Isotope record of Nd-Sr-Pb in deep sea sediments from the Pacific (Table 2)

Pelagic clay of the east-central Pacific province is shown to be a mixture of three primary detrital components, reflecting continental source areas in Asia, North America, and Central and South America. Relative contributions from each source area are a function of geography, and this distribution appears to have remained constant over the past five million years, despite changing flux rates. A Q-mode factor analysis of downcore records for Pb, Sr, and Nd isotopes identified three factors that account for 98% of the total variance. These factors represent the radiogenic isotopic signatures of 1) late Cenozoic Asian dust, which dominates in the central North Pacific; 2) North American continental hemipelagic/eolian sources, restricted mainly to the easternmost North Pacific at ~30 °N latitude; and 3) Central and South American sources, restricted to areas east of ~100 °W longitude. South of the Intertropical Convergence Zone (~6 °N), the Asian dust signature diminishes abruptly. We conclude that late Cenozoic Asian dust sources can be isotopically differentiated downcore from both North American and South and Central American sources in the eastcentral Pacific. This approach has a utility for identifying changes in long-term Cenozoic atmospheric circulation patterns.

U-Pb geochronology and Nd isotope contributions to the interpretation of a peculiar ring massif: the Santa Eulália plutonic complex (SW Iberia, Portugal)

The Santa Eulalia plutonic complex (SEPC) is a late-Variscan granitic body placed in the Ossa-Morena Zone. The host rocks of the complex belong to metamorphic formations from Proterozoic to Lower Paleozoic. The SEPC is a ring massif (ca. 400 km2 area) composed by two main granitic facies with different colours and textures. From the rim to the core, there is (i) a peripheral pink medium- to coarse-grained granite (G0 group) involving large elongated masses of mafic and intermediate rocks, from gabbros to granodiorites (M group), and (ii) a central gray medium-grained granite (G1 group). The mafic to intermediate rocks (M group) are metaluminous and show wide compositions: 3.34–13.51 wt% MgO; 0.70–7.20 ppm Th; 0.84–1.06 (Eu/Eu*)N (Eu* calculated between Sm and Tb); 0.23–0.97 (Nb/Nb*)N (Nb* calculated between Th and La). Although involving the M-type bodies and forming the outer ring, the G0 granites are the most differentiated magmatic rocks of the SEPC, with a transitional character between metaluminous and peraluminous: 0.00–0.62 wt% MgO; 15.00–56.00 ppm Th; and 0.19–0.42 (Eu/Eu*)N ; 0.08–0.19 (Nb/Nb*)N [1][2]. The G1 group is composed by monzonitic granites with a dominant peraluminous character and represents the most homogeneous compositional group of the SEPC: 0.65–1.02 wt% MgO; 13.00–16.95 ppm Th; 0.57–0.70 (Eu/Eu*)N ; 0.14–0.16 (Nb/Nb*)N . According to the SiO2 vs. (Na2O+K2O–CaO) relationships, the M and G1 groups predominantly fall in the calc-alkaline field, while the G0 group is essencially alkali-calcic; on the basis of the SiO2 vs. FeOt/(FeOt+MgO) correlation, SEPC should be considered as a magnesian plutonic association [3]. New geochronological data (U-Pb on zircons) slightly correct the age of the SEPC, previously obtained by other methods (290 Ma, [4]). They provide ages of 306  2 Ma for the M group, 305  6 Ma for the G1 group, and 301  4 Ma for the G0 group, which confirm the late-Variscan character of the SEPC, indicating however a faintly older emplacement, during the Upper Carboniferous. Recent whole-rock isotopic data show that the Rb-Sr system suffered significant post-magmatic disturbance, but reveal a consistent set of Sm-Nd results valuable in the approach to the magmatic sources of this massif: M group (2.9 < Ndi < +1.8); G1 group (5.8 < Ndi < 4.6); G0 group (2.2 < Ndi < 0.8). These geochemical data suggest a petrogenetic model for the SEPC explained by a magmatic event developed in two stages. Initially, magmas derived from long-term depleted mantle sources (Ndi < +1.8 in M group) were extracted to the crust promoting its partial melting and extensive mixing and/or AFC magmatic evolution, thereby generating the G1 granites (Ndi < 4.6). Subsequently, a later extraction of similar primary magmas in the same place or nearby, could have caused partial melting of some intermediate facies (e.g. diorites) of the M group, followed by magmatic differentiation processes, mainly fractional crystallization, able to produce residual liquids compositionally close to the G0 granites (Ndi < 0.8). The kinetic energy associated with the structurally controlled (cauldron subsidence type?) motion of the G0 liquids to the periphery, would have been strong enough to drag up M group blocks as those occurring inside the G0 granitic ring.

A Short Review on Lu-Hf Isotope System in Zircon: Implications for Crustal Evolution

Zircon has been recognized as the unaltered part of the Earth's history which preserves nearly 4 billion year record of earth's evolution. Zircon preserves igneous and metamorphic processes during its formation and remains unaffected by sedimentary processes and crustal recycling. U-Pb and Lu-Hf in zircon work as geochronometer and geochemical tracer respectively. Zircon provide valuable information about the source composition of the rocks and the intrinsic details of an unseen crust-mantle processes. The world wide data of U-Pb and Lu-Hf isotope systems in zircon reveal crustal evolution through geological history. Moreover, the U-Pb age pattern of zircons show distinct peaks attributed to preservation of crustal rocks or mountain building during supercontinent assembly. The histogram of continental crust preservation shows that nearly one-third of continental crust was formed during the Archean, almost 20% was formed during Paleoproterozoic and 14% in last 400 Ma.

Caracterização ambiental da bacia hidrogáfica do Rio São Domingos a partir da análise geoquímica e isotópica Pb/Pb

A bacia hidrográfica do rio São Domingos constitui uma das sub-bacias do rio Muriaé pertencente ao sistema Paraíba do Sul e, tem seus limites coincidentes com os limites do município de São José de Ubá, sendo este o segundo maior produtor de tomate do estado do Rio de Janeiro, com sua principal fonte econômica baseada na agropecuária. Este tipo de atividade resulta em utilização de produtos químicos nas lavouras e juntamente a ocupação inadequada resulta em modificação das paisagens e da mata nativa, resultando em diversos tipos de impactos no ambiente. Neste estudo foram abordados os impactos relacionados a concentração de metais e sua proveniência através das assinaturas isotópicas Pb/Pb, utilizando para tal o procedimento analítico de lixiviação dos sedimentos de corrente e abertura total de rochas para a obtenção de razões isotópicas e concentrações de metais por ICP-MS. Os resultados mostraram que as contribuições nos sedimentos de corrente se dão a partir de cinco fontes compreendidos no intervalo de assinatura isotópica 206Pb/207Pb 1,1229 e 1,1949, representadas em intervalos bem definidos. Por correlação com as respectivas concentrações se observa que, preferencialmente, existe maior influência das rochas do embasamento, seguido de atividade antrópicas como a urbanização e disposição de lixo doméstico. As maiores concentrações estão associadas ao cobre, chumbo, estrôncio, níquel e zinco. Contudo todas as concentrações de metais obtidas se encontram abaixo da legislação vigente. Desta forma a contaminação antrópica é limitada a regiões de maior densidade populacional e as influências naturais predominam na área da bacia.

Isotope shift studies in the rare earths and lead

Isotope shifts of K_α1 x-ray transitions were measured for the Neodymium isotopes Nd 142, 143, 144, 145, 146, 148 and 150, the Samarium isotopes Sm 147, 148, 149, 150, 152 and 154, the Gadolinium isotopes Gd 154, 155, 156, 157, 158 and 160, the Dysprosium isotopes Dy 162 and 164, the Erbium isotopes Er 166, 168 and 170, the Hafnium isotopes Hf 178 and 180 and the Lead isotopes Pb 204, 206, 207 and 208. A curved crystal Cauchois spectrometer was used. The analysis of the measurement furnished the variation of the mean square charge radius of the nucleus, δ˂r²˃, for 23 isotope pairs. The experimental results were compared with theoretical values from nuclear models. Combining the x-ray shifts and the optical shifts in Nd and Sm yielded the optical mass shifts. An anomaly was observed in the odd-even shifts when the optical and the x-ray shifts were plotted against each other.

Estudos de metais pesados e isótopos de Pb nos sedimentos da Baía de Sepetiba baseados em geoquímica e na distribuição pelas possíveis áreas fontes

A Baia de Sepetiba é uma laguna costeira separada do oceano por uma ilha barreira. Localiza-se a 60 km da cidade do Rio de Janeiro, em uma importante região geoeconômica do Brasil. O objetivo deste trabalho foi avaliar a distribuição espacial da contaminação dos metais Cu, Pb, V, Cr, Cd, Co, Ni e Zn nos sedimentos da Baia. O mapa das concentrações elaborado pelo método de lixiviação permitiu caracterizar anomalias ao entorno da foz do Rio Guandu, na área da Coroa Grande, do Porto de Itaguaí, da Ilha do Martins, e anomalias ao longo de faixa com direção NW-SE. Os resultados das concentrações totais indicam contaminação por Zn, Cd, próximo a Ilha da Madeira com Pb e Cr associados e Cu e Zn na Restinga de Marambaia, com Ni, Pb e Cr associados. Os resultados dos isótopos de Pb para as razões de 206Pb/207Pb entre 1,23 e 1,27 representam os resíduos industriais e ocorrem em duas áreas: na parte leste da Restinga e entre as Ilhas de Jaguanum e Itacuruçá. A leste/sudeste destas ilhas foi reportada uma razão ainda mais alta (1.30), ainda não identificável na literatura. As correntes marinhas desempenham a redistribuição dos sedimentos e metais associados na Baia, com transporte de oeste para leste da pluma sedimentar descarregada pelos rios. Os principais causadores da poluição da Baia de Sepetiba são uma pilha de rejeito de Zn abandonada, resíduos industriais e domésticos não tratados de forma eficaz, poluentes atmosféricos de siderúrgicas e veículos, e por ventura resíduos de atividades navais e militares.

Litogeoquímica, geocronologia (U-Pb) e geoquímica isotópica (Sr-Nd) dos granitoides do Domínio Cambuci (Faixa Ribeira) na região limítrofe dos Estados do Rio de Janeiro e Espírito Santo

Os granitoides do Domínio Cambuci, na região limítrofe entre os estados do Rio de Janeiro e Espírito Santo, foram separados em quatro principais grupos: (1) Complexo Serra da Bolívia (CSB) - Ortogranulitos e Ortognaisses Heterogêneos; Ortognaisse Cinza Foliado; e charnockitos da Região de Monte Verde (2) Leucogranitos/leucocharnockitos gnaissificados da Suíte São João do Paraíso (SSJP) (3) Granito Cinza Foliado (4) Leucogranito isotrópico. O CSB é caracterizado pelo magmatismo de caráter calcioalcalino do tipo I, oriundo em ambiente de arco vulcânico (Suíte Monte Verde) e retrabalhamento crustal (ortogranulitos leucocráticos). O Ortogranulito esverdeado fino, é considerado no presente estudo como rocha do embasamento para o Terreno Oriental, cristalizada durante o paleoproterozoico - Riaciano (2184,3 21 Ma) e recristalizada durante o evento metamórfico Brasiliano no neoproterozoico - Edicariano (607,2 1,5 Ma), cuja idade TDM é de 2936 Ma. O Ortogranulito leucocrático médio cristalizou-se no neoproterozoico Edicariano (entre 592 e 609 Ma) e idade TDM ca. 2100 Ma, ao qual apresenta registro de herança no paleoproterozoico. A Suíte Monte Verde caracteriza-se por um magmatismo calcioalcalino e a Suíte Córrego Fortaleza, por um magmatismo calcioalcalino de alto K, ambas com assinatura de arco magmático. Registram dois pulsos magmáticos, em no Neoproterozoico - Edicarano: um em 592 2 Ma, idade do charnoenderbito, com idade TDM 1797 Ma, e outro em 571,2 1,8 Ma (injeção de um charnockitoide). Para todas as rochas do CSB são registradas feições protomiloníticas, miloníticas e localmente ultramiloníticas. Os dados geoquímicos indicam que os granitoides da SSJP são da série calcioalcalina de alto K, gerados no Neoproterozoico (idades que variam desde 610,3 4,7 Ma até, 592,2 1,3 Ma. As idades TDM revelam valores discrepantes para duas amostras: 1918 Ma e 2415 Ma, sugerindo que tenham sido geradas de diferentes fontes. O Granito Cinza Foliado é da Série Shoshonítica, metaluminoso do tipo I e, de ambiência tectônica de granitos intraplaca. Entretanto, poderiam ter sido fomados em ambiente de arco cordilheirano, havendo contaminação de outras fontes crustais. Fato este pode ser confirmado pelas as idades TDM calculadas ≈ 1429 1446 Ma. O Leucogranito isotrópico ocorre em forma de diques de direção NW, possui textura maciça e é inequigranular. Dados geoquímicos revelam que são granitoides metaluminosos do tipo I da série shoshonítica, e, de acordo com a ambiência tectônica, são granitos intraplaca. O Leucogranito Isotrópico representa o magmatismo pós-colisional ao qual ocorreu entre 80 a 90 Ma de anos após o término do evento colisional na região central da Faixa Ribeira. O Leucogranito Issotrópico cristalizou-se no cambriano (512,3 3,3 Ma e 508,6 2,2 Ma) e com idades TDM ca. 1900

内蒙古龙头山Ag-Pb-Zn多金属矿床成矿模式及找矿模型

The recent years research indicated that middle-south section of Da Hinggan Mountains metallogenic belt has two periods(Hercynian and Yanshanian) characteristics of metallogenesis, as well as the most of ore deposits in the area closely relate to Permian strata. Longtoushan ore deposit discovered in 2004 is an Ag-Pb-Zn polymetallic ore deposit born in Permian and located in the east hillside of the metallogenic belt, which has considerable resources potentials. It has important research value for its good metallogenic location and blank research history. Base on the detail field geology studies, the geology characteristics of "two stages and three kinds of metallogensis" has established. According to further work through geochemistry research including trace element, REE, S, Pb and Sr isotope, as well as petrography, microtemperature measurement, Laser Raman analysis and thermodynamics calculation of fluid inclusion, origin and characteristic of the ore-forming material and fluid has been discussed. And a new technology of single pellet Rb-Sr isochrones has been tried for dating its born time. Bae on above work, study of ore deposit comparison has been carried out, and metallogesis controlling factor and geological prospecting symbol have been summarized. Finally, metallogenic model and prospecting model have been established. According to above, the next step work direction has been proposed. Main achievement of the paper are listed as follow: 1.Longtoushan ore deposit has experienced two metallogenic periods including hot-water sedimentation period and hydrothermal reformation period. There are three kinds of metallizing phase: bedded(or near-bedded) phase, vein-shaped phase and pipe-shaped phase. The mian metallogenic period is hot-water sedimentation period. 2.Ore deposit geochemistry research indicated that the metal sulfides have charcateristic of hot-water sedimentation metallogensis, but generally suffered later hydrothermal transformation. The barite mineral isotope content is homogenous, showing the seabed hot-water sedimentation origin characteristic. Wall rock, such as tuff is one of metallogenic material origins. Both of Pb model age and Rb-Sr isochrone research older age value than that of strata, possibly for been influenced by hydrothermal transformation, and interfusion of ancient basis material. 3.There are two kinds of main metallogenic fluid inclusion in barite of the Longtoushan ore deposit, which are rich gas phase( C type) and liquid phase (D type). Their size is 2～7um, and principal components is H2O. Both kinds of fluid inclusion have freezing point temperature -7.1～-2.4℃ and -5.5～-0.3℃, salinity 4.0～10.6wt% and 0.5～8.5wt%, homogeneous temperature 176.8～361.6℃ and 101.4～279.9℃, which peak value around 270℃ and 170℃, respectively. Density of the ore-forming fluid is 0.73～0.97g/cm3, and metallogenic pressure is 62.3×105～377.9×105Pa. Above characteristic of the fluid inclusion are well geared to that of ore deposit originated in seabed hot-water sedimentation. 4.Through the comparison research, that Longtoushan ore deposit has main characteristic of hot-water sedimentation ore deposit has been indicated. Ore-forming control factor and prospecting symbol of it has been summarized, as well as metallogenic model and prospecting model. Next step work direction about prospecting has also been proposed finally.

Oxygen isotope thermometry in carbonatites, Fuerteventura, Canary Islands, Spain

Crystallization temperatures of the oceanic carbonatites of Fuerteventura, Canary Islands, have been determined from oxygen isotope fractionations between calcite, silicate minerals (feldspar, pyroxene, biotite, and zircon) and magnetite. The measured fractionations have been interpreted in the light of late stage interactions with meteoric and/or magmatic water. Cathodoluminescence characteristics were investigated for the carbonatite minerals in order to determine the extent of alteration and to select unaltered samples. Oxygen isotope fractionations of minerals of unaltered samples yield crystallization temperatures between 450 and 960degreesC (average 710degreesC). The highest temperature is obtained from pyroxene-calcite pairs. The above range is in agreement with other carbonatite thermometric Studies. This is the first study that provides oxygen isotope data coupled with a CL study on carbonatite-related zircon. The CL pictures revealed that the zircon is broken and altered in the carbonatites and in associated syenites. Regarding geological field evidences of syenite-carbonatite relationship and the close agreement of published zircon U/Pb and whole rock and biotite K/Ar and Ar-Ar age data, the most probable process is early zircon crystallization from the syenite magma and late-stage reworking during magma evolution and carbonatite segregation. The oxygen isotope fractionations between zircon and other carbonatite minerals (calcite and pyroxene) support the assumption that the zircon would correspond to the early crystallization of syenite-carbonatite magmas.