Crustal structure of the Hatton and the conjugate east Greenland rifted volcanic continental margins, NE Atlantic

Abstract

[1] We show new crustal models of the Hatton continental margin in the NE Atlantic using wide-angle arrivals from 89 four-component ocean bottom seismometers deployed along a 450 km dip and a 100 km strike profile. We interpret prominent asymmetry between the Hatton and the conjugate Greenland margins as caused by asymmetry in the initial continental stretching and thinning, as ubiquitously observed on ''nonvolcanic'' margins elsewhere. This stretched continental terrain was intruded and flooded by voluminous igneous activity which accompanied continental breakup. The velocity structure of the Hatton flank of the rift has a narrow continent-ocean transition (COT) only $40 km wide, with high velocities (6.9 -7.3 km/s) in the lower crust intermediate between those of the continental Hatton Bank on one side and the oldest oceanic crust on the other. The high velocities are interpreted as due to intrusion of igneous sills which accompanied the extrusion of flood basalts at the time of continental breakup. The variation of thickness (h) and P wave velocities (v p ) of the igneous section of the COT and the adjacent oceanic crust are consistent with melt formation from a mantle plume with a temperature $120-130°C above normal at breakup, followed by a decrease of $70-80°C over the first 10 Ma of seafloor spreading. The h-v p systematics are consistent with the dominant control on melt production being elevated mantle temperatures, with no requirement for either significant active small-scale mantle convection under the rift or of the presence of significant volumes of volatiles or fertile mantle.

Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental breakup

“…A common assumption describes a close spatial relationship between the SDRs and HVLC, whereby the HVLC represents intrusive equivalents of the erupted lavas which form the SDRs (White et al, 2008;White and Smith, 2009;Blaich et al, 2009). HVLC can make up a large part of the total magmatic output along volcanic rifted margins, and as studies in the North Atlantic have shown, variations in size and physical properties of the HVLC in these settings hold important clues to mantle melting scenarios (Fernàndez et al, 2010;Kelemen and Holbrook, 1995;Korenaga et al, 2002;Ridley and Richards, 2010;Voss et al, 2009;White et al, 2008).…”

A review of the NE Atlantic conjugate margins based on seismic refraction data

“…At magmarich margins, the interpretation of the COT becomes even more complicated as remnants of thinned continental crust may become indistinguishable from oceanic crust due to the break-up-related magmatic overprint. In the paper by White & Smith (2009), the COT was defined as the zone where a seaward increase in the average lower-crustal velocity is observed, indicating magmatic intrusions into older, seismically slower crust. With a dense spacing of seismic receivers, it is possible to determine the lower-crustal velocity distribution with sufficient resolution.…”

“…However, when velocity models from conjugate margins in the NE Atlantic are compared, there are often inconsistencies. For example, the initial seafloor spreading between SE Greenland and the Hatton margin seems to be highly asymmetrical, with a higher spreading rate on the Greenland side (White & Smith 2009). If this asymmetry is real or just perceived depends largely on the correct identification of the continent-ocean boundary (COB).…”

Controls on the location of compressional deformation on the NW European margin

“…This hypothesis bears similarities to that of Mjelde et al (2003Mjelde et al ( , 2005 in which the distribution of compressional structures was influenced by rigid blocks underlain by HVLC. There is a possible analogue on the Hatton margin, where the compressional structures lie just inboard of the approximately 40 kmwide zone adjacent to the ocean margin affected by mafic intrusion White & Smith 2009). …”

“…A magmatic origin has also been the preferred interpretation for the HVLC detected adjacent to the ocean margin in a series of seismic refraction experiments further south. Near the Faroe Islands and beneath the northern part of Hatton Bank, the iSIMM experiments revealed a 40 -50 km-wide zone of HVLC that was interpreted to be due to the intrusion of basic igneous sills at the time of break-up (White et al 2008;Roberts et al 2009;White & Smith 2009). Funck et al (2008) identified an extension of the HVLC beneath the northern part of the Hatton Basin below crystalline crust about 10 km thick, and interpreted this to be due to magmatic additions to the crust rather than partial serpentinization of the upper mantle.…”