In 1972, geophysicist Dan McKenzie was among the first to recognize that patterns of fault block motion along the active zone of continental collision in Eurasia are best explained in terms of rigid microplates that act as dies or indenters. Indenters, such as Arabia, bulldoze the less rigid (plastic) crustal domains ahead into folded welts (e.g. Iran) and push some blocks aside (e.g. Turkey). The geometry of deformation around indenters is controlled by the shape of the impinging rigid face and to the boundary conditions of the surrounding plastic rocks at depth. As a working hypothesis, Chamberlin and Anderson (1989) suggested that structural patterns in the Laramide Zuni uplift are much smaller but otherwise quite similar to indentation-extrusion domains observed between India and south China. We suggest that the narrow NNE-trending El Morro gravity high represents a relatively rigid mafic crustal beam, a stiletto heel, that focused compressive stresses and progressively pushed up the core of the Zuni Mountains at its hard northern tip. Slip patterns of microthrusts on the NE flank of the Zuni uplift imply that the core of the uplift moved northward with time (Chamberlin et.al, 1989; Chamberlin and Anderson, 1991). These limited observations provide some support for the indentation hypothesis. More field work is needed to address the slip characteristics inferred zones of lateral shear on the north and west flank of the uplift . The concept that large rigid crustal blocks or microplates can control patterns of deformation in surrounding plastic rocks is also useful in viewing extended terranes in the Cordillera of western North America. With this concept, the Colorado Plateau, Idaho Batholith and Sierra Nevada-Great Valley microplates appear as large rigid rafts surrounded by a sea of westward drifting crustal slivers that resemble pack ice.
|Photo: Stiletto heel mimics hypothetical indentation process along the south flank of the Zuni Mountains.|
- Chamberlin, R. M., and Anderson, O. J., 1989, The Laramide–Zuni uplift, southeastern Colorado Plateau: A microcosm of Eurasian-style indentation–extrusion tectonics?: New Mexico Geological Society, Guidebook 40, p. 81–90. (Reprints available on request)
- Chamberlin, R. M., and Anderson, O. J., 1991, A microindentation–extrusion tectonic model for the Laramide Zuni uplift, west-central New Mexico, USA [abs.]: Geological Society of America Abstracts with Programs, v. 23, no. 5, p. A482.
- Chamberlin, R. M., Anderson, O. J., Lucas, S. G., Maxwell, C. H., and Love, D. W., 1989, Second-day road log from Grants to El Malpias, Fence Lake, Zuni Pueblo and Gallup, 1989: New Mexico Geological Society, Guidebook 40, p. 1–24. (see p.27, Stop 1).
O. J., and Chamberlin, R. M., 1990, New insight and
hypothesis on Zuni Basin fold structures, New Mexico: Exploration
significance [abs.]: American Association of Petroleum Geologists Bulletin,
v. 74/8, p. 1314.