The SE China-NW Palawan conjugate continent ocean transitions; insights for mechanism of continental breakup

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https://meetingorganizer.copernicus.org/EGU2019/EGU2019-6554.pdf
Author(s): Nirrengarten, Michael; Mohn, Geoffroy; Kusznir, Nick; Despinois, Frank; Pubellier, Manuel; Chang, Sung-Ping
Author Affiliation(s): Primary:
Université de Cergy Pontoise, Laboratoire Géosciences et Environnement Cergy, Neuville sur Oise, France
Other:
University of Liverpool, United Kingdom
TOTAL-Scientific and Technical Center Jean Féger, France
Ecole Normale Superieure de Paris, France
Volume Title: European Geosciences Union general assembly 2019
Source: Geophysical Research Abstracts, Vol.21; European Geosciences Union general assembly 2019, Vienna, Austria, April 7-12, 2019. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: Recent high-quality seismic acquisitions on rifted margins around the world highlight the variability of the architecture of Continent-Ocean Transitions (COT). Drilling control, to determine the basement nature and timing of deformation, combined with the analysis of conjugate sections are essential to constrain tectono-magmatic evolution of rifting and breakup. With the recent deep-sea drillings (IODP 349-367 & 368), the high-resolution seismic data and potential field data, the SE China-NW Palawan margins provide an ideal natural laboratory to investigate the mechanisms of continental breakup and for comparison with the evolutionary models developed on the Atlantic margins. Seismic architecture of the drilled segment of the SE China COT is characterized from NW to SE by a basement high (the so-called Outer Margin High, OMH) that thins oceanward, three faulted basement ridges (A, B and C) and a 6 km thick oceanic crust. Deep sea drilling across the SE China COT presents significant basement lithology variations across these distinct structural features. From continent to ocean, pre-rift sediments (OMH), metamorphic rocks (OMH), highly altered basalt (Ridge A) and fresh pillow basalt (Ridge B) were recovered. Gravity anomaly inversion and joint inversion performed on seismic profiles show an increase of the average crustal basement density between ridges A and B interpreted as representing the transition from continental basement to igneous crust. Ridge A is composite, late syn-rift magmatism is emplaced within thinned continental crust, which shows the interactions between MORB magmatism and tectonic thinning. Ridges B and C are made of igneous crust subsequently faulted. At the NW Palawan margin, in contrast to the SE-China margin, no extensional faults have been observed in the igneous crust. Moreover, the older interpreted oceanic magnetic anomaly (C11) is only identified on the SE China side, whereas the magnetic anomaly C10 is observed on both side and located oceanward. Based on our results, we propose a tectono-magmatic model constrained in time and space for the breakup of this segment of the South China Sea. The main observations are: 1) MORB magmatism increases concomitant with crustal/lithospheric thinning; 2) The SE China and NW Palawan COT are asymmetric with tectonic extension in igneous crust and magnetic anomaly C11 only observed on the SE China side; 3) the formation of igneous crust occurs 2 Ma before the initiation of steady state sea-floor spreading; 4) extension at the SE China COT during this time lag is accommodated by the interplay between magmatic accretion and faulting. These results show that breakup leading to the formation of a steady state sea-floor spreading is not instantaneous, and involves a period during which magmatism and tectonic extension are not yet localized. [Copyright Author(s) 2019. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]
Year of Publication: 2019
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Arctic Ocean; Asia; Atlantic Ocean; Basalts; Cape Verde Rise; China; Continental crust; Crust; DSDP Site 349; DSDP Site 368; Deep Sea Drilling Project; Extension tectonics; Far East; Geophysical methods; Geophysical surveys; Igneous rocks; Integrated Ocean Drilling Program; Jan Mayen Ridge; Leg 38; Leg 41; Magmatism; Mid-ocean ridge basalts; North Atlantic; North Pacific; Northwest Pacific; Norwegian Sea; Oceanic crust; Pacific Ocean; Palawan; Philippine Islands; Plate tectonics; Rifted margins; Rifting; Seismic methods; South China Sea; Southeastern China; Surveys; Tectonics; Volcanic rocks; West Pacific
Coordinates: N050000 N330000 W0100000 W0220000
Record ID: 2019050552
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany