Abstract
The Labrador Sea and Baffin Bay form an extinct Palaeogene oceanic spreading system, divided by a major continental transform, the Davis Strait, with the whole region defined as the Northwest Atlantic. The Davis Strait hosts the Ungava Fault Zone and is the central structural element of the Davis Strait Large Igneous Province (DSIP) that formed broadly coeval with continental breakup to its north and south. While constraints on the crustal structure in this region primarily exist in the offshore, crustal models are limited onshore, which makes an interpretation of regional structures as well as the extent, and therefore origin of the DSIP extremely difficult to ascertain. Here, we have collected all available teleseismic data from the Northwest Atlantic margins and applied a receiver function inversion to retrieve station-wise velocity models of the crust and uppermost mantle. We integrate the outcomes with published controlled-source seismic data and regional crustal models to make inferences about the crustal structure and evolution of the Northwest Atlantic. In particular, we focused on constraining the spatial extent and origin of high velocity lower crust (HVLC), and determining whether it is generically related to the Davis Strait Igneous Province, syn-rift exhumed and serpentinised mantle, or pre-existing lower crustal bodies such as metamorphosed lower crust or older serpentinised mantle rocks. The new results allow us to better spatially constrain the DSIP and show the possible spatial extent of igneous-type HVLC across Southwest Greenland, Northwest Greenland and Southeast Baffin Bay. Similarly, we are able to relate some HVLC bodies to possible fossil collision/subduction zones/terrane boundaries, and in some instances to exhumed and serpentinised mantle.
Highlights
The Northwest Atlantic, here defined as the Labrador Sea and Baffin Bay (e.g. Abdelmalak et al, 2019), forms an extinct early Cenozoic spreading system separated by the Ungava Fault Zone underlying the Davis Strait bathymetric high (Figure 1 and 2)
The Labrador Sea-Baffin Bay oceanic basins and rifted margins are heavily segmented both structurally and in terms of igneous products (Skaarup et al, 2006; Heron et al, 2019) not least by the Davis Strait, which has acted as a transform between the offset Baffin Bay and Labrador Sea basins and hosts the Davis Strait Igneous Province (DSIP)
The Moho depth estimates from receiver function (RF) inversion in the study area are comparable to previously published data and regional models that are almost entirely based on independent data (Welford & Hall, 2013; Welford et al, 2018; Lebedeva-Ivanova et al, 2019),which is a good first indication that the estimates are geologically meaningful
Summary
The Northwest Atlantic, here defined as the Labrador Sea and Baffin Bay (e.g. Abdelmalak et al, 2019), forms an extinct early Cenozoic spreading system separated by the Ungava Fault Zone underlying the Davis Strait bathymetric high (Figure 1 and 2). Following initial continental rifting, beginning in the Early Cretaceous or possibly earlier (Larsen et al, 2009), the Labrador Sea-Baffin Bay spreading system is thought to have evolved in three stages – Palaeocene, Eocene, and Oligocene to present – including major changes in extension direction (Oakey & Chalmers, 2012). The DSIP formed largely coeval to continental breakup in the region (Abdelmalak et al, 2019; Clarke & Beutel, 2020). This structural and magmatic segmentation is to a larger degree controlled by pre-existing structures (Peace et al, 2018a; Peace et al, 2018b; Heron et al., 2019; Schiffer et al, 2020), but the dominant mechanism driving continental breakup in the region is debated
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