%0 Journal Article
%A Fanning, C.M.
%A Pankhurst, R.J.
%A Rapela, Carlos W.
%A Baldo, Edgardo G.
%A Casquet Martín, César
%A Galindo Francisco, María Del Carmen
%T K-bentonites in the Argentine Precordillera contemporaneous with rhyolitevolcanism in the Famatinian Arc
%D 2004
%@ 0016-7649
%U https://hdl.handle.net/20.500.14352/49503
%X New U–Pb radiometric dates for K-bentonite horizons within the Lower Cambrian to MiddleOrdovician platform carbonates from the Precordillera terrane of NWArgentina provide further constraints onmodels for the allochthonous or parautochthonous accretion of this terrane. Two K-bentonite layers from theTalacasto section yield indistinguishable sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircondates of 469.5  3.2 Ma and 470.1  3.3 Ma respectively. These are within uncertainty of the U–Pb SHRIMPzircon date of 468.3  3.4 Ma for a porphyritic rhyolite from the Famatinian magmatic arc, Sierra de lasPlanchadas, near Rio Chaschuil. Geochemical and isotope data also demonstrate the similarity of the Kbentoniteand Chaschuil rhyolite parent magmas. Thus, it is highly probable that the Famatinian arc volcanoesprovided the ash for the K-bentonite horizons, suggesting proximity to the Precordillera terrane during thedeposition of the Lower Cambrian to Middle Ordovician platform carbonates. This implication supports amid-Ordovician collision model, but could also be compatible with a parautochthonous model for docking ofthe Precordillera terrane, by movement along the Pacific margin of Gondwana, rather than across the IapetusOcean.
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