A complete structural model and kinematic history for distributed deformation in the Wharton Basin

Duncan E Stevens,Lisa C Mcneill,Timothy J Henstock,Matthias Delescluse,Nicolas Chamot-Rooke,Jonathan M Bull

doi:10.1016/j.epsl.2020.116218

Abstract

The equatorial eastern Indian Ocean hosts a diffuse plate boundary, where widespread deformation accommodates the relative motion between the Indian, Australian and Capricorn sub-plates. We integrate IODP Expedition 362 borehole data, which for the first time provides an accurate, ground-truthed chronostratigraphy of the sedimentary sequence east of the Ninety East Ridge (NER), with 2D seismic reflection profiles and multibeam bathymetry to assess the styles of faulting between the NER and the Sunda subduction zone, timing of activity and comparison with physical and rheological properties. We identify four distinct fault sets east of the NER in the northern Wharton Basin. N-S (350-010°) orientated faults, associated with the N-S fracture zones formed at the now extinct Wharton spreading centre, are still active and have been continuously active since at least 10 Ma. NNE- and WNW-trending fault fabrics develop between the fracture zones. The orientations and likely sense of displacement on these three sets of faults defines a Riedel shear system responding to ∼NNE-SSW left-lateral strike-slip activity at depth, demonstrated by the recent 2012 great intraplate earthquakes. We also find evidence of ∼NE-SW reverse faults, similar in style to E-W reverse faults observed west of the NER, where reverse faulting is more dominant. We show that the activity of this strike-slip system increased ca. 7-9 Ma, contemporaneous with reverse faulting and intraplate deformation west of the NER.

Highlights

The oceanic lithosphere of the equatorial Indian Ocean hosts a 3000 km wide (West to East) zone of complex deformation representing a diffuse plate boundary between the Indian, Capricorn and Australian plates (DeMets et al, 1990; Stein and Okal, 1978; Sykes, 1970; Wiens et al, 1986)
Biostratigraphic tie points from the International Ocean Discovery Program (IODP) (Fig. 3) borehole data show two distinct periods of sediment deposition in our study area occurring at different rates (McNeill et al, 2017a, 2017b)
Mostly still active, fault sets in the northern Wharton Basin formed in response to the regional stress field and influenced by combinations of proximity to the Sunda subduction zone and compressional deformation related to continental collision

Summary

Introduction

The oceanic lithosphere of the equatorial Indian Ocean hosts a 3000 km wide (West to East) zone of complex deformation representing a diffuse plate boundary between the Indian, Capricorn and Australian plates (DeMets et al, 1990; Stein and Okal, 1978; Sykes, 1970; Wiens et al, 1986). West of the NER, deformation is characterised by crustal shortening (Bergman and Solomon, 1985; Bull, 1990; Stein and Okal, 1978; Wiens et al, 1986), whereas in the equatorial Indian Ocean, at the northern end of the NER and east of the NER (the northern Wharton Basin, Fig. 1), primarily left-lateral strike-slip motion dominates (Deplus, 2001; Deplus et al, 1998; Sager et al, 2013). Fan sediments are dominated by siliciclastic sediment gravity-flow deposits (e.g., turbidity currents and debris flows), that range from clay to silty clay to fine-grained sand. These are underlain by pelagic and tuffaceous sediments overlying ocean basement (McNeill et al, 2017b). With lithified sediments only encountered in the deepest intervals

Methods

Results

Conclusion