Environmental Engineering Reference
In-Depth Information
strength, carving and cutting mode: dimensional
stone, farming or “lavoura” stone and sawed or
lumber stone.
through the hawaiite and mugearite (França,
et al., 2003).
Most of the geological formations that occur in
the azores archipelago from which extrusive rocks
are used as natural stone, are distributed by two
very different sets:
a. The first set comprises compact and/or porous
and vacuolar lavic rocks represented by basaltic
flows (s.l.) and trachytic flows (s.l.).
b. The second set comprises pyroclastic rocks
resulting from explosive activity. in fact, there
is a wide variety of materials, from huge blocks
to very fine ash, through intermediate terms
as “bagacina”, “gravel”, “lapilli” and “areão”
(coarse sand) exhibiting vesicular and spongy
structure, among which bombs frequently can
be found. however, these pyroclasts exhibit
some consolidation (welded materials), and in
some cases they look like heterometric breccia
and in other cases they look like tuff (Gomes &
silva, 1997).
The quarries of natural stone in the island of
são Miguel are more numerous than those in the
island of santa Maria.
in the island of são Miguel, given the demand
for natural stone of diverse lithology, natural stone
from distinctive volcanic complexes, such as: com-
plexo Vulcânico dos Picos (1), complexo Vulcânico
do Fogo (2), complexo Vulcânico das Furnas
(1) and complexo Vulcânico da Povoação (1),
has been studied.
With the exception of the complexo Vulcânico
dos Picos of fissural nature, all the others being
studied
2
GeoloGical seTTinG anD
locaTion oF naTURal sTone
QUaRRies
The azores archipelago is composed of nine islands
and several islets that are located in the north
atlantic ocean between latitudes 37º and 40ºn and
longitudes 25º and 31º W, spread over 610 km long
in a direction WnW-ese. Due to its geographic
distribution, the archipelago is organized into three
groups: the Western Group which includes the
islands of Flores and corvo, the central Group
is composed of the islands of Terceira, Graciosa,
são Jorge, Pico and Faial, and the eastern Group
which includes the islands of são Miguel and santa
Maria, and the islets of Formigas.
azores is located in an area where three major
tectonic plates converge—the eurasian, african
and north american—and where other minor tec-
tonic structures occur. These are arranged along a
set of tectonic alignments of general orientation
WnW-esse (França et al ., 2003). This general
trend is usually also found, in the shape of most
of the islands.
The dynamics of its tectonic Framework ( Figure 1 )
is the element responsible for the petrological and
geochemical characteristics of lavas ejected by
regional volcanic apparatus (França et al ., 2003).
Regional volcanism determines that stones
from azores are primarily basaltic, although
there are also acidic stones, with less representa-
tion (França, et al., 2003). While santa Maria,
são Jorge and Pico islands are mainly formed by
basalts and alkali basalts, the other islands have a
variety of lithologies, from alkali basalt to trachyte,
comprise
central
volcanic
structures
( Figure 2 ) .
in the case of the island of santa Maria, the two
studied natural stones are included in the com-
plexo Vulcânico dos anjos which occupies most
of the west sector of the island and consists of
basaltic lava flows of metric thickness, sometimes
alternating with thin layers of pyroclasts. Veins are
frequently seen cutting the basaltic flows.
Table 1 contains the references, the sources, the
technical-commercial names, and the exploiting
Figure 2. location in the island of são Miguel of the
quarries where natural stone has been sampled.
Figure 1. Geodynamic context of the azores (modified
from França, et al., 2003).
 
Search WWH ::




Custom Search