142 Undergraduate and Graduate Geoscience Student Lightning Talk Showcase (Posters)

This hybrid session offers undergraduate and graduate students the opportunity to present research findings in a brief, one-slide oral presentation (morning) and a poster presentation (afternoon). This session promotes science communication skills to audiences in multiple formats.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Geochemical Analysis of Shuksan Greenschist and Blueschist from the Easton Metamorphic Suiet in the Central Cascades, Washington State.

Paper number: 142-5
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Petrography and whole-rock geochemistry was done to help infer the tectonic origin of the Shuksan greenschist and blueschist of the Cretaceous Easton Metamorphic Suite. We analyzed 15 samples from the Hicks Butte and Kachess Lake inliers. The greenschist and blueschist are lepidoblastic to nematoblastic. The blueschist contain glaucophane and epidote. All samples plot in the field for basalt on the Ti/Zr vs. Nb/Y classification diagram.

All samples on a N-MORB normalization diagram have negative Th-Nb anomalies and look like modern arc settings. Most of the samples on the N-MORB normalized diagram display patterns similar to modern back-arc basin basalts. Three samples display enriched island arc tholeiite N-MORB normalization patterns. The last four samples have similar N-MORB normalization patterns to modern boninites. These four greenschist also have high V and low Ti, and plot in the boninite fields on discrimination diagrams; and they classify as both low- and high-Si boninites.

The majority of samples on the Th/Yb-Nb/Yb diagram plot within the mantle array near the average value for N-MORB. The four boninite samples have higher Th/Yb ratios and plot in the arc array but at depleted Nb/Yb ratios. The three enriched arc samples have high Th/Yb ratios and plot in the arc array at higher Nb/Yb ratios than other samples. The blueschist have higher Ti than the greenschist.

All samples have arc geochemical affinities. Geochemistry suggests a majority of the samples formed in a back-arc basin. The four boninites have geochemistry suggesting they formed in a forearc. The remaining three samples formed in a more enriched arc setting. The back-arc basin basalts are located in both inliers. The boninites are located only in the Hicks Butte inlier and the enriched island arc tholeiites are only in the Kachess inlier.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412394

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