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TitlePetrology and tectonic significance of seamounts within transitional crust east of Orphan Knoll, offshore eastern Canada
AuthorPe-Piper, G; Meredyk, S; Zhang, Y; Piper, D J WORCID logo; Edinger, E
SourceGeo-Marine Letters vol. 33, no. 6, 2013 p. 433-447,
Alt SeriesEarth Sciences Sector, Contribution Series 20130094
PublisherSpringer Nature
Mediaon-line; digital
File formathtml; pdf
ProvinceNewfoundland and Labrador
NTS1; 2; 10; 11; 12A; 12B; 12C; 12D; 12F; 12G; 12H; 12I; 12J; 12O; 12P; 21A; 21B; 21G; 21H; 21I
AreaOrphan Knoll; Canada; Ireland
Lat/Long WENS -47.5000 -44.5000 51.2500 50.7500
Lat/Long WENS -68.0000 -52.0000 52.7500 43.0000
Subjectsmarine geology; igneous and metamorphic petrology; tectonics; geochemistry; tectonic interpretations; tectonic environments; seamounts; bathymetry; petrography; petrogenesis; whole rock geochemistry; alteration
Illustrationslocation maps; images; photographs; tables; profiles; ternary diagrams
ProgramOffshore Geoscience
Released2013 10 11
AbstractThe Early Cretaceous separation of Newfoundland from Iberia - Ireland is a classic example of a magma-poor continental margin with hyperextension and with widespread minor magmatism resulting in seamounts. This study defines the distribution of seamounts east of Orphan Knoll, and documents and interprets the geochemical character of the one recovered lava sample. Video imagery of lava outcrops, and the sample, were obtained by ROV from Orphan seamount, one of a linear series of small seamounts overlying transitional thinned continental crust on the seaward side of Orphan Knoll. New multibeam bathymetry and legacy seismic data show several seamounts that extend irregularly along the fault-bound NE margin of Orphan Knoll. Whole rock geochemistry shows the sample to be highly alkaline basanite or possibly tephrite. Diopside - hedenbergite, kaersutite and K-feldspar phenocrysts were analyzed by electron microprobe and scanning electron microscope, and alteration minerals including kaolinite were identified by X-ray diffraction. The highly alkaline character of the basanite is similar only to Early Cretaceous volcanic and sub-volcanic rocks erupted through thick continental crust of the Mesoproterozoic Grenville Orogeny. The location of the linear set of seamounts is related to margin-parallel faults on the seaward side of Orphan Knoll that provided a pathway for magma, although ENE-trending lineaments in individual seamounts or seamount groups suggest the influence of oceanic fracture zones. A lower gradient crest to Orphan seamount above 2,200 m suggests subaerial erosion, consistent with the presence of kaolinite as an alteration product and the absence of lava pillows at and above this depth.
Summary(Plain Language Summary, not published)
This study documents a unique basalt sample from a seamount east of Orphan Knoll, offshore eastern Canada. The seamount formed on transitional extremely stretched crust before the beginning of normal ocean spreading. The seamount was at one time above sea level. It records a distinctive type of source for lava in the earth's mantle.

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