Peter Betts

Crustal evolution and geodynamic setting of the Sefwi Greenstone Belt, WAC. The Palaeoproterozoic West African Craton (2.25 - 2.07 Ga) represents one of the youngest, large provinces of juvenile crust on Earth. It displays lithological and architectural similarities to a numberof late Archean Provinces, including the Abitibi-Opatica terrane, Superior Province and Karelian and Kola cratons of the Fennoscandian Shield. Forming just after the Archean-Palaeoproterozoic transition, the magmatic evolution and geodynamic setting of juvenile crust formation of the WAC continues to stimulate scientific debate.

This paper presents a plate tectonic model for the evolution of the Australian continent between ca. 1800 and 1100 Ma. Between ca. 1800 and 1600 Ma episodic orogenesis occurred along the southern margin of the continent above a north-dipping subduction system. During ...

Craton margins undergo intense deformation influenced by the pre-existing crustal and lithospheric architecture, rheology, and far-field kinematics. The role of rheological contrasts and weak zones at the edge of the craton has been discussed, but it is unclear whether deformation in the upper crust is influenced by the geometry of the craton margin itself (i.e., whether the margin dips towards or away from the interior of the craton). Our analogue experiments are aimed at studying the influence of craton margin geometry on structures formed during rifting and inversion, as craton margins are prone to reworking and reactivation during superimposed tectonic events.The experiments are designed based on the geometries of the eastern and southern margins of the North Australian Craton which has experienced multiple stages of extension and shortening. The inward vs. outward dipping craton margins in these areas were interpreted from crustal-scale seismic reflection data.  In our experime...

Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

... 08120090802266600 ARA Aitken a * , PG Betts a , BF Schaefer a & SE Rye a pages 1127-1138. ... Evolution of a crustal scale transpressive shear zone in the Albany–Fraser Orogen, SW Australia: 1. P–T conditions of Mesoproterozoic metamorphism in the Coramup Gneiss. ...

Magmatic-hydrothermal ore deposits in suprasubduction environments are abundant in the Andes, where they are associated with the eastward subduction of the Nazca plate beneath the continental South American plate during the last 200 Ma. These deposits do not seem to correspond with progressive subduction processes but are concentrated at distinct regions that experienced pulses of intense metallogenic activity. An example is the Miocene metallogenic belt in the central Andes that was formed during a relatively short period between 15-5 Ma, and is characterised by clusters of mineral deposits in northern Peru and in central Chile. We propose that a key factor for the occurrence of metallogenic episodes during progressive subduction is related to bathymetric heterogeneities within the subducting oceanic plate. Such heterogeneities are manifested by the subduction of topographic anomalies that affected the whole dynamics of the subduction system and triggered metallogenic processes. Our study shows that the spatial and temporal distribution of Miocene ore deposits in the Peruvian Andes correspond with the arrival of relatively buoyant topographic anomalies, namely the Nazca Ridge in central Peru and the now-consumed Inca Plateau in northern Peru, at the subduction zone. Plate reconstruction shows a rapid metallogenic response to the arrival of the topographic anomalies at the subduction trench. This is indicated by clusters of ore deposits situated within the proximity of the laterally migrating zones of ridge subduction. It is accordingly suggested that tectonic changes associated with aseismic ridge subduction, (i.e. a change in the state of stress, flattening of the subducting slab, temporal quiescence in the volcanic activity and partial melting of the subducting slab) may trigger the formation of ore deposits in metallogenically fertile suprasubduction environments.

Tectonic models for the latest Paleoproterozoic to earliest Mesoproterozoic evolution of eastern Australia (circa 1620–1500 Ma) are diverse and either emphasize plume or plate margin activity, neither of which satisfactorily explains all geological observations. The dichotomy ...

The Australian continent records c. 1860–1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth (c. 1860–1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-Nor...

ABSTRACT Detailed structural mapping from the northern Mount Painter Province indicates that the metasediments of the Radium Creek Group underwent both Mesoproterozoic and Palaeozoic poly-deformation (Figure 1). Early north directed D1-D2 deformation is accompanied by upper amphibolite facies metamorphism. This deformation is characterised by recumbent folds that are preserved in the hinges of NE-SW trending doubly-plunging upright F3 folds (Armit et al., 2012). U-Pb-Hf dating of zircons from the Radium Creek Group identifies a consistent maximum depositional age for the Radium Creek Metamorphics of ca. 1596-1592 Ma across the Paralana Fault with a εHf range between -5.5 and +4. The timing of D1-D2 is constrained between this ca. 1592 Ma maximum depositional age and the minimum depositional age indicated by the truncation of the S1-S2 fabrics during the shallow-level emplacement of the ca. 1585-1569 Ma (Elburg et al., 2001; Fraser and Neumann, 2010; Neumann, 2001; Neumann et al., 2009) porphyritic Mount Neill Granite. This indicates that the Radium Creek Group were deposited, buried to mid-crustal levels and exhumed within 7 Myrs between 1592 and 1585 Ma before switching once again during the onset of NW-SE directed shortening during D3 (Armit et al., 2012). This time-frame is similar to that of modern orogens such as the Late Miocene-Present Kaikoura Orogeny of southern New Zealand (Landis and Coombs, 1964; Kamp, 1984). An S3 fabric overprints the earlier S1-S2 fabrics in the metasediments and extends into the Mount Neill Granite as a steeply dipping NE-SW trending gneissosity. The D3 event is constrained by the presence of this S3 foliation in the ca. 1585-1569 Ma Mount Neill Granite, the ca. 1552 Ma emplacement age (Fraser and Neumann, 2010) of the undeformed Hodgkinson Granodiorite and dating of ca. 1555 Ma metamorphic overgrowths on zircons from the Radium Creek Group (Armit et al., 2012). Repeated reactivation of the Proterozoic basement architecture constitutes significant deformational phases in the Mount Painter Province. During the development of the Neoproterozoic Adelaidean basins a series of shallow north-plunging quartz defined stretch lineations along the NE-SW trending Paralana Fault Zone record a phase of transtensional movement. NW-SE directed D5 deformation produced reverse movement along the Paralana Fault and tightened the pre-existing upright F3 folds producing a shallow NE-SW trending crenulation lineation on the steeply dipping bedding surfaces of the Radium Creek Group. NE-SW directed D6 shortening warped the existing structures producing type 2 interference patterns with the rotation of F3 and F5 folds axes. These Palaeozoic D5-D6 deformational events most likely reflect the ca. 500 Ma (Dutch et al., 2005; Foden et al., 2006; Harrison and McDougall, 1981; Sandiford et al., 1998) Delamerian Orogeny but might relate to deformation during the Ordovician Alice Springs Orogeny (McLaren et al., 2002). Further brittle deformation that overprints the D6 structures along the Paralana Fault such as a hematite bearing fault breccia at the Mount Neill Granite and metasediment interface highlight the protracted geodynamic evolution of the Paralana Fault Zone. The Mesoproterozoic geodynamic evolution component of the Mount Painter Province differs to that of the southern Gawler Craton and Curnamona Province, but correlates better with the Mount Isa Inlier and the northern Gawler Craton (Figure 2). This provides important Early Mesoproterozoic constraints for future tectonic models of eastern Proterozoic Australia.

... (1998, 2003a) and Betts and Lister (2001, 2002 ... 1997; Page 1998) (Figure 6). Remnants of the Isa Superbasin are also preserved in the Tommy Creek Block (Figures 3, 4) where ca 1630–1620 Ma felsic and mafic igneous rocks are intercalated with siltstone, marble, sandstone ...

... Isograd pattern and regional low-pressure, high-temperature metamorphism of pelitic, mafic and calc-silicate rocks along an east – west section through the Mt Isa Inlier. Australian Journal of Earth Sciences , 53: 167–186. [Taylor & Francis Online], [Web of Science ®] View all ...

... The largely pelitic, commonly carbonaceous metasediments and volcanics of the upper Maronan Supergroup (Toole Creek Volcanics), the Marimo Slate, Staveley Formation, Answer Slate andTommy Creek Beds are post-rift sequences that were deposited between 1.66 and ...

Palaeozoic continental growth and accretionary tectonism along the eastern margin of Gondwana is characterised by the inversion of back-arc basins and accretion of the magmatic arc terranes and micro-continental ribbons. The use of high resolution continental-scale geophysical data has allowed for the interpretation of a series of folded micro-continental ribbons (oroclines) in the Tasmanides of eastern Australia (Cayley et al., 2012; Cayley and Musgrave, in prep; Hoy et al., 2014; Li and Rosebaum (2014), Mochales et al., 2014; Rosenbaum and Lister, 2004a,b; Rosenbaum and Donchak (2012); Rosenbaum and Rubatto (2012) which are considered to be predominantly controlled by changes in plate boundary conditions such as subduction roll-back (Lonergan and White, 1997; Lucente & Speranza 2001; Moresi et al., 2014; Schellart & Lister, 2004)

The Earth is punctuated by relatively transient periods of continental lithospheric amalgamation to form supercontinents. The Nuna Supercontinent formed between ca 2000 and 1800 Ma and is one of the largest episodes of continental amalgamation in Earth's history. In most Nuna configurations Australia occupies a central and important component of the supercontinent. From an Australian perspective, Nuna amalgamation involved rapid accretion in which approximately 60% of the continent formed between ca 1870 Ma and 1800 Ma, and was terminated by the accretion of the West Australian Craton (micro-continent). This amalgamation involved episodic accretion of small crustal fragments, continental ribbons and continental arcs along several continental sutures that are imaged in continent-scale magnetic and gravity datasets and regional seismic reflection data. Major suture zones have been imaged in seismic reflection and potential field data, providing insights into major terrane boundari...

Three-dimensional inversion modelling of airborne magnetic data acquired in the Prince Charles Mountains, East Antarctica, provides an insight into the sub-ice distribution, and three-dimensional geometry of a Neoproterozoic sedimentary basin. A three-dimensional starting model was ...

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This study utilises U-Pb geochronology, Lu-Hf, Sm-Nd isotopes and geochemistry to constrain the timing of deposition, metamorphism and provenance characteristics of buried Palaeoproterozoic meta-sedimentary and meta-igneous rocks in the northern Gawler Craton, Australia. The data suggest that sedimentary sequences were deposited between ca. 1780 –1740 Ma across a wide region accompanied by syn-depositional magmatism. Restricted zircon age spectra, relatively radiogenic whole-rock Hf-Nd and in-situ zircon Hf isotopic compositions and enriched REE signatures support the notion of a connected series of basins or a single large basin, which developed on a common Neoarchaean substrate across the northern Gawler Craton during the Late Palaeoproterozoic. Temporal and isotopic correlation of these indurated rocks with Palaeoproterozoic basins throughout the North Australian Craton suggests they may form part of an extensive basin system that developed across the Australian continent during the Late Palaeoproterozoic. The meta-sedimentary and meta-igneous rocks of the northern Gawler Craton record high-grade crustal anatexis during the ca. 1730-1690 Ma Kimban Orogeny and subsequent Early Mesoproterozoic re-working.

Structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and Bouguer gravity data to develop a multi-scale kinematic and relative overprinting chronology for the Palaeoproterozoic Tallacootra Shear Zone, Australia. D2 mylonitic fabrics at outcrop record Kimban-aged (ca. 1730–1690Ma) N–S shortening and correlate with SZ1 movements. Overprinting D3 sinistral shear zones record the partitioning of near-ideal simple shear and initiated Riedel to regional-scale SZ2 strike-slip on the Tallacootra Shear Zone (SZ2). Previously undocumented NE–SW extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the (ca. 1595–1575Ma) Hiltaba magmatic event. D4 dextral transpression during the (ca. 1470–1450Ma) Coorabie Orogeny reactivated the Tallacootra Shear Zone (SZ2–R4) exhuming lower crust of the northwestern Fowler Domain within a positive flower structure. This latest shear zone movement is related to a system of west-dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening. These methods demonstrate the value of integrating multi-scale structural analyses for the study of shear zones with limited exposure.

... in fold superposition and the development of fold interference patterns are well understood (eg Ramsay, 1962; Thiessen and Means ... The eastern Allendale Mine Area comprises garnet and sillimanite rich metasediments of the Parnell Formation, and the western Allendale Mine ...