2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 227-1
Presentation Time: 9:00 AM

FROM RODINIA TO PANGEA: EASTERN NORTH AMERICAN THOLEIITES RECORDING A SUPERCONTINENT CYCLE


CALLEGARO, Sara1, MARZOLI, Andrea1, BERTRAND, Hervé2, CHIARADIA, Massimo3, REISBERG, Laurie4 and BELLIENI, Giuliano1, (1)Geoscienze, Università di Padova, via Gradenigo 6, Padova, 35100, Italy, (2)Laboratoire de Géologie de Lyon, Ecole Normale Superieure de Lyon, 46 allée d’Italie, Lyon, 5276, France, (3)Département de Minéralogie, Université de Genève, rue des Maraîchers 13, Genéve, Switzerland, (4)Crpg, CNRS, Nancy, CNRS, France

The south Eastern North American (SENA) margin is intruded by tholeiitic dykes and sills of the Central Atlantic Magmatic Province (CAMP) dated at 202-195 Ma. In the same region crop out older (Late Neoproterozoic) mafic rocks related to the early stages of Rodinia disruption, namely the Bakersville dykes (ca. 730 Ma) and the Catoctin magmatism (710-560 Ma).

CAMP dykes display enriched 87Sr/86Sri (0.70438-0.70880) and 143Nd/144Ndi (0.51251-0.51204) ratios typical of the low-Ti CAMP field, but Pb isotopes (206Pb/204Pbi 17.46-18.85, 207Pb/204Pbi 15.54-15.65, 208Pb/204Pbi 37.47-38.76) are particular to this area of the CAMP. Along with crustal-like trace element patterns and low 187Os/188Osi (0.127-0.144, incompatible with significant crustal assimilation), these traits are explained through shallow recycling of subducted lower and upper crustal materials within the upper mantle.

The Bakersville dykes and Catoctin magmatism are less studied, but the available data (87Sr/86Sri~ 0.7035-0.7044; Badger and Sinha, 1988; Goldberg et al., 1986) show more depleted characteristics compared to ENA CAMP. Assuming that they derive from the same upper mantle, an enrichment of the source is suggested between the Rodinia and Pangea breakup events (ca. 600 Ma and 200 Ma, respectively). This enrichment may be linked to the Late Ordovician subduction of the Rheic ocean under Laurentia (441-459 Ma; Sinha et al., 2012) or to the Carboniferous Acadian-Neoacadian subduction (ca. 410-330 Ma; Badger and Sinha, 1988).

Melts generated from sediments and delaminated portions of lower continental crust brought into the mantle during Paleozoic subduction mat have reacted with the ambient shallow lherzolitic mantle, forming enriched (pyroxenitic) zones. Enrichment and heterogeneities were thus preserved and are reflected in the different isotopic signatures of closely spaced SENA-CAMP dykes.

The ENA margin is thus an example of how extensional magmatism can record the geochemical evolution of the upper mantle during an entire Wilson cycle.

Badger, R.L., Sinha A.K., 1988. Geology 16, 692-695.

Goldberg, S.A., Butler, J.R., Fullagar, P.D., 1986. Am. J. Sci. 286, 403-430.

Sinha, A.K., Thomas, W., Hatcher, R.D., Harrison, T.M., 2012. Am. J. Sci. 312, 907–966.

Session No. 227

Structural Geology and Tectonics: Tectonics of Orogenic Cycles, Rift Processes and Basins (Posters)
Tuesday, 21 October 2014: 9:00 AM-6:30 PM
Exhibition Hall C (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.558
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