Selective reactivation of inherited fault zones driven by stress field changes: Insights from structural and paleostress analysis of the Pocuro Fault Zone, Southern Central Andes (32.8°S). (October 2022)

• Record Type: Journal Article
• Authors: Taucare, Matías; Roquer, Tomás; Heuser, Gert; Pérez-Estay, Nicolás; Arancibia, Gloria; Yáñez, Gonzalo; Viguier, Benoît; Figueroa, Ronny; Morata, Diego; Daniele, Linda
• Is Part Of: Journal of South American earth sciences. Volume 118(2022)
• Publication Date: 2022-10
• Subjects: Structural geology -- Paleostress inversion -- Polyphase deformation -- Tectonic inversion -- Mechanical strengthening -- Western andean front; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2022.103914
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: This study aims to explain the selective reactivation of normal faults during the Andean orogeny at the Southern Central Andes western flank. We conducted a structural mapping and paleostress field reconstruction in the regional-scale Pocuro Fault Zone (PFZ) at 32.8°S. Results reveal that the architecture of the PFZ results from at least two deformation phases, each revealing an individual progressive and gradual evolution. The earliest deformation phase is recorded by two ∼ NS-striking normal faults involving a 5 km wide damage zone characterized by quartz-laumontite and calcite veins that were developed under an extensional regime with a WNW-ESE-trending σ3-axis. The latest deformation phase is recorded by one NS-striking reverse-dextral fault with goethite-hematite syn-tectonic precipitation and two NW-striking reverse-sinistral faults. Reverse faults were developed under a compressional/transpressional regime characterised by an ENE-WSW-trending σ1-axis with a σ2-/σ3-axis permutation. From a geophysical data reassessment, we inferred that observed faults in the surface within the PFZ are regional-scale deep-seated structures. Considering previous geochronological data, we correlated the earliest and latest phases with the Abanico Basin extension (middle Eocene-early Miocene) and its subsequent inversion (Miocene). Given the neotectonic evidence (geomorphic markers and deformation of unconsolidated deposits), the latter phase likely remains active. Quartz-laumontite cementation of the fault core's cataclastic material promotes mechanical strengthening leading to negative feedback for the reactivation of inherited normal faults as reverse ones. Conversely, the concentration of fractures in the damage zone between the normal faults promotes mechanical weakening resulting in a preferential area for the propagation of reverse fault during the compressive/transpressional phase. Highlights: We discuss the selective reactivation of inherited normal fault planes during the Western Andean Front tectonic evolution. Pocuro Fault Zone reveals a polyphase deformation history with an extensional phase overprinted by a compressional/transpressional one. Mineral precipitation promotes the fault core's mechanical strengthening, leading to negative feedback for fault inversion. Fracture concentration in the normal faults' damage zone promotes mechanical weakening and propagation of reverse faults as new independent planes. Mineral precipitation and fracture concentration allow for the coexistence of normal and reverse faults in the same area.