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esearchers, here we suggest that the age range
of the Tuchengzi Formation in northern
Hebei-western Liaoning is from 147 Ma to
136 Ma. It implied that the Tuchengzi
Formation was mainly formed in the Early
Cretaceous.
2009020557
粤 北 早 侏 罗 世 岩 浆 作 用 : 霞 岚 杂 岩
SHRIMP 锆 石 U-Pb 年 代 测 定 = The Early
Jurassic magmatism in northern Guangdong
Province, southeastern China: Constraints
from SHRIMP zircon U-Pb dating of Xialan
complex. ( 英 文 ). Yu Xinqi; Di Yongjun; Wu
Ganguo; Zhang Da; Zheng Yong; Dai Yanpei.
Science in China Series D: Earth
Sciences, 2009, 52(4): 471-483
This paper reports SHRIMP zircon U-Pb
ages of 196±2 Ma for granite, and 195±1
Ma for gabbro from the Xialan complex in the
Meizhou area, northern Guangdong Province.
These results shed new light on the calm stage
of magmatic activity in southeastern China
during 200–180 Ma, and revealed that the
back-arc extension induced by the subduction
of the western Pacific plate may have begun at
195 Ma at least. Field observation on the fresh
outcrops allows us to recognize some features
formed by magma mixing. A part of the
gabbro has a fine-grained rim of 20–30 cm at
the margin, and thins gradually toward the
granite; numerous dark fine-grained to
microcrystalline dioritic enclaves developed in
the granite. These enclaves vary in shape and
size, dark minerals concentrated at the margin
of enclaves, and the contact between enclaves
and host rock is either obvious or obscure, or
gradational. In addition, needle-shaped
apatites are included in the enclaves. The REE
patterns of gabbros, as well as the trace
element patterns, are generally consistent with
those of granitic rocks. The above characters
further suggest that in the Early Jurassic the
injection of basic magma had melted deep
continental crust and produced acidic magma,
and the Xialan complex was produced by the
mixing of them.
2009020558
龙 门 山 断 裂 带 中 生 代 和 新 生 代 的 构 造 演 化
= Mesozoic and Cenozoic tectonic evolution
of the Longmenshan fault belt. ( 英 文 ). Wang
Erchie; Meng Qingren. Science in China
Series D: Earth Sciences, 2009, 52(5): 579-
592
The giant earthquake (M s=8.0) in
Wenchuan on May 12, 2008 was triggered by
oblique convergence between the Tibetan
Plateau and the South China along the
Longmenshan fault belt. The Longmenshan
fault belt marks an important component of
the tectonic and geomorphological boundary
between the eastern and western part of China
and has a protracted tectonic history. It was
first formed as an intracontinental transfer
fault, patitioning the differential deformation
between the Pacific and Tethys tectonic
domains, initiated in late Paleozoic-early
Mesozoic time, then served as the eastern
boundary of the Tibetan Plateau to
accommodate the growth of the plateau in
Cenozoic. Its current geological and
geomorphological frameworks are the result
of superimposition of these two tectonic
events. In Late Triassic, the Longmenshan
underwent left-slip oblique NW-SE shortening
due to the clockwise rotation of the Yangtze
Block, which led to the flexural subsidence of
the Sichuan foreland basin, but after that, the
subsidence of the Sichuan Basin seems no
longer controlled by the tectonic activity of
the Longmenshan fault belt. The Meosozoic
tectonic evolution of the Songpan-Ganzi fold
belt differs significantly compared with that of
the Yangtze Platform, featured by intensive
northeast and southwest shortening and
resulted in the close of the Paleo-Tethys.
Aerial photos taken immediately after main
shock of the giant May 12, 2008 earthquake
have documented extensive rock fall and
landslides that represent one of the most
destructive aspects of the earthquake. Both
rock avalanches and landslides delivered a
huge volume of debris into the middle part of
the Minjiang River, and formed many
dammed lakes. Breaching of these natural
dams can be catastrophic, as occurred in the
Diexi area along the upstream of the Minjiang
River in the year of 1933 that led to
devastating floodings. The resultant flood
following the breaching of these dams flowed
through and out of the Longmenshan belt into
the Chengdu Plain, bringing a huge volume of
sediments. The oldest alluvial deposits within
the Chengdu Plain are estimated to be Late
Miocene (8–13 Ma). We suggest that the
flooding that transported the course-grained
sediments into the Chengdu Plain occurred in
late Cenozoic, resulted from both the climate
and the historical earthquakes similar to the
May 12 earthquake. Estimated age of the
sediments related to earthquakes and coeval
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