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Soto J.I.,University of Granada | Fernandez-lbanez F.,Fermin Fernandez lbanez GeoMechanics International | Talukder A.R.,Australian Resources Research Center | Martinez-Garcia P.,University of Granada
AAPG Memoir

The Alboran Basin is a back-arc basin in the Mediterranean developed during the Miocene by the extensional collapse of the thick continental orogen known as the Betic-Rif arc. Collision and basin formation occurred in the Neogene as a result of oblique convergence of the Eurasian and African plates. A major, curved depocenter (with sedimentary accumulations >10 km [>6 mi]) is located to the west of this basin, containing a diapiric province with overpressured shales and mud volcanoes. This study presents a detailed reconstruction of the three-dimensional geometry of the diapirs and associated minibasins in the northern margin of this major depocenter (offshore Spain). Basin formation began in the early Miocene when rapid initial subsidence of the basin floor was accompanied by massive sedimentation and burial of fine-grained sediments. Gravity-driven tectonics and continuous basement subsidence during the Miocene led to downslope migration of mobile shales, whereas the basin margins were affected by synsedimentary extension, and associated shale-cored thrusts occurred in the basin depocenter. Extension occurred by means of low-angle normal faults coalescing with the basement surface, which represents a master detachment surface. Thin-skinned extension during the Miocene was accompanied by punctuated diapir ascent and the advance of shale sheets. Downslope Copyright © 2010 by The American Association of Petroleum Geologists. Source

Thiele S.T.,University of Western Australia | Micklethwaite S.,University of Western Australia | Micklethwaite S.,Monash University | Bourke P.,University of Western Australia | And 2 more authors.
Journal of Structural Geology

Two novel techniques, photo based reconstruction (photogrammetry) and computed tomography (CT), are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from Cape Liptrap, Southern Victoria, and to provide constraint on models for their development. The accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional (3D) model. The photogrammetric model was found to be accurate to at least 0.25mm and substantially more detailed than the laser scan. A methodology was developed by which 3D structural measurements could be extracted from the photogrammetric model. This was augmented with the CT model which, through its capacity to elucidate internal structure, was used to constrain the geometry and linkage of structures within the rock volume. The photogrammetric and CT data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample.The angle between the sigmoidal vein margins and an inferred shear zone, as well as the orientations of the crystal fibres, were found to imply a rotation of >27°. However coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by ~10°, an observation not easily explained using existing models for sigmoidal vein formation.A new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams. The process involves strain partitioning onto pressure solution seams, which leads to exaggeration of sigmoidal vein geometries. If not accounted for, the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type. Furthermore, the CT data demonstrated that in 3D the veins are continuous and channel-like, implying a far higher degree of connectivity and fluid transport than is suggested by their 2D form. © 2015 Elsevier Ltd. Source

Herwegh M.,University of Bern | Poulet T.,Australian Resources Research Center | Karrech A.,University of Western Australia | Regenauer-Lieb K.,Australian Resources Research Center | Regenauer-Lieb K.,University of Western Australia
Journal of Geophysical Research: Solid Earth

Numerical simulation experiments give insight into the evolving energy partitioning during high-strain torsion experiments of calcite. Our numerical experiments are designed to derive a generic macroscopic grain size sensitive flow law capable of describing the full evolution from the transient regime to steady state. The transient regime is crucial for understanding the importance of microstructural processes that may lead to strain localization phenomena in deforming materials. This is particularly important in geological and geodynamic applications where the phenomenon of strain localization happens outside the time frame that can be observed under controlled laboratory conditions. Ourmethod is based on an extension of the paleowattmeter approach to the transient regime. We add an empirical hardening law using the Ramberg-Osgood approximation and assess the experiments by an evolution test function of stored over dissipated energy (lambda factor). Parameter studies of, strain hardening, dislocation creep parameter, strain rates, temperature, and lambda factor as well asmesh sensitivity are presented to explore the sensitivity of the newly derived transient/steady state flow law. Our analysis can be seen as one of the first steps in a hybrid computational-laboratory-field modeling workflow. The analysis could be improved through independent verifications by thermographic analysis in physical laboratory experiments to independently assess lambda factor evolution under laboratory conditions. © 2014. American Geophysical Union. Source

McGregor F.,Australian Resources Research Center | Ramanaidou E.,Australian Resources Research Center | Wells M.,Australian Resources Research Center
Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science

This paper summarises Phanerozoic ooidal ironstone deposits worldwide, including Australian deposits such as the well-known channel iron deposits (CIDs). Nearly 400 occurrences have been catalogued based on stratigraphy, geographical coordinates, facies, grade, tonnage and ironbearing ore minerals. Descriptions include details on the geochemistry, genetic models and main references. Brief statistical analysis provides an overview of the variation between these deposits. This compilation offers a basis for better understanding of the ooidal ironstone deposits and a global evaluation of this important resource. © 2010 Maney Publishing. Source

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