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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

SEDIMENTOLOGY AND STRATIGRAPHIC EVOLUTION OF THE PARADOX BASIN IN THE MIDDLE-LATE JURASSIC, WESTERN UNITED STATES

Ejembi, John Idoko 01 December 2018 (has links)
The Middle-Upper Jurassic sedimentary rocks (i.e., the Entrada Sandstone, Wanakah Formation, and Morrison Formation) in western Colorado were mostly deposited in the Paradox Basin and form part of the modern-day Colorado Plateau in the Cordilleran foreland region. These rocks were deposited in the Mesozoic during periods of active tectonic processes in western and eastern Laurentia due to the Cordilleran magmatism and continued rifting of Pangaea, respectively. The Middle-Late Jurassic sedimentary record in the Paradox Basin shows rapid transition in depositional environments, pulses in sedimentation, post-depositional alteration, and changes in provenance. This dissertation project utilizes three main scientific tools to address pertinent geologic questions regarding the stratigraphic evolution of these units in the Paradox Basin. U-Pb detrital zircon geochronology of sandstones from these units show local and distal provenance sources. The anisotropy of magnetic susceptibility (AMS) of sediments and rock magnetism attribute the post-depositional alteration to percolation of ferruginous fluids driven by an adjacent regional uplift. Multi-geochemical proxies in paleosols suggest variable redox conditions, and a sub-humid to humid paleoclimate with seasonal precipitation during sedimentary hiatus in the Paradox Basin.
2

Middle-Late Jurassic Cu-Pb-Zn-bearing and W-bearing granitoids and their skarn mineralization in the Nanling Range, South China : the Tongshanling and Weijia deposits / Les granitoïdes du jurassique moyen et les skarns à Cu-Pb-Zn et à W associées dans la région de Nanling (Chine du Sud) : les gisements de Tongshanling et de Weijia

Huang, Xu-Dong 28 October 2018 (has links)
Les granitoïdes associés aux skarn à Cu-Pb-Zn et au W, dérivent, respectivement, de la fusion partiellede roches mafiques à amphiboles dans la croute inférieure et de roches métas-édimentaires riches enmuscovite dans la croute moyenne-supérieure. Ces sources fertiles mobilisées pour la formation de cesplutons a permis la formation de gisements à Cu-Pb-Zn, et W au cours du Jurassique moyen. L’originedans la croûte moyenne de la granodiorite de Tongshanling, associée aux minéralisations à Cu-Pb-Zn, aété montrée par l’étude des enclaves microgranulaires dioritiques qui sont des restites remaniées issuesde la fusion partielle des amphibolites de la croûte inférieure. Le Cu et le Zn associées à ces plutons sontprobablement issus de la croûte inférieure et ces métaux ont probablement étés remobilisés au cours dela fusion partielle. Le Pb issue de la croute supérieur a été collecté lors de l’ascension du magma qui adonné la granodiorite. Lors de leur mise en place ces granitoïdes ont exprimé leur potentielminéralisateur. L’étude structural montre que la géométrie des corps minéralisés et en lien avec ladéformation induite par la mise en place des plutons. Les différentes expressions de la minéralisationdans le district à Cu-Mo-Pb-Zn-Ag de Tongshanling sont génétiquement lié à l’hydrothermalisme et à sonévolution lors du développement du skarn. Le granite de Weijia a cristallisé à partir d’un magma saturéen eau et riche en Fluor. Les facteurs qui ont contrôlé la formation de ce skarn magnésien riche en W,suppose l’existence d’une source enrichie en W dans les sources métasédimentaires et d’un magmariche en Fluor très différentia par cristallisation fractionnée. / The Middle-Late Jurassic Cu-Pb-Zn-bearing and W-bearing granitoids in the Nanling Range were mainlyderived from non-simultaneous partial melting of the mafic amphibolitic rocks in the lower crust and themuscovite-rich metasedimentary rocks in the upper-middle crust, respectively. The fertile sources in theNanling Range are beneficial to the formation of Cu-Pb-Zn and W deposits during Middle-Late Jurassic.The lower-crust origin of the Cu-Pb-Zn-bearing granodiorites is further demonstrated by the dioriticmicrogranular enclaves in the Tongshanling granodiorite which are reworked restite enclaves derivedfrom partial melting of the mafic amphibolitic source. The Cu and Zn associated with these intrusionswere most probably released from the mafic amphibolitic lower crust by partial melting, whereas, Pb wasextracted from the upper crust by ascending granodioritic magmas. The emplacement of these orebearinggranitoid magmas may have a structural connection with the subsequent polymetallicmineralization in some way. For instance, the exoskarn and sulfide-quartz veins in the Tongshanling Cu-Pb-Zn deposit are evidently controlled by magma emplacement-induced wall-rock deformation. Thedifferent mineralization types and ore deposits in the Tongshanling Cu-Mo-Pb-Zn-Ag ore district aregenetically linked together in the same skarn system as the productions of evolution and zonation. TheWeijia granite was crystallized from a F-rich and water-saturated magma. The key factors controlling theoccurrence of unusual magnesian skarn W mineralization during Late Jurassic in the Nanling Rangemainly include a W enriched metasedimentary source, a fluorine-rich magma, a strong crystalfractionation, and a fluorine-rich hydrosaline melt

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