Seismic signature of subduction termination from teleseismic P- and S-wave arrival-time tomography: the case of northern Borneo

Abstract

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 postsubduction evolution of continental lithosphere can be significant.

Collision‐Induced Subduction Polarity Reversal Explains the Crustal Structure of Northern Borneo: New Results From Virtual Deep Seismic Sounding (VDSS)

“…In this scenario, intra‐oceanic subduction of the PSCS leads to the continent‐continent collision of the Dangerous Grounds Block and northern Borneo, which gives rise to the Crocker Range, the root of which is clearly revealed in Figure 3. This is followed by slab break‐off, with recent tomographic images from nBOSS data (Pilia et al., 2021a, 2022) showing clear evidence for PSCS slab remnants in the upper mantle and initiation of Celebes Sea subduction. Roll‐back of the Celebes Sea slab produces rifting in the back‐arc that goes on to form the Sulu Sea in the northeast, but only causes localized extension in northern Borneo (see Figure 3) owing to the presence of continental crust.…”

“…For northern Borneo, we used the S‐wave relative arrival‐time residuals from Pilia et al. (2022). The average difference between the VDSS traces obtained using method B with and without the incorporation of the calculated ∆ t is 1.6 ± 0.5 km, which is relatively small and within an acceptable error range.…”

“…The difference between the two arrival-time residuals (∆t) is used to adjust the T SsPmp-Ss travel time, thus mitigating the effect of mantle heterogeneity located between and beneath the virtual source and the receiver. For northern Borneo, we used the S-wave relative arrival-time residuals from Pilia et al (2022). The average difference between the VDSS traces obtained using method B with and without the incorporation of the calculated ∆t is 1.6 ± 0.5 km, which is relatively small and within an acceptable error range.…”