Field evidence suggests that the contact between the A and B divisions of the peridotitic komatiites, exposed at Spinifex Ridge, La Motte Township, Quebec, is erosional. The B division commonly shows parallel and (or) oblique layering which may occur in sequences. Reverse grading of hopper olivine crystals is observed at the top of the B division, whereas the underlying more equant, solid olivine crystals may be normally graded. These observations suggest that, for the La Motte komatiites, the spinifex (A) division formed first causing a diminution of the hydraulic radius of the conduit, leading to an increased velocity and turbulent underflow that produced the structures observed in the B division.

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