Between a Rock and a Hard Place

Random science

Using garnet geochemistry to investigate the lithospheric mantle beneath northern Tanzania

November 19, 2013

Sorcha McMahon is a third year PhD student in the School of Earth Sciences at the University of Bristol. Sorcha is investigating how strange igneous rocks called carbonatites may have formed, using both natural samples and high-pressure experiments.

As part of my undergraduate MSci course at the University of Cambridge, I carried out a project investigating a collection of thin sections from peridotite xenoliths from northern Tanzania. The main aim of this research was to constrain the petrogenetic evolution of the lithospheric mantle beneath the East African Rift (EAR) and adjacent Tanzanian Craton. Techniques employed included the electron microprobe (EMPA) and LA-ICP-MS to characterise the major and trace element contents of constituent minerals in garnet-bearing lherzolite and harzburgite mantle xenoliths. For the first time globally, we found ultra-depleted pyrope garnets from Lashaine peridotites displaying rare earth element (REE) patterns similar to those of hypothetical garnets proposed to have formed in the subcontinental lithospheric mantle prior to any metasomatism*.

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Power within the rift

October 28, 2013

Lying just under the Earth’s surface, the East African Rift is a region rich in geothermal resources. Exploitation of this clean and green energy source is steadily been gaining momentum. What is the geological mix that makes the Rift Valley ripe for geothermal power and how is it being tapped?

The East African Rift, stretching from Djibouti to Mozambique, marks the trace of a continent slowly tearing apart. At rates of about 1-2 cm per year, the African continent will one day split into two separated by a new ocean.

When continental rifting occurs, volcanism shortly follows. As the continent steadily stretches apart, the Earth’s crust thins allowing an easier path for buoyant magma to rise up. Where the magma cracks the surface, volcanoes build up. Dotting the Rift Valley are many active, dormant and extinct volcanoes. Famously active ones include Nyiragongo in the Democratic Republic of Congo, Ol Doinyo Lengai in Tanzania and the bubbling lava lake at Erta Ale volcano in Ethiopia. [Read More]

An ode to metamorphism

October 21, 2013

On finding out my ‘profession’, there’s one fact that people proudly announce to me on a regular basis: “I know the three rock types: sedimentary, igneous and metamorphic!”. What usually emerges from deeper probing is that most people are comfortable with the concept of sediments and magma, but metamorphism is a bit of an enigma. Like the mysterious stranger, lurking in a dark forgotten corner, it is true to say that for most people, this holds even throughout undergraduate geology courses.

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Rocky secrets – fifty shades darker?

October 14, 2013

Mel Auker is an Earth Sciences PhD student in the School of Earth Sciences at the University of Bristol. A mathematician by trade, Mel’s PhD uses numerical approaches to better understand past, present, and future global volcanic hazard and risk.

You might remember Charly’s “Fifity Shades of Grey” post, highlighting the colourful spectrum of rocks; fifty shades of grey they are not. On a purely aesthetic level, rocks are incredibly varied and interesting.

But the thing is, a lot of the samples us volcanology and petrology PhD students spend our time looking at are some shade of grey. The trick to staying interested in all things grey is to learn to read between the lines. Grey volcanic ash, for example, has a whole host of dark secrets to share if you know what to look for… [Read More]