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Mt. Erciyes (3917 m), the highest stratovolcano in Central Anatolia, Turkey, is considered active based on three recently dated early Holocene dome eruptions that were also correlated with tephras in the Mediterranean and the Black Sea. Despite the demonstrated Holocene activity of Mt. Erciyes, the eruptive chronostratigraphy of these events and their hazard potential for the nearby Kayseri metropolitan area (population ~1.4 million) remain poorly constrained. Here, we apply zircon double-dating (ZDD) based on (U–Th)/He thermochronology and U–Th–Pb crystallization ages, where intra-grain crystallization age differences were used for disequilibrium correction. Individual ZDD ages were refined via sequence modeling to reconstruct the eruption timing of four early Holocene domes peripheral to Mt. Erciyes. Sequence modeling, which incorporated petrological, volcanological, and stratigraphic constraints, yielded the following eruption ages (uncertainties stated at 1σ): 8.8 ± 0.8 ka for stratigraphically directly superimposed Perikartın and Karagüllü, 8.9 ± 0.5 ka for Dikkartın, and 9.4 ± 1.3 ka for previously undated Yılanlı Dağ, located within the perimeter of Kayseri. A model where all four early Holocene domes are assumed to have erupted simultaneously suggests an age of 8.9 ± 0.4 ka. Earlier eruptive phases of Mt. Erciyes were identified by ZDD at ca. 85–88 ka (fall-out deposits and Çarik Tepe lava) and at ca. 105 ka (xenoliths from two peripheral scoria cones). Zircon crystallization ages reveal protracted magmatic activity beneath Mt. Erciyes since ca. 800 ka, in agreement with dated volcanic activity, and preceding magmatic phases at ca. 2–3 Ma that included the eruption of the widespread Valibaba Tepe Ignimbrite with a U–Pb zircon age of 2.73 ± 0.02 Ma. A volume estimate for the Quaternary edifice of ~300 km3 translates into an integrated long-term eruptive magma flux of ~0.4 km3/ka for post-collisional Mt. Erciyes, within uncertainty of the Late Pleistocene–Holocene flux estimate of >0.1 km3/ka based on dome volumes and eruption ages. The near-synchronous eruptions of a suite of four evolved domes, in three cases with sizable early explosive venting, calls for a hazard assessment that combines the impact of multiple simultaneous eruptions. Image 1 • Yılanlı Dağ located within Kayseri metropolis newly identified as a Holocene dome. • Petrological, volcanological, and stratigraphic constraints refined (U–Th)/He ages. • Sequence modeling indicates four nearly-coeval early Holocene Mt. Erciyes eruptions. • Zircon crystallization ages reveal protracted magmatic activity since ca. 800 ka. • Eruptive flux of ~0.4 km3/ka similar to neighboring post-collisional Mt. Hasan. [ABSTRACT FROM AUTHOR]

Mt. Hasan (3262 m) is the second highest stratovolcano in Central Anatolia, Turkey, and is considered active based on a ca. 9 ka explosive summit eruption that was arguably depicted in a Neolithic mural at the nearby Çatalhöyük archaeological site. Besides evidence for Holocene activity of Mt. Hasan, its eruptive chronostratigraphy and hazard potential remain poorly constrained. Here, we apply (U–Th)/He thermochronology in combination with U–Th–Pb crystallization ages (zircon double-dating), including a novel population-based approach to disequilibrium correction of (U–Th)/He data, in an attempt to determine the eruption ages of strategically sampled lavas and pyroclastic deposits and to refine the Late Pleistocene chronostratigraphy of Mt. Hasan. During the Late Pleistocene, Mt. Hasan erupted multiple interfingering andesitic lava flows along with block-and-ash-flows. Seven of these lava flows, typically the stratigraphically youngest in a particular segment around the two central vents of the volcano, yielded Late Pleistocene eruption ages between 91.9 ± 3.9 and 18.1 ± 2.4 ka (uncertainties stated at 1σ). An even younger block-and-ash-flow was deposited on the western flank of the volcano at 13.5 ± 1.5 ka, which together with a ca. 9 ka small-volume explosive summit eruption define the youngest activity at the main edifice of Mt. Hasan. Collectively, these data indicate a Late Pleistocene recurrence of at least one eruptive phase every ca. 5–15 ka. New volume estimates for the Quaternary edifice of ~130–180 km3 translate into an integrated long-term eruptive magma flux of ~0.3 km3/ka, which is just slightly higher than Late Pleistocene flux estimates based on lava flow geochronology and volumes determined by analysis of digital elevation models. This long-term eruptive flux estimate is similar to those of stratovolcanoes in continental arcs, indicating that eruptive productivity in post-collisional settings can match that of active continental margins. All Mt. Hasan eruptions, including the Holocene event, sampled zircon which crystallized coeval with earlier eruptive phases, indicating longevity of the magma plumbing system. Along with ongoing fumarole activity and evidence for mid-crustal low seismic velocity zones, this suggests that a subvolcanic magma reservoir remains active to the present day. Unlabelled Image • New population-based disequilibrium corrections improved (U–Th)/He age accuracy. • Late Pleistocene recurrence of at least one eruptive phase every 5–15 ka at Mt. Hasan. • Eruptive fluxes presented as differential volumes vs. ages to accent recent trends. • Long- and short-term fluxes of post-collisional volcanism similar to arc settings. • Protracted zircon crystallization supports Mt. Hasan as an active volcanic center. [ABSTRACT FROM AUTHOR]

Mt. Erciyes (3917 m a.s.l.) and Mt. Hasan (3253 m a.s.l.), the two highest stratovolcanoes ofCentral Anatolia, Turkey, exhibit magmatic activity since at least 300 ka. Due to their closevicinity of only 120 km, their magmatic evolutions in a post-collisional intraplate setting canbe compared and contrasted. Here, we present U-Th disequilibrium and U-Pb (crystallization)and (U-Th)/He (eruption) ages and trace elements of zircon rims and interiors andmagnetite-ilmenite thermometry for a comprehensive set of 38 samples from both volcanoes.Samples comprise lava and pyroclastic deposits of intermediate to evolved compositions(63 – 76 wt. % SiO2). Zircon rims from both volcanoes show continuous crystallization age spectra. Zirconinterior age spectra for Mt. Hasan are also continuous, whereas those for Mt. Erciyes showdistinct crystallization peaks at ca. 10, 90 and 280 ka. These pulses coincide with intenseeruptive phases separated by quiescent episodes for Mt. Erciyes, whereas eruptive recurrenceat Mt. Hasan is at briefer intervals of ca. 5 – 15 ka over the last 60 ka. Eruptiontemperatures average 810 ˚ C for Mt. Erciyes’ early Holocene rhyodacitic domes Karagüllü,Dikkartın and Perikartın, their related pyroclastics, and the dacitic Yılanlıdağ dome. ForMt. Hasan, eruption temperatures are around 850 ˚ C for most dacitic lavas andblock-and-ash-flows, but in some cases up to 1040 ˚ C. Thus, eruption temperatures areusually 50 – 120 ˚ C hotter than mean Ti-in-zircon crystallization temperatures of 730 and750 ˚ C, respectively, emphasizing the significant reheating of erupted magmabatches. Long-term magma fluxes are estimated at 0.5 – 5 km3/ka based on zircon crystallizationage spectra for both Mt. Erciyes and Mt. Hasan. Episodes of intensified zircon growth anderuptive activity at Mt. Erciyes may be related to transient recharge at higher rates. Protractedzircon rim crystallization indicates continuous presence of small fractions of melt in bothsystems. This is explained by minor but frequent magma recharge, supported byfrequent eruptions in case of Mt. Hasan. The overall longevity of zircon crystallizationsuggests that magmatic activity persists to the present day at both volcanoes. Meltpresence and Holocene eruptive activity (previously unrecognized for Mt. Erciyes)emphasize the hazard potential for the population in the surroundings of Mt. Hasan andMt. Erciyes including the metropolis of Kayseri with 1.4 million inhabitants inclose proximity to Mt. Erciyes, calling for further investigations of both volcanoes. [ABSTRACT FROM AUTHOR]