HR: 16:15h
AN: T44C-02    [Abstracts]
TI: Geomorphologic study of the serpentine seamounts in the Mariana forearc region
AU: * Yokose, H
EM: yokose@sci.kumamoto-u.ac.jp
AF: Marine Volcanology, Graduate School of Sci. & Tech., Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan
AU: Maekawa, H
EM: maekawa@p.s.osakafu-u.ac.jp
AF: Dept. Physical Sci., Graduate School of Sci., Osaka Prefecture university, 1-1 Gakuen-cho, Naka-ku Sakai, Osaka, 599-8531, Japan
AU: Fujioka, K
EM: fujiokak@jamstec.go.jp
AF: JAMSTEC IFREE, 3175-25 Showa-Machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AB: In order to understand the origin of serpentine seamounts in the Mariana forearc region, we obtained new bathymetric map, which cover approximately 770 km with an area of 52000 km² along the arc, during cruises YK03-07 in 2003 and KR06-15 in 2006. We synthesized with the precise bathymetric map and previously reported geological papers, and classified the geomorphologic characteristics of the serpentine seamounts into three types: the conical type, the dome (including coin shape) type, and the plateau type. The plateau type seamount is considered to be a horst relatively uplifted oceanic crust with serpentine layers. On the otherhand, the other two types indicate a circular or orbital boundary in the bathymetric maps. These shapes imply that effusive materials are supplied from a central vent. Conical-type serpentine seamounts have concave or straight slopes in profile around the summit.Acoustically high reflective areas, which thier outlines are similar to a basaltic lava flow shape, around the summit. The edifices, which may be a mud flow deposit, are not thick enough for their morphological outlines to be detectable. At the same time, wrinkled slopes are observed on their flanks. Dome-type serpentine seamounts have convex upward slopes in profile around the summit. Some small domes, which are less than 10 km in diameter and 500 m in height, are located on the summit. Some of the domes have ramp structures on their boundaries. Remarkable wrinkled slopes are present and often indicate a curved ridge, approximately 100 m high, on their surface, known as an ogive ridge. This slope morphology is very similar to a viscous silicic coulee. The thickness is assumed to be more than 200m. Some of the dome-type seamounts have remarkable ramp structures, 100-150 m high, on their boundaries. These geomorphologic characteristics imply that the serpentine seamounts are produced by highly viscous materials expelled episodically from the central vent. If serpentine seamounts are a result of the accumulation of thin, less than 10 m, serpentine mud flows as proposed previously, the shape of serpentine seamounts should be similar to that of the shield volcano. The above geomorphologic characteristics indicate the presence of 22 serpentine seamounts including nine of which are newly identified. These 22 serpentine seamounts are not evenly distributed along the arc, but are localized in three areas: a northern area, N18° to N20°, a central area, N15° to N15°10', and a southern area, N14° to N14°40'. In the northern and central areas, the effusive centers of the serpentine seamounts are located roughly on the edge of the polygonal graben delineated by faults. The geomorphologic characteristics of the serpentine seamounts and their geometric arrangement are analogous to those of silicic lava domes developed on a caldera rim. These common characteristics suggests that the distribution pattern of the serpentine seamounts is more closely related to the polygonal depressions than to the tectonic setting.
DE: 3641 Extrusive structures and rocks
DE: 8003 Diapir and diapirism
DE: 8150 Plate boundary: general (3040)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8426 Mud volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting