cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454217
title: Global and regional palaeoceanographic changes as recorded in the mid-Cretaceous (Aptian–Albian) sequence of the Ionian zone (NW Greece)

description: Micropalaeontological and chemostratigraphic results from the mid-Cretaceous ‘upper siliceous zone’ of the Ionian zone, studied in two localities of NW Greece (Paliambela and Panaya), provide new insights into the palaeoceanographic evolution of Tethys and better correlation with well-studied Italian successions. <em>δ</em><sup>13</sup>C carbonate and organic-carbon isotope stratigraphy allows an improved correlation of the early Aptian Fourcade Level with Oceanic Anoxic Event 1a. Calcareous nannofossils point to intervals of reduced sedimentation within the late Aptian part of the limestones overlying the Fourcade Level. Combined calcareous nannofossil, radiolarian and planktonic foraminiferal biostratigraphy suggests that the overlying radiolarites (named herein the ‘Dercourt Member’) are essentially mid-Albian in age. Radiolarites of this age and thickness have not been identified in the well-explored Italian sections or in southern Albania. It is therefore likely that the Dercourt radiolarites reflect a high-productivity event localized in the Greek area of the Ionian zone, possibly caused by a bathymetrically induced upwelling of intermediate to deep waters that entered the Ionian trough following the opening of new oceanic gateways in the Eastern Mediterranean Tethys.
DOI: 10.6084/m9.figshare.3454217.v1
title: Global and regional palaeoceanographic changes as recorded in the mid-Cretaceous (Aptian–Albian) sequence of the Ionian zone (NW Greece)

description: Micropalaeontological and chemostratigraphic results from the mid-Cretaceous ‘upper siliceous zone’ of the Ionian zone, studied in two localities of NW Greece (Paliambela and Panaya), provide new insights into the palaeoceanographic evolution of Tethys and better correlation with well-studied Italian successions. <em>δ</em><sup>13</sup>C carbonate and organic-carbon isotope stratigraphy allows an improved correlation of the early Aptian Fourcade Level with Oceanic Anoxic Event 1a. Calcareous nannofossils point to intervals of reduced sedimentation within the late Aptian part of the limestones overlying the Fourcade Level. Combined calcareous nannofossil, radiolarian and planktonic foraminiferal biostratigraphy suggests that the overlying radiolarites (named herein the ‘Dercourt Member’) are essentially mid-Albian in age. Radiolarites of this age and thickness have not been identified in the well-explored Italian sections or in southern Albania. It is therefore likely that the Dercourt radiolarites reflect a high-productivity event localized in the Greek area of the Ionian zone, possibly caused by a bathymetrically induced upwelling of intermediate to deep waters that entered the Ionian trough following the opening of new oceanic gateways in the Eastern Mediterranean Tethys.
DOI: 10.6084/m9.figshare.3454214
title: Dating of the Ameralik dyke swarms of the Nuuk district, southern West Greenland: mafic intrusion events starting from <strong><em>c</em></strong>. 3510 Ma

description: This paper presents SHRIMP U–Pb zircon dating on four Meso- to Palaeoarchaean amphibolite-facies Ameralik dykes of differing compositions scattered throughout the Palaeoarchaean (3850–3600 Ma) amphibolite–granulite-facies Itsaq Gneiss Complex in the Nuuk district, southern West Greenland. In the north of the complex near the Isua supracrustal belt, an east–west-oriented, &gt;50 m thick metanoritic dyke, with abundant relicts of original opx + plag ± ol igneous mineralogy, gave an age of 3512 ± 7 Ma interpreted as the intrusion age (in general agreement with previous isotope dilution thermal ionization mass spectrometry data). In the same area, the best estimate for the intrusion age of a metadolerite dyke with the same orientation and similar degree of preservation is 3265 ± 15 Ma. At the mouth of Ameralik (fjord) 150 km to the SW, a large noritic Ameralik dyke, the Ugpik metadolerite, was largely recrystallized to amphibolite in the later Archaean. Relict magmatic zircon in this body implies an intrusion age of ≥3453 ± 16 Ma. In Itilleq (fjord) 60 km to the east of the Ugpik metadolerite, a dioritic component of a composite, dioritic–gabbroic intrusion cutting older, more deformed Ameralik dykes has yielded an age of 3257 ± 14 Ma for the time of intrusion. These new sensitive high-resolution ion microprobe dates on magmatic crystallization support previous field observations that the Ameralik dykes consist of several unrelated sets of dykes different in age by up to 250 Ma. The magmatic zircons in three of the dykes have 2700–2500 Ma overgrowths, interpreted to have grown during late Archaean amphibolite-facies tectonothermal events in the region. The original name ‘Ameralik dykes’ might propagate confusion that all such bodies can be regarded as the same age. Thus we recommend retaining the original definition of the Ameralik dykes but using the term ‘Ameralik dyke swarms’ to emphasize that unrelated intrusions of more than one age are present.
DOI: 10.6084/m9.figshare.3454214.v1
title: Dating of the Ameralik dyke swarms of the Nuuk district, southern West Greenland: mafic intrusion events starting from <strong><em>c</em></strong>. 3510 Ma

description: This paper presents SHRIMP U–Pb zircon dating on four Meso- to Palaeoarchaean amphibolite-facies Ameralik dykes of differing compositions scattered throughout the Palaeoarchaean (3850–3600 Ma) amphibolite–granulite-facies Itsaq Gneiss Complex in the Nuuk district, southern West Greenland. In the north of the complex near the Isua supracrustal belt, an east–west-oriented, &gt;50 m thick metanoritic dyke, with abundant relicts of original opx + plag ± ol igneous mineralogy, gave an age of 3512 ± 7 Ma interpreted as the intrusion age (in general agreement with previous isotope dilution thermal ionization mass spectrometry data). In the same area, the best estimate for the intrusion age of a metadolerite dyke with the same orientation and similar degree of preservation is 3265 ± 15 Ma. At the mouth of Ameralik (fjord) 150 km to the SW, a large noritic Ameralik dyke, the Ugpik metadolerite, was largely recrystallized to amphibolite in the later Archaean. Relict magmatic zircon in this body implies an intrusion age of ≥3453 ± 16 Ma. In Itilleq (fjord) 60 km to the east of the Ugpik metadolerite, a dioritic component of a composite, dioritic–gabbroic intrusion cutting older, more deformed Ameralik dykes has yielded an age of 3257 ± 14 Ma for the time of intrusion. These new sensitive high-resolution ion microprobe dates on magmatic crystallization support previous field observations that the Ameralik dykes consist of several unrelated sets of dykes different in age by up to 250 Ma. The magmatic zircons in three of the dykes have 2700–2500 Ma overgrowths, interpreted to have grown during late Archaean amphibolite-facies tectonothermal events in the region. The original name ‘Ameralik dykes’ might propagate confusion that all such bodies can be regarded as the same age. Thus we recommend retaining the original definition of the Ameralik dykes but using the term ‘Ameralik dyke swarms’ to emphasize that unrelated intrusions of more than one age are present.
DOI: 10.6084/m9.figshare.3454211
title: Transitional geometries between gently plunging and steeply plunging folds: an example from the Lower Palaeozoic Brabant Massif, Anglo-Brabant deformation belt, Belgium

description: Although many studies have dealt with markedly different fold orientations and associated cleavage–fold relationships within individual, single-phase deformed fold belts, there are very few descriptions of possible gradual, transitional fold geometries. The Lower Cambrian steep core of the single-phase deformed Brabant Massif contains steeply plunging, west-facing folds with a Z-shaped asymmetry, whereas the Ordovician–Silurian southern rim consists of gently plunging, upward facing folds. A gradual transition is observed between these end-member orientations, in a NW–SE-trending zone 1–1.5 km wide, in which the folds appear to be strongly curvilinear and locally downward facing. The structural geometries within this transition zone are described in detail and the geometric changes analysed in the light of the fold transition. The strongly variable fold orientations are tentatively attributed to a bulk oblate tectonic strain. The transition zone overlies an aeromagnetic lineament, classically interpreted as a dextral shear zone. The steeply plunging folds, the transition zone and the aeromagnetic lineaments are all attributed to a local dextral transpression, in which deformation is partitioned both vertically and laterally. The results indicate that within zones of heterogeneous transpression, the different deformation domains are not necessarily always fault bounded.
DOI: 10.6084/m9.figshare.3454211.v1
title: Transitional geometries between gently plunging and steeply plunging folds: an example from the Lower Palaeozoic Brabant Massif, Anglo-Brabant deformation belt, Belgium

description: Although many studies have dealt with markedly different fold orientations and associated cleavage–fold relationships within individual, single-phase deformed fold belts, there are very few descriptions of possible gradual, transitional fold geometries. The Lower Cambrian steep core of the single-phase deformed Brabant Massif contains steeply plunging, west-facing folds with a Z-shaped asymmetry, whereas the Ordovician–Silurian southern rim consists of gently plunging, upward facing folds. A gradual transition is observed between these end-member orientations, in a NW–SE-trending zone 1–1.5 km wide, in which the folds appear to be strongly curvilinear and locally downward facing. The structural geometries within this transition zone are described in detail and the geometric changes analysed in the light of the fold transition. The strongly variable fold orientations are tentatively attributed to a bulk oblate tectonic strain. The transition zone overlies an aeromagnetic lineament, classically interpreted as a dextral shear zone. The steeply plunging folds, the transition zone and the aeromagnetic lineaments are all attributed to a local dextral transpression, in which deformation is partitioned both vertically and laterally. The results indicate that within zones of heterogeneous transpression, the different deformation domains are not necessarily always fault bounded.
DOI: 10.6084/m9.figshare.3454208
title: Ductile shearing, hydrous fluid channelling and high-pressure metamorphism along the basement-cover contact on Sikinos, Cyclades, Greece

description: On the island of Sikinos in the Cyclades a schistose carapace separates a marble-blueschist cover sequence from underlying basement rocks. The basement ‘core’, comprising metapelitic gneisses, biotite-bearing granodiorites and aplites, becomes increasingly strained towards the carapace with progressive obliteration of earlier structures and intensification of a mylonitic foliation that becomes pervasive within the carapace. Granodiorites in the ‘core’ can be traced into microcline schists within the carapace, whereas metapelitic gneisses are converted to garnet-mica schists. The carapace is therefore a simple shear zone comprising basement rocks mylonitized during overthrusting of the cover. Biotite clusters in granodiorites of the basement ‘core’ are partially altered to phengite, whereas plagioclase shows incipient sericitization. In more strained rocks these hydration reactions show enhanced progress, until biotite and plagioclase are finally eliminated in the carapace. Rare glaucophane and chloritoid inclusions within garnets of metapelitic gneisses adjacent to the carapace are also attributed to hydration reactions. The association of higher strain with increased hydration in the basement suggests localization of fluids in the strained carapace zone, with limited percolation into underlying rocks. The restricted availability of water outside the carapace may be responsible for preservation of pre-Alpine assemblages in large parts of the Cycladic basement.
DOI: 10.6084/m9.figshare.3454208.v1
title: Ductile shearing, hydrous fluid channelling and high-pressure metamorphism along the basement-cover contact on Sikinos, Cyclades, Greece

description: On the island of Sikinos in the Cyclades a schistose carapace separates a marble-blueschist cover sequence from underlying basement rocks. The basement ‘core’, comprising metapelitic gneisses, biotite-bearing granodiorites and aplites, becomes increasingly strained towards the carapace with progressive obliteration of earlier structures and intensification of a mylonitic foliation that becomes pervasive within the carapace. Granodiorites in the ‘core’ can be traced into microcline schists within the carapace, whereas metapelitic gneisses are converted to garnet-mica schists. The carapace is therefore a simple shear zone comprising basement rocks mylonitized during overthrusting of the cover. Biotite clusters in granodiorites of the basement ‘core’ are partially altered to phengite, whereas plagioclase shows incipient sericitization. In more strained rocks these hydration reactions show enhanced progress, until biotite and plagioclase are finally eliminated in the carapace. Rare glaucophane and chloritoid inclusions within garnets of metapelitic gneisses adjacent to the carapace are also attributed to hydration reactions. The association of higher strain with increased hydration in the basement suggests localization of fluids in the strained carapace zone, with limited percolation into underlying rocks. The restricted availability of water outside the carapace may be responsible for preservation of pre-Alpine assemblages in large parts of the Cycladic basement.
DOI: 10.6084/m9.figshare.3454202
title: SIMS U–Pb zircon ages for the Upper Devonian Snobs Creek and Cerberean Volcanics from Victoria, with age uncertainty based on UO<sub>2</sub>/UO v. UO/U precision

description: Sensitive high-resolution ion microprobe (SHRIMP) zircon <sup>206</sup>Pb/<sup>238</sup>U ages for the Snobs Creek Volcanics and the overlying Cerberean Volcanics in central Victoria are analytically indistinguishable at 373.2 ± 1.8 and 375.0 ± 2.0 Ma (2σ). The SHRIMP data provide a refined numerical age for interbedded freshwater fish fauna of the Taggerty Formation and, together with its recently revised Givetian age based on independent faunal correlations, provide a new calibration point on the Devonian time scale. The use of Pb<sup>+</sup>/UO<sub>2</sub><sup>+</sup> rather than Pb<sup>+</sup>/U<sup>+</sup> in secondary ionization mass spectrometry (SIMS) dating reduces the range of secondary ion discrimination from zircon. Between-spot correlations observed between UO/U and UO<sub>2</sub>/UO ratios give quantitative estimates for external SIMS uncertainty per spot age that are independent of assumed uniformity in zircon Pb/U. They can exceed internal uncertainties by up to 1.5% dependent on the analytical session. This has important effects on the calibration of SIMS ages at the sub-percent level using imperfect reference zircons subject to small-scale perturbations of the U/Pb system.
DOI: 10.6084/m9.figshare.3454202.v1
title: SIMS U–Pb zircon ages for the Upper Devonian Snobs Creek and Cerberean Volcanics from Victoria, with age uncertainty based on UO<sub>2</sub>/UO v. UO/U precision

description: Sensitive high-resolution ion microprobe (SHRIMP) zircon <sup>206</sup>Pb/<sup>238</sup>U ages for the Snobs Creek Volcanics and the overlying Cerberean Volcanics in central Victoria are analytically indistinguishable at 373.2 ± 1.8 and 375.0 ± 2.0 Ma (2σ). The SHRIMP data provide a refined numerical age for interbedded freshwater fish fauna of the Taggerty Formation and, together with its recently revised Givetian age based on independent faunal correlations, provide a new calibration point on the Devonian time scale. The use of Pb<sup>+</sup>/UO<sub>2</sub><sup>+</sup> rather than Pb<sup>+</sup>/U<sup>+</sup> in secondary ionization mass spectrometry (SIMS) dating reduces the range of secondary ion discrimination from zircon. Between-spot correlations observed between UO/U and UO<sub>2</sub>/UO ratios give quantitative estimates for external SIMS uncertainty per spot age that are independent of assumed uniformity in zircon Pb/U. They can exceed internal uncertainties by up to 1.5% dependent on the analytical session. This has important effects on the calibration of SIMS ages at the sub-percent level using imperfect reference zircons subject to small-scale perturbations of the U/Pb system.
DOI: 10.6084/m9.figshare.3454199
title: <sup>40</sup>Ar/<sup>39</sup>Ar geochronology of Carboniferous-Permian volcanism in the Midland Valley, Scotland

description: Twenty-one new <sup>40</sup>Ar/<sup>39</sup>Ar step-heating experiments on mineral separates from intrusive and extrusive Carboniferous and Permian igneous rocks in the Midland Valley of Scotland yielded 17 concordant experiments with a relative age precision better than 1% (2σ). These ages resolve inconsistencies between existing K-Ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales. The precise <sup>40</sup>Ar/<sup>39</sup>Ar dates are stratigraphically constrained to stage level and can contribute to Carboniferous timescale tie points at the Tournaisian-Visean boundary, within the Visean and at the Carboniferous-Permian boundary. Situated in the extending Variscan foreland, two distinct phases of extension-related transitional-alkaline volcanism have been resolved in the Dinantian: the Garleton Hills Volcanic Formation in the eastern Midland Valley near the Tournaisian-Visean boundary, 342.1 ± 1.3 and 342.4 ± 1.1 Ma; and the Clyde Plateau Volcanic Formation in the western Midland Valley during the mid-Visean, 335 ± 2–329.2 ± 1.4 Ma. Alkaline basic sills near Edinburgh, previously thought to be Namurian, appear to be coeval with the Clyde Plateau Volcanic Formation at 331.8 ± 1.3–329.3 ± 1.5 Ma. The new ages allow correlation between these short-lived Dinantian magmatic pulses and extensional and magmatic phases in the Northumberland-Solway and Tweed basins to the south. After late Westphalian, end-Variscan, compression and a regionally important tholeiitic intrusive phase at <em>c.</em> 301–295 Ma, alkaline magmatism related to post-Variscan extension occurred in the central and western Midland Valley during the latest Carboniferous or Permian from 298.3 ± 1.3 to 292.1 ± 1.1 Ma. This correlates well with post-Varsican extension and magmatism observed across the NW European foreland from 300 to 280 Ma.
DOI: 10.6084/m9.figshare.3454199.v1
title: <sup>40</sup>Ar/<sup>39</sup>Ar geochronology of Carboniferous-Permian volcanism in the Midland Valley, Scotland

description: Twenty-one new <sup>40</sup>Ar/<sup>39</sup>Ar step-heating experiments on mineral separates from intrusive and extrusive Carboniferous and Permian igneous rocks in the Midland Valley of Scotland yielded 17 concordant experiments with a relative age precision better than 1% (2σ). These ages resolve inconsistencies between existing K-Ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales. The precise <sup>40</sup>Ar/<sup>39</sup>Ar dates are stratigraphically constrained to stage level and can contribute to Carboniferous timescale tie points at the Tournaisian-Visean boundary, within the Visean and at the Carboniferous-Permian boundary. Situated in the extending Variscan foreland, two distinct phases of extension-related transitional-alkaline volcanism have been resolved in the Dinantian: the Garleton Hills Volcanic Formation in the eastern Midland Valley near the Tournaisian-Visean boundary, 342.1 ± 1.3 and 342.4 ± 1.1 Ma; and the Clyde Plateau Volcanic Formation in the western Midland Valley during the mid-Visean, 335 ± 2–329.2 ± 1.4 Ma. Alkaline basic sills near Edinburgh, previously thought to be Namurian, appear to be coeval with the Clyde Plateau Volcanic Formation at 331.8 ± 1.3–329.3 ± 1.5 Ma. The new ages allow correlation between these short-lived Dinantian magmatic pulses and extensional and magmatic phases in the Northumberland-Solway and Tweed basins to the south. After late Westphalian, end-Variscan, compression and a regionally important tholeiitic intrusive phase at <em>c.</em> 301–295 Ma, alkaline magmatism related to post-Variscan extension occurred in the central and western Midland Valley during the latest Carboniferous or Permian from 298.3 ± 1.3 to 292.1 ± 1.1 Ma. This correlates well with post-Varsican extension and magmatism observed across the NW European foreland from 300 to 280 Ma.
DOI: 10.6084/m9.figshare.3454196
title: Yarlung Zangbo ophiolites (Southern Tibet) revisited: geodynamic implications from the mineral record

description: We present mineral chemistry data and petrological evidence from the Yarlung Zangbo suture zone ophiolites (Southern Tibet) suggesting that they represent a collage of heterogeneous massifs. Mantle sections in these ophiolites consist of harzburgite and lherzolite cut by several generations of gabbroic to diabasic intrusions, all affected by high-temperature deformation. Pyroxenitic bands are parallel to the mantle foliation. Crustal plutonic sections, consisting of dunite, wehrlite and gabbro, are thin or absent and have been observed only in the Dazhuqu massif. Plagioclase is an additional phase associated with crustal peridotites. The mineral chemistry of silicate minerals and spinel in the mantle and crustal rocks varies widely and is believed to reflect complex melt percolation and reaction. The massifs record polybaric exhumation steps from at least 50 km depth to the plagioclase stability field. Pyroxene has re-equilibrated compositions from 1200 °C down to medium-grade metamorphic conditions. The mantle peridotites are interpreted as the residues of 10–40% partial melting of a fertile lherzolitic source. High Cr number, low TiO<sub>2</sub> content and relatively high Fe<sup>3+</sup> number of spinels suggest that the ophiolitic massifs were generated in a suprasubduction zone (arc or back-arc) environment.
DOI: 10.6084/m9.figshare.3454196.v1
title: Yarlung Zangbo ophiolites (Southern Tibet) revisited: geodynamic implications from the mineral record

description: We present mineral chemistry data and petrological evidence from the Yarlung Zangbo suture zone ophiolites (Southern Tibet) suggesting that they represent a collage of heterogeneous massifs. Mantle sections in these ophiolites consist of harzburgite and lherzolite cut by several generations of gabbroic to diabasic intrusions, all affected by high-temperature deformation. Pyroxenitic bands are parallel to the mantle foliation. Crustal plutonic sections, consisting of dunite, wehrlite and gabbro, are thin or absent and have been observed only in the Dazhuqu massif. Plagioclase is an additional phase associated with crustal peridotites. The mineral chemistry of silicate minerals and spinel in the mantle and crustal rocks varies widely and is believed to reflect complex melt percolation and reaction. The massifs record polybaric exhumation steps from at least 50 km depth to the plagioclase stability field. Pyroxene has re-equilibrated compositions from 1200 °C down to medium-grade metamorphic conditions. The mantle peridotites are interpreted as the residues of 10–40% partial melting of a fertile lherzolitic source. High Cr number, low TiO<sub>2</sub> content and relatively high Fe<sup>3+</sup> number of spinels suggest that the ophiolitic massifs were generated in a suprasubduction zone (arc or back-arc) environment.