Description: The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization 238U–230Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W‐Fall (130 +16/−14 ka) and I‐Fall eruptions (56 +8.2/−7.7 ka), which under‐ and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for 〉80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km3 is obtained (volcanic explosivity index VEI 〉 8), which confirms the LCY eruption as the first‐ever recognized supereruption in Central America.

Description: Deutsche Forschungsgemeinschaft SCH 2521/6‐1

Description: Highlights • Temporally close-spaced double eruption within a couple of hundreds of years. • Magmas are variably tapped from zoned magma chambers during eruptions due to changing magma discharge rates and/or vent migration. • Eruptions started with a series of fallouts featuring stable eruption columns followed by fluctuating and partially collapsing eruption columns. • Eruptive volumes sum up to a total of 25.6 km3 and 40.5 km3 tephra volume, eruption column heights have been between 20–33 km. • Potential hazards from similar sized eruptions around Coatepeque Caldera are indicated even in the distal regions around San Salvador. Abstract The Coatepeque volcanic complex in El Salvador produced at least four Plinian eruptions within the last 80 kyr. The eruption of the 72 ka old Arce Tephra formed the Coatepeque Caldera and was one of the most powerful explosive eruptions in El Salvador. Hitherto it was thought that the Arce tephra had been emplaced only by one, mostly Plinian, eruptive event that ended with the deposition of a thick ignimbrite. However, our stratigraphic, geochemical, and zircon data reveal a temporally closely- spaced double eruption separated by a gap of only a couple of hundred years, and we therefore distinguish Lower and Upper Arce Tephras. Both eruptions produced in the beginning a series of fallout units generated from fluctuating eruption columns and turning wind directions. The final phase of the Upper Arce eruption produced surge deposits by several eruption column collapses before the terminal phase of catastrophic ignimbrite eruption and caldera collapse. Mapping of the individual tephra units including the occurrences of distal marine and lacustrine ash layers in the Pacific Ocean, the Guatemalan lowlands and the Caribbean Sea, result in 25.6 km3 tephra volume, areal distribution of 4 × 105 km2 and eruption column heights between 20–33 km for the Lower Arce eruption, and 40.5 km3 tephra volume, including 10 km3 for the ignimbrite, distributed across 6 × 105 km2 and eruption column heights of 23–28 km for the Upper Arce eruption. These values and the detailed eruptive sequence emphasize the great hazard potential of possible future highly explosive eruptions at Coatepeque Caldera, especially for this kind of double eruption.

Description: Highlights • Five Pleistocene and Holocene explosive eruptions of Mt. Erciyes dated. • Holocene Dikkartın and Perikartın pumices chemically equal Mediterranean S1 tephra. • Karagüllü dome eruption identified as the source of a Black Sea cryptotephra. • Eastward dispersal of Dikkartın fall-out consistent with probabilistic modeling. • Southerly S1 tephra occurrence suggests low altitude ash dispersal from Mt. Ericyes. Abstract Deposition of early Holocene Eastern Mediterranean S1 tephra and a Black Sea cryptotephra coincides with cultural transitions in the Fertile Crescent termed the Neolithic Revolution as well as sapropel formation during climate variability of the African humid period, classifying them as paramount regional marker horizons for archaeology as well as paleoclimatology. Their correlations with specific eruptions of the Mt. Erciyes stratovolcanic complex (Central Anatolia) remained inconclusive though. Here, we use zircon double-dating by (U–Th)/He and U–Th disequilibrium methods, major and trace element tephra glass geochemistry, and probabilistic modeling of tephra dispersal in an attempt to characterize all major late Quaternary proximal tephras of Mt. Erciyes, and to correlate them with distal deposits. Furthermore, we discuss contrasting proximal and distal tephra dispersal. Three nearly-coeval rhyolitic satellite domes (Dikkartın, Perikartın, and Karagüllü) erupted at Mt. Erciyes in the early Holocene, and their dome extrusions were all preceded by explosive phases producing pyroclastic material that formed tephra fall and pyroclastic flow deposits. The new eruption age of 9.03 ± 0.55 ka (1σ uncertainty here and elsewhere) for proximal Dikkartın pumice is consistent with 14C-based S1 tephra chronologies in distal locations averaging 8.92 ± 0.03 cal ka BP. Perikartın pyroclastic flow deposits predate S1 tephra by ca. 0.8 ka according to a pair of published 14C ages, and stratigraphically overlie Karagüllü fall-out, here dated to 8.2 ± 1.8 ka. Previously undated proximal tephras of Mt. Erciyes erupted in the Late (85.2 ± 4.9 ka) and Middle Pleistocene (154.5 ± 5.3 ka). S1 tephra glass is chemically similar to that of Dikkartın fall-out, but also indistinguishable from that of Perikartın fall-out. Karagüllü pumice is characterized by a distinct glass chemical composition, which correlates with that of unnamed cryptotephra reported for the southeastern Black Sea instead, where these results call for a re-evaluation of existing age models. Maximum lithic clast size isopleths for proximal Dikkartın fall-out indicate eastward dispersal of a 20 ± 5 km high eruption plume by stratospheric winds, in agreement with results of probabilistic tephra dispersal modeling. This azimuth contrasts with the known distribution of S1 tephra at distal locations that are all south of Mt. Erciyes. Significant tephra occurrences at up to 1300 km distance and orthogonal to prevalent stratospheric wind directions either result from very atypical wind conditions (probability ≪10 %), or are caused by tephra transport by prevailing low altitude winds. Two scenarios are proposed for low altitude transport: eolian reworking of primary fall-out (more likely from the more widespread Dikkartın deposits), or co-ignimbrite ash cloud dispersal (more likely from the Perikartın eruption which predominantly produced pyroclastic flows). Because S1 tephra is chemically indistinguishable from both Dikkartın and Perikartın by major and trace element glass compositions, its exact source and dispersal mechanism remain ambiguous, although existing 14C ages for Perikartın predating those for S1 tephra favor Dikkartın as its source.

Description: We present geochemical major and trace element glass data for tephra samples from International Ocean Discovery Program (IODP) Expeditions 349 and 367/368 from four drilling sites in the South China Sea. Overall, we obtained data for 55 samples and identified 46 as tephra layers, with dominant volcanic glass shards in the component inventory (in the 63–125 µ fraction). In total, we performed 720 single glass shard analyses using an electron microprobe for major element compositions, as well as 130 single glass shard analyses using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) for trace element compositions. The compositions of the samples range from basaltic, (trachy-) andesitic to trachytic, and rhyolitic and fall mainly into the calc-alkaline and K-rich calc-alkaline magmatic series. One sample falls into the shoshonitic series. Tephras from Expedition 349 Site U1431 span the whole compositional range, whereas tephras from the other sites are limited to rhyolitic composition. Tephra ages, calculated applying sedimentation rates, range to ~2 Ma at Site U1431, ~0.8 Ma at Expedition 367 Site U1499, ~0.6 Ma at Expedition 368 Site U1501, and ~0.9 Ma at Expedition 368 Site U1505.

Description: Highlights • Syn-rift sediments in the northern South China Sea are from the East Cathaysia block. • Rivers delivered sediments migrated from eastern to western region. • Tributaries catchment of the Pearl River started to migrate since the late Eocene. • The migration of the river catchment is related to the west-east topographic swap. • Topographic change was possibly related to the local tectonic uplift and exhumation. We examined an International Ocean Discovery Program (IODP) drilling core from Site U1501, located on the distal margin of the northern South China Sea (SCS) basin to unravel the sediment provenance evolution in the Paleogene and the evolution of river catchments during basin opening. We attempt to understand the major factors driving river development in a rift basin by utilizing provenance tools to constrain sediment transport pathways and compare these with the regional tectonics during the Paleogene in order to resolve competing models for drainage evolution and test their relationships with the evolving topography of SW China and the SE Tibetan Plateau. For this purpose, ten samples were collected from a 200-m-thick, syn-rift Eocene/pre-Eocene interval. Detrital zircon U-Pb data were collected by LA-ICP-MS to identify the sediment provenance and differentiate fluvial sources. Bulk rock geochemistry data was utilized to shed light on chemical weathering conditions and compositional maturity to further decipher sediment transportation patterns. We compare our data with adjacent IODP Site U1435 and several industrial boreholes located in the Pearl River Mouth Basin (PRMB). We applied multiple statistical tests, including K-S, Monte Carlo mixing and multidimensional scaling testing, to evaluate U-Pb age spectra similarities and to estimate endmember contributions from a variety of source areas. Our results from Site U1501 show that sediments deposited as fluvial sands during the rifting stage, were predominantly derived from the East Cathaysia block, probably from local sources. A progressive increase in older detrital zircon U-Pb ages peaks (〉200 Ma) was observed at Site U1435 and in PRMB strata, signaling a spatial shift in sediment provenance from east to west occurring between the late Eocene and the early Oligocene. This trend reflects a transition in sediment delivery from local small-catchment streams to a more regional drainage eroding the east and north of the South China Block. Westward drainage expansion is likely impacted by the uplift of the Tibetan Plateau.

Description: Defining a precise timeline for past eruptions from explosive volcanoes in continental arcs is imperative to forecast future hazards and mitigate volcanic disasters in these often densely populated regions. However, establishing reliable ages for Quaternary eruptions in the Central American Volcanic Arc has been challenging due to the common lack or alteration of suitable K-rich phases for 40Ar/39Ar geochronology, but also from their position in time beyond the reach of 14C dating. This especially holds for the active Amatitlán caldera in Guatemala, from which at least six explosive silicic eruptions have produced tephra blanketing neighboring regions that are today inhabited by millions of people. Zircon, a common datable accessory mineral in Amatitlán caldera magmas, is used here to retrieve eruption ages by applying the novel zircon double-dating method (ZDD) that integrates 238U–230Th disequilibrium dating and (U–Th)/He thermochronology. This approach yielded the first-ever radioisotopic ages of 24 ± 3 ka and 48 ± 6 ka (1σ), respectively, of two of Amatitlán caldera's most recent eruptions (J-tephra and E-tephra). Remarkably, both zircon crystallization and ZDD eruption ages for the older and voluminous T-tephra and L-tephra units significantly post-date existing plagioclase 40Ar/39Ar dates by ca. 26 and 70 kyr, respectively. The ZDD eruption age for T-tephra is 93 ± 4 ka, whereas zircon crystallization ages for L-tephra yield a maximum model eruption age of ca. 124 ka. The strong eruption age divergence between ZDD and plagioclase 40Ar/39Ar dating argues for the presence of inherited or xenocrystic plagioclase in Amatitlán caldera eruptive products. Statistical analysis based on the updated eruptive history suggests a recurrence interval of ca. 17 kyr, which is significantly shorter than previously estimated. The new age data, thus, suggest a more frequent eruptive activity of Amatitlán caldera than formerly thought and underscores the necessity to better understand the current underlying magmatic system and to constrain its past eruptive history more precisely.

Description: Volcanic islands export clastic material to their surrounding oceans by explosive eruptions, lava emissions, biogenic production on their shelves, and failure of their slopes, amongst other processes. This raises the question of whether geological events (in particular, eruptions and landslides) can be detected offshore and dated, and whether any relationships (for example, with climate changes) can be revealed using sediment cores. The volcanically active central Azorean islands (Faial, Pico, São Jorge, and Terceira), with their neighboring submarine basins, are potentially good candidates for such an analysis. Here, chronostratigraphies of four gravity cores collected amongst the islands are constructed based on twelve radiocarbon dates and two dates derived by geochemically correlating primary volcaniclastic turbidites with ignimbrites on Faial and Terceira Islands. Age-depth models are built from the hemipelagic intervals to estimate individual turbidite dates. Volumes of turbidites are modeled by multiplying basin areas with bed thickness, allowing for various turbidite thinning rates and directions. The volumes of landslide-generated turbidites are only comparable with the largest volumes of their adjacent upper-slope submarine landslide valleys; therefore, such turbidites in the cores likely derive from these largest landslides. Emplacement intervals between turbidites originating from both landslides and pyroclastic density currents are found to be mostly a few thousand years. Frequencies of landslide-generated turbidites and hemipelagic sedimentation rates were both highest in the past 8 k.y. compared to preceding periods up to 50 k.y. High hemipelagic sedimentation rates are interpreted to be related to sea-level rise, allowing more shelf bioproduction and release of particles by coastal erosion. The coincident increased frequencies of submarine landslides may also be associated with the increased sediment supply from the islands, resulting in a more rapid build-up of unstable sediments on submarine slopes. Notably, the emplacement frequencies of turbidites of pyroclastic density current origins do not suggest the decreased eruption frequency toward the Holocene that has been found elsewhere.

Description: The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization 238U–230Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 +16/−14 ka) and I-Fall eruptions (56 +8.2/−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for 〉80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km3 is obtained (volcanic explosivity index VEI 〉 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.

Description: We use the tephrostratigraphic framework along the Aegean Volcanic Arc established in part 1 of this contribution to determine hemipelagic sedimentation rates, calculate new tephra ages, and constrain the minimum magnitudes of (sub)plinian eruptions of the last 200 kyrs. Hemipelagic sedimentation rates range from ∼0.5 cm/kyr up to ∼40 cm/kyr and vary laterally as well as over time. Interpolation between dated tephras yields an eruption age of ∼37 ka for the Firiplaka tephra, showing that explosive volcanism on Milos is ∼24 kyrs younger than previously thought. The four marine Nisyros tephras (N1 to N4) identified in part 1 (including the Upper (N1) and Lower (N4) Pumice) have ages of ∼57 ka, ∼63 ka, ∼69 ka, and ∼76 ka, respectively. Eruption ages for the Yali-1 and Yali-2 tephras are ∼55 ka and ∼34 ka, respectively. The Yali-2 tephra comprises two geochemically and laterally distinct marine facies. The southern facies is identical to the Yali-2 fall deposit on land but the western facies has slightly less evolved glass compositions. Overall, erupted plinian and co-ignimbrite fall tephra volumes range from 〈1 to 56 km3 (excluding possible caldera fillings and ignimbite volumes), and 80% of the eruptions had magnitude 5.5〈M≤7.2 (M=log(m)-7; m = erupted magma mass in kg). Twenty percent of the tephras represent 3.2〈M〈5.5 eruptions. The long-term average tephra magma mass flux through highly explosive eruptions of Santorini is estimated at ∼40 kg/s. The analogous data for the Kos-Yali-Nisyros volcanic complex is less-well constrained but similar to Santorini.

Description: The Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U-230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of 〈10 kyr for major mineral phases in TBJ. This dichotomy is explained by a process of rhyolitic melt segregation from a crystal-rich refractory residue that incorporates zircon, whereas a new generation of major mineral phases crystallized shortly before eruption. Ti-in-zircon temperatures and amphibole geothermobarometry suggest that rhyolitic melt was extracted from different storage zones of the magma reservoir as indicated by distinct but synchronous thermochemical zircon histories among the TB suite eruptions. Zircon from TBJ and TB2 suggests magma differentiation within deeper and hotter parts of the reservoir, whereas zircon from TB3 and TB4 instead hints at crystallization in comparatively shallower and cooler domains. The assembly of the voluminous TBJ magma reservoir was also likely enhanced by cannibalization of hydrothermally altered components as suggested by low-δ18O values in zircon (+4.5 ± 0.3‰).