Regional-scale paleofluid system across the Tuscan Nappe–Umbria–Marche Apennine Ridge (northern Apennines) as revealed by mesostructural and isotopic analyses of stylolite–vein networks

Nicolas Beaudoin (1) , Aurélie Labeur , Olivier Lacombe (2) , Daniel Koehn , Andrea Billi , Guilhem Hoareau (1) , Adrian Boyce , Cédric M John , Marta Marchegiano , Nick M Roberts , Ian L Millar , Fanny Claverie (3) , Christophe Pécheyran (3) , Jean-Paul Callot (1)

1 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs
2 iSTeP - Institut des Sciences de la Terre de Paris
3 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux

We report the results of a multiproxy study that combines structural analysis of a fracture-stylolite network and isotopic characterization of calcite vein cements and/or fault coating. Together with new paleopiezometric and ra-diometric constraints on burial evolution and deformation timing, these results provide a first-order picture of the regional fluid systems and pathways that were present during the main stages of contraction in the Tuscan Nappe and Umbria-Marche Apennine Ridge (northern Apennines). We reconstruct four steps of deformation at the scale of the belt: burial-related stylolitization, Apenninic-related layer-parallel shortening with a contraction trending NE-SW, local extension related to folding, and late-stage fold tightening under a contraction still striking NE-SW. We combine the paleopiezometric inversion of the roughness of sedimen-tary stylolites-that constrains the range of burial depth of strata prior to layer-parallel shortening-with burial models and U-Pb absolute dating of fault coatings in order to determine the timing of development of mesostructures. In the western part of the ridge, layer-parallel shortening started in Langhian time (∼ 15 Ma), and then folding started at Torto-nian time (∼ 8 Ma); late-stage fold tightening started by the early Pliocene (∼ 5 Ma) and likely lasted until recent/modern extension occurred (∼ 3 Ma onward). The textural and geo-chemical (δ 18 O, δ 13 C, 47 CO 2 and 87 Sr/ 86 Sr) study of cal-cite vein cements and fault coatings reveals that most of the fluids involved in the belt during deformation either are local or flowed laterally from the same reservoir. However, the western edge of the ridge recorded pulses of eastward migration of hydrothermal fluids (>140 • C), driven by the tec-tonic contraction and by the difference in structural style of the subsurface between the eastern Tuscan Nappe and the Umbria-Marche Apennine Ridge.

Domaines: Matériaux; Chimie analytique; Polymères; Chimie théorique et/ou physique

Nicolas Beaudoin, Aurélie Labeur, Olivier Lacombe, Daniel Koehn, Andrea Billi, et al.. Regional-scale paleofluid system across the Tuscan Nappe–Umbria–Marche Apennine Ridge (northern Apennines) as revealed by mesostructural and isotopic analyses of stylolite–vein networks. Solid Earth, 2020, 11 (4), pp.1617 - 1641. ⟨10.5194/se-11-1617-2020⟩. ⟨hal-02957355⟩