ABSTRACT
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.
Susanne Petra Vogel 1993. Trace-element modelling of melting in
spinel peridotites.
Unpublished MSc. thesis, State University of New York at Albany.
140 pp., +xii
University at Albany Science Library call number: SCIENCE
Oversize (*) QE 40 Z899 1993 V64
thesis (scanned
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