Giampiero Venturelli

Crustal anatexis and melt extraction during deformation in the restitic xenoliths at El Joyazo (SE Spain)

Abstract The dacite of El Joyazo contains abundant metapelitic xenoliths. These can be divided into two main types: garnet-biotite-sillimanite and spinel-cordierite xenoliths. In the xenoliths the widespread occurrence of rhyolitic glass as interstitial films, foliation-parallel layers and primary melt inclusions in all mineral phases indicates that these assemblages developed in the presence of a melt phase, i.e. during anatexis. The composition of the interstitial glass is comparable to that of the melt inclusions, suggesting that melt was locally produced. Phase equilibria indicate that anatexis occurred at P−T conditions of 5−7 kbar and 850±50°C . Several microstructural lines of evidence show that melt extraction was assisted by deformation during foliation development, and that on the scale of the xenoliths (up to 50 cm) melt escaped mainly by flow along foliation planes. The development of a syn-anatectic foliation also suggests that metapelitic rocks were involved in high-grade metamorphism and partial melting prior to fragmentation and dispersion in the host dacite. Mass balance calculations, based on the chemical composition of interstitial glass and melt inclusions in minerals, the bulk xenoliths and representative samples of potential pelitic sources support a model wherein the xenoliths represent restites after the extraction of 30 to 55 wt.% melt from graphitic metapelite protoliths similar to the rocks constituting the surrounding Alpujarride metamorphic complex.

Petrology of melilite-bearing rocks from the Montefiascone Volcanic Complex (Roman Magmatic Province): new insights into the ultrapotassic volcanism of Central Italy

Abstract The products of Montefiascone Volcanic Complex (MVC) encompass one of the most distinct association of potassic to ultrapotassic rocks of the Roman Magmatic Province (RMP), ranging in composition from trachybasalts to tephritic leucitites. New discovery of leucite melilitites, occurring as small lava flows, and of kalsilite–melilite pyroclastic ejecta, further expand the compositional range of the MVC products towards the extreme ultrapotassic compositions of the nearby Umbria-Latium Intra Apenninic Volcanism (IAV). Both lavas and ejecta are characterized by strong LILE and Th enrichments coupled with HFSE depletion, very radiogenic 87 Sr/ 86 Sr (0.7104–0.7106) and unradiogenic 143 Nd/ 144 Nd (0.51209–0.51213). Mineral and whole-rock chemistry indicate that the leucite melilites are transitional between ultrapotassic larnite-free, Roman-type magmas and kamafugites, whereas the ejecta (kalsilite melilitolites and clinopyroxene–kalsilite melilitolites) can be considered as intrusive kamafugites. Significant interactions with country rocks (mainly limestones and marls) have been excluded on the basis of trace elements and Sr–Nd isotopes, showing that low SiO 2 , high (Ca+Na+K)/Al ratios and relatively high CO 2 contents (leading to crystallization of interstitial carbonates in both lavas and ejecta), are primary features of the melts which yielded the melilites and melilite-bearing ejecta. Petrogenesis of the whole range of MVC products is related to melting in the deepest part of a thinned lithosphere characterized by carbonate-bearing phlogopite–clinopyroxene veins with highly radiogenic 87 Sr/ 86 Sr and unradiogenic 143 Nd/ 144 Nd; progressive dilution of a vein-derived, K-rich (kamafugitic) end-member by a basaltic melt originated from a relatively depleted mantle would be able to explain the entire compositional range of MVC magmas. The common geochemical and isotopic signatures of MVC and IAV volcanics suggest that the same petrogenetic processes were simultaneously active in both regions, involving similar mantle domains metasomatized by carbonate–silicate or carbonatitic melts.

WEATHERING OF ULTRAMAFIC ROCKS AND ELEMENT MOBILITY AT MT. PRINZERA, NORTHERN APENNINES, ITALY

Abstract The weathering of the Mt. Prinzera serpentinites (Parma province, Northern Apennines, Italy) produced dominant smectite and minor Fe-hydroxides. The mobility of the elements during weathering has been estimated using the ratio Ki = MSi/MRi, where Mi indicates the mass of a generic component i before (R) and after (S) the weathering, and using TiO2 as a practically immobile component. For prevalently to tendentially mobile elements, the degree of mobility, which in our case increases as Ki decreases, is in the order Mn ≈ Cr = Fe < V ≈ Zn ≈ Co < Ni < Si < Mg < Ca. The elements Ti, Ga, Al and Zr are prevalently immobile. The mass chemically removed by the circulating waters during weathering may reach very high values (on average 52% of the original mass of serpentinite) and the main contribution to the mass loss is due to Si and Mg. The composition of the perennial and ephemeral springs in the area is in agreement with the degree of the element mobility at least for Cr, Mg and Ca.

Sulphide-bearing waters in Northern Apennines, Italy : general features and water rock interaction

Sulphide-bearing Ca-carbonate, Na-carbonate, Na-hydroxide, Na-chloride and Ca-sulphate waters from Northern Apennines were investigated in order to determine their main chemical and isotopic composition and draw inferences on water-rock interaction. δ2H and δ18O values suggest an origin mostly meteoric for the analysed waters but a well drilled in Miocenic sediments. The Na-carbonate and the Ca-sulphate waters are the most interesting geochemically. Na-carbonate type, which sometimes reaches extreme composition (Na/Ca up to 228, equivalent ratio), may have been derived through prolonged interaction of Ca-carbonate waters with rocks containing feldspar, montmorillonite and illite under calcite saturation/oversaturation; the high F and pH and the very low PCO2 agree with prograde dissolution of silicates and lasting water-rock interaction. However, Ca–Na ion exchange, involving clays of marine origin, cannot be excluded in addition. The Ca-sulphate waters, occurring in Messinian gypsum-bearing sediments, are saturated in gypsum and calcite and exhibit very high total H2S (up to 219 mg dm-3) and PCO2 (up to 0.32 bar). Mass balance of sulphate sulphur, sulphide sulphur and delta34S suggests sulphate – derived from gypsum – as source for H2S; CH4 and organic matter generate the reducing conditions and sulphate reduction is mediated by bacteria. One Na-chloride water from a well in Miocenic sediments has unusual composition, containing about 700 mgdm-3 of potential CaCl2 and having δ2H and δ18O (-47.5 and -4.9‰ respectively) which plot far from the meteoric water lines; probably it is derived by mixing of meteoric and formation waters. The Na-hydroxide water, with very high pH (11.2), is generated through protracted interaction of meteoric waters with ultramafites.

Stable isotope study on ancient populations of central sudan: Insights on their diet and environment

OBJECTIVES A contribution to the knowledge of the economy and the environmental surroundings of the populations living along the Nile valley in three different periods. MATERIALS AND METHODS This study reports stable isotope analyses on apatite bone samples of 139 humans, 48 mammals, and 43 fish from the Al Khiday archaeological sites in Sudan. The bones belong to four archaeological periods: pre-Mesolithic, Mesolithic, Neolithic, and Meroitic. Data were processed statistically. RESULTS A significant difference exists between the pre-Mesolithic and Mesolithic mean δ(18) Ow value and the mean of the modern Nile. The mean δ(18) Ow values for the Neolithic humans and bovids are very similar (+1.5‰ ±4‰, and -2‰, respectively) and more positive than the mean values of Mesolithic mammals and Pre-Mesolithic humans. The water ingested by Meroitic humans (+7‰ ± 2.5‰) is enriched in (18) O in respect to the water ingested by the Neolithic population. There is a separation in the δ(13) Cdiet values between the pre-Mesolithic humans (-14‰ ± 1‰) and Mesolithic mammals (-12‰ ± 2‰) group and the Neolithic humans (-18‰ ± 1‰), Meroitic humans (-19‰ ±1‰), Neolithic mammals (-21‰), and the modern (mean δ(13) Cdiet  = -19‰ ±2‰) mammal group. DISCUSSION The climate became warmer and more arid from the pre-Mesolithic/Mesolithic to the Meroitic period. The environmental conditions influenced the strategies of subsistence and, in particular, the changes occurring from the pre-Mesolithic to the Neolithic can be considered contemporaneous to the transition from hunting-gathering-fishing to cultivation-herding. Am J Phys Anthropol 160:498-518, 2016.

Characterisation and provenance of stones used in the mosaics of the domus dei Coiedii at Roman Suasa (Ancona, Italy)

Abstract The mosaics covering the floors of the rooms of the domus dei Coiedii at Suasa (Ancona, Italy) may be dated archaeologically and artistically between the late republican-Augustan age (end of the first century B.C.-beginning of first century A.D.) and the second century A.D.-first half of third century A.D. The floors were made mostly in opus tessellatum , only one in opus sectile . Tesserae used in opus tessellatum are made mainly of local stones, belonging to the so-called Umbro-Marchigiana Sedimentary Sequence: the white to pinkish and reddish tesserae consist prevalently of limestones belonging to the ‘Scaglia Rosata’ Formation (Late Turonian-Middle Eocene), and subordinately to the ‘Calcare Massiccio del Burano’, which is part of the ‘Calcare Massiccio s.l.’ Formation (Late Triassic-Early Lias). Most dark to black tesserae are composed of not fossiliferous marls and marly clays, which probably derive from the local ‘Marne a Fucoidi’ Formation; a number of them are made of very fine grained sandstones, which are found as pebbles in the alluvial sediments of the Cesano river close to Suasa, and, some, of aphyric leucite-bearing basanites from the potassic Quaternary magmatic province of central-southern Italy. Artificial glasses (red and green, rich in Pb and low in Sb; light blue, low in Pb and high in Sb), containing microliths of Pb-rich phase(s) and of wollastonite, were also used in some floors. The stones used in opus sectile are (1) sedimentary: nodular limestones belonging to the ‘Rosso Ammonitico’, which occurs in the Umbro-Marchigiana Sedimentary Succession; black marls and marly clays similar to those used in opus tessellatum ; onyx marble; (2) magmatic: porphyrites (‘porfido verde antico’) and gabbros (ophite); (3) marbles: different kinds of coloured marbles, comprising ‘marmo cipollino’, ‘rosso antico’, ‘pavonazzetto’, ‘portasanta’, ‘giallo antico’, ‘bigio antico’, ‘brecce coralline’. White marbles from Marmara and Carrara were also employed.

Post-magmatic apatite + hematite + carbonate assemblage in the Jumilla lamproites. A fluid inclusion and isotope study

Abstract The lamproitic rocks of Jumilla (southeastern Spain) consist of magnesian olivine, phlogopite, clinopyroxene, F-apatite, sanidine and analcime in variable amounts, and of Cr-rich spinel (mostly included in olivine and clinopyroxene), K-rich amphibole, Ti-magnetite, ilmenite and late calcite. In a small area, a post-magmatic apatite + hematite + carbonate assemblage occurs in the form of thin veins. F-apatite, hematite and calcite are the dominant phases. Apatite is rich in several generations of fluid (sensu lato) inclusions. The prevalent primary inclusions are filled in part with a solidified saline melt and in part with a very low density gas; the solid/gas volume ratio in the inclusions is not constant suggesting that, at the time of entrapment in apatite, a vapour phase was coexisting with the saline melt. The final melting temperature of the solids contained in the inclusions is mostly in the range 630–700°C, which represents the minimum temperature of entrapment. Other inclusions are concentrated along healed fractures. Some of them are similar to the solid salt inclusions described above, but most of them contain liquid, vapour and, sometimes, abundant daughter minerals. The temperature of initial melting of frozen liquid-bearing inclusions is variable (ca. −54°C, −35/−39°C, ca. −11°C, ca. −2/−3°C) suggesting that aqueous fluids carrying different components were entrapped at different times. The strontium isotope ratios and the high content of fluorine and REE suggest that apatite crystallized from fluids prevalently segregated from the lamproitic magma. Strontium as well as oxygen and carbon isotopes of the carbonates associated with apatite suggest that the parent fluids were poligenic (magmatic and sedimentary components) or of prevalent sedimentary provenance.

Weathering of granodiorite and micaschists, and soil pollution at Mt. Mottarone (northern Italy)

Abstract At the top of Mt. Mottarone a thin level of micaschist, covered by soil, rests on granodioritic rocks. Both rock types underwent weathering with generation of new minerals and variation of the original chemical composition. The weathering produced phyllosilicates and Fe- and Al-hydroxides. Mass balance calculations on the basis of Zr immobility indicate that at least As, Bi, Cd, Mo and Sb were added to the micaschist, whereas the other elements were removed; the soil was also enriched in As, Bi, Cd, Mo and Sb during weathering. Dry and wet pollution was responsible for the addition of the elements listed above. On the other hand, Ca, Na, Mo and Sr were surely removed from the granodiorite during weathering, whereas Bi and Cu were added by percolation from the overlying micaschist. The chemical features of a spring issuing from granodiorite agree well with the element budget as deduced from the rock transformation. This is not the case, however, for a spring issuing from the micaschist.