Structural Evolution of the Rifted Margin off Northern Labrador: The Role of Hyperextension and Magmatism

Abstract

AbstractHigh‐quality seismic reflection data from the offshore northern Labrador rifted margin allow imaging of the extended and rifted crust both along and across the continental margin and are described in conjunction with available seismic velocity and gravity data. The margin formed within cold, thick cratonic lithosphere. Both Archean continental basement and a discrete, undulating, high‐amplitude, deep reflection about 10 km below basement are observed. The deeper reflection can be correlated with the crust‐mantle boundary as measured on previous wide‐angle seismic data in the region. This reflection, termed here the L‐reflection, appears to be the equivalent to other top‐mantle detachments found elsewhere on magma‐poor rifted margins. However, normal mantle velocities have been observed to lie just below the reflection, suggesting that it may not be related to the formation of weak serpentinized mantle. A high‐velocity and density zone occupies the outer shelf seaward of the L‐reflection where basement is transparent, which may represent highly mafic crust or serpentinized mantle. A crustal reconstruction of this margin and its conjugate shows marked asymmetry, with a wider zone of crustal thinning on the Greenland margin. These crustal thinning profiles are comparable to those on other conjugate margins within cratonic lithosphere. While some of the attributes of this margin are those of a magma‐poor system, at the ocean‐continent transition, thick igneous crust created a magma‐rich zone in Paleocene time when a hot spot was active in the Davis Strait to the north. Thus, this margin exhibits characteristics of both magma‐rich and magma‐poor systems.