Microstructures of epidote-prehnite bearing damaged granitoids (northern Victoria Land, Antarctica): clues for the interaction between faulting and hydrothermal fluids

Abstract

Exhumed faults in granitoids along the Lanterman Fault-Rennick Graben Fault system (northern Victoria Land, Antarctica) show superposed ductile to brittle deformation and pervasive hydrothermal fluid-rock interaction. These processes triggered multiple brittle slip events producing crosscutting epidote and prehnite-rich fault veins, ultracataclasites and pseudotachylytes of crushing origin. Combined microstructural and minerochemical investigations on fault damage zones show three types of alteration: (i) albitization of K-feldspar and Caplagioclase; (ii) crystallization of prehnite and calcite in veins; (iii) alteration of magmatic phases by secondary hydrous minerals (e.g. chlorite, white mica, epidote and prehnite). The fault experienced various episodes of strain weakening and hardening, due to alteration of minerals and precipitation of epidote and prehnite within ultracataclastic intervals, at decreasing temperature conditions (200 < T • C < 450) and varying CO 2 fugacity of the fluids. Cyclic crystallization of epidote/prehnite within the fault cores caused cementation and locking of faults, concentration of deformation at weaker horizons and a progressive broadening of the fault zone. Our results indicate that multiple co-seismic slip and syntectonic fluid flow very likely occurred prior to the Cenozoic brittle reactivation of inherited anisotropies in the northern Victoria Land crust along the Lanterman Fault-Rennick Graben Fault system and underlines its high potential for polyphasicity.

Multiple Reactivations of the Rennick Graben Fault System (Northern Victoria Land, Antarctica): New Evidence From Paleostress Analysis

“…The RGF is an intraplate shear corridor where Meso‐Cenozoic tectonics reactivated regional‐scale shear zones to accommodate, as transform fault, the relative kinematics between the EAC to the west and the VL to the east. The long‐lived regional shear zones parallel to the western and eastern shoulders of the Rennick graben propagate southward in the Mountaineer Range (Capponi et al., 1999; Malatesta et al., 2021, e.g., Figure 1b). In NVL, the existence of a major fracture swarm striking 165°–180° (Step A: Figure 11a), nearly parallel to the fault network oriented in a NNW‐SSE direction (Figures 1c and 6), indicates the tectonic control exerted on the brittle reactivation of the RGB by the intraplate propagation of far field stresses and the relative motion between the eastern and western blocks (e.g., the Usarp and Bowers domains).…”

“…This corridor of deformation includes a net of regionally sized faults (Figure 1b), with the Rennick and Lanterman faults representing the major tectonic lineaments and are interpreted as crustal scale discontinuities on the basis of geophysical signatures (gravimetric and magnetic, Ferraccioli et al., 2002, 2009; Jordan et al., 2013, Zanutta et al., 2018). These faults have been characterized by a polyphased ductile to brittle tectonic history since the Cambrian‐Ordovician (e.g., Capponi et al., 1999; Crispini et al., 2014; Federico et al., 2006, 2010; Läufer & Rossetti, 2003; Malatesta et al., 2021; Rossetti et al., 2002). The more recent Meso‐Cenozoic tectonics were mainly characterized by strike‐slip movements, both sinistral and dextral (e.g., Bozzo et al., 1999; Damaske & Bosum, 1993; Dubbini et al., 2010; Ferraccioli & Bozzo, 2003; Läufer & Rossetti, 2003; Rossetti et al., 2000, 2002; Salvini et al., 1997; Tessensohn et al., 1994).…”

“…The rectangular area indicates the study area, the stars locate the onshore earthquakes with Mw > 5 recorded since 1973 (data from Reading, 2002, and integrated with GeoMappApp database [http://www.geomapapp.org]). Faults after Capponi et al., 1999, Federico et al., 2006, Kleinschmidt & Läufer 2006, Ferraccioli & Bozzo 2003, Ferraccioli et al., 2009 and integrations from Salvini et al., 1997, Läufer & Rossetti, 2003, and Malatesta et al., 2021. Background image is a MODIS mosaic of Antarctica.…”