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
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