The mechanisms of continental growth are a crucial part of plate tectonic theory, yet a clear und... more The mechanisms of continental growth are a crucial part of plate tectonic theory, yet a clear understanding of the processes involved remains elusive. Here we determine seismic Rayleigh wave phase anisotropy variations in the crust beneath the southern Tasmanides of Australia, a Paleozoic accretionary margin. Our results reveal a complex, thick‐skinned pervasive deformation that was driven by the tectonic interaction between the proto‐Pacific Ocean and the ancient eastern margin of Gondwana. Stress‐induced effects triggered by the collision and entrainment of a microcontinent into the active subduction zone are evident in the anisotropy signature. The paleofracturing trend of failed rifting between Australia and Antarctica is also recorded in the anisotropy pattern as well as a tightly curved feature in central Tasmania. The observed patterns of anisotropy correlate well with recent geodynamic and kinematic models of the Tasmanides and provide a platform from which the spatial exten...
ABSTRACT The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed... more ABSTRACT The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed in response to east–west crustal extension in the Early Devonian. The rift is filled mostly with Lower Devonian volcanic and volcaniclastic rock of the Snowy River Volcanics. Although the structure and geometry of the Buchan Rift and its major bounding faults are well mapped at the surface, a discrepancy exists between the surface distribution of the thickest rift fill and its expected potential field response. To investigate this variation, two new detailed land-based gravity surveys, which span the rift and surrounding basement rocks in an east–west orientation, have been acquired and integrated with pre-existing government data. Qualitative interpretation of the observed magnetic data suggests the highly magnetic rocks of the Snowy River Volcanics have a wider extent at depth than can be mapped at the surface. Forward modelling of both land-based gravity data and aeromagnetic data supports this interpretation. With the Snowy River Volcanics largely confined within the Buchan Rift, resolved geometries also allow for the interpretation of rift boundaries that are wider at depth. These geometries are unusual. Unlike typical basin inversions that involve reactivation of rift-dipping faults, the bounding faults of the Buchan Rift dip away from the rift axis and thus appear unrelated to the preceding rifting episode. Limited inversion of previous extensional rift faults to deform the rift-fill sequences (e.g. Buchan Synclinorium) appears to have been followed by the initiation of new reverse faults in outboard positions, possibly because the relatively strong igneous rift fill began to act as a rigid basement ramp during continued E–W crustal shortening in the Middle Devonian Tabberabberan Orogeny. Overthrusting of the rift margins by older sediments and granite intrusions of the adjacent Tabberabbera and Kuark zones narrowed the exposed rift width at surface. This scenario may help explain the steep-sided geometries and geophysical expressions of other rift basins in the Tasmanides and elsewhere, particularly where relatively mechanically strong basin fill is known or suspected.
... This section presents the latest mapping, regional structural data, and deep crustal seismic ... more ... This section presents the latest mapping, regional structural data, and deep crustal seismic reflection data to highlight the structure of the Victorian crust ... GSV mapping (eg Cayley & McDonald, 1995;VandenBerg et al., 1995, 2000; Cayley & Taylor, 1997, 2000, 2001; Willman et al ...
The Stavely Project is a federal and state government collaboration that aims to increase greenfi... more The Stavely Project is a federal and state government collaboration that aims to increase greenfields mineral exploration in western Victoria across an area that preserves a number of structurally dismembered prospective Cambrian volcanic belts (collectively termed the Stavely Arc), the majority of which are under younger cover rocks. These belts developed along with eastern margin of the proto-Australian continent (Delamerian Craton) during west-directed subduction. The region contains numerous features in common with well-endowed volcanic arc terranes worldwide. The project aim was achieved by collecting new geoscientific datasets to better characterise the subsurface Cambrian geology in order to de-risk exploration efforts in the region. Restoration of the volcanic belts to Cambrian-time results in three strikepersistent (~1160 km composite length), sub-parallel belts that are prospective for a series of arc-related mineral systems (porphyry, epithermal and volcanic-hosted massiv...
Mineralised Cu±Mo porphyries were discovered in belts of Cambrian andesite in the Stavely region ... more Mineralised Cu±Mo porphyries were discovered in belts of Cambrian andesite in the Stavely region of western Victoria in the late 1970s. Thick regolith complicates geochemical exploration. Some of the initial aircore exploration drilling failed to penetrate the regolith before refusing so that sampling to define geochemical anomalies was not fully effective. Through to the mid-2000s various companies only completed a small number of follow up diamond drill holes to depths of 100-300 m. This drilling encountered sub-economic grades (typically 0.1-0.3% Cu) mostly in propylitic and phyllic alteration associated with dacitic porphyry dykes intruding up into andesite host rocks. This lack of early success and low gold content, when combined with no historic indicators of viable mineralisation such as artisanal mining and uncertainty over the geological context, meant there was little appetite to persevere. There was no deeper drilling to test for the presence of porphyry bodies as a sourc...
The period between 480 Ma and 410 Ma in the Lachlan Orogen of southeastern Australia is the most ... more The period between 480 Ma and 410 Ma in the Lachlan Orogen of southeastern Australia is the most important metallogenically in eastern Australia, having contributed over half of the mineral wealth in the Tasman Element (or Orogen). The period of intense mineralisation is interpreted to be related to the development of the Lachlan Orocline at the very end of the Ordovician and into the Silurian. Formation of this orocline was triggered by the oblique accretion of the VanDieland crustal fragment, which includes the present day Melbourne Zone in Victoria and western Tasmania. Prior to this event, eastern Australia was characterised by a west-dipping convergent margin with associated smallto moderate-sized volcanic-hosted massive sulphide (VHMS: Girilambone, Mount Windsor and Balcooma) and calc-alkaline porphyry Cu-Au deposits (Copper Hill, Marsden) with ages of 480 Ma to 450 Ma. Orocline development was initiated by the accretion of the VanDieland at ~445 Ma, which was accompanied orog...
The mechanisms of continental growth are a crucial part of plate tectonic theory, yet a clear und... more The mechanisms of continental growth are a crucial part of plate tectonic theory, yet a clear understanding of the processes involved remains elusive. Here we determine seismic Rayleigh wave phase anisotropy variations in the crust beneath the southern Tasmanides of Australia, a Paleozoic accretionary margin. Our results reveal a complex, thick‐skinned pervasive deformation that was driven by the tectonic interaction between the proto‐Pacific Ocean and the ancient eastern margin of Gondwana. Stress‐induced effects triggered by the collision and entrainment of a microcontinent into the active subduction zone are evident in the anisotropy signature. The paleofracturing trend of failed rifting between Australia and Antarctica is also recorded in the anisotropy pattern as well as a tightly curved feature in central Tasmania. The observed patterns of anisotropy correlate well with recent geodynamic and kinematic models of the Tasmanides and provide a platform from which the spatial exten...
ABSTRACT The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed... more ABSTRACT The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed in response to east–west crustal extension in the Early Devonian. The rift is filled mostly with Lower Devonian volcanic and volcaniclastic rock of the Snowy River Volcanics. Although the structure and geometry of the Buchan Rift and its major bounding faults are well mapped at the surface, a discrepancy exists between the surface distribution of the thickest rift fill and its expected potential field response. To investigate this variation, two new detailed land-based gravity surveys, which span the rift and surrounding basement rocks in an east–west orientation, have been acquired and integrated with pre-existing government data. Qualitative interpretation of the observed magnetic data suggests the highly magnetic rocks of the Snowy River Volcanics have a wider extent at depth than can be mapped at the surface. Forward modelling of both land-based gravity data and aeromagnetic data supports this interpretation. With the Snowy River Volcanics largely confined within the Buchan Rift, resolved geometries also allow for the interpretation of rift boundaries that are wider at depth. These geometries are unusual. Unlike typical basin inversions that involve reactivation of rift-dipping faults, the bounding faults of the Buchan Rift dip away from the rift axis and thus appear unrelated to the preceding rifting episode. Limited inversion of previous extensional rift faults to deform the rift-fill sequences (e.g. Buchan Synclinorium) appears to have been followed by the initiation of new reverse faults in outboard positions, possibly because the relatively strong igneous rift fill began to act as a rigid basement ramp during continued E–W crustal shortening in the Middle Devonian Tabberabberan Orogeny. Overthrusting of the rift margins by older sediments and granite intrusions of the adjacent Tabberabbera and Kuark zones narrowed the exposed rift width at surface. This scenario may help explain the steep-sided geometries and geophysical expressions of other rift basins in the Tasmanides and elsewhere, particularly where relatively mechanically strong basin fill is known or suspected.
... This section presents the latest mapping, regional structural data, and deep crustal seismic ... more ... This section presents the latest mapping, regional structural data, and deep crustal seismic reflection data to highlight the structure of the Victorian crust ... GSV mapping (eg Cayley & McDonald, 1995;VandenBerg et al., 1995, 2000; Cayley & Taylor, 1997, 2000, 2001; Willman et al ...
The Stavely Project is a federal and state government collaboration that aims to increase greenfi... more The Stavely Project is a federal and state government collaboration that aims to increase greenfields mineral exploration in western Victoria across an area that preserves a number of structurally dismembered prospective Cambrian volcanic belts (collectively termed the Stavely Arc), the majority of which are under younger cover rocks. These belts developed along with eastern margin of the proto-Australian continent (Delamerian Craton) during west-directed subduction. The region contains numerous features in common with well-endowed volcanic arc terranes worldwide. The project aim was achieved by collecting new geoscientific datasets to better characterise the subsurface Cambrian geology in order to de-risk exploration efforts in the region. Restoration of the volcanic belts to Cambrian-time results in three strikepersistent (~1160 km composite length), sub-parallel belts that are prospective for a series of arc-related mineral systems (porphyry, epithermal and volcanic-hosted massiv...
Mineralised Cu±Mo porphyries were discovered in belts of Cambrian andesite in the Stavely region ... more Mineralised Cu±Mo porphyries were discovered in belts of Cambrian andesite in the Stavely region of western Victoria in the late 1970s. Thick regolith complicates geochemical exploration. Some of the initial aircore exploration drilling failed to penetrate the regolith before refusing so that sampling to define geochemical anomalies was not fully effective. Through to the mid-2000s various companies only completed a small number of follow up diamond drill holes to depths of 100-300 m. This drilling encountered sub-economic grades (typically 0.1-0.3% Cu) mostly in propylitic and phyllic alteration associated with dacitic porphyry dykes intruding up into andesite host rocks. This lack of early success and low gold content, when combined with no historic indicators of viable mineralisation such as artisanal mining and uncertainty over the geological context, meant there was little appetite to persevere. There was no deeper drilling to test for the presence of porphyry bodies as a sourc...
The period between 480 Ma and 410 Ma in the Lachlan Orogen of southeastern Australia is the most ... more The period between 480 Ma and 410 Ma in the Lachlan Orogen of southeastern Australia is the most important metallogenically in eastern Australia, having contributed over half of the mineral wealth in the Tasman Element (or Orogen). The period of intense mineralisation is interpreted to be related to the development of the Lachlan Orocline at the very end of the Ordovician and into the Silurian. Formation of this orocline was triggered by the oblique accretion of the VanDieland crustal fragment, which includes the present day Melbourne Zone in Victoria and western Tasmania. Prior to this event, eastern Australia was characterised by a west-dipping convergent margin with associated smallto moderate-sized volcanic-hosted massive sulphide (VHMS: Girilambone, Mount Windsor and Balcooma) and calc-alkaline porphyry Cu-Au deposits (Copper Hill, Marsden) with ages of 480 Ma to 450 Ma. Orocline development was initiated by the accretion of the VanDieland at ~445 Ma, which was accompanied orog...
Micro-continental ribbons can develop in several tectonic settings. Some form during continental ... more Micro-continental ribbons can develop in several tectonic settings. Some form during continental break-up in response to type 1 passive margn development, in which micro-continental ribbons are trapped by oceanic crust caused by mid-ocean-ridge jumping. The Mascarene Plateau is a modern example of such a micro-continent. The second mechanism that develops large ribbons is subduction roll-back. Elongate ribbons oriented parallel with convergent margin are “ripped” from the over-riding plate during back arc basin development. The Lord Howe Rise represents a modern analogue of this type of ribbon. The two episodes of significant continental growth of the Australian continent are profoundly influenced by ribbon tectonics by modifying the plate geometry as well as increasing the aerial extent of the continent.
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