Geochemistry of the oldest Atlantic oceanic crust suggests mantle plume involvement in the early history of the central Atlantic Ocean Philip E. Janney *, Paterno R. Castillo Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0220, USA Received 21 March 2001; received in revised form 27 June 2001; accepted 16 July 2001 Abstract Controversy has surrounded the issue of whether mantle plume activity was responsible for Pangaean continental rifting and massive flood volcanism (resulting in the Central Atlantic Magmatic Province or CAMP, emplaced around 200 Ma) preceding the opening of the central Atlantic Ocean in the Early Mesozoic. Our new Sr^Nd^Pb isotopic and trace element data for the oldest basalts sampled from central Atlantic oceanic crust by deep-sea drilling show that oceanic crust generated from about 160 to 120 Ma displays clear isotopic and chemical signals of plume contamination (e.g., 87 Sr/ 86 Sr i = 0.7032^0.7036, O Nd (t) = +6.2 to +8.2, incompatible element patterns with positive Nb anomalies), but these signals are muted or absent in crust generated between 120 and 80 Ma, which resembles young Atlantic normal mid-ocean ridge basalt. The plume-affected pre-120 Ma Atlantic crustal basalts are isotopically similar to lavas from the Ontong Java Plateau, and may represent one isotopic end-member for CAMP basalts. The strongest plume signature is displayed near the center of CAMP magmatism but the hotspots presently located nearest this location in the mantle reference frame do not appear to be older than latest Cretaceous and are isotopically distinct from the oldest Atlantic crust. The evidence for widespread plume contamination of the nascent Atlantic upper mantle, combined with a lack of evidence for a long-lived volcanic chain associated with this plume, leads us to propose that the enriched signature of early Atlantic crust and possibly the eruption of the CAMP were caused by a relatively short-lived, but large volume plume feature that was not rooted at a mantle boundary layer. Such a phenomenon has been predicted by recent numerical models of mantle circulation. ß 2001 Elsevier Science B.V. All rights reserved. Keywords: Atlantic Ocean; mantle plumes; oceanic crust; Mid-ocean ridge basalts; £ood basalts; Pangaea 1. Introduction The ¢rst major stage in the Mesozoic disinte- gration of the Pangaean super-continent was the opening of the central Atlantic Ocean in the Early Jurassic. The opening of this ocean basin was im- mediately preceded by a brief episode of areally extensive £ood volcanism at about 200 Ma (coin- 0012-821X / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved. PII:S0012-821X(01)00452-6 * Corresponding author. Present address: Department of Geology, The Field Museum of Natural History, 1400 S. Lake Shore Dr., Chicago, IL 60605, USA. Tel.: +1-312-665-7099; Fax: +1-312-665-7641. E-mail address: pjanney@fmnh.org (P.E. Janney). Earth and Planetary Science Letters 192 (2001) 291^302 www.elsevier.com/locate/epsl