博士 / 國立臺灣大學 / 海洋研究所 / 86 / To map the upper mantle structure in the Southeast Indian Ocean,we have in
verted Rayleigh wave group velocities to two-dimensionaltomographic images for
periods from 22 to 67 s. Most of the eventsused are located on the ridge and
stations are in the southernAustralia, with Rayleigh wave paths boundedbetwee
n 95 and 150 E.Most remarkable on these maps is theincrease of group velocity
withthe age of the seafloor, representing cooling of the upper mantle asit spr
eads away from the ridge. The ocean-continent transition inthe upper mantle a
s indicated by the abrupt change in velocity nearcontinent primarily mirrors t
he 60-90 Ma isochrons on the surface.High velocity anomalies are found to fram
e the morphologicallydifined Australian-Antarctic Discordance (AAD) zone (120-
128 E).This observation is at odds with the general notion that the coldanomal
y is centered right beneath the AAD corridor. On the otherhand, the along-axi
s variations suggest that the upper mantle beneaththe AAD is still faster than
segments to the east and west. Fromthese group velocity maps, we invert for
three-dimensional model ofshear velocity of the upper mantle. In the upper 60
km whereresolution is acceptable, we also find similar off-axis velocityanoma
lies on both sides of the AAD zone. On the corss-sectionsin the spreading dir
ection, the shear velocity in the upper mantleolder than 30 Ma is considerably
faster than those predicted fromcooling of oceanic lithosphere both verticall
y and laterally fromthe relatively cool continental shield. This feature may
imply that the thermal structure in the old upper mantle is affectedwith the t
hick Australian continental root as it moves northward.Our tomographic images
sensitive to asthenospheric depths posetight constraints on various mantle flo
w models that producecertain thermal signatures in this region.
| Identifer | oai:union.ndltd.org:TW/086NTU00274006 |
| Date | January 1998 |
| Creators | Liang, Wen-Tzong, 梁文宗 |
| Contributors | Ling-Yun Chiao, Ban-Yuan Kuo, 喬凌雲, 郭本垣, --- |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 140 |
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