26 research outputs found
Contact metamorphism associated to the Penamacor - Monsanto granitic intrusion (Central Portugal): geochemical, isotopic and mineralogical features
Contact metamorphism related to Variscan and late-Variscan granitic plutons in the Iberian Peninsula is superimposed on medium-grade regional metamorphism, making it often difficult to evaluate per se the thermal effects due to those intrusions and explaining the paucity of scientific literature on the subject. An exhaustive set of geochemical, isotopic and mineralogical data on the contact-zone metasediments hosting the Penamacor-Monsanto granite (Central Iberian Zone, Portugal) provides a significant contribution to the characterization of low- to intermediate-grade contact metamorphism in geological contexts formerly affected by regional metamorphism.
The metasediments hosting the Penamacor-Monsanto pluton belong to the extensive detrital sequence of the ante-Ordovician Schist-Greywacke Complex. Bulk geochemistry, oxygen isotope data and crystal-chemistry of key minerals from those contact-zone and neighbouring metasediments have made it possible to infer metamorphic conditions on the contact zone of this granitic intrusion, and to distinguish them from late boron-metasomatism at the exocontact.
Mineral paragenesis (muscovite + biotite + chlorite quartz plagioclase cordierite, in spotted-schists; biotite + chlorite quartz plagioclase ( cordierite), in hornfelses) and the composition of these coexisting mineral phases indicate that most of the contact rocks reached the biotite zone (or even the cordierite zone, in some cases), equivalent to upper greenschist – lower amphibolite metamorphic grade. The relatively narrow range of O-isotope temperatures estimated for the crystallization of the marginal granites (550-625ºC) explains the absence of significant effects of thermal flow anisotropy on the contact-zone rocks. Besides, textural, paragenetic, mineralogical, isotopic and geochemical nuances observed in hornfelses and spotted-schists seem mainly related to the local host-rock heterogeneities, rather than to thermal effects.
The relatively low temperatures estimated for granitoid emplacement and their restricted isotopic and mineralogical impacts on the metasedimentary host-rocks account for the narrow metamorphic aureole associated with the Penamacor-Monsanto pluton, and suggest this massif may correspond to the outcropping tip of a larger granitic intrusion at depth.Las intrusions graníticas Varíscicas y tardivaríscicas de la Península Ibérica dieron lugar a un metamorfsmo de contacto
que afecta a un encajante previamente sometido a un metamorfsmo regional de grado medio, lo que difculta separar los
efectos térmicos de aquellos regionales, y explica la escasez de estudios sobre el mismo. El estudio detallado de la zona
de contacto entre el Granito de Penamacor-Monsanto (Zona Centro-Ibérica; Portugal) y su encajante metasedimentario
mediante técnicas geoquímicas, mineralógicas e isotópicas supone una notable contribución al conocimiento y caracterización del metamorfsmo de contacto de grados bajos a intermedios en contextos geológicos previamente afectados por
metamorfsmo regional. El encajante metasedimentario del Plutón de Penamacor-Monsanto es parte de la amplia secuencia detrítica ante-Ordovícia conocida como Complejo Esquisto-Grawackico. Datos geoquímicos de roca total y cristaloquímicos
de los minerales más característicos, y relaciones isotópicas de oxígeno en la zona de contacto y metasedimentos aledaños
permiten inferir las condiciones metamórfcas en la zona de contacto de dicha intrusión, y diferenciarla de aquella afectada
por metasomatismo tardío por B. La paragénesis mineral (muscovita + biotita + clorita ± cuarzo ± plagioclasa ± cordierita
en los esquistos moteados; biotita + clorita ± cuarzo ± plagiclasa (± cordierita) en corneanas) y la composición de las fases
minerales coexistentes indican que la mayoría de rocas del contacto alcanzaron la zona de la biotita (e incluso, en algunos
casos, aquella de la cordierita), equivalente a la parte alta del grado metamórfco de los esquistos verdes, o a la parte baja de
las anfbolitas. El rango relativamente pequeño de temperaturas de cristalización de los granitos marginales (550-625°C),
calculado mediante isótopos de oxígeno, explica la carencia de anisotropías térmicas signifcativas en las rocas del contacto.
Las sutiles diferencias texturales, paragenéticas, mineralógicas, isotópicas y geoquímicas en esquistos moteados y corneanas
parecen relacionadas con heterogeneidades locales de los encajantes, y no con efectos térmicos diferenciados. Las temperaturas relativamente bajas estimadas durante la intrusión del granito de Penamacor-Monsanto, y el limitado efecto mineralógico
e isotópico sobre el encajante metasedimentario, dan lugar a una aureola de contacto estrecha, y sugieren que este macizo
puede corresponder al techo de una intrusión mayor en profundidad.Funding was provided by FCT—Fundação para a Ciên cia e Tecnologia, through project METMOB (PTDC/CTE-GIX/116204/2009
A Guide to Medications Inducing Salivary Gland Dysfunction, Xerostomia, and Subjective Sialorrhea: A Systematic Review Sponsored by the World Workshop on Oral Medicine VI
Multiple crustal sources for post-tectonic I-type granites in the Hercynian Iberian Belt
A post-tectonic plutonic array of felsic I-type
granites crops out in the western Hercynian Iberian Belt.
Isotope (Sr, N d, Pb) data favour the absence of an important
input of juvenile magmas in late- to post- tectonic
Hercynian felsic magmatism in western Iberia, but suggest
a reworking of different crustal protoliths, including
oceanic metabasic rocks accreted to mid-to-Iower crustal
levels during the early stages of the collision. I-type granites
were derived from different meta-igneous protoliths ranging
from metabasic to felsic compositions depending on their
geographical position from the external (e.g. Galicia-N
Portugal, GNP) to the innermost continental areas (Spanish
Central System and Los Pedroches Batholiths). The GNP 1-
type pIu tons related to eo-Hercynian accretional terranes
have lower initial 87Sr/86Sr ratios, lower negative εNd
values, and higher 206PbP04Pb ratios than other I-type granites of the Central Iberian zone. These more isotopically
primitive Hercynian I-type granites are important in
tracking pre-Hercynian accreted oceanic lithosphere
terranes
U–Pb isotopic ages and Hf isotope composition of zircons in Variscan gabbros from central Spain: evidence of variable crustal contamination
Ion microprobe U–Pb analyses of zircons from
three gabbroic intrusions from the Spanish Central System
(SCS) (Talavera, La Solanilla and Navahermosa) yield
Variscan ages (300 to 305 Ma) in agreement with recent
studies. Only two zircon crystals from La Solanilla massif
gave slightly discordant Paleoproterozoic ages (1,848 and
2,010 Ma). Hf isotope data show a relatively large variation
with the juvenile end-members showing ɛHfi values as high
as +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa and
Talavera gabbros, respectively. These positive ɛHfi values up
to +6.9 might represent the composition of the subcontinental
mantle which generates these SCS gabbros. This ɛHfi
range is clearly below depleted mantle values suggesting the
involvement of enriched mantle components on the origin of
these Variscan gabbros, and is consistent with previous
whole-rock studies. The presence of zircons with negative
ɛHfi values suggest variable, but significant, crustal contamination
of the gabbros, mainly by mixing with coeval granite
magmas. Inherited Paleoproterozoic zircons of La Solanilla
gabbros have similar trace element composition (e.g. Th/U
ratios), but more evolved Hf-isotope signatures than associated
Variscan zircons. Similar inherited ages have been
recorded in zircons from coeval Variscan granitoids from the
Central Iberian Zone. Granitic rocks have Nd model ages
(TDM) predominantly in the range of 1.4 to 1.6 Ga,
suggesting a juvenile addition during the Proterozoic.
However, Hf crustal model ages of xenocrystic Proterozoic
zircons in La Solanilla gabbro indicate the presence of
reworked Archean protoliths (TDM2 model ages of 3.0 to
3.2 Ga) incorporated into the hybridized mafic magma
U–Pb geochronology and zircon composition of late Variscan S- and I-type granitoids from the Spanish Central System batholith
Andalusite and Na- and Li-rich cordierite in the La Costa pluton, Sierras Pampeanas, Argentina: textural and chemical evidence for a magmatic origin
The La Costa pluton in the Sierra de Velasco
(NW Argentina) consists of S-type granitoids that can be
grouped into three igneous facies: the alkali-rich Santa
Cruz facies (SCF, SiO2 *67 wt%) distinguished by the
presence of andalusite and Na- and Li-rich cordierite
(Na2O = 1.55–1.77 wt% and Li2O = 0.14–0.66 wt%), the
Anillaco facies (SiO2 *74 wt%) with a significant proportion
of Mn-rich garnet, and the Anjullo´n facies (SiO2
*75 wt%) with abundant albitic plagioclase. The petrography,
mineral chemistry and whole-rock geochemistry of
the SCF are compatible with magmatic crystallization of
Na- and Li-rich cordierite, andalusite and muscovite from
the peraluminous magma under moderate P–T conditions
(*1.9 kbar and ca. 735C). The high Li content of cordierite
in the SCF is unusual for granitic rocks of intermediate
composition
Pb–Zn–Cd–As Pollution in Soils Affected 1 by Mining Activities in Central and Southern 2 Spain: a Scattered Legacy Posing Potential 3 Environmental and Health Concerns
In this chapter, published geochemical data for soils from several Pb–Zn mine sites and districts from Spain are reviewed. Although most of the mines have closed down, a legacy of highly polluted soils still remains throughout the sites constituting a potential hazard for the environment and human health. The fate of the studied metals and metalloids in these soils is mainly controlled by factors such as mining methods, concentration and metallurgical operations, mineralogy of the ore, gangue and host rock, fracturing of the host rocks, physiography, climate, and soil types (pedogenic evolution). It can be concluded that the most polluted soils (identified on the basis of an enrichment factor) are those of the Sierra Minera (La Unión District – SE Spain), at more than 488 (Pb), 163 (Zn), 99 (Cd), and 1698 (As) times the background values from non-contaminated soils. Pb is usually related to As, which in turn is bound to Fe oxides and oxyhydroxides.Metal bearing jarosite and other soluble phases also play a relevant role in the studied soil–water systems, because these minerals are dissolved during intense rainy events, thus resulting in high rates of metal leaching and mobilization by runoff