Lithospheric Drip
Monday, 1. June 2009, 06:48:26
In a recent post at Adventures in the world of Geology Anna wrote that she had never heard about lithospheric drips - well, neither had I, in fact, until recently.
A lithospheric drip has been defined as a geological phenomenon in which a heavy rock formation sinks in a lighter rock formation, the latter having been made plastic by high temperature and pressure. A long trail is left behind the heavy material, like honey dripping off a spoon. Such a lithospheric drip has been discovered, and documented, below the Great Basin in Nevada.
A study by West et al. about this lithospheric drip was published in the 24 May 2009 issue of the journal Nature Geoscience under the title Vertical mantle flow associated with a lithospheric drip beneath the Great Basin. This is not open access, but requires a subscription. The findings were however also presented at the 2009 EarthScope National Meeting in Boise, Idaho, 12-15 May 2009, and an abstract is available from here (scroll down to the third last abstract). On page 2 of this abstract there is a figure showing a 3-D tomography of the phenomenon.
What strikes me is that the (more or less cylinder-formed) “drip” merges with a much larger structure in the mantle at approximately 500 km depth. This structure is possibly a detached slab from earlier subduction. Such a slab detachment or break-off is not unusual. I mentioned one recently in my post on the Vrancea Earthquake. In 2007 it was suggested that descent of the ancient Farallon slab drives localized mantle flow below the New Madrid, Missouri, seismic zone (see my post here) with a much debated earthquake cluster.
My personal guess is that the downwelling of the lithosphere beneath the Great Basin is caused by a detached subducted slab pulling it down.
For tens of millions of years all of the Great Basin has been undergoing extension - but a smaller area is currently undergoing contraction. West et al. found that portions of the lithosphere had sunk into the more fluid upper mantle beneath the Great Basin and formed a large cylindrical blob of cold material far below the surface of central Nevada. A so-called lithospheric drip. A lithospheric drip can be envisioned as honey dripping off of a spoon, where an initial lithospheric blob is followed by a long tail of material. When a small, high-density mass is embedded near the base of the crust and the area is warmed up, the high-density piece will be heavier than the area around it and it will start sinking. As it drops, material in the lithosphere starts flowing into the newly created conduit. Seismic images show the drip as a large cylindrical mass 100 km wide and at least 500 km tall.
• http://thrustacline.blogspot.com/2009/05/lithospheric-drip.html
• http://asunews.asu.edu/20090526_greatbasin
• http://www.livescience.com/environment/090526-giant-blob.html
• http://www.redorbit.com/news/science/1695713/blob_of_material_found_beneath_nevada/index.html?source=r_science
• http://www.terradaily.com/reports/A_Hidden_Drip_Drip_Drip_Beneath_Earth_Surface_999.html
• http://www.eurekalert.org/pub_releases/2009-05/nsf-ahd052609.php
• http://www.geologytimes.com/research/A_hidden_drip_drip_drip_beneath_Earths_surface.asp
• http://www.littleabout.com/news/15102,large-cylindrical-blob-cold-material-b.html
• http://www.iris.edu/hq/esreg/page/abstracts
A lithospheric drip has been defined as a geological phenomenon in which a heavy rock formation sinks in a lighter rock formation, the latter having been made plastic by high temperature and pressure. A long trail is left behind the heavy material, like honey dripping off a spoon. Such a lithospheric drip has been discovered, and documented, below the Great Basin in Nevada.A study by West et al. about this lithospheric drip was published in the 24 May 2009 issue of the journal Nature Geoscience under the title Vertical mantle flow associated with a lithospheric drip beneath the Great Basin. This is not open access, but requires a subscription. The findings were however also presented at the 2009 EarthScope National Meeting in Boise, Idaho, 12-15 May 2009, and an abstract is available from here (scroll down to the third last abstract). On page 2 of this abstract there is a figure showing a 3-D tomography of the phenomenon.
What strikes me is that the (more or less cylinder-formed) “drip” merges with a much larger structure in the mantle at approximately 500 km depth. This structure is possibly a detached slab from earlier subduction. Such a slab detachment or break-off is not unusual. I mentioned one recently in my post on the Vrancea Earthquake. In 2007 it was suggested that descent of the ancient Farallon slab drives localized mantle flow below the New Madrid, Missouri, seismic zone (see my post here) with a much debated earthquake cluster.
My personal guess is that the downwelling of the lithosphere beneath the Great Basin is caused by a detached subducted slab pulling it down.
For tens of millions of years all of the Great Basin has been undergoing extension - but a smaller area is currently undergoing contraction. West et al. found that portions of the lithosphere had sunk into the more fluid upper mantle beneath the Great Basin and formed a large cylindrical blob of cold material far below the surface of central Nevada. A so-called lithospheric drip. A lithospheric drip can be envisioned as honey dripping off of a spoon, where an initial lithospheric blob is followed by a long tail of material. When a small, high-density mass is embedded near the base of the crust and the area is warmed up, the high-density piece will be heavier than the area around it and it will start sinking. As it drops, material in the lithosphere starts flowing into the newly created conduit. Seismic images show the drip as a large cylindrical mass 100 km wide and at least 500 km tall.
• http://thrustacline.blogspot.com/2009/05/lithospheric-drip.html
• http://asunews.asu.edu/20090526_greatbasin
• http://www.livescience.com/environment/090526-giant-blob.html
• http://www.redorbit.com/news/science/1695713/blob_of_material_found_beneath_nevada/index.html?source=r_science
• http://www.terradaily.com/reports/A_Hidden_Drip_Drip_Drip_Beneath_Earth_Surface_999.html
• http://www.eurekalert.org/pub_releases/2009-05/nsf-ahd052609.php
• http://www.geologytimes.com/research/A_hidden_drip_drip_drip_beneath_Earths_surface.asp
• http://www.littleabout.com/news/15102,large-cylindrical-blob-cold-material-b.html
• http://www.iris.edu/hq/esreg/page/abstracts
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