Studies attempting to gain new insights into the last stage of the subduction cycle are typically challenged by limited direct observations owing to a lack of recent post-subduction settings around the world. Central to unravelling how the subduction cycle ends is an understanding of crust and mantle processes that take place after subduction termination. Northern Borneo (Malaysia) represents a unique natural laboratory because it has been the site of two sequential subduction episodes of opposite polarity since the mid-Paleogene. The region exhibits several enigmatic post-subduction (after ∼ 10 Ma) features, including: subsidence followed by rapid uplift, localised intraplate volcanism, possible orogen collapse, and a pluton that emerged to become the third highest peak in southeast Asia, Mt Kinabalu (4095 m). Arrival-time residuals from distant earthquake data recorded by the nBOSS seismic network have been used to investigate P- and S-wavespeed variations in the crust and underlying upper mantle beneath northern Borneo. Our 3-D tomographic images consistently show a high-velocity perturbation in western Sabah that we associate with an upper-mantle remnant of the Proto South-China Sea slab, thus providing important constraints for tectonic reconstructions of SE Asia. The tomographic models, combined with other seismological and geological information, reveal evidence for lithospheric removal in eastern Sabah via a drip instability. Our results suggest that lithospheric drips can be smaller than previously thought, yet their effects on the post-subduction evolution of continental lithosphere can be significant.
S.P. acknowledges support from the Natural Environmental Research Council (NERC) Grant NE/R013500/1 and from the European Union's Horizon 2020 Research and Innovation Program under Marie Skłodowska-Curie Grant Agreement 790203. We thank the TanDEM-X Science Communication Team (German Aerospace Center (DLR) e.V.) for providing TanDEM topographic data. We thank the NERC Geophysical Equipment Facility for loan 1038 and seismometers loaned by the University of Cambridge and Aberdeen. We would like to thank Zhong-Hai Li and an anonymous reviewer for their constructive feedback during the review process.
Data Availability StatementData and software availability
Waveform data from the nBOSS network will be publicly accessible through the IRIS Data Management (https://www.iris.edu/
mda) from February 2023 (see for details https://doi.org/10.7914/
SN/YC_2018). Details on the status of this database may be
obtained from N.R. Access to waveform data from the Malaysian
national network (https://www.fdsn.org/networks/detail/MY/) is
restricted. The final P- and S-wave tomographic models can be
downloaded from the following digital object identifier
The source code for the Adaptive Stacking method used to compute the arrival time residuals is available at https://www.iearth.
edu.au/codes/AdaptiveStacking/. The source code and manual for
FMTOMO are available at https://iearth.edu.au/codes/FMTOMO/.
Supplementary data to this article can be found online at
- Teleseismic tomography
- Subduction termination
- Lithospheric drip
- Proto-South China Sea
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