cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454193
title: Grampian orogenesis and the development of blueschist-facies metamorphism in western Ireland

description: Rb–Sr and <sup>40</sup>Ar/<sup>39</sup>Ar step-heating and <em>in situ</em> <sup>40</sup>Ar/<sup>39</sup>Ar laserprobe dating of fabric-forming micas provide new constraints on the timing of Grampian orogenesis and the associated development of blueschist-facies metamorphism at the Laurentian margin in NW Ireland. Early (MP<sub>1</sub>) blueschist-facies assemblages were developed in metabasites of the Dalradian Supergroup deposited near the edge of the incipient Laurentian margin, contemporaneous with Barrovian metamorphism in the Dalradian closer to the Laurentian foreland. The regional D<sub>2</sub> event is associated with the formation of orogen-scale fold nappes and is constrained in the Dalradian by S<sub>2</sub> muscovite ages of <em>c</em>. 460 Ma, which are probably recording crystallization. Importantly, the Clew Bay Complex, previously considered as an exotic terrane (correlated with the Highland Border Complex of Scotland) and the Dalradian are in structural continuity. Muscovite from the S<sub>2</sub> nappe fabric in the Clew Bay Complex also yields identical <em>c</em>. 460 Ma ages. During D<sub>3</sub>, dextral shearing tilted the recumbent D<sub>2</sub> nappes into a vertical, downward-facing orientation adjacent to the Laurentian margin. D<sub>3</sub> is constrained by S<sub>3</sub> muscovite ages of <em>c</em>. 448 Ma. Synchronous deformation of the Dalradian Supergroup and the Clew Bay Complex in the mid-Ordovician Grampian orogeny casts doubt on both the validity of Silurian microfossil dates obtained from the Clew Bay Complex and the exotic status of both this ‘terrane’ and the correlative Highland Border Complex of Scotland.
DOI: 10.6084/m9.figshare.3454193.v1
title: Grampian orogenesis and the development of blueschist-facies metamorphism in western Ireland

description: Rb–Sr and <sup>40</sup>Ar/<sup>39</sup>Ar step-heating and <em>in situ</em> <sup>40</sup>Ar/<sup>39</sup>Ar laserprobe dating of fabric-forming micas provide new constraints on the timing of Grampian orogenesis and the associated development of blueschist-facies metamorphism at the Laurentian margin in NW Ireland. Early (MP<sub>1</sub>) blueschist-facies assemblages were developed in metabasites of the Dalradian Supergroup deposited near the edge of the incipient Laurentian margin, contemporaneous with Barrovian metamorphism in the Dalradian closer to the Laurentian foreland. The regional D<sub>2</sub> event is associated with the formation of orogen-scale fold nappes and is constrained in the Dalradian by S<sub>2</sub> muscovite ages of <em>c</em>. 460 Ma, which are probably recording crystallization. Importantly, the Clew Bay Complex, previously considered as an exotic terrane (correlated with the Highland Border Complex of Scotland) and the Dalradian are in structural continuity. Muscovite from the S<sub>2</sub> nappe fabric in the Clew Bay Complex also yields identical <em>c</em>. 460 Ma ages. During D<sub>3</sub>, dextral shearing tilted the recumbent D<sub>2</sub> nappes into a vertical, downward-facing orientation adjacent to the Laurentian margin. D<sub>3</sub> is constrained by S<sub>3</sub> muscovite ages of <em>c</em>. 448 Ma. Synchronous deformation of the Dalradian Supergroup and the Clew Bay Complex in the mid-Ordovician Grampian orogeny casts doubt on both the validity of Silurian microfossil dates obtained from the Clew Bay Complex and the exotic status of both this ‘terrane’ and the correlative Highland Border Complex of Scotland.
DOI: 10.6084/m9.figshare.3454190
title: <sup>40</sup>Ar/<sup>39</sup>Ar ages in mantle xenolith phlogopites: determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands

description: Kimberlites are extraordinary natural phenomena, ascending through the Earth’s lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to est whether other mantle phlogopite cores may yield meaningful ages. Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9–6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2–15 hours (assuming the same magma temperature).
DOI: 10.6084/m9.figshare.3454190.v1
title: <sup>40</sup>Ar/<sup>39</sup>Ar ages in mantle xenolith phlogopites: determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands

description: Kimberlites are extraordinary natural phenomena, ascending through the Earth’s lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to est whether other mantle phlogopite cores may yield meaningful ages. Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9–6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2–15 hours (assuming the same magma temperature).
DOI: 10.6084/m9.figshare.3454187
title: Linking growth episodes of zircon and metamorphic textures to zircon chemistry: an example from the ultrahigh-temperature granulites of Rogaland (SW Norway)

description: <em>In-situ</em> U-Th-Pb analyses by ion-microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon. This approach helps: (a) to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the Rogaland anorthosite-norite intrusive complex; and (b) to constrain the age of M<sub>2</sub> ultrahigh-temperature (UHT) metamorphism and the subsequent retrograde M<sub>3</sub> event. All samples yield magmatic inherited zircon of <em>c.</em> 1035 Ma, some an additional group at <em>c.</em> 1050 Ma. This suggests that loss of Pb by volume diffusion in non-metamict zircon is not an important factor even under extreme crustal conditions. Furthermore, the identical inheritance patterns in aluminous (garnet, cordierite ± osumilite-bearing) migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite. Results for the M<sub>1</sub> metamorphic event at <em>c.</em> 1000 Ma BP are consistent in all samples, including those from outside the orthopyroxene-in isograd. The latter do not show evidence for zircon growth during the M<sub>2</sub> metamorphic episode. Zircon intergrown with or included within M<sub>2</sub> metamorphic minerals (magnetite, spinel, orthopyroxene) give an age of 927 ± 7 Ma (2<em>σ, n</em> = 20). The youngest observed results are found in zircon outside M<sub>2</sub> minerals, some overgrown by M<sub>3</sub> mineral assemblages (late garnet coronas, garnet + quartz and orthopyroxene + garnet symplectites) and yield a slightly younger pooled age of 908 ± 9 Ma (2<em>σ, n</em> = 6). These textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the UHT event. These youngest age groups are consistent with the emplacement age of the Rogaland intrusive complex and the last magmatic activity (Tellnes dyke intrusion), respectively. This is direct and conclusive evidence for UHT metamorphism in the regional aureole being caused by the intrusions, and corrects earlier notions that the events are not linked. Trace element behaviour of zircon (Tb/U and Y content) has been tracked through time in the samples and shows variations both within and between samples. This heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of ‘rules of thumb’ in the interpretation of zircon chemistry, but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism.
DOI: 10.6084/m9.figshare.3454187.v1
title: Linking growth episodes of zircon and metamorphic textures to zircon chemistry: an example from the ultrahigh-temperature granulites of Rogaland (SW Norway)

description: <em>In-situ</em> U-Th-Pb analyses by ion-microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon. This approach helps: (a) to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the Rogaland anorthosite-norite intrusive complex; and (b) to constrain the age of M<sub>2</sub> ultrahigh-temperature (UHT) metamorphism and the subsequent retrograde M<sub>3</sub> event. All samples yield magmatic inherited zircon of <em>c.</em> 1035 Ma, some an additional group at <em>c.</em> 1050 Ma. This suggests that loss of Pb by volume diffusion in non-metamict zircon is not an important factor even under extreme crustal conditions. Furthermore, the identical inheritance patterns in aluminous (garnet, cordierite ± osumilite-bearing) migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite. Results for the M<sub>1</sub> metamorphic event at <em>c.</em> 1000 Ma BP are consistent in all samples, including those from outside the orthopyroxene-in isograd. The latter do not show evidence for zircon growth during the M<sub>2</sub> metamorphic episode. Zircon intergrown with or included within M<sub>2</sub> metamorphic minerals (magnetite, spinel, orthopyroxene) give an age of 927 ± 7 Ma (2<em>σ, n</em> = 20). The youngest observed results are found in zircon outside M<sub>2</sub> minerals, some overgrown by M<sub>3</sub> mineral assemblages (late garnet coronas, garnet + quartz and orthopyroxene + garnet symplectites) and yield a slightly younger pooled age of 908 ± 9 Ma (2<em>σ, n</em> = 6). These textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the UHT event. These youngest age groups are consistent with the emplacement age of the Rogaland intrusive complex and the last magmatic activity (Tellnes dyke intrusion), respectively. This is direct and conclusive evidence for UHT metamorphism in the regional aureole being caused by the intrusions, and corrects earlier notions that the events are not linked. Trace element behaviour of zircon (Tb/U and Y content) has been tracked through time in the samples and shows variations both within and between samples. This heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of ‘rules of thumb’ in the interpretation of zircon chemistry, but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism.
DOI: 10.6084/m9.figshare.3454184
title: Effect of metamorphic reaction history on the U-Pb dating of titanite

description: Drill core samples of garnet-clinopyroxene granulite at Tirschheim and a reference sample at Waldheim (Saxon Granulite Massif, Germany) endured the same P-T conditions, but developed variable mineral assemblages due to differences in bulk chemistry, reaction progress, deformation and retrogression. Titanite formed during peak-metamorphic conditions of 22–24 kbar and 1020–1050 °C. Dating titanite from the various samples should yield the same age for all. The observed age variation, which exceeds the duration of the entire metamorphic cycle, originates from the contrasting preservation of isotopic inheritance during peak metamorphism and from post-peak re-equilibration. (1) Pb inheritance observed in some peak-metamorphic titanite demonstrates that geochronologically relevant elements are redistributed among remaining reactants and reaction products during prograde metamorphism and that the sequence of metamorphic reactions does not result in isotopic homogenization. Instead, metamorphic minerals inherit the radiogenic signatures of the precursor minerals and may in extreme cases approach the age of the precursor mineral. (2) Titanite that formed at peak-metamorphic conditions is characterized by high A1 contents and X<sub>F</sub> ≈ 0.8−1. Texturally comparable titanite that re-equilibrated during cooling (reduced Al contents and X<sub>F</sub>) yields too young U-Pb ages. The age of such re-equilibrated titanite does not correspond to the age of the event indicated by the texture.
DOI: 10.6084/m9.figshare.3454184.v1
title: Effect of metamorphic reaction history on the U-Pb dating of titanite

description: Drill core samples of garnet-clinopyroxene granulite at Tirschheim and a reference sample at Waldheim (Saxon Granulite Massif, Germany) endured the same P-T conditions, but developed variable mineral assemblages due to differences in bulk chemistry, reaction progress, deformation and retrogression. Titanite formed during peak-metamorphic conditions of 22–24 kbar and 1020–1050 °C. Dating titanite from the various samples should yield the same age for all. The observed age variation, which exceeds the duration of the entire metamorphic cycle, originates from the contrasting preservation of isotopic inheritance during peak metamorphism and from post-peak re-equilibration. (1) Pb inheritance observed in some peak-metamorphic titanite demonstrates that geochronologically relevant elements are redistributed among remaining reactants and reaction products during prograde metamorphism and that the sequence of metamorphic reactions does not result in isotopic homogenization. Instead, metamorphic minerals inherit the radiogenic signatures of the precursor minerals and may in extreme cases approach the age of the precursor mineral. (2) Titanite that formed at peak-metamorphic conditions is characterized by high A1 contents and X<sub>F</sub> ≈ 0.8−1. Texturally comparable titanite that re-equilibrated during cooling (reduced Al contents and X<sub>F</sub>) yields too young U-Pb ages. The age of such re-equilibrated titanite does not correspond to the age of the event indicated by the texture.
DOI: 10.6084/m9.figshare.3454181
title: Exhumation of the Ronda peridotite and its crustal envelope: constraints from thermal modelling of a <em>P</em>–<em>T</em>–time array

description: The Ronda peridotite in the Betic Cordillera of southern Spain is a relic of the sub-orogenic lithospheric mantle that was exhumed during earliest Miocene time from about 66 km depth. Overlying crustal rocks show an apparently coherent metamorphic zonation from high-pressure granulite-facies rocks at the contact to unmetamorphosed rocks 5 km higher in the structural sequence, indicating drastic tectonic thinning of the whole orogenic crust during exhumation. <em>P</em>–<em>T</em> paths from the peridotite and its crustal envelope indicate decompression with rising temperature to shallow depths. U–Pb ion microprobe dating of zircon, Ar/Ar dating of hornblende, Ar/Ar laserprobe dating of muscovite and biotite, and fission-track analysis of zircon and apatite reveal that cooling was extremely rapid in the interval 21.2–20.4 Ma. One-dimensional thermal modelling of the array of <em>P</em>–<em>T</em>–time paths indicates that an asthenospheric heat source at an initial depth of about 67.5 km is required to explain heating during exhumation, and that the main period of exhumation lasted 5 Ma, starting at around 25 Ma. Exhumation must therefore have directly followed removal of most, but not all, of the lithospheric mantle beneath the Betic orogen, and was coeval with a period of late orogenic extension that profoundly modified the crustal structure and created the present-day Alboran Sea in the western Mediterranean.
DOI: 10.6084/m9.figshare.3454181.v1
title: Exhumation of the Ronda peridotite and its crustal envelope: constraints from thermal modelling of a <em>P</em>–<em>T</em>–time array

description: The Ronda peridotite in the Betic Cordillera of southern Spain is a relic of the sub-orogenic lithospheric mantle that was exhumed during earliest Miocene time from about 66 km depth. Overlying crustal rocks show an apparently coherent metamorphic zonation from high-pressure granulite-facies rocks at the contact to unmetamorphosed rocks 5 km higher in the structural sequence, indicating drastic tectonic thinning of the whole orogenic crust during exhumation. <em>P</em>–<em>T</em> paths from the peridotite and its crustal envelope indicate decompression with rising temperature to shallow depths. U–Pb ion microprobe dating of zircon, Ar/Ar dating of hornblende, Ar/Ar laserprobe dating of muscovite and biotite, and fission-track analysis of zircon and apatite reveal that cooling was extremely rapid in the interval 21.2–20.4 Ma. One-dimensional thermal modelling of the array of <em>P</em>–<em>T</em>–time paths indicates that an asthenospheric heat source at an initial depth of about 67.5 km is required to explain heating during exhumation, and that the main period of exhumation lasted 5 Ma, starting at around 25 Ma. Exhumation must therefore have directly followed removal of most, but not all, of the lithospheric mantle beneath the Betic orogen, and was coeval with a period of late orogenic extension that profoundly modified the crustal structure and created the present-day Alboran Sea in the western Mediterranean.
DOI: 10.6084/m9.figshare.3454178
title: A tectonostratigraphic synthesis of the Sub-Andean basins: inferences on the position of South American intraplate accommodation zones and their control on South Atlantic opening

description: It has been shown in the accompanying paper that the Sub-Andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains. To test the hypothesis that changes in palaeo-depositional setting rely on the presence of a series of transverse zones of structural accommodation, data have been digitally compiled from across the South American continent. Spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries (structural accommodation zones), and patterns of subsidence and intraplate deformation. The results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which, on a regional scale, interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization. Their strong spatial relationship with Mesozoic, intraplate, alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during Gondwana breakup. These localized zones of high heat flow have important implications for source rock maturity in the interior, Phanerozoic intracratonic basins of South America. On the South Atlantic margin, the majority of these crustal lineaments correlate with failed arms of triple-junction rifts and define the boundaries to tectonostratigraphic domains recognized along the South Atlantic Rift System.
DOI: 10.6084/m9.figshare.3454178.v1
title: A tectonostratigraphic synthesis of the Sub-Andean basins: inferences on the position of South American intraplate accommodation zones and their control on South Atlantic opening

description: It has been shown in the accompanying paper that the Sub-Andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains. To test the hypothesis that changes in palaeo-depositional setting rely on the presence of a series of transverse zones of structural accommodation, data have been digitally compiled from across the South American continent. Spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries (structural accommodation zones), and patterns of subsidence and intraplate deformation. The results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which, on a regional scale, interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization. Their strong spatial relationship with Mesozoic, intraplate, alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during Gondwana breakup. These localized zones of high heat flow have important implications for source rock maturity in the interior, Phanerozoic intracratonic basins of South America. On the South Atlantic margin, the majority of these crustal lineaments correlate with failed arms of triple-junction rifts and define the boundaries to tectonostratigraphic domains recognized along the South Atlantic Rift System.
DOI: 10.6084/m9.figshare.3454175
title: A tectonostratigraphic synthesis of the Sub-Andean basins: implications for the geotectonic segmentation of the Andean Belt

description: The tectonic, structural and depositional history of 19 Sub-Andean foreland and eight southern Caribbean basins has been synthesized and is summarized by regional geohistory charts. These charts recapitulate the subsidence regimes recognized and have been used to evaluate correlations between genetically related stratigraphic sequences. Based on spatial and temporal changes in palaeo-depositional setting, the Sub-Andean region can be subdivided longitudinally into several tectonostratigraphic domains. The differential amount of subsidence between two adjacent tectonostratigraphic provinces or sub-provinces relies on the presence of a transverse zone of structural accommodation. The location of these transfer zones correlates with a number of known and several newly identified zones of intracontinental deformation. Combined with changes in the structural geometry of the Andean Fold and Thrust Belt and the relative dominance of basement fault systems along the length of the Andean foreland, it is suggested that the Andean Belt can be separated into five tectonic domains (which are themselves bounded by transverse, structural accommodation zones). Representing the multiphase reactivation of pre-existing basement fault systems, the influence of these broad zones of transcontinental deformation is most apparent during the Triassic–Jurassic period, suggesting that they were intimately associated with accommodating intraplate stresses during the breakup of the Gondwana Supercontinent.