high-K Granitoids Research Articles

Geochemistry and petrogenesis of magnesian high-K granitoids from Bundelkhand Craton, Central India: New insights into crustal evolution

Geochemistry and petrogenesis of magnesian high-K granitoids from Bundelkhand Craton, Central India: New insights into crustal evolution

Early Triassic high-K granitoids and enclaves of the Daheba pluton, West Qinling (China): Implications for relative contributions of crust and mantle

Early Triassic granitoids are widespread in the northwestern West Qinling Orogen, China, but their petrogenesis and geodynamic implications remain unclear. In this study, we integrated new field and petrological observations, mineralogical compositions, zircon U-Pb dating, Hf isotopic and whole-rock geochemical analyses for the early Triassic granitic pluton in the Daheba area to determine its magma source and geodynamic scenario. The pluton is composed of granodiorite and syenogranite and carries microgranular enclaves (MEs) which formed at ca. 253–249 Ma. The granitoids show wide SiO2 contents of 63.73–77.49 wt% (av. 69.89), high K2O contents of 3.4–5.4 wt% (av. 4.1) and moderate Mg# of 16–51 (av. 36), belonging to high-K, calc-alkaline I-type granites. These rocks have high radiogenic but uniform Hf isotopic compositions with 176Hf/177Hf and ɛHf(t) of 0.282511–0.282658 and −3.85 – +1.25, respectively. The MEs hosed within the granite are characterized by high Mg# of 35–58 (av. 46) and variable εHf(t) of −4.64 – +9.35, which likely represent a hybridized melt derived from a slab-modified mantle and lower crust. In combination with coeval magmatic rocks in the western Gonghe-East Kunlun area, we propose a genetic model where mafic magmas derived from an enriched mantle and underplated beneath the overlying lower crust are considered to have produced the high-K felsic magma. Further, the hybridized melt ascended to shallower crustal levels to generate a series of rocks ranging from dioritic MEs to granodiorite to syenogranite. Mass balances modeling suggests that the generation of these rocks involved 36 % of the lower crustal-derived melt and 64 % of the SCLM (R2 = 0.9). Our new data, in tandem with published results suggest that the Daheba pluton formed during the subduction stage of the Paleo-Tethyan Ocean and that a local extensional episode occurred at 253–249 Ma in the western Gonghe area.

The Role of Fluids in Melting the Continental Crust and Generating Granitoids: An Overview

Granite is a distinctive constituent part of the continental crust on Earth, the formation and evolution of which have long been hot research topics. In this paper, we reviewed the partial melting processes of crustal rocks without or with fluid assistance and summarized the role of fluids and volatiles involved in the formation of granitic melts. As a conventional model, granitoids were thought to be derived from the dehydration melting of hydrous minerals in crustal basement metamorphic rocks in the absence of external fluids. However, the external-fluid-assisted melting of crustal metamorphic rocks has recently been proposed to produce granitoids as extensive fluids could be active in the deep continental crust, especially in the subduction zones. It has been demonstrated experimentally that H2O plays a crucial role in the partial melting of crustal rocks, in which H2O can (1) significantly lower the solidus temperature of the melted rocks to facilitate partial melting; (2) affect the melting reaction process, mineral stability, and the composition of melt; and (3) help the melt to separate more easily from the source area and aggregate to form a large-scale magma chamber. More importantly, dissolved volatiles and salts in the crustal fluids could also lower the solidus temperature of rocks, affect the partitioning behaviors of trace elements between minerals and melts, and facilitate the formation of some distinctive granitoids (e.g., B-rich, F-rich, and high-K granitoids). Furthermore, various volatiles dissolved in fluids could result in elemental or isotopic fractionation as well as the diversity of mineralization during fluid-assisted melting. In-depth studies regarding the fluid-assisted partial melting of crustal rocks will facilitate a more comprehensive understanding of melting of the Earth’s crust, thus providing strong theoretical constraints on the genesis and mineralization of granitoids as well as the formation and evolution of the continental crust.

Neodymium Isotope Constraints on the Origin of TTGs and High-K Granitoids in the Bundelkhand Craton, Central India: Implications for Archaean Crustal Evolution

Abstract The Bundelkhand craton in central India consists mainly of abundant high-K granitoids formed at the Archaean-Proterozoic boundary and several enclosed rafts of TTGs (tonalite-trondhjemite-granodiorites) up to 3.5 Ga. Therefore, the Bundelkhand craton is a key locality for studies on Archaean crustal growth and the emergence of multisource granitoid batholiths that stabilised a supercontinent at 2.5 Ga. Based on their geochemical characteristics, the high-K granitoids are divided into low silica–high Mg (sanukitoids and hybrids) and high silica–low Mg (anatectic) groups. We aim to provide new insights into the role of juvenile versus crustal sources in the evolution of the TTG, sanukitoid, hybrid, and anatectic granitoids of the Bundelkhand craton by comparing their key geochemical signatures with new Nd isotope evidence on crustal contributions and residence times. The ages and geochemical signatures as well as εNd(t) values and Nd model ages of TTGs point towards partial melting of a juvenile or short-lived mafic crust at different depths. Paleoarchaean TTGs show short crustal residence times and contributions from the newly formed crust, whereas Neoarchaean TTGs have long crustal residence times and contributions from the Paleoarchaean crust. This may reflect the transition from melting in a primitive oceanic plateau (3.4-3.2 Ga) in plume settings, resulting in a Paleoarchaean protocontinent, to 2.7 Ga subduction and island arc accretion along the protocontinent. The 2.5 Ga high-K granitoids formed at convergent subduction settings by partial melting of the mantle wedge and preexisting crust. Sanukitoids and hybrid granitoids originated in the mantle, the latter showing stronger crustal contributions, whereas abundant anatectic granitoids were products of pure crustal melting. Our Nd data and geochemical signatures support a change from early mafic sources to strong crust-mantle interactions towards the A-P boundary, probably reflecting the onset of supercontinent cycles.

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.

The generation and evolution of the Archean continental crust: The granitoid story in southeastern Brazil

The Archean Eon was a time of geodynamic changes. Direct evidence of these transitions come from igneous/metaigneous rocks, which dominate cratonic segments worldwide. New data for granitoids from an Archean basement inlier related to the Southern São Francisco Craton (SSFC), are integrated with geochronological, isotopic and geochemical data on Archean granitoids from the SSFC. The rocks are divided into three main geochemical groups with different ages: (1) TTG (3.02–2.77 Ga); (2) medium- to high-K granitoids (2.85–2.72 Ga); and (3) A-type granites (2.7–2.6 Ga). The juvenile to chondritic (Hf-Nd isotopes) TTG were divided into two sub-groups, TTG 1 (low-HREE) and 2 (high-HREE), derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts. The compositional diversity within the TTG is attributed to different pressures during partial melting, supported by a positive correlation of Dy/Yb and Sr/Zr, and batch melting calculations. The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs, indicating the presence of subduction processes concomitant with TTG emplacement. From ∼2.85 Ga to 2.70 Ga, the dominant rocks were K-rich granitoids. These are modeled as crustal melts of TTG, during regional metamorphism indicative of crustal thickening. Their compositional diversity is linked to: (i) differences in source composition; (ii) distinct melt fractions during partial melting; and (iii) different residual mineralogies reflecting varying P–T conditions. Post-collisional (∼2.7–2.6 Ga) A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms, and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle. The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening, regional metamorphism and crustal melting, and post-collisional extension, similar to that seen in younger Wilson Cycles. It is compelling evidence that plate tectonics was active in this segment of Brazil from ∼3 Ga.

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.

Monazite EPMA-CHIME dating of Sangmelima granulite and granitoid rocks in the Ntem Complex, Cameroon: Implications for Archean tectono-thermal evolution of NW Congo craton

Electron microprobe (EPMA) monazite Th–U – Pb ages have been determined from a suite of granulite and granitoids rocks of the Sangmelima granite-greenstone Belt (SGB) of the Ntem Complex in Cameroon or NW Congo Craton. The monazite-bearing rocks include charnockitic gneiss, migmatitic tonalite-trondhjemite-granodiorite (TTG) gneisses, granodiorite, monzogranite and a late pegmatite intrusion. The monazites of Sangmelima can be classified as monazite-Ce. Based on published ages and EPMA Th–U – Pb monazite age data from the SGB, the geodynamic evolution of the NW Congo Craton was refined through its tectonometamorphic and magmatic events. The major charnockitic and TTG magmatism event in Ntem Complex occurred between ~2950 and 2850 Ma. This Mesoarchean crystalline basement underwent two major ductile tectonothermal events M1 – D1 and M2 – D2. (1) The onset of M1 – D1 corresponds to the migmatization of TTG at 2843 Ma coeval with the emplacement of syn-kinematic granite dykes (monzogranites) at 2840–2825 Ma. The S1 regional penetrative foliation (D1) was progressively generated during the M1 metamorphic event, which led to the formation of associated hypersthene-garnet-bearing granulitic mineral assemblage that peaked at ~2830 Ma. (2) The M2 – D2 event between 2760 and 2740 Ma corresponds to the folding of S1 regional foliation by F2 folds and development of C2 shear zones synchronous with the anatexis event that generated the high-K granitoids at 2750 Ma. Late Neoarchean granitic pegmatite/aplite dikes and/or veins emplaced during the brittle deformation D3 and protracted cooling of the Ntem Complex between ~2700 and 2550 Ma. Our new EPMA monazite U–Th – Pb ages from the SGB highlight similar magmatic and tectonothermal events of the adjacent northern Gabonese domain and the Chaillu Massif in Gabon part of the NW Congo craton (ca. 3.0–2.5 Ga).

Discovery of multi-crustal rejuvenations for the formation of the Lincang granitic batholith, Southwest China: magmatism relating to Changning–Menglian Paleo–Tethyan termination

ABSTRACT The consumption of the Changning–Menglian Palaeo-Tethys ocean in the Triassic formed the Lincang granitic batholith in the southwestern China, once the oceanic supra-subduction zone. The batholith provides us a critical window to understand the nature of the crustal basements and the process of Palaeo-Tethyan termination. Here we report zircon U-Pb ages and Hf isotopes, and whole-rock elements and Sr-Nd isotopes of granitic samples from the central part of the Lincang batholith. The geochemical results reveal two genetic types of granites indicated by low-K and high-K affinities, respectively. The Group 1 low-K granitoids dated at 237–229 Ma are low-K calc-alkaline and metaluminous to peraluminous (A/CNK = 0.75–1.29), with K2O contents of 0.13–1.33 wt%, K2O/Na2O ratios of 0.03–0.30, Rb/Sr ratios < 0.18, and initial 87Sr/86Sr = 0.71693 and εNd(t) = −10.8. In contrast, the Group 2 high-K granitoids dated at 239–200 Ma are calc-alkaline and peraluminous (A/CNK = 1.02–1.20), with higher K2O contents (3.15–4.7 wt%), K2O/Na2O ratios (1.15–2.00) and Rb/Sr ratios (0.77–2.62), and more enriched isotopic compositions (initial 87Sr/86Sr = 0.73129 to 0.74037, εNd(t) = −13.1 to −11.0) as well as highly negative zircon εHf(t) values of −16.8 to −6.7. The formation time of these granitoids is compatible with that of the post-collision of the Palaeo-Tethys, subsequently to the magmatic gap (250–240 Ma) coupling with the syn-collision stage. The magmatic source discriminations suggest that the low-K granitoids were derived from partial melting of the dehydrated low-K amphibolite source and the high-K granitoids were dominantly from the psammitic source with minor mantle-derived magma involvement. Using the geochemical variations of the granitic rocks related to the Palaeo-Tethyan closure, we reveal melting of multiple crustal sources rather than a sole source to construct the Lincang batholith.

Petrogenesis of Magnesian High-K Granitoids From Bitkine (Centrechad Massif): Major and Trace Elements Constraints

Major and trace element data were used to constrain the nature and origin of the Bitkine gabbro-diorite magma.The gabbro-diorites of Bitkine within the Guéra Massif, and associated microgranular enclaves consist of plagioclase, k-feldspar, clinopyroxene, amphibole, biotite and quartz. Gabbro-diorites and enclaves are basic to intermediate rocks. They are high-K magnesian calc-alkaline with shoshonite affinity. ΣREE range from 132 to 436 ppm in gabbro-diorites, while they are from 134 to 207 ppm in enclaves. LREE are weakly enriched compared to HREE (La/Yb)N = (12.23 -41.40) and (6.20-31.86) respectively in gabbro-diorites and enclaves. These rocks show a weak negative anomaly in europium (Eu/Eu* = 0.78-1.07). They are rich in Ba and Sr, and show negative anomalies in Nb, Ta and Ti. The Nb/Ta, Rb/Cs and Ba/Nb ratios of the Bitkine gabbro-diorites and their enclaves indicate that they are derived from mantle magma modified by subducted fluids. This magma during its evolution by fractional crystallization was contaminated by crustal materials.

Paleoproterozoic sources for Cordilleran-type Neoproterozoic granitoids from the Araçuaí orogen (SE Brazil): Constraints from Hf isotope zircon composition

The Araçuaí orogen of SE Brazil exposes numerous amounts of magnesian, metaluminous, calc-alkaline, and medium- to high-K granitoid batholiths that were emplaced during early convergence between the São Francisco and Congo cratons during West Gondwana assembly in the late Neoproterozoic. Previously proposed sources for these pre-collisional granitoids include the Paleoproterozoic basement and mantle-derived magma based on isotopic signatures, abundant microgranular enclaves and contemporaneous mafic intrusions. Zircons from migmatitic basement gneiss, a noritic intrusion and five granitoid intrusions were analysed for U–Pb–Hf isotopes to evaluate their magma source. Paleoproterozoic migmatites represent addition of juvenile crust in an accretionary orogenic setting at ca. 2.2–2.0 Ga evidenced by their positive zircon εHf values. The Hf isotopic composition of zircon from pre-collisional granitoids has a large range of negative εHf values between −28.8 and −1.7 indicating crustal protoliths. This range of unradiogenic Hf isotopic compositions is explained by inefficient mixing of magmas derived from felsic and mafic Paleoproterozoic sources that hybridised during incremental growth of the plutons. Zircon grains of contemporaneous mafic intrusions display slightly higher, yet enriched, Hf isotopic compositions consistent with crustal contamination of mantle magmas. The new Hf isotope data, integrated with other chemical and isotopic evidence, suggest derivation of the pre-collisional granitoids from lower crustal sources of the Paleoproterozoic basement, with only minor contributions from mantle-derived magmas. Thus, magmatism of the Araçuaí orogen related to the assembly of West Gondwana was dominantly a crustal-reworking event.

Mesoarchean geodynamic regime evidenced from diverse granitoid rocks in the Anshan-Benxi area of the North China Craton

The petrogenesis and inner genetic relations of Mesoarchean granitoid rocks have been poorly researched in the Anshan-Benxi (AB) area of the North China Craton. These Mesoarchean granitoids are mainly composed of ~3.14 Ga Lishan trondhjemitic gneisses (LSTG), and 2.95–3.01 Ga Donganshan – Jinjialing trondhjemitic to monzogranitic gneisses (DTMG) and Tiejiashan – Gongchangling high-K granitoid gneisses (TGKG), which show essentially consistent ages of magmatic crystallization.The LSTG are characterized by SiO2 (70.71–73.72 wt%) and Al2O3 (14.25–15.99 wt%) contents, and low MgO (0.46–1.12 wt%) contents with low Mg# values (32–49) and K2O/Na2O values of 0.43 to 0.66, and total rare earth elements (TREE) of 97 to 151 ppm with (La/Yb)N ratios of 14.19 to 83.15. Integrated with Hf–O isotope characteristics from previous research and partial melting simulation, the geochemical characteristics of LSTG indicate that the trondhjemitic magma was generated by the partial melting of the source consisting of dominant ~3.3 Ga juvenile crustal material and some Paleo- to Eoarchean sediments at the lower crust level. In contrast with the LSTG, the DTMG shows higher SiO2 (73.10–75.99 wt%) contents, slightly lower Al2O3 (13.41–15.00 wt%) and MgO (0.21–0.61 wt%) contents with Mg# values (18–48), higher K2O/Na2O values (0.53–1.26) and similar TREE contents of 85 to 162 ppm, (La/Yb)N ratios (30.78–125.02), and εHf(t2) values from −5.38 to 3.16. Detailed petrogenetic investigations suggest that the magma of the DTMG was derived from the partial melting of the source comprising main ~3.3 Ga basaltic material and more Mesoarchean sediments at the lower crust level, then experienced slight plagioclase fractionation crystallization. The TGKG is characterized by the highest SiO2 (72.86–77.57 wt%) concentrations, but the lowest Al2O3 (11.96–14.47 wt%) and MgO (0.01–0.54 wt%) contents with K2O/Na2O values of 0.86 to 2.53 and Mg# values of 2 to 41. The wide TREE contents (142–766 ppm) and (La/Yb)N ratios (6.41–86.87), εHf(t2) value range of −9.71 to −2.14, suggesting that the magma of TGKG formed from the partial melting of abundant Eo- and Paleoarchean recycled sediments and igneous rocks. This petrogenesis of TGKG magma indicates that Eo- to Paleoarchean supracrustal material may exist under the Tiejiashan – Gongchangling area.Integrating previous studies on the AB area, these diverse granitoids record two episodes of major crust growths at ~3.65–3.8 Ga and ~3.3 Ga. Subsequently, the geological processes were dominated by the recycling of ~3.3 Ga basaltic material and Eo- to Paleoarchean crustal materials during ~3.14–2.95 Ga. The petrogenesis of Mesoarchean diverse granitoids indicates that voluminous supracrustal materials with different ages were transferred into the lower crust level during 2.95–3.14 Ga, revealing that pre-subduction buckling convergence may be the most probable Mesoarchean geodynamic regime in the AB area of the North China Craton.

Constraining provenance for the uraniferous Paleoproterozoic Francevillian Group sediments (Gabon) with detrital zircon geochronology and geochemistry

The Paleoproterozoic sandstones of the ca. 2.1 Ga Francevillian Group, southeast Gabon, host the oldest known redox-controlled high-grade uranium (U) deposits. Uranium-bearing detrital minerals (e.g., monazite) in the Francevillian Group sediments were derived by erosion of Archean basement rocks from the East Gabonian block of the northwestern Congo craton surrounding the Francevillian Basin. They are viewed as primary sources for U, but the nature of these sources remains poorly constrained. Here, U-Pb ages and Hf isotope data for detrital zircon grains are combined with literature geochemical data for igneous rocks from the Archean basement, to characterize the nature, age, and origin of the provenance for the Francevillian Basin and the ultimate source of U for the high-grade uranium deposits.Detrital zircon ages range from ca. 3.1 to 2.6 Ga with a dominant population between ca. 2.90 and 2.80 Ga, suggesting a major contribution from ca. 2.88 to 2.81 Ga high-K granitoids with a limited contribution from ca. 3.1 to 2.84 Ga TTGs and 2.75 to 2.7 Ga granitoids of the East Gabonian block. Most detrital zircon grains share similar depleted-mantle Hf model ages between ca. 3.08 and 3.30 Ga, indicating significant recycling of a Paleoarchean to Mesoarchean crust. We suggest that ca. 2.9 to 2.8 Ga high K, U, and Th granitoids, which reflect hybrid melts of both mantle and crustal parentage were the major detrital sources of U to the Francevillian Basin and, ultimately, for the U deposits. We propose that ca. 2.9 to 2.8 Ga detrital zircons with Hf TDM ages between ca. 3.1 and 3.3 Ga may thus allow for vectoring U deposits in sedimentary basins across the Congo craton.

Neoarchean and Rhyacian TTG-Sanukitoid suites in the southern São Francisco Paleocontinent, Brazil: Evidence for diachronous change towards modern tectonics

The southern portion of the São Francisco Palaeocontinent in Brazil is denoted by Archean nuclei and Paleoproterozoic magmatic arcs that were amalgamated during Siderian to Orosirian orogenic processes (ca. 2.4–2.1 ​Ga). New isotopic U–Pb in zircon and Sm–Nd whole rock combined with major and trace element composition analyses constrain the crystallization history of the Neoarchean Piedade block (at ca. 2.6 ​Ga) and the Paleoproterozoic Mantiqueira Complex (ca. 2.1–1.9 ​Ga). These therefore display quite different magmatic histories prior to their amalgamation at ca. 2.05 ​Ga. Sm–Nd and Rb–Sr isotopes imply a mixed mantle-crustal origin for the samples in both units. A complete Palaeoproterozoic orogenic cycle, from subduction to collision and collapse, is recorded in the Piedade Block and the Mantiqueira Complex. Rhyacian to Orosirian subduction processes (ca. 2.2–2.1 ​Ga) led to the generation of coeval (ca. 2.16 ​Ga) TTG suites and sanukitoids, followed by late (2.10–2.02 ​Ga) high-K granitoids that mark the collisional stage. The collisional accretion of the Mantiqueira Complex against the Piedade Block at 2.08–2.04 ​Ga is also recorded by granulite facies metamorphism in the latter terrane, along the Ponte Nova suture zone. The collisional stage was closely followed by the emplacement of within-plate tholeiites at ca. 2.04 ​Ga and by alkaline rocks (syenites and enriched basic rocks) at ca. 1.98 ​Ga, marking the transition to an extensional tectonic regime. The discovery of two episodes of TTG and sanukitoid magmatism, one during the Neoarchean in the Piedade Complex and another during the Rhyacian in the Mantiqueira Complex, indicates that the onset of subduction-related melting of metasomatized mantle was not restricted to Neoarchean times, as generally believed, but persisted much later into the Paleoproterozoic.

The late Neoarchean transition from low- to high-K granitoids in western Liaoning Province, NE China: Clues from geochemistry and zircon U–Pb–Hf–O isotopes

High-K granitoids are among the most abundant rock types in many Archean cratons. Late Neoarchean monzogranitic to syenogranitic gneisses with high-K affinities are widely distributed in the Anshan, Suizhong, Qinhuangdao, and Aolaishan areas on the northeastern margin of the North China Craton (NCC). In this contribution, we present an integrated study of zircon U–Pb–Hf–O isotopic compositions and whole-rock elemental compositions of amphibolites and trondhjemitic and monzo–syenogranitic gneisses of the Jinzhou area in the metamorphic basement of eastern Hebei–western Liaoning, with the aim of constraining their petrogenesis and geodynamic setting. Emplacement ages of the amphibolites and trondhjemitic–monzogranitic gneisses are 2543 ± 27, 2532 ± 19, and 2513 ± 7 Ma, respectively. The amphibolites are tholeiitic in composition with SiO2 contents of 49.7–50.8 wt%, variable degrees of light rare-earth-element (LREE) enrichment and high-field-strength element (HFSE) depletion, and high zircon εHf(t) values of +2.6 to +6.3, suggesting a depleted lithospheric mantle origin. The major- and trace-element compositions of the trondhjemitic gneisses are similar to those of the low-pressure tonalite–trondhjemite–granodiorite (TTG) suite. The zircon Hf (εHf(t) = +1.6 to +3.9) and O (δ18O = +3.76‰ to +5.73‰) isotopic compositions of the trondhjemitic gneisses indicate a juvenile basaltic source at the base of a thickened magmatic arc. The monzogranitic gneisses differ from their TTG counterparts in that they have lower SiO2 and higher MgO, K2O, and incompatible-element (especially Ba, Th, Sr, P, and LREE) contents. They also have slightly evolved zircon εHf(t) values (+0.6 to +3.8) and higher δ18O values (+4.69‰ to +6.13‰). These features suggest that the monzogranitic gneisses represent sanukitoid-type rocks, with a mantle source modified by crust-derived melts. The weakly deformed syenogranitic gneisses are characterized by high SiO2 and K2O, and very low MgO, Cr, and Ni contents, suggesting that they were formed by partial melting of local TTG rocks. Our results, together with those of previous investigations, suggest that the 2554–2513 Ma low- to high-K magmatism in the Jinzhou area most likely originated in an arc–back-arc tectonic setting on the northern margin of the NCC. The large volumes of high-K granitoids in eastern Hebei–western Liaoning are related to extensive mantle–crust interactions and crustal reworking in such a setting.

Geochemistry and Petrogenesis of the ca. 2.5 Ga High-K Granitoids in the Southern North China Craton

Archean high-K granitoids, generally formed after tonalite-trondhjemite-granodiorite (TTGs), are important for understanding crustal reworking of ancient cratons. The Linshan Archean high-K granitoids from the southern Trans-North China Orogen (TNCO) provide a window into the continental crustal evolution of the North China Craton (NCC). They mainly consist of monzogranite and granodiorite which were formed during 2 542–2 503 Ma. The high-K granitoids have high SiO2 (65.86 wt.%–78.08 wt.%), K2O (3.29 wt.%–7.62 wt.%) and low P2O5 (0.01 wt.%–0.27 wt.%). They display right inclined REE patterns with negative Eu anomalies (Eu/Eu*=0.20–0.81). Their spider diagram is characterized by enrichment of Rb, K, Th, U and depletion of Nb, Ta, Zr, Ti. The rocks have positive and variable zircon eHf(t) (+2.5 to +6.6) and whole-rock eNd(t)(+0.7 to +4.5) with two-stage model ages (TDM2Hf=2.87–2.64 Ga; TDM2Nd=2.77–2.50 Ga) similar to those of the Archean TTG-type rocks, amphibolites and diorites in the area. These evidences suggest that the high-K granitoids were produced by partial melting of juvenile crustal rocks. The Linshan high-K granitoids show relatively high whole-rock zircon saturation temperatures (694–889 oC) and low Sr/Y ratios (0.27–21.1), indicating low pressure partial melting. Combined with other geological evidences, the Linshan high-K granitoids are suggested to have been produced by partial melting of the continental crust in a post-collision extensional environment after an arc-continent collision. Thus, the NCC did not amalgamate together until ca. 2.5 Ga. Compiled zircon U-Pb ages and Hf isotopes reveal that the ca. 2.5 Ga magmatism represents reworking of the continental crust.

Neoarchean crust-mantle interactions in the Yishui Terrane, south-eastern margin of the North China Craton: Constraints from geochemistry and zircon U-Pb-Hf isotopes of metavolcanic rocks and high-K granitoids

The Neoarchean Yishui Terrane (YST) is situated in the east of Western Shandong Province (WSP), south-eastern margin of the North China Craton (NCC). The metavolcanic rocks of the YST are fine-grained hornblende plagioclase gneisses (Group #1) and fine-grained amphibolites (Group #2) in the Yangzhuangzhen area and fine- to medium-grained amphibolites (Group #3) in the Leigushan area. The high-K granitoids associated with Groups #1 and 2 are dominated by fine- to medium-grained monzogranitic gneisses. Zircon LA-ICP-MS U-Pb dating reveals that the magmatic precursors of Groups #1 and #2 were formed at 2641 Ma and the magmatic precursors of concomitant monzogranitic gneisses were emplaced from 2615 to 2575 Ma, whereas Group #3 represents a later 2500 Ma volcanic eruption, and all these metamorphic volcanic rocks and monzogranitic gneisses were subjected to subsequent 2470–2460 Ma metamorphism.The metamorphic volcanic rock samples in Group #1 exhibit the chemical compositions of calc-alkaline andesites, showing fractionated chondrite-normalized REE patterns ((La/Yb)N = 10.48–19.30) and negative Nb, Ta and Ti anomalies ((Nb/La)PM = 0.13–0.22), which are akin to those of typical high-Mg andesites (HMAs) in the subduction-related settings. The magmatic precursors of the Group #1 samples were derived from partial melting of a fluid- or melt-metasomatized depleted mantle wedge at deep levels in the upper mantle. Samples in Group #2 show calc-alkaline chemical compositions with less fractionated chondrite-normalized REE patterns ((La/Yb)N = 2.24–3.34) and negative Nb, Ta and Ti anomalies ((Nb/La)PM = 0.47–0.76), which are consistent with those of the volcanic rocks in the Aleutian island arc. The magmatic precursors of Group #2 were generated by partial melting of a fluid-metasomatized depleted mantle wedge at shallow levels in the upper mantle. The monzogranitic gneisses exhibit high SiO2 and K2O contents with high-K calc-alkaline affinities and peraluminous characteristics. Based on their distinct HREE contents and chondrite-normalized REE patterns, these granitoid samples are subdivided into low-Yb monzogranitic gneisses (LYMGs) and high-Yb monzogranitic gneisses (HYMGs). The LYMG magma was derived from partial melting of a mixed source of juvenile two-mica pelites and minor basic-intermediate igneous rocks at lower crustal levels with pyroxene + amphibole + garnet as the main residual phases, and the HYMG magma was derived from partial melting of multi-sourced juvenile two-mica pelites at middle to lower crustal levels with pyroxene + amphibole and subordinate plagioclase and garnet as the main residual phases. In addition, Group #3 resembles tholeiitic back-arc basalts in the Okinawa Trough and displays flat chondrite-normalized REE patterns ((La/Yb)N = 1.22–2.08) and slightly negative Nb and Ta anomalies ((Nb/La)PM = 0.35–0.59). This group was most likely derived from partial melting of a depleted mantle source that had been modified by the addition of subducted slab-derived fluids at shallow levels in the upper mantle. These metavolcanic rocks and concomitant high-K granitoids record important Neoarchean crust-mantle interactions involving the first modification and partial melting of the lithospheric mantle induced by oceanic crust subduction; then, upwelling and underplating of mantle-derived magmas triggered partial melting of the middle to lower crust and mixing between crust- and mantle-derived magmas. These processes imply that Neoarchean crust-mantle interaction played a crucial role in the evolution of the southeastern margin of the NCC.Available whole-rock Sm-Nd and zircon Lu-Hf isotopic data from metamorphic volcanic rocks and plutonic granitoids from this study and previous studies reveal that YST experienced three crucial juvenile crustal growth events from ~2.78–2.69 Ga, ~2.64–2.56 Ga and ~2.54–2.50 Ga.

Contrasting granitic magmatism of the Kalba fold belt (East Kazakhstan): Evidence for Late Paleozoic post-orogenic events

The paper presents new original data and a review of previous studies on the Late Carboniferous – Early Permian granitoids of the Kunush and Kalguty intrusive complexes from the Kalba fold belt (East Kazakhstan). These rocks formed at the initial post-collisional stage of the Irtish-Zaisan orogen in the western Central Asian Orogenic Belt (CAOB). The granitoids form isometric or NW linear intrusions inside the Late Devonian - Early Carboniferous metasediments which overlap the accretionary lithology of the Kalba fold belt in front of the Altai active margin of the Siberian continent. These granitoids contain zircon grains with U-Pb ages of ca.308–291 Ma, synchronous with the peak post-orogenic magmatic event at ∼300 Ma in the CAOB. The Kunush high-Na granitoids, with high SiO2 (67–72%) and Al2O3 (15–18%) contents and the Na2O/K2O ratio (1.94–6.43), and low HREEs (Yb = 0.22–0.93 ppm) but moderate Sr/Y ratios (47–179), Mg# (35–55) and Ni, Cr, are generally common to high-Al TTG-series with non-subduction geochemical signatures. The Kalguty granitoids mostly belong to calc-alkalic to subalkalic high-K series, have non-corundum CIPW-norm compositions and mainly weakly peraluminous (ASI = 0.97–1.09) characteristics. Their Fe∗ = 0.7–1 at 62–74 wt.% SiO2 and relatively high Y/Nb (2–4) and Rb/Nb (9–18) ratios are similar to transitional compositions reported for fractionated I- and A2-type post-orogenic granites worldwide. The Kunush high-Na and Kalguty high-K granitoids formed at different depths in the crust and the parent melts were derived from metabasaltic (MORB; P = 10–15 kbar) and metagranitic (TTG-like; P < 10 kbar) protoliths, respectively. We propose that relaxation of tangential compression after oblique collision and the following thermal impact of mafic magma that acted simultaneously at different crustal depths, along with decompressional partial melting, may be a basic petrological scenario for synchronous formation of geochemically different granitoids.

Petrogenesis of late Neoarchean high-K granitoids in the Western Shandong terrane, North China Craton, and their implications for crust-mantle interactions

Late Neoarchean plutonic rocks in the eastern range of the Western Shandong (WSD) terrane, North China Craton, consist of fine-grained monzogranites (Group #1), fine-grained monzogranitic gneisses (Group #2), coarse-grained granodioritic gneisses (Group #3) and coarse-grained gabbro-diorites (Group #4). The first three groups of granitoids exhibit high SiO2 and K2O contents and plot in the quartz monzonite, granodiorite and granite fields in the TAS classification diagram and the high-K calc-alkaline series field in the SiO2 and K2O diagram. These granitoids show meta- to peraluminous characteristics in the A/NK versus A/CNK plot. In contrast, the gabbro and diorite samples display low SiO2 and K2O contents. LA-ICP-MS zircon U-Pb isotopic dating reveals that the high-K granitoids (Groups #1, 2 and 3) were emplaced at ∼2511–2497 Ma and that the gabbro-diorites were emplaced at ∼2511 Ma. All of these samples generally underwent regional metamorphism at ∼2475–2451 Ma. Detailed petrogenetic and geochemical studies suggest that the fine-grained monzogranites (Group #1) were derived from the hydrous partial melting of juvenile sediments at mid-crustal levels, while the fine-grained monzogranitic gneisses (Group #2) were most likely derived from the partial melting of metagreywackes at lower to mid-crustal levels. The gabbro-diorites (Group #4) were derived from the partial melting of a fluid-metasomatized mantle source at relatively deeper levels of the upper mantle. The granodioritic gneisses (Group #3) were generated from magma mixing between melts derived from the partial melting of metagreywackes (∼90%) and melts derived from a metasomatized depleted mantle source (∼10%) with minor ancient basement material additions.These findings, combined with previously obtained zircon U-Pb dating and Lu-Hf isotope data, suggest that crust-mantle interaction constituted the essential mechanism for the formation of high-K granitoids in the WSD terrane. The upwelling and underplating of mantle-derived magmas (Group #4) not only provided sufficient heat for melting crustal materials at various levels (Group #1 and #2) but also mixed mantle materials with crustal-derived melts, thereby generating the magmatic precursors of the granodioritic gneisses (Group #3).

Geochronological and geochemical evidences for extension-related Neoarchean granitoids in the southern São Francisco Craton, Brazil

New LA-SF-ICP-MS U-Pb zircon dating of high-K granitoids from the Campo Belo metamorphic complex, southern São Francisco Craton (Brazil), reveals a long period (ca. 100My) of Neoarchean granitic magmatism that post-date the TTG magmatism. The oldest studied pluton is a highly porphyritic biotite orthogneiss emplaced at 2748±5Ma, followed by a hornblende-biotite orthogneiss (2727±7Ma). Both granitic bodies were affected by a deformation event prior to the emplacement of the Rio do Amparo, Bom Sucesso and Lavras granitoid plutons at 2716±6Ma, 2696±6Ma and 2646±5Ma, respectively. The Neoarchean granitic magmatism ended with the intrusion of peraluminous leucogranitic dikes at 2631±4Ma.The 2.73–2.65Ga Campo Belo granitoids share chemical features of A-type granites, such as high apatite- and zircon-saturation temperatures (mostly>800°C), relatively high Fe-number, high total alkalis and characteristic enrichment in LREE and HFSE although most samples of the Rio do Amparo granite have lower HFSE and LREE content that typical A-type granites but very high Th. The high Th content of the Rio do Amparo and Bom Sucesso granites may suggest involvement of Th-orthosilicate in their sources. The trace element composition permits to classify the Campo Belo granitoids as A2-type granites, suggesting derivation from partial melting of TTG-crustal sources likely in an extensional setting.Significant reworking of Mesoarchean crust is suggested by mostly negative εNdi values (Rio do Amparo: −2.0 and +3.1; Bom Sucesso: −3.6, −3.1 and +0.9; Lavras: −2.5 and −0.2) and old Nd model ages (TDM close to 3.1Ga), although with probable involvement of juvenile material (TDM of 2.7–2.9Ga). This contrasts with Neoarchean granites of the northern São Francisco and Congo cratons characterized by negligible juvenile imprint.The 2.75–2.63Ga Campo Belo granitoids witness the thermal stabilization of the Archean lithosphere through a major episode of high-K granitoid magmatism between 2760 and 2600Ma, which affected the whole São Francisco Craton and the northern Congo Craton.