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1.
UThPb systematics of the eucrite “Juvinas”: Precise age determination and evidence for exotic lead
The U-Th-Pb isotope systematics of the eucrite “Juvinas” have been studied in whole rock fragments as well as in plagioclases and pyroxenes. The results show that this monomict breccia crystallized with a very high initial ratio at T = 4.539 ± 0.004 AE ago. There is evidence for a less radiogenic Pb component (; ; ) interpreted as “exotic lead” induced by a meteoritical impact at the surface of the Juvinas parent body, 1.92 ± 0.06 AE ago. 相似文献
2.
R. Montigny H. Bougault Y. Bottinga C.J. Allegre 《Geochimica et cosmochimica acta》1973,37(9):2135-2147
Abundances of major elements, rare earth elements, transition metals, alkali metals and alkaline earth metals have been measured in a representative suite of samples from the Pindos (Greece) ophiolitic complex. Our data indicate that the igneous members of the complex are genetically related. An ocean floor origin of the complex is suggested. 相似文献
3.
Jean Louis Birck Serge Fourcade Claude J. Allegre 《Earth and Planetary Science Letters》1975,26(1):29-35
Internal isochrons for two Apollo 15 rocks give an age of(3.34 ± 0.09)and(3.46 ± 0.04) × 109 years with an identical87Sr/86Sr initial ratio of 0.69928. Considering the possibility for the line obtained in a87Sr/86Sr,87Rb/86Sr diagram to be a mixing line, the significance of these results are discussed. 相似文献
4.
Claude J. Allegre Dalila Ben Othman Mireille Polve Pierre Richard 《Physics of the Earth and Planetary Interiors》1979,19(4):293-306
The neodymium-strontium isotopic correlation observed in most of the Earth mantle materials is evaluated by means of direct modelling. Several geochemical models are quantitatively developed to explain the observations. The main results of this modelling are that such a correlation is not geochemically trivial and that it corresponds to specific conditions in chemical fractionation. These specific conditions seem to be satisfied by solid-liquid partitioning in magmatic conditions. The discussion of the experimental data supports a continuous convecting-magmatic fractionation model for a large proportion of the mantle. 相似文献
5.
Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. εNd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a εNd-εSr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high87Sr/86Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago. 相似文献
6.
Résumé Nous étudions l'évolution du rapport isotopique du Sr et du Rb au cours du temps dans les minéraux triés aussi bien que dans la roche totale.Pour exemple nous avons choisi des granites de l'Anti-Atlas et de la Montagne Noire.
The evolution of the isotopic ratio of Sr/Rb is being studied with regard to its time sequence, in each mineral as well as in the totality of a granite.This study deals with granits of the Anti-Atlas and of the Montage Noire.
Zusammenfassung Die Entwicklung der Isotopen-Verhältnisse von Sr/Rb werden in ihrer zeitlichen Folge in den Einzelmineralien sowie im Gesamtbestand eines Granites untersucht.Als Beispiel dienen Granite des Anti-Atlas und der Montagne Noire.
, (, , ).相似文献
7.
西天山喇嘛苏铜矿成矿斑岩的岩石学、地球化学特征及成因探讨 总被引：7，自引：3，他引：4
位于西天山别珍套-科古琴晚古生代岛弧西段的喇嘛苏铜矿床是区内最大的铜矿床,与成矿作用有着密切关系的斑岩体为英云闪长斑岩、花岗闪长斑岩,是同源岩浆分异演化的产物,且花岗闪长斑岩可能属于岩浆演化晚期的产物。本区成矿斑岩的主量、微量元素和Sr-Nd同位素地球化学特征表明,其富集大离子亲石元素,而相对亏损高场强元素,出现了较为明显的Ta、Nb负异常,初始锶同位素ISr和εNd(t=390Ma)值分别为0.7072～0.7076和-0.32～0.17,显示壳幔混合源的特征,利用Sr和Nd同位素估算其源区物质约有50%来源于地壳。岩石地球化学特征指示了其为典型钙碱性火山弧花岗岩,暗示其形成于大陆弧环境。结合区域地质背景,推测本区成矿斑岩是在洋壳俯冲作用下发生部分熔融,交代原先的地幔楔,并混合了部分下地壳的物质,经历分离结晶作用的产物,其形成可能与晚古生代准噶尔洋板块向南的俯冲作用有关。结合东西天山的成矿斑岩的地球化学特征对比研究,岩浆源区的差别可能导致不同类型斑岩型矿床的形成,斑岩型铜矿床的形成较斑岩型钼矿床可能有更少的地壳物质贡献。 相似文献
8.
A preliminary study of photomosaic maps of Mars suggests that large lateral relative motions of a relatively thick lithosphere may have occurred. Transform faults (at two different stages of their evolution) are described, together with a possible triple junction. Diffuse diverging plate boundaries can be found, whereas converging ones remain a problem. 相似文献
9.
Groundwater plays an important role in New Zealand water supplies and hence monitoring activities are conducted regularly. Most monitoring programmes aim to evaluate groundwater chemistry and almost completely overlook the microbial component in this ecosystem. In our present study, the bacterial community structure of groundwater in the Wairarapa Valley was examined using the terminal restriction fragment length polymorphism (T-RFLP), and relationships between bacterial community structure and groundwater chemistry, aquifer confinement and groundwater usage were explored. In addition, the results from this study were compared with a previous T-RFLP survey of the same area in an attempt to detect changes in bacterial community structure over time. The data obtained suggested that bacterial community structure was related to groundwater chemistry, especially to redox conditions. Species composition showed minimal variation over time if groundwater chemistry remained unchanged. These findings reflect the potential of using bacterial communities as biological indicators to evaluate the health of groundwater ecosystems. We suggest that it is important to include this type of broad bacterial diversity assessment criteria into regular groundwater monitoring activities. 相似文献
10.