The Paleoproterozoic North Hebei Orogen: North China craton's collisional suture with the Columbia supercontinent

Understanding the geologic history and position of the North China craton in the Paleoproterozoic Columbia supercontinent has proven elusive. Paleoproterozoic orogenic episodes (2.00–1.85 Ga) are temporally associated with ultimate stabilization of the North China craton (NCC), followed by the development of extensive craton-wide rift systems at 1.85–1.80 Ga. The age difference between the sedimentary cover and the metamorphic basement is up to 500–700 Ma, suggesting that uplift and doming of cratonic basement occurred in the latest Paleoproterozoic. Mafic dike swarms (1.80–1.77 Ga) and anorogenic magmatism (1.80–1.70 Ga) record the extensional breakup and dispersal of the North China craton during this stage. The late Paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the NCC within the Late Paleoproterozoic supercontinent of Columbia.An east-west striking thousand kilometer long belt of khondalites (granulite facies metapelites) stretches along the northern margin of the North China craton, on the cratonward side of the Northern Hebei orogenic belt. This granulite belt includes Mg–Al (sapphirine bearing) granulites that reached ultrahigh-temperature “peak” metamorphic conditions of  1000 °C at 10 kbars at 1927 ± 11 Ma. Following peak ultrahigh-temperature conditions, the rocks underwent initial isobaric cooling and subsequent isothermal decompression, and these trajectories are interpreted to be part of an overall anti-clockwise P-T evolution indicating that the northern margin of the craton experienced continental collision at 1.93–1.92 Ga. The position of the khondalite belt south of the Northern Hebei orogenic belt makes it analogous to Tibet, a continental collision-related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth. We suggest that the tectonic evolution of the NCC during this period was closely related to the assembly and break-up of the Columbia supercontinent, and that the NCC was adjacent to the Baltic and Amazonian cratons in the period 2.00–1.70 Ga. Craton-wide extension occurred within 100–150 Ma of collision along the northern margin of the craton at 1.93–1.92 Ga. It is concluded that mantle upwellings are chiefly responsible for the breakup of the NCC from the Paleoproterozoic supercontinent.     

New U-Pb titanite age data on the rocks from the Karelian craton and the Belomorian mobile belt, Fennoscandian Shield

We test the possibility of applying titanite as indicator of the boundaries between the Belomorian mobile belt and the Karelian craton of the Fennoscandian Shield. U-Pb isotope dating established wide variations of titanite ages in the Belomorian mobile belt and the Karelian craton. The titanites from the Karelian craton are mainly Archean in age (2.52–2.86 Ga), whereas the Belomorian mobile belt contains, with few exceptions, Paleoproterozoic titanites (1.74–1.95 Ga). In the Karelian craton, the age of titanite, in general, records the cratonization of the Earth’s crust (2.8 Ga and 2.6–2.7 Ga, respectively). In the Belomorian mobile belt, it presumably reflects the timing of the exhumation of tectonic nappes from the mid-crustal depths during the collisional stage of the evolution of the Lapland-Kola orogen.     

SHRIMP U–Pb zircon dating of the Neoproterozoic Penglai Group and Archean gneisses from the Jiaobei Terrane, North China, and their tectonic implications

Archean basement gneisses and supracrustal rocks, together with Neoproterozoic (Sinian) metasedimentary rocks (the Penglai Group) occur in the Jiaobei Terrane at the southeastern margin of the North China Craton. SHRIMP U–Pb zircon dating of an Archean TTG gneiss gave an age of 2541 ± 5 Ma, whereas metasedimentary rocks from the Neoproterozoic Penglai Group yielded a range in zircon ages from 2.9 to 1.8 Ga. The zircons can be broadly divided into three age populations, at: 2.0–1.8 Ga, 2.45–2.1 Ga and >2.5 Ga. Detrital zircon grains with ages >2.6 Ga are few in number and there are none with ages <1.8 Ga. These results indicate that most of the detrital material comes from a Paleoproterozoic source, most likely from the Jianshan and Fenzishan groups, with some material coming from Archean gneisses in the Jiaobei Terrane. An age of 1866 ± 4 Ma for amphibolite-facies hornblende–plagioclase gneiss, forming part of a supracrustal sequence within the Archean TTG gneiss, indicates Late Paleoproterozoic metamorphism. Both the Archean gneiss complex and Penglai metasedimentary rocks resemble previously described components of the Jiao-Liao-Ji orogenic belt and suggest that the Jiaobei Terrane has a North China Craton affinity; they also suggest that the time of collision along the Jiao-Liao-Ji Belt was at 1865 Ma.     

A Late Archean foreland fold and thrust belt in the North China Craton: Implications for early collisional tectonics

The Archean North China craton is divided into the Western and Eastern blocks along the Central Orogenic belt. A 1600 km long Archean foreland basin and thrust belt fringes the eastern side of the Central Orogenic belt. Rocks in the orogen form tectonically-stacked east-vergent fold and thrust sheets including foreland basin sediments, 2.50 Ga ophiolitic mélange, and an island arc complex. Foreland basin sediments overlie a passive margin sequence, and include a 2.50 Ga deep-water turbidite sequence that grades upward and westward into shallow-water molasse, now disposed in structurally imbricated east-verging thrusts and asymmetric folds that gradually migrated craton-ward with deformation, uplift, and erosion of the orogen. There is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the North China craton along the Central Orogenic belt at 2.50 Ga. The Qinglong foreland basin and Central Orogenic belt of the North China craton represents one of the best-preserved Archean orogen-to-craton transitions in the world. Its classic internal to external zonation, and flexural response to loading, demonstrate that convergent tectonics in the Archean were broadly similar to Phanerozoic convergent margin processes.     

Isotopic geochronological evidence for the Paleoproterozoic age of gold mineralization in Archean greenstone belts of Karelia, the Baltic Shield

The Rb-Sr age of metasomatic rocks from four gold deposits and occurrences localized in Archean granite-greenstone belts of the western, central, and southern Karelian Craton of the Baltic Shield has been determined. At the Pedrolampi deposit in central Karelia, the dated Au-bearing beresite and quartz-carbonate veins are located in the shear zone and replace Mesoarchean (～2.9 Ga) mafic and felsic metavolcanic rocks of the Koikar-Kobozero greenstone belt. At the Taloveis ore occurrence in the Kostomuksha greenstone belt of western Karelia, the dated beresite replaces Neoarchean (～2.7 Ga) granitoids and is conjugated with quartz veins in the shear zone. At the Faddeinkelja occurrence of southern Karelia, Aubearing beresite in the large tectonic zone, which transects Archean granite and Paleoproterozoic mafic dikes, has been studied. At the Hatunoja occurrence in the Jalonvaara greenstone belt of southwestern Karelia, the studied quartz veins and related gold mineralization are localized in Archean granitoids. The Rb-Sr isochrons based on whole-rock samples and minerals from ore-bearing and metasomatic wall rocks and veins yielded ～1.7 Ga for all studied objects. This age is interpreted as the time of development of ore-bearing tectonic zones and ore-forming hydrothermal metasomatic alteration. New isotopic data in combination with the results obtained by our precursors allow us to recognize the Paleoproterozoic stage of gold mineralization in the Karelian Craton. This stage was unrelated to the Archean crust formation in the Karelian Block and is a repercussion of the Paleoproterozoic (2.0–1.7 Ga) crust-forming tectonic cycle, which gave rise to the formation of the Svecofennian and Lapland-Kola foldbelts in the framework of the Karelain Craton. The oreforming capability of Paleoproterozoic tectonics in the Archean complexes of the Karelian Craton was probably not great, and its main role consisted in reworking of the Archean gold mineralization of various genetic types, including the inferred orogenic mesothermal gold concentrations.     

华北克拉通古元古代区域构造格架及其板块构造演化探讨

华北克拉通古元古代区域构造至少可以划分出三大构造单元：（１）陆内裂谷带（２．３０～２．６０Ｇａ）;（２）陆缘造山带（２．３０～２．６０Ｇａ）;（３）再造的太古代克拉通区（麻粒岩相带）（大于２．５０Ｇａ）．太古代末—古元古代重要的区域性构造－热事件序列依次为：（１）克拉通中部不同地壳层次伸展及裂谷盆地的发育;（２）克拉通北缘构造活动、增生及陆壳基底再造;（３）与大陆裂谷盆地闭合过程相联系的板内造山－前陆盆地发育．板块构造模式可以很好地解释上述构造作用类型．     

New constraints for the source characteristics,deposition and age of the 2.1–1.9 Ga metasedimentary cover at the western margin of the Karelian Province

The Paleoproterozoic cover sequence at the 100–150 km wide western margin of the Archean Karelian Province is dominated by deep water Lower and Upper Kaleva metasediments. We present here an interpretation of Sm–Nd isotope and geochemical data on 36 samples, TIMS multi-grain U–Pb zircon analyses on nine samples, and ca. 100 SIMS analysis of detrital zircon grains from four Upper Kaleva and one Lower Kaleva samples.The Lower Kaleva is characterized by autochthonous–parautochthonous, lithologically heterogeneous metaturbidites showing common enrichment in quartz. All the analysed detrital zircons are of a local Neoarchean source but t_DM variation up to 2.4 Ga combined with geochemical data indicate abundant mixing of Paleoproterozoic mafic material, presumably from 2.1 Ga plateau lavas and dykes, in most of the Lower Kaleva samples.The Upper Kaleva is dominantly allochthonous with tectonically enclosed fragments of ophiolite bodies, and it is characterized by lithological and geochemical-isotopic homogeneity. Geochemical, isotopic and detrital zircon data favour material derived from an orogenic domain, comprising both Archean and Proterozoic units, followed by effective mixing during the transport. The Archean zircon grains (25%) are mostly Neoarchean. The Paleoproterozoic grains lack zircons at 2.5–2.2 Ga and plot dominantly (92%) between 1.92 and 2.05 Ga. The indicated maximum deposition ages vary from 1.95–1.94 Ga to 1.92 Ga. The main source area proposed is the Himalaya-type Lapland-Kola orogen (now) in the northeast, which experienced mountain building and erosion at 1.95–1.91 Ga.The western margin of the Karelian Province shows evidence of rifting and lithosphere thinning from 2.1 to 1.95 Ga but it is still under debate whether the craton breakup occurred at 2.06 Ga in a volcanic or later at 1.95 Ga in a non-volcanic margin setting. One hypothesis is that the onset of collision in the northeast changed plate motion and lead to a new spreading within the pre-existing passive margin at 1.97–1.95 Ga. Thus, both a volcanic margin at 2.06 Ga and a non-volcanic margin at ca. 1.95 Ga could have been operated at the western margin of the Karelian Province.     

朝鲜北部狼林地块构造归属与地壳形成时代

朝鲜半岛北部的狼林地块一直被认为是中朝克拉通的重要组成部分。传统认为,它向南与我国辽东半岛的辽南太古宙地体相接,与其北部的鞍山-辽北-吉南太古宙地体(龙岗地块)具有基本类似的物质组成。两大太古宙地体之间是著名的以辽河群、集安群和老岭群为代表的辽吉古元古代岩系。辽吉岩系目前最主要的学术争论是,它是原本一体的太古宙地体的裂解产物,还是两个性质不同的太古宙地体拼合的结果。无论采用何种模型,学术界都普遍接受狼林地块主要由太古代岩石组成这一基本假定。为准确厘定狼林地块的地壳性质与形成时代,本文选择大同江、清川江、城川江、长津江、厚州川、厚昌江和秃鲁江中的河沙样品作为研究对象。这些河流均发源于狼林山脉,是狼林地块的核心区域,因而这些河流沉积物能够较好地全面反映狼林地块的物质组成情况。上述河流不同部位8件样品的分析结果显示,狼林地块主要由18~19亿年的古元古代岩石组成,太古宙岩石比例极为有限。但锆石Hf同位素模式年龄集中在28亿年左右,与华北克拉通全岩样品的Nd同位素模式年龄基本一致。结合狼林地块大量麻粒岩相变质表壳岩系和古元古宙花岗岩的发育,本文认为狼林地块是与辽吉岩系基本类似的古元古代地体,它可能是华北克拉通在古元古代期间东南大陆边缘的巨型造山带,我们可将其简称为辽-吉-朝古元古代造山带。因此,先前认为狼林地块主要由太古宙岩石组成的观点需要重新检查和认识。     

Nd isotopic composition of Paleoproterozoic volcanic and granitoid rocks of Vila Riozinho: implications for the crustal evolution of the Tapajós gold province, Amazon craton

Nd data from the Paleoproterozoic magmatic rocks of Vila Riozinho and Jamanxim (Tapajós gold province) indicate that original magmas were not produced exclusively by the remelting of Archean sialic crust and point to dominant Paleoproterozoic sources. ε_Nd(T) values preclude derivation from mantle sources for the ca. 2.0 Ga Vila Riozinho volcanics and older São Jorge granite. They may represent a subduction-related magmatic arc with magmas modified by interaction with crust or a post- to late-orogenic remelting of an older Paleoproterozoic juvenile arc with minimal contribution from the Archean crust. The origin of the 1.88 Ga Parauari, Maloquinha, Iriri, and Moraes Almeida igneous associations and the Jamanxim rhyolites has been attributed to large-scale taphrogenesis that marked the breakup of a large Paleoproterozoic continent. Derivation of the original magmas from the remelting of crustal sources older than ca. 1.9 Ga is consistent with geochemical and Nd isotopic data. Archean remnants probably occur between the Paleoproterozoic terrains of the Ventuari-Tapajós province. Archean terrains of the Amazon craton extend from the Xingu to the Itaituba region but have not been identified in the southern Guyana shield. Thus, data reveal that the boundaries between the central Amazon and Ventuari-Tapajós provinces need better definition and more detailed field and geochronological work.     

U/Pb and Sm/Nd geochronologic studies of the eastern Borborema Province, Northeastern Brazil: initial conclusions

The Borborema Province of NE Brasil comprises the central part of a wide Pan-African-Brasiliano orogenetic belt that formed as a consequence of late Neoproterozoic convergence and collision of the São Luis-West Africa craton and the São Francisco-Congo-Kasai cratons. New Sm/Nd and U/Pb results from the eastern part of this province help to define the basic internal architecture and pre-collisional history of this province, with particular emphasis on delineating older cratonic terranes, their fragmentation during the Mesoproterozoic, and their assembly into West Gondwana during the Pan African-Brasiliano orogeny at ca. 600 Ma.The region can be divided into three major geotectonic domains: a) Rio Piranhas-Caldas Brandão massif, with overlying Paleoproterozoic to Neoproterozoic supracrustal rocks, north of the Patos Lineament; b) the Archean to Paleoproterozoic São Francisco craton (SFC) to the south; and c) a complex domain of Paleoproterozoic to Archean basement blocks with several intervening Mesoproterozoic to Neoproterozoic fold belts in the center (south of Patos Lineament and north of SFC). The northern and central domains comprise the Borborema Province.Archean basement gneiss and Transamazonian granulite of northern SFC are exposed in the southern part of the central domain, underlying southern parts of the Sergipano fold belt. Basement in the Rio Piranhas massif appears to consist mostly of Transamazonian (2.1 to 2.2 Ga) gneissic rocks; Nd model ages (T_DM) of ca. 2.6 Ga for 2.15 Ga gneisses indicate a substantial Archean component in the protoliths to these gneisses. The Caldas Brandão massif to the east yields both Transamazonian and Archean U/Pb zircon and Nd (T_DM) ages, indicating a complex architecture. Metasedimentary rocks of the Jucurutu Formation yield detrital zircons with original crystallization ages as young as 1.8 Ga, indicating that these rocks may be late Paleoproterozoic and correlate with other ca. 1.8 Ga cratonic supracrustal rocks in Brazil such as the Roraima Group and Espinhaço Group.Most metavolcanic and pre-Brasiliano granitic units of the Sergipano (SDS), Pajeú-Paraíba (SPP), Riacho Pontal (SRP), and Piancó-Alto Brígida (SPAB) fold belts in the central domain formed ˜ 1.0 ± 0.1 Ga, based on U/Pb ages of zircons. Nd model ages (T_DM) for these same rocks, as well as Brasiliano granites intruded into them and large parts of the Pernambuco-Alagoas massif, are commonly 1.3–1.7 Ga, indicating that rocks of the fold belts were not wholly derived from either older (> 2.1 Ga) or juvenile (ca. 1.0 Ga) crust, but include mixtures of both components. A simple interpretation of Brasiliano granite genesis and the Nd data implies that there is no Transamazonian or Archean basement underlying large parts of these fold belts or of the Pernambuco-Alagoas massif. An exception is a belt of syenitic Brasiliano plutons (Syenitoid Line) and host gneisses between SPAB and SPP that clearly has a Transamazonian (or older) source. In addition, there are several smaller blocks of Archean to Transamazonian gneiss that can be defined within and among these fold belts. These blocks do not appear to constitute a continuous basement complex, but appear to be isolated older crustal fragments.Our data support a model in which ca. 1.0 Ga rifting was an important tectonic and crust-forming event along the northern edge of the São Francisco craton. Our data also show that significant parts of the Borborema Province are not remobilized Transamazonian to Archean crust, but that Mesoproterozoic crust is a major feature of the Province. There are several small remnants of older crust within the area dominated by Mesoproterozoic crust, suggesting that the rifting event created several small continental fragments that were later incorporated into the Brasiliano collisional orogen. We cannot at present determine if the Rio Piranhas-Caldas Brandão massifs and the older crustal blocks of the central domain were originally part of the São Francisco craton or whether some (or all) of them came from more exotic parts of the Proterozoic Earth. Finally, our data have not yet revealed any juvenile terranes of either Transamazonian or Brasiliano age.     

1891–1883 Ma Southern Bastar–Cuddapah mafic igneous events, India: A newly recognized large igneous province

A newly recognized remnant of a Paleoproterozoic Large Igneous Province has been identified in the southern Bastar craton and nearby Cuddapah basin from the adjacent Dharwar craton, India. High precision U–Pb dates of 1891.1 ± 0.9 Ma (baddeleyite) and 1883.0 ± 1.4 Ma (baddeleyite and zircon) for two SE-trending mafic dykes from the BD2 dyke swarm, southern Bastar craton, and 1885.4 ± 3.1 Ma (baddeleyite) for a mafic sill from the Cuddapah basin, indicate the existence of 1891–1883 Ma mafic magmatism that spans an area of at least 90,000 km² in the south Indian shield.This record of 1.9 Ga mafic/ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south-eastern margin of the south Indian shield is a widespread geologic phenomenon on Earth. Similar periods of intraplate mafic/ultramafic magmatism occur along the margin of the Superior craton in North America (1.88 Ga Molson large igneous province) and in southern Africa along the northern margin of the Kaapvaal craton (1.88–1.87 Ga dolerite sills intruding the Waterberg Group). Existing paleomagnetic data for the Molson and Waterberg 1.88 Ga large igneous provinces indicate that the Superior and Kalahari cratons were at similar paleolatitudes at 1.88 Ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a Limpopo-like 2.0 Ga deformation zone in the Superior Province. The widespread occurrence of 1.88 Ga intraplate and plate margin mafic magmatism and basin development in numerous Archean cratons worldwide likely reflects a period of global-scale mantle upwelling or enhanced mantle plume activity at this time.     

Proterozoic zircon growth in Archean lower crustal xenoliths, southern Superior craton – a consequence of Matachewan ocean opening

Granulite-grade, anorthositic and mafic xenoliths recovered from a Jurassic kimberlite pipe near Kirkland Lake, Ontario are fragments of the lower crust that underlies the ca. 2.7 Ga Abitibi greenstone belt of the Superior craton. Cathodoluminescence imaging and/or backscatter electron microscopy of zircon from four individual xenoliths reveals a complex crystallization history, characterized by two main stages of zircon growth. The age of the two stages has been constrained by combining imaging results with isotope dilution U-Pb dating of grain fragments and single grains. Minimum ages for the first crystallization stage in individual xeno liths are 2584 ± 7 Ma, 2629 ± 8 Ma, 2633 ± 3 Ma, whereas an approximate crystallization age for a fourth sample is 2788 ± 57 Ma. The second main stage of growth consists of chemically and isotopically distinct metamorphic zircon overgrowths. Times of solid-state zircon growth are most broadly constrained in three samples to the interval between 2.52 Ga to 2.40 Ga, and most precisely dated in a meta-anorthosite at 2416 ± 30 Ma. These complex zircons are intergrown with garnet and clinopyroxene of the host granulite-facies assemblage, and thus the Paleoproterozoic ages of the metamorphic overgrowths are interpreted to reflect an interval of isobaric, granulite-grade metamorphism of the lower crust beneath the greenstone belt approximately 150 million years after craton formation. This interval of metamorphism is broadly coeval with the intrusion of the Matachewan dyke swarm across the southern Superior craton, and with mafic magmatism and deposition of Huronian rift-margin sediments 200 km to the south during the opening of the Matachewan ocean. It is proposed that a significant volume of magma intruded the crust-mantle interface during rifting, promoting isobaric metamorphism and zircon growth in the deep levels of the Superior craton. Subsequent major rifting events along this margin apparently failed to produce a similar lower crustal response. The results have important implications for the structure of lithosphere beneath Archean continental crust. Received: 3 October 1995 / Accepted: 11 February 1997     

Lithospheric architecture and tectonic evolution of the Hudson Bay region

Hudson Bay conceals several fundamental tectonic elements of the North American continent, including most of the ca. 1.9–1.8 Ga Trans-Hudson orogen (THO) and the Paleozoic Hudson Bay basin. Formed due to a collision between two cratons, the THO is similar in scale and tectonic style to the modern Himalayan–Karakorum orogen. During collision, the lobate shape of the indentor (Superior craton) formed an orogenic template that, along with the smaller Sask craton, exerted a persistent influence on the tectonic evolution of the region resulting in anomalous preservation of juvenile Proterozoic crust. Extensive products of 2.72–2.68 Ga and 1.9–1.8 Ga episodes of subduction are preserved, but the spatial scale of corresponding domains increases by roughly an order-of-magnitude (to 1000 km, comparable to modern subduction environments) from the Archean to the Proterozoic. Based on analysis of gravity and magnetic data and published field evidence, we propose a new tectonic model in which Proterozoic crust in the southeastern third of Hudson Bay formed within an oceanic or marginal-basin setting proximal to the Superior craton, whereas the northwestern third is underlain by Archean crust. An intervening central belt truncates the southeastern domains and is interpreted to be a continental magmatic arc.Thick, cold and refractory lithosphere that underlies the Bay is well imaged by surface-wave studies and comprises a large component of the cratonic mantle keel beneath North America. The existence of an unusually thick mantle root indicates that subduction and plate collision during the Trans-Hudson orogeny were ‘root-preserving’ (if not ‘root-forming’) processes. Although the Hudson Bay basin is the largest by surface area of four major intracratonic basins in North America, it is also the shallowest. Available evidence suggests that basin subsidence may have been triggered by eclogitization of lower-crustal material. Compared to other basins of similar age in North America, the relatively stiff lithospheric root may have inhibited subsidence of the Hudson Bay basin.     

Further evidence for 1.85 Ga metamorphism in the Central Zone of the North China Craton: SHRIMP U–Pb dating of zircon from metamorphic rocks in the Lushan area, Henan Province

This paper reports SHRIMP zircon U–Pb dating of Precambrian supracrustal and granitic rocks from the Lushan area, Henan Province, in the southern portion of the Central Zone (also referred to as the Trans-North China Orogen) of the North China Craton. A graphite–garnet–sillimanite gneiss (Sample TW0006/1) of the Shangtaihua ‘Group’ gives a range of inherited zircon ages from 2.73 to 2.26 Ga and a metamorphic zircon age of 1.84 ± 0.07 Ga. A garnet-bearing gneissic granitoid (Sample TWJ358/1), which is considered to intrude the Shangtaihua ‘Group’, gives a magmatic zircon age of 2.14 ± 0.02 Ga and a metamorphic zircon age of 1.87 Ga. The metamorphic zircon ages of 1.87–1.84 Ga obtained in this study indicate that an important tectonothermal event occurred at the end of the Paleoproterozoic in the Lushan area. This supports the southern continuation of a Central Zone in the North China Craton that workers have recently considered to result from continent–continent collision. It is also evident that the Shangtaihua ‘Group’ was formed during the Paleoproterozoic (between 2.26 and 2.14 Ga), and not during the Archean, as previously considered.     

Electron microprobe U–Th–Pb monazite dating of the Transamazonian metamorphic overprint on Archean rocks from the Amapá Block, southeastern Guiana Shield, Northern Brazil

The Amapá Block, southeastern Guiana Shield, represents an Archean block involved in a large Paleoproterozoic belt, with evolution related to the Transamazonian orogenic cycle (2.26 to 1.95 Ga). High spatial resolution dating using an electron-probe microanalyzer (EPMA) was employed to obtain U–Th–Pb chemical ages in monazite of seven rock samples of the Archean basement from that tectonic block, which underwent granulite- and amphibolite-facies metamorphism. Pb–Pb zircon dating was also performed on one sample.Monazite and zircon ages demonstrate that the metamorphic overprinting of the Archean basement occurred during the Transamazonian orogenesis, and two main tectono-thermal events were recorded. The first one is revealed by monazite ages of 2096 ± 6, 2093 ± 8, 2088 ± 8, 2087 ± 3 and 2086 ± 8 Ma, and by the zircon age of 2091 ± 5 Ma, obtained in granulitic rocks. These concordant ages provided a reliable estimate of the time of the granulite-facies metamorphism in the southwest of the Amapá Block and, coupled with petro-structural data, suggest that it was contemporaneous to the development of a thrusting system associated to the collisional stage of the Transamazonian orogenesis, at about 2.10–2.08 Ga.The later event, under amphibolite-facies conditions, is recorded by monazite ages of 2056 ± 7 and 2038 ± 6 Ma, and is consistent with a post-collisional stage, marked by granite emplacement and coeval migmatization of the Archean basement along strike-slip shear zones.     

Age of the Siberian craton crust beneath the northern kimberlite fields: Insights to the craton evolution

Comprehensive studies of zircon xenocrysts from kimberlites of the Kuoika field (northeastern Siberian craton) and several kimberlite fields of the eastern Anabar shield, along with data compilation on the age of kimberlite-hosting terranes, reveal details of the evolution of the northern Siberian craton. The age distribution and trace element characteristic of zircons from the Kuoika field kimberlites (Birekte terrane) provide evidence of significant basic and alkaline–carbonatite magmatism in northern Siberia in the Paleozoic and Mesozoic periods. The abundance of 1.8–2.1 Ga zircons in both the Birekte and adjacent Hapchan terranes (the latter hosting kimberlites of the eastern Anabar shield) supports the Paleoproterozoic assembly and stabilization of these units in the Siberian craton and the supercontinent Columbia. The abundance of Archean zircons in the Hapchan terrane reflects the input of an ancient source other than the Birekte terrane and addresses the evolution of the terrane to west (Magan and Daldyn terranes of the Anabar shield). The present study has also revealed the oldest known remnant of the Anabar shield crust, whose 3.62 Ga age is similar to that of another ancient domain of Siberia, the Aldan shield. The first Hf isotope data for the Anabar shield coupled with the U–Pb systematics indicate three stages of crustal growth (Paleoproterozoic, Neoarchean and Paleoarchean) and two stages of the intensive crustal recycling in the Paleoproterozoic and Neoarchean. Intensive reworking of the existing crust at 2.5–2.8 Ga and 1.8–2.1 Ga is interpreted to provide evidence for the assembly of Columbia. The oldest Hf model age estimation provides a link to Early Eoarchean (3.7–3.95 Ga) and possibly to Hadean crust. Hence, some of the Archean cratonic segments of the Siberian craton could be remnants of the Earth's earliest continental crust.     

An early Paleoproterozoic high-K intrusive complex in southwestern Tarim Block, NW China: Age, geochemistry, and tectonic implications

Systematic geochronologic, geochemical, and Nd isotopic analyses were carried out for an early Paleoproterozoic high-K intrusive complex exposed in southwestern Tarim, NW China. The results provide a better understanding of the Paleoproterozoic tectonic evolution of the Tarim Block. Zircon U–Pb age dating indicates two Paleoproterozoic magmatic episodes occurring at ca. 2.41 Ga and ca. 2.34 Ga respectively, which were followed by a ca. 1.9 Ga metamorphic event. The 2.41 Ga granodiorite–adamellite suite shares characteristics of late to post-orogenic metaluminous A-type granites in its high alkalinity (Na₂O + K₂O = 7.6–9.3%), total REE (410–788 ppm), Zr (370–660 ppm), and Y (21.7–58.4 ppm) contents. εNd(t) values for the suite range from − 3.22 to − 4.71 and accordingly the Nd modal ages (T_2DM) vary between 3.05 Ga and 3.17 Ga. Based on geochemical data, the 2.34 Ga suite can be subdivided into two sub-suites, namely A-type and S-type. However, both types have comparable Nd isotope compositions (εNd(t) ≈ − 0.41 to − 2.08) and similar narrow T_2DM ranges (2.76–2.91 Ga).Geochemical and Nd isotopic data for the high-K intrusive complex, in conjunction with the regional geological setting, suggest that both the 2.41 Ga suite and the 2.34 Ga A-type sub-suite might have been produced by partial melting of the Archean mafic crust in a continental rift environment. The S-type sub-suite is thought to have formed by partial melting of felsic pelites and/or metagreywackes recycled from Archean crust (TTG?). Gabbro enclaves with positive εNd(t) value (2.15) have been found to be intermingling within the 2.34 Ga suite; ca. 2.34–2.36 Ga gabbroic dykes and adamellites have previously been documented in eastern Tarim. These observations indicate that the high-K intrusions may reflect the emergence of depleted mantle upwelling beneath the Tarim Block at that time. We suggest a three-stages model for the Precambrian crustal evolution in the Tarim Block: (1) the formation of proto-crust (TTG) by ca. 2.5 Ga, (2) episodes of felsic magmatism possibly occurring in continental rift environments at ca. 2.41 Ga and ca. 2.34–2.36 Ga, and (3) ca. 1.9 Ga metamorphism that may represent the solidification of the Precambrian basement of the Tarim Block.     

Petrogenesis of the Paleoproterozoic rapakivi A-type granites of the Archean Carajás metallogenic province, Brazil

Three Paleoproterozoic A-type rapakivi granite suites (Jamon, Serra dos Carajás, and Velho Guilherme) are found in the Carajás metallogenic province, eastern Amazonian craton. Liquidus temperatures in the 900–870 °C range characterize the Jamon suite, those for Serra dos Carajás and Velho Guilherme are somewhat lower. Pressures of emplacement decrease from Jamon (3.2±0.7 kbar) through Serra dos Carajás (2.0±1.0 kbar) to Velho Guilherme (1.0±0.5 kbar). Oxidizing conditions (NNO+0.5) characterized the crystallization of the Jamon magma, the Velho Guilherme magmas were reducing (marginally below FMQ), and the Serra dos Carajás magmas were intermediate between the two in this respect. The three granite suites have Archean T_DM model ages and strongly negative _Nd values (−12 to −8 at 1880 Ma), and they were derived from Archean crust. The Jamon granite suite may have been derived from a quartz dioritic source, and the Velho Guilherme granites from K-feldspar-bearing granitoid rocks with some sedimentary input. The Serra dos Carajás granites either had a somewhat more mafic source than Velho Guilherme or were derived by a larger degree of melting. Underplating of mafic magma was probably the heat source for the melting. The petrological and geochemical characteristics of the Carajás granite suites imply considerable compositional variation in the Archean of the eastern Amazonian craton. The oxidized Jamon suite granites are similar to the Mesoproterozoic magnetite-series granites of Laurentia, and they were derived from Archean igneous sources that were more oxidized than the sources of the Fennoscandian rapakivi granites. The Serra dos Carajás and Velho Guilherme granites approach the classic reduced rapakivi series of Fennoscandia and Laurentia. No counterparts of the Mesoproterozoic two-mica granites of Laurentia have been found, however. Following the model of Hoffman [Hoffman, P., 1989. Speculations on Laurentia's first gigayear (2.0 to 1.0 Ga). Geology 17, 135–138], the origin of the 1.88 Ga Carajás granites is related to a mantle superswell beneath the Trans-Amazonian supercontinent. This caused breakup of the continent and was associated with magmatic underplating and resultant crustal melting and generation of A-type granite magmas. The Paleoproterozoic continent that included the Archean and Trans-Amazonian domains of the Amazonian craton was assembled at 2.0 Ga; its disruption was initiated at 1.88 Ga, at least 200 Ma earlier than in Laurentia and Fennoscandia. The Carajás granites were related to the breakup of the supercontinent, not to subduction processes.     

内蒙古白云鄂博地区基底岩石锆石年代学及对构造背景的指示

白云鄂博地区的克拉通基底岩石主要由糜棱岩化花岗片麻岩(2588±15Ma),正长岩、花岗闪长岩(2018±15Ma)和黑云母花岗片麻岩、含石榴石蓝晶石花岗片麻岩(～1890Ma)等组成,白云鄂博超大型稀土矿床就位于华北克拉通太古代基底之上。太古代克拉通基底在早元古代中晚期(2.0Ga)又经历了一次强烈的碰撞造山运动,造成了闪长质与花岗质岩浆侵位,以及1.9Ga片麻岩相变质事件。     

Neoproterozoic accretionary and collisional events on the western margin of the Siberian craton: new geological and geochronological evidence from the Yenisey Ridge

The geological, structural and tectonic evolutions of the Yenisey Ridge fold-and-thrust belt are discussed in the context of the western margin of the Siberian craton during the Neoproterozoic. Previous work in the Yenisey Ridge had led to the interpretation that the fold belt is composed of high-grade metamorphic and igneous rocks comprising an Archean and Paleoproterozoic basement with an unconformably overlying Mesoproterozoic–Neoproterozoic cover, which was mainly metamorphosed under greenschist-facies conditions. Based on the existing data and new geological and zircon U–Pb data, we recognize several terranes of different age and composition that were assembled during Neoproterozoic collisional–accretional processes on the western margin of the Siberian craton. We suggest that there were three main Neoproterozoic tectonic events involved in the formation of the Yenisey Ridge fold-and-thrust belt at 880–860 Ma, 760–720 Ma and 700–630 Ma. On the basis of new geochronological and petrological data, we propose that the Yeruda and Teya granites (880–860 Ma) were formed as a result of the first event, which could have occurred in the Central Angara terrane before it collided with Siberia. We also propose that the Cherimba, Ayakhta, Garevka and Glushikha granites (760–720 Ma) were formed as a result of this collision. The third event (700–630 Ma) is fixed by the age of island-arc and ophiolite complexes and their obduction onto the Siberian craton margin. We conclude by discussing correlation of these complexes with those in other belts on the margin of the Siberian craton.