Paleomagnetic inclinations in DSDP Hole 417D reconsidered: Secular variation or variable tilting?

Abstract

In Deep Sea Drilling Program (DSDP) Hole 417D in the western central North Atlantic, dips of pillow margins measured in the upper and lower part of basement correlate with tilts predicted from paleomagnetic inclinations in the corresponding parts of the hole. A ∼40° westward dip of the seafloor around 417D matches the tilt predicted from inclinations and pillow margin dips in the uppermost lavas. The correlation suggests that most of the large long-wavelength inclination variation in Hole 417D is caused by variable tilting about an axis more or less parallel to the paleo rift rather than by secular variation. The variable tilt in Hole 417D is interpreted as the sum of rotation due to lava loading along the Mesozoic paleo rift and a later block rotation of ∼40° in the rift valley walls. This interpretation allows a reconstruction of the paleo rift environment in which the 417D upper crust formed.