Topographic Development History of the Range

Item Type Poster

Authors Davis, Kailyn N.

Download date 26/09/2021 22:08:57

Link to Item http://hdl.handle.net/11122/3442 CNSM Topographic Development History of the Davis, Kailyn N., [email protected], Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, AK 99775; Benowitz, Jeff, [email protected], Geophysical Institute, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, AK 99775; Roeske, Sarah M., [email protected], Earth and Planetary Sciences Department, University of California Davis

Abstract: The overall goal of this project is to use variations in sediment source through time as a Methods: We collected sandstone and sand samples from the Usibelli Group and Nenana Gravels proxy for deciphering the uplift history of the Alaska Range (Fig. 1). In particular, we tracked variations at the Suntrana Type Section (Healy Creek site). We then separated out >~50 grains of muscovite in sediment provenance through time for the Oligocene to present Tanana Basin. The three from each sample and applied 40Ar/39Ar geochronology to deconvolve their original source region. In main sediment source regions are north of the Alaska Range, south of the Alaska Range, and from addition, we collected sand from the modern Nenana River both north and south of the Range, a the Alaska Range itself (Fig. 2). Furthermore, we will use the sediment source interpretation to test the schist bedrock sample at the Suntrana type section, and a metasedimentary rock from the headwaters hypothesis that the Nenana River changed direction during the Miocene (23 Ma to 5.3 Ma) (e.g. of the Nenana River and applied 40Ar/39Ar muscovite geochronology to supplement existing regional Brennan, 2012). river and bedrock 40Ar/39Ar geochronology data sets.

° ° W155 W153 Heavy mineral zircon U-Pb ages more often reflect magmatic ages, whereas light mineral muscovite 40 39 Ar/ Ar ages reflect metamorphic ages. For our purposes, muscovite was the mineral of choice Sample Areas because of its stability during transportation and deposition, low specific density, and because the N65.5° potential source regions have bedrock lithologies that are abundant in muscovite with distinct age Upper populations from north and south of the Alaska Range and from within the Alaska Range itself. Lower Tanana River

Tanana River Delta River A muscovite sample from the Grubstake Formation and the Nenana River headwaters has yet to be dated, and we are currently in the process of dating more samples of the Sanctuary Formation and Alaska Range: When did these mountains arise to become sediment source topographic highs N64.5° Fairbanks Nenana River (Tatlanika Bridge) Lignite Formation, and change drainage patterns?

Nenana River (Cantwell) Conclusions: During the deposition of the Healy Creek Formation in the paleo-Tanana Basin, the Upper Nenana Gravels Upper Tanana River (n=46) paleo-Nenana River likely flowed south to Cook Inlet draining the Yukon-Tanana Highlands (21% of Nenana River (n=92) 250-201 Ma=2% 250-201 Ma=1% y y

t muscovite grains) (Fig. 6a). By the time of the deposition of the early-Miocene Sanctuary Formation, the t i i l

(Nenana) l i 201-153 Ma=11% i 201-153 Ma=1% b b a a 153-120 Ma=51% paleo-Nenana River was both sourcing the uplifted Alaska Range (5% of muscovite grains) and the b Suntrana 153-120 Ma=17% b o Healy o r Yukon River 120-50 Ma=70% r 120-50 Ma=47% P Type Section P Talkeetna Arc (43% of muscovite) and flowing north (Fig. 6b). The mid-Miocene Suntrana formation had (Circle) 0 50 100 150 200 250 300 50-0 Ma=0% 0 50 100 150 200 250 300 50-0 Ma=0% Age (Ma) Age (Ma) a large contribution from Triassic rocks (13% of muscovite grains) implying a spatially variable history of DE Yukon River NA drainage patterns and rock uplift in the Alaska Range. During the deposition of the Nenana Gravels, LI (Circle) FA Lower Nenana Gravels Lower Tanana River UL there is a large population of muscovite grains sourced from the Yukon-Tanana Highlands (28%) Nenana River Delta River T (n=36) (n=89) GE 250-201 Ma=3% 250-201 Ma=0% y y t t implying sediment recycling as the southern extent of the Healy Creek formation was uplifted and eroded. N i i l

l 201-153 Ma=1%

N A i

i 201-153 Ma=16%

R b b a A a 153-120 Ma=28% 153-120 Ma=39%

K b The modern Nenana River near Cantwell has an 87% contribution of muscovite grains from the Alaska b

S o o r LA r 120-50 Ma=53% 120-50 Ma=60% P 100km A P Range and no Talkeetna Arc-aged grains, implying continued drainage reorganization after the 0 50 100 150 200 250 300 50-0 Ma=0% 0 50 100 150 200 250 300 50-0 Ma=0% Age (Ma) Age (Ma) deposition of the Nenana Gravels (see modern Nenana River Figs. 1 and 2). This is supported by the Broad Pass Fault likely being active during the Pliocene (Haeussler et al., 2008). These Figure 1. Regional Map with study area, bedrock, and modern river sample locations annotated. We Lignite Creek Formation Delta River (n=18) (n=66) results are in general agreement with past work in which Brennan (2012) applied a U-Pb geochronology sampled the uplifted Paleo-Tanana Basin at the Suntrana Type Section. 250-201 Ma=0% 250-201 Ma=3% y y t t i source-to-sink approach to the paleo-Tanana Basin. In summary, the Alaska Range was uplifted by the i 201-153 Ma=50% l 201-153 Ma=36% l i i b b a

a 153-120 Ma=0% 153-120 Ma=14%

b early Miocene, the Nenana River drainage changed direction by this time period, and continued b o o

120-50 Ma=50% r

r 120-50 Ma=47% P P drainage reorganization has occurred to the recent past. W145 W144 0 50 100 150 200 250 300 50-0 Ma=0% 0 50 100 150 200 250 300 50-0 Ma=0% Age (Ma) Age (Ma) Yukon composite terrane 40 39 (Paleozoic-Mesozoic accreted) Continued Work: Our next step in this project is to complete the muscovite Ar/ Ar dating for the Suntrana Formation Nenana River - Tatlanika r e (n=81) Grubstake Formation, Nenana Glacier headwaters, and additional Lignite and Sanctuary Formations v Upper Cretaceous igneous rocks (n=76) i

R 250-201 Ma=1%

250-201 Ma=13.5% y t

a y i sample analysis. To further expand and support our preliminary conclusions, we also plan on applying t l i n i

l 201-153 Ma=5% i a Triassic-Paleozoic undifferentiated 201-153 Ma=22% b

n b a

e a 153-120 Ma=13.5% b 153-120 Ma=6% the same radiometric dating approach to different paleo-Tanana Basin outcrops outside the Suntrana b

N o r o

r 120-50 Ma=88% 120-50 Ma=50% P Paleocene-Oligocene igneous rocks P Type Section. 0 50 100 150 200 250 300 50-0 Ma=1% 0 50 100 150 200 250 300 50-0 Ma=0% r N64 e Age (Ma) Age (Ma) v Wrangellia composite terrane i

R (A) Oligocene Yukon-Tanana Highlands a t l Nenana River - Cantwell 140-120 Ma e Upper Cretaceous Valdez Group Sanctuary Formation D (n=56) (n=30) (Healy Creek Formation) Hine 250-201 Ma=2% 250-201 Ma=0% s C y

r y ee t t k F i i aul l l t Middle Jurassic igneous rocks 201-153 Ma=43% i 201-153 Ma=0% i b b a a 153-120 Ma=12.5% 153-120 Ma=0% b BP Denali Fault b West

o East o r ~40 Ma plutons r 120-50 Ma=37.5% 120-50 Ma=13% P

r P a Rive Subduction-related D Nenan 0 50 100 150 200 250 300 50-0 Ma=5% 0 50 100 150 200 250 300 50-0 Ma=87% F Nenana Gravel arc magmatism Talkeetna Arc Age (Ma) Age (Ma) 201-153 Ma (?) CMF N63 Usibelli Group Healy Creek Formation Nenana River - Nenana (n=66) (n=31) CI 250-201 Ma=2% 250-201 Ma=0% Fluvial-estuarine y y t t

i forearc-basin i l l

Sample area i i 201-153 Ma=3% 201-153 Ma=3% b

b deposition a a 153-120 Ma=3% 153-120 Ma=21% b b BP = Broad Pass o o r Healy Creek Schist r 120-50 Ma=74% 120-50 Ma=94% P P Subduction of CMF = Castle Mountain Fault 0 50 100 150 200 250 300 50-0 Ma=0% 0 50 100 150 200 250 300 50-0 Ma=0% Pacific oceanic crust DF = Denali Fault Metasedimentary bedrock sample Age (Ma) Age (Ma) 100 km CI = Cook Inlet River = Alluvial fans Yukon River - Dalton Bridge (n=82) = Fluvial drainages Fault Figure 4. Normalized probability-density plots for 250-201 Ma=1% y

t = Topography i

N l 50 km 40 39 i 201-153 Ma=17% b Yukon-Tanana Highlands

the detrital Ar/ Ar muscovite age data set from a (B) Early Miocene = Active volcanism b 153-120 Ma=9% 140-120 Ma o r 120-50 Ma=73% the Suntrana Type Section (Fig. 3) along with P (Sanctuary Formation) = Paleoflow direction Figure 2. Geological Map. Triassic-aged rocks are present in the Alaska Range. The 201-153 Ma 0 50 100 150 200 250 300 multiple river samples (Fig. 1). A probability- 50-0 Ma=0% Talkeetna Arc lies south of the Alaska Range; ~140 Ma to ~120 Ma-aged sources lie north of the Alaska Age (Ma) BP density plot is a histogram that takes into account West ~37 Ma East Range in the Yukon-Tanana Highlands. There are plutons and metasedimentary rocks within the Alaska Yukon River - Circle error. Subduction-related D Range that have the distinct age of ~40 Ma. Map modified from Trop and Ridgway, 2007. (n=67) F 250-201 Ma=3% arc magmatism y t

i Talkeetna Arc l 201-153 Ma=36% i CMF b 201-153 Ma The brown box indicates ages from the Triassic a 153-120 Ma=15% b o

r 120-50 Ma=46% CI

period (250-200 Ma); the green boxes represent P 0 50 100 150 200 250 300 50-0 Ma=0% Fluvial-estuarine forearc-basin the range for the Talkeetna Arc sources (201- Age (Ma) deposition Shallow subduction 153 Ma); the purple boxes represents ages of oceanic plateau reflecting a metamorphic event predominantly experienced throughout the Yukon-Tanana Highlands Subduction of (Yakutat microplate) Pacific oceanic crust (153-120 Ma); the pink lines indicate ages similar to the Healy Schist bedrock (104.3 " 1.1 Ma); the 100 km yellow lines represents bedrock sources from within the Alaska Range (36.7 " 0.3 Ma); and Upper Nenana Gravels Fm. 120-50 Ma ages are non-unique throughout the data sets. Graphs inspired by Brennan, 2012. Lower Nenana Gravels Fm. Figure 6 (A,B). Tectonic baseball diagrams of the paleodrainage patterns of the region of study both 10CH05B MU#L1 Age spectrum Grubstake Fm. 01SUNSCHIST MU#L1 Age spectrum during the Oligocene and the Early Miocene. Modifed from Ridgway et al., 2012. 200 40 Lignite Creek Fm.

Suntrana Fm. Integrated Age: 104.3 ± 1.1 Ma Plateau age: 104.8 ± 1.5 Ma Brennan, Patrick R.K. “Lithospheric Structure and Geologic Development of a Collisional Orogen: 150 N: 7 out of 10 30 Sanctuary Fm. MSWD: 1.98 Insights from the Central Alaska Range.” (2012): 171-218. Print. % release: 96.9 % Integrated age: 36.7 ± 0.3 Ma Plateau age: 36.4 ± 0.2 Ma Healy Creek Fm. a Haeussler, P.J., et al. “Evidence for Pliocene to present thrust faulting on the south side of the Alaska a

M N: 5 out of 13

M

20 n MSWD: 0.34 Range in the vicinity of the Peters Hills piggyback basin.” AGU Fall Meeting Abstracts. Vol. 1. 2008 100 i n

i

% release: 90.4 % e e g Ridgway, K.D., Trop, J.M., And Finzel, E.S., 2012, Modification of continental forearc basins by flat-slab g A A subduction processes: A case study from southern Alaska, in Busby, C., And Azor, A., Eds., 50 10 Tectonics of Sedimentary Basins: Recent Advances, Blackwell Publishing, p. 327-346.. Trop, Jeffrey M., And Kenneth D. Ridgway. “Mesozoic and Cenozoic Tectonic Growth of Southern Alaska:

0 0 A Sedimentary Basin Perspective.” (2007): 57-58. Print 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Fraction of 39Ar Released Fraction of 39Ar Released Wartes, Marwan A., Robert J. Gillis, Trystan M. Herriott, Richard G. Stanley, Kenneth P. Helmold, C. Figure 3. Photograph of the upper part of the Usibelli Group at the Suntrana Type Section. Samples Shaun Peterson, and Jeffrey A. Benowitz. “Summary of 2012 Reconnaissance Field Studies Related to the Petroleum Geology of the Nenana Basin, Interior Alaska.” (2012): 8. Print. were collected from Healy Creek, Sanctuary, Suntrana, Lignite Creek, and Grubstake Formations Figure 5. Age spectra for the Healy Creek Schist (bedrock formerly known as Birch Creek Schist) along with the Nenana Gravels. Note the car for scale in the lower center of the photo. Photo and text and the Alaska Range showing integrated ages of 104.3 " 1.1 Ma and 36.7 " 0.3 Ma respectively. Acknowledgements: USRA Funding, Geophysical Insistute Geochronology Facility modified from Wartes et al., 2013. We would also like to acknowledge Dr. Paul Layer for his help and contribution to the geochronological analysis.