Prof. Oliver Tschauner [Univ. of Nevada Las Vegas, USA]

Title: Mineralogy of the deep mantle

Time: 10:00 - 11:00 AM, Tuesday July 10, 2018

Place: Conference room 410, HPSTAR (Shanghai)

Host: Ho-Kwang Mao

Polycom: 02120004

Abstract:

Understanding complex systems like the Earth requires proper correlation of a very large number of parameters. Within the context of the Earth’s interior these parameters are studied by different sub-disciplines: Geophysics, geochemistry, petrology, mineralogy, mineral physics. Wherever rocks are available, results from these different disciplines can be well placed in context. For instance, minerals that occur in a rock are compared to the phases that form in experiments at known pressure and temperature. Composition and abundance of mineral species guide experiment design and in turn the experimental results constrain the formation process of this rock.

However, pristine rock samples are not available for sublithospheric mantle (below 150 km depth) and studies of most parts of the Earth’s mantle has relied on the combination of seismic, geochemical, and mineral-physical data only.

Inclusions in diamonds extend the range of available natural samples to ~ 800 km depth. They can provide this important constraint on compositional space, abundance, and actual redox conditions that avail within the deeper mantle. Traditionally, microscopic inclusions are retrieved from their host diamonds and examined by chemical and isotope-geochemical methods. Using synchrotron-based techniques we have extended this research to sub-microscopic inclusions and to in situ examination of properties. This allows for a) examination of non-retrievable inclusions such as former fluids, b) assessment of current residual pressure, which establishes one end point of a nearly isochoric path whereof the P and T of entrapment are the other end point. Thus, we can constrain source regions of fluids and coexisting phases in the deep mantle with unprecedented accuracy.  

I discuss implications for deep mantle fluid recycling, open questions, and how high-pressure mineral physics complements this new field of research.

Biography of the Speaker:





Prof. Oliver Tschauner is working in the Department of Geoscience, UNLV. He is mineralogist and crystallographer. My main interest is in the examination of minerals that occur at high pressures with emphasis on the deep Earth (transition zone and deeper). I also study processes during large asteroid impacts. Experimental studies of deep Earth materials are quite established but the actual mineralogy of the deep Earth is an open field: Centered on studies of naturally occuring specimens it complements experimental approaches. Natural specimens always bring surprises. The intrinsic complexity of their composition and their history of pro- and retrograde transformation are beyond what any realistic experimental program can ever examine.

Though rare and usually sub-microscopic, remnant high-pressure minerals are the pieces of a mosaic that represents the deeper Earth. The design has to be drawn by geochemistry and geophysics but without the actual pieces it cannot be made.