Disappearing ink: How pseudotachylytes are lost from the rock record |
| |
| Institution: | 1. Earth and Planetary Sciences, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA;2. Earth and Planetary Sciences, McGill University, 3450 University St., Montréal, QC H3A 0E8, Canada;3. Department of Geological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7707, South Africa |
| |
| Abstract: | Melt-origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record. However, reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults, suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed. In this paper, we document the processes whereby pseudotachylytes are overprinted, destroyed and otherwise removed from the rock record. We present examples of recrystallized, altered, and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults. Based on these observations, we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes. Our results imply that pseudotachylytes are vastly under-reported due to their vulnerability to destruction and the resulting difficulty in identification. As a consequence, the significance of frictional melting is underestimated. The criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record. |
| |
| Keywords: | Pseudotachylyte Frictional melt Fault rocks Rock record of earthquakes Paleoseismology |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
