Early Paleoproterozoic Research Articles

Polymetamorphic evolution of the Vestfold Block in East Antarctica and implications for the amalgamation of terranes

The Vestfold Block, a typical polymetamorphic Archean terrane in East Antarctica, is a key area to understand amalgamations of Rodinia and East Gondwana continents. However, multiphase overprinting makes it difficult to determine the timing and nature of each tectonothermal event. In this study, we present P–T estimates, zircon, monazite U(–Th)–Pb and biotite/K–feldspar Rb–Sr isochron ages of paragneisses from the SE Vestfold Block. One paragneiss sample, which is assigned to the Chelnok Paragneiss, has experienced a protracted metamorphism from the Neoarchean to the early Paleoproterozoic. Phase equilibria modeling constrained the peak P–T conditions to 7.2–9.6 kbar and 850–880 ℃, and the post–peak metamorphism to 4.2–5.6 kbar and 720–790 ℃, respectively. On the other hand, a paragneiss sample close to the ice sheet documented a high–grade metamorphic event at 918 ± 23 Ma, with peak P–T conditions of 6.0–8.0 kbar and 860–880 ℃. Biotite/K–feldspar Rb–Sr dating for these two samples yields isochron ages of 474 ± 12 and 442 ± 7 Ma, respectively, representing the cooling ages of the Pan–African reworking. Collectively, an integrated application of diverse chronometers, combined with published data, indicates that the Vestfold Block may have experienced at least three major thermal events with variable intensities and extents. Initially, the supracrustal rocks in this region pervasively underwent a protracted high–grade thermal event from the Neoarchean to the early Paleoproterozoic, which formed the backbone of the block. Thereafter, the southern Vestfold Block experienced a Grenvillian granulite facies metamorphism, indicating that the Vestfold Block has been locally involved in the Rayner orogeny (i.e. the late Mesoproterozoic/early Neoproterozoic collision between the Indian craton and East Antarctica). Ultimately, the whole Vestfold Block may have been reworked under relatively low temperatures during the Pan–African Prydz tectonic event.

Earliest Paleoproterozoic arc magmatism in the western Yangtze Block, South China and its geological implications

The Archean – Early Paleoproterozoic tectono-magmatic history of the Yangtze Block is inadequately constrained owing to the scarcity of coeval magmatic outcrops. Herein, we report on the Earliest Paleoproterozoic (2498 ± 17 Ma) meta-diabase dike in the Bajiaojing area of the western Yangtze Block, which may represent the oldest known mafic magmatism in the block. Whole-rock geochemical and mineral chemical proxies (e.g., U/Nb, Sc/Yb, and La/Yb) demonstrated that the Bajiaojing meta-diabase was likely emplaced in a continental arc setting. Positive zircon εHf(t) values (> 8) and incompatible elemental ratios (e.g., Gd/Yb, Sm/Yb, and Lu/Hf) further indicated that the mafic dike was derived from a depleted asthenospheric mantle source, which was modified by fluid and sediment from the subducting slab. The subduction-related modification also accounted for the compositional heterogeneity in the mantle source, which was observed in the wide range of Zr/Nb (1.05–4.38), Ce/Pb (6.11–81.59), and Nb/U (7.96–78.72) values. By combining the Precambrian evolutionary history of the Yangtze Block, we determined that an essential magmatic episode occurred in the Earliest Paleoproterozoic that was likely linked to crustal growth in the block. Therefore, the 2.5 Ga magmatism represented by the Bajiaojing meta-diabase was a potential provenance for the synchronous detrital zircons from Precambrian basement rocks.

Tracing the crustal evolution of the Precambrian Southern Granulite terrane in East Gondwana: New insights from zircon U-Pb/Hf geochronology

The Precambrian Southern Granulite terrane of south India has a crustal evolution history broadly bracketed between the late Archean and Cambrian with records of polyphase deformation, metamorphism, and magmatism. The Southern Granulite terrane comprises distinct crustal blocks bounded by shear/suture zones that have been variably correlated with supercontinent fragments including Madagascar, Sri Lanka, Africa, Eastern Ghats, and Antarctica. However, the timing and mechanism of assembly of different crustal blocks within the Southern Granulite terrane and its linkages with counterparts in East Gondwana are highly debated. This study aimed to unravel the complex crustal evolutionary pattern of the terrane by generating robust zircon U-Pb/Hf isotopic data from basement charnockites, gneisses, granitoids, and alkaline intrusive units from the central part of Southern Granulite terrane and comparing these results with similar data from different East Gondwanan terranes. The study identified four distinct crustal growth episodes in the Madurai block: (1) Neoarchean−early Paleoproterozoic, (2) Rhyacian−Orosirian, (3) late Tonian, and (4) Ediacaran−Cambrian. Analysis of zircon Hf isotope data revealed that the first two events are marked by juvenile magmatic signatures, whereas the latter two are distinctly associated with intense reworking and remelting of older crust with no significant juvenile input. Our new results combined with existing data from other Gondwanan terranes suggest a common Paleoproterozoic ancestry for the Southern Granulite terrane and its corresponding Gondwanan fragments, proposing a revision to the existing geodynamic models.

Petrogenesis of the Early Paleoproterozoic Felsic Metavolcanic Rocks from the Liaodong Peninsula, NE China: Implications for the Tectonic Evolution of the Jiao-Liao-Ji Belt, North China Craton

The early Paleoproterozoic (ca. 2.2–2.1 Ga) tectonic evolution of the Jiao–Liao–Ji belt (JLJB) is a continuous hot topic and remains highly controversial. Two main tectonic regimes have been proposed for the JLJB, namely arc-related setting and intra-continental rift. Abundant ca. 2.2–2.1 Ga volcanic rocks were formed in the JLJB, especially in the Liaodong Peninsula. These ca. 2.2–2.1 Ga volcanic rocks therefore could host critical information for the evolution of the JLJB. In this study, we report a suit of ca. 2.2–2.1 Ga felsic metavolcanic rocks in the Liaodong Peninsula of the JLJB to provide new insights into the above issue. Zircon U-Pb dating reveals that the felsic metavolcanic rocks were erupted at 2185–2167 Ma. They have variable εHf(t) values (−0.70 to +9.69), high SiO2 (66.30–75.30 wt.%) and relatively low TiO2 (0.03–0.78 wt.%), tFe2O3 (0.55–5.03 wt.%), MgO (0.17–8.76 wt.%), Cr (9.16–67.30 ppm), Co (2.01–7.00 ppm) and Ni (3.90–25.70 ppm) contents with enrichments in light rare earth element (REE) and large ion lithophile element (LILE), and depletions in heavy REE and high field strength element (HFSE). Geochemical and isotopic results indicate that the felsic metavolcanic rocks were sourced from partial melting of ancient Archean TTG rocks and juvenile lower crustal materials. Combined with coeval A-type granites, bimodal volcanic rocks and the absence of typical arc magmatism, the most likely tectonic regime at ca. 2.2–2.1 Ga for the JLJB is an intra-continental rift.

Isotopic Constraints on the Nature of Primary Precipitates in Archean–Early Paleoproterozoic Iron Formations from Determinations of the Iron Phonon Density of States of Greenalite and 2L- and 6L-Ferrihydrite

Iron formations (IFs) are chemical sedimentary rocks that were widely deposited before the Great Oxidation Event (GOE) around 2.4–2.2 Ga. It is generally thought that IFs precipitated as hydrated Fe3+ oxides (HFOs) such as ferrihydrite following surface oxidation of Fe2+-rich, anoxic deep waters. This model often implicates biological oxidation and underpins reconstructions of marine nutrient concentrations. However, nanoscale petrography indicates that an Fe2+ silicate, greenalite, is a common primary mineral in well-preserved IFs, motivating an alternative depositional model of anoxic ferrous silicate precipitation. It is unclear, however, if Fe2+-rich silicates can produce the Fe isotopic variations in IFs that are well explained by Fe2+ oxidation. To address this question, we constrain the equilibrium Fe isotopic (56Fe/54Fe) fractionation of greenalite and ferrihydrite by determining the iron phonon densities of states for those minerals. We use ab initio density functional theory (DFT + U) calculations and nuclear resonant inelastic X-ray scattering spectroscopy to show that ferrous greenalite should be isotopically lighter than ferrihydrite by ∼1–1.2‰ at equilibrium, and fractionation should scale linearly with increasing Fe3+ content in greenalite. By anchoring ferrihydrite–greenalite mineral pair fractionations to published experimental Fe isotopic fractionations between HFOs and aqueous Fe2+, we show that ferrous greenalite may produce all but the heaviest pre-GOE Fe isotopic compositions and mixed valence greenalites can produce the entire record. Our results suggest that heavy Fe isotope enrichments alone are not diagnostic of primary IF mineralogies, and ferrihydrite and partially oxidized or even purely ferrous greenalite are all viable primary IF mineralogies.

Early Paleoproterozoic tectonic evolution of the Yinshan Block in the North China Craton: Constraints from the geochronology and geochemistry of basic to felsic magmatic rocks in the Guyang area

The earliest Paleoproterozoic magmatic rocks have recorded the transition from the Neoarchean cratonization of the NCC to its post-Archean tectonic evolution, which will provide insight into the onset of the modern-style subduction. This study focuses on the early Paleoproterozoic granodiorite, monzonitic diorite, alkali feldspar granite and gabbro in the Guyang area to decipher the early Paleoproterozoic tectonic evolution of the Yinshan Block. Zircon U–Pb dating indicates that these rocks were emplaced at ca 2.46 – 2.41 Ga. The ∼ 2.46 Ga granodiorite samples have high Sr contents, low Y and Yb contents with high Sr/Y ratios, similar to the characteristics of adakitic rocks. Based on their high Mg# values, Na2O/K2O ratios, Cr, Co and Ni concentrations, and positive εNd(t) values, we propose that the granodiorite was likely produced by partial melting of subducting oceanic slab. The contemporary monzonitic diorite samples are characterized by high Nb concentration, which are similar to those of Nb-enriched basalt/andesite. The monzonitic diorite samples are characterized by LREE-enriched patterns with negative Eu anomalies and have negative εNd(t) values (-0.4 – −1.4), which suggest that they were derived from partial melting of fertile mantle peridotite metasomatized by adakitic melts. The ∼ 2.44 Ga alkali feldspar granite samples have negative εNd(t) values (-4.0 – −1.9) and show geochemical characteristics of A-type granites, indicating an extension background. The distinct geochemical characteristics of ca. 2.46 – 2.44 Ga Guyang adakatic granodiorite, Nb-enriched monzonic diorite and A-type alkali feldspar granite suggest that a slab window was opened in the southern margin of the Yinshan Block. The gabbros were emplaced at ∼ 2.41 Ga revealed by U-Pb dating. The enriched LREEs and relatively flat HREEs patterns with negative Nb-Ta anomalies of gabbros indicate a subducting tectonic setting. Their high Ba/Th and low Nb/Y ratios imply that the mantle source was metasomatized by slab-derived fluids. This special rock association not only constrains the tectonic evolution in the southern margin of the Yinshan Block, but also indicates modern-style subduction operated already in the early Paleoproterozoic.

Petrogenesis of the ca. 2.5 Ga dioritic-TTG and granitic gneisses from the Huai'an Complex and its implications for crustal evolution and tectonic settings of the North China Craton

The diversity and petrogenesis of Archean granitoid rocks, including tonalite-trondhjemite-granodiorite suites (TTGs), sanukitoids, and K-rich granites, is essential to understanding the geodynamic process of crust-mantle interaction and the origin and evolution of the continental crust. In this study, we investigate the petrogenesis, geochronology, and Sr-Nd-Hf isotopes of Neoarchean granitoids from the Huai'an Complex in the North China Craton (NCC) to gain insight into the crustal evolution during the Late Neoarchean–Early Paleoproterozoic. Five groups of plutonic gneisses of dioritic-tonalitic-trondhjemitic (DTT) and granitic gneisses in the Huai'an Complex are distinguished by their compositions. LA-ICP-MS zircon U-Pb dating constrains their emplacement ages from ca. 2.53 to 2.47 Ga and metamorphic ages at ca. 2.46 Ga and 1.86–1.82 Ga. The ca. 2.5 Ga DTT gneisses have consistent Sr-Nd-Hf isotopic compositions with positive whole-rock ɛNd(t) (+1.0 to +5.1), zircon εHf(t) (0.0 to +6.2) values, and older two-stage Hf model ages of 2.7–3.0 Ga, indicating they are cogenetic and derived from the partial melting of preexisting mafic crust. The dioritic gneisses with elevated MgO (3.09–4.94 wt%) and compatible element compositions (e.g., Cr and Ni) originated from a mafic crustal source modified by mantle-derived melts. The high Sr/Y values (104–661) and positive Eu anomalies (Eu/Eu⁎ = 1.05–2.76) of trondjemitic gneisses are controlled by plagioclase accumulation. The granitic gneisses are slightly peraluminous with high K2O (5.00–6.29 wt%) and low FeOT and MgO contents, indicating they were formed from the remelting of preexisting tonalitic crusts. The DTT and granitic plutonic gneisses in the Huai'an Complex were likely derived from crust-mantle interaction and crustal reworking in a subduction-related arc setting. The diverse geochemistry of these ca. 2.5 Ga granitoids is significantly controlled by source compositions, magmatic mixture, and accumulation. The prominent ca. 2.5 Ga TTG and granitic magmatism in the NCC likely represent a dominated internal reworking of the continental arc crust with subordinate crustal growth involving a subduction environment.

Modern-style subduction during the late Neoarchean to early Paleoproterozoic? Geochemical evidence from ca. 2.45 Ga arc-type magmatism in the Feidong Complex, northeastern Yangtze Craton, South China

The late Neoarchean to early Paleoproterozoic tectonic evolution of the Yangtze Craton remains poorly constrained as a result of the poor exposure of contemporaneous basement rocks. This study presents new zircon U–Pb–Hf isotopic data and whole–rock geochemical and Sr–Nd isotopic data for orthogneisses from the Feidong Complex of the northeastern Yangtze Craton. Two orthogneiss samples yielded weighted mean ages of 2416 ± 21 and 2436 ± 21 Ma, respectively, indicating the timing of protolith formation. These samples contain relatively high concentrations of SiO2 (54.04–63.25 wt%), but low concentrations of Na2O (3.29–4.12 wt%) and K2O (1.87–2.84 wt%), indicating they are calc–alkaline intermediate rocks. They are enriched in the light ion lithophile elements (LILE) and the light rare earth elements (LREE) but are depleted in Nb–Ta, Ti, the heavy REE (HREE), and Y. They also plot within the arc affinity fields of (La/Yb)N vs. (Yb)N and Sr/Y vs. Y diagrams, consistent with their relatively high Th/Yb and Ta/Yb and low Ce/Pb and Nb/U values, all of which are indicative of rocks formed by arc–type magmatism. The two orthogneiss samples have zircon εHf(t) values that vary between –6.83 and +2.54 with two–stage model ages (TDM2) of 3.35–2.79 (peak at 3.2 Ga) and with similar Nd isotopic compositions. The high total REE contents and Nb–Ta depletions within the orthogneiss samples may reflect derivation from magmas sourced from regions containing fluids released from a subducting slab. These data indicate that the calc–alkaline protoliths of these orthogneisses formed from magmas generated by the partial melting of mantle wedge material driven by the addition of fluid released from a subducted slab. This process induced the partial melting of ca. 3.2 Ga lower crustal material in a manner similar to that associated with modern arc–type magmatism. Taken collectively, the regional magmatism recorded by the ca. 2.50–2.47 Ga tonalite–trondhjemite–granodiorite (TTG) gneisses of the Douling Complex, the ca. 2.45 Ga calc–alkaline arc-type magmatic rocks in the Feidong Complex, and contemporaneous metamorphism within the north margin of Yangtze Craton all provide evidence that modern–style subduction occurred within the northeastern Yangtze Craton between the late Neoarchean and the early Paleoproterozoic.

Petrogenesis of the ca. 2.32 Ga low-δ18O gabbroic diorites and granites in the Xiaoshan area, southern North China Craton: Implications for the early Paleoproterozoic tectonic evolution

The database of global zircon ages shows a marked age gap at 2.45–2.2 Ga, which was postulated associated with the global magmatic and plate tectonic “shutdown” or “slowdown”. But in recent years, a great deal of ∼ 2.3 Ga magmatism has been identified in the North China Craton (NCC). Nevertheless, tectonic evolutionary scenario of the NCC during early Paleoproterozoic is still in hot debate. This study focuses on the gabbroic diorites and biotite granites in the Xiaoshan area, southern margin of the NCC. They were emplaced at ∼ 2.32 Ga. The gabbroic diorites have low SiO2, high Mg#, Cr, Ni values, and characterized by LREE-enriched, HREE-depleted trends, slightly positive Eu anomalies with pronounced negative Nb-Ta anomalies. Meanwhile, the samples have low-δ18O value of 2.05–5.35 ‰, they show negative zircon εHf (t) (−5.8 to − 4.1) and whole-rock εNd (t) (−2.36 to − 1.77) values, with TDM1 ages of 2.81–2.88 Ga and 2.80–2.86 Ga respectively, and crustal assimilation was limited during magma ascent, indicating a lithospheric mantle (CLM) source, which has been refertilized by metasomatic processes. The biotite granites have low 10000 Ga/Al ratios, Zr, Zr + Nb + Ce + Y concentrations, and calculated zircon saturation temperature (697–776 °C), belonging to metaluminous I-type granite. Their highly fractionated REE patterns, high Sr/Y and La/Yb ratios, low Dy/Yb and Gd/Yb ratios indicating that they were derived from partial melting of a lower crust source with both garnet and amphibole in the residue. Besides, they have δ18O values ranging from 2.41 ‰ to 5.11 ‰, variable zircon εHf (t) (−1.1 to + 1.4) and whole-rock εNd (t) (−0.76 to + 0.29) values, implying they were formed mainly by reworking of the pre-existing ancient crust, which was probably triggered by underplated mantle-derived mafic magmas. In combination with previous studies on the great diversity 2.45–2.2 Ga mafic-felsic rock assemblages and their geochemical features, we prefer that the extensional tectonic regime, which can result in thermal anomaly to account for the lithospheric mantle and crustal melting, is reasonable in the early Paleoproterozoic Era, at least for the southern NCC.

A refined Archean-Paleoproterozoic magmatic framework of the Cuoke Complex, SW China, and its implications for early Precambrian evolution of the Yangtze Block

New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent.

ISOTOPE-GEOCHEMISTRY EVIDENCE FOR GLOBAL CHANGES IN THE HYDROSPHERE COMPOSITION IN PALEOPROTEROZOIC OF SARMATIA

In the carbonate rocks of the Kursk block of Sarmatia, evidence of global perturbations in the atmosphere and hydrosphere of the Earth has been recorded. Dolomites of the Rogovskaya Formation accumulated on the passive continental margin and are characterized by a chondrite Y/Ho ratio, the absence of Ce* anomalies, and δ 13 C and δ 18 O values typical of Neoarchean and Early Paleoproterozoic marine carbonates. Therefore, their accumulation took place before the GOE . Limestones of the Tim Formation are contrastingly distinguished by negative Ce* anomalies, superchondrite Y/Ho ratio, and anomalously high values of δ 13 C = 10.4 to 12.1 ‰ V-PDB. It follows from this that carbonates of the Tim Formation were formed after the GOE during the Yatuli-Lomagundi event. Their Pb-Pb age of 2233 ± 8 Ma is close to its lower boundary.

Chronological framework of Precambrian Dantazi Complex: Implications for the formation and evolution of the northern North China Craton

The Dantazi Complex in the North Hebei Terrane is located in the middle segment of the northern North China Craton, and plays a crucial role for understanding the early Precambrian crustal evolution of the craton. The Dantazi Complex is composed mainly of late Neoarchean tonalites-trondhjemites-granodiorites, potassic granites, sanukitoid granodiorites-monzodiorites and quartz syenites, which were emplaced by Paleoproterozoic gabbroic stocks. SHRIMP and LA–ICP–MS zircon dating analyses have revealed that the Neoarchean diversified granitoids of the Dantazi Complex were formed in ∼2.52–2.47 Ga, and preserved ∼2.60–2.53 Ga inherited/captured zircon ages. All these rocks experienced early metamorphism and deformation at ∼2.40 Ga, later granulite facies metamorphism at ∼1.80 Ga, and alterations at ∼1.73 Ga. Whole-rock chemical characteristics and Sm–Nd–Lu–Hf isotopes indicate that (1) The ∼2.52 Ga tonalites-trondhjemites-granodiorites were derived from partial melting of juvenile mafic crust; (2) the ∼2.51 Ga sanukitoid monzodiorite-granodiorite series came from slab-mantle interaction with different melt/rock ratios; (3) The ∼2.50–2.47 Ga potassic granites were generated by intracrustal recycling of metagreywacks that sourced from the mixture between juvenile and ancient crustal materials; and (4) The ∼2.50 Ga quartz syenites were originated from fractional crystallization of mantle-derived magmas. These petrogenetic processes reveal that the subduction-related crust-mantle interaction is the key reason for the diversity of late Neoarchean granitoids in the Dantazi Complex. Regional comparison indicates that the Precambrian North Hebei Terrane show distinct structure in the chronology and lithological assemblages from other basement terranes in the trans-North China Orogen and Western Block, implying that they were formed in different crust-mantle dynamic systems. Therefore, the Precambrian North Hebei Terrane was probably an independent micro-continental block at least until the early Paleoproterozoic. In the Archean crystalline basement range of the North Hebei–West Liaoning–East Hebei, from NW to SE, the magmatic crystallization ages gradually became older, and the granitoid assemblages transformed from sodium-rich to potassium-rich, the spatio-temporal evolution of chemical composition and lithological assemblages further indicates that the North Hebei Terrane was most likely developed in an arc environment with continuous retreat subduction caused by the slab roll-back.

Whole-rock geochemistry and zircon O-Hf isotope compositions of ca. 2.35 Ga strongly peraluminous granites: Implications for increase in zircon δ18O values during the Paleoproterozoic

Zircon oxygen isotope ratios have been used to trace the incorporation of sedimentary rocks into magmas. The dramatic increase in maximum zircon δ18O values in the Paleoproterozoic observed in global databases coincides with changes in surface environments (e.g., the rise of subaerial and oxidative weathering), implying a connection between elevated zircon δ18O and these changes. Zircon δ18O between 2.5 and 2.2 Ga, however, is relatively under-constrained owing to limited available data in this age range. To augment data from this critical time period and understand potential causes for the elevated zircon δ18O values, we report U-Pb zircon ages and δ18O values of zircon, as well as, whole-rock major and trace element geochemistry of Paleoproterozoic strongly peraluminous granites (SPGs) from the southwestern margin of the Yangtze Block (China). Our geochronological data demonstrate that these SPGs crystallized at ∼2.35 Ga and that inherited zircon with ages of 2428–2721 Ma are present in these granites, indicating the source rocks of these granites were deposited, subsequently metamorphosed, and partially melted between 2.43 and 2.35 Ga. Synmagmatic zircon from samples dated in this study have εHf(t) values of −6.4 to −0.9 and high δ18O values of 7.6–9.9‰, elevated above the maximum value observed in Archean zircon (∼7‰). These granites can be divided into two groups based on whole-rock geochemistry. Both Group 1 and Group 2 granites were derived from a similar high δ18O, metapelitic source, but were generated by dehydration melting and hydrous melting, respectively. Our results demonstrate that the fine-grained sedimentary rocks from which the SPGs were derived had relatively high δ18O (as compared to older sedimentary rocks) by 2.43–2.35 Ga. The depositional time interval of the high-δ18O sedimentary sources for SPGs studied here coincides with the emergence of continental crust above sea level and the Great Oxidation Event. Supporting the findings of previous studies, the contemporaneity of our dataset with these changes in Earth’s surface environments suggests that subaerial and potentially oxidative weathering contributed (at least partially) to the elevation of δ18O of fine-grained sedimentary rocks. Recycling of these high-δ18O sedimentary rocks into magmas contributed to the dramatic change in δ18O of magmatic zircon in the earliest Paleoproterozoic. In addition, although this study is focused on a single locality, our results suggest that the abrupt shift observed in global zircon δ18O data sets likely occurred by 2.35 Ga. Last, a literature compilation of zircon δ18O data from SPGs suggested that zircon δ18O values may have also experienced a stepwise increase in the Neoproterozoic to Phanerozoic from 12 to 14‰. The coincidence of these increases in zircon δ18O values with global oxygenation events suggests that atmospheric oxygenation may have contributed to the increase in δ18O of sedimentary rocks.

U-Pb dating reveals multiple Paleoproterozoic orogenic events (Hamersley orogenic cycle) along the southern Pilbara margin (Australia) spanning the onset of atmospheric oxygenation

Abstract The early Paleoproterozoic was a time of unprecedented change in Earth's climate and surface environment. The key to resolving some of the controversies surrounding the timing and causes of these changes lies with supracrustal sequences, such as the 2.45–2.22 Ga Turee Creek Group in the southern Pilbara craton, northwestern Australia. The group preserves a predominantly siliciclastic sequence; however, its precise age, tectonic setting, and postdepositional history are disputed. Although it is interpreted to have been deposited in a foreland basin setting shortly after 2.45 Ga, the oldest well-recognized deformational event, marked by northward folding and thrusting, is the 2.20–2.15 Ga Ophthalmia orogeny. Evidence for a pre-Ophthalmia fabric-forming tectonic event north of the Archean Sylvania Inlier, southeast Pilbara craton, which is marked by tight to isoclinal folding, has been largely overlooked. In this area, we report in situ U-Pb geochronology of authigenic monazite and xenotime in shale with a well-developed tectonic cleavage from the ca. 2.63 Ga Jeerinah Formation. Monazite porphyroblasts, which are locally wrapped by strain fringes aligned in a tectonic cleavage, yielded weighted mean 207Pb/206Pb ages at 2370 ± 11 Ma and 2312 ± 8 Ma, whereas xenotime, which overprints a crenulation cleavage, gave a weighted mean 207Pb/206Pb age of 2291 ± 11 Ma, constraining fabric development to between 2.31 Ga and 2.29 Ga. Our results confirm the existence of a pre-Ophthalmia deformational event in the southeastern Pilbara craton, herein referred to as the Sylvania orogeny, which is part of an ~300 m.y. interval (2.45–2.15 Ga) of northward-directed compression (“Hamersley orogenic cycle”). This orogenic cycle is marked by east-west and northwest-southeast folding, cleavage development, veining, hydrothermal gold mineralization, and isotopic resetting across the southern Pilbara craton. Our results indicate that the syn–Great Oxidation Event Turee Creek Group was deposited in one or more foreland basins after 2.45 Ga. Our results provide a new tectonostratigraphic and geodynamic framework for understanding the timing and origin of geochemical records in a key succession deposited during an interval of global environmental change.

Geological history and supercontinent cycles of the Arctic

AbstractThe geological history of the Arctic is constrained within the framework of the assembly and breakup of three supercontinents. The first of these was preceded by the crystallization of the oldest dated rocks on Earth and consolidation of the Arctic region’s Archean cratons between 2.82 and 2.54 Ga. Following the emplacement of regional mafic dike swarms between 2.51 and 2.03 Ga, the cratons were amalgamated into the Nuna (Columbia) supercontinent between 2.0 and 1.6 Ga, and the distribution of low-thermalgradient eclogite (indicative of continental subduction) and ophiolite (indicative of obduction of oceanic crust onto a continental margin) suggests that diagnostic plate-tectonic processes were well in place by the early Paleoproterozoic. Basin formation, flood basalts, and dike swarms are features of the partial(?) breakup of Nuna (Columbia) by 1.5–1.27 Ga. The extent to which specific dike swarms led to continental breakup and a rift-to-drift transition remains unclear. Assembly of the second supercontinent (Rodinia, 1.4–0.9 Ga) is recorded by a network of Grenvillian and Sveconorwegian collisional orogenic belts. Prominent features of Rodinia breakup (780–615 Ma) in the Arctic are extensive dike swarms and regional-scale glacial-periglacial deposits associated with the Sturtian (717–661 Ma) and Marinoan (ca. 645 ± 6 to ca. 635 Ma) snowball Earth glaciations. Assembly of the third supercontinent, Pangea, between 600 Ma and ca. 250 Ma, was accomplished through stitching of four orogens in the Arctic (Timan-Varanger, Caledonian, Ellesmerian, and Urals-Taymyr). Pangea breakup (rifting since 250 Ma and oceanic spreading since the Cretaceous) led to the emplacement of Cretaceous and Paleogene flood basalts, new oceanic crust in the Labrador Sea, North Atlantic Ocean, and Arctic Ocean, and orogens characterized by relatively small but far-traveled accreted terranes with provenance in Laurentia, Baltica, and Siberia. Paleogeographic similarities and geological correlations among Laurentia, Baltica, Siberia, and the North China craton suggest that Rodinia formed following incomplete breakup of Nuna (Columbia) and/or by introversion, whereas unique paleogeographic traits for Pangea within the Arctic region point to supercontinent formation by extroversion.

Late Paleoproterozoic magmatism in North Hengshan: Final collapse of the Trans-North China Orogen

Post-collisional magmatism carries important information for understanding when and how an ancient continental collisional orogen unrooted and collapsed. However, the post-collisional magmatic response to the final collapse of the Trans-North China Orogen, one of the 2.1–1.8 Ga collisional orogens that formed in coincidence with the assembly of the Paleo–Mesoproterozoic Columbia supercontinent, remains controversial. Here we present the results of a combined geochronological and geochemical investigation on a suite of Late Paleoproterozoic potassic granites in the North Hengshan terrane of the Trans-North China Orogen, the North China Craton. In situ zircon U-Pb dating shows that these potassic granites, as the last phase of Precambrian magmatism in this terrane, were emplaced between 1790 Ma and 1774 Ma. Their enriched bulk-rock Nd and zircon Hf isotopic compositions point to an ancient crustal source, and their zircon O isotopic variation indicates the involvement of weathered supracrustal rocks in their sources. Considering their bulk-rock major and trace elements, the Late Paleoproterozoic potassic granites in North Hengshan are best explained to be produced by melting of immature metagraywacke that belonged to the Neoarchean–Early Paleoproterozoic sedimentary sequences, at middle–lower crustal depths. The 1.79–1.77 Ga potassic granites in North Hengshan postdated the main phase of the Late Paleoproterozoic collisional orogeny, and were a magmatic response to the final collapse of the Trans-North China Orogen. These 1.79–1.77 Ga potassic granites, along with other 1.80–1.75 Ga magmatism in the Trans-North China Orogen, were most likely generated in a post-collision extensional setting, possibly superimposed by an Andean-type continental arc at its southern margin. The 1.80–1.75 Ga magmatism marked the end of collision between the Western and Eastern Blocks that gave rise to the final consolidation of the North China Craton and the assembly of the Columbia supercontinent, and recorded the outgrowth of this supercontinent through accretion at its continental margins.

Geochemistry, Zircon U-Pb Dating and Sr-Nd-Hf Isotopes of Dioritic-Tonalitic-Trondhjemitic and Granitic Gneisses from the Huai'An Complex, North China Craton: Implications for the Late Neoarchean–Early Paleoproterozoic Crustal Reworking

Geochemistry, Zircon U-Pb Dating and Sr-Nd-Hf Isotopes of Dioritic-Tonalitic-Trondhjemitic and Granitic Gneisses from the Huai'An Complex, North China Craton: Implications for the Late Neoarchean–Early Paleoproterozoic Crustal Reworking

Archean-Proterozoic unconformity on the Fennoscandian Shield: Geochemistry and Sr, C and O isotope composition of Paleoproterozoic carbonate-rich regolith from Segozero Lake (Russian Karelia)

Precambrian paleoweathering profiles provide insight into environmental changes and mark stratigraphic boundaries. However, the well-preserved and exposed stratigraphic boundaries, not affected by tectonics, are rare for the Precambrian. We report sedimentological, geochemical and Sr, C and O isotopic data for the Paleoproterozoic weathering profile in Chapanshary Island on Lake Segozero, Central Karelia, the eastern part of the Fennoscandian Shield. The Chapanshary Island weathering crust contains a unique carbonate caliche, rarely developed on the Archean granite-gneiss basement. The crust laterally grades into carbonate-cemented boulder conglomerate, which is overlain by sedimentary carbonate. The chemical index of alteration (CIA; 60–67) and plagioclase index of alteration (PIA; 53–82) values for the weathering crust correspond to weathered felsic/mafic substrate and to illite and K-rich composition of the regolith. The δ18O values of carbonate cement and sedimentary carbonate are highly negative (−22.3 to −17.6‰ V-PDB). The 87Sr/86Sr values of Fe- and Mn-rich carbonate of the regolith, boulder conglomerate cement and sedimentary carbonate are 0.7133 to 0.7242 and are exceptionally high for marine Paleoproterozoic carbonate. The high δ13C values (+3.9 to + 5.2‰ V-PDB) of carbonate cement and sedimentary carbonate indicate deposition during the ca. 2.22–2.06 Ga Lomagundi-Jatuli carbon isotope excursion of the early Paleoproterozoic. The Chapanshary Island weathering profile developed in a terrestrial setting with arid to semi-arid climate ca. 2.2–2.1 Ga ago under atmosphere with high CO2 content. The overlying sedimentary carbonates were deposited in a shallow-water setting (ephemeral ponds and lakes) evolved in the inner part of Fennoscandia.

Sedimentary evidence for the early Paleoproterozoic tectono-magmatic lull: Detrital zircon provenance of the 2.47–2.17 Ga Langzishan Formation, Liaohe Group, Eastern Block of the North China Craton

As one of the most ancient cratons in Asia, the North China Craton (NCC) provides an opportunity to examine the evolution of the early earth. However, it is poorly known about the tectonic setting of the Eastern Block of the NCC at 2.47–2.17 Ga. In this study, zircon U-Pb dating was conducted to constrain the provenance, depositional age, and depositional environment of the Langzishan Formation in the Liaodong peninsula, to investigate the tectonic setting of the Eastern Block during the earliest Paleoproterozoic. Provenance analysis suggests that the basal sandstones (protolith of quartzite) in the Langzishan Formation were sourced from 3.8 to 2.5 Ga continental crust, while the overlying sandstone and pelite units were sourced exclusively from 2.5 Ga continental crust. The distribution of detrital zircon ages shows that the basal sandstones of the Langzishan Formation were deposited at 2.47–2.2 Ga, during which the tectonic setting changed from an early collisional setting (2.47–2.35 Ga) to a stable continental margin (2.35–2.2 Ga), whereas pelites in the upper layer of the Langzihsan Formation were deposited at 2.2–2.17 Ga, and also experienced a transition in tectonic setting from a passive continental margin to an active continental margin. The Langzishan Formation is believed to be the lowest sedimentary unit in the Eastern Block. The transition of tectonic setting of this formation shows that the Eastern Block probably has undergone the same transition at 2.47–2.17 Ga, from a collisional setting to a passive continental margin, and then to an active continental margin, possibly related to both onset of the 2.3–2.2 Ga Paleoproterozoic tectono-magmatic lull (TML) and its cessation.

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.