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 Pub Date : 1900-01-01 DOI:10.1130/2019.2542(13)

J. Belza, W. Álvarez, E. Tavarnelli, F. Vanhaecke, J. Baele, P. Claeys

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引用次数: 3

Abstract

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

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下白垩统亚平宁海底灰岩中的膨胀角砾岩:II。它们起源的地球化学限制

分析了辉晶石封方解石膨胀角砾岩、方解石脉和寄主碎屑的锶(87Sr/86Sr)和氧碳(δ18O、δ13C)稳定同位素特征。角砾岩产于下白垩统马爵利卡组。在意大利翁布里亚马奇-亚平宁褶皱冲断带的上白垩统至始新统Scaglia Rossa组中，在少数地方发现了相关但不同的角砾岩。我们认为流体超压水力压裂可能是这些地层中角砾岩形成的一种机制。我们的数据与水力裂缝角砾岩的假设相一致，该角砾岩是由富含二氧化碳的流体的旋回堆积和快速减压形成的，由构造和地层密封圈闭二氧化碳产生超压。锶和氧同位素比值数据表明，富co2流体可能由Belza, J.， Alvarez, W.， Tavarnelli, E.， Vanhaecke, F.， Baele, J.- m .;Claeys, P.， 2019，下白垩世亚平宁海底石灰岩中的膨胀角砾岩:II。地球化学对它们起源的限制，见Koeberl, C和Bice, d.m.，编。，意大利中部的2.5亿年地球历史:庆祝Coldigioco地质观测站25年:美国地质学会特别论文542,p. 251-269, https://doi.org/10.1130/2019.2542(13)。©2019美国地质学会。版权所有。请联系editing@geosociety.org获取复制权限。252 Belza等人。SPE542-13第二页252

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250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco

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