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Progresses on CCSD project and UHP
metamorphic terrane
Xu Zhiqin
( PI of CCSD project, Institute of Geology, Chinese Academy of
Geological Sciences)
CCSD is a national key
scientific engineering project of China. The drill site of CCSD is located
in Donghai, Jiangsu Province, the eastern part of the Dabie-Sulu UHP
metamorphic belt, which possesses global geological significance. From the
spud on June 25, 2001 to April 6, 2002, the 2000m pilot hole was finished
with a total core recovery of 88.7% and an average well inclined angle of
3~4 degrees. Until August 14, 2002, the depth of main hole has reached
1871m. The pilot hole provides valuable, continuous and fresher 2000m
core, cuttings, fluid and gas samples as well as logging data. At the same
time, significant scientific achievements have been obtained.
Lithological profile, structural profile, core scanning profile, core
gamma anomaly profile, mineralized profile, petrophysical profile, fluid
chemical profile, and dozens of different log profile have been recorded.
3D seismologic exploration around the drill site and VSP seismologic
profile have been completed which revealed detailed crustal structure
around drill site.
In the pilot hole of the 2000 m cores, the accumulative thickness of
eclogite with special geological significance reaches more than 1000 m.
The thickness of mantle peridotite reaches more than 80 m for thickness.
The new rutile deposit ranged from 1600 to 2000m in depth has been found.
Since solving the problem of core orientation and depth reconstruction,
a high-reliable structural profile is established. And seven petrophysical
parameters of the first 500 m cores have been acquired as well. After
eliminating the disturbance of drilling and mud, the anomaly of methane
(CH4), ethane (C2H6), propane (C3H8), butane (C4H10), helium (He), carbon
dioxide (CO2) and carbonic oxide (CO) has been found. Preliminary study
shows that the fluid and gas are characterized by multi-generations.
The DNA analysis probably shows existence of microbes in the eclogite
core at the depth of 1080 m, which could provide some very important clue
for studying the origin of life.
All the scanned images of 2000m cores and drilling data have been input
into the newly developed database of Drilling Information System (DIS).
Thousands of web pages have been published on the INTERNET.
The new progresses on UHP metamorphic terrane are as follows:
1) Coesites in Zircons from different types of country rocks of eclogite
are widely distributed in South Sulu UHPM belt and new evidence of
super-deep subduction through microstructure studies has been found which
indicates that huge amount crustal material has been subducted to more
than 200km depth.
2) New metamorphic rock units of various types of UHP metamorphic rocks
have been re-classified according to their origin, occurrence and
composition. These units have been marked in the newly mapped 1: 250,000
geological map. New structural framework of this area has been built.
3) The seismic tomographic cross-section of the southern Sulu HP-UHP
metamorphic belt reveals that the Xiangshui Fault located between the Sulu
belt and Yangzi craton and the Tan-Lu Fault are two super-lithospheric
faults, both exceed to more than 250 km in depth.
4) The discovery of the North Qaidam coesite-bearing UHP metamorphic belt
of 350 km long, the Western part of China and the suggestion of the huge
Central-China UHP metamorphic belt of about 4000km long can be regarded as
significant contribution to the UHPM study of China and world. Recently,
the UHP mineral has been found at the conjunction part of the Dabie-Sulu
UHPM belt and the North-Qaidam UHPM belt, which provided an important new
evidence for such a huge Central China UHPM belt.
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