Modeling of dike-induced graben nucleation in the Elysium region, Mars: The role of planetary gravity

Rivas‐Dorado, Sam; Ruíz, Javier; Romeo, I.

doi:10.1016/j.jsg.2022.104778

Cited by 3 publications

(3 citation statements)

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“…thus driving a Mohr stress circle of small diameter (𝜎𝜎v -𝜎𝜎h where 𝜎𝜎v is the earlier vertical effective stress and major principal stress and 𝜎𝜎h is the earlier horizontal effective and minor principal stress) against the failure envelope at a point where it crosses the normal stress (𝜎𝜎) axis so that tensile fractures form with the plane of rupture perpendicular to the minor principal stress (Russell, 1972(Russell, , 1973Rivas-Dorado et al, 2023). Similar models are presented in Nahm et al (2016) and by Stähler et al (2022) who model dyke injection to mid-crustal level as interpreted from the first focal mechanisms of marsquakes (Brinkman et al 2021;Kedar et al, 2021 ).…”

Section: Figure 5 Proposed Model For Geofracture Formation In Ireland...mentioning

confidence: 99%

“…It is speculated here that the same is likely true for geofractures in Ireland in the early Carboniferous. Nearer the surface, as pore fluids gain access and escape up and along permeable cross structures, pore pressures drop and the stress circle retreats to the right despite a drop in tensile strength, so that Gf1(CF3) and Gf2(CF2) do not reach the surface (Russell, 1969;Rivas-Dorado et al, 2023). No increase in pore pressures occurs in the region to the east so a similar type of failure cannot take place.…”

Section: Figure 5 Proposed Model For Geofracture Formation In Ireland...mentioning

confidence: 99%

“…No increase in pore pressures occurs in the region to the east so a similar type of failure cannot take place. Instead, at a correspondingly greater distance from Gf2(CF2) the horizontal compressive stress 𝜎𝜎h is reduced by an amount x so that the Mohr stress circle of relatively large diameter touches the fracture envelope to the right of the shearing stress (𝞽𝞽) axis and normal fault failure results (Russell, 1969;Rivas-Dorado et al, 2023). The double headed arrows signify the tensile stress concentrations associated with the bottom of the geofractures which attract fluids from a degassing mantle, thus providing engine-like feedback and so concentrating the heat required to drive the hydrothermal systems (Russell, 1972;Bailey, 2012;Davidheiser-Kroll et al, 2014).…”

Section: Figure 5 Proposed Model For Geofracture Formation In Ireland...mentioning

confidence: 99%

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On Irish bacteriometallogenesis and its wider connotations

Russell

2023

Irish-Type Zn-Pb Deposits Around the World

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Rapid and widespread access of surface waters to jostling segments of the upper crust marks the first step to metallogenesis in the Irish early Carboniferous. Overall, siting of these ore-forming systems involves two types of fluid-charged autocatalytic cracking engines. The more obvious is a province-wide diffuse type, excavating downward from the generally submarine surface to where waters are heated, dissolve metals and become buoyant enough to exploit channel ways back to the surface. Another, rather more obscure engine, starts near the mantle-crust boundary and either produces a through-going crustal structure to vectorially guide pressurized mantle volatiles and perhaps accompanying magma toward the surface, or it autonomously drills its way through the entire crust by penetrative convection, as in a diatreme. Either way ore-forming solutions are perhaps best incubated where both engines interact within the crust. But precipitation of minable metal requires structural down warp basins and associated saline, sulphate-reducing microbiome traps. So, whilst there is no unique ex-planation for the distribution of the orebodies, the Navan orebody, its southwest extension (SWEX) and its neigh-bour to the south, Tara Deep, do fall on a putative N-S Geofracture (Gf 3) first proposed in 1968/1969. But the N-S Geofracture hypothesis runs strongly against the “academic” grain! Moreover, no further discoveries can be unequivocally assigned to the hypothesis. So why persist with the notion at all? Well, there have been some other indications of such structures in adjacent countries and, most notably and farthest afield, on Mars which acts as a time machine for our planet! There the seismically active Cerberus Fossae structures have similar crustal joint aspect ratios of 40 to 55km, as with the putative Irish (and Scottish) examples. And five cold springs, sequentially younger to the east, happen to lie well-spaced along a 250km stretch of the northernmost Fossa. Yet there are no signs of mineral sulphide accumulations on Mars. Perhaps lacking there were sulphate-reducing bacteria required for the deposition of economic ores as in Ireland. Indeed, it was the discovery of light sulphate sulphur in the Irish ores, along with lithochemical and geological evidence for an exhalative aspect to them, that inspired the submarine alkaline vent theory (AVT) for the emergence of life. In this theory exothermic serpentinization drives hydrothermal convection cells to produce the exhalations into the Hadean Ocean. Here the free-energy convert-ing iron minerals (oxyhydroxides and sulphides) act as nano-engines in spontaneously precipitated membranes to generate the appropriate organic molecules required for life’s onset from volatile and hydrothermal delivery of CO2, H2, CH4 and the trace elements. These prebiotic nanoengines are powered by the electrical and pH disequilibria focused across the mineral membranes amounting to ~1 volt.

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