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]