Further evidence for a single polarity and a common source for the quartz-porphyry intrusions of the Arran area

Abstract

SYNOPSISNew evidence supports the proposition that all the Tertiary quartzporphyry intrusions of Arran and Bute, which have a geographic span of 35 km, are normally magnetised. This is the only known correlation between magnetic polarity and petrography in the British Tertiary Igneous Province. It is most easily explained by a single magma source supplying all the quartz-porphyry bodies. The bodies were probably intruded during a single normal magnetic interval lasting about \ Ma, about 58 Ma ago. This significant correlation between petrography and polarity could help to erect the Tertiary igneous succession of Arran by use of the quartz-porphyry intrusions as a 'marker horizon'.

Magma Ascent along a Major Terrane Boundary: Crustal Contamination and Magma Mixing at the Drumadoon Intrusive Complex, Isle of Arran, Scotland

“…Petrologically, these intrusions have been considered to be part of the same intrusive event, examples of which are seen throughout Arran and the Isle of Bute (Smellie, 1914;Brown, 1929;Buist, 1952). Palaeomagnetic studies also suggest that these intrusions are members of the same phase of regional rhyolitic magmatism, related to a normal magnetic reversal, chron 26n (58•7^58•2 Ma) (Dagley et al, 1978;Mussett et al, 1987Mussett et al, , 1989Hodgson et al, 1990;Gradstein et al, 2004).…”

“…Previous palaeomagnetic work on both the quartz-and feldspar-phyric rhyolite suite and the Northern Granite has suggested that all the intrusions formed within the same period of normal polarity (chron 26n) (Mussett et al, 1987(Mussett et al, , 1989Hodgson et al, 1990;Table 11). However, in light of the more precise radiometric dates from both this study and that of Chambers (2000), it seems that the Northern Granite may lie within chron 26n, whereas the Drumadoon Sill was intruded during a period of normal polarity within chron 26r (Fig.…”

“…Although assimilation of (Ogg et al, 2008), with superimposed recent radiometric dates for the Drumadoon porphyritic rhyolite intrusions and the Northern Granite. Palaeomagnetic data were previously used to suggest that these intrusions all lay within chron 26n (Mussett et al, 1987(Mussett et al, , 1989Hodgson et al, 1990).…”