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- Zibra, Ivan, et al.
(författare)
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Regional-scale polydiapirism predating the Neoarchean Yilgarn Orogeny
- 2020
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951. ; 779
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Tidskriftsartikel (refereegranskat)abstract
- Gneiss domes occur in a wide variety of orogenic and anorogenic domains of the continental crust, and play a major role in lithosphere dynamics by allowing upwards transfer of heat and mass. They commonly contain a core of granites and/or migmatites, overlain by a mantle of lower-grade rocks. Evolutionary models of many gneiss domes are controversial. Here we use new structural and zircon isotopic data to unravel the tectono-magmatic evolution of the Yalgoo dome and surroundings, at the margins of the Neoarchean Yilgarn Orogen, Western Australia. The study area includes at least seven granite–migmatite domes (5–70km in average diameter), and several subdomes within the larger domes, all showing comparable structural features and age. In each dome, a concentric domal foliation is concordant with granite–greenstone contacts, bearing a radial, outward-plunging lineation. The bulk of the structures in each dome reflect magmatic flow, with pervasive subsolidus fabrics occurring only along the outer dome margins, and reflecting dome-up kinematics. Narrow greenstone keels pinched between domes and subdomes display vertical constriction, in an area regionally dominated by flattening along the steep sides of the deeply-eroded domes, and along the flat-laying dome roofs. The regional structural pattern and the kinematics of the high-strain zones are best explained by sequential emplacement of nested diapirs, which delivered large volumes of granitic magma in a c. 20Myr time-span. The dome-and-keel regional architecture and the internal structures of each dome resulted therefore from multiscale polydiapirism. These diapirs were later weakly overprinted by a tectonic fabric that developed during the Neoarchean Yilgarn Orogeny. The contrast between the Yalgoo region and the rest of the craton, which was strongly reworked by this orogeny, highlights the dichotomy of tectonic styles in Archean terranes, demonstrating that diapirism dominated in times of tectonic quiescence.
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2. |
- Zibra, Ivan, et al.
(författare)
-
Tectono-magmatic evolution of the Neoarchean Yalgoo dome (Yilgarn Craton): Diapirism in a pre-orogenic setting
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Gneiss domes occur in any orogenic and anorogenic domain of the continental crust, from Precambrian cratons to present-day active orogens. They commonly contain a core of granitic rocks and/or high-grade metamorphic rocks, overlain by a mantle of lower-grade rocks. Evolutionary models of many gneiss domes are controversial. We use new structural and geochronological data to constrain the tectono-magmatic evolution of the Yalgoo dome in the Yilgarn Craton of Western Australia. The granite–migmatite core of the dome shows an overall domal foliation pattern, associated with radial and outwardsplunging lineations. A high-strain zone with top-outwards sense of shear (the Badja decollément) occurs along the granite–greenstone boundary. The greenstone sequence contains an angular unconformity that likely developed during doming. We show that doming, associated with outward flow of supracrustal material, was accompanied by the emplacement of large volumes of granitic magma at 2760–2750 Ma. The dome-scale finite strain pattern resulted from diapiric granite emplacement into the greenstone cover, with negligible background regional stress. Granitic plutons flanking the Yalgoo dome show a similar, first-order structural architecture. The dome-forming fabric is locally overprinted by a discordant, north-trending foliation caused by folding that likely developed at c. 2700 Ma, during the Neoarchean Yilgarn orogeny.
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