Magmatische Prozesse und Kontinentalzerspaltung: Eine integrierte Untersuchung mittels numerischer Modellierung und geophysikalischer Beobachtungen
Zusammenfassung der Projektergebnisse
DFG funding was received to support work on understanding the processes involved with continental rifting and breakup and the establishment of seafloor spreading systems. It is now recognized that rifted margins have a variety of volcanic characteristics, ranging from those with large amounts of magmatism to those that are magmatically starved. The underlying causes and processes responsible for the remarkable diversity in magmatic productivity associated with continental breakup remain poorly understood and are a matter of intense current research and debate. The work funded by this project included numerical modeling of the magmatic processes associated with breakup and work on observational evidence from key rifted margins. Volcanic rifted margins are manifested by the accretion of exceptionally thick new crust during the first 2-3 Myr of seafloor spreading. Crustal thicknesses on the order of 15 km, or double the average for oceanic crust worldwide, are typical and extremes of as much as 30 km have been interpreted. The commonly agreed source of excess volcanism, deep seated mantle plumes, is still questioned by several authors. Several alternative mechanisms have been proposed, including the possibility of edge-driven convection that may develop near steep lithospheric boundaries. The other end member is dominated by tectonic extension with only minor amounts of melt production. On these margins, extension is accommodated by block faulting and mechanical exhumation of the mantle, which then interacts with seawater to form a layer of serpentinite with crust-like seismic velocities, not unlike Hess’s original proposal for the nature of the world’s oceanic basins. As it is generally assumed that the thermal state of the asthenosphere is such that it is very close to the solidus temperature, the apparent lack of pressure release melting on these margins is particularly enigmatic. A key aspect of rifted margin evolution is the importance of asymmetry and pre-existing structure. This is well established for amagmatic margins and understanding the causes and consequences of asymmetry has received significant recent attention. It has been hypothesized that magmatic asymmetry on volcanic margins is possible and could be important for understanding magmatic accretion during breakup. This is has now been clearly demonstrated for the case of SE Greenland / Hatton Bank conjugate pair, where nearly two-thirds of the new crust created during first 3 Myr of spreading accreted to the Greenland margin. Asymmetry may thus be a fundamental aspect of breakup and the establishment of a seafloor spreading system.
Projektbezogene Publikationen (Auswahl)
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2003. Mantle Melting during Continental Breakup. 8th European Workshop on Numerical Modeling of Mantle Convection and Lithospheric Dynamics, Hruba Skala, Czech Repulic, Sept. 13-18
Hopper, J. R., and T.K. Nielsen
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2003. Modeling Mantle Melting During Continental Breakup: Implications for Anomalous Volcanic Productivity at Rifted Margins. Eos Trans. AGU, 84 (46), Abstract V31A-03
Hopper, J.R., and T.K. Nielsen
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2004. From Rift to Drift: Mantle Melting During Continental Breakup. Geochem. Geophys. Geosys. 5, Q07003
Nielsen, T.K., and J.R. Hopper
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2004. Magmatic Processes and Continental Breakup. GDP03, DGG annual meeting, Berlin
Hopper, J. R., T.K. Nielsen, J. Phipps-Morgan
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2004. Numerical Modeling of Melting During Continental Breakup. InterMARGINS workshop: IMEDL, Pontresina, Switzerland July 11-16, 2004
Hopper, J.R., and T.K. Nielsen
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2004. Rifting Between Iberia and Newfoundland: New Results from SCREECH Line 1 Show First-Order Asymmetries. InterMARGINS workshop: IMEDL, Pontresina, Switzerland July 11-16, 2004
Hopper, J.R., T. Funck, B.E. Tucholke, H.C. Larsen, W.S. Holbrook, K.E. Louden, D. Shillington, and H. Lau
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2004. Volcanic Productivity During Continental Breakup from Numerical Models of Mantle Convection with Application to Atlantic Rifted Margins. Eos Trans. AGU, 85 (17), Abstract T31D-02
Hopper, J.R., and T.K. Nielsen
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2006. A Deep Seismic Investigation of the Flemish Cap Margin: Implications for the Origin of Deep Reflectivity and Evidence for Asymmetric Breakup between Newfoundland and Iberia. Geophys. J. Inter. 164, 501–515
Hopper, J.R., T. Funck, B.E. Tucholke, K.E. Louden, W.S. Holbrook, and H.C. Larsen
