Mercury in sediments from gold and copper exploitation areas in the Camaquã River Basin,Southern Brazil

Mercury concentrations were determined in stream sediments from the Camaquã River Basin, located in the shield region of the state of Rio Grande do Sul, southern Brazil. The resulting geochemical data show that overbank floodplain deposits exhibit higher concentrations than sediments collected from the active channel bed. In addition, higher Hg concentrations were measured in the fine(<63 μm) sediment fraction of the samples. Total Hg concentrations in the fine fraction of active stream sediments from Lavras do Sul County, which have been influenced by past gold mining activities, have decreased during the last five years to values ≤142 ng g⁻¹. However, in a settling pond containing abandoned mine wastes, the Hg concentration of a bulk sample remained exceptionally high (5220 ng g⁻¹). Preliminary speciation results show that Hg⁰ is the predominant species in most of the samples. This was the form of Hg released by the gold amalgamation activities in the area, and appears to be relatively stable under the existing E_h and pH conditions.     

Composition and diagenesis of Neoproterozoic Guaritas Group sandstones in the Minas do Camaquã fault zone,Camaquã Basin

Geological structures influence the formation and evolution of sedimentary rocks. The Minas do Camaquã fault zone is a primary structure of the Camaquã Basin, controlling the uplift of the ore-bearing units of the Santa Bárbara Group. To the south of the Camaquã River, the fault zone deforms alluvial and eolian sequences attributed either to the Santa Bárbara or Guaritas groups. In this study, a facies and petrographic composition and diagenetic analysis are presented to understand the evolution of the fault zone. Facies analysis was accomplished using high-resolution orthophoto mosaics and field surveys. Seven sedimentary facies were defined, grouped into three facies associations. Facies associations correspond to a succession of climate-influenced depositional environments. The transition from humid to dry conditions occurs from a fluvial (facies association 1) to eolian environments (facies association 2). These deposits are overlaid at the top by a high energy environment deposits characterized by amalgamated gravelly and sandy bodies, corresponding to an alluvial environment (facies association 3). Despite a small compositional variation, sandstones present a continental block provenance which may be related to mixed anorogenic or orogenic provenance. Diagenetic features are similar in the three facies associations, suggesting the same burial history for the sedimentary deposits separated by the fault zone. The Minas do Camaquã fault zone in the study area is an intraformational structure, as analyzed sequences are attributed to the Guaritas Group, implying a relatively high degree of deformation late after its deposition.     

Illite authigenesis in sandstones of the Guaritas Allogroup (Early Paleozoic): Implications for the depositional age,stratigraphy and evolution of the Camaquã Basin (Southern Brazil)

Several analytical studies performed on alluvial-eolian sandstones of the Early Paleozoic Guaritas Allogroup (Camaquã Basin, southern Brazil) indicate illite to be abundant, showing different morphologies as authigenic grain rims and pore-bridging filaments. Authigenic illite separates of variable grain sizes from distinct stratigraphic intervals of the Guaritas Allogroup yielded ⁴⁰K–⁴⁰Ar ages from 521.7 ± 10.3 to 473.7 ± 9.4 Ma. These ages, interpreted to record the timing of illite authigenesis, are coincident with the age of emplacement of the Rodeio Velho andesites (470 ± 19 Ma). Moreover, field structures suggest interaction between hot, andesite lava flows and wet, poorly consolidated sediments of the Pedra Pintada Alloformation (lower strata of the Guaritas Allogroup). This set of data indicates that the Rodeio Velho volcanism could have been responsible for a widespread remobilization of interstitial fluids and consequent authigenic illite precipitation in the sandstones of the Guaritas Allogroup.     

Petrology of a Subduction-related Caldera and Post-Collisional,Extension-related Volcanic Cones from the Early Cambrian and Middle Ordovician (?) of the Camaquã Basin,Southern Brazil

The region studied, located in southern Rio Grande do Sul State, Brazil, 25 km to the northeast of Lavras do Sul, records two volcanic events. The first is the eruption of pyroclastic material and localized flows of alkali-basalt, trachyandesite and andesite composition, corresponding to the early Cambrian Hilário Formation. This event in the region, through tectonic reactivation and explosive expulsion of a large amount of material from the magmatic reservoir chamber, which later faulted and collapsed, has generated an elliptical caldera of 7.2 km × 3.0 km. The rocks in the caldera have derived from partial melting of a spinel lherzolitic or garnet lherzolitic mantle, in a typically orogenic, calc-alkaline environment. They were generated during the final phase of subduction of the Adamastor plate beneath the Rio de la Plata plate in the early Cambrian. The second event occurred in a post-collisional tectonic setting in the Middle Ordovician?, when alkaline magma was emplaced through deep fractures, generating four cones within the collapsed caldera. The rocks in the cones bear the geochemical signature of a more evolved magma when compared to the rocks in the caldera, having been formed through low fusion rates of a garnet-depleted source in the upper mantle. It represents the last phase of the Pan-African-Brasiliano Orogeny, which occurred right after the collision of the Rio de La Plata and Kalahari continental plates, in a retroarc setting.     

Basin evolution and stratigraphic correlation of sedimentary-exhalative Zn–Pb deposits of the Early Cambrian Zarigan–Chahmir Basin,Central Iran

The Zarigan–Chahmir basin is placed in the southern part of a crustal domain known as the Central Iranian microcontinent, at the northwestern margin of Gondwana. This basin hosts abundant mineral deposits, particularly of the iron oxide–apatite (IOA), Fe–Mn exhalative, and Zn–Pb sedimentary-exhalative (SEDEX) types. The evolution of this basin is governed by the Proto-Tethys oceanic crust subduction beneath the Central Iranian microcontinent and by the resulting continental arc and back-arc. This evolution followed two major stages of rifting: (I) Stage I or syn-rift phase, related to intra-basin extension, is indicated by coarse-grained detrital sedimentary rocks and bimodal volcanism (basis of the Early Cambrian Volcano-Sedimentary Sequence; ECVSS), which filled half-graben systems. During this stage, tuff-hosted stratiform, exhalative Fe–Mn deposits along with Kiruna-type IOA deposits formed. The former deposits (e.g., Narigan) are related to early submarine rhyolithic volcanism of the rift-phase sequence, whereas the latter (e.g., Esfordi, Choghart, Chadormalu, Chahgaz) are connected to hydrothermal activity directly linked to the arc calk-alkaline magmatism. (II) Stage II or sag-phase involved the deposition of calcareous shales, siltstones and carbonates (upper part of the ECVSS). Sedimentation during this phase was controlled by basin subsidence and by the reactivation of the half-graben faults. SEDEX deposits are hosted within a carbonaceous, black siltstone unit of the sag-phase sequence, which was deposited during a period of rapid basin subsidence and under anoxic conditions. The location of synsedimentary faults and the prevalence of poorly-oxygenated bottom water conditions were key factors controlling SEDEX mineralization processes in the basin. A high geothermal gradient caused by maximum syn-rift magmatism and sub-crustal lithospheric thinning, affecting primarily the center, western and northwestern basin, may have driven a basin-scale hydrothermal fluid circulation. This finding explains the occurrence of larger, well correlable SEDEX deposits in the northwestern and central parts of the Zarigan–Chahmir basin.     

Contribution of SHRIMP U–Pb zircon geochronology to unravelling the evolution of Brazilian Neoproterozoic fold belts

The South-American continent is constituted of three major geologic–geotectonic entities: the homonym platform (consolidated at the end of the Cambrian), the Andean chain (essentially Meso-Cenozoic) and the Patagonian terrains, affected by tectonism and magmatism through almost all of the Phanerozoic. The platform is constituted by a series of cratonic nuclei (pre-Tonian, fragments of the Rodinia fission) surrounded by a complex fabric of Neoproterozoic structural provinces.     

SHRIMP U–Pb zircon geochronology and Nd signatures of supracrustal sequences and orthogneisses constrain the Neoproterozoic evolution of the Pernambuco–Alagoas domain,southern part of Borborema Province,NE Brazil

The Borborema Province is the western part of a major Brasiliano belt that extends from Brazil through NW Africa in pre-drift reconstructions. This province resulted from convergence and collision among the West African, Congo-São Francisco, and Amazonian cratons about 600 Ma. This study focuses on the Pernambuco–Alagoas (PEAL) domain, which is a complex of magmatic, migmatitic, and metamorphic rocks, located in the southern part of the Borborema Province. U–Pb geochronology and Sm–Nd data for metasedimentary sequences (Rio Una, Inhapi) of the PEAL domain and a sample from a sequence of the Transversal Zone domain suggest that their deposition occurred during a Cryogenian extensional event, within the interval 850–631 Ma (or slightly younger). This extensional event occurred in the PEAL, Transversal Zone, and Sergipano domains before the onset of the Brasiliano collision and was followed by syn- and post-collisional magmatism. The Rio Una sequence and the sequence from Transversal Zone domain were deposited over a Rhyacian (ca. 2.0–2.2) basement having a juvenile Palaeoproterozoic Nd signature, whereas the Inhapi sequence was deposited over an Early Neoproterozoic (Tonian) basement. The deposition of the studied sequences is coeval with metasedimentary sequences to the north and south in other domains of the Borborema Province. However, differences in Nd isotopic signatures between the sequences from PEAL, Transversal Zone, and Sergipano domains suggest that they were formed in distinct basins. Metasedimentary sequences from the PEAL domain have Meso- and Palaeoproterozoic T _DM model ages. These data suggest that the orogens where the metasedimentary sequences are located have a strong ensialic component. T _DM model ages of ca. 1.0 Ga and εNd (0.6 Ga) values around zero recorded in granites from the southern part of the PEAL, suggesting that juvenile material was accreted to the southern part of the PEAL domain crust during the Tonian. The migmatites from the PEAL domain have a wide range of T _DM ages along with a wide range of εNd (0.6 Ga) values. The transition between the northern and southern parts of the PEAL domain denotes the approximate northern margin of a Late Mesoproterozoic to Early Neoproterozoic rift.     

Structural evolution and U–Pb SHRIMP zircon ages of the Neoproterozoic Maria da Fé shear zone,central Ribeira Belt – SE Brazil

The Maria da Fé Shear Zone (MFSZ) is a sinistral strike-slip kilometric-scale structure developed in the late Neoproterozoic during the assembly of Gondwana. The MFSZ development is related to the NW–SE collision between the São Francisco Paleocontinent and the Rio Negro Magmatic Arc, which formed the Ribeira Belt. This paper describes the shear zone in detail, concluding that the orientation and age are consistent with NW–SE shortening during the afore mentioned collision. A U–Pb SHRIMP Concordia age of 586.9 ± 8.7 Ma is reported from zircon grains of a granitic dyke that crystallised synkinematically to the main tectonic activity of the shear zone. Another group of zircon grains from the same sample generated an upper intercept age of 2083 ± 43 Ma anchored in the younger Concordia age. These zircon grains are interpreted as relict grains of the basement from which the granite dyke was generated by partial melting. The temperature during mylonitization in the MFSZ was estimated in the range from 450 to 600 °C, based on microstructures in quartz and feldspar. An earlier collision in the same region, between 640 and 610 Ma, led to an extensive nappe-stack with tectonic transport to ENE, integrating the southern Brasilia Belt. One of the thrust zones between these nappes in the studied area is the Cristina Shear Zone with mylonites that were generated under upper amphibolite to granulite facies conditions. Brittle-ductile E–W metric-scale shear zones are superimposed on the MFSZ, which were active in similar, but probably slightly cooler, metamorphic conditions (≈500 °C).     

The tectonic evolution of the Neoproterozoic Brasília Belt,central Brazil,based on SHRIMP and LA-ICPMS U–Pb sedimentary provenance data: A review

The Brasília Belt is a Neoproterozoic orogenic belt in central Brazil, developed between the Amazon, São Francisco-Congo and Paranapanema cratons. It consists of a thick sedimentary pile, made up of several stratigraphic units, which have been deformed and metamorphosed along the western margin of the São Francisco Craton during the Brasiliano orogenic cycle. In the western part of the belt, a large, juvenile magmatic arc is exposed (the Goiás Magmatic Arc), consisting of calc-alkaline plutonic suites as well as volcano-sedimentary sequences, ranging in age between ca. 860 and 650 Ma. Regional-scale, west-dipping thrusts and reverse faults normally mark the limits between the main stratigraphic units, and clearly indicate tectonic transport towards the east. The age of deposition and tectonic significance of the sedimentary units comprising the Brasília Belt have been a matter of continuous debate over the last three decades. In the present paper, recent provenance data based on LA-ICPMS U–Pb ages of detrital zircon grains from several of these units, are reviewed and their significance for the age of deposition of the original sediments and tectonic evolution of the Brasília Belt are discussed.The Paranoá, Canastra and the Vazante groups, in the central part of the Belt, have detrital zircon grains with ages older than ca. 900 Ma and are interpreted as representative of the passive margin sequence deposited on the western margin of the São Francisco Craton. On the other hand, samples from the Araxá and Ibiá groups have a much younger population of Neoproterozoic zircon grains, as young as 650 Ma, and have been interpreted as syn-orogenic (fore-arc?) deposits. The Bambuí Group, exposed in the easternmost part of the belt and covering large areas of the São Francisco Craton also has young zircon grains and is interpreted, at least in part, as the foreland basin of the Brasília Belt.     

U–Pb (SHRIMP) Zircon Age of Granitoid Pebbles from the Kukkarauk Conglomerates of the Vendian Asha Group (Alatau Anticlinorium,Southern Urals)

Doklady Earth Sciences - The lack of reliable geochronological data for the Vendian deposits of the Urals and other regions is one reason why there is still uncertainty in the age estimates of the...     

Implications of U–Pb SHRIMP zircon data on the age and evolution of the Felbertal tungsten deposit (Tauern Window, Austria)

U–Pb SHRIMP analyses of zircons from various lithologies and ore bodies of the Felbertal scheelite deposit (western and eastern ore field) and neighbouring areas allow the reconstruction of the pre-Alpine magmatic and metamorphic processes responsible for the tungsten mineralization. The ore deposit belongs to the Magmatic Rock Formation, which is tectonically squeezed between the Habach Phyllite Formation and the Basal Schist Formation (all members of the Habach Group). In both the eastern and western ore field, the pre-mineralization geological processes are marked by the emplacement of basalts (547±27?Ma). Ensialic back-arc extension provided pathways for gabbroic and pyroxenitic melts as well as normal "I-type" granitoids (minimum crystallization age of 529±18?Ma). The rock assemblage forms a magmatic arc on an approximately 2?Ga continental Gondwana (?) margin. Post-emplacement tectonism and metamorphism have converted the basalts to fine-grained amphibolites, the gabbroic and pyroxenitic rocks to coarse-grained amphibolites and hornblendites, and the granitoids to leucocratic orthogneisses, respectively. Tungsten mineralization is intimately related to small patches and dikes of differentiated granitoids in the eastern ore field and the K2 ore body in the western ore field. The granitic melts have supposedly been generated by ongoing differentiation of calcalkaline magmas. They cut the older lithologies and intruded along the same pathways as the earlier melts. Fluids have been carried up along a major line in the eastern ore field. They caused the formation of an elongate ore body with a scheelite-quartz stockwork zone (scheelite-bearing quartz veinlets and veins) and an overlying, likewise elongate, 900-m-long, scheelite-rich quartzite lens. In the western ore field, accompanying fluids produced the K2 ore body. In this ore body, an eruption breccia occurs above a mineralized quartzite. The breccia (younger than 529±18?Ma) contains mineralized quartzite clasts as well as barren fine-grained amphibolite clasts and leucocratic orthogneiss-clasts that are similar to the surrounding host rock equivalents. The quartzite, which represents the main mineralization stage of the K2 ore body, is unsuitable for dating. However, the scheelite-rich quartzite lens of the eastern ore field is probably coeval. This lens locally lies on top of a differentiated and strongly mineralized gneiss. The crystallization age of this gneiss is 529±17?Ma, and marks the peak of tungsten input in the eastern ore field. Small, differentiated granitic dikes, which cut both the K2 eruption breccia and the K2 quartzite in the western ore field, contain only minor scheelite and mark a decrease in mineralization at 519±14?Ma. Thus, a period between 530 and 520?Ma and a setting between magmatic arc and (ensialic) back-arc may properly explain the likely scenario for the primary tungsten input (stage-1 scheelite) by differentiated granitic melts of calcalkaline character. Surprisingly, a second stage-2 scheelite formation was induced in the western ore field by a Variscan granite intrusion (K1–K3 gneiss; 336±19?Ma), the emplacement time of which is pre-dated by a cross-cutting dacitic dike of 340±5?Ma. This mineralization, which occurs in small quartz veins and within a quartz aureole atop the intrusion as well as an even younger mineralization in shear zones (yellowish-fluorescent stage-2 scheelite porphyroblasts), is bracketed between 355?Ma (the upper age limit of the K1–K3 gneiss precursor) and 335?Ma (the lower age limit of the dacitic dike, which is stage-2 scheelite free). Supposedly, long-lasting Variscan (amphibolite facies) metamorphic conditions till 282±2?Ma extended the scheelite remobilization. They caused a further dispersion of scheelite and induced the growth of individual grains and of rims around older grains (bluish-fluorescent stage-3 scheelite). The Alpine metamorphism of lower amphibolite to upper greenschist facies conditions caused a further, minor scheelite remobilization, especially along some faults and quartz veins, including sparse, but large, whitish-bluish-fluorescent crystals (stage-4 scheelite).     

First SHRIMP U–Pb zircon dating of granulites from the Kontum massif (Vietnam) and tectonothermal implications

The Kontum massif in Central Vietnam represents the largest continuous exposure of crystalline basement of the Indochina craton. The central Kontum massif is chiefly made of orthopyroxene granulites (enderbite, charnockite) and associated rocks of the Kannack complex. Mineral assemblages and geothermobarometric studies have shown that the Kannack complex has severely metamorphosed under granulite facies corresponding to P–T conditions of 800–850°C and 8±1 kbars. Twenty-three SHRIMP II U–Pb analyses of eighteen zircon grains separated from a granulite sample of the Kannack complex yield ca 254 Ma, and one analysis gives ca 1400 Ma concordant age for a zoned zircon core. This result shows that granulites of the Kannack complex in the Kontum massif have formed from a high-grade granulite facies tectonothermal event of Indosinian age (Triassic). The cooling history and subsequent exhumation of the Kannack complex during Indosinian times ranged from ∼850°C at ca 254 Ma to ∼300°C at 242 Ma, with an average cooling rate of ∼45°C/Ma.     

LA–ICP–MS U–Pb Geochronology of Detrital Zircon in the Guanzhong Basin, China and Its Tectonic Response

正Objective The Guanzhong Basin in the transitional zone of the Qinling orogenic belt and the southern margin of the Ordos Basin has been extensively studied in recent years.Although some results have been obtained,some problems such as whether the materials from the North China craton and the Qinling orogenic belt are detrital sedimentary rocks of the Guanzhong Basin still remain unresolved.     

U–Pb TIMS age constraints on the evolution of the Neoproterozoic Meatiq Gneiss Dome,Eastern Desert,Egypt

Ages are used to constrain the temporal evolution of the Meatiq Gneiss Dome, Eastern Desert, Egypt, by dating (ID-TIMS) pre-, syn-, and post-tectonic igneous rocks in and around the dome. The Um Ba’anib Orthogneiss, comprising the deepest exposed structural levels of the dome, has a crystallization age of 630.8 ± 2 Ma. The overlying mylonites are interpreted to be a thrust sheet/complex (Abu Fannani Thrust Sheet) of highly mylonitized metasediments (?), migmatitic amphibolites, and orthogneisses with large and small tectonic lenses of less-deformed intrusives. Two syn-tectonic diorite lenses in this complex have crystallization ages of 609.0 ± 1.0 and 605.8 ± 0.9 Ma, respectively. The syn-tectonic Abu Ziran diorite, cutting across the tectonic contact between mylonite gneisses of the Abu Fannani Thrust Sheet and a structurally overlying thrust sheet of eugeoclinal rocks (“Pan-African nappe”), has a magmatic emplacement age of 606.4 ± 1.0 Ma. Zircons from a gabbro (Fawakhir ophiolite) within the eugeoclinal thrust sheet yielded a crystallization age of 736.5 ± 1.2 Ma. The post-tectonic Fawakhir monzodiorite intrudes the ophiolitic rocks and has an emplacement age of 597.8 ± 2.9 Ma. Two other post-tectonic granites, the Arieki granite that intrudes the foliated Um Ba’anib Orthogneiss, and the Um Had granite that cuts the deformed Hammamat sediments, have emplacement ages of 590 ± 3.1 and 596.3 ± 1.7 Ma, respectively. We consider formation of the Meatiq Gneiss Dome to be a young structural feature (<631 Ma), and our preferred tectonic interpretation is that it formed as a result of NE–SW shortening contemporaneous with folding of the nearby Hammamat sediments around 605–600 Ma, during oblique collision of East and West Gondwana.     

Neoproterozoic SHRIMP U–Pb zircon ages of silica-rich Dokhan Volcanics in the North Eastern Desert,Egypt

Chronology of Neoproterozoic volcanosedimentary successions remains controversial for many regions of the Arabian–Nubian Shield, including the Dokhan Volcanics of NE Egypt. New U–Pb zircon SHRIMP ages have been obtained for 10 silica-rich ignimbrites and two subvolcanic dacitic bodies, mapped as Dokhan Volcanics, from the North Eastern Desert of Egypt. Crystallization ages range between 592 ± 5 and 630 ± 6 Ma (Early Ediacaran). Apparently, the late consolidation of the Arabian–Nubian Shield was accompanied by the evolution of isolated volcanic centres and basin systems which developed during a period of approx. 40 Ma, independently in space and time and probably under changing tectonic regimes. The obtained age data together with other previously published reliable ages for Dokhan Volcanics suggest two main pulses of volcanic activity: 630–623 Ma and 618–592 Ma. Five samples contain inherited zircons, with ages of 669, 715–746, 847 and 1530 Ma, supporting models that North Eastern Desert crust is mainly juvenile Neoproterozoic crust.     

U–Pb geochronology and palynology from Lopingian (upper Permian) coal measure strata of the Galilee Basin,Queensland, Australia

This study presents the first chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U–Pb zircon ages from tuffs in Lopingian (upper Permian) strata of the Galilee Basin, Queensland and reassigns the B coal-seam to the ‘Burngrove Formation equivalent.’ Five Lopingian tuffs were dated: four from the CRD Montani-1 drill hole including three from the ‘Fair Hill Formation equivalent’ (255.13 ± 0.09, 254.41 ± 0.07 and 254.32 ± 0.10 Ma) and one from the ‘Burngrove Formation equivalent’ (252.81 ± 0.07 Ma, approximately the age of the Yarrabee Tuff in the adjacent Bowen Basin); and a single tuff from the Black Alley Shale in the GSQ Tambo-1-1A drill hole (254.09 ± 0.06 Ma). In the Galilee Basin, all three units are constituents of the Betts Creek Group, here formally elevated in nomenclatural status from the Betts Creek beds. On the western margin of the basin, the group thins, and the ‘J and K’ seams (formerly known as the Crossmore and Glenaras sequences, respectively) in the GSQ Muttaburra-1 drill hole have been interpreted through palynology as Cisuralian–early Guadalupian (spore-pollen assemblage APP3.2). This corroborates the exclusion of the ‘J and K’ seams from the overlying Lopingian Betts Creek Group (spore-pollen assemblage APP5), and the underlying lower to mid-Cisuralian Aramac Coal Measures (spore-pollen assemblage APP2.2), which represent the uppermost unit of the Joe Joe Group. It is proposed that the ‘J and K’ seams are restricted to a depocentre in the Hulton–Rand structure. The recognition of these strata containing APP3.2 spore-pollen assemblages suggests that the mid-Permian hiatus is locally reduced to 12–13 My from 30 Ma (where the ‘J and K’ seams are absent). The results of the radiometric dating and palynological analysis in the Galilee Basin support the proposed, albeit informal stratigraphy, that is given in terms of equivalents of formational units in the Bowen Basin and on the intervening Springsure Shelf.     

Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm–Nd, Pb–Pb and SHRIMP data

Whole-rock geochemical analyses using major and trace elements in combination with the Sm–Nd and Pb–Pb isotope systems, together with SHRIMP age dating on metasedimentary rocks from the Sierras de Chepes, the Sierras de Córdoba, the Sierra Norte and the San Luis Formation in the Sierra de San Luis, have been carried out to unravel the provenance and the geodynamic history of the Eastern Sierras Pampeanas, Central Argentina. The geochemical and the Sm–Nd data point to a slightly stronger mafic and less-fractionated material in the provenance area of the Sierras de Córdoba when compared to the other units. The T_DM model ages from the Sierras de Chepes (~1.82 Ga) and the Sierra Norte (~1.79 Ga) are significantly older than the data from the Sierras de Córdoba (1.67 Ga). The Pb data are homogeneous for the different units. Only the ²⁰⁸Pb/²⁰⁴Pb ratios of some samples from the Sierras de Córdoba are higher. A late Pampean detrital zircon peak around 520 Ma from the Sierras de Chepes is in accordance with the new data from the San Luis Formation. This is similar to the literature data from the Famatina Belt located to the northwest of the Sierras de Chepes and also fits the detrital zircon peaks in the Mesón group. These maximum depositional ages were also reported from some locations in the Puncoviscana Formation but are absent in the Sierras de Córdoba. An improved model for the development of the Eastern Sierras Pampeanas in the area between the Sierras de Córdoba and the Puncoviscana Formation is provided. This gives new insights into the late Pampean development of the Sierra de San Luis and the complex development of the Eastern Sierras Pampeanas. This new model explains the younger detrital ages in the Puncoviscana Formation compared with the older ages of the Sierras de Córdoba. Another model of the Sierra de San Luis explains the younger depositional ages of the Pringles Metamorphic Complex and the San Luis Formation when compared to the Nogolí Metamorphic Complex and the Conlara Metamorphic Complex. Additionally, the rather fast change of the high-grade metamorphic conditions in the Pringles Metamorphic Complex and the low-grade metamorphic conditions in the San Luis Formation is explained by extension, the ascent of (ultra) mafic material and later folding and erosion.     

Silurian U–Pb zircon age (LA-ICP-MS) of granitoids from the Zelenodol Cu–porphyry deposit,Southern Urals

The Zelenodol porphyry Cu-(Au, Mo) deposit located about 65 km SSW of the city of Chelyabinsk is confined to the western part of the West Uralian Volcanogenic Megazone. The concordant U-Pb age of zircons from ore-bearing island-arc diorite porphyryis 418.3 Â ± 2.9 Ma.     

Emplacement Ages of the Molybdenum–bearing Granites in the Jinduicheng Area of East Qinling, China: Constraints from Zircon U–Pb Ages and Hf Isotopes

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