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Lack of internal textural evidence for flow tops and small chemical variability among late Proterozoic basalt samples suggest the presence of a single flow at Henley Harbour, Labrador, Canada, despite spectacular, m-scale layering in outcrop. Total chemical variation just slightly exceeds analytical uncertainty for many elements. Multidimensional scaling (MDS) enhances "effective" analytical precision by allowing all data (elements and samples) to be compared simultaneously. Scaling of elements reveals element associations/patterns consistent with igneous controls on distribution, even for alteration-sensitive (Na, K, Sr) elements. MDS also shows that the m-scale layering has a chemical fingerprint. However, to explain chemical variability between layers using mass balance calculations and averaged whole-rock data requires unreasonable (low temperature) phenocryst compositions. Textural features of the m-scale layering record changes in cooling regime between the bottom and center of the flow but chemical variation may reflect changing magma compositions during formation of an inflated flow. However, mass balance calculations suggest that large-scale chemical variation reflects the migration of residual liquid, perhaps as vesicle plumes, within an initially chemically homogeneous flow. Low in the flow (layer 1), metres-long but cm-scale raised and eroded subhorizontal "bands" superficially resemble segregation veins but lack coarse-grained textures. MDS confirms that raised and eroded samples are chemically distinct. Mass balance indicates that banding is not related to phenocryst percentages but may reflect the abundance of a residual liquid resembling the liquid explaining compositional variation between large-scale layers. Alignment of microlites and variations in the quantity of altered residual-liquid glass suggest that banding is related to magma movement during extrusion. It is possible that banding of this type has not been recognized before. RESUME L'absence d'attestation texturale interne des sommets d'ecoulement et la faible variabilite chimique entre les echantillons de basalte du Proterozoique tardif laissent supposer la presence d'un ecoulement unique a Henley Harbour, Labrador, Canada, malgre la stratification spectaculaire a moyenne echelle de l'affleurement. La variation totale des compositions chimiques depasse tout juste legerement l'incertitude analytique de nombreux elements. L'analyse multidimensionnelle (AMD) ameliore la precision analytique « effective » en permettant une comparaison simultanee de toutes les donnees (elements et echantillons). L'analyse des elements revele des associations/dispositions d'elements correspondant a des controles ignes de la repartition, meme dans le cas des elements sensibles a l'alteration (Na, K, Sr). L'AMD revele par ailleurs que la stratification a moyenne echelle presente une empreinte chimique. L'explication de la variabilite chimique entre les couches au moyen de calculs du bilan ponderal et de moyennes des donnees sur la roche totale necessite cependant des compositions de phenocristaux excessives (basse temperature). Les caracteristiques texturales du fil de stratification a moyenne echelle changent en regime de refroidissement entre le fond et le centre de l'ecoulement, mais la variation des compositions chimiques peut correspondre a des compositions magmatiques changeantes pendant la formation d'un ecoulement gonfle. Les calculs du bilan ponderal laissent toutefois supposer que la variation des compositions chimiques a grande echelle temoigne de la migration de liquides residuels, peut-etre sous forme de panaches de vacuoles a l'interieur d'un ecoulement initialement homogene du point de vue chimique. Au bas de l'ecoulement (premiere strate), des « bandes » subhorizontales de plusieurs metres de longueur mais erodees et soulevees de quelques centimetres ressemblent superficiellement a des filons d'exsudation mais sont depourvues de textures a grain grossier. L'AMD confirme que les echantillons souleves et erodes sont chimiquement distincts. Le bilan ponderal revele que le rubanement n'est pas lie au pourcentage de phenocristaux, mais qu'il temoigne de l'abondance d'un liquide residuel ressemblant au liquide expliquant la variation des compositions entre les strates a grande echelle. L'alignement des microlites et les variations de la quantite de verre soluble residuel altere laissent supposer que le rubanement est apparente a un deplacement magmatique survenu pendant l'extrusion. Il est possible qu'on n'ait pas decele un rubanement de ce genre auparavant.

A petrochemical study of basaltic layering at Henley Harbour, Labrador, using multidimensional scaling