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Walvis Ridge MV1203 Expedition

Weekly Report 1 -- Wednesday, 7 March 2012


Determining the Age of a Rock with the K/Ar System (Part 1)

Utilizing the radioactive decay of elements, we can date the rocks that we find on the ocean floor.  One of the most common systems that we use is the decay of the Potassium (K) 40 isotope to the Argon (Ar) 40 isotope.  As the K 40 in a rock breaks down, it converts to Ar 40 over a measureable period of time at a constant rate.  In the case of the Walvis seamounts that we are exploring, we want to establish when the lava that formed these structures was erupted.  When magma is generated deep in the earth it heats up everything in it and around it.  Any Ar 40 decay product that existed in solid phases before this magma creation is released from those solid phases at high temperatures.  When this magma erupts in a volcanic event, and basaltic rocks are formed, all pre-existing Ar 40 state was erased and the “clock” measuring the conversion of K 40 to Ar 40 is reset to zero.  Once the magma cools below what is known as a blocking temperature, the decay of K 40 to Ar 40 resumes and the clock begins ticking again.  Thus, using the K/Ar age dating technique, one can measure when the volcanic event occurred that created the rocks building the structures of the Walvis ridge. 

Part 2: Where in a rock do we find the argon we are looking for? 

Julia Klath