Fault–slip analysis and transpressional tectonics: A study of Paleozoic structures in northern Victoria Land, Antarctica
Introduction
Antarctica presents many challenges to structural geologists due to its remote location and, in many areas, relatively poor exposure. Rocks now exposed in northern Victoria Land were part of the over 4000 km long paleo-Pacific margin of East Gondwana during the Paleozoic. This margin was the site of protracted convergence, with terrane accretion and collision(s) of arc and/or microcontinental masses (e.g., Veevers, 2000, Cawood, 2005, Vaughan and Pankhurst, 2008). The Ross–Delamerian (hereafter Ross) Orogeny (Cambrian–Early Ordovician; e.g., Bradshaw, 1987, Bradshaw, 1989, Kleinschmidt and Tessensohn, 1987, Findlay et al., 1991, Ferraccioli et al., 2002) was the most pervasive tectonic event of the area, responsible for the regionally dominant deformations. Following that event, an outboard migration of the subduction plane possibly occurred inducing less intense deformations typical of foreland areas during the Devonian–Carboniferous, together with a magmatic pulse (Kleinschmidt and Tessensohn, 1987, Fioretti et al., 1997). Finally, the fragmentation of Gondwana and, in particular, the separation between Australia and Antarctica was responsible for strike-slip to transtensional deformations during the Cenozoic (e.g., Salvini et al., 1997, Rossetti et al., 2003). The area was, therefore, the site of multiple tectonic events, with recurrent reactivation of major faults, in particular the trans-lithospheric faults that represent terrane-bounding structures (e.g., Lanterman Fault and Leap Year Fault, Fig. 1, Fig. 2).
The Cenozoic brittle tectonics of the northern Victoria Land has been widely documented in the published literature (Salvini et al., 1997, Salvini and Storti, 1999, Rossetti et al., 2000, Rossetti et al., 2002, Rossetti et al., 2003, Storti et al., 2001) whereas older brittle structures related to post-Ross orogenic phases are less well known (Wodzicki and Robert, 1986, Jordan et al., 1984, Capponi et al., 1999).
In this study we analyse and interpret the deformation patterns from outcrops located in an area that straddles the Lanterman and Leap Year faults focusing on the brittle structures related to pre-Cenozoic tectonics. A complex fault network is preserved, with dominant steeply-dipping reverse and oblique–slip faults, locally forming positive flower structures. The fault system is associated with quartz–carbonate veining and cuts and thus postdates the Ross Orogeny-related ductile deformation structures.
The aim of this work is to unravel the Paleozoic post-Ross Orogeny tectonic evolution, by characterising the tectonic event responsible for the development of the pre-Cenozoic fault system and related stress state. Regional correlations with the formerly adjoining fragments of Gondwana, namely SE Australia, are also discussed.
To achieve this aim, we conducted field work, investigating cross-cutting relationships, mesoscale fault geometries, and collecting fault–slip data. The inversion of fault–slip data is a well-established technique that has increasingly been used to unravel very complex tectonic histories, responsible for the formation of heterogeneous fault populations (e.g., Wang and Neubauer, 1998, Lamarche et al., 1999, Matenco and Schmid, 1999, Saintot and Angelier, 2002, Burg et al., 2005, De Paola et al., 2005, Bergerat et al., 2007, Laó-Dávila and Anderson, 2009, De Vicente et al., 2009, Sippel et al., 2009). Fault–slip inversion techniques have a number of critical assumptions and limitations (as discussed, for instance, by Pollard et al., 1993, Dupin et al., 1993, Twiss and Unruh, 1998, Marrett and Peacock, 1999), so we applied several different inversion methods and a variety of open-source computer programs to calculate resolved stress tensors (F.S.A. v. 28.5 by Célérier, 1999 and MIM 5.31 by Yamaji et al., 2005a) and P–B–T axes (Faultkin v. 4.3.5 by Allmendinger et al., 1994).
Section snippets
Northern Victoria Land
The tectonic architecture of northern Victoria Land (Fig. 1, Fig. 2) was predominantly established during the Neoproterozoic to early Paleozoic Ross Orogeny.
This event led to the accretion of three terranes to the East Antarctic craton: from west to east these are: the Wilson; Bowers; and Robertson Bay terranes (e.g., Bradshaw et al., 1985, Kleinschmidt and Tessensohn, 1987, Ricci et al., 1997, Federico et al., 2006). The Wilson and Bowers terranes are juxtaposed by the Lanterman Fault (e.g.,
Field data
We investigated the mesoscale fault pattern in the area of the Bowers Mountains between the Lanterman Fault and Leap Year Fault (Fig. 1, Fig. 2). We collected fault–slip data from 153 striated fault planes at 10 localities (Fig. 3), scattered between 70°45′–71°45′ Lat. S and 162°00′–163°45′ Long. E (Fig. 2).
In the study area the sparse number of outcrops of Devonian–Triassic sediments (Beacon Supergroup) and/or Jurassic rocks (Ferrar Dolerite and Kirkpatrick Basalt) make finding age constrains
Inversion of fault–slip data
Most fault–slip inversion techniques use one or two fundamental assumptions:
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They impose a geometrical constraint requiring that slip on the fault plane takes place parallel to the direction of maximum resolved shear stress (Wallace, 1951, Bott, 1959, so-called "Wallace–Bott hypothesis"),
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Alternatively or additionally, they include a frictional constraint that the fault plane must form with an orientation that fulfils the Mohr–Coulomb yield criterion, e.g., the shear-to-normal stress ratio equals
Results
Most of the fault populations are heterogeneous, as illustrated by the different orientations of strain axes calculated by Faultkin and of stress axes calculated from FSA and MIM (Fig. 3). Where possible, we have separated different subsets (whose significance is discussed below), whilst in other cases, if the data set was too small, just one stress tensor was calculated, or the faults don’t fit, they have been grouped in the “Rest” column of Table 1. For each stress tensor we show the misfit
Paleostress inversion method
A good agreement exists between stress calculations and field data. All the reactivated faults identified in the field were either assigned to two different stress tensors or were assigned to one stress tensor and to the “rest” group by the software. In contrast, when single fault planes with a curved geometry have been identified (4 cases), the software was able to fit them into the same stress tensor in just one case. As a consequence, caution needs to be taken performing analysis of
Conclusions
In the present study, fault–slip data were inverted to calculate reduced palaeostress tensors through a stepwise procedure that allowed us to compare results obtained from different methods. We found good agreement between FSA and MIM results and a first-order agreement of principal stress axes and P–B–T axes calculated by Faultkin. Paleostress inversion methods correctly separated faults of different populations when overprinting relationships had been observed, and in general agree well with
Acknowledgments
Fieldwork benefitted from the excellent support of Helicopter NZ; special thanks to Jeff McClintock and Ricky Park.
The Authors thank Blanka Sperner for kindly providing the software FLUMO together with useful suggestions. Richard Allmendinger, Bernard Célérier and Atsushi Yamaji are acknowledged for kindly providing for free the softwares Faultkin and Stereonet, F.S.A. and M.I.M., respectively.
Careful reviews by F. Storti, R. Holdsworth and an anonymous reviewer are greatly appreciated.
This
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2021, Journal of Structural GeologyCitation Excerpt :Northern Victoria Land (nVL) is located at the Pacific end of the Transantarctic Mountains. Its basement results from the juxtaposition of three lithotectonic units during the late Neoproterozoic to early Paleozoic Ross Orogeny (e.g., Bradshaw and Laird, 1983; Weaver et al., 1984; Bradshaw et al., 1985; GANOVEX Team, 1987; Kleinschmidt and Tessensohn, 1987; Stump, 1995; Capponi et al., 1999; Roland et al., 2004; Federico et al., 2006, 2010). These are, from W to the E, the polymetamorphic and magmatic Wilson Terrane, the central island-arc- or arc/back-arc-related metasedimentary to –volcanic Bowers Terrane, and the external turbidite succession of the Robertson Bay Terrane (e.g., Wright et al., 1984; Borg and Stump, 1987; GANOVEX Team, 1987; Black and Sheraton, 1990; Capponi et al., 1999; Di Vincenzo and Rocchi, 1999; Rocchi et al., 2003, 2011; Roland et al., 2004; Schüssler et al., 2004; Federico et al., 2006; Bracciali et al., 2009; Goodge et al., 2012, 2020; Estrada et al., 2016) (Fig. 1).
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2016, Journal of Structural GeologyCitation Excerpt :To elucidate the role of bedding in the evolution of meso- and microstructural fabrics in fault zones, detailed microscopic observations and bulk mineralogical and geochemical analyses were conducted on rock samples that contain the bedding-oblique and bedding-parallel faults described above. These analyses are also important for improving our understanding of the relationship between the morphology of secondary fractures and the displacement sense of slip surfaces, which is helpful in analyses of paleostresses (Yamaji et al., 2005; Federico et al., 2010; Tonai et al., 2011) and in determining whether faults are of tectonic or nontectonic origin (Anders et al., 2013; Wakizaka, 2015; Yamane et al., 2015). The Horonobe area, located on the eastern margin of a Neogene–Quaternary sedimentary basin on the western side of northern Hokkaido, Japan, is in an active Quaternary foreland fold-and-thrust belt located near the boundary between the Okhotsk and Amurian plates (Fig. 3).
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2016, TectonophysicsCitation Excerpt :This suggests that the analyzed fault-slip data population carries kinematically heterogeneous information about the faulting mechanism and evolution of the intra-arc zone. Following this, the strain analysis would not be representative without an arbitrary data selection (Angelier, 1984; Federico et al., 2010; Marrett and Allmendinger, 1990; Veloso et al., 2015; Yamaji, 2000). We analyze the fault-slip data by structural sites in an attempt to differentiate local-scale homogeneous strain fields recorded within the regionally heterogeneous fault-data set, as shown further along in the text.