Hydrothermally reset magmatic spinels in retrograde serpentinites: formation of “ferritchromit” rims and chlorite aureoles   总被引：1，自引：0，他引：1  

M.?Mellini  C.?Rumori  C.?VitiEmail author 《Contributions to Mineralogy and Petrology》2005,149(3):266-275

Serpentinized harzburgites from southern Tuscany (Italy) host different kinds of spinels: (a) relic, magmatic Al-spinels, (b) hydrothermally altered spinels, occurring as ferritchromit rims, (c) syn- and post-serpentinization magnetites. The composition of relic Al-spinels suggests 5–15% partial melting of a fertile, spinel lherzolite. After the main serpentinization, Al-spinels are progressively replaced by ferritchromit rims by a dissolution–recrystallization process. Transmission electron microscopic investigation shows that ferritchromit actually consists of a complex, nanometric association of Cr-magnetite (Mg_0.03 Fe_0.97²⁺ Al_0.11 Cr_0.89 Fe³⁺ _1.00 O₄), chlorite and lizardite, with (001)_chl/liz always parallel to (111)_Cr-mag. Mg and Al, released during the Al-spinel ferritchromit replacement, interact with mesh-textured serpentine, giving rise to chloritic aureoles (i.e., randomly intergrown chlorite, lizardite and septechlorite) that overgrow and postdate mesh textures.  相似文献   

Thermal transformations in laser-heated chloritized annite     

C.?VitiEmail author  G. Di?Vincenzo  M.?Mellini 《Physics and Chemistry of Minerals》2004,31(2):92-101

Chloritized annite from the Irizar granite has been used for laser-heating experiments, following the procedures used for ⁴⁰Ar–³⁹Ar dating (heating steps in the 600–1080 °C temperature range). Four runs, at different temperatures, have been characterized using transmission electron microscopy, electron diffraction, micro-Raman and micro-IR spectroscopies. The water loss was evaluated by thermogravimetry. The chlorite domains break down first forming (001) amorphous layers, that later coalesce to rounded, equant inclusions and finally recrystallize to olivine and spinels plus silica glass. These phases occur within negative crystals hosted in ordered dehydrated annite, produced by dehydration and annealing of the starting annite. Dehydrated annite, olivine and spinels display topotactic relationships, determined by the common orientation of closely packed oxygen layers.  相似文献   

Radio maps of the Sun at λ = 1.95 cm     

Franca Chiuderi Drago  Marcello Felli 《Solar physics》1970,14(1):171-175

Two radio maps of the Sun at = 1.95 cm, taken at the N.R.A.O. (Green Bank) with a resolving power of 2.1 are studied and compared with H pictures: both bright and dark features appear to be strongly correlated. The emitted flux and the angular extent of the bright regions are given; from the observed radio-darkening of a region, the height of a prominence is derived.On leave from Osservatorio Astrofisico di Arcetri, Firenze.  相似文献   

Magnetic and microwave structure in solar active regions     

Marcello Felli  Giannina Poletto  Gianni Tofani 《Solar physics》1977,51(1):65-81

The structure of six active regions observed at 2.8 cm with the Stanford interferometer is compared with the configuration of the underlying photospheric magnetic fields, as given by the Kitt Peak magnetograph.The similar resolution and accuracy on the measured positions of both instruments allowed us to establish a more detailed spatial correspondence between radio and magnetic features than previously reached.The radio features which correspond to the cores of the active sources are always found to overlay regions of enhanced magnetic fields. Different spatial associations have been found depending on the brightness temperature of the sources. The possibility that this effect might be due to the development of the active region is also considered.  相似文献   

X-ray and HRTEM study of sursassite: Crystal structure,stacking disorder,and sursassite-pumpellyite intergrowth     

M. Mellini  S. Merlino  M. Pasero 《Physics and Chemistry of Minerals》1984,10(3):99-105

Sursassite is monoclinic, space group P2 ₁/m, a=8.70, b=5.79, c=9.78 Å, β=108.9°. The crystal structure was determined with X-rays and refined to R=0.065, obtaining Mn₂Al₃[(OH)₃(SiO₄)(Si₂O₇)] as ideal crystal chemical formula. Sursassite, isostructural with macfallite Ca₂Mn₃[(OH)₃(SiO₄)(Si₂O₇)], is closely related to pumpellyite Ca₂Al₃[(OH)₃(SiO₄)(Si₂O₇)]. In fact both sursassite and pumpellyite, apart from the different chemical composition, are built up by common structural layers, which are repeated by different stacking vectors. As a result, faulted stacking sequences are energetically possible. Examination by high resolution transmission electron microscopy (HRTEM) shows that frequent (001) pumpellyite-like lamellae are intergrown with thicker (001) sursassite lamellae. Usually, the guest lamellae are a few unit cells thick along [001] and continuous along the (001) plane, although also rare interrupted lamellae are found.  相似文献   

Niocalite revised: Twinning and crystal structure     

Dr. M. Mellini 《Mineralogy and Petrology》1982,30(4):249-266

Summary Niocalite (monoclinicPa, a=10.863(3),b=10.431(3),c=7.370(2) Å, =110.1(1)°) belongs to the cuspidine group. Its crystal structure has been refined toR ₁=0.069 andR _w=0.046, using 2411 independent reflections. Niocalite is isostructural with cuspidine and lavenite, but topologically distinct from the related mineral wöhlerite.The present model differs, from the structure proposed byLi Te Yü et al. (1966) because of the different choice of space group (Pa instead ofP2₁). The previous erroneous space group identification was due to neglecting the usual twinning of niocalite. In fact, the X-ray diffraction patterns and the electron optical images show that the mineral occurs as a dense intergrowth of twinned lamellae, having (100) as the twin composition plane and 100–1000 Å thickness.The chemical analysis, together with the results of the structure refinement, gives the crystal chemical formula Nb₂Ca₁₄(Si₂O₇)₄O₆F₂.The structure refinement seemed to indicate disordered distribution of niobium and calcium atoms within two different sites. In any case, this apparent disorder is supposed to be fictitious and would be due to the occurrence of twinning. Namely, the crystal structure would consist of twin related domains, each of them being characterized by ordered distribution of calcium and niobium atoms.

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Zur Kristallstruktur und Verzwillingung von Niocalit

Zusammenfassung Niocalit (monoklinPa, a=10,863(3),b=10,431(3),c=7,370(2) Å, =110,1(1)°) gehört zur Cuspidin-Gruppe. Seine Kristallstruktur wurde verfeinert aufR ₁=0.069 undR _w=0,046, auf der Basis von 2411 unabhängigen Reflexen. Niocalit ist isotrukturell mit Cuspidin und Låvenit, aber topologisch verschieden von dem verwandten Mineral Wöhlerit.Das vorgelegte Modell unterscheidet sich von der Struktur, dieLi Te Yu et al. (1966) vorgeschlagen haben, vor allem wegen der verschiedenen Wahl der Raumgruppe (Pa anstatt vonP2₁). Die Tatsache, daß die Raumgruppe früher nicht korrekt bestimmt werden konnte, geht darauf zurück, daß die verbreitete Verzwillingung von Niocalit nicht beachtet wurde. Diffraktometeraufnahmen und elektronenoptische Bilder zeigen, daß das Mineral als eine enge Verwachsung von verzwillingten Lamellen, mit (100) als Verwachsungsebene und 500–1000 Å Durchmesser auftritt.Die chemische Analyse, zusammen mit den Ergebnissen der Strukturverfeinerung geben die kristallchemische Formel Nb₂Ca₁₄(Si₂O₇)₄O₆F₂.Die Strukturverfeinerung schien anzudeuten, daß eine ungeordnete Verteilung von Niobium- und Kalzium-Atomen innerhalb von zwei verschiedenen Positionen vorliegt. Diese scheinbare Unordnung ist nicht reell und ist dieser Verzwillingung zuzuschreiben. Die Kristallstruktur besteht aus zwillingsbezogenen Bereichen, jeder von ihnen wird durch eine geordnete Verteilung der Kalzium- und Niobium-Atome charakterisiert.

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With 7 Figures  相似文献   

Role of stratospheric dynamics in the ozone–carbon connection in the Southern Hemisphere     

Chiara Cagnazzo  Elisa Manzini  Pier Giuseppe Fogli  Marcello Vichi  Paolo Davini 《Climate Dynamics》2013,41(11-12):3039-3054

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New insights on diapirism in the Adriatic Sea: the Tremiti salt structure (Apulia offshore,southeastern Italy)   总被引：1，自引：0，他引：1  

Vincenzo Festa  Gianvito Teofilo  Marcello Tropeano  Luisa Sabato  Luigi Spalluto 《地学学报》2014,26(3):169-178

The reinterpretation of public seismic profiles in the Adriatic offshore of Gargano (Apulia, southern Italy) allowed the detection of a kilometre‐scale salt‐anticline, the Tremiti diapir, within the larger Tremiti Structure. This anticline was generated by diapirism of Upper Triassic anhydrites within a thick Mesozoic to Quaternary sedimentary succession. Both internal stratal patterns and shapes of Plio‐Quaternary units, and the occurrence of an angular unconformity between early Tortonian and Pliocene rocks on the Tremiti Islands, suggest that halokinesis began during the late Miocene and is still active today. An ancient extensional SE‐dipping fault, cutting an older Mesozoic low‐amplitude anhydritic ridge, played an important role during salt mobilization, which was promoted by NW‐SE shortening. The diapir grew in the footwall of this fault, causing its upward propagation. In some places, the ancient fault served as a preferential channel for the upward migration of the anhydrites.  相似文献