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

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 UmbriaMarche 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 Belza, J., Alvarez, W., Tavarnelli, E., Vanhaecke, F., Baele, J.-M., and Claeys, P., 2019, Expansion breccias in Lower Cretaceous Apennine pelagic limestones: II. Geochemical constraints on their origin, in Koeberl, C., and Bice, D.M., eds., 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco: Geological Society of America Special Paper 542, p. 251–269, https://doi.org/10.1130/2019.2542(13). © 2019 The Geological Society of America. All rights reserved. For permission to copy, contact editing@geosociety.org. 252 Belza et al. SPE542-13 2nd pgs page 252