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Case Study of the Abrigo Ignimbrite, Tenerife, Canary Islands 127

concentration zone contains a larger variety of lithic types than shown in the
quantitative analysis including GVand FV1. Second, the quantitative analysis at San
Juan does not represent the lithic clast population of the entire west coast; in
particular, a larger variety of lithologies have been observed around Puerto de
Santiago to the north (S4, relatively common; S3, MV1, MV2 MV5, FV3, FV4,
FV6, C, A1 and 3 also observed; see Tables 1–4); dense, glassy volcanic clasts around
San Juan and Adeje; and welded pyroclastic breccia clasts around Adeje. Third,
syenite is common on the Diego Herna `ndez and La Fortaleza caldera wall sections
(S1, S2, G1 and G2 are common at La Fortaleza). Finally, gabbroid/syeno-gabbroid
clasts have only been observed on the eastern side of the Las Can ˜adas edifice in the
Orotava Valley, on the Tigaiga Massif and near San Miguel de Tajao.

3.5. Supporting evidence from juvenile clast and syenite geochemical
compositions
Spatial variations in juvenile clast geochemistry within temporally equivalent zones
across the Abrigo ignimbrite should reflect tapping and eruption of different parts
of the magma chamber. Such variations should complement regional variations in
lithic clast componentry. Field studies (Pittari, 2004) indicate that the proportion of
banded and/or mafic juvenile clasts increases from west to east across the Bandas del
Sur, although anomalously high proportions also occur near Puerto de Santiago on
the west coast. Fresh gabbro clasts have only been found in the eastern part of the
island.
Bulk rock geochemical analyses of major and trace elements within juvenile
pumice and dense glassy clasts, further constrain regional compositional variations
within the Abrigo deposit around the island. A detailed examination of the
geochemical data is beyond the scope of this paper; however, the data can be found
in Nichols (2001) and Pittari (2004). Juvenile clasts of the Abrigo ignimbrite follow
the basanite/tephrite–phonotephrite–tephriphonolite–phonolite trend, although
the majority are phonolitic in composition (Nichols, 2001). Individual localities of
the Abrigo deposit are characterised by one of the four geochemically distinct
juvenile clast populations identified in this study (South groups A and B, North
group, San Juan group, Figure 13a), and further constrained, especially the San Juan
group, by differences in the ranges of Mn, Zn and Nb/Zr associated with the
phonolitic portion of clasts (Figure 13b).

(a) South group A, which spans the southern coastline from Playas de las
Ame ´ricas to the Gu ¨imar Valley, has the broadest range in juvenile clast
compositions, and is distinct from the North group, spanning the northern
coastline and Puerto de Santiago on the west coast, which has a limited
variation (Figure 13a, b).
(b) South group B, which is localised between San Miguel de Tajao and the
Barranco de la Cera in Abrigo deposits that are within close proximity to
deposits of the more widespread South group A population, is dominated by
more evolved compositions (Figure 13a).