The abundance levels of K, Rb, Sr and Ba in pyroxenes, olivines and garnets of ultramafic rocks are too low to yield a satisfactory composition for an upper mantle composed of these phases. This deficiency can be corrected by incorporation of a combination of plagioclase, hornblende and phlogopite, all of which have been shown previously to be stable in upper mantle environments. Concentrations of these elements in the above minerals, as determined in the present work, have been employed to calculate the abundances in various model mantles. Empirically determined distribution coefficients have then been used to calculate the trace element characteristics of liquids derived by partial melting of these model mantles. Comparison of these calculated partial melts with oceanic tholeiitic and alkali basalts indicates that the presence of 2-5 % hornblende and trace amounts (< 1 2%) of phlogopite in the upper mantle are necessary for the generation of these basalts. Alkali basalts may be derived through 5-10 % partial melting of this mantle, and 20-30 % melts resemble oceanic tholeiites. Such an upper mantle will satisfy many other geophysical and geochemical requirements.
|Number of pages||26|
|Journal||Geochimica et Cosmochimica Acta|
|Publication status||Published - Nov 1969|