100 Snowballs, Unconformities, BIFs and Beyond: Navigating the Neoproterozoic Rock and Climate Records Using Geochronology

The Neoproterozoic comprised periods of upheaval in Earth’s climate which changed the course of life and resulted in unique geologic features and formations. We welcome contributions applying geochronometers to investigate the timing of events and processes which shaped the Neoproterozoic.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 304C

Hematite Double-Dating Defines Proterozoic Mineralization and Thermal History of Archean Banded Iron Formations, NE Minnesota, USA

Paper number: 100-9
Program: Technical Sessions
Time: 10:25 AM – 10:40 AM

Authors

Abstract

The age and origin of hematite deposits in the Vermilion District of Minnesota, Lake Superior region has been debated for over a century and inferred to be Neoarchean or Mesoproterozoic. Utilizing a new geochronological approach combining U-Pb and (U-Th)/He ‘double-dating’ of hematite, we present the first direct dates for hematite deposits at the Soudan mine, revealing a previously unknown Paleoproterozoic mineralization event and a thermal history recording the emplacement of the proximal Mesoproterozoic Midcontinent Rift System. Hematite phases yield U-Pb crystallization dates ranging between 1.8-1.6 Ga and (U-Th)/He dates in the range of 1.63-0.53 Ga, with a distinct cluster at ca. 1.1 Ga. We propose that replacement-style hematite mineralization was generated during Paleoproterozoic orogenic events, including the Yavapai (1.71-1.68 Ga) and/or Mazatzal (1.65-1.60 Ga) accretionary orogenies and associated magmatism related to the assembly of Laurentia that reactivated shear zones and facilitated hydrothermal alteration deep into the Archean craton. (U-Th)/He data suggest that hematite ore experienced a thermal overprint that did not reset the U-Pb system, with the most consistent dates coinciding with the establishment of the Midcontinent Rift System at ca. 1.1 Ga. Double-dating of hematite is demonstrated to directly link iron mineralization to thermal and tectonic events in Precambrian cratons and place constraints on genesis not available from coexisting accessory minerals.

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

doi: 10.1130/abs/2025AM-414941

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