Flowing asthenosphere and a slab window beneath the Coast Mountains Batholith, British Columbia

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					<h3>Flowing asthenosphere and a slab window beneath the Coast Mountains Batholith, British Columbia</h3>
					From: <a href="http://www.slideshare.net/drrocks1982/">drrocks1982</a>, 3 weeks ago<br /><br />
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					In a nutshell: Using seismology to understand the ongoing evolution of the mantle beneath northwestern North America.

Specifically: I use three well-developed techniques for shear-wave splitting analysis on high quality teleseismic recordings to develop a preliminary model of mantle deformation fabric beneath the Coast Mountain Batholith (CMB) in British Columbia. High quality results show a consistent shear-wave splitting trend of ~1.5 to 2 seconds for the highest signal-to-noise earthquake recorded during the Batholiths Continental Dynamics Experiment seismic deployment. These new observations show a pronounced trend of seismic anisotropy corresponding to an east-west striking fabric superimposed beneath the entire region, crossing several Mesozoic-age terrane boundaries as well as the Cenozoic-age CMB. This trend contrasts with previous work showing null or weak measurements of shear-wave splitting observed elsewhere along the Canadian Cordillera and continental margin. This distinct trend of splitting occurs near the inferred northern edge of the subducted Explorer Plate (Madsen et al., 2006). The anisotropy also strongly mirrors the trend of the 14-0 Ma Anahim Volcanic belt (Souther, 1986). The orientation of splitting coincides with neither the current absolute plate motion of North America, nor the predicted angle of convergence during subduction in the late Cretaceous and early Cenozoic. In addition, the magnitude of the splitting requires a layer of significant seismic anisotropy exceeding 100 km in thickness. These constraints imply that the fabric is a likely to have developed more recently, resides to a significant extent in the asthenosphere, and may relate to a dynamic interaction of the northern edge of the subducted Explorer Plate and the subcontinental mantle of the North American and Pacific Plates.<br /><br />
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Flowing asthenosphere and a slab window beneath the Coast Mountains Batholith, British Columbia

From drrocks1982, 3 weeks ago

In a nutshell: Using seismology to understand the ongoing evolutio more

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Slide 1: Flowing asthenosphere and a slab window beneath the Coast Mountains Batholith, British Columbia Andy Frassetto

Slide 2: Coast Mountains Batholith ?

Slide 4: Thorkelson & Taylor, 1989

Slide 5: How do slab windows influence volcanism?

Slide 6: How do slab windows influence deformation of the mantle?

Slide 7: Coast Mountains Anahim Volcanoes Madsen et al. 2006

Slide 9: Anisotropic Mineral Flow Aligned Minerals

Slide 10: Shear Wave Splitting Result R T Courtesy of Ed Garnero

Slide 14: e nd ah i m Tr An

Slide 15: “The Anahim hotspot is a Miocene-to-Holocene hotspot which is responsible for the volcanic activity...in central British Columbia.”

Slide 16: 1. N.A. plate pushes slab to the SW. 2. Pressured Pacific mantle escapes past slab edge, driving flow.

Slide 17: A Southern Analog? Zandt and Humphreys, 2008

Slide 18: Conclusion #1 A coherent trend of anisotropy is observed across the region.

Slide 19: Conclusion #2 Inferred fabric orientation does not match common models.

Slide 20: Conclusion #3 Fabric must reside predominantly in the asthenosphere.

Slide 21: Conclusion #4 Toroidal mantle flow occurs beneath the Coast Mountains batholith.

Slide 22: Thanks to… George Zandt, Berk Biryol, the Global Seismology and Tectonics Research Group University of Wyoming National Science Foundation PASSCAL Instrument Center