Geology, Geochemistry, Geochronology, and economic potential of the Taftan volcanic complex, southeastern Iran Open Access

[摘要] The late Miocene-Quaternary Taftan volcanic complex is located above the Makran subduction zone in Sistan and Baluchestan province of southeastern Iran. The earliest volcanic eruptions at Taftan started in the late Miocene (~8 Ma) by explosive eruption of andesitic to dacitic lava on the Cretaceous to Eocene volcanic and sedimentary paleosurface ~20 km to the northwest of the current edifice. Later Plio-Pleistocene volcanism consisted of voluminous andesitic and dacitic lavas and pyroclastic flows (~3.1-0.4 Ma). The major and trace element compositions of the Taftan volcanic rocks show calc-alkaline to high-K calc-alkaline affinity with depletions of Nb, Ta, and Ti and relative enrichment of large-ion lithophile elements (LILE) and Th and U; these are typical signatures of subduction-related arc magmas. From the late Miocene to the late Pleistocene La/Yb and Sr/Y ratios of the Taftan volcanic rocks increase, which likely reflects fractional crystallization of pyroxene and amphibole. Electron microprobe analysis of amphibole phenocrysts from the Taftan volcanic rocks show that amphibole chemistry changed from high-Al pargasite to low-Al magnesio-amphibole from the late Miocene to the Pleistocene. Detailed modelling of amphibole chemistry indicates that the host magmas were water saturated (>5 wt.% H2O) and underwent partial crystallization at various depths between ~20 to ~5 km in the upper crust prior to eruption. Temperature and oxidation state estimates obtained from magnetite-ilmenite mineral pairs from andesites and amphibole phenocrysts in andesites show that they crystallized at temperature from ~1000°C to ~800C under moderately oxidizing conditions (FMQ +1.7 ± 0.3). The presence of small porphyry and epithermal prospects such as the Kharestan Cu porphyry (6.10 ± 0.40 Ma) and Siah jangal epithermal Au deposit in the late Miocene, and several argillic to advanced argillic fumarolic alteration zones in the Taftan Plio-Pleistocene volcanic rocks suggest the potential for additional porphyry and epithermal style mineralization within the volcanic edifice at depth.

[发布机构] University of Alberta

[效力级别] Geology