Petrology, geochemistry, and diabase-granophyre relations of a thick basaltic sill emplaced into wet sediments, western Montana

Citation
Ma. Poage et al., Petrology, geochemistry, and diabase-granophyre relations of a thick basaltic sill emplaced into wet sediments, western Montana, CAN J EARTH, 37(8), 2000, pp. 1109-1119
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
CANADIAN JOURNAL OF EARTH SCIENCES
ISSN journal
0008-4077 → ACNP
Volume
37
Issue
8
Year of publication
2000
Pages
1109 - 1119
Database
ISI
SICI code
0008-4077(200008)37:8<1109:PGADRO>2.0.ZU;2-N
Abstract
The Plains Sill is a thick diabase-granophyre body that intruded the wet se diments of the Middle Proterozoic Prichard Formation of the Belt-Purcell Su pergroup. The diabase is a high-iron tholeiite geochemically compatible wit h large-volume mantle melting in an intracratonic rift environment. Evidenc e of emplacement into wet sediments includes thick zones of homogenized gra nosediments adjacent to the sill, soft-sediment deformation at sill contact s, and sedimentary ovoid structures possibly formed by local fluidization o f sediments. Utilizing sediment pore water and driven by heat from the sill , the diabase was metamorphosed during crystallization and cooling, leaving hornblende as the dominant mafic phase. Continued retrograde alteration re sulted in overgrowths of secondary hornblende and variable alteration of pl agioclase to epidote. A miarolitic granophyre layer, up to 150 m thick, cap s the diabase and appears igneous in origin. Locally the granophyre is anom alously thick, perhaps reflecting updip migration of granophyric fluid wher e the Plains Sill cuts upsection through the Prichard Formation stratigraph y.