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Author Topic: Ophiolites  (Read 4579 times)

Offline JimBob

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Ophiolites
« on: 24/04/2006 04:09:27 »
Two days ago I posted an article on a fossil magma chamber beneath the east Pacific. This rock was reported to be a gabbro in the article. This is mafic rock, but aparently did not penertate the dunnite ultra mafics of the lower ophiolite sequence. Neither did the synopsis of the Science artilce state the mineralogy of the gabbro - whether the pyroxines in the gabbro were clino or ortho - pyroxines.

The point is that two types of ophiolites defined and these have been recognized for a long time. The Harzbergite ultramafics are dominantly subduction zone ophiolites exposed after a two-plate collision. The oceanic ophioltes dominantly contain clinopyroxines. Something has been nagging me ever since then. I finnaly have it pegged.

My question is this. Why are rocks from two distinct processes and melting tempratures, even if the only differences are mineralogical, grouped under the same name? Is this a hitorical accident or is there another reason?



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Offline Ophiolite

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Re: Ophiolites
« Reply #1 on: 30/04/2006 14:21:24 »
I would view it as historical accident.

Remember that ophiolites are not a specific rock type, but rather an association of lithologies, often referred to as the Ophiolite Suite. This comprises a mix of black shales, cherts, pillow lavas, basaltic dykes, gabbros, and various ultra-basics.

This association had been identified in numerous locales globally, before its significance was fully understood. The Trudos massif in Cyprus, the complex in Oman, and the Bay of Islands in Newfoundland all spring to mind. For me though, the relatively minor outcrops south of Girvan (Scotland) spring to mind. They were my first real undergraduate mapping exercise.

Their distinction as true oceanic crust, generated at mid-ocean ridges, and subsequently welded to continents, was only appreciated later.


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Offline JimBob

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Re: Ophiolites
« Reply #2 on: 30/04/2006 16:48:53 »
Thank you, Opiolite. I was thinking along these lines but was unfamiliar with the complete history.



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Re: Ophiolites
« Reply #2 on: 30/04/2006 16:48:53 »

 

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