242-5 Barium Isotopes as Tracers of Sediment Recycling in Colombian and Mexican Arc Magmas

Abstract:

Subduction zones transport sediments into the mantle, enabling sediment-derived components and their geochemical signatures to be transferred to arc magmas. However, distinguishing biogenic from terrigenous or hydrothermal contributions remains challenging. The continental arcs of Colombia and Mexico offer an ideal geological setting to address this question because Ba-rich biogenic sediments are subducted with the Nazca plate beneath the Northern Volcanic Province of Colombia (NVPC), whereas terrigenous and hydrothermal sediments are subducted with the Rivera and Cocos plates beneath the Trans-Mexican Volcanic Belt (TMVB). Despite similar calc-alkaline affinities, their volcanic rocks differ markedly in average Ba concentrations. To investigate the origin of this contrast, we present the first high-precision ¹³⁵Ba–¹³⁷Ba double-spike-corrected Ba isotope dataset for lavas from the NVPC and TMVB. These measurements, combined with published geochemical data, allow us to test whether contrasting biogenic and terrigenous/hydrothermal sedimentary inputs impart distinguishable Ba isotope signatures to arc magmas. In the NVPC, high-Mg andesites from Nevado de Santa Isabel volcano, where the slab lies at a depth of ~140 km, display isotopically light δ¹³⁸Ba^/134Ba_NIST3104a values (-0.10‰ to -0.07‰), whereas lavas from Cerro Machín volcano, where the slab reaches a depth of ~160 km, record the heaviest Ba isotopic compositions of the Colombian suite (-0.04‰ to +0.01‰). The western TMVB exhibits the opposite relationship with slab depth, with lavas from Colima volcano, where the slab lies at ~90 km depth, yielding heavier compositions (-0.04‰ to -0.01‰) than those from the more landward Tequila volcano (-0.09‰ to -0.03‰), where the slab reaches an estimated depth of ~320 km. We suggest that the observed Ba isotope variability in lavas from the NVPC and TMVB reflects contributions from subducted barite reservoirs of contrasting marine origins. Whereas barite destabilization may be limited at shallower slab depths beneath Nevado de Santa Isabel and Colima, deeper breakdown of relatively heavy pelagic barite beneath Colombia and isotopically light hydrothermal barite beneath Mexico could shift Cerro Machín and Tequila lavas toward heavier and lighter Ba isotope compositions, respectively. These results highlight the potential of Ba isotopes to trace the cycling of biogenic and terrigenous/hydrothermal sedimentary components from the seafloor through the mantle wedge and back to the surface via arc volcanism.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-21675

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