Cobble of metamorphic rock with pseudotachylite (fossil earthquake)


I am indebted to Rick Sibson, expert on pseudotachylite and fault mechanics, who inspired me to tcollect a piece or two of pseudotachylite.  I first met Rick when he was teaching at University of California at Santa Barbara.  He showed me the first examples I had ever seen of pseudotachylite, and I immediately got a bad case of ‘pseudotachylite envy.’  Finally I took care of this condition in 2010, traveling for the first time in New Zealand.  In advance of the trip, Rick told me about several (largely) dry river beds where I might find a pebble or cobble of pseudotachylite.  I was lucky enough to find 2 pieces among the thousands and thousands of cobbles in Hare Mare River in Westland.  This was a rewarding experience!!

Age & Formation
Pseudotachylite (fossil earthquake) from Alpine fault zone, New Zealand. The black glassy material was generated during the last 10 Ma.