TDM Model Research Articles

U-Pb zircon and Sm-Nd geochronology of the dom Silvério group, SE Brazil: Implications for the evolution of the superposed Araçuaí and Minas-Bahia orogens

The Araçuaí orogen, the South American portion of the Brasiliano/Pan-African Araçuaí-West Congo orogenic system (AWCO), formed during the Ediacaran-Cambrian assembly of West-Gondwana. The basement of a substantial portion of the Araçuaí orogen comprises Archean and Paleoproterozoic rocks involved in the 2.1–2.0 Ga Minas-Bahia orogen. The Dom Silvério Group, which consists of mica schists containing layers and lenses of mafic, ultramafic, and Mn-rich rocks, as well as quartzites, graphite schists, marbles, and banded iron formations, defines a ca. 10 km-wide and 150 km-long belt in the southwestern portion of the Araçuaí orogen. This succession, currently interpreted as deep marine deposits or an ocean-floor assemblage of uncertain age - Paleoproterozoic or Neoproterozoic-, potentially records processes involved in critical evolutionary stages of the superposed Minas-Bahia and Araçuaí orogens. Aiming to characterize the age and tectonic significance of the Dom Silvério Group, we performed a geochronological and geochemical investigation on samples collected from selected lithotypes. U-Pb (LA-ICP-MS) determinations on detrital zircons revealed two distinct age spectra. Zircons extracted from the lower Dom Silvério schists define a spectrum characterized predominantly by Neoproterozoic age clusters with a maximum depositional age of 601 ± 10 Ma. Quartzites from the lower and upper sections of the group do not contain zircons younger than 1.9 Ga and show unimodal age distributions around 2067 Ma. The maximum depositional age estimated for these rocks is 2020 ± 6 Ma. The spectrum of the lower section schist indicates the turbidites of the Ediacaran Salinas Formation as their most probable correlative. In contrast, the quartzites and schists of lower and upper sections correlate with the Orosirian Itacolomi Group, the post-collisional assembly of the Minas-Bahia orogen. Sm-Nd isotope analyses and whole-rock geochemistry allow the discrimination of two generations of mafic rocks. The older generation, showing TDM model ages = 1.92 to 3.6 Ga and ƐNd(t) = -12.93 to +4.63, represents components of the basement. The younger generation, with TDM model ages = 1.0 Ga to 1.25 Ga and ƐNd(t) = +0.05 to +2.29, is similar to the ophiolitic rocks that occur imbricated with Ediacaran metasedimentary successions in the central portion of the Araçuaí orogen defining the Ribeirão da Folha accretionary belt. They show Th/Yb and Nb/Yb ratios of the EMORB-OIB mantle array and Nb/Y and Zr/Y ratios compatible with OIB and oceanic plateau basalts. The Dom Silvério Group is thus a complex that involves members of the Araçuaí and Minas-Bahia orogens. Their Ediacaran components materialize the southern extension of the Ribeirão da Folha accretionary wedge and, as such, provide further evidence for oceanic consumption during the development of the southern Araçuaí orogen.

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.

Geochemical and isotopic evidence for early neoproterozoic (ca. 1000 Ma) subduction-related magmatism in the central Borborema Province, Brazil

Early Neoproterozoic (1000-920 Ma) rocks related to the Cariris Velhos event in the central Borborema Province have been linked to either continental rifting or accretionary-collisional orogenesis. The Serra do Jatobá Suite is located in the southwestern part of the Alto Pajeú Terrane along with coeval metasedimentary sequences and Ediacaran granites. This suite is composed of alkali-calcic, meta-to peraluminous granodiorites to monzogranites that share similarities with both ferroan- and magnesian granite series. Chondrite normalized REE (Rare Earth Elements) patterns are moderately fractionated with pronounced negative Eu anomalies. Incompatible element spidergrams show a negative Nb–Ta anomaly, similar to those observed in Cordilleran-type granites. U–Pb zircon data constrain the crystallization ages at around 1000 Ma, whereas calculated εNd(t) values range between −1.74 and −0.94. Obtained TDM model ages range from 1.76 to 1.54 Ga, which corresponds with source ages for the Cariris Velhos magmatic rocks. Our findings suggest that subduction took place in the early Neoproterozoic in the Borborema Province, pointing to an accretionary nature for the Cariris Velhos event.

Petrogenesis and tectonic implications of the Bloubergstrand basaltic andesites, Tygerberg Formation, Malmesbury Group, Pan-African Saldania Belt, southwestern Africa

Abstract The Bloubergstrand Member, consisting of mafic to intermediate tuffs and flows within the Tygerberg Formation of the Malmesbury Group, is a crucial but understudied component of the western Saldania Belt in southwestern Africa. With a U-Pb zircon age of 555 ± 5 Ma, these volcanic rocks provide valuable insights into the origins and, more broadly, the tectonic setting of the Saldania Belt during the final stages of Malmesbury Group sedimentation in the context of the construction of southwestern Gondwana at approximately 560 to 540 Ma. The Bloubergstrand Member amygdaloidal volcanic rocks vary from basaltic andesitic to andesitic and have experienced varying degrees of alteration. The volcanic rocks are enriched in the large ion lithophile elements (LILE) relative to the high field strength elements (HFSE). When normalised to primitive mantle values, they show enrichment in Cs, Rb, K and Pb and mild enrichment in Th, U, Zr and Hf, with the light rare earth elements (LREE) enriched relative to the heavy rare earth elements (HREE). They are depleted in Ba, Nb, Ta, Sr, Eu, P and Ti. εNd(t) values are mildly negative ranging from -3.60 to -2.39, and Nd TDM model ages range from 1.4 to 1.7 Ga. Initial 87Sr/86Sr ratios vary from 0.70478 to 0.70620, with one higher value of 0.72270, the latter likely due to extensive alteration. The Bloubergstrand Member volcanic rocks exhibit characteristics suggesting their origin from partial melting of lithospheric to transitional asthenospheric upper mantle, influenced by sediment-derived melts and variable degrees of crustal contamination. With continental arc basalt compositions and similarities to shoshonites, the samples reflect variable degrees of partial melting and source heterogeneities. Fractional crystallisation of pyroxenes, hornblende, and plagioclase contributes to compositional variability. Erupting in a continental arc margin, likely part of the Arachania block of the Kalahari craton, separated during the Tonian break-up of Rodinia, the volcanics were associated with the Marmora basin formed by eastward-directed subduction below the western Kaapvaal Craton margin. Extruded in a distal position relative to the Cuchilla Dionisio Arc in present-day southern Brazil and Uruguay, these volcanic rocks preceded the closure of the southern Marmora basin. The mantle melting, possibly a result of slab roll-back, break-off, ridge subduction, or a combination, served as a precursor to the lower crustal heating that generated the granitic magmas of the Cape Granite Suite.

Petrology of the Cretaceous Riacho do Cordeiro dike swarm: Unraveling the giant low-Ti tholeiitic plumbing system of the Equatorial Atlantic Magmatic Province

The formation of the Early Cretaceous Equatorial Atlantic Magmatic Province (EQUAMP), northeastern Brazil, is related to the fragmentation of the West Gondwana supercontinent that culminated in the separation of South America and Africa, during the Lower Cretaceous. The EQUAMP is characterized by its intrusive nature, where mafic dike swarms intrude the Proterozoic basement of the Borborema Province. The other components of this province are represented by sill complexes hosted between the Paleozoic sediments in the Parnaíba Basin, described as the Sardinha Formation. The magmatism related to the EQUAMP is tholeiitic, with high-Ti, and low-Ti magmas compositions that with similar features that are observed in other Mesozoic igneous provinces of Gondwana. The Riacho do Cordeiro dike swarm (RCo) represents the southernmost manifestation of the EQUAMP, consisting of a series of igneous bodies aligned along the N45E trend, arranged in an en echelon pattern. This structure extends for about 350 km, cutting the Precambrian basement of the southern segment of the Borborema Province. The dikes have a composition similar to tholeiitic basalts and basaltic andesites, but they are distinguished from the other components of the EQUAMP by their exclusively low-Ti content (TiO2 = 1.7–1.2 wt%). Magmatic differentiation is the main petrogenetic mechanism of the low-Ti magmas, typified by the systematic fractionation of major elements with respect to the variation of MgO (6.4–2.4% wt%). Trace (including rare earth) element patterns show enrichment in incompatible elements and negative anomalies in NbTa, a pattern recognized in continental basalts derived from (or contaminated with) lithospheric mantle. The Sr (87Sr/86Sr(i) 0.7072 to 0.7091) and Pb (206Pb/204Pb 18.360 to 18.785) isotopic signatures, combined with negative values for εNd(i) (−4.8 to −6.1) and TDM model ages >1.2 Ga, confirm the involvement of reservoir(s) in the upper mantle possibly modified by ancient subduction processes. The first reported 40Ar/39Ar ages for the low-Ti tholeiites of the RCo indicate ages from 134.53 ± 3.10 to 132.19 ± 1.28 Ma. Geochemically, the low-Ti tholeiites of the RCo are equivalent to low-Ti dikes that constitute part of the Rio Ceará Mirim dike swarm, the main component of the EQUAMP. Besides that, in a scenario external to this province, the same compositional correspondence is found within the Cretaceous dikes of the Vitória-Colatina swarm, southeastern Brazil, and the low-Ti type lavas of the Paraná-Etendeka Province. This compositional and geochronological connection between the tholeiitic magmatism located north and south of the São Francisco craton supports a possible genetic connection between these two Early Cretaceous LIPs and serve as base to future investigations that deal with what would have been the (global) mechanisms that led to the rifting of the Atlantic, from the southern segment to the equatorial margin.

Nd isotope and element composition of shales from the Parnaíba Basin, NE Brazil: Insights for provenance shifts in a cratonic basin

Sm-Nd and Sr isotope compositions of 24 samples of fine-grained clastic rocks from eastern Parnaíba basin, NE-Brazil, are presented along with major and trace element compositions of 19 of these samples. Samples were collected from outcrops of the Paleozoic Canindé (Pimenteiras, Longá and Poti) and Balsas (Piaui Formation) groups, and from the Jurassic Pastos Bons Formation. Discrimination diagrams based on Th, Sc, La and Zr indicate sedimentary provenance from felsic dominant sources and high degrees of crustal recycling. PAAS-normalized REE diagrams show that the Pimenteiras and Longá Formations display flat patterns with slight REE enrichment, and initial εNd and 87Sr/86Sr around the average composition of the upper continental crust, respectively between −8.9 and −14.6 and between 0.711 and 0.760, indicating provenance from old Precambrian basement. The Nd TDM model ages of the Pimenteiras between 1.32 Ga and 2.00 Ga indicate heterogeneity of source areas during the Devonian, and TDM ages around 1.6 Ga in the Longá Formation samples suggest intense recycling of older sediments. The Poti formation samples yield TDM ages of 2.30 Ga and 2.32 Ga, respectively, suggesting tectonic reactivation and new input from Archean-Paleoproterozoic basement complexes. The Pastos Bons Formation samples show lower Th-Sc ratios, light-REE depletion, and less negative initial εNd, indicating contribution from mafic rocks, probably from the underlying Mosquito Formation intraplate tholeiitic basalts and dolerites.

Tonian rifting coeval with the last stages of amalgamation of Rodinia: Evidence from southern Borborema province, northeastern Brazil

During the last stages of assembly of the Rodinia supercontinent at 1000-900 Ma, rifting processes were occurring in places that would be part of Gondwana in the late Neoproterozoic. In the Borborema Province, northeastern Brazil, this event is known as Cariris Velhos. It is represented in the Alto-Pajeú Domain from the Central subprovince by a 700 km-long, 70 km-wide NE-SW belt comprising bimodal metavolcanic rocks and granitic orthogneisses. Orthogneisses with similar ages were found in previous works in the western Pernambuco-Alagoas Domain from the Southern subprovince immediately to the south of the ESE-trending dextral West Pernambuco shear zone. The Airi Complex comprises several elongate bodies that extend for at least 80 km. It consists of a bimodal sequence of metafelsic (granitic orthogneisses) associated with layers and enclaves of metamafic (amphibolites) rocks. Seven orthogneiss samples dated by LA-ICPMS yielded zircon U–Pb crystallization ages of 950–1011 Ma. Zircon Hf analyses from two samples yielded εHf(t) values ranging from −1.4 to 2.1 and TDM model ages of 1.7–1.9 Ga. Geochemical analyses allow to distinct different source rocks for the protoliths of the orthogneisses. Orthogneisses derived from metasedimentary sources have modal muscovite ± garnet, are ferroan, alkali-calcic and predominantly peraluminous, exhibiting strong negative Eu anomalies in chondrite-normalized rare earth elements diagrams. Orthogneisses derived from high-K mafic rocks are calc-alkalic, slightly peraluminous, with small or absent negative Eu anomalies. Orthogneisses from tonalitic sources are magnesian, calc-alkalic to alkali-calcic, and slightly peraluminous, without Eu anomalies. There is no correlation between crystallization ages and source rock types. The results indicate that the Airi Complex originated through partial melting of ancient heterogenous crustal sources. Therefore, its geochemistry reflects the nature of these sources, not the tectonic setting of intrusion. Emplacement of the complex was broadly coeval with well-documented extensional processes in the São Francisco/Congo Craton and represents a failed attempt to break-up a larger paleocontinent encompassing this craton and the basement of the Borborema Province.

Exploring the orogenic nature of the Cariris Velhos event (ca. 1000-920 Ma) of the Borborema Province (NE Brazil)

The Cariris Velhos event (ca. 1000-920 Ma) is a significant marker in the early Neoproterozoic lithospheric record of the Borborema Province in NE Brazil. Despite its importance, the nature of this event remains unresolved having been linked to either continental rifting or accretionary-collisional orogeny. In this study, we support a compressive setting for the Cariris Velhos event based on compiled geochemical and isotopic data (Sm–Nd and Lu–Hf) from metagranitic rocks in the Alto Pajeú Terrane (central Borborema) and in the Pernambuco-Alagoas Super Terrane, as well as in the Riacho do Pontal and Sergipano fold belts (Southern Borborema). Geochemistry of these rocks share similarities with calcic to alkali-calcic and ferroan magmas, along with some Cordilleran magnesian members. They also correspond to meta-to peraluminous I- and S-type granitic rocks. Trace element distribution on spider diagrams reveals negative anomalies of HFSE (high field strength elements) such as Nb and Ta, which are typically associated with subduction-related settings. Additionally, chondrite normalized REE (rare-earth element) diagrams indicate mixing of both crustal and mantle material. Tectonic discriminant diagrams using elements with low mobility supports the hypothesis of a continental margin subduction-related setting. Calculated εNd and εHf values vary from negative to slightly positive, suggesting contributions from juvenile inputs and reworking of Meso-Paleoproterozoic crust, as indicated by the associated TDM model ages. Although the nature of the Cariris Velhos event requires further investigation, we suggest that, at least partially, it corresponded to an orogenic episode that might have occurred concurrently with continental break-up, similar to modern continental arc-retro arc foreland settings.

Lower Cretaceous (Aptian-Albian) Bisbee Group, Arizpe area, northern Sonora, Mexico: Integrated biostratigraphy, age and provenance from U-Pb and Hf isotopes

New data on the stratigraphy, biostratigraphy, detrital zircon U-Pb, and Hf isotope geochronology of a Lower Cretaceous succession of the Bisbee Group in northern Sonora, Mexico that accumulated in the Altar-Cucurpe sub-basin help to constrain ages of their formations and documents the detrital provenance. These tectonically shortened strata, studied in the Arizpe area, crop out in the Cerro La Ceja block (CCB) composed of the upper Morita Formation, the complete Mural Limestone, and Cintura Formations, and the lower part of La Juana Formation. The Sierra Los Azulitos block (SAB), composed of the Mural Limestone, is thrust eastward over the CCB. A measured section of the Mural Limestone in the SAB block includes the upper Tuape Shale, Los Coyotes, Cerro La Puerta, and part of the Cerro La Espina members whose age is constrained as upper Aptian to lower Albian based on benthic and planktonic foraminifera, bivalves and echinoderms. The age of the boundary between the Morita and Tuape Shale Member is constrained by detrital zircon maximum depositional ages (MDA) of 115.8 ± 1.1 Ma and 113.9 ± 0.8 Ma, respectively. The MDA of the upper Mural is 111.6 ± 1.6 Ma and the MDA of basal Cintura Formation is 108.8 ± 1.1 Ma. The La Juana Formation has upper Albian bivalves and echinoderms.
 About one-quarter of the detrital zircon grains dated from the five sandstone samples have Proterozoic ages with age peaks that clearly indicate provenance from basement rocks of southwestern Laurentia. More than two-thirds of the grains are of Jurassic and Early Cretaceous age in about the same proportions, and have main peaks at 166, 150, and 118 Ma. The Jurassic grains may have sources in rocks of the Jurassic Cordilleran continental magmatic arc of southwestern North America, and the most probable sources for the Cretaceous grains are arcs of the Peninsular Ranges batholith that by that time were located adjacent to coastal Sonora. Jurassic and the Early Cretaceous zircons dated from 195.3 to 106.8 Ma both have mixed εHf(t) values that range from 9.53 to -21.28, and TDM model ages between 0.4 to 0.8 Ga for the primitive grains, and 0.8 to 1.3 Ga for the more evolved zircons. The probable source for the Jurassic grains with negative εHf values might be local granites of that age in northern Sonora that have Neoproterozoic TDM model ages. In contrast, sources for the Jurassic zircon with positive Hf values may be Jurassic igneous and metaigneous rocks of the Peninsular Ranges Batholith of the Californias, although data reported are scarce. Similarly, the Early Cretaceous detrital zircon grains with mixed positive and negative εHf values may have provenance from igneous rocks of the Peninsular Ranges Batholith-Sierra Nevada magmatic arc.

Peraluminous leucogranites generation during different stages of the Brasiliano Orogeny in the Borborema Province, NE Brazil

The Mamanguape pluton comprises muscovite, biotite syeno-to monzogranite intruded in metasedimentary rocks. Geochemically, the studied samples of the Mamanguape pluton peraluminous granites are ferroan and alkali-calcic. Furthermore, trace element distribution diagrams are characterized by troughs at Ba, Nb, Sr, P and Ti. The REE patterns are fractionated showing (Ce/Yb)N ratios ranging from 12 to 15, and deep negative Eu anomalies, with Eu/Eu* ratios varying between 0.18 and 0.25. The geochemistry of the two-mica granites of the Mamanguape pluton shows similarities with peraluminous leucogranites from the Borborema Province with crystallization ages related to the contractional (640–600 Ma) and transcurrent (590–545 Ma) stages of the Brasiliano/Pan-African Orogeny. Peraluminous, two-mica and biotite-leucogranites were emplaced through all Borborema Province with ages within 640–600 Ma and 590–545 Ma intervals. Their generation is interpreted as the result of partial melting of metasedimentary rocks involving muscovite dehydration. The crystallization age (574 ± 2 Ma) of the Mamanguape two-mica granites suggest intrusion related to the transcurrent stage of the Brasiliano Orogeny. Zircon grains extracted from two samples of a two-mica leucogranites of the Jurema and Jupi Plutons, Pernambuco-Alagoas Domain, show a large variation of εHf(t) values (−45 to −5) and Hf TDM model age between 1.2 and 3.9 Ga. Archean Hf TDM model ages were recorded in Cryogenian/Ediacaran zircon grains as well as Paleoproterozoic grains, suggesting contribution of an Archean component in the source of the granites. One sample of the Mamanguape Pluton, Transversal subprovince, have εHf(t) values ranging between −13.7 and + 1.4 and Hf TDM model age between 1.4 and 2.2 Ga, suggesting that the magma was generated by partial melting of metasedimentary rocks that received a large contribution of Neoproterozoic and Paleoproterozoic igneous sources. Small amount of mantle melt contributing to the source of the two-mica granites is supported by the presence of mafic enclaves and positive εHf(t) values.

Variability in the sources of North Gondwana Cadomian basins tracked by Nd isotopic systematics (Iberian Massif)

The Cadomian Orogeny encompassed the opening and closure of oceanic domains and associated sedimentary basins in the northern margin of Gondwana from Ediacaran to Early Cambrian time. In the Iberian Massif, these Cadomian basins are included in autochthonous and allochthonous (far-travelled) terranes of the Variscan Orogen. A compilation of Nd isotope information of Ediacaran-Lower Cambrian siliciclastic series supports previous proposal for variability in the sources along the North Gondwanan margin that continued during the Early Paleozoic. Older TDM model ages ranging from 1361 to 2357 Ma of the Variscan allochthonous Ediacaran-Lower Cambrian siliciclastic series indicate proximity to Archean and Paleoproterozoic old crustal sources of the West African Craton and represent deposition on a western Cadomian basin. In turn, the autochthonous Ediacaran-Lower Cambrian siliciclastic series show relatively younger TDM values ranging from 1179 to 2114 Ma, suggesting derivation from more juvenile magmatic rocks that are well represented further east. The Ediacaran-Lower Cambrian siliciclastic series of the autochthonous terranes formed in an eastern Cadomian basin located near the Sahara Metacraton, the Trans-Saharan Orogen and the Tuareg and Arabian-Nubian shields.

Tracking a magmatic arc within a confined orogen: New evidence from the Araçuaí orogen (SE Brazil)

By comparison with igneous rock assemblages of well-exposed modern magmatic arcs and their typical calc-alkaline, magnesian, I-type signatures, many deeply eroded magmatic arcs have been characterized worldwide, unraveling ancient plate margins. Since the 1980's, different assemblages of Ediacaran to Cambrian magmatic rocks have been systematically mapped and characterized according to their distinctive petrographic, structural, lithochemical, geochronologic, and isotopic features, allowing to establish the pre-collisional, collisional, and post-collisional stages of the Araçuaí orogen (SE Brazil). Among them, the tonalitic-granodioritic batholiths and stocks with calc-alkaline, magnesian, I-type signatures, rich in dioritic to mafic enclaves, and related metavolcano-sedimentary successions compose a magmatic arc formed in the early Ediacaran, the Rio Doce magmatic arc. Extending for more than 1000 km along the Araçuaí-Ribeira Orogenic System (AROS), the Rio Doce arc shows a hybrid isotopic signature and crustal inheritance, compatible with modern magmatic arcs built on continental active margins. We present new field, petrographic, and lithochemical studies, coupled with U–Pb (LA-ICPMS) geochronology and isotopic (in-zircon Lu–Hf and whole-rock Sm–Nd) analysis, unraveling the least evolved isotopic signatures ever found for tonalitic-granodioritic plutons of the Rio Doce magmatic arc, and a comprehensive data comparison with modern magmatic arcs. The studied Santa Tereza and Jequitibá suites comprise tonalitic-granodioritic and Opx-bearing charnockitic rocks, with calcic-to-alkali-calcic-magnesian I-type signature, associated with gabbroic rocks. Zircon U–Pb data yielded Concordia ages of 612 ± 3 Ma (Santa Tereza) and 594 ± 3 Ma (Jequitibá) for magmatic crystallization, and 580 ± 5 Ma to 571 ± 3 Ma for metamorphic recrystallization, with associated εNd(612Ma) values from −0.06 to −7.05 (TDM model ages: 1.4–2.04 Ga), and εNd(594Ma) values from −6.67 to −8.8 (TDM model ages: 1.64–1.87 Ga). The zircon εHf(t) (+2.3 to −4.8) and Hf TDM model ages (1.33–1.65 Ga) assigned a moderately juvenile to evolved signature for the Santa Tereza suite, while the Jequitibá suite (εHf(t): −1.7 to −36.4; TDM model ages: 1.33–3.21 Ga) shows a more evolved signature. Altogether, data from the Rio Doce arc are similar to typical continental-margin magmatic arcs with the involvement of mantle melts and/or melting of juvenile crust, suggesting a westward slab retreat during ocean-floor subduction within the Araçuaí confined orogen.

Petrogenesis of the late Neoproterozoic Carmo stock, northeastern Brazil: Implications for partial melting of oceanic crust and sediments in a syn-collisional setting

Granitic magmatism is undoubtedly the main geological feature of the Brasiliano Orogeny in the Borborema Province, northeastern Brazil. However, the petrogenesis and tectonic setting of the oldest magmatic pulse (640–620 Ma; Conceição-type granites) in the Central Subprovince is still hotly debated. The Carmo stock consists of calc-alkalic magmatic epidote-bearing Conceição-type porphyritic granodiorite and monzogranites that carry abundant mafic microgranular enclaves (MMEs). LA-ICP-MS zircon U–Pb data indicate crystallization around 615 Ma for these granitoids. Granitoids and MMEs exhibit similar chemical characteristics, both of which show high-K calc-alkalic, metaluminous and magnesian compositions. All studied rocks are enriched in large-ion lithophile elements (LILE) and light rare-earth elements (LREE), and depleted in high-field-strength elements (HFSE) and heavy rare-earth elements (HREE). Host granitoids are characterized by high initial 87Sr/86Sr ratios (0.707863–0.709677), weakly negative ε Nd(t) values (−2.1 to −3.1), and TDM model ages of 1.31–1.36 Ga. These geochemical and isotopic signatures, together with the low Ba/Th and Sm/La ratios and high La/Sm and Th/La ratios, suggest that granodiorites and monzogranites were generated from the partial melting of altered oceanic crust and subducted sediments. The MMEs have Sr–Nd isotopic compositions almost indistinguishable from their host granitoids, with initial 87Sr/86Sr ratios of 0.708895, ε Nd(t) values of −2.8 and TDM model ages of 1.40 Ga. The similarity in isotopic compositions and the petrographic evidence indicate that magma mixing and mingling played an important role in the formation of MMEs. Based on the new geochemical and isotopic data, together with regional geological features, we infer that the Carmo stock rocks, as well as Conceição-type granites, were most likely formed in a syn-collisional tectonic setting following the early break-off of a relatively weak oceanic slab.

Comparative analysis of the TDM model and the DMO model planned for Hungarian tourism areas

Magyarország Kormánya 2020 végén helyezte hatályba a turisztikai térségek meghatározásáról szóló 429/2020. (IX. 14.) kormányrendeletet. A rendelet egy új turisztikai intézményrendszer kialakítását vetíti elő, ami – a desztinációs logikát követve – több hasonlóságot mutat a korábban már aktívan működő turisztikai desztinációmenedzsment (TDM) rendszerrel (NTS 2005). A desztinációmenedzsment szervezetekből (DMSZ) álló új ágazatirányítási szint szervezeti modelljét a Nemzeti Turizmusfejlesztési Stratégia 2030 – Turizmus 2.0 (NTS 2021) tartalmazza. A kutatás elsősorban a 2020-ban kijelölt turisztikai térségek (429/2020. (IX. 14)) földrajzi határait veti össze a korábban kiépített TDM-rendszer működési területével, majd értékeli a két rendszer alapvető hasonlóságait és eltéréseit a szervezeti modell, a feladatellátás és a finanszírozás szintjén primer adatgyűjtés és az NTS 2021 tartalomelemzése alapján.

Petrogenesis of the late Ediacaran A-type granites of the western part of the Moroccan Anti-Atlas belt: Insights from U–Pb dating, geochemistry and Sr–Nd isotopes of the Sidi El Houssein, Tafraout and Taourgha intrusions

The U–Pb zircon age carried out on three distinct late Ediacaran granites through the Anti-Atlas yielded 207Pb/235U ages of 584 ± 2.29/579 ± 3.83 Ma for Sidi El Houssein granite (Zenaga Inlier), 581 ± 2.05 Ma for Tafraout granites (Kerdous inlier) and 580 ± 3.02 Ma for the Taourgha intrusion (Bas-Drâa inlier). These pink granites display high SiO2 contents that range from 69.19 to 77.3 wt %. They are mainly peraluminous to weak metaluminous and subalkaline and ferron granites with LILE (Rb, K, Th) and HFSE (Ta, Zr, Hf) enrichment, with depletions in Ba, Nb, Sr, and Ti. These rocks have relatively high zircon saturation temperatures (700–900 °C), high Zr + Nb + Ce + Y contents >350 ppm), and 10,000 × Ga/Al ratios> 2.6 that are typical of A-type granites. Isotopic compositions show that the granitoids have variable (87Sr/86Sr)i ratios (0.67–0.73), εNd(t) values (−2.9 to-7.63) and TDM model ages of 1.49–2.53 Ga Suggesting that they were derived from the partial melting of the continental crust with a moderate contribution of the mantle. The late Neoproterozoic granitoids of the Anti-Atlas belt were probably generated during a transtensional regime due to an asthenosphere upwelling that followed the lithospheric delamination related to the collapse of the Panafrican belts.

Petrogenesis of potassic granite suites along the southern margin of the Zimbabwe Craton

AbstractAn integrated approach embracing field studies, petrographic and geochemical investigations together with zircon U-Pb-Hf data was used to investigate the petrogenesis of potassic granite suites along the southern margin of the Zimbabwe Craton. Zircon U-Pb geochronology identifies age relationships, revealing coeval magmatism of the ca. 2 635 ± 5 to 2 625 ± 3 Ma Chilimanzi Suite, and the ca. 2 627 ± 7 Ma Razi Suite. Both suites represent syn- to late-tectonic, high-K, calc-alkaline, and metaluminous to weakly peraluminous granites and granodiorites with I-type affinity. The granite suites contain xenocrystic zircons, with the Chikwanda Pluton of the Chilimanzi Suite yielding a grain of up to 3 206 Ma old. Both granite suites exhibit eHf values of between -5.6 ± 1.3 and -7.3 ± 1.6 and TDM model ages of ca. 3.4 to 3.5 Ga which suggests a similar crustal source. The unradiogenic zircon Hf isotopic compositions are consistent with formation of the granite suites through partial melting of pre-existing crustal protoliths, including Palaeoarchaean tonalite-trondhjemite-granodiorites (TTGs) of the Zimbabwe proto-craton. Partial melting of lower crust gave rise to granitic melts that became emplaced over a relatively short time interval from 2 635 to 2 625 Ma and heralded the stabilisation of the Zimbabwe Craton.In addition to virtually identical ages, the Razi and Chilimanzi suites have similar geochemistry. Small geochemical differences between the Chilimanzi and the Razi suites are attributed to the crustal level at which they are preserved, the modal mineralogy and the extent to which the melts are evolved. The Razi Suite melts were generated from lower crust partial melting of thickened charnockite-enderbite source rocks rich in heat producing elements. The partial melting occurred under fluid-absent conditions and magmas were emplaced at lower to mid crustal levels. The Chilimanzi Suite magmas were similarly derived by the partial melting of TTG lower crust and were emplaced at upper crustal levels. Accordingly, the Chilimanzi Suite exhibits more evolved magmatic fractionation indices indicated by high Rb/Sr, as well as low K/Rb ratios relative to the Razi Suite. Both suites reveal varying degrees of enrichment in incompatible elements including Rb, Th, and U, as well simultaneous depletions in Ba, Sr, and Hf which underscores the role of fractional crystallisation in the evolution of the granitic magmas.

Cadomian arc recycling along the northern Gondwana margin: Source-inherited composition of Miaolingian rift-related rhyolitic rocks (Ossa-Morena Zone, SW Iberia)

Rhyolites and rhyolitic tuffs of the Freixo-Segóvia Volcanic-Sedimentary Complex of the Cambrian of the Ossa-Morena Zone (Variscan belt, SW Iberia) were analyzed for petrography, major and trace element geochemistry, Sm–Nd isotopes and U–Pb zircon geochronology in order to deduce magma sources. New U–Pb zircon age data indicate that Freixo-Segóvia rhyolitic rocks, previously assigned to the Terreneuvian, formed during the Miaolingian (ca. 509-505 Ma). These rhyolitic rocks exhibit calc-alkaline signature, LREE enrichment, nearly flat HREE patterns, negative Eu, Nb and Ti anomalies, and are chemically similar to the bulk continental crust. Freixo-Segóvia rhyolitic rocks have negative to slightly positive εNd(T) values (−2.8; 0.5) resulting in TDM model ages (1.0–1.3 Ga) that overlap the range defined by Terreneuvian Malcocinado andesites, formed in the transition of the Cadomian (West-African) arc to continental rifting in northern Gondwana margin. Based on the Sm–Nd isotopic data, the Freixo-Segóvia rhyolitic rocks may have resulted from of partial melting of andesitic crust. The presence of Ediacaran-age zircon in the Freixo-Segóvia rhyolitic rocks indicates inheritance from the Cadomian arc. Inherited zircon grains with West African affinity were probably transferred into the rhyolitic magma from an older igneous source formed in the Cadomian arc. Based on their major and trace element composition, combined with isotopic and geochronological data, the Freixo-Segóvia rhyolitic rocks record recycling of arc crust during a Late Cambrian rifting event along the northern Gondwana margin. The transition from Cadomian accretion to peri-Gondwana break-up leading to the opening of the Rheic Ocean is also known in other parts of the Variscan belt.

Meso- to Neoproterozoic terrane accretion: Insights from juvenile mafic magmatism from the Votuverava Group and Embu Complex, southern Ribeira Belt, Brazil

Terranes of the Neoproterozoic Ribeira Belt record processes related to West Gondwana assembly. However, the evolutionary history of the belt in the preceding Rodinia supercontinent cycle and its role in the transition to West Gondwana assembly is poorly known. New geochemical and geochronological data of mafic magmatism from Meso- to early Neoproterozoic rock units (1500–900 Ma) integrated with published data provides new constraints to unravel the tectonic setting of the Ribeira Belt. Geochemical and isotopic data from the Votuverava Group and Embu Complex from the southern Ribeira Belt record three distinct periods of juvenile magmatism. Mafic rocks from the Votuverava Group define the oldest magmatism as Calymmian (1490–1475 Ma) and Ectasian (1300–1260 Ma). Both age groups display Th/Yb ratios greater than N-MORB, low Ta/Yb and Nb/La ratios, low Nb and Zr concentrations, negative Nb anomaly, whole-rock ɛNd(T) from +2.25 to +4.01, an Nd two-stage TDM model age spanning 1629–1471 Ma, and zircon εHfT mainly between +5 and +10, characteristics of juvenile mantle source arc-related magmatism. The third event occurred during early Tonian (900 Ma) and is recorded in the mafic rocks from the Embu Complex. Geochemical data indicate that these mafic rocks belong to the tholeiitic series with low LREE enrichment, negative Nb and Ta anomalies, low Nb and Zr contents and low Nb/La and Zr/Y ratios, consistent with arc-related basalts. Whole-rock Sm–Nd isotopic data yielded ɛNd(T) of +0.72 and Nd two-stage TDM model age of 1921 Ma, with zircon Hf isotopes indicating juvenile mantle sources to the mafic magmatism with ɛHfT between +4.5 and +17.2. Thus, mafic rocks from the southern Ribeira Belt record multiple periods of accretion and convergence settings associated with assembly of Rodinia and Gondwana.

Petrogenesis of the Helong Granites in Southern Jiangxi Province, China: Constraints from Geochemistry and In Situ Analyses of Zircon U–Pb–Hf Isotopes

The Jinzhuping and Changkeng granites are related to the Helong W–Sn ore field in southern Jiangxi Province, China. Three different phases can be found in the Jinzhuping pluton, and their LA-ICP-MS zircon U–Pb ages are 155.2 ± 0.68 Ma, 154.0 ± 0.56 Ma, and 153.4 ± 0.99 Ma, respectively, indicating two types of granitic rocks. All granites in the Helong ore field have similar geochemical characteristics, they have high contents of SiO2 (73.99 wt.%–77.68 wt.%), and total alkali (7.56 wt.%–8.76 wt.%) and are weakly to strongly peraluminous. They are slightly enriched in HREE and depleted in Eu, Ba, Sr, P, and Ti. Zircon εHf(t) values of the Jinzhuping three granites are from −14.4 to −10.4, from −15.3 to −11.4, and from −18.1 to −10.5, and the Hf TDM model ages range from 1.83 to 2.06 Ga, from 1.89 to 2.14 Ga, and from 1.83 to 2.31 Ga, respectively. Whole-rock geochemistry and Hf isotope analysis indicate that the Helong granites experienced a high degree of differentiation and evolution derived by partial melting of the Late Paleoproterozoic crustal materials, and they formed in a backarc caused by low-angle subduction of the Paleopacific plate.

Geological processes defining the formation of plumasite-type corundum in the Paleoproterozoic Isertoq Terrane, South-East Greenland

Plumasite-type corundum occurrences in the Nattivit area in South-East Greenland offer a unique opportunity to study corundum formation in-situ where pegmatites intruded into metamorphosed lherzolite and dunite of the Archean-Paleoproterozoic continental crust. The Nattivit area, located in the Isertoq Terrane of North Atlantic Craton, forms part of the overriding plate during convergence of the Nagssugtoqidian orogen (1910-1840 Ma). New field observations and elemental and isotopic geochemical analysis provide further insights in the history of crustal convergence, its exhumation and how corundum was formed. The continental crust in the area consists of metamorphosed mafic to ultramafic rocks and tonalite-trondhjemite-granodiorite (TTG) gneisses, where the mafic rocks in the Isertoq Terrane yield a εNd TDM model age of 3000–2800 Ma. Dunite and lherzolite sills/dikes intruded the mafic rocks before the intrusion of the TTG sheets. The intrusion ages for the TTG obtained from zircon U-Pb geochronology are 2818 ± 8 Ma, 2760 ± 13 Ma to 2667 ± 7 Ma. U-Pb zircon data, zircon textures and Th/U ratios indicate metamorphism occurred at 2698 ± 7 Ma to 2629 ± 11 Ma, 2500–2400 Ma and 1900–1600 Ma. Whole rock geochemical data of mafic to ultramafic rocks show a continental arc affinity, with negative Ta, Nb and positive Pb anomalies. A metasomatic event at 2390 ± 70 Ma partly reset the isotopic signature in the mafic to ultramafic rocks. A marked absence of ages between 2350 and 2100 Ma in the TTG zircon age populations exists, indicating a period with minimal magmatic and/or metamorphic activity. The metamorphic mineral assemblages of the schist, amphibolite, ultramafic rocks and metasomatic reaction zones in ultramafic rocks indicate upper to medium–high amphibolite facies conditions. Kyanite in the metasomatic reaction zones in ultramafic rocks indicate the higher end of the temperature and pressure range above 4.2–10 kbar and 530–800 °C, similar to estimates from dolerite dikes in the Kitak area. The syn-tectonic pegmatites with an intrusion age of 1843 ± 4 Ma formed corundum. The new data indicate that the pegmatite melt/fluid and the geotectonic setting are defining factors for generating plumasite-type corundum.