Structural history of the Arthur Lineament, northwest Tasmania: An analysis of critical outcrops

Abstract

The Arthur Lineament of northwestern Tasmania is a Cambrian (510 Ϯ 10 Ma) high-strain metamorphic belt. In the south it is composed of metasedimentary and mafic meta-igneous lithologies of the 'eastern' Ahrberg Group, Bowry Formation and a high-strain part of the Oonah Formation. Regionally, the lineament separates the Rocky Cape Group correlates and 'western' Ahrberg Group to its west from the relatively low-strain parts of the Oonah Formation, and the correlated Burnie Formation, to its east. Early folding and thrusting caused emplacement of the allochthonous Bowry Formation, which is interpreted to occur as a fault-bound slice, towards the eastern margin of the parautochthonous 'eastern' Ahrberg Group metasediments. The early stages of formation of the Arthur Lineament involved two folding events. The first deformation (CaD1) produced a schistose axial-planar fabric and isoclinal folds synchronous with thrusting. The second deformation (CaD2) produced a coarser schistosity and tight to isoclinal folds. South-plunging, north-south stretching lineations, top to the south shear sense indicators, and south-verging, downward-facing folds in the Arthur Lineament suggest south-directed transport. CaF1 and CaF2 were rotated to a north-south trend in zones of high strain during the CaD2 event. CaD3, later in the Cambrian, folded the earlier foliations in the Arthur Lineament and produced west-dipping steep thrusts, creating the linear expression of the structure.KEY WORDS: Arthur Lineament, Cambrian, strain, structure, Tasmania, Tyennan Orogeny.*Corresponding author and present address: Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia (Oliver.Holm@ga.gov.au).Formation amphibolites, which the granitoid intrudes, have been correlated with the Kanunnah Subgroup, which has a preferred age of 650-580 Ma (Crawford 1992). We conclude that the Bowry Formation cannot be a lithostratigraphic correlative of the Kanunnah Subgroup or any part of the Ahrberg Group. Turner and Bottrill (2001) discussed the problems associated with large differences in metamorphic history between the Bowry Formation and other parts of the 'Timbs Group' and concluded that the Bowry Formation had a faulted margin against the remainder of the 'Timbs Group', with a metamorphic grade difference across the fault. The western section of the 'Timbs Group' is interpreted here as a parautochthonous slice of the Ahrberg Group, and is referred to in this paper as the 'eastern' Ahrberg Group. The autochthonous Ahrberg Group is referred to as the 'western' Ahrberg Group. The Bowry Formation is referred to here as a separate unit with no specific correlates. The Bowry Formation is fault bounded in the southern Arthur Lineament, has internal evidence of a different metamorphic history (Turner & Bottrill 2001) and is probably much older. There are other fault-bounded units within the Arthur Lineament, in particular, east of the Bowry Formation and faulted against the high-strain Oonah Formation is a block of material that is similar in appearance to t...

Palaeozoic suturing of eastern and western Tasmania in the west Tamar region: Implications for the tectonic evolution of southeast Australia

“…In contrast, Cambrian structures in the Badger Head Group allochthon compare well to those 100 km to the west, in and adjacent to the Arthur Lineament (Figure 1). There, tectonic vergence during the Cambrian was approximately south [D 1 & D 2 (Holm & Berry 2002)] and then east [D 3 (Holm & Berry 2002)], closely matching the southeast‐ (D 1 ) and east‐ (D 2 ) vergence, respectively, of structures in the Badger Head Group. Open folding and a spaced crenulation cleavage of D 3 age in the Arthur Lineament, however, contrasts with the tight to isoclinal folding and slaty cleavage for similarly east‐verging structures in the Badger Head Group (D 2 ).…”

“…Holm and Berry (2002 ) proposed westward emplacement of the mafic–ultramafic complexes followed by a change in tectonic vergence toward the south to reconcile differences in tectonic vergence between structures in the Arthur Lineament and west‐directed emplacement of the mafic–ultramafic complexes. However, this change does not readily explain the east‐verging structures present in both the Arthur Lineament and the Badger Head Group.…”

SHRIMP U–Pb detrital zircon ages from Proterozoic and Early Palaeozoic sandstones and their bearing on the early geological evolution of Tasmania

“…2001), but not the Mathinna Supergroup samples of the present study. The Bowry Formation is part of the Arthur Metamorphic Complex and is a unit for which the correlation is uncertain and for which an allochthonous origin has been proposed (Turner & Bottrill 2001; Holm & Berry 2002). The Forest Conglomerate is the basal unit of the Upper Neoproterozoic Togari Group, unconformably overlying the Rocky Cape Group.…”

“…1994; Meffre et al . 2000; Turner & Bottrill 2001; Holm & Berry 2002). Fingerprinting the sandstones by means of detrital‐zircon age distributions should help clarify the relationships of the different inliers, by testing for commonalities in the ages of source terranes.…”

Geochemistry and tectonic settings of meta‐igneous rocks in the Arthur Lineament and surrounding area, northwest Tasmania*

“…in press), where it is transected by a major northeast‐trending structural zone, the Arthur Lineament (Figure 1). This study reports geochemical and geochronological investigations of the variably deformed Late Neoproterozoic rift sequences and adjacent rocks now incorporated in the Arthur Lineament of northwestern Tasmania (Holm 2002; Holm & Berry 2002). The aim of this study is to define the magmatic affinities and correlations of the Neoproterozoic mafic igneous rocks in northwestern Tasmania within and adjacent to the Arthur Lineament, and hence provide better constraints on their tectonic setting.…”