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- Augustsson, Carita, et al.
(författare)
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0.3 byr of drainage stability along the Palaeozoic palaeo-Pacific Gondwana margin; a detrital zircon study
- 2015
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Ingår i: Journal of the Geological Society. - : The Geological Society of London. - 0016-7649 .- 2041-479X. ; 172, s. 186-200
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Tidskriftsartikel (refereegranskat)abstract
- The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U–Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3–0.9 Ga and they can be correlated with ‘Grenvillian’ age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2–1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeo-Pacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted.
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| 2. |
- Torres Sánchez, Sonia Alejandra, et al.
(författare)
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Magmatic source and metamorphic grade of metavolcanic rocks from the Granjeno Schist : Was northeastern Mexico a part of Pangaea?
- 2016
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Ingår i: Geological Journal. - : Wiley. - 0072-1050. ; 51:6, s. 845-863
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Tidskriftsartikel (refereegranskat)abstract
- The geochemistry of the metavolcanic rocks from the Granjeno Schist in northeastern Mexico indicates an origin in different tectonic environments: mid-ocean ridge and ocean island. High ratios of Hf/Th and Th/Nb (4.4-14 and 0.08-0.15), low ratios of LaN/YbN and LaN/SmN (0.74-1.7 and 0.60-1.4) and depleted LREE patterns in metabasalt display mid-ocean ridge characteristics. In contrast, the pattern of trace-element ratios and REEs in metabasalt and metapillow lava 60km to the west indicates a magma source with ocean-island basalt characteristics. Both areas were metamorphosed during the Late Carboniferous (300±4Ma). Estimated metamorphic conditions deduced from white mica and chlorite compositions, distinguish greenschist facies (350°C and 4kbar) for the mid-ocean ridge basalt, and prehnite-pumpellyite facies (250°C and 2.5kbar) for the ocean-island-type basalt. This metamorphism took place at an active continental margin during Pennsylvanian time. Our new tectonic model, which differs from earlier models, suggests that the origin of the Granjeno Schist is related to a subduction zone located at the western margin of Pangaea, active after Laurentia-Gondwana collision.
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