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KERR ANDREW C.; TARNEY JOHN; KEMPTON PAMELA D.; PRINGLE MALCOLM; NIVIA ALVARO 《Journal of Petrology》2004,45(9):1877-1906
The fault-bounded Bolívar Ultramafic Complex (BUC) onthe eastern fringes of the Western Cordillera of Colombia wastectonically accreted onto the western coast of South Americain the late Cretaceous–early Tertiary, along with pillowbasalts of the Caribbean–Colombian Oceanic Plateau (CCOP).The complex consists of a lower sequence of ultramafic cumulates,successively overlain by layered and isotropic gabbroic rocks.The gabbros grade into, and are intruded by, mafic pegmatitesthat consist of large magnesiohornblende and plagioclase crystals.These pegmatites yield a weighted mean 40Ar–39Ar step-heatingage of 90·5 ± 0·9 Ma and thus coincidewith the timing of peak CCOP volcanism. The chemistry of theBUC is not consistent with a subduction-related origin. However,the similarity in Sr–Nd–Pb–Hf isotopes betweenthe CCOP and the BUC, in conjunction with their indistinguishableages, suggests that the BUC is an integral part of the plume-derivedCCOP. The parental magmas of the Bolívar complex wereprobably hydrous picrites that underwent 20–30% crystallization.The residual magmas from this fractionation contained 相似文献
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DAVID R. MARCHANT GEORGE H. DENTON JAMES G. BOCKHEIM SCOTT C. WILSON REW R. KERR 《Boreas: An International Journal of Quaternary Research》1994,23(1):29-43
Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. 3 He and 10 Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma. 相似文献
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Basaltic oceanic plateaux are important features in the geologicalrecord. Not only do they record ancient mantle plume activity,but they also are believed to be important building blocks inthe formation of the continental crust. In this paper we reviewthe salient features of two Cretaceous oceanic plateaux (theOntong Java and the Caribbean–Colombian): thick sequencesof predominantly homogeneous basalt; the occurrence of high-MgObasalt, including komatiites; and an apparent absence of sheeteddyke complexes. In addition, pyroclastic deposits may be scarce.We then explore ways of distinguishing plateaux from basalticsequences erupted in different tectonomagmatic settings: continentalflood basalt provinces; island arcs; back-arc basins; oceanislands and mid-ocean ridges. Using these criteria, potentialArchaean and Proterozoic oceanic plateaux are reviewed and identified.Finally, we explore how these remnant oceanic plateaux becameincorporated into the continents, by reviewing the proposedaccretion mechanisms for the Cretaceous Caribbean–Colombianoceanic plateau, on the basis of evidence from South Americaand the tonalites of the southern Caribbean island of Aruba. KEY WORDS: oceanic plateau; basalt geochemistry; large igneous provinces; plumes 相似文献
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Major Element Records of Variable Plume Involvement in the North Atlantic Province Tertiary Flood Basalts 总被引：4，自引：3，他引：1
Major element variations in North Atlantic Tertiary Provinceprimitive, early erupted, alkaline-transitional-tholeiite basalts,recalculated to a restricted value of MgO, give insights intothe process of plume-related magmatism. Basalts primitive enoughto be crystallizing only olivine were recalculated to a proposedprimary magma composition of 15 wt % MgO. The recalculated datasetshows clear inter-element correlations including a strong, significant,negative correlation between Fe and Si indicating polybaricmelt segregation. Overlap between basalt compositions and experimentalmelts from a fertile, Fe-rich, low mg-number (85.5) peridotitesuggests that, relative to normal peridotite with mg-number> 89, the North Atlantic basalt source was Fe rich. Linearregression of the experimental data gives apparent pressuresof magma segregation of 17·5–37 kbar, with intra-regionvariability in the depth derivation from the melt column foreach sample, thus suggesting that lithospheric thickness ‘lid-effect’control on magma generation may have been overemphasized inrecent studies. Comparable source composition, magma segregationdepth and calculated mantle potential temperature (1440–1460°C)throughout the Province supports the previously suggested plumeimpact model, arriving below East Greenland, derived from avariably enriched and depleted lower-mantle source. Given thegood agreement between conclusions drawn from major elementdata and previously published results we suggest that restricted-MgOrecalculated datasets may be usefully applied to study otherlarge igneous provinces. KEY WORDS: basalt; Fe-rich mantle; large igneous provinces; North Atlantic Tertiary Province; restricted-MgO major element datasets 相似文献
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P. VITTOZ R.A. OLIVER G. VIVIER S.A. KERR F. HOYLER 《Geostandards and Geoanalytical Research》1987,11(1):43-47
Eleven USGS geological reference materials and twelve French geological reference materials have been measured for B, Sm and Gd concentrations by prompt-gamma activation analysis. For those materials that have already been analysed, our data is in agreement with published recommended values. These values constitute the first measured data for several French geological reference materials 相似文献
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