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41.
Katja Ruschel Lutz Nasdala Andreas Kronz John M. Hanchar Daniel M. T?bbens Radek ?koda Friedrich Finger Andreas M?ller 《Mineralogy and Petrology》2012,105(1-2):41-55
This study addresses whether Raman spectra can be used to estimate the degree of accumulated radiation damage in monazite-(Ce) samples whose chemical composition was previously determined. Our results indicate that the degree of disorder in monazite–(Ce), as observed from increasing Raman band broadening, generally depends on both the structural state (i.e., radiation damage) and the chemical composition (i.e., incorporation of non-formula elements). The chemical effects were studied on synthetic orthophosphates grown using the Li-Mo flux method, and non radiation-damaged analogues of the naturally radiation-damaged monazite–(Ce) samples, produced by dry annealing. We found that the “chemical” Raman-band broadening of natural monazite–(Ce) can be predicted by the empirical formula, $$ {\hbox{FWHM}} {\hbox{[c}}{{\hbox{m}}^{ - {1}}}{]} = {3}{.95} + {26}{.66} \times {\hbox{(Th}} + {\hbox{U}} + {\hbox{Ca}} + {\hbox{Pb)}} {\hbox{[apfu]}} $$ where, FWHM = full width at half maximum of the main Raman band of monazite–(Ce) (i.e., the symmetric PO4 stretching near 970?cm?1), and (Th+U+Ca+Pb) = sum of the four elements in apfu (atoms per formula unit). Provided the chemical composition of a natural monazite–(Ce) is known, this “chemical band broadening” can be used to estimate the degree of structural radiation damage from the observed FWHM of the ν1(PO4) band of that particular sample using Raman spectroscopy. Our annealing studies on a wide range of monazite–(Ce) reference materials and other monazite–(Ce) samples confirmed that this mineral virtually never becomes highly radiation damaged. Potential advantages and the practical use of the proposed method in the Earth sciences are discussed. 相似文献
42.
Jaroslava Hajná Ji?í ?ák Václav Kachlík Martin Chadima 《International Journal of Earth Sciences》2012,101(7):1855-1873
The Teplá–Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal ‘median massif’ above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU. For the first time, we describe the crustal-scale NE–SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well-preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (~380–370?Ma). On the basis of structural, microstructural, and anisotropy of magnetic susceptibility data from the KSZ, we propose a new synthetic model for the deformation partitioning in the Teplá–Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá–Barrandian convergence was nearly frontal during ~380–346?Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion. The synconvergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at ~346–337?Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345?Ma onwards. 相似文献
43.
Paleo- and Neoproterozoic magmatic and tectonometamorphic evolution of the Isla Cristalina de Rivera (Nico Pérez Terrane, Uruguay) 总被引:1,自引:0,他引:1
Pedro Oyhant?abal Martin Wagner-Eimer Klaus Wemmer Bernhard Schulz Robert Frei Siegfried Siegesmund 《International Journal of Earth Sciences》2012,101(7):1745-1762
The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage magmatic and metamorphic evolution. Based on SHRIMP U–Pb zircon, Th–U–Pb monazite (CHIME-EPMA method) and K–Ar age data from key units several events can be recognized: (1) multistage magmatism at 2,171–2,114?Ma, recorded on zircon of the granulitic orthogneisses and their 2,093–2,077?Ma overgrowths; (2) a distinct amphibolite facies metamorphism at ~1,980?Ma, recorded by monazite; (3) greenschist facies reworking and shearing at ca. 606?Ma (monazite and K–Ar on muscovite) along the Rivera Shear Zone, and finally (4) intrusion of the post-tectonic Sobresaliente and Las Flores granites at around 585?Ma. Lithological similarities, geographic proximity and coeval magmatic and metamorphic events indicate a similar tectonometamorphic evolution for the Isla Cristalina de Rivera, the Valentines Block in Uruguay and the Santa María Chico Granulitic Complex in southern Brazil, since at least 2.1?Ga. 相似文献
44.
本文对松辽盆地东南部后五家户气田划分出22种沉积微相,建立7种相层序,分析了扇三角洲及三角洲沉积环境对天然气成藏的控制作用。指出了扇三角洲前缘砂体和三角洲前缘砂体较为发育,沉积物源来自气田东北部和东南部两个方向。后五家户气田多为构造—岩性气藏和岩性气藏。 相似文献
45.
Carbon isotope fractionation in phospholipid fatty acid biomarkers of bacteria and fungi native to an acid mine drainage lake 总被引:3,自引:0,他引:3
Benjamin R. Cowie Gregory F. Slater Luc Bernier Lesley A. Warren 《Organic Geochemistry》2009,40(9):956-962
This study identifies isotope signatures associated with autotrophic and heterotrophic microbial communities that may provide a means to determine carbon cycling relationships in situ for acid mine drainage (AMD) sites. Stable carbon isotope ratios (δ13C) of carbon sources, bulk cells, and membrane phospholipids (PLFA) were measured for autotrophic and heterotrophic microbial enrichment cultures from a mine tailings impoundment in northern Ontario, Canada, and for pure strains of the sulfur oxidizing bacteria Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The autotrophic enrichments had indistinguishable PLFA distributions from the pure cultures, and the PLFA cyc-C19:0 was determined to be a unique biomarker in this system for these sulfur oxidizing bacteria. The PLFA distributions produced by the heterotrophic enrichments were distinct from the autotrophic distributions and the C18:2 PLFA was identified as a biomarker for these heterotrophic enrichments. Genetic analysis (16S, 18S rRNA) of the heterotrophic cultures indicated that these communities were primarily composed of Acremonium fungi.Stable carbon isotope analysis revealed that bulk cellular material in all autotrophic cultures was depleted in δ13C by 5.6–10.9‰ relative to their atmospheric CO2 derived carbon source, suggesting that inorganic carbon fixation in these cultures is carbon limited. Individual PLFA from these autotrophs were further depleted by 8.2–14.6‰ compared to the bulk cell δ13C, which are among the largest biosynthetic isotope fractionation factors between bulk cell and PLFA reported in the literature. In contrast, the heterotrophic bulk cells were not significantly fractionated in δ13C relative to their carbon source and heterotrophic PLFA ranged from 3‰ enriched to 4‰ depleted relative to the isotopic composition of their total biomass. These distinct PLFA biomarkers and isotopic fractionations associated with autotrophic and heterotrophic activity in this laboratory study provide potential biomarkers for delineating autotrophic and heterotrophic carbon cycling in AMD environments. 相似文献
46.
47.
This study combines different methods, including grain size, macrofossil, and pollen analyses, to reconstruct paleogeographical and paleoclimatological conditions for periods before, during, and after the isolation of a small lake (Lake Kachishayoot) in northern Québec. After the retreat of the Laurentide Ice Sheet around 8000 14C yr B.P., the area was submerged by the Tyrrell Sea. The transition from marine to lacustrine environment occurred about 5400 yr B.P. Two major periods of water-level fluctuations were inferred from organic and mineral sediments: a high water level that occurred after 3200 yr B.P. and a low water level that started before 2200 yr B.P. Our chronological data for the first period are consistent with those from nearby Lac des Pluviers and from other lakes in east central Canada and in the northeastern United States. During the low-water-level period, however, there is no evidence for minor fluctuations, whereas other lakes in northern Québec and east-central Canada underwent several brief lowerings. Long-term changes in atmospheric circulation caused by changing global boundary conditions likely explained long-term water-level fluctuations of Lake Kachishayoot. 相似文献
48.
Elisabetta?Brizi Sabrina?NazzareniEmail author Francesco?Princivalle Pier?Francesco?Zanazzi 《Contributions to Mineralogy and Petrology》2003,145(5):578-584
Optically homogeneous augite xenocrysts, closely associated with spinel–peridotite nodules, occur in alkali basalts from Hannuoba (Hebei province, China). They were studied by electron and X-ray diffraction to define the occurrence and significance of pigeonite exsolution microtextures. Sub-calcic augite (Wo34) exsolved into En62–62Fs25–21Wo13–17 pigeonite and En46–45Fs14–14Wo40–42 augite, as revealed by TEM through diffuse coarser (001) lamellae (100–300 Å) and only incipient (100) thinner ones (<70 Å). C2/c augite and P21/c pigeonite lattices, measured by CCD-XRD, relate through a(Aug)?a(Pgt), b(Aug)?b(Pgt), c(Aug)≠c(Pgt) [5.278(1) vs 5.189(1)Å] and β(Aug)≠β(Pgt) [106.55(1) vs 108.55(2)°]. Cell and site volumes strongly support the hypothesis that the augite xenocrysts crystallised at mantle depth from alkaline melts. After the augite xenocrysts entered the magma, (001) lamellae first formed by spinodal decomposition at a Tmin of about 1,100 °C, and coarsened during very rapid transport to the surface; in a later phase, possibly on cooling, incipient (100) lamellae then formed. 相似文献
49.
The world-class Idrija mercury deposit (western Slovenia) is hosted by highly deformed Permocarboniferous to Middle Triassic sedimentary rocks within a complex tectonic structure at the transition between the External Dinarides and the Southern Alps. Concordant and discordant mineralization formed concomitant with Middle Triassic bimodal volcanism in an aborted rift. A multiple isotopic (C, O, S) investigation of host rocks and ore minerals was performed to put constraints on the source and composition of the fluid, and the hydrothermal alteration. The distributions of the 13C and 18O values of host and gangue carbonates are indicative of a fracture-controlled hydrothermal system, with locally high fluid-rock ratios. Quantitative modeling of the 13C and 18O covariation for host carbonates during temperature dependent fluid-rock interaction, and concomitant precipitation of void-filling dolomites points to a slightly acidic hydrothermal fluid (13C–4 and 18O+10), which most likely evolved during isotopic exchange with carbonates under low fluid/rock ratios. The 34S values of hydrothermal and sedimentary sulfur minerals were used to re-evaluate the previously proposed magmatic and evaporitic sulfur sources for the mineralization, and to assess the importance of other possible sulfur sources such as the contemporaneous seawater sulfate, sedimentary pyrite, and organic sulfur compounds. The 34S values of the sulfides show a large variation at deposit down to hand-specimen scale. They range for cinnabar and pyrite from –19.1 to +22.8, and from –22.4 to +59.6, respectively, suggesting mixing of sulfur from different sources. The peak of 34S values of cinnabar and pyrite close to 0 is compatible with ore sulfur derived dominantly from a magmatic fluid and/or from hydrothermal leaching of basement rocks. The similar stratigraphic trends of the 34S values of both cinnabar and pyrite suggest a minor contribution of sedimentary sulfur (pyrite and organic sulfur) to the ore formation. Some of the positive 34S values are probably derived from thermochemical reduction of evaporitic and contemporaneous seawater sulfates.Editorial handling: P. Lattanzi 相似文献
50.
Gerd?RantitschEmail author Thomas?Rainer 《International Journal of Earth Sciences》2003,92(2):195-209
Vitrinite reflectance was measured in Late Carboniferous to Triassic shales, siltstones and marls of the Karawanken Range. Thermal models of the central South-Karawanken Range were calibrated on the basis of these data. They suggest an eroded overburden of more than 3,200 m of Jurassic to Cretaceous sediments and a heat flow in the range of 42 to 60 mW m?2 during the time of maximum subsidence. Because the reconstructed thermal history of the South-Karawanken Range is very similar to the thermal history of the Generoso basin (western Southern Alps), these data provide strong evidence for a deep basinal position of the Southern Karawanken Range during Jurassic to Cretaceous times. A vitrinite reflectance anomaly at the northern margin of the South-Karawanken Range is explained by advective heat transport during the Oligocene. The heat source for the anomalies at the western margin of the Seeberg Rise and in the area between the Periadriatic Lineament and the Donat Fault Zone is unknown. Vitrinite reflectance in Late Triassic sediments indicates the South-Karawanken Range and the South-Zala Unit of the Pannonian basement as exotic blocks in the Sava Composite Unit. This is explained by Miocene displacement of structural units, which were derived from different paleogeographical segments of the Permo-Mesozoic western Tethyan margin. 相似文献