cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454745
title: Petrology, Sr–Nd–Hf isotopic geochemistry and zircon chronology of the Late Palaeozoic volcanic rocks in the southwestern Tianshan Mountains, Xinjiang, NW China

description: The Late Palaeozoic volcanic rocks, mainly consisting of basalt, trachyte, trachy-andesite, andesite and rhyolite, widely distributed in the southwestern Tianshan Mountains, have been proven to be formed during Late Devonian to Late Carboniferous time (&gt;361–313 Ma) based on zircon sensitive high-resolution ion microprobe dating. The geochemistry demonstrates that the studied volcanic rocks represent a continental arc formed during the subduction of the Palaeo-southern Tianshan Ocean. The ε<sub>Hf(T)</sub> values of zircons in these volcanic rocks vary from +1.4 to +15.6 with weighted average values of +9.5 (Late Devonian), +8.9 (Early Carboniferous) and +10.3 (Late Carboniferous), suggesting a depleted mantle origin. However, the Late Devonian basaltic samples have negative ε<sub>Nd(T)</sub> values (from −5.16 to −3.07) and high initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7073–0.7098), whereas the Early Carboniferous volcanic rocks mostly have positive ε<sub>Nd(T)</sub> values (from −0.18 to +3.07) with low initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7044–0.7067), and the Late Carboniferous volcanic rocks are characterized by high ε<sub>Nd(T)</sub> values (+2.79 to +5.89) and low initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7032–0.7054). The assimilation–fractional crystallization (AFC) model is used to explain the isotope characteristics of the Late Devonian volcanic rocks in the southwestern Tianshan Mountains. Calculation shows that the Late Devonian samples could be formed by the AFC process between depleted mantle and continental crust. The Carboniferous basaltic rocks originated by partial melting of the mantle wedge.
DOI: 10.6084/m9.figshare.3454745.v1
title: Petrology, Sr–Nd–Hf isotopic geochemistry and zircon chronology of the Late Palaeozoic volcanic rocks in the southwestern Tianshan Mountains, Xinjiang, NW China

description: The Late Palaeozoic volcanic rocks, mainly consisting of basalt, trachyte, trachy-andesite, andesite and rhyolite, widely distributed in the southwestern Tianshan Mountains, have been proven to be formed during Late Devonian to Late Carboniferous time (&gt;361–313 Ma) based on zircon sensitive high-resolution ion microprobe dating. The geochemistry demonstrates that the studied volcanic rocks represent a continental arc formed during the subduction of the Palaeo-southern Tianshan Ocean. The ε<sub>Hf(T)</sub> values of zircons in these volcanic rocks vary from +1.4 to +15.6 with weighted average values of +9.5 (Late Devonian), +8.9 (Early Carboniferous) and +10.3 (Late Carboniferous), suggesting a depleted mantle origin. However, the Late Devonian basaltic samples have negative ε<sub>Nd(T)</sub> values (from −5.16 to −3.07) and high initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7073–0.7098), whereas the Early Carboniferous volcanic rocks mostly have positive ε<sub>Nd(T)</sub> values (from −0.18 to +3.07) with low initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7044–0.7067), and the Late Carboniferous volcanic rocks are characterized by high ε<sub>Nd(T)</sub> values (+2.79 to +5.89) and low initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.7032–0.7054). The assimilation–fractional crystallization (AFC) model is used to explain the isotope characteristics of the Late Devonian volcanic rocks in the southwestern Tianshan Mountains. Calculation shows that the Late Devonian samples could be formed by the AFC process between depleted mantle and continental crust. The Carboniferous basaltic rocks originated by partial melting of the mantle wedge.
DOI: 10.6084/m9.figshare.3454742
title: Eclogite–high-pressure granulite metamorphism records early collision in West Gondwana: new data from the Southern Brasília Belt, Brazil

description: Nappes in the southern sector of the Southern Brasília Belt record suturing of the Paranapanema Block and Socorro–Guaxupé Arc with a subducted passive margin on the western side of the São Francisco Craton. We report secondary ion mass spectrometry U–Pb zircon ages that for the first time constrain the age of: (1) retrograded eclogite from a block along the tectonic contact beneath the uppermost nappe in a stack of passive margin-derived nappes; (2) high-pressure granulite-facies metamorphism in the uppermost passive margin-derived nappe; (3) high-pressure granulite-facies metamorphism in the overlying arc-derived nappe. Rare zircons from a retrograded eclogite yield a <sup>206</sup>Pb/<sup>238</sup>U age of 678 ± 29 Ma, which we interpret as most likely to date close-to-peak-<em>P</em> metamorphism and to provide a minimum age for detachment of the overlying passive margin-derived nappe from the subducting plate. Zircon associated with ilmenite in samples from two structural levels in the passive margin-derived high-pressure granulite nappe yields <sup>206</sup>Pb/<sup>238</sup>U ages of 648 ± 12 and 647 ± 11 Ma, and Ti-in-zircon crystallization temperatures from <em>c</em>. 860 °C down to <em>c</em>. 785 °C, but skewed toward the lower part of the range. These data indicate zircon formation during cooling from around peak <em>T</em> to the solidus, consistent with the high-<em>T</em> retrograde <em>P</em>–<em>T</em> path deduced from microstructures linked to phase assemblage fields in isochemical phase diagrams. Rb–Sr multi-mineral–whole-rock isochrons from two samples from close to the bottom of this nappe date formation of a retrograde sillimanite-bearing penetrative fabric to <em>c</em>. 590 Ma at temperatures of <em>c</em>. 750 °C (based on Ti-in-quartz thermometry). Rare zircons from leucosome in high-pressure granulite from the overlying arc-derived nappe yield a <sup>206</sup>Pb/<sup>238</sup>U age of 622 ± 28 Ma and Ti-in-zircon crystallization temperatures from <em>c</em>. 970 °C down to <em>c</em>. 820 °C, which we interpret to record formation of zircon during cooling from peak high-pressure granulite-facies conditions. These ages indicate that the first stage of craton amalgamation in West Gondwana may have occurred earlier than previously inferred.
DOI: 10.6084/m9.figshare.3454742.v1
title: Eclogite–high-pressure granulite metamorphism records early collision in West Gondwana: new data from the Southern Brasília Belt, Brazil

description: Nappes in the southern sector of the Southern Brasília Belt record suturing of the Paranapanema Block and Socorro–Guaxupé Arc with a subducted passive margin on the western side of the São Francisco Craton. We report secondary ion mass spectrometry U–Pb zircon ages that for the first time constrain the age of: (1) retrograded eclogite from a block along the tectonic contact beneath the uppermost nappe in a stack of passive margin-derived nappes; (2) high-pressure granulite-facies metamorphism in the uppermost passive margin-derived nappe; (3) high-pressure granulite-facies metamorphism in the overlying arc-derived nappe. Rare zircons from a retrograded eclogite yield a <sup>206</sup>Pb/<sup>238</sup>U age of 678 ± 29 Ma, which we interpret as most likely to date close-to-peak-<em>P</em> metamorphism and to provide a minimum age for detachment of the overlying passive margin-derived nappe from the subducting plate. Zircon associated with ilmenite in samples from two structural levels in the passive margin-derived high-pressure granulite nappe yields <sup>206</sup>Pb/<sup>238</sup>U ages of 648 ± 12 and 647 ± 11 Ma, and Ti-in-zircon crystallization temperatures from <em>c</em>. 860 °C down to <em>c</em>. 785 °C, but skewed toward the lower part of the range. These data indicate zircon formation during cooling from around peak <em>T</em> to the solidus, consistent with the high-<em>T</em> retrograde <em>P</em>–<em>T</em> path deduced from microstructures linked to phase assemblage fields in isochemical phase diagrams. Rb–Sr multi-mineral–whole-rock isochrons from two samples from close to the bottom of this nappe date formation of a retrograde sillimanite-bearing penetrative fabric to <em>c</em>. 590 Ma at temperatures of <em>c</em>. 750 °C (based on Ti-in-quartz thermometry). Rare zircons from leucosome in high-pressure granulite from the overlying arc-derived nappe yield a <sup>206</sup>Pb/<sup>238</sup>U age of 622 ± 28 Ma and Ti-in-zircon crystallization temperatures from <em>c</em>. 970 °C down to <em>c</em>. 820 °C, which we interpret to record formation of zircon during cooling from peak high-pressure granulite-facies conditions. These ages indicate that the first stage of craton amalgamation in West Gondwana may have occurred earlier than previously inferred.
DOI: 10.6084/m9.figshare.3454739
title: Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK

description: The Late Jurassic was a time of increasing aridity in NW Europe. Here, a new clay mineral dataset is presented from a 600 m thick composite core through the Kimmeridge Clay Formation, southern England. Clay mineral assemblages comprise mainly illite and kaolinite, with minor randomly interstratified illite–smectite mixed-layer clays. SEM observations indicate that clay minerals are mainly detrital, except in silty strata of late Tithonian age, which contain abundant pore-filling kaolinite aggregates. Th/K ratios determined from gamma-ray spectrometry mirror palaeoclimatically significant variations in kaolinite/illite ratios, with notable exception where diagenetic kaolinite occurs. Comparison with age-equivalent strata identifies regional cyclic variations in clay minerals at the 100–300 m scale. Small-scale (10–20 m) variations in clay minerals and Th/K also occur. It is proposed that the region experienced progressively intense humidity through the Kimmeridgian, followed by a return to more arid conditions during the early Tithonian. Following a mid-Tithonian peak in aridity (the ‘Hudlestoni Event'), more humid climatic conditions returned prior to the development of latest Tithonian intense aridity. Late Jurassic climate was apparently subject to synchronously cyclic changes across a broad area of the Laurasian continent. Such changes could not have resulted from mountain building or continental rotations.
DOI: 10.6084/m9.figshare.3454739.v1
title: Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK

description: The Late Jurassic was a time of increasing aridity in NW Europe. Here, a new clay mineral dataset is presented from a 600 m thick composite core through the Kimmeridge Clay Formation, southern England. Clay mineral assemblages comprise mainly illite and kaolinite, with minor randomly interstratified illite–smectite mixed-layer clays. SEM observations indicate that clay minerals are mainly detrital, except in silty strata of late Tithonian age, which contain abundant pore-filling kaolinite aggregates. Th/K ratios determined from gamma-ray spectrometry mirror palaeoclimatically significant variations in kaolinite/illite ratios, with notable exception where diagenetic kaolinite occurs. Comparison with age-equivalent strata identifies regional cyclic variations in clay minerals at the 100–300 m scale. Small-scale (10–20 m) variations in clay minerals and Th/K also occur. It is proposed that the region experienced progressively intense humidity through the Kimmeridgian, followed by a return to more arid conditions during the early Tithonian. Following a mid-Tithonian peak in aridity (the ‘Hudlestoni Event'), more humid climatic conditions returned prior to the development of latest Tithonian intense aridity. Late Jurassic climate was apparently subject to synchronously cyclic changes across a broad area of the Laurasian continent. Such changes could not have resulted from mountain building or continental rotations.
DOI: 10.6084/m9.figshare.3454736
title: Smothering of microbial mats by macrobiota: implications for the Ediacara biota

description: Recent advances in understanding the preservation of the soft-bodied Neoproterozoic Ediacara biota have centred upon the role of microbes in casting the morphologies of static or dead macrobiota on the Precambrian sea floor. This experimental study explores the preservational effects brought about by the passive movement of dead macro-organisms upon a pre-established marine microbial mat under laboratory conditions. This demonstrates the potential for making multiple impressions of body tissues on the surface of microbial mats by means of passive transport alone. This throws doubt on the evidence for active feeding in Ediacaran fossils such as <em>Dickinsonia</em> and <em>Yorgia</em>.
DOI: 10.6084/m9.figshare.3454736.v1
title: Smothering of microbial mats by macrobiota: implications for the Ediacara biota

description: Recent advances in understanding the preservation of the soft-bodied Neoproterozoic Ediacara biota have centred upon the role of microbes in casting the morphologies of static or dead macrobiota on the Precambrian sea floor. This experimental study explores the preservational effects brought about by the passive movement of dead macro-organisms upon a pre-established marine microbial mat under laboratory conditions. This demonstrates the potential for making multiple impressions of body tissues on the surface of microbial mats by means of passive transport alone. This throws doubt on the evidence for active feeding in Ediacaran fossils such as <em>Dickinsonia</em> and <em>Yorgia</em>.
DOI: 10.6084/m9.figshare.3454733
title: Tectonomagmatic events during stretching and basin formation in the Labrador Sea and the Davis Strait: evidence from age and composition of Mesozoic to Palaeogene dyke swarms in West Greenland

description: Mesozoic to Palaeogene intrusive igneous rocks in West Greenland range from a large, coast-parallel dyke swarm to small, poorly defined dyke swarms or single intrusions. New age and geochemical data indicate that intrusion forms and melt compositions changed with time, dependent on changing stress fields and increasing lithospheric attenuation. During the period <em>c</em>. 220–150 Ma (Late Triassic to Late Jurassic) incipient stretching is reflected in the production of highly alkaline, volatile-rich melts formed in small volumes in the deep lithosphere. Around 150 Ma (Kimmeridgian), increased extension took place and melts were intruded in a 60 km long swarm of scattered alkaline dykes. In the Early Cretaceous, 140–133 Ma, the regional stress field was intense, upwelling asthenospheric mantle started to melt, and alkali basaltic magmas were emplaced in a 400 km long coastal dyke swarm parallel to large linear faults offshore. In the Palaeocene, continental break-up took place and flood basalts (62–60 Ma) were extruded in the Nuussuaq Basin. Large basalt sills and dykes extend the region with Palaeocene activity 150 km southwards and form a link between the Nuussuaq Basin and the Sisimiut Basin offshore. Dykes with ages of 57–51 Ma indicate widespread younger volcanic activity.
DOI: 10.6084/m9.figshare.3454733.v1
title: Tectonomagmatic events during stretching and basin formation in the Labrador Sea and the Davis Strait: evidence from age and composition of Mesozoic to Palaeogene dyke swarms in West Greenland

description: Mesozoic to Palaeogene intrusive igneous rocks in West Greenland range from a large, coast-parallel dyke swarm to small, poorly defined dyke swarms or single intrusions. New age and geochemical data indicate that intrusion forms and melt compositions changed with time, dependent on changing stress fields and increasing lithospheric attenuation. During the period <em>c</em>. 220–150 Ma (Late Triassic to Late Jurassic) incipient stretching is reflected in the production of highly alkaline, volatile-rich melts formed in small volumes in the deep lithosphere. Around 150 Ma (Kimmeridgian), increased extension took place and melts were intruded in a 60 km long swarm of scattered alkaline dykes. In the Early Cretaceous, 140–133 Ma, the regional stress field was intense, upwelling asthenospheric mantle started to melt, and alkali basaltic magmas were emplaced in a 400 km long coastal dyke swarm parallel to large linear faults offshore. In the Palaeocene, continental break-up took place and flood basalts (62–60 Ma) were extruded in the Nuussuaq Basin. Large basalt sills and dykes extend the region with Palaeocene activity 150 km southwards and form a link between the Nuussuaq Basin and the Sisimiut Basin offshore. Dykes with ages of 57–51 Ma indicate widespread younger volcanic activity.
DOI: 10.6084/m9.figshare.3454724
title: Late Devonian tetrapod habitats indicated by palaeosols in Pennsylvania

description: Late Devonian (Famennian) tetrapods from the Duncannon Member of the Catskill Formation, near Hyner (Pennsylvania, USA) have been found within palaeosols that offer a new line of evidence for their ancient environments. Hyner has yielded at least two fossil tetrapod species, <em>Hynerpeton basseti</em> and <em>Densignathus rowei</em>. Subhumid Vertisol palaeosols and semiarid Aridisol palaeosols alternate at Hyner, as in other Catskill Formation sedimentary cycles attributed to Milankovitch-eccentricity periods (100 ka). Tetrapods were found in palaeosols of subhumid, not semiarid, phases of 100 ka palaeoclimate cycles. In addition, palaeosols at Hyner record an unusually warm and wet climatic episode compared with other palaeosols of the Catskill Formation, and correlated with the European <em>Annulata</em> black shale event. Tetrapod bones are cracked and disarticulated in red palaeosols of an oxbow lake margin, as if victims of dry-season death, decay, and subaerial weathering. Vegetation-choked swales and floodplains would have afforded shelter from 3–4 m long predatory fish (<em>Hyneria lindae</em>) of open water, and offered food of large dead fish, small live fish, arachnids, myriapods and scorpions. If these early tetrapods lived on land at all, it was during wet seasons of feeding and breeding, rather than fatally dry seasons.
DOI: 10.6084/m9.figshare.3454724.v1
title: Late Devonian tetrapod habitats indicated by palaeosols in Pennsylvania

description: Late Devonian (Famennian) tetrapods from the Duncannon Member of the Catskill Formation, near Hyner (Pennsylvania, USA) have been found within palaeosols that offer a new line of evidence for their ancient environments. Hyner has yielded at least two fossil tetrapod species, <em>Hynerpeton basseti</em> and <em>Densignathus rowei</em>. Subhumid Vertisol palaeosols and semiarid Aridisol palaeosols alternate at Hyner, as in other Catskill Formation sedimentary cycles attributed to Milankovitch-eccentricity periods (100 ka). Tetrapods were found in palaeosols of subhumid, not semiarid, phases of 100 ka palaeoclimate cycles. In addition, palaeosols at Hyner record an unusually warm and wet climatic episode compared with other palaeosols of the Catskill Formation, and correlated with the European <em>Annulata</em> black shale event. Tetrapod bones are cracked and disarticulated in red palaeosols of an oxbow lake margin, as if victims of dry-season death, decay, and subaerial weathering. Vegetation-choked swales and floodplains would have afforded shelter from 3–4 m long predatory fish (<em>Hyneria lindae</em>) of open water, and offered food of large dead fish, small live fish, arachnids, myriapods and scorpions. If these early tetrapods lived on land at all, it was during wet seasons of feeding and breeding, rather than fatally dry seasons.
DOI: 10.6084/m9.figshare.3454718
title: High spatial resolution <sup>40</sup>Ar/<sup>39</sup>Ar dating of pseudotachylites: geochronological evidence for multiple phases of faulting within basement gneisses of the Outer Hebrides (UK)

description: Pseudotachylites within the Neoarchaean to Palaeoproterozoic basement of the Lewisian Gneiss Complex have been analysed using the high spatial resolution <sup>40</sup>Ar/<sup>39</sup>Ar UV laserprobe technique. It has been possible to measure <sup>40</sup>Ar/<sup>39</sup>Ar age and ‘apparent' age variations that would be beyond resolution by lower spatial resolution or bulk <sup>40</sup>Ar/<sup>39</sup>Ar dating methods. We report a range of complexities including significantly younger narrow (&lt;1 mm) margins on much older pseudotachylite veins, and heterogeneous excess argon contamination. We also report pseudotachylite veins of varying magnitudes that have been subject to later thermal reheating, whereby there is a relationship between vein thickness and extent of argon loss. In spite of these it is still possible to determine geologically meaningful <sup>40</sup>Ar/<sup>39</sup>Ar ages for pseudotachylite-forming events. In Lewis the <em>c</em>. 1900 Ma event may relate to early stages of Laxfordian reworking. In Barra and South Uist a 1300–1200 Ma event is recorded, whereas in Barra, South and North Uist a second event is recorded at <em>c</em>. 700 Ma, which is likely to be associated with NW- and west-directed thrusting, and could represent far-field effects of tectonic events recorded at this time east of the Moine Thrust in NW Scotland.
DOI: 10.6084/m9.figshare.3454718.v1
title: High spatial resolution <sup>40</sup>Ar/<sup>39</sup>Ar dating of pseudotachylites: geochronological evidence for multiple phases of faulting within basement gneisses of the Outer Hebrides (UK)

description: Pseudotachylites within the Neoarchaean to Palaeoproterozoic basement of the Lewisian Gneiss Complex have been analysed using the high spatial resolution <sup>40</sup>Ar/<sup>39</sup>Ar UV laserprobe technique. It has been possible to measure <sup>40</sup>Ar/<sup>39</sup>Ar age and ‘apparent' age variations that would be beyond resolution by lower spatial resolution or bulk <sup>40</sup>Ar/<sup>39</sup>Ar dating methods. We report a range of complexities including significantly younger narrow (&lt;1 mm) margins on much older pseudotachylite veins, and heterogeneous excess argon contamination. We also report pseudotachylite veins of varying magnitudes that have been subject to later thermal reheating, whereby there is a relationship between vein thickness and extent of argon loss. In spite of these it is still possible to determine geologically meaningful <sup>40</sup>Ar/<sup>39</sup>Ar ages for pseudotachylite-forming events. In Lewis the <em>c</em>. 1900 Ma event may relate to early stages of Laxfordian reworking. In Barra and South Uist a 1300–1200 Ma event is recorded, whereas in Barra, South and North Uist a second event is recorded at <em>c</em>. 700 Ma, which is likely to be associated with NW- and west-directed thrusting, and could represent far-field effects of tectonic events recorded at this time east of the Moine Thrust in NW Scotland.
DOI: 10.6084/m9.figshare.3454715
title: Exhumation of an active magmatic–hydrothermal system in a resurgent caldera environment: the example of Ischia (Italy)

description: Ischia is a rare case of a well-exposed caldera system that has experienced rapid recent resurgence, which can be used to dissect the anatomy of an otherwise inaccessible active hydrothermal system developed in a caldera-forming environment. Integrated analyses of melt and fluid inclusions, mineralogy and stable isotopic compositions of pumices, tuffs and syenitic xenoliths of the Ischia volcanic system provide strong physico-chemical constraints on the shallow magmatic reservoir and the hydrothermal system. The hydrothermal system has been exposed by the rapid uplift of the Mt. Epomeo resurgent block. The engine of the hydrothermal system of Ischia can be identified in the shallow magmatic system (at around 2 km depth) that hosts hot (<em>c</em>. 1000 °C) trachytic magma. The hydrothermal system developed principally within thick intracaldera ignimbrite deposits, and extended to a depth of at least 1 km, defining a series of facies characterized by associations of alteration mineral assemblages typical of a seawater-dominated high-temperature geothermal system.