Highly deformed metaconglomerates, mafic to felsic in composition, characterize the eastern Lanterman Range (northern Victoria Land, Antarctica). In the literature the mafic and felsic metaconglomerates are known as Husky Conglomerate and Lanterman Conglomerate respectively. They occur in a 25 km long strip along the Lanterman Fault, which is a major tectonic boundary between the Wilson and the Bowers terranes. New field observations show that there is a gradual transition from mafic to felsic metaconglomerates: this supports a stratigraphical continuum from Husky to Lanterman Conglomerate, and indicates that they belong to the same sedimentary succession. Structural analysis indicates that Husky and Lanterman conglomerates suffered the same structural evolution. From all these evidences, there is no reason to distinguish two types of metaconglomerates, apart from the diversity in the lithological features. However the two terms “Husky Conglomerate” and “Lanterman Conglomerate” can be still used to refer to the mafic and felsic facies of the same sedimentary succession. On the basis of their lithology the Husky Conglomerate can be derived from the Glasgow volcanic arc, whereas the felsic clasts of the Lanterman Conglomerate may be derived from a continental basement below the Glasgow arc or from a continental block bounding the Bowers trough.
In the Cambrian, the paleo-Pacific margin of the Gondwana supercontinent included East Antarctica, Australia, Tasmania and New Zealand and was affected by the major Ross-Delamerian Orogeny. In Antarctica, evidence suggests that this resulted from oblique subduction and that in northern Victoria Land it was accompanied by the opening and subsequent closure of a back-arc basin. Comparison of the type and timing of sedimentary, magmatic and metamorphic events in areas noted above shows strong similarities between northern Victoria Land and New Zealand. In both regions Middle Cambrian volcanites are interpreted as arc/back-arc assemblages produced by westdirected subduction; sediments interbedded with the volcanites show provenance both from the arc and from the Gondwana margin and therefore place the basin close to the continent. Back-arc closure in the Late Cambrian was likely accomplished through a second subduction system.
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.
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