Resumen: The Global Boundary Stratotype Section and Point
(GSSP) for the Aalenian
Stage, formally defined at the
base of bed FZ107 in the Fuentelsaz section, Castilian
Branch of the Iberian Range (Spain), has been ratified
by the IUGS. Multidisciplinary biostratigraphical data,
based on ammonites, brachiopods, ostracods, bivalves,
foraminifera, calcareous nannofossils assemblages and
palynomorphs, assure worldwide correlations; magnetostratigraphic
data increase this correlation power.
The position of the boundary coincides with the first
occurrence of the ammonite assemblage characterized
by Leioceras opalinum and Leioceras lineatum and corresponds
with a normal polarity interval correlated with
the up-to-date Jurassic magnetic polarity time scale
(Gradstein and others, 1994; Ogg, 1995).
Resumen: This paper is organized in two distinct parts. In the first section, the theoretical framework is laid regarding the functions of language, as Smith has them envisaged, and their relationship to the division of labor. And although this idea is original to Smith, the broader topic itself has been eluded to many times, as far back as the Ancient Philosophers, and more recently by William Petty and Bernard Mandeville. Nevertheless, the notion that persuasion
is intrinsically linked to the division of labor is a concept exclusive to Smith. Moreover, the existence of the two types of communication, persuasive and empathetic, is established in Smith, in which both styles of communication are compared in relation to the behavior of exchange or trade.
In the second section of this article I will argue that both exchange, or trade, and linguistic communication have their roots in the empathetic style of interaction outlined previously. After all, it is the empathetic style that favors both speaker and listener in an even exchange, while persuasive communication necessarily assumes a greater benefit for the speaker. Obviously, the notions of contractual interaction and trade must imply some sort of mutuality, if not trade would not occur. And even though one participant may come out of the deal with a greater benefit than the other, this is a matter of perspective and dependent on the point of view of the participants in the interaction.
Resumen: Magma flow in dykes is still not well understood; some reported magnetic fabrics are contradictory
and the potential effects of exsolution and metasomatism processes on the magnetic
properties are issues open to debate. Therefore, a long dyke made of segments
with different
thickness, which record distinct degrees of metasomatism, the Messejana–Plasencia dyke
(MPD), was studied. Oriented dolerite samples were collected along several cross-sections
and characterized by means of microscopy and magnetic analyses. The results obtained show
that the effects of metasomatism on rock mineralogy are important, and that the metasomatic
processes can greatly influence anisotropy degree and mean susceptibility only when rocks
are strongly affected by metasomatism. Petrography, scanning electron microscopy (SEM)
and bulk magnetic analyses show a high-temperature oxidation-exsolution event, experienced
by the very early Ti-spinels, during the early stages of magma cooling, which was mostly
observed in central domains of the thick dyke segments. Exsolution reduced the grain size
of the magnetic carrier (multidomain to single domain transformation), thus producing composite
fabrics involving inverse fabrics. These are likely responsible for a significant number
of the ‘abnormal’ fabrics, which make the interpretation of magma flow much more complex.
By choosing to use only the ‘normal’ fabric for magma flow determination, we have
reduced by 50 per cent the number of relevant sites. In these sites, the imbrication angle of the
magnetic foliation relative to dyke wall strongly suggests flow with end-members indicating
vertical-dominated flow (seven sites) and horizontal-dominated flow (three sites).
Palabras clave: Magnetic fabrics and anisotropy; Rock and mineral magnetism; Large igneous
provinces; Magma migration and fragmentation; Europe
Resumen: Andalusite occurs as an accessory mineral in many types of peraluminous
felsic igneous rocks, including rhyolites, aplites, granites,
pegmatites, and anatectic migmatites. Some published stability
curves for And = Sil and the water-saturated granite solidus permit
a small stability field for andalusite in equilibrium with felsic melts.
We examine 108 samples of andalusite-bearing felsic rocks from
more than 40 localities world-wide. Our purpose is to determine the
origin of andalusite, including the T–P–X controls on andalusite
formation, using eight textural and chemical criteria: size—
compatibility with grain sizes of igneous minerals in the same rock;
shape—ranging from euhedral to anhedral, with no simple correlation
with origin; state of aggregation—single grains or clusters of
grains; association with muscovite—with or without rims of monocrystalline
or polycrystalline muscovite; inclusions—rare mineral
inclusions and melt inclusions; chemical composition—andalusite
with little significant chemical variation, except in iron content
(0.08–1.71 wt % FeO); compositional zoning—concentric, sector,
patchy, oscillatory zoning cryptically reflect growth conditions;
compositions of coexisting phases—biotites with high siderophyllite–
eastonite contents (Alw Ɉ 268 ñ 007 atoms per formula
unit), muscovites with 0.57–4.01 wt % FeO and 0.02–
2.85 wt % TiO2, and apatites with 3.53 ñ 0.18 wt % F.
Coexisting muscovite–biotite pairs have a wide range of F contents,
and FBt = 1.612FMs + 0015. Most coexisting minerals have
compositions consistent with equilibration at magmatic conditions.
The three principal genetic types of andalusite in felsic igneous rocks
are: Type 1 Metamorphic—(a) prograde metamorphic (in thermally
metamorphosed peraluminous granites), (b) retrograde
metamorphic (inversion from sillimanite of unspecified origin) (c) xenocrystic (derivation from local country rocks), and (d) restitic
(derivation from source regions); Type 2 Magmatic—(a) peritectic
(water-undersaturated, T↑) associated with leucosomes in migmatites,
(b) peritectic (water-undersaturated, T↓), as reaction rims on
garnet or cordierite, (c) cotectic (water-undersaturated, T↓) direct
crystallization from a silicate melt, and (d) pegmatitic (watersaturated,
T↓), associated with aplite–pegmatite contacts or pegmatitic
portion alone; Type 3 Metasomatic—(water-saturated,
magma-absent), spatially related to structural discontinuities in
host, replacement of feldspar and/or biotite, intergrowths with
quartz. The great majority of our andalusite samples show one or
more textural or chemical criteria suggesting a magmatic origin. Of
the many possible controls on the formation of andalusite (excess
Al2O3, water concentration and fluid evolution, high Be–B–Li–P,
high F, high Fe–Mn–Ti, and kinetic considerations), the two most
important factors appear to be excess Al2O3 and the effect of
releasing water (either to strip alkalis from the melt or to reduce
alumina solubility in the melt). Of particular importance is the
evidence for magmatic andalusite in granites showing no significant
depression of the solidus, suggesting that the And = Sil equilibrium
must cross the granite solidus rather than lie below it. Magmatic
andalusite, however formed, is susceptible to supra- or sub-solidus
reaction to produce muscovite. In many cases, textural evidence
of this reaction remains, but in other cases muscovite may
completely replace
