Spherulite crystallization induces Fe-redox redistribution in silicic melt

Castro, Jonathan M.; Cottrell, Elizabeth; Tuffen, Hugh; Logan, M. Amelia V.; Kelley, K. A.

doi:10.1016/j.chemgeo.2009.09.006

Cited by 24 publications

(13 citation statements)

References 38 publications

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“…If true, then our estimated spherulite nucleation temperatures of ~600-700 °C are equivalent to undercoolings of 300-400 °C, values similar to those determined in comparable experiments. Furthermore, quartz and alkali feldspar were experimentally estimated to grow at rates of 0.1-6 mm hr -1 , which are largely consistent with our estimates (Swanson, 1977;Baker and Freda, 2001;Castro et al, 2009). The cooling rate estimates determined independently from both techniques described herein can be interpreted to provide a firstorder constraint on the longevity of a largevolume prehistoric lava.…”

Section: Spherulite Geospeedometrysupporting

confidence: 54%

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Spherulites as in-situ recorders of thermal history in lava flows

Befus¹,

Watkins²,

Gardner³

et al. 2015

Geology

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Spherulites in rhyolitic obsidian provide a record of the thermal history of their host lava during the interval of spherulite growth. We use trace element concentration profiles across spherulites and into the obsidian host from Yellowstone National Park (USA) to reconstruct the conditions that existed during spherulite formation. The measured transects reveal three behaviors: expulsion of the most diffusively mobile elements from spherulites with no concentration gradients in the surrounding glass (type 1); enrichment of slower-diffusing elements around spherulites, with concentration gradients extending outward into the glass (type 2); and complete entrapment of the slowest-diffusing elements by the spherulite (type 3). We compare the concentration profiles, measured by laser ablation-inductively coupled plasma-mass spectrometry and Fourier transform infrared spectroscopy, to the output of a spherulite growth model that incorporates known diffusion parameters, the temperature interval of spherulite growth, the cooling rate of the lava, and data on the temporal evolution of spherulite radius. Our results constrain spherulite nucleation to the temperature interval 700-550 °C and spherulite growth to 700-400 °C in a portion of lava that cooled at 10 -5.2 ± 0.3 °C s -1 , which matches an independent experimental estimate of 10 -5.3 °C s -1 measured using differential scanning calorimetry. Maximum spherulite growth rates at nucleation are on the order of 1 mm hr -1 and are inferred to decrease exponentially with time. Hence, spherulites may serve as valuable in-situ recorders of the thermal history of lava flows.

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Section: Spherulite Geospeedometrysupporting

confidence: 54%

“…Past experimental studies have examined how felsic minerals crystallize from melt in response to variable degrees of undercooling (Fenn, 1977;Swanson, 1977;Baker and Freda, 2001;Castro et al, 2009). Spherulites were the stable form in experiments that experienced large undercoolings ranging from 100 to 400 °C.…”

Section: Spherulite Geospeedometrymentioning

confidence: 98%

Spherulites as in-situ recorders of thermal history in lava flows

Befus¹,

Watkins²,

Gardner³

et al. 2015

Geology

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“…The uncertainties in oxygen isotope geothermometry limit ΔT estimates to sizable ranges. The estimates are consistent with experiments that performed spherulite growth at ΔT ranging from 100 to 400°C [Lofgren, 1974;Fenn, 1977;Kirkpatrick et al, 1979;Baker and Freda, 2001;Castro et al, 2009]. The Δ 18 O Qtz-Kfs temperature estimates are also comparable with constraints inferred from advection-diffusion modeling of incompatible constituent profiles surrounding spherulites in the same sample from Pitchstone Plateau [Befus et al, 2015].…”

Section: Discussionsupporting

confidence: 84%

“…The new estimate for spherulite growth is similar to the slower growth rates determined from experiments but is largely similar to results from advection‐diffusion modeling [ Fenn , ; Swanson , ; Baker and Freda , ; Castro et al , ; Arzilli et al , ; Befus et al , ]. Much of the discrepancy between the new rates and the faster rates determined from past experiments is simply a result of dissimilar materials.…”

Section: Discussionmentioning

confidence: 99%

Crystallization kinetics of rhyolitic melts using oxygen isotope ratios

Befus

2016

Geophysical Research Letters

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Crystals provide the means to understand igneous systems, but natural constraints on crystallization kinetics are rare because thermal conditions and crystallization timescales are typically unknown. Oxygen isotope ratios in quartz and alkali feldspar crystals in spherulites provide a natural record of the temperature interval of crystallization and crystal growth rates in rhyolitic melts. Oxygen isotope compositions in both phases change progressively with position from the spherulite core to rim. Quartz δ18O increases from 5.0 ± 0.3‰ in the core to 5.6 ± 0.3‰ at the rims, whereas alkali feldspar decreases from 3.7 ± 0.4‰ in the core to 2.7 ± 0.9‰ at the rims. Fractionation therefore increases from 1.3 ± 0.7‰ in the cores to 2.9 ± 1.1‰ at the rims. Oxygen isotope thermometry tracks crystallization temperature with position. Spherulites nucleate at 578 ± 160°C and continue to grow until 301 ± 88°C. The in situ analyses demonstrate that spherulites self‐contain a record of their thermal history and that of the host lava.

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“…Watkins et al (2009) argue that spherulite growth is lim ited by diffusivity of OH -, which is 10 -6 mm 2 /s in obsidian, and because thermal diffusivity is orders of magnitude higher, latent heat is con ducted away well before temperature can rise. However, theoretical spherulite growth times reported by Castro et al (2008) are shorter than those of Watkins et al (2009) and are verified by experimentally grown spherulites (Castro et al, 2009) on June 1, 2015 geosphere.gsapubs.org Downloaded from Secondary structures of ignimbrites is a limiting growth factor in nonporous obsid ian, it is less likely to constrain growth in partly permeable tuffs. Lastly, Watkins et al's (2009) analysis ignores scale effects, as is shown next.…”

Section: New Observationsmentioning

confidence: 53%

Relations between thermal history and secondary structures of ignimbrites exclusive of rheomorphism

Riehle¹

2015

Geosphere

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Newly calculated model density profiles of ignimbrites also provide model thermal his tories, which serve as a framework to help analyze the development of cooling joints, devitrification textures, and lithophysal cavi ties. Only those parts of sections of Rattle snake Tuff in central Oregon that resided >600 °C for at least two years show devitrifi cation. Low tensile strength means that joints form by thermoelastic contraction after cool ing by as little as 25 °C. This means that columnar joints formed in as little time as a few weeks after deposition of the Aravaipa Tuff in SE Arizona. Compaction is rapid as well, so both columnar jointing and compac tion are complete before the onset of devitri fication in deposits <40 m thick.A section of Rattlesnake Tuff shows strata bound occurrences of devitrified spots and cavities; devitrification appears to have begun at scattered spots. Most spots are bounded by crescentic cavities in formerly ductile shards. The equation for conductive cooling of a spherical heat source shows that for rock volumes larger than ~15 cm diam eter, the rate of cooling is insufficient to pre vent heating by latent heat by as much as 12 °C. Inflation therefore appears to have been caused by vapor released by devitri fication and its slight adiabatic expansion. Eventual wholesale devitrification of matrix resulted in moredevitrified spots scattered in less devitrified matrix. Lithophysal cavi ties in the Rattlesnake Tuff and in the Peach Springs Tuff in NW Arizona are more abun dant in lower density horizons, showing that cavity growth is favored in permeable zones between impermeable horizons.The Peach Springs Tuff and other depos its described in the literature have horizon tal joints that formed during cooling and whose origin has yet to be deterministically modeled. The longest joints are most closely spaced in the zone of cavities and formed after columnar joints. It is inferred that after formation, each vertical column responds independently to evolving stresses; at this time, asperities together with gas pressures accompanying cavity formation result in horizontal joints. Columnar joints do not completely relieve growing gas pressures during devitrification, likely because of seal ing by wholesale inflation of the rock mass and by mineral deposition.Some devitrified horizons of Rattlesnake Tuff and Peach Springs Tuff are densely frac tured, resulting in a rubbly surface. These small fractures show zigzag traces, bifur cations, abrupt terminations, and pinch andswell walls, similar to ductile fractures described by Eichhubl (2004). Their origin is interpreted to be the result of tensile stress due to porosity increase during later stages of devitrification.Closely adjacent sections of Rattlesnake Tuff at one site differ by 18% in thickness, reflecting buried paleotopography. Each sec tion is devitrified. The thicker profile has a zone of lithophysal cavities near its base; the thinner profile has few cavities. The greater thickness translates to only 0.18 MPa addi tional lithostatic p...

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Spherulite crystallization induces Fe-redox redistribution in silicic melt

Cited by 24 publications

References 38 publications

Spherulites as in-situ recorders of thermal history in lava flows

Spherulites as in-situ recorders of thermal history in lava flows

Crystallization kinetics of rhyolitic melts using oxygen isotope ratios

Relations between thermal history and secondary structures of ignimbrites exclusive of rheomorphism

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