cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454577.v1
title: Timing of migmatization and granite genesis in the Northwestern Terrane of Svalbard, Norway: implications for regional correlations in the Arctic Caledonides

description: U–Pb ion microprobe investigations of zircons from gneisses, granites and migmatites of the pre-Devonian Smerenburgfjorden and Richarddalen Complexes constrain the tectonic evolution and origin of Svalbard's Northwestern Terrane. Field relationships combined with U–Pb age data indicate that a late Meso- to Neoproterozoic metapelitic protolith was intruded by Tonian (<em>c</em>. 960 Ma) granitoids and suggest that the entire Northwestern Terrane is underlain by early Neoproterozoic granitoids intruding older metasediments. Both rock types were later involved in Caledonian deformation, with subsequent migmatization and granite genesis at <em>c</em>. 435–420 Ma. Ages of inherited zircons in granites and migmatites reflect anatexis of this late Meso- to Neoproterozoic protolith, with zircon xenocrysts ranging in age from <em>c</em>. 1030 to 1820 Ma. Pronounced lithological, geochronological and tectonothermal similarities to NE Svalbard (Nordaustlandet) and the Krummedal supracrustal sequence of East Greenland suggest a strong correlation between Svalbard and East Greenland prior to Caledonian orogenesis.
DOI: 10.6084/m9.figshare.3454574
title: Probing the basement of southern Tibet: evidence from crustal xenoliths entrained in a Miocene ultrapotassic dyke

description: A variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung–Tsangpo suture zone in southern Tibet. Garnet–clinopyroxene–plagioclase–quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130–1330 °C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of <em>c</em>. 16 °C km<sup>−1</sup>. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920–1130 °C and 17–24 kbar, whereas felsic granulites equilibrated at 870–900 °C at an inferred pressure of 17 kbar. <em>In situ</em> U–(Th)–Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean <sup>206</sup>Pb/<sup>238</sup>U ages of 16.8 ± 0.9 Ma and 15.6 ± 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean <sup>208</sup>Pb/<sup>232</sup>Th age of 14.4 ± 0.4 Ma. These results show that the southern Tibet basement reached a thickness of <em>c</em>. 80 km by 17–14 Ma at the latest and has remained unchanged until the present day.
DOI: 10.6084/m9.figshare.3454574.v1
title: Probing the basement of southern Tibet: evidence from crustal xenoliths entrained in a Miocene ultrapotassic dyke

description: A variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung–Tsangpo suture zone in southern Tibet. Garnet–clinopyroxene–plagioclase–quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130–1330 °C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of <em>c</em>. 16 °C km<sup>−1</sup>. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920–1130 °C and 17–24 kbar, whereas felsic granulites equilibrated at 870–900 °C at an inferred pressure of 17 kbar. <em>In situ</em> U–(Th)–Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean <sup>206</sup>Pb/<sup>238</sup>U ages of 16.8 ± 0.9 Ma and 15.6 ± 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean <sup>208</sup>Pb/<sup>232</sup>Th age of 14.4 ± 0.4 Ma. These results show that the southern Tibet basement reached a thickness of <em>c</em>. 80 km by 17–14 Ma at the latest and has remained unchanged until the present day.
DOI: 10.6084/m9.figshare.3454571
title: Constraints on <sup>87</sup>Sr/<sup>86</sup>Sr of Late Ediacaran seawater: insight from Siberian high-Sr limestones

description: In SE Siberia, carbonate formations with δ<sup>13</sup>C<sub>carb</sub> values ranging between −12‰ and −7‰ (V-PDB) and Sr concentrations of up to 2.5% occupy an area of 40 000 km<sup>2</sup>. Several successions exceed 1000 m in thickness and represent the world's largest known exposures of sedimentary carbonates exhibiting extreme depletion in <sup>13</sup>C. The carbonates were deposited on a carbonate platform evolving from a mixed carbonate–siliciclastic ramp to a carbonate ramp, and then from a peritidal rimmed shelf to a deep-water open shelf. All sequences reveal a facies-independent, upward rise in marine δ<sup>13</sup>C<sub>carb</sub> from −12‰ to −7‰. The trend and magnitude of the values mimic those that are characteristic of the 600–550 Ma Shuram–Wonoka isotope event. A coincident stratigraphic rise in <sup>87</sup>Sr/<sup>86</sup>Sr from 0.70802 to 0.70862 in several sections of limestones, containing 4400 μg g<sup>−1</sup> Sr on average, is considered to be by far the best available constraint on a temporal variation of seawater isotopic composition through the Late Ediacaran. If the greatest temporal rate of change in seawater <sup>87</sup>Sr/<sup>86</sup>Sr observed in the Cenozoic is applied to the Siberian sections, the calculated minimum duration for the Suram–Wonoka event is 10 Ma.
DOI: 10.6084/m9.figshare.3454571.v1
title: Constraints on <sup>87</sup>Sr/<sup>86</sup>Sr of Late Ediacaran seawater: insight from Siberian high-Sr limestones

description: In SE Siberia, carbonate formations with δ<sup>13</sup>C<sub>carb</sub> values ranging between −12‰ and −7‰ (V-PDB) and Sr concentrations of up to 2.5% occupy an area of 40 000 km<sup>2</sup>. Several successions exceed 1000 m in thickness and represent the world's largest known exposures of sedimentary carbonates exhibiting extreme depletion in <sup>13</sup>C. The carbonates were deposited on a carbonate platform evolving from a mixed carbonate–siliciclastic ramp to a carbonate ramp, and then from a peritidal rimmed shelf to a deep-water open shelf. All sequences reveal a facies-independent, upward rise in marine δ<sup>13</sup>C<sub>carb</sub> from −12‰ to −7‰. The trend and magnitude of the values mimic those that are characteristic of the 600–550 Ma Shuram–Wonoka isotope event. A coincident stratigraphic rise in <sup>87</sup>Sr/<sup>86</sup>Sr from 0.70802 to 0.70862 in several sections of limestones, containing 4400 μg g<sup>−1</sup> Sr on average, is considered to be by far the best available constraint on a temporal variation of seawater isotopic composition through the Late Ediacaran. If the greatest temporal rate of change in seawater <sup>87</sup>Sr/<sup>86</sup>Sr observed in the Cenozoic is applied to the Siberian sections, the calculated minimum duration for the Suram–Wonoka event is 10 Ma.
DOI: 10.6084/m9.figshare.3454568
title: The Cleveland Dyke in southern Scotland

description: There have been a number of recent papers on ‘giant dykes’, i.e. dykes exceeding 100 km in length. This paper extends the known length of the Tertiary (Palaeogene) Cleveland Dyke (CD) by about 64 km, giving a total proven length of <em>c.</em> 260 km. The results of a detailed investigation using ground magnetic surveys have discovered 26 additional exposures in southern Scotland, allowing magnetic, petrographic and geochemical measurements and magnetic modelling to be carried out, resulting in one of the most detailed studies of a ‘giant’ dyke. The structure of the CD complex in the Southern Uplands of SW Scotland has been influenced by pre-existing structures, in particular faults and granitic intrusions. It is chemically heterogeneous without systematic trend along its length. This heterogeneity, plus segmentation along strike, numerous offsets, in particular one of 5 km along the Water of Ken, en-échelon structure, narrow width at many localities (2.3–0.8 m) with lack of baking of adjacent country rocks, all argue strongly against lateral intrusion from the Mull intrusive complex, as has been proposed. Instead, aeromagnetic surveys and wide-angle seismic and gravity surveys make it probable that the dyke relates to a regional magma reservoir beneath the Southern Uplands.
DOI: 10.6084/m9.figshare.3454568.v1
title: The Cleveland Dyke in southern Scotland

description: There have been a number of recent papers on ‘giant dykes’, i.e. dykes exceeding 100 km in length. This paper extends the known length of the Tertiary (Palaeogene) Cleveland Dyke (CD) by about 64 km, giving a total proven length of <em>c.</em> 260 km. The results of a detailed investigation using ground magnetic surveys have discovered 26 additional exposures in southern Scotland, allowing magnetic, petrographic and geochemical measurements and magnetic modelling to be carried out, resulting in one of the most detailed studies of a ‘giant’ dyke. The structure of the CD complex in the Southern Uplands of SW Scotland has been influenced by pre-existing structures, in particular faults and granitic intrusions. It is chemically heterogeneous without systematic trend along its length. This heterogeneity, plus segmentation along strike, numerous offsets, in particular one of 5 km along the Water of Ken, en-échelon structure, narrow width at many localities (2.3–0.8 m) with lack of baking of adjacent country rocks, all argue strongly against lateral intrusion from the Mull intrusive complex, as has been proposed. Instead, aeromagnetic surveys and wide-angle seismic and gravity surveys make it probable that the dyke relates to a regional magma reservoir beneath the Southern Uplands.
DOI: 10.6084/m9.figshare.3454562
title: Construction, solidification and internal differentiation of a large felsic arc pluton: Cathedral Peak granodiorite, Sierra Nevada Batholith

description: The Tuolumne Batholith (TB), Sierra Nevada Batholith (USA), is an archetypal large, zoned arc intrusion (<em>c</em>. 1200 km<sup>2</sup>). Previous work proposed that compositional zonation observed in the TB was produced <em>in-situ</em> by inward differentiation of a large magma chamber and/or large-scale, intrachamber magma mixing. Recent geochronology shows that the TB was intruded over 8–9 Ma, making single pulse fractionation or mixing in a magma chamber of TB dimensions unlikely. We examine processes responsible for compositional variation in the Cathedral Peak Granodiorite, which is the largest mapped unit of the TB. New field, geochemical and geochronological work along a roughly contact-perpendicular 5 km transect indicates: (1) magmatic foliation is steeply-dipping (&gt;60°); (2) field evidence for repeated separation of crystals from melt and local magma mixing is observed; (3) U–Pb zircon ages at opposing ends of the transect are indistinguishable within error (<em>c</em>. 87.5 Ma); (4) bulk composition varies only modestly but trace elements show variable degrees of scatter; (5) εNd(t) and <sup>87</sup>Sr/<sup>86</sup>Sr(i) have small variation compared with that in the whole TB. Geochemical and isotopic data are compatible with fractionation of major silicates and accessory minerals. However, the geochemical spatial variation, minor isotopic variation and field evidence suggest that fractionation was highly disorganized and also involved mixing with new input magma and remobilization of crystal mush as the pluton solidified. Our observations are consistent with the construction of a large and dynamic magma system within the last <em>c</em>. 1 Ma of TB growth.
DOI: 10.6084/m9.figshare.3454562.v1
title: Construction, solidification and internal differentiation of a large felsic arc pluton: Cathedral Peak granodiorite, Sierra Nevada Batholith

description: The Tuolumne Batholith (TB), Sierra Nevada Batholith (USA), is an archetypal large, zoned arc intrusion (<em>c</em>. 1200 km<sup>2</sup>). Previous work proposed that compositional zonation observed in the TB was produced <em>in-situ</em> by inward differentiation of a large magma chamber and/or large-scale, intrachamber magma mixing. Recent geochronology shows that the TB was intruded over 8–9 Ma, making single pulse fractionation or mixing in a magma chamber of TB dimensions unlikely. We examine processes responsible for compositional variation in the Cathedral Peak Granodiorite, which is the largest mapped unit of the TB. New field, geochemical and geochronological work along a roughly contact-perpendicular 5 km transect indicates: (1) magmatic foliation is steeply-dipping (&gt;60°); (2) field evidence for repeated separation of crystals from melt and local magma mixing is observed; (3) U–Pb zircon ages at opposing ends of the transect are indistinguishable within error (<em>c</em>. 87.5 Ma); (4) bulk composition varies only modestly but trace elements show variable degrees of scatter; (5) εNd(t) and <sup>87</sup>Sr/<sup>86</sup>Sr(i) have small variation compared with that in the whole TB. Geochemical and isotopic data are compatible with fractionation of major silicates and accessory minerals. However, the geochemical spatial variation, minor isotopic variation and field evidence suggest that fractionation was highly disorganized and also involved mixing with new input magma and remobilization of crystal mush as the pluton solidified. Our observations are consistent with the construction of a large and dynamic magma system within the last <em>c</em>. 1 Ma of TB growth.
DOI: 10.6084/m9.figshare.3454556
title: Uniform processes of melt differentiation in the central Izu Bonin volcanic arc (NW Pacific)

description: The intra-oceanic Izu Bonin arc (NW Pacific) has produced a bimodal spectrum of melts with maxima in the basaltic andesitic (<em>c</em>. 53–54 wt% SiO<sub>2</sub>) and rhyolitic range (<em>c</em>. 70–72 wt% SiO<sub>2</sub>) since arc inception <em>c</em>. 48–49 million years ago. Composition of phenocrysts and accessory minerals from 21 contemporaneous fallout tephras from ODP Site 782A confirm the bimodality and uniformity of the erupted melts. The basaltic andesite melts equilibrated with calcic plagioclase (<em>c</em>. An<sub>70–95</sub>), high-Mg# clino- and orthopyroxene and low-Ti titanomagnetite. Dacitic and rhyolitic melts crystallized sodic plagioclase (<em>c</em>. An<sub>40–60</sub>), low-Mg# clino- and orthopyroxene, apatite, Ti-rich titanomagnetite in addition to occasional ilmenite and amphibole. The Izu melts are inferred to crystallize at oxygen fugacities between <em>c</em>. 0 to +2.5 log<sub>10</sub> units relative to FMQ, at temperatures between <em>c</em>. 775° and 1100 °C and at pressures between <em>c</em>. 300 and <em>c</em>. 1100 MPa, corresponding to <em>c</em>. 5–35 km lithospheric depth. The compositional uniformity of the tephra layers, which are spaced on average 230 ± 380 ka apart, suggest uniform processes of differentiation since at least <em>c</em>. 42 Ma ago. The tephra record shows no indication of periodic or progressive crustal growth that might correlate with the alternate periods of arc formation, arc rifting or backarc spreading, or would suggest an increasingly efficient ‘crustal filter’ with time. The tephra data tentatively conform to a model where crust grows steadily through intrusions of mafic and evolved melt body batches whereby buoyancy controls the level of solidification. While the tephra compositions demonstrate the uniformity of the processes of melt formation and differentiation through time, the data do not permit the differentiation processes themselves to be constrained. These may comprise fractional crystallization, crustal fusion, fusion of non-peridotitic sub-crustal lithologies, or any combination of these processes.
DOI: 10.6084/m9.figshare.3454556.v1
title: Uniform processes of melt differentiation in the central Izu Bonin volcanic arc (NW Pacific)

description: The intra-oceanic Izu Bonin arc (NW Pacific) has produced a bimodal spectrum of melts with maxima in the basaltic andesitic (<em>c</em>. 53–54 wt% SiO<sub>2</sub>) and rhyolitic range (<em>c</em>. 70–72 wt% SiO<sub>2</sub>) since arc inception <em>c</em>. 48–49 million years ago. Composition of phenocrysts and accessory minerals from 21 contemporaneous fallout tephras from ODP Site 782A confirm the bimodality and uniformity of the erupted melts. The basaltic andesite melts equilibrated with calcic plagioclase (<em>c</em>. An<sub>70–95</sub>), high-Mg# clino- and orthopyroxene and low-Ti titanomagnetite. Dacitic and rhyolitic melts crystallized sodic plagioclase (<em>c</em>. An<sub>40–60</sub>), low-Mg# clino- and orthopyroxene, apatite, Ti-rich titanomagnetite in addition to occasional ilmenite and amphibole. The Izu melts are inferred to crystallize at oxygen fugacities between <em>c</em>. 0 to +2.5 log<sub>10</sub> units relative to FMQ, at temperatures between <em>c</em>. 775° and 1100 °C and at pressures between <em>c</em>. 300 and <em>c</em>. 1100 MPa, corresponding to <em>c</em>. 5–35 km lithospheric depth. The compositional uniformity of the tephra layers, which are spaced on average 230 ± 380 ka apart, suggest uniform processes of differentiation since at least <em>c</em>. 42 Ma ago. The tephra record shows no indication of periodic or progressive crustal growth that might correlate with the alternate periods of arc formation, arc rifting or backarc spreading, or would suggest an increasingly efficient ‘crustal filter’ with time. The tephra data tentatively conform to a model where crust grows steadily through intrusions of mafic and evolved melt body batches whereby buoyancy controls the level of solidification. While the tephra compositions demonstrate the uniformity of the processes of melt formation and differentiation through time, the data do not permit the differentiation processes themselves to be constrained. These may comprise fractional crystallization, crustal fusion, fusion of non-peridotitic sub-crustal lithologies, or any combination of these processes.
DOI: 10.6084/m9.figshare.3454553
title: New U–Pb and Rb–Sr constraints on pre-Acadian tectonism in North Wales

description: A new U–Pb date of 615.2 ± 1.3 (2σ) Ma for the Twt Hill Granite, North Wales, contrasts with an Rb–Sr isochron age of 491 ± 12 (2σ) Ma from the same body. The latter age is thought to result from isotope resetting during regional low-grade metamorphism or fault reactivation. The Rb–Sr age also coincides with the onset of latest Cambrian to Early Tremadoc regression and is taken to reflect tectonic uplift prior to the Arenig overstep at around 478 Ma. It is proposed that this in turn reflects plate-scale processes along the contemporary peri-Gondwanan continental margin.
DOI: 10.6084/m9.figshare.3454553.v1
title: New U–Pb and Rb–Sr constraints on pre-Acadian tectonism in North Wales

description: A new U–Pb date of 615.2 ± 1.3 (2σ) Ma for the Twt Hill Granite, North Wales, contrasts with an Rb–Sr isochron age of 491 ± 12 (2σ) Ma from the same body. The latter age is thought to result from isotope resetting during regional low-grade metamorphism or fault reactivation. The Rb–Sr age also coincides with the onset of latest Cambrian to Early Tremadoc regression and is taken to reflect tectonic uplift prior to the Arenig overstep at around 478 Ma. It is proposed that this in turn reflects plate-scale processes along the contemporary peri-Gondwanan continental margin.
DOI: 10.6084/m9.figshare.3454550
title: New SIMS U–Pb zircon ages from the Langavat Belt, South Harris, NW Scotland: implications for the Lewisian terrane model

description: Secondary ionization mass spectrometry (SIMS) U/Pb dating of zircon has been applied to rocks of the Lewisian Complex of South Harris (Outer Hebrides, NW Scotland), yielding insights into the complex geological evolution of this region and enhancing our understanding of terranes in the Lewisian Gneiss Complex. Results show that tonalite–trondhjemite–granodiorite magmatism occurred in the Tarbert Terrane between <em>c</em>. 2850 and 2830 Ma, equivalent to similar rocks in other parts of the Outer Hebrides. Magmatism was accompanied or closely followed by high-grade metamorphism at <em>c</em>. 2830 Ma, the first reported occurrence of such an event at this time. These rocks were affected by a subsequent high-grade metamorphic event at <em>c</em>. 2730 Ma, which has correlatives both in the Outer Hebrides and in the mainland Lewisian Gruinard Terrane. These data suggest that the ‘terranes’ forming the Outer Hebrides and parts of the mainland Lewisian were once contiguous and were fragmented by post-2730 Ma events. The <em>c</em>. 1700–1660 Ma ages from felsic sheets and pegmatites within the Langavat Shear Zone may record the reassembly of these crustal fragments.
DOI: 10.6084/m9.figshare.3454550.v1
title: New SIMS U–Pb zircon ages from the Langavat Belt, South Harris, NW Scotland: implications for the Lewisian terrane model

description: Secondary ionization mass spectrometry (SIMS) U/Pb dating of zircon has been applied to rocks of the Lewisian Complex of South Harris (Outer Hebrides, NW Scotland), yielding insights into the complex geological evolution of this region and enhancing our understanding of terranes in the Lewisian Gneiss Complex. Results show that tonalite–trondhjemite–granodiorite magmatism occurred in the Tarbert Terrane between <em>c</em>. 2850 and 2830 Ma, equivalent to similar rocks in other parts of the Outer Hebrides. Magmatism was accompanied or closely followed by high-grade metamorphism at <em>c</em>. 2830 Ma, the first reported occurrence of such an event at this time. These rocks were affected by a subsequent high-grade metamorphic event at <em>c</em>. 2730 Ma, which has correlatives both in the Outer Hebrides and in the mainland Lewisian Gruinard Terrane. These data suggest that the ‘terranes’ forming the Outer Hebrides and parts of the mainland Lewisian were once contiguous and were fragmented by post-2730 Ma events. The <em>c</em>. 1700–1660 Ma ages from felsic sheets and pegmatites within the Langavat Shear Zone may record the reassembly of these crustal fragments.
DOI: 10.6084/m9.figshare.3454547
title: Tectonic response of the central Chilean margin (35–38°S) to the collision and subduction of heterogeneous oceanic crust: a thermochronological study

description: Along-strike geological segmentation in the Andean chain has been recognized at various scales and is usually attributed to changes in plate motion vectors, as well as the upper-plate expression of differing subducted slab age, strength and composition. We present new multi-phase <sup>40</sup>Ar/<sup>39</sup>Ar, apatite fission-track and zircon and apatite (U–Th)/He data from a north–south-oriented traverse between 35 and 38°S along the Principal Andean Cordillera of Chile that reveal (1) rapid cooling at 18 and 15 Ma, which can be attributed to both thermal relaxation following magmatic intrusion and regional-scale exhumation, and (2) along-strike differences in the extent of exhumation since 7.5 Ma that may be a consequence of the subduction of the Juan Fernandez Ridge above the flat-slab segment at 32°, since 10 Ma. A comparison of the response of the South American Plate to the collision of the Carnegie, Nazca and Juan Fernandez ridges suggests that slab flattening is not the dominant driving force that exhumes the upper plate in these settings. Rather, the extent of exhumation is controlled by pre-existing structural weaknesses, the time duration of the dynamically supported topography, and climate.