CRUSTAL STRUCTURE OF THE WEST GREENLAND IGNEOUS PROVINCE – IMPLICATIONS FOR TECTONO-MAGMATIC EVOLUTION

The Labrador Sea and Baffin Bay form an extinct early Cenozoic spreading system, between Greenland and North America. The two basins are separated by the Davis Strait, which is underlain by continental crust, has accommodated major strike-slip motion and hosts voluminous igneous rocks as part of the West Greenland Igneous Province (WGIP), which formed coevally with continental breakup. The WGIP includes various basaltic flows and intrusions on- and offshore. The formation of these features is poorly understood, but may be linked to interactions between plate kinematic changes, pre-existing structure and sub-lithospheric processes.

Information on the crustal structure is provided by sparse deep geophysical models offshore and only few seismic stations onshore. This inhibits estimates of extent and volumes of volcanics, and models of magmatic processes. Furthermore, uplift and erosion may have removed much of the geological record and the Greenland ice sheet limits mapping inland.Here, we investigate the crustal structure by means of joint inversion of receiver functions and P-wave polarisation at seismic stations along the West Greenland margin, with focus on the high velocity lower crust (HVLC) that may be indicative of intruded lower crust.

The results indicate ~4.5 km thick HVLC beneath southern Disko Island, the southern limit of the onshore basalts. The thickest HVLC is estimated further south across Disko Bay, where no volcanic rocks are present. On the mainland east of Disko Island, no indication for HVLC is found, suggesting that magmatism terminated in Disko Bay.

Further north, coincident with volcanic flows, the HVLC is estimated to be ~4.5-5.5 km thick. Just to the north of the onshore volcanics ~3.5 km thick HVLC is found, while the northernmost station shows no signs of HVLC.

HVLC is also absent ~200 km south of Disko Bay, and 150 km inland, while at the southernmost station, Nuuk, a ~3.5 km thick HVLC is estimated. Nuuk is ~200 km away from the magma-rich margin, indicating that volcanism extended this far inland.

The presence of HVLC generally coincides with areas covered by subaerial volcanics. Immediately north and south of the onshore basalt flows, the results suggest a larger extent of the area affected by magmatism than surface rocks suggest. The results also provide spatial limits of magmatic activity east of Disko Island. The new models provide information on the spatial distribution, thicknesses and potentially compositions of deep intrusions and thereby contribute to our understanding of how the WGIP was formed.