Dear All:
I have obtained a few samples of scoria from deep waters (1800-2000 m depth) off northern Chile. I am most interested to know where they have been produced: if in-situ as submarine scoria or dragged down from a terrestrial (above-ground) origin.
The areas where these rocks were found (25°19' S; 70°50' W) are apparently exempt of volcanic activity, and the only possible volcanism in the are may be explained by petite-spot volcanism as explained by Hirano (2006, 2011), however it has so far applied to offshore areas in the Nazca Plate.
Is there any measurement which can be done on these samples to ascertain its origin? If there are any interest in these rocks I can easily send a few samples to anybody interested. I am very interested in collaborating in the matter.
Best regards,
Juan Francisco.
At first, it could be interesting to evaluate the fabric of this scoria.
I presume that it will give to us indication of the subaerial or submarine environment of genesis.
Maybe you can post a photo. It will be a first approach to the problem!
Ciao
Federico
There are some characteristics on pyroclastic particles that could indicate several processes. For example: the interaction of a pyroclastic surge with water could be represented by quenches cracks and chemical pitting visualized on grain surfaces by scanning electron microscope.
Antonio Pola
Dear Juan-Francisco,
in 1966 I had the opportunity to stay a couple of hours on Surtsey south of Iceland. During that stay little Jolnir, in the sea, about 400 m away from Surtsey and its crater a bit open to the sea, erupted phreatomagmatically and almost continuously. Basaltic clasts, up to several cm in size, drifted on the sea and some got stranded at the beach of Surtsey. I collected some of them. They were so vesicular that per definition the represent pumice, but basaltic pumice. Later, back in Mainz University, I put some of these highly vesicular clasts in a large beaker filled with water and replaced regularly the amount water that had evaporated. The reason was that I was interested how long it would take the pumiceous clasts to soak up sufficient water to subisde finally in the “sweet“water. It took three months. I had had used salt water of sea water salt content it would probably have taken even longer. Thus my question I would have is how vesicular are your scoria clasts? If they had been pumiceous basaltic clasts they could have drifted on the sea surface for months and it would be very difficult to work out their origin.
With kind regards
Volker
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