DOES THE CENTRAL ATLANTIC MAGMATIC PROVINCE (CAMP) REPRESENT A PLUME INDUCED LITHOSPHERE MELTING?

The Mesozoic age CAMP, erupted during Pangea breakup, may represent the largest subaerial flood basalt event on the planet. The absence of a Jurassic hotspot track or triple junction rift structures argue against a deep mantle origin for CAMP.

New geochemical data for tholeiite basalt and diabase from the Culpepper Basin in Virginia has TiO₂ ranging from 0.44-1.25, MgO from 4.1-11.7, and shows strong subduction related trace element characteristics, e.g. (La/Sm)n 1.5-1.9, Nb/La 0.36-0.62 and Th/Ta 4.6-9.1. Initial ratios at 200 Ma are ⁸⁷Sr/⁸⁶Sr 0.7055-0.7109, εNd -2.4-1.6, εHf -2.2-8.7, ²⁰⁶Pb/²⁰⁴Pb 18.25-19.09, ²⁰⁷Pb/²⁰⁴Pb 15.62-15.67, ²⁰⁸Pb/²⁰⁴Pb 38.15-38.9. The Pb isotopes have SCLM-like +Δ207Pb and +Δ208Pb. The CAMP radiogenic isotopes are broadly similar to the late Proterozoic Catoctin flood basalts (CVP) formed during Rodinia breakup. Both LIPs, associated with two discrete Wilson cycles, are nearly co-incident in location in Virginia. In the εNd_t-εHf_t initial plot CAMP has higher εHf, suggesting that the CAMP was derived from the residual source of the CVP. In Pb-Sr-Nd isotope plots the CAMP define binary-like trends between SCLM sources and a C-like source.

In the Central Atlantic, numerous plume tracks occur along the western African continental margin. Their activity dates back to the early opening of the Atlantic (180-150 Ma). Tomographic images (Montelli et al.) show that central Atlantic plumes have complex roots connecting to the lower mantle. For example, Azores, Canary, and Cape Verde plumes merge at depth before reaching the deep mantle. Isotopic data for these hotspots, like CAMP suggest a common C-like source that mixed with various SCLM and MORB sources. Similarity in source components for the central Atlantic hotspot/plume lavas and CAMP suggests that the LIP event resulted from heat associated with buoyant mantle plumes, rooted in the peripheries of the African superswell (e.g. Torsvik et al.), that rose beneath thin lithosphere associated with the breakup of Rodinia. We suggest that the trapped plume material and associated heat transferred from the lower mantle caused the thinned lithosphere to melt and triggered the CAMP flood basalt eruption during initial rifting of Pangea.

Montelli et al, Science (2004) 303

Torsvik et al., Geophys. J Int. (2006) 167