Nav: Home

Homologues temperature of olivine links deformation experiments and rheology of the upper mantle

June 15, 2016

The homologous temperature of a crystalline material is defined as the ratio between temperature and the melting (solidus) temperature (Tm) in Kelvin. Because Tm of a crystalline material is controlled by the bonding force between atoms, T/Tm has been widely used to compare the creep strength of crystalline materials. As the most abundant mineral in the upper mantle, olivine is the solid solution of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Recent deformation experiments have revealed the influence of water, temperature, pressure, stress and partial melting on fabric development of olivine. However, how to extrapolate laboratory results to mantle deformation is still under debate.

In a recent review in Science China Earth Sciences, Qin Wang from Nanjing University established the phase diagram of dry olivine up to 6.4 GPa using previous melting experiments and the generalized means. She found that the change of T/Tm of olivine with depth allows us to compare the strength of the upper mantle with different thermal states and olivine composition. The transition from semi-brittle to ductile deformation in the upper mantle occurs at a depth where T/Tm of olivine equals to 0.5 (Figure 1).

In addition, T/Tm is used to analyze fabric transitions of olivine. The results indicate that the effect of water on olivine fabrics is closely related with pressure. Below 6.4 GPa (<200 km) and under the strain rate low stress in upper mantle, [100](010) slip system (a-type fabric) becomes dominant when t> 0.55-0.60. When T/Tm < 0.55-0.60, [001] slip is easier (Figure 1). Low T/Tm favors the operation of [001](100) slip system (C-type fabric). This is consistent with the widely observed A-type fabric in naturally deformed peridotites, and the C-type fabric in peridotites that experienced deep subduction in ultrahigh-pressure metamorphic terranes. However, the [001](010) slip system (B-type fabric) will develop under high stress and relatively low T/Tm.

This study provides new information on tracing mantle flow from seismic anisotropy. Seismic anisotropy of the upper mantle is controlled by the A-type fabric of olivine in most regions, where the fastest P-wave velocity and the polarization direction of the faster S-wave velocity are parallel to the mantle flow direction. However, olivine in subduction zones may develop the B- or C-type fabric, making the fastest P-wave velocity and the polarization direction of the faster S-wave velocity normal to the mantle flow direction. Seismic anisotropy of the upper mantle beneath cratons can be simulated using a four-layer model with different fabrics.

It is noteworthy that when pressure is higher than 6.4 GPa, the melting behavior of iron-rich olivine and the incorporation mechanism of hydrogen in olivine are different from those at low pressure. The lack of melting experiments on hydrogen-bearing olivine at high pressure hampers our estimation of its homologous temperature. Such knowledge will improve our understanding of the role of water in mantle rheology and planetary evolution.
This research was funded by the NSFC projects (41590623 and 41172182) and grant (201311178-3) from the Ministry of Land Resources.

See the article: Wang, Q., "Homologous temperature of olivine: Implications for creep of the upper mantle and fabric transitions in olivine," Science China Earth Sciences, (2016) 59:1138-1156. doi: 10.1007/s11430-016-5310-z

This article was published online

Science China Press

Science China Press

Related Water Articles:

Water, water, nowhere
Researchers at the University of Pittsburgh's Swanson School of Engineering have found that the unusual properties of graphane -- a two-dimensional polymer of carbon and hydrogen -- could form a type of anhydrous 'bucket brigade' that transports protons without the need for water, potentially leading to the development of more efficient hydrogen fuel cells for vehicles and other energy systems.
Advantage: Water
When water comes in for a landing on the common catalyst titanium oxide, it splits into hydroxyls just under half the time.
What's really in the water
Through a five-year, $500,000 CAREEER Award from the National Science Foundation, a civil and environmental engineering research group at the University of Pittsburgh's Swanson School of Engineering will be developing new DNA sequencing methods to directly measure viral loads in water and better indicate potential threats to human health.
Jumping water striders know how to avoid breaking of the water surface
When escaping from attacking predators, different water strider species adjust their jump performance to their mass and morphology in order to jump off the water as fast and soon as possible without breaking of the water surface.
Water, water -- the two types of liquid water
There are two types of liquid water, according to research carried out by an international scientific collaboration.
Just add water? New MRI technique shows what drinking water does to your appetite, stomach and brain
Stomach MRI images combined with functional fMRI of the brain activity have provided scientists new insight into how the brain listens to the stomach during eating.
UM researchers found shallow-water corals are not related to their deep-water counterparts
A new study led by scientists at the University of Miami Rosenstiel School of Marine and Atmospheric Science found that shallow-reef corals are more closely related to their shallow-water counterparts over a thousand miles away than they are to deep-water corals on the same reef.
Saline water better than soap and water for cleaning wounds, researchers find
Researchers found that very low water pressure was an acceptable, low-cost alternative for washing out open fractures, and that the reoperation rate was higher in the group that used soap.
UTA research predicting lake levels, moving water to yield better data for water providers
A University of Texas at Arlington environmental engineer is creating an integrated decision support tool for optimal operation of water supply systems that will allow water providers to make better decisions about when to turn on pumps to transfer water from one reservoir system to another and when to release water downstream from the reservoirs.
Surfing water molecules could hold the key to fast and controllable water transport
Scientists at UCL have identified a new and potentially faster way of moving molecules across the surfaces of certain materials.

Related Water Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...