Acigol rhyolite field, central Anatolia (part II): geochemical and isotopic (Sr-Nd-Pb, delta O-18) constraints on volcanism involving two high-silica rhyolite suites


SIEBEL W., Schmitt A. K. , KIEMELE E., DANISIK M., AYDİN F.

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, cilt.162, ss.1233-1247, 2011 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 162 Konu: 6
  • Basım Tarihi: 2011
  • Doi Numarası: 10.1007/s00410-011-0651-2
  • Dergi Adı: CONTRIBUTIONS TO MINERALOGY AND PETROLOGY
  • Sayfa Sayıları: ss.1233-1247

Özet

The Acigol rhyolite field erupted the most recent high-silica rhyolites within the Cappadocian Volcanic Province of central Anatolia, Turkey. It comprises two sequences of domes and pyroclastic rocks with eruption ages of similar to 150-200 ka (eastern group) and similar to 20-25 ka (western group). Compositionally, the eastern rhyolite group lavas are less evolved (SiO2 = 74-76 wt%), whereas the western group has higher silica abundance (SiO2 = similar to 77 wt%) with extremely depleted feldspar-compatible trace elements. Within each group, compositional variability is small and Nd-143/Nd-144 (0.51257-0.51265) and Pb isotope compositions (Pb-206/Pb-204 = 18.87-18.88, Pb-207/Pb-204 = 15.65-15.67 and Pb-208/Pb-204 = 38.94-38.98) are homogeneous. The western group rhyolites have delta O-18(zircon) overlapping mantle values (5.7 +/- A 0.2aEuro degrees), whereas eastern group rhyolites are enriched in delta O-18 by similar to 0.5aEuro degrees, consistent with a tendency to lower epsilon Nd values. By contrast, western group rhyolites have markedly more radiogenic Sr-87/Sr-86 ratios (0.7065-0.7091) compared to those of the eastern group (0.7059-0.7065). The presence of angular granitic xenoliths and a correlation between hydration (based on loss on ignition data) and Sr-87/Sr-86 in the western lavas, however, indicates that Sr was added during the eruption or post-eruption alteration. Isotope constraints preclude the possibility that the rhyolite magmas formed by partial melting of any known regional crystalline basement rocks. Basalts and andesites erupted in the periphery of the Acigol field are characterised by Sr-87/Sr-86 ratios between 0.7040 and 0.7053, Nd-143/Nd-144 = 0.51259-0.51300, Pb-206/Pb-204 = 18.85-18.87, Pb-207/Pb-204 = 15.646-15.655, Pb-208/Pb-204 = 38.90-38.97. The isotopic and trace element data favour an origin of the rhyolites by mixing of basaltic/andesitic magmas with minor amounts of crustal melts and followed by extensive fractional crystallization.