Conceptual model for small-volume alkali basalt petrogenesis: implications for volcanic hazards at the proposed Yucca Mountain nuclear waste repository

Abstract

Today, 31 countries operate ∼ 450 nuclear power reactors supplying electric power to ∼ 1 billion people, ∼ 15% of the world population. Nuclear reactors generate ∼ 17% of global electric power needs and a number of industrialized countries depend on nuclear power for at least half of their electricity. In addition, ∼ 30 nuclear power reactors are presently under construction worldwide (Macfarlane and Miller, 2007). A comprehensive summary of the principles, practices, and prospects for nuclear energy may be found in Bodansky (1996). Concerns regarding energy resource availability, climate change, air quality and energy security imply a continuing demand for nuclear power in the world energy budget (Craig et al., 2001). However, to date no country has solved the problem of long-term disposal or storage of nuclear waste. Without a long-term solution, the viability of nuclear energy as an increasingly significant contributor to power generation in the long-range future remains unclear. There is broad consensus that geologic disposal is the safest feasible longterm solution to high-level waste and spent-fuel disposal. Although a number of countries have ongoing geologic repository research programs, there is presently no operational geologic repository for spent fuel or high-level waste on Earth. In the United States, where spent nuclear fuel and high-level waste amounts to ∼ 50 000 metric tons, ∼ 15% of the world total, implementation has proven to be challenging both technically and politically. Nuclear waste is currently stored on-site at existing nuclear power stations and at several temporary storage facilities. Permanent geologic disposal, like the siting of a nuclear power plant, requires careful site selection. For geologic disposal, lithology that can isolate radioactive waste from the surrounding environment and biosphere at geologic timescales ∼ 10 4 −10 6 a are a minimum requirement (Macfarlane and Ewing, 2006). Of particular importance in this regard are the nature, consequences and probabilities of volcanic hazards that can potentially compromise public, environmental and biospheric safety at long-term nuclear waste storage sites. Yucca Mountain (YM) in Nevada, USA was identified in the early 1980s as a potential geologic repository for nuclear waste. Yucca Mountain is made up of silicic volcanic tuffsrocks composed chiefly of pyroclastic flow and fall deposits. The proposed Yucca Mountain Repository (YMR) lies on the western boundary of the Nevada Test Site (NTS) within the Basin and Range geologic province (Zoback et al., 1981; Thompson and Burke, 1974). This region is geologically active, with transtensional deformation manifested by faulting, related Small-volume alkali basalt petrogenesis 197 YMR involves an event at a specific location where volcanism has not occurred in the last 10 Ma. Volcanic hazard evaluation and prediction at YM therefore involves the coupled and difficult problems of predicting the timing, location, volume and eruptive style of possible eruptive events. Any single one of the...

Mechanisms of low-flux intraplate volcanic fields—Basin and Range (North America) and northwest Pacific Ocean

“…Heterogeneities or patches relatively enriched in hydrous phases have slightly depressed solidus temperatures and elevated degrees of partial melt under ambient conditions. Thermodynamic calculations suggest that the patches contained 5%-10% (by mass) partial melt of candidate fertile peridotite sources (with water contents of ~0.2 wt%), at temperatures between ~1120 and 1300 °C, and depths of ~50-70 km (Spera and Fowler, 2009).…”

“…2C) and lack of a crustal contamination signature in the isotopic compositions suggest that Southwest Nevada volcanic fi eld dikes, once triggered at source depths, ascended rapidly through the crust with little or no storage in magma chambers; fractionation probably occurred during ascent and mainly at depths >30 km (Valentine and Perry, 2007;Spera and Fowler, 2009). In contrast, northwest Pacifi c Ocean magmas experienced variable degrees of fractionation and contamination as they ascended through the lithosphere ( Fig.…”

“…It is likely that many small veins and dikes are triggered along shear bands, and these coalesce upward to feed one or a few major dikes (see Ito and Martel, 2002) that ascend into the upper lithosphere and potentially feed monogenetic events. This zone of dike and vein coalescence is likely where much of the deep fractionation recorded in the Southwest Nevada volcanic fi eld takes place (Spera and Fowler, 2009). The relationship between melt collection/ascent and tectonic deformation (stress relief) results in a time-predictable relationship between eruption volume and repose time (Valentine and Perry, 2007).…”

Evolution of the East African Rift System from trap-scale to plate-scale rifting

“…Moreover, the widespread distribution of easily fusible lithospheric metasomes within the continental lithosphere mantle might have facilitated magma generation without the need for substantial lithospheric thinning or elevated mantle potential temperatures (Rooney et al, 2014). Thus, a deformation-driven collection of already existing partial melts in a heterogenous mantle, as described by Valentine and Perry (2007), Spera and Fowler (2009) Valentine and Hirano (2010), Smith et al (2021), could have produced a tectonically controlled magmatism. We therefore interpret the timing of the alkaline volcanism along the Pan-African mobile belts, synchronously with main changes in the spreading ridge dynamics, as primarily controlled by the increase of extension stresses.…”

Lunar Crater volcanic field (Reveille and Pancake Ranges, Basin and Range Province, Nevada, USA)

“…Detailed whole-rock and mineral chemistry data from two episode 3 eruptive centers (Cortés et al, 2015) suggest that the magmas may have originated by 3%-5% partial melting of an olivine websterite-lherzolite source at depths of 60-130 km. The magmas partially crystallized at depths of 30-45 km, either while stalled near the base of the crust (30-35 km thick) or during ascent in that depth interval, after having risen directly from source depths (Spera and Fowler, 2009;Rasoazanamparany et al, 2015;Cortés et al, 2015). After ~50% crystallization, the magmas then ascended rapidly to the surface, with no geochemical evidence for crustal contamination.…”