Comments on: Mt Taranaki: Hmmm http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/ geology and planetary science. done good. Thu, 17 Mar 2011 11:08:56 +0000 hourly 1 http://wordpress.org/?v=3.1 By: Chris http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-947 Chris Sat, 18 Apr 2009 15:01:09 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-947 Mole: There's no doubt it's a subduction-driven volcano due to being at the tail end of the Tonga-Kermadec arc. The "Hmmm" bit is the geochemical disassociation with the rest of the TVZ, the lack of a line of back arc volcanism leading up to Taranaki, and that Taranaki has a little volcanic arc of its own which trends SE/NW whereas the Tonga-Kermadec trends SW/NE. Below I've made little map to show the trend of Taranaki volcanism, of which Taranaki and the smaller Fanthoms peak are the modern active vents, while the Pouakai complex and the Kaitake range are the older, seemingly extinct vents: <img src="http://www.goodschist.com/images/TaranakiTrend.png" width="400"> And here's the trend of the TVZ vs that of the Taranaki region: <img src="http://www.goodschist.com/images/TVZTrend.png" width="400"> I've been out of the loop for while, though, so I'm a little hazy on the region. Mole: There’s no doubt it’s a subduction-driven volcano due to being at the tail end of the Tonga-Kermadec arc. The “Hmmm” bit is the geochemical disassociation with the rest of the TVZ, the lack of a line of back arc volcanism leading up to Taranaki, and that Taranaki has a little volcanic arc of its own which trends SE/NW whereas the Tonga-Kermadec trends SW/NE. Below I’ve made little map to show the trend of Taranaki volcanism, of which Taranaki and the smaller Fanthoms peak are the modern active vents, while the Pouakai complex and the Kaitake range are the older, seemingly extinct vents:

And here’s the trend of the TVZ vs that of the Taranaki region:

I’ve been out of the loop for while, though, so I’m a little hazy on the region.

]]> By: Mole http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-944 Mole Sat, 18 Apr 2009 06:12:09 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-944 If you look there is actually a second volcanic trend to the kermadec arc behind the main trend which forms the TVZ. If we account for the curve of both arcs with the plate boundary, Taranaki lies along this second trend, and the basaltic andesite composition and structure (strato) points to arc-volcanism. Many Arc systems have two trends/lines of activity, see the marianas trench bathymetry for a great example. This is due to dehydration of the subducting slab with depth. Metamorphic reactions which occur at various depths release fluis (minly water) into the overlying mantle wedge, causing it to melt and produce magm which eventually forms the arc system. The reason there are two lines of volcanism is that there are two reactions which release the fluid, and this occur at different depths (dehydration of amphibolite and dehydration of ecologite and also possibly serpentinite). The shallower reaction (amphibolite) forms the first trend, and the deeper reaction forms the secondary trend (distances can depend on the slab angle... in some areas no secondary trend occurs as subduction ocurs too steeply (i.e. the andes). It looks like taranaki lies along the second trend... If you look there is actually a second volcanic trend to the kermadec arc behind the main trend which forms the TVZ. If we account for the curve of both arcs with the plate boundary, Taranaki lies along this second trend, and the basaltic andesite composition and structure (strato) points to arc-volcanism. Many Arc systems have two trends/lines of activity, see the marianas trench bathymetry for a great example.

This is due to dehydration of the subducting slab with depth. Metamorphic reactions which occur at various depths release fluis (minly water) into the overlying mantle wedge, causing it to melt and produce magm which eventually forms the arc system. The reason there are two lines of volcanism is that there are two reactions which release the fluid, and this occur at different depths (dehydration of amphibolite and dehydration of ecologite and also possibly serpentinite). The shallower reaction (amphibolite) forms the first trend, and the deeper reaction forms the secondary trend (distances can depend on the slab angle… in some areas no secondary trend occurs as subduction ocurs too steeply (i.e. the andes).

It looks like taranaki lies along the second trend…

]]> By: goodSchist » Art, Lore and Legend http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-236 goodSchist » Art, Lore and Legend Sun, 15 Jun 2008 14:35:14 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-236 [...] and why it is where it is. I’ve talked about Taranaki in a previous Accretionary Wedge “Things that make you go hmmmm“, it’s definately an oddly positioned volcano. But this time I’m going to talk [...] [...] and why it is where it is. I’ve talked about Taranaki in a previous Accretionary Wedge “Things that make you go hmmmm“, it’s definately an oddly positioned volcano. But this time I’m going to talk [...]

]]> By: The Accretionary Wedge #6: Geohmms « The Accretionary Wedge http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-88 The Accretionary Wedge #6: Geohmms « The Accretionary Wedge Tue, 11 Mar 2008 03:10:15 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-88 [...] the volcano scale, Chris wonders why Mt. Taranaki is so far west, relative to the rest of New Zealand’s volcanoes. I’ve only seen Taranaki from the plane, and [...] [...] the volcano scale, Chris wonders why Mt. Taranaki is so far west, relative to the rest of New Zealand’s volcanoes. I’ve only seen Taranaki from the plane, and [...]

]]> By: Chris http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-66 Chris Sun, 24 Feb 2008 10:19:13 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-66 Andrew: I don't think any other 5 word geology joke has made me giggle so much :) Andrew: I don’t think any other 5 word geology joke has made me giggle so much :)

]]> By: Andrew Alden http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-65 Andrew Alden Sun, 24 Feb 2008 06:00:46 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-65 Clearly it's a mantle plume! Clearly it’s a mantle plume!

]]> By: Garry Hayes http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/comment-page-1/#comment-64 Garry Hayes Sun, 24 Feb 2008 05:15:15 +0000 http://www.goodschist.com/2008/02/24/mt-taranaki-hmmm/#comment-64 You have a great "hmmm" there. I have no real expertise in volcanism, but looking at the diagram I am reminded of the Cascades arc, and the fact that St Helens is placed noticiably west of the main arc. In our flat Central Valley in California we have a possible remnant of the Cascades arc in the Sutter Buttes, which lie well west of the ancient arc, and are in fact the only interruption to the topography of the valley for a great distance. I don't know why. Hmmm? You have a great “hmmm” there. I have no real expertise in volcanism, but looking at the diagram I am reminded of the Cascades arc, and the fact that St Helens is placed noticiably west of the main arc. In our flat Central Valley in California we have a possible remnant of the Cascades arc in the Sutter Buttes, which lie well west of the ancient arc, and are in fact the only interruption to the topography of the valley for a great distance. I don’t know why. Hmmm?

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