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Sahand volcano along with the two neighbouring volcanic systems of Saray and Sabalan are three Late Miocene-Quaternary volcanoes that formed in the wake of the collision between the Arabian and Eurasian continental plates along the Neo-Tethyan suture zone in northwestern Iran. Sahand volcano is an isolated, extensive (3707 m elevation; >3000 km2 area) stratovolcanic complex, which is located ~165 km north of the Neo-Tethyan suture zone and was constructed over ~45 km thick continental crust. Andesitic to dacitic pyroclastic deposits, ignimbrites, and lava flows form the now strongly eroded Paleo- and Meso-Sahand edifice. Paleo-Sahand rocks are mostly restricted to the central part the edifice, where they underlie Meso-Sahand deposits. By contrast, Neo-Sahand volcanic rocks intruded older volcanic successions within and outside a largely eroded caldera margin, which likely formed during the Meso-Sahand stage. Neo-Sahand units comprise several basaltic andesitic to rhyolitic domes in the center of the complex as well as small parasitic cones along with subvolcanic dikes. High spatial resolution and sensitivity U-Pb geochronology using secondary ionization mass spectrometry (SIMS) define the formation of Paleo-, Meso-, and Neo-Sahand to ca. 8 to 3 Ma, ca. 1 Ma, and ca. 600 to <173 ka, respectively, with dating mostly focusing on Neo-Sahand. Antecrystic zircon crystals in Sahand volcanic deposits also indicate that post-collisional magmatism initiated locally at about the same time or slightly earlier than at Saray volcano to the west of Sahand. The initiation of volcanic activity subsequently migrated to the northeast over a distance of ~300 km away from the Neo-Tethyan suture, where activity started at Sabalan volcano at ca. 4.5 to 2.9 Ma. This time corresponds to a magmatic lull of Sahand before the Meso-Sahand eruptive activity resumed at ca. 1 Ma. Subsequently, Neo-Sahand and Neo-Sabalan erupted synchronously throughout the middle and possibly into the late Pleistocene. Paleo- and Neo-Sahand volcanic rocks are characterized by enrichments of large-ion lithophile (LILE) and light rare earth elements (LREE) relative to high-field strength and heavy rare earth elements (HREE), respectively, and prominent negative Ti, Nb, and Ta anomalies relative to primitive mantle compositions. The least evolved magmas at Sahand have formed by 1–5% partial melting of garnet- and spinel-peridotite and were subsequently overprinted through assimilation – fractional crystallization (AFC) processes acting in the continental crust. Although Sahand and Sabalan volcanic rocks share many geochemical characteristics indicative of a continental subduction setting, Sahand is less potassic and less enriched in incompatible trace elements compared to Sabalan. Another difference is that Sahand primitive magmas were formed by smaller degrees of partial melting in the mantle than is the case for Sabalan. Both effects likely result from variable distances from the suture zone and crustal thickening away from the suture towards the northeast. Overall, the apparent age progression and geochemical variation of the post-collisional volcanism, lack of asthenospheric mantle components, and the subduction-affinity of Sahand and Sabalan volcanic rocks supports a scenario where mantle melting was triggered by slab roll back and break-off shortly after continental collision, followed by migration of the slab edge towards the northeast at plate-like velocities. Unlabelled Image • Sahand volcano in northwestern Iran formed in three major stages • New U-Pb zircon ages for Sahand Paleo-, Meso-, and Neo-Sahand stages • Subduction-modified mantle melted following collision and subsequent slab rupture • Post-collisional magmatism controlled by mantle wedge and crustal thicknesses • Onset of volcanism consistent with slab migration at velocities of 2–3 cm per year [ABSTRACT FROM AUTHOR]

The Santa María-Santiaguito volcanic complex collectively is one of the most active and dangerous volcanoes in the entire Central American volcanic arc. Within 20 years of the destructive Plinian eruption of the Santa María stratocone (Guatemala) in 1902, the Santiaguito volcanic dome complex started to form by parasitic vent eruptions which have lasted over nearly a century. Because of the frequent eruptions of Santiaguito, it offers unique opportunities to study secular changes in its subvolcanic magma reservoir at high temporal resolution. Ash collected days and hours after eruptions of Santiaguito during an unusually explosive interval in August 2016 represents some of the least evolved compositions (60–62% SiO 2) with the lowest 87Sr/86Sr isotope ratios ever reported for the system. This extends the multi-decadal trend of Santiaguito to progressively less evolved magma compositions with time, relative to the 1902 event which erupted overwhelmingly dacitic pumice. Santiaguito's geochemical changes are indicative of increasingly larger contributions of fresh basaltic andesite magma recharge mixing with dacitic magma that remained after the 1902 eruption. High-resolution secondary ion mass spectrometry (SIMS) 238U-230Th disequilibrium dating and geochemistry of zircon from Santiaguito ash and Santa María 1902 pumice reveal the presence of evolved and zircon-saturated melts over the entire ca. 100 kyr interval of basaltic andesite eruptions that constructed the Santa María central cone. Quartz diorite basement xenoliths (~55% SiO 2) with Eocene zircons are common in the Santa María 1902 deposits, and a few equally old zircon xenocrysts within Santiaguito ash suggest that vestiges of assimilated Eocene crustal rocks are present in the modern magma system. Zircon crystals in andesitic Santiaguito tephra are identical in age and trace element signature to those in the 1902 pumice. This is direct evidence for the persistence of residual evolved magma with crystals dating back to the Santiaguito cone-forming stage between ca. 100 and 25 ka and the pre-1902 eruptive quiescence which lasted for ca. 25 kyr. It also indicates that residual dacite still contributes to Santiaguito andesitic magmas. Zircon survival in Santiaguito andesite requires comparatively brief timescales of magma mixing between basaltic andesite and resident dacite magmas because otherwise zircon would become resorbed. • 2016 Santiaguito ash has the least evolved composition in the volcano's history. • Whole-rock Sr isotopes among the most primitive ever reported for Santiaguito. • U-series zircon ages suggest evolved magma coeval to Santa María basaltic magmatism. • Zircon dating reveals Eocene (ca. 41 Ma) crustal basement below Santiaguito. • Andesite originated by mixing of dacite leftover and basaltic andesite recharge. [ABSTRACT FROM AUTHOR]

The provenance and nature of palygorskite clay used by Mayas for the creation of the outstanding Maya Blue pigment and pottery in the Yucatán peninsula has not been analyzed thoroughly. Especially the hypothesis of palygorskite being a diagenetic product of volcanic glass has remained uncertain. Here, we present a detailed study of zircon extracted from palygorskite-rich materials (sak lu'um) collected in the interior of the Sacalum cenote and near Chapab village, to evaluate the potential of zircon as an indicator mineral for tephra-derived palygorskite or clay-rich deposits intercalated with carbonate rocks. U-Pb zircon geochronology and correlative trace element analyses from stratigraphically different palygorskite-rich horizons indicate a restricted Eocene age range, which is coeval to the deposition of the host carbonates, and discrete airborne emplacement events of silicic tephra into warm and shallow waters at ca. 50 Ma and 41 Ma, likely derived from volcanoes in a continental magmatic arc. Our findings also indicate that palygorskite deposits in the Yucatán peninsula are not inherited from continental sources but rather formed in-situ partly from weathering of volcanic glass that sourced Si and Al required for palygorskite formation. • Silicic tephra is a precursor component for palygorskite in Yucatán, Mexico. • Eocene zircon in palygorskite deposits are coeval to carbonate formation. • Trace elements in zircon suggest ash derivation from a continental arc setting. • Tephra origin as fall-out from western Central American or Caribbean arcs. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Edifice growth of Bazman volcano in southeastern Iran started around 1.37 Ma. • Bazman volcano evolved in four major eruption episodes with the youngest eruption at <41 ka. • Quaternary volcanism was preceded by Neogene (8.61–4.12 Ma) volcanism. • Magmas formed via melting of subduction-modified mantle and crustal contamination. • Makran-Chagai volcanic arc remained stationary throughout the Quaternary. Abstract Bazman is an isolated voluminous (3497 m elevation; >300 km2) composite volcano that is located within the western segment of the Makran-Chagai arc. This arc obliquely tracks the modern EW-trending trench offshore the Oman sea coast of Iran and Pakistan, with several Quaternary stratovolcanoes (Bazman and Taftan in SE Iran, and Kuh-i-Sultan in western Pakistan) superimposed on a preexisting Neogene arc. High spatial resolution and high sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry (SIMS) yielded four clusters of zircon ages for Bazman volcanic rocks which range from ca. 8.6 Ma to 41 ka. Lava and pyroclastic materials erupted between 8.6 and 5.9 Ma forming a thick Neogene volcanic succession (Ngv). These deposits were intruded by hypabyssal andesite-dacite domes at ca. 4.1 Ma. The next younger group of the Quaternary Bazman center comprises several eruptive pulses at 1.37 Ma, 1.13 Ma, 0.943 Ma, 0.853 Ma and 0.635 Ma, which constructed the main edifice around a central vent through alternating eruptions of lava and pyroclastic rocks (Qtv and Qa2). Subsequently, ignimbrite flows also sourced from the main vent erupted at 0.59 and 0.47 Ma, and covered the earlier erupted deposits. The youngest dated eruptive phase (Qa3) comprises the emplacement of dacitic to andesitic lava around the top of volcano. Based on Uranium-series (238U-230Th) disequilibrium in Qa3 zircons, model ages of ca. 41 ka define a maximum eruption age of these lavas, which tapped a long-lived magma reservoir with zircon crystallization ages predating eruption by 10's to 100's of ka. Low- medium-K calc-alkaline basaltic-andesitic eruptions formed parasitic cones located on northeastern flanks of the edifice as the youngest unit (Qa4) of Bazman. Both Neogene and Quaternary rocks from Bazman volcano exhibit homogeneous trace element characteristics, including enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements (HFSE) and heavy rare earth elements (HREE), respectively. High Th/Yb and negative anomalies of Ta, Nb and Ti are consistent with an enriched mantle source in a continental subduction zone. Trace element modeling for the most primitive basalts erupted at Bazman suggests an origin of parental magmas through ∼15% partial melting of an enriched spinell-lherzolite mantle, whereas the genesis of Bazman acidic volcanic rocks with SiO 2 > 62% involves partial melting in the middle/lower continental crust which became subsequently overprinted through assimilation – fractional crystallization (AFC) processes. Compositional continuity of Quaternary Bazman volcanic rocks with their Neogene precursors implies a steady magma source above the subducted Oman slab. Consequently, subduction geometry in the Makran-Chagai arc has experienced little modification over the past few million years. [ABSTRACT FROM AUTHOR]

The chronologic record encoded in accessory minerals, based on the radioactive decay of U and Th, is indispensable to extract quantitative process rates over timescales encompassing Earth's evolution from the Hadean to the Holocene, and extending from terrestrial to extra-terrestrial realms. We have essentially three different U–Pb dating tools at hand, a high-precision, whole-grain bulk technique (isotope-dilution thermal ionization mass spectrometry, ID-TIMS), and two high-spatial resolution but less precise in-situ techniques (secondary ion mass spectrometry, SIMS, and laser ablation inductively-coupled plasma mass spectrometry, LA-ICP-MS), all of which are predominantly applied to the mineral zircon. All three have reached a technological and methodological maturity in data quality and quantity, but interpretational differences, which are often common (albeit at different temporal and spatial scales) to all isotopic dating techniques, remain largely unresolved. The choice to use one of these techniques should be governed by the scientific question posed, such as (1) the duration of the geological process to be resolved; (2) the size and abundance of the material to be analyzed; (3) the complexity of the sample material and of the geological history to be resolved; and (4) the number of dates needed to address the question. Our compilation demonstrates that, ultimately, the highest confidence geochronological data will not only result from the optimal choice of appropriate analysis technique and the accurate treatment of analytical and interpretational complexities, but also require comprehensive sample characterization that employs the full gamut of textural (e.g., cathodoluminescence, charge contrast imaging, electron backscatter diffraction) and compositional (e.g., trace element, stable and radiogenic isotope) analysis. [ABSTRACT FROM AUTHOR]

Geologic records of Earth's hydrosphere and meteoric precipitation older than 2 Ga are rare, although they provide insight into the past climate, rates of water-rock interaction, and intensity of plate tectonics. Here we report and describe in detail the lowest known δ13O (-16‰ to -25‰) terrestrial silicate rocks on Earth, found in Paleoproterozoic plagiogneisses from the Belomorian complex, Karelia, Russia. Geochronologic and oxygen isotopic data on zircons (+7‰ to -26‰) and monazite (-17.5‰) imply that the protoliths of these rockswere ca. 2.5 Ga metasediments and metavolcanics that were hydrothermally altered prior to 1.85 Ga within an intracontinental rift zone, and involved ultralow δ13O, <-25‰ meteoric water. Paleogeographic reconstructions indicate that Karelia was at low to middle latitudes throughout the Paleoproterozoic Era. Ultradepleted δ13O waters outside of polar regions or the interiors of large landmasses provide independent evidence for a moderately glaciated, so called "slushball" Earth climate between 2.45 and 2.4 Ga, in which low- or mid-latitude, midsize continents were covered with glaciers while the ocean remained at least partially unfrozen to allow for intracontinental isotopic distillation in a large temperature gradient. In addition to these climatic inferences, the data are more readily explained by a depleted -10‰ seawater reservoir during Paleoproterozoic time. [ABSTRACT FROM AUTHOR]

Pleistocene volcaniclastic turbidites drilled during IODP 340 (U1398B, ≤ 170 mbsf) in the Grenada basin west of Martinique (central Lesser Antilles) have been investigated for sediment provenance. U/Pb ages by ion microprobe from 323 detrital zircon grains at three U1398B levels reveal youngest population maximum ages which are interpreted to represent major eruption periods. Systematic age progression with depth defines a ~ 20 cm/ka depositional rate and provides a robust chronostratigraphic frame for the ≤167.5 mbsf (≤ 856 ± 10 ka) interval of U1398B, and confirms on-board paleomagnetic constraints for a possible late Matuyama age for the lowermost sampled parts of U1398B. The achieved chronostratigraphic frame yields sedimentation rates for carbonate ooze and of volcaniclastic sands and gravels of 8.2 and 7.6 cm/ky, respectively. Depth plots of cumulative thickness of these lithologies allow for a differentiation into periods of enhanced and reduced volcanic activity. Porphyritic lava and mineral fragments include plagioclase, diopside, augite and enstatite, as well as magnesio-hornblende and ferri-tschermakite. Geothermobarometry based on clinopyroxene and amphibole reveal the dominant role of upper crustal magma reservoirs. Ferri-tschermakite from 93 and 167.5 mbsf (~410 and 856 ka, respectively) records contributions from lower crustal, hot magma reservoirs. These temperature estimates are supported by Ti-in-zircon data. O-isotope ratios and trace elements in zircon reflect magmatic activity typical for an evolved island arc system. The bathymetry of the Grenada basin, the composition of lava clasts and minerals, scarcity of altered lava fragments, the narrow maximum age population of detrital zircon, and the O-isotope and trace element data on zircon suggest that the majority of U1398B volcaniclastic turbidites originated from the island of Dominica. The thick volcaniclastic units are most likely related to major eruption periods of andesitic magma that ascended from crustal reservoirs. Debris avalanche-related processes seem to be less important in U1398B at ≤170 mbsf. Mineral chemistry and O-isotope data obtained from plagioclase, pyroxene, amphibole, zircon and glass, separated from deep marine volcaniclastic turbidites, provide a chronostratigraphic frame for the sedimentary succession, and helps to genetically fingerprint the volcanic and magmatic evolution of the neighboring volcanic islands. While this is documented here for the well-constrained Pleistocene history of the central Lesser Antilles, the applied methods may also be used to characterize ancient marine volcaniclastic mass flow deposits and to reconstruct their volcanic source areas. • U/Pb ages of detrital zircon provide chronostratigraphic frame for Pleistocene volcaniclastic turbidites (U1398B, IODP 340). • SEM and microprobe data characterize central Lesser Antilles magmatic plumbing system, ≤ 856 ka. • Trace element and O isotope data on zircon give further independent evidence for the magmatic evolution. • Thickness/depth plots of carbonatic ooze and of volcanic sands and gravel indicate periods of enhanced volcanic activity. • Volcaniclastic turbidites mainly originated from Dominica. [ABSTRACT FROM AUTHOR]

Abstract: The suitability of in situ Secondary Ionisation Mass Spectrometry (SIMS) techniques for measuring O isotopes in speleothems is critically examined by applying this technique to a 500-year interval of the well-known Hulu Cave record (Wang, Y.J., Cheng, H, Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.C., Dorale, J.A., 2001. A high-resolution absolute dated late Pleistocene monsoon record from Hulu Cave, China. Science, 294: 2345–2348). This interval includes a large abrupt +2‰ shift in δ 18O at 16.07 ka, which may correlate to Heinrich Event I (H1). The high-resolution SIMS method provides annual to near-annual δ 18O data, thereby increasing the temporal resolution of the previously published Hulu Cave isotopic data by approximately tenfold. SIMS δ 18O data reveal that 75% of the abrupt isotopic shift at 16.07 ka occurred in just 1 to 2 years and the full +2‰ occurs over 6 years, compared with an upper limit of 20 years as previously determined by conventional methods employing micro-cutting, acid-digestion and CO2-gas source mass spectrometry methods. SIMS δ 18O data also reveal numerous high amplitude (1–3‰), high frequency (<20 year) fluctuations not resolvable with conventional data that are recorded in the several hundred years prior to 16.07 ka and may persist after the 16.07 ka event. These fluctuations are interpreted to represent more local rainfall changes while the +2‰ shift represents a rapid change in the underlying δ 18O mean driven by more complex processes that are maintained for 500 years. [Copyright &y& Elsevier]

Abstract: Rhyolite lavas and xenoliths from the Salton Sea geothermal field (Southern California) provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust. Salton Buttes rhyolite lavas contain xenoliths that include granophyres, fine-grained altered rhyolites (“felsite”), and amphibole-bearing basalts. Zircon is present in lavas and xenoliths, surprisingly even in the basaltic xenoliths, where it occurs in plagioclase-rich regions interpreted as pockets of crystallized partial melt. Zircons in the xenoliths are exclusively Late Pleistocene–Holocene in age and lack evidence for inheritance. U–Th isochron ages are: 20.5−1.2 +1.2 ka (granophyres), 18.3−3.5 +3.6 ka (felsite), 30.1−12.4 +14.1 ka and 9.2−6.6 +7.0 ka (basalts; all errors 1σ). The dominant zircon population in the rhyolite lavas yielded U–Th ages between ∼18 and 10 ka, with few pre-Quaternary xenocrysts present. δ 18Ozircon values are lower than typical crustal basement values, thus ruling out rhyolite genesis by melting of continental crust. Moreover, δ 18Ozircon values are ∼0.5–1.0‰ lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid-ocean ridge basalt, suggesting that basaltic crust and silicic plutons in the subsurface of the Salton Sea geothermal field isotopically exchanged with meteoric waters. This is evidence for deep-reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma. [Copyright &y& Elsevier]

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of eight zircon reference materials and synthetic zircon-hafnon end-members indicate that corrections for abundance sensitivity and molecular zirconium sesquioxide ions (Zr 2 O 3 + ) are critical for reliable determination of 230 Th abundances in zircon. Other polyatomic interferences in the mass range 223–233 amu are insignificant. When corrected for abundance sensitivity and interferences, activity ratios of ( 230 Th)/( 238 U) for the zircon reference materials we used average 1.001 ± 0.010 (1σ error; mean square of weighted deviates MSWD = 1.45; n = 8). This includes the 91500 and Plešovice zircons, which were deemed unsuitable for calibration of ( 230 Th)/( 238 U) by Ito (2014). Uranium series zircon ages generated by LA-ICP-MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on 230 Th such as those presented by Ito (2014) are potentially unreliable. [ABSTRACT FROM AUTHOR]

• Blueschist from serpentine mud volcano in Mariana forearc is ca. 50 Ma old. • The mineral assemblage records warm metamorphic conditions during IBM subduction initiation. • Blueschist rocks have resided in the subduction channel for at least 46 Ma. From ca. 50 Ma to present, the western Pacific plate has been subducting under the Philippine Sea plate, forming the oceanic Izu-Bonin-Mariana (IBM) subduction system. It is the only known location where subduction zone products are presently being transported to the surface by serpentinite-mud volcanoes. A large serpentine mud "volcano" forms the South Chamorro Seamount and was successfully drilled by ODP during Leg 195. This returned mostly partially serpentinized harzburgites enclosed in serpentinite muds. In addition, limited numbers of small (1 mm–1 cm) fragments of rare blueschists were also discovered. U–Pb dating of zircon and rutile from one of these blueschist clasts give ages of 51.1 ± 1.2 Ma and 47.5 ± 2.0 Ma, respectively. These are interpreted to date prograde high-pressure metamorphism. Mineral equilibria modelling of the blueschist clast suggests the mineral assemblage formed at conditions of ∼1.6 GPa and ∼590 °C. We interpret that this high-pressure assemblage formed at a depth of ∼50 km within the subduction channel and was subsequently exhumed and entrained into the South Chamorro serpentinite volcano system at depths of ∼27 km. Consequently, we propose that the material erupted from the South Chamarro Seamount may be sampling far greater depths within the Mariana subduction system than previously thought. The apparent thermal gradient implied by the pressure–temperature modelling (∼370 °C/GPa) is slightly warmer than that predicted by typical subduction channel numerical models and other blueschists worldwide. The age of the blueschist suggests it formed during the arc initiation stages of the proto-Izu-Bonin-Mariana arc, with the P – T conditions recording thermally elevated conditions during initial stages of western Pacific plate subduction. This indicates the blueschist had prolonged residence time in the stable forearc as the system underwent east-directed rollback. The Mariana blueschist shows that subduction products can remain entrained in subduction channels for many millions of years prior to exhumation. [ABSTRACT FROM AUTHOR]

High-spatial resolution zircon geochronology was applied to constrain the timescales of volcanic eruptions of the youngest, mostly explosive volcanic phase of Ciomadul volcano (Carpathian–Pannonian region, Romania). Combined U–Th and (U–Th)/He zircon dating demonstrates that intermittent volcanic eruptions occurred in a time range of 56–32 ka. The reliability of the eruption dates is supported by concordant ages obtained from different dating techniques, such as zircon geochronology, radiocarbon analysis, and infrared stimulated luminescence dating for the same deposits. The new geochronological data suggest that volcanism at Ciomadul is much younger (< ca. 200 ka) than previously thought (up to 600 ka). A dominantly explosive volcanic phase occurred after an apparent lull in volcanism that lasted for several 10's of ka, after a period of lava dome extrusion that defines the onset of the known volcanism at Ciomadul. At least four major eruptive episodes can be distinguished within the 56–32 ka period. Among them, relatively large (sub-plinian to plinian) explosive eruptions produced distal tephra covering extended areas mostly southeast from the volcano. The 38.9 ka tephra overlaps the age of the Campanian Ignimbrite eruption and has an overlapping dispersion axis towards the Black Sea region. The wide range of U–Th model ages of the studied zircons indicates prolonged existence of a low-temperature (< 800 °C) silicic crystal mush beneath Ciomadul. The main zircon crystallization period was between ca. 100 and 200 ka, coeval with the older, mostly extrusive lava dome building stage of volcanism. Even the youngest U–Th model ages obtained for the outermost 4 μm rim of individual zircon crystals predate the eruption by several 10's of ka. The zircon age distributions suggest re-heating above zircon saturation temperatures via injection of hot mafic magmas prior to eruption. Intermittent intrusions of fresh magma could play a significant role in keeping the intrusive silicic magmatic reservoir in a partially melted for prolonged period. The previous history of Ciomadul suggests that melt-bearing crystal mush resided beneath the volcano, and was rapidly remobilized after a protracted (several 10's of ka) lull in volcanism to trigger several eruptions in a comparatively short time window. This classifies Ciomadul as a volcano with ‘Potentially Active Magma Storage’ (PAMS) which we propose to be common among the seemingly inactive volcanoes in volcanic arc regions. The potential for reactivation of these systems should be included into volcanic hazard assessments. [ABSTRACT FROM AUTHOR]

• We conduct correlated microstructural and isotopic analysis of six eucrites. • U-bearing accessory minerals baddeleyite, zircon, and apatite were targeted. • No sample records ages around 3.9 Ga, the hypothesised late heavy bombardment. • Older (> 4.2 Ga) grains record no structural evidence of later shock deformation. • We find no evidence for a increased impact flux (LHB) in the studied eucrites. A long-standing paradigm in planetary science is that the inner Solar System experienced a period of intense and sustained bombardment between 4.2 and 3.9 Ga. Evidence of this period, termed the Late Heavy Bombardment is provided by the 40Ar/39Ar isotope systematics of returned Apollo samples, lunar meteorites, and asteroidal meteorites. However, it has been largely unsupported by more recent and robust isotopic age data, such as isotopic age data obtained using the U-Pb system. Here we conduct careful microstructural characterisation of baddeleyite, zircon, and apatite in six different eucrites prior to conducting SIMS and LA-ICP-MS measurement of U, Th, and Pb isotopic ratios and radiometric dating. Baddeleyite, displaying complex internal twinning linked to reversion from a high symmetry polymorph in two samples, records the formation of the parent body (4554 ± 3 Ma 2σ; n = 8), while structurally simple zircon records a tight spread of ages representing metamorphism between 4574 ± 14 Ma and 4487 ± 31 Ma (n = 6). Apatite, a more readily reset shock chronometer, records crystallisation ages of ∼4509 Ma (n = 6), with structurally deformed grains (attributed to impact events) yielding U-Pb ages of 4228 Ma (n = 12). In concert, there is no evidence within the measured U-Pb systematics or microstructural record of the eucrites examined in this study to support a period of late heavy bombardment between 4.2 and 3.9 Ga. [ABSTRACT FROM AUTHOR]

• Zircon spot ages suggest prolonged lifetime of the magma reservoir beneath Ciomadul. • Zircon and major mineral phase thermometry suggests near solidus conditions. • Low and steady-state magma flux can maintain parts of the reservoir above solidus. • 260 km3 magma injected in the upper crust of which 35 km3 is still partially molten. • Ciomadul is capable of sudden reawakening even after several 10's kyr dormancy. Ciomadul is the youngest volcano in eastern-central Europe. Although its last eruption occurred at ca. 30 ka, there are independent indications for a high-crystallinity magma reservoir persisting beneath the volcano until present. In order to further test the hypothesis of long-lived melt presence and to better constrain the nature and timescales associated with the subvolcanic magma storage system, over 500 zircon U-Th and U-Pb spot ages (crystal interiors and outer surfaces) were interpreted from dacitic rocks of the most productive eruptive period (the Young Ciomadul Eruptive Period; YCEP, 160-30 ka). Zircon surface ages from lava dome and pumice samples range from ca. 600 ka up to the youngest eruption event at 30 ka. They form a continuous age distribution and some single crystals reveal significant age zonation (>150 kyr difference from core to rim). The oldest zircon ages of YCEP overlap with the last eruption events of the Old Ciomadul Eruptive Period (1000–330 ka). The zircon age spectra, combined with textural data, point to a prolonged (several 100's kyr) residence in a highly crystalline mush state. The range in zircon crystallization temperature (from ∼750 °C to the solidus at ∼680 °C) is consistent with the results of thermometry on amphibole and plagioclase from felsic crystal clots, which represent crystal mush fragments. To maintain magma reservoir for such a long time above solidus, continuous magma input by deeper recharge is required. Zircon crystallization model calculations constrained by thermal modelling imply an average rate of magma input of about 1.3 × 10−4 km3/yr over 2 Myr. Such estimate allows us to calculate an extrusive/intrusive ratio of 1:25–1:30. The model calculations suggest that a crystal mush zone of about 35 km3 is still present within the subvolcanic magma reservoir. Importantly, the Ciomadul plumbing system thus remains thermally primed and renewed magma injection could lead to rapid reawakening and eruption of the apparently inactive volcano. [ABSTRACT FROM AUTHOR]

Melt inclusions in zircon represent time capsules, which provide deep insights into igneous rock formation including timing, physicochemical conditions, and the compositional evolution of cogenetic magmas with respect to major, trace, and volatile elements. However, their full potential as petrogenetic indicators, in particular their usability and consistency as geothermometers, is poorly investigated. Therefore, we present new mineralogical and chemical data for recrystallized and homogenized melt inclusions and host zircon from different mafic and felsic rocks of the Bushveld Complex (BC), South Africa. Samples include rutile-bearing cumulate rocks of the Marginal and Critical zones, as well as rutile-free, magnetite-ilmenite-titanite-bearing diorites and granites of the Upper Zone, Rashoop Granophyre and Lebowa Granite Suite. All melt inclusions, irrespective of rock type, have rhyolitic compositions with SiO 2 contents ranging from 65 to 78 wt.%, and H 2 O from 1.6 to 4.0 wt.%, whereas trace element contents differ systematically between rock types. In rutile-bearing mafic rocks, melt inclusions commonly show higher Ti contents (>800 ppm), higher Th/U ratios (up to 38), and lower REE contents (ƩREE < 150 ppm) compared to those in rutile-free mafic and felsic rocks (Ti < 800 ppm; Th/U < 5; ƩREE > 150 ppm). Liquidus temperatures of melt inclusions obtained from normative Qz-Ab-Or and rhyolite-MELTS modelling indicate melt entrapment mostly at 930–850 °C (at 200 MPa), tailing down in some samples to 700 °C. For rutile-bearing rocks, these temperatures overlap with those obtained by TiO 2 -in-melt and Ti-in-zircon geothermometry. For all rutile-free mafic and felsic rocks, reduced TiO 2 activities of a TiO 2 ∼ 0.3 are required for Ti-in-zircon geothermometry, and TiO 2 rutile ∼ 30 wt.% for TiO 2 saturation geothermometry, to match temperatures from other geothermometers. Furthermore, partition coefficients obtained from melt inclusion - host zircon pairs are within error identical for mafic and felsic rocks and also reveal no systematic dependency on melt inclusion size, composition and entrapment temperature. The results of this study demonstrate that melt inclusions in zircon are a powerful tool for geothermometry and to constrain magma compositions, H 2 O contents, and TiO 2 activities, which are critical for the understanding of magmatic processes shaping Earth's crust. [ABSTRACT FROM AUTHOR]

The Toba Caldera on Sumatra, Indonesia is the host of the Young Toba eruption (∼74 ka), globally one of the largest and most recognized eruptions during the Quaternary and regionally concentrated in the eastern Indian Ocean. Three older deposits (Middle, and Old Toba Tuff as well as Haranggaol Dacite Tuff) are also attributed to Toba caldera, with their eruption products distributed over the Indian Ocean. We present the Quaternary marine tephra record from an array of 14 sites and 28 holes from deep ocean drilling programs, complementing earlier work on distal to ultra-distal Indian Ocean sediment cores and terrestrial distribution data of Toba deposits. A unique set of major and trace element glass-shard compositions on 115 primary ash layers together with glass shard morphologies, core pictures and statistical analysis support geochemical fingerprinting between marine tephra layers and known deposits from Toba and five so far unidentified medium to large eruptions assigned to northern Sumatra. Additionally, zircon crystallization ages have been determined for the Haranggaol Dacite Tuff resulting in a new maximum eruption age of 1.42 ± 0.034 Ma. Tephra volumes and magma masses for the (co-ignimbrite) fallout are estimated based on the compiled marine tephra distribution that are complemented by published proximal ignimbrite volumes. For YTT the resulting tephra and DRE volumes of 5600 km3 and 3600 km3, respectively, are in between the previous estimates. For MTT (253 km3 DRE), ODT (1550 km3 DRE), HDT (129 km3 DRE), and the five additionally identified eruptions from Northern-Sumatran volcanoes, new magma volumes have been determined. Overall, the Indian Ocean tephra record reveals in one large eruption every 200 kyr in the Quaternary that is derived from northern Sumatra. The Toba Caldera on Sumatra, Indonesia, is a famous spot for volcanism since it is the host of one of the largest and most recognized eruptions on the world, the ∼74 ka Young Toba supereruption. It produced widespread volcanic particles (volcanic ash) that were distributed around the globe by winds, but most deposits are concentrated in the eastern Indian Ocean. Next to the Young Toba Tuff (YTT), three older deposits from probably similar large eruptions are known from this caldera that are also found as ash layers in the Indian Ocean. We investigated this marine tephra record, including 28 locations from the three phases of the deep ocean drilling program (DSDP, ODP, IODP), and created a unique set of glass-shard trace element (LA-ICP-MS) compositions that complements our major element (EMP) data on 115 primary ash layers. Comparing these compositions between the different marine locations and to known terrestrial deposits of the Toba eruptions is done by geochemical fingerprinting where the characteristic chemical "fingerprint" of marine ash layers is correlated between oceanic and to on-land deposits to find out from which eruption it originated. Glass shard morphologies, core pictures and statistical analysis complement this approach to support the correlations to four known tephras from Toba (Young, Middle, and Old Toba Tuff, as well as Haranggaol Dacite Tuff) and five so far unidentified eruptions from Northern Sumatra. The distribution of all tephras in the Indian Ocean allows to estimate erupted volumes by mapping out the occurrence and thicknesses of the tephras on the seafloor using drill cores. The resulting magma volumes amount to, for example, between 3600 km3 and 129 km3 magma for Young, Middle, and Old Toba Tuff as well as the Haranggaol Dacitic Tuff. Together with the five additionally identified (northern)Sumatra eruptions, these results indicate that one large eruption has happened every 200 kyr in northern Sumatra over the last 2.4 Ma. • Quaternary marine tephrostratigraphy of very large eruptions for the Eastern Indian Ocean • Chemical fingerprinting of marine tephras between each other and to terrestrial Toba deposits • Revised and new volume estimations for large Northern Quaternary Sumatran eruptions and respective repose times [ABSTRACT FROM AUTHOR]

Provenance studies of widely distributed tephra deposits are important to deduce systematic changes in the source, size, distribution, and temporal variation of regional explosive volcanism. Long-term deep ocean drilling sedimentary records are particularly useful for these kind of studies. In this study, we establish a robust tephrochronostratigraphy for 235 primary marine tephra layers collected during International Ocean Discovery Program Expeditions 353, 354, and 362, complemented by older drill cores from Deep Sea Drilling Program and Ocean Drilling Program Legs 22, 119, 120, 121, and 183. We infer at least two major phases of highly explosive arc volcanism during the Early Miocene to Pleistocene, as well as three episodes related to explosive ocean island volcanism located in the Kerguelen plateau, the Broken Ridge, and close to Réunion reaching back to the Paleogene. Twenty-two widespread arc-derived tephra layers from individual eruptions can be correlated by geochemical fingerprinting between multiple holes. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence including four new U Pb zircon ages. Provenance analysis of the marine tephra layers, which is based on glass composition, assign eleven of these layers to a Toba-like source, ranging from 24 Ma to 75 ka, with the youngest correlative being Young Toba Tuff. Based on distribution pattern, thickness decay, and compositional evidence another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance. First-order minimum eruptive volume estimates for the Neogene tephra layers imply eruptive magnitudes ranging from M = 6.5 to M = 7.5, proving a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene, as previously known from the Quaternary. Knowing the origin of large volcanic eruptions is important to deduce systematic changes in the source, size, distribution, and changes of regional explosive volcanism. In this study we use widely dispersed marine volcanic deposits in the Indian Ocean, so-called marine tephra layers, to reconstruct the history of a) Sumatran highly explosive eruptions over the last 24 Ma, and b) ocean island volcanism frequently observed in the Indian Ocean. The marine deposits are often the only evidence of major eruptions in the past because respective volcanic edifices and terrestrial deposits are often destroyed by subsequent eruptions, eroded or overlain by younger deposits. Deep ocean drilling provides the unique possibility to overcome these problems by recovering long, tephra-bearing marine sediment sequences in the drill cores. We present the results for 235 primary marine tephra layers that have been collected during eight deep drilling campaigns in the Indian Ocean. Twenty-two widespread connections of arc-derived tephra layers are established by comparing distinctive geochemical fingerprints of the tephras between multiple locations. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence. The origin of these marine tephra layers is determined based on the unique glass compositions of individual volcanoes and eruptions, assigning 11 of these layers to a Toba-Caldera-like source ranging from 24 Ma to 75 ka, with the youngest correlative being the iconic Young Toba Tuff. Another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance. Our record demonstrates a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene. We additionally infer (1) at least two major phases of highly explosive arc volcanism from the Sumatra-Andamen volcanic chain during Early Miocene to Pleistocene times, and (2) three episodes related to explosive ocean island volcanism found in the Kerguelen plateau, the Broken Ridge, and close to Réunion. • Cenozoic marine tephrostratigraphy and provenance of large explosive eruptions for the Eastern Indian Ocean • Long-term eruptive history for large explosive eruptions • Temporal compositional variations in explosive arc and ocean island volcanism of the Indian Ocean tephra inventory [ABSTRACT FROM AUTHOR]

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. • New and updated ages for explosive eruptions from Amatitlán caldera. • Zircon double-dating suggests a much younger eruptive history. • Existing plagioclase Ar eruption ages are ca. 26 to 70 kyr older than ZDD. • New eruption history suggests a shorter recurrence interval of ca. 17–24 kyr. [ABSTRACT FROM AUTHOR]

Sabalan Volcano (NW Iran) is an isolated voluminous (4821 m elevation; > 800 km 2 ) composite volcano that is located within the Arabia-Eurasia collision zone. Its edifice was assembled by recurrent eruptions of trachyandesite and dacite magma falling into a relatively restricted compositional range (56–67% SiO 2 ) with high-K calc-alkaline and adakitic trace element (Sr/Y) signatures. Previous K-Ar dating suggested protracted eruptive activity between 5.6 and 1.4 Ma, and a two stage evolution which resulted in the construction of the Paleo- and Neo-Sabalan edifices, respectively. The presence of a topographic moat surrounding Neo-Sabalan and volcanic breccias with locally intense hydrothermal alteration are indicative of intermittent caldera collapse of the central part of Paleo-Sabalan. Volcanic debris-flow and debris-avalanche deposits indicate earlier episodes of volcanic edifice collapse during the Paleo-Sabalan stage. In the Neo-Sabalan stage, three dacitic domes extruded to form the summits of Sabalan (Soltan, Heram, and Kasra). Ignimbrites and minor pumice fall-out deposits are exposed in strongly dissected drainages that in part have breached the caldera depression. Lavas and pyroclastic rocks are varyingly porphyritic with Paleo-Sabalan rocks being trachyandesites carrying abundant phenocrysts (plagioclase + amphibole + pyroxene + biotite). The Neo-Sabalan rocks are slightly more evolved and include dacitic compositions with phenocrysts of plagioclase + amphibole ± alkali-feldspar ± quartz. All Sabalan rock types share a common accessory assemblage (oxides + apatite + zircon). High spatial resolution and sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry yielded two clusters of zircon ages which range from 4.5 to 1.3 Ma and 545 to 149 ka, respectively (all ages are averages of multiple determinations per sample). U-Th zircon geochronology for selected Neo-Sabalan rocks agrees with the U-Pb ages, with the youngest zircon rims dating to ca. 110 ka. Because zircon crystallization predates eruption, this age represents the upper limit for the youngest eruptions of Sabalan. Valley-filling ignimbrites yielded variable U-Pb zircon ages which argue against these pyroclastic rocks being generated in a single caldera forming event. These results indicate that eruptions occurred more recently than previously indicated by K-Ar dating. Paleo-Sabalan and Neo-Sabalan volcanic rocks have similar geochemical characteristics, including enrichment of LILE and LREE relative to HFSE and HREE, respectively, and prominent negative Ti, Nb, and Ta anomalies. The trachyandesitic to dacitic rocks of Sabalan also share negative Eu anomalies. This, together with horizontal or slightly increasing Y vs. Rb trends, indicates fractionation of plagioclase-amphibole or plagioclase-clinopyroxene assemblages with negligible crustal assimilation (based on low and invariant Rb/Th). High degrees of mantle partial melting are inferred from high (La/Yb) N (from 28 to 48). Overall, the subduction-affinity of Sabalan volcanic rocks agrees with models of melt generation following a Quaternary slab break-off event coeval with continental collision. [ABSTRACT FROM AUTHOR]

We document the recent reappearance of anadromous sockeye salmon () that were thought to have been extirpated by the construction of hydroelectric dams on the Coquitlam and Alouette rivers in British Columbia, Canada, in 1914 and 1927, respectively. Unexpected downstream migrations of juveniles during experimental water releases into both rivers in 2005 and 2006 preceded upstream return migrations of adults in 2007 and 2008. Genetic (microsatellite and mitochondrial DNA) markers and stable isotope (δ34S and 87Sr/86Sr) patterns in otoliths confirm that both the juvenile downstream migrants and adult upstream migrants were progeny of nonanadromous sockeye salmon (kokanee) that inhabit Coquitlam and Alouette reservoirs. Low genetic diversity and evidence of genetic bottlenecks suggest that the kokanee populations in both reservoirs originated from relatively few anadromous individuals that residualized after downstream migration was largely prevented by the construction of dams. Once given an opportunity for upstream and downstream migration, both populations appear capable of reverting to a successful anadromous form, even after 25 generations. [ABSTRACT FROM AUTHOR]

Abstract: Phengite-bearing metasedimentary sequences preserving relict glaucophane from Serifos, western Aegean, are indicative of high-pressure conditions during Cycladic blueschist metamorphism. Depth-profiling and conventional SIMS U–Pb geochronology and O-isotope analysis on zircon from highly strained orthogneisses at the base of the sequence reveal xenocrystic zircon with varying degrees of recrystallization. One end-member population has needle-like or prismatic morphologies, is internally oscillatory-zoned, with little to no rim material created during recrystallization. These zircons yield Triassic to Carboniferous ages, elevated Th/U, and δ18O mostly ranging between ~4 and 11‰. In marked contrast, a separate zircon population has a spongy structure created by complete recrystallization of the pre-existing crystal. These zircons possess low Th/U and flat HREE patterns, and yield Eocene ages with δ18O ~7‰. Chondrite-normalized REE profiles are extremely depleted. Within this spectrum, other zircons show variable states of recrystallization and mixed ages. Regression of U–Pb data from three mylonitic orthogneiss samples that exhibit near complete recrystallization and similar age-depth profiles yields c. 40Ma ages. These new data are the first geochronological constraints that successfully demonstrate an Eocene metamorphic event in the western Cyclades, and new 40Ar/39Ar phengitic mica ages of 38–32Ma presented here suggest the metamorphic wedge was exhumed into the shallow crust shortly thereafter. [Copyright &y& Elsevier]

Abstract: The Kamchatka Peninsula in far eastern Russia represents the most volcanically active arc in the world in terms of magma production and the number of explosive eruptions. We investigate large-scale silicic volcanism in the past several million years and present new geochronologic results from major ignimbrite sheets exposed in Kamchatka. These ignimbrites are found in the vicinity of morphologically-preserved rims of partially eroded source calderas with diameters from ∼2 to ∼30km and with estimated volumes of eruptions ranging from 10 to several hundred cubic kilometers of magma. We also identify and date two of the largest ignimbrites: Golygin Ignimbrite in southern Kamchatka (0.45Ma), and Karymshina River Ignimbrites (1.78Ma) in south-central Kamchatka. We present whole-rock geochemical analyses that can be used to correlate ignimbrites laterally. These large-volume ignimbrites sample a significant proportion of remelted Kamchatkan crust as constrained by the oxygen isotopes. Oxygen isotope analyses of minerals and matrix span a 3‰ range with a significant proportion of moderately low-δ 18O values. This suggests that the source for these ignimbrites involved a hydrothermally-altered shallow crust, while participation of the Cretaceous siliceous basement is also evidenced by moderately elevated δ 18O and Sr isotopes and xenocryst contamination in two volcanoes. The majority of dates obtained for caldera-forming eruptions coincide with glacial stages in accordance with the sediment record in the NW Pacific, suggesting an increase in explosive volcanic activity since the onset of the last glaciation 2.6Ma. Rapid changes in ice volume during glacial times and the resulting fluctuation of glacial loading/unloading could have caused volatile saturation in shallow magma chambers and, in combination with availability of low-δ 18O glacial meltwaters, increased the proportion of explosive vs effusive eruptions. The presented results provide new constraints on Pliocene–Pleistocene volcanic activity in Kamchatka, and thus constrain an important component of the Pacific Ring of Fire. [Copyright &y& Elsevier]

Abstract: Fluid infiltration of high-grade terrains is commonly difficult to track; however, the use of secondary ionization mass spectrometry (SIMS) depth profiling analysis of zircon in high-grade metamorphic rocks allows acquisition of micron-scale U–Pb geochronology, Ti in zircon thermometry, and oxygen isotope measurements that can be used to decipher temporal and physicochemical records of orogens. This investigation focuses on a migmatite dome in a Cordilleran metamorphic core complex that records a long history of partial melting, deformation, and fluid flow during crustal thickening and/or rapid orogenic collapse. SIMS depth-profiling analyses of the outermost rims of zircon and monazite from samples representing a range of crustal levels elucidate the nature of the deep crustal environment during the final stages of extension and orogenic collapse from 58 to 50 Ma, following a major episode of granitoid emplacement and partial melt crystallization. The results from ultrathin (0.25 to 5.00 µm) outer rims of zircon demonstrate that fluid infiltration driven by amphibolite facies metamorphic devolatilization and/or igneous crystallization persisted at deep crustal levels until just before the time that the rocks were rapidly exhumed to upper crustal levels. Collectively, the results indicate that metamorphic fluids continued to infiltrate the gneiss dome from ca. 58 to 50 Ma. The overlap in ages from the zircon rims and monazite with argon cooling ages suggests that the dome cooled rapidly from >650 °C to 300 °C from 51–47 Ma. The results further demonstrate that the evolution of high-grade terrains, including the fluid history, can be revealed in unprecedented detail through the combination of depth profiling analyses of U–Pb age, Ti thermometry, and O isotopes. [Copyright &y& Elsevier]

Rhyolitic volcanism can provide important information about the mechanisms by which highly-evolved crystal-poor melts can be extracted from silicic crystal-mush reservoirs. In the Altiplano-Puna plateau (Central Andes), rhyolites are volumetrically less abundant than the high-volume, crystal-rich intermediate products emitted during the ignimbritic flare-up (ca. 10–1 Ma), and their geological and temporal relation with the widespread, upper crustal, dacitic mush systems is not well constrained. We studied the isotopic (U Pb ages), trace (U, Th, Hf, Y, Ti, P) and rare earth element compositions of zircon contained in the rhyolitic products of the Ramadas Volcanic Centre (late Miocene), which erupted extremely-aphyric, garnet-bearing tubular pumice during a single Plinian event (Corte Blanco Tuff; northern Puna plateau). Results reveal a complex pre-eruptive magmatic history characterized by variable crystallization conditions existing at different times within an upper-crustal crystal-mush reservoir. The unmixing model applied to magmatic zircon sharing textural and geochemical features (oscillatory texture, Th/U = 0.2–0.6; Eu/Eu* = 0.1–0.7) indicates the existence of at least two mush-related crystallization events, which are separated by a protracted hiatus (ca. 2 Ma), and are supported by independent isotopic ages. An episode of zircon crystallization (average disequilibrium-corrected 206Pb/238U age of 9.06 ± 0.19 Ma) coincides with the ages determined for accessory phases associated with garnet in pumice samples (9.163 ± 0.037 Ma, U Pb age determination on zircon; 8.70 ± 0.23 Ma, U-Th-Pb age determination on monazite). A further zircon crystallization event is recorded at ca. 6.64 ± 0.12 Ma, which is concordant with published radiometric ages dating the eruption at 6.3 ± 0.3 Ma (average 40Ar/39Ar age of glass shards from distal locations) and at 6.63 ± 0.28 Ma (fission track age of proximal obsidian). The existence of a late-stage to hydrothermal crystallization event is evident from another zircon population with low Th/U ratios (< 0.1) and a 206Pb/238U age of 6.514 ± 0.058 Ma, which crystallized in cold and highly-evolved parts of the reservoir resulting in negative Eu/Eu* and Ti depletion in zircon before these crystals were recycled into the erupting magma. The extreme aphyric character of the rhyolitic products and the nearly-complete lack of phenocrysts and glomerocrysts despite their evolved composition indicate that the Plinian eruption was preceded by effective extraction of crystal-poor melts from the mush zone, during which only micrometric antecrystic minerals (≤ 200 μm) were incorporated. Gas filter-pressing, combined with a compressional local stress field, likely contributed to melt-crystal separation, which was favoured by high volatile contents (H 2 Omelt 3–5 wt%) and shallow emplacement levels (< 10 km). Finally, the distribution of the U-Pb ages of zircon antecrysts suggests a correlation between the evolution of the Ramadas magmatic system and the fluctuating pattern characterizing the Altiplano-Puna Volcanic Complex flare-up activity, highlighting a possible geological and temporal connection between rhyolitic volcanism and the widespread dacitic mush systems in this sector of the Puna plateau. • Extremely aphyric rhyolites with heterogeneous mineral accessory association • Mechanical extraction of eruptible rhyolitic magma from Puna plateau mush system • Pre-eruptive mixing of antecrysts with different crystallization histories • Repeated episodes of melts segregation separated by a regional magmatic hiatus [ABSTRACT FROM AUTHOR]