Hi,
Could it be that the matrix would be strongly alkaline in composition? No missed nepheline?
Regards
>The attached photographs are of a felsic agglomerate which I found recently during mapping in an Archean greenstone belt. The matrix consists of fine grained quartz and plagioclase feldspar. Clasts are either of igneous origin(quartz and feldspar) or are country rock clasts (like quartzite; last photograph). Interesting thing is, there are reaction rims around magmatic (are they?) quartz and feldspar clasts (see the feldspar clast in hand specimen in second photograph or quartz clast in photomicrographs). Such rims consist of fine grained radiating amphibole needles (mostly actinolite, tremolite). The clast and matrix are not compositionally very different, so why this reaction rim occurs? Is it because of temperature difference between them or something else? Or is it a secondary texture? In the last photomicrograph, it is clearly seen that the matrix-clast (quartz) has a reaction relationship as the matrix material intrudes into clast (literally 'eating' it; second last photomicrograph). No rim is seen around quartzite clasts (see last field photo).
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>Trisrota Chaudhuri,
>Geologist,
>Geological Survey of India,
>India.
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Francois GUILLOT
Université de Lille, Laboratoire CNRS UMR 8187 - Laboratoire d'Océanologie et de Géosciences, batiment SN5 - Sciences de la Terre, F-59655 VILLENEUVE D'ASCQ CEDEX (France)
TEL 33(0)--320 43 6731 (office) /-320 43 49 10 (fax)
http://log.cnrs.fr/spip.php?article200
http://www.researcherid.com/rid/C-1224-2014
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