cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454481.v1
title: Pliocene–Pleistocene HT–LP metamorphism during multiple granitic intrusions in the southern branch of the Larderello geothermal field (southern Tuscany, Italy)

description: This work presents the results of a multidiscipinary study carried out in the southern branch of the Larderello geothermal field (Travale–Montieri area), which was based on the integration of field data with information on the deeper structures as derived from interpretation of seismic reflection profiles and the <em>P</em>–<em>T</em>–<em>t</em> history of the metamorphic substratum as reconstructed from borehole data. Our data document that the structural and metamorphic signature of the metamorphic substratum is chiefly related to a prograde HT–LP metamorphic overprint, ranging in age from <em>c</em>. 2.8 to 0.7 Ma. The metamorphic climax was attained within the K-feldspar zone and equilibrated at <em>P</em>–<em>T</em> conditions of about 0.2 GPa and 650 °C. We interpret these new findings as evidence of Pliocene–Pleistocene thermal metamorphism associated with multiple granite intrusions at shallow levels in the crust. These results (1) add strength to the interpretations emphasizing the contribution of Neogene thermal metamorphism to the tectonometamorphic signature of the basement rocks found at depth in the Larderello geothermal field, and (2) provide insights on the thermal structures of the crustal section hosting the geothermal field and on the modes through which the long-lived positive thermal anomaly operated in southern Tuscany.
DOI: 10.6084/m9.figshare.3454478
title: Age and evolution of late Mesozoic metamorphic core complexes in southern Siberia and northern Mongolia

description: Numerous Cretaceous metamorphic core complexes (MCCs) extend from Transbaikalia in Russia to northern Mongolia within the Central Asian Orogenic Belt. We investigated the Buteel and Zagan MCCs in detail. Shear sense indicators in mylonitized rocks show footwall-to-the-NW tectonic transport. Single zircon dating of footwall rocks in the Buteel MCC establishes the emplacement of granitoid orthogneiss precursors at 240–211 Ma, a felsic metavolcanic rock at 265.0 ± 1.2 Ma, a syenite at 265.5 ± 1.2 Ma and a metarhyolite of the pre-granitoid basement at 553.6 ± 2.9 Ma. A peralkaline granite intruding orthogneisses of the Zagan MCC has a new U–Pb zircon age of 151.6 ± 0.7 Ma. <sup>40</sup>Ar/<sup>39</sup>Ar ages of 133.5 ± 1.8 Ma of hornblende from amphibolite and 122.6 ± 1.8 Ma of biotite from mylonitized gabbro–dolerite of the Buteel MCC are interpreted as cooling ages representing the time of deformation in the footwall. Geological data suggest that the MCCs in Transbaikalia and northern Mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc-alkaline magmatism in an Andean-type setting on the border of the closing Mongol–Okhotsk ocean, by widespread collisional to post-collisional thrusting, and by extensive alkaline–peralkaline magmatism.
DOI: 10.6084/m9.figshare.3454478.v1
title: Age and evolution of late Mesozoic metamorphic core complexes in southern Siberia and northern Mongolia

description: Numerous Cretaceous metamorphic core complexes (MCCs) extend from Transbaikalia in Russia to northern Mongolia within the Central Asian Orogenic Belt. We investigated the Buteel and Zagan MCCs in detail. Shear sense indicators in mylonitized rocks show footwall-to-the-NW tectonic transport. Single zircon dating of footwall rocks in the Buteel MCC establishes the emplacement of granitoid orthogneiss precursors at 240–211 Ma, a felsic metavolcanic rock at 265.0 ± 1.2 Ma, a syenite at 265.5 ± 1.2 Ma and a metarhyolite of the pre-granitoid basement at 553.6 ± 2.9 Ma. A peralkaline granite intruding orthogneisses of the Zagan MCC has a new U–Pb zircon age of 151.6 ± 0.7 Ma. <sup>40</sup>Ar/<sup>39</sup>Ar ages of 133.5 ± 1.8 Ma of hornblende from amphibolite and 122.6 ± 1.8 Ma of biotite from mylonitized gabbro–dolerite of the Buteel MCC are interpreted as cooling ages representing the time of deformation in the footwall. Geological data suggest that the MCCs in Transbaikalia and northern Mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc-alkaline magmatism in an Andean-type setting on the border of the closing Mongol–Okhotsk ocean, by widespread collisional to post-collisional thrusting, and by extensive alkaline–peralkaline magmatism.
DOI: 10.6084/m9.figshare.3454475
title: West Gondwana amalgamation based on detrital zircon ages from Neoproterozoic Ribeira and Dom Feliciano belts of South America and comparison with coeval sequences from SW Africa

description: Neoproterozoic–Cambrian amalgamation of West Gondwana involved the collision of several terranes of older crust that are now in eastern South America and western Africa. U–Pb (SHRIMP) detrital zircon ages from representative metasedimentary units of the Ribeira and Dom Feliciano belts (South America) and Gariep and Damara belts (Africa) provide constraints on the possible sediment source areas across probable suture zones. Ribeira detrital zircons are Palaeoproterozoic and Archaean. For the Dom Feliciano Belt, a contribution of Meso- and Neoproterozoic zircons is present, which definitely indicate Neoproterozoic sedimentation. It is proposed that the inflow of material to the Ribeira basin was essentially derived from the Paranapanema and Rio de la Plata cratons, whereas for the Damara and Gariep–Rocha belts source areas were from the Namaqua Belt. The Dom Feliciano Belt received sediments from the South American side and to a lesser degree from African sources. These results highlight the differences in the detrital zircon signatures across a proposed West Gondwanan suture, with those in the west being derived from distinctive South American basement sources and those in the east from distinctive African sources.
DOI: 10.6084/m9.figshare.3454475.v1
title: West Gondwana amalgamation based on detrital zircon ages from Neoproterozoic Ribeira and Dom Feliciano belts of South America and comparison with coeval sequences from SW Africa

description: Neoproterozoic–Cambrian amalgamation of West Gondwana involved the collision of several terranes of older crust that are now in eastern South America and western Africa. U–Pb (SHRIMP) detrital zircon ages from representative metasedimentary units of the Ribeira and Dom Feliciano belts (South America) and Gariep and Damara belts (Africa) provide constraints on the possible sediment source areas across probable suture zones. Ribeira detrital zircons are Palaeoproterozoic and Archaean. For the Dom Feliciano Belt, a contribution of Meso- and Neoproterozoic zircons is present, which definitely indicate Neoproterozoic sedimentation. It is proposed that the inflow of material to the Ribeira basin was essentially derived from the Paranapanema and Rio de la Plata cratons, whereas for the Damara and Gariep–Rocha belts source areas were from the Namaqua Belt. The Dom Feliciano Belt received sediments from the South American side and to a lesser degree from African sources. These results highlight the differences in the detrital zircon signatures across a proposed West Gondwanan suture, with those in the west being derived from distinctive South American basement sources and those in the east from distinctive African sources.
DOI: 10.6084/m9.figshare.3454472
title: The nappe rule: why does it work?

description: The nappe rule stresses that imbrication emplaces nappes with higher metamorphic grade above those with lower grade. This means that the overriding nappes must be exhuming during nappe stacking; otherwise metamorphic grade would increase structurally downwards. The high-grade metamorphic internides of many orogens are characterized by a pervasive nappe-emplacement-related subhorizontal foliation indicative of vertical ductile shortening (thinning). By quantifying finite strain in the Gran Paradiso Massif, Italian Alps, we show that vertical ductile thinning associated with a nappe-emplacement-related subhorizontal foliation caused sufficient exhumation of the overriding nappes and can thus explain the occurrence of higher-grade rocks above lower-grade ones.
DOI: 10.6084/m9.figshare.3454472.v1
title: The nappe rule: why does it work?

description: The nappe rule stresses that imbrication emplaces nappes with higher metamorphic grade above those with lower grade. This means that the overriding nappes must be exhuming during nappe stacking; otherwise metamorphic grade would increase structurally downwards. The high-grade metamorphic internides of many orogens are characterized by a pervasive nappe-emplacement-related subhorizontal foliation indicative of vertical ductile shortening (thinning). By quantifying finite strain in the Gran Paradiso Massif, Italian Alps, we show that vertical ductile thinning associated with a nappe-emplacement-related subhorizontal foliation caused sufficient exhumation of the overriding nappes and can thus explain the occurrence of higher-grade rocks above lower-grade ones.
DOI: 10.6084/m9.figshare.3454469
title: Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

description: Contact-metamorphic mineral assemblages are described from Dalradian non-graphitic pelites and semipelites in the southern sector of the Etive thermal aureole, adjacent to the Quarry Diorite ring intrusion. Six metamorphic zones were mapped on the basis of incoming index minerals: I, Biotite; II, Cordierite; III, Andalusite+K-feldspar; IV, Corundum; V, Spinel; VI, Sillimanite. Garnet and orthopyroxene occur locally in high-grade quartz-bearing assemblages. Rocks of the Biotite and Cordierite zones retain their regional-metamorphic textures to a large extent, particularly S<sub>2</sub> crenulation cleavage. Above the Andalusite+K-feldspar isograd the rocks are hornfelses, but relict features of S<sub>2</sub> persist. Rocks of the upper Spinel and Sillimanite zones are agmatic/stromatic migmatites which preserve evidence of local partial melting in the form of S<sub>2</sub>-parallel leucosomes and thin fracture-filling vein leucosomes. All leucosomes are K-feldspar-rich. Vein leucosomes consist mainly of leucogranite with a metaluminous composition and, in the Sillimanite Zone, locally contain crystals of peritectic orthopyroxene and/or cordierite. The compositions of coexisting minerals, determined by EPMA, were used to constrain metamorphic reactions and, with equilibrium thermodynamic calculations, to refine estimates of the P-T conditions of metamorphism. Isograd reactions can generally be modelled satisfactorily in the CNKFMASH system as an isobaric sequence at P=2.2 kbar. An exception is the spinel isograd which occurs at anomalously low T due to the partitioning of Zn into spinel. Estimated isograd temperatures for the And+Kfs, Crn, Spl, melt and Sil isograds are 610°C, 630°C, 660°C, 680°C and 705°C, respectively. Calculated dehydration equilibria yield low values of water activity in the Sillimanite Zone, confirming that partial melting in the innermost aureole occurred under fluid-absent conditions. Leucosome textures and structures suggest that the siliceous microlithons of the former S<sub>2</sub> differentiated crenulation cleavage were the likely sites of melting and provided channels for the movement of melt into brittle fractures to form the vein leucosomes.
DOI: 10.6084/m9.figshare.3454469.v1
title: Contact metamorphism and partial melting of Dalradian pelites and semipelites in the southern sector of the Etive aureole

description: Contact-metamorphic mineral assemblages are described from Dalradian non-graphitic pelites and semipelites in the southern sector of the Etive thermal aureole, adjacent to the Quarry Diorite ring intrusion. Six metamorphic zones were mapped on the basis of incoming index minerals: I, Biotite; II, Cordierite; III, Andalusite+K-feldspar; IV, Corundum; V, Spinel; VI, Sillimanite. Garnet and orthopyroxene occur locally in high-grade quartz-bearing assemblages. Rocks of the Biotite and Cordierite zones retain their regional-metamorphic textures to a large extent, particularly S<sub>2</sub> crenulation cleavage. Above the Andalusite+K-feldspar isograd the rocks are hornfelses, but relict features of S<sub>2</sub> persist. Rocks of the upper Spinel and Sillimanite zones are agmatic/stromatic migmatites which preserve evidence of local partial melting in the form of S<sub>2</sub>-parallel leucosomes and thin fracture-filling vein leucosomes. All leucosomes are K-feldspar-rich. Vein leucosomes consist mainly of leucogranite with a metaluminous composition and, in the Sillimanite Zone, locally contain crystals of peritectic orthopyroxene and/or cordierite. The compositions of coexisting minerals, determined by EPMA, were used to constrain metamorphic reactions and, with equilibrium thermodynamic calculations, to refine estimates of the P-T conditions of metamorphism. Isograd reactions can generally be modelled satisfactorily in the CNKFMASH system as an isobaric sequence at P=2.2 kbar. An exception is the spinel isograd which occurs at anomalously low T due to the partitioning of Zn into spinel. Estimated isograd temperatures for the And+Kfs, Crn, Spl, melt and Sil isograds are 610°C, 630°C, 660°C, 680°C and 705°C, respectively. Calculated dehydration equilibria yield low values of water activity in the Sillimanite Zone, confirming that partial melting in the innermost aureole occurred under fluid-absent conditions. Leucosome textures and structures suggest that the siliceous microlithons of the former S<sub>2</sub> differentiated crenulation cleavage were the likely sites of melting and provided channels for the movement of melt into brittle fractures to form the vein leucosomes.
DOI: 10.6084/m9.figshare.3454463
title: The brittle evolution of a major strike-slip fault associated with granite emplacement: a case study of the Leannan Fault, NW Ireland

description: NE–SW-trending sinistral strike-slip deformation is widespread throughout the Highlands of Scotland and NW Ireland and has been interpreted as a response to the subduction of Iapetus and continental collision. The southwestern continuation of the Great Glen Fault zone is marked in NW Ireland by the Leannan Fault. Field evidence derived from the Tullagh Point Granite indicates its intrusion along the fault during ductile sinistral shearing. U–Th–Pb zircon geochronology yields a crystallization age of 422 ± 2 Ma for this granite. Detailed analysis of fracture patterns throughout the Malin Head region demonstrates that sinistral fractures (F<sub>1</sub>) developed at an acute angle to the main fault strands. These fractures display oblique internal alignment of K-feldspar and are overprinted by dilatational quartz-filled joints at a similar orientation. The trend of these joints is consistent with <em>c</em>. 90° rotation of the σ<sub>1</sub> axes relative to F<sub>1</sub> as a result of intrusion of the Malin Head Granite dated at 412 ± 3 Ma. Subsequent sinistral fractures developed after dissipation of granite-related forces. They define an anticlockwise rotation of the regional σ<sub>1</sub> and moved under a different stress tensor from F<sub>1</sub>. It is concluded that the Leannan Fault moved sinistrally at <em>c</em>. 422 Ma and after <em>c</em>. 412 Ma, and that granite emplacement had pronounced effects on the fault kinematics.
DOI: 10.6084/m9.figshare.3454463.v1
title: The brittle evolution of a major strike-slip fault associated with granite emplacement: a case study of the Leannan Fault, NW Ireland

description: NE–SW-trending sinistral strike-slip deformation is widespread throughout the Highlands of Scotland and NW Ireland and has been interpreted as a response to the subduction of Iapetus and continental collision. The southwestern continuation of the Great Glen Fault zone is marked in NW Ireland by the Leannan Fault. Field evidence derived from the Tullagh Point Granite indicates its intrusion along the fault during ductile sinistral shearing. U–Th–Pb zircon geochronology yields a crystallization age of 422 ± 2 Ma for this granite. Detailed analysis of fracture patterns throughout the Malin Head region demonstrates that sinistral fractures (F<sub>1</sub>) developed at an acute angle to the main fault strands. These fractures display oblique internal alignment of K-feldspar and are overprinted by dilatational quartz-filled joints at a similar orientation. The trend of these joints is consistent with <em>c</em>. 90° rotation of the σ<sub>1</sub> axes relative to F<sub>1</sub> as a result of intrusion of the Malin Head Granite dated at 412 ± 3 Ma. Subsequent sinistral fractures developed after dissipation of granite-related forces. They define an anticlockwise rotation of the regional σ<sub>1</sub> and moved under a different stress tensor from F<sub>1</sub>. It is concluded that the Leannan Fault moved sinistrally at <em>c</em>. 422 Ma and after <em>c</em>. 412 Ma, and that granite emplacement had pronounced effects on the fault kinematics.
DOI: 10.6084/m9.figshare.3454460
title: Petrology, geochronology, and tectonic implications of <em>c</em>. 500 Ma metamorphic and igneous rocks along the northern margin of the Central Asian Orogen (Olkhon terrane, Lake Baikal, Siberia)

description: A significant portion of the continental crust of northern Eurasia is thought to have formed during the evolution of the Central Asian Orogenic Belt at the time of accretion of continental terranes and island arcs. Records of this event are well preserved within the Siberian craton–Central Asian Orogenic Belt transition zone in Lake Baikal region, particularly in the Olkhon terrane. Our results establish granulite-facies conditions for peak metamorphism in the Olkhon terrane, and indicate that the granulites were derived from island arc mafic volcanic rocks and back-arc basin sediments. Sensitive high-resolution ion microprobe dating of metamorphic zircons from two mafic granulites yielded <sup>238</sup>U/<sup>206</sup>Pb ages of 507 ± 8 and 498 ± 7 Ma, and magmatic zircons from syntectonic syenite yielded an age of 495 ± 6 Ma. The main metamorphic event occurred at about 500 Ma, and was probably related to collision of the Barguzin microcontinent with the Siberian craton. Ages from 535 to 2750 Ma for detrital zircon cores in early Palaeozoic metasediments of the Olhkon terrane were obtained. Archaean ages of detrital zircons in such metasediments suggest that the Barguzin microcontinent was originally part of the Aldan Province of the Siberian craton that was detached in late Mesoproterozoic, and reattached to the craton during early Palaeozoic collision.
DOI: 10.6084/m9.figshare.3454460.v1
title: Petrology, geochronology, and tectonic implications of <em>c</em>. 500 Ma metamorphic and igneous rocks along the northern margin of the Central Asian Orogen (Olkhon terrane, Lake Baikal, Siberia)

description: A significant portion of the continental crust of northern Eurasia is thought to have formed during the evolution of the Central Asian Orogenic Belt at the time of accretion of continental terranes and island arcs. Records of this event are well preserved within the Siberian craton–Central Asian Orogenic Belt transition zone in Lake Baikal region, particularly in the Olkhon terrane. Our results establish granulite-facies conditions for peak metamorphism in the Olkhon terrane, and indicate that the granulites were derived from island arc mafic volcanic rocks and back-arc basin sediments. Sensitive high-resolution ion microprobe dating of metamorphic zircons from two mafic granulites yielded <sup>238</sup>U/<sup>206</sup>Pb ages of 507 ± 8 and 498 ± 7 Ma, and magmatic zircons from syntectonic syenite yielded an age of 495 ± 6 Ma. The main metamorphic event occurred at about 500 Ma, and was probably related to collision of the Barguzin microcontinent with the Siberian craton. Ages from 535 to 2750 Ma for detrital zircon cores in early Palaeozoic metasediments of the Olhkon terrane were obtained. Archaean ages of detrital zircons in such metasediments suggest that the Barguzin microcontinent was originally part of the Aldan Province of the Siberian craton that was detached in late Mesoproterozoic, and reattached to the craton during early Palaeozoic collision.
DOI: 10.6084/m9.figshare.3454454
title: Grenville-age pseudotachylite in the Lewisian: laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar ages from the Gairloch region of Scotland (UK)

description: Infrared laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar dating has been used to date pseudotachylite and host-rock minerals from a crush belt in the Lewisian basement of Scotland. It has revealed complexity in the pseudotachylite data that is attributable to the presence of refractory host-rock clasts and mineral fragments in the pseudotachylite. In conjunction with the host-rock mineral laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar data it has been possible to simplify the pseudotachylite data for the samples, and the preferred ages for these are: 980 ± 39 Ma, 999 ± 31 Ma and 1024 ± 30 Ma (2σ). These ages are the first record of Grenville-aged brittle deformation in the Lewisian. Further, this study serves to illustrate the complexity of dating pseudotachylites, and the advantages and limitations of the IR laserprobe applied to such materials.
DOI: 10.6084/m9.figshare.3454454.v1
title: Grenville-age pseudotachylite in the Lewisian: laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar ages from the Gairloch region of Scotland (UK)

description: Infrared laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar dating has been used to date pseudotachylite and host-rock minerals from a crush belt in the Lewisian basement of Scotland. It has revealed complexity in the pseudotachylite data that is attributable to the presence of refractory host-rock clasts and mineral fragments in the pseudotachylite. In conjunction with the host-rock mineral laserprobe <sup>40</sup>Ar/<sup>39</sup>Ar data it has been possible to simplify the pseudotachylite data for the samples, and the preferred ages for these are: 980 ± 39 Ma, 999 ± 31 Ma and 1024 ± 30 Ma (2σ). These ages are the first record of Grenville-aged brittle deformation in the Lewisian. Further, this study serves to illustrate the complexity of dating pseudotachylites, and the advantages and limitations of the IR laserprobe applied to such materials.