22 Undergraduate Research Poster Session II

Saturday, 29 March 2025
8:30 AM - 5:30 PM
North Great Hall

LOW-TEMPERATURE HYDROTHERMAL ALTERATION OF SLOW-SPREADING, NON-MORB OCEANIC CRUST AND ITS EFFECTS ON THE SEAWATER POTASSIUM BUDGET

Paper number: 22-30
Program: Theme Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

Low-temperature chemical exchanges between oceanic crust and seawater play a significant role in the biogeochemical cycle of many elements and help to regulate atmospheric CO2 concentrations over geological timescales. Understanding the timing, style and extent of these reactions is thus crucial to our knowledge of global climate feedback. Potassium (K) is a highly mobile element during low-temperature hydrothermal alteration and tends to accumulate in altered crust as it exchanges with seawater. As a result, K concentrations in altered oceanic crust (AOC) provide a direct window into the extent of reaction between crust and seawater. Recently, K-isotopes have been paired with K concentrations to shed light into the heterogeneous nature of oceanic crust alteration. However, existing data are limited to intermediate to fast spreading ridges with MORB-like lithologies. In this study, we expand on our knowledge of K cycling in AOC through the analysis of K-isotopic compositions of oceanic crust samples from a nearly 60-million-year-old piece of slow-spreading crust from the South Atlantic Ocean (~30oS). These rocks span compositions varying from MORB-like to enriched tholeiites and alkali basalts, thus covering a large range of initial K2O (wt%) contents. Our K-isotope data reinforce the dynamic and heterogeneous nature of low-temperature seawater-crustal exchange and indicate both gain and loss of K during crustal alteration. Depending on the global extent of these non-MORB lithologies, results from this study also suggest that our current picture of the effects of low-temperature hydrothermal alteration on the chemistry of seawater might need revision.

Geological Society of America Abstracts with Programs. Vol. 57, No. 3

doi: 10.1130/abs/2025NE-408905

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