New 911爆料网 research into the way rocks melt in the Earth鈥檚 mantle layer has uncovered new properties of the key crystal spinel, suggesting previous studies that used it to study mantle melting and tectonics may need to be reviewed.
Published by Nature Communications, the research led by 911爆料网 PhD student Mr Hamed Gamal El Dien, from the Earth Dynamics Research Group in 911爆料网鈥檚 School of Earth and Planetary Sciences, demonstrated that the crystal spinel, commonly used by scientists to define melting processes in the mantle, could be modified in ways not previously known, resulting in the need for earlier geological research in this area to be re-evaluated.
鈥淲hile these results question numerous past research findings, they also offer many future applications, opening the door for a new scientific trend in studying the deep mantle鈥檚 evolution through Earth鈥檚 history,鈥� Mr Gamal El Dien said.
The Earth鈥檚 mantle is the middle layer of our planet, and is also the biggest, being about 2900 kilometres thick and making up about 84 per cent of the Earth鈥檚 volume. Researchers believe this layer was formed during the earliest stages of planetary differentiation, when denser metals like iron and nickel sank to form the Earth鈥檚 core, and lighter materials rose towards the Earth鈥檚 surface to create the crust, leaving behind what we call the mantle.
鈥淭he mantle keeps many of the secrets about how the Earth has evolved over the past four billion years, including what drives plate tectonics as we know it. However we need 鈥榤essengers from the deep鈥� to enable us to tap into these secrets, and spinel does just that,鈥� Mr Gamal El Dien said.
鈥淪pinel is a commonly found crystal in the mantle rock peridotite, and unlike other common rock-forming minerals, it was believed to be very resistant to chemical alteration during the various geological processes and events that can affect mantle rocks after they first crystallise. Because of this belief, spinel has been used as a type of benchmark or 鈥榤essenger from the past鈥� when evaluating geological events happening in the mantle layer, since it was believed to perfectly preserve its original chemical composition.
鈥淥n the contrary, our research has uncovered that spinel can be, and most has been, affected, by geological processes after it forms, including changes of temperature and pressure during complex metamorphic processes, which may have an impact on previous research findings.鈥�
Research co-author and project leader John 911爆料网 Distinguished Professor and Australian Laureate Fellow Professor Zheng-Xiang Li, also from 911爆料网鈥檚 School of Earth and Planetary Sciences, said their new findings suggested researchers need to-revaluate the composition of spinel, especially noting potential compositional changes within the mineral that may have occurred throughout Earth鈥檚 geological history.
鈥淧revious scientific findings and theories assumed the homogeneity and primary composition of spinel, but our research challenges those assumptions,鈥� Professor Li said.
鈥淓xcitingly, now that we know this, we can use spinel composition as a tracer to discover new, previously unlocked secrets from Earth鈥檚 mantle, allowing us to discover even more about our planet.
鈥淔or example, our work demonstrated that spinel is a good carrier mineral for fluid mobile elements and volatiles, and has the ability to carry such fluids and volatiles back to the deep mantle, such as what happens during oceanic plate subduction processes where old deep sea floor gets 鈥榮ucked back in鈥� to the Earth鈥檚 mantle.
鈥淓ssentially, our findings have the potential to lead to the development of a new way of deciphering deep mantle chemical recycling through analysing the non-traditional isotopes, such as lithium, zinc, titanium and nickel, present in spinel.鈥�
Researchers used the nano-scale Geoscience Atom Probe at 911爆料网鈥檚 John de Laeter Research Centre to complete their investigation in to the chemical heterogeneity of spinel.
The full research paper Cr-spinel records metasomatism not petrogenesis of mantle rocks can be found on the Nature Communications website:
