May GEOSPHERE media highlightsBoulder, Colo. - The May issue of GEOSPHERE, published in electronic format only by the Geological Society of America, is now available online. Research published in GEOSPHERE spans all geology disciplines, with content ranging from comprehensive papers to brief notes, plus data and software contributions from the emerging field of geoinformatics. Contributions from geoscience education also appear in the journal.
Access the issue at http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=1553-040X
The Earth Has a Future
Steven Ian Dutch, University of Wisconsin-Green Bay, Green Bay, WI 54311, USA. Page 113.
A new way of visualizing geologic time is to look into the future. A thousand years in the future, a blink of the eyes in geologic terms, is still three times as remote as the future depicted in Star Trek. Events unknown in recorded history, like large meteor impacts and eruptions of supervolcanoes, become inevitable, even frequent, in the near geologic future. A million years in the future is such a vast concept we cannot remotely guess what human society will be like, if indeed humans will still even exist then, yet geologic changes in that time will be fairly modest. Nevertheless, some geologic changes can be seen even in a human lifetime, and seemingly eternal features like the Pyramids, Old Faithful, or the Cascade volcanoes may not even exist a million years from now.
Major ignimbrites and volcanic centers of the Copper Canyon area: A view into the core of Mexico's Sierra Madre Occidental
Eric R. Swanson, University of Texas at San Antonio, San Antonio, TX 78249-0663, USA; et al. Page 125
The Sierra Madre Occidental of western Mexico contains an enormous number of extinct volcanoes forming what geologists call a large igneous province. The plateau-like sierra is generally considered to constitute Earth's largest, intact example of a large igneous province of the type known as silicic. It is believed to hold the remains of hundreds of silicic caldera volcanoes. With its world-record concentration of active hot springs and geysers, the Yellowstone caldera is another active example of this volcano type. Although calderas are associated with much of the mineral wealth of western Mexico, little is known of the volcanic history of this large and mostly remote igneous province. This is particularly true for the central core of the province where for nearly 600 miles along its central axis the geology is virtually unknown. This paper reports the results of reconnaissance mapping in the core of the volcanic field in the western Mexican state of Chihuahua. The complex geology of that region has been unraveled and several new calderas located. Swanson et al.'s results are expected to guide further studies and future mineral exploration. This area is of particular interest to the general public because it includes the world-class tourist destination site of Copper Canyon, sometimes known as the Grand Canyon of Mexico. This paper provides the first explanation of the geology of that scenic and geologic attraction and the first detailed look into the core of the giant Sierra Madre Occidental volcanic field.
Reflectance spectroscopy (0.3-2.5 μ) at various scales for bulk-rock identification
Maria Sgavetti, University of Parma, Parma 43100, Italy; et al. Page 142.
Unveiling the inner secrets of rocks gives scientists a lot of information about what the planet is made of, its histories, and its climate changes. This paper probes these secrets, using spectrometers to reveal the chemistry and structure of rock minerals. Sgavetti et al. not only used laboratory-based spectrometers, they also walked on mountains with a portable version of a spectrometer and looked down through the eye of a spectrometer from an airplane and from a satellite orbiting around Earth.
Regional mapping of phyllic- and argillic-altered rocks in the Zagros magmatic arc, Iran, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and logical operator algorithms
John C. Mars and Lawrence C. Rowan, U.S. Geological Survey, Reston, VA 20151, USA. Page 161.
This paper documents a new method using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to map argillic- and phyllic-altered rocks of the Zagros magmatic arc in Iran. Logical operator algorithms using band ratios and band thresholds were used to map hydrothermal alteration. Each algorithm produced a byte image from each ASTER reflectance data set that was converted to vector data. The vector data were superimposed on a Landsat TM mosaic of the study area. This method can be used for regional mapping of hydrothermally altered rocks. The ASTER data set for the study area consisted of 62 scenes of ASTER reflectance data (1 ASTER scene is 60 km by 60 km). The new mapping method was validated in this study using ASTER and Airborne Visible Infrared Imaging Spectrometer data at Cuprite, Nevada. Regional hydrothermal alteration mapping of the Zagros magmatic arc illustrates distinct patterns of hydrothermally altered rocks associated with regional tectonic processes.
Slip analysis of the Kokoxili earthquake using terrain-change detection and regional earthquake data
Cara G. Schiek and José M. Hurtado, Jr., University of Texas at El Paso, Department of Geology, El Paso, TX 79968, USA. Page 187.
The Kokoxili earthquake occurred on 14 November 2001 along the Kunlun fault, a major strike-slip fault on the northern Tibetan plateau. To analyze the type of movement along segments of the fault, this study employed a new method of terrain change detection using ASTER satellite images. The method compared two images, one taken before and the other after the earthquake, and computed the amount of horizontal displacement that occurred. The results then allowed Schiek and Hurtado to model the tectonic stresses associated with the observed deformation. Three segments of the fault were analyzed, each with different types of movement. Their analysis detected left-lateral slip, a displacement of 3-11 m, and areas of both compression and tension along the Kunlun fault. These deformation results are consistent with field observations by previous workers and Schiek and Hurtado's stress analysis is consistent with the stress field obtained from regional earthquake data. They found that the pattern of deformation along the fault, and the associated stresses, are greatly influenced by the fault's geometry. In addition, this study demonstrates, for the first time, the utility of ASTER optical satellite imagery for acquiring quantitative measurements of surface movement.
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