Crystal fractionation processes at Baru volcano from the deep to shallow crust

Abstract

[1] Linking shallow and deep crustal processes at volcanic arcs is an important component in evaluating the growth and evolution of the continental crust. Commonly, deep crustal processes and the nature of subarc lithosphere are studied long after the volcanism has ceased in obducted arc terranes. In active arcs, studies of deep crustal processes focus on cumulates derived from middle-lower crustal levels. Although uncommon in the erupted magmas, these cumulates are required by crustal differentiation models of arc magmatism. Quaternary magmas at Baru volcano in Panama contain ubiquitous amphibole-bearing cumulates that provide an opportunity to probe the magma plumbing system of an active arc volcano. We have determined that these cumulates are related to their host magmas by crystal fractionation processes. Pressure and temperature estimates for amphiboles within these cumulates and the host rock are consistent with sampling of mush/magma zones from throughout the arc crust. These mush zones would be localized in deep hot crustal zones where magmatic differentiation of water-saturated arc magmas takes place by crystallization of amphibole-rich cumulates. The identification of middle-lower crustal cumulates is not exclusive to Baru volcano; similar cumulates are common throughout the Panamanian arc and are consistent with a widespread amphibole-rich layer present within the arc crust of Panama. Our results highlight the importance of amphibole fractionation in the differentiation sequence of island arcs effectively driving the residual magma to the average andesitic composition of the continental crust.

Amphibole stability in primitive arc magmas: effects of temperature, H2O content, and oxygen fugacity

“…These experimental studies along with studies of natural samples (Grove and Donnelly-Nolan 1986;Romick et al 1992;Davidson et al 2007) have shown that amphibole crystallizes from a wide variety of liquids at crustal pressures and can be an important fractionating phase in arc systems. Significant amphibole fractionation has been inferred to occur at arcs such as Panama (Hidalgo and Rooney 2010), Chile (Kratzmann et al 2010), and globally (Davidson et al 2007). Olivine-bearing, plagioclase-free amphibole cumulates have been identified in the Bonanza Jurassic arc in British Columbia (Larocque and Canil 2010), and the Adamello batholith (Tiepolo et al 2011).…”

Tracing changes in mantle and crustal influences in individual cone-building stages at Mt. Shasta using U–Th and Sr isotopes

“…Most arc lavas are highly differentiated and have mineral assemblages that are the product of shallow, relatively late crystallization processes (Davidson et al, 2007). Here we consider minerals other than those observed in erupted lavas as a possible control on Th/U ratios, including cryptic mineral fractionation in the mid-to lower-crust (e.g., Lee et al, 2006;Davidson et al, 2007;Hidalgo and Rooney, 2010). Although an uncommon eruptive product, garnet is observed where the lower crustal roots of arcs are exposed.…”

“…Although an uncommon eruptive product, garnet is observed where the lower crustal roots of arcs are exposed. Deep garnet fractionation imparts distinct chemical signatures on magmas, including HREE depletions, unusually high Sr/Y ratios, moderate Fe/Mg ratios, and, as a result of an affinity for U relative to Th (D U = 0.31, D Th = 0.074; Rubatto and Hermann, 2007), significant 230 Th-excesses may be produced (Ankney et al, 2013;Hidalgo and Rooney, 2010;Jicha et al, 2009b).…”

The Record of the Transition From an Oceanic Arc to a Young Continent in the Talamanca Cordillera

“…This process is possible as thermal models indicate that temperatures above the aqueous fluid saturated solidus are common along the top of most subducting plates worldwide (Conder, 2005;Kelemen et al, 1990;van Keken, Kiefer, et al, 2002;Peacock et al, 2005). Lower crustal fractionation (Hidalgo & Rooney, 2010;Hidalgo & Rooney, 2014) and/or anatexis of lower crust materials (Vogel et al, 2004) will later add to the evolution of primary magmas into even more felsic compositions. Lower crustal fractionation (Hidalgo & Rooney, 2010;Hidalgo & Rooney, 2014) and/or anatexis of lower crust materials (Vogel et al, 2004) will later add to the evolution of primary magmas into even more felsic compositions.…”