ResearchOnline@JCU This file is part of the following reference: Holm, Robert J. (2013) Magmatic arcs of Papua New Guinea: insights into the late Cenozoic tectonic evolution of the northern Australian plate boundary. PhD thesis, James Cook University. Access to this file is available from: http://researchonline.jcu.edu.au/32125/ The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact [email protected] and quote http://researchonline.jcu.edu.au/32125/ Magmatic arcs of Papua New Guinea: Insights into the Late Cenozoic tectonic evolution of the northern Australian plate boundary Thesis submitted by Robert J. Holm July 2013 For the Degree of Doctor of Philosophy in the School of Earth and Environmental Sciences of James Cook University Statement of Access I, the undersigned author of this thesis, understand that James Cook University will make this thesis available for use within the university library and allow access in other approved libraries after its submission. All users consulting this thesis will have to sign the following statement: In consulting this thesis I agree not to copy or closely paraphrase it in whole or in part without the written consent of the author; and to make proper public written acknowledgement for any assisstance which I have obtained from it. Beyond this, I do not wish to place any restrictions on access to this thesis. Robert J. Holm July 2013 I Declaration I declare that this thesis is my own work and has not been submitted in any form for another degree or diploma at any university or other institute or tertiary education. Information derived from the published or unpublished work of others has been acknowledged in the text and a list of references is given. Robert J. Holm July 2013 II Statement of Contribution by Others Names, Titles and Affiliations of Nature of Assistance Contribution Co-Contributors Intellectual Support Proposal writing Simon Richards (JCU) Simon Richards (JCU) Data analysis Carl Spandler (JCU) Mark Schmitz (Boise State) Carl Spandler (JCU) Editorial assistance Simon Richards (JCU) Gideon Rosenbaum (UQ) Barrick Australia Financial Support Field research (In-kind contribution) Stipend Australian Postgraduate Award SEES ($15,580) Research funding Research account of Simon Richards ($5,000) Richard Wormald (JCU) Data Collection Research assistance Yi Hu (JCU) III Statement of Contribution by Others Title of thesis: Magmatic arcs of Papua New Guinea: Insights into the Late Cenozoic tectonic evolution of the northern Auatralian plate boundary Name of candidate: Robert J. Holm Chapter Details of publication(s) on which chapter is Nature and extent of the intellectual input of # based each author Holm, R.J., Spandler, C., Richards, S.W., 2013. Melanesian arc far-field response to collision of the Ontong Java Plateau: I contributed to the writing and development of 3 Geochronology and pertrogenesis of the concepts Simuku Igneous Complex, New Britain, Papua New Guinea. Tectonophysics, In Press. I confirm the candidate's contribution to this paper and consent to the inclusion of the paper in this thesis. Name: Carl Spandler Signature: Date: Statement of Contribution by Others Title of thesis: Magmatic arcs of Papua New Guinea: Insights into the Late Cenozoic tectonic evolution of the northern Auatralian plate boundary Name of candidate: Robert J. Holm Chapter Details of publication(s) on which chapter is Nature and extent of the intellectual input of # based each author Holm, R.J., Spandler, C., Richards, S.W., 2013. Melanesian arc far-field response to collision of the Ontong Java Plateau: 3 I contributed to the development of concepts Geochronology and pertrogenesis of the Simuku Igneous Complex, New Britain, Papua New Guinea. Tectonophysics, In Press. Holm, R.J., Richards, S.W., 2013. A re- evaluation of arc-continent collision and along- I contributed to the writing and development of 7 arc variation in the Bismarck Sea region, concepts Papua New Guinea. Australian Journal of Earth Sciences, Accepted. I confirm the candidate's contribution to this paper and consent to the inclusion of the paper in this thesis. Name: Simon Richards Signature: Date: IV Acknowledgments There are many people who were involved or contributed in some way to my thesis work over the last three and a half years. Although they cannot all be thanked here individually, their help is greatly appreciated. I owe the greatest debt of thanks to my supervisors, Simon Richards, Carl Spandler and Gideon Rosenbaum. Firstly, a huge thanks Simon for the opportunity to study in such a region and his enthusiasm for the project and willingness to explore weird and wonderful ideas. An enormous thanks to Carl for reigning back some of the ideas and whose time and wide range of knowledge got me over the line. And lastly, great thanks to Gideon for all your time and effort, and input into the project. Simon, Carl, and Gideon, I look forward to working with you in the future. I would also like to thank Richard Wormald and Yi Hu for their time an effort for the zircon and LA-ICP-MS work, one of the most enjoyable and key aspects of my research. Thanks to all the staff at SEES for the last three and a half years who made this an enjoyable and worthwhile experience, and for all your time and help. And thanks to my fellow PhD and honours students over the years, particularly Johannes, Mark, Babo, Ryan, Grace and Jainrich (and those to come). As mates and colleagues you all provided plenty of advice and many fruitful discussions, as well as the many that were not so useful but entertaining nonetheless. I would like to thank Barrick Australia for making this project possible and particularly those in PNG for providing samples and assistance in the field. Also thanks to the AAC staff for assistance with analytical work, and Mark Schmitz for help with the TIMS analyses and dating. And finally, my parents for their support and always being interested in my work despite not understanding the details, and for putting up with two perennial students for sons. V Abstract Papua New Guinea, as part of the southwest Pacific, lies in a complex tectonic setting of oblique convergence between the Pacific and Australian plate, and trapped between the converging Ontong Java Plateau of the Pacific plate and the Australian continent. Through studying the tectonic evolution of Papua New Guinea we can gain insight into how the region formed through time and explore the relationships between the driving forces of tectonics and the responses or feedbacks reflected in the geology. At present we lack the evidence to fully constrain the evolution of Papua New Guinea, however, through the study of arc magmatism I illustrate how we might approach defining a geodynamic framework for the region and unraveling the complex tectonic history. In general, the deformation history of Papua New Guinea is well constrained but the same robust records do not exist for magmatism. To progress with unravelling the tectonic evolution of the region we require a time and cost effective means of robust age dating in young rocks. Investigation into the timing of two Quaternary magmatic occurrences by LA-ICP-MS U-Pb zircon dating compared with CA-TIMS and SHRIMP dating methods reveal good correlation and age agreement between dating methods. This is one of only few studies utilizing LA-ICP- MS U-Pb zircon dating for Quaternary ages. Uncertainty in such young rocks is relatively large due to potential matrix effects related to differential alpha dose accumulation and limitations on instrumental precision with an associated error threshold of 5% for a determined age. This makes LA-ICP-MS U-Pb dating a useful tool in regional studies of this nature. The Late Cenozoic tectonic evolution of Papua New Guinea is set in motion with initial convergence at the Australia-Pacific plate boundary from 45 Ma. Combined U-Pb zircon geochronology and geochemical investigation into the evolution of the Melanesian arc from the Simuku Igneous Complex of West New Britain, Papua New Guinea reveals development of the embryonic island arc from at least 43 Ma. Progressive arc growth was punctuated by distant collision of the Ontong Java Plateau and subduction cessation from 26 Ma. This change in subduction dynamics is represented by emplacement of the adakitic Simuku Porphyry Complex between 24 and 20 Ma. Petrological and geochemical affinities highlight genetic differences between contemporaneous “normal” arc volcanics and adakite-like signatures of Cu-Mo mineralized porphyritic intrusives. Not only is this one of few studies into the geology of the Melanesian arc, it is also among the first to address the distant tectono-magmatic effects of major arc/forearc collision events and subduction cessation on magmatic arcs. VI Understanding of the tectonic evolution of mainland Papua New Guinea throughout the Miocene is hampered by a lack of robust geological evidence. The Maramuni arc of Papua New Guinea represents the only continuous tectonic element throughout this dynamic period. I present the first detailed U-Pb geochronology and geochemical investigation of the Maramuni arc from intrusive rocks of the Kainantu region of the eastern Papuan Highlands. Arc magmatism related to north-dipping subduction at the Pocklington trough is punctuated by arrival of the Australian continent at approximately 12 Ma and growth of the New Guinea Orogen. Arc geochemistry from 12 Ma highlights a changing tectonic setting, marked by anomalous enrichments in high- field strength elements at 9 Ma. Crustal delamination from approximately 7 Ma is coincident with porphyry intrusion bearing similarities to adakitic rocks and renewed uplift of the New Guinea Orogen from 6 Ma.