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Foundering-driven lithospheric melting: The source of central Andean mafic lavas on the Puna Plateau (22°S–27°S)

By
Kendra E. Murray
Kendra E. Murray
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA
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Mihai N. Ducea
Mihai N. Ducea
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA, and Facultatea de Geologie Geofizica, Universitatea Bucuresti, Strada N. Balcescu Nr 1, Bucuresti, Romania
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Lindsay Schoenbohm
Lindsay Schoenbohm
Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
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Published:
January 01, 2015

Investigations of lithospheric foundering and related magmatism have long focused on the central Andes, where there are postulated links between the eruption of mantle-derived lavas and periodic loss of the lower lithosphere. Whole-rock elemental and Nd-Sr-Pb isotopic results from a suite of late Miocene–Quaternary mafic lavas erupted onto the Puna Plateau clarify the relationship between this hypothesized process and lava composition. Zinc and Fe provide a critical perspective because they are partitioned differently during the melting of asthenospheric and lithospheric mantle. All Puna lavas have Zn/FeT (×104) values >13, which requires clinopyroxene and perhaps garnet to be the dominant phase(s) in the melt source; this precludes a melt source of typical mantle asthenosphere. This result is contrary to classic models of delamination magmatism that suggest asthenospheric peridotite melts to generate these lavas. Pyroxenite (±garnet)–bearing lithospheric materials in the central Andes are likely common and heterogeneous in age, volatile content, and mineralogical composition, and if they are the melt source, this can explain the diversity in the elemental (La/Yb = 11–45; La/Ta = 22–40) and isotopic (87Sr/86Sr = 0.7055–0.7080; ε Nd = −1 to −7) compositions of these mafic magmas (MgO > 8%, Mg number > 60). We propose that compositionally diverse, gravitationally unstable pyroxenites both drive “dripping” of the lower lithosphere and are the source of the resulting melt. We also postulate that mantle-derived lavas erupted on the Puna Plateau were generated during localized foundering and melting of these materials. The cumulative effect of these drip events is a modern Puna Plateau with geodynamic anomalies including thin lithosphere and anomalously high surface elevation.

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GSA Memoirs

Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and Northern Chile

Peter G. DeCelles
Peter G. DeCelles
Department of Geosciences, University of Arizona, Tucson, Arizona, USA
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Mihai N. Ducea
Mihai N. Ducea
Department of Geosciences, University of Arizona, Tucson, Arizona, USA, and Universitatea Bucuresti, Facultatea de Geologie Geofizica, Strada N. Balcescu Nr 1, Bucuresti, Romania
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Barbara Carrapa
Barbara Carrapa
Department of Geosciences, University of Arizona, Tucson, Arizona, USA
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Paul A. Kapp
Paul A. Kapp
Department of Geosciences, University of Arizona, Tucson, Arizona, USA
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Geological Society of America
Volume
212
ISBN print:
9780813712123
Publication date:
January 01, 2015

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