Polyphase Magmatism During the Formation of the Northern East Greenland Continental Margin

Abstract

New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors, which are found to decrease in size both northward and southward from a central point at 75°N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the seaward dipping reflectors have been emplaced over a period of 2–4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40‐Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The breakup of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southward, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone.

Along‐Margin Variations in Breakup Volcanism at the Eastern North American Margin

“…Our 3‐D magnetic model assumed a constant magnetization of 5 A/m throughout the volcanic wedge with an inclination of 45° and a declination of −2° based on the estimates of the Jurassic geomagnetic pole (Austin et al, 1990; Talwani et al, 1995). This magnetization is consistent with drilling results that penetrated SDRs at other margins (see Davis et al, 2018, their figure 3) and is similar to the magnetization used in 2‐D magnetic modeling of volcanic wedges at both the ENAM (Figure S1) (Austin et al, 1990; Talwani et al, 1995) and other volcanic rifted margins (e.g., Bauer et al, 2000; Franke et al, 2019). We also validated this magnetization with a 2‐D magnetization inversion (Figure S3) (Parker & Huestis, 1974).…”

“…Along-axis magmatic segmentation is a feature of both presently active rifts (e.g., Beutel et al, 2010;Hammond et al, 2013;Hayward & Ebinger, 1996;Keir et al, 2013;Manighetti et al, 1998Manighetti et al, , 2001) and magma-rich rifted continental margins (Collier et al, 2017;Franke et al, 2019;Geoffroy, 2005;Koopmann et al, 2014). The greater amount of magma in the center of these segments is related to along-margin variations in extension during breakup (Ebinger & Casey, 2001;Geoffroy, 2001).…”

“…Horizontal volcanic flows are erupted subaerially before acquiring a seaward dip from either magmatic loading and thermal subsidence of the lithosphere or slip along bounding normal faults (Buck, 2017; Morgan & Watts, 2018). The volcanic wedge is associated with and likely responsible for a high‐amplitude, margin parallel magnetic anomaly (e.g., Berndt et al, 2001; Collier et al, 2017; Corner et al, 2002; Davis et al, 2018; Franke et al, 2019; Keen & Potter, 1995). The presence of breakup volcanic wedges has been confirmed by drilling at the Greenland and Norwegian margins (e.g., Eldholm et al, 1989; Vandamme & Ali, 1998), and analogous volcanic flows exist at modern rift sites, such as the Afar region of Ethiopia (e.g., Bastow & Keir, 2011; Beutel et al, 2010; Keir et al, 2013).…”

The extent of continental material in oceans: C-Blocks and the Laxmi Basin example

“…Because of their extrusive nature and seaward development with time (Geoffroy 2005 , Fig. 2), SDRs are associated with linear but segmented magnetic anomalies (Larsen & Jakobsdóttir 1988;Behn & Lin 2000;Stica et al 2014;Franke et al 2019). Pairs of magnetic anomalies are also found in Afar where magmatic continental break-up is underway (Bridges et al 2012).…”

Icelandia

“…The NE Atlantic Ocean basin also opened in a piecemeal way, but there, embryonic spreading ridges to the north and south of the Nagssugtoqidian orogen propagated in opposite directions (Franke et al, 2019;Gernigon et al, 2019). At ca.…”