REE Analyses Research Articles

Investigation on pretreatment method for the determination of rare earth elements in polymetallic mineral samples in Pan-Xi region by ICP-MS.

The polymetallic mineral samples in Pan-Xi region are rich in rare earth resources, and exploring an efficient and accurate analysis method is of great significance for their comprehensive utilization. In this study, the samples were decomposed by three methods, namely closed acid dissolution, open acid dissolution with five acid and alkali fusion with sodium peroxide, and the 15 REE were determined by inductively coupled plasma mass spectrometry (ICP-MS) with Rh and Re as internal standard correction elements. The comparative experiments were conducted using standard substances, and the results showed: (1) The detection limit of closed acid dissolution method was low with relative standard deviation (RSD) ranging from 2.51% to 9.56% and the accuracy of method (ΔlgC) ranging from 0.006 to 0.073, while the sample processing was long, and the results of some REE were low. (2) The RSD of open acid dissolution with five acid method ranged from 1.93% to 7.96%, and ΔlgC ranged from 0.004 to 0.045 with low results of the determination results of REE. (3) The alkali fusion with sodium peroxide method eliminated the influence of matrix effects by selecting instrument optimization, sample dilution, appropriate internal standard elements, etc. The RSD ranged from 1.24% to 6.49%, and ΔlgC ranged from 0.001 to 0.032. In conclusion, alkali fusion with sodium peroxide method has a fast analysis process, complete sample dissolution, and the accuracy and precision of test results can meet the requirements of specification (DZ/T0011-2015), which is most suitable for the analysis of REE in polymetallic mineral samples from Pan-Xi region.

Advances in Analytical Techniques and Applications in Exploration, Mining, Extraction, and Metallurgical Studies of Rare Earth Elements

The use of analytical techniques is important and critical in all areas related to REE, such as basic fundamental research, exploration, mining, extraction, and metallurgical activities at different stages by different industries. At every stage of these activities, rock, ore, minerals, and other related materials have to be analyzed for their REE contents in terms of elemental, isotopic, and mineralogical concentrations using different analytical techniques. Spectacular developments have taken place in the area of analytical instrumentation during the last four decades, with some of them having shrunk in size and become handheld. Among laboratory-based techniques, F-AAS, GF-AAS, ICP-OES, and MP-AES have become very popular. Because of high sensitivity, fewer interference effects, and ease of use, ICP-MS techniques, such as quadrupole ICP-MS, ICP-MS/MS, ICP-TOF-MS, MH-ICP-MS, HR-ICP-MS, and MC-ICP-MS, with both solution nebulization as well as direct solid analysis using laser ablation sample introduction methods, have become more popular for REE analysis. For direct analysis of solids, INAA, XRF, and LIBS techniques, as well as LA-based ICP-MS techniques, are being extensively utilized. The LIBS technique in particular requires little to no sample preparation. TIMS, SIMS, and SHRIMP techniques are being used for isotopic as well as dating REE depots. Portable analytical techniques, such as pXRF, pLIBS, and Raman spectrometers are able to perform in situ analysis even in the field, helping to make fast decisions during exploration studies. At present, hyperspectral remote sensing techniques including handheld, drone, and satellite-based techniques have become very popular in REE exploration studies because of their ability to cover larger areas in a limited time and, thus, became very cost-effective. Deployment of microanalytical devices/sensors mounted in remotely operated vehicles (ROV) is being successfully utilized in detecting REE-rich deposits in the deep oceans. Providing updated in-depth information on all these important aspects with suitable examples, especially from the point of view of REE research studies is the focal point of this review article.

REE Analyses in Some Geological Standard Reference Materials utilizing LA-ICP-MS and ICP-MS Techniques

REE Analyses in Some Geological Standard Reference Materials utilizing LA-ICP-MS and ICP-MS Techniques

Granitoids Geological and Geochemical Features Study at Akchatau Massif

. The aim of the work is to identify the geological and geochemical features of the granitoids of the Akchatau massif. This article discusses the petrochemical data of the first and second phase introduction of the Akchatau massif, as well as the petrogenesis of rocks and the distribution conditions of tungsten and molybdenum. To diagnose the distribution of elements, the data were normalized by UCC. According to the results of the analysis, it was found that the chemical analysis of REE for granites is less than for leukogranites. It was also found that the REE distribution graph in the rocks of the Akchatau massif repeats the line of the upper crust.

노인의 체육참여 영향요인 분석: 로지스틱 회귀분석과 의사결정나무 분석의 적용

Purpose: The purpose of this study is to identify factors influencing sports participation in older adults.BR Method: The subjects of this study were 9,799 older adults aged 65 and over selected through raw data from the 2017 National Survey of Older Koreans. The research tools were 16 variables extracted from the survey questions of the 2017 National Survey of Older KoreansD. ata processing was performed on SPSS Ver. 22.0, and was used to perform logistic regression analysis and decision tree analysis.BR Results: First, as a result of logistic regression analysis, factorsn ifluencing sports participation in older adults were ‘age’, ‘level of education’, ‘residence’, ‘income elvel’, ‘health status’, ‘muscle status’, ‘number of chronic diseases, ‘movement’ ‘Performance’, ‘depression’, ‘support from friends/neighbors’, ‘family support’, and ‘social activity. Second, as a result of the desciion tree analysis, it was found that ‘movement performance’, ‘social activities’, ‘residence’, ‘muscle state’ ,and ‘friend/neighbor support’ were important variables to distinguish whether to participate or not in sposrt. There were 8 node combinations that determine. Third, both logistic regression analysis and decisiont ree analysis showed that ‘movement performance’ was the factor that had the greatest influence on participation in sports for the elderly, and the influence of participation in sports for older adults was conrfmi ed through logistic regression analysis and decision tree analysis. The factors were ‘residence’, ‘social activity’, ‘muscle state’, and ‘friend/neighbor support’. Fourth, ‘gender’ and ‘age’ were found as variables with differences from previous studies.BR Conclusion: In this study, the level of physical function is found to haev the most important effect on participation in sports among older adults.

Garnet, zircon, and monazite age and REE signatures in (ultra)high‐temperature and high‐pressure rocks: Examples from the Caledonides and the Pamir

AbstractRare earth element (REE) signatures of high‐U/Pb and high‐Th/Pb accessory minerals are typically used to link their ages to specific petrological processes (‘petrochronology’)—most notably the growth or breakdown of garnet. Although this approach is powerful, gaps in our understandings of REE systematics in high‐grade rocks exist, particularly regarding the degree to which these minerals chemically equilibrate at extreme conditions. To investigate this, we performed comparative chronology and REE analysis of garnet, zircon, and monazite in (1) a fluid‐rich, ultrahigh‐pressure (UHP) migmatite from the Western Gneiss Region, Norway, and (2) dry felsic granulite xenoliths from the Pamir, Tajikistan. Zircon and monazite from the hydrous migmatite provided ages of 450–370 Ma and a range of Gd/Yb values across this time span. A Lu‐Hf garnet age of 422 ± 2 Ma coincides with the age at which zircon and monazite exhibit the highest Gd/Yb values, as well as the largest range therein. The degree of dispersion in these values is substantial, especially for monazite. Zircon and monazite in the dry xenoliths provide age clusters between 50 and 11 Ma, recording pulsed growth and recrystallization. The Lu/Hf garnet ages for these samples are 41–38 Ma. The accessory minerals of that age are texturally associated with garnet, yet have the lowest, not the highest, Gd/Yb values. In both cases, there is evidence that co‐genetic garnet and accessory minerals achieved REE equilibrium during growth. However, the age and compositional record of chronometric accessory minerals that were co‐genetic with garnet are distinctly different between the two case examples. In the hydrous migmatite, supply‐limited garnet growth in the presence of fluid phase resulted in strongly zoned garnet and a correspondingly large range in Gd/Yb values among co‐genetic zircon and monazite. The range in Gd/Yb values match among these phases and collectively capture the strong fluctuations in the REE composition of matrix micro‐domains caused by garnet growth. In this case, it is the range in Gd/Yb values, rather than a specific composition that is diagnostic for garnet growth. In the felsic granulites, garnet and accessory minerals growth occurred in a fluid‐limited regime, in which short fluid pulses triggered reactions that had been likely significantly overstepped. The seemingly contradictory pattern of increasing Gd/Yb after garnet growth in these samples is the result of garnet having high Gd/Yb and continued zircon growth forcing further HREE depletion of the matrix with time. The situation that high, rather than low, Gd/Yb values in zircon and monazite indicate equilibrium with garnet may be common in dry granulites and other anhydrous high‐temperature rocks. Our findings provide an improved framework for the reliable identification of the accessory minerals that equilibrated with garnet, even when the REE‐age record of these minerals is complex, dispersed, and seemingly contradictory. In addition, the combined zircon‐, monazite‐, and garnet‐age and REE‐record refines the regional tectonic interpretation of our samples.

Geochemical Distribution of REE and Grain Size Analysis of Heavy Mineral Associated with Tin Placer-Type Deposit, Bangka

Indonesia is included in the East Malaya Block of the Southeast Asian Tin Belt. Two types of tin deposits in Indonesia are primary and secondary tin deposits (placer). Factors that can cause the formation of placer tin deposits include S-type granite, weathering, transportation, and sedimentation. Factors that control the formation of placer tin deposits include the presence of source rock (granite type S), weathering processes, erosion, transportation and sedimentation, and the presence of basins or valleys where weathering materials are deposited. The transportation process has a major role in the grain shape of a material. This study aims to determine the geochemical distribution and characteristics of heavy mineral grains at the accumulation of placer tin deposits, e.g., colluvial, alluvial, and tailings, in which there are 62 sample points located Bangka Island, Indonesia. The research method used in this study was grain size analysis, radiation level measurement using a scintillometer, and geochemical analysis using ICP-MS.

Mineralogy and Geochemistry of JingFenCui (Rhodonite Jade) Deposit from Beijing, China

JingFenCui is a type of rhodonite jade from the Changping district of Beijing, China, which is a manganese skarn deposit formed through the metasomatism of the granite aplite and Cambrian limestone. The pink color of JingFenCui is richer and brighter than that of rhodonite jade from other deposits. The surface of JingFenCui exhibits dendritic iron and manganese oxides, which is the outstanding advantage of rhodonite jade for carving works. The zoning pattern of mineralogy between the contact zone with the wallrock is obvious. The main skarn minerals consist mainly of spessartine, diopside, augite, manganotremolite, clino-suenoite, rhodonite, galena, etc. Compared with rhodonite jade from the Makeng in Fujian and the Luziyuan in western Yunnan, vittinkiite (MnSiO3) is more concentrated in the rhodonite of the JingFenCui Deposit as a Mn-Ag-Pb-Zn-Fe polymetallic deposit. There is a good agreement among the rhodonite, amphibole, and galena in the spider diagrams of the trace elements. The results of trace elements and REE analysis show that the metallogenic fluids of the JingFenCui deposit are mainly from magma related to the Heixiongshan granite. It is suggested that the JingFenCui deposit is a manganese skarn deposit formed through the metasomatism of the manganese-bearing limestone and fine-grained granite of the Heixiongshan.

Genesis of the Eastern Adamello Plutons (Northern Italy): Inferences for the Alpine Geodynamics

The Corno Alto–Monte Ospedale magmatic complex crops out at the eastern border of the Adamello batholith, west of the South Giudicarie Fault (NE Italy). This complex includes tonalites, trondhjemites, granodiorites, granites and diorites exhibiting an unfoliated structure suggesting passive intrusion under extensional-to-transtensional conditions. Major, minor elements, REE and isotopic analyses and geochemical and thermodynamic modelling have been performed to reconstruct the genesis of this complex. Geochemical analyses unravel a marked heterogeneity with a lack of intermediate terms. Samples from different crust sections were considered as possible contaminants of a parental melt, with the European crust of the Serre basement delivering the best fit. The results of the thermodynamic modelling show that crustal melts were produced in the lower crust. Results of the geochemical modelling display how Corno Alto felsic rocks are not reproduced by fractional crystallization nor by partial melting alone: their compositions are intermediate between anatectic melts and melts produced by fractional crystallization. The tectonic scenario which favored the intrusion of this complex was characterized by extensional faults, active in the Southalpine domain during Eocene. This extensional scenario is related to the subduction of the Alpine Tethys in the Eastern Alps starting at Late Cretaceous time.

NanoSIMS and EPMA dating of lunar zirconolite

Zirconolite is a common Zr-rich accessary mineral in mafic rocks. It is also an ideal U–Pb/Pb–Pb chronometer because it commonly contains high U content (mostly 0.1–10 wt%) and negligible initial Pb. However, zirconolite is usually very small (e.g., ~ 1 μm in width) in lunar rocks, requiring a high spatial resolution analysis. We analyzed a single, large (25 μm × 20 μm) grain of zirconolite in lunar meteorite NWA 4485 using Pb–Pb dating by NanoSIMS and U–Th–Pb dating by EPMA. The resultant U–Th–Pb age is 4540 ± 340 Ma (2σ) with a spatial resolution of 1.3 μm. The Pb–Pb age by NanoSIMS is 4348.5 ± 4.8 Ma (2σ) with a spatial resolution of ~ 2 μm, consistent with the age of 4352 ± 10 Ma and 4344 ± 14 Ma reported in the same meteorite and its paired meteorite NWA 4472. Although U–Th–Pb age is somewhat older, it still includes the NanoSIMS results within the analytical uncertainty. This work demonstrates the potential application of the combined EPMA dating and REE analysis of lunar zirconolite, with the benefits of high spatial resolution, non-destructive, and readily accessibility of the instrument. The precision of the EPMA dating (7.6%, 2σ) can be improved by increasing the counting time for Pb, U and Th. We expect to apply this EPMA technique for a quick and non-destructive age survey and geochemical study of zirconolite grains from the lunar mare basalts newly returned by Chang’E-5 mission which landed on a very young (1.2–2.0 Ga by crater-counting chronology) basalt unit in Procellarum KREEP Terrain.

Ferruginous accumulations in hypogene karst conduits of Crimean Piedmont: Evidence for a deep iron source for the Kerch-Taman iron-ore province, north Black Sea region

This study documents ferruginous accumulations in hypogene karst cavities in the Eocene limestones of central-eastern Crimean Piedmont, including unusual quartz-goethite tubes in Tavrida Cave, and aims to reveal their origin and significance to the problem of iron source for the adjacent Kerch-Taman iron ore province. We employed speleological, petrographic, mineralogical, and geochemical (including REE analysis) methods. Ferruginous materials dominated by goethite precipitated in open cavities, although metasomatic replacement of the host rock also occurred. Although the formation of conduits/cavities enclosing ferruginous materials clearly predated the main phase of hypogene speleogenesis in Tavrida Cave, both speleogenetic phases were controlled by the same cross-formational flow paths. Geochemical characteristics of the studied materials in all sites are largely similar, pointing to their genetic affinity. REEY patterns in most of the samples are remarkably similar to those found in iron formations worldwide, for which significant hydrothermal contribution is established. We show that these accumulations had been formed from acidic, reduced, hydrothermal fluids rising from a deep source and intruding oxidizing environment of the karstified Eocene aquifer, where goethite had been precipitated at the boundary of the iron reduction/oxidation zone. This mechanism is consistent with the hypogene origin of host karst conduits. These findings have implications to the origin of iron ores in the adjacent Kerch-Taman province, where deposits are closely associated with mud volcanoes operating there since at least the Middle Miocene. Although the marine sedimentary (hydrogenetic) origin of these deposits is universally accepted, the source of iron is a matter of debate. Revealing of the deep fluid source of iron for the ferruginous accumulations in hypogene caves in Piedmont suggests that the deep fluid system associated with mud volcanism in the Kerch-Taman region could have been a significant, if not the major, supplier of iron for ore deposits in the Cimmerian basin.

A Lower Cretaceous Lagerstätte from France: a taphonomic overview of the Angeac‐Charente vertebrate assemblage

Terrestrial ecosystems from the Lower Cretaceous of Europe and bonebeds formed in swampy environments are poorly known. The Berriasian-early Valanginian Angeac-Charente site in France represents an example of both. Nine field campaigns have yielded thousands of fossils of over a hundred taxa, including 16 taxa from vertebrate macroremains with numerous trample and crocodile bite marks; 22 taxa from the abundant vertebrate microremains; >10 vertebrate coprolite morphotypes with plant and vertebrate inclusions; abundant sauropod and stegosaur tracks including some preserved in ‘4-D’; termite coprolites; mollusc moulds; ostracods and plants, including coniferous wood, cones, leaves and cuticle fragments, charophytes and pollen. The richness, diversity and preservation of the fossils qualify the site as a fossil-Lagerstätte. The site represents a ‘snapshot’ into a Lower Cretaceous ecosystem. This is supported by REE analyses of biogenic apatite and sediment samples, the fossils being found in a single stratigraphical interval and the record of sedimentological and taphonomic ‘frozen scenes’. The Angeac-Charente bonebed is highly diverse, dominated by an ornithomimosaur taxon, and contains both macro- and microfossils. This indicates a complex formation, likely primarily influenced by ecological and biologic processes, but also significant physical processes. These include crocodyliform predation and/or scavenging on turtles, ornithomimosaurs and fishes; probable mass mortality occurrence of an ornithomimosaur herd; possible social behaviour of stegosaurs; limited hydraulic transport of most sauropod bones and intense dinoturbation.

U–Pb geochronology and REE geochemistry of zircons in mafic granulites from the Lützow-Holm complex, East Antarctica: Implications for the timing and P–T path of post-peak exhumation and Antarctica–Sri Lanka correlation

We report new petrological and geochronological data, together with zircon REE patterns, of mafic granulites from the Lützow-Holm Complex (LHC), East Antarctica, and investigate the pressure-temperature-time (P-T-t) evolution of granulite-facies metamorphism in order to unravel the timing and tectonics of Neoproterozoic collisional processes related to the amalgamation of Gondwana. The LHC is composed of three tectonic units: a ca. 2.5 Ga continental fragment (Shirase Microcontinent), a ca. 1.0 Ga magmatic arc (Prince Olav–Vijayan Block; PVB), and a latest Neoproterozoic suture zone (Lützow-Holm Bay Suture Zone; LHSZ) separating the two. Mafic granulites from Tenmondai Rock and Sudare Rock, which belong to the PVB and the LHSZ, respectively, contain orthopyroxene + plagioclase symplectites around garnets, probably formed during post-peak decompression. The application of phase equilibrium modeling and geothermobarometry indicates similar peak P-T ranges of 850–860 °C/7.8–8.4 kbar (Tenmondai Rock) and 800–810 °C/8.5–9.0 kbar (Sudare Rock), together with clockwise P-T paths for both localities. LA-ICP-MS zircon U-Pb dating of the studied granulites yielded Mid-Neoproterozoic magmatic ages of >808 Ma (Tenmondai Rock) and >783 Ma (Sudare Rock) from igneous cores, and Late Neoproterozoic to Cambrian metamorphic ages of ca. 630–481 Ma from overgrown rims and/or structureless grains. Zircon REE analyses indicate that younger 560–510 Ma metamorphic zircons from the localities exhibit heavy-REE-enriched patterns and negative Eu anomalies, suggesting that the consumption of garnet and growth of plagioclase took place during zircon growth. This process was probably related to the formation of post-peak decompressional textures (orthopyroxene + plagioclase symplectite around garnet) observed in the mafic granulites. The results of this study therefore indicate that post-peak exhumation of the LHC started at ca. 560 Ma. Available U-Pb and REE data from 560 to 510 Ma metamorphic zircons of the Highland Complex, Sri Lanka, show similar heavy-REE-enriched patterns and Eu negative anomalies, suggesting that post-peak exhumation of both the LHC and the Highland Complex took place almost simultaneously at ca. 560 Ma. The results of this study further support the proposed tectonic model in which the Highland Complex and the LHSZ are parallel collisional sutures formed during the Late Neoproterozoic-Cambrian Gondwana amalgamation.

High‐P granulites of the Songshugou area (Qinling Orogen, east‐central China): Petrography, phase relations, and U/Pb zircon geochronology

AbstractHigh‐pressure (HP) granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems. The latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates. A continental arc, active c. 520–395 Ma ago, formed an enigmatic example of such a rock association in the Songshugou area, Qinling Orogen. To unravel the juxtaposition of the distinct rocks, this study combines petrography, phase equilibria modelling, conventional thermobarometry, and zircon U–Th–Pb–Ti–REE analysis. Two mafic HP granulites, which contain the mineral assemblages garnet–clinopyroxene–plagioclase–rutile–mesoperthite–quartz and garnet–clinopyroxene–plagioclase–rutile, experienced peak metamorphic conditions of ≤1.4 GPa, 860°C and ~1.3 GPa, ≥910°C, respectively. During decompression and cooling, at 489 ± 4 Ma, amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810–860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at 510 ± 4 Ma. Though the thermobarometric data are just within the methodological errors, the U/Pb zircon ages imply the HP granulites did not evolve coherently. The HP granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging‐wall plate. Published and new pressure–temperature–time–deformation paths converge at ~710°C, ~0.9 GPa, and ≲470 Ma, implying exhumation tectonics juxtaposed the HP granulites with a mélange of eclogite and mantle dunite at lower crustal levels. This study highlights that lower arc crust can comprise material of diverse evolution.

Conditions of Early Paleozoic Basaltic and Picritic Magmatism in West Siberia

Abstract ––Geological, petrological, isotope-geochemical (40Ar/39Ar analysis, petrochemical data, and geochemistry of trace elements and REE), and mineralogical researches testify that the formation of the early Paleozoic basalt and picrite complexes of the West Siberian Plate basement was related to the development of the Cambrian subduction zone of the Paleo-Asian Ocean. Using the compositions of clinopyroxenes and amphiboles (and also programs of computational modeling), we have established the Р–Т conditions of formation of early Paleozoic picrite complexes. Crystallization of clinopyroxenes began at significant depths (25–20 km) and at high temperatures (1300–1275 °C). Olivine might have formed at elevated pressures (8–7 kbar) and temperatures of 1540–1490 °C. Amphiboles formed, most likely, at 6.1–4.5 kbar and much lower temperatures, 1105–1060 °C. Petrochemical analysis and data on trace elements and REE in the rocks of the studied early Paleozoic complexes in West Siberia testify to their intricate formation involving magmatic systems with basalt (island arc and back-arc basins), picrite, and shoshonite (and also WPB type) melt characteristics. Taking into account the similar geochemical characteristics of the early Paleozoic basaltoids and picrites of the West Siberian Plate basement and the Kamchatka volcanics, we suggest that a considerable part of the studied ancient complexes formed by the model implying (as in the case of the Sredinnyi Ridge in Kamchatka) the action of enriched magmatic systems during the development of a destructive window (“slab-window”) under rupture of subducted plate on the background of common island arc magmatism.

석회암 내 희토류원소 분석법 고찰: 유도결합 플라스마 질량분석기를 이용한 석회암시료의 희토류원소 함량 분석 시에 발생하는 Ba 산화물의 영향

석회암 내 희토류원소 분석법 고찰: 유도결합 플라스마 질량분석기를 이용한 석회암시료의 희토류원소 함량 분석 시에 발생하는 Ba 산화물의 영향

Implication of weathering and mineral sorting on rare earth element geochemistry of Pleistocene–Holocene sediments from Cauvery delta, south India

REE analysis of sediments was carried out on representative samples from two cores drilled at Uttrangudi and Porayar locations from Cauvery delta in south India to better understand the patterns and textural and mineralogical control on REEs. Good correlation of REEs and their chondrite normalized ratios (Gd/Yb and La/Yb)N with Ti, Th and Y in both the cores suggest control of Allanite, Titanite and Monazite among heavy minerals on the REE distribution in sediments. Good to strong positive correlation among REEs and Al, Fe, Mg, Ni, Cr, Sc and Co in both the cores suggests partial control of mafic minerals and clay. The Eu/Eu* values show a significant negative correlation with the CIA values, suggesting that the Eu in sediments has been modified to some extent by the process of weathering, affecting its loss and consequently lowering of Eu/Eu* values particularly in Uttrangudi sediments. The correlation of various trace elements with Eu/Eu* suggests that the enrichment of LREE bearing heavy minerals (Allanite, Titanite and Monazite) has resulted in relatively higher increase in LREE and HREE in comparison to Eu that is dominantly held in feldspars, which has further resulted in decreased value of Eu/Eu*.

Timing and petrogenesis of metamafic-ultramafic rocks in the Southern Brasília orogen: Insights for a Rhyacian multi-system suprasubduction zone in the São Francisco paleocontinent (SE-Brazil)

A systematic investigation of amphibolites and a metaultramafite granofels was carried out in the southernmost Brasília Orogen, part of the reworked margin of the São Francisco paleocontinent. These rocks occur interleaved within Neoproterozoic metasediments and the Archean-Paleoproterozoic basement. The amphibolites from the Andrelândia, Liberdade and the Carrancas nappe system show an N-MORB signature, enriched to slightly depleted in LILE (Large Ion Lithophile Elements) and LREE (Light Rare Earth Elements) and depletion in the HFSE. They define a flat sub primitive mantle (PM) normalized curve with negative anomalies of Nb and Ce. The Lima Duarte nappe amphibolite has an andesitic basalt with an E-MORB signature and magmatic arc filiation. U-Pb (SHRIMP) zircon dating on the different samples yielded similar crystallization ages of ca. 2.15 Ga. Metamorphic conditions record amphibolitic facies for all the samples and can be linked to lower intercepts aged between 560 and 590 Ma. Whole rock Nd isotopic data suggest a juvenile source with TDM ages between 1.95 and 2.22 Ga. The associated metaultramafite, from Carrancas Klippe, highlights inherited cryptic layering and fractional crystallization processes from mineral and whole rock chemistry. It is enriched in LILE and shows negative anomalies of Th and Nb and positive anomalies of Sr and Zr. The Platinum group elements present a total PGE abundance of 16.5 and 30.8 ppb. The Iridium group defines a steep positive normalized curve while the Palladium group defines a gentle positive one, as expected for differentiated liquids. U-Pb zircon dating yielded three data clusters: i) the ca. 2.5 Ga, interpreted as inheritance, ii) the ca. 2.1 Ga, considered as the crystallization age and, iii) the youngest, being ca. 600 Ma, associated with the amphibolite facies metamorphic overprint. REE analyses on Rhyacian zircons suggest plagioclase crystallization under the influence of free-REE bearing minerals. A magmatic zircon grain containing a quartz inclusion, presents a distinctive REE pattern, with a positive normalized curve and a strong negative Eu anomaly. It suggests a hybridized crystallization under influence of plagioclase-rich and silica-saturated fluids prior or during the igneous crystallization, possibly due to the influence of slab derived materials. These data unravel new insights towards mafic-ultramafic rocks formation in different settings within a Rhyacian suprasubduction system in the southernmost part of the São Francisco paleocontinent, later reworked during the Gondwana amalgamation.

New evidence and interpretation of facies, provenance and geochemistry of late Triassic-early Cretaceous Tethyan deep-water passive margin-related sedimentary rocks (Ayios Photios Group), SW Cyprus in the context of eastern Mediterranean geodynamics

The late Triassic-early Cretaceous deep-sea sedimentary succession exposed in western Cyprus is used here to help understand the wider context of continental break-up and seafloor spreading in the easternmost Mediterranean region. The restored sequence begins with late Triassic, base-of-slope sandstone turbidites and mudrocks, and fines upwards into mudrocks, distal calciturbidites and metalliferous sediments. After a hiatus, late Jurassic-early Cretaceous non-calcareous mudstones and radiolarites accumulated beneath the carbonate compensation depth, together with redeposited shallow-water-derived carbonates, including calcirudites. The succession culminates in late Jurassic-early Cretaceous very thickly bedded and highly mature quartzarenites that accumulated by mass-flow processes. The fine-grained siliciclastic sediments are terrigenous in origin, as indicated by whole-rock, trace element and REE analysis. Fe, Mn and trace metal enrichment in the late Triassic represents hydrothermal input related to submarine volcanism that was probably triggered by the nearby onset of seafloor spreading. The late Triassic sandstones were derived from a low to intermediate-grade metamorphic source terrane. The late Jurassic-early Cretaceous sandstones reflect extreme physical and chemical maturity in the source area, followed by transport and mass flow to a deep-water base-of-slope setting. Regional facies variation and locally available palaeocurrent data suggest sediment supply, originally from a continental block, no more than tens of km to the west or north. Similar successions are exposed in W Turkey, represented by the Antalya Complex. In the light of alternatives, the sedimentary succession is restored as the base-of-slope apron of a rifted microcontinental block, adjacent to the northern margin of the S Neotethys. The overall succession indicates (unstable) passive margin development after regional latest Triassic-early Jurassic continental break-up, with implications for plate reconstructions and hydrocarbon exploration.

Petro-Geochemical and Statistic Studies of the Nimba Region in the Republic of Guinea

Petro-Geochemical and Statistic Studies of the Nimba Region in the Republic of Guinea