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Tucson, AZ, United States

Space-shuttle radar topography data from central Sulawesi, Indonesia, reveal two corrugated, domal landforms, covering hundreds to thousands of square kilometers, that are bounded to the north by an abrupt transition to typical hilly to mountainous topography. These domal landforms are readily interpreted as metamorphic core complexes, an interpretation consistent with a single previous field study, and the abrupt northward transition in topographic style is interpreted as marking the trace of two extensional detachment faults that are active or were recently active. Fault dip, as determined by the slope of exhumed fault footwalls, ranges from 4° to 18°. Application of critical-taper theory to fault dip and hanging-wall surface slope, and to similar data from several other active or recently active core complexes, suggests a theoretical limit of three degrees for detachment-fault dip. This result appears to conflict with the dearth of seismological evidence for slip on faults dipping less than ~. 30°. The convex-upward form of the gently dipping fault footwalls, however, allows for greater fault dip at depths of earthquake initiation and dominant energy release. Thus, there may be no conflict between seismological and mapping studies for this class of faults. © 2011 Elsevier B.V. Source

The Space-Shuttle Radar Topography Mission provided geologists with a detailed digital elevation model of most of Earth's land surface. This new database is used here for structural analysis of grooved surfaces interpreted to be the exhumed footwalls of three active or recently active extensional detachment faults. Exhumed fault footwalls, each with an areal extent of one hundred to several hundred square kilometers, make up much of Dayman dome in eastern Papua New Guinea, the western Gurla Mandhata massif in the central Himalaya, and the northern Tokorondo Mountains in central Sulawesi, Indonesia. Footwall curvature in profile varies from planar to slightly convex upward at Gurla Mandhata to strongly convex upward at northwestern Dayman dome. Fault curvature decreases away from the trace of the bounding detachment fault in western Dayman dome and in the Tokorondo massif, suggesting footwall flattening (reduction in curvature) following exhumation. Grooves of highly variable wavelength and amplitude reveal extension direction, although structural processes of groove genesis may be diverse. Source

Ferguson C.A.,Arizona Geological Survey | McIntosh W.C.,New Mexico Institute of Mining and Technology | Miller C.F.,Vanderbilt University
Geology | Year: 2013

Sanidine 40Ar/39Ar geochronology confi rms that Silver Creek caldera, which straddles the eastern edge of the Colorado River extensional corridor near Oatman, Arizona (United States), is the source of the Peach Spring Tuff. Eight new dates (fi ve from outfl ow, three from caldera fi ll) are analytically indistinguishable, and combined with the most precise previously published date give a weighted mean average age of 18.78 ± 0.02 Ma. A fragment of the caldera identifi ed in the midst of the extensional corridor is structurally juxtaposed with mesozonal plutons of identical age. The implied extension direction (182°-225°) is compatible with abundant previously published structural data for the region. © 2012 Geological Society of America. Source

Geologic investigations of late Miocene- early Pliocene deposits in Mohave and Cottonwood valleys provide important insights into the early evolution of the lower Colorado River system. In the latest Miocene these valleys were separate depocenters; the floor of Cottonwood Valley was ~200 m higher than the floor of Mohave Valley. When Colorado River water arrived from the north after 5.6 Ma, a shallow lake in Cottonwood Valley spilled into Mohave Valley, and the river then filled both valleys to ~560 m above sea level (asl) and overtopped the bedrock divide at the southern end of Mohave Valley. Sediment-starved water spilling to the south gradually eroded the outlet as silici clastic Bouse deposits filled the lake upstream. When sediment accumulation reached the elevation of the lowering outlet, continued erosion of the outlet resulted in recycling of stored lacustrine sediment into downstream basins; depth of erosion of the outlet and upstream basins was limited by the water levels in downstream basins. The water level in the southern Bouse basin was ~300 m asl (modern elevation) at 4.8 Ma. It must have drained and been eroded to a level <150 m asl soon after that to allow for deep erosion of bedrock divides and basins upstream, leading to removal of large volumes of Bouse sediment prior to massive early Pliocene Colo rado River aggradation. Abrupt lowering of regional base level due to spilling of a southern Bouse lake to the Gulf of California could have driven observed upstream river incision without uplift. Rapid uplift of the entire region immediately after 4.8 Ma would have been required to drive upstream incision if the southern Bouse was an estuary. © 2014 Geological Society of America. Source

Agency: NSF | Branch: Standard Grant | Program: | Phase: EarthCube | Award Amount: 100.00K | Year: 2012

EarthCube is focused on community-driven development of an integrated and interoperable knowledge management system for data in the geo- and environmental sciences. By utilizing a cooperative, as opposed to competitive, process like that which created the Internet and Open Source software, EarthCube will attack the recalcitrant and persistent problems that so far have prevented adequate access to and the analysis, visualization, and interoperability of the vast storehouses of disparate geoscience data and data types residing in distributed and diverse data systems. This awards funds a series of broad, inclusive community interactions to gather adequate information and requirements to create a roadmap for a critical capability (governance) in the development of EarthCube, a major new NSF initiative. Community/stakeholder buy-in and adoption of standards; common tools and aproaches, if possible; best practices; cyberinfrastructure protocols; and workflows are essential to any holistic approach to creating an interoperable and service-oriented architecture that serves the needs of the geoscience research community wishing to do data-enabled science. The funded series of online/virtual workshops that will engage a brod spectrum of the geoscience community were considered innovative and exciting, especially the proposed application of social networking outreach utilities to engage early career scientists and students. A prime deliverable of the project will be a road map of how to move forward in terms of setting up broadly agreed upon structures to oversee the development of EarthCube activities in the associated working groups and concept grants. Broader impacts of the work include converging on mutually agreed upon processes to allow decision making with regard to whether or not standards or specific protocols should be established, and if so what they should be. They also include the fostering of close interaction between communities that do not commonly interact with one another (the geosciences and those in cyberinfrastructure and computer science) and focusing them on the common goal of creating a new paradigm in data and knowledge management in the geosciences.

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