Early Cambrian U-Pb zircon age and Hf-isotope data from the Guasayán pluton, Sierras Pampeanas, Argentina: implications for the northwestern boundary of the Pampean arc

Abstract

An Early Cambrian pluton, known as the Guasayán pluton, has been identified in the central area of Sierra de Guasayán, northwestern Argentina. A U-Pb zircon Concordia age of 533±4 Ma was obtained by LA-MC-ICP-MS and represents the first report of robustly dated Early Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentary rocks and its magmatic assemblage consists of K-feldspar (phenocrysts)+plagioclase+quartz+biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessory minerals. Geochemically, the granitic rock is a metaluminous subalkaline felsic granodiorite with SiO2=69.24%, Na2O+K2O=7.08%, CaO=2.45%, Na2O/ K2O=0.71 and FeO/MgO=3.58%. Rare earth element patterns show moderate slope (LaN/YbN=8.05) with a slightly negative Eu anomalies (Eu/Eu*=0.76). We report the first in situ Hf isotopes data (εHft=-0.12 to -4.76) from crystallized zircons in the Early Cambrian granites of the Sierras Pampeanas, helping to constrain the magma source and enabling comparison with other Pampean granites. The Guasayán pluton might provide a link between Early Cambrian magmatism of the central Sierras Pampeanas and that of the Eastern Cordillera, contributing to define the western boundary of the Pampean paleo-arc.

Review of the Cambrian Pampean orogeny of Argentina; a displaced orogen formerly attached to the Saldania Belt of South Africa?

“…One sample from the Los Túneles Phyllites (TLT-2069) has been analysed for U-Pb SHRIMP zircon chronology and  18 O and Hf isotope measurements on dated zircon grains (analytical methods as in Rapela et al, 2016) (Lyons et al, 1997;Rapela et al, 1998;Stuart-Smith et al, 1999;Leal et al, 2003;Hauser et al, 2011;Escayola et al, 2007Escayola et al, , 2011Tibaldi et al, 2008;Aparicio Gonzalez et al, 2011;Hong et al, 2010;Siegesmund et al, 2010;Iannizzotto et al, 2013;von Gosen et al, 2014;Dahlquist et al, 2016) (Table 3). The metaluminous Sierra Norte-Ambargasta batholith was emplaced within a very short period of time: the main intrusive pulse took place between 537 ± 4 and 528 ± 2 Ma (based on 11 results) with most ages in the range 530 ± 4 Ma (Rapela et al, 1998;Leal et al, 2003;Iannizzotto et al, 2013;von Gosen et al, 2014; Table 3) and thus constitutes a magmatic flare-up.…”

Geocronologia e isotopia do magmatismo paleozoico na zona de diablillos, borda oriental da Puna austral (NW da argentina): evolução crustal do orógeno paleozoico inferior na margem ocidental de Gondwana

“…13a) and zircon Hf(t) values (Fig. 12) presented in this study and by Hauser et al (2011) and Dahlquist et al (2016), show that the interaction of a Mesoproterozoic crustal source of ~1.4 Ga and juvenile mantle-derived magmas, that were reworked during lower Paleozoic times in the Eastern Magmatic Belt, extended not only to the Cordillera Oriental geological province, east of the magmatic belt, but also to the Northern Sierras Pampeanas gological province (Fig. 14) south of the Eastern Magmatic Belt.…”

“…The intermediate rocks show enrichment of the LREE and a decreasing HREE pattern, compared to the basic rocks. Note the similarities between the CID and CEO rocks with those from the Ojo de Colorados Complex, Western Magmatic Belt (Zimmermann et al, 2014), Guasayán Pluton, Northern Sierras Pampeanas (Dahlquist et al, 2016), a Metadacite from Niño Muerto, Northeastern Magmatic Belt (Hauser et al, 2011) and the Tastil batholith, Cordillera Oriental (Hauser et al, 2011). (c) Upper crust-normalized trace element abundances (normalization after Taylor and McLennan, 1985).…”

“…(Hauser et al, 2011), the granitic dykes in Mojotoro (Aparicio González et al, 2011), and the Nevado de Chañi and Cañañi granitoids (Zapettini et al, 2008;Escayola et al, 2011, respectively) in the Cordillera Oriental. Also shown is the Guasayán pluton in the Northern Sierras Pampeanas (Dahlquist et al, 2016). Inset (a) shows the Probability Density Plot illustrating zircon U-Pb ages for the Eastern Magmatic Belt (Puna), from the CID, and the North and Geocronologia e isotopía do magmatismo paleozoico na zona de Diablillos, borda oriental da Puna austral (NW da Argentina): Evolução crustal do orôgeno paleozoico inferior na margem ocidental de Gondwana 13 LISTA DE TABELAS ANEXO Table 1.…”

“…The majority of the T DM ages are constrained between the red dotted lines, denoting T DM ages from 1.2 to 1.55 Ga. The red solid line indicates the most frequent T DM observed is 1.4 Ga. For comparison, the Ordovician Agustín Ortiz Yañez metadacite εHf(t) data from the Northern Eastern Magmatic Belt, the Cambrian Tastil batolith εHf(t) data from the Cordillera Oriental (Hauser et al, 2011), and the data by Dahlquist et al (2016) for the Cambrian Guasayán Pluton in the Sierras Pampeanas are also shown. Inset (a) Hf(t) histogram: The Hf(t) values for the selected samples range from + 2.0 to -2.0, whereby the latter value is observed more frequently.…”