"On human time-scales, continental
rifting is extremely slow at spreading rates of mm's per year but, on geologic time-scales,
rifting can be considered a catastrophic continental breakup event."
Thus, the continent--ocean transition is more complex than previously thought, and depth-dependent stretching and/or simple shear have been invoked to explain how mantle could be exhumed during the
rifting process, and lead to asymmetrical conjugate margins.
Finding the rift extension led the team to propose that the mountains are actually the result of multiple orogenies, or mountain building episodes, involving a unique combination of continental collision,
rifting and uplift processes not previously seen together in other mountain ranges.
The reappearance of banded iron is more likely related to episodes of continental
rifting in the Neoproterozoic and deposition in enclosed or restricted rift basins close to hydrothermal vents along incipient mid-ocean ridges.
He notes that some flood basalts might be related to continental
rifting, but he says the eruptions cause
rifting -- an idea in direct opposition to the theory that
rifting causes flood basalts.
"This work is a breakthrough in our understanding of continental
rifting leading to the creation of new ocean basins," said Ken Macdonald, professor emeritus in the Department of Earth Science at the University of California, Santa Barbara, and who is not affiliated with the research.
The age and style of
rifting describe the nature of the continental breakup phase preceding orogeny.
Previously, scientists seeking to explain the origin of this break have been unable to choose between two rival
rifting theories, but geophysicists recently pulled up evidence from the ocean floor that they say settles the debate.
