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9. The Diverse Habitats of Eclogite Formation: Insights From the Mesoproterozoic Glenelg Inlier, Scotland.

Author

Lucas, Nicholas A., Weller, Owen M., Copley, Alex, Mottram, Catherine M., Chapman, Glenn, and McMahon, William J.

Subjects
SEDIMENTARY rocks, METAMORPHIC rocks, ECLOGITE, GEOLOGICAL time scales, PHASE equilibrium, SUTURE zones (Structural geology)
Abstract

Eclogite‐facies rocks provide important constraints on the behaviour of convergent plate boundaries and the geometries of tectonic reconstructions due to the high to ultrahigh pressure conditions at which they form. Many eclogite occurrences are documented near the suture zone of active collisional settings where they are interpreted to mark the approximate location of former ocean basin subduction. Such observations influence tectonic interpretations for older eclogites within more deeply eroded and/or less well‐exposed terranes. The eclogitic Glenelg inlier in northwest Scotland is one such example, with c. 1 Ga eclogites having previously been interpreted as marking the trace of a Grenville‐aged collisional suture zone that defines a third 'arm' to the Grenville orogen alongside well‐defined sutures in North America and Scandinavia. Here we use a combination of geochronology, phase equilibrium modelling and accessory‐phase thermometry to show that the eclogite‐facies assemblages were produced at ∼$$ \sim $$18–19 kbar and 700°C–750°C from c. 1.1 to 1.0 Ga. Accounting for the foreland basin setting of equivalent‐aged sedimentary rocks in the region and demonstrating the thermal viability of this setting, we show that eclogite formation occurred in deforming foreland crust adjacent to the Grenville orogen, in a setting broadly analogous to fault‐bounded basement uplifts in the forelands of active deformation belts, such as the Himalayas and Andes. Our results demonstrate that eclogite‐facies rocks can form in a greater range of tectonic settings than are sometimes considered, with implications for tectonic reconstructions of collisional zones. In this instance, our results remove the need for a third 'arm' of the Grenville orogen by placing Glenelg in a foreland setting, reconciling the absence of plentiful Grenville‐aged metamorphic rocks in northwest Scotland, the sedimentological record and paleomagnetic data in the wider region. [ABSTRACT FROM AUTHOR]

Published
2025
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12. Tracking the porphyry-epithermal mineralization transition using U-Pb carbonate dating.

Author

Mottram, Catherine M., Kellett, Dawn A., Barresi, Tony, Chapman, Glenn G., and Halle, Jesse

Subjects
*URANIUM-lead dating, *CARBONATE minerals, *RENEWABLE energy transition (Government policy), *MINERALIZATION, *FLUID flow
Abstract

Key metals important for the green energy transition concentrate during magmatic-hydrothermal processes. In porphyry deposits, epithermal mineralization can overprint earlier higher-temperature systems. It is not well understood whether mineralization occurs in a single evolving system or forms during pulsed, episodic overprinting events. The timing and duration of fluid flow therefore remain key data gaps in deposit models, but they are essential factors for understanding metal (re)mobilization and concentration processes. Carbonates are common gangue minerals that precipitate during fluid flow and can be dated using the U-Pb method, thereby directly dating hydrothermal processes. Here, 41 new U-Pb dates from a fault-controlled porphyry-epithermal system in Yukon, Canada, reveal a >50 m.y. record of carbonate precipitation between ca. 77 and 19 Ma. Results support a model of pulsed, episodic fluid flow, rather than a single evolving system, where epithermal carbonate precipitation at ca. 74–67 Ma was both coeval with and significantly postdated Cretaceous porphyry-related magmatism. Overprinting events at ca. 62–56 Ma, ca. 51–47 Ma, and younger than 40 Ma were not responsible for primary metal deposition but may have contributed to metal enrichment. Carbonate dates coincide with periods of brecciation and fault slip. Fault movement therefore enabled episodic overprinting by epithermal mineralization, mobilizing and (re)concentrating metals. This comprehensive reconstruction of a long-lived magmatic-hydrothermal system tracks the transition from porphyry to epithermal environments, demonstrating the power of carbonate U-Pb dating for critical minerals research. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Using U–Pb carbonate dating to constrain the timing of extension and fault reactivation within the Bristol Channel Basin, SW England.

Author

Connolly, Joe, Anderson, Mark, Mottram, Catherine, Price, Gregory D., Parrish, Randall, and Sanderson, David

Subjects
SEDIMENTARY basins, FLUID pressure, GEOLOGICAL time scales, RIFTS (Geology), MESOZOIC Era
Abstract

The Bristol Channel Basin is a Mesozoic continental rift basin. The basin is an important analogue for offshore reservoirs. Relative cross-cutting relationships and correlation with adjacent sedimentary basins have previously been used to constrain the timing of basin development. In situ U–Pb carbonate geochronology has been used to date calcite slickenfibre development in the cores of normal, thrust and strike-slip faults in the East Quantoxhead and Kilve region of Somerset for the first time. Protracted north–south extension from c. 150 to 120 Ma formed normal faults. Subsequent north–south shortening from c. 50 to 20 Ma was accommodated by (1) mutually cross-cutting strike-slip faults, (2) minor east–west-striking thrust faults and (3) the reactivation of pre-existing normal faults. Throughout Cenozoic contraction, σ 2 and σ 3 remained similar in magnitude and periodically flipped to become vertical; this was probably controlled by local stress permutations and changes in fluid pressure. The timing of inversion is contemporaneous with dominant Pyrenean and later Alpine orogenic events, as well as the opening of the Mid-Atlantic Rift. Early inversion of the Bristol Channel Basin was probably driven by far-field Pyrenean deformation, with later contraction caused by Alpine forces. Ridge push from the Mid-Atlantic Rift exacerbated the reactivation of the basin. [ABSTRACT FROM AUTHOR]

Published
2024
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16. An integrated metamorphic and isotopic study of crustal extrusion along the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine Mary

Subjects
551.43
Abstract

Mountains form where the Earth's plates collide; during this upheaval rocks are deformed by massive forces. The Himalayan orogen represents the ideal natural laboratory to decode the record of the deformational processes encrypted in the rocks. In the eastern region of Sikkim, a unique series of 'time windows' are exposed by doming of a major ductile fault, revealing the inner workings of one of the major mountain-building structures that accommodated the India-Asia collision. The temporal and thermal evolution of the complex zone of deformation associated with this structure, the Main Central Thrust (MCT), was investigated using a combination of whole rock geochemistry (εNd), geochronology (U-Pb and ⁴⁰Ar/³⁹Ar), accessory and major phase geochemistry, and pressure-temperature modelling. The results demonstrate that: (1) isotope geochemistry can distinguish rock packages that have been juxtaposed over many hundreds of kilometres in complex ductile shear zones; (2) during prolonged ductile deformation of the MCT zone from ~21-9 Ma there was progressively downwards-penetrating deformation and accretion of colder original footwall material to the hotter hanging wall; (3) the associated zone of inverted Barrovian metamorphism documents a sequence of 'paleo-thrusts' that evolved as the thrust-zone deformed rocks at successively lower pressure and temperature conditions (< 500 to > 650°C and 8 to 10 kbar); (4) during the Miocene thrusting progressed at a rate of ~10 mm yr⁻¹ , followed by moderately rapid cooling at a rate of ~50-70°C Ma⁻¹. These findings are consistent with a tectonic model where rocks were accreted to a partially-molten mid-crustal channel of ductilely deforming material along the MCT. This study provides new insight into how deformation is accommodated along major thrust faults during mountain building and has implications for how geological tools such as linked geochronology-geochemistry and P-T modelling are used to aid the interpretation of rock deformation in the cores of evolving mountain belts.

Published
2014
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24. Multidisciplinary characterization of fluid sources in ductileshear zones (Armorican Massif, Variscan belt, France)

Author

Dusséaux, Camille, Gébelin, Aude, Boulvais, Philippe, Ruffet, Gilles, Gardien, Véronique, Dubois, Michel, Poujol, Marc, Cogné, Nathan, Branquet, Yannick, Mottram, Catherine, Barou, Fabrice, Mulch, Andreas, Plymouth University, Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Génie Civil et Géo-Environnement (LGCgE) - ULR 4515 (LGCgE), Université d'Artois (UA)-Université de Lille-Ecole nationale supérieure Mines-Télécom Lille Douai (IMT Lille Douai), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL), Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Métallogénie - UMR7327, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), University of Portsmouth, Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Goethe-Universität Frankfurt am Main-Senckenberg – Leibniz Institution for Biodiversity and Earth System Research - Senckenberg Gesellschaft für Naturforschung, Leibniz Association-Leibniz Association, University of Plymouth (UOP), Plymouth, UK, Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
fluid-rock interactions, thermometry, hydrogen isotope, shear zone, U(-Th)/Pb, meteoric fluids, 40Ar/39Ar, Variscan, fluid inclusions, [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy, detachment, Armorican Massif, oxygen isotope, [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology
Abstract

National audience; Ductile shear zones are sites of significant fluid circulation and hydrothermal alteration wheremetamorphic, magmatic and surface-derived fluids meet. Characterization of the meteoricsource of crustal fluids can be used to better understand ore deposition and mineralization atthe orogen scale or for stable isotope paleoaltimetry reconstructions. Microstructural,thermometry, geochronological and hydrogen (δD) and oxygen (δ18O) isotope data fromsyntectonic peraluminous granites from ductile shear zones in the Armorican Massif permit todetermine the source of fluids present during deformation. Furthermore, they allow to study thespatial and temporal evolution of localized deformation and fluid-rock interaction across theseVariscan fossil hydrothermal systems, including the timing and duration of fluid flow and watermineralisotope exchange.At the regional scale, a 41‰ difference in δDwater values amongst mylonitic leucograniteemplaced along strike-slip and detachment zones highlights a mixing relationship betweenmetamorphic/magmatic fluids (δDwater ~ -33‰) and meteoric fluids with δDwater values aslow as -74‰. The mixing between surface-derived and deep fluids is further supported by fluidinclusions aligned along synkinematic structural planes in quartz grains from detachmentfootwalls. They contain very low to medium salinity water (0 to 7 wt% eq. NaCl) and haveintermediate δD and δ18O values.We focus on the Quiberon detachment zone (QDZ) where synkinematic muscovite andtourmaline crystallized and equilibrated with deuterium-depleted surface-derived fluids duringhigh-temperature deformation supported by titanium-in-muscovite thermometry andmicrostructures. 40Ar/39Ar data on muscovite and U(-Th)/Pb geochronology on zircon,monazite and apatite from syntectonic leucogranites, together with microstructural data,suggest that meteoric fluid-rock-deformation interactions started at ~320 Ma and played amajor role in leaching uranium at ~305 Ma. U-Th/Pb data from migmatites located belowthe QDZ strengthen the idea that meteoric fluids infiltration, detachment activity, syntectonicleucogranite emplacement and migmatization were coeval and allowed the development of asustained hydrothermal system.

Published
2021

28. Multidisciplinary characterisation of fluid sources in ductile shear zones

Author

Dusséaux, Camille, Gébelin, Aude, Boulvais, Philippe, Ruffet, Gilles, Dubois, Michel, Poujol, Marc, Cogné, Nathan, Branquet, Yannick, Mottram, Catherine, Barou, Fabrice, Mulch, Andreas, School of Geography, Earth and Environmental Sciences [Plymouth] (SoGEES), Plymouth University, Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Université de Lille, University of Portsmouth, Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Goethe-Universität Frankfurt am Main, The Royal Society of London, Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), and Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Abstract

International audience; Ductile shear zones represent sites of significant fluid circulation and hydrothermal alteration where metamorphic, magmatic and surface-derived fluids meet. Characterization of the meteoric source of crustal fluids can be used to better understand ore deposition and mineralization at the orogen scale or for stable isotope paleoaltimetry reconstructions. Microstructural, thermometry, geochronology and hydrogen isotope data conducted on syntectonic peraluminous granites from crustal-scale shear zones in the Armorican Massif and the French Massif Central allowed the determination of the source of fluids present during deformation, and a better understanding of the spatial and temporal evolution of localized deformation and fluid-rock interaction across these Variscan fossil hydrothermal systems, including the timing and duration of fluid flow and mineral water isotope exchange.

Published
2020

30. Using U-Th-Pb petrochronology to determine rates of ductile thrusting: Time windows into the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B.W., Roberts, Nick M.W., Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B.W., and Roberts, Nick M.W.

Abstract

Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from ~50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of ~550°C and 0.8 GPa between ~21 and 18 Ma along the prograde path. Peak metamorphic conditions of ~650°C and 0.8–1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at ~17–14 Ma. This same process occurred at analogous metamorphic conditions between ~18–16 Ma and 14.5–13 Ma in the midsection of the thrust zone and between ~13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently ~4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr−1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

Published
2015

38. Using U-Th-Pb petrochronology to determine rates of ductile thrusting: time windows into the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B. W., Roberts, Nick M. W., Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B. W., and Roberts, Nick M. W.

Abstract

Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from ~50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of ~550°C and 0.8 GPa between ~21 and 18 Ma along the prograde path. Peak metamorphic conditions of ~650°C and 0.8–1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at ~17–14 Ma. This same process occurred at analogous metamorphic conditions between ~18–16 Ma and 14.5–13 Ma in the midsection of the thrust zone and between ~13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently ~4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr−1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

39. Tectonic interleaving along the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine M., Argles, T. W., Harris, N. B. W., Parrish, R. R., Horstwood, M. S. A., Warren, C. J., Gupta, S., Mottram, Catherine M., Argles, T. W., Harris, N. B. W., Parrish, R. R., Horstwood, M. S. A., Warren, C. J., and Gupta, S.

Abstract

Geochemical and geochronological analyses provide quantitative evidence about the origin, development and motion along ductile faults, where kinematic structures have been overprinted. The Main Central Thrust is a key structure in the Himalaya that accommodated substantial amounts of the India–Asia convergence. This structure juxtaposes two isotopically distinct rock packages across a zone of ductile deformation. Structural analysis, whole-rock Nd isotopes, and U–Pb zircon geochronology reveal that the hanging wall is characterized by detrital zircon peaks at c. 800–1000 Ma, 1500–1700 Ma and 2300–2500 Ma and an εNd(0) signature of –18.3 to –12.1, and is intruded by c. 800 Ma and c. 500–600 Ma granites. In contrast, the footwall has a prominent detrital zircon peak at c. 1800–1900 Ma, with older populations spanning 1900–3600 Ma, and an εNd(0) signature of –27.7 to –23.4, intruded by c. 1830 Ma granites. The data reveal a c. 5 km thick zone of tectonic imbrication, where isotopically out-of-sequence packages are interleaved. The rocks became imbricated as the once proximal and distal rocks of the Indian margin were juxtaposed by Cenozoic movement along the Main Central Thrust. Geochronological and isotopic characterization allows for correlation along the Himalayan orogen and could be applied to other cryptic ductile shear zones.

40. From source to emplacement: the origin of leucogranites from the Sikkim-Darjeeling Himalaya, India

Author

Srivastava, Tanya, Harris, Nigel, Mottram, Catherine, Joshi, Kumar, Wanjari, Nischal, Srivastava, Tanya, Harris, Nigel, Mottram, Catherine, Joshi, Kumar, and Wanjari, Nischal

Abstract

Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular. This paper aims to understand the melt source and emplacement age of the leucogranites from Sikkim in order to decipher the deep geodynamic processes of the eastern Himalayas. Zircon U-Pb analysis of the Higher Himalayan Sequence (HHS) metamorphic core reveals a prolonged period of crustal melting between >33 to ca. 14 Ma. Major and trace element abundances are presented for 27 leucogranites from North Sikkim that are classified into two-mica and tourmaline leucogranite types. They are peraluminous in composition, characterized by high SiO2 (70.91–74.9 wt.%), Al2O3 (13.69–15.82 wt.%), and low MgO (0.13–0.74 wt.%). Elemental abundances suggest that Sikkim Himalayan leucogranites are derived from crustal melts. The two-mica leucogranites are derived from a metagreywacke source, whereas the tourmaline leucogranites are sourced from metapelitic sources, with inherited zircons indicating an HHS origin for both types. U-Pb zircon geochronology of the two mica leucogranites indicates ages of ca. 19–15 Ma, consistent with crustal melting recorded in HHS gneisses from Darjeeling. Monazites from both the two-mica and tourmaline granites yield a crystallization age of ca. 14 Ma, coeval with movement on the Main Central Thrust and South Tibetan Detachment System which further provides constraints on the timing and mechanism of petrogenesis of leucogranites in the Sikkim Himalayas.

41. Using U-Th-Pb petrochronology to determine rates of ductile thrusting: time windows into the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B. W., Roberts, Nick M. W., Mottram, Catherine M., Parrish, Randall R., Regis, Daniele, Warren, Clare J., Argles, Tom W., Harris, Nigel B. W., and Roberts, Nick M. W.

Abstract

Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from ~50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of ~550°C and 0.8 GPa between ~21 and 18 Ma along the prograde path. Peak metamorphic conditions of ~650°C and 0.8–1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at ~17–14 Ma. This same process occurred at analogous metamorphic conditions between ~18–16 Ma and 14.5–13 Ma in the midsection of the thrust zone and between ~13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently ~4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr−1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

42. Tectonic interleaving along the Main Central Thrust, Sikkim Himalaya

Author

Mottram, Catherine M., Argles, T. W., Harris, N. B. W., Parrish, R. R., Horstwood, M. S. A., Warren, C. J., Gupta, S., Mottram, Catherine M., Argles, T. W., Harris, N. B. W., Parrish, R. R., Horstwood, M. S. A., Warren, C. J., and Gupta, S.

Abstract

Geochemical and geochronological analyses provide quantitative evidence about the origin, development and motion along ductile faults, where kinematic structures have been overprinted. The Main Central Thrust is a key structure in the Himalaya that accommodated substantial amounts of the India–Asia convergence. This structure juxtaposes two isotopically distinct rock packages across a zone of ductile deformation. Structural analysis, whole-rock Nd isotopes, and U–Pb zircon geochronology reveal that the hanging wall is characterized by detrital zircon peaks at c. 800–1000 Ma, 1500–1700 Ma and 2300–2500 Ma and an εNd(0) signature of –18.3 to –12.1, and is intruded by c. 800 Ma and c. 500–600 Ma granites. In contrast, the footwall has a prominent detrital zircon peak at c. 1800–1900 Ma, with older populations spanning 1900–3600 Ma, and an εNd(0) signature of –27.7 to –23.4, intruded by c. 1830 Ma granites. The data reveal a c. 5 km thick zone of tectonic imbrication, where isotopically out-of-sequence packages are interleaved. The rocks became imbricated as the once proximal and distal rocks of the Indian margin were juxtaposed by Cenozoic movement along the Main Central Thrust. Geochronological and isotopic characterization allows for correlation along the Himalayan orogen and could be applied to other cryptic ductile shear zones.

43. Directly dating deformation with calcite U-Pb; the good, the bad and the ugly!

Author

Mottram, Catherine, Coutand, Isabelle, Grujic, Djordje, and Kellett, Dawn

Subjects
*CALCITE, *GEOLOGICAL time scales, *BRITTLE fractures, *FLUID flow, *QUARTZ, *LOW temperatures, *GEOLOGY
Abstract

Deformation in the upper crust is commonly accommodated by brittle fracturing, faulting and dissolution-precipitation creep. These short-lived, low temperature deformation processes are notoriously difficult to date as minerals commonly used to record geological time (such as zircon and monazite) typically do not crystallise or recrystallize in response to deformation under these conditions. Brittle fractures provide pathways for fluids, resulting in abundant calcite/quartz veins in the earth's upper crust. Analytical techniques have recently been developed for direct dating of brittle structures using U-Pb in calcite slickenfibres and syn-tectonic veins (e.g. Roberts and Walker, 2016; Nuriel et al., 2017). This has opened up a whole new realm of possible tectonic investigations in the upper crust.This talk will explore the effectiveness of the U-Pb calcite dating technique for providing timing constraints for upper crustal deformation, fluid flow and mineralisation events. Like other unconventional geochronometers that have low U content and incorporate common Pb into their structures (e.g. titanite), calcite is not always suitable for U-Pb analysis and results can therefore be ambiguous to interpret. We present examples spanning the range of the 'good, bad and ugly' in the world of calcite U-Pb dating. Despite these challenges, we use case studies from continental-scale thrust and strike-slip faults including the Main Boundary Thrust in the Himalaya, the North Anatolian Fault, and the Big Creek Fault in the Yukon, Canadian Cordillera to demonstrate how U-Pb calcite dating can be successfully used to reconstruct the displacement history of these various first-order structures. Roberts and Walker, 2016, Geology, 44, p. 531; Nuriel et al., 2017, Geology, 45, p.587 [ABSTRACT FROM AUTHOR]

Published
2019

45. LETTERS.

Author

Taylor, Gordon, Cooper, Guy, McGee, Alan, Middleton, J. B., Pasley, A Du Gard, Baker, Deborah, Jones, Margaret, Marshall, R. J., Nicholls, Ian, Mottram, Catherine, Jacob, Jean, Weatherill, J. M., Williams, Trudie, Spencer, Ann, Hoar, Sue, Salt, Len, Woods, Jennifer, Shaw, Elspeth, Sculpher, John, and Hubbard, Sacha

Subjects
LETTERS to the editor, GARDEN centers, GARDEN design, GRASSES, GARDENING
Abstract

Several letters to the editor in response to articles in previous issues of "The Garden," including "Plant Sales Under Pressure," in the October 2005 issue, "Designing for an Extended Season," in the September 2005 issue, "Grasses for a New Generation," in the September 2005 issue are presented.

Published
2005

46. Dating fault reactivation at the northern Appalachian structural front, western Newfoundland, Canada.

Author

MCKEEN, DYLAN J., WHITE, SHAWNA, KELLETT, DAWN, MOTTRAM, CATHERINE, and WALDRON, JOHN W. F.

Subjects
*OROGENIC belts, *FAULT zones, *THRUST, *GEOLOGICAL time scales, *CALCITE, *LASER ablation inductively coupled plasma mass spectrometry, *EDIACARAN fossils
Abstract

The Appalachian orogen developed during multiple microcontinent and terrane accretions resulting from episodic, Cambrian through Devonian, closure of the Iapetus Ocean. In western Newfoundland, preserved folds and faults formed during the Taconian and Acadian orogenies. THe NW limit of deformation, or Appalachian structural front, extends along Newfoundland's west coast, and is defined by a tectonic wedge, the upper detachment of which is marked on the Port au Port Peninsula by the Tea Cove thrust. Stratigraphic relationships suggest west-directed wedge emplacement during the Early to Middle Devonian. THe Tea Cove thrust is cross-cut by the basement-cutting Round Head thrust, the motion of which is bracketed between the Early Devonian and Visean according to stratigraphic relationships. Preliminary U-Pb geochronology data obtained from LA-ICP-MS of calcite slickenfibres collected from small but pervasive conjugate thrust faults, oriented parallel to the Tea Cove thrust with horizontal NW-SE shortening direction, show Late Devonian ages of ~366 Ma for fault slip. Major faults, parallel to the Tea Cove THrust, preserve two generations of motion; a metre-wide fault zone with kinematic indicators indicating SE-directed back-thrusting and discrete, bedding-subparallel faults an opposite, normal sense of slip which bound the fault zone. U-Pb calcite slickenfibre ages from these discrete faults indicate latest Mississippian to Pennsylvanian slip at ~324 Ma. Later cross-cutting faults, with orientations consistent with post-Taconian basement faults, have sinistral sense calcite slickenfibres that yield late Pennsylvanian to Permian U-Pb ages of ~299 Ma. Future work will focus on dating early bituminous veins that are cross-cut by all major structures, to further constrain motion and reactivation on the structural front. THese novel calcite slickenfibre ages, some of the first reported in the Canadian Appalachians, demonstrate fault reactivation during late and post-orogenic stages along the Appalachian front. [ABSTRACT FROM AUTHOR]

Published
2023
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47. Applicability of geochemistry, Sm-Nd and Sr isotopes, and detrital zircon U-Pb ages for provenance studies of the Resende Basin alluvial deposits

Author

Carvalho, Manuela de Oliveira, manuela.carvalho.1989@outlook.com, Valeriano, Claudio de Morisson, Ramos, Renato Rodriguez Cabral, Mottram, Catherine, Souza, Miguel Antonio Tupinambá Araújo, Riccomini, Claudio, Mello, Claudio Limeira, and Guedes, Eliane

Subjects
Áreas-fonte contrastantes, Proveniência sedimentar, Geochronology, Riftes continentais, GEOCIENCIAS::GEOLOGIA [CIENCIAS EXATAS E DA TERRA], Geoquímica – Resende, Bacia de (RJ), Geologia isotópica – Resende, Bacia de (RJ), Rochas sedimentares – Resende, Bacia de (RJ), Continental rift, Geochemistry, Isótopos radiogênicos, Sedimentos (Geologia) – Resende, Bacia de (RJ), Contrasting source areas, Geocronologia, Sedimentary provenance, Radiogenic isotopes
Abstract

Submitted by Taciane CTC/C (taciane.silva@uerj.br) on 2021-11-11T14:05:40Z No. of bitstreams: 2 Tese - Manuela de Oliveira Carvalho - 2020 - Completa.pdf: 215259085 bytes, checksum: 044d3cc7671df16553300f49827534cb (MD5) Tese - Manuela de Oliveira Carvalho - 2020 - Parcial.pdf: 2465932 bytes, checksum: 823d06f98a4aeb78bebfeaa630b5c8a9 (MD5) Made available in DSpace on 2021-11-11T14:05:40Z (GMT). No. of bitstreams: 2 Tese - Manuela de Oliveira Carvalho - 2020 - Completa.pdf: 215259085 bytes, checksum: 044d3cc7671df16553300f49827534cb (MD5) Tese - Manuela de Oliveira Carvalho - 2020 - Parcial.pdf: 2465932 bytes, checksum: 823d06f98a4aeb78bebfeaa630b5c8a9 (MD5) Previous issue date: 2020-12-21 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ The Resende Basin is a halfgraben with a north tectonic border and about 240 km2 of area and 45 km in length on its NE-SW axis located in South-eastern Brazil. The thickness of the sedimentary filling reaches about 500 m and its registration comprises, at the base, Paleocene deposits of the Ribeirão dos Quatis Formation (pre- or syn- rifting tectonics fluvial system) underpinned by the syn-rift I sedimentary successions of the Resende Formation (braided-fluvial system with associated marginal alluvial fans). In the Oligocene, syn-rift II successions of the Pinheiral Formation (braided-fluvial system) were deposited. The Miocene deposits of the Floriano Formation (meandering fluvial system) mark the post-rift period of the basin. The present work intends to contribute to the knowledge of the evolution of the Resende Basin from studies of sedimentary provenance based on whole-rock geochemical analysis, whole-rock of Sm-Nd and Sr isotope analysis and U-Pb detrital zircon dating. Samples correspond to fluvial mudstones and sandstones and sediments from alluvial fans. The basement of the Resende Basin consists of Proterozoic rocks from the Ribeira Belt and Cretaceous alkaline rocks from the Itatiaia and Morro Redondo massifs. Both mudstones and sandstones of the Resende Formation have similar chemical signatures of trace and rare earth elements, as well as similar Sm-Nd and Sr isotopes signatures, whose variations are easily explained by differences in provenance due to different source areas and/or degrees of mixture of sources. There is a strong control of elements such as Rb and Ba, which can be associated with the presence of low-altered K-feldspars. Enrichments of Zr, Hf, Y and considerable variations in the values of the sum of rare earth elements, especially in mudstones, indicate the addition of heavy minerals (zircon and monazite). Mudstones and sandstones in the Resende Basin present values of εNd(40 Ma) and ratios of 87Sr/86Sr(40 Ma), respectively, between -4 and -21 and between 0.70603 and 0.80934. Sediments from alluvial fans have isotopic signatures like their adjacent basements, the Itatiaia fan with the Itatiaia Massif and the Penedo fan with Proterozoic rocks. Samples with εNd(40 Ma) > -10 and TDM < 1.25 Ga have a contribution of less radiogenic Cretaceous material, while samples with εNd(40 Ma) < -10 and TDM > 1.25 Ga may have or not Cretaceous contribution, revealed by the presence of Cretaceous zircons in samples with more radiogenic isotopic signatures. There is a limit on the proportion of less radiogenic content needed to interfere with Sm-Nd signatures. The Cretaceous content reflected in the isotopic signatures and in detrital zircon ages is more expressive in the westernmost portions of the Resende Structural High, Penedo Depocenter, when compared to the sediments deposited further east, Porto Real Depocenter. The content of Cretaceous zircons is also expressive in the easternmost portions of the basin, Quatis Depocenter. Probably the Resende Structural High already existed and compartmentalized the basin in two depocenters, blocking part of the sediments from the Itatiaia Massif brought from W-E direction channels to the easternmost portions of the basin. The results point to an expressive control of the basement at south-southwest in the supply of debris during the syn-rift filling A Bacia de Resende é um hemigráben com borda norte tectônica e cerca de 240 km2 e 45 km de comprimento em seu eixo NE-SW localizada no Sudeste do Brasil. A espessura do preenchimento sedimentar alcança cerca de 500 m e seu registro compreende, na base, depósitos paleocênicos da Formação Ribeirão dos Quatis (sistema fluvial entrelaçado pré ou sin-tectônica de rifteamento) sotopostos pelas sucessões sedimentares eocênicas de estágio sin-rifte I da Formação Resende (sistema fluvial entrelaçado com leques aluviais marginais associados). No Oligoceno, foram depositadas sucessões sin-rifte II da Formação Pinheiral (sistema fluvial entrelaçado). Os depósitos miocênicos da Formação Floriano (sistema fluvial meandrante) marcam o período pós-rifte da bacia. O presente trabalho pretende contribuir para os conhecimentos de evolução da Bacia de Resende a partir de estudos de proveniência sedimentar com base em análises geoquímicas de rocha-total, assinaturas isotópicas de Sm-Nd e Sr de rocha-total e datação U-Pb de zircão detrítico. Amostras correspondem a lutitos e arenitos fluviais e sedimentos de leques aluviais. O embasamento da Bacia de Resende é constituído por rochas proterozoicas do Orógeno Ribeira e rochas alcalinas cretáceas dos maciços de Itatiaia e Morro Redondo. Tanto lutitos, como arenitos da Formação Resende apresentam assinaturas químicas de elementos traço e terras raras e de isótopos de Sm-Nd e Sr similares, cujas variações são facilmente explicadas por diferenças na proveniência devido às diferentes áreas-fonte e/ou graus de mistura de fontes. Há forte controle de elementos como Rb e Ba, que podem ser associados a presença de K-feldspatos pouco alterados. Enriquecimentos de Zr, Hf, Y e variações consideráveis nos valores do somatório de elementos terras raras, especialmente nos lutitos, indicam adição de minerais pesados (zircão e monazita). Lutitos e arenitos da Bacia de Resende apresentam valores de εNd(40 Ma) e razões de 87Sr/86Sr(40 Ma), respectivamente, entre -4 e -21 e entre 0,70603 e 0,80934. Sedimentos de leques aluviais possuem assinaturas isotópicas similares aos seus embasamentos adjacentes, o Leque de Itatiaia com o Maciço de Itatiaia e, o Leque de Penedo com rochas proterozoicas. Amostras com valores de εNd(40 Ma) > -10 e TDM < 1,25 Ga apresentam contribuição de material menos radiogênico cretáceo, enquanto amostras com valores de εNd(40 Ma) < -10 e TDM > 1,25 Ga podem ter ou não contribuição cretácea, revelado pela presença de zircões de idade cretácea em amostras com assinaturas isotópicas mais radiogênicas. Há um limite de proporção de conteúdo menos radiogênico necessário para interferir nas assinaturas de Sm-Nd. O conteúdo cretáceo refletido nas assinaturas isotópicas e em idades de zircão detrítico é mais expressivo nas porções mais a oeste do Alto Estrutural de Resende, Depocentro Penedo, se comparado aos sedimentos depositados mais a leste do alto, Depocentro Porto Real. O conteúdo de zircões cretáceos também é expressivo nas porções mais a leste da bacia, Depocentro Quatis. Provavelmente, o Alto Estrutural de Resende já existia e compartimentava a bacia em dois depocentros, bloqueando parte dos sedimentos provenientes do Maciço de Itatiaia trazidos de canais de direção W-E para as porções mais a leste da bacia. Os resultados apontam para um controle expressivo do embasamento a sul-sudoeste no fornecimento de detritos durante o preenchimento sin-rifte

Published
2020

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