Cite abstracts as Author(s) (2008), Title, Eos
2008 Western Pacific Geophysics
Meeting
Trans. AGU,
89(23), West. Pac. Geophys. Meet. Suppl.,
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Abstract xxxxx-xx
Your query was:
taiwan
HR: 1800h
AN: V35A-01
TI:
Volcanology
Kueishantao,
and
Northeast
Geochemistry
Taiwan,
and
of
Their
Implications
AU: * Song, S
EM: srsong@ntu.edu.tw
AF: 1. Institute of Geosciences, National Taiwan
University, P.O. Box 13-318, Taipei, 106, Taiwan
AU: Chiu, C
EM: b5204008@yahoo.com.tw
AF: 1. Institute of Geosciences, National Taiwan
University, P.O. Box 13-318, Taipei, 106, Taiwan
AU: Tsao, S
EM: tsaosj@moeacgs.gov.tw
AF: CENTRAL GEOLOGICAL SURVEY, MOEA, P.O.BOX
968, Taipei County, 235, Taiwan
AU: Hsieh, Y
EM: hsiehyc@moeacgs.gov.tw
AF: CENTRAL GEOLOGICAL SURVEY, MOEA, P.O.BOX
968, Taipei County, 235, Taiwan
AU: Chen, C
EM: prochen@moeacgs.gov.tw
AF: CENTRAL GEOLOGICAL SURVEY, MOEA, P.O.BOX
968, Taipei County, 235, Taiwan
AB: The Kueishantao (KST) is a young volcanic island
located at the southernmost part of the Okinawa
Trough. TL dating of siltstone xenoliths collected
from the lower part of the pyroclastic deposit shows
the last eruption may be younger than 7 ka.
Furthermore, on-land fumaroles, active submarine
hydrothermal mounds and high heat flow around this
island all indicate that an active magmatic system
may exist underneath it. In addition, based on the
observation of drilling core at the northern flank and
surface outcrops, it shows the KST as a typical
stratovolcano with two volcanic centers which are
mainly composed of lava flows, pyroclastic flows,
lahars, and hydrothermal deposits. In KST, the
occurrence of xenoliths is common in volcanic rocks
and shows an increasing trend from the bottom of
drilling
core
to
the
top,
which
inferring
an
intensification of crustal contamination. Based on
major-element geochemistry, KST andesites can be
divided into two subgroups, in which Type I
Andesites are defined as possessing lower MgO and
SiO2, and Type II Andesites possessing higher MgO
and SiO2. In general, both of them reveal similar
trace-element compositions except that Type II
Andesites exhibit high Ni and Cr contents. In
primitive-mantle-normalized incompatible element
diagram and chondrite-normalized REE pattern, Type
I and II Andesites have highly similar patterns. They
are
characterized
by
enrichment
of
large
ion
lithophile elements (LILEs) and Th, U and Pb, and
depletion of high field strength elements (HFSEs).
Type I Andesites are in the lower part of core, and
Type II Andesites are distributed in the topper part,
indicating that KST magmatic evolution from low
MgO magmas transferring into high MgO magmas.
Base on the combination of results of chemical
analyses, isotopic compositions and petrographic
observation, we propose that magmatic evolution of
KST is as follows. Firstly, Type I Andesites were
produced by about 45% fractional crystallization of
basaltic magmas, which were derived from melting of
the mantle wedge induced by hydrous fluids released
during dehydration reactions in the subducting
Philippine oceanic lithosphere, prior to the opening
of the southern Okinawa Trough. Secondly, as a
result of the opening of the Okinawa Trough, quick
ascending of magma may shorten its storage time in
magma chamber and experienced less fractional
crystallization.
Finally,
magma
assimilated
the
continental crust materials (about 15-25%) during it
ascended through the upper continental crust and
then produced Type II Andesites.
DE: 8400 VOLCANOLOGY
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8413 Subduction zone processes (1031, 3060,
3613, 8170)
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2008 Western Pacific Geophysics Meeting