Emplacement of magmatic dikes and their tectonic interpretation: examples in tertiary rocks of the Sierra de Pachuca

Abstract

Magmatic dikes are intrusions that penetrate and displace the host rock, form conduits connecting with the magmatic chamber, and get emplaced into the upper crust through ascending flows. In this work, dikes are considered hydraulic tension fractures in the host rock, infilled with magma, and oriented perpendicularly to the minimum compressive stresses, s3, following Anderson’s theory. Consequently, a dike swarm of a single generation defines the stress field map associated with the tectonic regime that prevailed at the time of emplacement. Based on the structural attitude of outcropping diabase and granitoid dikes in Sierra de Pachuca, its geometry ant the orientation of the stress field in the upper crust are inferred (s₁, s_2, s₃). Despite the lack of radiometric ages for the different lithologic units of the Sierra de Pachuca, it is widely considered that these rocks were formed during Oligocene to Pleistocene times. Nevertheless, crosscutting relations among the host rock, the brittle structures, and dike emplacement, allow the establishment of the relative sequence of geologic events. Results indicate that the emplacement of dikes and brittle deformation are tectonically associated.