Picritic basalts from the Palaeocene lava field of west-central Skye, Scotland: evidence for parental magma compositions

Bell, Brian R.; Willamson, Ian T.

doi:10.1180/minmag.1994.058.392.01

Cited by 14 publications

(8 citation statements)

References 37 publications

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“…There are no observed major interlava non-lateritic sedimentary sequences; most hawaiites do, however, overlie a thick laterite. A single picritic basalt flow occurs close to the top of the preserved sequence on An Cruachan at [NG 384 225] (Bell & Williamson 1994) 2.1.5. The Glen Caladale Lava Group.…”

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confidence: 99%

“…Two occurrences of picritic basalt, characterised by phenocrysts of forsteritic olivine and chromespinel, are recognised from the lava field of west-central Skye: (i) within the Glen Brittle Formation of the Cruachan Lava Group, on the NE side of An Cruachan at [NG 384 225]; and, (ii) within the Tusdale Formation of the Glen Caladale Lava Group, in the cliff section E of Sgurr Beag at [NG 339 248]. The mineralogy and geochemistry of these unevolved flows are documented by Bell and Williamson (1994).…”

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The Palaeocene lava field of west-central Skye, Scotland: Stratigraphy, palaeogeography and structure

Williamson

Bell

1994

Transactions of the Royal Society of Edinburgh: Earth Sciences

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Palaeocene volcanic activity is represented in west-central Skye, Inner Hebrides, Scotland, by a laterally extensive and thick pile of sub-aerial lavas mainly belonging to the alkali olivine basalt—hawaiite—mugearite—benmoreite—trachyte suite. The lavas are typical of many continental flood basalt suites and were principally fed from fissure eruptions similar to those of present day Iceland. Intercalated with the lavas are rare beds of heterogeneous volcaniclastic material, including breccias, conglomerates, sandstones and mudstones. The sequence forms a major portion of a larger volcanic field preserved within the NNE-SSW-elongated ‘Sea of the Hebrides’ sedimentary basin.Significant hiatuses in the volcanic activity are marked by deep-weathering profiles and thin sedimentary sequences comprising mudstones, ironstones, coals, sandstones and conglomerates. Palaeocurrent indicators and clast lithologies within the clastic sedimentary rocks indicate that erosion of a massif dominated by the Palaeocene Rum Igneous Complex and its roof rocks, c. 20 km to the S, provided abundant detritus to a river system which drained towards the N. Such sedimentary intercalations aid the stratigraphical subdivision of the lava field. Eight lava groups, each most likely with a different focus of fissure eruption, and divisible into mappable formations, together with two sedimentary formations, are recognised.The alkali olivine basalts are typically thin, with a tendency to form compound flows with limited lateral extents, whilst the hawaiites and mugearites are considerably thicker and cover large areas. Only very rarely are flow terminations observed. The original extents of the single benmoreite and rare trachytes cannot be determined from their limited erosional remnants. The more evolved flows tended to occur after brief hiatuses in the volcanic activity, indicated by well-developed lateritic tops to the underlying flows.The youngest preserved lava is a columnar-jointed olivine tholeiite with a MORB-like composition. The flow is at least 120 m thick and apparently ponded in a steep-sided palaeo-valley within the lava field.Three fault trends are recognised: parallel, normal and marginally oblique to the main NW-SEtrending regional dyke swarm, and dissect the lava field into a number of discrete blocks. The more significant of these faults may have been active during the development of the lava field, and in some instances instrumental in controlling the distribution of the flows.Later Tertiary erosion has removed an unknown thickness of material from the upper part of the lava field, the preserved thickness of which is estimated to be about 1·5 km.

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The Palaeocene lava field of west-central Skye, Scotland: Stratigraphy, palaeogeography and structure

Williamson

Bell

1994

Transactions of the Royal Society of Edinburgh: Earth Sciences

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“…Chromian spinels from Hole 917A have rather similar compositions to those from the Scoresby Sund basalts (Larsen et al, 1989) and the Paleogene picritic lavas of west-central Skye, Scotland (Bell and Williamson, 1994), but they are much more depleted in chromium than those from the Kangerlussuaq picrites of East Greenland (Nielsen et al, 1981). Spinels from the Upper Series have slightly lower TiO 2 contents than those from the Lower Series, but these differences are too subtle to relate firmly to a change in the tectonic regime (Arai, 1992).…”

Section: Spinelsmentioning

confidence: 99%

Mineral chemistry of volcanic sequences from Hole 917A, southeast Greenland Margin

Demant¹

1998

Proceedings of the Ocean Drilling Program

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During Ocean Drilling Program Leg 152, a 779-m-thick volcanic sequence was drilled at Hole 917A, on the feather edge of the seaward-dipping reflector sequence. The volcanic succession, which erupted under subaerial conditions, was subdivided into three series (Upper, Middle, and Lower) and 92 flow units. The Upper Series comprises picrites and olivine-phyric basalts. The Middle Series basalts are more evolved, and dacitic lavas and tuffs were erupted at the base of this series. Lavas from the Lower Series show a wider compositional range. A detailed mineralogical study of the different petrographical types shows that olivine is the principal phenocryst phase in the basalts, whereas clinopyroxene and plagioclase are the main components of the groundmass. High-Mg olivines (up to Fo 92.4 ) with chrome-spinel inclusions are abundant in the picrites and olivine-phyric basalts. Fo-content of the olivine decreases as a function of the composition of the whole rock except in some aphyric basalts with ophitic textures where the olivine underwent further re-equilibration during cooling. Plagioclase exhibits a large compositional range from bytownite (An 91 ) in the more primitive basalts to oligoclase (An 21 ) for the late crystallizing feldspar in the ophitic textures. Plagioclases from the Upper Series lavas are very poor in K 2 O. The presence of bytownite phenocrysts (An 86− 66 ) associated with sodic sieve-textured plagioclase (An 36−26 ) in the dacite (Unit 54) clearly demonstrates that this lava is a mixed lava. Pyroxenes are mainly clinopyroxene, but pigeonite and orthopyroxene were found in the matrix of some differentiated basalts with ophitic textures. The low Ti contents of the pyroxenes and the evolution trends are typical of tholeiitic lavas. The development of sector zoning in pyroxene microphenocrysts of the more differentiated basalts has a scattering effect on the distribution of the points on the pyroxene quadrilateral. Opaque oxides crystallize late and are mainly titanomagnetite. Ilmenite is also present in some lavas.The volcanic succession drilled at Hole 917A presents many petrographical and mineralogical similarities to the flood basalts of the Scoresby Sund region in East Greenland. These thick basaltic sequences, which characterize the North Atlantic volcanic rifted margins, were emplaced during a short time interval during the phase of continental breakup. The Lower and Middle Series have evolved in crustal magma chambers. The frequency of picrites in the Upper Series emphasizes an easier access of more primitive magmas to the surface during the final phase of rifting.

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“…InWest Greenlanda ndon BaffinIslandac onsiderableproportion ofthe basalts formed duringthe early NAIP event ( c .6 2-58Ma)are picritic, withMgO concentrations of c .15-30% (Gill etal .1992). AtSkyea ndM ull,i nt he BritishV olcanic Province, MgO concentrations generally range between c .5%and14% ( Kerr 1995;Scarrow &C ox 1995)but locally reach 18% ( Bell & Williamson 1994). Basalts extruded duringthe laterNAIP event ( c .56-53Ma)inEast Greenlandandthe FaroeIslandsdominantly haveMgO concentrations of c .5-10%,except the so-called 'lava interval2'thathasaMgO content of c .24% (Larsen etal .1999a).…”

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NE Atlantic break-up: a re-examination of the Iceland mantle plume model and the Atlantic–Arctic linkage

Lundin

Doré²

2005

PGC

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Finalbreak-up ofPangaea -openingofthe NE Atlantic (NEA)andthe Arctic Eurasia Basin-was associated withsignificant magmatism (inthe NEA)andiscommonlyascribed to thermaleffects from aprotoIcelandplume.The plumeisoftenassumed to be fixed withrespecttothe Earth's coreandto havegoverned NEA break-up. Itisargued herethatt he Icelanda nomaly,past andpresent,c annot represent afi xed plume, nor be rooted att he core-mantleb oundary andthatt he Greenland-FaroesRidge isinconsistent withaclassic timetransgressiveh otspot track.Itiss hown thatt he Icelanda nomaly hasp robably beenl ocated att he constructive plateb oundary (Mid-Atlantic Ridge anda ntecedents) since its inception. Whilerecent studiesallow for some 'wandering'ofhotspots relativeto the coreandmantle, itisconsidered unlikely thatsuch driftofamantleplume wouldprecisely match lithospheric driftino rdert oachievec onstant centeringon the spreadingridge.The alternativeviewis,therefore, supported -thatthe anomaly isanuppermantleresponseto platebreak-up. The two pulseso fN EA magmatism arerelated to separatephaseso fN orthA tlantic break-up. Early Paleocene magmatism ( c .62-58Ma)wasgoverned byashort-lived attempt atseekinganewriftpath, intermediateintime andspace betweent he Labrador Sea-BaffinBayandthe NEA-Eurasia Basinr ifts. The voluminous Early Eocenemagmatism ( c .56-53Ma)alongthe NEA margins wasrelated to finalbreak-up ofPangaea,exploiting the collapsed Caledonianfoldb elt. The interpretations herea rea to ddsw ithI celandrepresentingaclassic Morgan-typeplumeanditissuggested thatthe magmatism inthe NEA andthe Icelandanomaly represent a'topdown' effecto fplatetectonics.

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Picritic basalts from the Palaeocene lava field of west-central Skye, Scotland: evidence for parental magma compositions

Cited by 14 publications

References 37 publications

The Palaeocene lava field of west-central Skye, Scotland: Stratigraphy, palaeogeography and structure

The Palaeocene lava field of west-central Skye, Scotland: Stratigraphy, palaeogeography and structure

Mineral chemistry of volcanic sequences from Hole 917A, southeast Greenland Margin

NE Atlantic break-up: a re-examination of the Iceland mantle plume model and the Atlantic–Arctic linkage

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