David Burney

Igneous Petrology and Geochemistry of Iceland

            I quantified the textures and geochemistry of the crystalline cargo of an off-rift basaltic deposit on Western Iceland. The bulk of volcanism on Iceland is due to the divergence of lithospheric plates and allowing for the melting and eruption of large volumes of basalts. This rifting is a continuation of the mid-Atlantic ridge which is pushed upwards by a mantle plume which allows for the subaerial exposure of these rifting and volcanic processes. A string of monogenetic volcanic events are located in western Iceland in East-West orientated volcanic fields which are perpendicular and far from the North-South oriented main rift zones. The cause of volcanism in the West is unique from the predominant rifting processes occurring across the rest of Iceland, and thus the magma chamber dynamics are poorly constrained. My researched utilized a heavily porphyritic deposit named Vatnafell to investigate the magmatic plumbing system and crustal structure beneath this basalt flow. The geochemistry and textures of the entrained minerals, predominantly clinopyroxene and olivine, were used to calculate the depths and temperatures of crystallization and residence times. The results show a simpler magma chamber morphology than what is seen in the main rift zones as there are fewer locations within the crust for magma to stall and continue to crystallize. A wherlitic cumulate formed at the base of the crust which was then ripped up and incorporated into the surrounding magma as it ascended rapidly to subglacially erupt.

Planetary volatiles and geochemical signatures

            A large part of my research background involves analyzing planetary materials in an effort to understand the differentiation and evolution of other worlds. I have studied many lunar samples collected during the Apollo missions to investigate the role of volatiles on the Moon. Prior to, and soon after, the Apollo missions the Moon was hypothesized to be “dry” as the Giant Impact that created would have driven off any volatile species. Recent analyses have shown that highly volatile species such as water are actually present which has sparked a “volatiles renaissance” with respect to Lunar samples. My research was based on a suite of moderately volatile elements (MVEs: Zn, Se, Rb, Ag, Cd, In, Sb, Tl, Pb, and Bi) with the assumption that if highly volatile species survived the Giant Impact and subsequent differentiation and eruption, then the more robust moderately volatile species may be present as well. This suite of elements is poorly constrained in lunar material, but has become a very important tracer of volatiles throughout lunar evolution. I developed a method to measure this suite of elements in whole-rock samples using ICP-MS, then applied this method to over 60 different lunar lithologies. The incompatible nature of the MVEs in crystallizing phases means that they should become more concentrated in later forming lunar lithologies. This enrichment is not seen across the entire suite and must have endured two fundamental processes; 1.) They degassed as lunar evolution occurred, possibly from the lunar magma ocean before the crust had formed, during eruption, or possibly after the lunar crust had formed if crustal breaching impacts were able to expose the source regions for the erupted basalts. 2.) The source regions became quite well mixed to create a homogenous source region with respect to the MVEs that is not seen in the major element compositions used to differentiate the lunar lithologies. While many processes are at work throughout planetary differentiation and evolution, the MVEs have been used as another line of evidence to explore these processes. Many discussions are ongoing over the implications of my data with respect to individual sample suites, as well as understanding their part in lunar formation.

Impact Processes

            Meteorites are interesting geologic samples to interpret because they encompass so many more signatures than what terrestrial samples go through. While they have experienced similar fundamental igneous processes such as crystal formation and eruption or emplacement, they have also experienced dramatic high-energy events which alter them, as well as the material they impact. Meteorites also provide sample materials from distant bodies within our solar system that we have not been able to sample directly.  I have disentangling the geochemical signatures within lunar and Martian meteorites and impact lithologies to determine what they can tell us about their parent body, or what the impactor has changed here in terrestrial materials. I am interested in the geologic rock forming processes as well as the necessary analytical methods to process the materials and properly quantify the data necessary to conduct research in these and other areas of Earth Science.