Northwestern Italian Alps Research Articles

Biodemographic and molecular analysis of an isolated Alpine population (Postua)

Isolated populations have been the object of several genetic and anthropological studies, since endogamy and inbreeding often lead to the acquisition of a particular gene pool. In this context, we studied the small, ancient population of Postua in the north-western Italian Alps. We used biodemographic and molecular techniques to analyse the population structure in order to evaluate the relationship between geographical and genetic isolation. We examined about 26,000 certificates kept in the town and parish archives, concerning the period from 1640 to 1999. High rates of endogamy and isonymy, short marriage distances and a low ratio between the number of surnames and the number of individuals were inferred. In the molecular analysis, we compared the distribution of Y chromosome SNPs (single nucleotide polymorphisms) with those of mitochondrial variations and Y chromosomal microsatellites (short tandem repeat polymorphisms) in 102 healthy individuals originating from Postua. A control sample (94 individuals) was collected from a plain area, 50 km away. We examined 23 SNPs and an Alu repeat, located in the nonrecombinant portion of the Y chromosome. To further delineate Y chromosome lineages, the biallelic haplogroups were further resolved using Y microsatellite markers (DYS19, DYS391, DYS392, DYS393). Mitochondrial HVS-I and HVS-II regions were sequenced, and RFLP screening with the six classical enzymes was performed. Postua is similar to other populations living in northern Italy, but it shows a lower number of haplotypes. The samples were compared with other European populations. We calculated genetic distances according to Reynold and Nei and we carried out a phylogenetic analysis by phylogenetic trees and reduced median networks construction. Postua clusters with other samples from northern Italy but in a separate position, probably indicating drift phenomena. These relationships are supported by AMOVA (analysis of molecular variance). Our results suggest that the influence of neighbouring populations on the gene pool of Postua has been very low through both females and males.

Brittle post-metamorphic tectonics in the Gran Paradiso Massif (north-western Italian Alps)

New geological mapping (1:10.000 scale) and structural analysis in the Orco valley (NW Italian Alps), give insights on the post-metamorphic brittle tectonic evolution of the Gran Paradiso Unit and adjoining Piemonte Ophiolitic Unit and Sesia-Lanzo Unit. According to existing geochronological data, the metamorphic evolution of the studied domain ended in Early Oligocene and was followed by a progressive exhumation during Neogene. This work describes the brittle fault network developed during the post-metamorphic tectonic stages coeval to exhumation. The geometry and kinematics of this fault network allow to interpret the study area as a part of a larger lowstrain, fault-bounded block, whose main bordering discontinuities are located outside the mapped region. The post-metamorphic kinematic evolution was characterised by: (a) ESE-WNW extension, attested by NNE-SSW normal faults and extensional joints; (b) dextral shearing along a major E-W shear zone (Orco shear zone). The individual faults of the studied area are considered as P- or R-shears of the Orco shear zone, which could be in turn a part of a larger NE-SW regional shear zone bounded to the N by the Chamonix-Rhône- Simplon Line.

Past and present circulation of CO2-bearing fluids in the crystalline Gran Paradiso Massif (Orco Valley, north-western Italian Alps): tectonic and geochemical constraints

In the Orco Valley, inside the Gran Paradiso Massif, 3 main fault systems are present: (a) E–W striking faults dipping at 45–60° to the N, (b) high-angle NW–SE striking faults, and (c) high-angle NE–SW to NNE–SSW striking faults. The E–W striking faults and the interposed NW–SE-faults appear to represent a cogenetic structural association related to a larger scale transtensional shear zone, while the NE–SW faults are probably inherited by an older discontinuous deformation stage. Breccia bodies or veins, mostly consisting of carbonate (siderite–ankerite±calcite)+quartz with sulphide–Au mineralisation, recording a multistage mesothermal evolution, occur along both E–W and NW–SE fault systems. Three water types are recognised: type I, Ca2+–HCO3− waters, with minor SO42−; type II, (Ca2+/Na+)–HCO3− waters varying towards Na+–(HCO3−/Cl−) waters; and type III, Mg2+–HCO3− waters. Type I and type III groundwaters are freshly recharged waters, only slightly exchanged with rocks. Type II includes waters which come into contact with carbonate fracture fillings, and geochemical modelling indicates that dissolution of carbonates along fractures is the main process controlling the groundwater chemistry. These waters evolve in a system open to uprising CO2, and their strongly negative δ13CCO2 suggests a substantial organic component in the CO2 discharge. In the past, CO2-bearing fluids were likely responsible for the formation of Fe-bearing carbonate fracture fillings. The persistence through time of the CO2 flux in the region has important implications for the reconstruction of the Alpine tectonic evolution and deep structure.

The October 2000 flooding in Valle d'Aosta (Italy): Event description and land planning measures for the risk mitigation

On October 13–16th, 2000 heavy rainfalls in the Northwestern Italian Alps caused huge flooding and landslides with significant damages to houses and infrastructures and several life losses. In this paper a description of the main events that affected Valle d'Aosta's region and the subsequent land planning measures adopted for the risk mitigation are presented. After a first meteorological and hydrological framing, based on the data of the regional monitoring system (that pointed out rainfalls up to 236 mm in 24 h also in high‐altitude zones, because of the rise of the isotherm 0°C around 3000 m above sea level), the main effects of the event (extensive flooding, landslides, soil slips and debris flows) in the regional catchment of the Dora Baltea river are described. Through aerial and direct surveys those effects have been transferred into a thematic cartography within two months from the event, in order to have detailed elements for the technical, administrative and political land planning decisions, and, on this basis, a new regional directive containing detailed measures for the hydro‐geological risk mitigation and land safety has been adopted.

Quantifying fractured rock hydraulic heterogeneity and groundwater inflow prediction in underground excavations: the heterogeneity index

This paper presents an approach to quantify the degree of heterogeneity of a fracture network starting from the information that is collected for a geomechanical classification of rock masses. Six synthetic experiments have been used to prove the existence of a correspondence between the variability in fracture properties and in the direction and magnitude of flow. Statistical analyses conducted using fracture data collected at a tunnel crossing the north-western Italian Alps have also shown that variability in fracture characteristics is indeed related to the magnitude of inflows. These findings have proved that it is reasonable to estimate the degree of heterogeneity of a fracture network by combining the variance of those fracture characteristics that regulate both flow and the geomechanical behavior of a rock mass. An index comprising a combination of variances of fracture parameters at different scales is presented. Its dependence on scale showed that the heterogeneity of fractured rock increases with scale up to a certain scale and then gradually decreases at large scales.

Nicht-territoriale Systeme bei Corviden: das Beispiel des Tannenhähers (Nucifraga caryocatactes) in den Alpen

The Nutcracker is considered a territorial species even though some studies have shown that conflicts are rare. Previous research suggested that Nutcrackers from two Alpine sites did not use territories during autumn and winter. The aim of the present study was to describe the Nutcracker’s spacing system during the reproductive period to provide a general interpretation of its spacing ecology. The study was carried out from March to May in the Aleve forest (north-western Italian Alps) with radio-tracking and bird census techniques. Vocal activity was recorded throughout the year to make possible a better interpretation of the census results; recorded calls were also used for experimental play-back tests in the field. Home ranges were very small (median value of 22 ha, minimum convex polygon 95 %) and overlapped to a great extent (72 %, on average). No territorial confrontation was detected. Strangers were usually tolerated near the nest and a few experimental playback tests elicited no significant interaction initiatives. Present data indicate that the Nutcracker cannot be considered territorial, at least in our study area. We believe the spacing pattern of this species can be explained, at least partially, by its storing habit. In typical territorial systems, food resources are threatened by neighbours or strangers. In the Nutcracker’s spring spacing system, food stores are not threatened because their location is known only to the owner. Thus, border trespassing is tolerated because strangers or neighbours are not food competitors. Estimates of Nutcracker density varied significantly among months, habitats and years. Arolla pine forests were preferred over the other habitats, probably because of autumn seed availability there. Vocal activity, which was weather-dependent, significantly changed among periods. Seasonal variations in vocal activity suggest caution when densities are compared among different periods.

Do topographical constraints and space availability influence birds’ ranging behaviour ? The Alpine Chough (Pyrrhocorax graculus) as a study case

Summer home ranges and movements of Alpine Choughs Pyrrhocorax graculus radiotracked in a large Alpine top valley (Cervinia, Valtoumanche, northwestern Italian Alps) were compared with those radiotracked in a small Alpine top valley (Palanfrè, Val Grande, southwestern Italian Alps). Birds never flew beyond the mountain ridges delimiting the two areas. On average, home ranges at Cervinia were ten times as large as those at Palanfrè ; however, ratios between the extent of individual home ranges (MPC 100 %) and the area potentially available to birds were not significantly different in the two areas. Bird locations were rather scattered at Cervinia, whereas they were concentrated in a few cells at Palanfrè. The proportion of fixes spent at pastures and cliffs was lower at Cervinia than at Palanfrè. Finally, birds changed cells more often and flew for a longer distance at Cervinia than at Palanfrè. These results suggest that spatial structures of the landscape such as topographical constraints (high mountain ridges) and the extent of the area available to birds significantly affect movements and home ranges of the Alpine Chough. Movements also depend on mutual location of foraging and nesting sites and on typical ecological factors such as food availability and distribution. Therefore, we conclude that the summer ranging behaviour of the Alpine Chough is affected both by local topographical and ecological factors.

First Report of Heterobasidion annosum on Native European Pinus cembra.

Heterobasidion annosum (Fr.:Fr.) Bref. is one of the most widespread and damaging root and butt rot agents on conifers. In the summer of 1998, H. annosum was observed for the first time on the Swiss Stone Pine (Pinus cembra L.) in its natural range (1) at 1,900 m in the Aosta Valley in the northwestern Italian Alps. The affected tree was 14 m tall and about 60 years old. It was growing in a mixed spruce (Picea) and larch (Larix) forest severely affected by H. annosum. There were no clear crown symptoms but, after felling, an extensive butt rot was noticed up to 4 m from the collar. The pathogen was isolated from a disk cut at a height of about 40 cm. Its anamorphic form (Spiniger meineckellum (A. Olson) Stalpers) developed on this disk after 8 days of incubation at 20°C. H. annosum was also isolated from the central cylinder of the tree's primary roots and on the other roots down to a diameter of 0.5 cm. Sexual mating tests with single-spore testers for the P, S, and F intersterile groups (ISGs) showed that the isolate belonged to S-ISG. Biomolecular tests on this strain are in progress to confirm this. Reference: (1) T. G. Tutin et al. 1993. Flora Europaea. Cambridge University Press, Cambridge.

Seasonal variations in lipids of Xanthoria parietina growing at high elevations

Seasonal variations (from spring to winter) in the total lipid content, polar, non-polar and neutral lipids were detected in Xanthoria parietina growing naturally at high elevation in the northwestern Italian Alps (Piedmont). Various lipid classes were separated and the corresponding fatty acid methyl esters were analysed by GC-MS. The results obtained confirmed a clear response of the lipid metabolism of X. parietina growing at high elevations to changing seasonal environmental factors. They also indicated a typical increase in total lipid content from spring to winter and a direct relationship between the degree of fatty acid unsaturation and high temperature and precipitation levels.

Chemotaxonomy ofJuniperus communis, J. sibiricaandJ. intermedia

ABSTRACT The oil chemical composition was studied in several populations of Juniperus communis, J. sibirica (J. nana sensu Pignatti) and J. intermedia growing spontaneously in the northwestern Italian Alps. The oil of J. communis was characterized by high percentages of sabinene (32% to 47%) and low values of α-pinene (9% to 22%), whereas J. sibirica showed opposite values (respectively 0.3% to 25% and 9% to 46%). The oil chemical composition of J. intermedia showed intermediate values for both sabinene (28%) and α-pinene (20%) when compared to the other two taxa. The data obtained from GC/MS analyses of the oils were used to study the chemotaxonomic characters of the three taxa. Chemometrics included multivariate statistical analyses such as Principal Component Analysis (PCA), Cluster Analysis (CA) and Discriminant Analysis (DA). The results of this investigation indicated that most of the populations considered as J. intermedia showed a statistically significant different oil composition when compared t...

Late Alpine kinematics of the Aosta fault (northwestern Italian Alps)

Late Alpine kinematics of the Aosta fault (northwestern Italian Alps)

Cation ratios of fluid inclusions in a gold-quartz vein at Brusson, Val d'Ayas, northwestern Italian Alps: Comparison of bulk crush-leach results with SIMS analyses of individual inclusions

This study tests the widely made assumption that, with favourable fluid inclusion samples, bulk crush-leach analyses accurately reflect the electrolyte compositions of individual fluid inclusions. Secondary-ion mass spectrometric (SIMS) analyses of individual inclusions, calibrated by synthetic fluid inclusion standards, are compared to crush-leach analyses of the same natural quartz sample. Quartz from the Bechaz mesothermal Au vein at Brusson, northwestern Italian Alps, is dominated by fluid inclusions of uniform, low-salinity, low- X CO 2 composition. These inclusions represent the liquid phase of an originally immiscible hydrothermal system, whereas much rarer high- X CO 2 inclusions, of even lower salinity, represent the conjugate vapour phase. SIMS analyses of the low- X CO 2 inclusions yield mean molar K N = 0.050 and Ca Na = 0.016 . These results are identical, well within experimental uncertainty, to replicate crush-leach analyses made in two different laboratories. The excellent agreement between the SIMS and crush-leach results confirms the accuracy of both analytical methods. Despite the low salinity of the Bechaz fluid inclusions, and the rare muscovite and dolomite impurities in the host quartz, the crush-leach analyses are both highly precise and accurate. Furthermore, the agreement between methods demonstrates that SIMS analyses of natural, multi-component fluid inclusions may be reliably calibrated by synthetic inclusions with simple compositions. A SIMS analysis of a high- X CO 2 “vapour” inclusion yields K/Na and Ca/Na ratios that are not significantly different from those of the coexisting, low- X CO 2 inclusions. This suggests that, under the P- T conditions of immiscibility in the Bechaz vein (∼ 230°C and 600 bar), liquid-vapour fractionation of K and Ca, relative to Na, was only very slight.

Lead and oxygen isotope evidence for the origin of the Monte Rosa gold lode deposits (Western Alps, Italy); a comparison with Archean lode deposits

In the Monte Rosa area of the northwestern Italian Alps swarms of epigenetic, quartz sulfide gold-bearing veins occur within a terrane affected by Tertiary regional metamorphism of greenschist to amphibolite grade. They are preferentially associated with the felsic rocks of the upper Penninic nappes. Field evidence and available geochronologic data imply emplacement ages postdating the metamorphic peak (38 + or - 2 m.y.). The spatial distribution of the veins is related to late metamorphic large-scale tectonic disturbances, which displace, truncate, or fold the isograds.Lead isotope analyses of galenas and other sulfides were compared with those of feldspars, clinozoisites, and whole rocks from various unaltered host rocks. The data suggest derivation of the ore lead from Caledonian metapelites, with a possible contribution from Hercynian granitoids, but they rule out significant contributions from the neighboring ophiolitic greenstones and associated stratiform massive sulfide deposits. The separation of the ore leads into two distinct data fields is probably the result of ore deposition from at least two hydrothermal systems, which were separated in space and possibly also in time. The hypothesis of two distinct mineralization ages is also supported by geochronologic data.Oxygen isotope data indicate that the ore fluids had isotopic compositions consistent with a metamorphic origin, with the notable exception of the Val Toppa mine, where lighter, possibly surface-derived water was involved. Oxygen isotope fractionations between mineral pairs in metasediments and granites indicate metamorphic peak temperatures of 530 degrees to 605 degrees C, in agreement with those inferred from petrologic evidence. These temperatures and preliminary fluid inclusion data were used to predict oxygen isotope compositions of gangue quartz. The comparison of predicted with measured delta 18 O values shows consistency with the assumption that the fluids were generated by metamorphic devolatilization within the metapelites and granitoids, in agreement with the lead isotope data.The results suggest that the gold-bearing fluids and the lead were supplied by rocks derived from the continental crust, in opposition to the data from many greenstone-hosted Archean gold lode deposits, which indicate a mantle source. This implies that metamorphic-hosted quartz-gold lodes do not necessarily derive metals and fluids from source beds within a greenstone sequence. Therefore, the assumption that the Archean gold was derived from greenstones should be checked by isotope tracing studies. The common lead method appears to be particularly promising in distinguishing greenstone metamorphic from granitic sources in Precambrian terranes, in view of the contrasting U/Pb ratios usually stated in these lithologies.