Neoarchean Granitoids Research Articles

Zircon U-Pb-Hf isotopes constraints on the petrogenesis of Neoarchean granitic rocks from the Northeastern part of the Eastern Dharwar Craton, Southern India

In the present study, we integrate bulk rock chemistry and in-situ zircon U-Pb-Hf isotopes of high-K Neoarchean granitoids from the northeastern part of the Eastern Dharwar Craton (EDC) to investigate their source, petrogenesis, and plausible tectonic setting. Based on the mineral assemblage, in coherence with their geochemical characteristics, these granitoids are classified as Hornblende-biotite granite (HBG) with Microgranular enclaves (ME), Biotite granite (BTG) and Monzogranite (MG). Field observations and zircon U-Pb ages reveal coeval emplacement of these granitoids between 2.53 and 2.50 Ga. The HBG, including ME, has low silica, metaluminous affinity, and high ferromagnesian element content, consistent with their derivation from a mafic source. Some of the HBG and ME samples are strongly enriched in incompatible elements, similar to the sanukitoids. The geochemical attributes and strongly evolved zircon Hf isotopic compositions (ɛHf(t) = −4.3 to +1.8 and −7.3 to +0.2) of the HBG and ME suggest their derivation from a mantle source metasomatized by subducted sediments. The BTG and MG are compositionally similar, with high silica, low ferromagnesian element content, and moderate peraluminous affinity, suggesting the involvement of felsic crustal sources. The sub-chondritic to chondritic zircon Hf isotopic compositions (ɛHf(t) = −2.7 to +1.4 and −6.9 to +1.9) of these granitoids support the involvement of heterogeneous ancient crustal sources. While all granitoids exhibit similar zircon Hf isotopic compositions, their geochemical attributes suggest distinct sources. The HBG reflects juvenile crustal additions, whereas BTG and MG are products of the crustal reworking. We propose that these granitoids formed during the continent-continent collision between Western and Eastern Dharwar cratons, that took place after the break-off of the eastward subducting slab. The asthenospheric upwelling induced by slab break-off and/or lithospheric delamination of thickened crust led to the genesis of metasomatized mantle derived magma, which drove the crustal reworking. The observed zircon Hf isotopic composition of the EDC granitoids are similar to the present day Phanerozoic Alpine-Himalayan type orogenies supporting subduction followed by continental collision model for the stabilisation of Archean cratons. Evidence for the existence of Paleo- Mesoarchean felsic crust from this part of the EDC warrants further studies to test the three-terrane model for the Dharwar Craton.

Neoarchean granitoid magmatism and geodynamic process in the northeastern North China craton

The composition of Archean granitoid rocks changed from predominantly tonalite-trondhjemite-granodiorite (TTG) gneisses in the early Archean (4−3 Ga) to diversified granitoid rock assemblages in the late Archean (3.0−2.5 Ga), marking a crucial transformation in the geodynamic processes of early Earth. However, the reason for this major transition remains enigmatic because the petrogenetic features of different granitoid assemblages and their crust-mantle interactions during different periods are poorly understood. We use variations in the spatial-temporal distribution, lithological association, chemical composition, and petrogenesis of Neoarchean (2.7−2.5 Ga) granitoids and inferred correlative crust-mantle interactions in the Eastern Liaoning Range (ELR) of the northeastern North China craton to explore this geodynamic transition. The early Neoarchean (ca. 2.7 Ga) ELR granitoids were dominated by TTG gneisses, and the late Neoarchean (2.6−2.5 Ga) ELR granitoid typology and compositions became more complex, changing into TTGs and more K2O-rich granitoid rocks. The TTGs can be subdivided into a high-Ca group and a low-Ca group: The 2.71−2.68 Ga high-Ca group TTG magma originated from partial melting of subducted juvenile oceanic crust, and the low-Ca group TTG magma was derived from fractionation crystallization of the high-Ca group TTG magma. The chemical composition of the magmatic sources played a dominant role on the 2.60−2.50 Ga TTG magmatism: the high-Ca and low-Ca group TTG magmas came from low-K mafic rocks and tonalites, respectively. The 2.58−2.49 Ga K2O-rich granitoids can be divided into three petrogenetic series: (1) The high-Ca-Mg group K2O-rich granitoid magma originated from partial melting of high-K mafic rocks, (2) the low-Ca-Mg group K2O-rich granitoid magma was derived from partial melting of sedimentary rocks, and (3) the transition group K2O-rich granitoid magma was sourced from metagreywackes. The 2.71−2.68 Ga TTGs were generated in an island arc belt, and subducted slab melting and subsequent magmatic differentiation were the dominant mechanisms of the TTG magmatism. The 2.60−2.50 Ga diversified granitoids were formed in the oceanic-continental subduction process under the active continental margin; the complicated oceanic slab subduction and arc-arc and arc-continent collisions contributed to the diversity of late Neoarchean granitoid magmatism.

From 3.4 Ga TTG generation to 2.9 Ga crustal anatexis: The Archean crustal evolution of Porteirinha Complex (SE, Brazil)

The Porteirinha Block (PB) provides an important record of the origin and evolution of South American crust. The PB records the generation of Paleoarchean TTG, Mesoarchean anatexis, and Paleoproterozoic crustal reworking. It is exposed as a basement inlier in the Araçuaí Orogen as a result of a tectonic involvement of the continental margins of São Francisco Congo Paleocontinent (PSFC) during the collisional processes of Gondwana amalgamation at the Neoproterozoic. The PB basement unit is the Porteirinha Complex (PC), which consists of TTG orthogneisses, migmatites, amphibolites, metaultramafics rocks and Neoarchean granitoids. In this paper, we discuss the evolution of the TTG orthogneisses and migmatites from PC based on field, geochronological and whole-rock geochemistry data. Zircon U–Pb ages (LA-ICP-MS) show a complex and polycyclic evolution of these rocks. Concordant ages were obtained for crystallization of TTG magma at ca. 3.4 Ga and the geochemical signature supports the idea of TTG generation by partial melting of hydrated mafic crust under garnet-amphibolite facies conditions. Zircon U–Pb ages also suggest crustal reworking events at 3.1 Ga. Metatexite and diatexite domains related to partial melting of TTG orthogneisses are individualized. The migmatites record processes of crustal anatexis and melt generation that occurred between 2.8 and 2.9 Ga (LA-ICP-MS, U–Pb in zircon) and are linked to crustal reworking and heat generation events recognized regionally. The new data presented in this work allow us to establish correlations between Archean and Paleoproterozoic units of the PB and those that occur regionally, particularly those related to Gavião block, where a series of stages and events of early crustal evolution are shared.

Late Neoarchean plume-induced crust-mantle interaction and crustal reworking: Evidence from the Jianping Complex, North China Craton

The Archean basement of the North China Craton (NCC) is predominantly composed of 2.6–2.5 Ga lithological assemblages, while the tectonic regime that governed the formation and evolution of these Neoarchean basement rocks has been a controversial issue. Based on field relationships, petrographical features, whole-rock chemistry and zircon Hf isotope data, diverse late Neoarchean granitoids exposed in the Jianping Complex of the NCC are categorized into TTGs, sanukitoids and potassic granites. Their petrogenesis are associated with partial melting of metabasalts, melting of metasomatized mantle, and melting of crustal lithologies including tonalite and metasediments, respectively. Zircon U-Pb results suggest that different types of Neoarchean granitoids in the Jianping Complex are nearly coeval with crystallization ages of ∼ 2.54–2.52 Ga and metamorphic ages of ∼ 2.49–2.48 Ga. New Hf isotopic data reveal that these granitoids show positive εHf(t) values, with the tonalitic gneisses of εHf(t) values closer to the depleted mantle than those of granodioritic gneiss, sanukitoids and potassic granite. This result reflects potentially more enriched source for other granitoids than the tonalitic gneisses, which is linked with increasing level of crustal-mantle interaction and crustal reworking the late Neoarchean. Integrating other evidence from geochemical, structural and metamorphic studies, it is inferred that the plume activities play an important role in the emplacement of late Neoarchean granitoids in the Jianping Complex, with TTGs formed through the partial melting of juvenile crust induced by plume activity, sanukitoids produced from melting of metasomatized mantle resulted from sagduction process, and potassic granites formed by reworking of earlier crustal lithology caused by sustained underplating of mantle material. Overall, we interpreted that the late Neoarchean crustal growth and crustal-mantle interaction in the Jianping Complex can be attributed to upwelling of mantle plume and potential sagduction process in a vertical tectonic regime.

Temporal evolution of the early−late Neoarchean granitoid magmatism in the eastern North China Craton: Transition of geodynamic regime from mantle plume to continental marginal arc system

A study of tonalite−trondhjemite−granodiorite (TTG) suite and sanukitoids emplaced at different ages in the Archean can constrain the transition of early Earth’s tectonic regime, which remains a subject of debate. In this contribution, we report a systematic investigation of an early Neoarchean and late Neoarchean TTG-sanukitoid association from the eastern North China Craton based on mineralogical, petrological, and geochemical evidence. The geochemical features of the 2.7 Ga TTG rocks studied suggest that their magma was primarily generated by partial melting of garnet-amphibolite and eclogite. Moreover, they are characterized by relatively low values of MgO, Mg#, Cr, and Ni, and zircon ɛHf(t) that varies mostly with evolved signature, which suggests that the primary magma of the TTGs was generated in a setting of thickened lower crust. The 2.5 Ga high-K calc-alkaline granitoids studied show an affinity to Archean sanukitoids. Their representative major and trace elemental and isotopic features suggest that they were derived from partial melting of mantle wedge metasomatized by subducted fluids and slab- and sediment-derived melts, followed by varying degrees of mineral fractional crystallization. The eastern North China Craton may have developed a continental marginal arc system in the late Neoarchean attached to another craton in the global Kenorland supercontinent, which might have eventually resulted in its final cratonization. The distinct tectonic settings of the two types of granitoids may indicate a transition of the tectonic regime from vertical in the early Neoarchean to horizontal at the end of the late Neoarchean. Moreover, the low δ18O values found in this study as well as those in other areas of the globe suggest that they were probably related to cold climatic conditions and/or elevated latitudes or altitudes.

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.

Petrogenesis of newly identified Neoarchean granitoids in the Qingyuan of NE China: Implications on crustal growth and reworking of the North China Craton

• A new ca. 2.7–2.5 Ga granitoid suite was identified in the Qingyuan, NE China. • The 2.68 Ga TTG was derived from ancient lower crust as well as juvenile crust. • Qingyuan granitoids record two periods of crustal growth and reworking events. Discovery of ca. 2.7 Ga tonalite-trondhjemite-granodiorite (TTG) in the North China Craton (NCC) can provide the key clue to understanding the Neoarchean crustal evolution. Most recently, we mapped out ca. 2.7 Ga TTGs from the northern Qingyuan at the northeastern margin of NCC. Together with the associated ca. 2.6–2.5 Ga high-K granites and high-Mg diorites, this study provides new constraints on crustal growth and reworking during the Neoarchean. Zircon U–Pb dating indicates that the TTGs, high-K granites and high-Mg diorites were formed at ca. 2.68 Ga, ca. 2.56 Ga and ca. 2.54 Ga, respectively. All of these lithologies exhibit enrichments in large ion lithophile elements (e.g., Rb and Ba) but depletions in high field strength elements (e.g., Nb and Ta), with positive εHf(t) and εNd(t) values. The TTGs have moderate SiO 2 , low Al 2 O 3 and variable MgO contents with high Sr/Y and (La/Yb) N ratios. They were likely derived from partial melting of mafic lower crust. High SiO 2 and K 2 O but low MgO and Cr contents as well as high Sr/Y and (La/Yb) N ratios reflect an origin of recycling of ancient crustal rocks (e.g., pre-existing TTGs) for the high-K granites. The high-Mg diorites have high MgO and Cr contents but low Sr/Y and (La/Yb) N ratios, which indicate that they could be sourced from partial melting of metasomatized mantle peridotite. Combined with previous studies, the northeastern NCC experienced two major periods of ca. 2.7 Ga and ca. 2.6–2.5 Ga crustal growth and reworking events.

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.

Zircon U-Pb Dating and Metamorphism of Granitoid Gneisses and Supracrustal Rocks in Eastern Hebei, North China Craton

Granitoid gneisses dominated by tonalitic–trondhjemitic–granodioritic (TTG) compositions, with metamorphic supracrustal rocks consisting of sedimentary and volcanic rocks, are widely exposed in the Eastern Hebei terrane, North China Craton (NCC). This study presents systematic zircon U–Pb geochronological and whole-rock geochemical data of the Neoarchean granitoid gneisses and supracrustal rocks in Eastern Hebei. Zircon U–Pb isotopic dating for the representative samples reveals that magmatic precursors of granitoid gneisses were emplaced between 2524 ± 7 and 2503 ± 12 Ma, and the protoliths of the pelitic granulites were deposited in the Late Neoarchean era. Both of them have been subjected to granulite facies metamorphism during 2508 ± 10 to 2468 ± 33 Ma, coeval with the intrusion of syenogranitic pegmatite (2488 ± 5 Ma). Zircon ages of 2.45–2.01 Ga obtained from the analyzed samples were considered mixed data from 2.53–2.48 Ga and 1.9–1.8 Ga and were chronologically meaningless. Paleoproterozoic metamorphic zircon ages of 1.9–1.8 Ga were usually neglected because of hardly being obtained from TTG gneisses and supracrustal rocks. The tectonic regime during the Neoarchean era was considered to be dominated by vertical tectonism in the Eastern Hebei terrane.

Crustal maturation and cratonization in response to Neoarchean continental collision: The Suizhong granitic belt, North China Craton

The late Archean (3.0–2.5 Ga) is a pivotal period, when properties of the continental crust significantly changed and a fundamental shift of geodynamic processes took place. As the major felsic component in early Archean (> 3.0 Ga) crustal records, tonalite-trondhjemite-granodiorite (TTG) suites are compositionally different to the present-day felsic upper continental crust. But it remains unclear how and to what degree the felsic part of the continental crust evolved during the late Archean. The 250 km long Neoarchean Suizhong granitic belt in the North China Craton (NCC) is mainly composed of K-rich granitoids and compositionally distinct to the TTG-dominated early Archean upper continental crust. This belt is a natural laboratory to explore how the early Archean upper continental crust evolved in the late Archean. Combined with our new data (zircon U-Pb ages, bulk-rock geochemistry and zircon Hf isotopes), we provide an overview of the temporal and compositional features of the Neoarchean Suizhong granitic belt. Granitic magmatism in the Suizhong granitic belt mainly took place within 100 Myrs around the end of the Archean, and these rocks are primarily K-rich granitoids with minor TTGs and mafic magmatic enclaves (MMEs). The K-rich granitoids include sanukitoid-like granites and potassic granites; the former are hybrids between melts from Mesoarchean enriched mafic crust and enriched mantle, and the latter are melts from Hadean–Mesoarchean crustal lithologies. The volumetrically minor TTGs were sourced from Mesoarchean low-K mafic crust. MMEs are either cumulates or inclusions of captured enriched mantle melts. Overall, these Neoarchean granitoids are essentially intracrustal reworking products of ancient continental nuclei and are compositionally and temporally similar to syn- and post-collisional magmatism in Phanerozoic collisional orogenic belts. The Neoarchean crustal reworking process was most likely to be induced by amalgamation of micro-continents through collision. Through the collision-induced reworking, a variety of K-rich granitoids were introduced to the Neoarchean upper continental crust. As a result, layering of felsic upper and mafic lower crust was developed, and the maturity of Archean continental crust was significantly enhanced. Collisional orogenesis played a critical role in maturing the Archean continental crust and initial cratonization of the NCC during the late Archean.

Featured Neoarchean granitoid association in the central North China Craton: An indicator of warm plate subduction

Abstract Diverse Neoarchean granitoid assemblages, which generally include tonalites–trondhjemites–granodiorites (TTGs) and various K-rich granitoids, are prevalent in most basement terranes of the North China Craton. However, the Hengshan terrane is an exceptional case in the North China Craton; it is dominated by late Neoarchean sodic diorite-TTGs (DTTGs) and sanukitoids. These sanukitoids are the only high-K granitoids and show Mg-rich chemical features. The late Neoarchean DTTGs and sanukitoids were generated at ca. 2486–2537 Ma and show an intimate spatial association. The granitoid assemblages of the DTTGs and sanukitoids are characterized by high Mg# [100 × Mg/ (Mg + Fetotal)] values (43–65) and enriched in light rare earth elements, large ion lithophile elements, heterogeneous zircon Lu–Hf (εHf = −1.6 to +7.4), and whole-rock Sm–Nd (εNd = +0.9 to +4.2) isotopic components, which indicates that they may be derived from varying degrees of interactions between mantle peridotite and subduction-related materials. Combined with the relatively high apparent geothermal gradient (∼17 ± 2 °C/km) and the relatively low basal heat flow of continental crust (∼25 ± 5 mW m−2), the crustmantle interaction process indicates that the occurrence of late Neoarchean high-Mg magmatism was closely related to warm oceanic slab subduction in the Hengshan terrane, and the featured lithological association of DTTGs and sanukitoids most likely developed in the active continental margin at the end of the Archean.

Neoarchean granitoids and tectonic regime of lateral growth in northeastern North China Craton

The Archean Eastern Liaoning metamorphic basement block is located in the northeastern North China Craton (NCC), in which ∼2.9 to 3.8 Ga lithological assemblages are well developed. The region which exposed these ancient lithological assemblages is usually called as an ancient continental nucleus. Toward north from the northeastern margin of the ancient continental nucleus, ∼2.5 to 2.7 Ga lithological assemblages continuously developed, forming abundant ∼2.5 Ga tonalite- trondhjemite- granodiorite (TTG) and high-K granitoids. Some ∼2.7 Ga TTG gneisses and metamorphic calk-alkaline volcanic rocks have also been documented recently in the Eastern Liaoning to the Southern Jilin of northeastern NCC. Our geological investigations found that many big ∼2.7 Ga TTG gneiss enclaves are preserved in the ∼2.5 Ga granitoids in the northeastern NCC. The early Neoarchean (∼2.7 Ga) TTG gneisses are exposed in the Waitoushan-Baishan areas, together with many contemporaneous subduction-related metamorphic calk-alkaline volcanic rocks in the Helong area of Southern Jilin province, constituting a nearly E-W-trending ∼2.7 Ga island arc belt in the northeastern NCC. However, the ∼2.7 Ga geological record is absent within the Anshan-Benxi-Waitoushan ancient microblock (ABWN) domain, suggesting that the ∼2.7 Ga arc belt was formed far away from the ABWN domain. The petrogenesis of ∼2.52–2.59 Ga TTG and sanukitoid gneisses, integrating with contemporaneous top-to-the-NE thrusting structural features, indicate that the new oceanic crust in the Waitoushan-Weiziyu-Jiubing (WWJ) area subducted to the southwest from ∼2.53–2.60 Ga. At the Archean end, the northern Liaoning-eastern Hebei intraoceanic arc system subducted to the southeast, which led to the final amalgamation among the ABWN, WWJ and northern Liaoning areas. Subsequently (∼2.50–2.53 Ga), the subducted slab broke off and the collisions between the arc and ancient continental nucleus, as well as the arc and arc, resulted in the generation of extensive crust-derived high-K granitoids.

Zircon U-Pb-Hf isotope systematics of Limpopo Belt quartzites and igneous rocks, implications for Kaapvaal – Zimbabwe Craton accretion

There are ongoing debates about the nature and timing of Kaapvaal-Zimbabwe Craton accretion. A critical role in this discussion plays the Central Zone (CZ) of the Limpopo Belt, which represents a polymetamorphic gneiss terrane limited by the Kaapvaal Craton to the South and the Zimbabwe Craton to the North. Uncertainties mainly result from complex field relationships, the lack of age data, and the complexity of investigated zircon grains. In this study we present new results of combined U-Th-Pb and Lu-Hf isotope analyses of zircon grains from quartzite, granitoid, and metabasite samples from different areas of the CZ. These data indicate that the oldest lithologies are mafic rocks which were emplaced at 3.35–3.29 Ga from near-chondritic mantle source. They also reveal that quartzite precursors throughout the CZ were deposited during two major sedimentary cycles, with quartzite-I members between 3.36 and 2.64 Ga, and quartzite-II between 2.55 and 2.04 Ga, and that the detritus was supplied from distinct sources. Detrital zircon grains of quartzite-I were delivered from Eo- to Mesoarchean granite-gneiss terranes, affected by magmatism between 3.92 and 2.90 Ga, and characterized by hafnium model ages (TDM) between 4.40 and 3.30 Ga. In contrast, zircon grains of quartzite-II stem predominately from Neoarchean granitoids, which intruded between 2.73 and 2.62 Ga, and mostly show TDM of 2.88 ± 0.06 Ga (n = 8) or 3.09 ± 0.10 Ga (n = 4). Comparison with published age-εHft data and spatial relationships suggest quartzite-I being sourced mainly from the Zimbabwe Craton, which was connected to parts of the CZ since the Paleoarchean, and quartzite-II from granitoids of an independent Neoarchean terrane (with TDM 3.1–2.9 Ga), which was derived from the same mantle source as the crust of the adjacent Pietersburg Block (northern Kaapvaal Craton). All data in combination provide evidence that the CZ of the Limpopo Belt hosts a composite terrane that comprises relics of (1) Zimbabwe Craton-related crust, and (2) a south-to-north developing accretionary system of granite-greenstone terranes younger than 3.1 Ga, which finally collided with the Zimbabwe Craton at ca. 2.62 Ga.

Magnetic petrology of the Neoarchean granitoids in the Vila Jussara Suite, Carajás Province, Amazonian Craton

The Vila Jussara Suite (VJS) is formed by Neoarchean (~ 2.75 Ga) granites that are located in the Sapucaia Domain of the Carajás Province (CP), Amazonian Craton. Four petrographic varieties were identified in the VJS: biotite-hornblende monzogranite (BHMzG); biotite-hornblende tonalite (BHTnl); biotite monzogranite (BMzG); and hornblende-biotite granodiorite (HBGd). In terms of magnetic signature, BHMzG has two subgroups: the first subgroup has low magnetic susceptibility (MS) values (0.16 × 10-3 to 0.81 × 10-3) and more commonly contains ilmenite with titanite rims; the second subgroup shows moderate to high MS (1.91 × 10-3 to 6.02 × 10-3) and magnetite dominant over ilmenite. BHTnl has moderate MS (0.85 × 10-3 to 1.36 × 10-3) and dominance of pyrite followed by magnetite. BMzG and HBGd have comparatively high MS (3.35 × 10-3 to 19.3 × 10-3 and 2.14 × 10-3 to 25.0 × 10-3, respectively), with magnetite dominant over pyrite. The granite varieties of the VJS were formed under different oxygen fugacity (fO2) conditions, varying from reducing (< fayalite-magnetite-quartz (FMQ)) to oxidizing conditions (nickel-nickel oxide (NNO) to NNO+1). In addition, biotite-hornblende syenogranite occurs subordinately and shows high MS values and extremely high FeOt/(FeOt + MgO) ratios, both in whole-rock and amphibole and biotite. The granites of the VJS are similar to other Neoarchean granites of the Carajás province. The reduced VJS granites are akin to the ferroan granites of Planalto suite, Estrela Complex and Vila União area and the magnesian granites of VJS approach the magnesian granites of Vila União area.

Geochemical and Nd‐Hf Isotopic Constraints on the Petrogenesis of an Archean Granitoid in the Erguna Massif, NE China

AbstractCrystalline basement and Precambrian crustal growth of the continental massifs within the Central Asian Orogenic Belt (CAOB) are still pending problems. Our geological and geochemical investigations identified an Archean (2606 Ma) granitic pluton in the Biliya area of the Erguna Massif. The Neoarchean granitoids show high and positive in‐situ zircon ∊Hf(t) (+0.3 to +10.0), whole‐rock ∊Nd(t) (+4.8) and whole‐rock ∊Hf(t) values (+2.1). They are characterized by high Y + Ce + Zr + Nb (&gt; 220 ppm) and Zr contents and could be classified as A‐type granites. These granitoids are characterized by high Zr saturation temperatures (TZr) (796–836°C). They were derived from partial re‐melting of juvenile mafic lower crust in an intracontinental back‐arc extensional environment. This newly identified Neoarchean granitic pluton may represent the crystalline basement of the several continent massifs within the CAOB, and their high ∊Hf(t)–∊Nd(t) values may also indicate the occurrence of lateral crustal growth events in these massifs during the Neoarchean.

Crustal thickening and continental formation in the Neoarchean: Geochemical records by granitoids from the Taihua Complex in the North China Craton

The Earth’s lithosphere changed dramatically in many aspects during the Neoarchean era. In this period, the crust became more felsic and shows significant diversification in the composition of granitoids. Although this change has been noticed for many years, the mechanism that drove the change remains unclear. Here we report a geochemical study of Neoarchean granitoids from the Taihua Complex in the North China Craton. Zircon U-Pb dating reveals two episodes of granitoid magmatisms at ca. 2.65 Ga and ca. 2.55–2.50 Ga. Sodic TTGs at ca. 2.65 Ga are characterized by low K2O/Na2O ratios of < 0.6, high Sr/Y and (La/Yb)N ratios, positive Eu anomalies, positive zircon ɛHf(t) values of 0.9 to 5.2, and zircon δ18O values of 6.3–6.5‰, suggesting that they were derived from partial melting of the thickened oceanic crust. In contrast, K-rich granitoids at ca. 2.65 Ga have higher K2O/Na2O ratios, low Sr/Y and (La/Yb)N ratios, negative Eu anomalies, mostly positive zircon ɛHf(t) values of −0.4 to 8.0, and high zircon δ18O values of 7.0–8.4‰. The K-rich granitoids at 2.55–2.50 Ga show similarly high Sr/Y and (La/Yb)N ratios to the sodic TTGs at ca. 2.65 Ga. All these geochemical evidences suggest that these Neoarchean K-rich granitoids were derived from partial melting of the low-T seawater-hydrothermally altered oceanic basalt at different depths. Therefore, the sodic TTG and K-rich granitoids are linked to each other through both similarity and difference in their source compositions rather than magmatic processes such as partial melting and crystal fractionation. On the other hand, high-K granites at ca. 2.55–2.50 Ga are highly siliceous, have very high K2O/Na2O ratios of 4.0–7.9, and contain many relict zircons with U-Pb ages of ca. 3.49–2.68 Ga, indicating their formation by reworking of the pre-existing continental crust. Using a filtered global geochemical database, we find that the Neoarchean is the most important period for the growth of both sodic TTGs and K-rich granitoids. The Sr/Y and (La/Yb)N ratios of these granitoids also reach the maximum during this period, suggesting global-scale thickening of the oceanic crust caused by warm plate convergence. Once the orogenic lithospheric mantle was foundered for thinning, the thickened oceanic crust experienced partial melting at different depths. This gave rise to the different types of granitoid for growth of the continental crust along convergent plate boundaries. Therefore, partial melting of the thickened crust at different depths is a viable mechanism for the compositional transition of continental crust in the Neoarchean.

Magmatic epidote in Archean granitoids of the Carajás Province, Amazonian craton, and its stability during magma rise and emplacement

In the Rio Maria and Sapucaia Domains of the Carajás Province, during the Mesoarchean, tonalite-trondhjemite-granodiorite (TTG) series (2.98–2.92 Ga; Colorado Trondhjemite) and sanukitoid rocks (∼2.87 Ga; Rio Maria Suite of Ourilândia do Norte) were formed. They were followed, in the Neoarchean (2.75–2.73 Ga), by numerous stocks of granitoids similar to A-type granites (Vila Jussara Suite). Despite the compositional differences between these granitoids, epidote is a mineral phase common to all of them, with pistacite contents of 26–29 mol% in TTGs, 22–33 mol% in sanukitoids and 25–30 mol% in Neoarchean granitoids. The study of the dissolution kinetics of Archean epidotes of the Carajás Province reveals that the partial dissolution time of their crystals was ∼4–10 years, with corresponding magma ascent rates of 4–8 km/year. Magma viscosities at liquidus temperature were estimated at 105.3 Pa s for TTG magma and 102.5 Pa s for sanukitoid magma, whereas monzogranitic magmas of the Vila Jussara Suite exhibited a viscosity of 104.4 Pa s. In contrast, the viscosity of tonalitic magma of the Vila Jussara Suite was 103.5 Pa s. The preservation of magmatic epidote in Archean granitoids requires that the plutons grew in an incremental way, similar to their Phanerozoic counterparts, with the stacking of small sill-dykes of about 100 m thickness each intruded in a rather cold crust, allowing fast cooling rates so as to prevent complete dissolution of epidote at the final emplacement level.

Neoarchean Granitoids in the Western Part of the Tunguska Superterrane, Basement of the Siberian Platform: Geochronology, Petrology, and Tectonic Significance

Neoarchean Granitoids in the Western Part of the Tunguska Superterrane, Basement of the Siberian Platform: Geochronology, Petrology, and Tectonic Significance

Synchronous late Neoarchean Na- and K-rich granitoid magmatism at an active continental margin in the Eastern Liaoning Province of North China Craton

The appearance of voluminous K-rich granitoid rocks during Late Archean marks gradual maturation and stabilization of the continental crust. While most K-rich granitoid magmatism followed TTG magmatism, they occur synchronously sometimes, and this relationship is crucial for our understanding of the evolution of late Archean continental crust and its geodynamic setting.In this study, a series of ~2.57–2.52 Ga coeval and diverse granitoid rocks, including quartz dioritic-trondhjemitic and granodioritic to monzo-/syenogranitic gneisses, were identified in the southern Fushun area of Eastern Liaoning Province, North China Craton. The ~2.57 Ga quartz dioritic gneisses show moderate MgO (≤ 3.96 wt.%) and moderate to high Mg# (37.3–75.5). Geochemical modeling, together with mildly fractionated REE patterns and negative Eu anomalies and depleted zircon ƐHf(t2) (+2.1 − +7.4), suggest that they were differentiated from a depleted mantle source that was metasomatized by slab-derived fluids. The younger trondhjemitic gneisses (~2.55–2.52 Ga) are divided into two subgroups, i.e., an older subgroup (~2547–2540 Ma) characterized by mildly fractionated REE patterns and negative Eu anomalies, and a younger subgroup (~2533–2517 Ma) with strongly fractionated REE patterns and positive Eu anomalies. The trondhjemitic gneisses lack evidence for magma differentiation, and they are inferred to have been formed by reworking of amphibolites/greywackes at diverse crustal levels, with some inputs of mantle materials in the earlier subgroup. The coeval ~2550–2529 Ma granodioritic and monzo-/syenogranitic gneisses are characterized by high K2O/Na2O (0.67–2.45) but low MgO and Mg# (mostly <2 wt.% and < 50, respectively). Geochemical modeling data indicate that the granodioritic gneisses are less differentiated, which could have been derived from the partial melting of high-K mafic rocks (e.g., regional late Neoarchean calc-alkaline meta-basaltic rocks), as further supported by the constant A/CNK (1.00–1.14) and zircon ƐHf(t2) (+2.0 − +9.3) values. In comparison, the monzo-/syenogranitic gneisses show variable A/CNK (0.78–1.32) and zircon ƐHf(t2) (−2.4 − +7.8) values. They are explained to be formed by the partial melting of mixed sources of high-K mafic and sedimentary rocks, with the primary magmas showing plagioclase and apatite fractionation.Taken together, the above granitoid rocks record gradually decreasing zircon ƐHf(t2) values and increasing crustal thickness. Considering the petrogenetic information, regional geological data and the presence of some ~3.45–2.70 Ga crustal materials, the late Neoarchean granitoid magmatism of southern Fushun were likely generated via complex crust-mantle interaction processes at an active continental margin. It is further emphasized that Archean active continental margins are key sites for the initial maturation of the crust, and this tectonic scenario acted as a trigger for granitoid diversification during both the subduction and subsequent collisional stages.

Lithological and structural controls on the emplacement of a Neoarchean plutonic complex in the Carajás province, southeastern Amazonian craton (Brazil)

New geological and geochronological (Pb-Pb evaporation) data from the Vila Jussara suite, a representative of the Neoarchean granitoids of the Carajás province, southeastern Amazonian craton (Brazil), are discussed. The Vila Jussara suite crops out as a series of coalescing plutons elongated in the E-W direction. These plutons generally have sigmoidal shapes, and steep dips (75–85°) that follow the regional trend. The centermost areas of plutons are generally slightly deformed, while the marginal portions display mylonitic aspect and are delimited by sinistral shear zones belonging to the transcurrent system of the Itacaiúnas shear belt. These granitoids cover a large compositional spectrum, with four main lithotypes: (i) Seriated biotite-hornblende monzogranite; (ii) biotite-hornblende tonalite; (iii) porphyritic biotite monzogranite-granodiorite; and (iv) porphyritic hornblende-biotite monzogranite-granodiorite. The microstructural analysis of the studied rocks reveals: (i) microfractures in feldspar phenocrysts, filled with a quartz-feldspar matrix; (ii) preferred orientation of euhedral feldspar crystals in an igneous matrix; and (iii) evidence of moderate-to high-temperature of solid-state deformation (>500 °C). These microstructures and field observations point to a continuum of deformation, from the (sub) magmatic state down to sub-solidus conditions. Dating of three types of granitoids out of four gives ages of 2754 ± 2.2 Ma, 2752 ± 5.7 Ma and 2745 ± 3 Ma. The different granitoid varieties of the Vila Jussara suite were thus emplaced simultaneously. It is proposed that emplacement of the granitoids was controlled by shear zones reactivated during oblique collision and that plutons where constructed by multiple injections of magmas, generating extensive hybridization.