Abstract:
This dissertation discusses the experimental results designed to constrain the processes of
MORB generation. The main focus of this study is to investigate the location and the
related processes of the transformation boundary from spinel to garnet peridotite facies at
subsolidus conditions, because the presence of garnet in melting residues has significant
influence to the conclusion drawn from geochemical/geophysical observations. Using an
approach that monitors the rate of reaction progresses, the experimental results confirmed
the presence of a region that garnet and spinel coexist in peridotite compositions. The
trace element distribution among the product phases (opx and cpx) subsequent to the
garnet breakdown reaction is in disequilibrium, due to the differences of diffusivity
between major and trace elements. The presence of disequilibrium distribution in nature
may be used to infer time scales of geodynamic processes. Diffusion coefficients of A1 in
diopside are experimentally determined, and used for modeling the equilibration of major
elements in pyroxene during MORB genesis. In summary, this dissertation contributes
two major inferences: the location of the transformation boundaries of the gamet-spinel
peridotite; the presence of disequilibrium trace elements distribution with equilibrium
major elements distribution in mantle pyroxenes.
