Date of Award
Master of Science (MS)
This study addresses three independent topics related to trace element modeling of spinel peridotites that are suggested by the pioneering work of Johnson et al. (1990) on abyssal harzburgites.
First, the fractional non-modal melting equation derived by Johnson and coworkers (1990) is algebraically modified to present a "one-element/two-phase" model. This model suggests a simple test for estimating mantle heterogeneity in the source rock of spinel lherzolites. This model is applied to data from the literature for samples from Dreiser Weiher, Germany; San Luis Potosi, Mexico; and Western Victoria, Australia.
Second, trace elements in clinopyroxenes of abyssal peridotites and continental spinel Iherzolite nodules from multiple localities are compared. Plots of Ti versus Zr, Na2O and REEs show data overlap in their distribution trends, and they are thought to have originated from broadly similar ratios in the source rock prior to partial melting and by generally similar melting processes.
Third, a modal melting (MM) diagram for abyssal peridotites based on the Johnson et al. (1990) melting equation is constructed that illustrates how modal proportions of mineral phases in a spinel-lherzolitic mineral assemblage change as a function of F (degree of melting). In accordance with this model, a method is introduced that allows F to be calculated based solely on the modal composition for a particular sample. This model is "calibrated" with Ti data for Cpx in abyssal harzburgites, and the original mantle composition is calculated at F=0 and compared to other suggested primitive upper mantle compositions. The sensitivity of this diagram to variations in input parameters is also shown. A further calibration with experimentally-established reaction coefficients for the upper mantle melting reaction (Kinzler & Grove 1992a, b; Baker & Stolper 1993) is also carried out in order to test similarities between these two independent approaches. The calibration shows iterative values for the input parameter are in partial agreement with experimentally-derived reaction coefficients. While the resulting reaction coefficients confirm generation of olivine during melting as suggested by melting experiments, Opx and Cpx reaction coefficients show similar proportions (Cpx/Opx < 1). This observation does not concur with experimentally-determined mantle melt reaction (Cpx/Opx ~ 2 for Kinzler & Grove (1992a) and Baker & Stolper (1993)). A satisfactory link between trace-element modelling and high P-T melting experiments could therefore not be obtained through the MM-model.
Vogel, Susanne Petra, "Trace-element modelling of melting in spinel peridotites" (1993). Geology Theses and Dissertations. 93.