1,721,002 research outputs found
Potentially toxic elements in ultramafic rocks and soils: A case study from the Voltri Massif (NW Italy)
No full textHigh concentrations of potentially toxic elements (PTEs) in surface and near-surface environment may be attributed to both anthropogenic sources, including industrial and agricultural activity, and geogenic source, mainly due to natural weathering of rocks.
Considering the geogenic sources, ultramafic rocks (e.g., dunite, peridotite, pyroxenite, and serpentinites) are among the most critical from the environmental point of view; in fact, they are characterized by high contents of Cr, Ni, Co, and other PTEs which can have potential harmful impact on ecosystems and human health if released into soils and waters during weathering and pedogenic processes. As a matter of the fact, weathering of ultramafic rock produces ultramafic soil containing high concentration of PTEs, including Cr, Ni, and Co compared to soils derived from non-ultramafic bedrock.
Although ultramafic rocks and relative soils cover approximately 1% of the Earth’s surface, they are distributed worldwide and are commonly associated with ophiolite complexes; for this reason, they play an important role in environmental management.
The main objective of this PhD thesis was to determinate the mineralogy and the chemistry of PTEs of ultramafic soil profiles from the Voltri Massif and to evaluate how lithological, textural, and structural properties of the ultramafic bedrock with various degree of serpentinization and deformation may affect the PTEs re-distribution and the fate in the soils during pedogenesis, as well as to assess their environmental implications in the ecosystem.
The multidisciplinary and multiscale approach, used in this PhD thesis, has allowed to highlight a series of considerations that led to the following conclusions:
• In the studied rocks, Cr, Ni, and, subordinately, Co are invariably the PTEs with the highest concentrations; in addition, V, Cu, and Zn are generally found in high concentrations. The main factors controlling the PTEs distribution within the studied ultramafic rocks appeared to be the serpentinization degree and the deformation style and intensity. The main source of the PTEs are spinel-group minerals. Moreover, PTEs-bearing phases are also represented by the other rock-forming minerals (such as serpentines, olivines, pyroxenes, and chlorites) and some accessory phases (e.g., ilmenite and other oxides, sulfides).
• The studied ultramafic soil profiles vary in thickness from 35 to 80 cm and are characterized by weakly developed A and C horizons and a very thin O horizon (up to 5-10 cm). In general, in the soils the mineralogy of the skeleton (sandy and silty fractions) is closely related to bedrock mineralogy as expected for primitive A-C soils (in order of abundance: antigorite, chlorite, spinel-group minerals, pyroxenes, authigenic phases, quartz, olivine, and tremolite). The clay fraction is mainly composed by amorphous or low-crystalline Fe-oxyhydroxides, serpentines, smectite and illite/smectite mixed-layer clay, and clinochlore.
Cr and Ni values have very variable concentrations over a wide range. Cr and Ni decrease according to serpentinization degree of bedrock. Co, Zn, and Cu do not show a clear correlation with bedrock serpentinization. V increase with the serpentinization of the bedrock. The PTEs concentrations in the studied ultramafic soil profiles are linked both to the primary minerals, inherited by bedrocks (e.g., serpentines, spinel-group minerals, pyroxenes, chlorites), and to their stable authigenic products (Fe-oxyhydroxides and clay minerals). The PTEs leached from the primary minerals is mainly scavenge by goethite, and subordinate by clay.
• The results evidence that Cr, Ni, and, Co systematically exceed (up to one order of magnitude) the residential and industrial threshold values (CSC) according to Italian law (D.M. 471/1999; D.Lgs 152/2006) both in rocks and soils. However, combining all my results, I have demonstrated that the critical PTEs concentrations in the studied profiles have a geogenic origin and are linked both to the primary minerals, inherited by bedrocks, and to their stable authigenic products. Considering the high stability of authigenic products in supergenic environment, it is evident that this mineral species are effective and often permanent traps for the most important PTEs of ultramafic soils and bedrocks, thus reducing its bioavailability.
A study of this kind that combine the bulk chemistry of outcropping rocks and the relative soil profiles with their geological, structural, mineralogical, and crystallochemical data, can be also a useful tool in environmental concerns to determine the PTEs distribution, to evaluate their potential mobility and bioavailability as well as to discriminate the natural geochemical background from possible source of contamination
Lawsonite-bearing eclogite from a tectonic mélange in the Ligurian Alps: new constraints for the subduction plate-interface evolution
No full textLawsonite eclogites are rare rocks and have been described from only a few localities in the world. Lawsonite-bearing assemblages are highly unstable and physico-chemical processes linked to exhumation may destroy them; only aggregates interpreted as pseudomorphs after lawsonite could be often recognized. In this paper, we present a detailed structural and petrological study of an area in the northwestern sector of the metaophiolitic high-pressure Voltri Massif (Ligurian Western Alps, Italy). The study area is characterized by a lawsonite-bearing eclogitic metagabbro associated with carbonated serpentinites and glaucophanic metasediments. The metagabbro body reached eclogitic metamorphic peak conditions at T = 465–477 °C and P = 20.9–24.4 kbar, with H2 O continuously supplied to the system. H2O under-saturated conditions, with the occurrence of both lawsonite and epidote, characterized the exhumation path. Both the low temperature recorded by the body and the occurrence of variously carbonated serpentinites led us to interpret this area as a portion of the top of the subducted slab, coupled with a ‘cool’ mantle wedge, where both aqueous fluids and carbonate- rich fluids were present. The occurrence of rocks belonging to different paleogeographic domains (e.g. continent versus ocean) and the multiple deformations recorded by the metagabbro suggest that this area was nearby the slab–mantle interface. This sector was thus affected by a shear regime that acted in a low-viscosity serpentinite channel, bringing these high-pressure rocks back to the surface
Lawsonite-bearing eclogite from a tectonic mélange in the Ligurian Alps: new constraints for the subduction plate-interface evolution
No full textLawsonite eclogites are rare rocks and have been described from only a few localities in the world. Lawsonite-bearing assemblages are highly unstable and physico-chemical processes linked to exhumation may destroy them; only aggregates interpreted as pseudomorphs after lawsonite could be often recognized. In this paper, we present a detailed structural and petrological study of an area in the northwestern sector of the metaophiolitic high-pressure Voltri Massif (Ligurian Western Alps, Italy). The study area is characterized by a lawsonite-bearing eclogitic metagabbro associated with carbonated serpentinites and glaucophanic metasediments. The metagabbro body reached eclogitic metamorphic peak conditions at T = 465–477 °C and P = 20.9–24.4 kbar, with H2 O continuously supplied to the system. H2O under-saturated conditions, with the occurrence of both lawsonite and epidote, characterized the exhumation path. Both the low temperature recorded by the body and the occurrence of variously carbonated serpentinites led us to interpret this area as a portion of the top of the subducted slab, coupled with a ‘cool’ mantle wedge, where both aqueous fluids and carbonate- rich fluids were present. The occurrence of rocks belonging to different paleogeographic domains (e.g. continent versus ocean) and the multiple deformations recorded by the metagabbro suggest that this area was nearby the slab–mantle interface. This sector was thus affected by a shear regime that acted in a low-viscosity serpentinite channel, bringing these high-pressure rocks back to the surface
Cr, Ni, and other Potentially Toxic Elements (PTEs) in serpentine soils from different ophiolite complexes (Liguria, Italy)
No full textGeodynamic evolution of a subduction plate interface: constraints from the study of lawsonite-bearing eclogite in the mélange of the Voltri Massif (Ligurian Alps, Italy)
No full textLawsonite (lws) blueschists and eclogites are expected to be the prevailing lithotypes developing during deep subduction of the oceanic crust and should therefore be quite abundant in exhumed subduction complexes. Nevertheless, lws-bearing eclogites have been described only from few localities in the world. Moreover the occurrence of lws- bearing high-pressure metamorphic rocks, associated with eclogite facies rocks, could give important constraints on the coupling mechanisms between different tectonometamorphic slivers in subduction zones and on the interaction with fluids along the subducting slab.
Here we present the structural and petrological study of a lws-bearing eclogitic metagabbro, cropping out in the north-western sector of the metaophiolitic Voltri Massif (Ligurian western Alps, Italy).
The Voltri Massif occurs at the eastern end of the western Alps and in the study area is characterised by ocean-, continental- and mantle-derived slices of tectonometamorphic units, involved in the Alpine orogenesis.
The metagabbro body is a 20-m sized lens and shows a peculiar alternation of Na-amphibole-rich blue and Na- pyroxene-rich green layers, with a mylonitic texture. Both layers include isoclinal intrafoliar folds, which are the oldest recognizable deformation. The metagabbro was affected by a superimposed folding event, testified by isoclinal folds, deforming all the previous structures and causing the alternating green and blue banding. This body is in contact with glaucophane-bearing metasediment and both are interlayered with serpentine schists. Ophicalcites and serpentinites with a variable degree of carbonation (till their complete transformation into listvenites) also crop out in the area.
The thermodynamic modelling suggests that the metagabbro body reached metamorphic peak conditions at relatively low temperature (T = 465-477°C, P = 20.9-24.4 kbar), in a setting where H2O was continuously provided to a cold system. H2O under-saturated conditions, with the occurrence of both lawsonite and epidote, characterised the exhumation path.
The occurrence of carbonated serpentinites suggests that an intense and long-lasting circulation of CO2-rich fluids affected the area. Further evidence of this circulation comes from an adjoining outcrop (La Pesca locality) some hundreds meters far; we therefore compared the two areas to constrain the timing of CO2 fluid circulation and its role in the lawsonite preservation.
The metamorphic peak conditions recorded by the metagabbro body and the occurrence of variously carbonated serpentinites suggest that this area can be interpreted as a portion of the top of the subducted slab, coupled with a “cool” mantle wedge, where both H2O- and CO2-rich fluids were present; in particular we think that this area was nearby the slab-mantle interface. This sector was thus involved in a low viscosity serpentinite channel, where it was affected by a shear regime that brought these high-pressure rocks back to the surface
Trace metal distribution in spinels from ultramafic bedrocks with different degree of serpentinization: insight from the HP-LT Voltri Massif (Ligurian Alps)
No full textCr, Ni, and other Potentially Toxic Elements (PTEs) in serpentine soils from different ophiolite complexes (Liguria, Italy)
No full textTrace metal distribution in spinels from ultramafic bedrocks with different degree of serpentinization: insight from the HP-LT Voltri Massif (Ligurian Alps)
No full textWater quality and dissolved load in the Chirchik and Akhangaran river basins (Uzbekistan, Central Asia)
Full text linkUzbekistan (Central Asia) is experiencing serious water stress as a consequence of altered climate regime, past over-exploitation, and dependence from neighboring countries for water supply. The Chirchik-Akhangaran drainage basin, in the Tashkent province of Uzbekistan, includes watersheds from the Middle Tien Shan Mountains escarpments and the downstream floodplain of the Chirchik and Akhangaran rivers, major tributaries of the Syrdarya river. Water in the Chirchik-Akhangaran basin is facing potential anthropogenic pressure from different sources at the scale of river reaches, from both industrial and agricultural activities. In this study, the major and trace element chemistry of surface water and groundwater from the Chirchik-Akhangaran basin were investigated, with the aim of addressing the geogenic and anthropogenic contributions to the dissolved load. The results indicate that the geochemistry of water from the upstream catchments reflects the weathering of exposed lithologies. A significant increase in Na+, K+, SO42-, Cl-, and NO3- was observed downstream, indicating loadings from fertilizers used in croplands. However, quality parameters suggest that waters are generally suitable for irrigation purposes, even if the total dissolved solid indicates a possible salinity hazard. The concentration of trace elements (including potentially toxic elements) was lower than the thresholds set for water quality by different regulations. However, an exceedingly high concentration of Zn, Mo, Sb, Pb, Ni, U, As, and B compared with the average river water worldwide was observed. Water in a coal fly-ash large pond related to the Angren coal-fired power plants stands out for the high As, Al, B, Mo, and Sb concentration, having a groundwater contamination potential during infiltration. Spring waters used for drinking purposes meet the World Health Organization and the Republic of Uzbekistan quality standards. However, a surveillance of such drinking-water supplies is suggested. The obtained results are indicators for an improved water resource management
Geodynamic evolution of a subduction plate interface: constraints from the study of lawsonite-bearing eclogite in the mélange of the Voltri Massif (Ligurian Alps, Italy)
No full textLawsonite (lws) blueschists and eclogites are expected to be the prevailing lithotypes developing during deep subduction of the oceanic crust and should therefore be quite abundant in exhumed subduction complexes. Nevertheless, lws-bearing eclogites have been described only from few localities in the world. Moreover the occurrence of lws- bearing high-pressure metamorphic rocks, associated with eclogite facies rocks, could give important constraints on the coupling mechanisms between different tectonometamorphic slivers in subduction zones and on the interaction with fluids along the subducting slab.
Here we present the structural and petrological study of a lws-bearing eclogitic metagabbro, cropping out in the north-western sector of the metaophiolitic Voltri Massif (Ligurian western Alps, Italy).
The Voltri Massif occurs at the eastern end of the western Alps and in the study area is characterised by ocean-, continental- and mantle-derived slices of tectonometamorphic units, involved in the Alpine orogenesis.
The metagabbro body is a 20-m sized lens and shows a peculiar alternation of Na-amphibole-rich blue and Na- pyroxene-rich green layers, with a mylonitic texture. Both layers include isoclinal intrafoliar folds, which are the oldest recognizable deformation. The metagabbro was affected by a superimposed folding event, testified by isoclinal folds, deforming all the previous structures and causing the alternating green and blue banding. This body is in contact with glaucophane-bearing metasediment and both are interlayered with serpentine schists. Ophicalcites and serpentinites with a variable degree of carbonation (till their complete transformation into listvenites) also crop out in the area.
The thermodynamic modelling suggests that the metagabbro body reached metamorphic peak conditions at relatively low temperature (T = 465-477°C, P = 20.9-24.4 kbar), in a setting where H2O was continuously provided to a cold system. H2O under-saturated conditions, with the occurrence of both lawsonite and epidote, characterised the exhumation path.
The occurrence of carbonated serpentinites suggests that an intense and long-lasting circulation of CO2-rich fluids affected the area. Further evidence of this circulation comes from an adjoining outcrop (La Pesca locality) some hundreds meters far; we therefore compared the two areas to constrain the timing of CO2 fluid circulation and its role in the lawsonite preservation.
The metamorphic peak conditions recorded by the metagabbro body and the occurrence of variously carbonated serpentinites suggest that this area can be interpreted as a portion of the top of the subducted slab, coupled with a “cool” mantle wedge, where both H2O- and CO2-rich fluids were present; in particular we think that this area was nearby the slab-mantle interface. This sector was thus involved in a low viscosity serpentinite channel, where it was affected by a shear regime that brought these high-pressure rocks back to the surface
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