Zoned, birefringent garnets from Thera Island, Santorini Group (Aegean Sea)
نویسنده
چکیده
A garnetite that occurs locally in phyllitic schists exposed by the Santorini caldera consists mainly of euhedral garnet crystals showing alternating isotropic and birefringent lamellae. X-ray diffraction revealed two garnets with unit cell dimensions a of I2.o52:ko-oo2 and I~'984-ko-oo5 A, corresponding respectively to almost pure andradite and a granditic phase. Mean compositions determined by microprobe analysis are An97SplAlm~ for the isotropic and about An~aGr~aSpiAlma for the birefringent layers. The garnets are deduced to have been produced mainly by thermal metamorphism of the schists. Although cyclic variations in the composition of circulating fluids could have brought about the zoning, this may just as well be the result of temperature fluctuations, individual garnet compositions being indicative of the respective formation temperature.
منابع مشابه
Pumice from thera (santorini) identified from a greek mainland archeological excavation.
Pumice fragments recovered from an archeological excavation on the Greek mainland have been correlated by means of index of refraction measurements with the Late Bronze Age volcanic eruption on the island of Thera (Santorini) in the Aegean Sea. Pottery from the strata containing the pumice dates from the 15th century B.C.
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