Zircon LA-ICPMS geochronology of the Cornubian Batholith, SW England

Neace, Erika R.; Nance, R. Damian; Murphy, J. Brendan; Lancaster, Penelope J.; Shail, RK

doi:10.1016/j.tecto.2016.04.002

Cited by 11 publications

(7 citation statements)

References 56 publications

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“…Williams 1995Williams , 2001Appleby et al 2009;Gao et al 2016), and the anomalously old U-Pb bulk zircon age (~310 Ma) published by Neace et al (2016) demonstrate that the Dartmoor granitic magmas did contain such inherited zircon. Many of the discordant zircon crystals studied by Neace et al (2016) have Grenvillian (Mesoproterozoic) ages, though, as these authors point out, their discordancy precludes them from being used to definitively identify the source rocks for the magmas. In any case, for Dartmoor, the likely overall picture is one of mid-crustal fluiddeficient partial melting involving muscovite and some biotite breakdown, leading to the formation of a variety of granitic magmas, the more mafic of which contained significant but varying proportions of entrained peritectic minerals, as well as some inherited zircon.…”

Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 97%

“…The Ba contents of melts are likely to be joint functions of source-rock Ba content (or mineralogy, if the source contains a high K-feldspar content) and melting temperature (e.g., Clemens 2014). In contrast to these elements, Zr concentrations are likely to be influenced by the proportions of restitic zircon crystals entrained into the magmas (Clemens and Stevens 2012;Clemens 2014), and the Dartmoor zircons do contain inherited cores (Neace et al 2016). This influence would be especially the case if the partial melting were at relatively low T, resulting in generally low Zr solubility in the melts (e.g., Watson and Harrison 1983).…”

Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 99%

“…S-type granitic magmas commonly contain inherited zircon (e.g. Williams 1995Williams , 2001Appleby et al 2009;Gao et al 2016), and the anomalously old U-Pb bulk zircon age (~310 Ma) published by Neace et al (2016) demonstrate that the Dartmoor granitic magmas did contain such inherited zircon. Many of the discordant zircon crystals studied by Neace et al (2016) have Grenvillian (Mesoproterozoic) ages, though, as these authors point out, their discordancy precludes them from being used to definitively identify the source rocks for the magmas.…”

Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 99%

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Origins and Scales of Compositional Variations in Crustally Derived Granitic Rocks: The Example of the Dartmoor Pluton in the Cornubian Batholith of Southwest Britain

Clemens

Helps

Stevens

et al. 2021

The Journal of Geology

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The c. 280 Ma, post-orogenic, S-type Dartmoor pluton was assembled from numerous sheets of granitic magma, emplaced into the shallow crust. The main magma source lies in the middle crust, and is most probably Proterozoic metagreywackes, with minor metapelites and metavolcanic or plutonic rocks, possibly formed in a syn-collisional environment. Partial melting of this source may have occurred under fluid-deficient conditions, and the magmas most likely had relatively high initial H2O contents. The pluton contains substantial, wholerock-Sr and quartz-O isotope heterogeneities on scales down to a metre or less, and such small-scale heterogeneities are probably common in granitic intrusions derived from heterogeneous protoliths. Thus, variations in source terranes may not be fully captured with the sample numbers and scales commonly applied in studies of granitic plutons. The preservation of both large-and small-scale isotopic heterogeneities suggests that the 2 Dartmoor magmas were never efficiently homogenised by flow-driven mechanical mixing. This implies a source terrane with lithological variations on scales of tens of metres or less.The granitic rocks form five texturally, chemically and isotopically distinct groups, each of which had somewhat different sources or mixtures of sources. The main chemical variations cannot have been formed through fractionation of any combination of the major minerals in the rocks. Instead, entrainment of variable proportions of peritectic plagioclase, orthopyroxene and ilmenite was responsible, together with local crystal fractionation. Lowdensity, late-magmatic melts and aqueous fluids produced patchy enrichment in light elements, and extreme enrichment in some of the highly silicic, two-mica microgranites.However, although they are also enriched in light elements, the 'aplites' were not produced through fractionation, and seem to have had independent magmatic origins.

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Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 97%

Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 99%

Section: Source Rocks and Their Melting Conditionsmentioning

confidence: 99%

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Origins and Scales of Compositional Variations in Crustally Derived Granitic Rocks: The Example of the Dartmoor Pluton in the Cornubian Batholith of Southwest Britain

Clemens

Helps

Stevens

et al. 2021

The Journal of Geology

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“…3), do reflect lower plate basement but are undated (Goode & Merriman 1987). Rare inherited Mesoproterozoic and late Devonian zircons in the Early Permian Cornubian Batholith (Neace et al 2016), and Lower Paleozoic zircons in the Palaeocene Lundy Granite (Charles et al 2017), do not provide substantive constraint.…”

Section: Pre-devonian Basementmentioning

confidence: 97%

Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

Alexander¹,

Shail

Leveridge³

2019

Self Cite

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The Rheic Ocean is a persistent feature of Paleozoic palaeogeographies whose closure contributed to the development of the Variscan orogen and formation of Pangaea. Geological and geophysical data indicate repeated episodes of Paleozoic rifting and plate convergence around SW England and the adjacent offshore areas. SW England occupied a lower plate position during the Devonian-Carboniferous, on the northern passive margin of the short-lived Rhenohercynian Ocean that had formed near a recently closed segment of the Rheic Ocean. Variscan plate convergence resulted in the development of the composite southwardsdipping Rheic-Rhenohercynian suture zone by the latest Devonian and inversion of the lower plate basins during the Carboniferous. Early Permian NNW-SSE extensional reactivation of this suture zone controlled the development of the Western Approaches Basins in its hangingwall and provides an excellent example of Wilson Cycle structural inheritance. The onshore expression of this episode includes shear zones and detachment faults consistent with top-to-the SSE extensional reactivation of Variscan thrust faults. There is a progression to higher-angle brittle extensional faults that cutout earlier structures. Exhumation of the lower plate was accompanied by Early Permian mantle and concomitant crustal partial melting, the construction of the Cornubian Batholith, and W-Sn-Cu fracture-hosted mineralisation.

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“…Zircon U-Pb geochronological studies focussed on the crystallisation of the Cornubian Batholith have been largely avoided since S-type granites typically retain a large proportion of inherited zircon grains (Chesley et al, 1993;Neace et al, 2016). In addition, zircon grains hosted in evolved granites typically contain high U (>>100 ppm) concentrations and can therefore, rapidly become metamict (Romer et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Zircon perspectives on the age and origin of evolved S-type granites from the Cornubian Batholith, Southwest England

Smith

Darling

Bullen³

et al. 2019

Lithos

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Granite stocks across southwest England have played a significant role in the genesis of world-class polymetallic mineralisation. This study presents the first geochemical and geochronological dataset for the composite Crownhill stock, placing it into the newly emerging geochronological framework for the Cornubian Batholith. The Crownhill stock comprises kaolinised two-mica granite in the north and variably-grained biotite granite in the south that encloses pods of tourmaline granite. All granites are peraluminous (A/CNK>1) and the biotite (BG) and tourmaline granites (TG) are related by the replacement of biotite by tourmaline and secondary muscovitization. Integrated LA-ICP-MS and CA-ID-TIMS geochronology indicate two-phase magmatism, where zircon cores yield 288.9 ± 5 Ma and 286.4 ± 5 Ma and rims yield 277.74 ± 0.33 Ma and 278.35 ± 0.35 Ma, for BG and TG respectively. The zircon cores crystallised during initial magmatism, that formed the two-mica and muscovite granites (e.g., Carnmenellis, Bodmin, and Hemerdon) exposed in the north of the Crownhill stock. The zircon rims crystallised from the second phase of magmatism the formed the biotite and tourmaline granites (e.g., Dartmoor and St. Austell). This indicates that zircon crystals were assimilated from older twomica and muscovite granites and entrained in the second phase of magmatism. Trace element compositions of zircon grains suggest that the rims crystallised from a more evolved magma, where zircon grains hosted in tourmaline granites are broadly more evolved than those from biotite granites. This is likely a result of elevated volatile concentrations delaying zircon fractionation. Trace cassiterite has been observed within interstitial tourmaline in the tourmaline granites, where crystallisation was likely induced by the removal of boron through tourmaline fractionation, coupled with the addition of Sn sourced from the alteration of biotite. The assimilation and over-printing of older granites by second-stage magmatism suggests that the initial phase of magmatism could be more widespread than initially thought and that tourmalinisation may have been responsible for leaching and remobilising Sn from the biotite-rich granites.

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Zircon LA-ICPMS geochronology of the Cornubian Batholith, SW England

Cited by 11 publications

References 56 publications

Origins and Scales of Compositional Variations in Crustally Derived Granitic Rocks: The Example of the Dartmoor Pluton in the Cornubian Batholith of Southwest Britain

Origins and Scales of Compositional Variations in Crustally Derived Granitic Rocks: The Example of the Dartmoor Pluton in the Cornubian Batholith of Southwest Britain

Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

Zircon perspectives on the age and origin of evolved S-type granites from the Cornubian Batholith, Southwest England

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