Os Isotopes and the Origin of the Tasmanian Dolerites   总被引：3，自引：0，他引：3  

BRAUNS  C. M.; HERGT  J. M.; WOODHEAD  J. D.; MAAS  R. 《Journal of Petrology》2000,41(7):905-918

New Os isotope data obtained for oxides separated from samplesof the Jurassic dolerites of Tasmania (Australia) are used toconstrain the petrogenesis of the Ferrar continental flood basaltprovince. It is proposed here that the unradiogenic initialOs ratio (¹⁸⁷Os/¹⁸⁸Os = 0·145 ± 0·049 2  相似文献   

U-Pb Zircon Studies of Mid-crustal Metasedimentary Enclaves from the S-type Deddick Granodiorite, Lachlan Fold Belt, SE Australia   总被引：2，自引：0，他引：2  

MAAS  R.; NICHOLLS  I. A.; GREIG  A.; NEMCHIN  A. 《Journal of Petrology》2001,42(8):1429-1448

High-grade metasedimentary enclaves in granites can be usedto directly characterize the lower and mid crust. Enclaves inthe Silurian S-type Deddick Granodiorite, SE Australia, havechemical and Nd–Sr isotopic compositions broadly similarto Ordovician–Silurian clastic sedimentary rocks throughoutthe fold belt. SHRIMP U–Pb ages of detrital zircons inthe enclaves indicate Early Ordovician maximum depositionalages for their psammitic–pelitic precursors. Patternsof zircon inheritance show the same  相似文献   

Petrology and Geochemistry of Intraplate Basalts in the South Auckland Volcanic Field, New Zealand: Evidence for Two Coeval Magma Suites from Distinct Sources   总被引：4，自引：1，他引：3  

COOK  CRAIG; BRIGGS  ROGER M.; SMITH  IAN E. M.; MAAS  ROLAND 《Journal of Petrology》2005,46(3):473-503

The South Auckland Volcanic Field is a Pleistocene (1·59–0·51Ma) basaltic intraplate, monogenetic field situated south ofAuckland City, North Island, New Zealand. Two groups of basaltsare distinguished based on mineralogy and geochemical compositions,but no temporal or spatial patterns exist in the distributionof various lava types forming each group within the field: GroupA basalts are silica-undersaturated transitional to quartz-tholeiiticbasalts with relatively low total alkalis (3·0–4·6wt %), Nb (7–29 ppm), and (La/Yb)_N (3·4–7·6);Group B basalts are strongly silica-undersaturated basanitesto nepheline-hawaiites with high total alkalis (3·3–7·9wt %), Nb (32–102 ppm), and (La/Yb)_N (12–47). GroupA has slightly higher ⁸⁷Sr/⁸⁶Sr, similar _Nd, and lower ²⁰⁶Pb/²⁰⁴Pbvalues compared with Group B. Contrasting geochemical trendsand incompatible element ratios (e.g. K/Nb, Zr/Nb, Ce/Pb) areconsistent with separate evolution of Groups A and B from dissimilarparental magmas derived from distinct sub-continental lithosphericmantle sources. Differentiation within each group was controlledby olivine and clinopyroxene fractionation. Group B magmas weregenerated by <8% melting of an ocean island basalt (OIB)-likegarnet peridotite source with high ²³⁸U/²⁰⁴Pb mantle (HIMU)and enriched mantle (EMII) characteristics possibly inheritedfrom recycled oceanic crust. Group A magmas were generated by<12% melting of a spinel peridotite source also with HIMUand EMII signatures. This source type may have resulted fromsubduction-related metasomatism of the sub-continental lithospheremodified by a HIMU plume. These events were associated withMesozoic or earlier subduction- and plume-related magmatismwhen New Zealand was at the eastern margin of the Gondwana supercontinent. KEY WORDS: continental intraplate basalts; geochemistry; HIMU, EMII; Sr, Nd, and Pb isotopes; South Auckland; sub-continental lithospheric sources  相似文献   

Mantle-melt Evolution (Dynamic Source) in the Origin of a Single MORB Suite: a Perspective from Magnesian Glasses of Macquarie Island   总被引：2，自引：0，他引：2  

KAMENETSKY  VADIM S.; MAAS  ROLAND 《Journal of Petrology》2002,43(10):1909-1922

The effects of source composition and source evolution duringprogressive partial melting on the chemistry of mantle-derivedmid-ocean ridge basalt (MORB) melts were tested using a comprehensivegeochemical and Sr–Nd–Pb isotopic dataset for fresh,magnesian basaltic glasses from the Miocene Macquarie Islandophiolite, SW Pacific. These glasses: (1) exhibit clear parent–daughterrelationships; (2) allow simple reconstruction of primary meltcompositions; (3) show exceptional compositional diversity (e.g.K₂O/TiO₂ 0·09–0·9; La/Yb 1·5–22;²⁰⁶Pb/²⁰⁴Pb 18·70–19·52); (4) preserve changesin major element and isotope compositions, which are correlatedwith the degree of trace element enrichment (e.g. La/Sm). Conventionalmodels for MORB genesis invoke melting of mantle that is heterogeneouson a small scale, followed by binary mixing of variably lithophileelement-enriched melt batches. This type of model fails to explainthe compositions of the Macquarie Island glasses, principallybecause incompatible element ratios (e.g. Nb/U, Sr/Nd) and Pbisotope ratios vary non-systematically with the degree of enrichment.We propose that individual melt batches are produced from instantaneous‘parental’ mantle parageneses, which change continuouslyas melting and melt extraction proceeds. This concept of a ‘dynamicsource’ combines the models of small-scale mantle heterogeneitiesand fractional melting. A dynamic source is an assemblage oflocally equilibrated mantle solids and a related melt fraction.Common MORB magmas that integrate the characteristics of numerousmelt batches therefore tend to conceal the chemical and isotopicidentity of a dynamic source. This study shows that isotoperatios of poorly mixed MORB melts are a complex function ofthe dynamic source evolution, and that the range in isotoperatios within a single MORB suite does not necessarily requiremixing of diverse components. KEY WORDS: mid-ocean ridge basalt; Macquarie Island; radiogenic isotopes; mantle; geochemistry  相似文献   

A simple model for the three-dimensional, thermally and wind-driven ocean circulation     

LEO R. M. MAAS 《地球，A辑:动力气象学与海洋学》1994,46(5):671-680

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