INVESTIGADORES
GONZALEZ Pablo Diego
congresos y reuniones científicas
Título:
Cambrian magmatism and Cambro-Ordovician tectono-metamorphic event in Nahuel Niyeu Formation, Northpatagonian Massif, Argentina.
Autor/es:
GRECO GERSON; GONZÁLEZ, SANTIAGO; GONZÁLEZ PABLO DIEGO; SATO ANA MARÍA; LLAMBÍAS EDUARDO; COLOMBO TASSINARI CELSO; BASEI MIGUEL; SATO, KEY; VARELA RICARDO
Lugar:
San Pablo
Reunión:
Simposio; 9th South American Symposium on Isotope Geology; 2014
Institución organizadora:
CPGeo-IG-USP, Brazil
Resumen:
Nahuel
Niyeu Formation metasediments are interbedded with metamafic sills between
Valcheta and Aguada Cecilio towns, Rio Negro Province, Argentina. The sills display
clear intrusive contacts, concordant with relict, sedimentary S0 bedding.
Their composition is dominantly gabbroic, with minor granodioritic and even
granitic differentiates. A main tectono metamorphic event (D1-D2-M1) at
greenschist facies affects both the sedimentary and interbedded igneous protoliths.
Muscovite leucogranites, equivalent to the Valcheta Pluton of 470 Ma (Ar-Ar, Gozalvez 2009), and therefore of possible Ordovician
age, crosscut the sills and metasediments in postorogenic relationship.
Zircon
crystals were collected from a granitic differentiate of a sill and analysed by
SHRIMP U-Pb method at the Centro de Pesquisas Geocronologicas, Geosciences
Institute, University of São Paulo. Cathodoluminescence (CL), Secondary
Electron (SE), and binocular lens images were used for choosing the sites for analysis on the basis of
internal structure and fracturing degree of the grains. The crystals are
prismatic, amber colour or colourless and transparent, they present low luminescence
and show oscillatory and sector zoning, typical of magmatic zircon. The U-Pb
SHRIMP analysis yielded a Cambrian concordia age of 513.6 ± 3.3 Ma (MSWD =
0.84). This result is interpreted as the age of magmatic crystallization of the
sill.
From
the above, a Cambrian magmatism (513.6 ± 3.3 Ma) of mainly basic composition is
confirmed. This magmatism is coeval with the deposition of the sedimentary
protoliths of the Nahuel Niyeu Formation, since their maximum deposition age is
around 515-507 Ma (Pankhurst et al. 2006; Rapalini et
al. 2013). Furthermore, the first and main tectono metamorphic event (D1-D2-M1)
may be constrained between 513.6 and 470 Ma, on the basis of the equivalence of
the postorogenic leucogranites with the 470 Ma, Valcheta Granite.