MANTLE FLOW PATTERNS ABOVE SUBDUCTED CONTINENTAL CRUST USING OLIVINE LATTICE PREFERRED ORIENTATIONS FROM THE BJORKEDALEN PERIDOTITE, WESTERN NORWAY

Lattice preferred orientations (LPO) of olivine within the Bjorkedalen Peridotite in western Norway were analyzed using electron backscatter diffraction (EBSD) to determine the flow pattern and emplacement mechanism of the mantle above a subducted continental slab. Water content, temperature, and stress are the three main factors that affect how LPOs record patterns of flow. Other studies of olivine LPO within peridotite have concluded that the three most common types of slip are interchangeable when water content, temperature, and stress are varied. Overall, the bulk mantle is thought to be dominated by [100] (010) type slip. Olivine deformed in i) dry, high-temperature, and low-stress environments produces [100] (010) slip; ii) high-water content, lower-temperature, and high-stress produces [001] (010) slip; and iii) high-water content, high-temperature, and moderate-stress environment produces [001] (100) slip. Knowledge of olivine LPO thus reveals the boundary conditions accompanying flow above a subducting plate.

The samples were collected from the boundaries to center of the peridotite body, to illustrate the olivine LPO transition from the slab interface up into the overlying mantle. The samples range from highly serpentinized peridotites with a weak to absent foliation and lineation, to strongly foliated and lineated peridotites, to undeformed peridotites. The fabric becomes progressively more prominent and less serpentinized moving from the boundary towards the center of the Bjorkedalen Peridotite; the central parts of the body, however, are not foliated. The slip system present in the Bjorkedalen Peridotite will be illustrated with the results of the olivine LPOs thus representing the conditions present and flow pattern of the mantle above a subducted continental slab.