Search results for "petrography"

New mineral activity-composition relations for thermodynamic calculations in metapelitic systems

2014

New activity–composition (a–x) relations for minerals commonly occurring in metapelites are presented for use with the internally consistent thermodynamic dataset of Holland & Powell (2011, Journal of Metamorphic Geology, 29, 333–383). The a–x relations include a broader consideration of Fe2O3 in minerals, changes to the formalism of several phases and order–disorder in all ferromagnesian minerals where Fe–Mg mixing occurs on multiple sites. The a–x relations for chlorite, biotite, garnet, chloritoid, staurolite, cordierite, orthopyroxene, muscovite, paragonite and margarite have been substantially reparameterized using the approach outlined in the companion paper in this issue. For the fir…

Using calculated chemical potential relationships to account for replacement of kyanite by symplectite in high pressure granulites

2015

Calculated mineral equilibria are used to account for the formation of sapphirine-plagioclase, spinel-plagioclase and corundum-plagioclase symplectites replacing kyanite in quartz-plagioclase-garnet-kyanite granulite facies gneisses from the Southern Domain of the Athabasca granulite terrane, a segment of the Snowbird tectonic zone in northern Saskatchewan, Canada. Metamorphic conditions of >14 kbar and 800 °C are established for the high pressure, garnet-kyanite assemblage using constraints from P-T pseudosections and Zr-in-rutile thermometry. Replacement of kyanite by symplectites reflects the reaction of kyanite with the matrix following near-isothermal decompression to <10 kbar. The che…

A mineralogical-petrographic analysis of samples of Sicilian archeological earthen mortars

2011

Carthage's military installations of the First Punic War on Monte Pellegrino (Palermo)

2019

The excavation in the park of Villa Belmonte (Monte Pellegrino, Palermo) has brought to light several warehouses, made with a “pseudo-frame” technique, probably with a straw roof, used for the storage of foodstuffs, given the large quantity of Punic-type amphorae found in situ, datable to around the middle of the third century BC. In addition, a section of road - about 3 m wide that proceeds in the direction of WNW- ESE, consisting of two layers of use - has been intercepted. We believe to have tracked down part of a strategic/military station used by the Carthaginian army during the crucial years of the First Punic War.

The scientific instruments of the historical Mineralogical Museum of Palermo: testimonies of almost two centuries of mineralogical and petrographic s…

The scientific collections of the historic Museum of Mineralogy of Palermo are located on the second floor of via Archirafi 36 and are preserved by the Dipartimento di Scienze della Terra e del Mare (DiSTeM) of the University of Palermo. The historical edifice was designed by the architect Antonio Zanca and completed in the years 1933-1934. From the beginning, it has hosted the Institute of Physics at the ground and first floors, today entitled in honour of the famous physicians Emilio Segrè, and the Institute of Mineralogy at the second floor, which has kept one of the richest and ancient collections of Sicilian minerals. Today, the collections are partially exposed and are the subject of …

Direct synthesis of pure brannerite UTi2O6

2019

International audience; A new method based on the precipitation of uranium(IV) and titanium(IV) hydroxide precursors was developed to prepare pure brannerite UTi2O6 samples. In fact, U(IV) dissolved in HCl (6 mol L−1) was mixed to Ti (IV) alkoxyde before a basification step with an excess of NH4OH to obtain a highly reactive nanometric (U,Ti)(OH)4 powder. The obtained powder was then dried under vacuum, pressed into pellets and finally fired at 1300 °C. This method led to the formation of pure brannerite in contrast to previous reported protocols, which showed the formation of impurities such us UO2 and TiO2. The refined unit cell parameters of UTi2O6 led to a = 9.8113(2) Å, b = 3.7681(1) Å…

Territorial and socio-economic organisation in Le Grand-Pressigny

2012

In and around Le Grand-Pressigny (Indre-et-Loire, France), a petrographic study was implementedon 92 ceramic samples from the Final Neolithic sites of Le Petit-Paulmy and Bergeresse (Abilly).Analyses showed that the sediments used were extracted from local sources: Claise and Creusealluvium, local substrate and loessic silts. Quantitatively, the study showed that almost all the ceramicmaterials in Bergeresse and more than half of those in Le Petit-Paulmy come from the valley of theCreuse. The mineralogical compositions of three samples from Le Petit-Paulmy, including one ofunusual form, indicate sources from an exogenous region, the Massif Central (perhaps the alluviumof the Loire or the Al…

Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks: Rationale and Implications

2005

RECEIVED JULY 16, 2004; ACCEPTED MARCH 16, 2005ADVANCE ACCESS PUBLICATION APRIL 29, 2005We introduce a modification to the current IUGS classificationsystem for igneous rocks to include ultramafic lamprophyres, whicharecurrentlyentirelyomitted.Thisisdonebyincludinganewstepinthe sequential system, after the assignment of pyroclastic rocks andcarbonatites, that considers ultramafic inequigranular textured rockswith olivine and phlogopite macrocrysts and/or phenocrysts. At thisstepultramaficlamprophyresareconsideredtogetherwithkimberlites,orangeites (former Group 2 kimberlites) and olivine lamproites.This proposal allows the correct identification and classificationof ultramafic lamprophyres w…

Volcanological evolution of Pantelleria Island (Strait of Sicily) peralkaline volcano: a review

2022

International audience; Pantelleria volcano has a particularly intriguing evolutionary history intimately related to the peralkaline composition of its explosively erupted magmas. Due to the stratigraphic complexity, studies over the last two decades have explored either only the pre-Green Tuff ignimbrite volcanism or the post-Green Tuff activity. We here focus on the whole evolutionary history, detailing the achievements since the first pioneering studies, in order to illustrate how the adoption and integration of progressively more accurate methods (40 Ar/ 39 Ar, paleomagnetism, petrography, and detailed field study) have provided many important independent answers to unresolved questions…

Evidence from Antarctic mantle peridotite xenoliths for changes in mineralogy, geochemistry and geothermal gradients beneath a developing rift

2006

Abstract Garnet and spinel peridotite xenoliths associated with the Phanerozoic Lambert–Amery Rift in eastern Antarctica contain evidence for several stages in the development of the mantle beneath the rift. Despite the fact that equilibria were only partly attained, a combination of petrography, whole-rock geochemistry, mineral chemistry and thermobarometry can be used to decipher four stages prior to entrainment of the xenoliths in the host magma during the initial stages of the breakup of Antarctica, India and Madagascar. The first chronological stage is represented by harzburgitic protoliths represented by rare occurrences of low-Ca olivines and orthopyroxenes in spinel lherzolites: the…