||6 March 2006
GSA Release No. 06-07
February Media Highlights: Geosphere
Boulder, Colo. - The February issue of GEOSPHERE, published in electronic format only by the Geological Society of America, is now available online.
- Evaluating geoscience information systems in the classroom: A case study of Discover Our Earth
Carrie Brindisi, Institute for the Study of the Continents (INSTOC), Cornell University, Ithaca, New York 14853; Dogan Seber (corresponding author), University of California, San Diego, San Diego Supercomputer Center, La Jolla, CA 92093, USA; et al. Pages 1-10.
- Internet-based information and knowledge systems are being tested in classroom settings to evaluate the potential benefits of allowing students to access scientific data sets via easy-to-use Web-enabled interfaces. This study shows that student involvement in learning increases when students are provided with inquiry-based online data access and manipulation tools. A geoscience learning resource, Discover Our Earth (www.discoverourearth.org), has been evaluated in middle school classroom environments. This paper concluded that Discover Our Earth improved student engagement and allowed students to experiment with their own ideas and theories to reach scientific conclusions, a significant improvement compared to being told what they need to know by their teachers.
- Cenozoic to Recent plate configurations in the Pacific Basin: Ridge subduction and slab window magmatism in western North America
J.K. Madsen, Simon Fraser University, Burnaby, BC V5A 1S6, Canada; et al. Pages 11-34.
- This paper presents new U-Pb age determinations for Eocene forearc igneous rocks on Vancouver Island and a tectonic model of oceanic plate configurations for the Pacific Basin (in movie format) from 53 million years ago to the present. The model also shows where mid-ocean spreading ridges intersected the continental margin, and the shapes of resulting slab windows (gaps between the subducting oceanic plates) beneath western North America.
- Late Cenozoic shortening in the west-central Alborz Mountains, northern Iran, by combined conjugate strike-slip and thin-skinned deformation
Bernard Guest, University of California-Los Angeles, Los Angeles, CA 90095, USA; et al. Pages 35-52.
- The Alborz Mountains of northern Iran is a poorly understood actively growing mountain range that has probably developed to its present size over the last 12 million years. The active nature of this range makes it important for understanding the regional plate tectonic development of Iran and the Middle-Eastern region in general. Furthermore, the location of large, growing population centers like Tehran and Karaj on the southern flanks of this earthquake prone mountain range makes studying the growth of the range and the related faulting processes doubly important. In this paper, Guest et al. present a large amount of new geologic data in the form of geologic maps and cross sections, which has allowed them to make new interpretations of the tectonic development of the west-central segment of the range. These interpretations result in a new estimate for the total amount of tectonic contraction across the Alborz (53 ± 3 km, up from a loose estimate of 30 to 35 km) and indicate strong differences in the amount of shortening along the range (53 ± 3 km in the eastern part of the study area and only 15 to 18 km in the western part of the study area). Also, their interpretation of the structures (faults and folds) to the north and west of Tehran and Karaj suggests that these cities lie in a region that is tectonically similar to Southern California and that this area should be studied in greater detail so as to facilitate a better understanding of the seismic risk faced by these large metropolitan areas.
- Geoinformatic approach to global nepheline syenite and carbonatite distribution: Testing a Wilson cycle model
Kevin Burke, University of Houston, Houston, TX 77004, USA; and Shuhab Khan, Carnegie Institution of Washington, Washington, DC 20005, USA. Pages 53-60.
- On a grand scale, the history of Earth's surface consists of complex interwoven cycles of the opening and closing of ocean basins. Burke and Khan report on using an information technological approach to spatial data on the distribution of alkaline igneous rocks and carbonatites. That approach is proving powerful in helping to identify places where continents have ruptured and also where ancient oceans have closed.
- Retrograded eclogite-facies pseudotachylytes as deep-crustal paleoseismic faults within continental basement of Lofoten, north Norway
Mark G. Steltenpohl, Auburn University, Auburn, AL 36849, USA; et al. Pages 61-72.
- Steltenpohl et al. report the discovery of rare rocks exposed in the Lofoten Islands of arctic Norway that preserve ancient earthquakes and hold clues to understanding how earthquakes occur deep in Earth today. The "fossilized" earthquakes occur as black veins of ultra-fine grained rock called pseudotachylyte. Pseudotachylyte veins form when fault movements are abrupt and so extremely fast that enough frictional heat is generated to cause the host rock to locally melt. This catastrophic failure releases tremendous amounts of seismic energy and is the cause of earthquakes. The pseudotachylyte melts inject into fractures within the relatively cold host rock bounding the fault where they are quenched and eventually brought to the surface by later faulting and/or erosional uplift. Scientists who study modern earthquakes (i.e., seismologists) are stymied because they must rely on remote methods (e.g., seismometers) to make inferences about what might be happening at depth in Earth when an earthquake occurs. Pseudotachylites are paleoseismic faults, however, and they provide the only opportunity to directly observe the actual products of an earthquake. They provide direct information on the strengths of the rocks, the mechanisms involved in their failure, and the geometry of fault movements at the focal point of an earthquake. What makes the Lofoten pseudotachylites even more exciting, however, is that high-resolution microscopy reveals high-pressure minerals documenting crystallization at tremendous depths, as much as 30 miles below the surface. Earthquakes occur at these great depths today beneath the Himalayas where India is actively being subducted beneath Asia. The deadly 8 October, 2005, earthquake in Pakistan formed much shallower, however, at roughly 16 miles deep. The Lofoten pseudotachylites formed before 430 million years ago in a very similar plate tectonic setting where the proto-European margin was subducted beneath proto-Greenland and the Caledonian Mountains formed. Lofoten is only the third locality on Earth where deep-crustal paleoseismic faults are reported. Steltenpohl et al. explore the processes controlling the mechanical strength of the deep crust and the generation of deep-foci earthquakes, which has direct application for modern continental seismic zones.
To review the abstracts for these articles, go to www.gsajournals.org.
To view the complete table of contents for the current issue of GEOSPHERE,
go to www.gsajournals.org/.
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