Origin of the Breno and Esino dolomites in the western Southern Alps (Italy): Implications for a volcanic influence
Articolo
Data di Pubblicazione:
2016
Citazione:
Origin of the Breno and Esino dolomites in the western Southern Alps (Italy): Implications for a volcanic influence / Y. Hou, K. Azmy, F. Berra, F. Jadoul, N.J.F. Blamey, S.A. Gleeson, U. Brand. - In: MARINE AND PETROLEUM GEOLOGY. - ISSN 0264-8172. - 69(2016), pp. 38-52. [Epub ahead of print] [10.1016/j.marpetgeo.2015.10.010]
Abstract:
The Esino Limestone of the western Southern Alps represents a differentiated Ladinian-Lower Carnian (?)
carbonate platform comprised of margin, slope and peritidal inner platform facies up to 1000 m thick. A
major regional subaerial exposure event lead to coverage by another peritidal Lower Carnian carbonate
platform (Breno Formation). Multiphase dolomitization affected the carbonate sediments. Petrographic
examinations identified at least three main generations of dolomites (D1, D2, and D3) that occur as both
replacement and fracture-filling cements. These phases have crystal-size ranges of 3e35 mm (dolomicrite
D1), 40e600 mm (eu-to subhedral crystals D2), and 200 mm to 5 mm (cavity- and fracture-filling anhedral
to subhedral saddle dolomite D3), respectively.
The fabric retentive near-micritic grain size coupled with low mean Sr concentration (76 ± 37 ppm)
and estimated d18O of the parent dolomitizing fluids of D1 suggest formation in shallow burial setting at
temperature ~ 45e50 C with possible contributions from volcanic-related fluids (basinal fluids circulated
in volcaniclastics or related to volcanic activity), which is consistent with its abnormally high Fe
(4438 ± 4393 ppm) and Mn (1219 ± 1418 ppm) contents. The larger crystal sizes, homogenization
temperatures (D2, 108 ± 9 C; D3, 111 ± 14 C) of primary two-phase fluid inclusions, and calculated
salinity estimates (D2, 23 ± 2 eq wt% NaCl; D3, 20 ± 4 eq wt% NaCl) of D2 and D3 suggest that they
formed at later stages under mid-to deeper burial settings at higher temperatures from dolomitizing
fluids of higher salinity, which is supported by higher estimated d18O values of their parent dolomitizing
fluids. This is also consistent with their high Fe (4462 ± 4888 ppm; and 1091 ± 1183 ppm, respectively)
and Mn (556 ± 289 ppm and 1091 ± 1183 ppm) contents, and low Sr concentrations (53 ± 31 ppm and
57 ± 24 ppm, respectively).
The similarity in shale-normalized (SN) REE patterns and Ce (Ce/Ce*)SN and La (Pr/Pr*)SN anomalies of
the investigated carbonates support the genetic relationship between the dolomite generations and their
calcite precursor. Positive Eu anomalies, coupled with fluid-inclusion gas ratios (N2/Ar, CO2/CH4, Ar/He),
high F concentration, high F/Cl and high Cl/Br molar ratios suggest an origin from diagenetic fluids
circulated through volcanic rocks, which is consistent with the co-occurrence of volcaniclastic lenses in
the investigated sequence.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Carbonate diagenesis
Dolomitization
Stable isotopes
Rare earth elements
Microthermometry
Fluid-inclusion gases
Triassic
western Southern Alps (Italy)
Elenco autori:
Y. Hou, K. Azmy, F. Berra, F. Jadoul, N.J.F. Blamey, S.A. Gleeson, U. Brand
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