cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3453782.v1
title: Sedimentary provenance, age and possible correlation of the Iona Group SW Scotland

description: Most clast lithologies within the basal conglomerate of the Iona Group, exposed on Iona, Inner Hebrides, SW Scotland, resemble the adjacent Archaean–Palaeoproterozoic Lewisian Gneiss Complex, supporting the hypothesis that the Iona Group unconformably overlies Lewisian gneisses on Iona. Moreover, a whole-rock Sm–Nd t<sub>DM</sub> age of 2512 Ma from one of these clasts supports its lithological correlation with granitic pegmatites in the underlying gneisses, while a second quartz-rich paragneiss clast with a Sm–Nd t<sub>DM</sub> age of 2745 Ma, is similar to Lewisian paragneisses on Coll. However, whole-rock t<sub>DM</sub> ages of 1755–2060 Ma and pronounced <em>c</em>. 1780–1800 Ma peaks in U–Pb detrital zircon and titanite data for Iona Group metasediments suggest additional distal sources of Laurentian affinity including the Rhinns Complex as well as Labradorian, Pinwarian and Archaean detritus. The Iona Group was deposited and deformed after <em>c</em>. 1490 Ma and before <em>c</em>. 422 Ma, constrained by the youngest detrital zircon and titanite and the intrusion of the Ross of Mull Granite, respectively. The detrital data permit correlation of the Iona Group with the Colonsay Group and the Glenshirra Subgroup of the Dalradian Grampian Group, although correlation with parts of the Torridonian cannot be excluded.
DOI: 10.6084/m9.figshare.3453779
title: Magmatic volatile distribution as recorded by rhyolitic melt inclusions in the Taupo Volcanic Zone, New Zealand

description: The central Taupo Volcanic Zone (TVZ) is an actively rifting continental arc and is well known for its exceptionally high rate of rhyolitic magma generation and frequent caldera-forming eruptions. Two end-member types of rhyolites (R1 and R2) have been previously identified based on differences in their bulk-rock chemistry and mineral assemblage with hydrous phases crystallizing in the R1 type, which are not present or only rare in R2 rhyolites. Here we present new trace element and volatile data from rhyolitic melt inclusions measured in several representative eruptive deposits (R1 and R2 rhyolites) from the central TVZ to examine their volatile concentrations and origin. R1 and R2 show very distinct Cl concentrations, with R2 rhyolites being enriched in Cl by <em>c.</em> 1000 ppm. H<sub>2</sub>O is slightly higher in the R1 rhyolites, whereas CO<sub>2</sub> concentrations are similar between the two end-member types. The origin of these volatile disparities between R1 and R2 melts is assigned to differences in the initial bulk volatile content of the parental magma, possibly associated with distinct input of fluids from the subduction zone. These disparities in bulk volatile concentrations can lead to variations in relative timing of exsolution of volatile phase(s) prior to melt inclusion entrapment.
DOI: 10.17632/3sdss7h6ry.3
title: Data for: Decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle-fabric analysis

description: One of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement. Here we explore particle shape-fabric within samples from the column-collapse pyroclastic density current (PDC) deposits generated by the 18 May 1980 eruption of Mt. Saint Helens (MSH). Particle shape-fabric is the mutual alignment of particles within the samples, which is dependent of shearing conditions at the time of deposition. Here, particle shape-fabric is used to address the following hypotheses: (1) particle shape-fabric will align with previous interpretations of PDC flow direction during the 1980 event; (2) samples extracted from PDC deposits immediately above a basal contact will show higher extents of fabric development (i.e. clast alignment) relative to samples extracted well above the contact; and (3) samples extracted from the proximal bedded deposits, located on the steep flanks of the volcano, will have higher extents of fabric development relative to samples extracted from the massive facies found in the gently dipping pumice plain. We find that fabric orientations approximate previous flow direction interpretations well for massive PDC deposits, validating the method of using particle-shape fabric to determine flow direction. However, while samples extracted immediately above the PDC deposit-substrate contact do not show a higher measure of clast alignment relative to samples taken well above flow contacts, the typical clast bimodality suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs. Samples extracted from the proximal bedded deposits do not show higher extents of fabric development relative to the massive deposits, supporting previous interpretations that these deposits formed from a rapidly sedimenting, concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow. Finally, observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step-wise aggradation during deposition. This work demonstrates that particle shape-fabric analyses can aid in decoding PDC flow conditions, and future, complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear within the lower flow boundary zone of PDCs.
DOI: 10.6084/m9.figshare.3453779.v1
title: Magmatic volatile distribution as recorded by rhyolitic melt inclusions in the Taupo Volcanic Zone, New Zealand

description: The central Taupo Volcanic Zone (TVZ) is an actively rifting continental arc and is well known for its exceptionally high rate of rhyolitic magma generation and frequent caldera-forming eruptions. Two end-member types of rhyolites (R1 and R2) have been previously identified based on differences in their bulk-rock chemistry and mineral assemblage with hydrous phases crystallizing in the R1 type, which are not present or only rare in R2 rhyolites. Here we present new trace element and volatile data from rhyolitic melt inclusions measured in several representative eruptive deposits (R1 and R2 rhyolites) from the central TVZ to examine their volatile concentrations and origin. R1 and R2 show very distinct Cl concentrations, with R2 rhyolites being enriched in Cl by <em>c.</em> 1000 ppm. H<sub>2</sub>O is slightly higher in the R1 rhyolites, whereas CO<sub>2</sub> concentrations are similar between the two end-member types. The origin of these volatile disparities between R1 and R2 melts is assigned to differences in the initial bulk volatile content of the parental magma, possibly associated with distinct input of fluids from the subduction zone. These disparities in bulk volatile concentrations can lead to variations in relative timing of exsolution of volatile phase(s) prior to melt inclusion entrapment.
DOI: 10.6084/m9.figshare.3453776
title: The thermal history of the western Irish onshore

description: We present here a low-temperature thermochronological study that combines the apatite fission-track and (U + Th)/He dating methods with a pseudo-vertical sampling approach to generate continuous and well-constrained temperature–time histories from the onshore Irish Atlantic margin. The apatite fission-track and (U + Th)/He ages range from the Late Jurassic to Early Cretaceous and the mean track lengths are relatively short. Thermal histories derived from inverse modelling show that following post-orogenic exhumation the sample profiles cooled to <em>c</em>. 75 °C. A rapid cooling event to surface temperatures occurred during the Late Jurassic to Early Cretaceous and was diachronous from north to south. It was most probably caused by <em>c</em>. 2.5 km of rift-shoulder related exhumation and can be temporally linked to the main stage of Mesozoic rifting in the offshore basins. A slow phase of reheating during the Late Cretaceous and Early Cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in <em>c</em>. 1.5 km of burial. Our data imply a final pulse of exhumation in Neogene times, probably related to compression of the margin. However, it is possible that an Early Cenozoic cooling event, compatible with our data but not seen in our inverse models, accounts for part of the Cenozoic exhumation.
DOI: 10.6084/m9.figshare.3453776.v1
title: The thermal history of the western Irish onshore

description: We present here a low-temperature thermochronological study that combines the apatite fission-track and (U + Th)/He dating methods with a pseudo-vertical sampling approach to generate continuous and well-constrained temperature–time histories from the onshore Irish Atlantic margin. The apatite fission-track and (U + Th)/He ages range from the Late Jurassic to Early Cretaceous and the mean track lengths are relatively short. Thermal histories derived from inverse modelling show that following post-orogenic exhumation the sample profiles cooled to <em>c</em>. 75 °C. A rapid cooling event to surface temperatures occurred during the Late Jurassic to Early Cretaceous and was diachronous from north to south. It was most probably caused by <em>c</em>. 2.5 km of rift-shoulder related exhumation and can be temporally linked to the main stage of Mesozoic rifting in the offshore basins. A slow phase of reheating during the Late Cretaceous and Early Cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in <em>c</em>. 1.5 km of burial. Our data imply a final pulse of exhumation in Neogene times, probably related to compression of the margin. However, it is possible that an Early Cenozoic cooling event, compatible with our data but not seen in our inverse models, accounts for part of the Cenozoic exhumation.
DOI: 10.6084/m9.figshare.3453770
title: Marine cements reveal the structure of an anoxic, ferruginous Neoproterozoic ocean

description: Neoproterozoic oceans provided the setting for the rise of animals, yet little is known of their chemical composition. Marine carbonates from the Cryogenian Oodnaminta Reef Complex, South Australia, reveal the chemical structure of a Neoproterozoic ocean. Pseudo-depth profiles from shallow- to deep-water reef facies have been constructed from geochemical and sedimentological analysis of marine cements. Evidence suggests that under a peritidal oxic–anoxic chemocline, the water column was largely anoxic, strongly ferruginous and had a chemistry profoundly different from that of modern seawater. These geochemical data suggest early Archaean-like conditions for this late Cryogenian ocean, posing problems for metazoan evolution in extremely anoxic conditions.
DOI: 10.6084/m9.figshare.3453767
title: Alpine Tethys closure as revealed by amphibole-rich mafic and ultramafic rocks from the Adamello and the Bergell intrusions (Central Alps)

description: U–Pb ages and Hf isotope data were obtained for zircon from amphibole-rich mafic to ultramafic rocks from the Adamello batholith and the Bergell pluton, the largest Palaeogene intrusions of the Alpine Orogen. The <sup>206</sup>Pb/<sup>238</sup>U age pattern of U–Pb concordant dates from the Adamello mafic rock shows a major crystallization event at <em>c</em>. 41 Ma and older age peaks at <em>c</em>. 50 and <em>c</em>. 45 Ma. Hornblendite and amphibole gabbro samples of the Adamello batholith have zircon with initial ϵHf of <em>c</em>. +9.0 and <em>c</em>. +7.0, respectively. Amphibole gabbro and diorite samples of the Bergell pluton yield a younger age of <em>c</em>. 31 Ma and have zircon with lower initial ϵHf (<em>c</em>. +4.0). We propose that the amphibole-rich rocks from the Adamello batholith originated from a depleted mantle source activated by the subduction of the Ligurian–Piedmontese Basin. The amphibole-rich rocks from the Bergell pluton formed 10–15 Ma later than the Adamello counterparts by melts derived from a mantle sector metasomatized by the subduction of the Valais Basin. The enriched Hf isotopic signature of the amphibole-rich rocks from the Bergell pluton is therefore interpreted to reflect the peculiar lithostratigraphy of the Valais Basin or a primary feature of the newly activated mantle source.
DOI: 10.6084/m9.figshare.3453767.v1
title: Alpine Tethys closure as revealed by amphibole-rich mafic and ultramafic rocks from the Adamello and the Bergell intrusions (Central Alps)

description: U–Pb ages and Hf isotope data were obtained for zircon from amphibole-rich mafic to ultramafic rocks from the Adamello batholith and the Bergell pluton, the largest Palaeogene intrusions of the Alpine Orogen. The <sup>206</sup>Pb/<sup>238</sup>U age pattern of U–Pb concordant dates from the Adamello mafic rock shows a major crystallization event at <em>c</em>. 41 Ma and older age peaks at <em>c</em>. 50 and <em>c</em>. 45 Ma. Hornblendite and amphibole gabbro samples of the Adamello batholith have zircon with initial ϵHf of <em>c</em>. +9.0 and <em>c</em>. +7.0, respectively. Amphibole gabbro and diorite samples of the Bergell pluton yield a younger age of <em>c</em>. 31 Ma and have zircon with lower initial ϵHf (<em>c</em>. +4.0). We propose that the amphibole-rich rocks from the Adamello batholith originated from a depleted mantle source activated by the subduction of the Ligurian–Piedmontese Basin. The amphibole-rich rocks from the Bergell pluton formed 10–15 Ma later than the Adamello counterparts by melts derived from a mantle sector metasomatized by the subduction of the Valais Basin. The enriched Hf isotopic signature of the amphibole-rich rocks from the Bergell pluton is therefore interpreted to reflect the peculiar lithostratigraphy of the Valais Basin or a primary feature of the newly activated mantle source.
DOI: 10.6084/m9.figshare.3453764
title: Effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics: Gunung Merapi 2010 eruption

description: In 2010, Gunung Merapi (Central Java, Indonesia) generated two violent eruption sequences on 26 October and 5 November culminating in widespread pyroclastic density currents (PDCs) associated with the destruction of lava domes. Tephra from PDC deposits were analysed to examine pre-dome collapse volatile behaviour and evidence of carbonate assimilation. Secondary-ion mass spectroscopy (SIMS) depth profiles of plagioclase phenocrysts reveal that the <sup>7</sup>Li/<sup>30</sup>Si ratios in 26 October products are higher in the glass compared to the crystal, indicating a build-up of Li in the groundmass not observed in the 5 November samples. Higher Li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 October explosion, which was only captured through the behaviour of quickly diffusing Li and not H<sub>2</sub>O. Following the explosion-induced decompression, juvenile magma rapidly ascended in great volume to generate extremely destructive PDCs following subsequent dome collapses, particularly on 5 November. Additionally, 26 October tephras contain carbonate grains in the ash component and abundant CO<sub>2</sub> within the lava lapilli groundmass glass, which supports previous studies indicating assimilation of calc-silicate lithologies by the Merapi magma at depth in the plumbing system prior to the onset of 2010 activity.
DOI: 10.6084/m9.figshare.3453764.v1
title: Effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics: Gunung Merapi 2010 eruption

description: In 2010, Gunung Merapi (Central Java, Indonesia) generated two violent eruption sequences on 26 October and 5 November culminating in widespread pyroclastic density currents (PDCs) associated with the destruction of lava domes. Tephra from PDC deposits were analysed to examine pre-dome collapse volatile behaviour and evidence of carbonate assimilation. Secondary-ion mass spectroscopy (SIMS) depth profiles of plagioclase phenocrysts reveal that the <sup>7</sup>Li/<sup>30</sup>Si ratios in 26 October products are higher in the glass compared to the crystal, indicating a build-up of Li in the groundmass not observed in the 5 November samples. Higher Li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 October explosion, which was only captured through the behaviour of quickly diffusing Li and not H<sub>2</sub>O. Following the explosion-induced decompression, juvenile magma rapidly ascended in great volume to generate extremely destructive PDCs following subsequent dome collapses, particularly on 5 November. Additionally, 26 October tephras contain carbonate grains in the ash component and abundant CO<sub>2</sub> within the lava lapilli groundmass glass, which supports previous studies indicating assimilation of calc-silicate lithologies by the Merapi magma at depth in the plumbing system prior to the onset of 2010 activity.
DOI: 10.6084/m9.figshare.3453761
title: The 1970 eruption on Deception Island (Antarctica): eruptive dynamics and implications for volcanic hazards

description: In the southern winter of 1970, a phreatomagmatic eruption occurred in the northern part of Deception Island (South Shetland Archipelago, Antarctic Peninsula). The eruption, with no eye-witnesses to the event, occurred in the same general area as the 1967 eruption, but with new, more widely distributed vents. Two contrasting groups of craters were formed in the 1970 eruption, showing that different active fissures and eruptive dynamics were operating. One group consists of ‘maar-like’ craters, whereas the other comprises conical edifices. The 1970 eruption can be classified as volcanic explosivity index (VEI) 3, with mainly phreatomagmatic phases that generated a bulk volume of about 0.1 km<sup>3</sup> of pyroclastic material and an eruptive column at least 10 km high, from which fallout deposits are recognized more than 100 km to the NE. The 1970 eruption was similar to that of 1967 and together these two eruptive events show how eruption dynamics can be controlled by the uppermost part of the volcano substrate and the width and orientation of the eruptive fissure. These influence magma–water interaction and hence may imply different eruptive phases and associated volcanic hazards.
DOI: 10.6084/m9.figshare.3453761.v1
title: The 1970 eruption on Deception Island (Antarctica): eruptive dynamics and implications for volcanic hazards

description: In the southern winter of 1970, a phreatomagmatic eruption occurred in the northern part of Deception Island (South Shetland Archipelago, Antarctic Peninsula). The eruption, with no eye-witnesses to the event, occurred in the same general area as the 1967 eruption, but with new, more widely distributed vents. Two contrasting groups of craters were formed in the 1970 eruption, showing that different active fissures and eruptive dynamics were operating. One group consists of ‘maar-like’ craters, whereas the other comprises conical edifices. The 1970 eruption can be classified as volcanic explosivity index (VEI) 3, with mainly phreatomagmatic phases that generated a bulk volume of about 0.1 km<sup>3</sup> of pyroclastic material and an eruptive column at least 10 km high, from which fallout deposits are recognized more than 100 km to the NE. The 1970 eruption was similar to that of 1967 and together these two eruptive events show how eruption dynamics can be controlled by the uppermost part of the volcano substrate and the width and orientation of the eruptive fissure. These influence magma–water interaction and hence may imply different eruptive phases and associated volcanic hazards.
DOI: 10.6084/m9.figshare.3453758
title: Interaction of arc magmas with subvolcanic hydrothermal systems: insights from compositions and metasomatic textures of olivine crystals in fresh basalts of Daisen and Mengameyama, Western Honshu, Japan

description: Pleistocene basalts from Daisen and Mengameyama in the SW Japan volcanic arc of western Honshu are characterized by an abundance of olivine crystals with Fe-rich rims. At Daisen, these have previously been interpreted to have formed from their host melt by equilibrium crystal fractionation and by disequilibrium fractionation during supercooling. Here we use combined electron probe microanalysis, isotopography, transmission electron microscopy and selected area electron diffraction to show that crystal rims are significantly enriched in aluminium (up to <em>c.</em> 1 wt%) and hydrogen (up to <em>c.</em> 10 000 ppm) hosted in oriented low-density amorphous domains. These domains are interpreted to have formed by melting of deuteric and/or post-deuteric metasomatic alteration minerals upon uptake of older olivine crystals into fresh, initially aphyric host melts up to a few hours prior to eruption. It is argued that uptake of variably altered crystals into initially aphyric or sparsely phyric melts may be a common process at subduction zones, and can account for typical disequilibrium textures displayed by arc magmas erupted in SW Japan and elsewhere. Analyses of the altered crystal cargo in arc volcanic rocks therefore provides an important tool for understanding subvolcanic hydrothermal systems and the interaction of ascending melts with such systems.
DOI: 10.6084/m9.figshare.3453758.v1
title: Interaction of arc magmas with subvolcanic hydrothermal systems: insights from compositions and metasomatic textures of olivine crystals in fresh basalts of Daisen and Mengameyama, Western Honshu, Japan

description: Pleistocene basalts from Daisen and Mengameyama in the SW Japan volcanic arc of western Honshu are characterized by an abundance of olivine crystals with Fe-rich rims. At Daisen, these have previously been interpreted to have formed from their host melt by equilibrium crystal fractionation and by disequilibrium fractionation during supercooling. Here we use combined electron probe microanalysis, isotopography, transmission electron microscopy and selected area electron diffraction to show that crystal rims are significantly enriched in aluminium (up to <em>c.</em> 1 wt%) and hydrogen (up to <em>c.</em> 10 000 ppm) hosted in oriented low-density amorphous domains. These domains are interpreted to have formed by melting of deuteric and/or post-deuteric metasomatic alteration minerals upon uptake of older olivine crystals into fresh, initially aphyric host melts up to a few hours prior to eruption. It is argued that uptake of variably altered crystals into initially aphyric or sparsely phyric melts may be a common process at subduction zones, and can account for typical disequilibrium textures displayed by arc magmas erupted in SW Japan and elsewhere. Analyses of the altered crystal cargo in arc volcanic rocks therefore provides an important tool for understanding subvolcanic hydrothermal systems and the interaction of ascending melts with such systems.
DOI: 10.6084/m9.figshare.3453755
title: Late Jurassic amphibolite-facies metamorphism in the Intra-Pontide Suture Zone (Turkey): an eastward extension of the Vardar Ocean from the Balkans into Anatolia?

description: The palaeogeography of Neotethys during its closure is still a matter of debate. This study provides new insights into the Neotethys closure by the discovery in the Intra-Pontide Suture Zone (Turkey) of an accretionary complex that recorded a Late Jurassic (<em>c</em>. 163 Ma) amphibolite-facies metamorphism. Results are discussed in the framework of the accretionary events that occurred at the southern margin of Laurasia. The resulting picture supports a new model in which the Vardar suture zone, in the Balkans, and the Intra-Pontide Suture Zone, in Anatolia, represent remnants of the same elongate oceanic basin.