Papers by Alexander Cruden
Surface Deformation on Venus Driven by Downwelling: Results of Scaled Analogue Experiments
AGU Fall Meeting Abstracts, Dec 1, 2006
ABSTRACT
Intrusion tip velocity controls the emplacement mechanism of sheet intrusions
Geology, Nov 27, 2023
We investigate the conditions under which saucer-shaped sills form through the upper crust and th... more We investigate the conditions under which saucer-shaped sills form through the upper crust and their geometries. We performed a series of scaled laboratory experiments that employ visco-elastic-plastic Laponite RD® (LRD) gels to model upper crustal rocks, and Newtonian paraffin oil as the magma analogue. Both homogenous and layered analogue upper crust is considered. In homogenous 3 wt. % LRD, the injected oil formed a saucer-shaped intrusion with the shortest inner sill observed among all of the experiments. Saucer-shaped sills always formed in experiments with a two-layer upper crust. These experiments show sharp transitions from an inner flat sill to outer inclined sheets, which are characterised by non-planar margins. The experimental results show that: (1) the transition from an inner flat sill to outer inclined sheet occurs when the sill radius to overburden depth ratio (r/H) is between 0.5 and 2.5; (2) the inclined sheets propagate upwards with angles, θ = 15°to 25°; (3) the ratio of the Young's modulus (E*) between the layers controls when the inner flat sill to outer inclined sheet occurs; and (4) irregular finger-like and/or lobe segment geometries form at the propagating tip of the intrusion. The results also suggest that there is no strict requirement for high horizontal stresses to form natural saucer-shaped sill geometries. We conclude that the layered visco-elastic-plastic crustal analogues better represent natural, complex saucer-shaped sill geometries. Furthermore, the observed sharp transitions between inner and outer sills are compatible with brittle-elastic fracture mechanisms operating at the intrusion scale.
EarthArXiv (California Digital Library), Feb 16, 2021
Laponite ® is a synthetic clay that, depending on concentration, temperature and curing time, for... more Laponite ® is a synthetic clay that, depending on concentration, temperature and curing time, forms a clear, transparent thixotropic fluid or brittle visco-elasto-plastic gel when mixed with water. Here we present the results of rheological and mechanical testing of gel-forming Laponite RD (LRD) to evaluate its suitability as a rock analogue in laboratory analogue experiments. Rheological tests of 2 -4 wt. % concentrations of LRD in deionised water were carried out at temperatures between 20 and 50 °C, and after curing times of 3 to 14 days. Our results show that LRD gels change from a brittle, elastic-dominant, linear viscoelastic material to a plastic material as shear strain increases. The linear viscoelastic region occurs at shear strains, γ < 10 % after which the material yields and then undergoes strain hardening before a peak stress occurs at γ = 15 -20 %. LRD then strain softens up to γ < 26.2 %, beyond which it behaves as a plastic material. Empirical equations are provided that predict increases in the Young's and complex shear moduli of LRD with increasing concentration and ageing time. LRD can be used to model elastic deformation when γ < 10 % at a shear strain rate of 0.1 s -1 and plastic deformation when γ > 26.2%. LRD is an ideal material for modelling the behaviour of rocks during the emplacement of magma and the propagation of brittle fractures in the upper crust. Its ease of preparation, low surface tension, full transparency, chemical and biological stability and photoelastic properties provide further advantages for analogue laboratory modelling compared to other frequently used visco-elastic gels, such as pig skin gelatine.
Dyke propagation and linkage: Insights from high resolution aperture data captured by drone
EGU General Assembly Conference Abstracts, Apr 1, 2019
Interactions between propagating rifts and pre-existing linear rheological heterogeneities: insights from 3D analogue experiments of rotational extension
EGU General Assembly Conference Abstracts, Apr 1, 2017
Emplacement and growth of plutons: implications for rates of melting and mass transfer in continental crust
Fault-Assisted Vertical Pluton Growth: Coastal Cordillera, North Chilean Andes
AGU Fall Meeting Abstracts, Dec 1, 2004
Immense volumes of plutonic rocks exposed in magmatic arcs challenge our ability to understand fu... more Immense volumes of plutonic rocks exposed in magmatic arcs challenge our ability to understand fundamental interactions between deformation and magma emplacement at convergent margins. Although close temporal and spatial relationships between fault activity and emplacement of arc plutons have been inferred, the hypothesis that there is always a direct link between faults and plutons in magmatic arcs remains controversial. It
Hadean to Neoarchean Crustal Evolution in a Single Sample of the Cedar Lake Gneiss, Western Superior Province, Canada
GSA 2020 Connects Online, 2020
The Giant-Con gold deposits: Preliminary intergrated structural and mineralization history
Structure of the Archean English River subprovince: implications for the tectonic evolution of the western Superior Province, Canada
Canadian Journal of Earth Sciences, Jul 1, 2006
The English River subprovince is one of two metasediment-dominated terranes in the western Superi... more The English River subprovince is one of two metasediment-dominated terranes in the western Superior Province. It has been interpreted as an accretionary complex, a foreland, or a fore-arc basin that developed and was subsequently deformed between the metavolcanic-rich Uchi subprovince and the orthogneiss- and metaplutonic-dominated Winnipeg River subprovince during a prolonged transpressive orogeny. To test these hypotheses, we combined a satellite image, aeromagnetic image, and Lithoprobe reflection seismic profile interpretation with detailed structural mapping to better characterize the internal geometry and significance of structural features in the western part of the subprovince in Ontario. Northward-directed subduction and collision of the Winnipeg River subprovince with the Uchi subprovince at ca. &gt;2713–2698 Ma can account for the deposition of the sedimentary rocks, initial metamorphism, and the main phase of deformation in the subprovince, whereas the subduction of Wabigoon crust generated extensive tonalite magmatism in the Winnipeg River and English River subprovinces during the same period. A period of extension, after the docking of the Winnipeg River and Wabigoon subprovinces at ca. 2698 Ma, punctuated the compressive phases of the orogeny and was responsible for high-grade metamorphism, upward bending of the Moho, and localized deposition of late, coarse, alluvial–fluvial metasedimentary rocks. Renewed compression caused by the docking of the Wawa subprovince at ca. 2689–2684 Ma is likely responsible for a largely unrecognized regional upright folding and faulting event that controls the dominant structural geometry of the subprovince. Late in its tectonic evolution, strain was partitioned into dextral deformation that was strongly domainal and limited to the subprovince margins.
Inheritance of Penetrative Basement Anisotropies by Extension‐Oblique Faults: Insights From Analogue Experiments
Tectonics, May 1, 2021
During rifting, pre‐existing penetrative basement fabrics can affect new faults in cover rocks by... more During rifting, pre‐existing penetrative basement fabrics can affect new faults in cover rocks by a mechanism that does not appear to involve reactivation. This subtle form of inheritance can significantly impact fault network architecture in rift basins above laterally variable basement domains with geomechanical anisotropies. Here we use multi‐layer, brittle‐ductile, crustal‐scale analogue experiments to study the influence of penetrative basement anisotropies on fault patterns in the overlying cover during a single phase of orthogonal rifting. The experiments were designed to test whether basement anisotropies, oriented 45° to the extension direction, can lead to the formation of rift faults that are oblique to both the imposed extension direction and basement anisotropies. Our experiments show that a penetrative, vertically layered, mm‐wide basement anisotropy creates extension‐oblique faults in the overlying cover. We interpret this to arise when local strike‐slip kinematics along the interfaces of mechanically contrasting materials in the basement combine with the regional imposed orthogonal extension, creating a transtensional regime. The width and spacing of alternating “strong” and “weak” basement zones interact with rift kinematics, impacting the orientation, kinematics and spacing of new faults in the cover. New insights on the influence of penetrative, pre‐existing basement fabrics on localized re‐orientation of 3D strain in the cover have implications for understanding complex fault systems in rift basins and transfer zones.
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Papers by Alexander Cruden