Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6431358 | Journal of South American Earth Sciences | 2014 | 10 Pages |
â¢Three Nd-Sr isotopic domains were recognized in the RÃo Bonete region of NW Argentina.â¢Greenschists suggest contribution from a Mesoproterozoic juvenile mantle source.â¢A garnet amphibolite and a quartz-phyllite show more enriched isotope compositions.â¢Data has strong similarities with meta-igneous rocks from WSP and some Ullum xenoliths.â¢Overlap with the Llano granites and the Catoctin volcanics supports the Laurentian origin of Precordillera.
The Precordillera terrane (Cuyania) in western Argentina is commonly accepted as an exotic fragment derived from Laurentia in the Early Paleozoic. Evidence supporting such an interpretation is manly based on similarities in the sedimentary cover successions and their paleontological content. Little is known about the basement of the Precordillera terrane. Its isotopic characterization is essential to better constrain the present areal distribution of the terrane and it may provide more insight into the pre-rifting evolution of the Precordillera terrane along the Iapetan margin of Laurentia. We present new Sr and Nd isotope data of pre-Late Ordovician meta-igneous rocks from the RÃo Bonete region in NW Argentina, interpreted as the northernmost extent of the Precordillera. The Nd systematics of the RÃo Bonete basement rocks including greenschists and metagabbros (εNd(470) = +2.14-â0.19; TDM = 0.99-1.2 Ga), a garnet-amphibolite (εNd(470) = â0.53; TDM = 1.32 Ga) and a quartz-phyllite (εNd(470) = â3.83; TDM = 1.55 Ga), are similar to other pre-Ordovician meta-igneous rocks from Sierra de Umango, Pie de Palo and the Ullum xenoliths, usually interpreted as the basement of the Precordillera terrane. Nd model ages around 1.2 Ga are also typical from the Mesoproterozoic Grenvillian basement of southern North America, currently exposed in the Llano region. In addition, the greenschists and metagabbros show a robust correlation with the Late Neoproterozoic Catoctin volcanics in the central Appalachians. The Sr isotope data (when not disturbed) also supports this novel interpretation and suggests the presence of the Blue Ridge rifting event in Precordillera. According to our interpretation, some lithotypes included within the basement complex of the RÃo Bonete area belonged to the basement of the Precordillera terrane supporting previous correlation between both regions.