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Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador) |
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| Authors: | SAMANIEGO PABLO; MARTIN HERVE; MONZIER MICHEL; ROBIN CLAUDE; FORNARI MICHEL; EISSEN JEAN-PHILIPPE; COTTEN JOSEPH |
| Institution: | 1 DEPARTAMENTO DE GEOFÍSICA, ESCUELA POLITÉCNICA NACIONAL, AP. 17-01-2759, QUITO, ECUADOR 2 UNIVERSITÉ BLAISE PASCAL, LABORATOIRE MAGMAS ET VOLCANS, UMR 6524, 5 RUE KESSLER, 63038 CLERMONT-FERRAND, FRANCE 3 IRD, UR 031, LABORATOIRE MAGMAS ET VOLCANS, 5 RUE KESSLER, 63038 CLERMONT-FERRAND, FRANCE 4 IRD, UMR GÉOSCIENCES AZUR, UNIVERSITÉ DE NICE-SOPHIA ANTHIPOLIS, PARC VALROSE, 06108 NICE CEDEX 2, FRANCE 5 UMR 6538, UNIVERSITÉ DE BRETAGNE OCCIDENTALE, BP 809, 29285 BREST, FRANCE |
| Abstract: | In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at  1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the Wadati–Benioff zone and favouring slab partialmelting. KEY WORDS: adakites; 40Ar/39Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes |
| Keywords: | : adakites 40Ar/39Ar dating Cayambe volcano Ecuador mantle metasomatism Andes |
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