Click here to load reader

dissertation.pdf · PDF file VRIJE UNIVERSITEIT INTERCALIBRATION OF 40AR/39AR GEOCHRONOLOGY AND IN SITU TERRESTRIAL COSMOGENIC 3HE Two scientific methods join at Earth's surface ACADEMISCH

  • View
    0

  • Download
    0

Embed Size (px)

Text of dissertation.pdf · PDF file VRIJE UNIVERSITEIT INTERCALIBRATION OF 40AR/39AR...

  • VU Research Portal

    Intercalibration of 40AR/39AR geochronology and in situ terrestrial cosmogenic 3HE

    Schneider, B.S.H.

    2012

    document version Publisher's PDF, also known as Version of record

    Link to publication in VU Research Portal

    citation for published version (APA) Schneider, B. S. H. (2012). Intercalibration of 40AR/39AR geochronology and in situ terrestrial cosmogenic 3HE: Two scientific methods join at Earth's surface. http://dare.ubvu.vu.nl/handle/1871/33215

    General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.

    • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ?

    Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

    E-mail address: [email protected]

    Download date: 10. Feb. 2021

    https://research.vu.nl/en/publications/3b8630fe-bb19-4367-b21e-cd4893406bcf http://dare.ubvu.vu.nl/handle/1871/33215

  • VRIJE UNIVERSITEIT

    INTERCALIBRATION OF 40AR/39AR GEOCHRONOLOGY AND IN SITU TERRESTRIAL COSMOGENIC 3HE

    Two scientific methods join at Earth's surface

    ACADEMISCH PROEFSCHRIFT

    ter verkrijging van de graad Doctor aan de Vrije Universiteit Amsterdam, op gezag van de rector magnificus

    prof.dr. L.M. Bouter, in het openbaar te verdedigen

    ten overstaan van de promotiecommissie van de faculteit der Aard- en Levenswetenschappen

    op woensdag 11 april 2012 om 11.45 uur in het auditorium van de universiteit,

    De Boelelaan 1105

    door

    Björn Sven Harald Schneider

    geboren te Huerth, Duitsland

  • promotor: prof.dr. P.A.M. Andriessen copromotor: prof.dr. J.R. Wijbrans

  • Für Daniel…Du bist nicht vergessen… The Reading Committee Dr. L.A. Morgan Dr. F.M. Stuart Dr. T.J. Dunai Dr. J.M. O’Connor Dr. A. Hildenbrand This research was carried out at the Vrije Universiteit Amsterdam Department of Isotope Geochemistry, Faculty of Earth and Life Sciences De Boelelaan 1085 1081 HV Amsterdam, The Netherlands and the Scottish Universities Environmental Research Centre NERC Cosmogenic Isotope Analysis Facility Rankine Avenue Scottish Enterprise Technology Park East Kilbride G75 0QF, Scotland The project was kindly supported by the Marie Curie Initial Training Network CRONUS-EU Project number 511927 and The Netherlands Research Centre for Integrated Solid Earth Science (ISES).

  • Table of content Introduction and summary 2 (Introductie en samenvatting) I. Geological Setting Geology of the Canary Islands 16 Fuerteventura 20 Geochronological Framework 21 Geomorphology and Climate 22 II. Sampling, sample characteristics and sample preparation Sampling strategy 27 Sampling sites and sample field characteristics 27 Sample petrography 30 Sample preparation 31 Geochemistry 31 Summary 35 III. 40Ar/39Ar dating with a commercial grade triple filter quadrupole mass spectrometer Introduction 38 40Ar/39Ar geochronology: theory and application 39 Mass spectrometer line setup and methodology 43 Procedure development 49 Conclusions 68 Theory and application of in situ Terrestrial Cosmogenic Nuclides Introduction 70 Principle of Cosmogenic Nuclide applications 70 Applications and methodology for in situ noble gas TCNs 77 In situ cosmogenic 3He methodology and approach in this work 79

    V. Volcanic and exposure geochronology from Fuerteventura Introduction 82 Methodology 83 Results 88 Discussion 98 Conclusions 103 Synthesis and Conclusions This study and the Marie Curie initial training network 106 Synthesis 106 Perspectives 110 References 111 Acknowledgements 121 Appendices 123

  • Chronos, the god of time (sculpture by Franz Ignaz Gunther, 1765 – 1770, Bayerisches

    Nationalmuseum, Munich, Germany)

     

  • Introduction, rationale and outline of this study

    2

    Introduction, rationale and outline of this study One of the great challenges in Earth Sciences is to date ever younger events and processes with

    satisfactory precision and accuracy. This is an important step towards linking past and present

    behaviour of processes and potentially predicting future trends. Geochronology needs therefore

    refinement of existing methods and development of new ones, including intercalibration of

    methods, and their validation and testing. Radiometric dating is based on the fact that by knowing

    the production or decay of an isotope an age of a sample containing the isotope can be made. One

    of the challenges is that it is not possible to use a single dating method as all depend on suitable

    material and only achieve satisfactory precision within certain time intervals. For example, the

    radiocarbon method depends on the decay of 14C in a specimen over time. It is effectively extinct

    in 10 half-lives, one half- life being 5730 ka. Most other isotopic dating techniques are

    accumulation methods, i.e. they rely on the in-growth of the radiogenic daughter isotope by in situ

    decay of a radioactive isotope, or as will be shown, by continued exposure to a field of cosmic rays

    at the interface between the lithosphere and the atmosphere. All isotopic dating techniques relying

    on accumulation are also constrained by a detection limit of their daughter isotope at the younger

    end of their range of applicability.

    This study was initiated to improve our knowledge about the production rate of in situ terrestrial

    cosmogenic nuclides (TCN) within the framework of the CRONUS-EU Research Training

    Network. The primary aims of this network were to improve our understanding of TCN

    systematics and to train the next generation of scientists in using the TCN technique. CRONUS-

    EU and the parallel United States based network initiative CRONUS-Earth also aimed to unify the

    various existing scaling methods and production rates. Prior to these initiatives the best

    characterized calibration sites for the Holocene where clustered on Hawaii and for the Pleistocene

    in the Western USA and on the Canary Islands (Dunai, 2001 and references therein). During the

    CRONUS-EU initiative new sites emerged as potential calibration sites, e.g. Mt Etna and

    Stromboli in Italy and the Canary and Cape Verde Islands in the Atlantic Ocean.

    The research described in this thesis focused on calibration of the cosmogenic 3He exposure dating

    method using 40Ar/39Ar dated lava flows from the Canary Islands. It re-evaluated the Canary

    Islands as a low latitude and low altitude calibration site for cosmogenic nuclides by changing the

    sampling area from Lanzarote to Fuerteventura. This site was part of a natural target network

    spanning a wide range of latitudes from Mt Kilimanjaro at 3 degrees South to Iceland at 64

  • Introduction, rationale and outline of this study

    3

    degrees N. It provided also an opportunity for testing new approaches in measuring argon isotopes

    for 40Ar/39Ar geochronology and extracting helium from olivine phenocrysts. With the successful

    calibration of the cosmogenic 3He exposure dating improvements in production rate knowledge

    would be possible and help to decrease the uncertainties involved in cosmogenic nuclide

    applications.

    Technical improvements for dating younger rock samples

    Both the K/Ar and 40Ar/39Ar techniques are well established dating methods. This study uses the 40Ar/39Ar method as an independent dating tool to validate the results of cosmogenic nuclide

    measurements.

    Since its development from the K/Ar method, the 40Ar/39Ar technique (Merrihue & Turner, 1966)

    has been used to date rocks spanning a wide age range extending from the earliest geological

    records to palaeoanthropological timescales and even the history of Rome in the Classic Era

    (Renne et al., 1997; Ludwig & Renne, 2000). As ongoing analytical improvements in mass

    spectrometry reduce the uncertainties in isotope measurements the uncertainties in K/Ar standard

    ages and irradiation and decay constants have become increasingly important in 40Ar/39Ar

    geochronology (Kuiper et al., 2008; Renne et al., 2008; Min et al., 2000). These analytical

    improvements were necessary because dating increasingly younger samples was hindered by their

    low radiogenic 40Ar content. This problem is particularly accute with ages less than a few 100 ka.

    An additional problem is that the 40Ar/39Ar plateau method assumes the trapped non-radiogenic

    argon component has an atmospheric is

Search related