EGU2020-14296
https://doi.org/10.5194/egusphere-egu2020-14296
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Tectono-magmatic and thermal evolution of the SE China margin-NW Palawan breakup

Geoffroy Mohn1, Michael Nirrengarten1, Andrea Schito2, Nick Kusznir3, Sveva Corrado2, Stephen Bowden4, Manuel Pubellier5, François Sapin6, and Hans-Christian Larsen7
Geoffroy Mohn et al.
  • 1Université de Cergy-Pontoise, Departement de Geosciences et Environnement, Neuville sur Oise, France (geoffroy.mohn@u-cergy.fr)
  • 2Università degli Studi di Roma Tre, Dipartimento di Scienze, Sezione di Scienze Geologiche, Largo San Leonardo Murialdo 1, 00146 Rome, Italy
  • 3University of Liverpool, Department of Earth and Ocean Sciences, Liverpool, UK (L69 3BX)
  • 4University of Aberdeen, Department of Geology and Petroleum Geology, Aberdeen AB24 3UE, UK
  • 5Laboratoire de Géologie, UMR 8538, École Normale Supérieure, CNRS, Paris, France
  • 6Total SA Frontier Exploration R&D Program, CSTJF, Pau, France
  • 7Geological Survey of Denmark and Greenland, Copenhagen, Denmark

Continent Ocean Transitions (COTs) record the processes leading to continental breakup and localized oceanic accretion initiation. The recent IODP Expeditions 367-368 and 368X at the SE China margins combined with high quality multi-channel seismic profiles provide a unique dataset to explore the tectono-magmatic and thermal evolution from final rifting to early seafloor spreading. To investigate these issues, we developed a multi-disciplinary approach combining reflection seismic interpretations with geophysical quantitative analysis calibrated thanks to drilling results, from which we measured and modelled the thermal maturity in pre-/syn- to post-rift sediments.

Drilling results show that the transition from the most thinned continental crust to new, largely igneous crust is narrow (~20 km). During final rifting, decompression melting forming Mid-Ocean Ridge type magmatism emplaced within thinned continental crust as deep intrusions and shallow extrusive rocks concomitant with continued deformation by extensional faults. The initial igneous crust of the conjugate margins is asymmetric in width and morphology. The wider and faulted newly accreted domain on the SE China side indicates that magmatic accretion was associated with tectonic faulting during the formation of initial oceanic lithosphere, a feature not observed on the conjugate Palawan side. We suggest that deformation and magmatism were not symmetrically distributed between the conjugate margins during the initiation of seafloor spreading but evolved asymmetrically prior to the spreading ridge stabilising.

Organic matter from post-rift sediments has low thermal maturities due to limited burial and the absence of late post-rift magmatism. In contrast, pre to syn-rift sediments show significant variability in thermal maturities across the COT. Localised high thermal maturities for the pre- to syn-rift sediments requires that significant additional heat be imparted at shallow depths during breakup, likely related to magmatic intrusion or subsurface expressions of volcanism. The heterogeneous variation in thermal maturity observed across the COT reflects localised thermal perturbations caused by magmatic additions.

How to cite: Mohn, G., Nirrengarten, M., Schito, A., Kusznir, N., Corrado, S., Bowden, S., Pubellier, M., Sapin, F., and Larsen, H.-C.: Tectono-magmatic and thermal evolution of the SE China margin-NW Palawan breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14296, https://doi.org/10.5194/egusphere-egu2020-14296, 2020

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  • CC1: Comment on EGU2020-14296, Agustin Cardona, 05 May 2020

    Hello, very interestig research. Yo didn´t mention the role of hydrothermal activity on heating or the proximity to major faults. On your presentation you mention the presence of highly hydrothermally altered basalts. How does it fits on the thermal model.

    Thanks

    • AC1: Hydrothermalism at Site U1502, Geoffroy Mohn, 05 May 2020

      Hello Augustin,

      Yes, sorry I didn’t have time to develop more. Yes, at Site U1502 (IODP expedition 368, last piece of highly thinned continental crust associated with late syn-rift magmatic additions), we drilled strongly altered pillow basalt directly overlain by marble (10 meters thick). We interpreted this marble to be of hydrothermal origin. Above the marble, the 720m of post-rift sequence show no hydrothermal alteration. Near this site, we interpreted the occurrence of normal faults although we cannot really address their role for fluid pathway.

      We performed analyses of the thermal maturity (vitrinite reflectance and biomarker data) showing 0.43Ro% on the marble just above the basalts. Following our thermal modelling we can explain this value by burial assuming high heat flow conditions during the rifting (275mW.m-2).

      In general, the impact of hydrothermal conditions is an interesting question. For sure, hydrothermal fluids can impact the thermal maturity as already reported. Key question is the duration of the hydrothermalism, it has to sustain during a sufficient duration to impact organic matter.

      Please don’t hesitate to let me know if you need any additional precisions, I would be happy to answer.

      You can find more information in Nirrengarten et al. 2020,

      Cheers

      Geoffroy

  • CC2: Comment on EGU2020-14296, Yanghui Zhao, 06 May 2020

    Hi Geoffroy,

    I very much like your presentation. And congratulations to Michael's new MPG paper. Do you think syn-rift magmatism was mainly located in the future northern conjugate margin? If so, what causes the asymmetry? 

    Thanks,

    Yanghui

    • AC2: Reply to CC2, Michael Nirrengarten, 06 May 2020

      Hi Yangui,

      Thank you for the question, which is not easy to answer, but I will try to bring a partial answer. If you look on Fig. 9 of the MPG paper you see that between the COB and magnetic anomaly C10 there are ~47 km on the SE China side and ~31 km on the NW Palawan side, so approximatively 30% less distance on the S side compare to the N side. The SE China margin presents numerous oceanward dipping fault which are absent on the conjugate side. We sum the heaves of these faults and calculate that the tectonic extension account for 20 % of the distance between COB and C10. Which means that there is only 10% more magmatic material on the SE China side compared to the NW Palawan.

      To explain the asymmetry of the distal margin and first oceanic crust we suggest a process of trailing flank described by Stein et al. (1977) on seafloor spreading ridges induced by absolute plate motion. However, it is just a suggestion and there are still questions to understand the asymmetry of the system.

      Michael

  • AC3: Comment on EGU2020-14296, Manuel Pubellier, 06 May 2020

    Thanks for your question. There is much less magmatic evidence on the southern margin. However a large part is highly sedimented by clastics during Eocene and Oligocene and a lot of platform carbonate afterwards covering underlying material. There a a lot of Late Neogene occurences though, particularly south of Reed Bank. Some very limited magmatism at time of rifting exist in Palawan (Mt Capoas) but it is Middle to Late Miocene (just after the cessation of rifting).

    Manuel