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Thread: Island Arcs in the Caribbean

  1. #1 Island Arcs in the Caribbean 
    exchemist
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    I've just got back from holiday in Martinique, during which I climbed Montagne Pelée and went to a video presentation about it. I was interested to see the islands were apparently built up in two distinct phases of volcanism, the earlier phase being a bit further East than the later one. Does anyone know what accounts for this? I realise the volcanism in this region arises from subduction of the W. Atlantic plate beneath the Caribbean plate but can't think what might cause the volcanism to move westward. Are there other examples of this, at other subduction zones?


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  3. #2  
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    Think of the Galapagos Islands. It's not that the volcanism moves. It's the land moving over the volcanic hotspot. Galápagos hotspot - Wikipedia, the free encyclopedia

    Though I notice on that wiki page that there's no hotspot displayed in the Caribbean region. I presume there are other processes or descriptions which relate to separating the land surface from the tectonic/volcanic actions beneath.


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    WYSIWYG Moderator marnixR's Avatar
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    i'm not sure if it's really the same with island arches
    as far as i'm aware island arches are part of a subduction system where part of the subducting plate rises as it melts to form an arch of volcanoes
    why this takes the shape of an arch (as in the Caribbean and Indonesia) and other times not (as in the Andes) i'm not sure
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  5. #4  
    exchemist
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    Quote Originally Posted by adelady View Post
    Think of the Galapagos Islands. It's not that the volcanism moves. It's the land moving over the volcanic hotspot. Galápagos hotspot - Wikipedia, the free encyclopedia

    Though I notice on that wiki page that there's no hotspot displayed in the Caribbean region. I presume there are other processes or descriptions which relate to separating the land surface from the tectonic/volcanic actions beneath.
    No, as MarnixR says, these are island arcs, i.e. behind subduction zones, not hot spots. Think of the Philippines or Indonesia, as opposed to the Galapagos islands or the Hawaiian chain. According to the video, the Westward shift applies to the whole arc, not just to one volcano.

    I was thinking that maybe if the rate of seafloor spreading (and complementary subduction) had accelerated, this might shift the point at which the volcanism arises to the West. If that were the case it might show up in the magnetisation bands on the sea floor.

    Alternatively, if for some reason the angle of decent of the subduction slab has become more shallow, this too might shift the volcanism westward. I can't think immediately how this might be corroborated.

    I wonder if John G knows anything about this. If not, maybe there's a nice PhD thesis in there, in an agreeable part of the world, for some young geophysicist.
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    Universal Mind John Galt's Avatar
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    The plate geometry in the Caribean is very complex. It is not a region I have really looked at - partly because I knew its complexity would do my head in. I'll try to do some reading on it and if I can make any sense present a simplified overview later. Probably after the plates have moved a metre further west!
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  7. #6  
    exchemist
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    Quote Originally Posted by John Galt View Post
    The plate geometry in the Caribean is very complex. It is not a region I have really looked at - partly because I knew its complexity would do my head in. I'll try to do some reading on it and if I can make any sense present a simplified overview later. Probably after the plates have moved a metre further west!
    OK John I'd be interested if it is not too much trouble, but will understand if it gets too complicated to follow up.

    By the way I also got some interesting insights into the role of water in subduction zone volcanism and into the processes that lead to the high viscosity of the local magma, which is evidently what makes volcanoes such as Montagne Pelée and the two (or is it three?) Soufrières so dangerous. I might start threads on these some time as well. Fascinating stuff.
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