Reference frame, angular momentum, and porphyroblast rotation |
| |
Authors: | Dazhi Jiang Paul F Williams |
| |
Institution: | aDepartment of Geology, University of Maryland, College Park, MD 20742, USA;bDepartment of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, NB, Canada E3B 5A3 |
| |
Abstract: | Rotation of small rigid objects in a deforming ductile matrix can produce two different types of microstructure: a shape fabric due to alignment of the principal axes of a population of elongate objects and the inclusion trail microstructure preserved in syntectonic porphyroblasts. We use numerical modeling to show that inclusion trails of elongate porphyroblasts are expected to be extremely complex. In contrast, snowball garnets are readily interpretable. But misuse of reference frame and kinematic misconceptions have obfuscated the discussion on the formation of porphyroblast inclusion trails in general and snowball garnet inclusion trails in particular. We clarify this point. Models for snowball garnet formation that are based on the notion of garnets being irrotational with respect to the earth can be rejected on a geometrical and kinematic basis. Further, the notion that rigid objects embedded in a deforming ductile matrix generally do not rotate is unsound—it violates the fundamental physical law of balance of angular momentum. |
| |
Keywords: | Microstructure Porphyroblast Inclusion trail Rotation Snowball garnet Vorticity |
本文献已被 ScienceDirect 等数据库收录! |
|