Academic literature on the topic 'Orogenic belts – New South Wales'

ABSTRACT Early Ordovician to late Permian orogenies at different plate-boundary zones of western Pangea affected continental crust derived from the plates of North America (Laurentia), Europe (East European Craton including Baltica plus Arctida), and Gondwana. The diachronic orogenic processes comprised stages of intraoceanic subduction, formation and accretion of island arcs, and collision of several continents. Using established plate-tectonic models proposed for different regions and time spans, we provide for the first time a generic model that explains the tectonics of the entire Gondwana-Laurussia plate-boundary zone in a consistent way. We combined the plate kinematic model of the Pannotia-Pangea supercontinent cycle with geologic constraints from the different Paleozoic orogens. In terms of oceanic lithosphere, the Iapetus Ocean is subdivided into an older segment (I) and a younger (II) segment. Early Cambrian subduction of the Iapetus I and the Tornquist oceans at active plate boundaries of the East European Craton triggered the breakup of Pannotia, formation of Iapetus II, and the separation of Gondwana from Laurentia. Prolonged subduction of Iapetus I (ca. 530–430 Ma) culminated in the Scandian collision of the Greenland-Scandinavian Caledonides of Laurussia. Due to plate-tectonic reorganization at ca. 500 Ma, seafloor spreading of Iapetus II ceased, and the Rheic Ocean opened. This complex opening scenario included the transformation of passive continental margins into active ones and culminated in the Ordovician Taconic and Famatinian accretionary orogenies at the peri-Laurentian margin and at the South American edge of Gondwana, respectively. Rifting along the Avalonian-Cadomian belt of peri-Gondwana resulted in the separation of West Avalonian arc terranes and the East Avalonian continent. The vast African/Arabian shelf was affected by intracontinental extension and remained on the passive peri-Gondwana margin of the Rheic Ocean. The final assembly of western Pangea was characterized by the prolonged and diachronous closure of the Rheic Ocean (ca. 400–270 Ma). Continental collision started within the Variscan-Acadian segment of the Gondwana-Laurussia plate-boundary zone. Subsequent zipper-style suturing affected the Gondwanan Mauritanides and the conjugate Laurentian margin from north to south. In the Appalachians, previously accreted island-arc terranes were affected by Alleghanian thrusting. The fold-and-thrust belts of southern Laurentia, i.e., the Ouachita-Marathon-Sonora orogenic system, evolved from the transformation of a vast continental shelf area into a collision zone. From a geodynamic point of view, an intrinsic feature of the model is that initial breakup of Pannotia, as well as the assembly of western Pangea, was facilitated by subduction and seafloor spreading at the leading and the trailing edges of the North American plate and Gondwana, respectively. Slab pull as the plate-driving force is sufficient to explain the entire Pannotia–western Pangea supercontinent cycle for the proposed scenario.

ABSTRACT Early Ordovician to late Permian orogenies at different plate-boundary zones of western Pangea affected continental crust derived from the plates of North America (Laurentia), Europe (East European Craton including Baltica plus Arctida), and Gondwana. The diachronic orogenic processes comprised stages of intraoceanic subduction, formation and accretion of island arcs, and collision of several continents. Using established plate-tectonic models proposed for different regions and time spans, we provide for the first time a generic model that explains the tectonics of the entire Gondwana-Laurussia plate-boundary zone in a consistent way. We combined the plate kinematic model of the Pannotia-Pangea supercontinent cycle with geologic constraints from the different Paleozoic orogens. In terms of oceanic lithosphere, the Iapetus Ocean is subdivided into an older segment (I) and a younger (II) segment. Early Cambrian subduction of the Iapetus I and the Tornquist oceans at active plate boundaries of the East European Craton triggered the breakup of Pannotia, formation of Iapetus II, and the separation of Gondwana from Laurentia. Prolonged subduction of Iapetus I (ca. 530–430 Ma) culminated in the Scandian collision of the Greenland-Scandinavian Caledonides of Laurussia. Due to plate-tectonic reorganization at ca. 500 Ma, seafloor spreading of Iapetus II ceased, and the Rheic Ocean opened. This complex opening scenario included the transformation of passive continental margins into active ones and culminated in the Ordovician Taconic and Famatinian accretionary orogenies at the peri-Laurentian margin and at the South American edge of Gondwana, respectively. Rifting along the Avalonian-Cadomian belt of peri-Gondwana resulted in the separation of West Avalonian arc terranes and the East Avalonian continent. The vast African/Arabian shelf was affected by intracontinental extension and remained on the passive peri-Gondwana margin of the Rheic Ocean. The final assembly of western Pangea was characterized by the prolonged and diachronous closure of the Rheic Ocean (ca. 400–270 Ma). Continental collision started within the Variscan-Acadian segment of the Gondwana-Laurussia plate-boundary zone. Subsequent zipper-style suturing affected the Gondwanan Mauritanides and the conjugate Laurentian margin from north to south. In the Appalachians, previously accreted island-arc terranes were affected by Alleghanian thrusting. The fold-and-thrust belts of southern Laurentia, i.e., the Ouachita-Marathon-Sonora orogenic system, evolved from the transformation of a vast continental shelf area into a collision zone. From a geodynamic point of view, an intrinsic feature of the model is that initial breakup of Pannotia, as well as the assembly of western Pangea, was facilitated by subduction and seafloor spreading at the leading and the trailing edges of the North American plate and Gondwana, respectively. Slab pull as the plate-driving force is sufficient to explain the entire Pannotia–western Pangea supercontinent cycle for the proposed scenario.

ABSTRACT Rapid midcrustal cooling (>10 °C/m.y.) is typical of Phanerozoic orogens, but it is less commonly reported from Precambrian orogenic belts. Abundant new 40Ar/39Ar (predominantly plateau) dates reveal a period of late, rapid cooling following slow post- peak metamorphic cooling during the evolution of the Paleoproterozoic Cape Smith belt, a greenschist- to amphibolite-facies foreland thrust belt in the ca. 1.83–1.76 Ga Trans-Hudson orogen. We conducted 40Ar/39Ar step-heating analyses on biotite, hornblende, and/or muscovite from 38 samples sourced from the thrust belt and its footwall basement, the Archean Superior craton. The 40Ar/39Ar dates from the Cape Smith belt and re-equilibrated Superior craton ranged ca. 1948–1708 Ma in biotite, ca. 1801–1697 Ma in muscovite, and ca. 1764–1694 Ma in hornblende. Of these, ~70% were ca. 1740–1700 Ma plateau dates, which we interpret as cooling ages following Cape Smith belt metamorphism; gas-release spectra of older outlying dates exhibit characteristics of excess Ar. Following the metamorphic thermal peak, the belt cooled at slow rates of up to ~1 °C/m.y. until ca. 1740 Ma. Concordant biotite, muscovite, and hornblende cooling dates of ca. 1740–1700 Ma require fast, late cooling of the belt (≥4 °C/m.y.) through upper midcrustal levels (~500–300 °C), and they allow for very rapid cooling rates (≤200 °C/m.y.). Accelerated cooling rates may have been triggered by uplift in response to detachment of lower crust or subcontinental lithosphere, facilitated by the postcollisional relaxation of isotherms and structural uplift in basement-involved folds. In Superior craton basement, ca. 2704–2667 Ma 40Ar/39Ar hornblende plateau dates reflect undisturbed cooling ages following Neoarchean metamorphism, whereas younger and wide-ranging 40Ar/39Ar biotite dates (ca. 2532–1743 Ma) with variable gas-release spectra suggest spatially heterogeneous degrees of Ar resetting in biotite during Cape Smith belt tectonism. Partially reset 40Ar/39Ar biotite dates in the Superior craton up to ~100 km south of the belt suggest that the pre-erosional thrust wedge extended at least that far south, and that it imposed a widespread low-temperature (<300 °C) and/or short-lived thermal overprint on the footwall basement. Integration of multimineral 40Ar/39Ar data with structural and metamorphic constraints for the Cape Smith belt indicates that modern-style postcollisional exhumation and rapid cooling were viable processes during the middle Paleoproterozoic.

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