The volcanic province of southeastern Spain, which is of Miocene-Pliocene age,
is characterized in its first phase by the emission of calcalkaline materials
(andesites-dacites-riolites). In the last phase, which is Pliocene in age, basic
rocks were emitted, the composition of which varies from basanite to trachybasalt. The
ash cones of the Cartagena volcano field rest on a 22-km thick continental crust
containing Palaeozoic metamorphic rocks that appear as enclaves among vulcanites. Most
of these enclaves correspond to schists and gneisses showing different degrees
of assimilation by the magma. Metamorphic enclaves can also be found, mainly
with pyroxenites and dunites. The presence of metamorphic enclaves lies at the root
of the contamination of the volcanic rocks, with large amounts becoming
incorporated into the magma (13% assimilation). The origin of the magma source of the
basic rocks in the Spanish southeast was the melting of ultramafic rocks of the
mantle similar to those of the pyroxenite enclaves in the basanites.
The Cartagena volcano field is made up of a series of small ash cones and lapillis,
sometimes accompanied by short lava flows of basic composition (basanites and trachybasalts)
(Figure 1). This field is relatively young (age 2-4 million years) (Bellon and Brousse,
1977; Bellon and Letouzey, 1977 and Boivin, 1982) and came about through distensive
rifting affecting the western Mediterranean. The vulcanism of Cartegena shows a
petrogenetic relationship with recent basic vulcanism in other areas of the Iberian Peninsula.
The volcano field lies over a thinned crust, estimated by De Larouziere et al. (1988) to be some 22-km thick. The area has a strong geothermal gradient (Albert-Beltrán,
1979) and at a depth of 22 km, the temperature is estimated to be close to
800°C.The first studies to describe the mineralogy and geochemistry of the area's rocks
were those of Sagredo (1972), Rodríguez Badiola (1973), López Ruiz and Rodríguez
Badiola (1980), and Benito et al. (1999), although the plutonic (Sagredo, 1973, 1976; Dupuy et al., 1986; Capedri et al., 1988) and metamorphic enclaves (Navarro, 1973) within the
basanites were the main source of interest.
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