GMPV
Geochemistry, Mineralogy, Petrology & Volcanology

Geochemistry, Mineralogy, Petrology & Volcanology

#EGU2020 Sessions in the Spotlight: Evolution of the Earth’s upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites

#EGU2020 Sessions in the Spotlight: Evolution of the Earth’s upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites

The EGU 2020 abstract submissions are now open for the next two months! Every few days, we will highlight a geochemistry, mineralogy, petrology and/or volcanolo

gy session right here – great news if like me, you find choosing which session to submit to more difficult than choosing a decent movie on Netflix…

Today it’s the turn of GMPV 4.4. Evolution of the Earth’s upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites. This session is convened by Jacek Puziewicz, Costanza Bonadiman, Michel Grégoire and Károly Hidas. The convenors say:

Earth’s upper mantle consists of lithospheric mantle, which makes lower parts of tectonic plates, and asthenosphere, in which the plates are based. The nature of Earth’s lithospheric mantle is largely constrained from the petrological and geochemical studies of xenoliths. They are complemented by studies of orogenic peridotites and ophiolites, which show the space relationships among various mantle rock kinds, missing in xenoliths. Basalts and other mantle-derived magmas provide us another opportunity to study the chemical and physical properties the mantle. These various kinds of information, when assembled together and coupled with experiments and geophysical data, enable the understanding of upper mantle dynamics.

Ronda. Contact between mantle peridotites of the Ronda Massif in Spain and their gneissic surrounding. Difference between tree abundance shows that mantle rocks are poor in fertile components compared to the crust, demonstrating how important was formation of the crust for life in our planet.

This session’s research focus lies on mineralogical, petrological and geochemical studies of mantle xenoliths, orogenic and ophiolitic peridotites and other mantle derived rocks. We strongly encourage the contributions on petrology and geochemistry of mantle xenoliths and other mantle rocks, experimental studies, the examples and models of mantle processes and its evolution in space and time.

So are you TANTALised by the MANTLE (that one almost rhymed…)? Are you looking for some deep thinking and discussions (because the mantle is sort of deep…)? The submit here!

 

#EGU2020 Sessions in the Spotlight: Geochronology in hot and dynamic systems: approaches and tools to unravel the past

#EGU2020 Sessions in the Spotlight: Geochronology in hot and dynamic systems: approaches and tools to unravel the past

The EGU 2020 abstract submissions are now open for the next two months! Every few days, we will highlight a geochemistry, mineralogy, petrology and/or volcanology session right here – great news if you are paralysed by indecision or overwhelmed by the number of sessions.

Today it’s the turn of GMPV1.7, “Geochronology in hot and dynamic systems: approaches and tools to unravel the past”, convened by a team covering three continents (Silvia Volante (Curtin University), Alex Prent (John de Laeter Centre-Curtin University), Mahyra Tedeschi (Federal University of Minas Gerais), Massimo Tiepolo (University of Milan) and Jan Wijbrans (Vrije University)). The invited speakers will be Paola Manzotti (Stockholm University) and Urs Schaltegger (Université de Genève)

From the convenors:

The powerful combination of high-resolution geochronological data with petro-structural analysis, is continuously progressing our understanding of orogenic processes within the Earth’s dynamic lithosphere. Moreover, the development of new techniques and improvement of analytical equipment inspire future progress and development.

Despite being a powerful tool, geochronology of major and accessory minerals requires careful interpretation. The interplay of temperature, water and melt-content in magmatic and (ultra)high-temperature ((U)HT) metamorphic systems potentially affects geochronometers. Additionally, direct ages from time capsule minerals can be interpreted in different ways. For these reasons, reliable interpretation of geochronological data, essential to decipher the tectono- magmatic and metamorphic evolution of an orogenic system, is improved by using multiscale and multi-disciplinary approaches that complements geochronology with field observations, structural analysis, petrography, geochemistry, and petrology.

This session aims to highlight recent achievements and considerations in geochronology applied to igneous and (U)HT-metamorphic rocks from dynamic systems (orogens). We welcome contributions in which geochronology is coupled with petrology, major, trace elements and isotope geochemistry, thermodynamic modelling, and structural geology.

So if you think it’s time to think about time, or you have simply adore the ZrSiO4 (read: zee-ar-ess-i-oh-four, so it rhymes 🙂 ), then submit your abstract here, and have a great time in Vienna!

Can limestone digestion by volcanoes contribute to higher atmospheric carbon dioxide levels?

Can limestone digestion by volcanoes contribute to higher atmospheric carbon dioxide levels?

By Frances Deegan and Ralf Halama

Cartoon showing carbon fluxes in subduction zones. Source: Deep Carbon Observatory.

Carbon – the element on everyone’s lips. Carbon is unquestionably one of the most important elements on Earth – terrestrial life is carbon-based and so are many of our energy sources. From the perspective of a human time-scale, biological and anthropogenic (caused by human activity) carbon fluxes are very important (e.g. through industrial activity and burning fossil-fuels). However, if we consider time-scales spanning millions of years (the geological time-scale), then Earth degassing becomes an important control on the climate evolution of our planet. Volcanoes are major contributors to long-term Earth degassing and this is what brings us to Indonesia – one of the most volcanically-dense regions on Earth and home to some of the most active and dangerous volcanoes.

Where does volcanic carbon dioxide come from? Indonesia is located above a subduction zone, which is where two tectonic plates meet and one sinks into the Earth’s mantle. This is where crust is destroyed or “recycled” back into the Earth and where arc volcanoes form on the upper plate. The carbon dioxide released from volcanoes in subduction zones comes from a mixture of sources – some comes from the sedimentary rocks that were pushed into the mantle during subduction and some comes from the Earth’s mantle. Scientists have also discovered another source of carbon at subduction zones – the crust sitting on top of the subduction zone, on which the volcanoes are built (the “upper arc crust”).

The limestone-gas connection. Volcanoes located in areas where the bedrock is made of limestone often have an unusually high outflux of carbon dioxide. Could there be a link? Limestone is made of calcium carbonate, CaCO3, and when hot magma reacts with CaCO3 it rapidly breaks down to release large amounts of CO2, contributing to this unusually high outflux of CO2. The exact process during magma-limestone interaction at depth and the timescales over which this can happen have for a long time remained speculative.

Thermally metamorphosed limestone (calc-silicate) fragment entrained in Merapi lava. Source: Frances Deegan.

New research results. At Merapi volcano, a team of scientists from the universities of Keele (UK), Uppsala (Sweden) and Swansea (UK) have found pieces of thermally-altered limestone (calc-silicate xenoliths) among the volcano’s erupted products. They argue that these altered limestone samples record the processes in the underlying magma reservoir and allow them to gain insights into the processes accompanying liberation of CO2 from limestone. New research led by PhD researcher Sean Whitley from Keele University, investigated isotopic ratios of carbon and oxygen in crystals of the mineral calcite in these altered limestone fragments at the Edinburgh Ion-Microprobe Facility. Using these data, scientists can chemically fingerprint the processes that led to formation of calcite in the limestone fragments. Most intriguingly, the team found an unusual carbon isotopic signature that demonstrates highly efficient remobilisation of limestone-derived CO2 into the magmatic system. They further found that this CO2 release occurs over geologically short timescales of hundreds to thousands of years and that during non-eruptive episodes up to half of the CO2 emissions at Merapi derive from the digestion of limestone in the magma storage region, rising to 95% during volcanic eruptions.

Although Merapi is currently considered a relatively minor emitter of CO2 on a global scale, the new results from Sean Whitley and co-workers show that volcanic CO2 liberation can potentially release large amounts of limestone-derived CO2 during eruptive episodes. This increasingly recognised contribution of limestone-derived CO2 to volcanic carbon budgets now requires reconsideration of global carbon cycling models throughout Earth history.

Link to article: Whitley, S., Gertisser, R., Halama, R., Preece, K., Troll, V.R., Deegan, F.M. 2019: Crustal CO2 contribution to subduction zone degassing recorded through  calc-silicate xenoliths in arc lavas. Scientific Reports 9:8803, DOI: 10.1038/s41598-019-44929-2.

Do you want to write about your research, or highlight some new research, or just give blogging a go? Then get in touch!

#mineralmonday: tiptopite

#mineralmonday: tiptopite

#mineralmonday: your weekly* dose of obscure mineralogy, every Monday** [*not guaranteed; **or possibly Tuesday-Sunday]

tiptopite. Source: wikimedia.org.

What is it? Tiptopite: K2Na1.5Ca0.5Li3Be6(PO4)6(OH)2•(H2O)

What’s it made of?  Take a deep breath and recite after me: potassium, sodium, calcium, lithium, beryllium, phosphorus, oxygen and water (H2O).

Is it pretty? Yes, it’s a beautiful fibrous mineral. You wouldn’t put it on jewelry though, or even in your pocket, or you’ll end up with needles and dust.

Wikipedia defines ‘tip top’ as ‘a slang phrase which means of the highest order or excellent’. Is this true for this mineral? Not really, it doesn’t have any real use (we are more interested in the minerals that it is associated with, like beryl), is only found in one place (the ‘Tip Top’ mine in South Dakota), and only in some isolated areas in that mine. This mine was opened during world war 2 for strategic reasons, but then shut down again in the 1950s.

Beryllium metal. Not exactly a silver lining, but a shiny grey lining… source: wikimedia.org

Strategic mining you say? Presumably this was for mining dragon glass? Or maybe I’m mixing up my wars. Yes you are thinking of an earlier war. Dragons and white walkers were long extinct by the 1950s. This particular mine was for beryllium (the Be in the formula).

That sounds berylliant. What’s it for? Nothing fun, unfortunately. Beryllium has a useful property of being a neutron emitter and an alpha particle absorber. This makes it really useful as part of the triggering device of thermonuclear weapons. It also makes beryllium quite difficult to buy…

Is there a silver lining? Nope! Beryllium even has a couple of conditions named after it: berylliosis and acute beryllium poisoning. Luckily it’s hardly ever used these days, and the risks are well known.

It seems calling it ‘tip top’ was a little optimistic…

Do you have a favourite obscure mineral? Want to write about it? Contact us and give it a go!