Expansion breccias in Lower Cretaceous Apennine pelagic limestones: II. Geochemical constraints on their origin
J. Belza, W. Alvarez, E. Tavarnelli, F. Vanhaecke, J.-M. Baele, P. Claeys, "Expansion breccias in Lower Cretaceous Apennine pelagic limestones: II. Geochemical constraints on their origin", 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco, Christian Koeberl, David M. Bice
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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.
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250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco
Central Italy has been a cradle of geology for centuries. For more than 100 years, studies at the Umbria and Marche Apennines have led to new ideas and a better understanding of the past, such as the Cretaceous–Paleogene (K-Pg) boundary event, or the events across the Eocene–Oligocene transition from a greenhouse to an icehouse world. The Umbria-Marche Apennines are entirely made of marine sedimentary rocks, representing a continuous record of the geotectonic evolution of an epeiric sea from the Early Triassic to the Pleistocene. The book includes reviews and original research works accomplished with the support of the Geological Observatory of Coldigioco, an independent research and educational center, which was founded in an abandoned medieval hamlet near Apiro in 1992.