July 2009 Geology and GSA Today Media Highlights

Boulder, CO, USA - GEOLOGY articles extract information on forces shaping Earth's surface, solve the puzzle of LIPs on land, trace the leading edges of dispersing continents, expose magmatic plumbing, argue over gold deposits, show how fungi break down rocks, unveil tightly kept secrets about the Amazon River, investigate deep geological structures associated with the 2004 Sumatran earthquake, settle the debate over porphyroblasts, and define neptunian eruptions. GSA Today uncovers the impact of Cenozoic snow melt in the Rockies.

Beyond threshold hillslopes: Channel adjustment to base-level fall in tectonically active mountain ranges
William B. Ouimet et al., Dept. of Geology, Colorado College, Colorado Springs, Colorado 80903, USA. Pages 579-582.

Extracting information about the forces shaping Earth's surface directly from topography is an invaluable tool for all earth scientists, as well as engineers, planners, and managers who are faced with preparing for and dealing with the erosion of mountainous landscapes. Ouimet et al. utilize concentrations of cosmogenic nuclides extracted from river sand on the eastern margin of the Tibetan Plateau to explore relationships between millennial erosion rate, hillslope gradients, and channel gradients. The unique setting of the eastern margin allowed them to cover the majority of the globally known ranges for these topographic metrics with erosion rates ranging over two orders of magnitude, from about 0.03 to 3 mm/year. Their dataset offers insight into how hillslope and river channel morphology changes to accommodate higher rates of erosion and provides a critically needed test for advancing theoretical models of hillslope evolution and bedrock river incision in tectonically active settings.

The 132 Ma Comei-Bunbury large igneous province: Remnants identified in present-day southeastern Tibet and southwestern Australia
Di-Cheng Zhu et al., State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China. Pages 583-586.

A large igneous province (LIP) refers to a large area of Earth's surface covered with great volumes of igneous rocks of basaltic composition (with or without rhyolitic varieties) emplaced in a relatively short time period as a result of extensive decompressive melting of ascending mantle plume heads. Although there are exceptions, generation of many LIPs on land has been linked to breakups of supercontinents. A debate exists regarding the role of the Kerguelen mantle plume initiation in the India-Australia breakup. Zhu et al. report new zircon U-Pb age dates of the extensive Cretaceous igneous rocks exposed around the Comei area in southeastern Tibet. These data allow the recognition of a new 132-million-year-old LIP (i.e., the Comei LIP) that can be readily reconstructed in time and space to be related to the Bunbury basalts in present-day southwestern Australia. Until now, the expected LIP associated with the Kerguelen mantle plume and India-Australia breakup has been missing, and the best candidate was the volumetrically limited Bunbury basalts in southwestern Australia. With the recognition of the Comei LIP in southeastern Tibet, Zhu et al. have resolved the puzzle. Both the Comei LIP and the Bunbury basalts are tectonically isolated remnants of a previously unknown LIP, which is called the Comei-Bunbury LIP. These results are important in (1) resolving the above puzzle; (2) providing a broader context for understanding the Kerguelen mantle plume event, which appears to be a second stage of the Comei-Bunbury LIP; and (3) exploring the development of the 132-million-year-old Weissert oceanic anoxic event.