Late Miocene sills and dikes in the Paiute Ridge area of southern Nevada were emplaced in an extensional setting beneath a small volume, alkali basaltic volcano. Dikes (400-5000 m long, 1.2-9 m wide) mostly occupy pre-existing E-dipping normal faults. Three small sills (extending laterally up to ~500 m, and 20-46 m thick) and two larger sills (each having lateral dimensions ~1 km) locally branch off some dikes within ~250 m of the paleosurface. Individual small sills extend only into the hanging wall blocks of the faults that host their parent dikes, and are connected to the dikes by stems that are only a few tens of meters wide; elsewhere along their strikes the parent dikes extend above the sills. We infer that sill emplacement was caused by local rotation of principal stresses related to the intersection of the dike-hosting fault planes with the complex contact between relatively strong Paleozoic carbonates and weak Tertiary tuffs. This effect might have been accentuated by co- intrusive displacement along the faults as they were lubricated by magma, an interpretation that is corroborated by hydromechanical calculations. Orientation of bedding planes in the tuffs controlled the direction of sill propagation. The three most areally extensive sills formed lopoliths with sagging roofs, indicating interaction with the free surface. Both the bedding plane and free surface interactions contributed to the dish-shaped geometry of some of the sills (Ref: Earth Planet. Sci. Lett. 246, 217-230, 2006).
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 8486 Field relationships (1090;
- 8499 General or miscellaneous