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Ce Anomalies (ce + anomaly)
Selected AbstractsThe Cretaceous volcanic succession around the Songliao Basin, NE China: relationship between volcanism and sedimentationGEOLOGICAL JOURNAL, Issue 2 2002Pujun Wang Abstract With volume ratio of 8:1:1.5 amongst acidic, intermediate and basaltic rocks, the Cretaceous volcanics around the Songliao Basin are a series of high-K or medium-K, peraluminous or metaluminous, calc-alkaline rocks, lacking typical basalts and peralkaline members of typical rift-related types. Their eruption ages range between 133 and 127,Ma, 124 and 122,Ma and 117 and 113,Ma respectively. They are high in total (Rare earth element) REE contents (96.1,326,ppm), enriched in LREE and depleted in HREE (LREE/HREE,=,4.6,13.8), with negative Eu and Ce anomalies (Eu/Eu*,=,0.04,0.88; Ce/Ce*,=,0.60,0.97). They have enriched large-ion lithophile elements (e.g. K, Ba, Th) and depleted high field strength elements (e.g. Nb, Ti and Y), suggesting a subduction-related tectonic setting. The volcanic activities migrated from south to north, forming a successively northward-stepping volcanic series and showing a feature significantly different from the overlying sedimentary sequence striking northeast. Thus, an overlap basin model was proposed. Accompanied by opening of the basin, the volcanogenic succession was formed at the block-faulting stage (131,113,Ma) owing to the closure of the Mongolia,Okhotsk ocean in the Jurassic and early Cretaceous, while the overlying sedimentary sequence was unconformably deposited at the spreading stage (Albian,Maastrichtian) owing to the oblique subduction of the Pacific plate under the Eurasian plate. The volcanic succession constitutes the lower unit of basin filling and is the forerunner of further basin spreading. Copyright © 2002 John Wiley & Sons, Ltd. [source] Trace element concentrations in the Mexico-Belize ejecta layer: A link between the Chicxulub impact and the global Cretaceous-Paleogene boundaryMETEORITICS & PLANETARY SCIENCE, Issue 11 2007Jane Wigforss-Lange The ejecta deposits consist of a lower spheroid bed, containing clay and dolomite spheroids, and an upper diamictite bed with boulders and clasts of limestone and dolomite. The matrix of both beds is composed of clay and micritic dolomite. The rare earth element (REE) compositions in the matrix of both units show strong similarities in concentrations and pattern. Furthermore, the Zr/TiO2 scatter plot shows a linear correlation indicating one source. These results indicate that the basal spheroid bed has the same source and was generated during the same event as the overlying diamictite bed, which lends support to a single-impact scenario for the Albion Formation ejecta deposits. The elevated concentrations of non-meteoritic elements such as Sb, As, U, and Zn in the matrix of the lower spheroid bed are regarded to have been derived from the sedimentary target rocks at the Chicxulub impact site. The positive Eu and Ce anomalies in clay concretion and in the matrix of the lower part of the spheroid bed in Albion Island quarry is probably related to processes involved in the impact, such as high temperature and oxidizing conditions. Analogous trace element anomalies have been reported from the distal Cretaceous-Paleogene (K/T) boundary clay layer at different sites. Thus, the trace element signals, reported herein, are regarded to support a genetic link between the Chicxulub impact, the ejecta deposits along the Mexico-Belize border, and the global K/T boundary layer. [source] Formation of orange hibonite, as inferred from some Allende inclusionsMETEORITICS & PLANETARY SCIENCE, Issue 3 2001S. B. SIMON The melilite in the present samples is very Al-rich, averaging Åk6, Åk14, and Åk12 in the three samples studied. Hibonite in two inclusions, unlike that in Murchison, has low rare earth element abundances of <10 × CI; in the other inclusion, the hibonite, melilite and perovskite have Group II-like patterns. The hibonite and melilite in all three inclusions studied have excess 26Mg consistent with (26Al/27Al)I = 5 × 10,5. Much of the hibonite and some of the spinel in these inclusions is corroded. These phases are found enclosed in melilite, but based on bulk compositions and phase equilibria, hibonite should not be an early-crystallizing phase in these inclusions. We conclude that the hibonite and probably some of the spinel is relic. Reversely zoned melilite, rounded spinel and isotopically heavy Mg in the inclusions probably reflect reheating events that involved melting and evaporation. Alteration of the gehlenitic melilite gave rise to some rare phases, including corundum and nearly pure CaTs pyroxene. Studies have shown that blue hibonite contains Ti3+ while orange hibonite does not (Ihinger and Stolper, 1986; Beckett et al., 1988). Orange hibonite formed either under oxidizing conditions (such as at oxygen fugacities at least seven orders of magnitude greater than that of a solar gas at 1700 K), or under conditions reducing enough (e.g., solar) that it contained Ti3+, which was later oxidized in situ. Although V and Ce oxides are volatile at the temperature and range of oxygen fugacities at which orange hibonite is known to be stable, we find that (a) the hibonite is V-rich (,1 wt% V2O3) and (b) there are no negative Ce anomalies in Allende hibonite. This indicates that the hibonite did not form by condensation under oxidizing conditions. In addition, there are slight excesses of Ti + Si cations relative to Mg + Fe cations (up to 0.1 of 0.8 cations per 19 oxygen anions), probably reflecting the original presence of Ti3+. The results of this study strongly support the suggestion (Ihinger and Stolper, 1986) that Allende hibonite originally formed under reducing conditions and was later oxidized. Oxygen fugacities within ,2,3 orders of magnitude of that of a solar gas are implied; otherwise, strong Ce and V depletions would be observed. [source] Rare Earth Element and Trace Element Features of Gold-bearing Pyrite in the Jinshan Gold Deposit, Jiangxi ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010Guangzhou MAO Abstract: Jinshan gold deposit is located in northeastern Jiangxi, South China, which is related to the ductile shear zone. It has a gold reserve of more than 200 tons, with 80% of gold occurring in pyrite. The ,REE of gold-bearing pyrite is as higher as 171.664 ppm on average, with relatively higher light rare earth elements (LREE; 159.556 ppm) and lower HREE (12.108 ppm). The ,LREE/,HREE ratio is 12.612 and (La/Yb)N is 11.765. These indicate that pyrite is rich in LREE. The (La/Sm)N ratio is 3.758 and that of (Gd/Yb)N is 1.695. These are obvious LREE fractionations. The rare earth element (REE) distribution patterns show obvious Eu anomaly with average ,Eu values of 0.664, and ,Ce anomalies of 1.044. REE characteristics are similar to those of wall rocks (regional metamorphic rocks), but different from those of the Dexing granodiorite porphyry and Damaoshan biotite granite. These features indicate that the ore-forming materials in the Jinshan gold deposit derived from the wall rocks, and the ore-forming fluids derived from metamorphic water. The Co/Ni ratio (average value 0.38) of pyrite suggests that the Jinshan gold deposit formed under a medium,low temperature. It is inferred from the values of high-field strength elements, LREE, Hf/Sm, Nb/La, and Th/La of the pyrite that the ore-forming fluids of the Jinshan gold deposit derived from metamorphic water with Cl>F. [source] Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian, Weng'an, Guizhou ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Yong FU Abstract: The black shales of the Lower Cambrian Niutitang Formation in Weng'an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements (PGE) has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum (Mo), nickel (Ni), vanadium (V), lead (Pb), strontium (Sr), barium (Ba), uranium (U), arsenic (As), and rare earth elements (REE) in abundance. High uranium/thorium (U/Th) ratios (U/Th>1) indicated that mineralization was mainly influenced by the hydrothermal process. The ,U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements (LREE) (heavy rare earth elements (HREE) (LREE/HREE=5,17), slightly negative europium (Eu) and cerium (Ce) anomalies (,Eu=0.81,0.93), and positive Ce anomalies (,Ce=0.76,1.12). PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum (Pt), palladium (Pd), ruthenium (Ru) and osmium (Os). The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent. [source] Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, JapanRESOURCE GEOLOGY, Issue 4 2005Yasuhiro Kato Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today. [source] | ||||||||||