Preliminary report on the nature and age of the Blackstones Bank Igneous Centre, western Scotland

Durant, Graham P.; Dobson, M. R.; Kokelaar, B. P.; Macintyre, R. M.; Rea, W. J.

doi:10.1144/gsjgs.132.3.0319

Cited by 16 publications

(13 citation statements)

References 8 publications

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“…conventional K-Ar date of 72 Ma for a single dyke sample (Durant et al 1976) should be treated with caution. There are no palaeomagnetic polarities for any of these areas.…”

Section: Lundymentioning

confidence: 99%

Time and duration of activity in the British Tertiary Igneous Province

Mussett

Dagley

Skelhorn

1988

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S U M M A R Y:The time and duration of igneous activity in the separate component areas of the British Tertiary Igneous Province (BTIP) are investigated using radiometric dates that pass internal consistency tests, used in conjunction with palaeomagnetic polarities and the available stratigraphic information.Reliable results are available only for the currently subaerial parts of the Province. It is found that activity occurred within the approximate interval 63-52 Ma, with most activity at about 59 Ma. Later activity was predominantly of acid magmas though basic rocks preponderate in the province as a whole. The types and span of igneous activity in the separate areas followed no common pattern but areas of more complex geology tend to have had a longer span of activity.Magnetic polarities are predominantly reversed, with all the lavas having this polarity. This predominance is probably largely, but not entirely, due to reversed polarity intervals being longer than normal ones at this time, and with much activity occurring in a single reversed interval. The sequence of polarities found within the BTIP cannot be fully reconciled with the polarity timescales of either Harland et at. (1982) or Berggren et al. (1985).

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“…conventional K-Ar date of 72 Ma for a single dyke sample (Durant et al 1976) should be treated with caution. There are no palaeomagnetic polarities for any of these areas.…”

Section: Lundymentioning

confidence: 99%

Time and duration of activity in the British Tertiary Igneous Province

Mussett

Dagley

Skelhorn

1988

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“…These cast a corresponding suspicion on K-Ar ages for dolerites. Beckinsale (in Durant et al 1976) expressed considerable scepticism about the accuracy of K-Ar whole-rock ages for basalts and made the important and, to us, valid assertion that pristine mineralogy is no guarantee against argon loss. More recently Dagley et al (1978) have pessimistically dismissed any significance for a 69 Ma age-spread obtained from K-Ar analyses of fourteen fresh dolerites from Arran, "in the absence of independent evidence for their validity".…”

Section: Modification Of K -A R Systems In British Tertiary Doleritesmentioning

confidence: 99%

“…1985). K -A r analyses of northern and western Irish dolerites span a wide age-range of 73-50 Ma , and demonstrate the susceptibility of K -A r dating of mafic sheets to both inherited argon and to argon loss (Beckinsale in Durant et al 1976;Mussett 1978). O u r study of K -A r systems in the larger Tertiary dolerite sheets of West Connacht (Mohr 1982) reveals a regional, non-random modification of these 5 8 -5 4 Ma-old systems (Mohr et al 1984 across the width of the thickest, CI sheet, north of Killary, with additional samples from sheet axis and margin at selected CM sheet localities; (iii) samples from closely spaced localities at appreciably different elevations (i.e.…”

Section: Introductionmentioning

confidence: 99%

K–Ar systematics in Tertiary dolerites from West Connacht, Ireland

Mitchell

Mohr

1986

SJG

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Synopsis Thirty-four new K–Ar ages from West Connacht Paleocene dolerites reveal a systematic pattern of argon loss across the province. Four possible causes for this pattern are examined: thermal overprinting, nature of countryrock, depth of emplacement, and degree of microfracturing. Although some clear relationships emerge, no single cause can explain all the observed apparent ages. Nevertheless, the value of conventional K–Ar dating, as a supplement to 40 Ar/ 39 Ar dating, is emphasised as a means to obtaining regional geological insight into igneous provinces.

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“…Thus, the submarine occurrences on the continental shelf to the N and W of Britain (including the Anton Dohrn seamount, the Blackstones Complex, etc.) and the ash horizons in the chalk of eastern England probably date from this time (Macintyre et al 1975;Durant et al 1976;Pacey 1984).…”

mentioning

confidence: 99%

History of Tertiary igneous activity in the N Atlantic borderlands

Upton¹

1988

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S U M M A RY: Stretching and thinning of the Laurasian continental lithosphere, which had proceeded intermittently from late Palaeozoic through the Mesozoic, reached a climax in early Tertiary times with copious generation of basalt magma, invasion of the attenuated crust as dyke swarms and surface eruption, principally by fissure volcanism. Continued basin subsidence allowed basaltic lavas, erupted at near sea-level, to accumulate to thicknesses which in places (e.g. W Greenland, E Greenland, Faeroes) attained several kilometres. In some zones dyke-swarm injection and crustal attenuation led to sea floor spreading and generation of ocean crust. Fissure swarms not infrequently changed position so that there could be one or more 'unsuccessful' rifting events prior to establishment of a 'successful' spreading axis.While some uncertainty still exists regarding the precise timing of the onset of magmatism in the various zones of failure, the bulk occurred between 60 and 50 Ma. Across the British Isles basalt magmatism occurred early (ca. 60-59 Ma) whereas the great volumes of the E Greenland basalts appear to have erupted rapidly over the interval 54--52 Ma. The onset of magmatism in the Faeroes may have preceded that in E Greenland and possibly that of W Greenland-Baftin Island.Major sill swarms developed, commonly within the Mesozoic sedimentary strata. At favoured channels for magma ascent, commonly controlled by major faults, longer-lived central-vent volcanoes developed. Slow cooling of large magma bodies at such foci produced mafic and ultramafic cumulates; production of salic magmas was mainly confined to these central complexes, the majority of which are located close to the E Greenland coast between ca. 66 ~ and 74~ and a N-S zone through the British Isles from ca. 58~176 Although the salic magmas were predominantly silicic (rhyolitic), feldspathoidal (phonolitic) magmas were important in some of the E Greenland centres. Generation of salic magmas was generally late with respect to the main phases of basalt eruption in the various sectors of activity. However, notable sequences of peraluminous silicic lavas may have preceded basaltic eruption in the Rockall Trough and Voring Plateau areas. It is probable that magmatic activity in some of the sectors that had experienced the most intense early-phase volcanism persisted, on a small-scale, long after the sea floor spreading had been initiated and activity on the passive margins of both W and E Greenland may not have finally terminated until ca. 30 Ma.The total compositional range of early Tertiary magmas associated with the N Atlantic marginal regions was extensive. Whereas tholeiites, varying from FeTi-rich to N-type MORB, were erupted in greatest volume, compositions varied from picrites, through tholeiites to ferro-basalts, icelandites, dacites and rhyolites. More alkalic mafic magmas included alkali olivine-basalt (and its differentiated products), nephelinites, lamprophyres and melilitites, with some associated carbonatites. Salic magmas ranged widely from...

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Preliminary report on the nature and age of the Blackstones Bank Igneous Centre, western Scotland

Cited by 16 publications

References 8 publications

Time and duration of activity in the British Tertiary Igneous Province

Time and duration of activity in the British Tertiary Igneous Province

K–Ar systematics in Tertiary dolerites from West Connacht, Ireland

History of Tertiary igneous activity in the N Atlantic borderlands

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