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Ophiolites are tectonically transported assemblages of peridotite and other ultramafic rocks, gabbro, diabase, and mafic pillow lavas, commonly capped by chert or other pelagic sedimentary rocks.
1987, Precise U-Pb isotopic ages of diabase dykes and mafic to ultramafic rocks using trace amounts of baddeleyite and zircon, in Halls, H.
A similar age of activity is found in the "Southwestern USA Diabase Province", and in the Moores Lake sills of the Athabasca Basin (1000 km to the northwest).
Holes YD-07-37 and YD-07-42 on the western side of the Lower Boundary zone were either terminated for technical reasons (too much deviation from the intended target) or they intersected diabase dykes at the target horizon.
Irregular enclaves and sheets of diabase occur within this fine-grained granite, with textures suggesting that the mafic magma was immiscible (cf.
This was followed by the intrusion of andesite and diabase dikes.
Faulting was followed by crustal extension, the formation of sedimentary basins, diabase volcanism and, finally, kimberlite emplacement about 1 billion yr ago.
Subsequent tectonic activity forced magma into the Triassic sediments, forming extensive intrusive diabase sills, such as those exposed by later erosion at the Palisades Cliffs and Round Valley.
Low-grade lateritic bauxites are found on chlorite-amphibole schists and diabase porphyrite.
Hole YD06-31 was also completed in the area, but the zone was bisected by a diabase dyke.