TY - JOUR

T1 - The Permeability Evolution of Tuffisites and Implications for Outgassing Through Dense Rhyolitic Magma

AU - Heap, Michael J.

AU - Tuffen, Hugh

AU - Wadsworth, Fabian B.

AU - Reuschlé, Thierry

AU - Castro, Jonathan M.

AU - Schipper, C. Ian

N1 - An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union. This is the peer reviewed version of the following article:which has been published in final form at Heap, M. J., Tuffen, H., Wadsworth, F. B., Reuschlé, T., Castro, J. M., & Schipper, C. I. ( 2019). The permeability evolution of tuffisites and implications for outgassing through dense rhyolitic magma. Journal of Geophysical Research: Solid Earth, 124, 8281– 8299. https://doi.org/10.1029/2018JB017035 which has been published in final form at https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JB017035 ©2019. American Geophysical Union. All Rights Reserved.

PY - 2019/8/31

Y1 - 2019/8/31

N2 - There is growing evidence that outgassing through transient fracture networks exerts an important control on conduit processes and explosive-effusive activity during silicic eruptions. Indeed, the first modern observations of rhyolitic eruptions have revealed that degassed lava effusion may depend upon outgassing during simultaneous pyroclastic venting. The outgassing is thought to occur as gas and pyroclastic debris are discharged through shallow fracture networks within otherwise low-permeability, conduit-plugging lava domes. However, this discharge is only transient, as these fractures become clogged and eventually blocked by the accumulation and sintering of hot, melt-rich pyroclastic debris, drastically reducing their permeability and creating particle-filled tuffisites. In this study we present the first published permeability measurements for rhyolitic tuffisites, using samples from the recent rhyolitic eruptions at Chaitén (2008–2009) and Cordón Caulle (2011–2012) in Chile. To place constraints on tuffisite permeability evolution, we combine (1) laboratory measurements of the porosity and permeability of tuffisites that preserve different degrees of sintering, (2) theoretical estimates on grainsize- and temperature-dependent sintering timescales, and (3) H2O diffusion constraints on pressure-time paths. The inferred timescales of sintering-driven tuffisite compaction and permeability loss, spanning seconds (in the case of compaction-driven sintering) to hours (surface tension-driven sintering), coincide with timescales of diffusive degassing into tuffisites, observed vent pulsations during hybrid rhyolitic activity (extrusive behavior coincident with intermittent explosions), and more broadly, timescales of pressurization accompanying silicic lava dome extrusion. We discuss herein the complex feedbacks between fracture opening, closing, and sintering and their role in outgassing rhyolite lavas and mediating hybrid explosive-effusive activity.

AB - There is growing evidence that outgassing through transient fracture networks exerts an important control on conduit processes and explosive-effusive activity during silicic eruptions. Indeed, the first modern observations of rhyolitic eruptions have revealed that degassed lava effusion may depend upon outgassing during simultaneous pyroclastic venting. The outgassing is thought to occur as gas and pyroclastic debris are discharged through shallow fracture networks within otherwise low-permeability, conduit-plugging lava domes. However, this discharge is only transient, as these fractures become clogged and eventually blocked by the accumulation and sintering of hot, melt-rich pyroclastic debris, drastically reducing their permeability and creating particle-filled tuffisites. In this study we present the first published permeability measurements for rhyolitic tuffisites, using samples from the recent rhyolitic eruptions at Chaitén (2008–2009) and Cordón Caulle (2011–2012) in Chile. To place constraints on tuffisite permeability evolution, we combine (1) laboratory measurements of the porosity and permeability of tuffisites that preserve different degrees of sintering, (2) theoretical estimates on grainsize- and temperature-dependent sintering timescales, and (3) H2O diffusion constraints on pressure-time paths. The inferred timescales of sintering-driven tuffisite compaction and permeability loss, spanning seconds (in the case of compaction-driven sintering) to hours (surface tension-driven sintering), coincide with timescales of diffusive degassing into tuffisites, observed vent pulsations during hybrid rhyolitic activity (extrusive behavior coincident with intermittent explosions), and more broadly, timescales of pressurization accompanying silicic lava dome extrusion. We discuss herein the complex feedbacks between fracture opening, closing, and sintering and their role in outgassing rhyolite lavas and mediating hybrid explosive-effusive activity.

KW - HO diffusion

KW - lava dome

KW - permeability

KW - rhyolite

KW - sintering

KW - tuffisite

U2 - 10.1029/2018JB017035

DO - 10.1029/2018JB017035

M3 - Journal article

AN - SCOPUS:85070835508

VL - 124

SP - 8281

EP - 8299

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 8

ER -