I-type Magmas Research Articles

Variscan lithotectonic units of the Suchý massif in the Strážovské vrchy Mts., Western Carpathians – products of sedimentary, tectonometamorphic and granite forming processes

The present geological investigation of the Pre-Alpine structure of the western part of Strážovské vrchy Mts (the Suchý massif; Western Carpathians) has distinguished three lithologically distinct Variscan lithotectonic units, which originated (1) in the deeper parts of oceanic basin (prevailingly metapelites with different content of organic matter, metabasalts, metacarbonates?); (2) sediments of the continental slope (flyschoid sediments with a predominance of greiwacke sediments; both VmD0); (3) a unit of continent basement primarily of pre-VmD0 granitic composition (orthogneiss). These rock sequences of differing geotectonic provenances were amalgamated and metamorphosed in the pre-intrusive (Pre-Mississipian) stage; pre-VmD2). Regarding the Variscan polyorogenic evolution, Variscan processes in Tatricum represent the Meso-Variscan evolution (VmD). The maximum P-T conditions of orogenic (regional) metamorphism (up to 610 °C and 7.5–8.5 kbar) were not sufficient for more extensive anatexis. Field observations indicated that the production of a limited volume of granitoid melts occurred mainly at the contacts of amalgamated lithotectonic units. Probably due to the heat, produced by the hot line below the collisional orogen and contributing also to unroofing processes (in orogenic phase VmD2) there started new granitization process. This stage of Mississippian VmD2 granite formation is associated with the emplacement of various types of granitoid magma, encompassing the oldest granodiorites with frequent schliers, representing a poorly differentiated and poorly mobile crystal slurry (present in the SE part of the territory). In the highly evolved collision phase, masses of leucogranites intruded comformably with the deformation plan in the metamorphic complexes, interacting with surrounding metamorphic rocks in shallower crustal conditions and causing their contact metamorphic overprint (up to 590 °C and 3–4 kbar). The syn-deformation character of leucocratic granites is proved by the orientation of biotite flakes parallel to the deformation plane of surrounding metamorphites. Part of leucogranites, especially in the central parts of the bodies, is omnidirectional. The stress field acted not only during the intrusion of the leucogranite magma, but also in the subsolidus stage. The final stage of this process is the formation of large bodies of pegmatites in extensional VmD2 fractures oriented at a large angle to the main stress component. The texture of the grey blocky K-feldspar pegmatites and the lack of H2O-bearing minerals point to pneumatolytic fracturing in a subsequently opened environment in VmD2. The final stage of VmD2 is represented by intrusions of I-type granodiorites with indications of magma mixing, or mingling. The chemical dating of monazites in granitoids allowed to date individual phases of granitization process in the range of 360–345 Ma, which youngest ages correspond with the formation of pegmatites. Dating of monazite in metamorphic rocks points to their thermal overprint during granitization process (360–350 Ma), having already earlier metamorphic overprint (380–370 Ma). The scenario of placement of granitoid intrusions is consistent with the decompression regime (in VmD2) after the end of VmD1c crustal thickening until the fracturing of the crustal block with of I-type magma intrusions of deeper origin. After this period, the exhumation of crystalline blocks, partial diaphtoresis and later surface erosion continue until the Lower Triassic. The re-submergence of the crystalline complexes is associated with a low degree of Alpine metamorphic reworking.

Mesozoic crustal growth and recycling along the Southern margin of Eurasia: Magmatic rocks from the Sanandaj-Sirjan Zone of Iran

The Sanandaj-Sirjan Zone of western Iran is characterized by significant Mesozoic magmatic activity (from the early Jurassic to the late Cretaceous), with Cenozoic rocks being less common. Granitoids are prevalent in this zone, displaying A-, I-, and S-type geochemical characteristics. Despite several studies on these granitoids, there are still some questions regarding their sources– especially the S- and A-type granitoids – and the crustal growth and recycling in this zone, which require further studies using isotopes. This study focuses on the Aligoodarz, Kolah-Ghazi, and Golpayegan granitoids from the central SaSZ to better understand crustal growth and recycling in the Sanandaj-Sirjan Zone. The Aligoodarz and Kolah-Ghazi granitoids are identified as S-type granites, showing strong peraluminous signatures. Geochemical evidence suggests a mixture of melts from sub-crustal metasedimentary and meta-igneous sources, with factors such as source diversity and disequilibrium melting contributing to their formation. in contrast, the Golpayegan granitoids exhibit high total alkali (Na2O + K2O) contents and high field strength elements, indicating alkaline magmatic affinity. Their geochemical signatures suggest derivation from an enriched portion of an Indian MORB-like protolith. Golpayegan syenites share similarities with within-plate A1 granites, suggesting they are related to anorogenic silica-oversaturated granitoids. Golpayegan A-type granites probably originated from high-degree fractionation of alkali basic magmas. Golpayegan gabbros may be derived from a MORB or OIB-like mantle source, with characteristics indicating the presence of garnet in the mantle source and potentially deep melting from a mantle plume. Newly compiled zircon UPb data from the Sanandaj-Sirjan Zone show a complex magmatic chronology spanning from approximately 180 million years ago to the Eocene epoch, revealing peaks of magmatic activity at various intervals. Distinct phases of A-, I-, and S-type magmatism are identified, and synthesis of zircon UPb ages and HfO isotope data reveals the simultaneous occurrence of S-type and I-type magmas during specific periods. Furthermore, our study explores the tectonic settings underlying these magmatic processes and proposes scenarios involving subduction, continental rifting, and asthenospheric upwelling to elucidate the geological dynamics of the SaSZ.

Evidence for probable temporal and thermal trends among Devonian granitic magmas in central Victoria, and the composition of the Selwyn Block

This study provides new constraints on the causes of the chemical and isotopic variability in the central Victorian, Devonian, silicic, magmatic rocks and relates these to crustal architecture in the region. Synthesising present and previous work, it is concluded that the Selwyn Block, which forms the main source region for the Devonian silicic magmas (granitic and silicic volcanic rocks), is heterogeneous in three dimensions, on scales of 1 km and less. The sources of both the I- and S-type magmas were formed in Paleoproterozoic to Mesoproterozoic times, in the distal back-arc region of an Andean-type margin, in a basin that was extending and deepening eastward with time. The prominent rock types are high-grade metamorphosed greywackes, potassic andesites and dacites, with smaller volumes of pelitic rocks. The metasediment-dominated source rocks generally lie at deeper levels and reached higher metamorphic grades than the sources of the I-type magmas. This means that the I-type magmas were generally at lower temperatures and were also more hydrous than the S-type magmas. Heat for the metamorphism and partial melting of the source rocks of the silicic magmas was advected into the crust by mantle-derived magmas. These probably formed an underplate, to drive the regional metamorphism, but numerous, scattered, sill-like mafic bodies caused local contact anatexis and silicic magma production. Along with the emplacement of mafic magma bodies, the ascent of the silicic magmas to the upper crust rendered the deeper parts of the Selwyn Block denser and more mafic.

Nature of magma and ore-forming conditions at the Randu Kuning porphyry Cu-Au deposit, Indonesia: a comparative study with other Cu-Au deposits in the region

ABSTRACT The subduction-related Sunda-Banda arc hosts several giant and major Cu–Au–Mo porphyry and epithermal Au systems, making it one of the most important magmatic-related metallogenic belts in Indonesia. They are accompanied by a number of smaller systems, one of which is the recently discovered Randu-Kuning porphyry Cu-Au deposit on Java Island. The present study investigates the geochemical characteristics of this deposit through whole-rock and mineral geochemistry and mineral geothermobarometry, focusing on three sequential dioritic intrusions that make up the host igneous complex, two barren and the third mineralized. Moreover, a comparative analysis is performed between other porphyry deposits in the Sunda-Banda arc and with Grasberg in Papua. This study shows that the older porphyry deposits have mostly similar geochemical characteristics to the younger deposits, suggesting the same magma source, which is mantle-derived oxidized I-type magma. Amphibole geothermobarometry shows that the formation of syn-ore intrusion in the older porphyry was higher in temperature and pressure than those at the younger porphyry. The halogen and oxygen fugacities inferred from biotite and amphibole chemistry indicate an oxidized, water- and halogen-rich melt. Our study shows that combining amphibole and biotite chemistry and whole-rock geochemical data is useful to fingerprint the magmatic-hydrothermal processes, especially where multiple magmatic phases occur. This research also provides valuable insights into the magmatic-hydrothermal physiochemical conditions during the formation of the mineralized system.

Roles and perspectives of A- and I-type magmas in rare earth element and gold mineralization

A- and I-type magmas are commonly associated with rare earth element (REE) and gold (Au) mineralization. However, the behavior and solubility of the REEs and gold within the A- and I-type magmas and their synchronous magmatism remain unclear. This study focused on the synchronous Early Cretaceous A- and I-type magmatism that formed alkaline and granodioritic complexes within the Luxi and Jiaobei terranes of the central-eastern North China Block, terranes that contain the third largest known REE deposit in China and the third largest gold province in the world. Our integrated whole-rock geochemical and Nd isotopic data and zircon Hf-O isotopic data provide new insights into the petrogenesis of these contemporaneous A- and I-type magmas and their role in the generation of the REE and gold mineralization in this area. The alkaline magmas that formed the intrusions in the Luxi terrane had A- and I-type affinities, were oxidized, were fluorine-, sulfur-, and copper-rich, were H2O-poor, and were generated by low-pressure partial melting of a source region containing enriched lithospheric mantle material and minor amounts of Paleoproterozoic A-type granitic crust. In comparison, the granodioritic magmas within the Jiaobei terrane had I-type affinities, were relatively reduced, were sulfur-rich, contained low concentrations of Cu, were hydrous, and were formed by high-pressure partial melting of a source region containing enriched mantle material and large volumes of Archean to Paleoproterozoic crustal material. The A- and I-type magmas within the Luxi terrane also have higher high field strength element (HFSE; e.g., Th, Nb, Ta) and total light rare earth element (ΣLREE) concentrations as well as higher ΣLREE/total heavy rare earth element (ΣHREE) ratios than the I-type magmas enriched in large ion lithophile elements (LILEs; e.g., Ba, Sr) in the Jiaobei terrane. These characteristics suggest that the diversity of REE and gold mineralization was the result of interaction between the lithospheric mantle and hybrid sediment-derived melts and aqueous fluids under rutile-bearing eclogite-facies (>2.0 GPa) conditions within the Luxi terrane and with aqueous fluids under amphibolite- to eclogite-facies (>1.5 GPa) conditions within the Jiaobei terrane. Our study strongly suggests that the interaction between the lithospheric mantle and sediment-derived melts, the presence of coexisting REE- and fluorine-rich magmas, and low-pressure partial melting were all crucial factors in the formation of A-type intrusion-related REE deposits, whereas high-pressure partial melting and contemporaneous sulfur and chalcophile element enrichment were critical processes in the formation of I-type intrusions prospective for gold mineralization.

Constraining mixing and mingling processes from zoned magmatic enclaves: An example from the Taejongdae granite in Busan, Korea

Zoned magmatic enclaves (MEs) within granitic intrusions provide valuable insights into the pre-intrusive processes involved in the formation of granitic magmas. This study focuses on the Taejongdae granite in Busan, Korea, which features uniquely zoned MEs, and aims to constrain the processes involved in their formation. Through a whole-rock geochemistry analysis, SHRIMP U-Pb zircon dating, and Lu-Hf isotope data, we investigated the geochemical characteristics and origin of the two magmas responsible for the zoned MEs (that is, dioritic and host granite magmas). Our findings have shown that the host granite aligns with the Bulguksa granites in the Gyeongsang Basin, which represent the I-Type magma resulting from the fractionation of magma generated through partial melting of the continental crust. In contrast, the dioritic magma exhibits a low K2O composition, high Sr content, and a positive-to-no Eu anomaly, indicating its formation via amphibole-dominated fractional crystallization under different pressure–temperature conditions. Both magmas share the same Cretaceous age and Hf ratios. The zoned MEs in the study area provide compelling evidence of magma mixing processes that occur between the outer dioritic zone and mafic core of the enclaves. However, the relationship between the outer dioritic zone and the host granite suggests limited interaction between the enclaves and host granite. This implies that mixing within the zoned enclaves occurred prior to enclosure in the host granite. By highlighting the significance of zoned magmatic enclaves, this case study advances our understanding of the pre-intrusive processes involved in the formation of granitic magmas, including magmatic mixing, mingling, and fractionation. These results offer important insights into the origin and geochemical characteristics of the two magmas and their interactions, thus contributing to a broader understanding of crustal evolution in subduction-related settings.

Devonian ignimbrites of central Victoria: explosive magmas from multiple sources, and deep crustal structure in the Selwyn Block

The magmas that formed each Devonian, S-type, volcanic complex in central Victoria were generated through partial melting of a distinct assemblage of rock types in the crustal source region. The more silicic rhyolites were formed independently of the rhyodacitic to dacitic magmas, rather than as differentiates. Within every complex, each ignimbritic unit is also heterogeneous in its chemical and isotopic characteristics. Thus, in this part of Paleozoic Australia, magma heterogeneity occurred on at least three scales—the individual rock unit, the complex and across the region. This means that the Selwyn Block, the logical source of the ignimbrite magmas, is highly heterogeneous, probably in three dimensions. The statistically significant differences in the ages of the various complexes suggest that the heat sources for partial melting of the deep crust were themselves rather local in extent, and probably reflected numerous asynchronous intrusions of mantle-derived mafic magmas, most likely in relatively small batches. Thus, there should be no thick underplated or intraplated layer of gabbroic rock in the deep crust here. Thinner bodies of hot mafic magmas were probably emplaced in different places and at different levels, inducing local high-grade metamorphic conditions. Published radiometric dates for various volcanic units suggest that the magmatic heating of the crust occurred over a period of at least 17 Myr, although maximum intensity occurred between ca 375 and ca 371 Ma. Thus, a model of the deep crust here should involve numerous, perhaps thin metasedimentary units with highly variable ages and original clay contents, as well as sills of Late Devonian mafic rocks scattered both vertically and horizontally and intruded episodically. The dominantly meta-igneous sources of crustally derived I-type magmas generally lie at higher structural levels, where they did not experience metamorphic temperatures sufficient to cause the higher-temperature melting reactions needed to form I-type volcanic magmas. KEY POINTS Each Late Devonian, S-type, volcanic magma in central Victoria formed through melting of a distinct assemblage of crustal source rocks, most likely within the Selwyn Block. The rhyolites formed independently of the rhyodacitic to dacitic magmas, not as differentiates. The mafic magma heat sources for partial melting of the deep crust were emplaced as numerous, relatively small batches, in sheets distributed horizontally and vertically. The dominantly meta-igneous and shallower crustal sources of I-type magmas did not experience the higher temperatures required to form I-type volcanic magmas.

Mesozoic magmatism of Natuna Island, Indonesia: Implications for the subduction history of eastern Sundaland

Subduction beneath eastern Sundaland occurred throughout the Mesozoic forming a wide magmatic arc. This resulted in extensive magmatism, ophiolite formation, and development of a large accretionary complex that stretches north from Borneo, through Vietnam, and into China. However, much of this complex is currently submerged beneath the South China Sea, making the study of longitudinal variations in magmatic and subduction history difficult. This study focusses on the Mesozoic geology of Natuna, a remote island in the South China Sea, and uses fieldwork, whole-rock geochemistry, and zircon geochronology to determine the islands relationship to the subduction margin and how its magmatic history compares to examples from Borneo and Vietnam. Natuna records abundant subduction-related magmatism, with switches from extensional to compressional regimes driven by changes in the angle of subduction and rate of slab roll-back. Inherited zircons reveal the presence of Triassic–Early Jurassic crust beneath Natuna and indicate the formation of an Early Jurassic arc that has since eroded away. This is followed by Middle–Late Jurassic spreading in the fore-arc driven by slab-roll back and formation of the Pulau Tiga Ophiolite coeval with the deposition of cherts in the Bunguran Formation. A regional Late Jurassic–Early Cretaceous slab flattening then drove abundant I-type magmatism, however, the products of this are not observed on Natuna until the Late Cretaceous. Initial I/S-type granodiorite and porphyritic granite magmatism is recorded at 85–86 Ma and formed as mantle melts rose through and became partially contaminated by previously-formed arc crust. Following this, I/S-type granites record a period of crustal thickening and increased contamination from partially melted crust at 71–75 Ma. This crustal thickening marks the end of Palaeo-Pacific subduction beneath eastern Sundaland, compression in the fore-arc, ophiolite obduction, and formation of the Natuna Accretionary Complex along the Lupar Line.

Stenian sediments (

The Meso- to Neoproterozoic tectonic evolution of the Aravalli orogen in northwestern India is poorly understood because of limited combined isotopic-geochemical constraints on magmatic and sedimentary rocks. In this study, we present new zircon U-Pb-Hf isotope and whole-rock geochemical data for the Sendra Granitoid Suite and associated host quartzite of the Sendra Formation (Kumbhalgarh Group of the South Delhi Supergroup). Detrital zircon grains reveal a maximum age of deposition during the Stenian at 1065 Ma, and two major sources in the hinterland: (1) a Neoarchean to Paleoproterozoic basement (HfTDM = 2.7 – 2.0 Ga) affected by crustal reworking at 1.8–1.6 Ga, and (2) a juvenile terrain derived from the depleted mantle at ca. 1.6 Ga, and periodically reworked until 1.06 Ga in the Aravalli hinterland. Sediment deposition occurred in a passive margin setting. The post-collisional Sendra granitoids intruded during the Tonian between 1000 and 970 Ma from multiple sources. The highly superchondritic I-type granitoids (εHft = +10.8 to +12.1; HfTDM = 1.22 Ga) were formed from the fractional crystallisation of calc-alkaline mafic magma generated from partial melting of a mantle wedge. In contrast, the A-type granitoids originated either from melting of (1) relatively young, arc-related juvenile basaltic crust (εHf1.0 Ga = +10.3 to +15.3), (2) ancient felsic crust of the Aravalli continental margin (εHf1.0 Ga = -4.4 to −6.4; TDM = 2.08 Ga), and/or (3) by mixing of melts derived from different crust and mantle sources (εHf0.98 Ga = +0.8 to +3.1). All together, the new results provide evidence that NW India underwent transformation from a passive margin to an accretionary orogenic terrane between 1065 and 1000 Ma, followed by post-collisional magmatism and extension until 970 Ma.

Petrogenesis and Metallogenic Evolution of Leucogranites from the Paleoproterozoic Malanjkhand Granitoids, Central India

Abstract The Birsa and Devgaon leucogranites represent contemporaneous episodes of highly fractionated felsic magmatism associated with the Paleoproterozoic Malanjkhand granitoids in the Bastar craton, Central India. Major element oxides geochemistry reveals that two leucogranites are strictly granite in composition and both show calc-alkaline affinity. Geochemical discrimination diagrams inferred that these leucogranites shows affinity towards I-type magma with metaluminous characters. Geochemical classification inferred that the Birsa leucogranite preferred to be magnesian whereas Devgaon leucogranite designated to be ferroan type. Geothermobarometry estimation suggested that 1.2-4.5 kbar pressure and 750°-830°C temperature conditions at the shallow depth of the continental crust is responsible for the emplacement of leucogranites. Crystallization evolution of feldspar in the leucogranite provided evidences of late stage felsic magmatism in the Malanjkhand pluton. Molybdenum enrichment in the leucogranite possibly due to crystal fractionation under high oxygen fugacity conditions inherited from the magma chamber in the continental crust. Anomalous high concentration of Mo in the Devgaon leucogranite is contributed from episodic hydrothermal system with poor supply of sulphur. Occurrences of molybdenite in the Devgaon leucogranite provides high exploration potential to investigates granite molybdenite system in the Bastar craton.

Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin, western Yangtze: Implication for the magmatic origin and final closure of eastern Paleo-Tethys

The felsic volcanogenic tuffs named “green-bean rocks” (GBRs), characterized by a green or yellowish green color, are widely distributed in the western Yangtze platform and have a high lithium content (286–957 ppm). This paper studies the ages, origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U–Pb dating and Hf–O isotopes. The GBR samples from the Quxian and Beibei sections yielded zircon U–Pb ages of 245.5 ± 1.8 Ma and 244.8 ± 2.2 Ma. These samples can be used as the isochronous stratigraphic marker of the Early–Middle Triassic boundary (EMTB) for regional correlation. The whole-rock and zircon geochemistry, and zircon Hf–O isotopes exhibited S-type geochemical affinities with high positive δ18O values (9.28‰–11.98‰), low negative εHf(t) values (−13.87 to − 6.79), and TDM2 ages of 2150–1703 Ma, indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arc-related/orogenic tectonic setting. The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen, triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca. 247 Ma. This was marked by a major shift from I-type magmas with intermediate εHf(t) values to S-type magmas with low negative εHf(t) values. Collectively, our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.

U-Pb geochronology of the Silurian-Devonian Bega Batholith, south-eastern Australia: Insights into the origin and development of I-type granites

Earth’s continental crust is primarily composed of buoyant, felsic igneous (granitic) material that has been extracted from the mantle along convergent plate margins. Establishing the timescales of subduction-related granite batholith assembly is key to understanding the processes of magma generation, segregation, and transport that define the dynamics and rates of crustal growth. The ‘Cordilleran’ Bega Batholith is the largest I-type granite batholith in the Lachlan Fold Belt (LFB) of south-eastern Australia. The product of accretionary orogenesis along the Terra Australis Orogen, it has been extensively characterised by isotopic and geochemical studies yet lacks a robust geochronological framework. We present new ID-TIMS and SHRIMP U-Pb zircon ages for twenty-two plutonic rocks of the Bega Batholith. This geochronological survey indicates a prolonged duration for I-type magmatism, with crystallisation ages ranging from ca. 420 Ma in the west, to 385 Ma in the eastern Bega Batholith. These I-type granites collectively occupy ∼90,000 km3 and were emplaced over a period of ∼20–35 Ma, corresponding to a magma production rate of ∼8–15 km3/Ma km−1, considerably lower than that of S-type granites of the region and other subduction-related granite terranes globally. Fundamentally, the temporal overlap between the Bega I-type granites and S- and A-type granites also argues against a hiatus between each phase of granite magmatism in the LFB, suggesting a continuum between the granite types and derivation from common source components. This new geochronological data provides the first comprehensive compilation of U-Pb ages from across the Bega Batholith, establishing initial constraints on the development and evolution of I-type magmatism in south-eastern Australia. Our results demonstrate that I-type granite petrogenesis is linked with crustal growth processes, requiring the modification of global crustal growth curves during the Phanerozoic to account for new continental crust generated within I-type granite terranes of the Paleo-Pacific Gondwanan margin.

Emplacement conditions and exhumation of the Varvarco Tonalite and associated plutons from the Cordillera del Viento, Southern Central Andes

AbstractDuring the Late Cretaceous Andean orogeny, the compressive deformation associated with the shallowing of the subducting slab caused the development of the arc-related igneous rocks known as the Naunauco Belt. This study presents petrographic, mineralogical and anisotropy of magnetic susceptibility data for the Varvarco Intrusives (the Varvarco Tonalite, Butalón Tonalite and Radales Aplite), which crop out in the Cordillera del Viento, Neuquén Province, Argentina. The assembly of plutons was formed by mafic magma episodic injection. Amphibole and biotite compositions suggest that the Varvarco Tonalite is related to calc-alkaline, I-type magmas, typical of subduction environments. Different geothermobarometers based on amphibole and plagioclase compositions for the Varvarco Tonalite suggest shallow emplacement conditions (∼2–3 kbar, equivalent to ∼12 km depth). Apatite fission-track analyses give exhumation ages of 67.5 ± 8 Ma for the Varvarco Tonalite and 50.3 ± 5.9 Ma for the Butalón Tonalite. A calculated continuous fast exhumation rate of at least 330 °C Ma−1 is consistent with the shallow emplacement conditions, textural data and geobarometric estimations. In agreement with the thermal profile, the magmatic system was exhumed by ∼12 km within c. 2.1 Ma implying a geothermal gradient of ∼62.5 °C km−1. The last step of exhumation occurred between ∼65.3 and 56.9 Ma. The magmatic fabrics observed in the studied plutons reflect mostly magma chamber processes. The Varvarco Intrusives represent satellite calc-alkaline plutons of the North Patagonian Batholith which were emplaced syn- to post-tectonically with respect to a major deformation stage of the Southern Central Andes.

Tectonic switches recorded in a Paleoproterozoic accretionary orogen in the Alta Floresta Mineral Province, southern Amazonian Craton

The Alta Floresta Mineral Province (AFMP), southern Amazonian Craton, experienced extensive magmatic activity from ca. 2.03 to 1.75 Ga in an uncertain geodynamic setting. New and pre-existing geological, petrographic, geochemical, and zircon geochronological data show that magmatic rocks in the eastern AFMP comprise three magmatic sequences: 2.03–1.93, 1.90–1.85, and 1.83–1.75 Ga. Earlier magmas had garnet-bearing sources, whereas younger ones were derived from shallow, garnet-free sources. We propose a new, four-stage geological framework, comprising five domains, and featuring an accretionary orogen with tectonic switching that alternates between flat subduction and slab-rollback. During flat subduction and crustal thickening in stages A (2.03–1.97 Ga) and C (1.90–1.81 Ga), calc-alkalic to alkali-calcic I-type magmatism was produced, whereas alkali-calcic to alkalic A-type magmatism, and localized I-type granites, were generated during slab-rollback and crustal extension in stages B (1.96–1.94 Ga) and D (1.83–1.75 Ga). The last stage is associated with precious- and base metal porphyry- and epithermal-style systems. We interpret the eastern AFMP as a remaining cratonic block of the eastward Tapajós Domain within the ca. 1.95–1.80 Ga Ventuari-Tapajós Province, and recording 1.85–1.74 Ga magmatism of the Western Amazonia Igneous Belt within the ca. 1.80–1.55 Ga Rio Negro-Juruena Province. Similarities between the AFMP and the Svecofennian orogen (Fennoscandian Shield) suggest that parts of the Columbia supercontinent margins might have operated in similar fashion to Andean-type accretionary orogens.

Protracted intra- and inter-pluton magmatism during the Acadian orogeny: evidence from new LA-ICP-MS U-Pb zircon ages from northwestern Maine, USA

Devonian granitoid plutons comprise a major part of the bedrock of northwestern Maine representing the magmatic expression of the Acadian orogeny in this part of the northern Appalachian orogen. They are petrographically diverse with minerals characteristic of both I- and S-type granites, in some cases within the same intrusion, and some are compositionally zoned. New LA-ICP-MS ages presented here elucidate the timing and duration of this magmatism. The earliest phase of granitoid magmatism began around 410–405 Ma with the emplacement of the Flagstaff Lake Igneous Complex, and the presence of contemporaneous mafic rocks suggests that mantle-derived magmas were also produced at this time. Late Devonian ages, ca. 365 Ma, for many intrusions, such as the Chain of Ponds and Songo plutons, reveal that magmatism continued for 45 million years during which compositionally diverse I- and S-type magmas were produced. In addition, there is evidence that intrusive activity was prolonged within some plutons, for example the Rome-Norridgewock pluton and the Mooselookmeguntic Igneous Complex, with 10–15 myr between intrusive units. The new ages suggest a break in magmatism between 400 Ma and 390 Ma apparently separating Acadian magmatism into early and late pulses. The production of lower crustal I-type magmas appears to have been concentrated later, ca. 380–365 Ma, although several S-type granitoids were also emplaced during this period. These Late Devonian plutons display abundant zircon inheritance with ages around 385 Ma, which suggests that the crust was experiencing enhanced thermal perturbations during this extended timeframe. The new data for granitoid plutons in northwestern Maine are consistent with tectonic models for other parts of Ganderia which propose initial flat slab subduction followed by slab breakoff and delamination.

Geochronology, petrogenesis and tectonic importance of Eocene I-type magmatism in the Eastern Pontides, NE Turkey

Eastern Pontides are hosted to many granitoids with different composition, size and age ranges from Paleozoic to Cenozoic. Of these granitoids, especially those of the Cenozoic age are commonly observed in the southern part of the Eastern Pontides, and rarely in the northern part. This paper focuses on the Eocene aged Avliyana Granitoid, located south of the Eastern Pontides, intruding into Late Cretaceous and Eocene volcanic and sedimentary rocks. The Avliyana Granitoid is mainly diorite and tonalite and composed of plagioclase, quartz, orthoclase, hornblende, biotite, pyroxene, and Fe-Ti oxides. It shows granular, locally poikilitic and micrographic texture. The Avliyana Granitoid has I-type, medium to high-K calc-alkaline, and metaluminous character, and has a narrow SiO2 contents (57–64 wt.%). The rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile element (LILEs), and depleted in high field strength elements (HFSEs). Chondrite-normalized REE distributions are concave shaped (LaN/LuN = 5.87–11.92) and show negative Eu anomaly (Eu / Eu * = 0.55–0.81). Geochemical results show that plagioclase, pyroxene, hornblende, and Fe-Ti oxide fractionation are effective in the development of the rocks. The eNd(i) values of the rocks are between – 1.0 and – 0.1, 87Sr/86Sr(i) values are between 0.70531 and 0.70563, and the model ages (TDM) are between 0.79 and 0.93. U-Pb SHRIMP zircon ages of the Avliyana Granitoid rocks range from 45.60 ± 0.55 to 44.75 ± 0.36 Ma. In calculations made from zircon and apatite, the crystallization temperatures vary between 714 and 867 °C. The data revealed that the parental magma of the Avliyana Granitoid was derived from the enriched lithospheric mantle, and fractional crystallization and lesser assimilation played a role in the evolution of the rocks.

Geochemistry and geodynamic constraint of volcanic and plutonic magmatism within the Banfora Belt (Burkina-Faso, West-Africa): contribution to mineral exploration

Abstract Predominant volcano-plutonic (mafic–felsic) activity is expressed in the eastern Banfora Belt. The geochemical signature shows different geodynamic settings: (1) mafic rocks are tholeiitic, subalkaline and show high-Mg tendency, whereas pyroxenolite (MgO c. 15.4 wt%) has komatiite affinity; (2) felsic volcanic rocks are subalkaline; and (3) granitoids surrounding the Banfora Belt are alkaline to calc-alkaline, high K, peraluminous to metaluminous. The geochemistry of mafic volcanic rocks shows an unusual evolution from Mid Oceanic Ridge Basalt to Arc-related. The Western Granite and Eastern Granites were emplaced by fractional crystallization and partial melting, respectively, but sourced from igneous protolith (I-type magma) in a volcanic arc setting. The Sodingue granite was emplaced by fractional crystallization from A-type magma in a ‘within-plate setting’. Two-mica S-type granites located at the central portion of the belt relate to syn-collisional fractional crystallization. The paper highlights the complexity of the magma process through a diversity of sources, geochemical patterns and tectonic settings. An emphasis on the komatiite affinity of mafic magma is a challenge for related commodities, such as copper and gold resources.

A mineralogia acessória do Amazonita Pegmatito Serra Branca: classificação de um pegmatito NYF na Província Borborema, Nordeste do Brasil

O campo pegmatítico de Vieirópolis é caracterizado pela ocorrência de pegmatitos com amazonita e/ou berilo. Esse campo contém pegmatitos do tipo NYF (Nb-Y-F) inseridos no Domínio Rio Grande do Norte (DRGN), fora do contexto da Província Pegmatítica do Seridó (PPS). O principal pegmatito desse campo, o Amazonita Pegmatito Serra Branca, destaca-se pela mineralização de megacristais de amazonita e por sua exploração como rocha ornamental de elevado valor econômico. Para caracterizar a paragênese e a química mineral das fases acessórias do Amazonita Pegmatito Serra Branca, além de elucidar a classificação e a natureza petrogenética desse pegmatito, foram utilizados dados de campo, petrográficos, difração de raios X e química mineral. O Amazonita Pegmatito Serra Branca ocorre como dique tabular com aproximadamente 3 m de espessura, de direção NW-SE e caimento 45° WSW, caracterizado por apresentar uma zona composta por megacristais de amazonita e quartzo, e outra, por albita e quartzo sacaroidais. Apresenta vasta mineralogia acessória que compreende anglesita, biotita, bismutita, cerussita, columbita-(Mn), espessartina, helvina, fenaquita, fluorita, hematita, ilita, ilmenita, magnetita, montmorilonita, muscovita, piromorfita, pirocloro, rutilo e zircão. Destacando-se, também, atípicas mineralizações de sulfetos e a presença de beríliossilicatos reportados pioneiramente no contexto geológico da Província Borborema (PB). A paragênese mineral e a química dos minerais acessórios do Amazonita Pegmatito Serra Branca o classificam como pertence à família NYF da classe dos elementos raros, tipo da gadolinita, possivelmente associado a um magmatismo do tipo I.

The 2.26 to 2.18 Ga Arc-Related Magmatism of the Almas-Conceição do Tocantins Domain: An Early Stage of the São Francisco Paleocontinent Assembly in Central Brazil

Paleoproterozoic (Rhyacian) rocks dominate within the basement of the Neoproterozoic Brasília Belt and their genesis has been attributed to the orogenic amalgamation event that assembled the São Francisco-Congo paleocontinent from 2.18 to 2.07 Ga. However, the tectonic framework and genesis of the building blocks involved in this continent-wide amalgamation event are unclear, particularly in relation to terranes from the Almas-Conceição do Tocantins Domain, in the Goiás Massif, central Brazil. This work provides new whole-rock chemical and geochronological data, which indicate the generation of felsic to intermediate magmatism around 2.29 and 2.28 Ga corresponding to the Monzogranitic Unit and the Quartz-dioritic Suite, respectively. Later magmatic events occurred in a continental arc setting, around 2.26 to 2.2 Ga represented by metaluminous to peraluminous I-type magmatism of the Granodioritic to Tonalitic Suite (GTS) and the Serra do Boqueirão Suite. Around 2.2 to 2.18 Ga a peraluminous I-type magmatism took place and generated the Peraluminous Suite (PS). Our data show that after an earlier Siderian magmatic event around 2.45–2.34 Ga, reported in previous works, the Almas do Conceição do Tocantins Domain oversaw additional Rhyacian events of magmatic activity around 2.29 Ga to 2.18 Ga. Regional geotectonic correlations with the São Francisco Craton and other pericratonic belts indicate coeval magmatic events taking place during the early stages of the Columbia Supercontinent amalgamation.

Geochemical characteristics of the adakite-like Dodurga Pluton (Central Pontides, N Turkey): implications for Middle Triassic continental arc magmatism in southern Black Sea region

The tracing of Triassic arc magmatism is much-debated for a long time along the Sakarya Composite Terrane in Turkey and the southern Black Sea region. The Dodurga Pluton is located in the Central Pontides (N Turkey), one of the most complicated regions around the Black Sea region, and represents the first documented middle Triassic continental arc in the region. This pluton comprises of dacite porphyry and granodiorite, and displays calc-alkaline signatures, which is in agreement with arc-related and I-type magmas. The PM-normalized multi element and CN-normalized REE patterns are akin to volcanic arc granites, and characterized by LILEs and LREEs enrichments relative to HFSEs and HREEs coupled with negative Nb anomalies, which confirm derivation in a subduction-related tectonic setting. Moreover, the major and trace element systematics of the samples including higher Sr/Y ratios (22.93–101.36) and lower Yb contents (0.31–1.30 ppm) are consistent with those from adakitic melts compared to classical arc magmas. Therefore, this pluton also represents the first middle Triassic adakite-like magmatic occurrence in Turkey. Overall petrographic and geochemical signatures reported here indicate that the Dodurga Pluton might have been derived from a heterogeneous source, mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin. Based on the Tethyan evolution in the Anatolian realm, three geodynamic scenarios are possible for its formation, and it could have been formed as a result of northward or southward-subduction of the Paleotethys Ocean or northward-subduction of the northern branch of Neotethys Ocean during the middle Triassic.