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

Abstract

Subduction polarity reversal (SPR) is a key subduction initiation mechanism often associated with arc‐continent collision zones. Northern Borneo has long been recognized as a location where sequential but opposing subduction zones were present in the Miocene, but has not been examined in the context of SPR. Here, we exploit teleseismic data from northern Borneo to investigate crustal thickness variations using Virtual Deep Seismic Sounding (VDSS). Our results reveal a thick crustal root beneath the Crocker Range and an area of relatively thin crust in the southeast, which appears to extend northeast into the Sulu Sea, where back‐arc rifting behind the younger subduction zone developed. Overall, our findings are consistent with predictions from numerical models of SPR involving arc‐continent collision, but with several important differences—including a substantial mountain range and more limited back‐arc rifting that can be attributed to northern Borneo being an example of SPR involving continent‐continent collision.

Mantle Flow Induced by the Interplay of Downgoing Slabs Revealed by Seismic Anisotropy Beneath the Sula Block in Eastern Indonesia

“…The typical values of δt from SKS splitting in this study are more than 1 s, indicating that anisotropy primarily comes from the upper mantle beneath the Moho (Silver, 1996). More specifically, the average value of δt from SKS is 1.6 s, and more than 88% of values are larger than 1 s. A thin crust along the western part of the north arm of Sulawesi with about 20-25 km thickness has been proposed based on the receiver function analysis (Fauzi et al, 2021;Linang, 2023). Previous investigations in subduction zone settings support our inference that the dominant contributor of seismic anisotropy in the upper mantle is mantle wedge flow (e.g., Cao et al, 2021;León Soto & Valenzuela, 2013;Long & Wirth, 2013;Wang & He, 2020), though the upper plate crust and subducting slab may also contribute.…”

The Signature of Lithospheric Anisotropy at Post‐Subduction Continental Margins: New Insight From XKS Splitting Analysis in Northern Borneo

“…Recent geochemical analyses have indicated that an exposed ophiolitic complex around Telupid (central Sabah, see Figure 1) bears the signature of oceanic rifting, with radiometric U‐Pb ages dating these basalts to around 9 Ma (surface geology and geochemical dating shown in Figure S1 in Supporting Information ; Tsikouras et al., 2021). Furthermore, crustal thickness estimates have also revealed a degree of thinning in the crust that coincides with the exposed ophiolite, extending in from the Sulu Sea toward Telupid (Greenfield et al., 2022; Linang et al., 2022; Pilia et al., 2021). Together, these suggest that Sulu Sea rifting propagated into what is now northern Borneo, but ultimately failed to initiate extensive seafloor spreading.…”