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Lau, N, Tymofyeyeva E, Fialko Y.  2018.  Variations in the long-term uplift rate due to the Altiplano-Puna magma body observed with Sentinel-1 interferometry. Earth and Planetary Science Letters. 491:43-47.   10.1016/j.epsl.2018.03.026   AbstractWebsite

We present new Interferometric Synthetic Aperture Radar (InSAR) observations of surface deformation in the Altiplano-Puna region (South America) where previous studies documented a broad uplift at an average rate of similar to 10 mm/yr. We use data from the Sentinel-1 satellite mission to produce high-resolution velocity maps and time series of surface displacements between years 2014-2017. The data reveal that the uplift has slowed down substantially compared to the 1992-2010 epoch and is characterized by short-term fluctuations on time scales of months to years. The observed variations in uplift rate may indicate a non-steady supply of melt and/or volatiles from the partially molten Altiplano-Puna Magma Body (APMB) into an incipient diapir forming in the roof of the APMB. (C) 2018 Elsevier B.V. All rights reserved.

Khazan, Y, Fialko Y.  2005.  Why do kimberlites from different provinces have similar trace element patterns? Geochemistry Geophysics Geosystems. 6   10.1029/2005gc000919   AbstractWebsite

Analysis of the trace element contents in kimberlites from various provinces around the world, including South Africa, India, and Yakutia ( Siberia, Russia), reveals remarkable similarity of the maximum abundances. In addition, we find that abundances of the rare earth elements ( REE) in the South African kimberlites are highly coherent between individual elements. We suggest that the observed similarity of the trace element patterns may result from a common physicochemical process operating in the kimberlite source region, rather than from peculiar source compositions and magmatic histories. The most likely candidates for such a process are ( 1) partial melting at very low melting degrees and ( 2) porous melt flow and diffusive exchange with the host rocks. These two processes can produce the same maximum trace element abundances and similar undersaturated patterns. We argue that the porous flow, and the associated chromatographic enrichment, is preferred because it allows high saturations at relatively large melt fractions of similar to 1%. Observations of enrichment of the xenolith grain rims due to an exchange with metasomatizing melts of quasi- kimberlitic composition imply that the melt percolated beyond the source region, in agreement with basic assumptions of the percolation model. We demonstrate that the saturated REE patterns are in a good agreement with the maximum observed REE abundances in kimberlites from different provinces. The theoretical patterns are independent of the melt fraction and only weakly ( if at all) depend on the source modal composition. Characteristic diverging fan- like patterns of trace elements predicted by the percolation model are identified in kimberlites from South Africa. We propose that a high coherency of the REE patterns in the South African kimberlites results from a general dependence of all REE abundances on the calcium content. According to this interpretation, the overall depletion of the source rocks in REE with temperature ( and depth) postulated by our model is a natural consequence of a decrease in the calcium content along the lherzolite trend.

Fialko, Y, Khazan Y, Simons M.  2001.  Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy. Geophysical Journal International. 146:181-190.   10.1046/j.1365-246X.2001.00452.x   AbstractWebsite

We consider deformation due to sill-like magma intrusions using a model of a horizontal circular crack in a semi-infinite elastic solid. We present exact expressions for vertical and horizontal displacements of the free surface of a half-space, and calculate surface displacements for a special case of a uniformly pressurized crack. We derive expressions for other observable geophysical parameters, such as the volume of a surface uplift/subsidence, and the corresponding volume change due to fluid injection/withdrawal at depth. We demonstrate that for essentially oblate (i.e. sill-like) source geometries the volume change at the source always equals the volume of the displaced material at the surface of a half-space. Our solutions compare favourably to a number of previously published approximate models. Surface deformation due to a 'point' crack (that is, a crack with a large depth-to-radius ratio) differs appreciably from that due to an isotropic point source ('Mogi model'). Geodetic inversions that employ only one component of deformation (either vertical or horizontal) are unlikely to resolve the overall geometry of subsurface deformation sources even in a simplest case of axisymmetric deformation. Measurements of a complete vector displacement field at the Earth's surface may help to constrain the depth and morphology of active magma reservoirs. However, our results indicate that differences in surface displacements due to various axisymmetric sources may be subtle. In particular, the sill-like and pluton-like magma chambers may give rise to differences in the ratio of maximum horizontal displacements to maximum vertical displacements (a parameter that is most indicative of the source geometry) that are less than 30 per cent. Given measurement errors in geodetic data, such differences may be hard to distinguish.

Fialko, Y, Simons M, Khazan Y.  2001.  Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California. Geophysical Journal International. 146:191-200.   10.1046/j.1365-246X.2001.00453.x   AbstractWebsite

We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our brst-fitting model for the Socorro magma body is a sill with a depth of 19 km, an effective diameter of 70 km and a rate of increase in the excess magma pressure of 0.6 kPa yr(-1). We show that the corresponding volumetric inflation rate is similar to6 x 10(-3) km(3) yr(-1), which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle-derived melts into the middle crust beneath Socorro map have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of similar to 11 cm and a volume of 3.5 x 10(-2) km(3). Modelling of the InSAR data suggests that the observed deformation might be due to either a sill-like magma body at a depth of similar to 12 km or a pluton-like magma body at a depth of similar to8 km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two-colons laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7-9 km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions.

Fialko, Y.  2001.  On origin of near-axis volcanism and faulting at fast spreading mid-ocean ridges. Earth and Planetary Science Letters. 190:31-39.   10.1016/s0012-821x(01)00376-4   AbstractWebsite

At fast and superfast spreading mid-ocean ridges, such as the East Pacific Rise, a plate boundary is defined by a narrow (tens to hundreds of meters wide) neovolcanic zone within which the bulk of the upper oceanic crust is created. However, detailed near-bottom observations indicate that the volcanic construction may occasionally persist several kilometers off of the ridge axis. It has been proposed that off-axis volcanism manifests tapping of a wide melting region that supplies magma to the ridge axis, or spatial migration of magmatic sources in the crust and upper mantle. We demonstrate that off-axis eruptions may be a natural consequence of variations in magma supply rate even if the ridge axis is stationary in space, and the magma delivery is perfectly focussed at the ridge axis. Theoretical modeling and field observations indicate that off-axis volcanisin may result from magma emplacement in sills that propagate toward the surface after their characteristic horizontal size exceeds their emplacement depth. Volcanic construction and faulting due to sill intrusions may contribute to the formation of abyssal hills, arguably the most abundant relief form on Earth. (C) 2001 Elsevier Science B.V. All rights reserved.

Fialko, YA, Rubin AM.  1999.  What controls the along-strike slopes of volcanic rift zones? Journal of Geophysical Research-Solid Earth. 104:20007-20020.   10.1029/1999jb900143   AbstractWebsite

We investigate the dynamics of viscous pressure losses associated with lateral magma transport in volcanic rift zones by performing (I) coupled elastic-hydrodynamic simulations of downrift magma flow in dikes and (2) analog experiments mimicking lateral dike propagation in the presence of an along-rift topographic slope. It is found that near-source eruptions are likely to be favored by shallow slopes while distant downrift eruptions may be encouraged by steeper slopes, provided that along-rift variations in the tectonic stress are negligible or uncorrelated on the timescale of multiple dike intrusions. This implies the existence of a critical slope to which a volcanic rift zone would naturally evolve. Such behavior is produced by three-dimensional (3-D) elastic effects and is controlled by the ratio of the driving pressure gradient due to the along-strike topographic slope to the vertical gradient in the excess magma pressure in the dike. This model may be viewed as complementary to commonly cited mechanisms that appeal to magma viscosity and the dynamics of freezing of lava flows at the surface to explain the low profiles of basaltic shield volcanoes. Our estimated values of the critical slopes are in general agreement with observations in Hawaiian rift zones, but further development of fully 3-D models is required for more accurate predictions.