Carlo Alberto Ricci

Minette inclusions in the rhyodacitic lavas of Mt-Amiata (Central Italy): mineralogical and chemical evidence of mixing between Tuscan and Roman type magmas

Abstract Major-element, trace-element and mineralogical data are reported for a series of mafic inclusions occurring in the rhyodacitic lavas of Mt. Amiata (southern Tuscany, Italy), a volcanic complex belonging to the Tuscan Magmatic Province. The inclusions form, together with some subordinate mafic latitic lavas and the host rock rhyodacites, a continuous series, which varies from olivine and minor nepheline normative to quartz, hypersthene and corundum normative rock-types over a range of 48–67% SiO 2 . All of the rocks are characterized by high contents of potassium (5–6% K 2 O) and many trace elements, particularly the incompatible elements. Following straight-line correlation trends, Al, Fe, Mg, Ca, Ti, P, Sr and Ba decrease with increasing SiO 2 , whereas Na and Li increase, and K, Rb, Zr, La, Ce, Nb and Y remain virtually constant. The primary mineral assemblage of the inclusions consists of diopsidic pyroxene, forsteritic olivine and mica, and is representative for minettes. Xenocrysts of plagioclase, sanidine, orthopyroxene clinopyroxene, biotite, ilmenite and olivine occur in increasing amounts in the more siliceous samples. The composition of these xenocrysts is identical to that of the phenocryst assemblage in the rhyodacites. The latitic lavas are rich in xenocrysts and differ from the minettes mainly by the absence of primary mica. The data strongly suggest a magma mixing origin for the minettes, latites and possibly part of the rhyodacites. Injection of mafic magma into a siliceous magma chamber has resulted in the formation of hybrid inclusions and a latitic magma that could only reach the surface after eruption of the voluminous rhyodacitic lavas. The rhyodacites which erupted early and are slightly richer in SiO 2 than most of the other rhyodacites are considered to represent the acid mixing component, whereas the mafic end-member has close affinities to the potassic alkaline lavas of the adjacent Roman Province. The inclusions have the modal composition of a minette and this implies that volatiles were important constituents of the hybrid magmas. This may be attributed to the primary character of the Roman-type end-member involved, or explained by a process of selective enrichment operating during mixing. Although upper mantle derived Roman magmas have interacted with Tuscan magmas of crustal anatectic origin at Mt. Amiata and probably other volcanic centres in central Italy, the specific chemistry of lavas in both provinces cannot be explained by simple mixing of these magmas in shallow chambers.

Ultra-high-pressure metamorphism in felsic rocks: the garnet-phengite gneisses and quarzites from the Lanterman Range, Antarctica

Mesostructural and microstructural relations between eclogitic boudins and country gneisses in the Ross Orogen of the Lanterman Range (Northern Victoria Land, Antarctica) are in some areas characterized by interlayering with sharp contacts on a cm scale, which indicate that the two rock-types underwent a common metamorphic evolution. Contrary to many other UHP felsic rocks that only preserve a poor record of the HP stage, the studied rocks have recorded a metamorphic history ranging from initial prograde amphibolite facies through the eclogite facies to the retrogressive amphibolite facies. The prograde amphibolite stage is documented by garnet relics preserving prograde zoning and bearing biotite, plagioclase, muscovite, phengite and rutile inclusions. The eclogite stage is characterized by the coexistence of phengite with pyrope-grossu-larite rich garnet, the latter containing phengite and paragonite inclusions, and by radial fractures within garnet around quartz pseudomorphs after coesite. Symplectites have formed during the amphibolite-facies retrogression. They consist mainly of biotite + plagioclase around phengite and garnet; muscovite, biotite and plagioclase grew along the main foliation. The reconstructed metamorphic evolution, involves a steep prograde and retrograde PT path as well as a HP-T peak. Along with the geochronological evidence of fast exhumation, this supports a model of arc-continent collision, with the HP rocks belonging to the over-riding plate. Their exhumation is mainly controlled by extension related to renewed “rollback” of subduction in front of the orogenic zone.

SHRIMP dating of zircons in eclogite from the Variscan basement in north-eastern Sardinia (Italy)

SHRIMP (Sensitive High-Resolution Ion Microprobe) U-Pb ages of zircons from a single sample of mafic eclogite (Punta de li Tulchi, Sardinia, Italy) are reported. The study under cathodoluminescence (CL) reveals two groupsof metamorphic zircons and the SHRIMP analyses allow recognition of three ages: 1) 453 ′ 14 Ma; 2) 400 ′ 10 Ma, and 3) 327 ′ 7 Ma. The age of 453 ′ 14 Ma could be that of the magmatic protolith and an age of 327 ′ 7 Ma can reasonably be attributed to the main Variscan collisional event in Sardinia, which produced Barrovian-type metamorphism, and retrogression of eclogite under amphibolite-facies metamorphism. The intermediate age 400 ′ 10 Ma is difficult to interpret and it could represent either the age of the eclogite facies metamorphism or it is a result of Pb-loss during the main Variscan event at 327 ′ 7 Ma.

Importance of nicotinamide as an NAD precursor in the human erythrocyte.

The effect of variation in the concentration of inorganic phosphate and of the pyridine precursors nicotinamide (NAm) and nicotinic acid (NA) on pyridine nucleotide synthesis was studied using intact human erythrocytes. A wide range of incubation times was employed. The results showed that under physiological conditions the rate of synthesis of NAD from NAm exceeded that from NA twofold, while the reverse situation pertained at higher and unphysiological substrate levels. The two pathways had different regulation points. For NAm the rate-limiting factor was the initial step, namely its conversion into the mononucleotide, while for NA it lay at the second step, conversion of NA mononucleotide (NAMN) to its adenine dinucleotide. At physiological substrate levels the uptake of NA and conversion to NAMN were rapid, while the uptake and conversion of NAm were time dependent. This process was stimulated significantly by inorganic phosphate only for NAm. These results indicate that while NA is the predominant precursor of human erythrocyte NAD at high (unphysiological) substrate and phosphate levels, NAm is more efficient as an NAD precursor under physiological conditions, suggesting an important and hitherto unrecognized role for nicotinamide in NAD synthesis in vivo.

Purine and pyridine nucleotide production in human erythrocytes.

Human erythrocyte adenyl and pyridine nucleotide production has been tested in cell-free lysates and in intact cells. The main products obtained in cells incubated with adenine and nicotinic acid are adenosine triphosphate and nicotinate mononucleotide, respectively, under any experimental condition used (incubation time, base concentration). Adenine-phosphoribosyltransferase activity determined in crude lysates is about 100 times higher than nicotinate-phosphoribosyltransferase activity, while cellular adenyl nucleotide production is only three times higher than that of pyridine nucleotide. A strong intracellular regulation for the former, but not latter, synthetic process is thus suggested. Intact erythrocyte nicotinate nucleotide production is inhibited by adenine, while nicotinate-phosphoribosyltransferase activity is not. The possible regulation by adenyl nucleotides is discussed in light of the modulating action of ATP on nicotinate-phosphoribosyltransferase activity. The kinetic characteristics of both adenine- and nicotinate-phosphoribosyltransferases, determined on crude lysates, are reported.

First evidence of a “Barrovian”-type metamorphic regime in the Ross orogen of the Byrd Glacier area, central Transantarctic Mountains

Abstract The Selborne Group comprises two metamorphic rock units, the muscovite±dolomite bearing Madison Marble and the biotite-muscovite±quartz-calcite Contortion Schist, which contains thick lenses of variably deformed metabasalts and metaconglomerates. Petrological and structural data indicate a polyphase metamorphic evolution including: i) an early stage of upper greenschist regional metamorphism (P = ~0.15–0.3 GPa; T = ~380–450°C), ii) prograde metamorphism during D1 up to amphibolite facies peak conditions (P = 0.58–0.8 GPa, T = ~560–645°C), iii) syn-D2 unloading-cooling retrograde metamorphism, iv) a post-D2 contact metamorphic overprint at variable T between 450 and 550°C and ~0.2 GPa connected to the emplacement of granitic plutons and felsic dyke swarms. Geochronological data constrain the polyphase syn-D1/D2 evolution between ~ 510 and 492 Ma. A similar metamorphic path, including a medium P stage but at lower T conditions, is documented in greenschist facies metabasalts within the Byrd Group in the Mount Dick area. The metamorphic pattern and close lithostratigraphic matching between Selborne Group and Byrd Group sharply contrast with the high-grade Horney Formation that is exposed north of the Byrd Glacier and corroborate the hypothesis that the Byrd Glacier discontinuity marks a first-order crustal tectonic boundary crossing the Ross orogen.

Density increase and ageing of erythrocytes in stored blood

An increase in the density of erythrocytes was observed after storage of whole blood for 30 days at 4°C in either acid citrate – dextrose or citrate – phosphate – dextrose – adrenaline. Glucose- 6-phosphate dehydrogenase activity in unfractionated red blood cell lysates did not vary with the storage time. Enzyme activity in the lighter fraction separated by density gradient centrifugation was higher than that in heavier fractions. The decline in glucose-6-phosphate dehydrogenase activity with density was less marked after storage of whole blood for 30 days. It is suggested that density modifications are not related to the ageing of erythrocytes and additional mechanisms may be involved.

Formation of nicotinic acid nucleotides in the liver of nicotinamide-treated cats

Abstract Nicotinic acid mononucleotide and nicotinic acid-adenine dinucleotide were isolated by Dowex-1 chromatography from the liver of nicotinamide-treated cats. The compounds were identified on the basis of their paper Chromatographic behavior and their spectral and chemical characteristics. After the injection of nicotinamide, the level of NAD in cat liver is increased about 7-fold. The time course of accumulation of nicotinic acid, nicotinic acid mononucleotide, and nicotinic acid adenine dinucleotide suggests that these compounds are intermediates in the synthesis of NAD from nicotinamide.

Pyridine Nucleotide Metabolism: Purine and Pyrimidine Interconnections

The role of the pyridine coenzymes NAD and NADP in oxidation-reduction reactions, leading to energy production and to reductive synthesis, is well documented, and the characteristics of the proteins involved have been extensively studied. Since the balance between the oxidised and reduced form of pyridine coenzymes modulates both catabolic and synthetic pathways, their differing levels in different tissues, organs and cellular compartments indicate metabolic differentiations1. In addition to this role, pyridine coenzymes take part in a number of other cellular processes occurring in prokaryotes or eukaryotes or both2. These processes include the utilization of NAD for: protein ADP-ribosylations, mainly involved in the mechanism of action of bacterial toxins, affecting protein synthesis or some processes mediated by cAMP and G-proteins; poly-ADPribose synthesis, involved in the regulation of DNA repair and replication and in cellular differentiation; DNA ligase reactions, active in prokaryotes. NAD(P) involvement in the production of cytotoxic compounds and in phagocytosis process has also been described. Such findings revealed the versatility of the NAD(P) molecule in cell function, suggesting that its biological role is not yet fully appreciated.

Significance and Relevance of NAD Synthesis in Human Erythrocyte Life Span

NAD and NADP are known to play a key role in the general metabolism of human erythrocytes, owing to their involvement in all oxidative-reductive reactions occuring both in the energetic catabolism and in the processes preventing the cells from oxidative damage.