Abstract
Volcanic arc clusters are groups of adjacent volcanic edifices that allow the investigation of geochemical changes occurring through time within a limited area (< few hundreds of km2). As such they may increase our understanding of processes that lead to magma differentiation in arcs. Geochemical changes over time in volcanic clusters can be related to source or intracrustal processes. Here, we show that magmatic rocks of 9 edifices of the Chachimbiro-Pulumbura-Pilavo-Yanaurcu volcanic cluster, in the frontal arc of Ecuador, display temporal changes of major and trace elements as well as Pb isotopes during their ~13 Ma long life history (13 Ma to 6 ka). Additionally, geochemical compositions of magmatic rocks of these edifices also become more homogeneous through time. Fractionation, assimilation and recharge models suggest that the changes in geochemical composition and in the compositional spread of erupted materials of the cluster are controlled by an increased depth of magma evolution since ~300–400 ka ago. We propose two speculative scenarios to explain the deepening of magmatic evolutionary processes since ~300–400 ka in the studied cluster. Nonetheless, a higher geochronological and geochemical resolution is needed to determine the cause and exact timing of such a switch as well as its synchronicity or diachroneity with respect to the geochemical changes observed in other volcanic centers along and across the Ecuadorian arc.
Highlights
Arc magmas display first order major and trace element as well as isotopic changes across and along-arc, which are ascribed to changing slab-mantle wedge interactions and/or to mantle and crust composi tional heterogeneities (Barragan et al, 1998; Patino et al, 2000; Chiaradia and Fontbote, 2002; Bryant et al, 2006; Mamani et al, 2010; Turner et al, 2016; Ancellin et al, 2017; Chiaradia et al, 2020)
We show that magmatic rocks of 9 edifices of the Chachimbiro-Pulumbura-Pilavo-Yanaurcu volcanic cluster, in the frontal arc of Ecuador, display temporal changes of major and trace elements as well as Pb isotopes during their ~13 Ma long life history (13 Ma to 6 ka)
We propose two speculative explanations to the temporal shift of geochemical and isotopic signatures in the volcanic edifices of the Chachimbiro clusters that could apply to the approximately coeval geochemical changes recorded by other volcanic edifices of Ecuador: (1) The deeper evolution of young magmatic systems (
Summary
Arc magmas display first order major and trace element as well as isotopic changes across and along-arc, which are ascribed to changing slab-mantle wedge interactions and/or to mantle and crust composi tional heterogeneities (Barragan et al, 1998; Patino et al, 2000; Chiaradia and Fontbote, 2002; Bryant et al, 2006; Mamani et al, 2010; Turner et al, 2016; Ancellin et al, 2017; Chiaradia et al, 2020). Understanding the meaning of such changes is important to fully characterize the genesis of arc magmas and their relationships to Earth-scale significant processes like the formation of continental crust (e.g., Tang et al, 2019) and of economic porphyry-type deposits (e.g., Lee and Tang, 2020; Chiaradia and Caricchi, 2017; Chiaradia, 2020) Under this point of view, volcanic clusters, i.e., occurrences of in dividual volcanic edifices spatially adjacent to each other, are useful to understand the meaning of temporal changes at a local scale (Grunder et al, 2006; Klemetti and Grunder, 2008; Walker et al, 2010). The variability and typology of chemical signatures of magmas from vol canoes in a cluster can be related to: (i) changes in the mantle source through time: these may be difficult to evaluate if primitive magmatic rocks are lacking; (ii) magmatic processes occurring at deep crustal levels (hot zones of Annen et al, 2006); (iii) magmatic processes occurring at shallow levels prior to eruption
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