Estimating complete dyke dimensions from partial exposures

Abstract

Knowledge of complete dyke dimensions is crucial to determine the actual aspect ratio which is indispensable in estimating their magma overpressure, depth of origin and even explosivity potential of fissure eruptions. A dearth of completely exposed dykes imposes considerable uncertainty on estimates of their aspect ratios. Therefore, we have pioneered a method of estimating complete dyke dimensions from their partial exposures lacking any tip. Considering dykes as dominantly opening mode fractures, the method is built upon the idealized canonical model of opening mode fractures and utilizes differential equation of ellipse, which is the predicted shape of fracture opening in the model, to estimate their full length, maximum width and aspect ratio from limited outcrop measurements. The validity of the method has been tested against ground data and published data. From its application to two partially exposed mafic dykes devoid of tips, one each from the Western and Eastern Dharwar Cratons of India we generated results from which we further calculate their magma overpressures and depths of origin. Although developed for dykes, the method has potential for wider application, since it can be used fundamentally to predict complete dimensions of any elliptical shaped natural features from their partial exposures.