Ž . Lithos 43 1998 197–217 Isotopic and trace-element indications of lithospheric and asthenospheric components in Tertiary alkalic basalts, northeastern Brazil R.V. Fodor a, ) , S.B. Mukasa b , A.N. Sial c a Department of Marine, Earth, and Atmospheric Sciences, North Carolina State UniÕersity, Raleigh, NC 27695, USA b Department of Geological Sciences, UniÕersity of Michigan, Ann Arbor, MI 48109, USA c Departamento de Geologia, UniÕersidade Federal de Pernambuco, Recife, PE, Brazil Received 8 January 1997; accepted 3 April 1998 Abstract Plate reconstructions at 30 Ma place northeastern Brazil over the Fernando de Noronha hotspot, presently ;250 km offshore northeastern Brazil. Tertiary basaltic centers in northeastern Brazil may therefore be products of the Fernando de Noronha hotspot. We examined alkalic basalt from seven ;30–13 Ma old centers in Rio Grande do Norte and Pernambuco states to assess this possible link. Compositions are primitive, where MgO concentrations range from 12.5 to 17 wt.%, and SiO from ;41 to 48 wt.%. Trace-element abundances and Sr, Nd, and Pb isotopic compositions compare well with those 2 of ocean island basalt: 87 Srr 86 Sr s;0.7038–0.7051, 143 Ndr 144 Nd s;0.51266–0.51280, and 206 Pbr 204 Pb s;18.52– 19.35. There are correlations among SiO -undersaturation, incompatible-element abundances, relative percentages of partial 2 Ž . melting based on LarYb and LarY ratios , and the degree of isotopic ‘enrichment’ inherited from mantle sources. There is Ž . Ž . also a negative correlation for LarNb ;0.6–0.86 vs. BarNb 6.6–10.6 , where lower LarNb samples represent larger percentages of melting of a source comparatively enriched in radiogenic Sr. We attribute these compositional relationships to the lavas representing mixing of melts mainly from asthenosphere of largely HIMU plus DM characterization, probably the Fernando de Noronha plume, with melts from subcontinental lithosphere that was isotopically closer to EM1. Isotopic and trace-element compositions of the northeastern Brazil basalts are generally similar to those of Fernando de Noronha lavas Ž . Ž 12–2 Ma , and some minor trace-element differences observed e.g., more Zr, Nb, and less Th compared to northeastern . Brazil basalts are probably due to heterogeneity within the asthenospheric plume and to melt contributions from delaminated subcontinental lithosphere that may underlie Fernando de Noronha. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Basalt; Brazil; Trace-elements; Isotopes; Mineral compositions 1. Introduction Plate reconstructions for the South Atlantic Ž . Morgan, 1983; O’Connor and Duncan, 1990 place ) Corresponding author. northeastern Brazil over or near the oceanic Fer- nando de Noronha hotspot about 30 Ma ago. The ; 30–13 Ma old alkalic-basalt centers in the north- eastern corner of Brazil at ; 5830 X S and 358W may therefore have overlain or been in the proximity of the Fernando de Noronha hotspot, presently ; 250 0024-4937r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0024-4937 98 00012-7