Rare-earth element distribution in the metabasic rocks of the Land's End

ABSTRACT. Rock samples from the various metabasic hornfelses ofthe Land's End granite aureole were analysed for major elements by X-ray fluorescence analysis and for rare-earth elements (REE) by instrumental neutron activation analysis (INAA). The REE patterns of the unaltered olerites of the area seem to be analogous to those of the alkali basalts, taking into account a slight mobilization of the light REE during low-grade metamorphism. The REE content of the metabasic rocks of the aureole has increased relative to that of the unaltered olerites due to the introduction ofREE, along with K, from the granite by the action of hydrothermal solutions. The parallel increase in REE with the increase in K is demonstrated. The metasomatic hornfelses of igneous origin form two groups howing slightly different REE patterns and different rates of increase in REE content. The REE patterns of the two groups how a Eu anomaly increasing with the increase in REE content for the first group and decreasing with the increase in REE content for the second group, A qualitative model of the distribution of the REE in the metabasic aureole rocks is given. T tie great variety of the metamorphic-metasomatic hornfelses which exist in the Land's End granite aureole, as well as the rich mineral veining of the area, have attracted the interest of a great number of geologists since the beginning of the last century. A detailed review of the previous research on the Land's End granite aureole is given in Mitropoulos (1979). The mineralogically, petrologically, and chemically different aureole rock types are regarded as derived by metamorphism, coupled with meta-somatism, of basic igneous and sedimentary ocks resulting from the introduction of the granite. It has been shown (Mitropoulos, 1982) that the metasedimentary hornfelses of the Land's End granite aureole show similar REE patterns, highly enriched in light REE relative to the heavy REE. The REE content of the metasedimentary hornfelses of the aureole has increased relative to the REE content of the unaltered sediments of the area du