Large Igneous Provinces, Seward Dipping Refectors, and Central Atlantic Magmatic Province
Gregory McHone, Co-Leader
Manik Talwani, Co-Leader
The largest igneous province, still being defined, is the central Atlantic magmatic province (CAMP). It now appears that dikes and lava flows were spread over portions of a region that surrounded the initial Pangaean rift zone, plus areas of West Africa and South America that were far from the rift. An area of 7 x 106 km2 is indicated. Recent high quality dates point toward a brief time period for most of the magmatism, perhaps less than 1 or 2 m.y. around 200 Ma.
CAMP raises important questions that involve rift tectonic events, ocean opening events, and mass extinction events. A drilling program can be devised in regard to three fundamental questions:
1) How are CAMP basalts related to continental rifting, that is, to the tectonic activity that formed basins and ultimately split Pangaea?
2) What is the connection, if any, between the continental CAMP and the oceanic seaward dipping reflectors (SDRs)?
3) Can CAMP/SDR volcanism be related to the Tr-J mass extinction?
We suggest that several transects, or corridors, would focus new petrological and geophysical studies in conjunction with deep-drill sites to answer these questions.
The first transect extends across the South Georgia rift system, possibly including a drill site on land in southern Georgia or farther west. Other drill sites include the shallow continental shelf, and the SDR (into the thinner inland section of the basalt wedge). The material recovered can be used to correlate CAMP dikes, the South Georgia rift basalts (the "J horizon"), and the southern end of the SDR where it intersects the J basalt. The correlations will require geochemical analyses and careful radiometric dating (probably Ar/Ar). To the east, this transect could include the Senegal basin, which is a large but poorly correlated feature of the conjugate margin.
A second transect would be the mid-Atlantic U.S. coast, targeting both subsurface and exposed basins to the west with relatively shallow drill sites as well as the deeper SDR near the Baltimore Canyon trough. This section has particularly good seismic data that characterize its SDR.
A third transect may match a new drill site in the Fundy basin with the deeper oceanic basins at the northern end of the east coast SDR. There is much new interest in this region from energy companies, which invites cooperative efforts to understand the basin and rift history.
A fourth transect would cross the later (Cretaceous) rift zone between northern South America and southern West Africa. Early Mesozoic basins are not present, but field mapping and sampling, plus structural interpretations from geophysical work (magnetic, seismic) are needed for correlating dikes and sills, and for modeling their tectonic history.
We also wish to model the tectonic history of basins to account for orientations of dike swarms, which record variations of rift stresses through time.
These data must also link known lavas with their source dikes. We can then better estimate the original extent, thicknesses, and times of intrusion of the various CAMP magmas. Such volumetric data will be converted to estimates of aerosols produced at the fissure eruption sites, especially CO2, SO2, and halides. These are potential causes of an environmental disaster like the Tr-J boundary extinction. Stratigraphic studies of this boundary could allow overlap of CAMP/SDR magmatism with this event.
Finally, we wish to point out that this project has great significance as the first integrated geological/geophysical analysis of continental breakup and contemporaneous flood basalt volcanism.