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Distribution of basaltic volcanism on Tenerife, Canary Islands: Origin and dynamics of the rift systems

Adelina Geyer1 & Joan Martí2

1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, BS8 1RJ, Bristol (UK) A.GeyerTraver@bristol.ac.uk
Now at : CIMNE International Center for Numerical Models in Engineering, Spain ageyer@cimne.upc.edu

2Laboratory of Simulation of Geological Processes (SIMGEO), Department of Geophysics and Geohazards, Institute of Earth Sciences "Jaume Almera", CSIC, Lluis Solé Sabaris s/n, 08028 Barcelona (Spain). joan.marti@ija.csic.es

 

This webpage is a summary of: Geyer, A., J. Martí, The distribution of basaltic volcanism on Tenerife, Canary Islands: Implications on the origin and dynamics of the rift systems, Tectonophysics, 483, 310-326, 2010.

 

Introduction

In Tenerife, Canary Islands (Figure 1), two rift zones run NW-SE and ENE-WSW and are marked by parallel rows of aligned cones and eruptive fissures (e.g., Ancochea et al., 1990; Carracedo, 1994; Carracedo, 1996; Martí et al., 1996) and fault/dyke swarms (e.g., Walter & Schmincke, 2002; Walter et al., 2005). These are the Santiago del Teide (STR) and the Dorsal rifts (DR), respectively (Figure 1). In the southern part of the island, the Southern Volcanic Zone (SVZ), basaltic volcanism is characterized by scattered vents and non-coherently orientated eruptive fissures. Some authors have associated the SVZ with a third rift zone orientated N-S, which may comprise, with the Dorsal and the Santiago del Teide rifts, a three-armed or “Mercedes Star” rift structure (Carracedo, 1994; Carracedo, 1996; Walter & Troll, 2003).

 

Figure 1: Map of mafic emission centres and vent alignments on Tenerife Island. Coordinates refer to 20-km squares of the Spanish national grid (UTM).

Contrasting genetic explanations have been proposed for the origin and evolution of this three-armed rift system. The rift zones are believed to result either from inflation of the volcano due to mantle upwelling (Carracedo, 1994, 1996; Figure 2a), or to volcano spreading (Walter, 2003; Figure 2b). The most controversial point is whether the rift zones have been present throughout the entire history of Tenerife as a response to mantle upwelling (Carracedo, 1994, 1996) or, in contrast, whether they developed later as a result of volcano spreading (Walter, 2003). In the latter case, the rift structures would not be directly related to the origin of the island and their effect on the evolution of Tenerife would be restricted to more evolved stages.

 

Figure 2: a) A hotspot-based schematic model for the genesis of a complex three-armed rift zone on one of the Canary Islands. The concentration of recent eruptive activity and depressions that may have been generated by gravitational slides are indicated. (Modified from Carracedo, 1994). b) Experimental results of Walter (2003). Three separate sand cones spread for 32 hours (equivalent to 3 Ma). A rift is visible between ‘‘Teno’’ and ‘‘Roque del Conde’’ (RC). Then a fourth cone formed in the center, deforming the composite edifice for 16 hours (~1 Ma). Three main extensional zones formed. The best-developed rift is directed to the most distant cone (here: Anaga).

Geological and tectonic framework of Tenerife Island

Tenerife is the largest (2058 km2) and highest (3718 m) island of the Canarian archipelago. Ancochea et al. (1990) proposed that the three old massifs located at the three corners of the island, Teno in the northwest (6.7– 4.5 Ma), Anaga in the northeast (6.5–3.5 Ma), and Roque del Conde in the south (12–6.4 Ma), represent three independent edifices, each with its own volcanic history.

Around 3.5 Ma volcanic activity apparently migrated to the midpoint of the three old edifices forming the Cañadas edifice, which progressively connected the subaerial portions of the once-separated edifices. However, other authors do not share this view (Martí et al., 1996; Ablay & Kearey, 2000, Araña et al., 2000; Gottsmann et al., 2008).

The evolution of subaerial volcanism on Tenerife has been controlled mainly by the ENE-WSW and NW-SE oriented tectonic trends (Martí et al., 1996; Figure 1). Evidence comes from geophysical studies of the oceanic basement around and below the Canary Islands (Dash & Bosshard, 1969; Bosshard & Macfarlane, 1970; Mezcua et al., 1992; Verhoef et al., 1991; Roest et al., 1992.; Watts et al., 1997; Mantovani et al., 2007) and from dyke distributions and the alignments of recent mafic vents.

In the SVZ, basaltic volcanism corresponds to scattered vents that cover an area of over 600 km2 with a dispersal angle of around 125° relative to Pico Teide located at the central part of the island (Figure 1). Some of these vents are aligned but the orientation of the different alignments is highly variable (Figure 1). This area is considered by different authors (e.g., Carracedo, 1994; Walter, 2003) to be a third N-S trending rift zone that corresponds to the third branch of a three-armed rift structure.

Numerical models

In order to determine whether the basaltic volcanism at the SVZ corresponds to the third N-S running branch of a three-armed rift system or, in contrast, if it just results from the interaction between the NW-SE and the ENE-WSW rift zones, we performed 2-D modelling considering the two main rift zones as two intersecting finite fractures of 120 m width (Figure 3).

 

Figure 3: Sketch of the numerical models calculated. a) Sketch of the whole computational domain and a zoom in on the area studied, which covers the whole of Tenerife island. The dashed-line rectangles mark the areas shown in Figures 4 and 5. A zoom in on one of the rift axes shows the disposition of the overpressure applied to the rift limits. The computational domain is shaded grey. The overpressure assigned to the boundaries of the model is a requisite for finite-element calculation. b) Sketch of the overpressure conditions for the different numerical models.

We assume that the crust behaves as a linear homogeneous elastic material and we apply plain strain, i.e., the studied area is a section of a very long prismatic body with standard values of Young’s modulus E = 40 GPa and Poisson’s coefficient n= 0.25. The opening of the rift structures was simulated by excess pressure on the rift axis limits (Figure 3b).

Figure 4 shows the values of σ3 (maximum tensile stress or minimum compressive stress) and Figure 5 the stress trajectories of σ1 (maximum compressive stress). The contour fill values of σ3 give us the area with higher extension and consequently the zone where emission centres have the highest probability of appearing. Furthermore, we studied the trajectories of σ1 which allowed us to infer the preferred orientation of eruptive fissures and vent alignments.

 

Figure 4: Values of σ3 for the different numerical examples. Black dots correspond to mafic emission centres observed in the field. The figure area is defined in Figures 1 and 2. Click here or on Figure for enlargement.

 

Figure 5: Trajectories of σ1 for the different numerical examples. Black lines correspond to eruptive fissures observed in the field. Grey circles mark those fissures whose orientation is in agreement with the trajectories of σ1 obtained with the corresponding numerical model.

In short, the overpressure value modifies the extensive character of the zone but it is the overpressure relation between both axes that exerts the main control on the distribution and location of the extensive area propitious for the location of basaltic vents in the south of Tenerife. Furthermore, variations in the pressure ratio of the rift axis lead to a change in the orientation of the σ1 trajectories.

Discussion

The third N-S rift zone and the origin of the Tenerife rift zones

Authors favouring the idea of a three-armed rift system in Tenerife (Carracedo, 1994, 1996; Walter, 2003) have ignored the fact that the vent alignments in the south show a relatively wide range of orientations (Figure 1), implying that not all of them formed under the same stress field, as shown in the numerical models. Our numerical results favour the Santiago del Teide and Dorsal rift zones being related to crustal NW-SE and ENE-WSW tectonic structures that were present in the basement on which Tenerife has grown. This agrees with the results from detailed structural studies on Tenerife and other Canary islands (e.g., Staudigel et al., 1986; Marinoni & Pasquarè, 1994; Marinoni & Gudmundsson, 2000; Gee et al., 2001; Blanco-Montenegro et al., 2003; Klügel et al., 2005; Muñoz et al., 2005; Ancochea et al., 2008). These rifts zones have been used to drive mantle-derived mafic magmas to the surface during the entire history of the island and have been active simultaneously or alternately during different time periods. Thus, they have played a fundamental role in the origin and evolution of the island, not only in controlling recent basaltic volcanism.

Evolution of Tenerife Island

The origin of Tenerife is closely related to the presence of pre-exiting tectonic structures in the crust. Volcanic activity began as fissural volcanism along these structures and the accumulation of the basaltic series gave rise to the construction of the composite shield volcano (the Old Basaltic Complex; Figure 6). We assume that volcanism concentrated along the NW-SE and ENE-WSW fissures, especially at their junction, where more eruptives accumulated and thu differential growth occurred compared to other parts of the shield. This resulted in the formation of the dense core of the shield volcano (Boca de Tauce edifice; e.g., Ablay & Kearey, 2000; Gottsmann et al., 2008). The increase in height of the central part of the shield complex allowed ascending mafic magma to accumulate in the basaltic construct, forming shallow magma chambers, evolving phonolitic compositions and driving the construction of the Tenerife central volcanic complex (the Cañadas edifice).

 

 

Figure 6: a) Time-spatial evolution of Tenerife. Dark- and light-coloured edifices correspond to the Old Basaltic Series and the Cañadas edifice, respectively. b) Cross-section cutting the Old Basaltic Series and the Cañadas edifices. The increase in height of the central part of the shield complex allowed ascending mafic magmas to stop and accumulate in the interior of the basaltic construct, forming shallow magma chambers. There, they evolved phonolitic compositions and drove the construction of the Tenerife central volcanic complex (the Cañadas edifice). Click here or on Figure for enlargement.

 

The presence of shallow magma chambers during the construction of the central volcanic complex has not influenced the dynamics of the rift systems and their associated stress field. On the contrary, the shallow magmatic system has been strongly influenced by the rift structures, as is demonstrated by two facts:

  1. the Cañadas phonolitic dykes, which are clearly associated with the existence of several shallow magma chambers, show the NE-SW and ENE-WSW predominant orientations of the two rift systems (Martí et al., 1994); and
  2. these magma chambers formed successively during the construction of the Cañadas central complex and fed different volcanic centres that migrated along the western side of the Dorsal rift, younging from west to east (Martí & Gudmundsson, 2000).

Relationship between the Canary Islands and the Atlas Mountains

Regional and local tectonics are relevant to understanding the evolution of the Canary Island archipelago as a whole (Hérnandez-Pacheco & Ibarrola, 1973; Anguita & Hernan, 1975; Anguita & Hernan, 2000). In the African continent the Atlas chain (Figure 7), built through the tectonic inversion of a Triassic and Jurassic intracratonic rift (Jacobshagen et al., 1988) and associated with the opening of the North Atlantic, is characterized by post-Cretaceous Atlas thrusts faults (Mattauer et al., 1977; Proust et al., 1977; Binot et al., 1986) and mostly sinistral strike-slip faults (Herbig, 1988; Jacobshagen, 1992). Most faults strike NNE (in the High Atlas), NE (in the Middle Atlas), or NW (dispersed though less marked), although there are also abundant N-S structures. The South Atlas lineament comprised a discontinuous NNE structure or megashear, active from Palaeozoic times on. This lineament is considered to be a part of a newly defined strike-slip sinistral megastructure more than 1000 km long, the Trans-Alborán Fault system (TAF; Bousquet & Montenat, 1974; Sanz de Galdeano, 1990) which runs along the High Atlas and Middle Atlas and crosses the Alborán (Mediterranean Sea; Figure 7a).

Figure 7: (a) Tectonic alignments in the Atlas Mountains, (b) schematic model that proposes a common lineament and melt source for both the Atlas Mountains and the Canary Islands. Click here or on Figure for enlargement.

In the Atlantic ocean, marine geophysicists have found an array of tectonic structures such as antiforms, synforms and unconformities (Dillon, 1974; Uchupi et al., 1976; Dañobeitia & Collette, 1989). A NE striking submarine fault some 50 km long, with transcurrent (left-lateral) and reverse components lies between Tenerife and Gran Canaria (Mezcua et al., 1992). This fault is similar to the sinistral transcurrent faults associated with folds on the border of the Atlas (Piqué et al., 1998).

There are a number of volcanic areas in the Atlas Mountains and adjacent zones (Figure 7). Magmatism occurred in three different periods: Eocene to Oligocene (45-35 Ma), Miocene (14-6 Ma; Middle Atlas) and 1.8-0.5 Ma. The same rock types as are present in the Atlas Mountains are also represented in the Canary Islands and the rock ages are similar as well.

Anguita & Hernán (2000) suggested a residual fossil plume under North Africa, the Canary Islands, and western and central Europe, on the basis of seismic tomography (Hoernle & Schmincke, 1993; Figure 7b) [Ed: See also Interpreting Seismic Velocity page]. Thus, volcanism is assumed to occur there where an efficient fracture system allows magma to ascend (Anguita & Hernán, 2000). Volcanism in Europe, the western Mediterranean, Iberia, the Canary Islands and Cape Verdes have all been attributed to this (Hoernle et al., 1995) [Ed: See also Europe and Italy pages].

Tectonic studies at different islands have shown trends in fault and volcanic alignments consistent with oceanic and continental structures e.g., Lanzarote, (Marinoni & Pasquarè, 1994) and Gran Canaria, (Anguita et al., 1991). The main fractures in the islands and ocean floor comprise two families (Hernandez-Pacheco & Ibarrola, 1973): Atlantic “oceanic” (N160-180°E, N120-135°E) and African “continental” (strikes: N20°E, N45°E, N75°E), depending on their relation with the opening of the Atlantic or the tectonics of the Atlas range in the African continent (Anguita & Hernán, 1975: Fuster, 1975; Carracedo, 1984; Emery & Uchupi, 1984; Dañobeitia, 1988). The Atlantic alignment is oriented parallel to transform faults of the mid-Atlantic ridge (Rona, 1980). Additionally, alternating periods of magmatism in the islands, and compression in the Atlas Mountains and Atlantic suggests that during the tensional periods, the fractures served as conduits for the ascent of magma (Cousens et al., 1990; Anderson, 1999; Anguita & Hernán, 2000), while in the compressive epochs they cause uplift of the islands as sets of flower structures (Figure 3b; Anguita & Hernán, 2000).

Conclusions

Tenerife began with fissural volcanism along pre-existing crustal structures, progressively forming a composite shield volcano (the Old Basaltic Complex). Initial mafic volcanism concentrated along the NW-SE and ENE-WSW fissures, especially at their junction. This resulted in formation of the core of the shield volcano (Boca de Tauce edifice) and, with time, allowed the ascending mafic magma to pause and accumulate in the interior of the basaltic edifice, forming shallow magma chambers. There, it evolved phonolitic compositions and triggered the construction of the Tenerife central volcanic complex (the Cañadas edifice).

In terms of volcanic hazard related to basaltic volcanism, the present structural configuration of Tenerife suggests that the maximum probability of new vents forming is along the rift zones, preferentially the Santiago del Teide rift, according to the concentration of the most recent and historical volcanism.

Acknowledgments

This research was partially funded with MEC grants BTE-2003-08026 and CGL-2006-13830. AG is grateful for her MEC post-doctoral fellowship (2007-0400).

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