Earth and Environmental Sciences (SEES)

Crustal Evolution Research Group

 At Portsmouth our group is particularly focussed on the development of Plate Tectonics throughout Earth history. We are addressing fundamental questions with respect to the Earth system such as when did Plate Tectonics begin operating and what changes can be documented in the style and rate of plate movement and subduction through time. Most people are satisfied that some form of Plate Tectonics has been occurring since the Archaean, but how different was it to the modern observable record and when and how did we change from the ancient mode to the modern?

Alongside that we are interested in documenting the rate of continental crustal growth and recycling through time and how any changes in tectonics have influenced the rates of crustal growth and preservation. These are fundamental challenges underpinning all we know about our dynamic planet and perhaps others. These processes, and their secular change, undoubtedly govern many other variables, such as the origins of atmospheric oxygen and therefore evolution of life and the controls of Earth’s climate system, through tectonic influence on ocean circulation and weathering, with its control on CO2 drawdown to the deep Oceans.

Our group comprises four full-time academics (Dr Craig Storey, Dr Rob Strachan, Dr Mike Fowler and Dr Dean Bullen) along with a full-time Research Associate (Dr Emilie Bruand from March 2011) and a PhD student (Ms Florentina Enea). Our research facilities include a laser ablation ICP-MS lab (New Wave UP213 Nd:YAG laser coupled to an Agilent 7500CS ICP-MS), full access to an SEM equipped with EDS and CL, XRF, XRD, rock-crushing, full mineral separation and thin section lab, as well as research-grade microscopes.

Staff with brief details:

Dr Craig Storey

Principal Research Fellow (Director of group)

Research interests: evolution and growth of the continental crust, the onset of modern-style plate tectonics, Pliocene to recent evolution of Greenland’s ice sheet

Dr Rob Strachan

Head of School

Research interests: nature of orogenic processes within the middle crust; the application of geochronological techniques to deceipher reworked metamorphic terrains; Neoproterozoic tectonics of the North Atlantic region.

Mike Fowler

Principal Lecturer

Research interests: Granite petrogenesis. Comparative petrology of high Ba-Sr granites and sanukitoids. Their significance to the onset and evolution of modern plate tectonics. Caledonian plutonism of the Northern Highlands and Shetland.

Dean Bullen

Senior Lecturer

Research interests: Magma genesis in different plate tectonic settings; magmatic processes through time; ore formation; revisiting Archaean terranes in search of impact sites.

Current Research:

Evolution of high-pressure metamorphism from the Archaean to the present day and its bearing on the onset of modern plate tectonics

Craig Storey, Horst Marschall, (Bristol) and Florentina Enea

High-pressure rocks are notoriously difficult to preserve within the rock record due to metastability. Whilst medium to high temperature eclogites are present back to the Archaean, suggesting thickened crust, blueschists are only present back to the Neopropterozoic around 800 Ma ago. The latter are of extreme importance since they are indicative of the modern observable mode of plate tectonics, that is steep and deep subduction of oceanic crust resulting in lowered geotherms in benioff zones and consequent low temperature, high  pressure metamorphism. Equally, the oldest records of ultrahigh pressure metamorphism, from rapid ultradeep subduction and exhumation of continental crust, only extends back as far as possibley c.600 Ma ago. Our research attempts to use new methods via the accessory mineral rutile (TiO2) to test whether this situation is based on preservation or is refelective of the thermal evolution of Earth.

Provenance of the Greenland Ice Sheet from the Mid Pliocene to the Holocene

Craig Storey, Gavin Foster (Southampton), Ian Bailey (Southampton) and Simon Kelley (Open University)

Over the last 150 years or so the industrialisation of the human race has caused the climate of our planet to change.  The principal causes of this change are our emissions of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) due to burning fossil fuels, deforestation and cement making.  So far the amount of greenhouse warming is relatively small, only ~1 degC increase in mean annual temperature.  But as a consequence of this warming the continental ice sheets and valley glaciers are already beginning to melt and the oceans have thermally expanded - both leading to ~15 cm rise in sea level.   Up to now these changes have been relatively minor, what is of more concern is the magnitude of the warming to come and the climate changes that will accompany it due to our continued and previous greenhouse gas emissions.

In an effort to better understand modern climate and to predict future climate change, numerical models have been developed in an attempt to simulate the effects of greenhouse gas emissions. These General Circulation Models (GCM), though extraordinarily complex, remain imperfect tools that require validation. Therefore, the study of distinct ancient climate systems is now an integral part in informing policy makers on climate change issues. If these models successfully reproduce large-scale climate changes that occurred in the past, this will give us more confidence in their prediction for the future.  The most informative analogues are in the recent geological past where geographical configurations, ocean currents and ecosystems are similar to today. The Mid-Pliocene (about 3 Myrs ago) is the most recent time in Earth's history when mean global temperatures were substantially warmer than today with a climate similar to that predicted for the end of this century if we continue to burn fossil fuels at the current rate.  Thus, there is potential for using the Mid-Pliocene as an analogue for future global warming and testing the veracity of climate models. 

Of particular concern with respect to our prediction of future climate is the role the continental ice sheets of Greenland and Antarctica will play in changing sea level.  For example, if all the ice on Greenland were to melt global sea level would be around 6-8 m higher.  During the Mid-Pliocene it is likely that there was less ice on Greenland than today although we currently do not have a good idea about how much of the island was covered in ice - was it as much as today? Or was it significantly less? The central aim of this proposal is to address these questions and determine for the first time the areal extent of the Greenland ice sheet during the Mid-Pliocene. 

We will achieve this greater understanding by examining sand sized grains from 3 million year old deep ocean sediments from the North Atlantic.  These grains were originally incorporated into the ice sheet by glacial erosion, transported to the ice margin, and incorporated into icebergs before being deposited as the iceberg melted in the open ocean around 3 to 3.3 million years ago.  We will first test whether the chemical and isotopic composition and age of modern grains accurately reflect the region of Greenland from which they were eroded.  Then, by carefully looking at grains from sediments from ~3 million years ago, we can get an estimate of which areas were covered in ice at that time.  This reconstruction can then be compared to existing model results to examine their performance. This will help inform our level of confidence in their predictions of the behaviour of the Greenland ice sheet in the future. 

Sanukitoid magmatism and its bearing on the onset of modern plate tectonics

Mike Fowler, Craig Storey and Jaana Halla (Helsinki)

Sanukitoids are an important group of LILE-enriched magmatic rocks that fist appear commonly in the rock record in the Neoarchaean. They most likely represent some change in the dynamics of subduction, either through a changing (cooling) thermal regime in the mantle or an increase in the sedimentary component within subduction systems. Understanding their petrogenesis and tectonic significance is thus crucial to informing the debate about when Earth began experiencing plate tectonics in a fashion that we can understand from modern observations, with steep subduction of oceanic crust, paired metamorphic belts, recycling of sediments into the mantle and the generation of large volumes of magma within arcs and back-arcs. Phanerozoic analogues of sanukitoids are well-exposed in the Scottish Highlands and known as high Ba-Sr granites. Our research is studying the petrogenesis of these granites as well as Neoarchaean sanukitoids from Finland. We are seeking to understand the nature of this magmatism and its imprint in the geological record, particularly within the accessory mineral archive, which may be accessed through the detrital mineral record for where parental records have been destroyed.

Neoproterozoic tectonics along the Laurentian margin of Rodinia

Rob Strachan, Mike Fowler, Peter Cawood (St Andrews), Martin Hand & Kathryn Cutts (Adelaide), Pete Kinny (Curtin), Tony Prave (St Andrews), Anna Bird & Matthew Thirlwall (Royal Holloway), Ian Millar (NIGL).

The supercontinent Rodinia formed at 1.1-1.0 Ga by the amalgamation of Laurentia, Baltica and Amazonia. Recent continental reconstructions imply that East Greenland, Svalbard and Scotland were close to an active plate margin along the edge of the supercontinent. Previously enigmatic orogenic events in the time span 950-750 Ma in these areas are now interpreted in terms of a newly-recognised accretionary orogen (the Valhalla orogen of Cawood et al. 2010). Current research in NW Scotland and in the Shetland Islands is aimed at integrating geochronological, petrological, geochemical and isotopic studies of these complex polymetamorphic rocks in an attempt to build up a clearer picture of the evolution of this orogenic tract. This is no trivial matter since all the areas affected by Neoproterozoic orogenic events have been strongly overprinted by Lower Palaeozoic Caledonian orogenesis. This has resulted in widespread reworking of Neoproterozoic metamorphic assemblages which may only be preserved in the cores of large porphyroblasts (Cutts et al. 2009a & b, 2010).

Caledonian magmatism and tectonics along the Laurentian margin

Rob Strachan, Mike Fowler, Ian Alsop (Aberdeen), Maarten Krabbendam & Graham Leslie (BGS), Pete Kinny (Curtin), Ian Millar (NIGL), Martin Hand & Kathryn Cutts (Adelaide), Bob Holdsworth (Durham).

Models for Caledonian orogenic events in Northern Scotland involve Grampian (480-465 Ma) deformation and metamorphism (arc-continent collision), followed by ductile reworking during the Scandian (435-425 Ma) event (Laurentia-Baltica collision). This model is being tested and refined by detailed structural and petrological studies and U-Pb geochronology aimed at understanding: 1) the deformational and metamorphic fabrics that formed within the mid-crust during these orogenic events, 2) the generation, emplacement mechanism and structural settings of pre- and syn-orogenic intrusions that can be used as time-markers, 3) the large-scale tectonic significance of different kinematic regimes, in particular the relative timing of thrusting and strike-slip displacements, 4) the relationships between regional Barrovian metamorphism and ophiolite emplacement, 5) the relative timing of ductile thrusting versus folding at different levels within the nappe pile.    

Recent Papers:

Murphy, J.B., Coussens, B.L, Braid, J.A., Strachan, R.A., Dostal, J, Keppie, J.D. & Nance, R.D. 2010. Highly depleted oceanic lithosphere in the Rheic Ocean: implications for Palaeozoic plate reconstructions. Lithos, in press.

Nance, R.D., Guitierrez-Alonso, G., Keppie, J.D., Linnemann, U., Murphy, J.B., Quesada, C., Strachan, R.A. & Woodcock, N.H. 2010. Evolution of the Rheic Ocean. Gondwana Research, 17, 194-222.

Cutts, K.A., Kinny, P.D., Strachan, R.A., Hand, M., Kelsey, D.E., Emery, M., Friend, C.R.L. & Leslie, A.G. 2010. Three metamorphic events recorded in a single garnet: coupled phase modelling with in situ LA-ICPMS, and SIMS geochronology from the Moine Supergroup, NW Scotland. Journal of Metamorphic Geology, 28, 249-267.

Cawood, P.A., Strachan, R.A., Cutts, K., Kinny, P.D., Hand, M. & Pisarevsky, S. 2010. Neoproterozoic orogeny along the margin of Rodinia: development of the Valhalla Orogen, North Atlantic. Geology, 38, 99-102.

Cutts, K.A., Hand, M., Kelsey, D.E., Wade, B., Strachan, R.A., Clark, C. & Netting, A. 2009b. Evidence for 950-930 Ma metamorphism in the Shetland Islands, Scottish Caledonides: implications for early Neoproterozoic tectonics in the Laurentia-Baltica sector of Rodinia. Journal of the Geological Society, London, 166, 1033-1047.

Prave, A.R., Strachan, R.A. & Fallick, A.E. 2009. Global C cycle perturbations recorded in marbles: a record of Neoproterozoic Earth history within the Shetland Islands, Scotland. Journal of the Geological Society of London, 166, 129-135.

Cutts, K.A., Hand, M., Kelsey, D.E. & Strachan, R.A. 2009a. Orogenic versus extensional settings for regional metamorphism: Knoydartian events in the Moine Supergroup revisited. Journal of the Geological Society, London, 166, 201-204.

Fowler, M.B., Kocks, H., Darbyshire, D.P.F. & Greenwood, P.B.  2008. Petrogenesis of high Ba-Sr granitoids from the Northern Highland Terrane of the British Caledonian Province.  Lithos, 105, 129-148.

J.R. Darling, C.J. Hawkesworth, C.D. Storey and P.C. Lightfoot, 2010, Shallow impact: Isotopic insights into crustal contributions to the Sudbury impact melt sheet, Geochimica et Cosmochimica Acta, 74, 5680-5696.

H.R. Marschall, C.J. Hawkesworth, C.D. Storey, B. Dhuime, P.T. Leat, H-P. Meyer and S. Tamm-Buckle, 2010, The Annandagstoppane Granite, east Antarctica: evidence for Archaean intracrustal recycling in the Kaapvaal-Grunehogna Craton from zircon O and Hf isotopes, Journal of Petrology, 51, 2277-2301.

M.P. Smith, C.D. Storey, T.E.R. Jeffries and C. Ryan, 2010, In-situ U-Pb and trace element analysis of accessory minerals in the Norrbotten IOCG district: New constraints on the timing and origin of mineralization, Journal of Petrology, 50, 2063-2094.

J.R. Darling, C.J. Hawkesworth, P.C. Lightfoot, C.D. Storey and E. Tremblay, 2010, Isotopic heterogeneity in the Sudbury impact melt sheet, Earth and Planetary Science Letters, 289, 347-356.

C.D. Storey, T.S. Brewer, R. Anczkiewicz, R.R. Parrish and M.F. Thirlwall, 2010, Multiple high-pressure metamorphic events and crustal telescoping in the northwest Highlands of Scotland, Journal of the Geological Society, London, 167, 445-468.

C.J. Hawkesworth, B. Dhuime, A. Pietranik, P. Cawood, A. Kemp and C. Storey, 2010, The generation and evolution of the continental crust, Journal of the Geological Society, London, 167, 229-248.

J. Darling, C. Storey and C. Hawkesworth, 2009, Impact melt sheet zircons and their implications for the Hadean crust, Geology, 37, 927-930.

A.I.S. Kemp, G.L. Foster,  A. Schersten, M. Whitehouse, J. Darling and C. Storey, 2009, Concurrent Pb-Hf isotope analysis of zircon by laser ablation multi-collector ICP-MS, with implications for the crustal evolution of Greenland and the Himalayas, Chemical Geology, 261, 244-260.

C. Hawkesworth, P. Cawood, T. Kemp, C. Storey and B. Dhuime, 2009, A Matter of Preservation, Science, 323, 49-50.

A. Pietranik, C.J. Hawkesworth, C.D. Storey, K. Sircombe and A.I.S. Kemp, 2008, Episodic, mafic crust formation from 4.5 to 2.7 Ga: new evidence from detrital zircons, Slave Province, Canada, Geology.

C.D. Storey, 2008, The Glenelg-Attadale Inlier, NW Scotland, with emphasis on the Precambrian high-pressure metamorphic history and subsequent retrogression: an introduction and review, Scottish Journal of Geology, 44, 1-16.

C.D. Storey, 2008, A Field Guide to the Glenelg-Attadale Inlier, NW Scotland, with emphasis on the Precambrian high-pressure metamorphic history and subsequent retrogression, Scottish Journal of Geology, 44, 17-34.

F. Wall, Niku-Paavola, V.N., Storey, C., Muller, A. and Jeffries, T, 2008, Xenotime-(Y) from Carbonatite dykes at Lofdal, Namibia: unusually low LREE:HREE ratio in Carbonatite, and the first dating of xenotime overgrowths on zircon, Canadian Mineralogist, 46, 861-877.