Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Orphan Knoll (Orphan Seamount)


Occurrence number: 
Longitude: -45.33333, Latitude: 50.08333

Orphan Knoll is a continental basement high located at least 1850 m deep in the Northern Atlantic Ocean, associated with a 1.7 km high seamount informally known as the Orphan seamount. The seamount is composed of basanite in the form of massive or pillow lavas below depths of 2700 m along with breccias representing mass transport deposits down the volcano flank. Layered lava with lava tubes present in places overlies pillow lava, rubbly lava, and uncommon massive lavas between 2700-2200 m depth. Above depths of 2200 m pillow lava is no longer seen, with massive lava outcrops dominating instead. The basanite has undergone alteration but is still identified to be composed of a mineral assemblage including clinopyroxene, kaersutite, titanomagnetite, and possible olivine and sanidine. A lower gradient crest above 2200 m depth, the presence of kaolinite, and lack of pillow lavas suggests the seamount was once partially subaerial. Bathymetry, seismic profiles, and submarine images along with whole rock major and trace element, and mineral chemical data can be found in Pe-Piper et al., (2013).

Albian to Late Cretaceous based upon subsidence rates (Pe-Piper et al., 2013)
PE-PIPER, G., MEREDYK, S., ZHANG, Y., PIPER, D.J.W. & EDINGER, E., 2013. Petrology and tectonic significance of seamounts within transitional crust east of Orphan Knoll, offshore eastern Canada. Geo-Marine Letters 33 pp 433-447
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