Origin and tectonic significance of the Early Cretaceous Fogo Seamounts

• Published in: Atlantic geology Vol. 42; no. 1; p. 108
• Main Authors: Piper, DJW, Pe-Piper, G, Jansa, L F
• Format: Journal Article
• Language: English
• Published: 01-03-2006
• Subjects: Marine; AN, North Atlantic; ANW, Canada, Newfoundland and Labrador, Newfoundland; ISE, USA, Hawaii; ANW, North America, Grand Banks; MED, Central Mediterranean, Mid-Ocean Ridge
• ISSN: 0843-5561

The Lower Cretaceous Fogo Seamounts were formed along the transform margin of the southwestern Grand Banks, at the northeastern extremity of the mid Jurassic - early Cretaceous central North Atlantic ocean, and have been partially buried by younger progradation of the continental margin. Volcanism of similar age is known from hydrocarbon exploration wells in the Orpheus Graben and the southern Grand Banks and slighdy younger volcanic rocks are found in the Newfoundland Seamounts and ODP Site 1276. Otherwise, the Iberia - Grand Banks rift is remarkably non-volcanic. The J-Anomaly Ridge was sampled by DSDP Site 384 and represents an area of anomalously thick crust formed at the mid-ocean ridge at the southeastern end of the Fogo Seamount chain. New samples were obtained from the Narwhal F-99 exploration well, which penetrated olivine basalts in the northwestern part of the chain and trachybasalt conglomerate was dredged from Seamount G in the central part of the chain. In chemical composition and radiogenic isotopes, the basalts range from mildly alkalic to mildly tholeiitic, with chemical analogues, for example, in Hawaii. The voluminous tholeiitic magmas result principally from decompression melting, with the ocean-island-basalt signature of the alkalic rocks also suggesting upwelling of deeper asthenosphere.