high-K Calc-alkaline Granitoids Research Articles

Protracted magmatism and crust–mantle interaction during continental collision: insights from the Variscan granitoids of the external western Alps

Variscan granitoids and associated mafic rocks exposed in the External Crystalline Massifs (ECM) of the Western Alps document the Variscan stages from the early Carboniferous collision to the early Permian post-collisional setting. Our study focuses on the Central part of the ECM, synthesizing newly acquired and existing geochronological, whole-rock geochemical and isotopic data. We identified two distinctive magmatic series: (i) high-K calc-alkaline granitoids, which range from magnesian (MgG) to ferro-magnesian (FeMgG) rocks; (ii) ultra-high-K metaluminous (UHKM) rocks (“durbachites”). These series were emplaced roughly simultaneously between ca. 350 and 300 Ma, with two main episodes during the Visean (ca. 348–335 Ma) and the late Carboniferous (305–299 Ma), with a more limited activity in between. A younger Permian event at ca. 280–275 Ma has also been identified in one granitoid pluton. Contemporaneous emplacement of these two series reflects concomitant crustal anatexis and melting of LILE–LREE-rich metasomatized lithospheric mantle. Trace elements and Nd–Sr isotopes reveal significant hybridization between these two magmatic end members, by magma mixing, or assimilation of crystallized mafic ultrapotassic enclaves in the high-K calc-alkaline granitoids. Granitoid composition evolves over time, especially SiO2, Mg#, Sr/Y, La/Yb and Nb/Ta, possibly explained by increasing differentiation of magmas over time, changes in the crust versus mantle sources mass-balance, and decrease in melting pressure due to the orogenic collapse. The εNdi values of both high-K calc-alkaline granitoids and durbachites decreases from [− 3.8; − 2.9] to [− 6.4; − 5.2] between 345 and 320 Ma, possibly indicating an increasing influence of subducted/relaminated crustal material contaminating the lithospheric mantle source. εNdi values then rise to [− 3.7; − 0.5] during the late Carboniferous, possibly due to progressive exhaustion of the enriched mantle source, or advection of the asthenosphere during the post-collisional stage.Graphic abstractPossible geodynamic scenario along the central-eastern segment of the Variscan Belt, which may account for the temporal evolution of Variscan magmatism in the External Western Alps.

Early Orosirian belts of the central Guiana Shield, northern Amazonian Craton: U-Pb geochronology and tectonic implications

The Cauarane-Coeroeni Belt (CCB), the Orocaima Igneous Belt (OIB) and the Rio Urubu Belt (RUB) are the main tectonic features of the central part of the Guiana Shield. The CCB is a sinuous NW-SE/NE-SW/NW-SE trending high-grade supracrustal belt, bordered to the north by the OIB, formed by volcanics and high-crustal level granitoids, and to the south by the RUB, made up of deeply emplaced granitoids and gneisses. We present 27 new U-Pb SHRIMP and LA-ICP-MS zircon ages for these belts.The geochronological data obtained for 10 granitoid samples of the OIB indicate that magma pulses of different typologies were coeval along the belt and confirm its continental scale extension. Crystallization ages obtained for the high-K calc-alkaline granitoids vary from 1990 ± 5 Ma to 1957 ± 17 Ma and those of reduced A-type granites vary from 1980 ± 14 Ma to 1974 ± 8 Ma.Only four samples of granitoids and gneisses of the RUB were analysed. Crystallization ages of 1964 ± 7 Ma and 1956 ± 8 Ma were calculated respectively for a granodiorite and for an orthogneiss and are in agreement with the 1.96–1.92 Ga age period regionally considered for the evolution of the RUB. However, an age of 1973 ± 7 Ma was calculated for a foliated S-type granite, indicating that slightly older granitoid rocks are also present within the RUB. In addition, an age of 1935 ± 10 Ma was calculated for the high-grade metamorphism along the belt.A microgranitic dyke that crosscuts the foliation of a gneiss of the RUB was dated at 1884 ± 7 Ma, and probably represents one of the feeder dykes for the large 1.89–1.87 Ga Uatumã magmatic event.Twelve samples of the CCB were analysed. The data for the detrital nuclei of the zircon crystals of the paragneisses and schists suggest an overall similar inheritance pattern along the length of the CCB, recording the contribution of Archean to early Orosirian sources, with a major participation of Rhyacian domains.The oldest detrital zircon crystals yielded an age of 3.65 Ga, but the age of most of the Archean zircon grains fall in the 3.50–2.50 Ga range and they were probably derived from the Imataca and Amapá blocks. Results in the 2.50–2.30 Ga age interval were obtained for detrital zircon grains of many samples, indicating the contribution of Siderian source-areas, possibly the Bacajá Domain, located outside the shield. Those terranes formed within the shield during the Rhyacian phase of the Transamazonian Cycle were probably the source of the 2.30–2.05 Ga detrital zircon grains. In addition, zircon grains with ages between 2.05 Ga and 2.03 Ga were possibly derived from the Trairão-Anauá terranes.The U-Pb SHRIMP zircon dating allowed to better constrain the metamorphic events along the CCB. The syn-kinematic M1 high-grade metamorphic phase could not be directly dated, and we suggest it occurred between 2025 Ma and 2000 Ma. The imprint of the thermal M2 metamorphic event is recorded by the presence of rims and cores of zircon crystals with very low Th/U ratios (<0.1), showing secondary texture. Upper intercept ages of 1983 ± 9 Ma, 1978 ± 9 Ma and 1967 ± 27 Ma were obtained for M2. Zircon grains with secondary textures and very low Th/U ratios (<0.1) from a sample collected in the vicinities of the RUB yielded an upper intercept age of 1955 ± 14 Ma, tentatively interpreted as reflecting M3.The ages obtained for the M2 and M3 metamorphic phases coincide, respectively with those measured for the rocks of the OIB and for the high-grade metamorphism in the RUB. We envisage that the M2 and M3 metamorphic overprints in the paraderived rocks of the CCB reflect important fluid input and thermal perturbation respectively during the emplacement of the OIB granitoids to the north, and the assemblage of granitoid bodies of slightly different ages, deformation and high-grade metamorphism within the RUB, south of the CCB.The early Orosirian terranes of the central part of the Guiana Shield were formed during Akawai Orogeny. The 2.04–2.03 Ga Trairão-Anauá terranes and the CCB supracrustal rocks represent the pre-collisional and collisional stages of the orogeny, the OIB records post-collisional, late-orogenic magmatism. The RUB is probably reflecting a post-collisional setting associated with transpressive deformation. The Akawai Orogeny is interpreted as the late stage of the Transamazonian Cycle, after the main Rhyacian orogeny of the cycle, and was responsible for the final amalgamation of this part of the Columbia paleocontinent.

Constraints on the source and petrogenesis of early Ediacaran shoshonitic mafic magmatism and high-K calc-alkaline granitoids in the Sergipano Orogenic System, Borborema Province, Brazil

The early Ediacaran Capela pluton (ca. 630 Ma) is intruded into the metasedimentary succession of the Sergipano Orogenic System along the oriental segment of the Macururé Domain, southeastern Borborema Province, NE Brazil. This body is an uncommon example of mantle-derived shoshonitic mafic rocks associated with high-K calc-alkaline granitoids emplaced in a pre- to early-collisional context. Here, we aim to unravel the petrogenesis of this plutonic association to determine the role of crustal contribution to magmatism and its geodynamical significance during the early stages of the Brasiliano/Pan-African Orogeny. The Capela pluton comprises cumulate hornblendites, gabbronorites, gabbros, diorites, granodiorites, quartz monzonites, and granites. Shoshonitic mafic rocks and high-K calc-alkaline granitoids show significant enrichments in LILE and LREE compared to HREE and HFSE. Ultramafic and mafic rocks display a conspicuous crustal signature, yielding subchondritic εNd(t) and zircon εHf(t) values, along with variable radiogenic Sr–Pb isotopic compositions. The dominant factors controlling the geochemical features of the mafic magmas were the enriched signature of the lithospheric mantle source and the degree of partial melting. Mantle source metasomatism is thought to have occurred by incorporating subducted sediments into the mantle wedge before the onset of the Brasiliano Orogeny. Geochemical modeling demonstrated that low partial melting degrees (5–10%) of phlogopite-bearing lithospheric mantle in the spinel stability field metasomatized by 5–10% subducted sediments may account for the main characteristics of the mafic rocks. Introducing sedimentary material into the mantle caused a decrease in Sm/Nd and Lu/Hf ratios while increasing the Rb/Sr, U/Pb, and Th/Pb ratios, which led to the time-integrated evolved isotopic signature observed in the mafic rocks. The coeval granitoids are metaluminous to slightly peraluminous and display Nd–Pb isotopic compositions similar to those of mafic–ultramafic rocks. The petrological and isotopic features of the granitoids are consistent with derivation from an ancient mafic lower crustal source. We argue that the ascent and emplacement of hydrous mantle-derived magmas as successive sills into the lower crust produced a deep hot zone beneath the Sergipano Orogenic System during the onset of the Brasiliano/Pan-African Orogeny. Aqueous fluids released from such potassic mafic magmas favored the partial melting of surrounding rocks, producing contemporary felsic magmatism.

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.

Isotopic spatial-temporal evolution of magmatic rocks in the Gangdese belt: Implications for the origin of Miocene post-collisional giant porphyry deposits in southern Tibet

Abstract Crustal growth is commonly associated with porphyry deposit formation whether in continental arcs or collisional orogens. The Miocene high-K calc-alkaline granitoids in the Gangdese belt in southern Tibet, associated with porphyry copper deposits, are derived from the juvenile lower crust with input from lithospheric mantle trachytic magmas, and are characterized by adakitic affinity with high-Sr/Y and La/Yb ratios as well as high Mg# and more evolved isotopic ratios. Researchers have argued, lower crust with metal fertilization was mainly formed by previous subduction-related modification. The issue is that the arc is composed of three stages of magmatism including Jurassic, Cretaceous, and Paleocene–Eocene, with peaks of activity at 200 Ma, 90 Ma, and ca. 50 Ma, respectively. All three stages of arc growth are essentially similar in terms of their whole-rock geochemistry and Sr-Nd-Hf isotopic compositions, making it difficult to distinguish Miocene magma sources. This study is based on ~430 bulk-rock Sr-Nd isotope data and ~270 zircon Lu-Hf isotope data and &amp;gt;800 whole-rock geochemistry analyses in a 900-km-long section of the Gangdese belt. We found large scale variations along the length of the arc where the Nd-Hf isotopic ratios of the Jurassic, Cretaceous, and Paleocene–Eocene arc rocks change differently from east to west. A significant feature is that the spatial distribution of Nd-Hf isotopic values of the Paleocene–Eocene arc magmas and the Miocene granitoids, including metallogenic ones, are “bell-shaped” from east to west, with a peak of εNd(t) and εHf(t) at ~91°E. In contrast, the Jurassic and Cretaceous arc magmas have different isotopic distribution patterns as a function of longitude. The isotopic spatial similarity of the Paleocene–Eocene and Miocene suites suggests that the lower crust source of the metallogenic Miocene magmas is composed dominantly of the Paleocene–Eocene arc rocks. This is further supported by abundant inherited zircons dominated by Paleocene–Eocene ages in the Miocene rocks. Another important discovery from the large data set is that the Miocene magmatic rocks have higher Mg# and more evolved Sr-Nd-Hf isotopic compositions than all preceding magmatic arcs. These characteristics indicate that the involvement of another different source was required to form the Miocene magmatic rocks. Hybridization of the isotopically unevolved primary magmas with isotopically evolved, lithospheric mantle-derived trachytic magmas is consistent with the geochemical, xenolith, and seismic evidence and is essential for the Miocene crustal growth and porphyry deposit formation. We recognize that the crustal growth in the collisional orogen is a two-step process, the first is the subduction stage dominated by typical magmatic arc processes leading to lower crust fertilization, the second is the collisional stage dominated by partial melting of a subduction-modified lower crust and mixing with a lithospheric mantle-derived melt at the source depth.

Age, genesis, and tectonic setting of the Qiushuwan Cu–Mo deposit in East Qinling (Central China): Constraints from Sr–Nd–Hf isotopes, zircon U–Pb and molybdenite Re–Os dating

The Qiushuwan Cu–Mo deposit, closely associated with porphyritic granodiorites, form part of the giant East Qinling Mo belt. To better constrain the genesis, timing and tectonic setting of this world-class Cu–Mo deposit, we present a combined study of whole-rock elemental and Sr–Nd isotopes, zircon U–Pb–Hf isotopes and molybdenite Re–Os systematic of the Qiushuwan deposit. The porphyritic granodiorites associated with the deposit are metaluminous, high-K calc-alkaline granitoids and possess high Sr/Y, La/Yb and characteristic REE patterns devoid of Eu anomalies, displaying typical features of adakitic rocks. Moreover, the rocks yielded moderate negative whole-rock εNd(t) (–7.8 to –7.5), variable zircon εHf(t) (–5 to +0.8) and low (87Sr/86Sr)i ratios (0.705728–0.706617), indicating that the mineralizing magma for the Qiushuwan deposit was largely derived from metasomatized mantle with minor contribution from crustal material. An integrated zircon U–Pb and molybdenite Re–Os dating constrain the magmatic-metallogenic event related to the formation of the Cu–Mo deposit at ~150 Ma, corresponding to the late Jurassic. In addition, geochemical discrimination plots place the Qiushuwan granodiorite within the field of I-type granitoid, probably emplaced in a post-collisional setting. The post-collision setting provided favorable condition for mantle upwelling, partial melting and magma generation from the lithospheric mantle with minor contribution from the lower crust. It is likely that the lithospheric mantle, metasomatized during the preceding subduction, was hydrous, rich in Cu–Mo materials and had high oxygen fugacity, which collectively favored the formation of large Cu–Mo deposits in the Qinling belt.

Petrogenesis and geochronology of Cenozoic intrusions in the Poboya and Sassak gold and copper districts in Western Sulawesi, Indonesia: Implications for the mineralization processes and magma sources

This paper presents petrographic, geochemical and geochronological data for intrusions that area spatially related to gold and copper mineralization in the Poboya and Sassak areas in western Sulawesi. These data coupled with previous studies are then used to discuss the implications for the mineralization processes and magma sources. In the Poboya area, gold-bearing quartz veins are related to high-K calc-alkaline granitoids that display a reduced nature, whereas in Sassak area porphyry Cu-Au mineralization is associated with monzonitic intrusions intruded by gabbroic and syeno-dioritic intrusions. Granitoids from Poboya have a metaluminous to mildly peraluminous character (mol. Al2O3/mol. CaO + Na2O + K2O = 1.0–1.04) and include both I-type and S-type varieties. The Poboya and Sassak intrusions have Rb-Sr isotopic ages of 3.94 ± 0.03 Ma, 2.97 ± 0.05 Ma and 10.7 Ma ± 0.11 Ma, respectively, which are interpreted to closely approximate the time of emplacement into their country rocks. Zircon U-Pb dating of gabbro and diorite from the Sassak area yielded crystallization ages of 10.8 ± 0.16 Ma and 10.6 ± 0.19 Ma, respectively. New Sr isotopic data (87Sr/86Sr ratios >0.709) are consistent with previous data obtained from the central and northern parts of western Sulawesi, Gondwana-derived Mesozoic granitoids and enriched-mantle or lower crustal equivalents are the most likely magma sources for the Poboya and Sassak igneous rock suites, respectively. The Poboya deposit is interpreted to represent the distal part of a reduced intrusion-related gold system.

Permo–Triassic granitoids, Hainan Island, link to Paleotethyan not Paleopacific tectonics

Abstract Hainan Island may have lain at the boundary between the Tethyan and Pacific domains since the late Paleozoic. Permo–Triassic granitoids outcropped on the island provide insight into Mesozoic tectonic evolution and potential dynamics. Based on analyses of zircon U-Pb geochronological and Hf-O isotopic data, along with whole-rock elemental and Sr-Nd isotopic data, the Permo–Triassic granitoids are divided into three groups: Late Permian (256–252 Ma) gneissic granitoids (Group 1), Early–Middle Triassic (247–244 Ma) massive granitoids (Group 2), and Middle-Late Triassic (242–225 Ma) massive granitoids (Group 3). Groups 1 and 2 exhibit similar elemental and Sr-Nd isotopic compositions with εNd(t) values ranging from –6.71 to –3.25. Group 1 is characterized by gneissic foliation and calc-alkaline I-type geochemical affinities with negative Nb-Ta and Ti anomalies; it has low εHf(t) (–4.2∼+0.2) and high δ18O values (9.35–10.46‰), possibly related to derivation of a metabasite source in a continental arc setting. The Group 2 samples are peraluminous massive granitoids with slightly high A/CNK ratios of 1.00–1.31, δ18O values (8.85–11.75‰), and high Sr/Y ratios but low εHf(t) (–8.7∼+1.6) values. They may have originated from the mixed source of greywacke and metabasite, indicating a compressive tectonic setting. The Group 3 high-K calc–alkaline granitoids have high zircon temperatures (842–867 °C) and show the geochemical signatures of A-type granites. They are featured by slightly low whole-rock εNd(t) and zircon εHf(t) values, suggestive of the derivation from a metabasite–greywacke source in an extensional setting. In combination with other geochronological and geochemical data from Hainan Island, it is proposed that the Permian–Triassic igneous magmatism in Hainan Island reflects a continuous amalgamation process from back-arc consumption (272–252 Ma) to orogenic assembly (251–243 Ma) and orogenic collapse (242–225 Ma) between the South China and Indochina Blocks. Such a temporal–spatial pattern for the Hainan granitoids is consistent with that along the Truong Son, Jinshajiang–Ailaoshan–Song Ma tectonic zone, suggesting dominant control of Paleotethyan domain instead of Paleopacific tectonics.

Geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Late Permian–Early Triassic granitoids in Eastern Kunlun Orogen, Northwest China: petrogenesis and implications for geodynamic setting

ABSTRACT The Eastern Kunlun Orogenic Belt (EKOB) in Northwest China, is an ideal area for understanding the tectonic evolution of the Palaeo-Tethys Ocean. The EKOB is marked by widespread Palaeozoic to Early Mesozoic magmatism. However, the Late Permian–Early Mesozoic tectonic evolution of the Palaeo-Tethys Ocean tectonic regime is poorly understood. Here, we report new zircon LA-ICP-MS U–Pb dating and geochemical analyses of Late Permian–Early Triassic intrusive rocks in the Xiangyanggouxi and Dageledong areas in the EKOB, Northwest China, to discuss their petrogenesis and geodynamic setting and reconstruct the tectonic evolution of Palaeo-Tethys oceanic tectonic regime. Zircon U-Pb dating results indicate that these granitoids crystallized during ca. 256–248 Ma, i.e. the Late Permian to Early Triassic. These granitoids are mainly comprised of granodiorites and monzonitic granites that possess high concentrations of SiO2 (66.81–75.98 wt.%), K2O+Na2O (6.21–7.92 wt.%), and low contents of MgO, CaO, Cr, Ni, and Mg# (<0.44). They are classified as medium- to high-K calc-alkaline and metaluminous I-type granitoids. These granitoids are rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. In addition, combined with the εHf(t) values of −2.4 to +2.4 with two-stage model ages ranging from 1409 Ma to 1027 Ma, and the εNd(t) values from −3.73 to −2.95, it is suggested that the primary magma of these granitoids was derived from the partial melting of the Late Meso–Proterozoic mafic lower crust. These findings, combined with spatio-temporal distributions of regional magmatism, reveal that the Late Permian and Early Triassic granitoids formed in a continental magmatic arc setting related to the northward subduction of the Palaeo-Tethys Ocean plate beneath the EKOB-Qaidam terrane.

Geochemical characteristics and origin of the Neoproterozoic high-K calc-alkaline granitoids in the northern part of Mandara hills, northeastern Nigeria

The high-K calc-alkaline granitoids in the northern part of the Mandara Hills are part of the well-exposed post-collisional plutons in northeastern Nigeria. The calc-alkaline rock association consists of quartz monzodiorite, hornblende biotite granite, biotite granites and aplite which intruded the older basement consisting mainly of low-lying migmatitic gneisses and amphibolites during the Neoproterozoic Pan-African Orogeny. Petrological and geochemical studies have revealed the presence of hornblende, iron oxide, and metaluminous to slightly peraluminous characteristics in the granitoids which is typical of I-type granite. The granitoids are also depleted in some high field strength elements (e.g. Nb and Ta) as well as Ti. Plots of Mg# versus SiO2 indicate that the granite was derived from partial melting of crustal sources. Lithospheric delamination at the waning stage of the Pan-African Orogeny possibly triggered upwelling of hot mafic magma from the mantle which underplated the lower crust. This, in turn, caused partial melting and magma generation at the lower to middle-crustal level. However, the peculiar geochemical characteristics of the quartz monzodiorite especially the enrichment in compatible elements such as MgO, Cr, and Ni, as well as LILE element (e.g. K, Ce, Cs, Ba, and Sr), signify that the rock formed from an enriched upper mantle source. The emplacement of high-K granites in the Madara Hill, therefore, marked an important episode of crustal reworking during the Neoproterozoic. However, further isotopic work is needed to confirm this model.

Petrogenesis of Maktali fractionated calc-alkaline younger granitoids, Central Eastern Desert, Egypt

The Egyptian calc-alkaline younger granitoids represent part of broadly distributed late collisional high-K calc-alkaline granitoids in the northern Arabian-Nubian Shield. In the Eastern Desert of Egypt, these granitoids have a significant economic value that they are commonly associated with rare metal-bearing granites. Maktali granitoids are located in Central Eastern Desert and they constitute a two-phase pluton, which consists of leucogranites and monzogranites. They intrude the country metavolcanics with sharp contacts. These granitoids are slightly peraluminous and moderately to highly fractionated high-K calc-alkaline granitoids. Leucogranites and monzogranites were emplaced at temperatures 699.8-8.28.8°C and 757.2–909.6°C and under pressure 1.22–4.8 and 2.36–2.98 kbars respectively. Leucogranites and monzogranites were emplaced at depths 3.28–22.96 km and 6.36–8.5 km and they were crystallized under log Oxygen fugacity between − 13.2 to − 16.1 and − 11.6 to − 14.7 respectively. They are magnetite-series granitoids and their crystallization was controlled by NNO fugacity buffer. Leucogranites and monzogranites share the same magmatic source and they were emplaced during late-collisional stage by melting of crustal source rocks may occur as a consequence of decompression following delamination of the lithospheric root and slab breakoff. Maktali leucogranites could be generated by partial melting and subsequent fractional crystallization of mafic lower crust with addition of melts from the mantle. Maktali monzogranites show distinctive characteristics of rare metal-bearing granites that they contain Fe-columbite and transitional micas. Field and textural evidences together with chemistry of columbite, micas, and trace element behavior suggest the magmatic origin of monzogranites. Moreover, REEs in monzogranites show a pronounced Eu anomaly and a well-visible tetrad effect, supporting their generation by fractional crystallization and fluid-rock interaction during the late stage of granite crystallization.

Petrochemistry and Manganese Mineralization Potentials of the Calc-alkaline Granitoids from Northeastern Hawal Massif, North-Eastern Nigeria

The High-K calc-alkaline granitoids in southern part of Hawal massif is an integral part of the well-exposed syn-to post collisional plutons in eastern Nigeria. The evolution of the rocks can be linked to the thermo-tectonic period of faulting, uplift, cooling, fractionation and high-level magmatism, which led to the intrusion of the granites and related rocks during the Palaeoproterozoic, about 580± 10 Ma. A total of nine granitic rocks, constituting seven biotite granites of varying grain sizes and two porphyritic granites were sampled in Mubi area to shed new light regarding their petrochemistry. Detailed field and laboratory investigations show that the area is characterized majorly by Pan African granitoids. The massif has S-type strongly peraluminous geochemical signature, high-K calc-alkaline, magnesian, granodiorite, exemplified by high ASI (averagely 0.81 to 1.59), low Na2O (average 2.09 wt. %), and CaO (average 2.37 wt. %). Moreso, they exhibit low FeOt/(FeOt + MgO) ratios (0.64 – 0.80 wt%), low to moderate Na2O+K2O-CaO ratio (2.41 – 5.41 wt%), high Na2O+K2O (average 6.42 wt%) and K2O/Na2O ratios (average 2.11 wt%), as well as high Mg# (30.49 – 50.22), low molar CaO/(MgO + FeOt) (0.19 – 0.63 wt%) and molar Al2O3/(MgO +FeOt) ratio (2.10 – 4.31 wt%). Discrimination diagram shows that the granitoids are products of sedimentary protolith (metagreywacke) formed within a syn-collision and supra-crustal setting. The constituent mineral assemblages in the granitoids (quartz, plagioclase, alkali feldspar, biotite, hornblende, titanite, iron oxides) from the northern Hawal massif are obviously related to the condition of evolution and compositions of the protolith.

Highlights on Geochemical Changes in Archaean Granitoids and Their Implications for Early Earth Geodynamics

The Archaean (4.0–2.5 Ga) continental crust is mainly composed of granitoids, whose geochemical characteristics are a function of their formation mechanisms and components, as well as physical conditions of their source. Therefore, revealing changes in Archaean geodynamic processes requires understanding of geochemical changes in Archaean granitoids. This paper compares key geochemical signatures in granitoid occurrences from the Eoarchaean to Neoarchaean Eras and aims to highlight changes or variations in their geochemical signatures. The study is performed by exploring and comparing geochemical and geochronological datasets of Archaean granitoids compiled from literature. The results show that two end-members of sodic TTGs (tonalite–trondhjemite–granodiorite) occur throughout the Archaean: low- and high-HREE (heavy rare earth elements) types. A profound change in granitoid geochemistry occurred between 3.0 and 2.5 Ga when multi-source high-K calc-alkaline granitoid batholiths emerged, possibly indicating the onset of modern-type plate tectonics.

Petrogenesis and tectonic implications of early Paleozoic granitoids in East Kunlun belt: Evidences from geochronology, geochemistry and isotopes

The East Kunlun Orogenic Belt (EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism. Here we report the petrology, bulk geochemistry, zircon U–Pb dating and, Lu–Hf and Sr–Nd isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U–Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450–430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their (87Sr/86Sr)i values range from 0.7059 to 0.7085, εNd(t) values from –1.6 to –6.0 and the zircon εHf(t) values show large variations from +9.1 to –8.6 with Hf model ages (TDM2) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.

1.88 Ga São Gabriel AMCG association in the southernmost Uatumã-Anauá Domain: Petrological implications for post-collisional A-type magmatism in the Amazonian Craton

In the southernmost Uatumã-Anauá Domain, central Amazonian craton (Brazil), crop out 1.98Ga basement inliers represented by (meta)leucosyenogranites and amphibolites (Igarapé Canoas Suite), 1.90–1.89Ga high-K calc-alkaline granitoids (Água Branca Suite), a 1.88–1.87Ga alkali-calcic A-type volcano-plutonic system (Iricoumé-Mapuera), Tonian SiO2-satured alkaline granitoids, 1.45–1.25Ga orthoderived metamorphic rocks (Jauaperi Complex) and Orosirian–Upper Triassic mafic intrusions. New data on petrography, multielementar geochemistry, in situ zircon U–Pb ages and Nd and Hf isotopes of alkali-calcic A-type granites (São Gabriel Granite, Mapuera Suite) and related rocks are indicative of a 1.89–1.87Ga volcano-plutonic system integrated to the São Gabriel AMCG association. Its magmatic evolution was controlled by the fractional crystallization combined with magma mixing and cumulation processes. Nd isotope values (εNdt values=−3.71 to +0.51 and Nd TDM model age=2.44 to 2.12Ga) and U–Pb inherited zircon crystals (2115±22Ma; 2206±21Ma; 2377±17Ma, 2385±17Ma) of the São Gabriel system indicate a large participation of Siderian–Rhyacian crust (granite-greenstones and granulites) and small contribution of Rhyacian mantelic magma. εHft values (+5.2 to −5.8) and Hf TDM ages (3.27–2.14Ga) also point to contribution of Paleoarchean–Rhyacian crustal melts and small participation of Siderian–Rhyacian mantle melts. Residual melts from the lower crust have been mixed with basaltic melts generated by partial melting of the subcontinental lithospheric mantle (peridotite) in a post-collisional setting at 1.89–1.87Ga. The mafic melts of such a mixture could have been originated through partial melting of residual ocean plate fragments (eclogites) which ascended onto a residual mantle wedge (hornblende peridotite) and melted it, resulting in modified basaltic magma which, by underplating, led heat to the anatexis of the lower continental crust. This widespread alkali-calcic A-type magmatism was caused by destabilization and magmatic reactivation in the Ventuari-Tapajós and Central Amazonian Provinces, resulting from the Ventuari-Tapajós collision periods. Younger igneous reactivations have been registered at 1.45 to 1.25Ga, ~1.0Ga and ~100Ma, culminating with the production of mafic and felsic alkaline magmas, along of the northern border of the Amazon Basin.

About this title ‐ Crust–Mantle Interactions and Granitoid Diversification: Insights from Archaean Cratons

This Special Publication sheds light on crust formation and tectonic processes in early Earth by focusing on Archaean granitoids and related rocks from West Greenland in the North Atlantic Craton, Karelia Province of the Fennoscandian Shield, Eastern Dharwar and Bundelkhand cratons in the Indian Shield and Bug Complex of the Ukrainian Shield. Resulting from the IGCP-SIDA 599 project ‘The Changing Early Earth’, this compilation of papers provides explanations on the nomenclature of Archaean granitoids and explores the petrology, element and isotope geochemistry, geochronology and metamorphism of granitoids and supracrustal rocks of variable metamorphic grade. This volume provides information on the increase and timing of crust-mantle interactions and granitoid diversification from early Archaean protoliths of island arc origin to the emergence of multi-source high-K calc-alkaline granitoid batholiths at convergent continental margins. The formation of abundant granitoid batholiths suggests a significant change in mantle dynamics and plate tectonics towards the end of the Archaean.

The diversification of granitoids and plate tectonic implications at the Archaean–Proterozoic boundary in the Bundelkhand Craton, Central India

Abstract The Bundelkhand Craton in Central India holds a large Archaean granitoid complex consisting of cores of TTG (tonalite–trondhjemite–granodiorite) gneisses of island arc or oceanic origin surrounded by abundant younger high-K calc-alkaline granitoids. Major and trace element groupings and ion probe U–Pb zircon datings of the groups show a time gap of 130 Ma between the main formation episodes of the TTGs (3.5/3.3–2.7 Ga) and the emplacement of the first high-K granitoids (2.57–2.54 Ga). Based on their geochemical diversity, the high-K calc-alkaline granitoids can be divided into low-silica high-magnesium (LSHM) granitoids such as sanukitoids and Closepet-type granitoids, and high-silica low-magnesium (HSLM) monzogranites with low-HREE and low-Eu subgroups. The former group points to mantle or mixed mantle and crustal sources, and the latter to pure crustal sources. All the varieties of the high-K granitoids formed within a narrow time span, which indicates large-scale partial melting and fluid activity in the mantle and crust, possibly resulting from a slab breakoff or delamination at the margin of an Archaean TTG continent. Supplementary material: Major and trace element concentrations and U-Pb results of granitoids from the Bundelkhand Craton are available at https://doi.org/10.6084/m9.figshare.c.3576377

Petrology and geochemistry of charnockites (felsic ortho-granulites) from the Kerala Khondalite Belt, Southern India: Evidence for intra-crustal melting, magmatic differentiation and episodic crustal growth

The Kerala Khondalite Belt (KKB) of the southern India encompasses volumetrically significant magmatic components. Among these, orthopyroxene-bearing, felsic ortho-granulites, popularly known as charnockites in Indian context, constitute an important lithology. In contrast to the well-known phenomena of arrested charnockitization, the geochemical characteristics and petrogenesis of these ortho-granulite suites remain poorly studied, leaving geodynamic models envisaged for the KKB highly conjectural. In this paper, we try to bridge this gap with detailed results on orthopyroxene-bearing, felsic ortho-granulites spread over the entire KKB and propose a new petrogenetic and crustal evolution model.Based on geochemical characteristics, the orthopyroxene-bearing, felsic ortho-granulites (charnockites sensu lato) of KKB are classified into (1) tonalitic (TC), (2) granitic (GC), and (3) augen (AC) suites. Members of the TC follow sodic (characterized by decreasing CaO/Na2O), whereas those of the GC and AC follow calc-alkaline trends of differentiation. Geochemical patterns of the TC resemble those of the Archaean tonalite–trondhjemite–granodiorite (TTG) suites, with slightly magnesian character (average Mg#=33), moderate LREE (average LaN=154), low HREE (average YbN=6) and Y (1–53ppm; average 11ppm). The TC is also characterized by positive to slightly negative europium anomalies (Eu/Eu*=0.7 to 1.67). The GC and AC suites, on the other hand, resemble post-Archaean arc-related granites. The GC displays ferroan nature (average Mg#=22), low to moderate degrees of REE fractionation (average [La/Yb]N=34.84), high contents of Y (5–128ppm; average 68), and low Sr/Y (1–98) ratios. Significant negative Eu anomalies (Eu/Eu*=0.18–0.91; average 0.50) and low Sr (65–690ppm) are also noted in the GC. Similar chemical characteristics are shown by the AC, with ferroan nature (average Mg#=21), low to moderate degrees of REE fractionation (average [La/Yb]N=26), high contents of Y (71–99ppm; average 87), and low Sr/Y (average 2) ratios with significant negative Eu anomalies (Eu/Eu*=0.03–0.31; average 0.23) and low Sr (average 160ppm) contents. The protoliths of the TC are interpreted as being derived from partial melting of thickened oceanic-arc crust composed of Archaean mafic composite source rocks (i.e., eclogite and/or garnet amphibolite) with a garnet amphibolite residue. Geochemical features of the GC, such as high Rb/Sr (average 1.80) and Ba/Sr ratios (average values >6), are considered as evidence for crustal reworking in their genesis, suggesting remelting of a quartzo-feldspathic (TTG) source, within the plagioclase stability fields.The geochemical features of the felsic ortho-granulite suite, substantiated with published geochronological data on members of the TC, GC, and AC suites, suggest a four-stage crustal evolution of the KKB. The first stage is marked by the formation of an over-thickened oceanic-arc. Zircon Hfc model ages of the TC and GC suites constrain the time of this juvenile magmatic crust-forming event as Meso- to Neoarchaean (2.8 to 2.6Ga). The second stage corresponds to the production of TTG magmas by melting of the over-thickened oceanic-arc crust, subsequent to basaltic underplating during Palaeoproterozoic (ca. 2.1Ga). The third stage was initiated by a transition in subduction style from shallow to steep due to continent-arc accretion. This stage is marked by the formation of granitic magmas through partial melting of the TTG crust and their differentiation into GC and TC. The zircon crystallization ages (1.89 and 1.85Ga) of the GC indicate arc accretion occurred during the Palaeoproterozoic. The fourth stage of crustal evolution is correlated with the Mesoproterozoic (~1.5Ga) emplacement of megacrystic K-feldspar granites (protoliths to the AC and augen gneisses). The distinct petrography, geochemistry and crystallization ages of the AC suggests recurrence of megacrystic, high-K calc-alkaline granitoids as the product of final phases of crustal-remelting marking subduction cessation. All these magmatic events are fairly well correlated with the major episodes of crustal growth observed in the once contiguous continental fragments (Sri Lanka and Madagascar) and worldwide events (2.7, 1.9, and 1.2Ga) implying similar episodic nature in the lower crustal evolution of the KKB.

Crystallization conditions of porphyritic high-K calc-alkaline granitoids in the extreme northeastern Borborema Province, NE Brazil, and geodynamic implications

An integrated textural and chemical study on amphibole, biotite, plagioclase, titanite, epidote, and magnetite was conducted in order to estimate crystallization conditions, along with possible geodynamic implications, for six Ediacaran porphyritic high-K calc-alkaline granite plutons (Monte das Gameleiras, Barcelona, Acari, Caraúbas, Tourão, and Catolé do Rocha) intrusive into Archean to Paleoproterozoic rocks of the São José do Campestre (SJCD) and Rio Piranhas-Seridó (RPSD) domains, northern Borborema Province. The studied rocks include mainly porphyritic leucocratic monzogranites, as well as quartz-monzonites and granodiorites. Textures are marked by K-feldspar megacrysts (5–15 cm long) in a fine-to medium-grained matrix composed of quartz, plagioclase, amphibole, biotite, as well as titanite, epidote, FeTi oxides, allanite, apatite, and zircon as accessory minerals. Amphibole, biotite and titanite share similar compositional variations defined by increasing Al and Fe, and decreasing Mg contents from the plutons emplaced into the SJCP (Monte das Gameleiras and Barcelona) towards those in the RPSD (Acari, Caraúbas, Tourão, and Catolé do Rocha). Estimated intensive crystallization parameters reveal a weak westward range of increasing depth of emplacement, pressure and temperature in the study area. The SJCD plutons (to the east) crystallized at shallower crustal depths (14–21 km), under slightly lower pressure (3.8–5.5 kbar) and temperature (701–718 °C) intervals, and high to moderate oxygen fugacity conditions (+0.8 < ΔFQM < +2.0). On the other hand, the RPSD plutons (to the west) were emplaced at slightly deeper depths (18–23 km), under higher, yet variable pressures (4.8–6.2 kbar), temperatures (723–776 °C), and moderate to low oxygen fugacity conditions (−1.0 < ΔFQM < +1.8). These results reinforce the contrasts between the tectono-strutuctural domains of São José do Campestre and Rio Piranhas-Seridó in the northern Borborema Province.

Magma sources and petrogenesis of the early–middle Paleozoic backarc granitoids from the central part of the Qilian block, NW China

The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447Ma for the S-type and 419–451Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu*=0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu*=0.71–1.16). The initial (87Sr/86Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The εNd(450Ma) values are −8.9–−4.1 and −9.7–+1.9 for the S-type and I-type granitoids, respectively. The TDM values are 1.5–2.4Ga for the S-type and 1.0–2.3Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60millionyears after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50millionyears. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0Ga for the Qilian block.