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Universitaet Wien (1998)

Application of spectroscopic methods to the study of selected geochemical problems

Abate, B.

Titre : Application of spectroscopic methods to the study of selected geochemical problems

Auteur : Abate, B.

Akad. Grad : Thesis.Doctoral 1998

Université de soutenance : Institut fuer Geochemie ; Formal- und Naturwissenschaftliche Fakultaet ; Universitaet Wien

Résumé
Impact craters are products of a complex sequence of events and processes, which include the formation of the crater by a hypervelocity impact of an extraterrestrial body on the surface of the earth and the subsequent modification of the crater by terrestrial processes, such as weathering, erosion, sedimentation, tectonics, or volcanism. Recognition of impact craters as common geological features on the surface of planets is a major conceptual revolution in the Earth sciences during recent years. Impact craters can be distinguished by a set of criteria, such as morphology, associated geophysical and geochemical anomalies, and shock metamorphic effects. Some impact craters are known to host economically important mineral deposits and hydrocarbon reserves. Six different spectroscopic methods were used to obtain chemical data on the rocks of the studied areas. These are X-ray Fluorescence Spectroscopy (XRF), Atomic Absorption Spectroscopy (AAS), Direct Current Plasma Atomic Emission Spectroscopy (DCP-AES), Instrumental Neutron Activation Analysis (INAA), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Thermal Ionization Mass Spectrometry (TIMS). The subject of this study were samples from four different areas, Lake Tana area (north-central Ethiopia), Shakiso area (southern Ethiopia), BP and Oasis impact structures Libya, and the Zhamanshin impact crater, Kazakhstan. Petrographic and geochemical studies show that the Lake Tana and the Gimjabet-Kosober areas are covered by dominantly two main types of volcanic rocks. These are rhyodacitic and alkali basalts. Rhyodacites occur in the area east of Lake Tana, and the alkali basalts cover most of the area within the Lake Tana (e.g., Dek island), and the Gimjabet- Kosober areas. The rare earth element (REE) and incompatible element patterns of rhyodacites east of Lake Tana display evidence of differentiation and crustal contamination. The major, trace, and REE data suggest that the young volcanic rocks of the Ethiopian plateau and the Main Ethiopian Rift (MER) have a common central magma source. Petrographic and geochemical studies of rocks around Shakiso area were performed to constrain previously suggested evidence of shock metamorphism around the town of Shakiso. This study did not reveal any evidence for shock metamorphism and the existence of the suggested impact crater around the town of Shakiso could not be confirmed. In this research the impact origin of the BP and Oasis structures was confirmed from petrographic study target rocks. From geochemical and isotopic studies of target rocks from the two Libyan structures, it is concluded that rocks from the BP and Oasis structures, Libya, may be the source rocks of the Libyan Desert Glass. Drill core samples and surface target rocks from the Zhamanshin impact crater were investigated to study the geochemical characteristics of target rocks and associated impact glasses. Major element, trace element, and isotopic data were supported by mixing calculations.

Mots clé :
Impaktkrater / Isotopenchemie / Aethiopien / Libysches Wuestenglas / Roentgenstrahl-Fluoreszenzspektroskopie / Massenspektroskopie / Tana See
impact crater / isotope / geochemistry / Ethiopia / Libyan desert glass / Zhamanshin / X-ray fluorescence spectroscopy / mass spectroscopy / Lake Tana

Présentation : Österreichische Dissertationsdatenbank

Page publiée le 11 juin 2008, mise à jour le 14 mars 2019