Post on 03-Jul-2015
description
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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