CLASTIC DYKES IN THE DUNNAGE MELANGE, HALFMOON BAY, NORTHEAST NEWFOUNDLAND

• Main Authors: J. C. Pollock, Harold Williams
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Newfoundland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.536.9799; http://www.nr.gov.nl.ca/mines%26en/geosurvey/publications/cr2000/pollock.pdf

Recent studies have examined the presence and significance of clastic dykes in the Dunnage Melange, at Halfmoon Bay. They resemble pebbly shale, polymictic dykes that are between 2 and 30 cm wide and are up to 10 m in length. Grain size varies from fine to coarse, having equant and irregular clasts that include native and/or exotic rock types. The dykes cut both the shale melange matrix and volcanic blocks, as well as all cleavages in the melange. Injections of dyke matrix into internal joints and fractures in the clasts indicate that at some stage, the matrix was highly fluidized. The variety and irregular shape of clasts requires significant flow and mixing, probably over distances of hundreds of metres. The Dunnage Melange is the locus for intrusions, especially small bodies of the Coaker Porphyry that occur throughout the entire melange and make up about one third of the Dunnage Melange area. Intricate patterns of melange matrix shale and Coaker Porphyry have been interpreted as mud–magma mixtures. Clastic dykes in localities such as Halfmoon Bay are most plentiful and obvious where mud–magma mixing is most spectacular. The timing of clastic dyke emplacement has an important bearing on several struc-tural and plutonic events in melange evolution. Injection is a more important process in the entire Dunnage Melange devel-opment than previously considered.