Origin of silicic volcanic rocks in Central Costa Rica: a study of a chemically variable ash-flow sheet in the Tiribí Tuff

Abstract

Chemical heterogeneities of pumice clasts in an ash-flow sheet can be used to determine processes that occur in the magma chamber because they represent samples of magma that were erupted at the same time.The dominant ash-flow sheet in the Tiribí Tuff contains pumice clasts that range in composition from 55.1 to 69.2 wt% SiO 2 . It covers about 820 km 2 and has a volume of about 25 km 3 dense-rock equivalent (DRE). Based on pumice clast compositions, the sheet can be divided into three distinct chemical groupings: a low-silica group (55.1-65.6 wt% SiO 2 ), a silicic group (66.2-69.2 wt% SiO 2 ), and a mingled group (58.6-67.7 wt% SiO 2 ; all compositions calculated 100% anhydrous). Major and trace element modeling indicates that the lowsilica magma represents a mantle melt that has undergone fractional crystallization, creating a continuous range of silica content from 55.1-65.6 wt% SiO 2 . Eu/Eu*, MREE, and HREE differences between the two groups are not consistent with crystal fractionation of the low-silica magma to produce the silicic magma. The low-silica group and the silicic group represent two distinct magmas, which did not evolve in the same magma chamber. We suggest that the silicic melts resulted from partial melting of relatively hot, evolved calc-alkaline rocks that were previously emplaced and ponded at the base of an over-thickened basaltic crust. The mingled group represents mingling of the two magmas shortly before eruption. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.

Discriminant model and hydrogeochemical processes for characterizing preferential flow paths in four interconnected volcanic aquifers in Costa Rica

“…In the Colima Formation, the lavas of the Lower Colima Member are trachyandesites and porphyritic andesites, containing phenocrystals of plagioclase, e.g., anorthite, Puente Mulas Member is composed of tuffs and ignimbrites, whereas the lavas from the Upper Colima Member are aphyric andesites with only 4% phenocrysts (Kussmaul 1988)-Table S1 of the electronic supplementary material (ESM). The Tiribí Formation corresponds to a pack of chemically variable tuffs and ignimbrites, ranging from andesites transitional to shoshonitic dacites (Kussmaul 1988;Kussmaul and Sprechmann 1982), basaltic-andesites, trachytes, and trachydacites (Hannah et al 2002), with trachyandesites being the dominant composition (Pérez et al 2006), bearing 1-10% of plagioclases (Table S1 of the ESM). In the Barva Formation, the lavas of the Bermudez Member exhibit highly fractured porphyritic basaltic andesites (Arredondo Li and Soto 2007;Echandi 1981) with plagioclase and anorthite phenocrysts (Table S1 of the ESM).…”

“…Particularly, further enrichment in Colima might have also been obtained due to the infiltration of groundwater through the acidic ignimbrites, tuffs, and pumice-rich layers of the overlying Tiribí Formation (BGS/SENARA 1988). Tiribí lithologies are acid, based on their SiO 2 content (from 55.1 to 69.2 wt%; Hannah et al 2002), and comprise andesites, trachyandesites, and dacites (Pérez et al 2006) and elevated contents of Na 2 O and K 2 O (Kussmaul 1988). Higher magnesium concentrations in UC1 and LC, compared to LB, could be related to longer flow paths and residence times and consequent hydrolysis of the ferromagnesic minerals, i.e., hypersthene, augite, olivine.…”

Basalts From the Chukchi Borderland: 40Ar/39Ar Ages and Geochemistry of Submarine Intraplate Lavas Dredged From the Western Arctic Ocean

“…Trace element concentrations were determined on the same fused glass disks using an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) with a hexapole collision cell (Micromass Platform ICP-MS) coupled with a UV laser ablation system Cetac LSX200+, also at Michigan State University. Details of the analytical techniques and procedures are given in Hannah et al (2002). A few of the samples were analyzed in the Geoanalytical Laboratory of Washington State University using XRF spectrometry for major oxides and an HP-4500 Quadrupole ICP-MS for trace elements, both following methods outlined in Knaak et al (1994) and Johnson et al (1999).…”

Evolution of geochemical variations along the Central American volcanic front

“…Sample locations documented with GPS are reported in Table 1. Major element (wt%) data for the Balsamo samples were obtained using by X-ray fluorescence (XRF) at Michigan State University following procedures outlined in Hannah et al [2002]. Data are reported in Table 1.…”