Major element, trace element, and Sr, Nd and Pb isotope studies of Cenozoic basalts from the South China Sea

The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh basaltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cumulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.

Genesis of Th-230 excess in basalts from mid-ocean ridges and ocean islands: Constraints from the global U-series isotope database and major and rare earth element geochemistry

Based on Th-230-U-238 disequilibrium and major element data from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs), this study calculates mantle melting parameters, and thereby investigates the origin of Th-230 excess. (Th-230/U-238) in global MORBs shows a positive correlation with Fe-8, P (o), Na-8, and F-melt (Fe-8 and Na-8 are FeO and Na2O contents respectively after correction for crustal fractionation relative to MgO = 8 wt%, P (o)=pressure of initial melting and F (melt)=degree of melt), while Th-230 excess in OIBs has no obvious correlation with either initial mantle melting depth or the average degree of mantle melting. Furthermore, compared with the MORBs, higher (Th-230/U-238) in OIBs actually corresponds to a lower melting degree. This suggests that the Th-230 excess in MORBs is controlled by mantle melting conditions, while the Th-230 excess in OIBs is more likely related to the deep garnet control. The vast majority of calculated initial melting pressures of MORBs with excess Th-230 are between 1.0 and 2.5 GPa, which is consistent with the conclusion from experiments in recent years that D (U)> D (Th) for Al-clinopyroxene at pressures of > 1.0 GPa. The initial melting pressure of OIBs is 2.2-3.5 GPa (around the spinel-garnet transition zone), with their low excess Ra-226 compared to MORBs also suggesting a deeper mantle source. Accordingly, excess Th-230 in MORBs and OIBs may be formed respectively in the spinel and garnet stability field. In addition, there is no obvious correlation of K2O/TiO2 with (Th-230/U-238) and initial melting pressure (P (o)) of MORBs, so it is proposed that the melting depth producing excess Th-230 does not tap the spinel-garnet transition zone. OIBs and MORBs in both (Th-230/U-238) vs. K2O/TiO2 and (Th-230/U-238) vs. P (o) plots fall in two distinct areas, indicating that the mineral phases which dominate their excess Th-230 are different. Ce/Yb-Ce curves of fast and slow ridge MORBs are similar, while, in comparison, the Ce/Yb-Ce curve for OIBs shows more influence from garnet. The mechanisms generating excess Th-230 in MORBs and OIBs are significantly different, with formation of excess Th-230 in the garnet zone only being suitable for OIBs.

One century record of contamination by polycyclic aromatic hydrocarbons and polychlorinated biphenyls in core sediments from the southern Yellow Sea

Sixteen polycyclic aromatic hydrocarbons (PAHs) and 28 polychlorinated biphenyls (PCBs) were measured at a 2-cm interval in a core sample from the middle of the southern Yellow Sea for elucidating their historical variations in inflow and sources. The chronology was obtained using the Pb-210 method. PAHs concentrations decreased generally with depth and two climax values occurred in 14-16 cm and 20-22 cm layers, demonstrating that the production and usage of PAHs might reach peaks in the periods of 1956-1962 and 1938-1944. The booming economy and the navy battles of the Second World War might explain why the higher levels were detected in the two layers. The result of principal component analysis (PCA) revealed that PAHs were primarily owing to the combustion product. Down-cored variation of PCB concentrations was complex. Higher concentrations besides the two peaks being the same as PAHs were detected from 4 to 8 cm, depositing from 1980 to 1992, which probably resulted from the disposal of the out-dated PCB-containing equipment. The average Cl percentage of PCBs detected was similar to that of the mixture of Aroclor 1254 and 1242, suggesting they might origin from the dielectrical and heat-transfer fluid. The total organic carbon (TOC) content played a prevalent role in the adsorption of high molecular weight PAHs (>= 4-ring), while no obvious relationship among total PCBs, the concentration of congeners, and TOC was found.

The distribution, enrichment and source of potential harmful elements in surface sediments of Bohai Bay, North China

A geochemical study of Bohai Bay surface sediments was carried out to analyze the potential harmful element (PHE: Ge, Mo, In, Sn, Sb,Te, Tl, Bi and V) concentrations, transportation and deposition, enrichment factors and sources. Germanium, Mo, In, Sn, Sb, Te, Tl, Bi and V concentrations in the surface sediments were: 1.43-1.71, 0.52-1.43, 0.04-0.12, 2.77-4.14, 1.14-2.29, 0.027-0.085, 0.506-0.770, 0.27-0.63 and 70.35-115.90 mu g/g, respectively. The distributions of total PHE concentrations, together with sequential extraction analyses, showed that the PHEs were mainly due to natural inputs from the continental weathering delivered to the bay by rivers and atmospheric transportation and deposition. However, high Mo, Sb, Te, Bi and V occurred in non-residual fractions, suggesting some anthropogenic inputs in addition to the natural inputs. Besides sources, the distributions of PHEs were influenced by the coupling of physical, chemical and biological processes. Enrichment factor (EF) was computed for each site for each element in order to assess the polluting elements and the degree of pollution at each site. Results revealed that the EFs were generally lower than 1.0, particularly for Ge, Mo, In, Sn, Tl and V; however, the EFs were higher (>1.5), particularly for Sb, Te and Bi, revealing moderate contamination. (C) 2010 Elsevier B.V. All rights reserved.

Assessment of metal contamination in surface sediments of Jiaozhou Bay, Qingdao, China

An assessment of metal contamination in surface sediments of the Jiaozhou Bay, Qingdao, one of the rapidly developing coastal economic zones in China, is provided. Sediments were collected from 10 stations and a total of 15 heavy metals were analyzed. Concentrations of metals show significant variability and range from 210 to 620 ppm for Ti, 2.7 to 23 ppm for Ni, 4.2 to 28 ppm for Cu, 5.2 to 18 ppm for Pb, 12 to 58 ppm for Zn, 0.03 to 0.11 ppm for Cd, 5 to 51 ppm for Cr, 1.5 to 9.9 ppm for Co, 5.3 to 19 ppm for As, 12 to 32 ppm for Se, and 19 to 97 ppm for Sr. Based on concentration relationships and enrichment factor (EF) analyses, the results indicate that sediment grain size and organic matter played important roles in controlling the distribution of the heavy metals in surface sediments of the Jiaozhou Bay. The study shows that the sediment of the Jiaozhou Bay has been contaminated by heavy metals to various degrees, with prominent arsenic contributing the most to the contamination. The analysis suggests that the major sources of metal contamination in the Jiaozhou Bay are land-based anthropogenic ones, such as discharge of industrial waste water and municipal sewage and run-off. Notably, the elevated heavy metal concentrations of the Jiaozhou Bay sediments could have a significant impact on the bay's ecosystem. With the rapid economic development and urbanization around the Jiaozhou Bay, coastal management and pollution control should focus on these contaminant sources, as well as provide ongoing monitoring studies of heavy metal contamination within the bay.

Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater

A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods (BEMs) coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT (show strain rate test) in seawater.

塔里木盆地塔中—巴楚地区早二叠世岩浆岩地球化学特征及其成因

Tazhong-Bachu region is located in the Western Tarim basin.The early Permian magmatic rocks occur in the earth surface of Tazhong-Bachu region are mainly distributed in Kepintag,Mazhartag and Wajilitag region. There are a lot of wells, in which researchers found the early Permian magmatic rocks,in desert cover area.Most magmatic rocks are basic rocks, a few of which are ultrabasic rocks and intermediate-acid magmatic rocks.The ultrabasic rocks are are mainly occur in the Cryptoexplosive Breccia Pipes ,which is located in the volcanic complex body of Wajilitag region.The basic rocks can be divided into three rock types：The first type of the magmatic rocks in Tazhong-Bachu region is volcanic rock ,which occurs in the Lower Permian Kupukuziman Formation and Kaipaizileike Formation. Most Volcanic rocks are basalts,a few of which are volcanic breccias and pyroclastic rocks.The basalts are distributed in stratiform occurrences and interbeded the clastic rocks in Kepintag region.The attitudes of the basalts are nearly horizontal.Columnar Joints, gas pore textures and amygdaloidal structure are to develop in basalts.The second type of the magmatic rocks in Tazhong-Bachu region is diabase,which occurs in Mazhartag region.Diabase dike swarms occur in the stratums of Silurian, Devonian, Carboniferous and Lower Permian.They make from NNW direction to SSE direction, the obliquity of stratum is greater than 60°, and the dike thickness is form several cm to several meters. Diabasic texture is found in the rocks .The first type of the magmatic rocks in Tazhong-Bachu region are gabbro- pyroxenite rocks ,which occur in the Wajilitag igneous complex body. The intermediate-acid magmatic rocks, which are mainly syenites, are located in Mazhartag and Wajiltag region. But they are small in the whole Tazhong-Bachu region.There are intermediate-acid magmatic rocks,which are mainly dacite,in the northeast part of the wells in Tazhong-Bachu region.But ,it is not found in earth surface.Through systematical geochemical research of early Permian magmatic rocks,which are distributed in Kepintag,Mazhartag, Wajilitag region and the wells such as F1 well、Z1 well、Z13 well、TZ18 well、H3 well、H4 well et al., the focus on the geochronologic characteristics, the main element,trace element and REE geochemistry, the mineralogic characteristics, the Sr-Nd and Pb isotopic characteristics are put forward. The main points are: 1、A combined study of CL imaging and LA-ICP-MS U-Pb dating were carried out for zircon grains of the magmatic rocks in the Tazhong-Bachu region from the Tarim basin.The results of the systematic zircon LA-ICP-MS U-Pb dating reveal 272±6Ma to 291±10Ma for the magamatic rocks. It indicated that Early Permian is an important period of magmatic acvivity in the Tazhong-Bachu region. 2、There are a big hunch in the curves of primitive mantle-normalized trace element concentrations in the early Permian magmatic rocks from Kepintag, Mazhartag, Wajilitag region and the 14 wells. Light rare earth elements are comparatively rich and heavy rare earth elements are comparatively poor. The slope rates are same between light rare erath elements and heavy rare earth elements. It is not like the curves of the basalts in the convergent margin of plate , in which the slope rates of light rare erath elements is bigger than the alope rates of heavy rare erath elements, and the curves of heavy rare earth elements are comparatively flat. The magmatic rocks of Tazhong-Bachu region rarely have the characteristics of the basalts in the convergent margin of plate, which is that Tantalum, Niobium and Titanium are much poor, and Zirconium, Hafnium and Phosphorus are moderately poor. The magamatic rocks are mostly alkaline, which is indicated by the dots of the (Na2O+K2O)-SiO2 identification diagram. All of these indicate that the early Permian magmatic rocks were formed in an extension environment of intraplate. 3、The Thorium abundance is high and Tantalum abundance is low in most magmatic rocks from Tazhong-Bachu reguion, which is formed for crustal contamination.In the Th/Yb-Ta/Yb identification diagram，most dots are in the region, which means active continental margin, but a few dots are in the region, which means mantle source. It indicated the feeding of continental crust materials. 4、The magnesium content of the olvines from Wagilitag region is richest, and the olvines from Kepintag region is poorest in the tree region. 5、Through the the Sr-Nd and Pb isotopic study of the basalts and diabases from the F1 well core, Z1 well core, Z13 well core,TZ18 well core, and the basalts，gabbros, diabases(diabase-prophyrites) and pl-peridotites from Kepintag,Mazhartag, Wajilitag region , it indicated that all isotopic data is similar and close to enriched mantle.

东天山镁铁-超镁铁岩铜镍硫化物矿床通道式成矿机制与岩体含矿性评价研究

A mafic-ultramafic complex belt well developed in Eastern Tianshan, Xinjiang, NW China, which contains a series of Cu-Ni sulfide deposits. This area is the important production basis for Cu-Ni deposits, including Tulargen deposit, Hulu deposit, Huangshan-Huangshandong deposit, Hulu deposit, Xiangshan deposit, Tianyu deposit, Chuanzhu deposit. In China, especially Eastern Tianshan, it is prevalent that large Cu-Ni deposits occurred in small intrusions, typically including Jinchuan, Kalatongke, et al., so the ore-forming mechanism and evaluation rule for those small intrusions are very meaningful and of universal significance. On the basis of the research to typical Cu-Ni deposits, ore-forming conditions and processes are summarized through which to evaluate the ore-bearing potential for barren intrusions and unexplored mafic-ultramafic intrusions. By the contrast, metallogenic rule and mechanism of ore genesis are concluded, and evaluation system is preliminarily set up on the basis of these conclusions. Quantitatively simulation for the composition of olivine is introduced for the first time in China to discuss the interaction between magma and sulfide, and a new method to calculate the Mg-Fe composition of primitive magma is developed. Interaction between magma and sulfide liquid is used to get the Ni content in sulfide liquid. Sulfur isotopic characteristics in sulfide minerals in country rocks and ores are used to judge crustal sulfur introduction, which is applied for the first time in China. Re-Os isotopic characteristics are related to the ore-forming process, to interpret the process of enrichment of chalcophile elements. On the basis of the evaluation system, Mati, Chuanzhu, Luodong, Xiadong, those intrusions are evaluated to their ore-bearing potential. According to the studies to typical Cu-Ni deposits, conduit-type ore-forming model is set up, and the characteristics of the model are concluded systematically. The evaluation system and conduit-type ore-forming model can be helpful to the evaluation of mafic-ultramafic intrusions in this and similar mafic-ultramafic intrusion belts. The studied typical deposits and mafic-ultramafic intrusion include Tulargen deposit, Hulu deposit, Huangshandong deposit, Chuanzhu deposit, Mati intrusion，Luodong intrusion, Xiadong intrusion, and others. Through studies, there are similar characteristics for Tulargen and Hulu deposits in magma origin, composition of primitive magma（MgO=12.5%, FeO=12% and MgO=11%, FeO=10.5% respectively）, magma evolution, mechanism of sulfide segregation and conduit-type ore-forming process. By Re-Os isotopic system, the ore forming date of Tulargen deposit is 265.6±9.2Ma, which is consistent to regional metallogenic event, but little younger. The Mg-Fe composition of primitive magma of Baishiquan, Huangshandong area, Kalatongke is lower than that of Tulargen and Hulu deposit, showing common basalt composition. The Mg# value（Mg#=(Mg/Mg+Fe）increases gradually from Kalatongke to Baishiquan to Huangshan-Huangshandong East. Baishiquan intrusions show relatively higher crustal contamination by evidence of trace element, which indicates the lower magma original source, from depleted mantle to crust. One break is the discovery of komatiitic intrusion, Xiadong intrusion, which shows characteristics of highly magnesium (Max Fo=96). The primitive magma is calculated of MgO=28%，FeO=9%, belonging to komatiitic magma. Tectonic evolution of Eastern Tianshan is discussed. By the statistics of ore-forming data of porphyry copper deposits, magmatic sulfide Cu-Ni deposits, orogenic hydrothermal gold deposits, we believe that those deposits are the successive products of oceanic subduction, are and back-arc basin collision and post-orogenic extention. And Cu-Ni sulfide deposits and orogenic gold deposits occurred in the stage of post-orogenic extention. According to the conclusions, the conduit-type ore-forming mechanism of magmatic sulfide deposit is set up, and its characteristics and conditions are concluded as well. The conduit-type ore-forming system includes magma generation, sulfide segregation, enrichment of chalcophile elements, interaction of sulfide and magma, sulfide collection in limited space in magma conduit and bottom of the chamber, which make a whole ore-forming system.The ore-forming process of Cu-Ni sulfide deposits is concluded as three steps: 1. mantle derived magma rises upward to the middle-upper crust; 2. magma suffers crustal contamination of different degrees and assimilates crustal sulfur, which leads to sulfur saturation and sulfide segregation. Sulfide liquid interacts with magma and concentrates chalcophile elements; 3. enriched sulfide located in the conduit(Tulargen) or bottom of the chamber (Hulu). Depleted magma rises upward continuously to form barren complexes. For the practical cases, Tulargen deposit represents the feeding conduit, and Hulu deposit represents the bottom of the staging magma chamber. So the deeper of west of Tulargen and southwest of Hulu are the favorite locate for ore location. The evaluation for ore potential can be summarized as follows: (1) Olivine can be served as indicator for magma evolution and events of sulfide segregation; (2) Sulfur isotopic characteristics is an efficient method to judge sulfur origin for magmatic sulfide deposit; (3) Re-Os content of the ores can indicate interaction between sulfide and silicate magma and crustal contamination; (4) PGE mineralization is effected by degree of partial melting of mantle; (5) Cu/Zr is efficient parameter to judge sulfide segregation; (6) The effects of multiple magma fractionation and emplacement are important, for inverse order shows the destruction to previous solid lithofacies and orebodies. Mati, Chuanzhu, Xiadong, Luodong, mafic-ultramafic intrusions are evaluated using evaluation system above. Remarkable Ni depletion is found in olivine of Mati, and southwest of the intrusion can be hopeful location for ore location. Chuanzhu intrusion has remarkable evidence of sulfide segregation, but the intrusion represents the narrow feeder conduit, so the wide part of the conduit maybe the favorite location for sulfide to deposit. The ore potential of Luodong and Xiadong is not good. Both the intrusions show no Ni depletion in olivine, and there is no sulfide in country rocks, so no crustal sulfur is added into the magmatic system. For Sidingheishan, a very large intrusion, the phenomenon of sulfide segregation is found, but there are no favorite places for sulfide to deposit. So the Cu-Ni ore potential maybe not good, but PGE mineralization should be evaluated further.

新增生岩石圈与软流圈的相互作用：来自地幔橄榄岩捕虏体的证据

The petrology and geochemistry of peridotites entrained in Beiyan Cenozoic alkaline basalts within the middle segment of Tan-Lu fault zone and clinopyroxene megacrysts in the late Mesozoic and Cenozoic alkaline basaltic rocks from the North China Craton, have been systematically investigated. The main conclusions are obtained as follows. The peridotites entrained in alkaline basalts at Beiyan, Shandong Province, China are comprised of dominantly spinel lherzolites and spinel wehrlites with porphyroclastic, granuloblastic textures to resorption textures. The xenoliths are fertile in major element compositions (High CaO, TiO2, Low MgO, Cr2O3). The olivine Fo (= 100×Mg / (Mg+Fe) possesses a low and very large range of 81.0 to 91.0. The peridotites contain high percentages (Lherzolites: 10 - 19% in volume; Wehrlites: 24 - 28% in volume) of clinopyroxene with spongy textures. The Sr and Nd isotopic ratios of clinopyroxene separates from peridotites and pyroxenite xenoliths have a depleted and small range fall within the area of MORB, similar to newly-accreted lithospheric mantle. However, the appearance of many wehrlites and highly enriched LREE pattern suggest that this newly-accreted lithospheric mantle was considerably modified and reconstructed recently through the peridotite-asthenospheric melt interaction. The upwelling of asthenosphere from late Cretaceous to Eogene and upper mantle shearing of the Tan-Lu fault played an important role in the modification and reconstruction of the newly-accreted lithospheric mantle. The clinopyroxene megacrysts in the late Mesozoic and Cenozoic alkaline basaltic rocks from the eatern North China Craton are different in aspects of major elements, trace elements and isotopic composition. The characteristics of texture, mineral compositions and geochemistry as well as the Fe-Mg partitioning between the crystal and the melt indicates that the Al-augites in the Cenozoic basalts represent high-pressure crystallization products of alkaline basaltic melts. Thus, both of clinopyroxene megacrysts and host basalts could be derived from a same primitive magma. However, the Al-augites in the late Mesozoic basaltic rocks represent accidentally-included xenocrysts of basaltic components which had crystallized in the depth from a previously melting episode. The more depleted Sr-Nd isotopic compositions of Cenozoic megacrysts compared with those of host alkaline basalts and tholeiites demonstrate that even the alkali basalts could not completely represent primitive magma initiating in asthenosphere. That is to say, the Cenozoic alkaline basalts were more or less modified by some enriched Sr-Nd isotopic components during their eruption. Meanwhile, the tholeiites were not the products formed only by fractional crystallization of alkaline basaltic magma or different degrees of partial melting. It may result from the contribution of lithospheric mantle materials or crust contamination in magma chamber to alkali basaltic magmas.

晚中生代松辽盆地形成的大地构造环境及成因机制

Directed by the theory of "Collision Tectonic Facies", the tectonic setting and dynamic mechanism of the formation of Songliao basin in late Mesozoic (J_3-K_1) are studied in the present thesis with the methods of petrology, petrochemistry, geochemistry and isotopic geochronology. The research contents in this paper include as followings. Firstly, the general tectonic frame is made up of different tectonic facies formed from Mid-late Proterozoic to Mesozoic, which are Huabei plate, the Chengde-Siziwangqi melange (Pz_1), the Wenduermiao magmatic arc (Pz_1), the Hegenshan-Chaogenshan melange (Pz_2), the accretion arec (Pz_1-P), the Raohe-Hulin melange (Mz), the magmatic arc (Mz) and the pull-apart basin on the magmatic arc (Mz). Secondly, the volcanic rock assemblages of Songliao basin and its adjacent area in late Mesozoic is the typical calc-alkaline of the magmatic arc. The types of volcanic rocks in the study area include basalts, basaltic andesites, andesites, dacites and rhyolites, and basic-intermediate volcanic rocks have higher alkalinity. The volcanic rock series in this area is the high-K calc-alkaline series. Thirdly, the total REE of volcanic rocks in Songliao basin and its adjacent area is higher than that of the chondrite. The pattern of the REE normalized by the chondrite shows the characteristics similar to that of the typical island arcs or the active continental margins in the earth, that is enrichment of LREE and depletion of Eu. The spider-diagram of the trace element normalized by the primitive mantle also expresses the similar features to that of the typical island arcs or the active continental margins, it has distinctive valleies of Nb, Ta, Sr, P, and Ti, as well as the peaks of La, Ce, Th, U, and K. The incompatible elements show that the high field strength elements, such as Nb, Ta, Ti, and P, are depletion while the low field strength elements, such as K, U, Pb, and Ba, are enrichment. These features are similar to those of orogenic volcanic rocks and imply the formation of the volcanic rocks in this area is related to the subduction. The degrees of both the enrichment of the HFS elements and depletion of the LFS elements become more obvious from basic to acid volcanic rocks, which suggests crustal contamination enhances with the magmatic crystallization and fractionation. The concentration of the compatible elements is W-shape, and anomalies in Cr and Ni suggest there is the contamination during the magmatic crystallization and fractionation. Fourthly, the isotopic age data prove the volcanic activity in the Songliao basin and its adjacent area started in the early-middle Jurassic, and ended in the end of the early Cretaceous-the beginning of the Cretaceous. The volcanism summit was the late Jurassic-the early Cretaceous (100 - 150Ma). Finally, the tectonic setting of volcanism in the late Mesozoic was magmatic arc, which originated the subduction of Raohe-Hulin trench to the northwest Asian plate. The subduction began in the middle Jurassic, and the collision orogenesis between the Sikhote-Alin arc and Asian continent was completed in the end of the early Cretaceous-the beginning of the late Cretaceous. The results of above tectonic processes were finally to format Nadanhada orogenic belt symbolized by the Raohe-Hulin suture or melange belt. The violently oblique movement of the Izanagi plate toward Asian plate in the late Mesozoic was the dynamic mechanism of above tectonic processes. At the same tome, the left-lateral strike-slip shear caused by the oblique movement of the Izanagi plate produced a series of strike-slip faults in east Asian margin, and the large scale displacements of these strike-slip faults then produced the pull-apart basing or grabens on the magmatic arc. Conclusively, the tectonic setting during the formation of the grabens of Songliao basin in the late Mesozoic was magmatic arc, and its dynamic mechanism was the pull-apart. In a word, there was a good coupling relation among the oblique subduction of the oceanic plate, collisional orogene between island arc and continental plate, strike-slip shear of the faults and the formation of the grabens in Songliao basin and its adjacent area in late Mesozoic. These tectonic processes were completed in the unoin dynamic setting and mechanism as above description.