Hybrid Granitoids Research Articles

Neoarchean magmatism and Rhyacian reworking in the northeast of the Amapá Block, southeastern Guiana Shield, Brazil: Geochemistry, U–Pb geochronology, and Hf–Nd isotopes

This study investigates the age, geochemical nature, sources, and Rhyacian reworking of the Neoarchean magmatism at the northeastern portion of the Amapá Block, southeastern Guiana Shield (northeast Amazonian Craton). This block consists of a large Archean continental landmass strongly reworked during the Transamazonian orogeny (2.26–1.95 Ga). We provide the very first geochemical results for Archean basement units of the Amapá Block, which are the Mesoarchean Tumucumaque and Neoarchean Guianense complexes, and Neoarchean Mungubas Granite. The first two exhibited geochemical affinity with enriched TTG-type and hybrid granitoids, respectively, while the Mungubas Granite showed affinity with biotite granites. Such affinity with C-type granitoids indicates that the genesis of these units involves partial melting of crustal sources. LA-MC-ICP-MS zircon U–Pb and Lu–Hf, and whole-rock Sm–Nd data were obtained for the Neoarchean Mungubas Granite and Guianense Complex. In both units, zircon U–Pb dating provided a distribution of dates that span ∼50 Ma forming two groups with distinct mean 207Pb/206Pb ages of ∼2.70 Ga and ∼2.65 Ga, respectively. The older age is considered as the crystallization/emplacement age of the Mungubas Granite and the Guianense orthogneiss protolith, while the younger one is ascribed to concealed Pb loss. The recognition of Mesoarchean inherited zircon core and xenocryst with ages of 2.84 Ga and 2.99 Ga suggest that these units reworked older basement rocks from the Amapá Block. Subchondritic ԐHf(2.70 Ga) of zircon and ԐNd(2.70 Ga) of whole-rock, along with their respective Hf-TDMC (3.6–3.2 Ga) and Nd–TDM (3.6 Ga) model ages, for both units, reflect the substantial crustal reworking of predominant Paleoarchean sources during the Neoarchean in the northeastern Amapá Block. In addition, U–Pb dating on titanite crystals from the Guianense orthogneiss yielded an unprecedented ∼2.05 Ga age, arguing that a Late Rhyacian metamorphic event affected the Archean orthogneisses. This 2.05 Ga event coincides with the emplacement of Rhyacian granitoids in the area, as well as with the 2.06–2.04 Ga late orogenic HT granulite facies and amphibolite facies metamorphic events identified, respectively, at the northern border and in the central-southern portion of the Amapá Block.

The Amaros and Dois Córregos plutons: Mesoarchean and Orosirian magmatism in the northern Guanhães basement inlier, Araçuaí orogen, Brazil

In this paper we present new field, geophysical, petrographic, geochemical and geochronological data from granitic rocks newly recognized at the northern Guanhães block, one of the basement inliers of the Araçuaí orogen, eastern South America. Our data allowed the identification of two granitic units, namely Amaros and Dois Córregos plutons, intrusive in the Archean orthogneisses of the Guanhães Complex. In the studied area, the Guanhães Complex comprises muscovite-biotite gneisses, hornblende-biotite gneisses and clinopyroxene-hornblende-biotite gneisses. These rocks have distinct chemical characteristics, which range from TTG series to Late Archean hybrid granitoids. The Amaros pluton is composed of muscovite-bearing biotite metasyenogranites. These rocks are high-K calc-alkaline, magnesian and peraluminous, and were interpreted as a product of partial melting of an older TTG crust. U–Pb ICP-MS dating of zircons yielded a crystallization age of 2916 ± 19 Ma for Amaros pluton, which makes it the first Mesoarchean granite pluton delimited and detailed within the Guanhães block. Mesoarchean magmatism (ca. 2.9 Ga) similar in composition to the Amaros pluton is well known at the Porteirinha block, another basement inlier to the north of the Guanhães block, which raises questions about a connection between the two domains. The Dois Córregos pluton, firstly identified through geophysical analysis, is composed of hornblende-bearing biotite syenogranite crystallized at 2045.5 ± 24 Ma Ma (U–Pb in zircons, ICP-MS). These rocks are alkali-calcic to alkalic, magnesian to ferroan, ranging from per-to metaluminous and were interpreted as a product of the partial melting of continental crust, in a late-collisional stage of the Minas-Bahia orogeny, during the amalgamation of São Francisco-Congo paleocontinent.

The Andaluca plutonic unit, Vinquis Intrusive Complex, Argentina: An assessment of mantle role in the genesis of Early Carboniferous weakly peraluminous A-type granites in the pre-Andean SW Gondwana margin

During the Early Carboniferous, significant intracontinental magmatism was developed in the retro-arc region of the SW margin of Gondwana between ca. 27° and 31°S. This magmatism consisted of metaluminous to weakly peraluminous A-type granites, strongly peraluminous A-type granites (A- to S- hybrid granitoids) and, in a lesser extent, (sub-)volcanic felsic (rhyolites and trachytes) and mafic (alkaline basalts and lamprophyres) rocks. The Vinquis Intrusive Complex (VIC) registers these two compositional varieties of A-type granites: the Vinquis Unit (VU) represents the strongly peraluminous granites and the Andaluca Unit (AU) the weakly peraluminous granites. The adjacent Zapata Intrusive Complex (ZIC) also contains metaluminous to weakly peraluminous A-type granites. The AU is a semi-elliptical plutonic body of approximately 60 km 2 located in the southwestern part of the VIC, intruding the Vinquis Unit. The AU comprises three dominant rock types: i) quartz monzonite, ii) syenogranite and iii) alkali feldspar granite that can be classified as F-rich (calculated F content: 1950–5700 ppm), ferroan (FeO t /(FeO t + MgO) = 0.86–0.95) and weakly peraluminous (ASI = 1.03–1.10) A-type (Zr + Nb + Ce + Y = 364–570 ppm; Ga = 20–23 ppm) granitoids (SiO 2 wt% = 67.8–75.4% wt%). This unit was emplaced in early Carboniferous time (U Pb zircon crystallization ages of 346 ± 3 Ma and 342 ± 3 Ma). The AU has 87 Sr/ 86 Sr t , εNd t and εHf t values ranging from 0.7092 to 0.7140, −2.6 to −3.6 and − 16.5 to −3.3, respectively. These isotopic suggest that the parental magma of AU dominantly involved variable mixtures of mantle-derived components (magmas/fluids) and peraluminous continental crust. The extremely felsic granites of the AU (SiO 2 > ~72%) with a strongly fractionated composition (Rb > 336 and Sr < 70 ppm and Eu/Eu* < 0.22) supports extensive fractional crystallization. The high contents of fluorine and HFSE in AU could be explained as derived from an F- HFSE- and alkali-rich parental mafic magma plus contributions from F-bearing minerals assimilated from the country rock. Likewise, the magmatic differentiation processes from these reduced mafic magmas could explain the ferroan character of the AU granitoids. We envision three stages in the origin of these rocks: (1) fluids and magmas from the asthenospheric mantle metasomatize and melt the subcontinental lithospheric mantle (SCLM), the alkali-rich mafic melts produced are emplaced at the base of the crust, transfer heat to the crust and melt it, generating strongly peraluminous A-type magmas; (2) continued introduction of alkali-rich mafic magmas into the deep crust produce extensive assimilation of the preheated crust in equilibrium with mafic cumulates (generated by reaction and/or fractionation); (3) the hot magmas so produced migrate into the middle-upper crust to produce ferroan weakly peraluminous A-type granitoids. • The Andaluca plutonic unit of the Vinquis Intrusive Complex crystallized between 346 ± 3 Ma and 342 ± 3 Ma. • Andaluca Unit shows a F-rich weakly peraluminous ferroan A 2 -type affinity. • The high contents of fluorine and HFSE in Andaluca Unit can be explained from an F-rich parental alkaline mafic magma. • The Andaluca Unit granitoids can be generated through combined crustal assimilation and fractional crystallization of magmas derived from the metasomatized subcontinental lithospheric mantle.

Investigating assembly timing of Ediacaran Serra dos Órgãos batholith – Hints on prolonged magmatism at Ribeira belt, SE Brazil

The Pan-African/Brasiliano orogeny, result of the West-Gondwana assembly from the Neoproterozoic to Ordovician, had produced the Ribeira and Araçuaí belts at the edges of the São Francisco and Congo cratonic margins. In the central Ribeira belt, the docking of accretionary systems to the reworked continental margin of the São Francisco paleoplate culminated in a complex Ediacaran granite production event. Syn-to late-collisional I- and S-type granites and hybrid granitoids intruded the reworked margins and accreted continental masses, as well as the Tonian to Ediacaran juvenile magmatic arcs represented by the Serra da Prata and Rio Negro Complexes. The Serra dos Órgãos batholith is the main intrusion emplaced at the juvenile crust, forming an elongated NE-SW trending tabular body that crops out in the highland region of Rio de Janeiro State, Southeast Brazil. Geochemical and geochronological data in addition to field and petrological evidence was gathered to explore the assembly timing of the SOB granitic end-member. Zircon U–Pb SHRIMP and LA-ICP-MS geochronological data yield a prolonged emplacement timelapse for the studied granites and, along with published U–Pb ages of the SOB granodioritic end-member, enable the characterization of the Serra dos Órgãos as a composite batholith. The wide time interval of heat input inside intermediate crust is consistent with a prolonged, slow-cooling hot orogenic belt model for the Araçuaí-Ribeira Orogenic System.

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.

Rhyacian-Orosirian tectonic history of the Juiz de Fora Complex: Evidence for an Archean crustal reservoir within an island-arc system

The southern São Francisco Paleocontinent (SFP) comprises Archean nuclei and Paleoproterozoic complexes encompassing magmatic arcs juxtaposed during a Rhyacian to Orosirian orogenic event. The Juiz de Fora Complex (JFC) represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and later accreted to the southeastern margin of the SFP. Here we report new petrological, geochemical, whole-rock Nd and Sr data, as well as zircon U–Pb ages from felsic and mafic orthogranulites from the JFC. The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episodes in the context of the consolidation of São Francisco Paleocontinent during the Rhyacian–Orosirian. Pre collisional Island Arc tholeiites (IAT), Tonalites-Trondhjemites-Granodiorites (TTGs) and sanukitoid magmatism occurred from 2200 Ma to 2085 Ma. This was followed by post-collisional magmatism, which is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks. Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negative εNd(t) associated with Meso- to Neoarchean Nd TDM model ages as well as inherited zircon grains from the hybrid granitoids. The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc, but here we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC, suggesting a Mesoarchean crustal source involved in the JFC evolution.

Crustal melting vs. fractionation of basaltic magmas: Part 2, Attempting to quantify mantle and crustal contributions in granitoids

Granitic melts may form either directly, by melting of pre-existing crustal rocks, or by fractionation of mafic to intermediate magmas, typically mantle-derived. Each model is applicable to distinct portions of the Earth at different times. Whenever there is an important flux of mafic magmas from the mantle, differentiation of basaltic magmas dominates. In contrast, locations with a lower mafic magma flux, elevated thermal gradients and/or a fertile, thick crust are dominated by crustal melting and reworking. This only partly overlaps with the dichotomy between magmatic arcs and collision zones, as places like e.g. inverted back-arcs also feature large-scale crustal melting, whereas post-collisional domains include a sizeable mantle-derived component. Petrogenesis of individual granitic suites probably cannot be accounted for by pure, end-member models, as these suites typically feature a fair proportion of hybrid or ambiguous granitoids. Thus, we explore various petrogenetic and geological scenarios leading to the formation of hybrid granitoids at various scales. Finally, we outline possibilities to quantify the respective contributions of crust and mantle involved in their formation – hopefully, paving the way for a better understanding and more rigorous discussion of the mechanisms of crustal growth and recycling.

Granitik Buzul Çakıllarında Zirkon Tipolojisi Çalışması: Toridler’den Örnek Bir Çalışma (Türkiye)

The Late Ordovician glacial rocks from the northern part of the Gondwana are encountered in Taurides and Southeast Anatolia Autochtone Zone. In this study, zircon typology and zircon saturation temperature invetigations are performed on zircon minerals separated from the granitic glacial pebbles from the Feke-Saimbeyli-Ceralan and Feke-Gokmenler (Adana) areas in the east Taurides and Silifke-Ovacik (Mersin) in the central Taurides. Based on the zircon typology method, among the studied samples, DPK-30 is described as calc-alkaline hybrid granitoids bearing mafic enclaves, DPK-44 is identified as granitoids formed from wholly or partly continental crust with rare mafic microgranular xenoliths and low mantle contribution, and DPK-72 is defined as alkaline series granitoids, which are mantle originated rocks observed in subvolcanic and anorogenic complexes pointing out to hot and dry magma source. These descriptions are generally agreeable with the previous geochemical assessments, including isotopic data, on these rocks. Formation temperatures of studied granitic rocks are suggested as 750°C and 789°C for DPK-30, 700°C and 845°C for DPK-44, and 650°C and 790°C for DPK-72, based on zircon typology method and by zircon saturation temperature calculation, respectively. These temperature ranges show similarities to the present temperature data in literature on the Neoproterozoic granitoids from the Sina Peninsula and the Eastern Egypt Desert. As a result, zircon typology method and zircon saturation temperature calculation studies, combined with the other analytical data, can be beneficial in determining the source regions of the granitic glacial pebbles.

Peel-back controlled lithospheric convergence explains the secular transitions in Archean metamorphism and magmatism

The preserved archive of continental crust suggests that various secular geologic and geochemical transitions took place during the Mesoarchean and Neoarchean (∼3.2–2.5 Ga). These transitions, which are imprinted in the metamorphic and magmatic rock-record, include the emergence of paired metamorphism, an increasing depth of tonalite-trondhjemite-granodiorite (TTG) formation, the widespread appearance of granites and changes in the composition of mafic rock. Previous studies have argued that these secular transitions reflect secular cooling of the mantle and herald a gradual transition from pre-plate tectonic to plate tectonic regimes. However, their tectonic driver remains elusive, in part due to a lack of detailed understanding of lithospheric dynamics prevalent during this transitional period when the mantle was warmer compared to the present-day. Here, we demonstrate that lithospheric convergence driven by peel-back (/peeling) process under warmer mantle conditions – termed as peel-back convergence – may explain the late Archean secular transitions. This tectonic phenomena features large-scale peeling (a form of delamination, but not dripping) of the mantle lithosphere with or without lower crustal rocks during convergence. We simulated numerical models of peel-back convergence under Archean crust-mantle conditions and predicted the pressure-temperature (P-T) conditions of crustal metamorphism and melting. The evolution of peel-back convergent setting features juxtaposition of a colder, compressional regime with thickened crust that forms at the site of peeling, and a warmer, extensional regime with thinned crust forming behind it. The metamorphic and magmatic P-T conditions prevalent in these two tectonothermal sites replicate the features of the late Archean rock record, including the: appearance of coeval high-T/P and intermediate-T/P metamorphic rocks; greater abundance of high-T/P relative to intermediate-T/P metamorphic rocks; dominant formation of TTGs at higher pressures where garnet ± rutile is stable in the residue; reworking of pre-existing felsic rocks/sediments to produce potassic granites; and interaction of crustal melts and mantle to form hybrid granitoids. Thus, peel-back convergence can explain the thermobaric bimodality of late Archean rocks within an asymmetric tectono-thermal framework. However, unlike modern convergent plate boundaries, the asymmetry is controlled by lithospheric peeling.

Geology and geochemical constraints on the origin of the Mesoarchean granitoids from Carajás province, Amazonian craton

The Carajás province (CP) is the largest preserved Archean core of the Amazonian craton. In this paper we present a detailed work about the Tucumã area located in the northwestern portion of the Rio Maria domain of the CP, where more detailed studies had not yet been carried out. The new geological and geochemical data obtained allowed the identification of Mesoarchean granitoids of different natures that resemble typical late-Archean granitoids (TTG, leucogranites, sanukitoids and hybrid granites) identified in several cratons around the world. The most extensive unit in the Tucumã area is the Leucomonzogranitic batholith which is intrusive in a tonalite crust of TTG affinity, that exhibits an older N-S structural pattern commonly found in oldest rocks (greenstone belt sequence). The batholith is coeval with small granitoid intrusions that occur as lenses controlled by NE-SW and E-W direction anastomosed shear zones. Apart from the tonalite, these granitoids show affinity with the calc-alkaline series and are individualized in four units. The porphyritic granodiorite is a magnesium-rich unit that has moderate K2O/Na2O ratio and higher levels of Ba, K and Th, indicating similarities with the Transitional TTG suites (Yilgarn craton). Equigranular granodiorites are equivalent of sanukitoid suites; they show enrichment in Sr and compatible elements (Mg, Cr, and Ni) and depletion in HREE. Hybrid granitoids were identified as High-HFSE granites (medium- and high-Ba) that share some geochemical affinities with Closepet granite of the Dharwar craton. The Leucomonzogranite is enriched in LILE and exhibit negative Eu anomalies, which indicate crustal reworking processes. This granitoids are syntectonic bodies that underwent a progressive deformation processes that started before the magma crystallization was complete, under high temperatures (>500 °C) conditions compatible with those of the amphibolite facies. Two phases of magmatism are recorded in the RMD, which would be responsible for the formation of these granitoids. The first phase (2.98-2.92 Ga) is related to formation of a thick TTG crust from parcial melting of an oceanic plateau or a thickened mafic crust. The second magmatism phase (~2.87 Ga) initiated due to thermal events in a collisional setting, where both crustal rework processes and generation of juvenile magmatism occurred at the same time, resulting in the formation of heterogeneous plutons, at different crustal levels that were emplaced by mechanisms analogous to diapirs.

Crustal anatexis and mantle-derived magmas forming Neoarchean A-type granitoids in Carajás Province, northern Brazil: Petrological evidence and tectonic control

Neoarchean hybrid granitoids from the Vila União suite are located in the central portion of the Canaã dos Carajás domain, Carajás Province (Amazonian craton, Brazil), and suggest that magma mixing events played an important role in their origin. According to complete evidence, including field observations, petrography, geochemical modeling, zircon SHRIMP and LA-MC-ICP-MS U-Pb ages, and Nd-Hf isotope data, we propose a geodynamic model based on initial mafic underplating promoted by lower crustal delamination, which generated mantle-derived mafic melts that were injected into the lower/middle crust (composed of Mesoarchean felsic granulite) and caused partial melting, producing leucogranitic melts. The interaction between these contrasting felsic and mafic magmas occurred by both mixing and mingling processes. The hybrid magma ascent and emplacement occurred in a N–S pure shear-dominated transpressional tectonic regime, with an E–W sinistral sense of tectonic movement, in which the hybrid melt was channeled into pre-existing shear zones trending E–W (Itacaiúnas shear zone). This tectonic regime (transpressional) proceeded coevally with the hybrid magma cooling, producing 2.75–2.73 Ga Neoarchean deformed A-type granitoids with a syntectonic nature in the Vila União suite, in addition to the Pium diopside-norite, which represents the mafic endmember generated by underplating.

The epilogue of Paleo-Tethyan tectonics in the South China Block: Insights from the Triassic aluminous A-type granitic and bimodal magmatism

Triassic aluminous A-type granitoids, mostly peraluminous biotite granites, occur in various areas in the South China Block. Here, we focus biotite granites from three plutons and one granitic dike that provide new insights into the Triassic tectono-magmatic evolution of South China Block. The peraluminous biotite granites from Zhulanbu, Xiaotao and Wengshan plutons all emplaced at ca. 225 Ma and contain Fe-rich biotites. Their high FeOT/(FeOT + MgO) and Ga/Al ratios and HFSE contents imply an aluminous A-type affinity. The geochemical features and heterogeneous Sr-Nd-Hf isotopic compositions of these A-type granitoids, together with previous results, indicate their derivation from disequilibrium partial melting of a sedimentary source or fractional crystallization of coeval monzonitic melts. The Xiamao granitic porphyry dike emplaced synchronously with the nearby Xiamao diabase dike at ca. 225 Ma. This granitic dike is highly siliceous and its geochemical characteristics imply derivation from crustal assimilation and fractional crystallization (AFC) of mafic melt. Closure of Paleo-Tethyan oceanic basin and final collision of the South China Block with the Indochina and the North China Blocks were completed by ca. 230 Ma. The onset of A-type granitic magmatism occurred near Triassic dextral shear zones or surrounded by Triassic NE-SW strike-slip shear zones that generated localized extension under an overall compressional regime until 230 Ma. The subsequent formation of abundant A-type granitoids, bimodal dikes and hybrid granitoids hosting mafic microgranular enclaves implies the tectonic regime to a within-plate post-collision extensional setting with more intense mafic magmas underplating, marking the epilogue of Paleo-Tethyan tectonics in the South China Block.

Zircon U–Pb ages and geochemistry of the late Archaean granitoids in the Zanhuang Complex: Records of an arc–continent collision event at the end of Archaean

The late Archaean witnessed a critical transition of the composition of the continental crust from predominantly sodic tonalite‐trondhjemite‐granodiorites (TTGs) to a combination of TTGs and increasing proportion of potassic calc‐alkaline granitoids. This shift is also well recorded in the Zanhuang Complex located in the central part of the North China Craton (NCC). In this work, we present a detailed geochemical study of these granitoids and subdivide them into four groups, that is, TTGs, sanukitoids, crustal‐sourced granitoids, and hybrid granitoids. The TTGs in the Zanhuang Complex may have formed at a longer and earlier period during ~2.7 to ~2.5 Ga as the first stage. They show typical TTG characteristics, such as high SiO2, Na2O, and Sr/Y and depletion of Nb, Ta, Ti, and HREE. The TTGs are interpreted to have formed in a subduction‐related environment. The other three groups of granitoids formed at a shorter and later stage. The sanukitoid sample shows high MgO and Mg# and other geochemical signatures of typical Archaean sanukitoid affinity, yielding a weighted mean zircon 207Pb/206Pb age of 2,517 ± 5 Ma as the crystallization age. The sanukitoid magma derived from partial melting of a hydrous mantle peridotite source metasomatized by slab‐derived melts or fluids. The crustal‐sourced granitoids, including a new sample (~2,510 Ma) in this work, the Jiandeng granite (~2,490 Ma), and the Huangcha/Wangjiazhuang granite (2,488 to 2,517 Ma) show signatures of a mainly crustal source such as high SiO2 and K2O, low MgO and Mg# values, and weakly peraluminous. The hybrid granitoids represented by the Haozhuang granitoid (2,511 to 2,528 Ma) are characterized by enrichment in both incompatible (LILE and LREE) and compatible (Mg, Ni, and Cr) elements and may have formed by mixing/contamination of multiple magmas or sources. The temporal and spatial distributions of these groups of granitoids indicate that the Zanhuang Complex experienced a subduction–collision event between the Fuping arc and the Eastern Block of the NCC at the end of Archaean.

Oligocene subduction-related plutonism in the Nodoushan area, Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO2 = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO2 = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045–0.707959, εNd(t) = −3.23 to +3.80, and the Nd model ages (TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.705513 to 0.707275 and εNd(t) from −1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.

КОНТАМИНАЦИЯ МАГМЫ, ОСОБЕННОСТИ ПЕТРОГЕНЕЗИСА И РАСПРЕДЕЛЕНИЕ РУДНОГО ВЕЩЕСТВА В ПОРОДАХ НИКЕЛЕНОСНОЙ ФОРМАЦИИ СРЕДИННО-КАМЧАТСКОГО МАССИВА (часть третья)

This is the final article that describes various for petro- and oreogenesis consequences of the contamination of nickel-bearing magma with siliceous material (quartzites), which led to the replacement of ultrabasic ore-hosting rocks (cortlandites) with ultramafic (amphibole orthopyroxenites). Besides, the paper describes the products of metamagmatic variations of pyroxene ore cumulates in biotite-amphibole rocks inported by water-potassium fluid. The author shows the unconventional results of fluid influence on similar cumulates with relics of quartzite xenoliths accompanied by the formation of ore granophyric autobreccies, as well as ore-bearing derivatives from the process of magma mixing (auto-contamination). We introduce an intraformational classification of copper-nickel ores by their associations with host rocks of different composition and origin — from juvenile magmatic ultrabasites, contaminated and ultramafites and melanodiorites to hybrid granitoids. The dynamics of the formation of intrusive ore-magmatic systems and the plausible reason of differences in the ore content of large and small intrusions are discussed.

Tonalite–Trondhjemite and Leucogranodiorite–Granite Suites From the Rio Maria Domain, Carajás Province, Brazil: Implications For Discrimination and Origin of the Archean Na-Granitoids

Abstract The Mesoarchean Na-granitoids exposed in the Rio Maria domain, southeastern Amazonian craton, are represented by tonalite–trondhjemite and leucogranodiorite–granite suites. The 2.98–2.92 Ga tonalite–trondhjemites are the most voluminous rock type in the Rio Maria domain and host 2.86 Ga leucogranodiorite–granite plutons. These rocks share common geochemical characteristics, such as relatively high Al 2 O 3 and Na 2 O and low Yb and Y contents, as well as the behavior of the REE. However, based on an extensive geochemical data set, it is possible to show that the leucogranodiorite–granites have higher K 2 O, Ba, Sr, and Rb and lower CaO contents than the tonalite–trondhjemites. The latter are compositionally similar to typical tonalite–trondhjemite–granodiorite (TTG) series and probably originated from partial melting of garnet amphibolites, derived from tholeiitic rocks or from metabasalts of the Identidade greenstone belt, at pressure conditions suitable to produce high, medium, and low La/Yb tonalite–trondhjemite groups. The leucogranodiorite–granites show geochemical affinity with the Transitional TTG of the Yilgarn craton and are related to the Hybrid granitoid group. The ambiguous geochemical character of the Rio Maria leucogranodiorite–granite suite, which shares some characteristics that are typical of the tonalite–trondhjemite rocks and others more commonly observed in the sanukitoid suites, may be related to complex processes involving TTG and sanukitoid magmas. The discrimination of these two Na-granitoid groups helps us estimate the true volume of TTG magmatism in the Rio Maria domain and in understanding the dynamics of petrogenetic processes in the terrane at the end of the Archean.

Granites: petrology, structure, geological setting, and metallogeny

1. What is a granite? 2. Origin of granitic magmas 3. Segregation of granitic melt 4. Genesis of hybrid granitoids: mingling and mixing 5. Transport of granitic magma 6. Emplacement and shape of granite plutons 7. Thermomechanical aspects in the country rocks around granite plutons 8. Crystallization of granitics magmas 9. Microstructures and fabrics of granites 10. Magnetic fabrics in granites 11. Zoning in granite plutons 12. Granites and plate tectonics 13. Precambrian granitic rocks 14. Granite metallogeny

Study of the mineralization potential of the intrusives around Valis (Tarom-Iran)

&lt;p&gt;The study area is located in northwestern Iran in the central Iran zone, specifically the western Alborz sub-zone south of the Tarom-Hashtjin metallogenic zone. The exposed rock units in this area generally include Eocene volcanic rocks (lava flows and pyroclasts belonging to the Karaj formation) and Oligocene granitoid intrusive bodies. The intrusive bodies in the area have a petrographic composition of granite, syenite and monzonite and are mostly metaluminous. The dual characteristics of these intrusives (for example, the behavior of elements such as Rb, P, Ga/Al, Y/Nb, K/Na, and FeO/Fe2O3, the Rb/Nb ratios, the A/CNK molar ratios and the ACF and A/CNK-Fe2O3+FeO diagrams), some of which are consistent with the I nature and others with the S and A natures, show that the rocks are among hybrid granitoids and, in terms of the tectonic setting, lie within the WPG range. According to the Rb/Sr, Zr/Hf, K/Rb ratios, the granite melts that form the aforementioned bodies are not extremely evolved and have not undergone post magmatic activity, which would lead to mineralization. The Sm/Eu and Rb/Ba ratios and the behavior of Rb, Ba and Sr within the aforementioned granitoids show that the rocks are similar to average granitoids unrelated to Li, Be, Sn, W and Ta deposits; they fall within the range of barren granitoids but are partially fertile in Cu.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Resumen&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;El área de este estudio está localizada en el noroeste de la zona central de Irán, específicamente en el oeste de la subzona de Alborz y al sur de la zona metalogénica de Tarom-Hashtjin. Las unidades de roca expuesta en esta área se clasifican generalmente como rocas volcánicas del Eoceno (flujos de lava y piroclastos pertenecientes a la formación Karaj) y como cuerpos granitoides intrusivos del Oligoceno. Los cuerpos intrusivos en el área tienen una composición petrográfica de granito, sienita y monzonita mayormente metaluminosa. Las características duales de estas intrusiones (por ejemplo, el comportamiento de de elementos como Rb, P, Ga/ Al, Y/Nb, K/Na, y Feo/Fe2O3, los índice de Rb/Nb, la proporción molar de los A/CNK y los diagramas ACF y A/CNK-Fe2O3+FeO), algunas de las cuales son consistentes con la índole I y otras con las índoles S y A, muestran que las rocas son granitoides híbridos y, en términos de orden tectónico, subyacen en la cadena WPG. De acuerdo con los índices Rb/Sr, Zr/Hf, K/Rb, los granitos fundieron la forma de los cuerpos sin desarrollarse completamente y sin registrar actividad magmática posterior, lo que llevó a la mineralización. Los índices Sm/Eu y Rb/Ba y el comportamiento del Rb, Ba y Sr al interior de los granitoides mencionados muestran que las rocas son similares al promedio de los granitoides no relacionados con los depósitos de Li, Be, Sn, W y Ta; estos incluyen en el rango de granitoides estériles, pero son parcialemente fértiles en Cu.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;br /&gt;&lt;/strong&gt;&lt;/p&gt;

Geochemical characteristics of the Kuh-e Dom intrusion, Urumieh–Dokhtar Magmatic Arc (Iran): Implications for source regions and magmatic evolution

The Kuh-e Dom Pluton is located along the central northeastern margin of the Urumieh–Dokhtar Magmatic Arc, spanning a wide range of compositions from felsic rocks, including granite, granodiorite, and quartz monzonite, through to intermediate-mafic rocks comprising monzonite, monzodiorite, diorite, monzogabbro, and gabbro. The Urumieh–Dokhtar Magmatic Arc forms a distinct linear magmatic complex that is aligned parallel with the orogenic suture of the Zagros fold-thrust belt. Most samples display characteristics of metaluminous, high-K calc-alkaline, I-type granitoids. The initial isotopic signatures range from εNd (47Ma)=−4.77 to −5.89 and 87Sr/86Sr(i)=0.7069 to 0.7074 for felsic rocks and εNd (47Ma)=−3.04 to −4.06 and 87Sr/86Sr(i)=0.7063 to 0.7067 for intermediate to mafic rocks. This geochemical and isotopic evidence support a mixed origin for the Kuh-e Dom hybrid granitoid with a range of contributions of both the crust and mantle, most probably by the interaction between lower crust- and mantle-derived magmas. It is seem, the felsic rocks incorporate about 56–74% lower crust-derived magma and about 26–44% of the enriched mantle-derived mafic magma. In contrast, 66–84% of the enriched mantle-derived mafic magma incorporates 16–34% of lower crust-derived magma to generate the intermediate-mafic rocks. According to the differences in chemical composition, the felsic rocks contain a higher proportion of crustal material than the intermediate to mafic ones. Enrichment in LILEs and depletion in HFSEs with marked negative Nb, Ba, and Ti anomalies are consistent with subduction-related magmatism in an active continental margin arc environment. This suggestion is consistent with the interpretation of the Urumieh–Dokhtar Magmatic Arc as an active continental margin during subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent.

Monazite to the rescue: U–Th–Pb dating of the intrusive history of the composite Karkonosze pluton, Bohemian Massif

The large (~700km2) composite Karkonosze (Krkonoše) pluton in the West Sudetes, on the border between Poland and the Czech Republic, consists mainly of porphyritic and equigranular granitoids, but contains a range of lithologies from lamprophyre to leucogranite. The absolute age and duration of the plutonism have proved difficult to determine. Previous age measurements by Rb–Sr, Ar–Ar and U–Pb range from ~330 to 290Ma, with more recent results converging to ~320–300Ma. Dating of zircon and monazite from samples of a variety of major and minor lithologies by SIMS U–Th–Pb, several from the geochemical study of Słaby and Martin (2008), has narrowed the possible age range further. U–Pb ages measured on eight of ten zircon and monazite samples are in the range ~314–311Ma. Zircon ages measured on the two major types of porphyritic granitoid are 313±3 and 311±4Ma, and monazite ages are 312±2, 313±3 and 311±3Ma. Monazite from one hybrid granitoid has an age of 314±3Ma, and zircon from another an age of 314±4Ma. Zircon from a composite dyke has an age of 311±6Ma. The monazite U–Pb age of an equigranular granite, at 318±6Ma, is consistent with geological evidence that it is older than the porphyritic granitoids but, because of the relatively large uncertainties, is not conclusive. Zircon from one microgranular enclave is anomalously young, 302±4Ma. Evidence is mounting that the main porphyritic granitoids, hybrid granitoids and composite dykes were emplaced within a short time interval between 314±4 and 311±3Ma. Given the uncertainties, emplacement of these units could have been effectively simultaneous. The larger difference between the ages from the equigranular granite and microgranular enclave, however, indicates that the whole Karkonosze thermal episode possibly lasted as long as 15Ma.