A complex strain and intrusion fabric related to trans-solidus deformation: The Wolf Mountain Intrusion, Llano Uplift, Texas.
Robert M. Reed, Department of Geological Sciences, University of Texas, Austin, TX 78712
The Wolf Mountain Intrusion (WMI) is as chevron-shaped (phacolithic) granite body which occupies an upright synform that plunges shallowly to the southeast. The WMI is one of many Proterozoic porphyritic granite intrusions in the Grenvillian Llano Uplift of central Texas that have previously been considered post-orogenic to anorogenic. Deformation during and after the emplacement of the granitic magma has produced a complex internal fabric including foliations with magmatic and tectonic components, multiple diking events, and shearing. This internal fabric is most complex in the hinge region of the intrusion where the history is as follows:
The internal structure of the granite is much simpler in the limbs of the intrusion, suggesting concentration of strain in the hinge zone during regional folding of the crystallizing intrusion.
The WMI provides evidence for late synorogenic intrusion of granite in the Llano Uplift, tying what were considered to be "anorogenic" granites to an orogenic event. The WMI also provides an example of the complexities that arise from deformation occurring synchronous with solidification. Deformation is not just concentrated at the pluton margin but within an area in the interior. The localization of deformation in one area with reduced deformation elsewhere points out the need for caution in labeling a pluton "undeformed" based on an examination of only part of its area.
(from 1996)
