The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greens... more The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greenstone terrains on Earth, and is inferred to have developed on an older (> 3.8 Ga), possibly Hadean, continental substrate. Such ancient crust has, however, never been identified in outcrop. Here, we show that metamorphosed gabbroic, leucogabbroic and anorthositic rocks of the South Daltons area, in the western part of the Shaw Granitic Complex, formed at 3.59-3.58 Ga and were intruded by granitic magma at 3.44 Ga. The 3.59-3.58 Ga gabbroic rocks, here named the Mount Webber Gabbro, represent the oldest, unambiguous igneous rock emplacement in the Pilbara Craton and significantly predate the oldest volcanic activity of the 3.53-3.23 Ga Pilbara Supergroup within the East Pilbara Terrane. We interpret the Mount Webber Gabbro samples to represent fragments of a dismembered layered mafic intrusion. Mantle-like zircon δ 18 O and Hf isotope signatures indicate derivation from a chondritic to near chondritic mantle at~3.59 Ga, and do not support the existence of a > 3.8 Ga basement to the East Pilbara Terrane. These results strengthen the notion of an approximately chondritic > 3.5 Ga mantle beneath the Pilbara Craton, and provide further evidence that recent estimates of Archean stabilised continental volumes, based on the assumption of crust extraction from a global, convecting depleted mantle reservoir, may be overestimated.
... Osinski, GR, Spray, JG, Bunch, TE, Grieve, RAF, Schutt, JW and Lee, P. . Post-impact hydrothe... more ... Osinski, GR, Spray, JG, Bunch, TE, Grieve, RAF, Schutt, JW and Lee, P. . Post-impact hydrothermal activity at the Haughton impact structure, Devon Island, Nunavut, Canada. ... [CrossRef], [Web of Science ®] View all references), although the Hickman Crater is much smaller. ...
Australian Journal of Earth Sciences, May 12, 2014
ABSTRACT Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations i... more ABSTRACT Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations in the Fortescue and Hamersley Groups have been further investigated to test their potential stratigraphic relationships. This work has included new observations related to the ca 2.63 Ga Jeerinah Impact Layer (JIL) and impact spherules associated with the 4th Shale-Macroband of the Dales Gorge Iron Member (DGS4) of the Brockman Iron Formation. A unit of impact spherules (microkrystite) correlated with the ca 2.63 Ga JIL is observed within a > 100 m-thick fragmental-intraclast breccia pile in drill cores near Roy Hill. The sequence represents significant thickening of the impact/tsunami unit relative to the JIL type section at Hesta, as well as relative to the 20-30 m-thick ca 2.63 Ga Carawine Dolomite spherule-bearing mega-breccia. The ca 2.48 Ga-old Dales Gorge Member of the Brockman Iron Formation is underlain by an similar to 0.5 m-thick rip-up clast breccia located at the top of the ca 2.50 Ga Mt McRae Shale, and is interpreted as a tsunami deposit. We suggest that the presence of impact ejecta and tsunami units stratigraphically beneath a number of banded iron-formations, and units of ferruginous shale in the Pilbara and South Africa may result from a genetic relationship. For example, it could be that under Archean atmospheric conditions, mafic volcanism triggered by large asteroid impacts enriched the oceans in soluble FeO. If so, seasonal microbial and/or photolytic oxidation to ferric oxide could have caused precipitation of Fe2O3 and silica. In view of the possible occurrence of depositional gaps and paraconformities between impact ejecta units and overlying ferruginous sediments, these relationships require further testing by isotopic age studies.
Geological Society of America Bulletin, Aug 1, 1999
... HJ Hofmann, K. Grey, AH Hickman and RI Thorpe Australia Origin of 3.45 Ga coniform stromatoli... more ... HJ Hofmann, K. Grey, AH Hickman and RI Thorpe Australia Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western ... (1992) as 3.46 Ga. 1256 Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western Australia ...
At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thi... more At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thick. To the north and west the quartzite units wedge out and the succession thins to about 5 km. This regional disparity is attributed to major facies changes and not structural ...
The early Archaean East Pilbara Terrane of the Pilbara Craton represents the archetypical granite... more The early Archaean East Pilbara Terrane of the Pilbara Craton represents the archetypical granite dome-greenstone keel terrain and preserves much of the primary geological features of dome-and-keel formation. Here we present the first detailed lithostratigraphic and structural transect from marginal gneisses of the Muccan Granitic Complex through 6 km of steeply dipping strata of the western Doolena Gap greenstone belt. Based on overprinting relationships, we identified five deformational events (D 1-D 5) that can be correlated between four structural domains: (i) marginal orthogneisses of the polyphase Muccan Granitic Complex, (ii) a dominantly mylonitic shear zone (South Muccan Shear Zone) representing a granite dome-greenstone keel detachment zone, (iii) a Central Fold Belt of dominantly mafic greenschists, and (iv) a lower greenschist-to sub-greenschist facies southern Low-Strain Belt. The D 1 event in the Low-Strain Belt is recorded in syn-depositional normal faulting (f 1) during eruption of deep water low vesicular pillow basalts of the ca. 3.47 Ga Mount Ada Basalt, followed by a conformable transition towards shallow water stromatolites in the Duffer Formation. We interpret the D 1 event as the result of upper-crustal extension and subsequent uplift above the Muccan Granitic Complex. The D 2 event shows the most intense deformation with syn-anatectic tight folds within the Muccan Granitic Complex and tight to isoclinal transposed folds (F 2) and fluid-induced normal faults (f 2) within the Central Fold Belt. The D 2 event resulted in a regional EW composite S 1/2 foliation, and in the development of the mylonitic South Muccan Shear Zone along the dome-keel interface and within the Central Fold Belt, mineral lineations (L 2) in conjunction with increasing southward D 2 L-tectonite. This D 2 event is not observed in a $1 km-thick sandstone package (ascribed to the <3.43 Ga Strelley Pool Formation) in the Low-Strain Belt that was deposited over an angular unconformity indicating 45°SSW tilting of the underlying Mount Ada Basalt and Duffer Formation. This constrains the D 2 event to between 3.47 and 3.43 Ga. We propose that the D 1 and D 2 events record locally significant initiation of Muccan Granitic Complex doming and associated sagduction of greenstone keel rocks, suggesting that partial convective overturn initiated early in the evolution of the East Pilbara Terrane.
Synopsis Moinian and Lower Dalradian metasediments between Glen Roy and Lismore are folded by str... more Synopsis Moinian and Lower Dalradian metasediments between Glen Roy and Lismore are folded by structures belonging to two main phases of deformation. D1 folds are isoclinal and regionally recumbent whereas D2 folds are tight to isoclinal and upright. New information indicates that two structures previously regarded as major recumbent synclines can no longer be accepted as D1 folds. One, the Ballachulish Syncline, was postulated on false stratigraphic criteria and is considered to be non-existent. The other, the Appin Synform, is a D2 fold which locally refolds D1 isoclines, an example being the Balygrundle Syncline† on Lismore. Recumbent folds up to 20 km in amplitude are confined to the area between Kinlochleven and Loch Treig where the Treig Syncline† underlines the Kinlochleven Anticline. Both these structures are refolded by the Blackwater Synform and the Inverlair Antiform†. (†Structure described for the first time)
The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greens... more The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greenstone terrains on Earth, and is inferred to have developed on an older (> 3.8 Ga), possibly Hadean, continental substrate. Such ancient crust has, however, never been identified in outcrop. Here, we show that metamorphosed gabbroic, leucogabbroic and anorthositic rocks of the South Daltons area, in the western part of the Shaw Granitic Complex, formed at 3.59-3.58 Ga and were intruded by granitic magma at 3.44 Ga. The 3.59-3.58 Ga gabbroic rocks, here named the Mount Webber Gabbro, represent the oldest, unambiguous igneous rock emplacement in the Pilbara Craton and significantly predate the oldest volcanic activity of the 3.53-3.23 Ga Pilbara Supergroup within the East Pilbara Terrane. We interpret the Mount Webber Gabbro samples to represent fragments of a dismembered layered mafic intrusion. Mantle-like zircon δ 18 O and Hf isotope signatures indicate derivation from a chondritic to near chondritic mantle at~3.59 Ga, and do not support the existence of a > 3.8 Ga basement to the East Pilbara Terrane. These results strengthen the notion of an approximately chondritic > 3.5 Ga mantle beneath the Pilbara Craton, and provide further evidence that recent estimates of Archean stabilised continental volumes, based on the assumption of crust extraction from a global, convecting depleted mantle reservoir, may be overestimated.
... Osinski, GR, Spray, JG, Bunch, TE, Grieve, RAF, Schutt, JW and Lee, P. . Post-impact hydrothe... more ... Osinski, GR, Spray, JG, Bunch, TE, Grieve, RAF, Schutt, JW and Lee, P. . Post-impact hydrothermal activity at the Haughton impact structure, Devon Island, Nunavut, Canada. ... [CrossRef], [Web of Science ®] View all references), although the Hickman Crater is much smaller. ...
Australian Journal of Earth Sciences, May 12, 2014
ABSTRACT Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations i... more ABSTRACT Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations in the Fortescue and Hamersley Groups have been further investigated to test their potential stratigraphic relationships. This work has included new observations related to the ca 2.63 Ga Jeerinah Impact Layer (JIL) and impact spherules associated with the 4th Shale-Macroband of the Dales Gorge Iron Member (DGS4) of the Brockman Iron Formation. A unit of impact spherules (microkrystite) correlated with the ca 2.63 Ga JIL is observed within a &gt; 100 m-thick fragmental-intraclast breccia pile in drill cores near Roy Hill. The sequence represents significant thickening of the impact/tsunami unit relative to the JIL type section at Hesta, as well as relative to the 20-30 m-thick ca 2.63 Ga Carawine Dolomite spherule-bearing mega-breccia. The ca 2.48 Ga-old Dales Gorge Member of the Brockman Iron Formation is underlain by an similar to 0.5 m-thick rip-up clast breccia located at the top of the ca 2.50 Ga Mt McRae Shale, and is interpreted as a tsunami deposit. We suggest that the presence of impact ejecta and tsunami units stratigraphically beneath a number of banded iron-formations, and units of ferruginous shale in the Pilbara and South Africa may result from a genetic relationship. For example, it could be that under Archean atmospheric conditions, mafic volcanism triggered by large asteroid impacts enriched the oceans in soluble FeO. If so, seasonal microbial and/or photolytic oxidation to ferric oxide could have caused precipitation of Fe2O3 and silica. In view of the possible occurrence of depositional gaps and paraconformities between impact ejecta units and overlying ferruginous sediments, these relationships require further testing by isotopic age studies.
Geological Society of America Bulletin, Aug 1, 1999
... HJ Hofmann, K. Grey, AH Hickman and RI Thorpe Australia Origin of 3.45 Ga coniform stromatoli... more ... HJ Hofmann, K. Grey, AH Hickman and RI Thorpe Australia Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western ... (1992) as 3.46 Ga. 1256 Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western Australia ...
At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thi... more At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thick. To the north and west the quartzite units wedge out and the succession thins to about 5 km. This regional disparity is attributed to major facies changes and not structural ...
The early Archaean East Pilbara Terrane of the Pilbara Craton represents the archetypical granite... more The early Archaean East Pilbara Terrane of the Pilbara Craton represents the archetypical granite dome-greenstone keel terrain and preserves much of the primary geological features of dome-and-keel formation. Here we present the first detailed lithostratigraphic and structural transect from marginal gneisses of the Muccan Granitic Complex through 6 km of steeply dipping strata of the western Doolena Gap greenstone belt. Based on overprinting relationships, we identified five deformational events (D 1-D 5) that can be correlated between four structural domains: (i) marginal orthogneisses of the polyphase Muccan Granitic Complex, (ii) a dominantly mylonitic shear zone (South Muccan Shear Zone) representing a granite dome-greenstone keel detachment zone, (iii) a Central Fold Belt of dominantly mafic greenschists, and (iv) a lower greenschist-to sub-greenschist facies southern Low-Strain Belt. The D 1 event in the Low-Strain Belt is recorded in syn-depositional normal faulting (f 1) during eruption of deep water low vesicular pillow basalts of the ca. 3.47 Ga Mount Ada Basalt, followed by a conformable transition towards shallow water stromatolites in the Duffer Formation. We interpret the D 1 event as the result of upper-crustal extension and subsequent uplift above the Muccan Granitic Complex. The D 2 event shows the most intense deformation with syn-anatectic tight folds within the Muccan Granitic Complex and tight to isoclinal transposed folds (F 2) and fluid-induced normal faults (f 2) within the Central Fold Belt. The D 2 event resulted in a regional EW composite S 1/2 foliation, and in the development of the mylonitic South Muccan Shear Zone along the dome-keel interface and within the Central Fold Belt, mineral lineations (L 2) in conjunction with increasing southward D 2 L-tectonite. This D 2 event is not observed in a $1 km-thick sandstone package (ascribed to the <3.43 Ga Strelley Pool Formation) in the Low-Strain Belt that was deposited over an angular unconformity indicating 45°SSW tilting of the underlying Mount Ada Basalt and Duffer Formation. This constrains the D 2 event to between 3.47 and 3.43 Ga. We propose that the D 1 and D 2 events record locally significant initiation of Muccan Granitic Complex doming and associated sagduction of greenstone keel rocks, suggesting that partial convective overturn initiated early in the evolution of the East Pilbara Terrane.
Synopsis Moinian and Lower Dalradian metasediments between Glen Roy and Lismore are folded by str... more Synopsis Moinian and Lower Dalradian metasediments between Glen Roy and Lismore are folded by structures belonging to two main phases of deformation. D1 folds are isoclinal and regionally recumbent whereas D2 folds are tight to isoclinal and upright. New information indicates that two structures previously regarded as major recumbent synclines can no longer be accepted as D1 folds. One, the Ballachulish Syncline, was postulated on false stratigraphic criteria and is considered to be non-existent. The other, the Appin Synform, is a D2 fold which locally refolds D1 isoclines, an example being the Balygrundle Syncline† on Lismore. Recumbent folds up to 20 km in amplitude are confined to the area between Kinlochleven and Loch Treig where the Treig Syncline† underlines the Kinlochleven Anticline. Both these structures are refolded by the Blackwater Synform and the Inverlair Antiform†. (†Structure described for the first time)
Geological Survey of Western Australia Report 160, 2016
The northwest Pilbara Craton provides an exceptionally well-preserved record of Archean crustal e... more The northwest Pilbara Craton provides an exceptionally well-preserved record of Archean crustal evolution from c. 3280 Ma to c. 2830 Ma. A major change in tectonic processes occurred at c. 3220 Ma when mantle plume-related volcanism and vertical deformation was abruptly replaced by plate tectonic evolution. This change, commencing with deep rifting of the 3530–3223 Ma volcanic plateau of the East Pilbara Terrane, caused northwest separation of the Karratha Terrane and established a northeast–southwest trending rift basin floored by juvenile basaltic crust (Central Pilbara Basin). Much thinner, less rigid, and significantly hotter than the adjacent continental plates of the Karratha and East Pilbara Terranes, this basin became the focus of almost all tectonic and magmatic activity in the Pilbara Craton until c. 3068 Ma. A c. 3160 Ma metamorphic event in the Karratha Terrane coincided with the northwest separation of the Karratha Terrane being halted and change to convergence back towards the East Pilbara Terrane. In this report it is inferred that this reversal was due to c. 3160 Ma collision of the Karratha Terrane with another plate northwest of the Pilbara Craton. Convergence resulted in obduction of juvenile basaltic crust of the Central Pilbara Basin (Regal Formation) onto the Karratha Terrane to form the Regal Terrane. It also resulted in the development of a subduction zone within the Central Pilbara Basin producing the 3130–3093 Ma arc volcanism and granitic intrusion of the Sholl Terrane. At c. 3068 Ma the convergence culminated in accretion of three northwest Pilbara terranes (Karratha, Regal, and Sholl) to form the West Pilbara Superterrane and collision of this superterrane with the East Pilbara Terrane resulting in the 3068–3066 Ma Prinsep Orogeny. Crustal relaxation and extension following the Prinsep Orogeny initiated development of a shallow-water intracontinental basin (3066–3015 Ma Gorge Creek Basin) that covered the entire northern half of the Pilbara Craton. By c. 3023 Ma this extensional phase had been replaced by renewed northwest–southeast convergence between the Pilbara Craton and the inferred plate to the northwest. During convergence a continental volcanic arc (3009–2991 Ma Whim Creek Basin) was developed immediately southeast of a 3006–2982 Ma belt of granitic intrusion (Maitland River Supersuite). Southeast of the volcanic arc a back-arc basin (Mallina Basin) evolved from c 3015 Ma until its development was terminated by 2954–2919 Ma plate collision (North Pilbara Orogeny). Geochronological evidence of the second phase of Mesoarchean convergence and subduction in the northwest Pilbara is provided by a southeasterly migration of granitic intrusion from c. 3023 Ma to c. 2919 Ma. The final event in the crustal evolution of the northwest Pilbara Craton was the intrusion of 2851–2831 Ma post-orogenic granites (Split Rock Supersuite). Most Archean mineralization in the northwest Pilbara was related to plate tectonic processes and included VHMS Cu–Zn within arc volcanism, Ni–Cu, PGE, and V–Ti in layered ultramafic–mafic intrusions, and lode Au in and adjacent to major strike-slip shear zones.
Uploads
Papers by Arthur Hickman
Crustal relaxation and extension following the Prinsep Orogeny initiated development of a shallow-water intracontinental basin (3066–3015 Ma Gorge Creek Basin) that covered the entire northern half of the Pilbara Craton. By c. 3023 Ma this extensional phase had been replaced by renewed northwest–southeast convergence between the Pilbara Craton and the inferred plate to the northwest. During convergence a continental volcanic arc (3009–2991 Ma Whim Creek Basin) was developed immediately southeast of a 3006–2982 Ma belt of granitic intrusion (Maitland River Supersuite). Southeast of the volcanic arc a back-arc basin (Mallina Basin) evolved from c 3015 Ma until its development was terminated by 2954–2919 Ma plate collision (North Pilbara Orogeny). Geochronological evidence of the second phase of Mesoarchean convergence and subduction in the northwest Pilbara is provided by a southeasterly migration of granitic intrusion from c. 3023 Ma to c. 2919 Ma. The final event in the crustal evolution of the northwest Pilbara Craton was the intrusion of 2851–2831 Ma post-orogenic granites (Split Rock Supersuite).
Most Archean mineralization in the northwest Pilbara was related to plate tectonic processes and included VHMS Cu–Zn within arc volcanism, Ni–Cu, PGE, and V–Ti in layered ultramafic–mafic intrusions, and lode Au in and adjacent to major strike-slip shear zones.
KEYWORDS: Archean, plate tectonics, convergence, obduction, subduction, orogeny, mineralization.