cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454346
title: Subglacial bedrock welding associated with glacial earthquakes

description: A &lt;3 mm thick, intensely brecciated layer associated with Marinoan (<strong><em>c</em></strong>. 635 Ma) glacial striations on a Neoproterozoic sandstone pavement is documented. Only instantaneous solidification could have preserved the breccia <strong><em>in situ</em></strong>. Glacier speeds of <strong><em>c</em></strong>. 0.3 m s<sup>−1</sup> would have induced peak flash temperatures sufficient (&gt;1130 °C) to cause partial frictional welding of the deformed quartzitic bedrock beneath an ice-loaded clast. These results support suggestions that glacial seismicity is due to episodic very rapid shifts of large ice masses over the substrate (stick–slip movement). They also indicate that significant effective normal stresses occur at the base of glaciers.
DOI: 10.6084/m9.figshare.3454346.v1
title: Subglacial bedrock welding associated with glacial earthquakes

description: A &lt;3 mm thick, intensely brecciated layer associated with Marinoan (<strong><em>c</em></strong>. 635 Ma) glacial striations on a Neoproterozoic sandstone pavement is documented. Only instantaneous solidification could have preserved the breccia <strong><em>in situ</em></strong>. Glacier speeds of <strong><em>c</em></strong>. 0.3 m s<sup>−1</sup> would have induced peak flash temperatures sufficient (&gt;1130 °C) to cause partial frictional welding of the deformed quartzitic bedrock beneath an ice-loaded clast. These results support suggestions that glacial seismicity is due to episodic very rapid shifts of large ice masses over the substrate (stick–slip movement). They also indicate that significant effective normal stresses occur at the base of glaciers.
DOI: 10.6084/m9.figshare.3454343
title: Widespread arc-related melting in the mantle section of the northern Oman ophiolite as inferred from detrital chromian spinels

description: We examined detrital chromian spinels, in recent river beds, derived from the mantle section to deterrmine whether the mantle peridotite of the northern Oman ophiolite is of oceanic or arc origin. The Cr-number (= Cr/(Cr + Al) atomic ratio) of the detrital chromian spinels mostly ranges from 0.4 to 0.8, and more than 60% of them have Cr-numbers higher than 0.6. This indicates a significant extent of island-arc nature because chromian spinels seldom have Cr-numbers higher than 0.6 in ocean-floor rocks. The high-Cr-number (&gt;0.6) spinels, which are also low in TiO<sub>2</sub> (&lt;0.3 wt%), are probably derived from an arc setting. Lherzolite with spinel Cr-numbers &lt;0.2 is absent except near the base of the section. The high-Cr-number detrital chromian spinels are more abundant from the mantle section with more frequent discordant dunite pods. Post-deformational discordant dunite and adjacent harzburgite include the high-Cr-number spinels in outcrops. The upper mantle of the northern Oman ophiolite was formed at a fast-spreading ridge and was later modified by island-arc magmatism in a subduction-zone environment. This switch of tectonic setting from a mid-oceanic ridge to an island arc is essential in the explanation of obduction of a slice of oceanic lithosphere onto a continental margin as an ophiolite.
DOI: 10.6084/m9.figshare.3454343.v1
title: Widespread arc-related melting in the mantle section of the northern Oman ophiolite as inferred from detrital chromian spinels

description: We examined detrital chromian spinels, in recent river beds, derived from the mantle section to deterrmine whether the mantle peridotite of the northern Oman ophiolite is of oceanic or arc origin. The Cr-number (= Cr/(Cr + Al) atomic ratio) of the detrital chromian spinels mostly ranges from 0.4 to 0.8, and more than 60% of them have Cr-numbers higher than 0.6. This indicates a significant extent of island-arc nature because chromian spinels seldom have Cr-numbers higher than 0.6 in ocean-floor rocks. The high-Cr-number (&gt;0.6) spinels, which are also low in TiO<sub>2</sub> (&lt;0.3 wt%), are probably derived from an arc setting. Lherzolite with spinel Cr-numbers &lt;0.2 is absent except near the base of the section. The high-Cr-number detrital chromian spinels are more abundant from the mantle section with more frequent discordant dunite pods. Post-deformational discordant dunite and adjacent harzburgite include the high-Cr-number spinels in outcrops. The upper mantle of the northern Oman ophiolite was formed at a fast-spreading ridge and was later modified by island-arc magmatism in a subduction-zone environment. This switch of tectonic setting from a mid-oceanic ridge to an island arc is essential in the explanation of obduction of a slice of oceanic lithosphere onto a continental margin as an ophiolite.
DOI: 10.6084/m9.figshare.3454340
title: Zircon thermometry and U–Pb ion-microprobe dating of the gabbros and associated migmatites of the Variscan Toledo Anatectic Complex, Central Iberia

description: In the Central Iberian Zone there are several large thermal domes in which small bodies of ultramafic, mafic and intermediate rocks appear intimately associated with crustal granites and migmatites. The closest spatial association between the ultramafic, mafic and intermediate rocks and migmatites is in the Toledo Anatectic Complex, where field relationships suggest that these rocks are coeval and have an age close to 340 Ma. This, and the recent discovery in the neighbouring Ossa Morena Zone of a large mid-crustal seismic reflector interpreted as a 335–350 Ma mafic sill, reinforce the hypothesis that heat for crustal melting was supplied from early Variscan mantle magmas emplaced in the middle crust. However, precise ion-microprobe U–Pb zircon dating and Ti-in-zircon thermometry in Toledo do not support this idea. Whereas the mean age of four mafic bodies is 307 ± 2 Ma, the migmatites are <em>c</em>. 25 Ma older. The migmatites hosting ultramafic, mafic and intermediate bodies have the same age and Ti-in-zircon temperatures as migmatites far from any mafic intrusion. These data reveal that ultramafic, mafic and intermediate magmas are late Variscan; they were emplaced in already cooling anatectic zones once the extensional collapse was initiated, and their thermal impact on the mid-crustal Variscan anatexis of Central Iberia was negligible.
DOI: 10.6084/m9.figshare.3454340.v1
title: Zircon thermometry and U–Pb ion-microprobe dating of the gabbros and associated migmatites of the Variscan Toledo Anatectic Complex, Central Iberia

description: In the Central Iberian Zone there are several large thermal domes in which small bodies of ultramafic, mafic and intermediate rocks appear intimately associated with crustal granites and migmatites. The closest spatial association between the ultramafic, mafic and intermediate rocks and migmatites is in the Toledo Anatectic Complex, where field relationships suggest that these rocks are coeval and have an age close to 340 Ma. This, and the recent discovery in the neighbouring Ossa Morena Zone of a large mid-crustal seismic reflector interpreted as a 335–350 Ma mafic sill, reinforce the hypothesis that heat for crustal melting was supplied from early Variscan mantle magmas emplaced in the middle crust. However, precise ion-microprobe U–Pb zircon dating and Ti-in-zircon thermometry in Toledo do not support this idea. Whereas the mean age of four mafic bodies is 307 ± 2 Ma, the migmatites are <em>c</em>. 25 Ma older. The migmatites hosting ultramafic, mafic and intermediate bodies have the same age and Ti-in-zircon temperatures as migmatites far from any mafic intrusion. These data reveal that ultramafic, mafic and intermediate magmas are late Variscan; they were emplaced in already cooling anatectic zones once the extensional collapse was initiated, and their thermal impact on the mid-crustal Variscan anatexis of Central Iberia was negligible.
DOI: 10.6084/m9.figshare.3454331
title: Zircon age constraints on sediment provenance in the Caspian region

description: Sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages for detrital zircons from the Caspian region reveal the age ranges of basement terrains that supplied the sediment. One sample from the modern Volga river has groupings at <em>c</em>. 340–370 Ma, <em>c</em>. 900–1300 Ma and <em>c</em>. 1450–1800 Ma, with a small number of older zircons. This is consistent with derivation from the Precambrian basement of the East European Craton, and Palaeozoic arcs in the Urals. Mid- and Late Proterozoic components may be derived from beyond the present Volga drainage basin, such as the Sveconorwegian orogen. A Bajocian sandstone from the Greater Caucasus has 73% zircons that post-date 350 Ma. Ages cluster at <em>c</em>. 165–185 Ma, <em>c</em>. 220–260 Ma, <em>c</em>. 280–360 Ma and <em>c</em>. 440–460 Ma. This pattern suggests derivation from Palaeozoic basement of the Greater Caucasus itself and/or the Scythian Platform, and igneous rocks generated at a Jurassic arc in the Lesser Caucasus. Four samples from the Lower Pliocene Productive Series of the South Caspian Basin have common Phanerozoic grains, and groups between <em>c</em>. 900–1300 Ma and 1500–2000 Ma. Each sample contains zircons dated to <em>c</em>. 2700 Ma. The overall age patterns in the Productive Series samples suggest a combination of East European Craton and Greater Caucasus source components.
DOI: 10.6084/m9.figshare.3454331.v1
title: Zircon age constraints on sediment provenance in the Caspian region

description: Sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages for detrital zircons from the Caspian region reveal the age ranges of basement terrains that supplied the sediment. One sample from the modern Volga river has groupings at <em>c</em>. 340–370 Ma, <em>c</em>. 900–1300 Ma and <em>c</em>. 1450–1800 Ma, with a small number of older zircons. This is consistent with derivation from the Precambrian basement of the East European Craton, and Palaeozoic arcs in the Urals. Mid- and Late Proterozoic components may be derived from beyond the present Volga drainage basin, such as the Sveconorwegian orogen. A Bajocian sandstone from the Greater Caucasus has 73% zircons that post-date 350 Ma. Ages cluster at <em>c</em>. 165–185 Ma, <em>c</em>. 220–260 Ma, <em>c</em>. 280–360 Ma and <em>c</em>. 440–460 Ma. This pattern suggests derivation from Palaeozoic basement of the Greater Caucasus itself and/or the Scythian Platform, and igneous rocks generated at a Jurassic arc in the Lesser Caucasus. Four samples from the Lower Pliocene Productive Series of the South Caspian Basin have common Phanerozoic grains, and groups between <em>c</em>. 900–1300 Ma and 1500–2000 Ma. Each sample contains zircons dated to <em>c</em>. 2700 Ma. The overall age patterns in the Productive Series samples suggest a combination of East European Craton and Greater Caucasus source components.
DOI: 10.6084/m9.figshare.3454328
title: Lower crustal rheological expression in inverted basins

description: Although lithospheric modelling has provided extraordinary insights into the processes that shape the continental crust, considerable uncertainty surrounds the basic rheology that governs behaviour at geological timescales. In part, this is because it has proved difficult to identify the geological observations that might discriminate, or unify, models of lithospheric rheology. In particular, the relative strength of lower crust and upper mantle remains a contentious aspect of continental lithospheric rheology. We show that various models for lower crustal rheology may produce distinct patterns of inversion in extensional sedimentary basins, consistent with some of the observed natural variability of inversion styles. Inversion of basin interiors, as is common in European Mesozoic basins, is favoured by a lithospheric rheology more sensitive to lateral thermal structure than to changes in the depth of the Moho, consistent with there being little strength contrast between the lower crust and upper mantle in these settings. In contrast, inversion of basin margins, particularly involving basinward verging structures, is consistent with a rheological sensitivity to the depth of Moho as would apply for a lower crust much weaker than the upper mantle. We use an example from central Australia to demonstrate this latter response, together with thermochronologic data that suggests that a relatively weak lower crust in this setting may reflect abnormally high geothermal gradients.
DOI: 10.6084/m9.figshare.3454328.v1
title: Lower crustal rheological expression in inverted basins

description: Although lithospheric modelling has provided extraordinary insights into the processes that shape the continental crust, considerable uncertainty surrounds the basic rheology that governs behaviour at geological timescales. In part, this is because it has proved difficult to identify the geological observations that might discriminate, or unify, models of lithospheric rheology. In particular, the relative strength of lower crust and upper mantle remains a contentious aspect of continental lithospheric rheology. We show that various models for lower crustal rheology may produce distinct patterns of inversion in extensional sedimentary basins, consistent with some of the observed natural variability of inversion styles. Inversion of basin interiors, as is common in European Mesozoic basins, is favoured by a lithospheric rheology more sensitive to lateral thermal structure than to changes in the depth of the Moho, consistent with there being little strength contrast between the lower crust and upper mantle in these settings. In contrast, inversion of basin margins, particularly involving basinward verging structures, is consistent with a rheological sensitivity to the depth of Moho as would apply for a lower crust much weaker than the upper mantle. We use an example from central Australia to demonstrate this latter response, together with thermochronologic data that suggests that a relatively weak lower crust in this setting may reflect abnormally high geothermal gradients.
DOI: 10.6084/m9.figshare.3454325
title: Convergent morphology in small spiral worm tubes (‘<em>Spirorbis</em>’) and its palaeoenvironmental implications

description: Calcareous tube-worms generally identified as <strong><em>Spirorbis</em></strong> range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent <strong><em>Spirorbis</em></strong> is a polychaete annelid, details of tube structure in pre-Cretaceous ‘<strong><em>Spirorbis</em></strong>’ suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true <strong><em>Spirorbis</em></strong>. Recent <strong><em>Spirorbis</em></strong> is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian–Triassic. Anomalies in the palaeoenvironmental distributions of fossil ‘<strong><em>Spirorbis</em></strong>’ are explained with the recognition of this striking convergence between microconchids and true <strong><em>Spirorbis</em></strong>.
DOI: 10.6084/m9.figshare.3454325.v1
title: Convergent morphology in small spiral worm tubes (‘<em>Spirorbis</em>’) and its palaeoenvironmental implications

description: Calcareous tube-worms generally identified as <strong><em>Spirorbis</em></strong> range from Ordovician to Recent, often profusely encrusting shells and other substrates. Whereas Recent <strong><em>Spirorbis</em></strong> is a polychaete annelid, details of tube structure in pre-Cretaceous ‘<strong><em>Spirorbis</em></strong>’ suggest affinities with the Microconchida, an extinct order of possible lophophorates. Although characteristically Palaeozoic, microconchid tube-worms survived the Permian mass extinction before being replaced in late Mesozoic ecosystems by true <strong><em>Spirorbis</em></strong>. Recent <strong><em>Spirorbis</em></strong> is stenohaline but spirorbiform microconchids also colonized freshwater, brackish and hypersaline environments during the Devonian–Triassic. Anomalies in the palaeoenvironmental distributions of fossil ‘<strong><em>Spirorbis</em></strong>’ are explained with the recognition of this striking convergence between microconchids and true <strong><em>Spirorbis</em></strong>.
DOI: 10.6084/m9.figshare.3454322
title: Geochemistry and U–Pb protolith ages of eclogitic rocks of the Asís Lithodeme, Piaxtla Suite, Acatlán Complex, southern Mexico: tectonothermal activity along the southern margin of the Rheic Ocean

description: Recent data indicating that the Piaxtla Suite (Acatlán Complex, southern Mexico) underwent eclogite-facies metamorphism and exhumation during the Devono-Carboniferous suggest an origin within the Rheic Ocean rather than the Iapetus Ocean. The Asís Lithodeme (Piaxtla Suite) consists of polydeformed metasediments and eclogitic amphibolites that are intruded by megacrystic granitoid rocks. U–Pb (zircon) data indicate that the metasediments were deposited after <em>c</em>. 700 Ma and before intrusion of <em>c</em>. 470–420 Ma quartz-augen granite. The metasedimentary rocks contain abundant Mesoproterozoic detrital zircons (<em>c</em>. 1050–1250 Ma) and a few zircons in the range of <em>c</em>. 900–992 and <em>c</em>. 1330–1662 Ma. Their geochemical and Sm–Nd isotopic signature is typical of rift-related, passive margin sediments derived from an ancient cratonic source, which is interpreted to be the adjacent Mesoproterozoic Oaxacan Complex. Megacrystic granites were derived by partial melting of a <em>c</em>. 1 Ga crustal source, similar to the Oaxacan Complex. Amphibolitic layers exhibit a continental tholeiitic geochemistry, with a <em>c</em>. 0.8–1.1 Ga source (<em>T</em><sub>DM</sub> age), and are inferred to have originated in a rift-related environment by melting of lithospheric mantle in the Ordovician. This rifting may be related to the Early Ordovician drift of peri-Gondwanan terranes (e.g. Avalonia) from Gondwana and the origin of the Rheic Ocean.
DOI: 10.6084/m9.figshare.3454322.v1
title: Geochemistry and U–Pb protolith ages of eclogitic rocks of the Asís Lithodeme, Piaxtla Suite, Acatlán Complex, southern Mexico: tectonothermal activity along the southern margin of the Rheic Ocean

description: Recent data indicating that the Piaxtla Suite (Acatlán Complex, southern Mexico) underwent eclogite-facies metamorphism and exhumation during the Devono-Carboniferous suggest an origin within the Rheic Ocean rather than the Iapetus Ocean. The Asís Lithodeme (Piaxtla Suite) consists of polydeformed metasediments and eclogitic amphibolites that are intruded by megacrystic granitoid rocks. U–Pb (zircon) data indicate that the metasediments were deposited after <em>c</em>. 700 Ma and before intrusion of <em>c</em>. 470–420 Ma quartz-augen granite. The metasedimentary rocks contain abundant Mesoproterozoic detrital zircons (<em>c</em>. 1050–1250 Ma) and a few zircons in the range of <em>c</em>. 900–992 and <em>c</em>. 1330–1662 Ma. Their geochemical and Sm–Nd isotopic signature is typical of rift-related, passive margin sediments derived from an ancient cratonic source, which is interpreted to be the adjacent Mesoproterozoic Oaxacan Complex. Megacrystic granites were derived by partial melting of a <em>c</em>. 1 Ga crustal source, similar to the Oaxacan Complex. Amphibolitic layers exhibit a continental tholeiitic geochemistry, with a <em>c</em>. 0.8–1.1 Ga source (<em>T</em><sub>DM</sub> age), and are inferred to have originated in a rift-related environment by melting of lithospheric mantle in the Ordovician. This rifting may be related to the Early Ordovician drift of peri-Gondwanan terranes (e.g. Avalonia) from Gondwana and the origin of the Rheic Ocean.
DOI: 10.6084/m9.figshare.3454319
title: Late Neoproterozoic proto-arc ocean crust in the Dariv Range, Western Mongolia: a supra-subduction zone end-member ophiolite

description: An unusual late Neoproterozoic (<em>c</em>. 572 Ma) ophiolite is exposed in the Dariv Range (western Mongolia), which contains intermediate to acidic lavas and sheeted dykes, and an igneous layered complex consisting of gabbro–norites, websterites, orthopyroxenites and dunites underlain by serpentinized mantle harzburgites. Based on the compositions of the crustal units and the crystallization sequences in the mafic and ultramafic cumulates we conclude that the entire oceanic crust, including the cumulates, was made from arc magmas with boninitic characteristics. The Dariv rocks bear a strong resemblance to rocks recovered from the modern Izu–Bonin–Mariana fore-arc, a fragment of proto-arc oceanic basement, and we propose that the Dariv Ophiolite originated in a similar tectonic setting. A metamorphic complex consisting of amphibolite- to granulite-facies metasedimentary and meta-igneous rocks was thrust over the ophiolite. This metamorphic complex probably represents a Cambrian arc. Thrusting started before 514.7 ± 7.6 Ma as constrained by new sensitive high-resolution ion microprobe U–Pb zircon analyses from a syn- to post-tectonic diorite. The Dariv Ophiolite is a type-example of a proto-arc ophiolite, a special class of supra-subduction zone ophiolites.
DOI: 10.6084/m9.figshare.3454319.v1
title: Late Neoproterozoic proto-arc ocean crust in the Dariv Range, Western Mongolia: a supra-subduction zone end-member ophiolite

description: An unusual late Neoproterozoic (<em>c</em>. 572 Ma) ophiolite is exposed in the Dariv Range (western Mongolia), which contains intermediate to acidic lavas and sheeted dykes, and an igneous layered complex consisting of gabbro–norites, websterites, orthopyroxenites and dunites underlain by serpentinized mantle harzburgites. Based on the compositions of the crustal units and the crystallization sequences in the mafic and ultramafic cumulates we conclude that the entire oceanic crust, including the cumulates, was made from arc magmas with boninitic characteristics. The Dariv rocks bear a strong resemblance to rocks recovered from the modern Izu–Bonin–Mariana fore-arc, a fragment of proto-arc oceanic basement, and we propose that the Dariv Ophiolite originated in a similar tectonic setting. A metamorphic complex consisting of amphibolite- to granulite-facies metasedimentary and meta-igneous rocks was thrust over the ophiolite. This metamorphic complex probably represents a Cambrian arc. Thrusting started before 514.7 ± 7.6 Ma as constrained by new sensitive high-resolution ion microprobe U–Pb zircon analyses from a syn- to post-tectonic diorite. The Dariv Ophiolite is a type-example of a proto-arc ophiolite, a special class of supra-subduction zone ophiolites.
DOI: 10.6084/m9.figshare.3454316
title: Linking the Palaeoproterozoic Nagssugtoqidian and Rinkian orogens through the Disko Bugt region of West Greenland

description: The parallel Trans-Hudson-aged Nagssugtoqidian Orogen and Rinkian Fold Belt of West Greenland have long been considered distinct orogenic belts separated by a zone of low or no Palaeoproterozoic strain in the intervening Disko Bugt region. New U–Pb geochronology confirms the continuity of Palaeoproterozoic deformation and metamorphism through this region, thereby directly linking the Nagssugtoqidian Orogen and Rinkian Fold Belt. Furthermore, two newly identified Archaean blocks in this region are interpreted to represent the southern and northern extensions of the Rae and North Atlantic cratons, respectively. Their boundary comprises a 15 km wide belt of distributed, NW-vergent ductile thrusts that deform ultramafic pods and is interpreted to represent the main collisional suture of a single, variably exhumed, &gt;1100 km wide Nagssugtoqidian–Rinkian orogenic system. We conclude that Palaeoproterozoic convergence of a northern Archaean craton carried a south-facing passive margin sedimentary sequence (Karrat Group) towards a south-dipping subduction zone along the North Atlantic Craton. Terminal collision created a high-grade core centred on the magmatic arc of the central Nagssugtoqidian Orogen and a NW-vergent fold and thrust belt in the Rinkian Fold Belt.