The role of syn-rift magmatism in the rift-to-drift evolution of the West Iberia continental margin: geophysical observations

Abstract

The presence of a well-defined ocean-continent transition (OCT) and the absence of large volumes of extrusive or intrusive rocks on the West Iberia margin make it a good place to investigate how the largely amagmatic rifting and break-up of continental lithosphere evolves into oceanic crust produced by magmatic sea-floor spreading. In the southern Iberia Abyssal Plain there is a broad OCT with a characteristic seismic and magnetic character, distinct from both thinned continental crust and normal oceanic crust, which supports the notion that it consists predominantly of exhumed and serpentinized mantle. Interpretations of magnetic and seismic data indicate that on average only small amounts of syn-rift melt exist within the OCT. Isolated, probably margin-parallel, intrusive melt bodies are scattered within the eastem part of the OCT well beneath the top of acoustic basement. Within the western part of the OCT, closer to unambiguous sea-floor spreading magnetic anomalies, such bodies were later(?) emplaced at higher levels and more closely together in the basement until eventually sea-floor spreading began. The evidence does not support the hypothesis that ultraslow sea-floor spreading can explain the magnetic anomalies observed within the wider parts of the West lberia OCT, where the OCT evolution is best resolved.

Geological setting and structural styles of Volcanic Massive Sulfide deposits in the northern Apennines (Italy): evidence for seafloor and sub-seafloor hydrothermal activity in unconventional ophiolites of the Mesozoic Tethys

“…Early geodynamic evolution of the basin occurred in a slowspreading center as a result of passive and asymmetric extension of the continental crust that caused exhumation of the upper mantle onto the seafl oor, formation of numerous, ephemeral magma chambers at low depth in the oceanic lithosphere and outfl ow of small volumes of extrusive volcanic rocks (Piccardo et al, 2002). The resulting unconventional oceanic crust may have its modern analogues in the northern Red Sea embryonic ocean (Barret, 1982;Nicolas, 1984;Piccardo et al, 2002) or in the ocean-continent transition of the western Iberia margin discovered at site 897 of the Ocean Drilling Program (Gibson et al, 1996;Whitmarsh et al, 2001).…”

Diachronous evolution of Late Jurassic–Cretaceous continental rifting in the northeast Atlantic (west Iberian margin)

“…In parallel, Michon and Merle [2003] have compared, and modeled, lithospheric extension on different passive margins, concluding that there is a shift in the principal locus of extension from interior rift basins to the deeper margin during the last stages of continental rifting, i.e., during the advanced rifting stage of Manatschal andBernoulli [1998, 1999]. In both evolution models, a period of $25 Ma of (synrift) stretching commonly precedes continental breakup [Whitmarsh et al, 2001].…”

Extension, hyperextension and mantle exhumation offshore Norway: a discussion based on 6 crustal transects

“…Ranero & Pérez-Gussinyé, 2010;Sutra et al, 2013). Since the dredging of serpentinised mantle rocks at the Iberian margin (Boillot et al, 1980) and their subsequent drilling by several ODP Legs (Shipboard Scientific Party, 1987a, b, 1994, 2004, pertinent questions at deep margins relate to the degree of crustal thinning and to whether mantle was exhumed to the seafloor during large-magnitude extension (Whitmarsh et al, 2001;Manatschal et al, 2007;Péron-Pinvidic & Manatschal, 2009;Lundin & Doré, 2011;Péron-Pinvidic et al, 2013). Since the geophysical properties of continental crystalline crust and serpentinised subcontinental mantle overlap considerably, this question cannot be answered easily for margins that were not drilled to crystalline basement.…”

“…Since the geophysical properties of continental crystalline crust and serpentinised subcontinental mantle overlap considerably, this question cannot be answered easily for margins that were not drilled to crystalline basement. Thus, one of the benchmarks of hyperextension identified in the Iberia-Newfoundland system, the exhumation of serpentinised mantle to the seafloor (Boillot et al, 1980;Manatschal et al, 2001;Whitmarsh et al, 2001), cannot be proven directly offshore Norway. Several workers have, however, discussed the possibility, and some have suggested that it may have occurred, based on interpretation of seismic reflection data, refraction data, potential field data and modelling (Ren et al, 1998;Osmundsen & Ebbing, 2008;Lundin & Doré, 2011;Reynisson et al, 2011;Péron-Pinvidic et al, 2012Rüpke et al, 2013).…”