October Geology and GSA Today media ...(of intense erosion accompanied initial l...)

Date:9/25/2007

of intense erosion accompanied initial land clearance in the Pre-Classic period when highly erodable soils were first exposed. These results suggest that the Maya had to contend with soil erosion long before their accelerated population growth and ultimate demise in the Classic period. This example of ancient human impact on the environment is relevant to contemporary issues of tropical deforestation and soil erosion.

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The tectonic significance of hgh-K2O volcanism in the Sierra Nevada, California
Keith Putirka, California State University, Fresno, Earth and Environmental Sciences, 2576 E. San Ramon Ave., MS/ST24, Fresno, California 93710, USA; and Cathy J. Busby, Department of Earth Science, University of CaliforniaSanta Barbara, Santa Barbara, California 93106, USA. Pages 923-926.

Putirka and Busby present new field and geochemical data from the central Sierra Nevada, California, that suggest a new model for Sierra Nevada volcanism and uplift. The rise of the Sierra Nevada has been attributed to the removal of dense rock that lies beneath the granitic crust, a process called "lithosphere delamination." This process works as would a block of wood, floating in water, with a metal plate underneath; remove the metal plate and the wood block rises. Seismic studies show that "lithosphere delamination" beneath the Sierra is nearly certainbut its timing and linkages to volcanism are not. This new data show that special volcanic rocks, high in the element potassium (K), erupt at the onset of transtensional "normal" faulting, not delamination. These normal faults, which control range uplift, began their activity 10 million years ago. This interpretation stands in contrast to earlier models that link the onset of delamination to volcanic activity 3.5 million years ago. Putirka and Busbys new age dates, and published dates, demonstrate that volcanism was initiated throughout the Sierra Nevada 10 million years ago. Putirka and Busby su
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Contact: Ann Cairns acairns@geosociety.org 303-357-1056 Geological Society of America Source:Eurekalert

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