December 2008 Geology and GSA Today media ...(coupled plasma-mass spectrometry. Samson...)

Date:11/26/2008

coupled plasma-mass spectrometry. Samson et al. have analyzed fluid inclusions from the El Mochito Zn-Pb-Ag deposit in Honduras using this technique and demonstrated that, despite being hosted by sedimentary rocks, the fluids responsible for mineralization were magmatic. Such data are also valuable for interpreting ore genesis in that they provide information on the metal contents of paleo fluids, allowing more accurate modeling of hydrothermal mineralizing processes.

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Anatomy of a young impact event in central Alberta, Canada: Prospects for the missing Holocene impact record

C.D.K. Herd et al., Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, Alberta T6G 2E3, Canada. Pages 955-958.

Based on the amount and frequency of meteorite falls and the formation of impact craters on the Earth, there should be over 20 impact craters in the < 100 m size range that formed within the past 10,000 years, yet only five such craters are known worldwide. Herd et al. report the discovery of a 36-m-diameter impact crater located in a forested area near the town of Whitecourt, Alberta, Canada. Although too overgrown to be seen in air photos or satellite images, the crater is revealed using a bare-Earth digital elevation model obtained through airborne Light Detection and Ranging (LiDAR). The crater formed in deglacial sediments, with impact ejecta burying a soil with a radiocarbon age of ~1100 years. Seventy-four iron meteorites (0.1-1196 g) have been recovered, most having an angular, shrapnel-like shape. These meteorites were buried at depths of < 25 cm and are interpreted to result from fragmentation of the original larger mass of the impactor, either at low altitude or during the impact event. Impact of the main mass formed the simple bowl-shaped impact structure associated with an ejecta blanket and crater fill. Herd et al. show that LiDAR may be a useful tool to look for additional sma
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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