40 Micro to Macro: Linking Structural Geology, Petrology, Geochronology, and Tectonics Across Scales (Posters)

Tuesday, 19 March 2024
9:00 AM - 1:00 PM
Armory Ballroom

FEASIBILITY OF THE U-PB HEMATITE CHRONOMETER IN SUPERIOR REGION MASSIVE IRON FORMATIONS

Paper number: 40-9
Program: Theme Sessions
Time: 9:00 AM – 1:00 PM

Authors

Abstract

The development of U-Pb geochronology in zircon unlocked unprecedented insight into Earth's dynamics in deep time. However, in non-magmatic successions without syn-depositional zircons, such as most of the thick, iron-rich chemical sedimentary rocks that record Earth’s oxygenation history, key temporal data remains out of reach. Throughout the Precambrian, deposition of iron-oxides records the state and evolution of marine oxygenation, while post-depositional enrichment of iron-oxides informs models of ore formation. Recently, novel techniques and approaches like the U-Pb hematite chronometer enable the acquisition of mineral-scale datasets to test models of iron-oxide deposition and enrichment. Hematite incorporates substituting cations such as U in octahedral-coordination with expected closure temperature similar to rutile. Here we test the feasibility of applying the U-Pb chronometer in Precambrian massive iron deposits from the Superior region Trommald and Ironwood Iron formations, using coupled petrographic and LA-ICP-MS mapping data. LA-ICP-MS mapping is an ideal tool to identify targets for successful U-Pb dating via detection of hematite with the greatest homogeneity, high U (>5 ppm) and lowest Pbc. Such analyses can help set the stage for applications of the novel U-Pb hematite chronometer to depositional, deep ore, and surface ore iron oxides to tease apart the timing of primary precipitation and test enrichment mechanisms.

Geological Society of America Abstracts with Programs. Vol. 56, No. 1

doi: 10.1130/abs/2024NE-397718

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