Department of Earth and Planetary Sciences Seminars
The Department of Earth and Planetary Sciences holds research seminars on a regular basis - please see below for the upcoming Department seminars. Staff and students are welcome to attend.
|28th May 2018, E7B 264 12 noon - 1 pm||Zsannet Pinter||The compositions of melts in the incipient melting region|
The composition of mantle-derived magmas suggest a remarkable variety in the abundances of volatiles in the upper mantle. Volatile components like H2O and CO2, generally depress the melting point of mantle considerably (Green, 2015). However, we have little knowledge about these first, incipient melts. We know incipient melts exist in a large temperature range (~300°C) in the upper mantle, but the chemical compositions of these melts are poorly constrained, and therefore the effect of volatiles on the various melt proportions could change the behaviour of melt significantly (Foley et al., 2011).
Nature provides us with limited samples of primitive mantle-derived melts, which have mostly suffered fractionation or weathering processes. Therefore it is necessary to simplify the picture for studying the primitive melts. Experimental petrology provides better insights into the incipient melting regime in mantle conditions. This project consists of a systematic study to determine the chemistry of incipient melts using different starting compositions (Green, 2015) with various volatile compositions. We are considering the effects of temperature (provide T range), and pressure (provide P range) in the incipient melt regime using piston cylinder apparatus. Our results show that melt compositions progress from carbonate-rich to carbonated silicate and are characterised by strong increase in SiO2 (2.75 to 39 wt%), as TiO2, Na2O and K2O decrease with increasing temperature. However, MgO shows little change at given pressures.
The project is a collaboration between Macquarie University (Sydney) and ANU RSES experimental group.References:
Foley, S.F. (2011) A reappraisal of redox melting in the Earth’s Mantle as a function of tectonic setting and time. Journal of Petrology 52:1363-1391.
Green, D.H. (2015) Experimental petrology of peridotites, including effects of water and carbon on melting in the Earth´s upper mantle. Physics and Chemistry of Minerals 42:95-122.
|8th of June 2018, E7B 263, 12 noon to 1 PM.||Juraj Farkas||Stable and Radiogenic Alkali/Alkaline Earth Metal Isotopes: Applications to Earth System Studies and Geochronology|
Alkaline earth metals, such as Mg, Ca and Sr, are major components of many geological and biological systems, and their biogeochemical cycles are closely linked to the global C cycle through the processes of silicate/carbonate weathering, marine carbonate formation, and/or seawater-basalt interactions at the mid-ocean ridges. These large-scale processes thus control the elemental and isotope budgets of alkaline earth metals in the oceans, and their past changes will be reflected in Mg, Ca, and Sr isotope records of seawater over geological time.
The stable and radiogenic isotope proxies of selected alkaline earth metals (d26Mg, d44Ca, d88Sr and 87Sr/86Sr), applied to marine carbonate archives, can be thus used to reconstruct the isotope composition of paleo-seawater over Phanerozoic and Neoproterozoic time scales, with implications for the Earth's system evolution. Specifically, stable Mg isotopes are used here to better constrain the past oceanic Mg fluxes, and plausible driving mechanism(s) behind the temporal changes in marine Mg/Ca ratios over Phanerozoic. A novel approach using both stable and radiogenic Sr isotopes (d88Sr, and 87Sr/86Sr) in carbonates will be applied to Neoproterozoic to infer past changes in Earth’s surface processes, i.e., carbonate weathering versus burial fluxes, during one of the most extreme environmental changes recorded on our planet.
Finally, new applications of in-situ dating and geochronology based on alkali/alkaline earth metal isotope systems, such as K/Ca and Rb/Sr radioactive decay pairs, will be illustrated on examples relevant to dating of sediments and low-temperature earth’s surface processes. These will include recent data on in-situ Rb/Sr dating (LA-QQQ) of glauconites and bulk shales.