From the Guajira Desert to the Apennines, and from Mediterranean Microplates to the Mexican Killer Asteroid: Honoring the Career of Walter Alvarez

This volume pays tribute to the great career and extensive and varied scientific accomplishments of Walter Alvarez, on the occasion of his 80th birthday in 2020, with a series of papers related to the many topics he covered in the past 60 years: Tectonics of microplates, structural geology, paleomagnetics, Apennine sedimentary sequences, geoarchaeology and Roman volcanics, Big History, and most famously the discovery of evidence for a large asteroidal impact event at the Cretaceous–Tertiary (now Cretaceous–Paleogene) boundary site in Gubbio, Italy, 40 years ago, which started a debate about the connection between meteorite impact and mass extinction. The manuscripts in this special volume were written by many of Walter’s close collaborators and friends, who have worked with him over the years and participated in many projects he carried out. The papers highlight specific aspects of the research and/or provide a summary of the current advances in the field.
Fluid-assisted brecciation of Lower Cretaceous Maiolica limestone in the Umbria-Marche Apennines: Hydrodynamical implications
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Published:June 21, 2022
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CiteCitation
Lung Sang Chan*, Walter Alvarez, Peter Geiser, Enrico Tavarnelli, 2022. "Fluid-assisted brecciation of Lower Cretaceous Maiolica limestone in the Umbria-Marche Apennines: Hydrodynamical implications", From the Guajira Desert to the Apennines, and from Mediterranean Microplates to the Mexican Killer Asteroid: Honoring the Career of Walter Alvarez, Christian Koeberl, Philippe Claeys, Alessandro Montanari
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ABSTRACT
The formation of the “expansion breccia” observed in the Lower Cretaceous Maiolica limestone in the Umbria-Marches region of Italy is attributable to a fluid-assisted brecciation process that occurred during the late Miocene exhumation of the Northern Apennines. The hydrothermal fluids probably originated as brine solutions trapped in the Burano anhydrite while it was in a plastic state. The migration of the Burano from the plastic to the brittle domain during unroofing resulted in liberation and injection of over-pressured hydrothermal fluids into the overlying limestone, causing hydraulic fracturing. Mapping of breccia morphology along a 400-m transect showed structures produced by different flow regimes, with chaotic and mosaic breccia characterizing the core parts of the section and mineral-filled fractures and veins in the margins. Based on the clast size in the chaotic breccia, the estimated velocities for fluidizing the aggregates of clasts and sustaining the clasts in suspension are, respectively, 15 cm/s and 65 cm/s. Crack growth was probably the main mechanism for the fragmentation of the limestone. Explosion fracturing patterns were only sporadically observed in the breccia, indicating substantial heat loss of the over-pressured fluids during their ascent to the Earth’s surface.
- Apennines
- breccia
- brecciation
- brines
- carbonate rocks
- Cenozoic
- clasts
- Cretaceous
- Europe
- exhumation
- fluid phase
- hydraulic conductivity
- hydrodynamics
- hydrothermal conditions
- Italy
- limestone
- Lower Cretaceous
- Maiolica Limestone
- Marches Italy
- Mesozoic
- migration
- Miocene
- Neogene
- permeability
- sedimentary rocks
- Southern Europe
- Tertiary
- Umbria Italy