229 Crustal Petrology (Posters)

This session explores various igneous and metamorphic processes that have shaped Earth’s crust. We welcome contributions from the micro- to macroscale, from the deep to shallow crust, and from field- to laboratory- to modeling-based.

Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Mafic Granulite Garnet Geochronology in the Deepest Section of the Athabasca Granulite Terrane

Paper number: 229-6
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Athabasca granulite terrane in the western Canadian Shield (AGT) with felsic and mafic granulites preserves paleodepths of 20-60 km and peak temperatures as high as 900-1000 °C in the Upper Deck domain of the AGT. Metamorphism of the felsic granulites has been dated at 2.6 Ga and 1.9 Ga using high precision ID-TIMS zircon 207Pb/206Pb dates and Th-U-total Pb dates of monazite using in situ electron probe microanalysis. The mafic granulites are not well dated and commonly yield complex discordant arrays of zircon dates between 2.55 Ga and 1.9 Ga, based on ID-TIMS U-Pb zircon geochronology. 176Lu/176Hf and 147Sm/143Nd dating of garnet offers potential answers to the crystallization date of the mafic granulites. Using a multi-collector inductively coupled plasma mass spectrometer to analyze bulk garnet separates and whole rock fractions, the 176Lu/177Hf data collected from six different samples at various paleodepths across the Upper Deck domain indicate apparent crystallization dates at around 2.1 Ga for five samples and 1.9 Ga for the remaining sample. The 147Sm/143Nd dates of the same six samples are 1.9 Ga for five samples and 2.1Ga for the last sample. The 2.1 Ga dates are inconsistent with known dates of regional tectonic events. The diffusion of trace elements in garnet during long term lower crustal residence (700 m.y.) could explain the inconsistency.

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

doi: 10.1130/abs/2025AM-413357

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