Conclusions
While there are some who would prefer not to accept a flat slab as a mechanism for Laramide deformation, it is for the most part widely accepted. What is currently disputed are the extents and impact of a
flat slab geometry. For instance, in their diagram shown before and seen here, Livaccari and Perry 1993 define a boundary near Las Vegas between mantle volcanics and mantle lithosphere volcanics. They draw
this boundary by assuming that signatures of mantle are due to late Cenozoic extension. However, some of the samples to the east of this boundary (in the lithosphere zone) show epsilon Nd values very
close to that of the mantle zone. As a result, this interpretation is up for debate.
Saleeby 2003 w/additions by C. Harig
1 - from Ducea and Saleeby 1998
2 - Lee et al., 2001
3 - from Miller et al. 2001
4 - Livaccari and Perry 1993
5 - from Farmer et al. 1989
The isotope geochemistry studies discussed previously have helped to define the area where mantle lithosphere persisted throughout the Laramide Orogeny and where it did not. When we examine the data
together, as in the diagram below, we can begin to get a picture of what the geometry of the flat slab might have looked like in Laramide time. Throughout the Mojave Desert, post-Laramide volcanic rocks
show isotopic signatures indicative of having been sourced in the mantle. To the north and to the southeast the rocks show signatures of a persisting mantle lithosphere.
Saleeby 2003 w/additions by C. Harig
As a result of these studies and other geophysical evidence, some have proposed a much narrower flat slab subduction zone than previously envisioned. Saleeby 2003 proposes that a slab originating from
the latitude of the Mojave Desert with motion in the direction of the North America - Farallon relative plate motion could cause the deformation seen in Wyoming and Colorado. This interpretation also
accommodates observed gradational features seen at the southern boundary of the Sierra Nevada Batholith. For example, there is a gradient in the igneous barometry of the edge of the SNB. So far this
interpretation appears to fit well with observed data; however continued study of the region will likely continue to yield valuable data.
References
Bird, P., Formation of the Rocky Mountains, Western United States; a continuum computer model, Science, 239, (4847), 1501-1507, 1988.
Bird, P., Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States: Comment, Geology, 22, (7), 670-671, 1994.
Bird, P., Kinematic history of the Laramide Orogeny in latitudes 35 degrees-49 degrees N, western United States, Tectonics, 17, (5), 780-801, 1998.
Ducea, M., The California arc: Thick granitic batholiths, eclogitic residues, lithospheric-scale thrusting, and magmatic flare-ups, GSA Today, 11, 4-10, 2001.
Dumitru, T. A., Gans, P. B., Foster, D. A., and Miller, E. L., 1991, Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction: Geology, v. 19, p. 1145-1148
Farmer, G. L., Perry, F. V., Semken, S., Crowe, B., Curtis, D., and DePaolo, D. J., 1989, Isotopic evidence on the structure and origin of sub continental lithospheric mantle in southern Nevada: Journal of Geophysical Research, v. 94, p. 7885-7898
Glazner, A. F., Farmer, G. L., Hughes, W. T., Wooden, J. L., and Pickthorn, W., 1991, Contamination of basaltic magma by mafic crust at Amboy and Pisgah craters, Mojave Desert, California: Journal of Geophysical Research, v. 96, p. 13,673-13,691
Lipman, P. W., 1992, Magmatism in the Cordilleran United States: progress and problems, in Burchfiel, B. C., Lipman, P. W., and Zoback, M. L., editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, p.481-514
Livaccari, R. F., and F. V. Perry, Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States, Geology, 21, (8), 719-722, 1993.
Maxson, J., and B. Tikoff, Hit-and-run collision model for the Laramide Orogeny, western United States, Geology, 24, (11), 968-972, 1996.
Perry, F. V., and R. F. Livaccari, Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States: Reply, Geology, 22, (7), 671-672, 1994.
Saleeby, J., Segmentation of the Laramide Slab - evidence from the southern Sierra Nevada region, Geol. Soc. Am. Bull., 115, 655-668, 2003.
Bird, P., Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States: Comment, Geology, 22, (7), 670-671, 1994.
Bird, P., Kinematic history of the Laramide Orogeny in latitudes 35 degrees-49 degrees N, western United States, Tectonics, 17, (5), 780-801, 1998.
Ducea, M., The California arc: Thick granitic batholiths, eclogitic residues, lithospheric-scale thrusting, and magmatic flare-ups, GSA Today, 11, 4-10, 2001.
Dumitru, T. A., Gans, P. B., Foster, D. A., and Miller, E. L., 1991, Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction: Geology, v. 19, p. 1145-1148
Farmer, G. L., Perry, F. V., Semken, S., Crowe, B., Curtis, D., and DePaolo, D. J., 1989, Isotopic evidence on the structure and origin of sub continental lithospheric mantle in southern Nevada: Journal of Geophysical Research, v. 94, p. 7885-7898
Glazner, A. F., Farmer, G. L., Hughes, W. T., Wooden, J. L., and Pickthorn, W., 1991, Contamination of basaltic magma by mafic crust at Amboy and Pisgah craters, Mojave Desert, California: Journal of Geophysical Research, v. 96, p. 13,673-13,691
Lipman, P. W., 1992, Magmatism in the Cordilleran United States: progress and problems, in Burchfiel, B. C., Lipman, P. W., and Zoback, M. L., editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, p.481-514
Livaccari, R. F., and F. V. Perry, Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States, Geology, 21, (8), 719-722, 1993.
Maxson, J., and B. Tikoff, Hit-and-run collision model for the Laramide Orogeny, western United States, Geology, 24, (11), 968-972, 1996.
Perry, F. V., and R. F. Livaccari, Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western United States: Reply, Geology, 22, (7), 671-672, 1994.
Saleeby, J., Segmentation of the Laramide Slab - evidence from the southern Sierra Nevada region, Geol. Soc. Am. Bull., 115, 655-668, 2003.