I Like Sills But Not A Fan Of The Popular Or My Friend’s Ex

I’m a contrarian.  Majority consensus makes me shudder.  I just like rooting for underdogs*.  Those undersea ridges at the boundaries of tectonic plates, spewing molten magma to form new crust are o’ so popular these days.

Spreading plate boundaries…meh.  What I do like is new research basically stating, and I am paraphrasing here, that spreading plate boundaries can suck it.

Let me explain. Over 30 miles away from these fancy spreading plate boundaries, the furthest distance ever documented, magma is rising below the seafloor surface.   However, this magma is stopped when it reaches the barrier of thick mud that covers the seafloor.  The magma forms a large horizontal sheet, a sill.  Think of that irritating girl your best friend dated long ago.  She wasn’t enough to break your friendship but she sure did intrude.  You and your friend are the mud and she is the magma. Welcome to the concept of intrusive volcanism.  “O’ pardon me.”

Unlike your best friend’s former girl, the sills are hot.  But like your former best friends girl, they produce 10 times as much carbon dioxide and methane gas.  This occurs because the sill heats the overlying mud and thermally alters it.  These rising gases can spawn biologically activity like hydrothermal vents, but all very far from the spreading center where vents were previously thought to be concentrated..

Bathymetry of a rift segment of the North Guaymas spreading center in the central Gulf of California shows a series of subsurface features. They are interpreted to be shallow sills intruded into the sediment-filled basin up to 50 km from the rift axis (lower left). High-resolution imaging by sidescan sonar revealed nearly 100 potential hydrothermal vent sites (yellow points) believed to result from widespread emplacement of magma over an area 10 times wider than expected at mid-ocean ridges. Deep-sea photographic surveys at some of the sites (red points) found elevated temperatures and methane concentrations in near-bottom waters and vibrant chemosynthetic animal communities (upper right, photo, about 5m across) containing tubeworms, clams, crabs, bacterial mats, and microbially precipitated carbonate deposits. The intrusion of magma into the sediments has the potential to release significant amounts of carbon from the sediments, previously thought to act as a long term carbon repository. (Credit: Graphic by S. Adam Soule, Woods Hole Oceanographic Institution)

More importantly, typically deep-sea mud is thought to store carbon, i.e. sequester carbon.  But this research suggest  these magma intrusion could potentially release significant amounts of carbon from the sediment.

*Go Butler

Lizarralde, D., Soule, S., Seewald, J., & Proskurowski, G. (2010). Carbon release by off-axis magmatism in a young sedimented spreading centre Nature Geoscience DOI: 10.1038/NGEO1006