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REE Contents (ree + content)
Selected AbstractsPetrology of Martian meteorite Northwest Africa 998METEORITICS & PLANETARY SCIENCE, Issue 5 2008Allan H. TREIMAN This 456-gram, partially fusion-crusted meteorite consists of (by volume) ,75% augite (core composition Wo39En39Fs22), ,9% olivine (Fo35), ,7% plagioclase (Ab61An35) as anhedra among augite and olivine, ,3.5% low-calcium pyroxenes (pigeonite and orthopyroxene) replacing or forming overgrowths on olivine and augite, ,1% titanomagnetite, and other phases including potassium feldspar, apatite, pyrrhotite, chalcopyrite, ilmenite, and fine-grained mesostasis material. Minor secondary alteration materials include "iddingsite" associated with olivine (probably Martian), calcite crack fillings, and iron oxide/hydroxide staining (both probably terrestrial). Shock effects are limited to minor cataclasis and twinning in augite. In comparison to other nakhlites, NWA 998 contains more low-calcium pyroxenes and its plagioclase crystals are blockier. The large size of the intercumulus feldspars and the chemical homogeneity of the olivine imply relatively slow cooling and chemical equilibration in the late- and post-igneous history of this specimen, and mineral thermometers give subsolidus temperatures near 730 °C. Oxidation state was near that of the QFM buffer, from about QFM-2 in earliest crystallization to near QFM in late crystallization, and to about QFM + 1.5 in some magmatic inclusions. The replacement or overgrowth of olivine by pigeonite and orthopyroxene (with or without titanomagnetite), and the marginal replacement of augite by pigeonite, are interpreted to result from late-stage reactions with residual melts (consistent with experimental phase equilibrium relationships). Apatite is concentrated in planar zones separating apatite-free domains, which suggests that residual magma (rich in P and REE) was concentrated in planar (fracture?) zones and possibly migrated through them. Loss of late magma through these zones is consistent with the low bulk REE content of NWA 998 compared with the calculated REE content of its parent magma. [source] REE, Mn, Fe, Mg and C, O Isotopic Geochemistry of Calcites from Furong Tin Deposit, South China: Evidence for the Genesis of the Hydrothermal Ore-forming FluidsRESOURCE GEOLOGY, Issue 1 2010Yan Shuang Abstract The Furong tin deposit in the central Nanling region, South China, consists of three main types of mineralization ores, i.e. skarn-, altered granite- and greisen-type ores, hosted in Carboniferous and Permian strata and Mesozoic granitic intrusions. Calcite is the dominant gangue mineral intergrown with ore bodies in the orefield. We have carried out REE, Mn, Fe, and Mg geochemical and C, and O isotopic studies on calcites to constrain the source and evolution of the ore-forming fluids. The calcites from the Furong deposit exhibit middle negative Eu anomaly (Eu/Eu*= 0.311,0.921), except for one which has an Eu/Eu* of 1.10, with the total REE content of 5.49,133 ppm. The results show that the calcites are characterized by two types of REE distribution patterns: a LREE-enriched pattern and a flat REE pattern. The LREE-enriched pattern of calcites accompanying greisen-type ore and skarn-type ore are similar to those of Qitianling granite. The REE, Mn, Fe, and Mg abundances of calcites exhibit a decreasing tendency from granite rock mass to wall rock, i.e. these abundances of calcites associated with altered granite-type and greisen-type ores are higher than those associated with skarn-type ores. The calcites from primary ores in the Furong deposit show large variation in carbon and oxygen isotopic compositions. The ,13C and ,18O of calcites are ,0.4 to ,12.7, and 2.8 to 16.4,, respectively, and mainly fall within the range between mantle or magmatic carbon and marine carbonate. The calcites from greisen and altered granite ores in the Furong deposit display a negative correlation in the diagram of ,13C versus ,18O, probably owing to the CO2 -degassing of the ore-forming fluids. From the intrusion to wall-rock, the calcites display an increasing tendency with respect to ,13C values. This implies that the carbon isotopic compositions of the ore-bearing fluids have progressively changed from domination by magmatic carbon to sedimentary carbonate carbon. In combination with other geological and geochemical data, we suggest that the ore-forming fluids represent magmatic origin. We believe that the fluids exsolved from fractionation of the granitic magma, accompanying magmatism of the Qitianling granite complex, were involved in the mineralization of the Furong tin polymetallic deposit. [source] The 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] Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: implications for allanite,monazite,xenotime phase relations from 250 to 610 °CJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008E. JANOTS Abstract The distribution of REE minerals in metasedimentary rocks was investigated to gain insight into the stability of allanite, monazite and xenotime in metapelites. Samples were collected in the central Swiss Alps, along a well-established metamorphic field gradient that record conditions from very low grade metamorphism (250 °C) to the lower amphibolite facies (,600 °C). In the Alpine metapelites investigated, mass balance calculations show that LREE are mainly transferred between monazite and allanite during the course of prograde metamorphism. At very low grade metamorphism, detrital monazite grains (mostly Variscan in age) have two distinct populations in terms of LREE and MREE compositions. Newly formed monazite crystallized during low-grade metamorphism (<440 °C); these are enriched in La, but depleted in Th and Y, compared with inherited grains. Upon the appearance of chloritoid (,440,450 °C, thermometry based on chlorite,choritoid and carbonaceous material), monazite is consumed, and MREE and LREE are taken up preferentially in two distinct zones of allanite distinguishable by EMPA and X-ray mapping. Prior to garnet growth, allanite acquires two growth zones of clinozoisite: a first one rich in HREE + Y and a second one containing low REE contents. Following garnet growth, close to the chloritoid,out zone boundary (,556,580 °C, based on phase equilibrium calculations), allanite and its rims are partially to totally replaced by monazite and xenotime, both associated with plagioclase (± biotite ± staurolite ± kyanite ± quartz). In these samples, epidote relics are located in the matrix or as inclusions in garnet, and these preserve their characteristic chemical and textural growth zoning, indicating that they did not experience re-equilibration following their prograde formation. Hence, the partial breakdown of allanite to monazite offers the attractive possibility to obtain in situ ages, representing two distinct crystallization stages. In addition, the complex REE + Y and Th zoning pattern of allanite and monazite are essential monitors of crystallization conditions at relatively low metamorphic grade. [source] Petrology and Geochemistry of the Huangshan Granitic Intrusion in Anhui Province, Southeast China: Implications for Petrogenesis and GeodynamicsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010Shu ZHANG Abstract: The Huangshan granitic intrusion in Anhui province, SE China, is tectonically located at the southeastern boundary of the Yangtze Block. Based on the contact relation and the petrography, the Huangshan granitic intrusion can be divided into four stages, from early to late, medium-grained monzogranite, coarse-grained porphyric granite, fine-medium grained porphyric granite, and fine-coarse grained granite. All rocks from the Huangshan granitic intrusion display similar petrological and geochemical characteristics, i.e. relatively high SiO2 (>75%) and alkali (7.85%,8.59%), low CaO(<1%), high Fe-number (FeOT/(MgO+FeOT) = 0.93,0.97) and A/CNK (atomic Al/(Ca+Na+K)) = 1.04,1.19. They are also enriched in rare earth elements (REE, except for Eu, with a total REE contents ranging from 116 ppm to 421 ppm), high strength field elements such as Zr, Hf, Nb, but depleted in Ba, Sr and Ni. The 10 000×Ga/Al ratios are higher than 2.6, which are consistent with the A-type granitoids. Based on the classification diagrams proposed by Eby, the Huangshan granite can be classified into the A2 group, which is usually believed to be formed under an extensional tectonic setting. Their Nd isotopic compositions suggest that the primary magmas of the Huangshan granite are predominantly derived from the Proterozoic andesitic rocks in the region, and this conclusion is also supported by REE modeling. The systemic investigations on the geochemistry of the Huangshan granitic intrusion can provide significant implications for the understanding of the petrogenesis and the geodynamic regime of southeastern China during the Late-Mesozoic. [source] REE Compositions of Lower Ordovician Dolomites in Central and North Tarim Basin, NW China: A Potential REE Proxy for Ancient SeawaterACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2008ZHANG Xuefeng Abstract: Rare earth element compositions of Lower Ordovician dolomites in the Central and Northern Tarim Basin are studied. Most dolomite samples are more or less contaminated by clay minerals. Their rare earth element compositions have been consequently changed, showing both seawater-like and non-seawater-like features. The clay contamination should be disposed before the REE data are used. Through ICP-MS and ICP-AES analyses, the REE features are well documented. The clay contamination is quantitatively determined by microscopic investigation, trace elements and REE contents. The dolomites, at least in the Tarim Basin, are thought to be pure when their total LREE contents are less than 3times10,6. Through comparison, the pure dolomites show similarities in REE patterns but differences in REE contents with co-existing pure limestone, which indicates that dolomitization may slightly change the REE compositions. Nevertheless, whatever the change is, the pure dolomites may act as a potential REE proxy for Ordovician seawater, which would be significant for ancient massive dolomite strata that lack limestone. 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