|
|
Now I have a question, Why would a old oceanic plate be subducted at a
steeper angle than a newer oceanic plate (unless the density of the older
plate is greater, but I don't think that is the case)?
To my knowledge, gravity does not care about age, just mass. Now if the
older plate crumbles upon interaction with the continental plate, it might,
perhaps, turn downwards quicker than a plate that exhibited more compression
strength.
If one could take a core sample of the plates, it would be easy to determine
where one began and the other ended, I would think, but there might be a
'zone of co-mingled plates', where particles from both plates existed.
"mirage" <mjohnson37@xxxxxxxxxxxxx> wrote in message
news:1140638829.112988.245900@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> SBC Yahoo wrote:
>> Generally speaking a oceanic plate is more dense than a continental
>> plate,
>> and the densest plate will slide beneath the lighter density plate.
>> (Subducted, I believe is the geologic term)
>>
>
> That part's clear. What I'm wondering about is the subduction angle.
> Very old, cold oceanic crust descends into the mantle at a pretty steep
> angle once it slips under lighter continental crust. In thinking about
> the spreading center from which the Farallon and Pacific plates
> emerged, the eastern edge of the Pacific plate is a single unit with
> the spreading center. In other words, the spreading center and the
> edge of the oceanic plate are a continuous physical structure (i.e.,
> there's no single, precise geologic demarcation where the spreading
> center ends and the oceanic plate begins). When the spreading center
> is overridden by the continental crust, the spreading center remains
> bouyant. As the oceanic crust follows the spreading center beneath the
> continental crust, the oceanic crust is still hot and physically
> contiguous with the already-subducted spreading center, which isn't
> descending toward the mantle. In such a case would the oceanic plate
> remain intact below, and parrallel to, the overlying continental crust?
> Or would it shear at some point, separating from the spreading center,
> and descend into the mantle?
>
> mirage
>
|
|