Deep velocity structure of rifted continental crust, U.S. Mid‐Atlantic Margin, from wide‐angle reflection/refraction data

Abstract

We present new ocean‐bottom, wide‐angle seismic data, collected during the 1990 EDGE Mid‐Atlantic multichannel seismic experiment, which provide a measurement of the deep velocity structure of rifted Appalachian continental crust beneath the U.S. East Coast continental margin. Reflections from the entire crust and Moho are visible from offsets of zero to 100 km. One‐dimensional inverse traveltime modeling reveals a 34‐km‐thick crust consisting of four layers beneath the post‐rift sediments, with velocities of 5.9, 6.3, 6.4, and 6.85 km/s. This velocity structure is indistinguishable from that found beneath several Appalachian terranes in the northern Appalachians of New England. The average velocity of 6.85 km/s in the lower crust limits the landward extent of the high‐velocity (7.2‐7.4 km/s) lower crust found farther seaward, and supports the interpretation of that layer as the result of rift‐related magmatic underplating, rather than as thinned, pre‐existing lower continental crust.

The Role of Premagmatic Rifting in Shaping a Volcanic Continental Margin: An Example From the Eastern North American Margin

“…The discovery of magmatic material, that was accreted during the latest stages of rifting and earliest seafloor spreading, led to the recognition of the volcanic nature of the ENAM (Austin et al, 1990;Holbrook et al, 1992Holbrook et al, , 1994Holbrook & Kelemen, 1993;Keen & Potter, 1995;Kelemen & Holbrook, 1995;LASE, 1986;Lizarralde & Holbrook, 1997;Talwani et al, 1995;Tréhu et al, 1989). Holbrook and Kelemen (1993) correlated intrusive and extrusive bodies, recognized on several wide-angle seismic profiles along the margin, to a margin-parallel positive magnetic anomaly known as the East Coast Magnetic Anomaly (ECMA, Figure 2).…”

“…The most pronounced characteristic of volcanic margins is the magmatic addition related to their latest stage of formation. These include a thick (<20 km) wedge of subaerially emplaced volcanic rocks, which were imaged on seismic reflection data as oceanward/seaward dipping reflectors (SDR) (Figure 1b; Hinz, 1981; Mutter et al, 1982; Planke et al, 2000) and an intruded and/or underplated lower crust (e.g., Abdelmalak et al, 2017; Eldholm et al, 1995; Holbrook et al, 1992; Menzies et al, 2002; White et al, 1987). SDR emplacement occurs on top of seaward tilting blocks composed of intruded continental or oceanic crust (Geoffroy, 2005; Stica et al, 2014).…”

Geologic transect across the Grenville orogen of Ontario and New York

“…To determine a true vertical depth of the crust-mantle boundary, the crustal velocity structure should be known. If the CMP profiles are not accompanied by refraction seismic studies, uncertainty in determination of depth can reach 5-6 % [Holbrook et al, 1992].…”

The role of pre-magmatic rifting in shaping a volcanic continental margin: An example from the Eastern North American Margin

“…The most pronounced characteristic of volcanic margins is the magmatic addition related to their latest stage of formation. These include a thick (<20 km) wedge of subaerially emplaced volcanic rocks, which were imaged on seismic reflection data as oceanward/seaward dipping reflectors (SDR) (Figure 1b; Hinz, 1981;Mutter et al, 1982;Planke et al, 2000) and an intruded and/or underplated lower crust (e.g., Abdelmalak et al, 2017;Eldholm et al, 1995;Holbrook et al, 1992;Menzies et al, 2002;White et al, 1987). SDR emplacement occurs on top of seaward tilting blocks composed of intruded continental or oceanic crust (Geoffroy, 2005;Stica et al, 2014).…”