Geophysics and Geodynamics Research at Colorado State University

Research in Progress

Continental Rifting and Formation of Rift Basins

Challenges to understanding the formation of rift basins and rifted continental margins are to define the processes controlling shifts in the locus of extension through time and the relationship between magma generation and extensional tectonics. Many rift systems initially undergo extension in areas that ultimately become quiescent, with continental breakup occurring elsewhere (thus stranding rift basins in shelf and onshore regions). Magmatism is equally enigmatic – some rift systems (dubbed Nonvolcanic Rift Margins, or NVRMs) proceed to continental breakup and production of new magmatic oceanic crust while producing very little syn-rift magmatic products. The G&G Research Group at CSU has been addressing the causes behind both shifts in extensional centers and the transition from amagmatic rifting to seafloor spreading through numerical simulations of extensional tectonics and related magma petrogenesis. The figure at right shows the results of a finite element model of extension on the Iberia/Newfoundland conjugate rift margins (crust is yellow, mantle is green). In this model, we have introduced small variations in the thickness of the pre-rift crust and a region with moderately weaker upper crust prior to extension. Extension is initially distributed over a broad region that includes deformation in what would be the Galicia Interior Basin on the Iberia shelf (where our upper crust weakness is prescribed). About 13 m.y. after rifting begins, deformation in the Galicia Interior Basin wanes and extension becomes focused in the area where the pre-rift crust was thickest. From this time forward, extension becomes progressively more focused in this area, leading to continental breakup seaward of the western edge of the Galicia Interior Basin. This style of deformation dramatically affects melt production. For the first 20 m.y., mantle thinning is distributed diffusely throughout the broad zone of extension. Beginning at around 20 m.y., after extension in the Galicia Interior Basin has shut down, mantle thinning becomes focused in the extensional zone west of the Galicia Interior Basin. By this time, sufficient space has been created for the upwelling asthenosphere to begin decompression melting. Once mantle necking begins in this area it focuses extensional stress in an ever-thinning cross section of the lithosphere. This promotes more rapid thinning, quickly leading to continental breakup within a few m.y. after melting begins. The model predicts a narrow region of very late stage syn-rift magmatism, and provides a simple explanation for how amagmatic rifting can end with sufficient melt production to create new oceanic crust.

The model shown here is described in more detail in Harry, D.L. and S. Grandell, A Dynamic Model of Rifting Between Galicia Bank and Flemish Cap During Opening of the North Atlantic Ocean, MARGINS Theoretical and Experimental Earth Science Series v. 3, G. Karner, G. Manatschal, L. Pinheiro (eds.), Columbia University Press, in press.

We currently have ongoing research activities in a variety of rift basins and rifted continental margins worldwide, including the North Atlantic, Gulf of Mexico, North America Cordillera, and West Antarctica (click on image for larger view).

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