Scientific article

Quaternary Sanukitoid-like Andesites Generated by Intracrustal Processes (Chacana Caldera Complex, Ecuador): Implications for Archean Sanukitoids

Published inJournal of petrology, vol. 55, no. 4, p. 769-802
Publication date2014

High-Mg diorites enriched in incompatible elements and their extru- sive equivalents are rare subduction-related rock types that have been found in modern arc settings and in Late Archean sequences, where they are associated with trondhjemite^tonalite^granodiorite (TTG) suites. Archean rocks with these geochemical features are known as sanukitoids and, despite their limited abundance, are con- sidered to be the indicators of the onset of modern plate tectonics because of their similarities to modern subduction-related high-Mg andesites and diorites. Understanding the genesis of sanukitoid rocks is thus an essential step towards understanding crustal growth processes. The accepted petrogenetic models for modern, enriched, high-Mg andesites and their Archean equivalents, the sanukitoids, consist of metasomatic enrichment of the mantle wedge by slab com- ponents and its subsequent partial melting, or the modification of siliceous slab components through continuous reaction with mantle peridotite during their ascent through the mantle wedge. We present new data on the petrography, mineral chemistry and whole-rock geo- chemistry (major and trace elements and Sr^Nd^Pb isotopes) of andesitic rocks from an 􏰀30 ka lava flow (Yuyos flow) from the Chacana Caldera Complex, Eastern Cordillera of Ecuador. These rocks show a remarkable geochemical affinity with Archean sanuki- toids, including high magnesium numbers (0·58-0·63) accompanied by high contents of incompatible elements (e.g. Th 17-23 ppm, U 6-7·5 ppm, Ba 1600-1800 ppm, Sr 1430-1565 ppm, La 74-94 ppm). Additionally, the sanukitoid-like andesites of Yuyos are associated with predominant silica-rich (adakite-like) andesites, which are widespread throughout the Quaternary arc of Ecuador. This makes the Quaternary Ecuadorian magmatic province a close equivalent of the Archean TTG^sanukitoid association. The bulk- rock geochemistry, petrography and mineral chemistry data indicate that the sanukitoid-like features of the andesites of the Yuyos flow derive from intracrustal recycling of the felsic-intermediate to mafic^ultramafic roots of the Quaternary volcanic arc of Ecuador by ‘normal' mantle-derived basaltic magmas with the geochemical characteristics of continental arc basalts or high-alumina basalts. In view of the similarities between the Yuyos andesites and Archean sanukitoids in terms of geochemistry and lithological association, we suggest that genetic models should consider the possibility of intracrustal recycling as a process responsible for the peculiar signa- tures of both Archean sanukitoids and modern enriched high-Mg andesites.

Citation (ISO format)
CHIARADIA, Massimo, MUNTENER, Othmar, BEATE, B. Quaternary Sanukitoid-like Andesites Generated by Intracrustal Processes (Chacana Caldera Complex, Ecuador): Implications for Archean Sanukitoids. In: Journal of petrology, 2014, vol. 55, n° 4, p. 769–802. doi: 10.1093/petrology/egu006
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Article (Published version)
ISSN of the journal0022-3530

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