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IODP Expedition 330 Louisville Seamount Trail

Daily Report 16 -- Monday, 27 December 2010 -- Reaching Volcanic Basement at Site U1372



Site U1372 on 26.5°S Guyot 26° 29' 35.9988" S, 174° 43' 45.0012" W
Louisville Seamount Trail
0 m above sea level

After five days of drilling at Site U1372 we have recovered many wonderful cores with many wonderful rocks of many kinds. In fact the cores already have provided us with lots of the rocks and minerals we require for our onshore research programs, which is a very good beginning of our expedition! We cored into a colorful volcaniclastic sediment of carbonate-cemented volcanic breccia. Some of the breccias have boulders in them that in themselves are very well-preserved, containing for example large amounts of fresh olivine crystals. This is quite an exceptional find as olivine crystals in contact with seawater and other fluids circulating in seamounts during their active eruption are the first crystals in the seamount rocks to start altering. So in most circumstances you never find fresh olivine but only the outlines of these crystals and the olivine crystal itself typically is replaced by a bright orange-red clay mineral called indingsite.

Most everybody and in particular the petrologists and geochemists onboard were extatic as these minerals will allow them to do very nifty and detailed analyses during their onshore investigations. For example, using olivine crystals they can assess the temperature and He isotopic composition of the magma source. This has never before been done for Louisville, mainly because this seamount has never been sampled in so much detail, but also because the sampling that has been done by dredging only recovered the surface rocks of this seamount. These dredge hauls in not a single case have resulted in any suitable olivine for these kind of highly-specialized measurements.

By now we have reached 150 mbsf (meters below the seafloor). The top of the volcanic basement was called around 45 mbsf with the identification of the first “in situ” lava flow and all subsequent cores returned even more lava flows, confirming that indeed we were in proper basement rocks now. However, after retrieving a whole sequence of many of these nice lava flows, the recovery rates decreased significantly as we entered a zone with mainly volcanic breccias with large basaltic clasts that are very fresh and occasionaly they become larger, even boulder-sized. Although we welcomed the variation in the rock types in our core, these new "rubbly rocks" were to present us with an unpleasant surprise in the days ahead of us!

Greetings Anthony Koppers