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Departmental Talks

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A collection of all the seminars going on at the Department, either on the downtown site, or out at the Bullard Laboratories
URL: http://talks.cam.ac.uk/show/index/15125
Updated: 1 hour 4 min ago

Wed 19 Feb 18:00: I know what you did last summer Pt3 version

Wed, 19/02/2025 - 10:51
I know what you did last summer Pt3 version

Come along to hear some of your favourite Part III students talk about what they did on internships and research placements this summer. From corals to chondrites we’ve got it all! Also an excellent way to find out about opportunities you could apply for when you’re not trudging through the rain on field trips. Speakers are: Alex C, Jenny D, Susannah S, Rosa W, Gio B, Rory M, Erica M, Zara C and Pippa L!

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Tue 11 Mar 12:00: From Sediment to Spodumene

Wed, 19/02/2025 - 09:33
From Sediment to Spodumene

In this talk I’ll synthesize recent research interrogating how variations in weathering regimes and sediment deposition have impacted the chemistry of igneous rocks. In particular, I will focus on a particular class of granites (often termed “S-type”) which form via partial melting of siliciclastic sedimentary rocks and are uniquely suited to capture how the chemical consequences of sedimentary incorporation into magmas have varied throughout Earth history. I will focus on how enhanced organic matter and clay deposition at various periods in Earth history are reflected in the chemistry of the granites and the implications these variations have for our understanding of the oxygenation of Earth’s atmosphere and the occurrence of Li mineral deposits.

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Tue 18 Mar 12:00: Title to be confirmed To meet with the speaker, contact Ali Mashayek (am3158@cam.ac.uk)

Tue, 18/02/2025 - 11:24
Title to be confirmed

Abstract not available

To meet with the speaker, contact Ali Mashayek (am3158@cam.ac.uk)

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Wed 19 Mar 14:00: Fault orientation in earthquake seismic precursors: Insights from the laboratory

Mon, 17/02/2025 - 17:13
Fault orientation in earthquake seismic precursors: Insights from the laboratory

Faults in the brittle crust lie at any orientation to the far-field stress. However, laboratory experiments designed to investigate earthquake physics commonly simulate favorably oriented faults, potentially overlooking the complexity of natural fault behavior. Here, we assess the role of stress field orientation in fault reactivation and earthquake precursors by conducting triaxial sawcut experiments with laboratory faults oriented at different angles to the maximum principal stress, ranging from 30° to 70°. The samples were instrumented with strain gauges and piezoelectric sensors. Laboratory well-oriented faults describe a rather simple system in which the elastic energy is stored via the deformation of the surrounding host rock during the inter-seismic period and released via on-fault slip during the co-seismic phase with associated precursor acoustic activity. Consistent with previous laboratory data, an abrupt increase in the on-fault acoustic emission rate occurs shortly before the laboratory earthquake. A more complex picture emerges when deforming laboratory misoriented faults. Particularly, acoustic emissions and strain gauge data indicate that when the fault is misoriented, off-fault permanent deformation occurs well before fault reactivation. The stress state in the host rock surrounding the fault is indeed far beyond the one required for the onset of inelastic deformation. In this case, acoustic activity distributed in the rock volume during the pre-seismic phase is associated with permanent deformation in the critically stressed host rock and is not a direct precursor to the following laboratory earthquake. Unlike well-oriented faults, laboratory misoriented faults lack detectable seismic precursors. The laboratory-observed increase in acoustic activity prior to, but not precursor of, misoriented fault reactivation impacts our understanding of earthquake precursors in natural faults.

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Wed 19 Feb 14:00: Catastrophic failure: sound and vision

Mon, 17/02/2025 - 15:05
Catastrophic failure: sound and vision

Catastrophic failure is the end result of progression and localisation of damage towards brittle failure on a variety of system scales in the Earth. However, the factors controlling this evolution, and that of the resulting seismicity, are not well constrained.  We address the question of how to relate the two, and the extent to which they can be controlled by feedback on the seismicity rate in a scale model experiment on a small rock sample deformed in a synchrotron. We image the underlying damage using x-rays and detect acoustic emissions, and show how they change during localisation, from distributed tensile cracking to a localised shear band containing a mixture of tensile cracking, grain rotation, and grain boundary shear, with shear becoming increasingly dominant and ultimately frictional sliding on a contiguous fault.  We confirm that using continuous servo-control based on acoustic emission event rate not only slows down deformation compared to standard constant strain rate loading, but also suppresses events of all sizes, including extreme events. We use this evolution to develop a mixture model for the stress history from damage mechanics, and find it is independently consistent with the observed stress history and acoustic emission statistics. Our results imply that including seismic event rate control may improve risk management of induced seismicity compared to feedback on the maximum magnitude alone. 

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Wed 19 Feb 14:00: Catastrophic failure: sound and vision

Mon, 17/02/2025 - 13:31
Catastrophic failure: sound and vision

Catastrophic failure is the end result of progression and localisation of damage towards brittle failure on a variety of system scales in the Earth. However, the factors controlling this evolution, and that of the resulting seismicity, are not well constrained.  We address the question of how to relate the two, and the extent to which they can be controlled by feedback on the seismicity rate in a scale model experiment on a small rock sample deformed in a synchrotron. We image the underlying damage using x-rays and detect acoustic emissions, and show how they change during localisation, from distributed tensile cracking to a localised shear band containing a mixture of tensile cracking, grain rotation, grain boundary shear, with shear becoming increasingly dominant and ultimately frictional sliding on a contiguous fault.  We confirm that using continuous servo-control based on acoustic emission event rate not only slows down deformation compared to standard constant strain rate loading, but also suppresses events of all sizes, including extreme events. We use this evolution to develop a mixture model for the stress history from damage mechanics, and find it is independently consistent with the observed stress history and acoustic emission statistics. Our results imply that including seismic event rate control may improve risk management of induced seismicity compared to feedback on the maximum magnitude alone. 

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Thu 20 Feb 11:30: Bubble growth in alkaline electrolysis

Mon, 17/02/2025 - 10:03
Bubble growth in alkaline electrolysis

In the production of hydrogen via electrolysis, bubbles of hydrogen and oxygen must grow and detach from the electrode. Discussion of factors effecting rate of bubble growth and final detachment volume, and their contribution to overall efficiency.

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Mon 03 Mar 13:00: Volcanoes, Rhinoceros and Cabbage

Sun, 16/02/2025 - 20:45
Volcanoes, Rhinoceros and Cabbage

Abstract not available

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Fri 09 May 16:00: The Magmatic Origin of the North Atlantic V-Shaped Ridges and Fractured Crust

Wed, 12/02/2025 - 12:03
The Magmatic Origin of the North Atlantic V-Shaped Ridges and Fractured Crust

Abstract not available

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Mon 17 Feb 18:00: How to run a library: 20 years of employment

Tue, 11/02/2025 - 17:06
How to run a library: 20 years of employment

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Fri 21 Feb 16:00: Title to be confirmed

Mon, 10/02/2025 - 13:04
Title to be confirmed

Abstract not available

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Fri 21 Mar 16:00: Title to be confirmed

Mon, 10/02/2025 - 13:04
Title to be confirmed

Abstract not available

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Fri 14 Mar 16:00: Normal mode coupling in an aspherical planet

Mon, 10/02/2025 - 13:03
Normal mode coupling in an aspherical planet

Abstract not available

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Fri 07 Mar 16:00: Channels or waves: controls on melt migration through the upper mantle

Mon, 10/02/2025 - 13:02
Channels or waves: controls on melt migration through the upper mantle

Abstract not available

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Fri 14 Feb 16:00: Reconciling seismic and thermo-chemical models of cratonic lithosphere

Mon, 10/02/2025 - 13:01
Reconciling seismic and thermo-chemical models of cratonic lithosphere

Abstract not available

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Mon 10 Feb 18:00: Growing a Carboniferous Forest: Planning, Developing and Executing a Unique Palaeontological Excavation & Visitor Attraction

Fri, 07/02/2025 - 12:46
Growing a Carboniferous Forest: Planning, Developing and Executing a Unique Palaeontological Excavation & Visitor Attraction

Dr Tim Astrop is a palaeobiologist, evolutionary biologist, general nerd and the resident palaeontologist (fossil coordinator) for the Brymbo Fossil Forest project at Stori Brymbo, an exciting new natural, industrial and social heritage attraction coming to Wrexham in 2025-26. The Brymbo Fossil Forest is a globally unique palaeontological treasure; it represents a 314 million year old in-situ fossilised forest within the grounds of the old Georgian ironworks in Brymbo, North-Wales. In 2025 the site will see the completion of a purpose-built structure erected to excavate the fossils in a protected environment while being completely publicly accessible. The working team will consist exclusively of students and volunteers making it the endeavour the first of it’s kind. In this lecture Tim will talk about the history of the Brymbo site, the discovery of the fossil forest & it’s inferred paleoecology as well as the future of the site as a scientific endeavour and visitor attraction

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Wed 12 Feb 17:30: Climate-ice sheet interactions in the long-term past and their importance for the long-term future

Fri, 07/02/2025 - 11:57
Climate-ice sheet interactions in the long-term past and their importance for the long-term future

The simulation of the last deglaciation (about 20.000 years before present to present) represents a hitherto unsolved challenge for comprehensive state-of-the-art climate models. During my presentation, I will introduce our novel coupled atmosphere-ocean-vegetation-ice sheet-solid earth model that is used to simulate the transient climate. An ensemble of transient model simulations successfully captures the main features of the last deglaciation, as depicted by proxy estimates. In addition, our model simulates a series of abrupt climate changes, which can be attributed to different drivers that will be discussed throughout the presentation. I will furthermore show, how the model can be applied for simulations of the long-term future. The future simulations show, that parts of the Antarctic ice sheet become unstable even under low-emission scenarios, with significant implications for the modelled climate response. Sensitivity experiments additionally show that, the Greenland ice sheet may exhibit multiple steady-states under pre-industrial climate conditions. This has significant implications for a potential regrowth, once disintegrated entirely.

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Thu 13 Mar 11:30: TBC

Wed, 05/02/2025 - 09:17
TBC

Abstract not available

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Thu 20 Feb 11:30: TBC

Wed, 05/02/2025 - 08:52
TBC

Abstract not available

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Wed 12 Feb 14:00: H, He, and seismic evidence for a bilithologic plume-fed asthenosphere

Tue, 04/02/2025 - 14:10
H, He, and seismic evidence for a bilithologic plume-fed asthenosphere

Chemical diffusion in the mantle has typically been viewed to play a negligible role in geodynamic processes. However, diffusion rates for water (H) and helium (He) are large enough that they lead to observable differences between pyroxenite-rich melting associated with ocean island volcanism (OIB) and more peridotite-rich melting associated with mid-ocean ridge basalts (MORB). Laboratory measurements of diffusion rates of H and He at ambient mantle temperatures in olivine are of order 10 km/1.7Gyr for He and 250 km/1.7 Gyr for H. If the mantle is an interlayered mixture of recycled oceanic basalts and sediments surrounded by a much larger volume of residual peridotites, then chemical diffusion can shape the mantle in two important ways. Hydrogen will tend to migrate from peridotites into adjacent pyroxenites, because clinopyroxene (and its high-pressure metamorphs) has a much stronger affinity for water than the olivine and orthopyroxene that form the bulk of mantle peridotites. Therefore pyroxenite lithologies will typically have twice or more the water content of their surrounding damp peridotites. This will strongly favor the enhanced melting of pyroxenites that is now mostly agreed to be a common feature of the OIB source. Radiogenic 4He will have the opposite behaviour — it will tend to migrate from where it is produced in recycled incompatible-element-rich (e.g. U and Th-rich) pyroxenites into nearby, larger volume fraction, but U+Th-poorer peridotites, while the radioisotopes of Ar and Ne that are also produced by the decay of the incompatible elements K, U, and Th will diffuse much less, and thus remain within their original pyroxenite source. This effect leads to lower 4He/21Ne and 4He/40Ar ratios in OIB in comparison to the predicted values based on the mantle’s bulk geochemistry, and complementary higher 4He/21Ne and 4He/40Ar ratios in the MORB source that is formed by the plume-fed asthenospheric residues to OIB melt extraction at plumes.

The recent observation of a 150-km-deep positive shear velocity gradient (PVG) beneath non-cratonic lithosphere (Hua et al., 2023) is further evidence for the initiation of pyroxenitic melting at this depth within the asthenosphere. It also implies that lateral temperature variations at this depth are quite small, of order ±75°C. This near uniformity of temperatures near both mantle plumes and mid-ocean ridges is, in turn, strong evidence in favor of the hypothesis that the asthenosphere is fed by mantle plumes. We propose that two filtering effects occur as plumes feed the asthenosphere, removing both the hottest and coldest parts of upwelling plume material. First, the peridotite fraction in the hottest part of upwelling plume material melts enough for it to dehydrate, thereby transforming this fraction into a more viscous and buoyant hotspot swell root that moves with the overlying plate, not as asthenosphere. Second, since plume material is warmer than average mantle, it is more buoyant, creating a natural density filter that prevents any cooler underlying mantle from upwelling through it. Preferential melt-extraction from denser pyroxenites at mantle plumes also makes the asthenosphere compositionally buoyant with respect to its underlying, more pyroxene-rich mantle. These rheological and density filters will tend to make the asthenosphere sampled by melting at mid-ocean ridges have a more uniform temperature than its typical underlying mantle.

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Department of Earth Sciences
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Cambridge. CB2 3EQ

✉︎ godwinlab@esc.cam.ac.uk

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