Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

Abstract

International audienceMinor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic. The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ 18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa and Huambo basement may be plausible contaminants

Across‐arc versus along‐arc Sr‐Nd‐Pb isotope variations in the Ecuadorian volcanic arc

“…Arc zonation is visible as alkaline content at given SiO 2 increases away from the trench. Composition of other Andean volcanic zones are displayed, the Central Volcanic Zone (CVZ) by the green shaded area [ Davidson and de Silva , ; Feeley and Davidson , ; Delacour et al ., ; Hora et al ., ; Mamani et al ., ; Sørensen and Holm , ] and the Southern Volcanic Zone (SVZ) by the red shaded area [ Hickey‐Vargas et al ., ].…”

Reconstruction of the volcanic history of the Tacámbaro-Puruarán area (Michoacán, México) reveals high frequency of Holocene monogenetic eruptions

“…Nonetheless, examination of the list of Holocene volcanic fields compiled by Simkin (2002-2011), inspection of satellite images using GoogleEarth, as well as a review of recent papers on selected areas, provide some insight into the characteristics of young monogenetic fields in volcanic arcs wordwide (here, we only consider groups of >5 volcanoes with published Holocene ages). Many of these fields occur in extensional back-arc settings (e.g., Auckland volcanic field, New Zealand, Molloy et al 2009; Los Volcanes field, Argentina, Germa et al 2010;Sredinny Range, Kamchatka, Ponomareva et al 2007) and only a few near the arc front (e.g., Andahua, Perú, Delacour et al 2007;Sand Mountain, Oregon, Wood and Kienle 1990;Tolbachik, Kamchatka, Braitseva et al 1984). The TMVB is certainly unique in the world by having such large numbers of monogenetic centers not only in the back but also along the front (e.g., Sierra Chichinautzin, Jorullo, Tacámbaro-Puruarán; Fig.…”

Role of magma mixing in the petrogenesis of tephra erupted during the 1990–98 explosive activity of Nevado Sabancaya, southern Peru

“…Some basaltic lavas (51.6-52.7 wt% SiO 2 ) from minor centres in southern Peru ca. 30 km WSW of Nevado Sabancaya are characterised by enriched isotopic signatures (Delacour et al 2002), with 87 Sr/ 86 Sr ratios of about 0.707 and d 18 O spanning a 7.1-7.5 range, which are very similar to the magmatic enclave compositions. These basalts have mineralogical and compatible trace element compositions typical of poorly evolved magmas, suggesting they have been erupted quite rapidly from their source region without long residence within upper crustal magma chambers.…”