%0 Journal Article
%A Colombo, F.
%A Baldo, Edgardo G.
%A Casquet, César
%A Pankhurst, R.J.
%A Galindo Francisco, Mª del Carmen
%A Rapela, Carlos W.
%A Dahlquist, Juan A.
%A Fanning, C.M.
%T A-type magmatism in the sierras of Maz and Espinal: A new record of Rodiniabreak-up in the Western Sierras Pampeanas of Argentina
%D 2009
%@ 0301-9268
%U https://hdl.handle.net/20.500.14352/49538
%X Two orthogneisses have been recognized in the sierras of Espinal and Maz (Western Sierras Pampeanas,NW Argentina) that were emplaced within a Grenvillian metasedimentary sequence. Microcline, plagioclaseand quartz are the main rock-forming minerals, with accessory zircon, apatite-(CaF), magnetite,biotite (Fe/(Fe + Mg) = 0.88–0.91), ferropargasite (Fetotal/(Fetotal + Mg) = 0.88–0.89), titanite (with up to1.61 wt% Y2O3) and an REE-rich epidote. REE-poor epidote and zoned garnet (Ca and Fe3+-rich) are metamorphicminerals, while muscovite, carbonates and chlorite are secondary phases. Texture is mylonitic.Two representative samples are classified as granite (from Sierra de Espinal) and granodiorite/tonalite(from Sierra de Maz) on the grounds of immobile trace elements. Some trace element contents are ratherhigh (Zr: 603 and 891 ppm, Y: 44 and 76 ppm, 10,000×Ga/Al: 2.39–3.89) and indicate an affiliation withA-type granites (more specifically, the A2 group). Both samples plot in the field of within-plate granitesaccording to their Y and Nb contents.Concordant crystallization ages (zircon U–Pb SHRIMP) are 842±5 and 846±6 Ma, respectively.87Sr/86Sri (845) ratios are 0.70681 and 0.70666; εNdi (845) values are −1.5 and +0.3 and depleted-mantle Ndmodel ages (2TDM*) are 1.59 and 1.45 Ga, respectively. These values indicate the involvement of an isotopicallyevolved source. 2TDM* values are compatible with the presence of inherited zircon crystals of upto 1480Ma in one of the rocks, thus implying that magmas incorporated material from Mesoproterozoiccontinental source. This is also indicated by the relatively high contents of Y, Ga, Nb and Ce compared tomagmas derived from sources similar to those of oceanic-island basalts.These orthogneisses represent a period of extension at ca. 845Ma affecting the Western Sierras Pampeanascontinental crust that was already consolidated after the Grenvillian orogeny (1.2–1.0 Ga). Theyare thus a record of the early stages of Rodinia break-up. Metamorphic conditions during the subsequentFamatinian orogenic cycle (ca. 420 Ma, SHRIMP U-Pb on zircon) attained 7.7±1.2 kbar and 664±70 ◦C.
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