Mantle Flow Patterns Above Subducted Continental Crust Using Olivine Lattice Preferred Orientations from the Bjørkedalen Peridotite, Western Norway

O'Daniel, Jamie Lee
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Lattice preferred orientations (LPO) of olivine within the Bjørkedalen 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. Few studies have been performed on large in-situ peridotite bodies to analyze how slip varies based on its location within the body. Water content, temperature, and stress are the three main factors affecting LPO development, thus such data reveal the boundary conditions accompanying flow above a subducting plate.

The samples were collected from margins to center of the peridotite body, to illustrate the texture and olivine LPO transition from the slab interface up into the overlying mantle. The samples range from highly serpentinized peridotite with a weak or absent foliation and lineation, to strongly foliated and lineated, or undeformed peridotite. The fabric becomes progressively less prominent and less serpentinized from the boundary towards the center of the peridotite; the central parts of the body are weakly foliated. The texture present within the peridotite body varies from porphyroclastic transitioning into equigranular to equigranular texture. The sparse equigranular texture is located in a thin strip oriented E-W just above the syncline fold axes. The porphyroclastic transitioning into equigranular texture is found throughout.

Results showed that the Bjørkedalen Peridotite utilized [001] {110}, [001] (100), and [100] (001) slip systems. The peridotite body was emplaced during subduction with a dominant slip system of [001] {110} and [001] (100) implying conditions of i) low to moderate temperature; ii) high pressure; iii) low to moderate water content, and iv) moderate to high stress.

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Continental Subduction, EBSD, LPO, Mantle Flow, Olivine, Peridotite