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mantle. Lead isotopes plot well inside the
field of island arcs, overlapping the
values of pelagic sediments.
They suggest that prior to partial melting there have been crust mantle mixing
due to subduction related process. The chemical and isotopic differences observed
between the northern and southern sectors of the magmatic region were possibly
due to the presence of a carbonate-rich component in the south, and an ancient
silicate metasedimentary slab in the north.
4.8.5 Volcanic Province of Spain
Ultrapotassic lamproitic rocks occur in the southeastern part of Spain in association
with calc-alkalic, high K-alkalic and shoshonitic rocks (Fuster et al. 1967; Lopez
Ruiz; Badiola 1980; Fig.
4.27
). The volcanic history of the area ranged between
middle Miocene and ended at the beginning of Pliocene (17
6 Ma ago). A careful
look at the chemistry of the rocks shows a progressive increase in the K
2
O content
of the rocks towards north. The ages of these rocks also decrease progressively in
the same direction.
Potassic lavas in southern Spain are composed of jumillite, fortunites and verites.
Although most well-known localities include Murcia and Almaria (Fig.
4.27
), they
are found in many other scattered localities (Borley 1967). The type locality of
verite is the village Vera, southwest of the town
-
. Fortunites occur in a
locality between Fortuna and Orihuela. The later occurs towards east of Murcia
(Borley 1967). Jumillites are post-Miocene lavas occurring 40 km north
'
Murcia
'
northwest
of Fortuna.They appear in a locality between Hellin and Jumilla, where they out-
crop as small hills. Borley described jumillites as surface
-
flows and not as intru-
sives. They are characterized by the presence of green diopside (containing small
amounts of Cr
2
O
3
), forsteritic olivines (Fo
85.5
±
3
), Ti-rich phlogopite, kataphoritic
amphibole, sanidine and rare leucite. Pyroxenes are of two generations, those of
later type occur as minute laths. The pleochroic scheme of mica is as follows:
ʱ
= red brown.
Verites are melanocratic rocks, and often occur as breccia. Mineralogically they
are similar to jumillite, but have fewer phenocrysts of forsteritc olivine (Fo
90.5
-
91.5
),
diopside, phlogopite and leucite, but amphibole is absent.
According to Lopez Ruiz and Badiola (1980), the essential difference in min-
eralogy amongst jumillites, cancalites, fortunites and verites lie in the relative
proportion of constituent minerals, e.g. olivine, phlogopite, clinopyroxene, sanidine
and K-richterite. Leucite is present only in jumillites and verites. Accessory min-
erals include apatite, calcite and rutile. K-analcite occurs in jumillites, verites and
fortunites. Analyses of lamproitic rocks from Spain are summarized in Table
4.17
.
= pink,
ʲ
= yellow and
ʳ
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