Expansion breccias in Lower Cretaceous Apennine pelagic limestones: II. Geochemical constraints on their origin

Joke Belza, Walter Alvarez, Enrico Tavarnelli, Frank Vanhaecke, Jean-Marc Baele, Philippe Claeys

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The geochemical signatures of sparry calcite-sealing expansion breccias, calcite veins, and host clasts were analyzed for their strontium (87Sr/86Sr) and oxygen and carbon (δ18O, δ13C) stable isotopic signatures. The breccias occur within
the Lower Cretaceous Maiolica Formation. Related but different breccias are found in a few places in the Upper Cretaceous to Eocene Scaglia Rossa Formation of the Umbria-Marche Apennines fold-and-thrust belt (Italy). We propose hydraulic fracturing by fluid overpressure as a possible mechanism for generation of the breccias in these formations. Our data are compatible with the hypothesis of a hydraulically fractured breccia formed by cyclic buildup and rapid decompression of CO2-rich fluids, with overpressures generated by entrapment of CO2 by structural and stratigraphic seals. Strontium and oxygen isotope ratio data suggest that the CO2-rich fluids may have originated from carbonate metasomatism of the mantle, resulting from subduction of carbonate-rich lithologies constituting the downgoing slab. This is consistent with previous conceptual models inferring that in the central part of the Northern Apennines, which is characterized by thick continental crust, CO2-rich fluids derived from mantle metasomatism would become trapped in structural seals, creating high
fluid overpressures.
Originele taal-2English
Titel250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco
RedacteurenChristian Koeberl, David Bice
Plaats van productieDenver
UitgeverijGeological Society of America, Boulder Co. USA
Hoofdstuk13
Pagina's251-269
Aantal pagina's19
Volume542
DOI's
StatusPublished - 11 sep 2019

Publicatie series

NaamSpecial Paper of the Geological Society of America
ISSN van geprinte versie0072-1077

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