37. STRUCTURES WITHIN HOLE 917A, SOUTHEAST GREENLAND RIFTED MARGIN1Hervé Cambray2,3 |
ABSTRACTDuring Ocean Drilling Program Leg 152 at Hole 917A, downhole electrical images along with standard logs were recorded in the flood basalts that formed the seaward-dipping reflector sequences on the southeast Greenland margin. The Formation MicroScanner electrical images of the borehole are analyzed here in terms of geometry, and related to fractures and lava beds observed in the core. Despite the good core recovery for hard rocks (52% average), these images are essential to provide a continuous and oriented record of structures vs. depth. More than 9000 structural events were mapped over 425 m of imaged flood basalts (22 per m on average). The steep fractures that dominate this interval are oriented mainly in an east-west strike direction with a seaward dip. The tilt of lava beds is also estimated from 15° to 30°, and appears to be distinctly higher below 180 meters below seafloor. Both fracture and bed measurements show evidence of a slight clockwise rotation of the strike with increasing depth. These results address questions regarding deformation of this part of the southeast Greenland margin (mainly antithetical fracturing) to discuss a two-main-events tilting story associated with a rotation of the extensional direction. |
|