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Discussion papers
https://doi.org/10.5194/se-2018-136
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2018-136
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Jan 2019

Research article | 03 Jan 2019

Review status
This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Solid Earth (SE).

Fault-controlled dolomitization in the Montagna dei Fiori Anticline (Central Apennines, Italy): Record of a dominantly pre-orogenic fluid migration

Mahtab Mozafari1, Rudy Swennen2, Fabrizio Balsamo1, Hamdy El Desouky2,3, Fabrizio Storti1, and Conxita Taberner4 Mahtab Mozafari et al.
  • 1NEXT – Natural and Experiment al Tectonics Research Group – Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Italy
  • 2Department of Earth and Environmental Sciences, KU Leuven, Belgium
  • 3Geology Department, Faculty of Science, Menoufia University, Menoufia, Egypt
  • 4Shell Global Solutions International B.V., Amsterdam, the Netherlands

Abstract. The Lower Jurassic platform and basinal deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) are pervasively affected by dolomitization. Based on the integration of field work, petrography, and geochemistry, two fault-related dolomitization events were recognized and interpreted as occurred before and during the Apenninic orogeny, respectively. Fluid inclusion analysis indicates moderate to elevated salinity values of 3.5 to 20.5 and 12.8 to 18.6 eq. wt. % NaCl, in the first and the second event, respectively. The estimated salinities, in combination with δ18O values and 87Sr/86Sr ratios, suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation. In addition, the 87Sr/86Sr ratios up to 0.70963 suggest the circulation of deep-sourced fluids that interacted with siliciclastics and/or the crystalline basement during the dolomitization events. The first dolomitization event which is also considered as the most pervasive one started prior to the significant burial conditions, as reflected in homogenization temperatures of their fluid inclusions being mostly below about 40–50 °C. Two major dolomite types (D1 and D2) were recognized as pertaining to this event, both postdated by high amplitude bed-parallel stylolites. This relationship supports a syn-burial, pre layer-parallel shortening dolomitization, interpreted as controlled by the extensional fault pattern affecting the carbonate succession before its involvement in the Apenninic thrust wedge. A possible geodynamic framework for this dolomitization event is Early to Late Jurassic rift-related extensional tectonism.

The second dolomitization event initiated with a dolomite type (D3) characterized by a slight temperature upturn (up to 73 °C), followed by a second type (D4) with markedly higher homogenization temperatures (up to 105 °C), interpreted as associated with the inflow of hydrothermal fluids, possibly related to major changes in the permeability architecture of faults during early- to syn-thrusting and folding activity. Eventually, D4 was overprinted by a late generation of dolomite veins (D5) interpreted as associated with late orogenic extensional faulting in the backlimb of the Montagna dei Fiori Anticline. Based on the timing of deformation in the Montagna dei Fiori Anticline, D3 to D5 dolomitization likely occurred in Late Miocene to Pliocene times. The findings regarding characteristics and timing of dolomitization here illustrates the long-term controlling role of the eveporitic detachments in dolomitization process. Our data shows the Mg-rich fluids most likely derived from these evaporites may prime the tectonically involved successions for repeated dolomitization, and formation of potential reservoirs in sequential tectonic modifications (extensional vs. compressional).

Mahtab Mozafari et al.
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Mahtab Mozafari et al.
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Short summary
The dolomitized intervals of the Lower Jurassic deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) have been investigated. Accordingly, two fault-related dolomitization events were recognised and interpreted as occurred before and during the Apenninic orogeny, respectively. The analyses suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation in the detachment level.
The dolomitized intervals of the Lower Jurassic deposits exposed in the Montagna dei Fiori...
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