Different Localities of Potassium-Rich Silica-Undersaturated Igneous Rocks and Their Silica-Rich Variants - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 166

Fig. 4.22 The volcanic
complex (solid dots)
associated with Bolsena
caldera showing adjacent
fields of Latera caldera (after
Turbeville 1993)

Torre Alfina

Orvieto

Acquapendente

Onano

S. Lorenzo N.

Sorano

Grotte
di. C.

Sovana

Vepe
Caldera

Bolsena

Bagnoregia

Lake
Bolsena

Ubriano

Pitigliano

Latera

Latera Caldera

Valentano

Isnia Di. C.

Capodimonte
Piansano

Monteliascone

Piaman Cellere

Tessannano

apino

Artena

Tuscania

Viterbo

N

10 Km

chaotic collapse. There was also subsidence in the northwestern sector. Deep
drilling has shown the presence of volcanic breccia in the southwestern section of
Latera caldera. There are four breccia layers (A, B, C and D) overlying earlier
activities of Paleo Bolsena and Bolsena complexes. This area is interpreted as a
source of oldest Latera ignimbrite. The Latera explosive activity shifted towards
northeastern side, where ignimbrites designated as E and F were erupted. The most
recent collapse of Latera Caldera affected the northwestern sector producing the
Veple caldera showing subsidence due to a ring-fractured system. Analyses of
K-rich rocks from Vulsini Complex are given in Table 4.16 .

4.8.4.3 Vico Complex

The Vico volcanic complex (Fig. 4.20 b) with six pyroclastic formations and lava

flows occur south of the Vulsini complex. The lavas are characterized by low
magnesia, iron and lime and relatively low SiO 2 contents, compared to most other
volcanic complexes of Italy. The lavas are porphyritic comprising leucite, clino-
pyroxene, alkali feldspar and plagioclase with accessory mica and Fe-Ti

Ti oxides
(up to a cm across). According to Cundari and Mattias (1974), the rock has
glomeroporphyritic texture, and clinopyroxene

-

± plagioclase ± mica is widespread

in the lavas. The rocks are mainly,

(1) Trachyte,
(2) Phonolite, and
(3) Tephrite and their variants.