magmas would derive from melting processes in the garnet stability field (>40 km depth), we suggest that this evident shift in TTG zircon O isotopic compositions records the onset of recycling of the mafic oceanic crust that underwent seawater hydrothermal alteration at low temperature. The onset of the enhanced recycling of supracrustal materials may also have developed elsewhere in other Archean cratons and reflects a significant change in the tectonic realm during craton formation and stabilization, which may be important processes for the operation of plate tectonics on early Earth. [ABSTRACT FROM AUTHOR]

The Neoarchean basement rocks of the Qixingtai region in the northwest of western Shandong, eastern North China Craton are divided into western and eastern domains, separated by a ductile shear zone. The western domain is mainly composed of early Neoarchean tonalitic and supracrustal rocks, and the eastern domain is composed of late Neoarchean crustally‐derived granite with diverse early Neoarchean enclaves up to several kilometres long of supracrustal and gneissic TTG‐diorite rocks. This study reports an integrated field, whole‐rock geochemistry and zircon U–Pb‐Hf study on the granites and their enclaves in the eastern domain. The supracrustal enclaves are mainly composed of meta‐basaltic and meta‐ultramafic rocks and are the same in lithological association and formation time as the 2,750–2,700 Ma Liuhang "Formation" in the western area. The TTG‐diorite enclaves can be divided into early and late groups. Magmatic zircons from early TTG‐diorite samples have U–Pb ages of 2,731 ± 17 to 2,748 ± 13 Ma and εHf(t) values of +2.7 to +9.5, whereas trondhjemite samples of the late group have U–Pb zircon ages of 2,588 ± 18 to 2,606 ± 12 Ma and εHf(t) values of +0.6 to +6.5. The Hf isotopic signatures on magmatic zircon from the >2,700 Ma diorite‐tonalites indicate that they are predominantly juvenile crustal additions, probably with minor involvement of older crust in their genesis, as given by tDM (Hf) ages ranging back to 2.92 Ga. The eastern granites range from monzogranite to syenogranite in composition and commonly have negative Eu anomalies, indicating residual plagioclase in the source region. Magmatic zircons from two granite samples have U–Pb ages of 2,516 ± 24 and 2,527 ± 18 Ma and εHf(t) values of +1.0 to +7.0. A fine‐grained syenogranite dyke contains inherited early Neoarchean zircons with εHf(t) values of +1.6 to +7.4. The isotopic signatures of the late Neoarchean granites that dominate the eastern domain show that they were derived from partial melting recycling of older continental crust recognized in the region – early Neoarchean rocks formed as a result of juvenile crustal additions. This is a common signature for late Archean crustal evolution throughout much of the North China Craton, and is the hallmark of some other Archean terranes, such as the Dharwar Craton of south India. The geodynamic explanations for the formation globally of vast amounts of crustally‐derived late Neoarchean granite are discussed. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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 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]