Insights into the tectonic development of the Klamath Mountains Province from thermal data and modeling

Rachel Piotraschke

Penn State Department of Geosciences

Graduate Student Colloquium

March 19, 2011

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Based on Ernst et al., 2008

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Modified from Kelsey et al., 1994

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What drove (is driving?) topographic development in the Klamath Mountains

Province?

Is it related to the northward migration of the Mendocino Triple Junction?

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When did the modern high topography of the KMP develop?

Are there post-accretionary structures that might tell us something about

timing and mechanisms of topographic development?

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Hypothesis:

• Unusual high topography of the Klamaths is a recent development

• Extensional faulting has played an important role in the Cenozoic tectonic development of the Klamath Mountains

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La Grange detachment

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Modified from Cashmanand Elder, 2002

Approach:

• Timing of exhumation

• Patterns and rates of exhumation—erosionalvs. tectonic

Thermal history

Exhumation history

Tectonic history

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• Apatite Fission Track (AFT) and apatite (U-Th)/He cooling ages from:– Plutons in lower

plate of detachment

– Plutons distal from detachment

– Plutons in upper plate?

Thermal history

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• Vitrinite reflectance (thermal maturity) data from:– Cretaceous rocks

from Western Klamaths (distal from detachment)

– Miocene rocks (from closer to detachment)

Thermal history

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Previously existing apatite (U-Th)/He data from lower plate plutons indicated Late Eocene exhumation

(Data from Batt et al., 2010) 12

New data shows north-to-south younging trend

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…indicating ages were locked in by removal of the upper plate along the detachment

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Back to the hypotheses:

• Extensional faulting was a significant driver of Cenozoic exhumation in the eastern Klamath Mountains

– Does this correspond with playing a significant role in the overall tectonics?

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Back to the hypotheses:

–After unroofing by detachment, plutonswere shallower than ~2.5 km depth

–Requires average erosion rates over last 20 Ma of less than ~0.13 mm/yr

–Is high topography of the Klamathsa recent development?

•Depends on modern erosion rates…

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Thanks to:

• Kevin Furlong

• Sue Cashman at Humboldt State University

• Peter Kamp and Martin Danišík at University of Waikato

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