Southeast Baffin volcanic margin and the North American-Greenland plate separation

Plate breakup over plumes is characterized by the development of margins sh owing extensive magma production both underplated at Moho level and extrude d as thick piles of seaward dipping lava formations. The Disko-Svartenhuk a rea in west Greenland is one of the few places in the world with exposed se award dipping basalts forming a prism whose thickness increases seaward. We present a quantitative tectonic study of this margin, which we tentatively restored in its geodynamic position during the different stages of plate s eparation between Greenland and North America. Our structural data are cons trained with recently published Ar-39/Ar-40 and new and coherent K-40/Ar-40 geochronology in dikes of different orientations. The first-order structur e is that of a tectonically-driven seaward crustal flexure linked to defini tive plate breakup between Greenland and Baffin Island during the Eocene, c oeval with the formation of the upper part of the exposed seaward dipping v olcanic prism. This flexing is associated with a significant crustal stretc hing associated with arrays of continentward dipping normal faults. This ac ross-strike structure is correlated to a fundamental along-strike segmentat ion with the three "segments" adopting a "zigzag" strike, There is a clear increase of extensional strain at the extremities of the segments, Eocene e xtension trended N060 on average in the northern and southern segments but was NW trending in the central NE trending Nugssuaq segment. We discuss the interpretation of such an extension perpendicular to the different margin segments. From a regional point of view the N060 extension is distinct in o rientation from the approximately N-S trend of plate separation between Nor th America and Greenland in the Baffin Bay during the Eocene. However, the extension recorded in the margin is nearly perpendicular to the obliquely s preading Eocene accretion axis in the Baffin Bay. This latter point suggest s a mantle or ridge control of the development of the margin over regional far-field lithospheric stress models.