Flux versus decompression melting at stratovolcanoes in southeastern Guatemala |
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| Institution: | 1. Faculty of Earth Science, Beni-Suef University, 621, Egypt;2. Laboratory of Quantum and Statistical Physics, LR18ES18, Monastir University, Faculty of Sciences of Monastir, Tunisia;3. Physics Department, Faculty of Science, Beni-Suef University, 621, Egypt;1. Department of Geosciences, The Pennsylvania State University, University Park, PA, USA;2. Institute for CyberScience, The Pennsylvania State University, University Park, PA, USA;1. Key Laboratory of Submarine Geosciences and Prospecting Techniques, Ministry of Education, Qingdao 266100, China;2. College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;3. National Oceanographic Center, Qingdao 266071, China;4. Shandong Institute for Ocean Resources Exploration, Qingdao 266555, China;5. Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China;1. Department of Geosciences, Virginia Tech, Blacksburg, VA, USA;2. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, Università di Napoli Federico II, Napoli, Italy;3. ISTerre, UMR 5275, CNRS, Université Grenoble Alpes, Grenoble, France;4. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia;5. Department of Geology and Andean Geothermal Centre of Excellence (CEGA), Universidad de Chile, Santiago, Chile;6. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum, Università di Bologna, Bologna, Italy |
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| Abstract: | The major and trace element geochemistry of lavas erupted from four volcanic front (VF) stratovolcanoes in southeastern Guatemala show differences in the relative importance of flux and decompression melting in a continental arc setting. The VF stratovolcanoes exhibit a wide compositional range from basalt to dacite, although modern Pacaya erupts basaltic lavas. The VF basalts have relatively low MgO contents and plot outside the field of primary arc magmas defined by melting experiments on hydrous peridotite. After subtracting the effects of the fractionation, assimilation, and alteration of some VF lavas, separate partial melting and mixing trends were identified for Agua–Pacaya and Tecuamburro–Moyuta.The distinct chemical signatures of the hemipelagic and carbonate sediments subducted off Guatemala provide constraints on material transfer processes that occurred between the slab and mantle wedge. Model fluids and melts from the subducted slab were calculated using recently published mineral–aqueous fluid partition coefficients. Wide separation of the model fluid and melt compositions on a U/La versus Ba/Th diagram creates diagnostic mixing curves with an enriched mid-ocean ridge basalt source. Fluid from mature ocean crust has high U/La, fluid from carbonate sediment has high Ba/Th, and fluid and melt from hemipelagic sediments have both high U/La and Ba/Th. In a simple single-stage model, a mantle metasomatized by fluid originating largely from the oceanic crust with only minor sediment fluid contributions best explains the overall large ion lithophile element composition of the VF lavas. (Th/Rb)N ratios of ～1 in the VF lavas from southeastern Guatemala require a component of sediment melting. Therefore, a more realistic two-stage model to describe the Guatemalan arc data involves an initial hemipelagic sediment melt input to the wedge followed by minor fluid additions from the oceanic crust or sediments. Correlation between measures of slab input and extent of melting in the older VF lavas from Tecuamburro and Moyuta favors flux-dominated melting near the base of the mantle wedge. In sharp contrast, the lack of a relationship between slab additions and melting in younger lavas from Agua and Pacaya volcanoes implies a significant role for decompression melting closer to the top of the wedge. In this melting scenario, the rate of crustal extension determines the extent of melting. |
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