Linking sill morphology to emplacement mechanisms by Nick Schofield A thesis submitted to The University of Birmingham For the degree of DOCTOR OF PHILOSOPHY Department of Earth Sciences School of Geography, Earth And environmental sciences The University of Birmingham May 2009 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ___________________________________________________________________________ Abstract ____________________________________________________________________ Mafic sill complexes are increasingly being shown to play a major role in the movement of magma around the upper crust in volcanic terranes and to have a role in mass extinction events in Earth history. Most of the current models of sill emplacement assume that brittle fracture operates at all points of sill emplacement. Within this thesis, a series of observations are presented from sheet intrusions in South Africa, USA and the UK showing that in certain situations, dependent on host rock lithology, the propagation of magma through normal brittle fracture can cease. In this circumstance a prevalent fluid/fluid or fluid/ductile relationship between host rock and intruding magma is often developed. Once this occurs, the evolution of a given sheet intrusion becomes distinctly different from that produced by normal brittle fracture alone. The break down in brittle fracture often leads to the development of magma fingers, which accelerate ahead of the main sheet of magma. It is important to note that it is ultimately the host rock lithology and its coupled response to intrusion of magma that dictates the ongoing evolution of the morphology of sheet intrusions in high-level magmatic systems. Words: 200 __________________________________________________________________________ Acknowledgement ___________________________________________________________________ Undertaking this PhD has been an interesting journey, it has been one of the best experiences of my life, but it has equally been tinged with much sadness. I’ve been very lucky throughout my PhD to have had five (having mysteriously gained another supervisor post-viva) excellent supervisors who have all contributed to this project in their own unique ways. Particular thanks/apologies should go to Prof. Tim Reston who took over lead supervision after Ken’s death. Although he has an unusual (possibly unhealthy) fascination with lithospheric stretching, he has equally been an invaluable source of advice and encouragement. A bottle of whisky is in order, however drink it properly Tim! Prof. Donny Hutton provided many discussions on sill emplacement, life and experiences. The field season which I spent with Donny in South Africa has provided me many good memories. Prof. Graham Westbrook provided critical discussions in general. He is also thanked for allowing me to take part in the HERMES TTR-16 cruise on the Norwegian Margin in June 2005. Dr. Carl Stevenson (one of the members of the Northern Ireland structural mob) deserves a big mention. He has been a both a good friend and a colleague. We have had many discussions on igneous emplacement, mainly at the Pub. So cheers mate, I couldn’t have done it without you. It should also be noted that the school of GEES decided post-viva that Dr. Stevenson was one of my supervisors! Talk about sitting on the fence! Thanks should also go to Dr. Jonathan Turner, who gave many words of encouragement during the PhD. “Alright Jonathan……Three lobster thermidor’s please”! Prof. John Underhill (Kens former PhD supervisor) is thanked for encouragement, advice, discussions and post-doc references! In bad times it was nice to know that I had somebody looking out for me back in Edinburgh. Dr Chris Cornelius of Cuadrilla Resources is thanked for his hospitality and introduction to the sills of the Raton Basin which cemented many of the ideas presented in the thesis. Dr Pete Turner of Cuadrilla Resources is thanked for help during the PhD and introducing me to Chris, as well as introducing me to plethora of ‘interesting’ individuals. The late Dr Bill Owens is thanked for early advice on AMS in Skye and for accompanying me in the field along with Donny on my first trip to the Trotternish Peninsula. He is sadly missed. John Smallwood of Hess is thanked for continued support and providing 3D seismic data sets. Funding from NERC studentship (NER/S/A/2005/13237) is gratefully acknowledged. AAPG Grants-In-Aid program is thanked for awarding the Horst & Jessie von Bandat Memorial Grant which enabled USA fieldwork to be undertaken. I would like to thank my examiners Dr. Mike Curtis (BAS) and Dr. Andy Chambers (Birmingham), I thank them both for seeing through my abysmal English skills to provide an opportunity for an in- depth and stimulating discussion on the thesis. Mike is particularly thanked for making me realise the need for complete precision and conciseness, as well as getting me to take more care in reading conclusions of papers! On more personal notes, several people deserve mentions; Dr. Neil Davies, did his best and succeeded in making the first half of my PhD a bizarre experience. Luckily for UK citizens, he is now in Canada. Fellow members of Rm 116 “The office of glory” a.k.a. “Subsurface office and Phil” deserve a mention. These include Craig “Magma” Magee, Ken “Keys” Mcdermot, Phil “Palynology” Jardine and Baba “Faults” Jibrin………………..I’m sure you are all destined for great things, how about “The School of the Subsurface and Phil”? Other mentions should go to people who have made my time at Birmingham very enjoyable. In no particular order, these include; Aruna Mistry, Ian Boomer, Paula Cole, Sarah King, Andy Rees, Richard Greswell, June Morris, Russel Exley, Simon Holford, Liam Herrigshaw, Andy Chambers, Kate Thatcher, Sam Spendlove, Ruth Hughes, Chloe Parker. Other notable mentions should also include the VMSG crew, who I have shared many a pint with over the years and in some cases ‘romantic’ sunset cruises under the Golden Gate bridge. The usual suspects consist of Dr Davie Brown (Glasgow), Dr Simon Passey (Faroes), Simon “Hang about, when I’m cleaning windows, fingers” Drake (UCL/Birkbeck). Finally I would particularly like to mention two people who have kept me on the right side of normality in recent years; My housemate, Kate Faloon a.k.a Loser, has been a source of very un-witty banter and given much amusement (often at her own expense, red-light bulbs maybe?). She has plied me with wine, whisky and chocolate brownies when the stress kicked in. In addition she has done my washing up on one to many occasions (well actually on most occasions to be trueful). For all this I am extremely grateful to her, but ultimately Kate, just remember………….I’m right, you’re wrong, so…...? The final thank mention goes to Holly who has been a source of great patience (generally). She has also kept a smile on my face in difficult times mainly due to her confusion with the general world around. So Holly in response to some of the questions you’ve raised or shown utter shock at in recent years (I know you don’t mind me saying these), the answers are as follows. 1) People do indeed eat monkeys 2) Clouds on the ground are generally referred to as fog and 3) The Bismarck did not take part in Falklands conflict and did not sink off the Falkland Islands. I hope this has cleared a few things up! ___________________________________________________________________________ Dedication ___________________________________________________________________ This thesis is dedicated to the memory of Dr. Ken Thomson (1966 – 2007) Ken unexpectedly passed away in April of 2007 while in the department. He was a brilliant supervisor, academic and polymath! Along with Donny he set an excellent PhD project which I’ve had the honour of getting my teeth into, for which I am extremely grateful. So Ken, if your about somewhere in the ether, I hope your happy with the result. It would have been nice to have a pint with you afterwards. “Sentries have come in from the hill, sir.... They report Zulus to the southeast. Four thousand of them” from the film Zulu (1965) “Mk.1 Eyeballs” – British military term Contents ________________________________________________________ Contents Chapter 1: Introduction and models of sill emplacement 1 1.1 Models of sill imitation and emplacement 1 1.1.1 Gilbert (1877) 1 1.1.2 Anderson (1951) 3 1.1.3 Mudge (1968) 3 1.1.4 Gretener (1969) 4 1.1.5 Johnson and Pollard (1973) 4 1.1.6 Leamen (1975) 4 1.1.7 Kavanagh et al. (2008) 4 1.2 Models of saucer-shaped sill emplacement (Pre 3D seismic) 5 1.2.1 Bradley (1965) 6 1.2.2 Francis (1982) 7 1.2.3 Chevalier and Woodford (1999) 7 1.3 Discussion 8 1.4 Preface to remaining chapter 8 Chapter 2: Contribution of 3D seismic data in the understanding of sill emplacement 10 mechanisms 2.1 3D seismic investigations of Sills 10 2.1.1 Sills in 3D seismic data – An introduction 10 2.1.2 Imaging of sills within seismic data 11 2.1.3 Opacity rendering 12 2.1.4 Sill feeding regimes 15 2.1.5 Exploitation of pre-existing