LATERAL TRANSPORT OF CAMP-RELATED MAGMAS BENEATH THE EASTERN NORTH AMERICAN RIFT SYSTEM AND MARGIN

Geophysical studies from passive margins of the North Atlantic have imaged complex networks of interconnected sills and dikes associated with breakup and the North Atlantic Igneous Province. These networks transported magma laterally away from the breakup site and upward into the continental crust over distances of several hundred kilometers. We propose that a similar plumbing system, dominated by lateral magmatic transport within the continental crust, affected the eastern North American (ENAM) rift system and margin during the short-lived, but intense, magmatic activity associated with the Central Atlantic Magmatic Province (CAMP, latest Triassic/earliest Jurassic, ~201 Ma). The style of the plumbing system varied spatially across ENAM, depending on the relative timing of rifting/breakup and CAMP magmatism, reflecting the evolving stress state during margin development.

The ENAM rift system comprises numerous parallel and en-echelon rift basins that are offset from the breakup site by tens to hundreds of kilometers. Numerical models suggest that extension was depth-dependent: broadly distributed within the continental crust producing a wide zone of offset rift basins and focused within the lithospheric mantle near the eventual breakup site. The cessation of rifting (and presumably the onset of breakup) was diachronous, occurring first in the south before CAMP and then in the central segment several million years after CAMP. In our conceptual model, CAMP-related magma preferentially accumulated beneath the thin lithosphere near the developing breakup site. In the south, where breakup occurred first and rifting ceased before CAMP, NW-striking dikes (subperpendicular to the margin) transported magma landward (westward) and upward into the continental crust, cutting across inactive rift basins. Igneous sheets developed where dikes intersected rift basins (intruding basin fill and/or deformed deep crust beneath them). In the central segment, where rifting continued during and for several million years after CAMP, interconnected sills and dikes facilitated the lateral propagation of magma landward and upward beneath and into active rift basins. Extension rates abruptly increased during CAMP, consistent with lateral magma networks propagating along and enhancing zones of crustal weakness.