BASALTIC VULCANISM OF SHOSHONITIC AFINITY IN ARCHEAN ARC ENVIRONMENT , GRÃO-PARÁ GROUP, SERRA DOS CARAJÁS-PARÁ. The N4 and N8 orebodies in the Carajás district are associated to the Archean volcano-sedimentary Grão-Pará Group. The volcanic portion of this group comprises mainly basalts and basaltic andesites with local basic to intermediate pyroclastic intercalations. Associated intrusive bodies occur locally. Volcanic rocks were extruded in a subaqueous environment and submitted to hidrothermal metamorphic event of the greenschist facies. The absence of penetrative structures and the conspicuous occurrence of several primary textures are important features of the volcanic rocks associated to the orebodies. Geochemically the metabasic rocks are characterized by high contents of K, Ba and Rb, and low Zr, Nb and Ti, typical of the shoshonitic series. Petrologically the basic rocks of the Grão-Pará Group indicate a subduction zone geotectonic environment.
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