Meeting/Event Information

AIPG MN May Luncheon - Mt. Draper and Mt. Stamy Plutons, Nunatak Fjord, Alaska!

May 01, 2018
11:45 AM to 1:00 PM
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Radisson Hotel Roseville
2540 North Cleveland Avenue
Roseville, MN 55113

Registration for the AIPG MN Section May Luncheon is now open online! The cost is $21 for non-members and $16 for members when registering before Monday, April 30, 2018 at 11:00 AM. Students may attend free of charge by registering in advance. Same-day luncheon registration cost is $25.  As always, non-geologists are welcome to attend!


Geochemistry, U-Pb Ages, and Hf Isotope Composition of the Mt. Draper and Mt. Stamy Plutons, Nunatak Fjord, Alaska: Implications for the Sanak-Baranof Plutonic Belt.


by Erin Arntson, Carleton College


Presentation Abstract


The Sanak-Baranof Plutonic Belt (SBPB) intrudes into the Chugach Prince William terrane (CPW), spanning the southern Alaskan margin. In southeastern Alaska, the Mt. Draper and Mt. Stamy plutons are confined to the Boundary block, which is situated outboard of the southeastern CPW: the Chugach Metamorphic Complex (CMC). Despite their confinement to the Boundary block, these plutons are part of the SBPB, evidenced by their ages and major element geochemistry. We report here LA-ICPMS U-Pb zircon dates from three different Mt. Draper two-mica granite samples that yield crystallization ages of 54.00 ± 0.60 Ma, 53.92 ± 0.82 Ma, and 53.06 ± 0.72 Ma. A gabbro most likely associated with the Mt Draper pluton, but collected from the Nunatak (5 km east of the main body of the pluton) yields an age of 52.78 ± 0.60 Ma, and the nearby Mt. Stamy pluton has a U-Pb date of 51.42 ± 0.66 Ma. Weighted mean εHf (t) values from two ~54 Ma Mt. Draper granites are +7.6 and +8.1, which correlates with a trend of increasing εHf (t) with younging in the central and eastern SBPB. Maximum depositional ages for the Schist of Nunatak Fjord, into which the Mt. Draper and Mt. Stamy plutons intrude, are as young as 53.2 Ma. This implies a rapid process of deposition, burial, and intrusion, which also occurs in the CMC, establishing a relationship between the CMC and the Boundary block. Geochemical, U-Pb, and Hf isotope data relate the Boundary block plutons to eastern Sanak-Baranof plutons, suggesting a common source and therefore close proximity at the time of intrusion. Building off of the Baranof-Leech River hypothesis, we propose that the Boundary block and Baranof Island were contiguous at Vancouver Island at ~50Ma before northward transport to their current locations along the Queen-Charlotte Fairweather fault system.



Speaker Biography


Erin Arntson is a senior geology major at Carleton College in Northfield, Minnesota, from which she will graduate in June. Erin is the Student Departmental Advisor for the geology department and has also worked as a teaching assistant for the past year. Besides studying geology, Erin works as a Student Manager in Carleton’s dining halls and dedicates a large amount of time to various dance clubs. She serves as the student director for Semaphore Repertory Modern Dance Company and a choreographer for Experimental Dance Board. Erin grew up in Grand Rapids, MN, and hopes to end up somewhere with snow next year!




$16.00 AIPG Member

$21.00 Non-Member

$0.00 Student