Antarctica — Before and after Gondwana

The Gawler craton is the major crustal province in the southern Australian Proterozoic and is pivotal in models seeking to describe the evolution of Proterozoic Australia. The craton is host to the Olympic Dam iron oxide Cu-Au-U-REE deposit, as well as a number of other iron oxide copper-gold (IOCG), Au, and iron ore deposits. The evolution of the Gawler craton is dominated by two major phases of tectonic activity, Late Archean and late Paleoproterozoic-early Mesoproterozoic, in total spanning ca. 1 billion years. The Late Archean (2560–2500 Ma) basin development was coeval with arclike felsic magmatism and mafic-ultramafic magmas, including komatiites. Collisional deformation between 2480 and 2420 Ma led to ca. 400 m.y. of tectonic quiescence, conceivably within an early Paleoproterozoic continental interior. The second major phase of tectonic activity was in the middle to late Paleoproterozoic and early Mesoproterozoic (2000–1450 Ma). Paleoproterozoic tectonism was initially dominated by rift-related events, which produced a series of basins over the interval ca. 1900 to 1730 Ma, some of which contain significant iron ore reserves. Transient contractional deformation at ca. 1850 Ma led to batholith-scale granitic magmatism, in part derived from melting of the late Archean basement. Major basin development was finally terminated by the 1730 to 1690 Ma Kimban orogeny, the effects of which are widespread and include the formation of crustal-scale shear systems, granitic magmatism, and low- to high-grade metamorphism. The Kimban orogeny was followed by a renewed period of extension between ca. 1680 and 1640 Ma, leading to local magmatism and sedimentation which appears in part to have been coeval with the high-grade ca. 1650 Ma Ooldean event in the western Gawler craton.

At ca. 1620 to 1615 Ma, the generation of the arc-related St. Peter Suite in the southern Gawler craton implies that craton components were located at an active plate margin. The arc environment was superseded by a transition to a continental interior regime, which coincided with the voluminous Gawler Range Volcanics (1595–1590 Ma) and Hiltaba Suite granitoids (1595–1575 Ma). The Hiltaba Suite is dominated by high T fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement. Emplacement of the Hiltaba Suite coincided with the major mineralizing interval in the Gawler craton. Regionally, two distinct mineral systems have been recognized: the Olympic IOCG province in the eastern part of the craton, and the gold-dominated systems within the central Gawler gold province. The spatial distribution of IOCG versus Au-dominated mineral systems appears to reflect regional variations in crustal composition and Hiltaba Suite petrogeneses. Hiltaba-aged granites in the Olympic IOCG province are isotopically more evolved, richer in U and Th, and oxidized compared to similar aged granites in the Au-dominated province. Modern-day heat flow in the IOCG province is significantly higher (90 ± 10 mWm−2) compared to the Au-dominated province (54 ± 5 mWm−2), suggesting there are important lithospheric compositional differences between the two metallogenic provinces, which may reflect an older phase of craton assembly.

Widespread northwest-southeast contractional deformation coeval with the emplacement of the Hiltaba Suite is expressed by the formation and/or reactivation of shear zones ranging up to crustal scale. Within this regime, northwest-trending structures such as those in the vicinity of the Olympic Dam deposit are likely to have accommodated dilation associated with strike-slip movements. Intersection between these structures and northeast-trending contractional faults may have formed suitable structural traps for 1590 to 1580 Ma mineralization. The timing of syn-Hiltaba deformation overlaps with transpression and medium to high-grade metamorphism associated with the ca. 1570 to 1540 Ma Kararan orogeny which dominates the geophysical architecture of the central northern part of the craton. The youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca. 1470 and 1450 Ma and regional cooling.

Tectonic Framework and Evolution of the Gawler Craton, Southern Australia

The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 19581. The preservation of Alpine topography in the Gamburtsevs2 may reflect extremely low long-term erosion rates beneath the ice sheet3, but the mountains’ origin remains problematic. Here we present the first comprehensive view of the crustal architecture and uplift mechanisms for the Gamburtsevs, derived from radar, gravity and magnetic data. The geophysical data define a 2,500-km-long rift system in East Antarctica surrounding the Gamburtsevs, and a thick crustal root4 beneath the range. We propose that the root formed during the Proterozoic assembly of interior East Antarctica (possibly about 1 Gyr ago), was preserved as in some old orogens5, 6 and was rejuvenated during much later Permian (roughly 250 Myr ago) and Cretaceous (roughly 100 Myr ago) rifting. Much like East Africa7, the interior of East Antarctica is a mosaic of Precambrian provinces affected by rifting processes. Our models show that the combination of rift-flank uplift, root buoyancy and the isostatic response to fluvial and glacial erosion explains the high elevation and relief of the Gamburtsevs. The evolution of the Gamburtsevs demonstrates that rifting and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere.

East Antarctic rifting triggers uplift of the Gamburtsev Mountains

Oligo-Miocene shearing along the Ailao Shan–Red River shear zone: Constraints from structural analysis and zircon U/Pb geochronology of magmatic rocks in the Diancang Shan massif, SE Tibet, China

The eastern Gawler craton hosts Australia's premier uranium-bearing iron oxide copper-gold (IOCG) belt, the >500-km-long Olympic Cu-Au-(U) province. In addition to the Olympic Dam Cu-U-Au and Prominent Hill Cu-Au deposits, numerous barren and weakly mineralized IOCG prospects are present in the province. New geochronological data for hydrothermal minerals combined with constraints from host-rock ages demonstrate that alteration and associated IOCG mineralization formed between ∼1570 and ∼1600 Ma in three districts of the province. This IOCG hydrothermal activity temporally overlaps with magmatism of the Hiltaba Suite and Gawler Range Volcanics. Titanites in paragenetically early magnetite-bearing alteration in the Olympic Dam and Prominent Hill districts yield U-Pb ion probe ages of 1576 ± 5 and 1567 ± 10 Ma, respectively. Molybdenite in veins crosscutting magnetite-biotite and albitic alteration in the Moonta-Wallaroo district have Re-Os ages of 1574 ± 6 and 1599 ± 6 Ma, respectively. These represent minimum ages of the IOCG alteration assemblages in this district. A muscovite 40Ar/39Ar age of 1575 ± 11 Ma provides a minimum age of paragenetically later hematitic alteration in the Olympic Dam district. Neodymium isotope compositions were determined for 44 whole-rock samples from barren and weakly mineralized Cu-Au prospects and host rocks in the Olympic Dam and Prominent Hill districts. The new geochronological framework enables comparison of the Nd isotope data across two IOCG districts at the time of formation of the Olympic Dam deposit (ca. 1590 Ma). Magnetite-ricH weakly Cu-mineralized alteration from five prospects yields a relatively narrow range eNd(1590) values of -5.8 to -4.1. Both hematite- and magnetite-rich alteration yield generally similar eNd(1590) values that match values from fresh and weakly altered Paleoproterozoic metasedimentary and metagranitic rocks (-6.6 to -3.5) as well as from most felsic Hiltaba Suite intrusions and Gawler Range Volcanics in the eastern Gawler craton (ca, -6 to -4). These data are consistent with crustal sources for REE and, by implication, for associated copper in the barren and weakly mineralized prospects. Mineralization and alteration in these minor IOCG systems can be geochemically discriminated from the giant Olympic Dam deposit, where greater inputs of mantle-derived REE and other ore components are evident. © 2007 Society of Economic Geologists, Inc.

/pdf/timing-of-iron-oxide-cu-au-u-hydrothermal-activity-and-nd-i7qvc0hw9n.pdf

Timing of Iron Oxide Cu-Au-(U) Hydrothermal Activity and Nd Isotope Constraints on Metal Sources in the Gawler Craton, South Australia

[1] Geological exposures in the Lambert Rift region of East Antarctica comprise scattered coastal outcrops and inland nunataks sporadically protruding through the Antarctic ice sheet from Prydz Bay to the southernmost end of the Prince Charles Mountains. This study utilized airborne magnetic, gravity, and ice radar data to interpret the distribution and architecture of tectonic terranes that are largely buried beneath the thick ice sheet. Free-air and Bouguer gravity data are highly influenced by the subice and mantle topography, respectively. Gravity stripping facilitated the removal of the effect of ice and Moho, and the residual gravity data set thus obtained for the intermediate crustal level allowed a direct comparison with magnetic data. Interpretation of geophysical data also provided insight into the distribution and geometry of four tectonic blocks: namely, the Vestfold, Beaver, Mawson, and Gamburtsev domains. These tectonic domains are supported by surface observations such as rock descriptions, isotopic data sets, and structural mapping.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JB005650

Basement interpretations from airborne magnetic and gravity data over the Lambert Rift region of East Antarctica

The emplacement of the ca 1590–1575 Ma Hiltaba Suite granites records a large magmatic event throughout the Gawler Craton, South Australia. The Hiltaba Suite granites intrude the highly deformed Archaean‐Palaeoproterozoic rocks throughout the craton nuclei. Geophysical interpretation of the poorly exposed central western Gawler Craton suggests that the region can be divided into several distinct domains that are bounded by major shear zones, exhibiting a sequence of overprinting relationships. The north‐trending Yarlbrinda Shear Zone merges into the east‐trending Yerda Shear Zone that, in turn, merges into the northeast‐trending Coorabie Shear Zone. Several poorly exposed Hiltaba Suite granite plutons occur within a wide zone of crustal shearing that is bounded to the north by the Yerda Shear Zone and to the south by the Oolabinnia Shear Zone. This wide zone of crustal shearing is interpreted as a major zone of synmagmatic dextral strike‐slip movement that facilitated the ascent of Hiltaba Suite granite i...

Geophysical constraints of shear zones and geometry of the Hiltaba Suite granites in the western Gawler Craton, Australia

Three gravity and magnetic profiles through the central and eastern part of the Melbourne Zone, Lachlan Fold Belt, have been modelled, with tight control from surface geology to investigate the deep crust. The largely non-magnetic upper crust (folded Ordovician to Lower Devonian strata of the Melbourne Zone intruded by Devonian granite plutons) has been modelled using recently acquired density measurements, providing a good match with the gravity profiles. The top of the basement is modelled at ∼10–15 km depth in the centre of the zone, and ∼8–10 km depth in the south of the zone, reflecting a thinning of the folded cover sequence toward the south, consistent with outcrops of basement Cambrian rocks on the south coast of Victoria. Long-wavelength magnetic anomalies in the Melbourne Zone are modelled as highly magnetic tabular bodies lying in the basement below the folded strata of the Melbourne Zone. The only rock type that matches the density and magnetic susceptibility is serpentinised ultramafic rock. ...

Gravity and magnetic modelling of crustal structure in central Victoria: what lies under the Melbourne Zone?

Three-dimensional inversion modelling of a Neoproterozoic basin in the southern Prince Charles Mountains, East Antarctica

Crustal cross-sections along the Mawson Escarpment and Mount Stinear, southern Prince Charles Mountains (East Antarctica): Correlating the Ruker Complex across the Lambert Glacier

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