Mantle compensation of active metamorphic core complexes at Woodlark rift in Papua New Guinea

Publication Type  Journal Article
Year of Publication  2002
Authors  Abers, G. A.; Ferris, A.; Craig, M.; Davies, H.; Lerner-Lam, A. L.; Mutter, J. C.; Taylor, B.
Journal Title  Nature
Volume  418
Issue  6900
Pages  862-865
Journal Date  Aug 22
ISBN Number  0028-0836
Accession Number  ISI:000177555600034
Key Words  lower-crust; dentrecasteaux islands; seismic evidence; beneath; origin; region; tomography; evolution; extension; flow
Abstract  

In many highly extended rifts on the Earth, tectonic removal of the upper crust exhumes mid-crustal rocks, producing metamorphic core complexes. These structures allow the upper continental crust to accommodate tens of kilometres of extension(1), but it is not clear how the lower crust and underlying mantle respond. Also, despite removal of the upper crust, such core complexes remain both topographically high and in isostatic equilibrium. Because many core complexes in the western United States are underlain by a flat Moho discontinuity(2,3), it has been widely assumed that their elevation is supported by flow in the lower crust(4-6) or by magmatic underplating(7). These processes should decouple upper-crust extension from that in the mantle. In contrast, here we present seismic observations of metamorphic core complexes of the western Woodlark rift that show the overall crust to be thinned beneath regions of greatest surface extension. These core complexes are actively being exhumed(8) at a rate of 5-10 km Myr(-1), and the thinning of the underlying crust appears to be compensated by mantle rocks of anomalously low density, as indicated by low seismic velocities. We conclude that, at least in this case, the development of metamorphic core complexes and the accommodation of high extension is not purely a crustal phenomenon, but must involve mantle extension.

Notes  

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URL  <Go to ISI>://000177555600034
DOI  Doi 10.1038/Nature00990