Page 147 - Caldera Volcanism Analysis, Modelling and Response

122 A. Pittari et al.

Figure 8 Field lithic clast analyses and sample locations on stratigraphic log at Locality 26,
La Mareta (see Figure 7 for legend of lithic clast abbreviations and numbers).

clasts in the Sur-C unit compared to the Sur-A unit across the Bandas del Sur. Near
Poris de Abona, from the base to the upper lithic concentration zone of the Sur-A
unit, there is an increase in mafic crystalline volcanic clasts (34–47%) along with
felsic crystalline volcanic, welded volcanic and clastic clasts, and a decrease in syenite
(13–7%) and altered lithic clasts (27–17%). Into and toward the top of the Sur-C
unit, the proportion of syenite clasts increases slightly and then remain constant,
mafic crystalline volcanic clasts first decrease to 26%, then increase upwards to 32%,
felsic crystalline volcanic clasts remain constant (28%), and altered lithic clasts first
increase to 33% and then decrease to 29%. The vertical trend at El Medano differs
from that at Poris de Abona in that syenite decreases and mafic crystalline volcanic
clasts become increasingly dominated by type MV1 (see Table 2, Figure 8) from the
Sur-A unit to the Sur-C unit.
The most significant variation over distances of 1.5–2 km downslope is an
increase in felsic crystalline volcanic clasts (20-35%, San Miguel de Tajao, Figure 9)
or mafic crystalline and welded volcanic clasts (Orotava Valley, Figure 11),