Subduction of oceanic crust at an unusually low-angle has been proposed as a model for the growth... more Subduction of oceanic crust at an unusually low-angle has been proposed as a model for the growth of continental crust older than about 2.5 Ga. At modern zones of low-angle-, or flat-subduction, magmatic additions to new crust come from partial melting of both the subducting oceanic crust (slab) and the thin wedge of mantle above the slab. Evidence for both a slab and wedge source is preserved in most late Archaean (3.0-2.5 Ga) terrains, but we find little evidence that a mantle wedge contributed to crustal growth prior to ∼3.1 Ga. This lack of evidence in part reflects a dearth of exposed crust aged between 3.0 and 3.3 Ga, but also suggests that subduction enriched mantle source regions did not develop before ∼3.3 Ga and possibly not before 3.1 Ga. In contrast to most modern terrains and some late-Archaean terrains, early Archaean (>∼3.3 Ga) continental crust evolved through direct melting of thick mafic crust. We invoke a process of subduction that does not include the development of a mantle wedge, and call this process Archaean flat-subduction to distinguish it from modern low-angle subduction.
Australians love energy. Almost all facets of our modern life depend on it. For much of Australia... more Australians love energy. Almost all facets of our modern life depend on it. For much of Australia’s European history, our major energy sources have been from hydrocarbons. These, however, are non-renewable and come with increasing environmental and other concerns. In a carbon-constrained future, where will Australia’s energy come from? What will power us into the next century and beyond? The answer is literally beneath our feet—our radioactive heritage. Australia is endowed with uranium (U), thorium (Th) and resultant thermal energy. The energy generated by the natural breakdown of radioactive elements is immense and can be captured not only by fission of U and Th in nuclear reactors, but by the use of geothermal energy, using Earth’s in-situ heat from this radioactive decay to generate electrical power. Both have potential to supply energy for Australia for thousands of years, particularly geothermal energy—it is renewable and environmentally friendly, and Australia has vast therma...
Deep seismic reflection data across the Archaean Eastern Goldfields Province, northeastern Yilgar... more Deep seismic reflection data across the Archaean Eastern Goldfields Province, northeastern Yilgarn Craton, Western Australia, have provided information on its crustal architecture and on several of its highly mineralised belts. The seismic reflection data allow interpretation of several prominent crustal scale features, including an eastward thickening of the crust, subdivision of the crust into three broad layers, the presence of a prominent east dip to the majority of the reflections and the interpretation of three east-dipping crustal-penetrating shear zones. These east-dipping shear zones are major structures that subdivide the region into four terranes. Major orogenic gold deposits in the Eastern Goldfields Province are spatially associated with these major structures. The Laverton Tectonic Zone, for example, is a highly mineralised corridor that contains several world-class gold deposits plus many smaller deposits. Other non crustal-penetrating structures within the area do not appear to be as well endowed metallogenically as the Laverton structure. The seismic reflection data have also imaged a series of lowangle shear zones within and beneath the granite-greenstone terranes. Where the low-angle shear zones intersect the major crustal-penetrating structures, a wedge shaped geometry is formed. This geometry forms a suitable fluid focusing wedge in which upward to subhorizontal moving fluids are focused and then distributed into the nearby complexly deformed greenstones.
The Archaean granites and granitic gneisses of the Eastern Goldfields in the Yilgarn Craton, West... more The Archaean granites and granitic gneisses of the Eastern Goldfields in the Yilgarn Craton, Western Australia, can be divided into two major groups (high-Ca and low-Ca), and three minor groups (high-HFSE (high field strength elements), mafic, and syenitic). The high-Ca group (68-77% SiO2) with high AIzO3, Na20 and Sr, and low Y, shares many features with typical Archaean tonalite-trondhjemite suites, but has higher K20, Rb, and Th contents. The low-Ca group (70-76% SiO2) differs from the high-Ca group in having lower A1203, CaO, and Na20, but higher K20, Rb, Th, Zr, Y, La and Ce contents. Granites of the high-HFSE, mafic and syenitic groups form a minor component (10-20%) of the Eastern Goldfields granites. The siliceous (74-77% SiOz) high-HFSE granites are restricted to a narrow NNWtrending zone and are characterised by high TiOz, total FeO, MgO, Y, Zr and Ce, but only moderate Rb, Th and Pb contents. The A-type syenites (50-68% SiOz) are distinguished by their high total alkalies and mainly occur along tectonic lineaments. The mafic group (55-70% SiO2) is lithologically diverse and exhibits a wide range of K20, Rb, Th, La and Ce contents. Granite emplacement occurred between 2.69 and 2.60 Ga, contemporaneous with, or postdating , greenstone formation, end values for the high-Ca, mafic and syenitic groups are similar (mostly 0.0 to +2.5), whereas those for the low-Ca group show a pronounced polarity, from-4.5 in the west to +2.0 in the east. Nd depleted-mantle model ages for the low-Ca granites range from 3.2 Ga in the west to 2.75 Ga in the east. Model ages for the high-Ca group (2.75-2.9 Ga) overlap with ages for inherited zircons from these granites. The high-Ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source (subducted oceanic crust, crustal underplate or thickened crust), or remelting of an older tonalitic source derived by such a process. If the high-Ca granites were largely crust derived, then their extensive source rocks must have formed less than 250 Ma prior to granite formation. The low-Ca granites appear to be the products of crustal reworking, probably from a tonalitic to granodioritic protolith that was progressively younger towards the east, perhaps in the order of several hundred million years younger, or involved an additional younger component. The localisation of the crustally-derived high-HFSE granites suggests either geochemical zonation of the crust or specific tectonic processes, such as rifting. The mafic granites, and possibly the syenites, imply a significant mantle contribution and new crustal growth, although the extent is equivocal. The crust of the Eastern Goldfields appears to have been generated by both lateral and vertical accretion over a significant period from, or before, 3.0 Ga until the time of granite emplacement.
... 4.1-4(e): Di Marco and Lowe, 1989a). 4.1-3.1.2. Kelly Group. Deposition of the Warrawoona Gro... more ... 4.1-4(e): Di Marco and Lowe, 1989a). 4.1-3.1.2. Kelly Group. Deposition of the Warrawoona Group was followed by a 75 My hiatus in volcanism, during which time the terrane was uplifted and eroded under at least locally subaerial conditions (Buick et al., 1995). ...
... Precision is better than ±1% of the reported values. Loss on Ignition (LOI) was determined by... more ... Precision is better than ±1% of the reported values. Loss on Ignition (LOI) was determined by gravimetry after combustion at 1100 °C. FeO abundances were determined by digestion and electrochemical titration using a modified method based on Shapiro and Brannock (1962). ...
The Boddington Gold Mine (BGM), Western Australia (current gold resource and past production&... more The Boddington Gold Mine (BGM), Western Australia (current gold resource and past production> 26 Moz Au) is one of the largest Au deposits in the world. The bedrock resource also contains a recoverable copper resource of 800 kt and appreciable amounts of ...
Subduction of oceanic crust at an unusually low-angle has been proposed as a model for the growth... more Subduction of oceanic crust at an unusually low-angle has been proposed as a model for the growth of continental crust older than about 2.5 Ga. At modern zones of low-angle-, or flat-subduction, magmatic additions to new crust come from partial melting of both the subducting oceanic crust (slab) and the thin wedge of mantle above the slab. Evidence for both a slab and wedge source is preserved in most late Archaean (3.0-2.5 Ga) terrains, but we find little evidence that a mantle wedge contributed to crustal growth prior to ∼3.1 Ga. This lack of evidence in part reflects a dearth of exposed crust aged between 3.0 and 3.3 Ga, but also suggests that subduction enriched mantle source regions did not develop before ∼3.3 Ga and possibly not before 3.1 Ga. In contrast to most modern terrains and some late-Archaean terrains, early Archaean (>∼3.3 Ga) continental crust evolved through direct melting of thick mafic crust. We invoke a process of subduction that does not include the development of a mantle wedge, and call this process Archaean flat-subduction to distinguish it from modern low-angle subduction.
Australians love energy. Almost all facets of our modern life depend on it. For much of Australia... more Australians love energy. Almost all facets of our modern life depend on it. For much of Australia’s European history, our major energy sources have been from hydrocarbons. These, however, are non-renewable and come with increasing environmental and other concerns. In a carbon-constrained future, where will Australia’s energy come from? What will power us into the next century and beyond? The answer is literally beneath our feet—our radioactive heritage. Australia is endowed with uranium (U), thorium (Th) and resultant thermal energy. The energy generated by the natural breakdown of radioactive elements is immense and can be captured not only by fission of U and Th in nuclear reactors, but by the use of geothermal energy, using Earth’s in-situ heat from this radioactive decay to generate electrical power. Both have potential to supply energy for Australia for thousands of years, particularly geothermal energy—it is renewable and environmentally friendly, and Australia has vast therma...
Deep seismic reflection data across the Archaean Eastern Goldfields Province, northeastern Yilgar... more Deep seismic reflection data across the Archaean Eastern Goldfields Province, northeastern Yilgarn Craton, Western Australia, have provided information on its crustal architecture and on several of its highly mineralised belts. The seismic reflection data allow interpretation of several prominent crustal scale features, including an eastward thickening of the crust, subdivision of the crust into three broad layers, the presence of a prominent east dip to the majority of the reflections and the interpretation of three east-dipping crustal-penetrating shear zones. These east-dipping shear zones are major structures that subdivide the region into four terranes. Major orogenic gold deposits in the Eastern Goldfields Province are spatially associated with these major structures. The Laverton Tectonic Zone, for example, is a highly mineralised corridor that contains several world-class gold deposits plus many smaller deposits. Other non crustal-penetrating structures within the area do not appear to be as well endowed metallogenically as the Laverton structure. The seismic reflection data have also imaged a series of lowangle shear zones within and beneath the granite-greenstone terranes. Where the low-angle shear zones intersect the major crustal-penetrating structures, a wedge shaped geometry is formed. This geometry forms a suitable fluid focusing wedge in which upward to subhorizontal moving fluids are focused and then distributed into the nearby complexly deformed greenstones.
The Archaean granites and granitic gneisses of the Eastern Goldfields in the Yilgarn Craton, West... more The Archaean granites and granitic gneisses of the Eastern Goldfields in the Yilgarn Craton, Western Australia, can be divided into two major groups (high-Ca and low-Ca), and three minor groups (high-HFSE (high field strength elements), mafic, and syenitic). The high-Ca group (68-77% SiO2) with high AIzO3, Na20 and Sr, and low Y, shares many features with typical Archaean tonalite-trondhjemite suites, but has higher K20, Rb, and Th contents. The low-Ca group (70-76% SiO2) differs from the high-Ca group in having lower A1203, CaO, and Na20, but higher K20, Rb, Th, Zr, Y, La and Ce contents. Granites of the high-HFSE, mafic and syenitic groups form a minor component (10-20%) of the Eastern Goldfields granites. The siliceous (74-77% SiOz) high-HFSE granites are restricted to a narrow NNWtrending zone and are characterised by high TiOz, total FeO, MgO, Y, Zr and Ce, but only moderate Rb, Th and Pb contents. The A-type syenites (50-68% SiOz) are distinguished by their high total alkalies and mainly occur along tectonic lineaments. The mafic group (55-70% SiO2) is lithologically diverse and exhibits a wide range of K20, Rb, Th, La and Ce contents. Granite emplacement occurred between 2.69 and 2.60 Ga, contemporaneous with, or postdating , greenstone formation, end values for the high-Ca, mafic and syenitic groups are similar (mostly 0.0 to +2.5), whereas those for the low-Ca group show a pronounced polarity, from-4.5 in the west to +2.0 in the east. Nd depleted-mantle model ages for the low-Ca granites range from 3.2 Ga in the west to 2.75 Ga in the east. Model ages for the high-Ca group (2.75-2.9 Ga) overlap with ages for inherited zircons from these granites. The high-Ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source (subducted oceanic crust, crustal underplate or thickened crust), or remelting of an older tonalitic source derived by such a process. If the high-Ca granites were largely crust derived, then their extensive source rocks must have formed less than 250 Ma prior to granite formation. The low-Ca granites appear to be the products of crustal reworking, probably from a tonalitic to granodioritic protolith that was progressively younger towards the east, perhaps in the order of several hundred million years younger, or involved an additional younger component. The localisation of the crustally-derived high-HFSE granites suggests either geochemical zonation of the crust or specific tectonic processes, such as rifting. The mafic granites, and possibly the syenites, imply a significant mantle contribution and new crustal growth, although the extent is equivocal. The crust of the Eastern Goldfields appears to have been generated by both lateral and vertical accretion over a significant period from, or before, 3.0 Ga until the time of granite emplacement.
... 4.1-4(e): Di Marco and Lowe, 1989a). 4.1-3.1.2. Kelly Group. Deposition of the Warrawoona Gro... more ... 4.1-4(e): Di Marco and Lowe, 1989a). 4.1-3.1.2. Kelly Group. Deposition of the Warrawoona Group was followed by a 75 My hiatus in volcanism, during which time the terrane was uplifted and eroded under at least locally subaerial conditions (Buick et al., 1995). ...
... Precision is better than ±1% of the reported values. Loss on Ignition (LOI) was determined by... more ... Precision is better than ±1% of the reported values. Loss on Ignition (LOI) was determined by gravimetry after combustion at 1100 °C. FeO abundances were determined by digestion and electrochemical titration using a modified method based on Shapiro and Brannock (1962). ...
The Boddington Gold Mine (BGM), Western Australia (current gold resource and past production&... more The Boddington Gold Mine (BGM), Western Australia (current gold resource and past production> 26 Moz Au) is one of the largest Au deposits in the world. The bedrock resource also contains a recoverable copper resource of 800 kt and appreciable amounts of ...
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