Tectonics of the Dalrymple Trough and uplift of the Murray Ridge (NW Indian Ocean)

Abstract

International audienceThe Dalrymple Trough is a 150-km-long, 30-km-wide basin located at the northern termination of the Owen Fracture Zone (OFZ), which is the present-day active India-Arabia plate boundary. The Dalrymple Trough is closely associated with the Murray Ridge, a complex of prominent bathymetric highs located on its eastern flank. Recent multibeam mapping of the connection between the Dalrymple Trough and the OFZ revealed a horsetail structure, which suggests a close relationship between geological histories of both structures. However, the 3-6 Ma age of initiation of the OFZ contrasts with the commonly accepted Early Miocene emplacement of the Dalrymple Trough. Recent seismic lines document a new tectonic history of the Dalrymple Trough, involving two major episodes of deformation along the India-Arabia plate boundary at ~ 8-10 Ma and ~ 1.9 ± 0.9 Ma. The 8-10 Ma episode is marked by a system of folds linked to the main uplift of the southern Murray Ridge and the first uplift of the northern Murray Ridge. This episode is related to a global plate reorganization event in the Late Miocene, well expressed by intraplate deformation in the Central Indian Ocean. The Dalrymple Trough opened at ~ 1.9 ± 0.9 Ma subsequently to the formation of a stepover at the India-Arabia plate boundary, coeval with the regional M-unconformity in the Oman abyssal plain, which marks a structural reorganization of the Makran accretionary wedge, and the last uplift of the northern Murray Ridge

The Geological Evolution of the Aden‐Owen‐Carlsberg Triple Junction (NW Indian Ocean) Since the Late Miocene

“…The reflector marking the opening of both the 20°N Basin and the Dalrymple Trough can be tracked from line to line, as far as the top of the southern Owen Ridge, where ODP Sites (721, 722, and 731) provide detailed stratigraphic constraints (Figure ; Shipboard Scientific Party, ). There, this key reflector is dated at 2.4 Ma, in agreement with age estimates from geological markers in the vicinity of the main pull‐apart basins (Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). The reflector recording the opening of the pull‐apart basins along the OFZ can be traced to the Oman abyssal plain, in front of the Makran accretionary wedge, where it merges with the M‐unconformity (Ellouz Zimmermann et al, ; Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ).…”

“…There, this key reflector is dated at 2.4 Ma, in agreement with age estimates from geological markers in the vicinity of the main pull‐apart basins (Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). The reflector recording the opening of the pull‐apart basins along the OFZ can be traced to the Oman abyssal plain, in front of the Makran accretionary wedge, where it merges with the M‐unconformity (Ellouz Zimmermann et al, ; Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). The regional‐scale seismic correlation of the key, 2.4‐Myr‐old reflector marking the opening of pull‐apart basins along the OFZ is provided in Figure .…”

“…Morphological offsets of the Owen Ridge on the order of 10–12 km are consistent with an age of emplacement of the OFZ around 3–6 Ma, assuming that the current motion of 3 ± 1 mm/year continued steadily for this time span (DeMets et al, ; Fournier et al, ; Rodriguez et al, ). The OFZ displays remarkable pull‐apart basins along its strike, including the 90‐km‐long, 35‐km‐wide 20°N Basin (Fournier et al, ; Rodriguez et al, , ), and the 150‐km‐long, 30‐km‐wide Dalrymple Trough (between ~22 and 23°N), which forms an horsetail structure at the northern termination of the OFZ (Edwards et al, ; Fournier et al, ; Gaedicke et al, ; Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). The reflector marking the opening of both the 20°N Basin and the Dalrymple Trough can be tracked from line to line, as far as the top of the southern Owen Ridge, where ODP Sites (721, 722, and 731) provide detailed stratigraphic constraints (Figure ; Shipboard Scientific Party, ).…”

“…Preliminary kinematic reconstructions based on magnetic anomalies from the Sheba and Carlsberg Ridges suggest about 80 km of dextral relative motion since ~20 Ma (Chamot‐Rooke et al, ). However, the significance of fracture zone offsets identified at the eastern edge of the Owen Ridge under the Indus turbidites remains ambiguous because of the lack of a clear sedimentary record (i.e., fanning configuration of the sediments and unconformities) of their activity (Rodriguez, Chamot‐Rooke, Huchon, Fournier, & Delescluse, ; Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). Early Miocene to Late Miocene sediments preserved on the top of the southern segment of the Owen Ridge display a fanning configuration, and a dense fault system, which may reflect either remnants of strike‐slip tectonics prior to the Owen Ridge uplift, or differential compaction processes, distinct from plate boundary tectonics (Rodriguez, Chamot‐Rooke, Huchon, Fournier, & Delescluse, ; Rodriguez et al, ).…”

“…A seismic data set acquired during the OWEN‐2 cruise in 2012 revealed that the uplift of the Owen Ridge, a series of bathymetric highs identified along the OFZ, began at 8.2–8.8 Ma (Rodriguez, Chamot‐Rooke, Huchon, Fournier, & Delescluse, ), and that major pull‐apart basins of the OFZ started opening at 2.4 Ma (Rodriguez et al, ; Rodriguez, Chamot‐Rooke, Huchon, Fournier, Lallemant, et al, ). Although these geological events suggest a complex evolution of the AOC triple junction since the Late Miocene, the precise timing of its changes of configuration remains unconstrained (Fournier et al, ).…”