The gravity field over the Ungava Bay region from satellite altimetry and new land-based data: implications for the geology of the area

Gravity data were obtained along two transects on the southern coast of Ung ava Bay, which provide continuous gravity coverage between Leaf Bay and Geo rge River. The transects and the derived gravity profiles extend from the S uperior craton to the Rae Province across the New Quebec Orogen (NQO). Inte rpretation of the transect along the southwestern coast of Ungava Bay sugge sts crustal thickening beneath the NQO and crustal thinning beneath the Kuu jjuaq Terrane, east of the NQO. Two alternative interpretations are propose d for the transect along the southeastern coast of the bay. The first model shows crustal thickening beneath the George River Shear Zone (GRSZ) and tw o shallow bodies correlated with the northern extensions of the GRSZ and th e De Pas batholith. The second model shows constant crustal thickness and b odies more deeply rooted than in the first model. The gravity models are co nsistent with the easterly dipping reflections imaged along a Lithoprobe se ismic line crossing Ungava Bay and suggest westward thrusting of the Rae Pr ovince over the NQO. Because no gravity data have been collected in Ungava Bay, satellite altimetry data have been used as a means to fill the gap in data collected at sea. The satellite-derived gravity data and standard Boug uer gravity data were combined in a composite map for the Ungava Bay region . The new land-based gravity measurements were used to verify and calibrate the satellite data and to ensure that offshore gravity anomalies merge wit h those determined by the land surveys in a reasonable fashion. Three paral lel east-west gravity profiles were extracted: across Ungava Bay (59.9 degr ees N), on the southern shore of the bay (58.5 degrees N), and onshore simi lar to 200 km south of Ungava Bay (57.1 degrees N). The gravity signature o f some major structures, such as the GRSZ, can be identified on each profil e.