New isotopic age data constrain the depositional age and accretionary history of the Neoproterozoic-Ordovician Mona Complex (Anglesey-Lleyn, Wales)

Asanuma, Hisashi; Fujisaki, Wataru; Sato, Terukazu; Sakata, Shuhei; Sawaki, Yusuke; Aoki, Kazumasa; Okada, Yoshihiro; Maruyama, Shigenori; Hirata, Takafumi; Itaya, Tetsumaru; Windley, Brian F.

doi:10.1016/j.tecto.2017.03.017

Cited by 6 publications

(10 citation statements)

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“…Peak metamorphic conditions were subgreenschist facies, typically meaning temperatures less than 300°C at burial depth less than 20 km (Kawai et al., 2006). Constraints on the depositional and deformational ages of these lithologies are uncertain; Neoproterozoic carbonates from the Gwna Complex in the north of Anglesey likely formed 880‒750 Ma (Horák & Evans, 2011) and Cambrian siliciclastic sediments on Llanddwyn Island were deposited after a maximum U‐Pd depositional age of 550 ± 24 Ma (Asanuma et al., 2017). Subduction of the Gwna Group likely began before 600 Ma, accreting the Gwna Complex at Llanddwyn Island after the deposition of the coarsest siliciclastic lithologies after 550 Ma (Asanuma et al., 2017) and continuing until the Ordovician (448 − 488 Ma; Kawai et al., 2007).…”

Section: Geological Setting Of the Gwna Complexmentioning

confidence: 99%

“…Constraints on the depositional and deformational ages of these lithologies are uncertain; Neoproterozoic carbonates from the Gwna Complex in the north of Anglesey likely formed 880‒750 Ma (Horák & Evans, 2011) and Cambrian siliciclastic sediments on Llanddwyn Island were deposited after a maximum U‐Pd depositional age of 550 ± 24 Ma (Asanuma et al., 2017). Subduction of the Gwna Group likely began before 600 Ma, accreting the Gwna Complex at Llanddwyn Island after the deposition of the coarsest siliciclastic lithologies after 550 Ma (Asanuma et al., 2017) and continuing until the Ordovician (448 − 488 Ma; Kawai et al., 2007). This relatively long‐lived, inferred history of convergence relates to the larger‐scale complex Cambrian‐Ordovician subduction‐collision Appalachian‐Caledonian belt, where post‐tectonic steepening of subduction‐related structures could relate to collisions of arcs and microcontinents (c.f.…”

Section: Geological Setting Of the Gwna Complexmentioning

confidence: 99%

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Heterogeneous Subgreenschist Deformation in an Exhumed Sediment‐Poor Mélange

et al. 2022

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Section: Geological Setting Of the Gwna Complexmentioning

confidence: 99%

Section: Geological Setting Of the Gwna Complexmentioning

confidence: 99%

Heterogeneous Subgreenschist Deformation in an Exhumed Sediment‐Poor Mélange

et al. 2022

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“…A subsequent age of ~474 Ma is interpreted as indicating the (Caledonian?) metamorphic event (Asanuma et al 2017). In addition, recent fossil finds also indicate a lower Cambrian (or younger) age for the Rhoscolyn Formation (e.g.…”

Section: Geological Settingmentioning

confidence: 99%

Syntectonic quartz vein evolution during progressive deformation

Lloyd

2018

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Two models to explain the progressive deformation of syntectonic quartz veins are derived from conventional theories for simple and pure shears. The simple shear model is based on reorientation and changes in length of linear vein elements and predicts initial orientations of veins for imposed shear strains, elongations and strain ratios. The pure shear model considers changes in length of lines variably oriented relative to the maximum compression direction and yields estimates of elongation strains and strain ratios. Expectations of both models are different, as illustrated by analysis of quartz veins from the Rhoscolyn Anticline, Anglesey, NW Wales. The simple shear model recognises three distinct initial orientations, which predict different strains across the fold; the pure shear model suggests veins were initially subparallel to the principal compression direction and predicts effectively constant strains across the fold. In addition, both models predict different patterns of fold vergence: for simple shear, vergence depends on magnitude and direction of shearing and may exhibit complex patterns; for pure shear, vergence patterns are predicted to be essentially constant. In general, the predictions of either model are critically dependent on the origin of the veins, particularly relative to the formation of the Rhoscolyn Anticline. The publication of 'Folding and Fracturing of Rocks' (Ramsay 1967) represented a step change in Structural Geology. It cemented the combination of rigorous field investigations augmented by mechanical and numerical analyses in the structural geological psyche and prepared the ground for ever more sophisticated investigations that persist to this day. However, it must be recognised that historically, the book represented a continuous progression of ideas that had developed albeit slowly over more than a century. Although folds and folding are central themes of Ramsay's book (Chapters 7-10), fracturing is actually of relatively minor consequence (i.e. there are no chapters dedicated to it specifically); in essence, the presentation is predicated on the significance of stress and particularly strain during geological deformation (Chapters 1-6). This contribution follows the philosophy inherent in 'Folding and Fracturing of Rocks' to interpret the evolution of syntectonic quartz veins during progressive deformation. The veins occur within (semi-)pelitic units folded by the Rhoscolyn Anticline, Anglesey, NW Wales (Fig. 1), a well-known location for both structural geology research and teaching. It begins with a brief description of the general geology of Rhoscolyn, including the recognition of various models to explain the evolution of the kilometre scale Rhoscolyn Anticline (e.g.

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“…19 b) consists of a succession of mixed metaclastic and metavolcanic rocks (Llanfachel Group) thrust over an undated unit (MONL) of mainly metaclastic rocks that are assumed to be younger (Schofield et al, 2020). Two detrital zircon data sets (Asanuma et al, 2017) show somewhat contrasting provenance. A diverse sample shows a typical "Ganderian" spectrum with varied Mesoproterozoic zircon but a large Cambrian peak at ~530 Ma.…”

Section: Monian Beltmentioning

confidence: 99%

“…The rocks are folded by early NW-vergent folds and at least two generations of younger SE-vergent structures. Of all the Monian slices the Porth y Felin has the most data on detrital zircon provenance (Collins and Buchan, 2004;Asanuma et al, 2017). A majority of samples show typical "Ganderian" distributions with abundant and diverse Mesoproterozoic zircon (Fig.…”

Section: Monian Beltmentioning

confidence: 99%