Tag: ta2.2

22-EPN3-092: Deciphering Traces of Life from the Dawn of Earth’s Biosphere

Visit by Nisha Ramkissooon (The Open University, UK) to TA2.2 VU (Exo)Planetary Interior Simulation Laboratory (PISL).
Dates of visit: 12-16 February 2024

Report Summary: In the search for evidence of ancient terrestrial life there are some obstacles. Purported biosignatures have been identified in a range of ancient mineral deposits, including silica. However, some of these signatures can also be generated under abiotic conditions, which brings into question their biological origin. In addition, the oldest fragments of the Earth’s crust are at least 3.8 Gyr, and would have experienced significant metamorphic alteration since their formation. Therefore, any preserved biosignatures could have also undergone extensive modification during metamorphism potentially making some of them unidentifiable. This project aimed to examine the effect of metamorphism on the modification of biosignatures preserved in silica deposits. 

Silica sinters were synthetically created in the laboratory via evaporation in the presence and absence of microbes. These samples were then exposed to simultaneous high temperature and high pressure conditions using the end-loaded piston-cylinder at the (Exo) Planetary Interior Simulation Laboratory (PISL), VU University, Amsterdam. Samples were individually subjected to pressures and temperatures of 650 °C and 12 kbar, respectively, for 20 hours. Raman spectroscopy and GC-MS will be used to assess changes in mineralogy and to quantify changes to organic molecules. Initial results obtained after returning to my home institution show that the high pressure and high temperature conditions experienced in these experiments led to changes in the crystalline structure of the samples. This resulted in samples transforming from silica glass to quartz. 

20-EPN2-91: Experimentally determined distribution of highly siderophile elements between sulfide and silicate melts at highly reduced conditions: implications for terrestrial late accretion models

Visit by Edgar Steenstra, Institute of Mineralogy, WWU Muenster (Germany) to TA2.2 VU (Exo)Planetary Interior Simulation Laboratory (PISL).
Dates of visit: 22 – 24 November 2022

Report Summary: Fifteen high-pressure experiments on the PISL end-loaded piston cylinder press were performed at 1 GPa and 1873 K to systematically investigate the effects of Cu and Ni on metal- and sulfide-silicate partitioning of highly siderophile elements (HSE) Pd, Ru, Pt and Ir. Run times at peak conditions varied around 60-90 minutes. The starting compositions consisted of silicate, sulfide and metal powders with added metallic Si. The experimental run products consist of well-segregated metallic and sulfide blobs in a silicate glass. The addition of metallic Si and the initial reduction of the experiments result in the suppression of nugget formation. The glass does contain minute specks typical of S- saturated silicate melts – subsequent LA-ICP-MS measurements of the run products show that these specks do not contain HSE, as initially hypothesized. Electron microprobe and LA-ICP-MS analyses further show that the experimental run products are homogeneous and no compositional zoning was observed. Initial results show that the addition of Cu and Ni to the sulfide liquid decreases the O content of that sulfide liquid at a given FeO value of the silicate melt. This will most certainly affect the partitioning of the elements of interest – preliminary results for Pt confirm this by its variation by three orders of magnitude at a given FeO content. Preliminary results also show that Pd, Ru, Pt, Ir are all preferentially partitioned into the metallic liquid instead of the sulfide melt, confirming their preference for S-poor alloys relative to S-rich liquids. 

20-EPN2-119: Distribution of sulfide-loving elements between major (mafic) mineral phases and silicate melts

Visit by Stephan Klemme and Edgar Steenstra, Institute of Mineralogy, WWU Muenster (Germany) to TA2.2 VU (Exo)Planetary Interior Simulation Laboratory (PISL).
Dates of visit: 22 – 24 November 2022

Report Summary: Twelve high-pressure experiments on a piston cylinder press were performed at 1 GPa and 1673-1873 K to systematically investigate the sulfide-silicate partitioning of chalcophile elements as a function of (non-FeO) silicate melt compositional terms. Run times at peak conditions varied around 70 to 220 minutes. The starting compositions consisted of silicate and sulfide powders. The experimental run products consist of well-segregated sulfide blebs in a silicate glass. The glass contains minute sulfur blebs but subsequent LA-ICP-MS measurements showed that these blebs do not contain the elements of interest and are composed of Fe-S-O.   Electron microprobe and LA-ICP-MS analyses further showed that the experimental run products are homogeneous and no compositional zoning was observed. 

Initial results show that variations in silicate melt composition affect the partitioning of chalcophile elements in a non-ideal way – i.e. FeO activity varies significantly across different melt compositions, thereby affecting the geochemical behavior of the elements of interest. Therefore, it can be expected that in an arc-type differentiation suite the sulfide-silicate partitioning behavior may vary significantly, purely due to variations in FeO activity due to variable silicate melt compositions.