Combining AMS and EBSD to unravel kinematic histories in granitic plutons
Roberts NIcolas, Hamilton College
Veronica Seixas, Hamilton College
Xavier Schlemmer, Hamilton College
Abstract
The Anisotropy of Magnetic Susceptibility of granitic rock samples can provide a robust orientation and geometry of magmatic solid-state fabric. This information is invaluable for interpreting the history of formation and deformation of plutons, but it lacks any kinematic information. This presentation explores how combining electron backscatter diffraction (EBSD) with AMS can help elucidate the kinematics associated with the formation and deformation of granitic plutons. Our case study is the Paleoarchean Mt Edgar dome in the East Pilbara Terrane, Western Australia. We use EBSD to compute the crystallographic preferred orientation (CPO) and the crystallographic vorticity axis (CVA) analysis. Polished thin sections from AMS cores were prepared, and EBSD maps were collected so that AMS data and EBSD data were collected on the same samples. EBSD analysis was performed using the MTEX Matlab package in an automated fashion. An advantage of our approach is that we examined EBSD data in both the fabric reference frame and the geographic reference frame. This shift in reference frame allows us to compare kinematic results directly to AMS fabric as well as the compare orientation of vorticity across the map area. Our results show CVA and CPO both vary systematically across the field area, despite the fact that granitic rocks are weakly deformed. We interpret that the AMS 3D structure within our area occurred from lateral flow within the granitic dome. Several interesting results require further investigation: 1) CPO and CVA results appear decoupled; and 2) CVA voracity axes do not always fall normal to the K1/K3 plane.
Session
Magnetic fabrics or other records of deformation