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The East Greenland coast-parallel dike swarm is exposed along ~250 km of the outermost coast south of the Iceland hotspot track manifest by the Iceland-Greenland Ridge. The dike swarm and associated plutonic centers were emplaced over a period extending from a few million years before µnal breakup to at least 7 m.y. after breakup ca. 56 Ma. The predominantly maµc dikes are hosted in Precambrian high-grade basement, but locally cut through early Tertiary plutonic complexes. Seaward, continental crust is replaced by 20-30-km-thick Icelandic-type igneous crust, including thick sequences of subaerially erupted lavas that dip oceanward. The orientations of dikes, dike thickness, dike density, µeld classiµcation, and relative sequence of emplacement of 1410 dikes within this region were studied in the µeld and by photogrammetry along 6 margin transects.Statistical treatment of the µeld data documents a shift in orientation of dikes from predominantly subvertical inland to predominantly landward dipping (as low as 40°) along the outer coast. The earliest dikes, largely intruded prior to breakup, have dip directions at right angles to the bedding of locally preserved lavas and sediments, implying subvertical intrusion of dikes followed by strong seaward rotation of the crust during breakup. Consistent with this, younger generations of dikes emplaced after breakup show steeper to almost vertical dips. The strikes of the earliest dikes suggest that these were intruded in an en echelon pattern and slightly oblique to the margin. These dikes are relatively thick (average 6-8 m) and may have been intruded subvertically from a deep source, possibly at the base of the crust. The other dikes deµne more curved, coast-parallel trajectories extending out from some of the major plutonic complexes and form partly overlapping dike swarm segments. Together with observed systematic decrease in dike density and increasing underrepresentation of thin dikes away from major igneous complexes, this suggests that with time crustal plutonic complexes became important reservoirs for lateral magma propagation along the margin.In cross section, the density of dikes increases seaward and reaches ~50% along the outer coast. The average dike thickness decreases from a maximum of 8 m inland to 3-4 m along the coast. A hinge line is located ~15 km inland and is deµned by landward rapidly decreasing dike density, maximum dike thickness, and, in general, subvertical orientation of dikes, except for a small population of early dikes that seems to have intruded along preexisting and landward-dipping faults. The parallel increase seaward in dike density and decreasing dike thickness suggests an ophiolitic sheeted dike complex (i.e., continent-ocean boundary) to be present offshore 20-40 km from the inland hinge line. The seaward ×exure of the crust is interpreted to re×ect initial tectonic extension by rotation of fault blocks followed by monoclinal ×exing due to loading by the

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U–Pb SHRIMP ages are reported for three rhyolite flows from the Lebombo rift region of the Karoo volcanic province. Two flows are interbedded with the Sabie River Basalt Formation and a third sample is from the overlying rhyolitic Jozini Formation. The interbedded rhyolites yield ages of 182.0 ± 2.1 and 179.9 ± 1.8 Ma, whilst the overlying Jozini Formation rhyolite yields an age of 182.1 ± 2.9 Ma. Combined with existing 40 Ar/ 39 Ar geochronology, the new SHRIMP data fine-tunes the chronology of the Karoo volcanic province and indicates the 12 km succession of volcanic rocks in the Lebombo rift were erupted in 1–2 million years and lends considerable support to the links between the Pleinsbachian–Toarcian extinction event and the global environmental impact of Karoo volcanism.