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Rock magnetic studies on the hominoid-bearing sediments at Zhupeng, Yuanmou Basin, southwestern China and its paleoclimatic significance

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Science Bulletin 2005年第15期 119-126页

作者： YAO Haitao1, LIU Qingsong1,2. Lü Lianqing1, CHANG Zhigang1 & ZHU Rixiang1 1. Paleomagnetism Laboratory, institute of Geology and geophysics, Chinese Academy of Sciences, Beijing 10002., China {2., university of cali-fornia, santa cruz, ca 95064, usa

It has been proposed that paleoclimatic changes and tectonic events strongly affect hominoid evolution. The Zhupeng section at Yuanmou Basin, southwestern China, with the hominoid-bearing fluvial-lacustrine sediments, is an ideal natural laboratory to test this hypothesis. This study provided an integrated magnetic study, including low-fre- quency susceptibility, the anisotropy of magnetic susceptibil-ity, temperature-dependent susceptibility, hysteresis loops, isothermal remanent magnetization, and anhysteretic rema-nent magnetization, on samples from the Baozidongqing section at Zhupeng. Results show that the dominant mag-netic carrier is hematite, with minor amount of magnetite. Both the composition and concentration of magnetic miner-als strongly correlate with the lithostratigraphy. At least eight short-term events defined by higher concentrations of magnetite were identified. These short events reflect that the subtropical dry-hot climate is similar to today’s climate. Basing on the lithostratigraphic and rock magnetic results, we suggest that Yuanmou Basin was in a steady deposition environment from about 11 to 7 Ma, which is characterized by alternating of long-term torrid-humid climate and short-term dry-hot climate. Our study provides invaluable environment information for understanding the climate shift and the relationship between paleoenvironment and homi-noid evolution in southwestern China during late Miocene.

关键词： Yuanmou Basin hominoid late Miocene rock magnet-ism paleoclimate.

Beamlet migration for complex structure and local angle-domain analysis

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Beamlet migration for complex structure and local angle-doma...

CPS/SEG 2.04 International Geophysical Conference

作者： Wu Rushan Modeling and imaging laboratory institute of geophysics and {2. university of california santa cruz ca 95064 Luo Mingqiu Chen Ling Presently at institute of geology and geophysics Chinese Academy of Sciences Beijing China 100101

＜正＞ Beamlet prestack migration is implemented in the shot domain. Both the source field and the receiver array field are decomposed into LCB beamlets and sinked down to image levels using beamlet propagators. Imaging condition can be applied either in beamlet domain or space domain. As an example, the 45 shots synthetic data of SEG/EAGE salt model are used for imaging. The results demonstrate the high resolution and high quality feature of the beamlet migration, that can be seen clearly from the images of the highly irregular top salt boundary. A method of local AVA （amplitude versus angle） analysis during the process of prestack depth migration in angle domain is proposed based on the local image matrix obtained through beamlet decomposition （wavelet transform along spatial axis） of both the incident and scattered wave field at the image locality. The local image matrices can be reduced to common refection-angle image （CRAI） gathers and common dip-angle image （CDAI） gathers. CDAI gathers can be used to determine the dip-angle of the reflector and CRAI gathers are then used for local AVA analysis. Preliminary numerical tests demonstrate the feasibility of the method.

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Rheological Strength of UHP Eclogite from Dabieshan: Evidences from High p-T Experiments

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Journal of Earth Science 2001年第3期 3-8页

作者： Zhang JunfengGraduate School, China university of Geosciences, Wuhan 430074 institute of {2. & planetary Physics, university of california, Riverside, ca 92.2., usaJin ZhenminFaculty of Earth Sciences, China university of Geosciences, Wuhan 430074

We present here experimental study of the rheological properties of UHP eclogite from Dabie at a pressure of 3 GPa by utilizing the 5 GPa Griggs type piston cylinder apparatus. The rheological constitutive equation of eclogite is determined with a stress exponent of 3.4, an activation energy of 480 kJ/mol and a preexponential factor of 103.3. Our!study shows that: (1) As a typical two phase rock, the flow strength of eclogite depends on the proportions of the strong phase (garnet) and the weak phase (omphacite); (2. The plastic deformation of eclogite is dominated by dislocation creep; (3) Based on that eclogite has the same strength as the upper mantle harzburgite, our study suggests that the delamination of the subducting crust component from the underlying upper mantle is unlikely. Therefore, the stretching after the collision orogeny coupled with the upwelling of the upper mantle may play a more important role in the exhumation of UHP rocks.

关键词： UHP eclogite rheological strength dislocation creep high p T experiment delamination Dabieshan.

A new high-precision furnace for paleomagnetic and paleointensity studies:minimizing magnetic noise emanating from heater-currents inside traditional thermal demagnetizers

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A new high-precision furnace for paleomagnetic and paleointe...

中国地球物理学会第二十六届年会、中国地震学会第十三次学术大会

作者： Zhong Zheng~1,Xixi Zhao~2.1 Geoscience Division,Sogokaihatsu Co,Ltd.,Nishi -Koiwa 1 -30- 16, Edogawa - ku,Tokyo 133 - 0057,Japan 2.institute of geophysics and {2. Physics,university of california,santa cruz,ca 95064,usa

Demagnetization is one of major lab measurements to recognize and remove secondary magnetization,and is routinely performed in paleomagnetic laboratories using thermal demagnetizers to heat specimens to specified temp... 详细信息

关键词： A new high-precision furnace for paleomagnetic and paleointensity studies:minimizing magnetic noise emanating from heater-currents inside traditional thermal demagnetizers

2.5D SH Wave Propagation in Heterogeneous Crustal Wave Guides Using the Phase Screen Method

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2.5D SH Wave Propagation in Heterogeneous Crustal Wave Guide...

中国科学院地质与地球物理研究所2.08学术年会

作者： Weijia Sun,Li-Yun Fu,and Ru-Shan Wu State Key Laboratory of Lithospheric Evolution institute of Geology and geophysics Chinese Academy of Sciences Beijing 10002.,China Modehng and Imaging Laboratory institute of geophysics and planetary Physics university of california,santa cruz 1156 High Street santa cruz,california 95064

One-way approximations for regional phases slice the half-space crastal wave guide into a number of slabs perpendicular to the propagation direction;the Moho discontinuity can be easily treated as a perturbation from the crustal background. The advantage of one-way propagation methods is their great saving of computing time and memory compared to full-waveform numerical methods,especially for 3D *** this article,we present general 2.5D SH formulas for the thin-slab method and a generalized screen propagator(GSP) for simulating SH wave propagation in the heterogeneous half-space crustal wave *** of numerical results with a finite-difference(FD) algorithm for a standard flat crustal model show excellent agreement,demonstrating the validity and accuracy of the 2.5D GSP for the half-space *** then compare the curves of energy attenuation calculated by the 2. and 2.5D *** comparison shows that the energy attenuation of the 2.5D case is about 1.5-3 times greater than that of the 2. case when the trapped mode is *** SH screen propagator is also used to simulate two laterally unvarying (in the y direction) crustal models,showing the path effects on regional wave propagation.

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深源地震：橄榄石→尖晶石相变诱发断层

地学前缘 1995年第1期2卷 19-25页

作者： Harry W. Green,Ⅱ(institute of geophysics and {2. Physics and Department of Earth Sciences,university of california,Riverstde,ca 92.2.,usa)

７０年代以来，人们已经知道在地球几百公里处有深源地震存在，在这个深处压力和温度不可能使岩石产生脆性剪切断裂。在３００ｋｍ之下，地震出现频率随深度增加而迅速减少，但是在６００ｋｍ处又再次增加，在７００ｋｍ处深源地震停止... 详细信息

７０年代以来，人们已经知道在地球几百公里处有深源地震存在，在这个深处压力和温度不可能使岩石产生脆性剪切断裂。在３００ｋｍ之下，地震出现频率随深度增加而迅速减少，但是在６００ｋｍ处又再次增加，在７００ｋｍ处深源地震停止。五年之前，我们发现这种深源地震与一种新的塑性不稳定性有关。在地球４００ｋｍ处，当上地幔最主要矿物橄榄石（Ｍｇ，Ｆｅ）＿２ＳｉＯ＿４发生相变时会导致一种新的断层类型产生。我们首先利用锗橄榄石Ｍｇ＿２ＧｅＯ＿４，（即晶体结构与镁铁橄榄石相同，而化学成分有所不同，它可以在比较低压力条件下发生相变）进行模拟实验，借以证明在上地幔很高压力条件下橄榄石也会发生相变。这种新的机制叫自组织类的脆性断裂（ｓｅｌｆ─ｏｒｇａｎｉｚｉｎｇｌｉｋｅｂｒｉｔｌｅｆａｉｌｕｒｅ），其特征是：在断层生长过程中会释发地震能量；在由很细尖晶石颗粒组成的“超塑性层”中会发生断层滑移（即所谓显微反向断裂，ｍｉｃｒｏａｎｔｉｃｒａｃｋ）。由这种机制形成的断层只在放热反应过程中产生，它可以用来解释为什么深源地震停止于７００ｋｍ，因为在这个深度，橄榄石到尖晶石相变为下地幔高密度矿物的吸热反应。深源地震的地震学证据与这种新机制是一致的。

关键词：深源地震断层橄榄石尖晶石相变地幔

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Seismic Lg-wave Q tomography in and around Northeast China

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Seismic Lg-wave Q tomography in and around Northeast China

中国科学院地质与地球物理研究所第十届(2.10年度)学术年会

作者： Lian-Feng Zhao,Xiao-Bi Xie,Wei-Min Wang,Jin-Hai Zhang,and Zhen-Xing Yao 1 institute of Geology and geophysics,Chinese Academy of Sciences, Beijing,China. 2.institute of geophysics and planetary Physics,university of california, santa cruz,santa cruz,california,usa. 3 institute of Tibetan Plateau Research,Chinese Academy of Sciences, Beijing,China.

[1]We investigate regional variations in the Lg-wave quality factor(Q)in Northeast China and its vicinity with a tomographic *** seismic data recorded at 2. broadband stations from 12. regional events are used to extract Lg-wave spectra. Tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0.05 and 10.0 *** simultaneously invert for the Lg-wave Q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the Q model and source *** best spatial resolution is approximately 1°×1°in well-covered areas for frequencies between 0.4 and 2.0 *** Lg Q shows significant regional variations and an apparent relationship with regional *** use a statistical method to investigate the regional variations of Lg Q and their frequency *** average Q(1 Hz Lg Q)in the entire investigated region is *** basins are usually characterized by lower average Q values (from 155 to 391),while volcanic mountain areas have relatively high average Q values (from 630 to 675).Lg Q generally increases with increasing ***,the frequency dependence has complex nonlinear features on a double-logarithmic scale, indicating that the commonly adopted power-law relationship may be oversimplified in a broad frequency *** frequency dependence varies in different geological areas,with larger variations seen at lower frequencies.

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Coesite inclusions in zircon from gneisses identified by laser Raman microspectrometer in ultra-high pressure zone of Dabie Mountains,China

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Science Bulletin 2001年第22期46卷 1912-1916页

作者： LIU Jingbo, YE Kai CONG Bolin, Maruyama Shegnori & FAN Hongruiinstitute of Geology and geophysics, Chinese Academy of Sciences, Beijing 10002., China Department of Earth and {2. Sciences, Tokyo institute of Technology, 2.12.1 Ookayama, Meguro Tokyo, 152. Japan institute of Geology and geophysics Chinese Academy of Sciences Beijing China Department of Earth and planetary Sciences Tokyo Institute of Technology Meguro Tokyo Japan

The mineral inclusions in zircon from gneisses in ultra-high pressure (UHP) zone of the Dabie Mountains were identified by using a laser Raman microspectrometer. Coesite occurs as inclusions in zircons from all types of gneiss. Other important minerals, such as jadeite, omphacite, aragonite, barite, and anhydrite were also found as inclusion minerals. These discoveries indicate that ( i) gneissic country rocks had metamorphosed at the same time as the enclosed eclogites; and (ii) SO4-2.-bearing fluids were presentin the UHP metamorphic process, which is manifested by occurrence of barite and anhydrite coexisting with coesite.

关键词： Coesite inclusions in zircon from gneisses identified by laser Raman microspectrometer in ultra-high pressure zone of Dabie Mountains,China high

NORMAL-SLIP ALONG THE NORTHERN ALTYN TAGH FAULT, NORTH TIBET

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地学前缘 2000年第S1期7卷 237-238页

作者： Yin An 1, George Gehrels 2. Chen Xunhua 3, Wang Xiao\|Feng 3, T. Mark Harrison 1, Shen Jie 1[WT5,5”BX](1 Department of Earth and Space Sciences and institute of geophysics and {2. Physics, university of california, Los Angeles, ca 90095\

The east\|west striking Northern Altyn Tagh Fault, about 2.0km long between Bashkaogong (90°E, 39°2.′N) and Lapeiquan (92.15′E, 39°2.′N), was previously mapped as a north\|dipping thrust, juxtaposing late Archean\|Mesoproterozoic gneisses in the hanging wall over Paleozoic volcanics, plutons, turbidite, and melange complexes in the footwall. In order to estimate the total magnitude of slip along the Cenozoic Altyn Tagh fault, we conducted geologic mapping along four traverses across the Jinyan Shan where the fault lies. Our field observations suggest that the fault is south\|dipping, with dip angles varying from 2.° in the east to about 40° in the west. The eastern fault zone exhibits mylonitic fabrics, whereas the western fault zone is characterized by cataclastic deformation. Kinematic indicators in the ductily deformed mylonitic shear zone consistently show a top\|to\|the\|south sense of shear, suggesting that the Northern Altyn Tagh fault is a south\|dipping normal fault, not a north\|dipping thrust.. The ductile shear zone is typically 30～40m thick, consisting of highly sheared metasediments (pelite and marble), granites, and granitic *** latter are systematically cut by small\|scale, south\|dipping ductile normal faults with displacements between 10s of cm to several meters, forming spectacular asymmetric boudinages in the sheared meta\|pelite *** minimum displacement along the detachment is about 2.km, as measured by the north\|south width of the exposed footwall gneisses. We renamed the Northern Altyn Tagh Fault in the Jinyan Shan region as the Lapeiquan detachment fault to avoid confusion with other east\|west trending Cenozoic faults to the west along the northern edge of the Altyn Tagh range (e.g., the Cenozoic Jianglisai fault near Qiemo), collectively known as the Northern Altyn Tagh fault system (see Cowgill et al., Geology,in press). The lower age bound of the Lapeiquan fault is Ordovician, as the fault cuts Ordovician volcanics and plut

关键词： detachment fault Northern Altyn Tagh Fault Tibet

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