Resumen: Entre los principales rasgos que caracterizan la obra del arquitecto gallego Antonio Palacios, cuyo interés geológico resulta excepcional, cabe destacar la materialidad pétrea de sus construcciones así como su apuesta por la conservación y difusión del patrimonio cultural. El estudio de la piedra natural que configura el legado
de Antonio Palacios permite entender mejor su pensamiento, atender al sustrato geológico próximo a los lugares donde construía o conocer los caracteres petrológicos de los materiales, que tan directamente participan en la textura que Palacios quiso otorgar a sus construcciones y que condicionan su estado de conservación. Además, posibilita conocer los motivos que favorecieron su selección, donde la situación por entonces de las canteras y de los medios de comunicación juegan un papel fundamental.
[ABSTRACT]
Among the main features that characterize the artwork of the architect Antonio Palacios, which geological interest is exceptional, the stonework of its constructions and its commitment with heritage conservation and dissemination should be mentioned. The study of natural stone which shapes Palacios´ legacy let its better understanding, to pay attention to the geological settings or to know the petrological characters of the buildings materials, so directly involved in the texture Palacios wanted to provide to its façades and with the materials decay. Besides, it enables to know the reasons that favored its selection, where the formerly quarries state and transport development play a fundamental role.
Palabras clave: Geología, Materiales pétreos, Conservación, Patrimonio construido, Canteras, Divulgación, Geology, Building materials, Conservation, Built heritage, Quarries, Dissemination
Resumen: El objetivo de esta 1ª Reunión Científica del IGEO es presentar la investigación desarrollada y las Unidades Técnicas de las que dispone el IGEO, mostrado su potencial investigador y facilitando la colaboración con otros organismos. En la reunión se presentaron las diferentes sublíneas de investigación que comprende el IGEO, comunicaciones cortas de investigaciones concretas y la actividad realizada por sus
Unidades Técnicas de Investigación, a disposición de toda la comunidad científica.
El IGEO nace con un importante compromiso para potenciar las investigaciones en Geología, Geodesia y Geofísica. Hay una excelente oportunidad para desarrollar ideas y metodologías que permitan la interacción de las tres disciplinas e incremente el valor del trabajo llevado a cabo, que sea útil para toda la comunidad científica y, sobre todo, para la sociedad.
[ABSTRACT]
The aim of the 1st Scientific Meeting of IGEO is to introduce the research developed and the Technical Units available in the IGEO, shown their research potential and providing collaboration with other agencies. The meeting presented the different research sublines involving the IGEO, short communications dealt with specific investigations and the activity conducted by its Research Technical Units, available to the entire scientific community.
The IGEO born with a commitment to enhance research in Geology, Geodesy and Geophysics. There is an excellent opportunity to develop ideas and methodologies in order to let the interaction of these three disciplines and to increase the value of the research carried out, to be useful for the scientific community and, above all, for society.
Resumen: The tectonothermal evolution of a polyorogenic terrane in the Variscan belt of NW Spain has been
constrained by 40Ar/39Ar laserprobe incremental heating experiments on mylonitic fabrics developed in major
structures. Transitional levels between HP–HT and IP
upper units in the O´ rdenes Complex where
metamorphic and structural records demonstrate two cycles of burial and exhumation were selected for dating.
Two groups of ages have been defined: (1) Silurian–Early Devonian, obtained from mylonites of the Forna´s
extensional detachment, here considered as the minimum age for the start of tectonic exhumation of the HP–
HT units and an upper age-limit for the HP–HT event itself; (2) Early to Mid-Devonian, from structures
related to the Variscan convergence in the area, which include top-to-the-east thrusts and extensional
detachments. A single, younger Carboniferous age obtained from the uppermost allochthonous sequences
possibly reflects the final stages of emplacement of the allochthonous complexes. Our data indicate a
polyorogenic character for a part of the Iberian allochthonous complexes, including Variscan (sensu stricto)
and Early Variscan convergence, as well as an older, Early Palaeozoic cycle.
Resumen: Many felsic pyroclastic units of various types are exposed in different sectors of Tenerife. New 40Ar/39Ar determinations allow them to be placed more precisely in the general volcano-stratigraphic succession. According to geographic distribution, stratigraphic position and isotopic ages, four
main pyroclastic phases may be identified. The first, San Juan de la Rambla phase (2.1 Ma), is only known in the north of Tenerife in the Tigaiga massif. The second, Adeje phase (1.8–1.5 Ma), is most completely developed in the southwest of the island, but occasionally occurs in the other sectors. The third, Las Américas phase (1 Ma), is only presently known in the southern region. The fourth, Bandas del Sur phase (0.7–0.15 Ma), is essentially exposed in the southeast sector. The results of this work emphasise the complexity of the pre-1-Ma eruptive history of Tenerife and underline the fact that explosive volcanic activity has taken place for at least the last 2 Ma. Vertical collapse structures have developed as a result of pyroclastic flow activity and these may be as old as 1.6–1.8 Ma, therefore much older than generally considered. The precise location of calderas is difficult to ascertain as a result of the repeated lateral flank collapse during the construction of the Cañadas volcano.
Resumen: A deformed ca. 570Ma syenite–carbonatite body is reported from a Grenville-age (1.0–1.2 Ga) terrane in
the Sierra de Maz, one of theWestern Sierras Pampeanas of Argentina. This is the first recognition of such a
rock assemblage in the basement of the
Central Andes. The two main lithologies are coarse-grained syenite
(often nepheline-bearing) and enclave-rich fine-grained foliated biotite–calcite carbonatite. Samples
of carbonatite and syenite yield an imprecise whole rock Rb–Sr isochron age of 582ñ60Ma (MSWD= 1.8;
Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of 206Pb–238Uages between
433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural
interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite
complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525ñ7Ma
(Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western
Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr
values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed
during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic
lower continental crust.
Resumen: A review of the general volcano-stratigraphy and geochronology of La Gomera, one of the lesser known Canary Islands, has led to the establishment of a new evolutionary model. The oldest edifice corresponds to the submarine stage built up between 20 and 15 Ma. The construction of the Submarine Edifice was followed by
an important break in the activity (about 4 Ma) and deep erosion of the edifice. About 10.5 Ma ago, the main present-day edifice (the Old Edifice 10.5–6.4 Ma) emerged, which was also submarine in its initial phases. Two different main stages are distinguishable. The first stage was represented by a large, some 22 km wide basaltic shield volcano (the Lower Old Edifice). Several lateral collapse events (Tazo and San Marcos avalanches) occurred during this time and were responsible for the removal of an important part of its northern flank. In the second growth stage (the Upper Old Edifice), the activity migrated southwards. A 25-km wide composite volcano arose covering part of the remaining earlier shield volcano. The felsic (trachytic to phonolitic) activity occurring in two separate episodes formed a significant component of this composite volcano. Finally, one more recent large edifice (the Young Edifice) built up from 5.7 to 4 Ma. The lava flows of this younger edifice covered completely the centre and the south of the island and filled deep ravines in the north. More evolved magmas, including significant felsic magmas (the third and last felsic episode), occurred in this phase of activity.
The growth of La Gomera was long-lasting, separated by an important gap in the activity in the Middle Miocene, with no Quaternary activity at all. At the same time on Tenerife (the nearest island east of La Gomera), three large edifices grew separately: Roque del Conde, Anaga and Teno (initially three separated islands). From the available data, it is inferred that the subaerial activity started earlier in the Roque del Conde Edifice, then on La Gomera and later in Teno in the NW and Anaga in NE of Tenerife, which is the youngest of all these edifices. These facts, together with the irregular general progress of the volcanic activity, support more complex views of the genesis for the Canary Islands than the simple hotspot model.
Palabras clave: La Gomera; Volcanic edifices; K/Ar geochronology; Canary Islands; Oceanic islands; Hot spot; Lateral collapse; Seamount
Resumen: The arc-derived upper terrane in the NW Iberia Variscan belt contains a 3000 m thick turbiditic formation at
its structural top. Most of the sandstones are feldspathic greywackes with a framework of quartz and weakly
altered plagioclase. Rock fragments of vitric and microgranular texture are common in
polymictic
conglomerates and coarse-grained greywackes, together with slates, cherts and bipyramidal volcanic quartz
fragments. Although recrystallization under greenschists facies conditions (chlorite and biotite zones) and the
presence of two cleavages hinder detailed textural analysis, the sandstones appear to be typically immature,
first-cycle sandstones. The metagreywackes have average major and trace element compositions similar to
PAAS (Post Archean Australian Shale), which is considered to reflect the composition of the upper continental
crust. Their trace element composition is very consistent and records deposition within a convergent tectonic
setting, probably in an intra-arc basin located in a volcanic arc built on thinned continental margin. Detrital
zircon populations suggest a Middle Cambrian maximum depositional age (530–500 Ma) and a Gondwanan
provenance located at the periphery of the West African Craton. Nd isotope data suggest mixing Ediacaran and
Paleoproterozoic sources for the provenance of the greywackes, with TDM ranging between 720 and 1215 Ma
with an average of 995 Ma (n=20)—an age range unrepresented in the detrital zircon population. The Nd
model ages are similar to those exhibited by West Avalonia, Florida or the Carolina terrane, but younger than
those of Cambrian and Ordovician sandstones and shales from the autochthonous realm. These data suggest
a westernmost location along the Gondwanan margin for the upper terrane of NW Iberia relative to other
terranes located in the footwall of the Variscan suture, consistent with several previously proposed
paleogeographic models for the NW Iberia terranes.
Resumen: The arc-derived upper units of the Órdenes Complex, NW Iberia, are emplaced above the Variscan suture and
contain a low-grade metasedimentary uppermost section, with a maximum depositional age of 510–530 Ma,
intruded by a number of mafic dykes. Three deformational events affect the metasedimentary section.
The
youngest deformation event (D3) is of undifferentiated Variscan age and consists of metre- to decametre-scale,
close upright folds with axes plunging gently towards N20°E. The most important D2 structure is a regional S2
foliation axial planar of minor foldswith dextral asymmetry. The presence of a stretching lineation parallel to the
D2 fold axes is related to a top-to-the-north sense of shearing in a context of regional extension. The oldestmeterscale
D1 folds are developed in suitable greywacke–pelite alternations and consist of tight folds with chevron and
similarmorphologies, axes plunging gently toward N20°E, and a continuous S1 axial planar foliation. The essential
characteristic of the D1 deformation event is depicted by a set of west-vergent folds with reverse limbs less than
2 kmin wavelength, that are affected in their lower part by the generalised presence of the regional S2 foliation.
The age of D2 and D1 structures is notwell constrained. The diabase dykes intruding the low-grade turbidites cut
the D1 folds and their field relationships suggest that they were emplaced at the end of the D2 shearing event
and prior to the upright D3 Variscan folds. Zircon grains obtained from one of the diabase dykes were analysed
for U–Pb at the SHRIMP-RG facility at Stanford University. An age of c. 510 Ma, based on the analysis of 31
individual zircon grains, is interpreted to date the crystallization of the Ares dyke. The tectonic and magmatic
evolution of the top turbiditic series of the Órdenes Complex is tentatively related to the dynamics of a peri-
Gondwanan arc developed during active subduction beneath Gondwana and suggests: (1) accretion beneath the
arc during west-vergent (present coordinates) nappe development (D1); (2) extension of the arc during top-tothe-
north shearing (D2); and (3) final intrusion of the diabasic dykes into an intra-arc turbiditic series. This
evolution spans the end of volcanic arc activity and the onset of the opening of the Rheic Ocean.
Resumen: U–Pb dating of zircons from a metagabbro of the Purrido
amphibolitic unit (Cabo Ortegal Complex, NW Iberian
Massif) yielded an age of 1159 ñ 39 Ma, interpreted to
approximate the crystallization age of the gabbroic protolith.
Considering the arc affinity of the metagabbroic rocks, the
unit is interpreted
as a pre-Rodinian ophiolite developed in a
back-arc setting. It is suggested that the ophiolite was
obducted over the West African terranes during the assembly
of Rodinia. There, this terrane remained tectonically stable
and facing an ocean for a long time, and eventually became
part of the Gondwanan margin. The ophiolite was finally
involved in the Variscan suture of Galicia where it is
sandwiched between Palaeozoic rocks. The Purrido unit is so
far the only example of a Mesoproterozoic ophiolite in the
European Variscan belt, where pre-Neoproterozoic rocks are
very scarce and restricted to small exposures.
