Earth’s surface is continuously reconfigured by the assembly and breakup of supercontinents. As part of this cycle, landmasses split apart at continental rifts, linear zones where the lithosphere is stretched and lowered and new oceanic crust forms.
Geologists have long understood that rifted margins are characterized by several types of normal faults that accommodate this extension, including steep faults with up to a few kilometers of vertical displacement and lower-angle faults that can accommodate tens of kilometers of horizontal motion. Although the growth of these steeper faults has been systematically studied in rift margins, the role that the lower-angle faults plays in these settings is not as well understood.
To bridge this gap, Osmundsen and Péron-Pinvidic studied the range of faults present along the mid-Norwegian margin, an important oil- and natural gas–producing area that experienced multiple episodes of rifting between the late Paleozoic and early Cenozoic. Using several sources of seismic reflection data collected in the Norwegian Sea between 1984 and 2008, the researchers identified five structural domains that formed via the linkage of large extensional faults.
The faults combined into what the authors call “breakaway complexes,” which distinguish the margin’s proximal and necking domains, with thicker continental crust and higher-angle faults, from its distal and outermost portions, which are recognized by increasingly isolated slivers of crystalline continental crust and the presence of lower-angle faults. Seaward of the outermost breakaway complex, nearly flat detachment faults prevail. The 3-D architecture of the rifted margin develops mainly through the lateral and downdip interaction between these faults.
By defining these structural domains in a novel way, this study places low-angle, high-displacement faults within a broader framework. This perspective will help researchers better understand the lateral variability of rift-forming processes and, ultimately, how these margins—and their economically important sedimentary deposits—evolve. (Tectonics, https://doi.org/10.1002/2017TC004792, 2018)
—Terri Cook, Freelance Writer
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