Arc‐parallel extrusion of the Timor sector of the Banda arc‐continent collision

Abstract

[1] Structural studies of synorogenic basins in Timor using field and remote sensing techniques provide new structural and geomorphic evidence for syn-collisional extension in the converging plate boundary zone between the Australian Plate and Banda Arc. Fault mapping and kinematic analysis at scales ranging from outcrop (<1 m 2 ) to the dimensions of the active orogen in East Timor (~100 km 2 ) identify a predominance of NW-SE oriented dextral-normal faults and NE-SW oriented sinistral-normal faults that collectively bound large (5-20 km 2 ) bedrock massifs throughout the island. These fault systems intersect at non-Andersonian conjugate angles of approximately 120 and accommodate an estimated 20 km of NE-directed extension across the Timor orogen based on reconstructions of fault-dismembered massifs. Major orogen-parallel ENE-oriented faults on the northern and southern sides of Timor exhibit normal-sinistral and normal-dextral kinematics, respectively. The overall pattern of deformation is one of lateral crustal extrusion sub-parallel to the Banda Arc. Stratigraphic relationships suggest that extrusion began prior to 5.5 Ma, before pronounced rapid uplift of the orogen. We link this to progressive coupling of the fore-arc to an underthrust plateau on the Australian Plate and subduction of its ocean crust. Our results enable us to track the structural evolution of the upper crust during dramatic plate-boundary reorganizations accompanying the transition from subduction to collision. The deformation structures that we document suggest that both upper and lower plate deformation during incipient island arc-continent collision was largely controlled by the geometry and topography of the lower plate.

Structural style in a young flexure-induced oblique extensional system, north-western Bonaparte Basin, Australia

“…Miocene, between 9.8 Ma BP and 5.7 Ma BP, causing interference in Timor and eventual jamming of the subduction zone at approximately 5.7 Ma BP. Whilst this age for collision is older than some other estimates (3.5e2 Ma BP; Audley-Charles, 2004;Spakman and Hall, 2010), it is consistent with other evidence for a regional tectonic event at approximately 8 Ma BP from both Timor and the adjacent Australian North West Shelf (McCaffrey et al, 1985;Reed, 1985;Berry and McDougall, 1986;Richardson and Blundell, 1996;Rutherford et al, 2001;Keep et al, 2002;Harris, 2011;Duffy et al, 2013). Timor Island seems to have first emerged by~4.5 Ma BP (Nguyen et al, 2013), and uplift accelerated at~3 Ma BP (Quigley et al, 2012;Nguyen et al, 2013).…”

Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste: Constraints on deformation processes in young orogens

“…Here ZHe data suggest exhumation of 2.7–4.6 km since 1.8 Ma only 15 km away from the Cailaco basin that has likely experienced less than a few hundred meters of exhumation. A normal fault located at the edge of the Cailaco River valley that juxtaposes the Aileu Complex with the Viqueque Sequence and Bobonaro Mélange accommodates much of the observed differential surface uplift between these two regions [ Duffy et al , ]. If this normal fault were driven by an island‐scale extensional tectonic setting on Timor, one would expect significant subsidence of the hanging wall and an alluvial sedimentary package within the hanging wall that is several kilometers thick.…”

“…Duplexing below both the footwall and hanging wall would cause uplift of both fault blocks, and a greater degree of duplexing below the Aileu Complex would cause more uplift of the footwall. Duffy et al [] have argued that duplexing below the footwall initiated motion along the Marobo fault, and our data suggest this duplexing continues today. Duplexing below the Aileu Complex is also consistent with the interpretation that a significant boundary in exhumation exists near the southern boundary of the Aileu slate belt.…”

“…Surface faulting is one mechanism that could cause such a sharp gradient in exhumation, but preliminary structural mapping demonstrates that surface faults of the Gondwana Sequence duplex are not currently active because they have been folded since the time that they were active thrusts [ Tate et al , ] and because no thrust faults within the Gondwana Sequence duplex are observed to cut the overriding Banda klippen [ Harris , ; Harris et al , ; Standley and Harris , ; Tate et al , ]. In addition, this transition from the southern foothills to the south‐central range in the eastern map area does not correlate with any of the proposed normal faults on the island [ Duffy et al , ]. Fault propagation folding due to a blind thrust in the subsurface could explain the sharp boundary in exhumation rates at the southern range front, but a single blind thrust would not explain the wide extent of fast exhumation rates continuing toward the hinterland in the northwest.…”

“…Within the area of thermochronology sampling mapping is from preliminary mapping by these authors. Outside of the thermochronology sampling area, mapping is compiled from previous mapping by Audley‐Charles [], Benincasa et al [], and Duffy et al []. Inset shows regional setting and surrounding bathymetry (from National Geophysical Data Center, NOAA), with Timor‐Leste in black and study area outlined in red.…”