Paleoproterozoic Crustal Evolution Research Articles

Lithogeochemistry and zircon U-Pb geochronology of the Granjeiro Complex and associated units, Curral Novo do Piauí, NW-Borborema Province, Brazil: implications for Archean to Paleoproterozoic crustal evolution

Lithogeochemistry and zircon U-Pb geochronology of the Granjeiro Complex and associated units, Curral Novo do Piauí, NW-Borborema Province, Brazil: implications for Archean to Paleoproterozoic crustal evolution

Paleoproterozoic crustal evolution of the Tarim Craton, NW China: Constraints from geochronology and geochemistry of orthogneisses and granitic veins in the Xingdi region of the Quruqtagh Block

The Archean–Paleoproterozoic basement rocks, exposed in the Xingdi region of the Quruqtagh Block, provide a great opportunity to characterize the early crustal evolution of the Tarim Craton and reconstruct the Columbia supercontinent. Here we report zircon U–Pb ages, Lu–Hf isotope compositions, and bulk-rock geochemical data of orthogneisses and granitic veins from the Xingdi region of the Quruqtagh Block in the northeastern margin of the Tarim Craton. The orthogneisses formed in the late Neoarchean to early Paleoproterozoic (2504 ± 33 Ma, 2419 ± 24 Ma and 2450 ± 27 Ma), and were metamorphosed in the late Paleoproterozoic (1789 ± 43 Ma and 1748 ± 35 Ma). The orthogneisses have relatively high Sr (312–710 ppm) contents, and low Y (5.3–13.8 ppm) and Yb (0.46–1.10 ppm) contents, resulting in high Sr/Y (32–118) and La/Yb (17–64) ratios that are characteristics of adakites. The relatively high Mg# (49–55) and depleted zircon Hf isotope characteristics (positive εHf(t), with TDM2 of ca. 2.5–2.8 Ga) indicate that the orthogneisses crystallized from partial melting of garnet-bearing amphibolite in a subduction environment. The granitic veins that intrude the orthogneisses formed during the late Paleoproterozoic (1760 ± 25 Ma), which is roughly contemporaneous with the metamorphic ages of the orthogneisses; the granitic veins are characterized by extremely high SiO2 (>80 %), enrichments in Rb, Ba and U, and depletions in Nb and Ta. It is inferred that the granitic veins formed by in situ anatexis of the orthogneisses during the late Paleoproterozoic. Based on the zircon ages with Hf isotope compositions, it is evident that the continental crust in the Xingdi region of the Tarim Craton largely formed between 2.5 and 2.8 Ga and was reworked at ca. 1.8 Ga; this evolutionary history is similar to that of the Dunhuang Block. Comparison of the Paleoproterozoic tectono-thermal events in the different terranes of the Tarim Craton, it is suggested that the Tarim Craton is composed of discrete terranes that detached from different ancient cratonic nuclei prior to the late Paleoproterozoic, and assembled within the Columbia supercontinent respectively.

Paleoproterozoic crustal evolution of the northern Borborema Province, NE Brazil: Insights from high-grade metamorphic rocks of the Canindé do Ceará Complex

Archean to Paleoproterozoic crustal segments are widely recognized as basement inliers within the Neoproterozoic orogenic belts of the Pan-African/Brasiliano orogeny. For example, the Canindé do Ceará Complex, in the northern Borborema Province, NE Brazil, comprises a large domain of Paleoproterozoic high-grade metamorphic rocks with a protracted tectonic history. This complex is dominantly represented by sillimanite- and graphite-bearing metasedimentary rocks with associated tonalitic to granodioritic orthogneisses. All these rocks are highly deformed and variably migmatized. Minor granitic intrusions and lenses of garnet amphibolites are also present. In this work, in order to discuss the tectonic evolution of the area, we present new U-Pb LA-ICPMS zircon dating, Sm-Nd isotopes, and whole-rock geochemistry for selected samples of the Canindé do Ceará Complex. The amphibolites show tholeiitic affinity and Sm-Nd TDM model ages of 2.22–2.52 Ga with positive εNd(t), attesting to an oceanic signature. The tonalitic/granodioritic orthogneisses show U-Pb ages of 2.19 to 2.12 Ga, Sm-Nd TDM model ages of 2.16 to 2.34 Ga, which probably reflect arc-related environments. The collisional event is marked by granitic intrusions (aplites) and diatexites, which display U-Pb ages ranging from 2.08 to 2.03 Ga. This event is also recorded in zircon recrystallized from tonalitic/granodioritic rocks, which show U-Pb age at 2.04 Ga. Therefore, from our results and literature information, the Rhyacian/Orosirian basement rocks of the Canindé do Ceará Complex show a protracted evolutionary history, ranging from 2.2 to 2.1 Ga arc-related environments, to 2.1–2.0 Ga continental collision and late Neoproterozoic metamorphic overprint.

Geochemistry, geochronology, and isotopic studies of Paleoproterozoic magmatic rocks from outer Kumaun Lesser Himalaya, India: Implication on petrogenesis and crustal evolution of northern Indian Block

Paleoproterozoic granite gneiss (GGn), mafic volcanics, and associated quartzite are exposed widely in the outer Kumaun Lesser Himalaya, which form an integral part of the Lesser Himalayan belt. Field relation, phase petrology, whole-rock geochemistry, and zircon U-Pb-Lu-Hf isotopes of GGn and enclosed microgranular enclaves (ME) have been investigated to infer the magmatic processes, tectonic setting and its implications on understanding the Paleoproterozoic crustal evolution of the north Indian block (NIB). The U-Pb zircon crystallization ages of GGn (1824 ± 16 Ma) and ME (1804 ± 16 Ma) underline their coeval nature. Modally, the GGn and the ME represent monzogranite and geochemically, they can be characterized as peraluminous, alkali-calcic, calc-alkaline, and ferroan types. Whole-rock elemental and biotite-zircon geochemistry reveal shallow level emplacement, reduced condition, and low water content of GGn magma similar to anorogenic A-type magma. The hybrid (crustal and mantle mixed) origin for the Paleoproterozoic GGn is envisaged, where synchronous mafic volcanics might have served as potential magma end-member. The present and published geochemical and zircon U-Pb-Lu-Hf isotopic record on the Lesser Himalayan felsic-mafic magmatic rocks propose a viable petrogenetic model for the evolution of Paleoproterozoic NIB crust that formed dominantly by the melting of ancient and juvenile crustal sources during 1.8–1.9 Ga.

Detrital zircon U-Pb-Hf isotope record of conglomerates in the southern Aravalli orogen, NW India: Implications for stratigraphy, provenance and Archean to Paleoproterozoic crustal evolution

The inconsistent stratigraphic framework of the Proterozoic successions in the Aravalli orogen, NW India hinders the detailed reconstruction of its geodynamic evolution during the Archean to Paleoproterozoic. In this study, we present new results of combined U-Pb-Hf isotope data of detrital zircon grains of two conglomerate samples from the southern Aravalli orogen, presently assigned to the upper unit of the Aravalli Supergroup. The youngest concordant zircon grains in both the conglomerates yield concordia ages of 1735 ± 13 Ma (n = 2) and 1736 ± 15 Ma (n = 2), respectively, interpreted as maximum ages of deposition. Older zircon grains mostly reveal Neoarchean to Paleoproterozoic age clusters at 2560–2550, 1870–1860 and 1760–1740 Ma, and minor Paleoarchean ages between 3558 ± 17 Ma and 3239 ± 14 Ma, corresponding to known magmatic events in the Aravalli orogen. Most detrital zircon grains show subchondritic εHft values (+6 to −20), signifying minor reworking of late Hadean/Eoarchean crust during the Paleoarchean, and substantial reworking of Paleo-to Neoarchean crust during the late Neoarchean and Paleoproterozoic, with only minor juvenile input. The maximum depositional ages indicate that the investigated conglomerates were deposited either synchronous or after the emplacement of extension-related A-type granites, which intruded the Aravalli orogen between 1733 ± 9 Ma and 1703 ± 5 Ma. Furthermore, the data suggest that the conglomerates do not belong to the upper Aravalli unit as envisaged by previously published stratigraphic concepts. Instead, these were deposited earlier, during opening of a rift-related basin, grading from a terrestrial into a marine environment, contemporaneous with other sedimentary successions exposed in the North Delhi basin, which are presently assigned to the North Delhi Supergroup. The compiled zircon age-Hf isotope data additionally provide evidence for a series of late Hadean to Archean juvenile crust formation events in hinterland of the Aravalli orogen at 4200–3300 Ma for east Indian cratonic blocks and 3550–3100 Ma for northern and southern cratonic nuclei, and 2700–2500 Ma all over India. Substantial crustal reworking took place during the late Neoarchean at 2500 Ma, and the late Paleoproterozoic at 1850 Ma and 1730–1700 Ma.

The Neoarchean and Paleoproterozoic crustal evolution of the Clearwater block, northwestern Laurentia: Implications for the assembly of supercontinents

We report new coupled zircon U-Pb age and Hf isotope data, along with whole-rock Hf-Nd isotope data for 20 samples from the Priest River and Clearwater complexes—Neoarchean and Paleoproterozoic basement exposures in northern Idaho, northwest Laurentia. The new zircon data reveal two well-defined periods of magmatism at ∼ 2.66 and ∼ 1.86 Ga in each complex, with no evidence of any intervening or older magmatic events. Positive zircon initial εHf values of the Neoarchean rocks (+1 to +3) indicate juvenile magmas derived from a depleted mantle source. The Paleoproterozoic rocks, in both complexes, share a much wider range of initial zircon εHf values (−7 to +6) which suggests magmas derived from a depleted mantle source intruded and assimilated pre-existing Neoarchean continental crust. The shared age and isotope compositions in the Priest River and Clearwater complexes suggest that the two complexes likely belong to a single crustal block—the Clearwater block.Based on these new zircon U-Pb ages and Hf isotopic data of the Neoarchean and Paleoproterozoic rocks, the Clearwater block is shown to be distinct from the nearby Wyoming Province, the Medicine Hat block, and components of the Great Falls tectonic zone. We also report new zircon Hf isotope data for the ∼ 1.58 Ga Laclede orthogneiss in the Clearwater block, which along with published U-Pb and Hf isotope constraints, support a paleogeographic connection between the Gawler craton, East Antarctica, and northwestern Laurentia during ∼ 1.9 Ga to ∼ 1.6 Ga. Comparison with other examples of co-existing Neoarchean and Paleoproterozoic igneous rocks present in other continents suggests that the global record of 2.7–2.5 Ga magmatism often represents new crustal additions from a depleted mantle reservoir. The record of 2.0–1.7 Ga rocks also represent additions of juvenile magma, but with significantly larger contributions from pre-existing continental crust. In many cases the 2.0–1.7 Ga crust preserved on Earth today was added during the assembly of the supercontinent Nuna.

Archean to Paleoproterozoic crustal evolution of the southern Yangtze Block (South China): U–Pb age and Hf-isotope of zircon xenocrysts from the Paleozoic diamondiferous kimberlites

Crustal zircon xenocrysts from mantle-derived magmatic rocks have the potential to probe the deep crust. Here we present integrated U–Pb dating and Hf-isotope analyses of zircons from a Paleozoic diamondiferous kimberlite dike in the Maping area of Zhenyuan County (southeastern Guizhou Province), with implications for the tectonothermal evolution of unexposed continental crust beneath the southern Yangtze Block, South China. All zircons (n = 236) show a wide range of U–Pb ages between Mesoarchean and middle Carboniferous. Among them, 96 zircons with 90–110% concordance yield concordant ages from 2942 ± 8 Ma to 342 ± 2 Ma, and form major age peaks at ∼2.9 Ga, ∼2.6 Ga and ∼2.0 Ga. The overwhelming majority of zircons are dominated by Mesoarchean–Paleoproterozoic U–Pb ages regardless of their concordance degrees. The zircon populations mainly consist of magmatic zircons, with minor metamorphic grains (Th/U < 0.10). The youngest magmatic zircon (Th/U = 0.43) with a well concordant 206Pb/238U age of 342 ± 2 Ma (M1-16) is interpreted as the maximum emplacement age of the Maping diamondiferous kimberlites. Most zircons with pre-eruption ages are considered to be xenocrysts, and they may be derived from the deep-seated continental crust through which kimberlite host magmas have passed. Their U–Pb ages and Hf isotopic compositions suggest the possible existence of a highly evolved Archean basement beneath the southern Yangtze Block, South China, which is much older than its known surface rocks. A lot of magmatic zircon xenocrysts reveal complex Precambrian crustal evolution in the southern Yangtze Block. These processes involved the important growth of continental crust at 2.6–2.5 Ga, and in the meantime, crustal reworking could be intermittently proceeding at 3.0–2.6 Ga. In addition, a group of xenocrystic zircons are identified to be of metamorphic origin, indicating that the proposed Archean basement beneath the southern Yangtze Block likely experienced a metamorphic event around 2.0 Ga. This geologically significant episode is consistent with the well-developed coeval metamorphism in other places of the Yangtze Block (e.g., Kongling Terrane), which has been considered to link to the assembly of the Paleoproterozoic Nuna/Columbia supercontinent. Our zircon data implies that the unexposed Archean basement beneath the southern Yangtze Block was affected by multiple thermal activities.

Incipient charnockite formation at the waning stage of Paleoproterozoic hot orogenesis, Yeongnam Massif, Korea

The incipient charnockite or orthopyroxene-bearing granitic orthogneiss is a relatively common constituent in ancient granulite-facies terranes, and its formation has been often attributed to an influx of CO2-rich fluid or a removal of aqueous melt. Temporal relationship between the orthopyroxene formation and the fluid or melt migration, however, remains debatable. Here we report the first finding of incipient charnockite hosted by garnet-biotite-bearing granitic gneisses in the Sancheong–Hadong anorthosite complex, Yeongnam Massif. Both lithologies preserve a variety of field and microstructural evidence for partial melting and subsequent melt crystallization, as manifested by granitic leucosomes and biotite-rich residua. Based on the phase equilibria modeling and geothermobarometric calculation, peak metamorphic conditions of migmatities were estimated to be 5.4–6.0 kbar and 800–850 °C, which led to the biotite dehydration melting together with the orthopyroxene formation in incipient charnockite. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses of zircon from an incipient charnockite and a host gneiss yielded the weighted mean 207Pb/206Pb ages identical within errors; 1880 ± 5 Ma and 1872 ± 6 Ma for the cores, and 1862 ± 4 Ma and 1861 ± 4 Ma for the rims, respectively. The former is interpreted to represent the time for magmatic crystallization of granitic protoliths, whereas the latter for subsequent anatexis typified by peritectic growth of orthopyroxene. Such a timeline is consistent with two distinct thermal events previously reported from the Sancheong-Hadong anorthosite complex. By contrast, monazite grains from a biotite-bearing granitic gneiss in the charnockite zone yielded the weighted mean 207Pb/206Pb ages of 1866 ± 14 Ma and 1835 ± 11 Ma for the core and rim, respectively. The latter is consistent with 1842 ± 8 Ma, estimated from monazite neoblasts of incipient charnockite. The monazite growth during a post-peak metamorphic stage at ca. 1.84 Ga is attributed to a fluid influx event, apparently concentrated in the charnockite zone. The charnockite formation in the Yeongnam Massif further attests to the longevity (>ca. 40 m.y.) of hot orogenesis that has governed the Paleoproterozoic crustal evolution in eastern North China Craton.

Neoarchean–early Paleoproterozoic crustal evolution in the Jiapigou terrane in the northeastern part of the North China Craton: Geochemistry, zircon U–Pb dating and Hf isotope constraints from the potassic granitic complex

Neoarchean granitic rocks are important components of Precambrian cratons, and their petrogenesis can provide constraints for understanding the evolution of continental crust. The Neoarchean potassic granites are widely distributed in southern Jilin Province, which is located in the northeastern part of the North China Craton. Newly obtained field geology observations and petrological, geochemical and geochronological data reveal that the Jiapigou potassic granitic complex is mainly composed of biotite granitic gneiss and medium- to coarse-grained granite. All the granitic gneisses and granites are high-K calcium–alkaline to shoshonite, metaluminous to peraluminous (A/CNK = 0.95–1.13; molar Al2O3/(CaO + Na2O + K2O)), enriched in LILEs and LREEs with strongly fractionated REE patterns ((La/Yb)N = 21–179), and depleted in Nb, Ta, Ti and P. The biotite granitic gneisses have low Rb/Sr ratios (∼0.06) and weak positive Eu anomalies (δEu = 1.26–1.51), while the granites have low Th, U and REEs and strong positive Eu anomalies (δEu = 7.27–16.92). The zircons of these granitic rocks generally have core–rim structures based on cathodoluminescence images and show inherited ages of 2729 ± 10 Ma, crystallization ages of 2523 ± 11 Ma to 2526 ± 15 Ma, and crystallization/metamorphism ages of 2480 ± 15 Ma to 2485 ± 9 Ma. The zircon Hf isotope results of the medium-grained monzogranite show that the εHf(t2) values vary from –2.2 to +5.3, and the two-stage model ages (TDM2) are 2.9–3.0 Ga. The magmatic zircons of the early Neoarchean (∼2.73 Ga) and the late Neoarchean (∼2.52 Ga) crystallized in high-temperature magmas (738–890 °C), whereas those of the early Paleoproterozoic (∼2.48 Ga) crystallized in relatively low-temperature (646–702 °C) magmas. These results indicate that the Jiapigou granitic rocks were products of intracrustal recycling during the late Neoarchean and the early Paleoproterozoic. The protoliths of the Jiapigou granitic gneisses were derived from the remelting of the early Neoarchean juvenile crustal rocks in the lower crust during the late Neoarchean. Subsequently, these granitic rocks underwent amphibolite-facies metamorphism and water-fluxed melting in the early Paleoproterozoic, resulting in the association of migmatic granitic gneisses and potassic granites at the shallow crust level. The cratonization in the Jiapigou terrane involved early Neoarchean (∼2.73 Ga) juvenile crust growth and late Neoarchean (∼2.53–2.52 Ga) to the early Paleoproterozoic (∼2.48 Ga) intracontinental reworking.

Mesoarchean to Paleoproterozoic Crustal Evolution of the Belomorian Province, Fennoscandian Shield, and the Tectonic Setting of Eclogites

Abstract—The Belomorian Province (BP) of the Fennoscandian Shield is a high-grade belt composed of Meso- to Neoarchean tonalite– trondhjemite–granodiorite (TTG) gneisses with subordinate supracrustal complexes. The Belomorian crust is underlined by a thick mantle keel, a structural element typical of Archean cratons. Belomorian rocks were metamorphosed under conditions of mainly high-pressure amphibolite to granulite facies in both Archean and Paleoproterozoic times. The TTG gneisses contain numerous blocks of almost completely retrogressed eclogite (eclogite-1). This paragenetic association of eclogite-1 and gneisses can be classified as an Archean eclogite–TTG gneiss mélange, a component of the Belomorian continental crust produced by subductional, accretionary, and collisional processes of the Belomorian collisional orogeny 2.9–2.66 Ga. The Paleoproterozoic history of the BP comprises of two prominent tectonic periods: (i) early Paleoproterozoic (~2.5–2.4 Ga), related to a superplume, and (ii) late Paleoproterozoic (2.0–1.85 Ga), resulted from crustal reworking during the Lapland–Kola collisional orogeny that produced strong penetrative metamorphic and local deformational overprint. The Paleoproterozoic highest-grade metamorphic overprint is represented by patches of eclogites (eclogite-2) in Paleoproterozoic mafic dikes and eclogite-1. Field relations between eclogite-1 and eclogite-2 are described in the Gridino area of the western coast of the White Sea. So, the BP is a high-grade polymetamorphic belt formed by a superposition of the Neoarchean Belomorian and Paleoproterozoic Lapland–Kola orogenies, whose characteristic features are eclogites produced by subduction and collision.

Late Neoarchean to Paleoproterozoic arc magmatism in the Shandong Peninsula, North China Craton and its tectonic implications

The transition in tectonic regime of our planet during the late Archean with the initiation broadly modern style subduction system is one of the major topics of interest in earth science. The North China Craton (NCC), one of the oldest cratonic nuclei in the world, preserves important records of Archean and Paleoproterozoic crustal evolution, cratonization and related geodynamic history that are important in understanding the continental growth of the early Earth. Here we investigate a suite of Archean to Paleoproterozoic rocks including hornblendite, amphibolite, gabbro, diorite, basalt, plagiogranite, granite porphyry and greenschist from Shandong Peninsula within the southwestern Jiaoliao block of the eastern NCC using zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemistry. We aim to understand the timing and petrogenesis of the rock suite and its implications on the geodynamic history of the NCC. Zircon U-Pb data show 207Pb/206Pb ages in the range of 2.68–1.83 Ga, and is divided into three groups of 2.68–2.43, 2.38–1.96 and 1.95–1.83 Ga. Among these, the 2.68–2.43 Ga group confirms with the major magmatic phase during Neoarchean-Paleoproterozoic transition in the eastern NCC, whilst the other groups of 2.38–1.96 and 1.95–1.83 Ga ages might represent the Paleoproterozoic orogenic events in the NCC. Zircon Lu-Hf isotopic data display εHf(t) values ranging from −0.4 to 10.0 and TDMC of 3074–2080 Ma, which are subdivided into one group with U-Pb ages of 2672–2445 Ma characterized by εHf(t) values from −0.4 to 7.0 and TDMC of 3074–2588 Ma and another group (2134–2009 Ma) with εHf(t) values in the range of 2.8–10.0 and TDMC ranging from 2458 to 2080 Ma. These results indicate that the magmas (2672–2445 Ma group) were sourced mainly from Late Mesoarchean to Neoarchean juvenile components with minor input of reworked Mesoarchean crustal components, whereas the 2134–2009 Ma group was derived from Paleoproterozoic juvenile components. Whole-rock geochemical data of the granite porphyry and plagiogranites show typical subduction-related arc signature with the enrichment of LREEs and LILEs and depletion of HREEs and HFSEs (e.g. Nb, Ta, Ti), and mainly belong to I-type granites generated at arc-related setting. The ultramafic–mafic magmatic suite corresponds with tholeiitic to calc-alkaline series which were formed by partial melting of enriched mantle within an island arc setting in an active continental margin. In conjunction with the results from previous studies in the NCC, we correlate the 2.68–2.43 Ga ages with Late Neoarchean amalgamation of microblocks and cratonization of the NCC driven by late Neoarchean oceanic plate subduction, and the 2.38–1.83 Ga ages represent Paleoproterozoic orogenic events including the assembly of major crustal blocks in the NCC within the Paleoproterozoic supercontinent Columbia, and the final collision of these crustal blocks and cratonization.

Paleoproterozoic (1.96–1.86 Ga) granites in Xinyang record zoned deep crustal structure and multi-stage reworking beneath the southern North China Craton

As one of the oldest cratons on Earth, the North China Craton (NCC) is a frequent area for geological research due to its complex crustal evolution. Regarding the Paleoproterozoic crustal evolution of the craton, most studies have focused on continental amalgamation (i.e. horizontal crustal evolution), but few on the vertical crustal evolution. Here we report whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotope geochemistry for the Xinyang granites to constraint the vertical crustal structure and evolution of the southern NCC. The studied granites comprise two-mica K-feldspar granite and garnet-bearing K-feldspar granite. All the rocks have high SiO2 and total alkali, but low CaO, MgO and Fe2O3T contents. Their A/CNK values (1.05–1.28) suggest that they are peraluminous rocks. These granites are enriched in LILE (Rb, Th and K), depleted in Sr, P and HFSE (Nb and Ti). The two-mica K-feldspar granites show obviously fractionated REE patterns ((La/Yb)N = 18.3–387) with negative or positive Eu anomalies (δEu = 0.47–1.03, 4.85–6.72), while the garnet-bearing K-feldspar granites have flat REE patterns ((La/Yb)N = 1.69–4.89) with extraordinary negative Eu anomalies (δEu = 0.22–0.42). The magmatic zircons of the two-mica K-feldspar granites yield crystallization ages ranging from ~ 1.86 Ga to ~ 1.90 Ga, and those of the garnet-bearing K-feldspar granites give crystallization ages of ~ 1.90 Ga. Previous work also reported a biotite K-feldspar granite pluton formed at ~ 1.96 Ga in the Xinyang area. Taken together, three major episodes of Paleoproterozoic granitoid events (~1.86 Ga, ~1.90 Ga and ~ 1.96 Ga) are recognized in the area. Combined with regional geochronological investigations, the peraluminous granitic magmatic activities occurring during 1.96–1.86 Ga in the Xinyang area could be linked to the collision between the Eastern and Western Blocks of the NCC. Alternatively, zircon Hf isotopic compositions suggest that these rocks derived from partial melting of pre-existing crust with heterogeneous compositions. Zircons from the ~ 1.86 Ga two-mica K-feldspar granites yield εHf(t) values of −5.2–1.7 with Tcrust of 2.40–2.86 Ga, compared to zircons from the ~ 1.90 Ga two-mica K-feldspar granites which yield wide range of εHf(t) values of −13.5–1.0 with Tcrust of 2.50–3.42 Ga. In contrast, the ~ 1.90 Ga garnet-bearing K-feldspar granites have homogeneous negative zircon εHf(t) values ranging from −11.8 to −10.4, with Tcrust ranging from 3.23 to 3.30 Ga. Moreover, zircons from the biotite K-feldspar granites have εHf(t) values of −0.6–2.6, corresponding to Tcrust of 2.44–2.77 Ga. Based on abovementioned geochemical signals, we propose that the Paleoproterozoic crust in the southern NCC likely consisted of two parts in vertical, the upper Middle-Late Archean crust and the lower early Paleoproterozoic crust with Eo-Paleoarchean crustal remnants. During the Paleoproterozoic, the southern NCC experienced multi-stage crustal reworking, indicating that a stable continental crust likely had been formed by the end of Archean.

Zircon U-Pb and Lu-Hf isotopes of Huai'an complex granites, North China Craton: Implications for crustal growth, reworking and tectonic evolution

The Huai'an Complex, located in the north-central North China Craton (NCC), consists of tonalite-trondhjemite-granodiorite (TTG) gneisses and minor intrusive bodies of granite. Its late Neoarchean to Paleoproterozoic crustal evolution is still unclear, and the study of this evolution will constrain the tectonic evolution of the NCC. The LA-ICP-MS zircon U-Pb ages of ten granites from the Huai'an Complex reveal three episodes of magmatism: 2.6–2.3 Ga, 2.0–1.7 Ga, and a few ages from ~2.3–2.0 Ga. The 2.6–2.3 Ga, 2.3–2.0 Ga and 2.0–1.7 Ga zircons have average εHf(t) values of 2.79, −4.0, and − 6.05, average TDM2 values of 2.78 Ga, 2.98 Ga, and 2.86 Ga, and average 176Lu/177Hf ratios of 0.033, 0.021, and 0.027, respectively, indicating that their magma sources were from the melting of the Neoarchean “mildly depleted” SCLM, the mafic Mesoarchean lower crust, and the mafic Meso-Neoarchean lower crust. Zircon geochemical characteristics indicate that the Huai'an Complex was a long-lived continental magmatic arc during 2.6–2.0 Ga. The juvenile crustal proportion was 100% during 3.1–2.6 Ga and decreased through 50% at 2.5 Ga to 20% at 2.45 Ga; it then increased to 45% at 2.3 Ga and finally decreased to 0% during 1.95–1.7 Ga, indicating that the crust experienced a growth stage during 3.1–2.5 Ga and reworking stage during 2.5–1.7 Ga and that the Huai'an Complex underwent compression-extension-compression processes during 2.6–1.7 Ga. The compression-dominant tectonic setting during 2.6–2.45 Ga may have been linked to the subduction and amalgamation of microblocks. The compressive setting during 2.3–1.7 Ga may have been related to amalgamation between the Eastern and Western Blocks. The modeled crustal growth curve suggests that approximately 67% of the existing continental crust of the Huai'an Complex formed before 2.6 Ga, which is similar to the NCC and several other cratons worldwide. Our results favor the two-stage cratonization model of the NCC.

Archean to paleoproterozoic crustal evolution in the Phan Si Pan zone, Northwest Vietnam: evidence from the U-Pb geochronology and Sr-Nd-Hf isotopic geochemistry

ABSTRACT We studied zircon U-Pb geochronology, Sr-Nd-Hf isotopes, and whole-rock geochemistry of Mesoarchean-Paleoproterozoic igneous rocks in the Phan Si Pan zone, NW Vietnam. The Mesoarchean-Paleoproterozoic magmatism in the area can be divided into three phases as represented by ca. 2.9 Ga Mesoarchean tonalite-trondhjemite-granodiorites (TTGs), ca. 2.3 Ga Paleoproterozoic mafic dykes, and ca. 1.8 Ga Paleoproterozoic granites. The ca. 2.9 Ga Mesoarchean TTGs serve as part of the oldest basement rocks in SE Asia, which have zircon εHf(t) and whole-rock εNd(t) values ranging from −2.8 to +2.1. Their ancient zircon Hf and whole-rock Nd isotopic model ages (TDM2) of 3.4 Ga to 3.2 Ga suggest an origin from partial melting of ancient crustal rocks. The ca. 2.3 Ga mafic dykes were affected by post-tectonic thermal events at ca. 1.9–1.8 Ga. Their zircon εHf(t) (+1.4 to +5.9) and whole-rock εNd(t) (−4.1 to −1.6) and 87Sr/86Sr ratio (0.703459 to 0.719079) isotopic characteristics show that they originated from partial melting of mantle components with a minor input of Archaean continental crust. The Paleoproterozoic granites in the Phan Si Pan zone crystallized at 1803–1864 Ma, and show negative εHf(t) values of −17.9 to −14.8 and zircon Hf model ages (TDM2) ranging from 3.48 to 3.66 Ga, suggesting a derivation by partial melting of Paleoarchean continental crust during Paleoproterozoic time. These isotopic results shed light on the Precambrian tectonic evolution of NW Vietnam and its relationship with continental blocks in Yangtze and India.

Archean and Paleoproterozoic crustal evolution and evidence for cryptic Paleoarchean-Hadean sources of the NW São Francisco Craton, Brazil: Lithochemistry, geochronology, and isotope systematics of the Cristalândia do Piauí Block

The Cristalândia do Piauí Block, located in the northwestern margin of the São Francisco Craton, represents the basement of the Rio Preto Fold Belt. It is composed of Archean orthogneisses of ca. 3.2 Ga reworked at 2.81 and 2.68 Ga with juvenile to moderately juvenile εHf values between −1.51 and −8.07, and high-K syenogranites dated at 2.65 Ga with crustal εHf values between −10.37 and −19.54, both with model ages (TDMc) varying from 3.57 to 4.33 Ga, indicating cryptic Paleo- to Eoarchean and even Hadean sources. Metamafic-ultramafic rocks, iron formations, metacherts, and graphite schists occur in association with the Archean orthogneiss. The whole set is intruded by Paleoproterozoic (ca. 2.2 Ga) metagranitoids with compositions varying from granodioritic with sanukitoid-type signatures to monzogranitic, and alkali-feldspar granitic with crustal signatures. They are related to the Rhyacian-Orosirian orogeny, responsible for the complex deformation patterns printed in the Archean basement. Orosirian metasedimentary rocks are represented by garnet-biotite paragneiss with maximum depositional age of ca. 1.95 Ga. Intrusive mafic dikes in the complex show ages of ca. 2.07 Ga and isotopic features of mantle-derived magmas. Considering the presented data, the Cristalândia do Piauí Block represents a metacratonic domain corresponding to part of the Guanambi-Correntina Paleoplate, wich had been involved in crustal accretion and reworking from the Archean to the Paleoproterozoic. Many of the elements of the evolutionary stages wich are present in the São Francisco-Congo Paleocontinent can be recognized, suggesting an evolution of this crustal segment amounts to the Eoarchean era and disclosing the existence of cryptic Paleoarchean or even Hadean nuclei, reworked in at least three metamorphic events during the Rhyacian-Orosirian orogeny.

Direct evidence for Archean crust in the Western Domain of the Karagwe Ankole Belt, Rwanda: Implications for Neoarchean to Paleoproterozoic crustal evolution

Neoarchean orthogneiss, dated at 2629 ± 9 Ma by SIMS zircon U-Pb, has been discovered in the Rusizian terrane of the Western Domain of the Karagwe Ankole Belt, Rwanda, redefining the NW margin of the Tanzania Craton. Metamorphism of the orthogneiss at 1959 ± 4 Ma was associated with Paleoproterozoic granitic arc magmatism in the Rusizian terrane over the period ca. 2000–1840 Ma. The major and trace element composition of the peraluminous, calc-alkalic orthogneiss is consistent with magmatism in an arc setting at an active continental margin. Its Nd depleted mantle model age of ca. 2800 Ma is consistent with derivation by partial melting and reworking of older crust at the NW margin of the Tanzania Craton. The Paleoproterozoic thermal event was related to the accretional collision between the Congo and Tanzania Cratons during the assembly of the Nuna supercontinent. Future tectonic modelling of the Karagwe Ankole Belt must take into account the presence of Archean basement beneath the Western Domain.

Late Paleoproterozoic crustal evolution in the Daqingshan area: Evidences from adakitic and A-type granitoids in the Guyang Changshengqu goldfield, Khondalite Belt, North China Craton

Granitic magmatism related to the collisional orogenic belt provides important information for the evolution of continental crust. We performed petrological, geochemical and zircon U-Pb-Hf isotopic studies on four granitoid samples from the Guyang Changshengqu goldfield, Daqingshan area, Khondalite Belt, North China Craton. The zircon U-Pb dating results indicate that the granitoids emplaced at 1950 ± 11 Ma, 1935 ± 12 Ma, 1846 ± 11 Ma, and 1812 ± 8.6 Ma, represent two periodic granitic magmatism in the Daqingshan area. The 1.95 and 1.93 Ga granites exhibit high SiO2, K2O, and Na2O contents with high Sr/Y and (La/Yb)N ratios, but low MgO, Cr, and Ni contents, indicating that they were produced by the partial melting of a thickened lower crust under relatively high-pressure conditions. The granites show negative-dominated zircon εHf(t) values (−5.7 to 1.9), and their zircon TDM2(Hf) values range between 2.9 and 2.5 Ga, indicating an ancient crust source with minor juvenile crustal material involved. The 1.85 and 1.81 Ga quartz monzonites exhibit high SiO2, K2O, Na2O, Zr, Nb, Ce, and Y but low MgO, Cr, and Ni contents, with high Ga/Al and FeOt/(FeOt + MgO) ratios, indicating an A-type granite affinity. The whole-rock geochemistry suggests that they were formed by dehydration re-melting of TTG and quartz diorite at high temperatures and shallow depths. The quartz monzonites show homogeneous εHf(t) values (−10.6 to −6.1) and the zircon TDM2(Hf) values range between 3.0 and 2.8 Ga, suggesting that they were derived from a Neoarchean ancient crust. The 1.95–1.93 Ga adakitic magmatism is associated with the 1.93–1.92 Ga mafic magmatism and UHT metamorphic in the eastern part of the Khondalite Belt; this suggests a tectonic transition from collisional compression to post-collisional extension. The 1.85–1.81 Ga A-type granitic magmatism indicates evident continental crust thinning and asthenospheric upwelling. The two unrelated magmatism are possibly induced by two collisional events from the Khondalite Belt and the Trans-North China Orogen, respectively. The collision of the western and eastern blocks at ca. 1.85 Ga may have played an important role in the A-type quartz monzonites origin and influenced the crustal evolution as far as the Daqingshan area in the Khondalite Belt.

Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: Implications for Archean–Paleoproterozoic Wilson cycle in the North China Craton

The North China Craton (NCC) offers a window to Archean–Paleoproterozoic crustal evolution. Following the amalgamation of microblocks during Neoarchean, the NCC witnessed another protracted Wilson cycle in the Paleoproterozoic with subduction-accretion-collision process. Here we report a newly identified suprasubduction zone ophiolite suite from the Miyun complex in the NCC where a rare and near-complete ophiolite succession is preserved including serpentinite, lherzolite, olivine clinopyroxenite, websterite, gabbro, dolerite, diorite, monzonite, metabasalts and trondhjemite, in association with Banded Iron Formation (BIF). The geochemical features of the suite are consistent with those of suprasubduction ophiolite complexes, with the mafic and intermediate members displaying Island Arc Tholeiite (IAT) and Mid-Ocean Ridge Basalt (MORB) affinity. Zircon grains from lherzolite define three groups of 207Pb/206Pb weighted mean ages at 2500 ± 12 Ma marking the formation age, and 2237 ± 47 Ma, and 1843 ± 30 Ma representing subsequent thermal events. The majority of zircon grains in olivine clinopyroxenite, gabbro, and quartz monzonite yield 207Pb/206Pb weighted mean ages of 2510 ± 19 Ma, 2495 ± 10 Ma, and 2486 ± 21 Ma respectively. Those from the trondhjemite show weighted mean age of 2476 ± 9.4 Ma. The compiled age data from all the rock types in the Miyun suite show two distinct age peaks at ca. 2486 Ma and 1832 Ma, corresponding to the timing of magma differentiation and subsequent metamorphism. The zircon Lu-Hf isotope data display distinct positive ɛHf(t) values in the range 0.35–7.05, suggesting magma derived from Neoarchean to Paleoproterozoic depleted mantle (juvenile) source. The zircon TDM ages show a peak at 2670 Ma, confirming Neoarchean components. The timing of magma formation in the Miyun ophiolite is broadly identical to those of the other rare Neoarchean – early Paleoproterozoic ophiolite suites described from the NCC including those from Yishui and Zunhua. Furthermore, evidence from the recently reported Alaskan-type intrusions and arc root mafic-ultramafic complexes around Miyun complex with ages in the range of 2.4–2.0 Ga suggest continued subduction-related magmatic processes, with final collision in latest Paleoproterozoic at around 1.84 Ga. We propose that following the assembly of ancient microblocks along multiple zones of ocean closure marked by major greenstone belts of 2.6–2.5 Ga, and high-grade metamorphism along the margins of the microblocks during Archean–Paleoproterozoic transition, the NCC went through another major Wilson cycle from early to late Paleoproterozoic involving prolonged subduction, accretion and collision of larger crustal blocks and intervening arc complexes, leading to final cratonization.

Paleoarchean to Paleoproterozoic crustal evolution in the Guanambi-Correntina block (GCB), north São Francisco Craton, Brazil, unraveled by U-Pb Geochronology, Nd-Sr isotopes and geochemical constraints

The north-central part of the São Francisco Craton (SFC) is one of the oldest terranes in the South American platform and experienced three regional magmatic events at 3.4–3.3, 3.1–2.7, and 2.1 Ga. Our new SHRIMP U-Pb data place the origin of Guanambi-Correntina block (GCB) in the Paleoarchean, contemporaneous with the Gavião block in central north SFC. Lithological, geochemical, and isotopic evidence indicate that the 3.4–3.3 Ga rocks of the Favelândia complex are derived from partial melting of E-MORB sources during flat subduction. The 3.1–2.7 Ga K-granitoids in the Santa Izabel complex are derived from a mixture of crustal and mafic sources, as evidenced by the slightly negative to positive ƐNd(T) and Sr/Sri between 0.700 and 0.706. The 3.1–2.7 Ga event is responsible for the recycling of the Paleoarchean TTG crust, generation of low- to high-K evolved crust, and juxtaposition of the Favelândia and Santa Izabel complexes. The youngest magmatic event at ca. 2.1 Ga produced felsic plutons, derived from anatexis of Archean felsic rocks and mantle components. The collisional process tectonically juxtaposed the Riacho de Santana greenstone belt and Archean felsic rocks at 2.1–2.0 Ga, determining the region’s current configuration. Based on the data reported in this study and previously published data, we suggest that the Guanambi-Correntina block was formed as an independent unit in the northern SFC.

Mesoarchean to Paleoproterozoic crustal evolution of the Taihua Complex in the southern North China Craton

The Taihua Complex is exposed mostly in the central-western part along the southern margin of the North China Craton (NCC). In this study, field geological, geochemical, LA-ICP-MS zircon U-Pb age dating and Lu-Hf isotopic analysis are applied to the orthorgneisses, felsic leucosomes, and granites of the Taihua Complex, in order to provide constraints on its crustal evolution from the Mesoarchean to Paleoproterozoic (ca. 2.9–1.8 Ga). The ca. 2.90–2.73 Ga magmatism was an important episode of contemporaneous crustal growth and crustal reworking. Among them, the ca. 2.90 Ga granodioritic enclaves have features similar to those of the Archean sanukitoids, and were generated by the direct partial melting of peridotitic mantle wedge in the subduction processes, representing the early continental nucleus. The ca. 2.84 Ga high Mg# TTGs were derived from the partial melting of subducted oceanic crust after interaction with mantle wedge, whereas the ca. 2.82–2.77 Ga low Mg# TTGs were originated from the partial melting of underplated basaltic crust, pointing to a series of continuous arc magmatic activities. The formation of the ca. 2.75–2.73 Ga crust-derived granites and felsic leucosomes in association with the contemporaneous metamorphism indicate the presence of a crustal anatexis, which probably was the result of an important magmatic underplating event. The magmatism between 2.9 Ga and 2.73 Ga indicates that the increased crust-mantle interaction and crustal differentiation stimulated the crust in the Taihua Complex to become more matural. The ca. 2.57–2.43 Ga magmatism represents another prominent magmatism in the Taihua Complex. The TTG gneisses and dioritic gneisses aged at ca. 2.57–2.50 Ga were derived from partial melting of the hydrated basalts under eclogite to garnet amphibolite facies conditions with interaction between initial melts and mantle wedge, indicating that incessant subduction led to the amalgamation of micro-blocks. The intrusion of granitic rocks, felsic leucosomes, TTG-like gneisses accompanied by metamorphism during ca. 2.50–2.43 Ga indicate that a dominant crustal anatexis event occurred in association with the cratonic stabilization processes. The ca. 2.36–2.24 Ga magmatism was also characterized by reworking of the basement rocks, which are represented by the intrusion of calc-alkaline monzogneisses, A-type granitic gneisses and mafic dykes. This scenario was coeval with the formation of volcanic-sedimentary sequences, indicating the presence of an extension event in the Taihua Complex. The ca. 1.96–1.85 Ga tectono-thermal event represented the last phase of compressional deformation and consequent metamorphism, leading to reworking of the pre-existed basement rocks. This event formed a WNW-ESE trending metamorphic belt that extends over 1000 km along the southern margin of the NCC and was well concordant with the world-wide orogeny associated with the amalgamation of Nuna supercontinent. Subsequently, widespread A-type granites, mafic dykes and volcanic rocks aged of ca. 1.84–1.74 Ga formed, marking the final consolidation of the crystalline basement at the Taihua Complex. Since then, the southern NCC became stable and entered into the stage of development of platform.