cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3453818.v1
title: The source of Proterozoic anorthosite and rapakivi granite magmatism: evidence from combined <em>in situ</em> Hf–O isotopes of zircon in the Ahvenisto complex, southeastern Finland

description: The isotope compositions of massif-type anorthosites in Proterozoic anorthosite–mangerite–charnockite–granite (AMCG) complexes are commonly dominated by crustal values. Olivine-bearing anorthositic rocks in several AMCG suites have, however, been shown to display juvenile character, suggesting that variably depleted mantle reservoirs were involved in their genesis. A coupled <em>in situ</em> zircon Hf–O isotope dataset from the 1.64 Ga Ahvenisto AMCG complex in the 1.54–1.65 Ga Fennoscandian rapakivi granite–massif-type anorthosite province reveals correlated juvenile isotope signals (δ<sup>18</sup>O<sub>zrn</sub> = 5.4–6.6‰; initial ϵ<sub>Hf</sub> = −1.1 to +3.4) in the most primitive gabbroic rock type of the suite suggesting a depleted mantle origin for the anorthositic rocks. This signal is not as prominent in the more evolved co-magmatic anorthositic rocks (δ<sup>18</sup>O<sub>zrn</sub> = 6.3–7.8‰; initial ϵ<sub>Hf</sub> = −0.8 to +2.0), most probably owing to contamination of the mantle-derived primary magma by crustal material. A rapakivi granite associated with the anorthositic rocks has different isotope composition (δ<sup>18</sup>O<sub>zrn</sub> = 7.4–8.6‰; initial ϵ<sub>Hf</sub> = −2.1 to +0.5) that points to a crustal source.
DOI: 10.6084/m9.figshare.3453809
title: Redefining the tectonostratigraphic and structural architecture of the Almora klippe and the Ramgarh–Munsiari thrust sheet in NW India

description: We integrate U–Pb zircon geochronology and ε<sub>Nd</sub>(0) values with field mapping to determine which tectonostratigraphic units are represented to the north, south and within the Almora klippe in Kumaun, NW India. Rock in the Almora klippe and north of the Main Central thrust (MCT) have Neoproterozoic (<em>c.</em> 900 Ma) detrital zircon ages, coupled with similar ε<sub>Nd</sub>(0) (−7.6 to −11.8) values, suggesting that these two units are the same tectonostratigraphic unit, and that the Almora klippe is the southern continuation of the MCT or another thrust in the Greater Himalayan thrust system. However, north of the Almora klippe, detrital zircon age populations establish the presence of Palaeoproterozoic rock instead of the previous interpretation of Neoproterozoic rocks. These Palaeoproterozoic Lesser Himalayan (LH) rocks are carried by the Ramgarh–Munsiari thrust (RMT) dipping south and folded underneath the klippe. South of the klippe, the RMT carries both the less metamorphosed Palaeoproterozoic and Neoproterozoic LH rocks, in disagreement with the idea that only Neoproterozoic–Cambrian LH rocks are present south of Almora klippe. These results suggest that previous cross-sections in Kumaun are incorrect and must be re-evaluated.
DOI: 10.6084/m9.figshare.3453809.v1
title: Redefining the tectonostratigraphic and structural architecture of the Almora klippe and the Ramgarh–Munsiari thrust sheet in NW India

description: We integrate U–Pb zircon geochronology and ε<sub>Nd</sub>(0) values with field mapping to determine which tectonostratigraphic units are represented to the north, south and within the Almora klippe in Kumaun, NW India. Rock in the Almora klippe and north of the Main Central thrust (MCT) have Neoproterozoic (<em>c.</em> 900 Ma) detrital zircon ages, coupled with similar ε<sub>Nd</sub>(0) (−7.6 to −11.8) values, suggesting that these two units are the same tectonostratigraphic unit, and that the Almora klippe is the southern continuation of the MCT or another thrust in the Greater Himalayan thrust system. However, north of the Almora klippe, detrital zircon age populations establish the presence of Palaeoproterozoic rock instead of the previous interpretation of Neoproterozoic rocks. These Palaeoproterozoic Lesser Himalayan (LH) rocks are carried by the Ramgarh–Munsiari thrust (RMT) dipping south and folded underneath the klippe. South of the klippe, the RMT carries both the less metamorphosed Palaeoproterozoic and Neoproterozoic LH rocks, in disagreement with the idea that only Neoproterozoic–Cambrian LH rocks are present south of Almora klippe. These results suggest that previous cross-sections in Kumaun are incorrect and must be re-evaluated.
DOI: 10.6084/m9.figshare.3453806
title: The Eoarchaean foundation of the North Atlantic Craton

description: The Archaean North Atlantic Craton underpins much of North America, Greenland and northern Europe, and incorporates the Earth's oldest extant continental crust. This paper reviews the current understanding of the region's crustal evolution, and considers our ability to investigate interrelationships between different fragments of the North Atlantic Craton. Detrital zircons from Mesoproterozoic to Cambrian basal sediments in NW Scotland have been re-examined in light of new data from the Archaean Tarbet supracrustal unit and the Palaeoproterozoic Rubha Ruadh granite. Hf model ages are recorded from 4160 to 1410 Ma, peaking at <em>c.</em> 3350 Ma, and are associated with U–Pb crystallization ages from 3670 to 1070 Ma, peaking at <em>c.</em> 2700 and 1700 Ma. The Rubha Ruadh granite is consistent with partial melting of Northern Region basement without contamination by juvenile magmas or supracrustal material, while the Tarbet Supracrustals record a minimum model age of <em>c.</em> 3200 Ma. Each of these units records Hf model ages that imply remelting of Eoarchaean (4000–3600 Ma) crust. Similar distributions of crystallization and model ages have been identified around the North Atlantic Craton, suggesting that Eoarchaean crust was once extensive in the region and constitutes the foundation of both Scotland and the North Atlantic Craton.
DOI: 10.6084/m9.figshare.3453806.v1
title: The Eoarchaean foundation of the North Atlantic Craton

description: The Archaean North Atlantic Craton underpins much of North America, Greenland and northern Europe, and incorporates the Earth's oldest extant continental crust. This paper reviews the current understanding of the region's crustal evolution, and considers our ability to investigate interrelationships between different fragments of the North Atlantic Craton. Detrital zircons from Mesoproterozoic to Cambrian basal sediments in NW Scotland have been re-examined in light of new data from the Archaean Tarbet supracrustal unit and the Palaeoproterozoic Rubha Ruadh granite. Hf model ages are recorded from 4160 to 1410 Ma, peaking at <em>c.</em> 3350 Ma, and are associated with U–Pb crystallization ages from 3670 to 1070 Ma, peaking at <em>c.</em> 2700 and 1700 Ma. The Rubha Ruadh granite is consistent with partial melting of Northern Region basement without contamination by juvenile magmas or supracrustal material, while the Tarbet Supracrustals record a minimum model age of <em>c.</em> 3200 Ma. Each of these units records Hf model ages that imply remelting of Eoarchaean (4000–3600 Ma) crust. Similar distributions of crystallization and model ages have been identified around the North Atlantic Craton, suggesting that Eoarchaean crust was once extensive in the region and constitutes the foundation of both Scotland and the North Atlantic Craton.
DOI: 10.6084/m9.figshare.3453803
title: Structural, geochronological and geochemical evidence for two distinct thrust sheets in the ‘Main Central thrust zone’, the Main Central thrust and Ramgarh–Munsiari thrust: implications for upper crustal shortening in central Nepal

description: Two orogen-scale thrusts structurally underneath Greater Himalayan (GH) rocks characterize the structural architecture of Himalaya in central Nepal. The Main Central thrust (MCT) is at the base of the GH with the Lesser Himalayan (LH) Robang Formation in the footwall, which is the hanging wall of the Ramgarh–Munsiari thrust (RMT). At Kodari-Tatopani and Malekhu, U–Pb detrital zircon age populations from the RMT sheet yield a maximum depositional age of <em>c.</em> 1838 and <em>c.</em> 1871 Ma. U–Pb analyses of igneous zircons from the RMT sheet yield a crystallization age of <em>c.</em> 1750 Ma at both Galchhi and Kodari-Tatopani. The εNd(0) values of pelitic rocks from the RMT sheet at Kodari-Tatopani range from <em>c.</em> −23 to −25; whereas, GH rocks have values from <em>c.</em> −12 to −18. These data indicate that the RMT sheet carries the Palaeoproterozoic LH rock and the MCT carries the GH rock. At Kodari-Tatopani, the thrust previously mapped as the MCT is interpreted to be the RMT. Positively identifying the RMT sheet in all three locations yields a more accurate kinematic evolution and confirms its orogenic-scale presence in central Nepal.
DOI: 10.6084/m9.figshare.3453803.v1
title: Structural, geochronological and geochemical evidence for two distinct thrust sheets in the ‘Main Central thrust zone’, the Main Central thrust and Ramgarh–Munsiari thrust: implications for upper crustal shortening in central Nepal

description: Two orogen-scale thrusts structurally underneath Greater Himalayan (GH) rocks characterize the structural architecture of Himalaya in central Nepal. The Main Central thrust (MCT) is at the base of the GH with the Lesser Himalayan (LH) Robang Formation in the footwall, which is the hanging wall of the Ramgarh–Munsiari thrust (RMT). At Kodari-Tatopani and Malekhu, U–Pb detrital zircon age populations from the RMT sheet yield a maximum depositional age of <em>c.</em> 1838 and <em>c.</em> 1871 Ma. U–Pb analyses of igneous zircons from the RMT sheet yield a crystallization age of <em>c.</em> 1750 Ma at both Galchhi and Kodari-Tatopani. The εNd(0) values of pelitic rocks from the RMT sheet at Kodari-Tatopani range from <em>c.</em> −23 to −25; whereas, GH rocks have values from <em>c.</em> −12 to −18. These data indicate that the RMT sheet carries the Palaeoproterozoic LH rock and the MCT carries the GH rock. At Kodari-Tatopani, the thrust previously mapped as the MCT is interpreted to be the RMT. Positively identifying the RMT sheet in all three locations yields a more accurate kinematic evolution and confirms its orogenic-scale presence in central Nepal.
DOI: 10.6084/m9.figshare.3453800
title: Muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

description: We present new muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages from thirteen Greater Himalayan rocks and one Lesser Himalayan rock collected from four north-trending transects across the southern Annapurna Range. Combining the new data with previously published ages leads to the following new insight into the tectonic development of the southern Annapurna. Muscovite cooling ages from Greater Himalayan rocks are <em>c.</em> 16–10 Ma in the western Annapurna and <em>c.</em> 6–2 Ma in the eastern Annapurna, revealing a decrease of 4–14 Ma from west to east. Similarly, the muscovite cooling age from one Lesser Himalayan rock in the west is <em>c.</em> 7 Ma and ages from several samples in the east are <em>c.</em> 5–2 Ma, indicating a decline of 2–5 Ma towards the east. Earlier cooling in the western Annapurna can be explained by along-strike differences in the geometry of the frontal ramp on the underlying thrust that carries these Greater and Lesser Himalayan rocks and/or by a NE-striking fault that cut these rocks. In Greater Himalayan rocks from the Modi river valley, one sample yielded muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages of 18.0±0.7 and 16.2±0.5 Ma for grain sizes of approximately 750 and 200 µm, respectively. In contrast, a sample collected 200 m structurally lower produced ages of 12.6±0.2 and 9.9±0.1 Ma for these two grain sizes. The north-dipping Bhanuwa fault has been proposed between these samples, with different authors arguing for normal or thrust-sense motion. Our newfound pattern of an older muscovite <sup>40</sup>Ar/<sup>39</sup>Ar age pair in the hanging wall supports arguments for the existence of the Bhanuwa fault and suggests normal sense motion.
DOI: 10.6084/m9.figshare.3453800.v1
title: Muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

description: We present new muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages from thirteen Greater Himalayan rocks and one Lesser Himalayan rock collected from four north-trending transects across the southern Annapurna Range. Combining the new data with previously published ages leads to the following new insight into the tectonic development of the southern Annapurna. Muscovite cooling ages from Greater Himalayan rocks are <em>c.</em> 16–10 Ma in the western Annapurna and <em>c.</em> 6–2 Ma in the eastern Annapurna, revealing a decrease of 4–14 Ma from west to east. Similarly, the muscovite cooling age from one Lesser Himalayan rock in the west is <em>c.</em> 7 Ma and ages from several samples in the east are <em>c.</em> 5–2 Ma, indicating a decline of 2–5 Ma towards the east. Earlier cooling in the western Annapurna can be explained by along-strike differences in the geometry of the frontal ramp on the underlying thrust that carries these Greater and Lesser Himalayan rocks and/or by a NE-striking fault that cut these rocks. In Greater Himalayan rocks from the Modi river valley, one sample yielded muscovite <sup>40</sup>Ar/<sup>39</sup>Ar ages of 18.0±0.7 and 16.2±0.5 Ma for grain sizes of approximately 750 and 200 µm, respectively. In contrast, a sample collected 200 m structurally lower produced ages of 12.6±0.2 and 9.9±0.1 Ma for these two grain sizes. The north-dipping Bhanuwa fault has been proposed between these samples, with different authors arguing for normal or thrust-sense motion. Our newfound pattern of an older muscovite <sup>40</sup>Ar/<sup>39</sup>Ar age pair in the hanging wall supports arguments for the existence of the Bhanuwa fault and suggests normal sense motion.
DOI: 10.6084/m9.figshare.3453797
title: An improved chronology for the Arthur’s Seat volcano and Carboniferous magmatism of the Midland Valley of Scotland

description: The Early Carboniferous Arthur’s Seat volcano in central Edinburgh is of geological significance and landscape value but lacks a precise chronology. New <sup>40</sup>Ar/<sup>39</sup>Ar step-heating plateau analyses date the lowest Lava 1 of the eruptive sequence to 341.2 ± 0.8 Ma (Visean, Holkerian), with Lava 3a at 336.7 ± 4.7 Ma. Intrusive or lava-lake basalts within the Lion’s Haunch Vent are precisely dated at 338 ± 0.6 Ma at Dunsapie and 335.1 ± 0.6 Ma at Crow Hill (Visean, Asbian). Taken together with existing <sup>40</sup>Ar/<sup>39</sup>Ar dates recalculated to recent decay constant and standard values, and U/Pb dates, a revised magmatic chronology consistent with biostratigraphy is presented for the Midland Valley of Scotland. The Garleton Hills Volcanic Formation is older than the Arthur’s Seat Volcanic Formation, whereas the Clyde Plateau and Arthur’s Seat volcanic formations are partly coeval, requiring minor re-adjustments to existing stratigraphy.
DOI: 10.6084/m9.figshare.3453797.v1
title: An improved chronology for the Arthur’s Seat volcano and Carboniferous magmatism of the Midland Valley of Scotland

description: The Early Carboniferous Arthur’s Seat volcano in central Edinburgh is of geological significance and landscape value but lacks a precise chronology. New <sup>40</sup>Ar/<sup>39</sup>Ar step-heating plateau analyses date the lowest Lava 1 of the eruptive sequence to 341.2 ± 0.8 Ma (Visean, Holkerian), with Lava 3a at 336.7 ± 4.7 Ma. Intrusive or lava-lake basalts within the Lion’s Haunch Vent are precisely dated at 338 ± 0.6 Ma at Dunsapie and 335.1 ± 0.6 Ma at Crow Hill (Visean, Asbian). Taken together with existing <sup>40</sup>Ar/<sup>39</sup>Ar dates recalculated to recent decay constant and standard values, and U/Pb dates, a revised magmatic chronology consistent with biostratigraphy is presented for the Midland Valley of Scotland. The Garleton Hills Volcanic Formation is older than the Arthur’s Seat Volcanic Formation, whereas the Clyde Plateau and Arthur’s Seat volcanic formations are partly coeval, requiring minor re-adjustments to existing stratigraphy.
DOI: 10.6084/m9.figshare.3453791
title: Geochemistry of a large impoundment, Part I: solute sources, mixing dynamics, and seasonal anoxia

description: Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO<sub>4</sub>-type waters with spatial distribution shifting from Na-Cl type to Ca-SO<sub>4</sub> type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics.
DOI: 10.6084/m9.figshare.3453791.v1
title: Geochemistry of a large impoundment, Part I: solute sources, mixing dynamics, and seasonal anoxia

description: Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO<sub>4</sub>-type waters with spatial distribution shifting from Na-Cl type to Ca-SO<sub>4</sub> type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics.
DOI: 10.6084/m9.figshare.3453785
title: The Southern Uplands Terrane in Scotland – a notional controversy revisited

description: Development of a regional geological interpretation for the Southern Uplands Terrane has been driven historically by advances in graptolite biostratigraphy, sandstone petrography and turbidite sedimentology (particularly the recognition of reliable way-up criteria), then, more recently, by a growing appreciation of the nature of accretionary processes at active plate margins. The latter has led to the widely held view of the terrane as an archetypal fossil accretionary prism, built up by the accretion at the margin of Laurentia of the sedimentary cover of Iapetus oceanic crust, the cover being stripped from the oceanic crust during its subduction beneath Laurentia. The achievement of this broad consensus has not been without controversy, which still persists in respect of some aspects of the overall model. Suggestions that the northernmost (Ordovician) part of the terrane might have originated in a back-arc basin have been disproved by a combination of mineral dating and basin thermal history analysis utilizing clay mineralogy. Nevertheless, it remains possible for that part of the terrane to have a continental margin, forearc depositional history. The southernmost (mid-Silurian) part of the terrane most probably developed in a foreland basin setting, as a fold-and-thrust belt overriding Avalonia, following the closure of the Iapetus Ocean. Progress in understanding the origins of the Southern Uplands Terrane has been achieved only by the collaborative application of multidisciplinary techniques – biostratigraphic, sedimentary, structural, geochemical and geophysical. This review is a tribute to all those who have contributed.
DOI: 10.6084/m9.figshare.3453785.v1
title: The Southern Uplands Terrane in Scotland – a notional controversy revisited

description: Development of a regional geological interpretation for the Southern Uplands Terrane has been driven historically by advances in graptolite biostratigraphy, sandstone petrography and turbidite sedimentology (particularly the recognition of reliable way-up criteria), then, more recently, by a growing appreciation of the nature of accretionary processes at active plate margins. The latter has led to the widely held view of the terrane as an archetypal fossil accretionary prism, built up by the accretion at the margin of Laurentia of the sedimentary cover of Iapetus oceanic crust, the cover being stripped from the oceanic crust during its subduction beneath Laurentia. The achievement of this broad consensus has not been without controversy, which still persists in respect of some aspects of the overall model. Suggestions that the northernmost (Ordovician) part of the terrane might have originated in a back-arc basin have been disproved by a combination of mineral dating and basin thermal history analysis utilizing clay mineralogy. Nevertheless, it remains possible for that part of the terrane to have a continental margin, forearc depositional history. The southernmost (mid-Silurian) part of the terrane most probably developed in a foreland basin setting, as a fold-and-thrust belt overriding Avalonia, following the closure of the Iapetus Ocean. Progress in understanding the origins of the Southern Uplands Terrane has been achieved only by the collaborative application of multidisciplinary techniques – biostratigraphic, sedimentary, structural, geochemical and geophysical. This review is a tribute to all those who have contributed.
DOI: 10.6084/m9.figshare.3453782
title: Sedimentary provenance, age and possible correlation of the Iona Group SW Scotland

description: Most clast lithologies within the basal conglomerate of the Iona Group, exposed on Iona, Inner Hebrides, SW Scotland, resemble the adjacent Archaean–Palaeoproterozoic Lewisian Gneiss Complex, supporting the hypothesis that the Iona Group unconformably overlies Lewisian gneisses on Iona. Moreover, a whole-rock Sm–Nd t<sub>DM</sub> age of 2512 Ma from one of these clasts supports its lithological correlation with granitic pegmatites in the underlying gneisses, while a second quartz-rich paragneiss clast with a Sm–Nd t<sub>DM</sub> age of 2745 Ma, is similar to Lewisian paragneisses on Coll. However, whole-rock t<sub>DM</sub> ages of 1755–2060 Ma and pronounced <em>c</em>. 1780–1800 Ma peaks in U–Pb detrital zircon and titanite data for Iona Group metasediments suggest additional distal sources of Laurentian affinity including the Rhinns Complex as well as Labradorian, Pinwarian and Archaean detritus. The Iona Group was deposited and deformed after <em>c</em>. 1490 Ma and before <em>c</em>. 422 Ma, constrained by the youngest detrital zircon and titanite and the intrusion of the Ross of Mull Granite, respectively. The detrital data permit correlation of the Iona Group with the Colonsay Group and the Glenshirra Subgroup of the Dalradian Grampian Group, although correlation with parts of the Torridonian cannot be excluded.