Gabbros and sulfides and chimneys, oh my! Part 1
So for the last 17 years I’ve wanted to “look inside” the ocean crust, as it were. I’ve been using data collected by the JR and the Juan de Fuca CORKs for the last 3 years, but I’ve never had the chance to get a good closeup look at the cores BEHIND the data! Of course you can imagine how excited I was to get to examine a cross section through the ocean crust by looking at cores from Hole 1256D (teaser image above). If I recall correctly, I jumped around a bunch and said things like “OOOOH!” and “This is SO COOL!”…while pointing at various parts of the core. I practically fell over when we pulled out the deepest core, which contains the contact between sheeted diabase dikes and cumulate gabbro! Hole 1256D was the first (and only) to penetrate into gabbros in the ocean crust…basically the Holy Grail of marine geologists and geophysicists. And I got to not only see the core, but even pick up the dike-gabbro contact! Remember, this little piece of rock came from over a kilometer below the seafloor…and here I was holding it in my hand. Amazing how the greatest scientific breakthroughs are often contained in tiny packages.
So without telling the Rockers ANYTHING about the core (am I mean or what? *laughs*), I had them describe it. Not surprisingly they quickly decided we were looking at an igneous rock sequence….and they promptly echoed my earlier sentiment once I clued them in on what they were looking at. Then we discussed how an eruption at the mid-ocean ridge forms the layers we see in the ocean crust. There was also a big discussion of heat flow, and how scientists knew about water circulating through the crust WAY before any hydrothermal vents were discovered in the late 1970s! Heat flow is a complicated subject, and I was really impressed by everyone’s questions! I also enjoyed their definition for advection, which is the heat transfer process that goes on during hydrothermal circulation: “convection with hitchhikers.”
I left the group with some questions for day 2 about water circulating in the crust: what does that do to the chemistry of the water? How about the rock?
Stay tuned for Part 2!