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| Titel |
Tectonic activities along the eastern flank of the Central Range in the active Taiwan orogen Inferred from river steepness index |
| VerfasserIn |
Yi-Wei Chen, J. Bruce H. Shyu, Chung-Pai Chang |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250073888
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| Zusammenfassung |
| The tectonic activity of the Taiwan orogenic belt has been well studied by different
methods in various time scales, such as long-term (>1 Ma) thermochronologic
data and short-term (yearly to decadal) geodetic analysis. However, constrains on
millennial-scale tectonic characteristics is limited, especially in the mountainous core of
the island. Recent studies show the channel networks in active orogens reflect the
pace at which landscapes respond to tectonic processes and provides a record of
relative changes in rock uplift. Therefore, we attempted to use river steepness index
(ksn) derived from the stream power incision model, combined with knick point
distributions from bedrock rivers to obtain the signature of tectonic forcing spatially and
temporally.
We analyzed 21 rivers along the eastern flank of the Central Range, Taiwan. We chose the
main trunk of each river system as the major branch flowing from the ridgeline of the Central
Range and perpendicular to the main structures and the strata. Our results show that the
ksn numbers of the rivers from slope and area plot fall in a wide range, from 60
to 570. The average of ksn is about 190 in the central part of our study area, and
decreases to 120 and 130 toward the north and south. Based on the characteristics
of the longitudinal profiles and the slop-area plot, we can divide these 21 rivers
into 6 distinctive groups. It is noteworthy that some of the rivers show ‘’anti-knick
points”, which are believed to be the results of the reduction of uplift rates. This
phenomenon has been discussed in theory, but may be the first time observed in the field
data.
We believe the differences in ksn in our results are related to tectonic activities in the
region, rather than influences of climate or lithologic controls, since all of the rivers are
located on windward side of the Taiwan orogen, and the similarity in metamorphic and
deformational degrees in the bedrocks reduced the differences of rock strength. The patterns
of the ksn variations are quite consistent with the patterns of tectonic evolution in Taiwan,
where in the southern part the orogen is growing, but in the northern part the active collision
and mountain-building has waned and the orogen is collapsing. Furthermore, our
results not only enabled us to better identify the transition area between rapid and
waning collisions in Taiwan, but also provides information to quantify the relative
rock uplift rates in the millennial time scale in the mountainous core of the island. |
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