Abstract
Structural, petrological and geochemical (δ13C, δ18O, clumped isotopes, 87Sr/86Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet (Southern Pyrenees). Five fracture events associated with the growth of the thrust-related Bóixols anticline and Coll de Nargó syncline during the Alpine orogeny are distinguished. These fractures were cemented with four generations of calcite cements, revealing that such structures allowed the migration of different marine and meteoric fluids through time. During the early contraction stage, Lower Cretaceous seawater circulated and precipitated calcite cement Cc1, whereas during the main folding stage, the system opened to meteoric waters, which mixed with the connate seawater and precipitated calcite cement Cc2. Afterwards, during the post-folding stages, connate evaporated marine fluids circulated through newly formed NW-SE and NE-SW conjugate fractures and later through strike-slip faults and precipitated calcite cements Cc3 and Cc4. The overall paragenetic sequence reveals the progressive dewatering of Cretaceous marine host sediments during progressive burial, deformation and fold tightening and the input of meteoric waters only during the main folding stage. This study illustrates the changes of fracture systems and the associated fluid-flow regimes during the evolution of fault-associated folds during orogenic growth.
Highlights
The integration of structural, petrological and geochemical analyses performed in fractureallowing the migration of a fluid from which calcite cement Cc2 precipitated
This is evidenced by the related calcite cements and host rocks constrains the spatiotemporal paleo-fluid system in the frontal presence of two striae sets showing dip-slip and strike-slip kinematics (Figure 8d) and the coexistence part of the Bóixols thrust sheet, the oldest thrust sheet of the South-Central Pyrenean Unit
These fracture sets and related and its temperature are interpreted as the infiltration of meteoric calcite cements reflect the evolution of the thrust/folding system and the relationship between the fluids during progressive uplift, folding and fossilization of the Bóixols thrust by the continental tectonic evolution and fluid migration: 1) During the early contraction, two bed-perpendicular NWPaleocene Garumnian facies, which mixed with previous local and connate marine waters (Figure 16)
Summary
Fluids play an important role on the Earth’s crust as, on one hand, they transport solutes and distribute heat, controlling mineral reactions including precipitation and dissolution [1,2,3,4,5,6,7,8], and on the other hand, they can change the effective stress, favoring the reactivation of existing fractures and the formation of new ones [9,10,11,12].Minerals 2019, 9, 117; doi:10.3390/min9020117 www.mdpi.com/journal/mineralsDuring the geodynamic evolution of fold and thrust belts and related foreland basins, fluid migration controls diagenetic processes and the propagation of fractures and faults. The fracture geometry and architecture conditions their role as either conduits or seals for fluids, controlling fluid distribution [13,14] In this geodynamic setting, the fluid sources change with time as foreland basins usually evolve from marine to continental conditions [15,16]. Studies integrating the evolution of fracture systems and related cements are needed to constrain the fluid-flow history of an area during orogenic growth and, understand the nature and origin of fluids that circulate through time, the diagenetic process evolution, changes in reservoir properties such as porosity and permeability and the distribution of minerals and hydrocarbons [28,29]
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