Caterina Gattuso* , Stefania Lanza, Giuseppe Panzera, Giuseppe Repaci, Giuseppe Sabatino and Maurizio Triscari "Caroselli": building elements typical of historic buildings in Calabria (southern Italy). Chemical-physical and mineralogical-petrographic characterisation and attribution of origin 19-34

ABSTRACT - Mineralogical and chemical analyses were performed in order to characterize the so-called "caroselli" a peculiar clay building material dating back to Byzantine period in Calabria (southern Italy). INAA and ICP chemical data, interpreted by means of cluster analyses and normalization were used, to recognize, amongst others, Ba, Cr, Cu, Ni, Pb, Rb, Sr, V, Zn and Zr, which may be usefully employed as discriminants. Petrographic observations identified the mineralogical composition of samples, showing that only specimens from Monterosso (Vibo Valentia area) can easily be distinguished from the others.
* Corresponding authors, E-mail: caterina.gattuso@unirc.it, maurizio@labcart.unime.it
[back]

Giulia Perini Sr-isotope and micro-isotope analyses of minerals: examples from some mafic alkaline potassic rocks

ABSTRACT - Evidence suggests that most silicic and mafic magmas evolve through open-system processes in which magma mixing and crustal contamination play an important role. In-situ Sr-isotope analyses help to decode the evolutionary history of silicic and mafic magmas that have been variously modified from their primary compositions. In-situ Sr isotope data on single minerals and separated bulk-minerals and rocks were acquired from two mafic alkaline potassic rocks erupted from the Pleistocene Vico volcano, central Italy. The rocks belong to high-potassium rock series (tephri-phonolite) and transitional series (olivine-latite). The higher ⁸⁷Sr/⁸⁶Sr of the clinopyroxene phenocrysts (⁸⁷Sr/⁸⁶Sr = 0.71093) with respect to sanidine core (⁸⁷Sr/⁸⁶Sr = 0.71063) enclosed in the tephri-phonolite may be explained by magma mixing between a less Sr radiogenic liquid (⁸⁷Sr/⁸⁶Sr ~0.7106), from which the sanidine megacryst crystallised, and a more radiogenic melt (⁸⁷Sr/⁸⁶Sr ~0.7109) from which the clinopyroxene crystallised. Before magma mixing the Sr isotope composition of the sanidine megacryst-bearing liquid changed, due to crustal contamination, as recorded by core-rim 87Sr/86Sr variation (⁸⁷Sr/⁸⁶Sr from 0.71063 to 0.71077). Magma mixing of more distinct radiogenic Sr end-members is also possible. The olivine-latite primitive magma (⁸⁷Sr/⁸⁶Sr ~0.7101) increased its Sr-isotope composition (⁸⁷Sr/⁸⁶Sr ~0.7103-0.7107) by crustal contamination and then decreased it by recharge with a similar Sr radiogenic mafic magma (87Sr/86Sr ~0.7101). This model accounts for the higher ⁸⁷Sr/⁸⁶Sr of the sanidine megacryst (⁸⁷Sr/⁸⁶Sr = 0.71067-0.71065) than the clinopyroxene (87Sr/86Sr = 0.71032) and for the less Sr radiogenic composition of the bulk rock (⁸⁷Sr/⁸⁶Sr = 0.71014). However, both sanidine megacrysts and clinopyroxene may have crystallised from different magmas, implying a further mixing event. The solid-liquid partition coefficient of Sr for sanidine suggests that the sanidine megacrysts crystallised from a mafic latitic melt. The similarity of Sr-isotope ratios in the cores of sanidine megacrysts (core ⁸⁷Sr/⁸⁶Sr in tephri-phonolite = 0.71063, core ⁸⁷Sr/⁸⁶Sr in olivine-latite = 0.71067) entrained in mafic and primitive potassic rocks belonging to distinct rock series suggests that they are co-genetic.
Present address: Museo Nacional de Ciencias Naturales, J.G.Abascal 2, 28006, Madrid, Spain.
E-mail: mcngp517@mncn.csic.es
[back]

Uwe Altenberger and Jörn H. Kruhl * Dry high-temperature shearing in the fossil Hercynian lower crust of Calabria (southern Italy)

ABSTRACT - In the Hercynian lower crust of Calabria, post-Hercynian shearing occurred during retrograde amphibolite to sub-greenschist facies conditions and was localised in mm to cm thick shear zones. With the aid of (i) petrological and microstructure-based thermobarometry, (ii) textural analyses, and (iii) infra-red spectroscopy, the timing, P-T conditions and kinematics of shearing are exemplified. (1) The general top-to-the-NW transport of the lower crustal section is reflected by the shear zone. (2) A period of annealing is bracketed by a stage of high-temperature and one of low-temperature shearing. (3) Even in ultramylonitic layers and in the greenschist facies, shearing occurred in dry conditions. (4) The shear zone was active for approximately 60 million years. (5) After the first formation of a shear zone, the concentration and continuation of movements was not necessarily governed by the infiltration of fluids but by the presence of a texturally weak zone. (6) Despite the general problems of exchange-reaction-based thermobarometry in shear zones, in specific cases - like the one presented here - reliable results may be obtained.
* Corresponding author, E-mail: Joern.Kruhl@geo.tum.de
[back]

Beatrice Moroni* and Giampiero Poli Provenance of materials employed in the construction of Orvieto Cathedral (Umbria, Italy)

ABSTRACT - A multivariate analytical approach was carried out in order to characterize travertine and "basaltina" which are the main building stones employed in the construction of Orvieto Cathedral. Results indicate the existence in the monument of three different lithotypes of "basaltina", "fine-grained", "coarse-grained" and "very fine-grained" distinguished on the basis of the size of leucite phenocrysts, and three distinct lithotypes of travertine, stromatolitic, phytohermal and detrital, distinguished on a textural basis. The multivariate approach was a powerful tool in checking historical sources on the provenance of the materials. Comparisons between samples from the Cathedral and homologous samples from ancient quarries and zones of excavation revealed a provenance from a quite narrow zone, between Orvieto and Bagnoregio, for all lithotypes. Comparisons, between homologous samples from different zones in the Cathedral shows that the areas of excavation of "basaltina" and travertine did not change with time.
* Corresponding author, E-mail: dottpetr@unipg.it
[back]

Francesco Morelli*, Robert Cullers*, Rocco Laviano* and Giovanni Mongelli* Geochemistry and palaeoenvironmental significance of Upper Cretaceous clay-rich beds from the Peri-Adriatic Apulia carbonate Platform, southern Italy

ABSTRACT - Clay-rich beds of Late Cretaceous age (from Cenomanian to Coniacian) interbedded with limestone in the Apulian Carbonate Platform, southern Italy, were analysed for mineralogy, major elements and trace elements. In addition, a number of size fractions of these beds were analysed for mineralogy and chemistry, including REE. Significant mineralogical and chemical differences were recognized between the beds. The Cenomanian unit is smectite-rich and shows high REE and high strength field element concentrations with a negative Eu/Eu* ratio (0.42), arguing for a fairly felsic source. The role of smectite in controlling most trace elements distribution is minor. The Turonian and Coniacian clay-rich beds are instead illite-rich and have flat REE patterns (normalized to the PAAS), higher Eu/Eu* ratios and lower REE and high strength field element concentrations. The control of illite on most trace elements distribution is also minor. During the Late Cretaceous the Apulian Carbonate Platform was sheltered from terrigeneous supply by deep troughs. Chemical indicators (i.e. Zr/Ti, (V+Ni+Cr)/Al₂O₃, Rb/K₂O), along with the absence of volcanic shards, lithic fragments and diagenetic minerals commonly associated with volcanically-derived clay beds, exclude a volcanic source for the clayey material. It is suggested that the clay-rich beds represent insoluble material, mostly wind-borne derived, from erosion of the exposed carbonate platform and deposited onto submerged portions of the platform itself. A calcareous breccia bed of Turonian age characterized by a kaolinite-rich reddish matrix was also studied. This bed formed in a warm and humid climate through dissolution of the platform limestone and accumulated on land. It is probably coeval with the karst bauxites of the Apulian Carbonate Platform and its composition has been used to test, in a binary mixing model, the parental relation of the karst bauxite. The (Eu/Eu*) and (Sm/Nd) values support a bauxite derivation from both intermediate composition pyroclastics and limestone residuum according, to the Late Cretaceous palaeotectonic restorations.
* Corresponding author, E-mail: f.morelli@geomin.uniba.it, rocco.laviano@geomin.uniba.it rcullers@ksu.edu mongelli@unibas.it
[back]

Giovanna Sapienza and Vittorio Scribano * Distribution and representative whole-rock chemistry of deep-seated xenoliths from the Iblean Plateau, south-eastern Sicily, Italy

ABSTRACT - Eighteen unpublished whole-rock chemical analyses on Iblean deep-seated xenoliths, combined with twenty-nine analyses reported in previous papers, form a data set representative of the various xenolith types as fixed by field and laboratory investigations lasting more than ten years. All Iblean xenoliths can be split into two main groups: ultramafic (UL) and feldspar-bearing (FB). The former, mostly representing the lithospheric mantle, consists of peridotites (UL-a) and various pyroxenites (UL-b-c-d). The peridotites exhibit a moderately refractory character, with some enrichment in LREE and other incompatible elements due to metasomatic event(s). The pyroxenites (spinel-websterites in most cases) derive from crystallisation and later sub-solidus re-equilibration of basic melts intruding the peridotites at different mantle depths. We distinguish Cr-rich and Al-poor pyroxenites (group UL-b, green) from those Cr-poor and Al-rich (groups UL-c, UL-d, black). Only the latter group keep their original igneous texture, but minor sub-solidus transformations occur. Garnet is found in some Al-rich pyroxenites, especially in those of group UL-d. The garnet, where modally abundant, controls the whole-rock distribution of some trace elements, especially REE. Fully recrystallized two-pyroxene granulites are the most common feldspar-bearing lithotypes (FB-e) together with minor cumulitic gabbros (group FB-f), variously recrystallized anorthosites (FB-g), rare metadiorites (FB-h) and plagioclase-websterites (FB-i). The representative whole-rock chemical compositions confirm such a division on a petrographic basis for most of the FB xenoliths. The chemical data set considered here, coupled with estimates of relative abundances of the various xenolith groups, may suggest the Iblean upper-mantle and inaccessible crust bulk compositions. The first exhibits a Primordial Mantle composition, due to the refertilizing effect of pyroxenites on the barren peridotites. Instead, the crust shows a roughly basaltic composition. Assuming that the Iblean xenoliths adequately represent all parts of the lithospheric column, which is probable for diatreme-related xenoliths, there is a marked absence of any felsitic upper crustal lithology. This fact may depend on (1) extreme lamination of a previous continental crust by rifting processes and concomitant magmatic intrusions and underplating, (2) severe erosion of the upper continental crust during an (unknown) period of exhumation, (3) the oceanic nature of the Iblean lithosphere.
* Corresponding author, E-mail: scribano@mbox.unict.it
[back]