ISOTOPIC AND REE CHARACTERISTICS OF THE INTRUSIVE CHARNOENDERBITE AND ENDERBITE GEOGRAPHICALLY ASSOCIATED WITH THE MATOK PLUTON, LIMPOPO BELT, SOUTHERN AFRICA

Intrusive charnoenderbite and enderbite in the Southern Marginal Zone of the Limpopo Belt are genetically linked with peak metamorphism (M1) during the 2700 Ma to 2650 Ma Limpopo Orogeny. They occur geographically associated with and are intruded by the granodiorite and granite of the Matok Pluton which were emplaced between the response phase (M2) and the rehydration phase (M3) of that Orogeny. Rb-Sr, Pb, REE and Sm-Nd elemental and isotopic data for whole rock samples and U-Pb data for populations of zircon suggest that the charnoenderbite and enderbite were intruded approximately 2671 Ma ago and were derived from a crustal precursor. The granodiorite and granite of the Matok Pluton were intruded at approximately the same time, between approximately 2667 Ma and approximately 2664 Ma ago; they also were derived from a crustal precursor. Nd model ages and REE patterns for the charnoenderbite and enderbite and the granodiorite are distinct. This relationship may imply that they are not cogenetic. Alternatively, these rock types could be cogenetic if the magma from which they were derived was assimilating older crustal material as it evolved. Nd isotopic data indicate that the magma giving rise to the charnoenderbite and enderbite formed by partial melting of rocks compositionally similar to some portions of the Baviaanskloof Gneiss. Data for the granodiorite are consistent with the possibility that this unit formed in a similar manner from rocks compositionally similar to other portions of the Baviaanskloof Gneiss. The close temporal relationship between the emplacement of the charnoenderbite and enderbite and the granitic rocks of the Matok Pluton indicates that the retrograde portion of the Limpopo Orogeny, beginning approximately 2670 Ma ago, occurred rapidly, perhaps over approximately 7 Ma.