Francesco Sassi

• University of Padua

We review a selection of case studies that highlight the fascination and complexity of metamorphic processes and mechanisms, as revealed in rocks from the crystalline basement of the frontal part of the Adria microplate. The examples from the Austroalpine metamorphic rocks south of the Tauern Window, and from the crystalline basement lying more sou...

The frontal northern part of the continental Adriatic microplate is formed by a stack of Austroalpine nappes and by the Southalpine basement and cover units. Both basement portions are now side by side, separated by the Periadriatic (Insubric) fault system, but they became juxtaposed only during the Alpine orogeny. Permian HT-LP metamorphism is now...

Petrologic, chemical, and polytype data are presented for dioctahedral potassic micas from K-feldspar-bearing metamorphic and igneous rocks of acidic composition unaffected by high-pressure (HP) conditions. The paper aims to demonstrate that: (1) under non-HP conditions, in both metamorphic and igneous plutonic environments, a given bulk-rock compo...

This special issue of the American Mineralogist honors the memory and life’s work of our friend, colleague, mentor, and consummate teacher of mineralogy and petrology, Charles V. Guidotti (1935–2005). These papers were largely derived from a special topical session held in his honor at the 2006 Annual Meetings of the Geological Society of America....

aBStraCt A crystal-chemical study of thirteen biotite (twelve of 1M polytype and one of 2M 1 polytype) and four muscovite samples was made. The biotite coexists with the muscovite. Samples are from metamorphic terranes and from granitic and granodioritic bodies occurring in three areas of western Maine. The metamorphic mineral zones identified by m...

The Lower Palaeozoic biostratigraphic records in the Alps are briefly reviewed and the result of a new study of the acritarch assemblage found by Sassi et al. (1984) in the greenschist facies black metapelites of the Southalpine metamorphic basement at Col di Foglia, and studied by Kalvacheva et al. (1986), is presented. The new taxonomic and biost...

Recently, in the Agordo area, some unquestionable fossils have been described: 1) Latest Cambrian acritarchs, within trivial black, fine grained phyllites (Col di Foglia); 2) Aeronian graptolites, within boudins along a recrystallized shear zone cutting low-grade metapelites (Ponte Alto); 3) Middle Devonian Rugosa corals, within metalimestone boudi...

Recently, in the Agordo area, some unquestionable fossils have been described: 1) Latest Cambrian acritarchs, within trivial black, fine grained phyllites (Col di Foglia); 2) Early Silurian graptolites, within boudins along a recrystallised shear zone cutting low-grade metapelites (Ponte Alto); 3) Middle Devonian Rugosa corals, within metalimestone...

Chemical data for 139 natural paragonite-muscovite (Pg-Ms) pairs illustrate the effects of ferromagnesian components on the P-T-X topology of the Pg-Ms solvus. The pairs were selected on the basis of: reasonably accurate knowledge of the P-T conditions of formation; evidence for close approach to equilibrium at peak metamorphic conditions; exclusio...

The statistical b(o) method is based on the fact that the cumulative b(o) values of white K-micas (WKM) from metapelites of a specific bulk composition can be used, in the lowermost T range of metamorphism, as a semiquantitative P indicator: mean b(o) values (and related celadonite content) in WKM increase with increasing P, thus characterizing the...

Much literature exists regarding processes by which shales are transformed into slates. Included are mechanical, physical, and chemical processes. We consider here some aspects not treated by previous authors. Specifically, we consider the manner in which, during such processes, certain special crystal-chemical and physical properties of phyllosili...

We report the discovery of Aeronian (Middle Llandovery) graptolites, and corals of probable Devonian age, in boudins hosted by greenschists, within the Southalpine Metamorphic Basement. These discoveries provide key constraints to the depositional age range of the protoliths. This remarkable occurrence of almost undeformed graptolites and compound...

We briefly review the state of the art on the metamorphic evolution of the crystalline basements of the Eastern Alps, with emphasis on the Italian sector. For each of the main structural units, Penninic, Austroalpine and Southalpine, we present a short outline followed by the most recent results obtained by the research team of metamorphic petrolog...

Most of the sedimentary rocks occurring in Italy are post-Carboniferous. All what lies below is considered basement, mostly metamorphic or igneous. Understand- ing the pre-Carboniferous evolution depends on the reconstruction of the sedimentary, metamorphic and igneous evolution of the basement. In general, the base- ment sedimentary protoliths wer...

Micas have been studied for many important and highly interesting reasons by a wide range of workers, e.g., engineers, physicists, chemists, and Earth scientists. Our focus includes only aspects related to the Earth sciences, specifically the mineralogy and petrology of natural metamorphic rocks, and particularly the occurrence of micas in such roc...

The incorporation of Fe, Mg, and Si into muscovite in response to increase of pressure (P) has long been recognized. In the context of the appropriate mineral assemblages, the extent of this substitution has been calibrated to serve as a very useful geobarometer for high-P parageneses. In marked contrast, little or no Fm i.e., S(Mg + Fetotal), subs...

The Rb/Sr whole-rock age of granitoid gneiss interlayered with marbles at the top of the Nevado-Filabride Complex cover is 247 ± 11 Ma (Permian-Triassic boundary). Tourmaline-rich metasediments were metasomatized by B-rich fluids from the igneous body. Hence the igneous rocks were emplaced in the sedimentary rocks that now host the gneiss body, pre...

End-members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas, and the interlayer-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemi...

In the last ten years much new work has been done on the petrogenetic significance of the Na-K white micas in metamorphic rock, both by the authors, and by numerous others. This paper reviews these new results. Special emphasis is given to the new advances on the Pg-Ms mineralogy and phase relations which the authors perceive as having direct petro...

Numerous new studies have been done over the last ten years on the minor isomorphous substitutions in Na-K white micas. These results, from over a hundred papers, are reviewed and critically discussed here. Special emphasis is given to the new advances which the authors perceive as having a direct petrogenetic significance for understanding metamor...

The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The definitions and recommendations presented were approved by the Commission. The report discusses mica definition, subdivisions, principles of classification, end-member formulae, modifiers, and suffixes, series...

End members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas and the interlayer-cation-deficient micas. The determination of the crys-tallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusua...

The northern Somali crystalline basement (NSB) consists of seven major rock complexes, five of which are mainly metasedimentary sequences with some meta-igneous intercalations, while two are plutonic complexes. Using the single grain evaporation method, the authors have dated zircons of six samples from three of these complexes exposed in the Hargh...

The northern Somali crystalline basement (NSB) consists of seven major rock complexes, five of which are mainly metasedimentary sequences with some meta-igneous intercalations, while two are plutonic complexes. Using the single gram evaporation method, the authors have dated zircons of six samples from three of these complexes exposed in the Harghe...

Reviews data concerning the crystalline basement of all tectonic units in Hungary. Their lithologic content, biostratigraphic data, metamorphic features and radiometric age data are presented and critically discussed. The effects of at least two regional metamorphic cycles have been definitely recognized, Alpine and Variscan, and some polymetamorph...

Detailed microstructural and microprobe analyses were carried out on some small garnet idioblasts from phyllonites and two garnet porphyroblasts, respectively from a representative amphibolite and phyllonite rock sample. A consistent sequence of growth stages has been ascertained in this way in the two porphyroblasts, suggesting, combined with the...

Illite and chlorite crystallinity indices (XRD peak widths, respectively IC and ChC for short) were determined and their variation compared in the Palaeozoic, pelitic-silty complex of the South-Alpine basement of the Eastern Alps. A suite of 238 samples derived from eight localities in Northern Italy was investigated. Metamorphic grade in this regi...

Data on the Na-K compositions and final equilibration temperatures of natural, quasibinary paragonite-muscovite (Pg-Ms) pairs (mole fraction of margarite in Pg < 0.05; Si/formula unit ≤ 6.2 and/or Σ(Mg + Fe2+ + Fe3+) ≤ 0.35 for Ms) have been plotted and analyzed to determine the P-T - X limits of the binary Pg-Ms solvus. There is considerable scatt...

Three parametric (nonthermodynamic) equations have been developed to calculate final equilibration temperatures for natural, quasibinary paragonite-muscovite (Pg-Ms) pairs (mole fraction margarite in Pg < 0.05, Si/formula unit [le] 6.2 and/or [Sigma](Mg + Fe[sup 2+] + Fe[sup 3+]) [le] 0.35 for coexistent Ms). The first two equations are paragonite-...

Potassic white micas occur in metamorphic rocks as polytype 2M1 and sometimes 3T. Metamorphic phengites typically crystallize under high-pressure/low-temperature conditions (occurrence type I), but they are also expected to be common in rocks of low metamorphic grade which have particular bulk compositions, specifically low in Al2O3 (occurrence typ...

The Southalpine crystalline basement in the Eastern Alps consists of thick phyllitic sequences, in which an acritarch assemblage was locally found suggesting a Late Cambrian to Tremadocian sedimentation age. This is the oldest sedimentation age recorded in the Alps. The presently available data on lithostratigraphy, interregional correlation, Paleo...

The nature of the Pg-Ms solvus and its geothermometric potential have been discussed in numerous previous papers. However, field, experimental and thermodynamic investigations of Pg-Ms solvus pairs have typically yielded conflicting results. For example, graphical and calculated Pg-Ms solvi based on experimental data for synthetic, binary Pg-Ms mic...

The Austro-Alpine quartzphyllites and related clastic- and volcanic-rich sequences are interpreted as the infilling of an Early Ordovician to Early Carboniferous basin. The basin may have been initially formed as a back-arc basin on a Late Cadomian/Pan-African metamorphic crust during the Ordovician. A pulse of renewed rifting during Silurian and E...

A model of lithostratigraphic sequence is presented, ranging from Cambrian to Devonian; its chronological frame is, however, mainly hypothetical due to the lack of fossils. The interposition of a volcano-sedimentary complex (VSC) makes the distinction between an upper (UPC) and a lower complex (LPC) possible, within this rather monotonous pelitic-p...

F.P. SASSI •, D. VISONA •, G. F'ERRARA ...., G.O. GATIO ......, H.A. IBRAHIM ........, A.A. SAID ,...,.,. and S. ToNARINl •• • Department of Mineralogy and Petrology, University of Padova, Corso Garibaldi 37, 35137 Padova, Italy. •• Department of Earth Sciences, University of Pisa, Via S.Maria 53, 56100 Pisa, Italy. ..,.,. Department of Geology, P...

Abstract The present paper reports and discusses the results on compositional variability of muscovites, obtained in the frame of a research project on the chemistry of biotites and muscovites in low-grade metapelites. The results on biotites have been reported in a separate paper, to which readers are deferred also because it gives the statement o...

The phengite peak at d≃1.5Å, formerly often labelled as 060, is a convolution of 331̄ and 060, whose intensities are in the ratio of about 2:1. Since both diffracting planes are practically perpendicular to (001), no preferred orientation can separate one diffraction peak from the other. By converting d331̄,060 to b, we introduce a systematic error...

Multivariant, second order regression equations have been developed to quantify the effects of Na* [=100 Na/(Na+K)] and Fm [=(FeT + Mg + Mn)] on the a, b, 1/2 c.sin β, and V cell parameters of muscovite (143 specimens) and paragonite (22 specimens). Na* substitutions occur on the XII sites of these micas, and it is assumed that all Fm substitutions...

Riassunto Sono state analizzate 140 lamelle di miche (76 muscoviti e 64 biotiti) da 4 campioni di metapeliti di basso grado provenienti da un grande affioramento di basamento sudalpino in Pusteria. Le lamelle sono state scelte:(i) in ski microstrutturali diversi (fianchi e cerniere di micropieghe);(ii) in microsistemi chimici diversi (domini granob...

Petrography, petrology, mineral chemistry, metamorphic evolution and geothermo-barometric estimations concerning the Pohorje eclogites are discussed. These rocks record a three-stage metamorphic evolution: (0 an older, dry, high-pressure/high-temperature recrystallization (eclogite stage);(ii) a later, lower-pressure/lower temperature symplectite s...

Chemical and X-ray diffraction data for 2M1 muscovites have been evaluated with the aim of quantifying the changes in a and b that occur with substitution of Mg, Fe2+ and Fe3+ for AlVI. Examination of old (63 muscovites) and newly acquired (79 muscovites) data for both natural and synthetic 2M1 muscovites reveals that a and b decrease with increasi...

Abundant but poorly preserved acritarchs have been found in black metapelites. The assemblage consists mainly of small (5–15 μm), smooth, thin-walled specimens, without processes. Eight subgroups are represented by 19 genera. Stratigraphically diagnostic acritarchs are: Ovulum saccatum, O. lanceolatum, Volkovia flagellata, Aranidium cf. confusum, V...

The contributions of radiometric geochronology to the reconstruction of the Alpine, Hercynian, 'Caledonian' and older events are critically discussed. All radiometric data available in the literature up to 1984 are listed in tables. Some specific problems involving geochronology in the Eastern Alps are discussed in detail. They include: 1) the radi...

The main metamorphic rock types outcropping in the Sopron area are discussed, using geobarothermometry, and an evolutional model proposed which distinguishes between pre-Alpine and Alpine effects. Their pre-Alpine development is interpreted as being due to the Hercynian or the 'Caledonian' event. Microprobe analyses of several minerals are given. -...

A sequence of events which has been recognized in the two basement regions of Somalia is outlined on the basis of new field and petrographic data and pre-existing published and unpublished reports. The evolution of the Somalian basement took place during the Pan-African event, However, much detailed work is necessary before the history of the basem...

The Rb/Sr whole rock method was used to carry out radiometric analyses on about forty samples from the Vedrette di Ries massif. The samples were arranged in five sample groups. The age of this massif was found to be Middle Oligocene, and the best-defined isochron (30±3 m. y.) was obtained with a group of nine samples from the Upper Anterselva Valle...

New b0 values were measured for 123 K-white mica specimens from the Sanbagawa Metamorphic Belt. The rather high b0 values have been obtained on 43 specimens from the quartzose schists and metabasites and the values are considered to be related to the bulk rock compositions. On 80 b0 values which has been obtained from the petapelites, we obtained t...

Synopsis Analyses are presented of the b 0 -spacing value of almost 200 potassic white micas from the low temperature zone of the Scottish Caledonides. These measurements, which provide a relative geobarometer, indicate a gradual transition in the facies series of metamorphism into the area of ‘Buchan’ metamorphism. The use of this method to accura...

In several places of the old crystalline basement of the Eastern Alps a classification of the pre-Alpine metamorphic effects into an older, high-to intermediate-pressure metamorphism (eclogites, kyanite) and a younger, lower-pressure one (andkycord) is recognizable. Some local geological situations allow a sharp chronological distinction to be made...

The b 0 of the potassic white micas was measured in 410 samples of low-grade pelitic schists from the Central Pyrenees, the Abukuma belt, Northern New Hampshire, the Eastern Alps, Otago, the Sanbagawa belt and the Central Pontic Chain. Temperature and rock bulk composition can be considered substantially constant all over the sample range, so that...

In the Eastern Alps the b0 values of potassic white micas of Hercynian low-grade schists differ sharply from those of Alpine isograde and isochemical rocks. These differences, which indicate variations in the phengite content present as solid solution in the white micas, are to be referred to differences in pressure. In this way it is possible to r...

Per la sua complessa storia geologica che comprende eventi magmatici e metamorfici avvenuti nel Caledoniano, Ercinico e Alpino, in contesti variabili di pressione, temperatura e deformazione, il basamento cristallino delle Alpi Orientali costituisce da quasi un secolo la "palestra" per le ricerche petrologiche di numerosi ricercatori. Questo Review...