The Northern Igneous Complex of Guernsey, Channel Islands

Topley, C. G.; Brown, Michael; D’Lemos, R. S.; Power, G. M.; Roach, Robert Allen

doi:10.1144/gsl.sp.1990.051.01.15

Cited by 10 publications

(5 citation statements)

References 11 publications

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“…Its southern half is dominated by high‐grade metamorphic basement rocks (Icart orthogneiss) of Palaeoproterozoic age, intruded by the Perelle diorite, which was foliated during the Cadomian (late Neoproterozoic) Orogeny. Igneous rocks found further north cover the entire range from gabbro to granite (Topley et al, ). The British Geological Survey last visited Guernsey 40 years ago and relatively little geological research has been carried out on the island since then.…”

Section: Application To Igneous Petrochronologymentioning

confidence: 99%

High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS

Vermeesch

Rittner

Petrou

et al. 2017

Geochem Geophys Geosyst

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The first step in most geochronological studies is to extract dateable minerals from the host rock, which is time consuming, removes textural context, and increases the chance for sample cross contamination. We here present a new method to rapidly perform in situ analyses by coupling a fast scanning electron microscope (SEM) with Energy Dispersive X‐ray Spectrometer (EDS) to a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LAICPMS) instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, Automated Phase Mapping (APM) by SEM/EDS produces chemical and mineralogical maps from which the X‐Y coordinates of the datable minerals are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic analysis. We apply the APM + LAICPMS method to three igneous, metamorphic, and sedimentary case studies. In the first case study, a polished slab of granite from Guernsey was scanned for zircon, producing a 609 ± 8 Ma weighted mean age. The second case study investigates a paragneiss from an ultra high pressure terrane in the north Qaidam terrane (Qinghai, China). One hundred seven small (25 µm) metamorphic zircons were analyzed by LAICPMS to confirm a 419 ± 4 Ma age of peak metamorphism. The third and final case study uses APM + LAICPMS to generate a large provenance data set and trace the provenance of 25 modern sediments from Angola, documenting longshore drift of Orange River sediments over a distance of 1,500 km. These examples demonstrate that APM + LAICPMS is an efficient and cost effective way to improve the quantity and quality of geochronological data.

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Section: Application To Igneous Petrochronologymentioning

confidence: 99%

High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS

Vermeesch

Rittner

Petrou

et al. 2017

Geochem Geophys Geosyst

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“…Late Cadomian (c. 600-540 Ma) intermediate to granitic plutonism is widespread. This magmatism is reviewed by with detailed descriptions provided by Auvray (1979); Topley, Brown & Power (1982); Topley et al (1990); Bland (1984;A. M. Bland, unpub.…”

Section: A Geological Settingmentioning

confidence: 99%

Sm–Nd isotope characteristics of late Cadomian granite magmatism in northern France and the Channel Islands

D’Lemos

Brown

1993

Geol. Mag.

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Sm–Nd isotopic studies of granites within the late Precambrian, Cadomian, orogenic belt of the North Armorican Massif (northwestern France) and Channel Islands reveal differences between arc-related granite magmatism in outboard terranes and intracrustal granite magmatism in inboard terranes. Late Cadomian (c. 570 Ma), arc-related granitoids exhibit a range of εnd( - 2 to - 6) and Nd model ages (TDM1.0–1.3 Ga) reflecting variable contamination between late Precambrian mantle derived magmas and ancient (c. 2.0 Ga?) continental crust. The contamination did not involve exposed granitic Icartian basement to anygreat degree, a more likely contaminant being unexposed lower crust of intermediate to acidic granulitic composition, or early Cadomian plutons which were themselves contaminated by lower crust. Voluminous granites of the Mancellian region (c. 550–540 Ma) share common isotopic characteristics (εNd-4 to -7, TDM1.5–1.7 Ga) with migmatites and anatectic granites produced by partial melting of metasedimentary sequences within the St Malo region consistent with a common source.

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“…On Guernsey, the Icartian gneisses and early Cadomian foliated plutons are intruded by post-tectonic igneous complexes (Fig. 2;Topley et al 1990) i^Castle Thomas, unpub. Ph.D. thesis, London Univ., 1978).…”

Section: Regional Geology Of Guernsey and Sarkmentioning

confidence: 99%

Neoproterozoic shear zone tectonics within the Icartian basement of Guernsey and Sark, Channel Islands

1996

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The Channel Islands of Guernsey and Sark are amongst the few localities within the Neoproterozoic, Cadomian orogenic belt where Palaeoproterozoic basement is exposed. Basement units collectively referred to as ‘Icartian’ comprise orthogneisses (e.g. the c. 2000 Ma Icart granite gneiss), metasediments and amphibolites. On Guernsey, the protolith to the Icart granite gneiss was intruded into metasediments already deformed during a D1 deformation event. Both were variably deformed during a D2 event within an approximately north—south trending, steeply dipping, oblique dextral shear zone. On Sark, metasediments and amphibolites carry a D1 fabric (not necessarily correlatable with that on Guernsey) which was deformed during D2 to form recumbent—gently inclined folds and tectonic fabrics which locally carry top-to-the-south kinematic indicators. Early Cadomian quartz diorites which intruded the Icartian basement carry variably developed magmatic and moderate temperature (400–550 °C) LS solid-state fabrics which are similarly oriented to D2 basement structures. This indicates that the quartz diorites were emplaced and deformed during a protracted D2 event. Published 40Ar/39Ar amphibole cooling ages of c. 600 Ma from Guernsey and Sark quartz diorites and a host Icartian amphibolite are consistent with reworking of basement units during the Cadomian Orogeny. The contrasting kinematic pattern during Cadomian deformation implies that a flat-lying shear zone on Sark may have accommodated oblique dextral strike-slip movement on Guernsey with an overall southerly direction of tectonic transport. Deformation most likely occurred in the hanging-wall of a major south-dipping Neoproterozoic subduction zone.

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The Northern Igneous Complex of Guernsey, Channel Islands

Abstract: The Northern Igneous Complex of Guernsey consists of four intrusive bodies,

Cited by 10 publications

References 11 publications

High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS

High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS

Sm–Nd isotope characteristics of late Cadomian granite magmatism in northern France and the Channel Islands

Neoproterozoic shear zone tectonics within the Icartian basement of Guernsey and Sark, Channel Islands

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