Tuesday, February 20, 2018 GSA Luncheon

 Topic: Cenozoic Off-set History of the Denali Fault System

Noon Luncheon 11:30-1:00 pm

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LUNCHEON ABSTRACT

No offset, no significant slip to recent times, and the large translation mobilists: Three different perspectives on the Cenozoic history of horizontal slip along the Denali Fault System

The Denali Fault System, at over ~800 km in length, is one of the major intra-continental strike-slip faults in the world and presents a significant seismic hazard to the state of Alaska and the Yukon Territory of Canada. Given the Denali Fault System’s prominence as a geographic trench andfeature clearly visible from space and as a tectono-lithospheric boundary, and given the highest mountain range in North America parallels its trace, it is surprising the published literature provides conflicting constraints on the Cenozoic horizontal displacement history along the different segments of this structure.

In this talk I will first review the many segments of the Denali Fault System and three different Denali Fault System displacement perspectives: A) Essentially no Cenozoic horizontal displacement has occurred, B) Horizontal displacements rates of ~10 mm/yr along the Denali Fault have only been occurring from approximately the Holocene to present, and C) Cenozoic horizontal displacement along the Denali Fault System has totaled around 400 km.

I will present new published piercing point and other geologic slip constraints from along the Totschunda Fault, Broxon Gulch Fault, and the segmented main Denali Fault from collaborators and myself. I will document that the initiation of many segments of the Denali Fault System are far older (ex. The Totschunda Fault is a Cretaceous structure) than previously considered. I will also make the case that ~400 km is a minimum horizontal total displacement along the Denali Fault System since ~57 Ma, and that Neogene slip rates mimic Holocene slip rates along many segments of the fault.

SPEAKER BIOGRAPHY

Dr. Jeff Benowitz, University of Alaska, Fairbanks

Jeff Apple Benowitz received a family photo postcard and a map of vast Alaska from Governor Jay Hammond as part of a 5th grade pen-pal writing project. When Jeff turned 19, he hitch-hiked to Alaska from his New York upbringing to a place where most mountains are named simply after their elevation. He spent his 20’s and 30’s writing climbing adventure stories about the Alaska Range. 26 years since originally sticking his thumb out, he is currently employed as the director of the University of Alaska Geophysical Institute Geochronology Facility.  Jeff now finds himself coaxing stories out of the rocks of Alaska that tell tales of where the mountains he calls home originate. He has studied the Brooks Range, Wrangell Mountains, Talkeetna Mountains, White Mountains, and of course the Alaska Range.

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