North-Central - 52nd Annual Meeting

Paper No. 38-6
Presentation Time: 8:00 AM-5:30 PM

MANTLE SOURCES FOR CENTRAL ATLANTIC MAGMATIC PROVINCE BASALTS FROM HF ISOTOPES


ELKINS, Lynne J.1, MARZOLI, Andrea2, BIZIMIS, Michael3, CALLEGARO, Sara4, MEYZEN, Christine5, SORSEN, Nathan1, LASSITER, John C.6 and ERNESTO, Marcia7, (1)University of Nebraska-Lincoln, Lincoln, NE 69588-0340, (2)Geoscienze, Università di Padova, via Gradenigo 6, Padova, 35100, Italy, (3)School of Earth, Ocean and the Environment, University of South Carolina, Columbia, SC 29208, (4)CEED - Centre for Earth Evolution ad Dynamics, University of Oslo, Sem Sælands vei 2A, Oslo, 0371, Norway, (5)Università di Padova, via Gradenigo 6, Padova, 35100, Italy; Geoscienze, Università di Padova, via Gradenigo 6, Padova, 35100, Italy, (6)Jackson School of Geosciences, The University of Texas at Austin, 2301 Speedway Stop, Austin, TX 78712, (7)University of Sao Paolo, Sao Paulo, 05508-010, Brazil

The Central Atlantic Magmatic Province (CAMP) was one of the most voluminous LIP events in Earth history and likely triggered the end-Triassic mass extinction. The tectonic and mantle processes that produced such significant magmatic emplacement are thus of broad geologic importance. To further explore the origins of CAMP, we present new 176Hf/177Hf isotope data for a broad geographic sampling of dikes, sills, and basalt flows. We find that basaltic intrusions from the Carolinas in Eastern North America trend along a shallower slope than the terrestrial array on a diagram of 176Hf/177Hf vs. 143Nd/144Nd. This trend may reflect the presence of recycled upper and lower crustal materials in the melt region, consistent with previous suggestions that the CAMP melt source has been modified by the addition of crustally derived material.

Distinct from the Carolina trend, we observe that low- and high-TiO2 basalts from Amazonia (Brazil) exhibit 176Hf/177Hf ratios along the terrestrial array. The high-TiO­2 basalts are overall isotopically depleted but trend towards EM1-type compositions, and may be asthenospheric melts that have experienced the addition of melt from local subcontinental lithospheric mantle (SCLM). For comparison, high-TiO2 CAMP basalts from Sierra Leone may likewise have incorporated melts of locally variable lithospheric mantle [Callegaro et al., in press, Jour. Petrology]. In contrast, low-TiO2 basalts from the same region in Brazil and of similar age to the high-TiO2 basalts have considerably lower Hf isotope ratios, indicative of a time-averaged source relatively enriched in incompatible elements. It remains unclear, however, whether the hypothesized SCLM sources represent intact lithospheric remnants, or if this material has reentered the convecting asthenosphere by delamination prior to melting. Neither ENA nor Amazonia CAMP require a mantle plume source to explain their Hf isotope systematics.