Tomáš Magna

Lithium in the Deep Earth: Mantle and Crustal Systems

Chapter 5 summarizes the current status of Li isotopic research in the Earths mantle and derivative melts as well as magmatic and metamorphic rocks of Earths crust. During the last decade a number of studies investigated samples from a range of settings and there is now better understanding of processes which drive Li isotopic fractionations at magmatic to sub-magmatic temperatures. Although this endeavor into the inner Earth is far from complete, comprehension of processes taking place in the mantle, during mantle melting, metasomatism, large-scale volcanism, and formation of crust has in recent years substantially increased. We focus on these major Earth reservoirs where Li predominantly resides.

Li Partitioning, Diffusion and Associated Isotopic Fractionation: Theoretical and Experimental Insights

Laboratory experiments on the partitioning of elements and isotopes between various phases (minerals, fluids, and melts) at thermodynamic equilibrium are fundamental to the interpretation of geochemical data. We compile and discuss in this chapter the measured partition coefficients of Li and Li isotopes between various phases (mineral–melt, mineral–fluid, and mineral–mineral), and the measured diffusion coefficients of Li in minerals, fluids, and melts. Furthermore, we present and discuss consequences of diffusive fractionation of Li isotopes. Based on the information compiled for partitioning and diffusion behavior of Li, we finally discuss experiments on fluid–rock interaction with special emphasis on the behavior of Li.

Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere

Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε54Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the 54Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ17O values as low as −0.22‰ in irghizites, however, are incompatible with a CI-like impactor. We suggest that the observed 17O depletion in irghizites relative to the terrestrial range is caused by partial isotope exchange with atmospheric oxygen (Δ17O = −0.47‰) following material ejection. In contrast, combined Δ17O–ε54Cr data for central European tektites (distal ejecta) fall into the terrestrial range and neither impactor fingerprint nor oxygen isotope exchange with the atmosphere are indicated.Identifying the original impactor from craters remains challenging. Here, the authors use chromium and oxygen isotopes to indicate that the Zhamanshin astrobleme impactor was a carbonaceous chrondrite by demonstrating that depleted 17O values are due to exchange with atmospheric oxygen.

The Surficial Realm: Low Temperature Geochemistry of Lithium

In this section we consider the variations shown by Li isotopes in materials related to near-surface (classically referred to as “low temperature”) systems, ranging from sediments and sedimentary rocks to natural waters and possible anthropogenic impacts. The combination of modest abundance in many minerals and fluid solubility make Li an element of interest in many surficial environments. The strong fractionation of Li isotopes has been exploited substantially in the examination of a variety of near-Earth-surface processes. In addition to their intrinsic value, many of these studies are critical toward the understanding of the cycling of Li between shallow and deep Earth reservoirs, as, relative to the latter, the bulk of the mass fractionation goes on in the former. Many studies aim also to develop Li isotopic tools for better quantifying processes in the shallow Earth, such as geothermometry of hydrothermal systems.

Summation: What Have We Learned and Where Can We Go?

In the 2004 review of the state of Li isotope research by Tomascak, a series of conclusions were put forth. Some of these were actually suggestions of where Li isotopes had either not been effectively applied or where the existing data failed to completely assess a topic. This concluding chapter revisits these points and indicates areas of prospective growth. Additionally, cautions are set out for future studies, especially of high-temperature materials where the effects of diffusion must be considered.

Methodology of Lithium Analytical Chemistry and Isotopic Measurements

At the time of the 19th century discovery and isolation of lithium, the future applications to various fields of human activities and far-reaching importance in several specific areas of industry were unimaginable. A long time had to elapse before the first inklings of utility in geoscience came about in the 1960s. At that stage, a plethora of chemical and instrumental methods to measure the abundances of two naturally occurring isotopes of Li to the highest possible degree of accuracy and precision began to be developed. This chapter synthesizes the pitfalls and success of these endeavours, with particular focus on the Earth and planetary sciences.