2018 Vol. 43, No. S2
Display Method:
2018, (S2): 1-15.
doi: 10.3799/dqkx.2018.572
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Abstract:
As a record of the process for expansion of the back-arc basin, the Xieyuanling diabase dyke swarms and the Yangling tuffs found interlayer in the flyschoids of Luojiamen Formation along the two sides of the Suzhuang-Shizhu fault in Kaihua area, western Zhejiang, and which is the eastern segment of Jiangnan orogeny. The U-Pb dating of zircon yields a lower limit age of 828.2±8.7 Ma for the Xieyuanling diabase,and another age of 830.9±4.9 Ma for the Yangling tuffs. Geochemical analysis indicates that the diabases have high Al2O3 (15.82%–17.09%), low TiO2 (0.64%–1.37%) and poor K2O (0.01%–0.04%). In the chondrite- and primitive mantle-normalized trace element diagram, all diabase samples show flat patterns,with (La/Yb)N=1.02–1.78 and (Ce/Yb)N=0.93–1.72, shows the similar characteristics of MORB or BABB. And they also enriched in Sr, Ba, Th and Pb, with Nb/U=11.67–28.17, La/Nb=1.21–2.02, Th/Ta=1.79–2.86, that indicate the formation process of diabase must have been contaminated by weak crustal materials. Therefore, a spreading of back-arc basin occurred with the paleo-South-China plate northwestwardly subducted in Neoproterozoic, it suggested the Shuangxiwu island arc rifted from the Yangtze block simultaneously, and the Yangtze block had not collided with the Cathaysia block at least at ca. 828 Ma or later.
As a record of the process for expansion of the back-arc basin, the Xieyuanling diabase dyke swarms and the Yangling tuffs found interlayer in the flyschoids of Luojiamen Formation along the two sides of the Suzhuang-Shizhu fault in Kaihua area, western Zhejiang, and which is the eastern segment of Jiangnan orogeny. The U-Pb dating of zircon yields a lower limit age of 828.2±8.7 Ma for the Xieyuanling diabase,and another age of 830.9±4.9 Ma for the Yangling tuffs. Geochemical analysis indicates that the diabases have high Al2O3 (15.82%–17.09%), low TiO2 (0.64%–1.37%) and poor K2O (0.01%–0.04%). In the chondrite- and primitive mantle-normalized trace element diagram, all diabase samples show flat patterns,with (La/Yb)N=1.02–1.78 and (Ce/Yb)N=0.93–1.72, shows the similar characteristics of MORB or BABB. And they also enriched in Sr, Ba, Th and Pb, with Nb/U=11.67–28.17, La/Nb=1.21–2.02, Th/Ta=1.79–2.86, that indicate the formation process of diabase must have been contaminated by weak crustal materials. Therefore, a spreading of back-arc basin occurred with the paleo-South-China plate northwestwardly subducted in Neoproterozoic, it suggested the Shuangxiwu island arc rifted from the Yangtze block simultaneously, and the Yangtze block had not collided with the Cathaysia block at least at ca. 828 Ma or later.
2018, (S2): 16-32.
doi: 10.3799/dqkx.2018.110
Abstract:
Neoproterozoic magmatic rocks, which extensively developed in the Northwest Zhejiang Province of the eastern Jiangnan orogen, are the key for discussing the pattern and evolution of the Jiangnan orogen. Although they have a great deal of research, their petrogenesis and tectonic setting remain ambiguous. In this paper, a set of basic-ultrabasic rocks from Qingdingshan area, Zhuji, Zhejiang Province are selected as objects, and detailed zircon chronology,Hf isotopic composition and geochemistry of rocks are studied. Zircon LA-ICP-MS U-Pb dating of Qingdingshan basic-ultrabasic rocks shows that these rocks were formed at 860 Maapproximately. The zirconε Hf(t ) values are 9.7 and 9.5, respectively. According to the geochemical characteristics of rocks, Qingdingshan basic-ultrabasic rocks are divided into two types: “low Al and high Mg” and “high Al and low Mg”. The former rocks are characterized by high TiO2, MgO, Fe2O3T, low Al2O3, rich in Cr-Ni and low Sr/Y value, while the latter is characterized by low TiO2, MgO, Fe2O3T, high Al2O3, poor Cr-Ni and high Sr/Y value. The geochemical characteristics and zircon Hf isotopic composition indicate that the Qingdingshan basic-ultrabasic rocks were formed in the oceanic island arc environment, and their genesis may be related to the subduction of the oceanic plate and the mantle wedge metasomatism at different depths. Based on the previous research results, the tectonic framework of the Neoproterozoic multi-arc-basin system in the eastern Jiangnan orogen has been preliminarily constructed for the “Longmenshan intraoceanic arc (1 172－840 Ma)-Anhui-Jiangxiinter-arcbasin (1 061－827 Ma)-Wannian continental margin arc (～840 Ma)-Jiangxi-Hunan back-arc basin (820－830 Ma)”. It provides a new perspective for the study of Jiangnan orogen.
Neoproterozoic magmatic rocks, which extensively developed in the Northwest Zhejiang Province of the eastern Jiangnan orogen, are the key for discussing the pattern and evolution of the Jiangnan orogen. Although they have a great deal of research, their petrogenesis and tectonic setting remain ambiguous. In this paper, a set of basic-ultrabasic rocks from Qingdingshan area, Zhuji, Zhejiang Province are selected as objects, and detailed zircon chronology,Hf isotopic composition and geochemistry of rocks are studied. Zircon LA-ICP-MS U-Pb dating of Qingdingshan basic-ultrabasic rocks shows that these rocks were formed at 860 Maapproximately. The zircon
2018, (S2): 33-48.
doi: 10.3799/dqkx.2018.131
Abstract:
The Baiyinwula area is located in the west segment of the Xing’an-Mongolia orogenic belt, the southeast margin of the Central Asian orogenic belt. Although voluminous Paleozoic magmas have been reported in this area, their activity sequences and tectonic settings are still in debate. According to the field relationships, the sequences of magmas in the study area are set up in this paper: breccia-bearing rhyolitic ignimbrite + grey phenocryst-poor rhyolite (wall rock)→ green-grey phenocryst-rich rhyolite→ brick-red rhyolite porphyry→alkaline granite. LA-ICP-MS zircon U-Pb dating reveals that the breccia-bearing rhyolitic ignimbrite contains two group ages of 312.2±2.8 Ma (n =5，MSWD=0.098) and 293±2 Ma (n =10，MSWD=0.95). The green-grey phenocryst-rich rhyolite and brick-red rhyolite porphyry were emplaced at 296±2 Ma (n =21, MSWD=1.4) and 294±2 Ma (n =18, MSWD=0.2), respectively, slightly older than the age of alkaline granite (290~285 Ma). As a result, the magmatism exposed regionally can be recognized with three episodes of ca. 311 Ma, 297 Ma, and 291 Ma respectively. Geochemically, the grey phenocryst-poor rhyolite and green-grey phenocryst-rich rhyolite are characterized by potassic calc-alkaline series.In contrast, the brick-red rhyolite porphyry and alkaline granite are sodic alkaline-peralkaline series. Those volcanic-intrusive rocks exhibit an evolution trend from calc-alkaline to alkaline-peralkaline, which are highly consistent with that of the magmatism in the northern magmatic belt of the Erenhot-Hegenshan area, and those of the post-collisional magmatism in the typical orogenic belts. Accordingly, it is proposed that the Late Carboniferous-Early Permian magmatic rocks in the northern magmatic belt of the Erenhot-Hegenshan area were formed in a post-collisional tectonic setting.
The Baiyinwula area is located in the west segment of the Xing’an-Mongolia orogenic belt, the southeast margin of the Central Asian orogenic belt. Although voluminous Paleozoic magmas have been reported in this area, their activity sequences and tectonic settings are still in debate. According to the field relationships, the sequences of magmas in the study area are set up in this paper: breccia-bearing rhyolitic ignimbrite + grey phenocryst-poor rhyolite (wall rock)→ green-grey phenocryst-rich rhyolite→ brick-red rhyolite porphyry→alkaline granite. LA-ICP-MS zircon U-Pb dating reveals that the breccia-bearing rhyolitic ignimbrite contains two group ages of 312.2±2.8 Ma (
2018, (S2): 49-59.
doi: 10.3799/dqkx.2018.202
Abstract:
Petrology, geochemical data and LA-ICP-MS zircon U-Pb dating have been obtained from the Xiaoheishan monzogranite and quartz diorite, with the aim of constraining the tectonic nature of the Beishan area. LA-ICP-MS zircon U-Pb age data indicate that the monzonite granite was formed during Middle Ordovician and the quartz diorite was emplaced during Early Silurian. Furthermore, the monzonite granite belong to high-K cal-alkaline, metaluminous-weakly peraluminous with features of rich SiO2 and Al2O3. They also show strong enrichment in LREEs and Rb, K, Th, U, depletion in HREEs and HFSEs (Nb, Ta, Ti). The quartz diorite belongs to cal-alkaline with metaluminous characteristics. In addition, they invariably exhibit relatively gentle light rare earth elements (LREE) enrichment with flat heavy rare earth elements (HREE) and weak negative Eu anomalies (δ Eu=0.69-0.92) in the chondrite-normalized REE patterns, depletion of Nb, Ta, P, Sr, Ti and enrichment of Rb, K. Based on the regional geology, the above characteristics reflect that the monzonite granite was formed under the tectonic setting of syn-collision, while the quartz diorite volcanic arc after collisional. This implies that the ocean basin represented by Hongliuhe-Niujuanzi-Xichangjing ophiolite mélange belt disappeared during 436.1-461.5 Ma.
Petrology, geochemical data and LA-ICP-MS zircon U-Pb dating have been obtained from the Xiaoheishan monzogranite and quartz diorite, with the aim of constraining the tectonic nature of the Beishan area. LA-ICP-MS zircon U-Pb age data indicate that the monzonite granite was formed during Middle Ordovician and the quartz diorite was emplaced during Early Silurian. Furthermore, the monzonite granite belong to high-K cal-alkaline, metaluminous-weakly peraluminous with features of rich SiO2 and Al2O3. They also show strong enrichment in LREEs and Rb, K, Th, U, depletion in HREEs and HFSEs (Nb, Ta, Ti). The quartz diorite belongs to cal-alkaline with metaluminous characteristics. In addition, they invariably exhibit relatively gentle light rare earth elements (LREE) enrichment with flat heavy rare earth elements (HREE) and weak negative Eu anomalies (
2018, (S2): 60-80.
doi: 10.3799/dqkx.2018.326
Abstract:
Aketenglongshan monzonitic granite is located in the south margin of South Altyn. Here we present whole-rock geochemistry, zircon U-Pb geochronology and Hf isotope analysis to study the petrogenesis and magmatic evolution of the granite, which belong to high-K calc-alkaline, weakly peraluminous series and I-type granite. The geochemical characteristics show strongly fractionation of the REEs, and enrichment in LREE, while depletion in HREE. It is infered that amphibole, apatite and rutile fractionation occurred during the magmatic evolution. The zircon U-Pb age of the granite is 435–449 Ma, representing the crystallization age of the granite. The half negative and half positive value of zirconε Hf(t ) indicates that the origin of the monzonitic granite is mixture of juvenile and ancient crust materials, and the granites were derived from the partially melted juvenile crust, and mixed with ancient crust materials during the upwelling, or derived from the partially melted mixture of juvenile and ancient crust materials, in extensional environment transformed from compressional environment after the break off of the subducted oceanic crust.
Aketenglongshan monzonitic granite is located in the south margin of South Altyn. Here we present whole-rock geochemistry, zircon U-Pb geochronology and Hf isotope analysis to study the petrogenesis and magmatic evolution of the granite, which belong to high-K calc-alkaline, weakly peraluminous series and I-type granite. The geochemical characteristics show strongly fractionation of the REEs, and enrichment in LREE, while depletion in HREE. It is infered that amphibole, apatite and rutile fractionation occurred during the magmatic evolution. The zircon U-Pb age of the granite is 435–449 Ma, representing the crystallization age of the granite. The half negative and half positive value of zircon
2018, (S2): 81-102.
doi: 10.3799/dqkx.2018.316
Abstract:
This study presents the granites from the Shahewan and Caoping plutons in South Qinling area, including their geochemical, geochronological, and zircon Lu-Hf isotopic compositions. Based on the geochemical analyses, the two plutons exhibit high alkali and MgO contents and belong to metaluminous I-type granite of high-K calc-alkaline series. The samples show evident fractionation of light rare earth elements (LREE) and heavy rare earth elements (HREE), as the samples are enriched in LREE and large ion lithophile elements (LILE, e.g. Rb, Ba and Sr) and relatively depleted in HREE and high-field-strength elements (HFSE, e.g., Nb, Ta, Ti, Y, and Yb). Most of the samples exhibit slightly or no positive Euanomalies except for one sample showing moderate negative anomaly. LA-ICP-MS U-Pb zircon age analyses indicate that the magmatic crystallization age of the Shahewan pluton is 214-207 Ma while the Caoping pluton is 215-212 Ma. Zircon Hf isotopic analyses show that the εHf(t) values are between -1.38 and +1.81 and the two-stage model ages (tDM2) are 1.30-1.11 Ga for the Shahewan pluton. Correspondingly, the εHf(t) values are -1.0 to +3.1 and tDM2 values of 1.29-1.03 Ga for the Caoping pluton. Nearly all the samples in the Shahewan and Caoping plutons display similar characteristics of petrology, geochronology, geochemistry and zircon Lu-Hf isotopes, indicating homologous evolution. It is concluded that the parental magma of the two plutons is a mixture of Mesoproterozoic crust and mantle and the plutons formed during the extensional delamination stage of the post-collisional stage. The Mianlue Ocean closed completely before the Late Triassic, at which time the collisional orogeny between the Yangtze and North China Blocks was in the late stage.
This study presents the granites from the Shahewan and Caoping plutons in South Qinling area, including their geochemical, geochronological, and zircon Lu-Hf isotopic compositions. Based on the geochemical analyses, the two plutons exhibit high alkali and MgO contents and belong to metaluminous I-type granite of high-K calc-alkaline series. The samples show evident fractionation of light rare earth elements (LREE) and heavy rare earth elements (HREE), as the samples are enriched in LREE and large ion lithophile elements (LILE, e.g. Rb, Ba and Sr) and relatively depleted in HREE and high-field-strength elements (HFSE, e.g., Nb, Ta, Ti, Y, and Yb). Most of the samples exhibit slightly or no positive Euanomalies except for one sample showing moderate negative anomaly. LA-ICP-MS U-Pb zircon age analyses indicate that the magmatic crystallization age of the Shahewan pluton is 214-207 Ma while the Caoping pluton is 215-212 Ma. Zircon Hf isotopic analyses show that the εHf(t) values are between -1.38 and +1.81 and the two-stage model ages (tDM2) are 1.30-1.11 Ga for the Shahewan pluton. Correspondingly, the εHf(t) values are -1.0 to +3.1 and tDM2 values of 1.29-1.03 Ga for the Caoping pluton. Nearly all the samples in the Shahewan and Caoping plutons display similar characteristics of petrology, geochronology, geochemistry and zircon Lu-Hf isotopes, indicating homologous evolution. It is concluded that the parental magma of the two plutons is a mixture of Mesoproterozoic crust and mantle and the plutons formed during the extensional delamination stage of the post-collisional stage. The Mianlue Ocean closed completely before the Late Triassic, at which time the collisional orogeny between the Yangtze and North China Blocks was in the late stage.
2018, (S2): 103-118.
doi: 10.3799/dqkx.2018.550
Abstract:
Lithospheric thermal structure is an integrated reflection of heat producing elements, deep thermal state and tectonic-thermal activities, and it also has a significant impact on the evolution of the lithosphere. Based on the correlativity between temperature and seismic wave velocity of deep rocks, we derived the uppermost mantle temperature distributions and thermal lithosphere thickness beneath the Junggar basin and its surroundings at the depths ranging from 75 to 250 km by the seismic tomography imaging model S2.9EA in this study. Utilizing the inverted temperature distribution at 75 km depth as the bottom boundary constraint and the surface temperature as the top boundary constraint, we calculated the crustal temperature structure and surface heat flow variations according to the one-dimensional steady heat conduction equation. A good agreement is found between the surface heat flow variations by the model prediction and the field measurements, which shows the reliability of the method and the calculated results in this study. The results show that lithospheric thermal structure in Junggar basin and its surroundings presents obvious lateral and vertical inhomogeneity, and the thermal structure distribution in shallow layer is consistent with the basin-mountain tectonic features and it has the trait of interchange with the temperature distribution below 150 km depth. Based on the spatial distribution characteristics of high and low temperature abnormal bodies in the upper mantle of study area, the thermal structure features of basins, contact relationships between basins and mountains, lithospheric delamination of Tianshan orogenic belt, tectonic thermal evolution process of basins and mountains, and the remote influence of India-Tibetan plateau collision on the lithospheric upper mantle thermal structure are synthetically analyzed, respectively, which further provide useful reference and information for the geotectonic and deep dynamic analysis of the study area.
Lithospheric thermal structure is an integrated reflection of heat producing elements, deep thermal state and tectonic-thermal activities, and it also has a significant impact on the evolution of the lithosphere. Based on the correlativity between temperature and seismic wave velocity of deep rocks, we derived the uppermost mantle temperature distributions and thermal lithosphere thickness beneath the Junggar basin and its surroundings at the depths ranging from 75 to 250 km by the seismic tomography imaging model S2.9EA in this study. Utilizing the inverted temperature distribution at 75 km depth as the bottom boundary constraint and the surface temperature as the top boundary constraint, we calculated the crustal temperature structure and surface heat flow variations according to the one-dimensional steady heat conduction equation. A good agreement is found between the surface heat flow variations by the model prediction and the field measurements, which shows the reliability of the method and the calculated results in this study. The results show that lithospheric thermal structure in Junggar basin and its surroundings presents obvious lateral and vertical inhomogeneity, and the thermal structure distribution in shallow layer is consistent with the basin-mountain tectonic features and it has the trait of interchange with the temperature distribution below 150 km depth. Based on the spatial distribution characteristics of high and low temperature abnormal bodies in the upper mantle of study area, the thermal structure features of basins, contact relationships between basins and mountains, lithospheric delamination of Tianshan orogenic belt, tectonic thermal evolution process of basins and mountains, and the remote influence of India-Tibetan plateau collision on the lithospheric upper mantle thermal structure are synthetically analyzed, respectively, which further provide useful reference and information for the geotectonic and deep dynamic analysis of the study area.
2018, (S2): 119-134.
doi: 10.3799/dqkx.2018.108
Abstract:
Jiajika super large lithium deposit is one of the most important lithium resources in China. The two-mica granite located in the southern of ore field is always regarded as mother rock of pegmatites. Systematical mineralogy study of the granite can not only provide basic data for mechanism of rare metals, but also has important meaning to the potential mineralization of rare metals. Based on systematical field work, the major and trace element compositions of micas from Jiajika two-mica granite were obtained by electron microprobe analysis (EMPA) and laser ablation plasma mass spectrometry (LA-ICP-MS), showing that the biotites are magmatic biotites. The biotites are extremely rich in Al and Fe, but poor in Mg. The biotites from Jiajika two-mica granite belong to siderophyllites (but close to protolithionite). Although muscovites from Jiajika two-mica granite show metasomatic reaction with biotites, they should still be regarded as magmatic muscovites after combining macroscopic characteristics of petrology, characteristics of chemistry and characteristics of petrographic. Muscovites are extremely rich in Al, poor in Fe and Mg. The muscovites from Jiajika two-mica granite belong to pure muscovites. According to test data, we make use of total-aluminium geobarmeter and titanium content geothermometry to calculate pressure and temperature of rock formation. The results show that the emplacement pressure varies from 430 MPa to 560 MPa, with the average pressure of 480 MPa；the crystallization temperature varies from 480 ℃ to 550 ℃, with the average temperature of 520 ℃. The calculated result of Si geobarmeter of muscovite is almost the same with that of biotite. In addition, according to the chemical composition of biotite, the oxygen fugacity of magma-hydrothermal system ranges from 10−17 to 10−18. The results also show that the oxygen fugacity increases from south to north. The study of major and trace elements composition of micas from Jiajika two-mica granite shows that rare metal elements are mainly hosted in micas. The content of rare metal elements in biotites is the highest. The geochemical analysis of biotites also shows that Jiajika two-mica granite belong to peraluminum S-type granite, and its formation is mainly related to the crustal magma. From the above, the study of composition of micas from two-mica granite suggests that the granite was formed in high pressure and oxygen-free environment. It provides significant instructions to prospecting of rare metals in Jiajika orefield.
Jiajika super large lithium deposit is one of the most important lithium resources in China. The two-mica granite located in the southern of ore field is always regarded as mother rock of pegmatites. Systematical mineralogy study of the granite can not only provide basic data for mechanism of rare metals, but also has important meaning to the potential mineralization of rare metals. Based on systematical field work, the major and trace element compositions of micas from Jiajika two-mica granite were obtained by electron microprobe analysis (EMPA) and laser ablation plasma mass spectrometry (LA-ICP-MS), showing that the biotites are magmatic biotites. The biotites are extremely rich in Al and Fe, but poor in Mg. The biotites from Jiajika two-mica granite belong to siderophyllites (but close to protolithionite). Although muscovites from Jiajika two-mica granite show metasomatic reaction with biotites, they should still be regarded as magmatic muscovites after combining macroscopic characteristics of petrology, characteristics of chemistry and characteristics of petrographic. Muscovites are extremely rich in Al, poor in Fe and Mg. The muscovites from Jiajika two-mica granite belong to pure muscovites. According to test data, we make use of total-aluminium geobarmeter and titanium content geothermometry to calculate pressure and temperature of rock formation. The results show that the emplacement pressure varies from 430 MPa to 560 MPa, with the average pressure of 480 MPa；the crystallization temperature varies from 480 ℃ to 550 ℃, with the average temperature of 520 ℃. The calculated result of Si geobarmeter of muscovite is almost the same with that of biotite. In addition, according to the chemical composition of biotite, the oxygen fugacity of magma-hydrothermal system ranges from 10−17 to 10−18. The results also show that the oxygen fugacity increases from south to north. The study of major and trace elements composition of micas from Jiajika two-mica granite shows that rare metal elements are mainly hosted in micas. The content of rare metal elements in biotites is the highest. The geochemical analysis of biotites also shows that Jiajika two-mica granite belong to peraluminum S-type granite, and its formation is mainly related to the crustal magma. From the above, the study of composition of micas from two-mica granite suggests that the granite was formed in high pressure and oxygen-free environment. It provides significant instructions to prospecting of rare metals in Jiajika orefield.
2018, (S2): 135-148.
doi: 10.3799/dqkx.2018.194
Abstract:
Yuanlingzhai porphyry Mo deposit is a newly discovered Mo-only deposit in the Nanling region. The Mo reserve in this deposit is estimated as 200 000 t. The mineralization developed in contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation.In this paper, we present a detailed research on fluid inclusions and stable isotope of the deposit reveals the characteristics of ore-forming fluids and mineralization. Research on fluid inclusions in quartz veins shows that they are distributed in groups, scattered random distribution or uniform distribution with long axes of 4–15 μm. The morphology of inclusions are mainly negative crystal, elliptical shape, elongated shape and irregular shape. The types of fluid inclusions include pure liquid, pure gas, two phase, three-phase inclusions containing liquid CO2, and multi-phase inclusions with daughterminerals. The liquid components of fluid inclusions are mainly Na+, Ca+, Cl−and SO42− and the gas components are mainly H2O, CO2, H2 implying that the ore-forming fluid belongs to CO2-H2O-NaCl(CaCl2) system with strong reducibility.The homogenization temperatures of the fluid inclusions vary remarkably from 170 to 350oC with an average of 257 oC. The NaCleq salinities of fluids range from 1.40% to 12.97% with an average of 6.236%. The fluid density ranges from 0.687 g/cm3 to 0.973 g/cm3with an average of 0.848 g/cm3. Therefore, the ore-forming fluid is characterized by medium to high temperature, medium to low salinity, and low density with depleted F enriched Cl. Besides, the fluid rich in Cu, Mo, Sb, Bi, etc. medium to high temperature ore-forming metallic elements, relatively rich in Co, Ni, suggests some connection with deep or mantle fluid.Theδ DV-SMOW value of the fluid inclusion in ore-forming stages ranges from −50.2‰ to −43.5‰, and δ OH2O value ranges from 2.69‰ to 5.69‰, which is the result of magmatic water and meteoric water mixing action. The δ 34S value of metal sulfide in ores ranges from −1.5‰ to 1.6‰, showing that ore-forming materials may have been derived from the deep. Fluid immiscibility (decompression boiling) and mixing of different fluids may be the main ore-forming mechanism of Yuanlingzhai Mo deposit.
Yuanlingzhai porphyry Mo deposit is a newly discovered Mo-only deposit in the Nanling region. The Mo reserve in this deposit is estimated as 200 000 t. The mineralization developed in contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation.In this paper, we present a detailed research on fluid inclusions and stable isotope of the deposit reveals the characteristics of ore-forming fluids and mineralization. Research on fluid inclusions in quartz veins shows that they are distributed in groups, scattered random distribution or uniform distribution with long axes of 4–15 μm. The morphology of inclusions are mainly negative crystal, elliptical shape, elongated shape and irregular shape. The types of fluid inclusions include pure liquid, pure gas, two phase, three-phase inclusions containing liquid CO2, and multi-phase inclusions with daughterminerals. The liquid components of fluid inclusions are mainly Na+, Ca+, Cl−and SO42− and the gas components are mainly H2O, CO2, H2 implying that the ore-forming fluid belongs to CO2-H2O-NaCl(CaCl2) system with strong reducibility.The homogenization temperatures of the fluid inclusions vary remarkably from 170 to 350oC with an average of 257 oC. The NaCleq salinities of fluids range from 1.40% to 12.97% with an average of 6.236%. The fluid density ranges from 0.687 g/cm3 to 0.973 g/cm3with an average of 0.848 g/cm3. Therefore, the ore-forming fluid is characterized by medium to high temperature, medium to low salinity, and low density with depleted F enriched Cl. Besides, the fluid rich in Cu, Mo, Sb, Bi, etc. medium to high temperature ore-forming metallic elements, relatively rich in Co, Ni, suggests some connection with deep or mantle fluid.The
2018, (S2): 149-161.
doi: 10.3799/dqkx.2018.115
Abstract:
Carbonate cements from sandstone-hosted uranium deposits have generally been considered as a tracer for ore-forming fluids. However, it is difficult to confirm whether carbonate cements occurred in the ore-forming period of the sandstone-hosted uranium deposits since they generally have characteristics of variable minerals and multiple depositional and diagenetic stages. The purpose of this study is to characterize the mineral species, occurrence, generation of the carbonate cements in the Qianjiadian uranium deposit, southern Songliao basin, based on a series of approaches such as core description, micropolariscope and scanning electron microscope (SEM). According to these data in combination with the spatial allocation of carbonate cements and uranium ore bodies, relationship between carbonate cementation and uranium mineralization are revealed. The key conclusions are summarized as follows: (1) Carbonate cements in the Qianjiadian uranium deposit are primarily composed of dolomite, siderite, ankerite and calcite. The dolomite cements with crystalline granular texture and contact cementation have the highest average content in the partial oxidation zone. Siderite cements with a large quantity of residual euhedral crystals often show as contact cementation, which have the highest average content in the reduction zone. Ankerite cements with mosaic granular structure generally present contact cementation and porous cementation. The average content of ankerite is the highest in the transition zone. Calcite cements with porous cementation and contact cementation mainly have mosaic granular texture, which have the highest average content in the weak oxidation zone. (2) The dolomite, siderite, ankerite and calcite are successively generated from early to late stages. Four evidences have been found in the thin sections. Firstly, the siderite and ankerite cements are included by the calcite. Secondly, the siderite is included by the ankerite. Thirdly, the dolomite is coated with ankerite. Finally, the dissolved pores of dolomite are filled by siderites. (3) It can be inferred that the siderite was formed during the diagenetic stage, and the dolomite may have occurred in penecontemporaneous or early diagenesis stages. It can be concluded that ankerite is associated with uranium mineralization. The calcite may have occurred after the metallogenic period. Therefore, the ankerite of carbonate cements is closely related to uranium mineralization in the Qianjiadian uranium deposit.
Carbonate cements from sandstone-hosted uranium deposits have generally been considered as a tracer for ore-forming fluids. However, it is difficult to confirm whether carbonate cements occurred in the ore-forming period of the sandstone-hosted uranium deposits since they generally have characteristics of variable minerals and multiple depositional and diagenetic stages. The purpose of this study is to characterize the mineral species, occurrence, generation of the carbonate cements in the Qianjiadian uranium deposit, southern Songliao basin, based on a series of approaches such as core description, micropolariscope and scanning electron microscope (SEM). According to these data in combination with the spatial allocation of carbonate cements and uranium ore bodies, relationship between carbonate cementation and uranium mineralization are revealed. The key conclusions are summarized as follows: (1) Carbonate cements in the Qianjiadian uranium deposit are primarily composed of dolomite, siderite, ankerite and calcite. The dolomite cements with crystalline granular texture and contact cementation have the highest average content in the partial oxidation zone. Siderite cements with a large quantity of residual euhedral crystals often show as contact cementation, which have the highest average content in the reduction zone. Ankerite cements with mosaic granular structure generally present contact cementation and porous cementation. The average content of ankerite is the highest in the transition zone. Calcite cements with porous cementation and contact cementation mainly have mosaic granular texture, which have the highest average content in the weak oxidation zone. (2) The dolomite, siderite, ankerite and calcite are successively generated from early to late stages. Four evidences have been found in the thin sections. Firstly, the siderite and ankerite cements are included by the calcite. Secondly, the siderite is included by the ankerite. Thirdly, the dolomite is coated with ankerite. Finally, the dissolved pores of dolomite are filled by siderites. (3) It can be inferred that the siderite was formed during the diagenetic stage, and the dolomite may have occurred in penecontemporaneous or early diagenesis stages. It can be concluded that ankerite is associated with uranium mineralization. The calcite may have occurred after the metallogenic period. Therefore, the ankerite of carbonate cements is closely related to uranium mineralization in the Qianjiadian uranium deposit.
2018, (S2): 162-178.
doi: 10.3799/dqkx.2018.196
Abstract:
The hadal zone (e.g. trench) is characterized by its unique V-shaped geological structure, hydrodynamic environment and material and energy circulation system, has relatively higher deposition flux and burial efficiency of biogenic elements (e.g.carbon) compared with other ocean environments. As the window and channel connecting the deep biosphere and the ocean, this unique area is the tremendous trapper of marine primary production and the sink of sedimentary organic carbon, and plays a very important role in the ocean and global carbon cycling. In this paper, the advances of the formation, distribution, living environment characteristics, internal carbon cycling, potential importance in the global carbon cycling and possible responses to the global climate change of the hadal zone are reviewed, and the biogeochemical processes of biogenic nutrients influenced by the living environment in the hadal zone are mainly discussed, from the point of coupling of “physical hydrology-chemical sedimentary environment-biological activity”. And the outlook of the developing tendency in the hadal zone is summarized.
The hadal zone (e.g. trench) is characterized by its unique V-shaped geological structure, hydrodynamic environment and material and energy circulation system, has relatively higher deposition flux and burial efficiency of biogenic elements (e.g.carbon) compared with other ocean environments. As the window and channel connecting the deep biosphere and the ocean, this unique area is the tremendous trapper of marine primary production and the sink of sedimentary organic carbon, and plays a very important role in the ocean and global carbon cycling. In this paper, the advances of the formation, distribution, living environment characteristics, internal carbon cycling, potential importance in the global carbon cycling and possible responses to the global climate change of the hadal zone are reviewed, and the biogeochemical processes of biogenic nutrients influenced by the living environment in the hadal zone are mainly discussed, from the point of coupling of “physical hydrology-chemical sedimentary environment-biological activity”. And the outlook of the developing tendency in the hadal zone is summarized.
2018, (S2): 179-191.
doi: 10.3799/dqkx.2018.209
Abstract:
Gravel layers were drilled at IODP 367 Site U1499 in northern South China Sea. A variety of possible genetic mechanism for gravel layers, which are incorrect or uncertain predictions from observations in geophysical data in advance, have been proposed through the lithostratigraphic units in the cored sediment at site U1499. Using tectonostratigraphy and sediment-filling dynamics, this study restores the palaeo-geomorphology during the gravel layers sedimentation period based on a high-resolution seismic database and IODP site data from the northern margin of the South China Sea. The results indicate that the gravel layers should be deposited in proximal delta sedimentation environment along Late Eocene-Early Oligocene lacustrine basin peripheral, whose provenance is mainly from Mesozoic erosion areas of Dongsha and Liyue. The top of the gravel layers corresponds to a coincidence boundary of T70 and T60 in seismic profiles. T70 unconformity is likely directly related to the continental breakup during the initial opening of the northern South China Sea. T70 boundary age is estimated to be at 33.0–228.4 Ma and is earlier in the east than that of the west. Besides, this paper suggests that the position of ocean-continent transition zone may be near the southern edge of a series of small extensional half-grabens in the northern South China Sea rather than a geomorphic abrupt domain with a water depth of 3 000 m.
Gravel layers were drilled at IODP 367 Site U1499 in northern South China Sea. A variety of possible genetic mechanism for gravel layers, which are incorrect or uncertain predictions from observations in geophysical data in advance, have been proposed through the lithostratigraphic units in the cored sediment at site U1499. Using tectonostratigraphy and sediment-filling dynamics, this study restores the palaeo-geomorphology during the gravel layers sedimentation period based on a high-resolution seismic database and IODP site data from the northern margin of the South China Sea. The results indicate that the gravel layers should be deposited in proximal delta sedimentation environment along Late Eocene-Early Oligocene lacustrine basin peripheral, whose provenance is mainly from Mesozoic erosion areas of Dongsha and Liyue. The top of the gravel layers corresponds to a coincidence boundary of T70 and T60 in seismic profiles. T70 unconformity is likely directly related to the continental breakup during the initial opening of the northern South China Sea. T70 boundary age is estimated to be at 33.0–228.4 Ma and is earlier in the east than that of the west. Besides, this paper suggests that the position of ocean-continent transition zone may be near the southern edge of a series of small extensional half-grabens in the northern South China Sea rather than a geomorphic abrupt domain with a water depth of 3 000 m.
2018, (S2): 192-202.
doi: 10.3799/dqkx.2018.189
Abstract:
In order to explain distribution characteristics of clay mineral composition in sediments from coastal rivers, and their contribution to sediments in the Northern South China Sea (NSCS), we collected sediment samples from six major rivers along the South China coast whose annual sediment discharge is greater than 500 thousand tons, together with surface sediment samples in the NSCS.The results show that (1) the total percentage of illite and kaolinite in sediments from the Han, Jiulong and Moyang Rivers is more than 90%, (2) smectite percentage in coastal river sediments is very low except for the Rong River (18%), (3) sediments in these six rivers have low chlorite percentage, and only the Jian and Pearl Rivers can reach 9%.The clay mineral assemblages in sediments from the above rivers are different from each other, which can be used to identify sediment sources in the NSCS.On the NSCS continental shelf, illite and chlorite mainly originate from the southwestern Taiwan, while kaolinite is primarily sourced from Jian, Moyang and Pearl Rivers.Smectite is largely derived from the Rong River, and area ranged from the Pearl River Delta to the Dapeng and Daya Bays.
In order to explain distribution characteristics of clay mineral composition in sediments from coastal rivers, and their contribution to sediments in the Northern South China Sea (NSCS), we collected sediment samples from six major rivers along the South China coast whose annual sediment discharge is greater than 500 thousand tons, together with surface sediment samples in the NSCS.The results show that (1) the total percentage of illite and kaolinite in sediments from the Han, Jiulong and Moyang Rivers is more than 90%, (2) smectite percentage in coastal river sediments is very low except for the Rong River (18%), (3) sediments in these six rivers have low chlorite percentage, and only the Jian and Pearl Rivers can reach 9%.The clay mineral assemblages in sediments from the above rivers are different from each other, which can be used to identify sediment sources in the NSCS.On the NSCS continental shelf, illite and chlorite mainly originate from the southwestern Taiwan, while kaolinite is primarily sourced from Jian, Moyang and Pearl Rivers.Smectite is largely derived from the Rong River, and area ranged from the Pearl River Delta to the Dapeng and Daya Bays.
2018, (S2): 203-213.
doi: 10.3799/dqkx.2018.130
Abstract:
Volcaniclastics is one of the important compositions of deep-sea sediments produced by volcanic eruptions. It is with great research values for studies on paleoenvironmental evolution in the deep-sea volcanic environment. The purpose of this work is to reveal the pattern of the Late Miocene benthic environment revolution in the central basin of the South China Sea (SCS) by analyzing the trace fossil assemblages in the volcaniclastic sequence drilled at site U1431 during the International Ocean Discovery Program (IODP) expedition leg 349. The study shows that trace fossils were developed well in siltstone and claystone during the Middle-Late Miocene (12.5–7.4 Ma, mainly in Late Miocene), and were dominated byZoophycos ,Thalassinoides ,Chondrites , and Planolites .The volcanoes in the central basin of the SCS experienced repeated alternations of eruption and quietness during Late Miocene. The trace fossil assemblage in site U1431 implies that the basin is a quiet deep-sea environment with sedimentary rate varying between 5–15 cm/ka during volcanic activity quiet periods. By analyzing the associations between the trace fossil assemblages and the lithologic stratigraphic features, the study shows that the composition of the trace fossil assemblage is limited by substrate lithology and the dissolved oxygen concentration in the water masses at the sediment/water interface. The study also suggests that during eruptions, submarine volcanic activities can potentially provide nutrients for surface seawaters, and these nutrients can promote phytoplankton growth and subsequently increase the supply of organic carbon to the seafloor. The organic carbon on the sea floor then may consume the dissolved oxygen in the sediment pore water, making it unfavorable to the activities of the benthic organisms. In contrast, during volcanic eruption quiet periods, flux of organic carbon to the seafloor possibly reduced. Consumption of the dissolved oxygen in the pore water thus reduced, and the growth of the benthic organisms subsequently developed.
Volcaniclastics is one of the important compositions of deep-sea sediments produced by volcanic eruptions. It is with great research values for studies on paleoenvironmental evolution in the deep-sea volcanic environment. The purpose of this work is to reveal the pattern of the Late Miocene benthic environment revolution in the central basin of the South China Sea (SCS) by analyzing the trace fossil assemblages in the volcaniclastic sequence drilled at site U1431 during the International Ocean Discovery Program (IODP) expedition leg 349. The study shows that trace fossils were developed well in siltstone and claystone during the Middle-Late Miocene (12.5–7.4 Ma, mainly in Late Miocene), and were dominated by
2018, (S2): 214-225.
doi: 10.3799/dqkx.2018.241
Abstract:
The dating of formation age of clastic rock is the premise of the division and correlation of sedimentary strata, reasonable reconstruction of prototype basin, better understanding of the regional tectonic evolutions and scientific evaluation of regional resources. According to the principle of " the temperature of sediments or sedimentary rocks increases with increasing burial depth ", the formation age of clastic rock can be determined by the initial burial warming time of thermal history which can be reconstructed by means of apatite fission track (AFT) thermal history simulation. Previous applications of AFT thermal history simulation and the example of sandstone sample of Liupanshan indicate that it is feasible to date the formation age of clastic rock by the simulated thermal evolution history, using clastic samples that experienced burial temperatures of less than the closure temperature in the thermal history simulation of fission track.
The dating of formation age of clastic rock is the premise of the division and correlation of sedimentary strata, reasonable reconstruction of prototype basin, better understanding of the regional tectonic evolutions and scientific evaluation of regional resources. According to the principle of " the temperature of sediments or sedimentary rocks increases with increasing burial depth ", the formation age of clastic rock can be determined by the initial burial warming time of thermal history which can be reconstructed by means of apatite fission track (AFT) thermal history simulation. Previous applications of AFT thermal history simulation and the example of sandstone sample of Liupanshan indicate that it is feasible to date the formation age of clastic rock by the simulated thermal evolution history, using clastic samples that experienced burial temperatures of less than the closure temperature in the thermal history simulation of fission track.
2018, (S2): 226-233.
doi: 10.3799/dqkx.2018.183
Abstract:
The Tertiary mudstone in the northern margin of Qaidam basin is the main regional caprock of oil and gas, characterized by lateral distribution stability and strong sealing ability. According to drilling, logging and breakthrough pressure data, the macroscopic development characteristics and microscopic sealing mechanism of the Tertiary mudstone caprock in Lenghu area of northern Qaidam basin were studied. Furthermore, the mudstone thickness, diagenetic stage, breakthrough pressure, overpressure coefficient and brittleness index are selected as evaluation parameters to quantitatively evaluate the sealing capacity of mudstone caprock. The results show that there is a series of mudstone caprock developed, such as Lulehe, Xiaganchaigou and Shangganchaigou Formations. Mudstone caprock diagenesis is in the early diagenetic stage A to the middle diagenetic stage B. The breakthrough pressure of mudstone caprock reaches 1.1 MPa, which has the ability of sealing commercial oil flow, and reaches 2 MPa, which has the ability to seal commercial gas flow. In general, the sealing ability of the upper member of Xiaganchaigou Formation and Lulehe Formation caprock is the best and the lower member of Xiaganchaigou Formation is relatively weak. The sealing ability of Shangganchaigou Formation is the worst. The results of sealing evaluation match with the exploration practice.
The Tertiary mudstone in the northern margin of Qaidam basin is the main regional caprock of oil and gas, characterized by lateral distribution stability and strong sealing ability. According to drilling, logging and breakthrough pressure data, the macroscopic development characteristics and microscopic sealing mechanism of the Tertiary mudstone caprock in Lenghu area of northern Qaidam basin were studied. Furthermore, the mudstone thickness, diagenetic stage, breakthrough pressure, overpressure coefficient and brittleness index are selected as evaluation parameters to quantitatively evaluate the sealing capacity of mudstone caprock. The results show that there is a series of mudstone caprock developed, such as Lulehe, Xiaganchaigou and Shangganchaigou Formations. Mudstone caprock diagenesis is in the early diagenetic stage A to the middle diagenetic stage B. The breakthrough pressure of mudstone caprock reaches 1.1 MPa, which has the ability of sealing commercial oil flow, and reaches 2 MPa, which has the ability to seal commercial gas flow. In general, the sealing ability of the upper member of Xiaganchaigou Formation and Lulehe Formation caprock is the best and the lower member of Xiaganchaigou Formation is relatively weak. The sealing ability of Shangganchaigou Formation is the worst. The results of sealing evaluation match with the exploration practice.
2018, (S2): 234-242.
doi: 10.3799/dqkx.2018.138
Abstract:
At the steep slope of the Shijiutuo uplift (Bohai bay basin), there is thick mixed-deposition of lacustrine carbonate and clastic in the first member of the Shahejie Formation (Es 1, 38.0－32.8 Ma), which is superimposed on the sandbody of fan delta. The cumulative thickness of the total reservoir is over 150 m, with tested productivity over 10×103 m3 and proven reservoir over 1×108 m3. Based on the analysis of thin section, electron probe, cathode luminescence, it is found that the freshwater diagenesis environment has played a decisive role in the reservoir formation and evolution. The dissolved pores in grains formed in the beach bar depositing lay a good foundation for later dissolution of gravels and lithology. Early exposure forms the atmosphere water seepage belt and undercurrent belt. There are vertical leaching seams, micro emulsion cementations and large amounts of fabric nonselective dissolution pores found in the seepage belt. In the upper part of the belt of undercurrent, fabric selective dissolution pores form a large number of oolitic mold and bioclastic mold, as well as the grain rim cements. The pores formed at the early leaching stage is important reservoir space，and also play a decisive role on dissolved pores formed by the later stage acid geofluids. The micro stalactitic cements, the grain rim cements, and the micrite envelope which formed in the freshwater diagenetic environment play a grid supported role to the preservation of the early formed pores.
At the steep slope of the Shijiutuo uplift (Bohai bay basin), there is thick mixed-deposition of lacustrine carbonate and clastic in the first member of the Shahejie Formation (E
2018, (S2): 243-255.
doi: 10.3799/dqkx.2018.204
Abstract:
Duoqing Co is located in the nearly South- North Pagri graben, which belongs to the southern part of Yadong-Gulu rift in Tibet. However, the water in the lake disappeared in half to one year (in the period from November, 2015 to April, 2016) after the Nepal earthquake. We think that the phenomenon was not caused by climate change and human activity based on the past meteorological and remote sensing data. And there may be buried fault with the direction of NNE at the east boundary of Duoqing Co under the remote sensing interpretation and surface investigation. We also found plenty of nearly NE extensional cracks on the dried-up lake, which may have been formed by the creep of the lake boundary fault zone. And we predicted that the water leaked from the fractured group likely. Under the investigation and tectonic analysis, we suggest that the stress of the Bhutan-Sikkim earthquake locking region located in Main Himalaya Thrust fault zone increased from slow to rapid causing elastic strain locally after 2015 Nepal earthquake. Therefore, the underground of Pagri graben generated nearly EW extension and expansion leading to resulting that the water flow into the water-beating stratum and lake drying up in a short time. Then, the strain relaxation and the fractures close, which caused the water recovery under the ground of rainy season of the plateau. If so, the abnormal phenomena are likely to be response to the further enhancement of stress-strain of Buhtan-Sikkim Himalayan segment. This would also imply that the crust has a sensitive or critical state and indicate that stress-strain hardening is a seismic precursor in the Main Himalaya thrust fault zone before a possibly huge earthquake. Further, the abnormal phenomenon on the surface in the Bhutan – Sikkim locking region, Himalaya Thrust fault zone, is worth paying attention to and being vigilant, especially against the background of the active phase of the large earthquake in the main thrust belt of Himalaya.
Duoqing Co is located in the nearly South- North Pagri graben, which belongs to the southern part of Yadong-Gulu rift in Tibet. However, the water in the lake disappeared in half to one year (in the period from November, 2015 to April, 2016) after the Nepal earthquake. We think that the phenomenon was not caused by climate change and human activity based on the past meteorological and remote sensing data. And there may be buried fault with the direction of NNE at the east boundary of Duoqing Co under the remote sensing interpretation and surface investigation. We also found plenty of nearly NE extensional cracks on the dried-up lake, which may have been formed by the creep of the lake boundary fault zone. And we predicted that the water leaked from the fractured group likely. Under the investigation and tectonic analysis, we suggest that the stress of the Bhutan-Sikkim earthquake locking region located in Main Himalaya Thrust fault zone increased from slow to rapid causing elastic strain locally after 2015 Nepal earthquake. Therefore, the underground of Pagri graben generated nearly EW extension and expansion leading to resulting that the water flow into the water-beating stratum and lake drying up in a short time. Then, the strain relaxation and the fractures close, which caused the water recovery under the ground of rainy season of the plateau. If so, the abnormal phenomena are likely to be response to the further enhancement of stress-strain of Buhtan-Sikkim Himalayan segment. This would also imply that the crust has a sensitive or critical state and indicate that stress-strain hardening is a seismic precursor in the Main Himalaya thrust fault zone before a possibly huge earthquake. Further, the abnormal phenomenon on the surface in the Bhutan – Sikkim locking region, Himalaya Thrust fault zone, is worth paying attention to and being vigilant, especially against the background of the active phase of the large earthquake in the main thrust belt of Himalaya.
2018, (S2): 256-262.
doi: 10.3799/dqkx.2018.987
Abstract:
The application of remote sensing is a commonly used approach to environmental monitoring in mine areas. The research on convolutional neural network (CNN) for recognition of opencast mining area in high-resolution remote sensing image could help to improve monitoring efficiency. This paper focused on the problem of low classification accuracy of opencast mining area based on CNN due to insufficient trained datasets, the experiment is designed with three types of transfer learning methods and tested in different pre-trained CNN models. The analysis shows that by contrast, fixed lower layers’ parameters in pre-trained CNN models and fine-tune higher layers’ parameters is the optimal training method, it achieved over 87% in both producer’s accuracy and user’s accuracy. This experimental results indicate that opencast mining area could be effectively recognized in high-resolution imagery based on this training method, therefore, the CNN which trained by this method can be used as an aid in remote sensing interpretation of opencast mining area.
The application of remote sensing is a commonly used approach to environmental monitoring in mine areas. The research on convolutional neural network (CNN) for recognition of opencast mining area in high-resolution remote sensing image could help to improve monitoring efficiency. This paper focused on the problem of low classification accuracy of opencast mining area based on CNN due to insufficient trained datasets, the experiment is designed with three types of transfer learning methods and tested in different pre-trained CNN models. The analysis shows that by contrast, fixed lower layers’ parameters in pre-trained CNN models and fine-tune higher layers’ parameters is the optimal training method, it achieved over 87% in both producer’s accuracy and user’s accuracy. This experimental results indicate that opencast mining area could be effectively recognized in high-resolution imagery based on this training method, therefore, the CNN which trained by this method can be used as an aid in remote sensing interpretation of opencast mining area.
2018, (S2): 263-275.
doi: 10.3799/dqkx.2018.312
Abstract:
Typhoon-triggered debris flow refers to the debris flow that was triggered by typhoon storm. By regression analysis, it is found that debris flow multi-outbreak and the huge rainfall intensity were almost synchronizing, but traditional debris flow initiating theory can hardly explain this phenomenon. On the basis of analyzing the initiating process of typhoon-triggered debris flow, a two-dimension limit equilibrium analytic model was introduced to analyze the failure process of the slope in the forming area of the debris flow watershed in terms of stability, while the huge rainfall intensity in short duration come along. It is supposed that in the early stage of the typhoon influence, the slope was on the underground water seepage stage, as the water infiltrated into the slope, the matric suction in the soil reduced, and effective stress descended. The huge rainfall intensity in short duration played a pivotal role; notable overland runoff appeared on the slope surface, the sliding force of the slope was expanded by the shearing force of the overland runoff fand the slope failed more quickly. It explained the synchronizing phenomenon well. Finally, through statistical analysis, it was found that the debris flow initiating efficiency is relevant to the proportion of the tributary ditch initiating.
Typhoon-triggered debris flow refers to the debris flow that was triggered by typhoon storm. By regression analysis, it is found that debris flow multi-outbreak and the huge rainfall intensity were almost synchronizing, but traditional debris flow initiating theory can hardly explain this phenomenon. On the basis of analyzing the initiating process of typhoon-triggered debris flow, a two-dimension limit equilibrium analytic model was introduced to analyze the failure process of the slope in the forming area of the debris flow watershed in terms of stability, while the huge rainfall intensity in short duration come along. It is supposed that in the early stage of the typhoon influence, the slope was on the underground water seepage stage, as the water infiltrated into the slope, the matric suction in the soil reduced, and effective stress descended. The huge rainfall intensity in short duration played a pivotal role; notable overland runoff appeared on the slope surface, the sliding force of the slope was expanded by the shearing force of the overland runoff fand the slope failed more quickly. It explained the synchronizing phenomenon well. Finally, through statistical analysis, it was found that the debris flow initiating efficiency is relevant to the proportion of the tributary ditch initiating.
