The Western Sierras Pampeanas: Protracted Grenville-age history (1330–1030 Ma) of intra-oceanic arcs,subduction–accretion at continental-edge and AMCG intraplate magmatism |
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| Authors: | CW Rapela RJ Pankhurst C Casquet E Baldo C Galindo CM Fanning JM Dahlquist |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, School of Scientific Research, China University of Geosciences, Beijing 100083, China;2. CSIRO Mineral Resources, Perth, WA 6151, Australia;3. School of Earth, Atmosphere and Environment, Monash University, Building 28, Clayton, Victoria 3800, Australia;4. The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;5. Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada;1. Departamento de Petrología & Geoquímica, Facultad de Ciencias Geológicas, Instituto de Geociencias (IGEO, CSIC), Universidad Complutense, 28040 Madrid, Spain;2. Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), CONICET, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 1611, Pab. Geol., X5016CGA Córdoba, Argentina;3. Centro de Investigaciones Geológicas, CONICET, Universidad Nacional de la Plata, 1900 La Plata, Argentina;4. Visiting Research Associate, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;5. Research School of Earth Sciences, Australian National University, Canberra, ACT, 0200, Australia |
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| Abstract: | New U–Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330–1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc–continental collision dated by zircon overgrowths at 1170–1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo–Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ～1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo–Ullún sector: (i) 1110 ± 10 Ma orthogneisses and basic amphibolites with geochemical fingerprints of emplacement in a more mature crust, and (ii) a 1027 ± 17 Ma TTG juvenile suite, which is the youngest Grenville-age magmatic event registered in the Western Sierras Pampeanas. The geodynamic history in both study areas reveals a complex orogenic evolution, dominated by convergent tectonics and accretion of juvenile oceanic arcs to the continent. |
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