Connie L. Dicken

Quick-look techniques for evaluating two-dimensional cross sections in detached contractional settings

For more than 30 yr, geologists and geophysicists have used balancing techniques to constrain their cross-sectional interpretations in detached contractional settings. The quality of the resulting interpretations commonly directly correlates to the quality of the data, the balancing and interpretational experience of the interpreter, and the time allotted for the interpretation. We demystify the balancing process and present quick-look techniques for quickly and effectively detecting and preventing common cross section balancing errors in detached contractional settings. Common balancing problems are highlighted through close scrutiny of hanging-wall and footwall ramps and flats; such analysis helps identify inconsistencies in the numbers of ramps and flats, in the strata and stratal thicknesses in corresponding ramps, and in displacement along the fault. These techniques possess the additional advantages of being useful at any stage of the interpretational process for time or depth sections and being easily comprehensible by students, geologists, geophysicists, and managers alike. The quick-look techniques, however, are not an all-encompassing panacea. They do not guarantee a unique and/or correct cross-sectional interpretation; instead, they serve to focus the interpreters attention on potentially problematic areas in the cross section that might require explanation and/or reinterpretation.

Undiscovered Phanerozoic Porphyry Copper Deposits—A Global Assessment

Porphyry copper deposits represent the principal source of global copper supply. To address the questions of where future copper supplies are likely to come from and how much copper could exist within the upper kilometer of the earth’s crust, the USGS led a cooperative international effort to assess the world’s undiscovered Phanerozoic porphyry copper deposits using a geologybased, probabilistic form of mineral resource assessment (Singer and Menzie, 2010). Globally, 175 tracts permissive for porphyry copper deposits were defined to include volcanic and intrusive rocks of specified ranges of age and composition. The rocks represent: (1) magmatic arcs that developed on continental crust above subducting oceanic plates, (2) island arcs that formed on oceanic crust, and(or) (3) postconvergent magmatic belts within continents. Quantitative assessments of undiscovered resources were done for 155 of those permissive tracts.

USGS national surveys and analysis projects: Preliminary compilation of integrated geological datasets for the United States: A section in Digital mapping techniques '06 - Workshop proceedings

The growth in the use of Geographic nformation Systems (G S) has highlighted the need for regional and national digital geologic maps attributed with age and rock type information. Such spatial data can be conveniently used to generate derivative maps for purposes that include mineral-resource assessment, metallogenic studies, tectonic studies, human health and environmental research. n 1997, the United States Geological Survey’s Mineral Resources Program initiated an effort to develop national digital databases for use in mineral resource and environmental assessments. One primary activity of this effort was to compile a national digital geologic map database, utilizing state geologic maps, to support mineral resource studies in the range of 1:250,000to 1:1,000,000-scale. Over the course of the past decade, state databases were prepared using a common standard for the database structure, fields, attributes, and data dictionaries. As of late 2006, standardized geological map databases for all conterminous (CONUS) states have been available on-line as USGS Open-File Reports. For Alaska and Hawaii, new state maps are being prepared, and the preliminary work for Alaska is being released as a series of 1:500,000-scale regional compilations. See below for a list of all published databases.