Isotopic age data from Scourian intrusive rocks on the Isle of Barra, Outer Hebrides, north-west Scotland

Francis, P. W.; Moorbath, S.; Welke, H. J.

doi:10.1017/s0016756800050913

Cited by 15 publications

(5 citation statements)

References 11 publications

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“…The veins have been dated by a whole rock Rb-Sr method at 2 450 m.y. (Francis et al 1971). If the Coll veins provide a similar age, the Scourian age of the granulite-facies event would be confirmed.…”

Section: Tentative Correlationsmentioning

confidence: 92%

The tectonic evolution of a Lewisian complex on Coll, Inner Hebrides

Drury

1973

SJG

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SYNOPSISThe heterogeneous Lewisian rocks of Coll show the effects of at least six phases of deformation. The absence of common, penetrative linear fabrics, and of representatives of the Scourie swarm of basic dykes, so useful in relative dating in most areas of Lewisian, limits rigorous analysis and regional correlation of tectonic events. To some extent the limitations have been overcome by examination of the effects of each phase on earlier structures, and of the geometry of the fold forms produced.Although some evidence points to earlier structures, the oldest decipherable event took place during granulite-facies metamorphism. Basic dykes were emplaced under the same conditions and were suitably modified. Since the intrusive episode the complex has been subjected to several tectonic episodes, each characterised by distinctive structural features. In each case, compositionally contrasted lithologies were affected in different ways. The rheological state of the whole complex is suggested to have varied during its evolution. CONTENTS 2 Scott.

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Section: Tentative Correlationsmentioning

confidence: 92%

The tectonic evolution of a Lewisian complex on Coll, Inner Hebrides

Drury

1973

SJG

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“…Throughout the course of his geological career, Stephen, with his research students and colleagues, made a great contribution to our understanding of the development of the Lewisian of northwest Scotland. Rb–Sr and Pb isotopic analysis of large suites of samples of the Lewisian grey (granitoid) gneisses from the Outer Hebrides (14, 25), from the mainland of northwest Scotland (12, 32, 55), and even from the Scardroy Mass to the east of the Moine Thrust (20), have established that a major episode of crust formation and high-grade metamorphism took place during the late Archaean between 2.9 and 2.6 billion years ago. Some areas of the Lewisian have suffered very little modification since that time.…”

Section: Scientific Contributionsmentioning

confidence: 99%

Stephen Moorbath. 9 May 1929 — 16 October 2016

Dewey¹,

Taylor²

2020

Biogr. Mems Fell. R. Soc.

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Stephen Moorbath was an intellectual with eclectic interests across the sciences and humanities. In 1939, as a ten-year-old, he fled from Germany to England with his father. Stephen spent almost the whole of the rest of his life—from schoolboy to university professor—in Oxford, where he became one of the world's leading isotope geochemists. His academic career began with setting up Europe's first radiometric rock and mineral dating laboratory. In this laboratory, together with numerous colleagues and students, he applied the lead–lead, rubidium–strontium, potassium–argon and, later, samarium–neodymium isotopic dating methods to the solution of many geological problems. He made major contributions in establishing the chronology for the geological and tectonic evolution of Precambrian crust in the Scottish Highlands and Islands, in West Greenland, Zimbabwe, South India, and Ghana. He developed isotopic criteria for assessing the relative contributions of mantle and crustal sources to Tertiary igneous rocks in Scotland, Andean volcanics and the late Archaean granitoids of West Greenland. He established dating methods for sedimentary rocks: Rb–Sr for shales and Pb/Pb for Archaean limestone. Stephen's abiding geological passion was the study of the early Archaean, especially the Godthåbsfjord and Isukasia areas of West Greenland.

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“…Two examples, recently measured in the authors' laboratory, are (1) the Q6rqut granite of West Greenland, with a Rb-Sr age of 2530 + 30 Ma (Moorbath et al 1981) and (2) Concerning the choice of appropriate dating methods in Precambrian terrains, we note the following three points: 1. In such cases, the error on the age is frequently minimized by a large spread of Rb/Sr and U/Pb ratios in individual intrusives.…”

Section: Precision Of Precambrian Age Measurementsmentioning

confidence: 99%

Precambrian geochronology and the geological record

Moorbath¹,

Taylor²

1985

Memoirs

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SummaryRb-Sr, Sm-Nd and Pb/Pb whole-rock isochron methods and the U-Pb zircon method have been widely applied to dating Precambrian igneous and meta-igneous rocks. Application of these methods in regional geochronological studies provides reliable constraints on the age and temporal evolution of rock units, even when some parent-daughter systems have suffered disturbance in metamorphic and/or metasomatic events which significantly post-date primary rock formation. Initial isotopic compositions of Sr, Nd and Pb aid geological interpretation of isochron age data, constrain crustal residence time of the protoliths and can be used to assess the relative contributions of mantle and crust in magma genesis.Precambrian sediments can be indirectly dated by reference to age data on interbedded volcanics, or by age-bracketing between dated basement rocks and dated cross-cutting intrusives. Significant progress has also been made in the direct dating of sedimentary rocks. Published isotopic age determinations on early Precambrian sediments containing biogenic remains are briefly reviewed. Provided that stratigraphical and geochronological correlations are correct, it appears that stromatohtic limestones were being deposited by c.3400 - 3300 Ma ago, and that true microfossils occur in rocks dated at c.3200 - 3000 Ma. Evidence relating to possible biogenic markers in sediments reliably dated at c.3800 - 3700 Ma is not yet definitive.

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Isotopic age data from Scourian intrusive rocks on the Isle of Barra, Outer Hebrides, north-west Scotland

Cited by 15 publications

References 11 publications

The tectonic evolution of a Lewisian complex on Coll, Inner Hebrides

The tectonic evolution of a Lewisian complex on Coll, Inner Hebrides

Stephen Moorbath. 9 May 1929 — 16 October 2016

Precambrian geochronology and the geological record

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