Isotopic and (trace) element studies of system Earth

Prof. dr. G.R. (Gareth) Davies, Dr. J.M. (Janne) Koornneef, Dr. P.Z. (Pieter) Vroon, Prof. dr. Wim van Westrenen, I.K. (Igor) Nikogosian, Dr. Monica Sanchez-Roman, Dr. F.M. (Fraukje) Brouwer, Prof K.F. (Klaudia) Kuiper and Dr. Graham Hagen-Parker

We focus on understanding the geological processes operating at all tectonic settings and throughout Earth’s history. We specialise in analysing (trace) element concentrations and radiogenic- and non- traditional stable isotopic compositions (Sr-Nd-Pb-Hf-Ca-Fe-Ba-Si-Mg) in (small) geological samples from: the mantle (xenoliths; ophiolites, diamonds); magmatic rocks (bulk rock, minerals and olivine-hosted melt inclusions); (UHP) crustal rocks; modern, experimental and ancient sediments (e.g. BIFs); and high-pressure, high-temperature experiments containing silicate mineral and melt phases and aim to understand: 1) cycling of elements between Earth’s deep and surficial reservoirs, 2) rates and timescale of tectonics and fluid flow processes, 3) the environments and timescales involved in the emergence of life, and 4) large-scale magmatic differentiation processes.

Specific areas of study include:

DEVELOPMENT OF STATE-OF-THE-ART ULTRA-LOW BLANK MASS SPECTROMETRY TECHNIQUES

The VU research group worked closely with Thermo Scientific to develop and validate techniques using amplifier technology equipped with 1013 Ω resistors to more precisely measure small ion beam currents. The mass spectrometry techniques are used in combination with specifically developed miniaturised low blank wet chemistry procedures to routinely analyse sub-ng amounts of Sr, Nd and Pb for their isotopic composition. The techniques were originally validated by thermal ionisation mass spectrometry (TIMS), but are now also applied in MC-ICPMS. The technological break-through has resulted in the development of novel applications that are being applied by the VU across Earth (see below), archaeology, cultural heritage and forensic sciences, see: Isotopic provenance studies. In Earth science applications the techniques are applied to various types of samples 1) minerals and their inclusions in volcanic rocks, 2) minerals from the lower oceanic crust 3) minerals from the lithospheric mantle, 4) inclusions in (fibrous) diamond, and 5) dust in ice cores for paleoclimate reconstruction.

Key papers:

Koornneef JM, Bouman C, Schwieters JB, Davies GR, 2014. Measurement of small ion beams by thermal ionisation mass spectrometry using new 1013 Ohm resistors. Anal Chim Acta, 819(0): 49-55..
Koornneef JM, Nikogosian I, van Bergen MJ, Smeets R, Bouman C, Davies GR, 2015. TIMS analysis of Sr and Nd isotopes in melt inclusions from Italian potassium-rich lavas using prototype 1013 Ω amplifiers. Chemical Geology, 397: 14-23..
Klaver M, Smeets RJ, Koornneef JM, Davies GR, Vroon PZ, 2016. Pb isotope analysis of ng size samples by TIMS equipped with a 1013 Ω resistor using a 207Pb-204Pb double spike. Journal of Analytical Atomic Spectrometry, 31(1): 171-178.

EARTH’S DEEP GEOCHEMICAL CYCLES

The unique element and isotopic analysis techniques at VU are applied to better quantify Earth deep geochemical cycles and the exchange between Earth’s interior and surficial reservoirs controlled by plate tectonic processes. We work on this broad topic by analysing small samples from a range of tectonic settings: convergent plate margins (Aegean, Italian & Mariana subduction zones); divergent plate margins (Mid-Atlantic-Ridge and East African Rift), plume related settings (Azores, Canary islands, Iceland) and the subcontinental lithospheric mantle (Botswana, South-Africa). The ERC-starting grant project “ReVolusions” (see fig.1) launched in 2018 aims to better quantify global recycling fluxes by comparing extreme subduction settings. We hence examine the geochemistry of volcanic rocks at subduction zones ranging from continental (Italy, Aegean) to oceanic (Lesser Antilles, Marianas). The isotopic composition of deeply formed melt inclusions (~100 μm; Fig. 2) in addition to bulk rocks are used to determine the elemental fluxes derived from sediments, volatiles and the subducting slab. The team furthermore focusses on how island arc systems evolved over time, and if tectonic changes in the subduction setting or overlying plate, influenced magma production rate and/or the evolution of magmas. In concert with the Ar geochronology facility at VU, precise Ar-Ar dating techniques of single minerals are combined with radiogenic isotopes to disentangle how processes change over time.

Key papers:

Klaver M, Blundy JD, Vroon PZ, 2018. Generation of arc rhyodacites through cumulate-melt reactions in a deep crustal hot zone: Evidence from Nisyros volcano. Earth and Planetary Science Letters, 497, 169-180
Klaver M, Davies GR, and Vroon PZ, 2016. Subslab mantle of African provenance infiltrating the Aegean mantle wedge. Geology 44, 367–370.
Koornneef JM, Nikogosian I, van Bergen MJ, Vroon PZ, Davies GR, 2019. Ancient recycled lower crust in the mantle source of recent Italian magmatism. Nature Communications, 10(1): 3237.
Lambart, S., Koornneef, J.M., Millet, M.-A., Davies, G.R., Cook, M., Lissenberg, C.J., 2019. Highly heterogeneous depleted mantle recorded in the lower oceanic crust. Nat. Geosci. 12, 482-486.
Stracke, A., Genske, F., Berndt, J., Koornneef, J.M., 2019. Ubiquitous ultra-depleted domains in Earth’s mantle. Nat. Geosci. 12, 851-855.

THE ORIGIN OF DIAMONDS AND THE DEEP CARBON CYCLE

Inclusions encapsulated in diamonds provide an unaltered record from Earth’s otherwise inaccessible interior and potentially key information to the changing nature of Earth’s deep carbon cycle. They provide insight into the evolution of Earth’s mantle back to at least 3.2 Ga spanning a period of major change in plate tectonics (e.g., onset of modern Wilson Cycle 3.5 – 3.2 Ga), the nature of crust formation and Earth’s atmosphere. The optimised the 1013 Ω technology is applied in the study of diamond genesis by analysing individual inclusions from different growth zones (see Fig. 3) and establishing that some diamonds required up to 2.0 Gyr to form.

In collaboration with multiple industrial partners the team is studying a suite of inclusion-bearing diamonds from across southern Africa, including a selection made from > 150,000 from Botswana. The methodology involves obtaining polished central plates to determine the growth history before C-N isotope analysis of the diamond (hyperlink to stable isotope lab?) and subsequent inclusion analysis. This allows both the timing and tectonic setting of diamond formation to be determined. The overall goal is to determine the timing and number of diamond forming events recorded beneath individual mines and the scale of diamond formation by comparing ages and inclusion chemistry between mines across southern Africa. A key question to resolve is if carbon was locally redistributed in the sub-continental lithosphere mantle or added by tectonic processes.

Understanding the temporal evolution of carbon is vital in establishing how the Earth differentiated and evolved, ultimately leading to the development and survival of life on Earth. Assessing the behaviour and changes in carbon fluxes from Earth interior over time and the possible recycling from the surface provides information about how our planet has evolved. Importantly, it may also help in developing better long-term climate models if the role of the deep carbon cycle is better understood. Obtaining a better understanding of the processes that control the deep carbon cycle on Earth also potentially has direct relevance to predicting how carbon cycles may operate on other planets in the Solar System and beyond (exoplanets).

The study of diamond involves major collaboration agreements with De Beers, Debswana and the Gemological Institute of America. We also collaborate with researchers at the Universities of Alberta (D.G. Pearson), Glasgow (J.W. Harris) and Nancy (E. Deloule). Current work focusses mainly on samples from Botswana but includes samples from South Africa, Siberia and Tanzania.

The group has produced a series of ground-breaking papers that demonstrate that the dating diamond growth with individual silicate inclusions is possible and that previously published ages using pooled inclusion populations need to be re-evaluated. The work also shows that multiple diamond populations occur beneath each diamond mine and the complex nature of diamond growth:

Key papers:

Davies GR, van den Heuvel Q, Matveev S et al. (2018). A combined cathodoluminescence and electron backscatter diffraction examination of the growth relationships between Jwaneng diamonds and their eclogitic inclusions. Mineralogy and Petrology 112, 231–242.
Gress, MU, Howell D, Chinn IL et al. (2018). Episodic diamond growth beneath the Kaapvaal Craton at Jwaneng Mine, Botswana. Mineralogy and Petrology 112, 219–229.
Koornneef JM, Gress MU, Chinn IL et al. (2017). Archaean and Proterozoic diamond growth from contrasting styles of large-scale magmatism. Nature Communications, 8(1): 648.
Timmerman S, Koornneef JM, Chinn IL, Davies GR (2017). Dated eclogitic diamond growth zones reveal variable recycling of crustal carbon through time. Earth Planet Sci Lett 2017, 463: 178-188.
Timmerman S, Chinn IL, Fisher D et al (2018). Formation of unusual yellow Orapa diamonds. Proc. of the 11th International Kimberlite Conference, Mineralogy and Petrology, 112, 209–218

RATES AND TIMESCALES OF TECTONIC PROCESSES, MINERAL TRANSFORMATIONS AND FLUID FLOW IN THE CRUST

The metamorphic geology research at VU investigates the rates and fluxes involved in crustal processes using a range of petrological, geochemical and geochronological techniques. Processes studied range from tectonics and exhumation of UHP terranes, terrane accretion, subduction initiation, impact of fluid-rock interaction on isotopic systems, and the impact of the PT-evolution of terranes on their Ar-age record. Petrochronological studies focus on (ultra)high-pressure and (ultra)high-temperature metamorphic terranes in China, Papua New Guinea, Norway, Sri Lanka, Greenland, Finland and Surinam. In combination with Ar-Ar geochronology ultrahigh-temperature metamorphic terranes are the focus of (in situ) elemental and isotopic analysis of single minerals and fluid/melt inclusions to constrain magmatic source domains and crustal residence times.

Key papers:
Brouwer FM, Groen M, Nebel O, Wijbrans JR, Qiu HN, Yang QJ, Zhao LH and Wu YB (2011), Coherence of the Dabie Shan UHPM terrane investigated by Lu-Hf and 40Ar/39Ar dating of eclogites. In: L.F. Dobrzhinetskaya, S. Cuthbert, S.W. Faryad and S. Wallis (Eds), Ultrahigh Pressure Metamorphism: 25 years after discovery of coesite and diamond, pp. 325-357.
Hu R, Wijbrans J, Brouwer FM, Wang M, Zhao L, Qiu H (2016) 40Ar/39Ar thermochronological constraints on the retrogression and exhumation of the ultra-high pressure (UHP) metamorphic rocks from Xitieshan terrane, North Qaidam, China. Gondwana Research 36, 157-175.
Li Y, Tong X, Zhu Y, Lin J, Zheng J, Brouwer, FM (2018). Tectonic affinity and evolution of the Precambrian Qilian block: Insights from petrology, geochemistry and geochronology of the Hualong Group in the Qilian Orogen, NW China. Precambrian Research 315, 179-200.
Li Y, Zheng J, Xiao W, Wang G, Brouwer FM (2020). ~2.5 Ga granitoids in the eastern North China Craton: Melting from ~2.7 Ga accretionary crust. GSA Bulletin 132, 817-834.
Uunk B, Brouwer FM, ter Voorde M, Wijbrans J (2018). Understanding phengite argon closure using single grain fusion age distributions in the Cycladic Blueschist Unit on Syros, Greece. Earth Planet. Sci. Lett. 484, 192-203.
van Hinsbergen DJJ, Maffione M, Plunder A, Kaykmakcı N, Ganerød M, Hendriks BWH, Corfu F, Gürer D, de Gelder GINO, Peters K, McPhee PJ, Brouwer FM, Advokaat EL, and Vissers RLM (2016). Tectonic evolution and paleogeography of the Kırşehir Block and the Central Anatolian Ophiolites, Turkey, Tectonics 35, 983-1014.

Buck Reef Chert, Barberton, South Africa, picture is 20x20cm

Silicate metal experiments

THE SEDIMENTARY RECORD TO STUDY THE EMERGENCE AND EVOLUTION OF LIFE ON EARTH

Sedimentology plays a vital role in the study of the early Earth evolution. Our current knowledge of the initiation of plate tectonics, the major changes in chemistry of the atmosphere and oceans, and emergence of life through deep time is underpinned by high precision radiogenic and stable isotope data obtained from Archaean and Proterozoic rocks and minerals. The VU team collaborates to study stable isotopes (Si, Fe, S) in ancient sediments on key localities including the Archaean Barberton Greenstone Belt and the East Pilbara Granite-Greenstone terrane. Additionally experimental work at the VU demonstrated that precipitation of amorphous silica induces kinetic isotope fractionation such that most Archaean cherts have silicon isotope signatures unsuitable for the determination of palaeo-ocean temperatures. The research team is exploring MC-ICPMS double spike approaches to analyses Mg-Si-Ca-Fe-Cu-Zn-Mo-Cd stable isotope variations to less than 0.01‰ to be able to determine isotope variations as well as metal and trace element partitioning in Archaean-Proterozoic samples and the products of well constrained experimental run products and modern analogues. The combination of detailed geological studies with experimental work aims to constrain the biological and inorganic processes in operation during the early Earth to better resolve hydrothermal from biological processes recorded in the geological rock record.

Marble Bar chert, Pilbara, Australia.