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Structural reorganization of the India-Arabia strike-slip
plate boundary (Owen Fracture Zone; NW Indian
Ocean) 2.4 million years ago
Mathieu Rodriguez, Philippe Huchon, Nicolas Chamot-Rooke, Marc Fournier,
Matthias Delescluse
To cite this version:
Mathieu Rodriguez, Philippe Huchon, Nicolas Chamot-Rooke, Marc Fournier, Matthias Delescluse.
Structural reorganization of the India-Arabia strike-slip plate boundary (Owen Fracture Zone; NW
Indian Ocean) 2.4 million years ago. Joao C. Duarte. Transform Plate Boundaries and Fracture Zones,
Elsevier, pp.146-155, 2019, �10.1016/B978-0-12-812064-4.00007-4�. �hal-02326725�
CHAPTER 7
Structural reorganization of the India-Arabia
strike-slip plate boundary (Owen Fracture
Zone; NW Indian Ocean) 2.4 million years ago
Mathieu Rodriguez
1
Philippe Huchon
2
Nicolas Chamot-Rooke
1
Marc Fournier
2
Matthias Delescluse
1
1
Laboratoire de Géologie, Ecole normale supérieure, CNRS UMR8538, PSL research university, Paris, France
2
Sorbonne Universités, UPMC Université Paris 06, CNRS UMR 7193, ISTeP, Paris, France
Abstract
The Owen Fracture Zone (OFZ) is the present-day, 800-km-long dextral India Arabia plate boundary,
with conspicuous pull-apart basins at stepover areas and at its terminations. We summarize geological
evidence documenting the age of formation of the OFZ, based on detailed analysis of geophysical and
drilling data in the vicinity of the main pull-apart basins. Although India-Arabia motion started in the
Late Cretaceous, we show that the present-day OFZ is a young structure formed at 2.4 Ma. This last
structural reorganization of the India-Arabia plate boundary is unrelated to any well-documented
kinematic change, leaving questions over its driver.
Keywords: Fracture zone – pull apart- horsetail- Indian Ocean
1 – Introduction
Strike-slip plate boundaries display a large variety of geological structures along their strike, especially
in areas where the layout of the displacement zone is discontinuous or curved (Mann, 2007). These step-over
areas favor the formation of releasing or restraining bends, according to the configuration of adjacent strike-slip
fault segments and the local stress field (Sylvester, 1988). Detailed tectonic and stratigraphic investigations have
revealed that strike-slip boundaries experience dramatic episodes of structural reorganization during their
lifetime, marked by the formation of new structures and the abandonment of older ones (ten Brink and Ben-
Avraham, 1989; Wakabayashi, 2007; Brothers et al., 2009; Schattner, 2010; ten Brink and Flores, 2012; Le
Pichon et al., 2001, 2013). Models of structural evolution have proposed that continental strike-slip boundaries
initiate as diffuse, en-_ echelon fault systems and become narrower with increasing maturity (Tchalenko, 1970;
Wesnousky, 2005; Dooley and Schreurs, 2012; Le Pichon et al., 2016). This pattern of structural evolution is
modulated by the layered rheology of the continental lithosphere (Le Pourhiet et al., 2014).
The structural evolution of oceanic strike-slip faults (with seismicity identified along their entire length) has been
investigated only for a few cases, including the MacQuarie Fault (Australia-Pacific boundary; Massel et al.,
2000; Meckel et al., 2005) or the Azores-Gibraltar transform fault (Nubia-Eurasia boundary; Zitellini et al.,
2009; Rosas et al., 2014; Miranda et al., 2014). Here we focus on the oceanic India-Arabia strike-slip plate
boundary, which initiated ∼90 Ma when India separated from Madagascar (Bernard and Munschy, 2000) and
started its motion toward Eurasia. The India-Arabia plate boundary experienced several episodes of migrations in
response to India-Eurasia or Arabia-Eurasia collision (Rodriguez et al., 2014a,b, 2016). Multibeam mapping of
the current India-Arabia plate boundary (Fig. 1), referred to as the Owen fracture zone (OFZ) in the Arabian Sea,
revealed dextral morphological offsets of the Owen Ridge on the order of 10 – 12 km (Fournier et al., 2008a,b,
2011)—the Owen Ridge being a series of bathymetric highs uplifted 8.7 Ma ago (Rodriguez et al., 2014a, b,
2018). Considering steady the current right-lateral motion of 3±1 mm yr
-1
(DeMets et al., 2010), these offsets
indicate a recent reorganization of the OFZ, younger than the Late Miocene.
Using multibeam and seismic data, tied to nearby ODP-DSDP sites, we performed detailed structural and
stratigraphic studies to investigate the age of formation of each major structure (mainly pull-apart basins)
observed along the OFZ in order to determine its age of formation. The results show that the present-day
expression of the entire, 800-km-long OFZ formed at 2.4 Ma, from the Aden-Owen-Carlsberg triple junction to
the Makran subduction zone (Fig. 1) and involved the opening of conspicuous pull-apart basins (from south to
north: the Beautemps-Beaupré Basin, Fig. 2; the 20° N Basin, Fig. 3; the Dalrymple Trough, Fig. 4).
2 – THE SEDIMENTARY RECORD OF STRIKE-SLIP TECTONICS ALONG
THE OWEN FRACTURE ZONE
2.1 The Indus Turbiditic Channels
The OFZ crosses the distal Indus turbidite fan, which is fed from the east by the Indus canyon cutting
through the NW Indian margin (von Rad and Tahir, 1997; Rodriguez et al., 2011, 2013, 2014a, b; Bourget et al.,
2013). Turbiditic channels are observed on both sides of the OFZ (Figs. 3 and 4). In terms of relative
chronology, the turbiditic channels observed west of the OFZ (in the Owen Basin) predate its formation and
indicate a period of limited tectonic activity, or a period when sedimentation rates were too high to record
tectonics. East of the OFZ, the turbiditic channels trapped or deviated by strike-slip structures postdate the
formation of the OFZ. Dating the different turbiditic systems provides good age brackets for the formation of the
OFZ. The age of a turbiditic channel is estimated from the age of the first pelagic layer that covers it.
2.2 Fault-Controlled Contourite Drifts
Bottom currents influence the geometry of deep-sea sedimentary deposits and build conspicuous
sedimentary formations referred to as contourite drifts (Rebesco et al., 2014). In the vicinity of the OFZ, several
fault-controlled contourite drifts are observed within the pelagic blanket lying over the turbiditic channels (Figs.
3 and 4). The opening of pull-apart basins along the OFZ induced local perturbations of bottom current. The base
of a fault-controlled drift indicates the minimum age of formation of the fault.
2.3 Angular Unconformities
Vertical motion of the seafloor (uplift or subsidence) related to faults results in major angular
unconformities within the Indus fan, sometimes outlined by conspicuous fanning configurations recording the
growth of the structure. Within the fanning configurations, numerous unconformities reflect the control of sea-
level variations at the 105 years time-scale over the Indus fan sedimentation (Bourget et al., 2013).
3 – AGE OF STRUCTURES ALONG THE OWEN FRACTURE ZONE
3.1 The Beautemps-Beaupré Pull-Apart Basin
The Beautemps-Beaupré Basin is a 120-km-long, 50-km-wide rhomboidal pull-apart basin located at
the southern termination of the OFZ (Fig. 2; Fournier et al., 2008a,b). The Beautemps-Beaupré Basin is almost
entirely filled in by Indus turbidites. The basin is bounded to the south by the Beautemps-Beaupré Ridge
(Rodriguez et al., 2018), which corresponds to a tilted section of Indus turbidites (Fig. 2). Numerous angular
unconformities are identified at the edges of the basin (Fig. 2), most of them being related to interruptions of
Indus sedimentation related to sea-level variations (Bourget et al., 2013). The onset of the uplift of the
Beautemps-Beaupré Ridge is recorded by a conspicuous angular unconformity and the base of the fanning
configuration of a sequence of Indus sediments (Fig. 2; Rodriguez et al., 2018). This unconformity can be
tracked within the Beautemps-Beaupré Basin, where it coincides with the onset of lateral variations in thickness
of turbidites, which marks the onset of seafloor subsidence there. Since its uplift above the level of turbidites
deposition, the Beautemps-Beaupré Ridge is blanketed by pelagic sediments that can be correlated with pelagic
sediments on top of the nearby Owen Ridge (Fig. 2), where ODP sites provide stratigraphic constraints
(Discoaster pentaradius; Shipboard Scientific Party, 1989). This unconformity is dated at 2.4 Ma (Rodriguez et
al., 2014b, 2018).
3.2 The 20°N Pull-Apart Basin
The 20° N Basin, named after its latitude, is an asymmetric, 90-km-long, 12-km-wide pullapart basin
(Fig. 3; Fournier et al., 2011). The OFZ constitutes the western flank of the 20° N Basin, while imbricated
systems of arcuate normal faults dissect its eastern flank (Fig. 3). The 20° N Basin is divided into three subbasins
by the transverse faults (Fig. 3). Fossil turbidite channels are identified west of the basin, whereas the currently
active channel is captured on the eastern side of the basin (Rodriguez et al., 2011; Bourget et al., 2013). The
most recent fossil turbidite channel to the west is dated at 3.4 ± 1.2 Ma (Rodriguez et al., 2013), which gives the
maximal age of the opening of the basin (Fig. 3). A fault-controlled contourite drift, with a typical sigmoid
geometry, is also identified on the top of the master fault (Fig. 3). The opening of the basin may have disturbed
the course of the bottom current and triggered the building of the drift. The reflector marking the base of the drift
can be correlated within the pelagic cover as far as the ODP sites located at the top of the Owen Ridge. The age
of this reflector is 2.4 Ma (Rodriguez et al., 2013, 2014b).
3.3 The Dalrymple Trough
The Dalrymple Trough marks the northern termination of the OFZ (Edwards et al., 2000; Ellouz
Zimmermann et al., 2007). The southern segment of the Dalrymple Trough is a 150-km-long, 30-km-wide
horsetail termination basin (Fig. 4), with numerous oblique splays connecting the OFZ (Fournier et al., 2011;
Rodriguez et al., 2014b). The Dalrymple Trough is flanked to the east by the Murray Ridge. Indus turbidite
channels dated at 3.7 ± 1 Ma to the west of the Dalrymple Trough predate its opening (Fig. 4). In contrast to the
20° N and Beautemps-Beaupré basins, the Dalrymple Trough has been isolated from the Indus infill
subsequently to the uplift of the Murray Ridge. On transverse seismic profile (Fig. 4), the core of the Dalrymple
Trough is expressed as a syncline. The last deformed layer can be fairly correlated with the Indus sequence at the
border of the basin (Fig. 4). It coincides with the reflector marking a major angular unconformity in front of the
Makran accretionary wedge (M-unconformity; Gaedicke et al., 2002; Ellouz Zimmermann et al., 2007).
Moreover, this reflector marks the base of a fault-controlled contourite drift close to the OFZ at the entrance of
the trough (Rodriguez et al., 2014b). Here again, this reflector within well-bedded pelagic layers can be
correlated from line to line to the location of the ODP sites. It is also dated at 2.4 Ma. However, the age of the
northern segment of the Dalrymple Trough, connecting the Ornach Fault in Pakistan, remains to be constrained.
4 – DISCUSSION AND PERSPECTIVES
Detailed tectono-stratigraphic studies indicate the present-day configuration of the entire 800-km-long
OFZ formed at 2.4 Ma, expressed by the coeval opening of the Beautemps-Beaupré basin to the south, the 20° N
basin, and the Dalrymple Trough to the north. Considering the 10 – 12 km-morphological offsets were formed
during the last 2.4 Ma implies a dextral rate of India-Arabia relative motion at ~ 4.2 ± 5 mm yr
-1
. The India-
Arabia boundary is located in this area since at least the Early Miocene and the first stages of seafloor accretion
at the Sheba Ridge ago (Fournier et al., 2010). The India-Arabia plate boundary has accommodated since then
about 80-km of dextral relative motion (Chamot-Rooke and Fournier, 2009). When the OFZ formed at 2.4 Ma,
the India-Arabia boundary was therefore already a mature system. The timing of the formation of the OFZ at 2.4
Ma does not correspond to a clearly identified kinematic change (DeMets et al., 2017), making the geodynamic
driver of its formation unknown. Either the corresponding kinematic change has not been detected so far, or
there is no kinematic change related to the onset of the OFZ. The formation of the OFZ may simply be the last
step of a series of transient adjustments of the India-Arabia plate boundary since the last major kinematic change
identified in the Indian Ocean between 6 and 8 Ma (DeMets and Merkouriev, 2016; DeMets et al., 2017). It is
also possible that the 2.4 Ma episode of intensification of the Indian Monsoon (An et al., 2001) might have
played a role in the evolution of the strike-slip system through its effect on the Indus sedimentation rates
(increase up to 500 m/Ma at 2.4 Ma; Shipboard Scientific Party, 1989).
Acknowledgments
This study is a synthesis of numerous works based on the multibeam and seismic dataset collected during the
AOC, OWEN 1 and 2 surveys in the last decade. All scientists and cruise members (R/V Beautemps-Beaupré,
SHOM) involved in these projects are warmly thanked for their help. We thank J. Duarte and T. Minshull for
their detailed comments that helped us to improve this synthesis.
Figure captions
Figure 1 Multibeam bathymetric map of the Owen fracture zone. Inset shows the plate tectonic context in the
northwestern Indian Ocean. (a) and (b) are enlargements of two areas where the lateral offset has been measured
(respectively 10 and 12 km).
Figure 2 (A) Multibeam bathymetric map of the Beautemps-Beaupré Basin (B
3
)[1], (B) North-South seismic
profile across the Beautemps-Beaupré Basin, and (C) its interpretation (in blue, the post – 2.4 Ma infill of the
basin, in black the 8.8 Ma discordance that marks the uplift of the Owen ridge).
Figure 3 (A) Multibeam bathymetric map of the 20°N Basin, OFZ: Owen Fracture Zone, SB1, SB2, SB3: sub-
basins, (B) West-East seismic profile across the sub-basin SB3 of the 20°N Basin, and (C) its interpretation (in
blue, the post – 2.4 Ma infill of the basin).
Figure 4 (A) Multibeam bathymetric map of the Dalrymple Trough (inset is a bird’s eye view from the
southwest), (B) West-East seismic profile across the southern part of the Dalrymple Trough, and (C) its
interpretation. The pink reflector dated at 2.4 Ma marks the beginning of the opening of the basin. The post – 2.4
Ma infill of the basin is shown in blue.
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