Analgesia
CH 2 OCH2OH
6. RESULTADOS
6.1. Disfunción inducida por dolor en la rata
Pyroxenes are typically magmatic minerals that have crystallized at high temperature with low water pressure. Therefore these are mostly minerals of volcanic and hypabyssal rocks.
In plutonic rocks, the pyroxenes are abundant in the initial terms (gab-bro, norite). They are rarer in differentiated terms (diorites) where they are replaced by amphibole. They are exceptional in granitoids. Hypersthene granitoids (charnockites) have crystallized in the granulite facies.
1 atmosphere - forsterite present
Fo + L T °C
1600
1500
1400
1300
1200
1100
1000 En
900
MgSio3 10 30 50 70 90 CaMgSi2o6
PEn HTEn
L
Di + L
Pi + Di
Pi + L Pi
PEn + Pi
En + Di
Di
Figure 3.24 Diopside–enstatite system (after Carlson, 1988, modified).
L = liquid; Fo = forsterite; PEn = protoenstatite.
HTEN = phase analogous to high temperature enstatite.
En = enstatite; Pi = pigeonite; Di = diopside (solid solution = endiopside/augite).
Pyroxenes of the alkaline series that occur in basic to intermediate rocks, augites close to the diopside–hedenbergite series or salites. These augite are richer in aluminium and titanium than in the subalkaline series, all the more aluminous and titaniferous as the series is more alkaline. In differentiated rocks, the pyroxene is aegirine and/or aegirine augite. In plutonic rocks (syenite, nepheline syenite, alkali granite), aegirine is commonly associated with riebeckite.
Hedenbergite appears with fayalite in rare alkali granites and quartz syenite, oversaturated in silica and highly under-saturated in alumina.
Basic and intermediate rocks of the subalkaline series contain two pyroxenes: an augite and calcium-poor pyroxene.
In the differentiated lavas (and hypabyssal rocks) of the tholeiitic series, this pyroxene is a pigeonite, forming both microlites and phenocrysts (in smaller quantities and more rare). In little or no differentiated lavas of these
aegyrine
peralkaline phonolites
phonolites trachytes
trachytes
ferrosilite benmor
eites
benmoreites mugearites
mugearites hawaites
hawaites basalts
basalts
hedenbergite diopside
80
60
40
20
0
0 20
50
40
30
enstatite
40 60 80
Figure 3.25 Pyroxenes of the Velay volcanic series, French Massif Central (unpublished data by E. Berger).
series, pigeonite is replaced by the enstatite/bronzite, because magnesian pigeonite crystallizes at higher temperatures (above 1300°C) than such mag-mas (which are about 1100 to 1200°C).
In tholeiitic plutonic complexes (anorthosite massifs, stratiform mafic–
ultramafic complex like the Bushveld and the Skaergaard (Figure 3.26), pigeonite and augite of primary crystallization, formed at high temperature, have undergone changes during subsolvus progressive cooling producing exsolutions lamellae of orthopyroxene in augite and transforming the pri-mary pigeonite into inverted pigeonite (hypersthene with exsolutions lamel-lae of augite). These stratiform complexes commonly contain accumulative pyroxenites (cumulates), like bronzitites and diopsidite.
The two pyroxenes of the calcalkaline series, volcanic or plutonic com-plexes ( Sudbury, Giant Mascott) (Figure 3.26) are augite and hypersthene.
In the plutonic complexes, augite, and to a lesser extent, hypersthene show the same type of exsolution as in tholeiitic plutonic complexes.
The diopside–enstatite phase diagram (Figure 3.24) shows that the tho-leiitic series (with pigeonite) crystallizes at higher temperatures and lower water fugacities than the calc-alkaline series (with hypersthene).
Pyroxenes are, with olivine, the major constituents of ultramafic rocks:
lherzolites (olivine + Opx + Cpx), harzburgite (olivine + Opx), wherlite (oli-vine + Cpx), websterite (Cpx + Opx) and pyroxenites.
wollastonite Casio3
pyroxenes of the mafic – ultramafic complexes Sudbury
Figure 3.26 Pyroxenes of the mafic–ultramafic complexes (data compiled by M. Besson and unpublished data by the same author).
Occurrences of ultramafic rocks are:
• bodies of cumulative origin associated with basic–ultrabasic complexes, in particular, as more or less stratiform levels in Bushveld type layered complexes;
• usually small ultramafic intrusions, as the Pyrenean lherzolites;
• inclusions in alkali basalts (basanite, nephelinite) and kimberlites; it may be either cumulates, or preserved fragments of the mantle, or relicts of a partial melting of the mantle;
• large bodies, made mostly of harzburgites (and minor lherzolites), in Alpine type ophiolites.
The upper mantle is composed of lherzolite: olivine, orthopyroxene, clinopyroxene (diopside–endiopside) and a minor aluminous phase, spinel or, at higher pressure/depth, garnet.
In summary, most ultramafic rocks are:
– either cumulates formed from basic magmas;
– or fragments of the mantle emplaced by tectonics or inclusions in vol-canic lava or kimberlites.
Stony meteorites (stones), chondrites and achondrites, which represent 90% of the meteorites, are composed of olivine, pyroxene and ore (less than 10%, as iron-nickel alloys and sulfides):
• iron-poor chondrites (L chondrites) with olivine and hypersthene;
• iron-rich chondrites (H chondrites) with olivine and bronzite;
• calcium poor achondrites with pigeonite or hypersthene;
• calcium-rich achondrites with diopside or augite.
Metamorphic rocks
Granulite facies (and that of pyroxene hornfels) are defined by the paragen-esis orthopyroxene + calcic plagioclase. This paragenesis appears in the basic rocks. In the orthogneisses with a composition of granitoids, orthopyroxene associated with potassium feldspar is formed in the place of the biotite of common granites. Orthopyroxene is rare in aluminous paragneisses: associ-ation garnet + K-feldspar replace aluminium-rich biotite (see chapter 3.2.1d on micas). Clinopyroxene may be present in basic rocks of the granulite and pyroxene hornfels facies. It is rare in basic rocks of the amphibolite facies, where it is commonly replaced by hornblende.
Aluminous diopside also occurs in calcic-magnesian, aluminous, silica-undersaturated (Tschermak molecule is under-saturated in silica compared to anorthite) rocks of high temperature (pyroxene hornfels facies, granulite facies and high temperature amphibolite facies).
The banded iron formations that have undergone high grade meta-morphism, contain iron-rich pyroxenes: orthopyroxene close to ferrosilite, hedenbergite, ferriaugite.
Clinopyroxenes of the diopside–hedenbergite series occur in carbon-ate rocks, impure marbles and calc-siliccarbon-ate-gneisses in a wide temperature range: the diopside isograd in these rocks corresponds roughly with that of aluminous silicates (garnet, cordierite, etc.) in metapelites.
Jadeite + quartz association defines a high-pressure sub-facies in blue-schist facies (pressure over 7–8 kb). But in the absence of quartz, jadeite can be stable at lower pressures. Some rocks deficient in silica and alumina, in particular iron-rich formations in blueschist facies, may contain aegir-ine associated with an amphibole of the glaucophane–riebeckite series (for instance, Saint-Veran, Hautes Alpes, France).
Pyroxenes of the eclogites are omphacite. But the composition of those omphacites depends on the type of eclogite: the relatively low temperature eclogites in the areas of Alpine metamorphism are rich in jadeite component.
Increase of temperature promotes the introduction of the Tschermak mol-ecule. Eclogites in enclaves in alkali basalts contain aluminous diopside.
Metasomatic rocks
Pyroxenes are major components of the skarns. In skarns of high tempera-ture (often at the magmatic stage) pyroxenes are commonly aluminous diopside. In most common hydrothermal skarns, pyroxenes belong to the diopside–hedenbergite–johannsenite series.
Aegirine appears in fenites, metasomatic halos around alkaline com-plexes, particularly carbonatites.