EARLY SERPENTINITE WEATHERING REACTIONS

This project explores the early weathering of serpentinites at two field localities: Pine Hill, Little Dear Isle, ME and Trinity Ultramafic Complex, Klamath Mountains, CA. Early weathering reactions in serpentinites are important because these reactions lead to porosity development that allows water to infiltrate into the low-porosity rock. The first mineral to dissolve within rocks is referred to as the “profile-controlling mineral”, which, even if present in small concentrations, may play a vital role in future soil formation.

Samples were collected from the soil, and to ~ 1 m within the bedrock at the Klamath Mountains site, while samples were taken to ~ 5 m depth in the bedrock at the Pine Hill site. Weathering profiles from both sites suggest that pyroxene weathers faster than serpentine, and that different serpentine polymorphs are present within both rocks with different weathering rates. SEM analysis shows the precipitation of secondary minerals, including manganese oxides and possible clays, within the top meter of the Pine Hill serpentinite. Normalized elemental concentration profiles show that calcium and titanium are depleted in the upper meter of the bedrock, while zinc and copper show depletion in soils followed by enrichment in the underlying bedrock. Major elements, including silicon and magnesium, show no changes. Fe-oxidizing bacteria have been detected within both the soils and weathered rock at the Klamath Mountains site, suggesting that bacteria could be contributing to weathering. In addition to field chemical weathering studies, we will conduct modeling using the reactive transport code CrunchFlow to quantitatively interpret the processes controlling weathering of serpentinites from bedrock to soil surface.