Stable mineral recrystallization is a recently identified process by which minerals exchange with ambient solution without overt mineralogical, compositional, or morphological changes. It is a phenomenon that has significant implications for the interpretation of geochemical proxies, and thus can impact mineral-based biosignatures and paleoclimatic reconstructions. Recent work suggests that significant mass fractions of minerals (~100% in some cases), such as iron oxides, exchange with ambient solutions over extremely short time scales. Similar behavior has also been observed in non-redox active minerals, such as calcite and barite, but generally to lesser extents. While there are clearly coherent proxy-based trends that reveal critical information about the past, it is also true that minerals interact with fluids over a range of time scales, and this has the potential to impact proxy-based reconstructions of the past.
In this talk, I will summarize recent experimental work conducted at Penn State in collaboration with Chris Gorski and Prachi Joshi, which suggests that neither the so-called “homogeneous” nor “heterogeneous” models are appropriate for explaining short-term stable mineral recrystallization. Instead, we contend that a hybrid model is appropriate. This model will be described in light of “respike experiments”, in which Fe-55 tracer is used to elucidate the extent of solid-fluid exchange over 60 days. This finding has signficant implications for the interpretation of past exchange data, and for the utility of Fe-oxides as proxy archievs, as well as mediators of environmental contamination. If there is time or interest from the audience, I can also briefly present the results, and interpretations, of recent exchange experiments conducted on carbonates.
About the Speaker – Matthew S. Fantle, Penn State University
Matthew S. Fantle is an Associate Professor in the Department in Geosciences. His current research program focuses in part on quantifying the effects of diagenetic processes, such as recrystallization, on the chemistry of carbonates, but also more generally on understanding the extent to which particles interact with coexisting fluids (and why) over a range of time scales. He is am interested in bringing a range of tools to bear on these questions, including neutron scattering, laser ablation, and nano-SIMS. His group has also been involved in NASA NAI sponsored work aimed at understanding the impact of organics on isotopic fractionation, and the use of isotopes as biosignatures. He constructed the Metal Isotope Laboratory (MIL) at PSU, which includes a Neptune Plus MC-ICP-MS, a Triton Plus TIMS, and clean lab facilities for dissolving and chromatographically purifying a range of natural samples.