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51.
Dr. T. D. Peterson Dr. S. Esperança Dr. A. N. LeCheminant 《Mineralogy and Petrology》1994,51(2-4):251-276
Summary Early Proterozoic ultrapotassic dikes, lava flows, and pyroclastic rocks of the Christopher Island Formation (CIF) erupted throughout an area 600 × 300 km within the Churchill Province of the Canadian Shield at 1.84 Ga. The rocks range from mafic lamprophyres (mg # 60; SiO2 47–54%, mean K2O/Na2O > 4) with phenocrysts of phlogopite + diopside + apatite ± olivine ± magnetite, to phenocryst-poor felsic rocks and sanidine porphyries (SiO255–69%). All samples have high incompatible element contents and display large depletions of high field strength elements relative to K, Rb, Sr, Ba, and Th. The CIF has geochemical and petrographic characteristics of both minettes and lamproites, but overall most closely resembles young Mediterranean lamproites. Felsic rocks of the CIF were produced by crystal fractionation and crustal contamination of mafic ultrapotassic magma, and include both high-silica lamproites strongly enriched in Zr, U, and Th, and weakly potassic to sodic rocks of trachytic composition. Flows and feeder dikes have relatively homogeneous Nd, 1840 Ma (–6 to –11) but highly variable ES., 1840 Ma (–40 to + 100); samples classified as lamproites have higher average Sr. Dike samples have highly variable present-day Pb isotope compositions, ranging from moderately to strongly nonradiogenic. Geochemical and isotopic data are consistent with contributions from depleted Archean lithospheric mantle, and OIB-type convecting mantle, both metasomatized by subduction-related processes during the Early Proterozoic. The lithospheric mantle probably contained Archean enriched domains as well. Proterozoic enrichment may have accompanied shallow underplating of subducted oceanic lithosphere beneath the Churchill Province during amalgamation of the Laurentian supercontinent. There are strong analogies in isotopic composition, and interpreted source region history, between the CIF and lamproites and minettes of the Wyoming Province and western Greenland, which suggest the existence of a Laurentian ultrapotassic superprovince.
With 7 Figures 相似文献
Geochemie und Entstehung der Proterozoischen ultrapotassischen Gesteine der Churchill Provinz, Kanada
Zusammenfassung Altproterozoische, ultrapotassische Gänge, Lavaströme und pyroklastische Gesteine der Christopher Island Formation (CIF), eruptierten in einem Gebiet von 600 × 300 km in der Churchill Provinz des Kanadischen Schildes vor 1.84 Ga. Die Zusammensetzung dieser Gesteine variiert von mafischen Lamprophyren (mg > 60; SiO2 = 47–54%, durchschnittliches K2O/Na2O > 4) mit Phänokristallent von Phlogopit + Diopsid + Apatit + Olivin + Magnetit, bis zu phänokristallarmen felsischen Gesteinen und Sanidinporphyren (SiO2 = 55–69%). Alle Proben zeigen hohe Gehalte an inkompatiblen Elementen und zeigen beträchtliche Verarmung an high field strength Elementen relativ zu K, Rb, Sr, Ba und Th. Die CIF hat geochemische und petrographische Eigenschaften sowohl von Minetten wie von Lamproiten, aber im allgemeinen ähnelt sie am stärksten jungen mediterranen Lamproiten. Felsische Gesteine der CIF wurden durch Fraktionierung und Krustenkontamination aus mafischen ultrapotassischen Magmen gebildet. Letztere umfassen sowohl siliziumreiche Lamproite, die deutlich an Zr, U und Th angereichert sind und schwach potassische bis sodische Gesteine von trachytischer Zusammensetzung. Lavenergüsse und zufuhrgänge zeigent ein relativ homogenes Nd, 1840 Ma (–6 bis –11) aber ein sehr variables Sr, 1840 Ma (-40 bis + 100); Proben die als Lamproite klassifiziert wurden, zeigent höhere durchschnittliche Sr-Werte. Proben von Gängen haben sehr variable Bleiisotopen-Zusammensetzungen, die von mäßig bis stark nichtradiogen variieren. Geochemische und Isotopendaten weisen auf Beiträge aus verarmtem archaischen lithosphärischen Mantel und aus konvektierendem OIB-Typ Mantel hin, die beide während des Alproterozoikums durch Subduktions-Vorgänge metasomatisiert wurden. Der lithosphärische Mantel enthielt wahrscheinlich auch angereicherte archaische Domänen. Proterozoische Anreicherungsvorgänge dürften seichtes Underplating subduzierter ozeanischer Lithosphäre unter der Churchill Provinz während der Amalgamation des laurentischen Superkontinentes begleitet haben. Es gibt starke Analogien in der Isotopenzusammensetzung und in der interpretierten Geschichte der Ursprungsregion, zwischen den CIF und Lamproiten und Minetten der Wyoming Provinz, und des westlichen Grönland. Diese weisen auf die Existenz einer laurentischen ultrapotassischen Superprovinz hin.
With 7 Figures 相似文献
52.
塔里木盆地是我国最大的含油气盆地,拥有巨大的油气资源潜力。但塔中地区奥陶系岩溶缝洞型储层埋藏深、类型复杂、储层非均质性强,所表现出的岩石地球物理特性不清楚。为了分析典型缝洞型储层模型含不同流体情形下的AVO特征,建立了过玉北1井的缝洞型储层地震地质模型,模型的3个储层段对应的孔隙度分别为10%,6%和8%,分别对应Ⅰ类储层、Ⅲ类储层和Ⅱ类储层,设计了3个储层段都充填气和3个储层段分别充填气、油、水3种不同流体时的2个模型,基于正演模拟共成像点道集记录(CMP),提取截距、梯度、纵横波反射系数及流体因子,采用AVO属性交汇分析方法,寻找油气识别的最佳属性组合,为叠前反演解释提供理论基础。 相似文献
53.
54.
Margarita Jambrina-Enríquez Clemente Recio Ildefonso Armenteros 《Environmental Earth Sciences》2018,77(2):49
The present multi-isotopic study (δ18O–δDwater, δ34S–δ18Odissolved-sulphate, δ13Cdissolved-inorganic-carbon, δ13C–δ18Oshells-modern-gastropods, δ13Cplants, and δ13Csedimentary-organic-matter) is aimed at assessing the hydrogeochemical changes and biogeochemical dynamics in a Mediterranean shallow lake fed by a Quaternary–Tertiary aquifer, the “Laguna del Cristo” (NW Iberian Peninsula), a system sensitive to climate fluctuations, between 2010 and 2011. Lake water is of the bicarbonate type, and there are no major pollutants. δ18O-δDwater values plot on a local evaporation line (δD=5.29δ18O–12.29) indicating that evaporative enrichment had a significant impact on lake water isotopic features. Periods of high water levels are characterized by lower δ34S–δ18Odissolved-sulphate and δ13Cdissolved-inorganic-carbon values and suggest sulphate derived from weathering of sulphides in the catchment area, delivered to the lake by surface run-off or via groundwater, and in situ decay of organic matter. During lower water levels, sulphate reduction and enhanced primary productivity lead to higher δ34Sdissolved-sulphate and δ13Cdissolved-inorganic-carbon values. Evaporation induced enrichment in 18Osulphate, 13Cdissolved-inorganic-carbon and 13C–18Oshells-Galba-Gyraulus. δ13Cplant confirms the C3 photosynthetic pathway. Enrichment in 13C submerged aquatic plants indicates that HCO3? is the main carbon source, except for 13C-depleted Potamogeton. The TOC, δ13Corg values, and TC/TN ratios in sediments all confirm the autochthonous character of organic matter contribution. This study provides a baseline for isotopic research into shallow, flow-through lakes fed by siliciclastic aquifers, and stresses the importance of evaporation and refilling (direct precipitation and groundwater discharge) in controlling the solute chemistry and stable isotopic composition in temperate regions with contrasting seasonal climates. The results also provide a snapshot of modern lake isotope variability that can be applied to paleoenvironmental reconstructions. 相似文献
55.
Groundwater systems in coastal aquifers may be affected by sea level change as increased seawater intrusion occurs with sea
level rise. Artificial pumping taking place at the same time will increase this impact. In order to estimate the vulnerability
of groundwater systems with sea level rise within coastal aquifers in South Korea, long-term groundwater data were analyzed
using basic statistics, trend analysis, and correlation analysis. Conductivity depth profiling was also periodically conducted.
Groundwater levels increased in wells with relatively low groundwater elevations but decreased in wells with higher groundwater
elevations. At the same time, conductivity variations were greater in wells located in reclaimed land areas, which vertical
conductivity profiles indicated were more affected by sea level variations, but decreased on the mainland. Results of auto-correlation
analysis showed a decreasing trend with cyclic variations and significant periodic patterns during dry seasons, indicating
that groundwater levels were not affected by artificial factors and that those in reclaimed land areas were less affected
by rainfall than on the mainland. These results coincided with those from cross-correlation analysis showing that groundwater
level was affected by sea level variation during the dry season. Sea level changes, which may be related to climate change,
as well as rainfall in South Korea can influence groundwater levels, and the groundwater system in reclaimed land areas may
be more affected than on the mainland, especially under dry conditions. 相似文献
56.
M. G. García K. L. Lecomte Y. Stupar S. M. Formica M. Barrionuevo M. Vesco R. Gallará R. Ponce 《Environmental Earth Sciences》2012,65(2):535-545
Symptoms of dental fluorosis have been observed in rural communities located in the Sierras Pampeanas de Córdoba, a mountainous
area in Central Argentina. The clinical assessment was performed in the Charbonier Department, where the fluoride (F−) intake was determined to be 3.90 ± 0.20 mg day−1 (n = 16). In this community, mild and severe fluorosis reach an incidence of 86.7% (total teeth surface = 636 teeth) among the
children population. To determine the origin and distribution of fluorine in natural waters from the Charbonier Department
and nearby regions, sampling was performed in the area covering the San Marcos River basin. The obtained results show that
F− concentrations vary between ~1 to ~2.5 mg l−1, with an outlier value of 8 mg l−1. The spatial distribution of F− shows that the lowest concentrations are found at the basin’s catchments. Maximum values are located in two sectors of the
basin: the Charbonier depression in the eastern part and at the San Marcos village, downstream the main collector, in the
western part of the basin. In these two regions, the F− contents in ground- and surface waters are >2.0 mg l−1 and nearly constant. Dissolved F− in natural waters from the study area has its origin in the weathering of F-bearing minerals present in the region’s dominant
lithology. The extent of mineral weathering is mostly determined by the residence time of water within the aquatic reservoir.
Longer residence times and a major solid–water interaction lead to enhanced release of F−. This explains the higher F− concentrations found in basin areas with lower run off. The removal of F− from water appears to occur by neither fluorite precipitation, nor by adsorption. Hence, variations in F− concentrations seem to be more related to regional hydrological conditions. 相似文献
57.
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
58.
Francisco González-Sánchez Antoni Camprubí Eduardo González-Partida Rafael Puente-Solís Carles Canet Elena Centeno-García Viorel Atudorei 《Mineralium Deposita》2009,44(3):343-361
Northeastern Mexico hosts numerous epigenetic stratabound carbonate-hosted low-temperature hydrothermal deposits of celestine,
fluorite, barite and zinc-lead, which formed by replacement of Mesozoic evaporites or carbonate rocks. Such deposits can be
permissively catalogued as Mississippi Valley-type (MVT) deposits. The deposits studied in the state of Coahuila are associated
with granitic and metasedimentary basement highs (horsts) marginal or central to the Mesozoic Sabinas Basin. These horsts
controlled the stratigraphy of the Mesozoic basins and subsequently influenced the Laramide structural pattern. The Sabinas
Basin consists of ~6,000-m-thick Jurassic to Cretaceous siliciclastic, carbonate and evaporitic series. The MVT deposits are
mostly in Barremian and in Aptian-Albian to Cenomanian formations and likely formed from basinal brines that were mobilized
during the Laramide orogeny, although earlier diagenetic replacement of evaporite layers (barite and celestine deposits) and
lining of paleokarstic cavities in reef carbonates (Zn–Pb deposits) is observed. Fluid inclusion microthermometry and isotopic
studies suggest ore formation due to mixing of basinal brines and meteoric water. Homogenization temperatures of fluid inclusions
range from 45°C to 210°C; salinities range from 0 to 26 wt.% NaCl equiv., and some inclusions contain hydrocarbons or bitumen.
Sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from Barremian to Cenomanian evaporites.
Regional geology and a compilation of metallogenic features define the new MVT province of northeastern Mexico, which comprises
most of the state of Coahuila and portions of the neighboring states of Nuevo León, Durango and, perhaps extends into Zacatecas
and southern Texas. This province exhibits a regional metal zonation, with celestine deposits to the south, fluorite deposits
to the north and barite and Zn–Pb deposits mostly in the central part. 相似文献
59.
S. Miko G. Koch S. Mesić M. Šparica-Miko M. Šparica R. Čepelak A. Bačani P. Vreča T. Dolenec S. Bergant 《Environmental Geology》2008,55(3):517-537
Due to their balneotherapeutic features, the organic-rich sediments in Makirina Cove are an important source of healing mud.
An environmental geochemistry approach using normalization techniques was applied to evaluate the anthropogenic contribution
of trace metals to sediments used as healing mud. Sediment geochemistry was found to be associated with land-use change and
storm events, as well as with proximity of a road with heavy traffic in the summer months. Local valley topography preferentially
channels lithogenic and pollutant transport to the cove. Concentrations and distribution of trace metals indicate lithogenic
(Ni, Cr, Co) and anthropogenic (Pb, Cu, Zn and Se) contributions to the sediments. The calculation of enrichment factors indicates
a moderate (EFs between 2–3.5) input of anthropogenic Cu and Pb in surficial sediments to a depth of 10 cm. Patients using
the Makirina Cove sediments as healing mud could be to some extent exposed to enhanced uptake of metals from anthropogenic
sources via dermal contact. 相似文献
60.
Michal Klaučo Bohuslava Gregorová Uglješa Stankov Vladimir Marković Polina Lemenkova 《Central European Journal of Geosciences》2013,5(1):28-42
The Sitno Natura 2000 Site covers an area of 935,56 hectares. The Sitno region is significant due to the number of rare and endangered species of plants, and as a result is considered a location of great importance to the maintenance of floral gene pools. The study area suffers human impacts in the form of tourism. The main purpose of this study is to the measure landscape elements, determine the ecological significance of habitats within the Sitno area, and from this data, organize the study area into conservation zones. The results of this landscape quantification are numerical values that can be used to interpret the quality of ongoing ecological processes within individual landscape types. Interpretation of this quantified data can be used to determine the ecological significance of landscapes in other study areas. This research examines the habitats of Natura 2000 Sites by a set of landscape metrics for habitat area, size, density, and shape, such as Number of patches (NP), Patch density (PD), Mean patch size (MPS), Patch size standard deviation (PSSD) and Mean shape index (MSI). The classification of land cover patches is based on the Annex Code system. 相似文献