6.6 Discussion
6.6.1 Active Tectonics
NW-SE present-day oblique convergence between the Eurasian and African plates at
a rate of 4.5 mm/year (DeMets et al. 2015) causes a regional NW-SE shortening and
orthogonal extension accommodated by tectonics structures (folds and faults) and
that produces a set of seafloor features of structural origin. Basically folded reliefs of
different magnitude, push-up ridges, linear scarps and lineations, and rhombic and
longitudinal depressions have been mapped (Vázquez et al. 2016).
Tectonics determines the development of large NE-SW to ENE-WSW antiforms
that delineates the shape of elongate seamounts (e.g. the Alboran Ridge, Xauen
Bank, and Francesc Pagès), the Alboran Trough, as well as smooth bulges anticlines
in the Adra margin region (Figs. 6.1b, 6.3b, 6.7 and 6.8a, b). Moreover, plate
convergence produced the presence of the two main fault sets, oriented N25
E
sinistral and N130
E dextral, where the resistant basement of the African plate
indents the thinned continental crust of the Alboran Sea (Estrada et al. 2018) that are
strongly marked in the morphology of the seafloor (Fig. 6.7). These faults have a
high level of seismic activity and are responsible for the NNE-SSW seismicity band
crossing the Alboran Sea, from Campo de Dalías to Al-Hoceima, where the recent
1993–1994, 2004, and 2016–2017 seismic series occurred (Figs. 6.1b and 6.7). The
Al Idrisi Fault and new faults developing westwards constitute the present-day most
active seismogenic faults in the Alboran Sea (Galindo-Zaldívar et al. 2018), located
on the northwestern border of the indenter. The dextral Yusuf Fault constitutes the
main WNW-ESE conjugate fault delineating the northern boundary (Figs. 6.1b and
6.7). NW-SE normal faults located along the northern boundary of the Alboran Sea,
like the Balanegra Fault (Galindo-Zaldívar et al. 2015) also play an important role in
accommodating the ENE-WSW extension related both to the indentation tectonics
and rollback processes. The orientation of the ENE-WSW Serrata-Carboneras Fault
with respect to the orthogonal NNW-SSE present-day convergence suggests that this
fault may currently have limited activity (Figs. 6.1b and 6.7).
The active tectonics is also attested by the fluid-flow features mapped on the
seafloor (Fig. 6.9). Fluids flowing from deep layers have been related to regional
tectonics. The diapir distribution in the Western Alboran Basin is related to extensional, compressional and strike-slip processes related to the geodynamic evolution
of the Alboran Basin (Pérez-Belzuz et al. 1997). Extensional processes reactive
though it punctuated diapiric activity during the Pliocene and early Quaternary, and
during the late Quaternary that activity was characterized by a generalised collapse
phase in many mud ridges (Pérez-Belzuz et al. 1997). The mud volcano activity is
related to the tectonically-driven diapirs whose mud forms the source of the focused
fluid-flow feeding the volcanoes (Pérez-Belzuz et al. 1997; Somoza et al. 2012).
These authors also suggest that active diapirism and mud volcanism was also
favoured in the African margin by differential loading generated by a contourite
sedimentation, specifically of the Ceuta plastered Drift (Pérez-Belzuz et al. 1997;
186
G. Ercilla et al.
6.6.1 Active Tectonics
NW-SE present-day oblique convergence between the Eurasian and African plates at
a rate of 4.5 mm/year (DeMets et al. 2015) causes a regional NW-SE shortening and
orthogonal extension accommodated by tectonics structures (folds and faults) and
that produces a set of seafloor features of structural origin. Basically folded reliefs of
different magnitude, push-up ridges, linear scarps and lineations, and rhombic and
longitudinal depressions have been mapped (Vázquez et al. 2016).
Tectonics determines the development of large NE-SW to ENE-WSW antiforms
that delineates the shape of elongate seamounts (e.g. the Alboran Ridge, Xauen
Bank, and Francesc Pagès), the Alboran Trough, as well as smooth bulges anticlines
in the Adra margin region (Figs. 6.1b, 6.3b, 6.7 and 6.8a, b). Moreover, plate
convergence produced the presence of the two main fault sets, oriented N25
E
sinistral and N130
E dextral, where the resistant basement of the African plate
indents the thinned continental crust of the Alboran Sea (Estrada et al. 2018) that are
strongly marked in the morphology of the seafloor (Fig. 6.7). These faults have a
high level of seismic activity and are responsible for the NNE-SSW seismicity band
crossing the Alboran Sea, from Campo de Dalías to Al-Hoceima, where the recent
1993–1994, 2004, and 2016–2017 seismic series occurred (Figs. 6.1b and 6.7). The
Al Idrisi Fault and new faults developing westwards constitute the present-day most
active seismogenic faults in the Alboran Sea (Galindo-Zaldívar et al. 2018), located
on the northwestern border of the indenter. The dextral Yusuf Fault constitutes the
main WNW-ESE conjugate fault delineating the northern boundary (Figs. 6.1b and
6.7). NW-SE normal faults located along the northern boundary of the Alboran Sea,
like the Balanegra Fault (Galindo-Zaldívar et al. 2015) also play an important role in
accommodating the ENE-WSW extension related both to the indentation tectonics
and rollback processes. The orientation of the ENE-WSW Serrata-Carboneras Fault
with respect to the orthogonal NNW-SSE present-day convergence suggests that this
fault may currently have limited activity (Figs. 6.1b and 6.7).
The active tectonics is also attested by the fluid-flow features mapped on the
seafloor (Fig. 6.9). Fluids flowing from deep layers have been related to regional
tectonics. The diapir distribution in the Western Alboran Basin is related to extensional, compressional and strike-slip processes related to the geodynamic evolution
of the Alboran Basin (Pérez-Belzuz et al. 1997). Extensional processes reactive
though it punctuated diapiric activity during the Pliocene and early Quaternary, and
during the late Quaternary that activity was characterized by a generalised collapse
phase in many mud ridges (Pérez-Belzuz et al. 1997). The mud volcano activity is
related to the tectonically-driven diapirs whose mud forms the source of the focused
fluid-flow feeding the volcanoes (Pérez-Belzuz et al. 1997; Somoza et al. 2012).
These authors also suggest that active diapirism and mud volcanism was also
favoured in the African margin by differential loading generated by a contourite
sedimentation, specifically of the Ceuta plastered Drift (Pérez-Belzuz et al. 1997;
186
G. Ercilla et al.