ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

area. Overall, the geomorphological changes of Tsengwen
coastal plain were caused by physical processes in long
term but modified strongly by human agency in the recent
time. The geomorphological changes have induced some
impacts on the human beings including the decline of port,
moving of village to prevent flooding, confusion of administrative
boundary, etc.
lIE CHEN 1, GUOYU DING 2 & GUOSHENG Qu 1
Arc tectonics in the northern margin
of the Pamir-Tibet Plateau
1 Institute of Geology, State Seismological Bureau, Beijing 100029, China
2 Center for Analysis and Prediction, State Seismological Bureau,
Beijing 100036, China
Arc tectonics is a key feature in intracontinental orogenic
belts in west China. Several rows of high-rising arcuate
mountain ranges, which caused by strongly lithospheric
compressing and uplifting owing to collision of the Indian
and Eurasian plates, mark the northern margin of the Parnir-Tibet
plateau. Two major arcs can be identified as the
Pamir-west Kunlun arc and the Altun-Qilianshan arc respectively
from west to east.
Analysis and comparison of accumulated neotectonic
deformation and of seismicity between these arcs has been
carried out recently on the basis of data related to sediment
strata deformation, geomorphic evolution, offset of
drainages, paleoearthquake events, and so on. Some results
have been gotten, even if they probably are unperfected.
1. These arcuate mountain ranges are alternated with intramountain
basins or piggy-back basins in space. From
the inner arcs to outer ones, their altitudes are getting
lower, their curvatures bigger, and their ages younger.
2. Every arc tectonic is composed of a series of varying
scales of sub-arc that is a separate fold-and-thrust sheet
with independent characteristics of geometry, kinematics
and mechanics and is a self-similar system as well.
3. The geometry and kinematics of arc tectonics changes
from thrusting at the top of the arc (where thrusts are with
gently dipping planes and has the largest slips) to oblique
thrusting and wrenching at the limbs (steeper faults with
sinistral wrenching at the left limb and dextral wrenching
at the right limb), and finally thrusting to the end of the
arc. For example, in the Pamir-west Kunlun arc which verges
to the north, the kinematics of arc changes from the
top (thrusting in the south of Kashigar) to the east limb
(dextral wrenching in the south of Yingjisha-Zepu, where
a large dextral pull-apart basin called the Tashikuergan basin
was developed as the result), and finally to the end (thrusting
in the south Yecheng).
4. These arc tectonics consist of frontal, lateral and oblique
ramps in deep, which merged downward into a series
of decollements in different depth.
5. Every earthquake deformation belt is probably related
to the independent arc tectonics one by one. Strong earthquakes
correspond to the large scale arcs, and middle to
small earthquakes to smaller ones.
ZHIMING CHEN
Analysis on the plate geomorphic effects in West China
Nanjing Institute of Geography and Limnology, Academia Sinica,
73 East Beijing Road, Nanjing 210008, China
The term «plate geomorphic effects» denotes that since
the end of Mesozoic era, especially since the continental
collision 40-45 MaBP under the drive of plate tectonics
and its stress field, there emerges a regional effect of systematic
geomorphic deformation or rejuvenation. Researches
indicate that during the Meso-Cenozoic period, the Indian
Plate made it a rule to subduct and collide against the Eurasian
Plate generally in a NNE direction. Thus, those
morphotectonics in west China and its adjacent areas have
taken place systematic deformation as the following:
1. Pattern of mountain system as vertically against the
main compressive axis: The trend of mountains and basins
in West China was generally in a vertical arrangement with
the principal compressive axis of the plate (NNE), whereas
its specific distribution had something to do with the geometric
forms of landmass boundaries. Moreover, in areas
ranging from Mt, Himalayan extending N -ward to Mts.
Kunlun-Altun-Qilian, Mts. South and North Tianshan,
and Mt. Altay, both the heights of mountain ranges (in the
average and in the highest) and the thicknesses of piedmont
molasses are becoming gradually lessened from
south to north:
2. Nappe-type mountains spreading extensively in the foreland
zones: After having undergone compressive stress
through longstanding stability, those marginallithospherical
substances of the orogenic belt were squeezed into and
thrusted above the old landmass, while the foreland crust
was underthrusted below the orogenic belt, as a result of
which these nappe-type mountains at all of the plateau
margin took shape. These nappe mountains, though varied
in age, became active violently in the Quaternary period, as
reflected conspicuously in relief. It is shown in the computer-aid
mapping from the piedmont relief, for example,
that there were inward plateau staircase planes contrary to
the normally tilted outward ones to be frequently seen;
3. Occurrence of the latest folded in semi-cemented strata:
in the region adjacent to the main compressive axis, due to
the fracture of rigid basement and the shortening of earth's
crust, the fluviolacustrine facies Tertiary and Quaternary
systems in some compresso-depressed basins gave rise to a
peculiar kind of the latest folded landform above their semicemented
caprocks. as shown in the considerable
amounts of massifs and hills in the satellite images from
those basins of Qaidamu, Junggar and Talimu.
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