Abstract
Three hundred stratigraphically constrained samples om the Reykjanes
Peninsula, SW Iceland, provide the basis for this study. This area
is an elevated section of mid-ocean ridge influenced by the Iceland
Plume. Selected chemical, Sr, Nd and laser-assisted fluorination
oxygen isotope data are presented. The dataset is subdivided into
groups bared on criteria which are independent of degree of fractionation:and
petrography. Two of these groups, Depleted and Stapafell, include
high-MgO aphyric samples with delta(18)O(olivine) values in equilibrium
with normal peridotite mantle. Deleted group samples have high Nd-143/Nd-144,
low Nb/Zr and low incompatible element abundances compared with the
dataset as a whole, the reverse of the Stapafell group. The majority
of the remaining samples have radiogenic isotope ratios, and incompatible
element concentrations and ratios intermediate between the Depleted
and Stapafell groups. Some samples, however define a range in Sr-87/Sr-86
and delta(18)O(olivine) at constant Nd-143/Nd-144, and others possess
positive Sr anomalies when normalized to primitive mantle values.
We explore the possibility that these and other chemical characteristics
have been produced by shallow crustal processes, including assimilation
of xenocrysts, cumulates and hydrothermally modified crust. We conclude
that although these processes are important, the major crustal process
acting to modify characteristics indicative of mantle heterogeneity
is magma mixing. Chemical variation previously thought to be a consequence
of dynamic melting is more readily explained by magma mixing.
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