229-7 Mafic Granulite Garnet Geochronology in the Deepest Section of the Athabasca Granulite Terrane

Session: Crustal Petrology (Posters)

Presenting Author:

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 Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8730

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