cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454547.v1
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.
DOI: 10.6084/m9.figshare.3454541
title: Chemical and Nd isotope constraints on granitoid sources involved in the Caledonian Orogeny in Scotland

description: Major- and trace-element data and Nd isotope compositions for granitoid samples from the Grampian Highlands in Scotland show a systematic evolution in the composition of their sources in the course of the Caledonian Orogeny. Granitoids of 511–451 Ma, related to the collision of the Midland Valley island arc with the Grampian terrane, show S-type affinity and fractionated REE patterns with minor Eu anomalies and low initial ϵ<sub>Nd</sub> values of −14.1 to −11.2 suggesting melting of predominantly Dalradian metasediments. Subsequently formed granitoids of 425–406 Ma derived from an assumed Andean plate margin comprise a wide spectrum of rock types including I-type granite–granodiorite, and S-type granitoids, monzonites and alkali granites. The trace-element patterns of these rocks and the range of initial ϵ<sub>Nd</sub> values of −2.1 to −6.9 are consistent with melting of variably rejuvenated crust as found in continental margin settings. We conclude that the Grampian Highlands were affected by two major crust-modifying events during the Caledonian Orogeny: predominantly recycling of older crust during docking of the Midland Valley arc and addition of juvenile, mantle-derived material to the crust during the convergence of Avalonia with Laurentia.
DOI: 10.6084/m9.figshare.3454541.v1
title: Chemical and Nd isotope constraints on granitoid sources involved in the Caledonian Orogeny in Scotland

description: Major- and trace-element data and Nd isotope compositions for granitoid samples from the Grampian Highlands in Scotland show a systematic evolution in the composition of their sources in the course of the Caledonian Orogeny. Granitoids of 511–451 Ma, related to the collision of the Midland Valley island arc with the Grampian terrane, show S-type affinity and fractionated REE patterns with minor Eu anomalies and low initial ϵ<sub>Nd</sub> values of −14.1 to −11.2 suggesting melting of predominantly Dalradian metasediments. Subsequently formed granitoids of 425–406 Ma derived from an assumed Andean plate margin comprise a wide spectrum of rock types including I-type granite–granodiorite, and S-type granitoids, monzonites and alkali granites. The trace-element patterns of these rocks and the range of initial ϵ<sub>Nd</sub> values of −2.1 to −6.9 are consistent with melting of variably rejuvenated crust as found in continental margin settings. We conclude that the Grampian Highlands were affected by two major crust-modifying events during the Caledonian Orogeny: predominantly recycling of older crust during docking of the Midland Valley arc and addition of juvenile, mantle-derived material to the crust during the convergence of Avalonia with Laurentia.
DOI: 10.6084/m9.figshare.3454535
title: Exhumation and deformation history of the lower crustal section of the Valstrona di Omegna in the Ivrea Zone, southern Alps

description: The Ivrea Zone (southern Alps) is one of the key regions interpreted as exposing a section of the lower continental crust and was the subject of several review-type articles. The Ivrea–Verbano Zone was rotated into an upright position along the Insubric mylonite belt. In the southeast, this unit is in contact with the Strona Ceneri Zone, which is interpreted as upper continental crust crossing the Permian Cossato–Mergozzo–Brissagio Line (CMB Line). The CMB mylonites are locally overprinted by the mylonites and cataclasites of the Pogallo Line, which was active during the Jurassic. In addition, the sinistral, steeply inclined Rosarolo shear zone was active over a long time span from the ductile into the brittle field, i.e. from the Early Permian (high-temperature ultra-mylonites) to the Neo-Alpine basic dykes and pseudotachylites. The high-temperature mylonites accommodated crustal extension and may be related to normal faults generated by magmatic underplating. The reactivation at different crustal levels during exhumation and tilting is documented by strain increments at decreasing P/T conditions. Its present subvertical orientation was attained during the Neo-Alpine deformation. Constraints on its exhumation history are based on new <sup>40</sup>Ar/<sup>39</sup>Ar hornblende ages, K–Ar biotite ages and zircon fission-track data along the NE–SW trending Valstrona section. A re-interpretation of existing U–Pb monazite ages is included, based on a higher closure temperature for monazite. The oldest monazite ages are observed in proximity to the Pogallo Line (<em>c</em>. 292 Ma). Heat input by mafic intrusions was sufficient to reset the U–Pb monazite system, as is evidenced by the youngest ages in the vicinity of the Insubric Line. The re-interpretation favours the hypothesis that the oldest monazite ages are the result of complete resetting by a Permian thermal event. The <sup>40</sup>Ar/<sup>39</sup>Ar hornblende ages and K–Ar biotite ages document the cooling after Permian heating. Roughly parallel age progressions decrease from the Pogallo Line (hornblende: 271 Ma vs. biotite: 227 Ma) towards the Insubric Line (hornblende: 201 Ma vs. biotite: 156 Ma). Zircon fission-track ages run parallel to the biotite ages in the upper part of the profile, whereas towards the Insubric Line a significant deviation from the biotite age progression is attributed to tilting of the basement during the Oligocene. Zircon fission-track ages around 38 Ma are found close to the Insubric Line. No age offset, neither at the CMB nor at the Pogallo Line, is observed. This confirms the hypothesis that the Pogallo Line is an oblique normal fault, and that the CMB Line has accommodated only minor vertical displacement. The capture of the different cooling ages confirms the tilting of the Ivrea–Verbano Zone during the Neo-Alpine deformation and contradicts the tilting of the Ivrea–Verbano Zone during the Permian.
DOI: 10.6084/m9.figshare.3454535.v1
title: Exhumation and deformation history of the lower crustal section of the Valstrona di Omegna in the Ivrea Zone, southern Alps

description: The Ivrea Zone (southern Alps) is one of the key regions interpreted as exposing a section of the lower continental crust and was the subject of several review-type articles. The Ivrea–Verbano Zone was rotated into an upright position along the Insubric mylonite belt. In the southeast, this unit is in contact with the Strona Ceneri Zone, which is interpreted as upper continental crust crossing the Permian Cossato–Mergozzo–Brissagio Line (CMB Line). The CMB mylonites are locally overprinted by the mylonites and cataclasites of the Pogallo Line, which was active during the Jurassic. In addition, the sinistral, steeply inclined Rosarolo shear zone was active over a long time span from the ductile into the brittle field, i.e. from the Early Permian (high-temperature ultra-mylonites) to the Neo-Alpine basic dykes and pseudotachylites. The high-temperature mylonites accommodated crustal extension and may be related to normal faults generated by magmatic underplating. The reactivation at different crustal levels during exhumation and tilting is documented by strain increments at decreasing P/T conditions. Its present subvertical orientation was attained during the Neo-Alpine deformation. Constraints on its exhumation history are based on new <sup>40</sup>Ar/<sup>39</sup>Ar hornblende ages, K–Ar biotite ages and zircon fission-track data along the NE–SW trending Valstrona section. A re-interpretation of existing U–Pb monazite ages is included, based on a higher closure temperature for monazite. The oldest monazite ages are observed in proximity to the Pogallo Line (<em>c</em>. 292 Ma). Heat input by mafic intrusions was sufficient to reset the U–Pb monazite system, as is evidenced by the youngest ages in the vicinity of the Insubric Line. The re-interpretation favours the hypothesis that the oldest monazite ages are the result of complete resetting by a Permian thermal event. The <sup>40</sup>Ar/<sup>39</sup>Ar hornblende ages and K–Ar biotite ages document the cooling after Permian heating. Roughly parallel age progressions decrease from the Pogallo Line (hornblende: 271 Ma vs. biotite: 227 Ma) towards the Insubric Line (hornblende: 201 Ma vs. biotite: 156 Ma). Zircon fission-track ages run parallel to the biotite ages in the upper part of the profile, whereas towards the Insubric Line a significant deviation from the biotite age progression is attributed to tilting of the basement during the Oligocene. Zircon fission-track ages around 38 Ma are found close to the Insubric Line. No age offset, neither at the CMB nor at the Pogallo Line, is observed. This confirms the hypothesis that the Pogallo Line is an oblique normal fault, and that the CMB Line has accommodated only minor vertical displacement. The capture of the different cooling ages confirms the tilting of the Ivrea–Verbano Zone during the Neo-Alpine deformation and contradicts the tilting of the Ivrea–Verbano Zone during the Permian.
DOI: 10.6084/m9.figshare.3454532
title: Volcanogenic nutrient fluxes and plant ecosystems in large igneous provinces: an example from the Columbia River Basalt Group

description: Research from biological and geological sources has highlighted the role of volcanoes in the outgassing of P, and thermal fixation and subsequent atmospheric oxidation of NO<em><sub>x</sub></em> in volcanic environments. The impact of these nutrient fluxes on biological systems has been demonstrated on present-day Hawai'i, and here we consider the impact on the plant communities within a large igneous province (LIP). The Miocene Columbia River Basalt Province, the youngest LIP on Earth, contains many sedimentary interbeds between the flows of the major extrusive phase, and these interbeds preserve variable but often diverse palynofloras. By integration of palynofloral analysis with analysis of macronutrient levels in the interbeds it can be suggested that there may have been significantly elevated levels of P within the lava field proximal to the source vents, a distribution mirrored by Ca and Mg. Evidence for potential volcanogenic eutrophication is restricted to &gt;10<sup>3</sup> year duration interbeds, contemporary with eruptive activity elsewhere in the LIP. The geochemistry and palynology of other interbeds demonstrate nutrient deficiency, with a potential route to nutrient sufficiency available from long-term symbiotic N-fixation. Elsewhere within the Columbia River Basalt Province, this process is short-circuited by the imput of felsic ash from the nearby Cascades Range of volcanoes.
DOI: 10.6084/m9.figshare.3454532.v1
title: Volcanogenic nutrient fluxes and plant ecosystems in large igneous provinces: an example from the Columbia River Basalt Group

description: Research from biological and geological sources has highlighted the role of volcanoes in the outgassing of P, and thermal fixation and subsequent atmospheric oxidation of NO<em><sub>x</sub></em> in volcanic environments. The impact of these nutrient fluxes on biological systems has been demonstrated on present-day Hawai'i, and here we consider the impact on the plant communities within a large igneous province (LIP). The Miocene Columbia River Basalt Province, the youngest LIP on Earth, contains many sedimentary interbeds between the flows of the major extrusive phase, and these interbeds preserve variable but often diverse palynofloras. By integration of palynofloral analysis with analysis of macronutrient levels in the interbeds it can be suggested that there may have been significantly elevated levels of P within the lava field proximal to the source vents, a distribution mirrored by Ca and Mg. Evidence for potential volcanogenic eutrophication is restricted to &gt;10<sup>3</sup> year duration interbeds, contemporary with eruptive activity elsewhere in the LIP. The geochemistry and palynology of other interbeds demonstrate nutrient deficiency, with a potential route to nutrient sufficiency available from long-term symbiotic N-fixation. Elsewhere within the Columbia River Basalt Province, this process is short-circuited by the imput of felsic ash from the nearby Cascades Range of volcanoes.
DOI: 10.6084/m9.figshare.3454529
title: Vertical ductile thinning and its contribution to the exhumation of high-pressure rocks: the Cycladic blueschist unit in the Aegean

description: The contribution of vertical ductile thinning to the exhumation of high-pressure rocks is evaluated by estimating finite strain in 75 exhumed high-pressure rocks of the Cycladic blueschist unit in the Aegean Sea, Greece, and western Turkey. Strain data indicate heterogeneous deformation; principal stretches are 1.24–5.03 for <em>S</em><sub><em>X</em></sub>, 0.63–2.53 for <em>S</em><sub><em>Y</em></sub> and 0.10–0.81 for <em>S</em><sub><em>Z</em></sub>, with a tensor average of <em>S</em><sub><em>X</em></sub>:<em>S</em><sub><em>Y</em></sub>:<em>S</em><sub><em>Z</em></sub>=1.52:1.28:0.51. A 1D numerical model, which integrates velocity gradients along a vertical flow path with a steady-state orogen, is used to estimate the contribution of ductile thinning of the overburden of the high-pressure rocks to exhumation. Using a strain-rate law that is proportional to depth, averaged results show that ductile flow contributed <em>c</em>. 20% to exhumation. A major implication is that the vertical strain in the exhumed rocks is an overestimate of the contribution that ductile flow makes to the total exhumation. A proportional strain-rate law that scales linearly with depth implies that material points rising towards the surface move quickly out of the more rapidly deforming part of the orogen. Therefore, very large vertical strains &gt;90% in deeply exhumed rocks are needed for vertical ductile thinning to be a major exhumation process.
DOI: 10.6084/m9.figshare.3454529.v1
title: Vertical ductile thinning and its contribution to the exhumation of high-pressure rocks: the Cycladic blueschist unit in the Aegean

description: The contribution of vertical ductile thinning to the exhumation of high-pressure rocks is evaluated by estimating finite strain in 75 exhumed high-pressure rocks of the Cycladic blueschist unit in the Aegean Sea, Greece, and western Turkey. Strain data indicate heterogeneous deformation; principal stretches are 1.24–5.03 for <em>S</em><sub><em>X</em></sub>, 0.63–2.53 for <em>S</em><sub><em>Y</em></sub> and 0.10–0.81 for <em>S</em><sub><em>Z</em></sub>, with a tensor average of <em>S</em><sub><em>X</em></sub>:<em>S</em><sub><em>Y</em></sub>:<em>S</em><sub><em>Z</em></sub>=1.52:1.28:0.51. A 1D numerical model, which integrates velocity gradients along a vertical flow path with a steady-state orogen, is used to estimate the contribution of ductile thinning of the overburden of the high-pressure rocks to exhumation. Using a strain-rate law that is proportional to depth, averaged results show that ductile flow contributed <em>c</em>. 20% to exhumation. A major implication is that the vertical strain in the exhumed rocks is an overestimate of the contribution that ductile flow makes to the total exhumation. A proportional strain-rate law that scales linearly with depth implies that material points rising towards the surface move quickly out of the more rapidly deforming part of the orogen. Therefore, very large vertical strains &gt;90% in deeply exhumed rocks are needed for vertical ductile thinning to be a major exhumation process.
DOI: 10.6084/m9.figshare.3454526
title: Provenance of Lower Cretaceous sediments in the Wandel Sea Basin, North Greenland

description: Detrital zircons in Lower Cretaceous sedimentary formations from the Wandel Sea Basin (Kilen, Peary Land) were dated by U–Pb and analysed for Hf isotopes by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Samples from Kilen and Peary Land display a wide range of U–Pb ages, with significant zircon populations at 1.0–1.1 and 1.8–2.0 Ga. Major hiati occur between 2.1 and 2.4 and from 0.48 to 0.91 Ga. Low initial ϵ<sub>Hf</sub> values indicate that recycled crust components are significant in Caledonian-aged zircons, and in Palaeoproterozoic (1.8–2.0 Ga) and Neoarchaean zircon populations. Other U–Pb age populations in the studied samples are dominated by zircons with positive ϵ<sub>Hf</sub> values indicating a significant contribution of mantle-derived material in these periods. A narrow range of ϵ<sub>Hf</sub> values is commonly seen within a given U–Pb age population, and the values seen in the samples are in general correlated with the different age populations and their frequency. One exception is the 1.8–2.0 Ga population, where variations suggest variable sources. The U–Pb and Hf data are consistent with Greenland as the sole source of zircon from the studied sandstones.
DOI: 10.6084/m9.figshare.3454520
title: Geochronology and geodynamics of Scottish granitoids from the late Neoproterozoic break-up of Rodinia to Palaeozoic collision

description: Thirty-seven granitoids from Scotland have been dated using the sensitive high-resolution ion microprobe zircon method. Granitoids were intruded during: (1) crustal stretching at <em>c</em>. 600 Ma after Rodinia broke up (A-types); (2) the Grampian event of crustal thickening when the Midland Valley Arc terrane collided with Laurentia at <em>c</em>. 470 Ma (S-types); (3) erosion and decompression of the over-thickened Laurentian margin at <em>c</em>. 455 Ma (S-types); (4) subduction of Iapetus Ocean lithosphere under Laurentia starting at 430 Ma (I-types); (5) roll-back beginning at 420 Ma (I-types); (6) bilateral slab break-off and lithospheric delamination at 410 Ma (I- and S-type granites) when Baltica hard-docked against the Northern Highland terrane and Avalonia soft-docked against the Grampian Highland terrane. Far-field Acadian events at 390 Ma were recorded by I-type granites intruded along active sinistrally transpressive faults. I-types formed in lower crustal hot zones above subduction zones, whereas S-types formed in lower crustal hot zones above lithospheric windows through which hot asthenosphere had risen.
DOI: 10.6084/m9.figshare.3454520.v1
title: Geochronology and geodynamics of Scottish granitoids from the late Neoproterozoic break-up of Rodinia to Palaeozoic collision

description: Thirty-seven granitoids from Scotland have been dated using the sensitive high-resolution ion microprobe zircon method. Granitoids were intruded during: (1) crustal stretching at <em>c</em>. 600 Ma after Rodinia broke up (A-types); (2) the Grampian event of crustal thickening when the Midland Valley Arc terrane collided with Laurentia at <em>c</em>. 470 Ma (S-types); (3) erosion and decompression of the over-thickened Laurentian margin at <em>c</em>. 455 Ma (S-types); (4) subduction of Iapetus Ocean lithosphere under Laurentia starting at 430 Ma (I-types); (5) roll-back beginning at 420 Ma (I-types); (6) bilateral slab break-off and lithospheric delamination at 410 Ma (I- and S-type granites) when Baltica hard-docked against the Northern Highland terrane and Avalonia soft-docked against the Grampian Highland terrane. Far-field Acadian events at 390 Ma were recorded by I-type granites intruded along active sinistrally transpressive faults. I-types formed in lower crustal hot zones above subduction zones, whereas S-types formed in lower crustal hot zones above lithospheric windows through which hot asthenosphere had risen.
DOI: 10.6084/m9.figshare.3454514
title: Geochronology of very low-grade Mesozoic Andean metabasites; an approach through the K–Ar, <sup>40</sup>Ar/<sup>39</sup>Ar and U–Pb LA-MC-ICP-MS methods

description: Multiple geochronological methods using different metamorphic minerals were combined to date the regional, very low-grade metamorphism affecting Upper Jurassic–Lower Cretaceous volcano-sedimentary successions in the Andes of central Chile. Early Late Cretaceous metamorphic ages (between 82 and 108 Ma) were obtained by the K–Ar and U–Pb methods for celadonite and titanite. A much younger thermal event is responsible for actinolite formation at 8 Ma, most probably related to the intrusion of proximal Miocene granitoids. Previous models for the metamorphism should be reinterpreted taking into account the absence of a greenschist-facies event. The combination of different metamorphic minerals and chronometers is regarded as a powerful analytical tool to date the very low-grade metamorphism associated with the Mesozoic extensional regime developed within the Andes.
DOI: 10.6084/m9.figshare.3454514.v1
title: Geochronology of very low-grade Mesozoic Andean metabasites; an approach through the K–Ar, <sup>40</sup>Ar/<sup>39</sup>Ar and U–Pb LA-MC-ICP-MS methods

description: Multiple geochronological methods using different metamorphic minerals were combined to date the regional, very low-grade metamorphism affecting Upper Jurassic–Lower Cretaceous volcano-sedimentary successions in the Andes of central Chile. Early Late Cretaceous metamorphic ages (between 82 and 108 Ma) were obtained by the K–Ar and U–Pb methods for celadonite and titanite. A much younger thermal event is responsible for actinolite formation at 8 Ma, most probably related to the intrusion of proximal Miocene granitoids. Previous models for the metamorphism should be reinterpreted taking into account the absence of a greenschist-facies event. The combination of different metamorphic minerals and chronometers is regarded as a powerful analytical tool to date the very low-grade metamorphism associated with the Mesozoic extensional regime developed within the Andes.