Trace and major elements in sedimentary and igneous processes: REE geochemistry of black shales and MORB and major element chemical variations in plume-generated basalts.

摘要

This study focused on the major element geochemistry, trace element geochemistry, and stable isotope geochemistry of organic-rich black shales (Part I) and basalts (Parts II and III).; Part I. This portion of the project concentrated on black shales deposited during the Caradocian (Late Ordovician) in the United States and Canada and prodeltaic shales deposited in the Greenhorn Sea during the Late Cenomanian through Early and Middle Turonian (early Late Cretaceous).; Chapter 2. Results indicate that the Taconic Foreland basin shales of the United States and Canada show a characteristic light rare earth element (LREE; La-Nd) depletion. The degree of LREE depletion relates directly to late diagenetic processes.; Chapter 3. The rare earth element geochemistry of the Tropic and Tununk shales of the Greenhorn Sea (Colorado and Utah) show remarkable uniformity across the basin. The stability of the source area over the course of the deposition of this sequence of shales provides significant information concerning relationship between sediment sorting and the development of stratigraphic cycles.; Chapter 4. Color variation couplets, magnetic susceptibility and stable isotopes ({dollar}deltasp{lcub}13{rcub}{dollar}C and {dollar}deltasp{lcub}18{rcub}{dollar}O) of the Collingwood-Blue Mountain formations of southern Ontario show the development of orbitally induced cycles on the order of Milankovitch frequencies.; Part II. This section concerns trace element analyses of glass samples from the equatorial Mid-Atlantic Ridge (MAR).; Chapter 5. Modeling of MAR glass trace element concentrations indicate the presence of three end-members. A new statistical modeling technique allows the composition of the end members to be determined. Additionally, the robustness of this technique affords its application to sedimentary systems.; Chapter 6. The Ce/Pb and Nb/U ratios of MAR glasses indicate at least three mantle source components. Correlations between trace element compositions and isotopic ratios are inconsistent with continental admixing. These results clearly demonstrate mantle Ce/Pb and Nb/U source heterogeneity.; Part III. This section discusses major element heterogeneity in the Hawaiian-Emperor seamount chain lavas and Siberian Flood Basalt province basalts.; Chapter 7. Examination of the major element geochemistry of the Hawaiian-Emperor seamount chain lavas clearly demonstrate that previously accepted views on the importance of fractional crystallization on the distribution of major elements is over estimated. The primary source geochemistry is not entirely obscured by crystal fractionation processes.; Chapter 8. Major element data and isotopic data of basalts from the Siberian Flood Basalt province indicate that major element heterogeneity is the direct result of partial melting with the bulk of the lavas showing lower mantle signatures.