EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The tectonic and volcanic evolution of the Mangatolu Triple Junction

Rebecca Mensing1,4, Margaret Stewart2, Mark Hannington1,3, Alan Baxter3, and Dorothee Mertmann4
Rebecca Mensing et al.
  • 1Marine Mineral Resources, Geomar - Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Department of Earth and Environmental Sciences, Mount Royal University, Calgary, Canada
  • 3Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, Canada
  • 4Geodynamics, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany

The Mangatolu Triple Junction (MTJ) is an intraoceanic back-arc spreading center that is host to at least 3 distinct hydrothermal systems. It is located in the NE Lau Basin, which opened due to rollback of the Pacific plate along the Tonga-Kermadec trench. At the MTJ, three spreading centers meet in a ridge-ridge-ridge (RRR)-type triple junction separating the Tonga plate in the east, the Niuafo’ou microplate in the southwest, and an unnamed microplate in the north. The MTJ is directly linked to the formation and evolution of the Northeast Lau microplate mosaic, as plate fragmentation inevitably results in the formation of triple junctions, but it remains unclear whether the spreading centers are the drivers of plate fragmentation or a consequence of stress relocation related to microplate rotation. Detailed investigation of the geology and structural setting of the MTJ therefore provides valuable insight into the development in the northeast Lau Basin. Here we present the first comprehensive 1:200,000 geological map of the MTJ, based on a compilation of marine geophysical data (hydroacoustics, magnetics, and gravity) derived from 7 research cruises that have investigated the region between 2004 and 2018. Analysis of the mapped geological formations at the MTJ shows the importance of relict arc crust originating from the Tofua Arc in the architecture of the triple junction, which includes three stages of back-arc crust development and extensive off-axis volcanism. The spreading centers along each arm of the MTJ exploit pre-existing crustal weaknesses, interpreted to have formed during initial Lau Basin opening. A reconstruction of the basin opening, based on the mapped features and published spreading rates, revealed that initiation of the MTJ commenced approximately 180,000 years ago, consistent with the very recent and ongoing dynamic evolution of the NE Lau Basin and emerging microplate mosaic. Intersecting fabrics indicate sequential evolution of the 3 arms of the triple junction, with extension along the northeast arm dominant in the early history and more recent extension along the southern and western arms. The results of this study contribute to our growing understanding of the tectonic framework of the northeast Lau Basin and the role of triple junctions in microplate formation.

How to cite: Mensing, R., Stewart, M., Hannington, M., Baxter, A., and Mertmann, D.: The tectonic and volcanic evolution of the Mangatolu Triple Junction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19897,, 2020

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Display material version 1 – uploaded on 03 May 2020
  • CC1: Comment on EGU2020-19897, Anouk Beniest, 07 May 2020

    Hey Rebecca,
    Thanks again for presenting your work! I really like your map. It is very neat!
    I have two more questions for you: what data did you use for your map, bathymetry and available data on rock samples? And lastly, are you thinking about including more structural features (like faults) on your map?

    • AC1: Reply to CC1, Rebecca Mensing, 07 May 2020

      Hey Anouk,
      I can only return the compliment, I really enjoyed your map and your display and same as Phillip during the Session would love to meet up eventually at Geomar to chat in person over the different mapping approaches.

      To answer your questions: 
      1 - I mainly used ship-derived Bathymetry and its derivatives integrated with the GMRT, and to some extend the global gravity and magnetics and some rock samples, but not too many.
      2 - I have mapped the faults and lineaments extensively (in total about 4500). However, since the map is usually not displayed at full scale the lineaments would cover the mapped units and the geology itself would get lost or barely even be visible. I am currently working on a Paper which should include the tectonic analysis and more, so be on the lookout for that, if you are interested.

      • CC2: Reply to AC1, Anouk Beniest, 07 May 2020

        Hey Rebecca,

        Cool! Thanks for your answers!

        I will definitely look out for your paper, and we will also meet up at GEOMAR for sure. Looking forward to it. Enjoy the rest of the week!