The origin and petrologic evolution of the Ordovician Famatinian-Puna arc

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Elemental chemistry, radiogenic isotopic data, and zircon U-Pb inheritance patterns for the Famatinian-Puna arc suggest that the primary petrogenetic process operating in the arc was mixing between subarc mantle-derived gabbroic magmas and metasedimentary materials without a substantial component of lower-crustal continental basement rocks. This mixing is observable in the fi eld and evident in variations of chemical elemental parameters and isotopic ratios, revealing that hybridization coupled with fractionation of magmas took place in the upper 25 km of the crust. Intermediate and silicic plutonic rocks of the Famatinia-Puna arc formed in a subduction setting where the thermal and material input of mantle-derived magmas promoted fusion of fertile metasedimentary rocks and favored mixing of gabbroic and dioritic magmas with crustal granitic melts. Whole-rock geochemical and isotopic data for the Famatinian-Puna magmatic belt as a whole demonstrate that the petrologic model studied in detail in the Sierra Valle Fertil–La Huerta section has the potential to explain generation of plutonic and volcanic rocks across the Early Ordovician western Gondwanan proto-Pacifi c margin. This example further underscores the signifi cance of passive-margin sedimentary accumulations in generating continental arcs. *ducea@email.arizona.edu Ducea, M.N., Otamendi, J.E., Bergantz, G.W., Jianu, D., and Petrescu, L., 2015, The origin and petrologic evolution of the Ordovician Famatinian-Puna arc, in DeCelles, P.G., Ducea, M.N., Carrapa, B., and Kapp, P.A., eds., Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and Northern Chile: Geological Society of America Memoir 212, p. 125–138, doi:10.1130/2015.1212(07). For permission to copy, contact editing@geosociety.org. © 2014 The Geological Society of America. All rights reserved. on September 24, 2014 memoirs.gsapubs.org Downloaded from