Ronda peridotites

Figure 5. Histogram Th/U for clinopyroxenes in peridotites and pyroxenites from the Ronda peridotite massif Concentrations were measured by isotope dilution mass spectrometry in acid-leached clinopyroxenes. This histogram shows that pyroxenites do not have larger Th/U ratios than peridotites. Thus, the correlation found between ( °Th/ U) and Th/U cannot be explained by mixing of peridotite and pyroxenite melts as advocated in Sigmarsson et al. (1998). Data from Hauri et al. (1994) and Bourdon and Zindler (unpublished). It can be shown with a simple Student t-test that the two populations are indistinguishable.

Most Ronda peridotites show thorium variations consistent with LREE variations. In other words, thorium generally plots on extrapolations of the LREE segments on the PM-normalized diagrams and Th/La is roughly correlated with La/Sm. Both ratios are generally lower than PM values in the Iherzolites, close to PM values in the harzburgites and variable in the dunites. 

Finally, the Ronda peridotites are generally characterized by negative anomalies of zirconium on PM-normalized diagrams, the amplitude of which increases from lherzolites (which have only subtle anomalies) to dunites. Zr/Sm is mostly in the range (O.S-l)XPM in the lherzolites. 

Davies G. R., Nixon P. H., Pearson D. G., and ObataM. (1993) Tectonic implications of graphitized diamonds from the Ronda peridotite massif, southern Spain. Geology 21, 471-474. 

Garrido C. and Bodinier J.-L. (1999) Diversity of mafic rocks in the Ronda peridotite evidence for pervasive melt/rock reaction during heating of subcontinental lithosphere by upwelling asthenosphere. J. Petrol. 40, 729-754. 

Lenoir X., Garrido C. J., Bodinier J.-L., Dautria J.-L., and Gervilla F. (2001) The recrystallization front of the Ronda peridotite evidence for melting and thermal erosion of subcontinental lithospheric mantle beneath the Alboran basin. J. Petrol 42, 141-158. 

Obata M. (1980) The Ronda peridotite Garnet-, Spinel-, and Plagioclase-lherzolite facies and the P—T trajectories of a high-temperature mantle intrusion. J. Petrol. 21, 533—572. Obata M. and Morten L. (1987) Transformation of spinel Iherzolite to garnet Iherzolite in ultramafic lenses of the Austridic crystalhne complex, Northern Italy. J. Petrol. 28, 599-623. 

Suen C. J. and Prey P. A. (1987) Origins of the mafic and ultramafic rocks in the Ronda peridotite. Earth Planet. Sci. Lett. 85, 183-202. 

Van der Wal D. and Bodinier J.-L. (1996) Origin of the recrystallization front in the Ronda peridotite by km-scale pervasive porous melt flow. Contrib. Mineral. Petrol. 122, 387-405. 

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