Tracking Reaction Assemblages in Iron-rich Chemical Sedimentary Rocks from Deposition through Burial, Metamorphism, and Multiple Generations of Fluid Alteration

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part I

Presenting Author:

Prof. Latisha Ashley Brengman

Authors:

Brengman, Latisha Ashley¹, Stewart, Esther K.², Bhuiyan, Farhan Ahmed³, Mitchell, Jennifer⁴, Banks, Madelyn⁵, Marin Lopez, Valentina⁶

(1) University of Minnesota Duluth, Earth and Environmental Sciences, Duluth, MN, USA, (2) Wisconsin Geological and Natural History Survey, Madison, WI, USA, (3) Iowa State University, Ames, IA, USA, (4) University of Minnesota, Minneapolis, MN, USA, (5) University of Minnesota Duluth, Duluth, MN, USA, (6) University of Minnesota Duluth, Duluth, MN, USA,

Abstract:

Many of early Earth’s fundamental, directional changes are archived within depositional systems affected by multiple orogenies and post-depositional mineral transformations. A framework to reconstruct low temperature mineral reaction assemblages in reactive iron-rich chemical sedimentary systems could help discriminate localized effects from regional or larger-scale depositional signals. Here we develop a low-temperature mineral reaction framework using a basinal transect that integrates mm-scale mineral, geochemical, and stratigraphic datasets from a sub-greenschist terrane. We document horizon- and basin-position-specific generations of fluid alteration associated with element mobility, and redox changes, in addition to tracking mineral-specific element exchange with increasing temperature in the same system across a metamorphic contact aureole. We then apply the low-temperature mineral reaction framework to track observed mineralogical and geochemical changes in higher temperature assemblages, comparing systems through time. Key findings include: (1) within one basin, we track systematic, localized geochemical changes that can be explained with different starting mineral assemblages; (2) complete mineral replacement reactions are common but traceable, resulting in mineralogical and geochemical information loss with increasing temperature; (3) partial reconstruction of deposition-linked low-temperature mineral assemblages in iron-rich chemical sedimentary rocks at the basin scale is possible using paired mineral chemistry and geochemical data placed within a well-constrained stratigraphic context; and (4) the low-temperature reaction assemblages observed in this study could inform disparate interpretations of geochemical data and distinguish signals of basin response to tectonic forcings in some early Precambrian assemblages.