Trail Lab

Early Earth and Experimental Geochemistry

Overview


Research conducted in our lab can be broadly classified as high temperature geochemistry. Much of our work involves the investigation of accessory minerals in the crust such as zircon, apatite, monazite, xenotime, and rutile. While these minerals make up a volumetrically minute fraction of the crust, their chemical and isotopic compositions hold a wealth of information. Accessory minerals are also important because in certain cases they represent the only available source of information. For example, zircons with ages that approach 4.4 billion years represent the only material available to investigate the Hadean Earth, as no known rocks exist from this time. We now have strong evidence that some of the pre-4.0 Ga zircons formed in igneous magmas that captured and archived a small fraction of the Earth's surface chemistry through re-melting of sedimentary rocks. We seek to "translate" this remnant chemical information from the formative stages of Earth into physical, chemical, and potentially planetary-wide constraints. Our strength lies in our ability to combine laboratory experiments with measurements of natural samples; that is, we do not think of our experiments as standalone contributions, but rather as a guide or impetus that leads us to conduct measurements on natural samples. A few recent projects are described below, though you will find more information on our 'publications' page.

Redox State of Early Earth Magmas. There is little question that the earliest atmosphere was influenced by the magmatic outgassing of Earth, especially since the first ~500 million years were the most active in our planet’s history. Magmatic gases can be composed of H, C, N, O, and S, but the composition of volatile emanations depends on the "pressure" of O2 in the magma, which is referred to as the oxygen fugacity. For example, if early Earth magmas had oxygen fugacities similar to the modern-day Earth, then CO2 would be stable, and would thus enter the atmosphere during outgassing. If reducing conditions prevailed, then a portion of the emanating gas mixture would be composed of carbon monoxide (CO). Our work has linked the (redox sensitive) chemistry preserved in magmatic zircon to the volatile gas composition, which showed that volcanic emanations were likely dominated by CO2, SO2, and H2O. You can read more about this research in Trail et al., 2011 (Nature), and 2012 (Geochim. Cosmochim. Acta). Below is an artist's conception of an Early Earth. For more artist conceptions of the early Earth such as this, see more work by the talented artist Don Dixon.

Artist conception of early earth.

Possible biosphere-lithosphere interactions preserved in minerals. One of our more recent contributions explores how biological processes (ancient and modern) could ultimately influence the chemical properties of magmas and minerals through the recycling of biomass. We examined the redox sensitive chemistry in zircons from Lachlan Fold Belt granitoids from two classes of rocks: (i) those that were likely derived from the melting of pre-existing igneous rocks, and (ii) those formed in granitoids magmas that assimilated buried sedimentary material with (reduced) biomass. We discovered that zircons from granitoids formed by re-melting of sediments grew under reducing conditions when compared to those formed from re melting of igneous rocks. This observation highlights one possible manner in which 'life' may modify the composition of igneous minerals. You can find more information in Trail et al., 2015 (Astrobiology).

A geospeedometer and peak temperature indicator for zircon. Our most recent contribution (as of March 2016) presents a possible geospeedometer for zircon. This approach relies on the zoning of Li in zircon to reveal temperature-time paths in the crust. Such work may be useful to zircon analysts that seek to establish peak thermal temperatures of detrital zircons with unknown thermal histories. Our work can also be applied to ~10 to ~100 year timescales of melt generation, storage, and eventual extraction of material during volcanic eruptions. See Trail et al., 2016 (Contributions to Mineralogy and Petrology) for more details; in this publication, you can find a few more important applications, including a possible application to exploring the time and intensity of Earth's early magnetic field.