TY - JOUR
T1 - O-Sr isotopic variations in Miocene granitoids from the Aegean
T2 - evidence for an origin by combined assimilation and fractional crystallization
AU - Altherr, Rainer
AU - Henjes-Kunst, Friedhelm
AU - Matthews, Alan
AU - Friedrichsen, Hans
AU - Hansen, Bent Tauber
PY - 1988/12
Y1 - 1988/12
N2 - Sr, O, and D/H isotopic compositions have been analyzed in Miocene metaluminous to slightly peraluminous (I-type) granitoids of the central Aegean. Individual plutonic complexes display significant variations in their δ18O and initial87Sr/86Sr compositions.δD and δ18O compositions of minerals and whole-rocks are mostly in the magmatic range. Some samples from Naxos and Mykonos/Delos show low δD and δ18O values characteristic of meteoric-water-hydrothermal interaction, but as a whole the changes in δ18O and Sr isotopic compositions as a result of hydrothermal alteration were slight, even in instances where marked alteration is petrographically observable. Consequently, the bulk-rock variations of δ18O from 8.1‰ to 12.0‰ and of87Sr/86Sr from 0.70438 to 0.71450 may be regarded as primary and indicative of the conditions of their evolution. Heterogeneous isotopic compositions observed in the individual plutons of Serifos, Ikaria, Samos and Kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses, with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization. The granitoids of Serifos, Ikaria and Kos display weak correlations between the initial87Sr/86Sr and δ18O and 1/Sr. The granitoid province shows a positive correlation between87Sr/86Sr and δ18O and a non-linear relationship between87Sr/86Sr and 1/Sr, whereby 1/Sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases. It is argued that assimilation of older continental material by mantle-derived arc magmas with combined fractionation (AFC) is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock-types trend from granodiorites in the (south)west, near the inferred Oligocene-Miocene suture, to granites in the center and monzonites in the (north)east of the province.
AB - Sr, O, and D/H isotopic compositions have been analyzed in Miocene metaluminous to slightly peraluminous (I-type) granitoids of the central Aegean. Individual plutonic complexes display significant variations in their δ18O and initial87Sr/86Sr compositions.δD and δ18O compositions of minerals and whole-rocks are mostly in the magmatic range. Some samples from Naxos and Mykonos/Delos show low δD and δ18O values characteristic of meteoric-water-hydrothermal interaction, but as a whole the changes in δ18O and Sr isotopic compositions as a result of hydrothermal alteration were slight, even in instances where marked alteration is petrographically observable. Consequently, the bulk-rock variations of δ18O from 8.1‰ to 12.0‰ and of87Sr/86Sr from 0.70438 to 0.71450 may be regarded as primary and indicative of the conditions of their evolution. Heterogeneous isotopic compositions observed in the individual plutons of Serifos, Ikaria, Samos and Kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses, with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization. The granitoids of Serifos, Ikaria and Kos display weak correlations between the initial87Sr/86Sr and δ18O and 1/Sr. The granitoid province shows a positive correlation between87Sr/86Sr and δ18O and a non-linear relationship between87Sr/86Sr and 1/Sr, whereby 1/Sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases. It is argued that assimilation of older continental material by mantle-derived arc magmas with combined fractionation (AFC) is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock-types trend from granodiorites in the (south)west, near the inferred Oligocene-Miocene suture, to granites in the center and monzonites in the (north)east of the province.
UR - http://www.scopus.com/inward/record.url?scp=0001203474&partnerID=8YFLogxK
U2 - 10.1007/BF00371381
DO - 10.1007/BF00371381
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AN - SCOPUS:0001203474
SN - 0010-7999
VL - 100
SP - 528
EP - 541
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 4
ER -