2021 Vol. 27, No. 4

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2021, 27(4): 封三-封三.
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2021, 27(4): 封二-封二.
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Chief Editor’s Address
2021, 27(4): 489-490.
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2021, 27(4): 491-496. doi: 10.12090/j.issn.1006-6616.2021.27.04.044
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Mesozoic tectonic deformation and its rock/ore-control mechanism in the important metallogenic belts in South China
ZHANG Da, LI Fang, HE Xiaolong, HU Bojie, ZHANG Xinming, BI Minfeng, WANG Sen, HUO Hailong, XUE Wei, LIU Songyan
2021, 27(4): 497-528. doi: 10.12090/j.issn.1006-6616.2021.27.04.045
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Since the Mesozoic, the convergence of the Tethys ocean plate and the Paleo-Pacific plate on the South China block has resulted in the multi-sequence tectonic deformation as well as the multi-stage magmatic and metallogenic events, and has formed many important polymetallic metallogenic belts in South China. In this context, mineralization stages, distribution of ore bodies and metallogenic mechanisms of typical skarn deposits in metallogenic areas were sorted out. And then the mineralization processes and genetic mechanisms of typical deposits are completed using the sequence of tectonic deformation and its rock/ore-control regularity. A structural deformation analysis was made on the southwestern Fe polymetallic metallogenic belt, the northeastern Jiangxi Taqian-fuchun W-Cu metallogenic belt and the Laojunshan W-Sn ore concentration area to set up three relatively complete periods of deformation sequence during the Indosinian period, the middle-late Jurassic and the Cretaceous, combined with previous research results; however, the three deformation sequences differ in duration of tectonics, structural property, scale and strength, and deformation style. The analysis of rock-control by tectonics together with the existing isotope chronology data both revealed that the magmatic or metamorphic thermal events were consistent with the deformation sequence occurred in each mineralization zone, and then the multi-stage magmatic events related to the Makeng-type Fe polymetallic deposit, the Zhuxi W-Cu deposit and the Nanyangtian W deposit were clarified using the corresponding laws between deformation sequence and magmatic stage. On this basis, we identified the multi-stage mineralization events and supposed that multi-stage superposition occurred in the mineralization process of all three typical deposits. From the point of view of structural control over the emplacement mechanism of the ore deposit, this paper analyzed the mechanism of the decentralized polymorphic orebody of the Makeng-type deposit, the vertical large-span mineralization and deep giant orebody of the Zhuxi deposit, and the stratiform-vein superposition orebody of the Nanyangtian deposit, which are controlled by the folding detachment of the ore-bearing strata, the large-scale thrust duplex and the two-stage tectonic compounding respectively. The dynamic background of tectonic deformation and magmatic mineralization in the important metallogenic belts of South China at different stages were discussed.
The migration rule of the ore-forming fluids in the Meso-Cenozoic Basins, Southwestern Tianshan, China
JIA Runxing, FANG Weixuan
2021, 27(4): 529-541. doi: 10.12090/j.issn.1006-6616.2021.27.04.046
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The Wulagen pb-zn deposit and the Sareke copper deposit, two most representative strata-bound glutenite deposits in the Meso-Cenozoic Basins in Southwestern Tianshan, are the subjects of our study. The Wulagen pb-zn deposit occurred in the coarse sandy fine conglomerates in the Section 5 of the Lower Cretaceous Kizilsu group(K1kz5) and have underwent weak tectonic reworking in the late period; The Sareke copper deposit occurred in anagenites in the upper section of Upper Jurassic Kuzigongsu formation (J3k2), and the northern part shows obvious tectonic reworking and enrichment mineralization, while the southern part shows discoloration and superposition mineralization after magmatic hydrothermal alteration. In order to study the migration law of ore-forming fluids and magmatic hydrothermal fluids in rocks, the porosity and permeability of the representative rocks dominated by sedimentation, tectonic reworking and magmatic hydrothermal alteration in the two mining areas were measured respectively. The test results show that the rocks in the Wulagen deposit area generally have low porosity and permeability than those in the Sareke deposit; the rocks in the Wulagen lead-zinc deposit and the northern part of the Sareke copper deposit have low porosity and permeability than their footwall rocks; the porosity and permeability of the rocks subjected to magmatic hydrothermal alteration in the southern part of the Sareke copper deposit are obviously lower than those not subjected to magmatic alteration, and the porosity and permeability of the footwall rocks of diabase dike are significantly lower than those of the upper rocks. According to the analysis of rock (ore) fabric, the changes of porosity and permeability after diagenesis and mineralization are closely related to the action of ore-forming fluids or magmatic hydrothermal fluids. In the Meso-Cenozoic strata-bound deposits in the southwestern Tianshan Mountains, rock strata with high porosity and permeability are preferred to be permeated, diffused, filled and metasomatized when ore-forming fluids rise along the cutting layer faults. The larger the gravel diameter is in the rock, the larger the gravel gap is; the greater the hardness of the rock, the easier it is to form structural cracks in the later tectonic deformation, and the more favorable it is for mineralization. This is also the important reason that the metal sulfide particles in the northern part of the Sareke copper deposit are obviously larger than those in the Wulagen lead-zinc deposit. In the process of magma intrusion, the alteration of the footwall quartz sandstone by the magmatic hydrothermal fluids is stronger than that of the hanging wall. The above results indicate that the stronger the mineralization of ore-forming fluids or magmatic hydrothermal fluids are in sedimentary basins, the lower the porosity and permeability of affected rocks will be after diagenesis and mineralization. The porosity and permeability of rocks can indirectly reflect the strength of mineralization and provides a theoretical basis for searching for ore shoots.
Geophysical data interpretation of the tectonic deformation lithofacies belts in the ore field: Application in ore prospecting
ZHANG Baolin, LYU Guxian, YU Jianguo, LIANG Guanghe, XU Xingwang, LI Zhiyuan, ZHANG Qipeng, SHI Xiaoming, WEI Junbin, XU Daoxue, LI Xu, ZHAO Peng
2021, 27(4): 542-556. doi: 10.12090/j.issn.1006-6616.2021.27.04.047
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Based on the physical parameters of the rocks (ores) and the genetic types of ore deposits, the geophysical exploration models have met issues of multiple solutions for deep prospecting prediction. It is necessary to find recognizable geological targets with high precision by geophysical methods. The ore prospecting practice over past years has demonstrated that the ore field tectonic deformation lithofacies belt is an outstanding target and significant prospecting results have been achieved. At present, the geophysical exploration work of large-scale mining area is heavy, while that of medium-scale ore field is limited, and both of them lack the strategic guidance at different levels. In order to establish the geophysical identification mark of the tectonic deformation lithofacies belt in ore field, it is necessary to clarify the complex time-space relationship between geology and geophysics, and strengthen the connection between geomechanics and geophysical exploration methods. In this paper, a method of processing and interpreting geophysical information at different levels is proposed. According to the "✳-shaped" structural features of the tectonic traces in the study area and the characteristics of the periodic development of the tectonic system, the geophysical exploration data of different scales and dimensions are analyzed from the two levels of ore field and deposit, and the information of tectonic deformation lithofacies belts is extracted. The specific operation procedures are as follows: (1) Making an area geophysical exploration within the scope of the ore field, interpreting the "✳-shaped" fault structure system, and then selecting the tensional and tension-torsional ore-bearing fault structures and predicting the prospecting direction; (2) Laying out large-deep geophysical profiles in the ore-bearing fault zone, analyzing the denudation degree and burial depth, and delineating the location of prospecting targets based on the geochemical exploration information. The application results of this method in the Chaihulanzi gold field in Chifeng, Inner Mongolia is introduced. The "✳-shaped" distribution of structural traces of the Neocathaysian tectonic system are interpreted from the geophysical data of the ore field, and then it is confirmed that the NNW and NWW trending tectonic deformation lithofacies belts are the main ore-bearing structural belts and there is a spatio-temporal sequential relationship between them in the two mining areas. These findings, provides a basis for deep ore prospecting and prediction.
On relationship between the superimposed mineralization systems and the zoning patterns of vertical tectonic lithofacies in the Gejiu concentration area of Sn-Cu-W and three rare metals in Yunnan
FANG Weixuan, GUO Yuqian, JIA Runxing, TONG Xiang, MA Zhenfei
2021, 27(4): 557-584. doi: 10.12090/j.issn.1006-6616.2021.27.04.048
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Based on the zoning pattern and the deformation sieving of tectonic lithofacies, as well as the macroscopic and microscopic studies of tectonic lithofacies, the superimposed mineralization systems and the Gejiu ore-concentrated area in Yunnan has been studied. The relationship among the enrichment mechanism of strategic key minerals, the superimposed mineralization, and the pattern of tectonic lithofacies has been uncovered. It was believed that the Triassic arc-back rift basin at the pre-magmatic intrusive stage, the tectonic system of magmatic intrusion at the syn-magmatic intrusive stage, and the karstic tectonic system at the post-magmatic intrusive stage, all of them are of syn-space superimposing lithofacies and mineralizations within different time domains and syn-time lithofacies differentiation. All of them had different controls on the Gejiu superimposed mineral system and Sn-Cu-W-Co-Cs-Rb mineralization. There are 9 vertical tectonic lithofacies zones (VTZs) in different patterns of VTZs around the Gejiu superimposed mineralization system. Firstly, the light-colored granite (VTZ8) and crystal-nucleus lithofacies of magmatic pneumatolytic hydrotherm (VTZ9), being the tectonic lithofacies of syn-magmatic intrusive stage for the biotite granite (γK2a-b-c), was formed at the top and on the edges of the granite intrusion. Secondly, skarn alteration lithofacies to skarn lithofacies (VTZ7) in the magma-contact metasomatic tectonic lithofacies zone is the tectonic lithofacies zone for coupling reaction by the strata and the magmatic system at the syn-magmatic intrusion.Thirdly, on the one hand, cryptoexplosive brecciation of magmatic pneumatolytic hydrotherm enriching in residual magma was forced into the Middle Triassic Gejiu Group, resulted in the magmatic hydrothermal plume and lithofacies zones of tourmaline-hydrothermal cryptoexplosive breccias (VTZ6). On the other hand, the upper part of the fault-fold-type carbonate layer (VTZ4), the marble lithofacies with cataclastic facies and the cataclastic tourmaline-marble lithofacies (VTZ5), and stratiform-like Sn-bearing dolomite with cataclastic facies (VTZ3) in the farthermost-end part, were formed by tectonic hydrothermal coupling derived in the syn-magmatic intrusive stage from the underlying magmatic hydrothermal plume. Fourthly, the alkaline picritic rocks and alkaline volcanicrocks, and their volcanic erupting structure in the Triassic arc-back rift basin were the tectonic lithofacies at the pre-magmatic intrusive stage. Fifthly, the erosion-level in the Yungui plateau (VTZ1) and the supergene karstic tectonic system (VTZ2) were formed in the post-magmatic intrusive stage; however, they (VTZ1, VTZ2) were superimposed on the tectonic system of the syn-magmatic intrusion (VTZ3, VTZ4, VTZ5, VTZ6, VTZ7, VTZ8, VTZ9). The above achievements are foundations of innovated theory for the deep-probe and the modeling prediction for the buried tectonic lithofacies in the area.
A preliminary study on the Mesozoic massive gold metallogenic mechanism of the deep-large fault coupling with critical water in the Jiaodong area, China
HU Baoqun, GAO Haidong, WANG Yun, ZHANG Baolin, LYU Guxian
2021, 27(4): 585-595. doi: 10.12090/j.issn.1006-6616.2021.27.04.049
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This study aims to study the reason why a huge accumulation of gold deposits occurred in the Jiaodong area. We summarized and analyzed the geological background and metallogenic characteristics of the Jiaodong gold deposits. In parallel, we highlighted the importance of depressurization-driven movement of ore-forming materials at two stages and the special properties of critical water (water at the critical value of both temperature and pressure, the same below) based on the theory of water phase change controlling metallogenesis in hydrothermal deposits. The above analysis results allow us to propose the Mesozoic massive gold metallogenic mechanism of deep-large fault coupling with critical water in the Jiaodong area, that is, the metallogenic mechanism of "one cake plus one knife". The old metamorphic rocks provide abundant ore-forming materials. In the early stage, a large-scale point-like depressurization results in acid intrusive complexes and various dykes, which were accompanied by a large amount of critical water over a long time to promote the activation and migration of ore-forming materials; In the late stage, the depressurization of the large linear fault caused the precipitation of ore-forming materials in a short time. The faults with open discontinuous space are dominated by ore-filling structures, while the fracture zones with continuous space are dominated by mineralized alteration with metasomatic structures. Abundant gold in metamorphic rocks, two stages of depressurization with different properties and unique properties of critical water are the main factors for the accumulation of massive gold deposits in the Jiaodong area.
Research progress on the fluid metallogenic mechanism of granitic pegmatite-type rare metal deposits
ZHENG Fanbo, WANG Guoguang, NI Pei
2021, 27(4): 596-613. doi: 10.12090/j.issn.1006-6616.2021.27.04.050
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Strategic rare metals have irreplaceable important use to emerging industry development. Granitic pegmatite is the main source of rare metals, and their fluid characteristics and metallogenic mechanism are hot topics. This paper mainly focuses on fluid properties and metallogenic mechanism of granitic pegmatite-type rare metal deposits. Ore-forming fluids of the granitic pegmatite-type rare metal deposits are generally enriched in volatile (B, P, F and H2O) and ore-forming elements, with low viscosity, low nucleation rate, but strong element solubility and mobility. The ore-forming fluids of the granitic pegmatite-type rare metal deposit were argued to be captured under the condition of high temperature and high pressure, or the temperature of as low as 350℃ under the condition of supercooling. The high crystallization differentiation evolution of granitic magma and the small proportion of crustal material rich in ore-forming elements are the two main mechanisms for the formation of ore-forming granitic pegmatite. Fluid immiscibility and constitutional zone refining are important means for further enrichment of rare metals in the process of magmatic hydrothermal evolution. The largest Jiajika granitic pegmatite-type lithium deposit in China is an ideal laboratory to study this kind of deposit.
Seismogenic, coseismic and postseismic deformation and stress evolution of the 2008 Wenchuan earthquake: Numerical simulation analysis
MENG Qiu, GAO Kuan, CHEN Qizhi, HU Caibo
2021, 27(4): 614-627. doi: 10.12090/j.issn.1006-6616.2021.27.04.051
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The 2008 MS 8.0 Wenchuan earthquake occurred in the Longmenshan fault zone, which has complex geological background, strong surface relief, and heterogeneous elastic-viscous structures; however, the seismic risk of the Longmenshan fault zone was underestimated before the Wenchuan earthquake due to the low seismicity and slight surface tectonic deformation. We established an elastic-viscous finite element model from the perspective of numerical simulation, taking multiple factors into consideration, such as initial topography, gravity, tectonic loading, and viscoelastic relaxation of the middle and lower crusts and the upper mantle. The effects of the mentioned factors on the dynamic process of seismogenic and coseismic deformations of the 2008 Wenchuan earthquake as well as the postseismic deformation in 150 years were analyzed. We quantitively studied the coseismic and postseismic deformations of the Yingxiu-Beichuan fault zone, and summerized the characteristics of stress accumulation, release, and adjustment in both the elastic and viscoelastic layers. The simulation results of the surface coseismic and postseismic displacements showed a good agreement with the geodetic data, and the aftershock distribution of the Wenchuan earthquake was explained in mechanics. The changes in preseismic, coseismic, and postseismic stress were calculated to analyze the dynamic cause of the Wenchuan earthquake and the influence on the seismic risk of surrounding areas.
Mechanism of the strong earthquake triggered by high pressure fluid in reservoir: A case study of the 5.12 Wenchuan earthquake
MAO Xiaoping, HE Liankang, LIU Jialin, LI Suisui, ZHANG Xueqiang, SU Yuchi, LU Pengyu
2021, 27(4): 628-642. doi: 10.12090/j.issn.1006-6616.2021.27.04.052
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At present, the mechanism of earthquake is still based on elastic rebound theory—Earthquake is caused by the release of elastic energy of rock strata due to fault dislocation. But more and more scholars began to question whether the elastic energy after fault faulting can really reach the huge energy released by the actual earthquake. Therefore, it is necessary to study the nature of destructive strong earthquake and its real energy source after the initial movement. According to the characteristics of the reservoir and its pressure in the sedimentary strata, it is concluded that there are a lot of high-pressure fluid in the reservoir, and its pressure can be released under certain conditions, resulting in fluid physical explosion, which may be an important part of strong earthquake energy. The calculation results show that when the fault ruptures and penetrates the reservoir with large area, the elastic energy produced by the pressure release can reach the energy released by the earthquake with magnitude above 8.0; Artificial engineering activities can also lead to the release of small-scale fluid pressure, such as blowout during drilling, earthquake induced by hydraulic fracturing, etc. At the same time, according to the analysis of the waveforms and propagation ray paths of the seismic stations close to the epicenter, it is considered that the strong earthquake wave may not be S-wave, but P-wave. Therefore, it cannot be ruled out that the strong earthquake might be caused by explosion. A large number of direct or indirect evidence, such as the time domain and frequency domain characteristics of seismic waves recorded by several stations during the Wenchuan earthquake, the explosion phenomena observed on the ground, and the cores obtained by scientific drilling after the earthquake, indicate the possibility of the release of this kind of fluid explosion energy. Finally, this paper proposes that the seismicity can be divided into three stages: The stage Ⅰ of micro rupture, in which there is fluid activity and electrokinetic effect, but the initial earthquake motion is not triggered; The stage Ⅱ of fault rupture after the initial earthquake motion; The strong earthquake stage Ⅲ, which is caused by the release of fluid pressure.
Experimental study on the dynamic rupture of coal and rock caused by high-pressure gas
DING Yanlu, YUE Zhongqi
2021, 27(4): 643-651. doi: 10.12090/j.issn.1006-6616.2021.27.04.053
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A special test apparatus has been designed and used to study the effect of high-pressure gas on the deformation and failure of coal and rock. Dynamic ruptures of coal and rock are carried out by gas decompression. The results show that low gas decompression rate only causes deformation of coal specimens slightly while high gas decompression rate leads to fracture and outburst phenomenon. The degree of damage of rocks depends on not only the gas decompression rate but also the gas pressure. Violent fragmentation occurs when gas decompression rate and high saturation pressure reach critical values. According to the relationship between the decompressed gas pressure and strain, the critical gas pressures are determined for the fracture and fragmentation of specimens.
Identifying intergranular pore types by distinguishing between cementation and dissolution of dotted calcite: A case study of the Xinhe Formation sandstones in the Yabrai Basin, China
WANG Jianguo, ZHOU Xiaofeng, TANG Haizhong, WEI Jun, HAN Xiaosong, GUO Wei
2021, 27(4): 652-661. doi: 10.12090/j.issn.1006-6616.2021.27.04.054
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There is still no consensus among researchers about whether intergranular pores in oil-bearing sandstone are primary pores or secondary pores. Distinguishing between cementation and dissolution of dotted calcite can effectively identify intergranular pore types. In this paper, taking the diagenetic environment evolution and diagenesis sequence as the thread, we carefully observed the casting slices from the Xinhe Formation sandstones in the Yabrai Basin and finely dissected the microphenomenon by focusing on the calcite cements in its relation between the origins of substance and dissolution fluids and the occurrence mode. The genesis of the dotted calcite was clarified thus, and then the intergranular pore types and reservoir space types in the sandstones were identified. The study results show that the dotted calcite in the intergranular pore is the dissolution residue of the disseminated calcite formed in the early diagenetic stage, and the dissolution type is the consistent dissolution. The dissolution fluid, organic acid fluid formed during the middle diagenetic stage, caused the secondary pores. Therefore, it is concluded that the reservoir space in the Xinhe Formation sandstones in the Yabrai Basin consists of the secondary intergranular pores and the secondary intragranular pores such as dissolution pores of cements of feldspar, lithoclast, lithoclast.
Seismogenic fault and it's rupture characteristics of the 21 May, 2021 Yangbi MS 6.4 earthquake: Analysis results from the relocation of the earthquake sequence
WANG Guangming, WU Zhonghai, PENG Guanling, LIU Zifeng, LUO Ruijie, HUANG Xiaolong, CHEN Haopeng
2021, 27(4): 662-678. doi: 10.12090/j.issn.1006-6616.2021.27.04.055
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According to China Earthquake Network Center (CENC), the MS 6.4 Yangbi earthquake struck northwestern Yunnan Province on 21 May, 2021 at 21:48(Beijing time). Figuring out the seismogenic fault and source rupture characteristics in time can provide a key basis for understanding the dynamic conditions in this region and estimating the risk of strong earthquakes in the future. We employed the double-difference relocation algorithm to relocate the Yangbi earthquake sequence, and obtained precise locations of 3, 863 earthquakes. In general, the result revealed a narrow 25-km-long, linear southeast seismicity trend concentrated in the 2~14 km depth range, and the orientation is 135°. The MS 6.4 mainshock located at (25.688°N, 99.877°E) after relocation, and the focal depth is 9.6 km. Based on the results of precise locations and focal mechanism solutions, the seismogenic fault might be a NW dextral strike-slip fault with southwest dip, and the dip angle tends to gradually decrease from NW to SE. The Yangbi earthquake sequence belongs to the "foreshock-mainshock-aftershock" type, revealed by the temporal and spatial evolution process of the earthquake sequence, and the fracture process mainly includes three stages: fracture nucleation stage, mainshock rupture stage, and tension rupture stage. In the first stage, small-scale fractures occurred at the relatively weak part of the seismogenic fault at the depth between 10~12 km, after two-days' nucleation, the fault entered into an unstably accelerated rupture state, resulting in the MS 5.6 foreshock. Under the joint influence of continuous loading of tectonic stress and surrounding small-scale fractures, the higher strength blocking area in the shallow part of the fault ruptured, and the MS 6.4 mainshock occurred. The tension rupture mainly occurred at the southeast end of the seimogenic fault. A horsetail splay with normal fault features was formed at the southeast end of the aftershock sequence, started by the largest aftershock of MS 5.2. In addition, the mainshock triggered small-scale fractures on a NEN sinistral strike-slip fault near the source area. The comprehensive study shows that the seismogenic fault of the Yangbi earthquake is not the well-known Weixi-Qiaohou fault, but the Caoping fault in the Lanping-Simao block. The Yangbi MS 6.4 mainshock is the result of the dextral strike-slip motion of the Caoping fault, which has been revived under the NWN-SES regional principal compressive stress, and the fault has obviously new fracture characteristics. This study indicates that the continuous southeastward extrusion of material from the Tibetan Plateau is leading to the reconnection and reactivation of the old faults in the junction zone between the eastern Lanping-Simao block and the Lijiang-Dali fault system, resulting in relatively frequent moderate-to-strong earthquakes in this area. Therefore, the reactivation of old faults and the generation of new faults in the southwestern boundary zone of Sichuan-Yunnan block are worthy to pay attention on the risk estimation and evaluation of regional moderate-to-strong earthquakes. We suggest that more attention should be paid to the possibility of further southern or northern migration (or expansion) of moderate-to-strong earthquakes.
The strong activities of the Namula fault zone in the eastern Himalayan syntaxis since Pliocene, constraints from thermochronological data
TU Jiyao, JI Jianqing, ZHONG Dalai, SUN Dongxia, ZHOU Jing
2021, 27(4): 679-690. doi: 10.12090/j.issn.1006-6616.2021.27.04.056
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To reveal the strong activities of the Namula fault zone in the eastern Himalayan syntaxis since Pliocene, this paper reports biotite 40Ar/39Ar and apatite fission track ages of 3 rock samples from the Namula fault zone, and quantitatively interpret these ages and the published ages from the adjacent areas, using a modeling code "Pecube". Biotite 40Ar/39Ar ages range from 4.44±0.71 Ma to 3.45±0.24 Ma, and apatite fission track ages range from 3.7±0.4 Ma to 1.8±0.2 Ma. The ages and simulation results show that, prior to ~3 Ma the highest exhumation rate had been located in the south of the Namula fault zone and was about 2.5 km/Ma, and the Namula fault zone had a motion feature of normal fault; Since ~3 Ma the highest exhumation rate have been located in the north of the Namula fault zone and was about 1.3 km/Ma, and the Namula fault zone had a motion feature of thrust fault. The evolution of the Namula fault zone's motion, probably have resulted from the south to north migration of the fast crust exhumation area in the eastern Himalayan syntaxis since ~8 Ma.