1,721,025 research outputs found
Subduction-related(?) ophiolitic metabasalts from Northern Apennines (Modena province, Italy)
No full textSprings and streams of the Taro–Ceno Valley(Northern Apennine, Italy): Reaction path modeling of waters interacting with serpentinized ultramafic rocks
No full textIn the area of the Taro–Ceno Valleys (Northern Apennine, Emilia-Romagna region, Italy), waters of meteoric origin interact with ophiolite rocks of the External Ligurides. Fresh water springs issuing from basalts have a Ca–HCO3 composition, whereas freshwater springs from ultramafites vary in composition from Ca–HCO3 or Mg–HCO3 to Na–OH or Na–SO4 types and in pH values from 7.3–8.8 up to pH 11, respectively. In addition, the
boron content of the alkaline waters is up to 13 mg/L, which is unusually high for freshwaters in general and ultramafites that have undergone oceanic serpentinisation in particular and gives a boric alkalinity to the waters. The springs waters show evidence of recent low-temperature continental serpentinisation and the
process is modeled by reaction paths using an updated geochemical thermodynamic database, consistent
with the local primary and secondary serpentinite paragenesis. For the model, bicarbonate waters evolve to alkaline waters supersaturated in Ca–(Mg)-carbonate, based on the assumption that the dissolution of serpentinite results in supersaturation with respect to kaolinite, ferrihydrite, vermiculite, Fe2+–Mg2+-
saponite, and poorly crystalline serpentine. The alkaline composition and the chloride content of the waters suggest a prolonged interaction with the rocks at depth that led to dissolution of albite and leaching of olivine-hosted fluid inclusions. A similar evolution is also proposed for the more developed springs issuing from the ultramafic rocks of the Voltri Group (Liguria region), where solutions are supersaturated in brucite and are in equilibrium with enstatite and/or chlorite
Geochemistry of basaltic and gabbroid metaophiolites from the Susa Valley, Italian Western Alps.
No full text
Magmatic evolution of the Gaussberg lamproite (Antartica): volatile content and glass composition.
No full textThe lamproite of Gaussberg is an ultrapotassic rock where leucite, olivine and clinopyroxene
microphenocrysts occur in a glass-rich groundmass, containing microliths of leucite, clinopyroxene,
apatite, phlogopite and rare K-richterite.
Abundant silicate melt inclusions occur in olivine, leucite and, rarely, in clinopyroxene
microphenocrysts. Raman investigations on melt inclusions showed the presence of pure CO2 in the
shrinkage bubbles. On the other hand, the glass of the groundmass is CO2-poor and contains up to
0.70 wt.% of dissolved H2O, as estimated by infrared spectra. It is inferred that CO2 was released at
every stage of evolution of the lamproite magma (CO2-rich shrinkage bubbles), whereas H2O was
retained for longer in the liquid. At Gaussberg, CO2 seems to have a major role at relatively high
pressure where it favoured the crystallization of H2O-poor microphenocrysts; the uprise of the magma
to the surface decreased the solubility of CO2 and caused a relative increase in water activity. As a
consequence, phlogopite and K-richterite appeared in the groundmass.
The glass composition of both the groundmass and melt inclusions suggests different evolutions for
the residual liquids of the investigated samples. Sample G886 shows the typical evolution of a
lamproite magma, where the residual liquid evolves toward peralkaline and Na-rich composition and
crystallizes K-richterite in the latest stage. Sample G895 derives from mixing/mingling of different
batches of magma; effectively glasses from melt inclusions in leucite and clinopyroxene are more
alkaline than those found in early crystallized olivine. Leucite and clinopyroxene crystallized early
from a relatively more alkaline batch of lamproite magma and, successively, a less alkaline, olivinebearing
magma batch assimilated them during its rise to the surface
- …
