A moderate melting model for the Voring margin (Norway) based on structural observations and a thermo-kinematical modelling: Implication for the meaning of the lower crustal bodies
|Author(s)||Gernigon Laurent1, 6, Lucazeau Francis2, Brigaud Frederic3, Ringenbach Jean-Claude4, Planke Sverre5, Le Gall Bernard1, 6|
|Affiliation(s)||1 : IFREMER, F-29280 Plouzane, France.
2 : CNRS, Inst Phys Globe, F-75252 Paris 05, France.
3 : Ctr Sci & Tech Jean Feger, Total Pau, F-64018 Pau, France.
4 : Total GSR PN, F-92078 Paris, France.
5 : VBPR, PGP, N-0349 Oslo, Norway.
|Source||Tectonophysics (0040-1951) (Elsevier), 2006 , Vol. 412 , N. 3-4 , P. 255-278|
|WOS© Times Cited||68|
|Keyword(s)||Mantle plume, Norwegian margin, Underplating, Breakup, Modelling, Rifting, Volcanic margins|
|Abstract||High P-wave velocities (7.1-7.8 km/s) lower crustal bodies (LCBs) imaged along volcanic margins are commonly interpreted as plume and break-up-related thick mafic underplating. This interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer Voring Basin (Norway). An exceptional strong amplitude reflection, the T Reflection, is particularly well defined below the North Gjallar Ridge (NGR) between 7 and 8 s TWT. The T Reflection is located near the volcanic lava flows emplaced during the NE Atlantic breakup (similar to 55-54 Ma ago) and coincides with the top of the LCB, forming a mid-crustal dome. Based on structural and temporal relationships, we show that the dome clearly influences the structural development of the NGR and predates the continental breakup at least by 10-15 Ma. Using a thermo-kinematical model, we tried also to investigate and quantify the relationships between the extension, LCB and the magmatic production. Modelling suggests that significant Paleocene-Early Eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the break-up initiation. The conclusion of 2D thermo-kinematical parametric analysis is that the magmatic model predicts, either little extension (beta < 2) with no melting or high extension (beta > 5) with significant melting along the outer Voring Basin. We suggest that the continental part of the LCB could not necessarily be breakup-related and so magmatic, as has often been stated previously. It is concluded here that the continental part of the LCB observed beneath the outer Voring Basin may be partly (or fully) attributed to inherited, high-pressure granulite/eclogite lower crustal rocks. The real amount of mafic material emplaced along the outer Voring Basin could be 20-40% less than thought.|