Polyphasic hydrothermal and meteoric fluid regimes during the growth of a segmented fault involving crystalline and carbonate rocks (Barcelona Plain, NE Spain)

Abstract

A polyphasic tectonic‐fluid system of a fault that involves crystalline and carbonate rocks (Hospital fault, Barcelona Plain) has been inferred from regional to thin section scale observations combined with geochemical analyses. Cathodoluminescence, microprobe analyses and stable isotopy in fracture‐related cements record the circulation of successive alternations of hydrothermal and low‐temperature meteoric fluids linked with three main regional tectonic events. The first event corresponds to the Mesozoic extension, which had two rifting stages, and it is characterized by the independent tectonic activity of two fault segments, namely southern and northern Hospital fault segments. During the Late Permian‐Middle Jurassic rifting, these segments controlled the thickness and distribution of the Triassic sediments. Also, dolomitization was produced in an early stage by Triassic seawater at shallow conditions. During increasing burial, formation of fractures and their dolomite‐related cements took place. Fault activity during the Middle Jurassic–Late Cretaceous rifting was localized in the southern segment, and it was characterized by hydrothermal brines, with temperatures over 180°C, which ascended through this fault segment precipitating quartz, chlorite, and calcite. The second event corresponds to the Paleogene compression (Chattian), which produced exhumation, folding and erosion, favouring the percolation of low‐temperature meteoric fluids which produced the calcitization of the dolostones and of the dolomite cements. The third event is linked with the Neogene extension, where three stages have been identified. During the syn‐rift stage, the southern segment of the Hospital fault grew by tip propagation. In the relay zone, hydrothermal brines with temperature around 140°C upflowed. During the late postrift, the Hospital fault acted as a unique segment and deformation occurred at shallow conditions and under a low‐temperature meteoric regime. Finally, and possibly during the Messinian compression, NW‐SE strike‐slip faults offset the Hospital fault to its current configuration.

Hydrothermal Carbonate Mineralization, Calcretization, and Microbial Diagenesis Associated with Multiple Sedimentary Phases in the Upper Cretaceous Bekhme Formation, Kurdistan Region-Iraq

“…Note another type of brecciation by pedogenic calcrete that caused an in situ fragmentation of the saddle and matrix dolomites (No. 3,6,8) and non-deposition period evidenced by marly bed (D). The HT cementation happened prior to the strong in situ brecciation of saddle dolomites (No.…”

“…The HT cementation happened prior to the strong in situ brecciation of saddle dolomites (No. 3,4,8). Photomicrographs (No.…”

“…Calcretization processes, contrary to HT processes, were widely recognized in environments submitted to various diagenetic conditions, either in the vadose zone related to pedogenetic alteration, or in the vicinity of the water table in the phreatic zone [6] and under low-temperature conditions (less than 50 • C [7]). Calcrete processes are also factors, which affect reservoir properties, mainly porosity [8].…”

Fracturing and Near-Surface Diagenesis of a Silicified Miocene Deltaic Sequence: The Montjuïc Hill (Barcelona)

“…This leaves two options to explain the low δ 18 O values at such shallow burial depths. Firstly, cement Cc2 precipitated from hydrothermal fluids, which have already been reported in several locations along the Catalan Coastal Ranges related to the Neogene extension [37,70,71], or secondly, the geothermal gradient may have been locally higher due to an increase of the lithospheric thinning towards the offshore, a fact that has been also suggested before [43,72,73].…”

“…In the Catalan Coastal Ranges (NE Spain), previous studies show that the main diagenetic processes linked to Cenozoic and Mesozoic deformation events are calcite cementation and dolomitization ( [15,[29][30][31][32][33][34][35][36][37]). Only two locations have been found to show extensive silicification, both related to the Neogene extension: the Camp dels Ninots (Caldes de Malavella) and the Montjuïc Hill (in the city of Barcelona).…”