Garnet petrochronology reveals the lifetime and dynamics of phonolitic magma chambers at Somma-Vesuvius

Somma-Vesuvius is one of the most iconic active volcanoes with historic and archeological records of numerous hazardous eruptions. Petrologic studies of eruptive products provide insights into the evolution of the magma reservoir before eruption. Here, we quantify the duration of shallow crustal storage and document the evolution of phonolitic magmas before major eruptions of Somma-Vesuvius. Garnet uranium-thorium petrochronology suggests progressively shorter pre-eruption residence times throughout the lifetime of the volcano. Residence times mirror the repose intervals between eruptions, implying that distinct phonolite magma batches were present throughout most of the volcano’s evolution, thereby controlling the eruption dynamics by preventing the ascent of mafic magmas from longer-lived and deeper reservoirs. Frequent lower-energy eruptions during the recent history sample this deeper reservoir and suggest that future Plinian eruptions are unlikely without centuries of volcanic quiescence. Crystal residence times from other volcanoes reveal that long-lived deep-seated reservoirs and transient upper crustal magma chambers are common features of subvolcanic plumbing systems

Resolving the timescales of magmatic and hydrothermal processes associated with porphyry deposit formation using zircon U–Pb petrochronology

Understanding the formation of economically important porphyry Cu–Au deposits requires knowledge of the magmatic-to-hydrothermal processes that act within the much larger magmatic system and the timescales on which they occur. We apply high-precision zircon geochronology (chemical abrasion–isotope dilution–thermal ionisation mass spectrometry; CA–ID–TIMS) and spatially resolved zircon geochemistry (laser ablation inductively coupled plasma mass spectrometry; LA-ICP-MS) to constrain the magmatic evolution of the underlying magma reservoir at the Pliocene Batu Hijau porphyry Cu–Au deposit. We then use this extensive dataset to assess the accuracy and precision of different U–Pb dating methods of the same zircon crystals. Emplacement of the oldest pre- to syn-ore tonalite (3.736±0.023&thinsp;Ma) and the youngest tonalite porphyry to cross-cut economic Cu–Au mineralisation (3.646±0.022&thinsp;Ma) is determined by the youngest zircon grain from each sample, which constrains the duration of metal precipitation to fewer than 90±32&thinsp;kyr. Overlapping spectra of single zircon crystallisation ages and their trace element distributions from the pre-, syn and post-ore tonalite porphyries reveal protracted zircon crystallisation together with apatite and plagioclase within the same magma reservoir over &gt;300&thinsp;kyr. The presented petrochronological data constrain a protracted early &gt;200&thinsp;kyr interval of melt differentiation and cooling within a large heterogeneous magma reservoir, followed by magma storage in a highly crystalline state and chemical and thermal stability over several tens of thousands of years during which fluid expulsion formed the ore deposit. Irregular trace element systematics suggest magma recharge or underplating during this final short time interval. The comparison of high-precision CA–ID–TIMS results with in situ LA-ICP-MS and a sensitive high-resolution ion microprobe (SHRIMP) U–Pb geochronology data from the same zircon grains allows a comparison of the applicability of each technique as a tool to constrain dates and rates on different geological timescales. All techniques provide accurate dates but with different precision. Highly precise dates derived by the calculation of the weighted mean and standard error of the mean of the zircon dates obtained by in situ techniques can lead to ages of unclear geological significance that are older than the maximum ages of emplacement given by the CA–ID–TIMS ages of the youngest zircons in each sample. This lack of accuracy of the weighted means is due to the protracted nature of zircon crystallisation in upper crustal magma reservoirs, suggesting that standard errors should not be used as a means to describe the uncertainty in those circumstances. We conclude from this and similar published studies that the succession of magma and fluid pulses forming a single porphyry deposit and similarly rapid geological events are too fast to be reliably resolved by in situ U–Pb geochronology and that assessing the tempo of ore formation requires CA–ID–TIMS geochronology.</p

The Function of Hypoxia-Inducible Factor (HIF) Is Independent of the Endoplasmic Reticulum Protein OS-9

The protein “amplified in osteosarcoma-9” (OS-9) has been shown previously to interact with the prolyl hydroxylases PHD2 and PHD3. These enzymes initiate oxygen-dependent degradation of the α-subunit of hypoxia-inducible factor (HIF), a transcription factor that adapts cells to insufficient oxygen supply (hypoxia). A new model has been proposed where OS-9 triggers PHD dependent degradation of HIF-α. It was the aim of our study to define the molecular mode of action of OS-9 in the regulation of PHD and HIF activity. Although initial co-immunoprecipitation experiments confirmed physical interaction between OS-9 and PHD2, neither overexpression nor lentiviral inhibition of OS-9 expression affected HIF regulation. Subcellular localization experiments revealed a distinct reticular staining pattern for OS-9 while PHD2 was mainly localized in the cytoplasm. Further cell fractionation experiments and glycosylation tests indicated that OS-9 is a luminal ER protein. In vivo protein interaction analysis by fluorescence resonance energy transfer (FRET) showed no significant physical interaction of overexpressed PHD2-CFP and OS-9-YFP. We conclude that OS-9 plays no direct functional role in HIF degradation since physical interaction of OS-9 with oxygen sensing HIF prolyl hydroxylases cannot occur in vivo due to their different subcellular localization

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu–PGE–Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190–700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu–Ni–PGE sulfides which require very high R factors, and settling of sulfide liquids

Reworking subducted sediments in arc magmas and the isotopic diversity of the continental crust: The case of the Ordovician Famatinian crustal section, Argentina

International audienceSince the onset of plate tectonics, continents have evolved through a balance between crustal growth, reworking, and recycling at convergent plate margins. The term "reworking" involves the re-insertion of crustal material into pre-existing crustal volumes, while crustal growth and recycling respectively represent gains from and losses to the mantle. Reworking that occurs in the mantle wedge ("source" contamination from slab material) or within the upper plate ("path" contamination), will have contrasting effects on crustal evolution. However, due to limited access to deep crustal and mantle rocks, quantifying source vs. path contamination remains challenging. Based on the 4-dimensional record of the fossil (Ordovician) Famatinian continental arc (Argentina), we demonstrate that source contamination plays a dominant role in imprinting mafic to granitic rocks with crustal oxygen-hafnium (O-Hf) isotopic compositions. We argue that source contamination at convergent plate margins significantly increased the diversity of O-Hf isotopic signatures of continents over geologic time. Our interpretation implies that crustal evolution models attributing this isotopic diversity dominantly to intra-crustal reworking may be over-simplistic and may underestimate continental growth in the last 2.5 billion years

Geochronology and geochemistry data for the Elbrus, Tyrnyauz, and Chegem magmatic centers, Greater Caucasus, Russia

The dataset presented here is associated with the article “Young Silicic Magmatism of the Greater Caucasus, Russia with implication for its delamination origin based on zir- con petrochronology and thermomechanical modeling”[1] . We present detailed sample descriptions and source locations for the rocks from the Chegem, Tyrnyauz, and Elbrus volcanic center localities presented in that study. The dataset presents extensive isotope and trace element geochemistry of zircon crystals from these rocks, major phenocrysts, and whole rock O and H isotopic and elemental compositions. Zircon ages, trace element compositions, and Hf and O isotopic composi- tions were obtained by both laser ablation ICP-MS and sec- ondary ionization mass spectrometry in situ techniques and chemical abrasion isotope dilution-thermal ionization mass spectrometry techniques. We also present whole-rock ma- jor element compositions obtained by X-ray fluorescence and trace element compositions obtained by solution inductively- coupled plasma mass spectrometry. We also report δ18 O analyses of phenocrysts and groundmass in samples, δ18 O- δ13 C analyses of limestones and limestone xenoliths in the Chegem ignimbrite, and coupled δ18 O- δD- Delta17 O analyses of glass and groundmass of rock samples from the Chegem ign- imbrites that show abundant evidence of post-emplacement interaction with meteoric waters. To supplement the associ- ated study [1] , this article also includes field photographs, cathodoluminescence images of zircons, plots of trace ele- ment compositions in zircon, plots of stable isotopic vari- ations in Chegem ignimbrites vs. stratigraphy, and selected trace elemental whole-rock diagrams

Young Silicic Magmatism of the Greater Caucasus, Russia, with implication for its delamination origin based on zircon petrochronology and thermomechanical modeling

Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegemvolcanic centers just to the east of Europe's highest mountain and active volcano, Mount Elbrus. This represents one of the world's best-preserved examples of silicic magmatism in a continental collision environment. We report results of amulti-method zircon petrochronologic (U–Pb,O–Hf isotopes, trace elements) investigation of six ignimbrites, lavas, and associated granodioritic porphyries from these localities.We observe two pulses of magmatismat 2.92 and 1.98 Ma related to Chegemand Tyrnyauz, respectively. High precision CA-ID-TIMS dating of zircons fromthe top and bottomof the Chegem ignimbrite and its associated porphyry yield indistinguishable age spectra recording 160 kyr of magma assembly and differentiation, with 2.9181± 0.0014 Ma eruption age as is constrained by the youngest dated zircon population. Togetherwith overlapping O and Hf isotopic values, this suggests that they represent a large volume of pre-eruptively homogenized magma with ~20% crystals. Zircons have isotopically diverse cores (δ18O = +3.4–6.7‰, εHf = +0.8 to +5.6) while the rims (+5.75 ± 0.20‰, εHf = 3.3 ± 0.7) are in isotopic equilibriumwith associated unaltered glass and major phenocryst phases. The neighboring and younger ignimbrites and granites of the nearby Elbrus and Tyrnyauz centers have overlapping higher δ18O and lower εHf zircon values and cluster narrowly in age around 1.98 Ma, suggesting a common source for all these ignimbrites, likely in the Tyrnyauz area. Isotopic data for Chegem, Elbrus and Tyrnyauz zircons and rocks require the contribution of a high proportion (25–55%) of Paleozoic crust to magma petrogenesis. The origin of sudden spikes of voluminous silicic magmatism is further investigated using thermomechanical modeling of the collisional environment. We show that the voluminous silicic volcanism at Chegem, Tyrnyauz and Elbrus is best explained by heating of the lower crust by asthenospheric upwelling after a relict slab detached and sank into the mantle at approximately 5 Ma. This timing is coincident with both the beginning of rapid uplift of the Greater Caucasus and initiation of major volcanism. After this initial melting, continuing delamination of the lithosphere and lower crust from the subducting plate produced broad mantle melting and basaltic volcanism, potentially explaining continued regional-scale magmatism in both the Greater and Lesser Caucasus

Tracking the evolution of large-volume silicic magma reservoirs from assembly to supereruption

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Age of the magma chamber and its physicochemical state under Elbrus Greater Caucasus, Russia using zircon petrochronology and modeling insights

Abstract Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U–Th–Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km 3 /1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km 3 , temporally oscillating δ 18 O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km 3 of melt in a vertically extensive system) and the potential for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by ~ 10 3 to 10 5 years reflecting protracted dissolution–crystallization histories