Basic and ultrabasic volcanic rocks from the Argyll Group (Dalradian) of NE Scotland
R. Macdonald
D. J. Fettes
D. Stephenson
C. M. Graham
10.6084/m9.figshare.3454304.v1
https://geolsoc.figshare.com/articles/dataset/Basic_and_ultrabasic_volcanic_rocks_from_the_Argyll_Group_Dalradian_of_NE_Scotland/3454304
<p>The Dalradian Supergroup of the Scottish Highlands is a largely metasedimentary succession of Neoproterozoic to Early Cambrian
age, metamorphosed during the Caledonian Orogeny. The rocks were deposited on the Laurentian margin during and following the
break-up of Rodinia. This rift setting is evidenced, in the upper half of the succession, by the presence of several volcanic
sequences. A significant development of these volcanic rocks occurs in the NE Grampian Highlands. There, the Blackwater Formation,
within the Argyll Group of the Huntly area, is dominated by basic and ultrabasic metavolcanic rocks, with intercalated metasedimentary
rocks. The rocks were metamorphosed in the amphibolite facies, with the Mg contents of their dominant amphiboles apparently
reflecting those of the whole-rock protoliths. The protoliths ranged from ultrabasic picritic types (MgO up to 35 wt%) through
high-magnesia basalts to basaltic andesites and andesites. The magmas feeding the volcanism were of tholeiitic affinity, broadly
similar to metavolcanic rocks elsewhere in the Dalradian. Higher-Nb and lower-Nb groups can be distinguished. The inferred
parental magmas were basalts with MgO <em>c.</em> 10 wt%. The ultrabasic rocks formed by accumulation of olivine and minor Cr-spinel within the parental basalts. Some more
evolved rocks show evidence of minor (5–10 wt%) accumulation of Fe–Ti oxides. Primary magmas of the Blackwater metavolcanic
rocks were generated from a mantle source, or sources, relatively enriched compared to the MORB source. It is speculated that
all the Dalradian metavolcanic rocks represent varying degrees of mixing of magmas from this source and a depleted, MORB-like,
mantle source.
</p>
2016-06-21 12:02:13
rocks show evidence
magma
NE Grampian Highlands
mantle source
Blackwater metavolcanic rocks
Dalradian metavolcanic rocks
Argyll Group
ultrabasic picritic types
MORB
intercalated metasedimentary rocks
ultrabasic metavolcanic rocks
Geology