An Investigation of AMS in Oman Ophiolite Gabbros

Crustal accretion processes at mid-ocean ridges are still poorly understood, and several competing models exist that try to explain exactly how magma from the mantle is incorporated into oceanic crust at a crustal spreading center. Ophiolites, or fragments of oceanic crust exposed on land, are useful sites at which to conduct rock fabric studies to understand oceanic crust formation processes. This study focuses on samples of upper foliated gabbros taken from the Oman ophiolite in order to characterize their fabric orientations and contribute to a better model of crustal formation. Much of the focus of this study is on using and interpreting anisotropy of magnetic susceptibility (AMS) as a method for measuring rock fabric directions. From our study site near the Maqsad diapir on the Sumail Massif, we found a magnetic foliation oriented NW-SE, subparallel to the nearest inferred spreading ridge and dipping steeply to the SW. The magnetic lineation from most of our samples was plunging moderately to the NW, towards the diapir. Comparison with shape-preferred orientation (SPO) measurements and other magnetic experiments indicate that our AMS fabrics match well with crystal fabrics, at least in foliation direction, and the magnetic susceptibility of our samples is largely due to secondary magnetite in serpentinized olivine.