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Find Your Science at GSA
7 December 2009
GSA Release No. 09-69
Christa Stratton
Director of Education, Communication, & Outreach
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December 2009 Geosphere Highlights

Boulder, CO, USA - The December issue of GEOSPHERE, The Geological Society of America’s Web science journal, is now online. The issue’s two articles examine (1) the Stateline fault along the southern California-Nevada border near Ivanpah Valley; and (2) magma chambers and crystal-rich magmas of the Tuolumne batholith in the Sierra Nevada range.

Highlights are provided below. Representatives of the media may obtain complementary copies of GEOSPHERE articles by contacting Christa Stratton at the address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOSPHERE in articles published. Contact Christa Stratton for additional information or assistance.

Review abstracts for these articles and the full table of contents at

Non-media requests for articles may be directed to GSA Sales and Service, .

Low-temperature thermochronologic constraints on the kinematic history and spatial extent of the Eastern California shear zone
K.H. Mahan et al., Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Boulevard, Pasadena, California 91125, USA; and Dept. of Geological Sciences, University of Colorado, 2200 Colorado Ave., Boulder, Colorado 80309, USA.

The 200-km-long Stateline fault occurs along the southern California-Nevada border and is part of a broad zone of active deformation that helps to accommodate relative motion between the Pacific and North American plates. We present evidence that explains how this fault system transfers dominantly right-lateral deformation along its main segments into dominant extension at its southern end near Ivanpah Valley. Part of this evidence is in the form of isotopic data that allows determination of the time at which rocks unroofed during this extensional process passed through a depth of approximately 1.5 km on their way to Earth's surface. These data also allow us to address important questions regarding rates of slip on the Stateline fault and to expand the known spatial extent of this particular style of active deformation along the western margin of North America.

Magmatic tubes, pipes, troughs, diapirs, and plumes: Late-stage convective instabilities resulting in compositional diversity and permeable networks in crystal-rich magmas of the Tuolumne batholith, Sierra Nevada, California
Scott R. Paterson, Dept. of Earth Sciences, University of Southern California, Zumberge Hall of Science, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, USA.

Funded in part by the NSF, this contribution examines a number of local magmatic structures that form by local convection, fractionation, and crystal sorting in crystal-rich magmas in the Tuolumne Batholith. An examination of these structures (tubes, troughs, pipes, diapirs, and thermal plumes) provides information about how magma chambers form and what sorts of physical and chemical processes occur during late movement in the magma chambers.