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Structural Geology
Mary Hubbard

Published papers in the field of structural geology continue to cover a broad range of subtopics that relate to processes at a variety of spatial scales and time scales. Many studies call on interdisciplinary approaches to solve problems in structure and tectonics. During this past year, a number of structural geologists in North America worked together to produce a white paper outlining some of the current topics of interest to the structural geology community. Resulting from a workshop in Denver in September 2002, which was sponsored by the Tectonics Program at the National Science Foundation, the report covers broad topics that encompass many of the recently published structural geology papers in leading journals. Thus the white paper serves to highlight current trends in structural research.

The first topic focuses on rheology and continental orogenesis. This topic includes studies of large-scale deformation in the mantle and crust such as those involving seismic tomography or regional global positioning systems (GPS). Large-scale deformability of a region certainly depends on crustal properties at the small scale too. Rock types, geothermal gradient, presence of fluids, localization of deformation and inherited fabric can all influence how deformation occurs over a large region. Seth Haines and colleagues in the February 2003 Tectonics present results of the INDEPTH III study of the deep crust in Tibet. This project applied active source seismic data to an interpretation of the crustal makeup of the Tibetan Plateau region.

Another topic of current interest featured in the white paper centers around the link between earthquake deformation experienced on an observable timescale and mountain-building processes that occur over millions of years. Geoscientists have a number of methods, such as GPS, interferometric synthetic aperture radar and earthquake seismology, that facilitate the understanding of short-term deformation. For longer-term deformation, they turn to the rock record in mountain belts and other deformed terrains. A particularly interesting area of study, however, bridges these two approaches and ultimately will provide greater insight on the interplay between earthquake events and mountain building. The linkage of these processes is also a function of rock types, geothermal gradient, presence of fluids, localization of deformation and inherited fabrics. Richard Bennett and co-workers (April 2003, Tectonics) used GPS to look at modern rates of relative motion for crustal regions within the western United States. Refined use of GPS methods in this region have clearly demonstrated the diffuse nature of the Pacific-North American plate boundary in this area.

The relationship between climate, Earth surface processes and tectonics is the third topic of the white paper. Although this topic has been popular for the past decade, the newest advances in technology are allowing more precise studies of existing landscapes and rates of recent erosion and deformation processes. These new technologies include satellite data acquisition, digital elevation mapping and dating of surface processes. Experimental studies of climate, tectonics and landscape development have also provided new insights on the interplay of these factors. Stéphane Bonnet and Alain Crave (February 2003, Geology) used a silica paste to create a "landscape," which they then subjected to different rates of uplift and rainfall in order to observe differences in the resulting landscape and sedimentation patterns in situations where either tectonics or climate had dominated.

A final topic of interest to the structural geology community is the link between tectonics and the evolution of Earth including the evolution of life. Data are beginning to emerge in the literature that shed light on issues of how Earth's thermal structure, magnetic field, past continental configurations, atmospheric chemistry and life forms have evolved through time. Geoscientists are working hard to decipher linkages between these different factors from the datasets. Limited outcrops make access to this information for Earth's earliest history difficult, however researchers made significant progress throughout the 1990s.

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Hubbard is head of the Department of Geology at Kansas State University. E-mail: mhub@ksu.edu.

Links:
Tectonics Program sponsored by NSF

References:
Haines, S.S., Klemperer, S.L., Brown, L., Jingru, G., Mechie, J., Meissner, R., Ross, A., and Wenjin, Z., 2003, INDEPTH III seismic data: from surface observations to deep crustal processes in Tibet: Tectonics, v. 22, no. 1, p. 1-1 to 1-17.
Bennett, R.A., Wernicke, B.P., Niemi, N.A., Friedrich, A.M., and Davis, J.L., 2003, Contemporary strain rates in the northern Basin and Range province from GPS data: Tectonics, v. 22, no. 2, p. 3-1 to 3-31.
Bonnet, S., and Crave, A., 2003, Landscape response to climate change: Insights from experimental modeling and implications for tectonic versus climatic uplift of topography: Geology, v. 31, no. 2, p. 123-126.


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