Print this pageActive Uplift and Its Annual Rate of the Saint Peter-Saint Paul Peridotite Ridge, Equatorial Atlantic Ocean
The Saint Peter Saint Paul Islets is situated at the Equatorial Atlantic Ocean on the top of the morphologic elevation of 90km in length, 25km in width, and 3800m in height constituted by abyssal mantle peridotite. This peridotite ridge is the only abyssal mantle exposure above sea level known up to the present. In addition, it is one of the places with possible occurrence of abiogenic hydrocarbonate generation by the serpentinization due to the reaction between the mantle peridotite and sea water. In this sense, the elucidation of the origin and evolution of this peridotite ridge are important to establish the standard example. The submarine morphology around the Saint Peter Saint Paulo Islets is highly accidental characterised by steep slopes and walls. The morphological features and the absence of large coral reef suggest that the islets are formed by recent tectonism that may continue up to the present. It is considered that the peridotite ridge top was present at the ocean bottom and it has just reached to the present sea level. The summit level map shows a wave-cut bench of 7~9 m above sea level. Considering this wave-cut bench to formed during the Flandrian Transgression, the uplift rate in recent 6000 years is calculated as 1.5 mm/year. The 14C datings for the coral fossils collected from the Belmont Island, the largest member of the Islets, indicate the uplift rate of 1.5 mm/years in recent 6600 years. If the peridotite ridge is a tectonically deformed megamullion, total uplift is 1500 to 3000m and the tectonism started at 1 to 2Ma. On the other hand, if the ridge is originated directly from subcrustal mantle, the total uplift becomes about 9000m and tectonism is active in recent 6 million years.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil