T59 Gradients at Hydrologic Interfaces as Indicators of Key Earth-Surface ("Critical-Zone") Processes (Posters)

GRADIENTS IN MINERALOGY AND ELEMENT COMPOSITION AT THE BEDROCK-REGOLITH INTERFACE RECORD MINERAL REACTION AND TRANSPORT RATES

Paper number: T59-2
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Basalt is the most common volcanic rock in the Earth's crust, and due to its quickly dissolving nature plays an important role in the composition of the Earth's waters. Additionally, about one third of the carbon dioxide currently being removed from the atmosphere by weathering silicate rocks is removed by weathering basalt. Basalt is also important to our understanding of the surface of Mars. However, despite its importance on both Earth and Mars, basalt weathering rates remain poorly understood.

We have studied elemental weathering profiles formed on basaltic parent material in three field weathering environments: tropical Costa Rica, temperate Pennsylvania, and arctic Svalbard (Norway). The gradients formed at these interfaces between parent rock and weathered rind or soil allow a comparison of basalt weathering under different climate regimes, duration of weathering, and physical erosion. The reaction front thickness over which primary minerals disappear from these profiles ranges from microns (Svalbard) to centimeters (Pennsylvania).

We also compare global mineral persistence data from soil environments to the studied weathering profiles. We present a compilation of field weathering rates for 8 common rock-forming phases (plagioclase, volcanic glass, quartz, feldspar, micas, pyroxene, amphibole, and olivine) collected from dated chronosequences representing a wide climatic spectrum ranging from -10°C to 30°C mean annual temperature and 400 mm to 4500 mm mean annual precipitation. This compilation helps constrain the rates at which primary phases weather under field conditions.

Understanding and interpreting basalt weathering profiles as well as mineral persistence in field environments allows us to better understand basalt weathering rates. This will help inform geochemical modeling, and enhance our understanding of the surface and aqueous history of both Earth and Mars.