Character of the Amerasia Basin Margin of the Lomonosov Ridge Microcontinent
Thomas E. Moore1 and Arthur Grantz2
1U.S. Geological Survey, Menlo Park, CA.
2Consulting Geologist, Palo Alto, CA.
The Lomonosov Ridge is a narrow, elongate microcontinent in the central Arctic Ocean formed by rift events during construction of the oceanic Amerasia basin in the Early Jurassic to mid-Early Cretaceous, and later during opening of the Eurasia basin in the late Paleocene. Much of the Amerasia basin margin of the microcontinent lies beneath sedimentary cover at abyssal depths, but can be identified by contrasts in magnetic anomaly patterns. High amplitude sub-parallel long-wavelength anomalies normal to the microcontinent in the eastern Podvodnikov basin are interpreted as oceanic crustal anomalies, whereas irregular low-amplitude anomalies in the western Podvodnikov basin correspond to Lomonosov continental crust identified by seismic refraction studies. The oceanic crustal anomalies wedge out in the Makarov basin and are replaced by irregular high frequency, high amplitude anomalies associated with the middle Cretaceous Alpha-Mendeleev Ridge large igneous province (LIP). The LIP is banked against or interfingers with the progradational sedimentary prism that overlies the Amerasia margin of the microcontinent from the Makarov basin to its end near Greenland. This prism was constructed on the continental margin when the microcontinent was attached to the Barents shelf prior to late Paleocene opening of the Eurasia. The progradational sedimentary prism overlies the Amerasia Basin transform fault, along which the Amerasia basin opened by rotational rifting about a pole in the lower Mackenzie Valley in the Early Jurassic to the mid-Early Cretaceous. The north-facing Marvin Spur escarpment, which has been thought to compose part of the transform, is interpreted here as a normal fault having Alpha-Mendeleev Ridge LIP rocks in its footwall. This requires a relatively young age for the escarpment, indicating the transform lies elsewhere, probably hidden beneath the progradational sedimentary prism closer to Lomonosov Ridge. The origin of the Marvin Spur escarpment is uncertain, but is most easily explained as a far-field effect of Paleocene extensional faulting in Eurasia basin.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia