Neoproterozoic granitic gneisses in the Chinese Central Tianshan Block: Implications for tectonic affinity and Precambrian crustal evolution
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Biotite from paragneiss of Gneiss Point, McMurdo Sound, Antarctica is dated at 520 m y by the A 40 /K 40 method. Metamorphism of Precambrian sediments at the close of Precambrian or in Cambrian time is indicated, but additional work is needed.
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With the recognition of the Hope Valley shear zone (HVSZ) as a terrane boundary, the Esmond-Dedham terrane (EDT) was subdivided, and the western division was named the Hope Valley terrane (HVT). The oldest rocks of the HVT consist of schist, gneiss and quartzite (Plainfield Formation), and metavolcanic and metaplutonic gneisses and amphibolites (Waterford Group), some of the latter yielding a radiometric age of 620 Ma. Members of the Sterling Plutonic Suite, consisting of granite gneiss and alaskite gneiss, intrude these older units. An exact radiometric age could not be determined for the alkaline pluton, Joshua Rock Granite Gneiss, but is...
Radiometric dating
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Banded iron formation
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Abstract Earth’s continental crust has evolved through a series of supercontinent cycles, resulting in a patchwork of Archean cores surrounded by terranes, fragments, and slivers of younger crustal additions. However, the dispersal (and/or stranding) of continental fragments during breakup is not well understood. Inherited structures from previous tectonic activity may explain the generation of continental terranes by controlling first-order deformation during rifting. Here, we explored the influence of lithospheric deformation related to ancient orogenesis, focusing on the impact of the Torngat orogen in the genesis of the Nain Province continental fragment in Eastern Canada. We present three-dimensional continental extension models in the presence of an inherited lithospheric structure and show that a narrow continental terrane could be separated and stranded by deep lithospheric scarring. The results show that continental terranes formed by this method would be limited to a width of 100–150 km, imposed by tectonic conditions during continental suturing. The findings have broad implications, demonstrating an original theory on the fundamental geologic problem of terrane generation and continent breakup.
Supercontinent
Continental Margin
continental collision
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The recognition of terranes and terrane accretion has fundamentally changed the way we view the development of continental crust. The terrane concept originated from studies of the western Cordillera of North America, where it was demonstrated in the 1970s that microplates had travelled substantial distances before being amalgamated to cratonic North America. Since these early studies, the terrane concept has been widely applied to older orogenic belts, including the Appalachians and most of the Precambrian shields. Despite the acceptance of the terrane concept, a number of fundamental questions remain regarding the process of terrane accretion and its interaction with transform faulting and igneous and metamorphic events. Still not fully understood are: the coupling processes of mantle with deeper crust, and of deeper crust with upper crust; how pieces of continental crust with different histories respond to juxtaposition; the mechanism of the Mono's formation; and the behavior of fluids (melt and aqueous) with the changing stress field during accretion.
Continental Margin
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Continental Margin
Island arc
Felsic
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Tonalitic orthogneiss from the Brookville Gneiss in southern New Brunswick has an igneous protolith age of $$605 \pm 3 Ma$$ based on U-Pb dating of zircon. Metamorphic titanite from the same sample gives a minimum age of $$564 \pm 6 Ma$$ for upper amphibolite facies metamorphism of the unit. Based on U-Pb analyses of single detrital zircons, a maximum sedimentary protolith age of about 641 Ma is suggested for associated paragneiss. These ages indicate that the igneous protolith of the orthogneiss was at most 35 Ma younger than the sedimentary rocks it intruded, and that the Brookville Gneiss is younger than the Green Head Group to which it was previously considered basement. Both orthogneiss and paragneiss in the Brookville Gneiss contain Proterozoic and Archean detrital zircon grains, suggesting an old, heterogeneous continental source. We conclude that the Brookville Gneiss does not represent the basement to the Avalon Terrane.
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