In situ U-Pb, O and Hf isotopic compositions of zircon and olivine from Eoarchaean rocks, West Greenland: New insights to making old crust

The sources and petrogenetic processes that generated some of the Earth's oldest continental crust have been more tightly constrained via an integrated, in situ (U-Pb, O and Hf) isotopic approach. The minerals analysed were representative zircon from four Eoarchaean TTG tonalites and two felsic volcanic rocks, and olivine from one harzburgite/dunite of the Itsaq Gneiss Complex (IGC), southern West Greenland. The samples were carefully chosen from localities with least migmatisation, metasomatism and strain. Zircon was thoroughly characterized prior to analysis using cathodoluminescence, scanning electron, reflected and transmitted light imaging. The zircon from all but one sample showed only minor post-magmatic recrystallisation. 207Pb/206Pb dating of oscillatory-zoned zircon using SHRIMP RG (n = 142) indicates derivation of the felsic igneous rocks from different batches of magma at 3.88, 3.85, 3.81, 3.80 and 3.69 Ga. Analyses of 18O/16O compositions of olivine from a harzburgite/dunite (n = 8) using SHRIMP II in multi-collector mode, indicate that the oxygen isotopic composition of this sample of Eoarchaean mantle (δ18OOl = 6.0 ± 0.4‰) was slightly enriched in 18O, but not significantly different from that of the modern mantle. Zircon δ18O measurements from the six felsic rocks (n = 93) record mean or weighted mean compositions ranging from 4.9 ± 0.7‰ to 5.1 ± 0.4‰, with recrystallised domains showing no indication of oxygen isotopic exchange during younger tectonothermal events. δ18OZr compositions indicate that the primary magmas were largely in equilibrium with the mantle or mantle-derived melts generated at similar high temperatures, while calculated tonalite δ18OWR compositions (6.7-6.9‰) resemble those of modern adakites. LA-MC-ICPMS zircon 176Hf/177Hf analyses were obtained from six samples (n = 122). Five samples record weighted mean initial εHf compositions ranging from to 0.5 ± 0.6 to -0.1 ± 0.7 (calculated using λ176Lu = 1.867 × 10-11 yr-1), while one sample records a composition of 1.3 ± 0.7, indicating the magmas were generated from a reservoir with a time averaged, near chondritic Lu/Hf. The derivation of TTG magmas from a chondritic Lu/Hf source implies either that there was not voluminous continental crustal growth nor major mantle differentiation leading to Lu/Hf fractionation during the Hadean or Eoarchaean, or alternatively that rapid recycling of an early formed crust allowed the early mantle to maintain a chondritic Lu/Hf. Previous studies have demonstrated that ancient TTG rocks were mostly produced by dehydration melting of mafic rocks within the stability field of garnet, probably in flatly-subducted or buried oceanic crust. The oxygen isotopic signatures measured here at high spatial resolution allow the source materials to be better defined. Melting of a mixed mafic source consisting of ∼80% unaltered gabbro (δ18OWR = 5.5‰) with ∼20% hydrothermally altered gabbro/basalt (δ18OWR = 4.0‰) would produce tonalite magmas within the average compositional range observed. 18O-enriched components such as altered shallow basaltic oceanic crust and pelagic or continental sediments were not present in the sources of these TTG melts. The absence of high 18O signatures may indicate either the rarity of low temperature altered sediments, or their effective removal from the down-going slab

Coupled Nd-142, Nd-143 and Hf-176 Isotopic Data from 3.6-3.9 Ga Rocks: New Constraints on the Timing of Early Terrestrial Chemical Reservoirs

Increasingly precise data from a range of isotopic decay schemes, including now extinct parent isotopes, from samples of the Earth, Mars, Moon and meteorites are rapidly revising our views of early planetary differentiation. Recognising Nd-142 isotopic variations in terrestrial rocks (which can only arise from events occurring during the lifetime of now extinct Sm-146 [t(sub 1/2)=103 myr]) has been an on-going quest starting with Harper and Jacobsen. The significance of Nd-142 variations is that they unequivocally reflect early silicate differentiation processes operating in the first 500 myr of Earth history, the key time period between accretion and the beginning of the rock record. The recent establishment of the existence of Nd-142 variations in ancient Earth materials has opened a new range of questions including, how widespread is the evidence of early differentiation, how do Nd-142 compositions vary with time, rock type and geographic setting, and, combined with other types of isotopic and geochemical data, what can Nd-142 isotopic variations reveal about the timing and mechanisms of early terrestrial differentiation? To explore these questions we are determining high precision Nd-142, Nd-143 and Hf-176 isotopic compositions from the oldest well preserved (3.63- 3.87 Ga), rock suites from the extensive early Archean terranes of southwest Greenland and western Australia

A idade e natureza da Fonte do Granito do Moinho, Faixa Ribeira, Sudeste do Estado de São Paulo

Este trabalho apresenta novos dados geocronológicos U-Pb SHRIMP em zircões e Sm-Nd em rocha total do Granito do Moinho, que ocorre nas imediações da cidade de Nazaré Paulista, Estado de São Paulo. Este granito apresenta característica sin- a tardi-tectônica em relação à Orogenia Brasiliana e é intrusivo nas seqüências mesoproterozóicas do Grupo Serra do Itaberaba, no segmento central da Faixa de Dobramentos Ribeira. Adicionalmente, foram reavaliados dados isotópicos de Pb obtidos em amostras de rocha total e feldspatos potássicos disponíveis na literatura. A idade U-Pb SHRIMP obtida em monocristais de zircões ígneos do granito foi de 620 ± 11 Ma, sendo interpretada como a época de cristalização desta rocha. As idades modelo Sm-Nd obtidas situaram-se entre 2,0 e 1,9 Ga, mostrando que o magma foi produzido por fusão parcial de rochas pré-existentes, derivadas do manto superior no Paleoproterozóico. As composições isotópicas de Pb das amostras do Granito do Moinho indicam, a exemplo dos isótopos de Nd, uma fonte também crustal e com participação de rochas do Grupo Serra do Itaberaba, de idade mesoproterozóica.U-Pb SHRIMP zircon ages and Sm-Nd isotopic analyses were carried out on the syn- to late tectonic Moinho Granite, intruded within the Mesoproterozoic Serra do Itaberaba Group. Six U-Pb SHRIMP analyses were undertaken on oscillatory zoned zircons. All yielded close to concordant Neoproterozoic ages, with a 206Pb/238U weighted mean age of 620 ± 11Ma, interpreted as the time of the granite crystallization. Sm-Nd isotopic analyses on samples from the Moinho Granite presented Paleoproterozoic depleted-mantle model ages between 2.0 and 1.9 Ga, and negative µNd values, indicating continental sources for the granitic magma. Previous Pb isotopic data suggest that the Mesoproterozoic Serra do Itaberaba metasedimentary sequence contributed to the magma genesis of the studied granitoid

U-Pb-Hf-REE-Ti zircon and REE garnet geochemistry of the Cambrian Attunga eclogite, New England Orogen, Australia: Implications for continental growth along eastern Gondwana

The timing and location of eclogite metamorphism is central to understanding subduction events responsible for the assembly of eastern Gondwana. The Attunga eclogite is one of only six eclogites in Australia and occurs as small blocks within a schistose serpentinite mélange known as the Weraerai terrane, along the Peel Fault of the southern New England Orogen. Our zircon data reveal the presence of high Th/U oscillatory zoned magmatic zircon with a weighted mean 206Pb/238U age of 534 ± 14 Ma and recrystallized metamorphic domains with an age of 490 ± 14 Ma. The latter have lower Th/U ratios, mostly no Eu anomalies and heavy rare earth element (HREE)‐depleted patterns. Garnet rims demonstrate that the final stages of garnet growth occurred in a HREE‐depleted environment, due to coeval formation with metamorphic zircon. Direct application of the Ti‐in‐zircon thermometer to metamorphic zircon yields temperatures of 770–610°C. Hf isotopic analyses of the zircons have an average εHf(t) of +13, indicating a juvenile crustal signature. We interpret the Attunga eclogite to be an indicator of Late Cambrian subduction beneath an oceanic suprasubduction zone prior to accretion against eastern Gondwanan in the latest Devonian. Phillips et al. (2015) suggest two metamorphic age populations within the Attunga eclogite, based on U‐Pb zircon and 40Ar/39Ar phengite data. These are ~515 Ma and ~480 Ma. We confirm these data, but our zircon trace element chemistry data indicate that the Early Cambrian age (530 Ma) represents igneous protolith formation rather than eclogite metamorphism

Biocompatibility for the new lasering surface titanium implant : Examination for cell and tissue reaction

松本歯科大学大学院歯学独立研究科博士（歯学）学位申請論文;健康増進口腔科学講座（主指導教員:八上　公利教授

Idades SHRIMP U-Pb do Complexo Sertânia: implicações sobre a evolução tectônica da Zona Transversal, Província Borborema

The Sertânia complex in the Alto Moxotó Terrane, Zona Transversal of the Borborema Province, Northeast Brazil, is a metasedimentary sequence with a subordinate metavolcanic component, metamorphosed under upper amphibolite facies conditions. Several previous regional geological surveys have included this rock assemblage in an undivided gneissic-migmatitic complex, due to the lack of a tectonostratigraphic model for this unit. This paper presents the first geochronological zircon U-Pb ages (SHRIMP U-Pb ages) and the first Sm-Nd isotopic data for this complex. Field and microscopic research reveals the existence of a volcanoclastic fraction of andesitic and dacitic composition, besides the dominant clastic components in these supracrustals. Furthermore, cathodoluminescence images of zircons show well formed little rounded crystals, thus suggesting reduced sediment transport prior to deposition. The calculated ages means with a 95% confidence level, based on a group of zircons of the same generation plot around 2.0 Ga, representing the episode of primary zircon crystallization. Some observed overgrowths testify to an additional Brasiliano overprint (ca. 0.6 Ga). Geochronological data on the supposed meta-plutonic rocks of the same complex point to the same Paleoproterozoic time interval, thus indicating contemporaneity with the sedimentation of the supracrustals. The obtained Nd model ages and µNd(t) parameters also confirm a contribution of Archean and Paleoproterozoic sources to these supracrustals rocks. These data clearly demonstrate contrast between the supracrustal rock assemblages of the Alto Moxotó Terrane and the supracrustals of other terranes of the Zona Transversal, which display Meso to Neoproterozoic ages, and imply that this crustal segment represents an independent lithotectonic domain.O Complexo Sertânia é uma seqüência metassedimentar com pequena contribuição metavulcânica, de facies anfibolito alto, que ocorre no Terreno Alto Moxotó, Zona Transversal da Província Borborema. Vários levantamentos geológicos têm incluído esta unidade num complexo gnáissico-migmatítico indiviso, questionando, por decorrência, a subdivisão de terrenos proposta para esse domínio litotectônico. O presente trabalho apresenta as primeiras idades geocronológicas U-Pb SHRIMP em zircão e dados isotópicos Sm-Nd desta unidade. Os dados de campo e microscópicos revelaram a presença de uma fração vulcanoclástica de composição andesítica e dacítica ao lado da dominante componente clástica dessas supracrustais. Por outro lado, as imagens de catodoluminescência dos zircões mostraram cristais bem formados ou pouco arredondados, sugerindo tratar-se de sedimentos pouco transportados. As idades calculadas são médias ponderadas com 95% de confidência, baseadas em agrupamentos de zircões de mesma geração. Foram obtidas idades em torno de 2,0 Ga, que representam a idade primária de cristalização dos zircões, localmente com sobrecrescimento brasiliano. As rochas metaplutônicas do suposto embasamento situam-se no mesmo intervalo de tempo, indicando uma contemporaneidade com a sedimentação das supracrustais. Os dados isotópicos de Nd (idade modelo T DM e µNd(t)) confirmam a presença de fontes arqueanas e paleoproterozóicas. Esses dados demonstram o contraste entre as supracrustais do Terreno Alto Moxotó com as de outros terrenos da Zona Transversal, de idade meso a neoproterozóicas, o que impede sua correlação e implica numa individualização desse terreno como um compartimento tectônico independente dos demais