Forming Europa’s folds: Strain requirements for the production of large-amplitude deformation

Bland, M. T.; McKinnon, William B.

doi:10.1016/j.icarus.2012.08.029

Cited by 17 publications

(20 citation statements)

References 99 publications

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“…Observational evidence for contraction is preserved in folds with small amplitudes [ Prockter and Pappalardo , ] though these folds do not record enough strain to accommodate the expansion elsewhere [ Dombard and McKinnon , ]. There are also no large‐amplitude folds with smaller strains [ Bland and McKinnon , ]. Bands [ Greenberg , ], strike‐parallel faults [ Sarid et al ., ], and ridges [ Patterson and Pappalardo , ] have been proposed as sites of convergence, though quantification of the magnitude has been limited.…”

Section: Discussionmentioning

confidence: 99%

Double ridges on Europa accommodate some of the missing surface contraction

et al. 2014

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Crosscutting relationships of tectonic lineaments on Europa record the history of surface deformation.We mapped the displacement and orientation of older features crosscut by two types of lineaments: bands and double ridges. These measurements allow us to determine both the strike-perpendicular and strike-parallel displacement along investigated features. Double ridges record both ridge-perpendicular contraction and expansion, with a mean of 0.16 ± 0.06 km (needs space) of contraction based on the analysis of 16 double ridges. Bands record expansion, with a mean of 3.33 ± 0.27 km for the six bands analyzed, but with perpendicular displacement less than their apparent morphologic widths of 3-24 km. The implied global surface strain for double ridges (including those that expand) and bands is 2.22 ± 0.76% contraction and 7.60 ± 3.7% expansion, respectively. Double ridges thus may accommodate part of the surface expansion recorded by bands. Most current models for double ridges do not predict contraction. The models that satisfy the observations for bands are "slow-spreading" models, cryovolcanism, and folding.

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Section: Discussionmentioning

confidence: 99%

Double ridges on Europa accommodate some of the missing surface contraction

et al. 2014

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“…The viscosity structure is determined by the vertical temperature profile. We examine heat fluxes ( q ) of 50, 75, and 100 mW m −2 , consistent with previous estimates of Europan fold formation [ Dombard and McKinnon , ; Bland and McKinnon , ]. The thermal conductivity of pure, solid water ice ( k ) is temperature dependent such that k =651 W m −1 / T , where T is the temperature [ Petrenko and Whitworth , ].…”

Section: Modeling Fold Formationmentioning

confidence: 77%

“…Surface temperatures were varied between 70 K and 120 K, consistent with diurnally averaged temperatures on Europa (see auxiliary material). Prescribing the heat flux rather than assuming a linear thermal gradient departs from previous modeling [e.g., Bland and McKinnon , ] and results in a modest increase in the strength contrast between the lithosphere and underlying ice “asthenosphere” but is more realistic. The increased strength contrast leads to modestly increased fold amplitudes for a given strain.…”

Section: Modeling Fold Formationmentioning

confidence: 91%

“…For numerical efficiency, we limit the maximum temperature ( T max ) at depth to 220 K. This temperature maximum slightly inhibits fold growth relative to a “real” ice shell where T max is near 270 K (for a conductive ice shell) or 250–260 K (for a convective shell). The T max used here is, however, 20 K greater than that used in Bland and McKinnon [], resulting in greater fold amplification at a given strain. Numerical tests increasing T max above 220 K yield only slightly greater fold amplification and at substantial computational cost.…”

Section: Modeling Fold Formationmentioning

confidence: 99%

“…Under arguably nominal conditions appropriate for the Astypalaea region of Europa (strain rate of 10 −13 s −1 , surface temperature of 80 K), the formation of 200 m amplitude folds required ∼6% shortening of the lithosphere (a number we revise downward in this paper). By decreasing the strain rate and/or the ice grain size (both of which affect effective viscosity), Bland and McKinnon [] found that Astypalaea‐like folds could be formed at strains as low as 2%, still an order of magnitude more than geometrical arguments suggested.…”

Section: Introductionmentioning

confidence: 99%

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Does folding accommodate Europa's contractional strain? The effect of surface temperature on fold formation in ice lithospheres

Bland

McKinnon

2013

Geophysical Research Letters

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[1] On Europa, the mechanism by which contractional strains are accommodated remains a mystery. Subtle folds have been observed in the polar regions, but if folding is a dominant accommodation mechanism, ubiquitous large-amplitude folds might be expected across Europa's surface. Here we use finite element modeling to show that fold growth rates are a strong function of surface temperature: warm temperatures result in lower rates, whereas cold temperatures result in higher rates. Combining diurnally averaged Europan surface temperatures derived from Galileo photopolarimeter-radiometer data and new numerical simulations, we show that forming moderateamplitude folds requires roughly twice the contraction, or shortening, in Europa's equatorial latitudes relative to polar latitudes. Relatively large contractional strains in Europa's equatorial and midlatitudes can therefore be accommodated primarily through passive shortening without producing obvious folds. Lithospheric folding and/or passive shortening therefore remain plausible mechanisms for strain accommodation on Europa.

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Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long‐wavelength topography

et al. 2013

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[1] The volcanic plains that fill the Caloris basin, the largest recognized impact basin on Mercury, are deformed by many graben and wrinkle ridges, among which the multitude of radial graben of Pantheon Fossae allow us to resolve variations in the depth extent of associated faulting. Displacement profiles and displacement-to-length scaling both indicate that faults near the basin center are confined to a~4-km-thick mechanical layer, whereas faults far from the center penetrate more deeply. The fault scaling also indicates that the graben formed in mechanically strong material, which we identify with dry basalt-like plains. These plains were also affected by changes in long-wavelength topography, including undulations with wavelengths of up to 1300 km and amplitudes of 2.5 to 3 km. Geographic correlation of the depth extent of faulting with topographic variations allows a first-order interpretation of the subsurface structure and mechanical stratigraphy in the basin. Further, crosscutting and superposition relationships among plains, faults, craters, and topography indicate that development of long-wavelength topographic variations followed plains emplacement, faulting, and much of the cratering within the Caloris basin. As several examples of these topographic undulations are also found outside the basin, our results on the scale, structural style, and relative timing of the topographic changes have regional applicability and may be the surface expression of global-scale interior processes on Mercury.Citation: Klimczak, C., C. M. Ernst, P. K. Byrne, S. C. Solomon, T. R. Watters, S. L. Murchie, F. Preusker, and J. A. Balcerski (2013), Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long-wavelength topography,

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Forming Europa’s folds: Strain requirements for the production of large-amplitude deformation

Cited by 17 publications

References 99 publications

Double ridges on Europa accommodate some of the missing surface contraction

Double ridges on Europa accommodate some of the missing surface contraction

Does folding accommodate Europa's contractional strain? The effect of surface temperature on fold formation in ice lithospheres

Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long‐wavelength topography

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