Structure of the SE Greenland margin from seismic reflection and refraction data: Implications for nascent spreading center subsidence and asymmetric crustal accretion during North Atlantic opening

Abstract

[1] Seismic reflection and refraction data from the SE Greenland margin provide a detailed view of a volcanic rifted margin from Archean continental crust to near-toaverage oceanic crust over a spatial scale of 400 km. The SIGMA III transect, located $600 km south of the Greenland-Iceland Ridge and the presumed track of the Iceland hot spot, shows that the continent-ocean transition is abrupt and only a small amount of crustal thinning occurred prior to final breakup. Initially, 18.3 km thick crust accreted to the margin and the productivity decreased through time until a steady state ridge system was established that produced 8-10 km thick crust. Changes in the morphology of the basaltic extrusives provide evidence for vertical motions of the ridge system, which was close to sea level for at least 1 m.y. of subaerial spreading despite a reduction in productivity from 17 to 13.5 km thick crust over this time interval. This could be explained if a small component of active upwelling associated with thermal buoyancy from a modest thermal anomaly provided dynamic support to the rift system. The thermal anomaly must be exhaustible, consistent with recent suggestions that plume material was emplaced into a preexisting lithospheric thin spot as a thin sheet. Exhaustion of the thin sheet led to rapid subsidence of the spreading system and a change from subaerial, to shallow marine, and finally to deep marine extrusion in $2 m.y. is shown by the morphological changes. In addition, comparison to the conjugate Hatton Bank shows a clear asymmetry in the early accretion history of North Atlantic oceanic crust. Nearly double the volume of material was emplaced on the Greenland margin compared to Hatton Bank and may indicate east directed ridge migration during initial opening.

Moho and basement depth in the NE Atlantic Ocean based on seismic refraction data and receiver functions

“…9). Between the Jan Mayen microcontinent and mid-Norway, the initial crustal thickness at break-up was around 11 km (Breivik et al 2006), which is less than that observed in SE Greenland at a similar distance from the Iceland plume (19 km: Hopper et al 2003). Close to the extinct Aegir Ridge, the crustal thickness is as little as 4 km (Breivik et al 2006).…”

“…Along this line, the Moho depth varies between 39 and 52 km, which is substantially more than the maximum Moho depth of 33 km on the two nearby lines 3 (Hopper et al 2003) and 4 (Holbrook et al 2001) of the SIGMA experiment. DLC 94 line 5 has a difficult geometry, with a crooked shot line along the coast and only three receivers onshore.…”

Regional distribution of volcanism within the North Atlantic Igneous Province

“…Gregg & Fornari 1998). The outer SDRs are interpreted to indicate a transition from shallow to deep water, where the water pressure prevents degassing and large sheets flows can form, similar to the subaerial eruptions (Gregg & Fornari 1998;Planke et al 2000;Hopper et al 2003). The seismic characteristics of both SDR units are similar, however (Fig.…”

“…Along the North Atlantic margins, they straddle the COB and the first identifiable seafloor spreading anomalies are typically within this volcanic facies unit. For example, along both the Vøring and SE Greenland margins, magnetic anomaly C24 is well identified and within the mapped inner SDRs (Hopper et al 2003;Breivik et al 2009;respectively). The COB is typically located near to where the thickest new igneous crust is observed, since oceanward the entire crust is volcanic whereas continentward, only a portion of the crust is volcanic.…”

“…An example from SE Greenland is shown in Figure 7. This example is based on the seismic reflection and refraction profile of Hopper et al (2003). The inner SDRs span a distance of over 100 km and the seawardmost extent are emplaced within unambiquous oceanic crust (Chron C24, see Hopper et al (2003)).…”