吉林东部大蒲柴河adakites锆石U-Pb年龄、Hf同位素特征及其意义

地球化学研究表明,大蒲柴河岩体具有典型的埃达克岩特征,来自加厚下地壳的部分熔融作用。本文采用激光等离子质谱对该岩体进行了U-Pb同位素定年,结果表明该岩体为晚侏罗世(165Ma)岩浆活动的产物。锆石的LA-MC-ICPMS Hf同位素研究结果显示,ε_(Hf)(165Ma)范围为-5.02～5.43,二阶段Hf模式年龄(t_(DM2)范围为965～1622Ma,暗示原始母岩浆为两种不同源区岩浆的混合。另外,Hf同位素研究表明,研究区在中-新元古代时(965～1304Ma)曾经历了一次重要的地壳增生事件。

雷琼地区晚新生代玄武岩地球化学:EM2成分来源及大陆岩石圈地幔的贡献

对雷琼地区21个晚新生代玄武岩样品的主量、微量元素和Sr、Nd、Pb同位素分别用湿化学法、ICP-MS和MC-ICPMS进行了测定。这些玄武岩主要为石英拉斑玄武岩,其次为橄榄拉斑玄武岩和碱性玄武岩。大多数样品的微量元素和同位素成分与洋岛玄武岩(OIBs)相似,而且随着SiO_2不饱和度增加,不相容元素含量也增加。除R4-1可能受到地壳混染外,其他样品相对均一的Nd同位素(ε_(Nd)=2.5～6.0)以及变化明显但范围有限的Sr同位素(0.703106～0.704481),可能继承了地幔源区的特征。^(87)Sr/^(86)Sr与^(206)Pb/^(204)Pb的正相关和^(143)Nd/^(144)Nd与^(206)Pb/^(204)Pb的负相关特征暗示DM(软流圈地幔)与EM2(岩石圈地幔)的混合。地幔捕虏体的同位素特征暗示EM2成分不可能存在于尖晶石橄榄岩地幔,而La/Yb和Sm/Yb系统表明岩浆由石榴石橄榄岩部分熔融产生,这意味着EM2成分可能存在于石榴石橄榄岩地幔。雷琼地区玄武岩的地球化学变化可以用软流圈地幔为主的熔体加入不同比例石榴石橄榄岩地幔不同程度熔融产生的熔体来解释:碱性玄武岩和橄榄拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较低程度(7%～9%)熔融体混合,而石英拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较高程度(10%～20%)熔融体的混合。

An Attempt to Analyze a Human Nervous System Algorithm for Sensing Earthquake Precursors

We statistically validate the 2011-2022 earthquake prediction records of Ada, the sixth finalist of the 2nd China AETA in 2021, who made 147 earthquake predictions (including 60% of magnitude 5.5 earthquakes) with a prediction accuracy higher than 70% and a confidence level of 95% over a 12-year period. Since the reliable earthquake precursor signals described by Ada and the characteristics of Alfvén waves match quite well, this paper proposes a hypothesis on how earthquakes are triggered based on the Alfvén (Q G) torsional wave model of Gillette et al. When the plume of the upper mantle column intrudes into the magma and lithosphere of the soft flow layer during the exchange of hot and cold molten material masses deep inside the Earth’s interior during ascent and descent, it is possible to form body and surface plasma sheets under certain conditions to form Alfven nonlinear isolated waves, and Alfven waves often perturb the geomagnetic field, releasing huge heat and kinetic energy thus triggering earthquakes. To explain the complex phenomenon of how Ada senses Alvfen waves and how to locate epicenters, we venture to speculate that special magnetosensory cells in a few human bodies can sense earthquake precursors and attempt to hypothesize an algorithm that analyzes how the human biological nervous system encodes and decodes earthquake precursors and explains how human magnetosensory cells can solve complex problems such as predicting earthquake magnitude and locating epicenters.

Mantle Redox State Evolution in Eastern China and Its Implications

Using the secondary spinel standard, the authors have precisely measured the Fe3+/∑Fe values of spinels in mantle xenoliths from Cenozoic basalts in eastern China, and estimated the oxygen fugacities recorded by 63 mantle xenoliths through olivine-orthopyroxene-spinel oxygen barometry. The results indicate that the oxygen fugacities of the lithospheric mantle in eastern China are higher in the south than in the north. Among them, the oxygen fugacity of the North China craton lithospheric mantle is the lowest, similar to that of the oceanic mantle, while that of Northeast and South China are the same as that of the global continental mantle. The variations of mantle redox state in eastern China are mainly controlled by the C-O-H fluids derived from the asthenospheric mantle. According to the mantle oxidation state, it can be concluded that the C-O-H fluids in the lithospheric mantle of eastern China consist mainly of CO2 and minor H2O, but CH4-rich fluids should come from the asthenosphere where the oxidation state is lower.

Comparison between Paleozoic and CenozoicLithospheric Mantle in Eastern Part of North China Block: With a Discussion of Mantle Evolution

Paleozoic diamond- and xenolith-bearing kimberlites and Cenozoic xenolith-bearing basalts,erupted in the eastern part of the North China block (NCB), provide excellent mantle probes for the research of intra-plate processes and the Phanerozoic evolution of the subcontinental lithosphere mantle (SCLM ). In this study, the mineral inclusions in diamond and xenoliths from Mengyin (Shandong Province) and Fuxian (Liaoning Province) kimberlites were chosen for constraining the nature of the Paleozoic SCLM. while xenoliths from the Shanwang and Qixia basalt (both in Shandong Province) were chosen for constraining the nature of the Cenozoic SCLM.Shanwang lies astride the Tancheng-Lujiang (Taulu) fault zone, a major lithospheric fault in Eastern China as well as in Eastern Asia, and Qixia lies east of the rault zone. Based on the research of the petrography of mantle xenoliths, petrochemistry, major and the trace element of mantle minerals, lithospheric thermal state, combiued with tbe modern geophysical data, it is concluded that the attenuation and replacement of Paleozoic SCLM by upwelling asthenospheric materials through thermal erosion and possibly delamination resulted in the rormation of irregular-shaPed hot bodies, mainly along weak zones within the mantle- The Tanlu fault zone played an importont role in the Mesozoic-Cenozoic replacemeni or the pre-existing lithospheric mantle.

Eocene magmatism(Maden Complex) in the Southeast Anatolian Orogenic Belt: Magma genesis and tectonic implications

The origin and geodynamic setting of the Maden Complex, which is situated in the Bitlis-Zagros Suture Zone in the Southeast Anatolian Orogenic Belt, is still controversial due to lack of systematic geological and geochemical data. Here we present new whole rock major-trace-rare earth element and Sre Nd isotope data from the Middle Eocene volcanic rocks exposed in Maden Complex and discuss their origin in the light of new and old data. The volcanic lithologies are represented mainly by basalt and andesite, and minor dacite that vary from low-K tholeiitic, calc-alkaline, high-K calc-alkaline, and shoshonitic in composition. They exhibit enrichments in large ion lithophile and light rare earth elements, with depletions in high field strength elements. Basaltic rocks have uniform Sr and Nd isotope ratios with high εNd(t) values varying from t5.5 to t6.7, in contrast to, andesitic rocks are characterized by low εNd(t) values ranging from à1.6 to à10. These geochemical and isotopic characteristics indicate that two end-members, a subduction-related mantle source and a continental crust, were involved in the magma genesis. Considering all geological and geochemical data, we suggest that the Eocene Maden magmatism occurred as a post-collisional product by asthenospheric upwelling owing to convective removal of the lithosphere during an extensional collapse of the Southeast Anatolian ranges.

3-D crustal-scale gravity model of the San Rafael Block and Payenia volcanic province in Mendoza,Argentina

The San Rafael Block(SRB)is part of one of the main retroarc volcanic provinces in southern Central Andes in Mendoza,Argentina.This block is located in the Andean foothills between the orogenic front and foreland basement uplifts of late Miocene age.In order to analyze the geochronological evolution of the Quaternary volcanism in the region,several geologic and geophysical studies have been conducted.Nevertheless,the crust,where the SRB is located,has not been well characterized yet.Based on gravimetric and magnetic data,together with isostatic and elastic thickness analyses,we modeled the crustal structure of the area.Information obtained has allowed us to understand the crust where the SRB and the Payenia volcanic province are located.Bouguer anomalies indicate that the SRB presents higher densities to the North of Cerro Nevado and Moho calculations suggest depths for this block between 40 and 50 km.Determinations of elastic thickness would indicate that the crust supporting the San Rafael Block presents values of approximately 10 km,being enough to support the block loading.However,in the Payenia region,elastic thickness values are close to zero due to the regional temperature increase.

Subsoil Natural Physico-Chemical Reactor:Regularity of Natural Processes of Synthesis of Perfect Diamond Crystals

Studies of inclusions(defects)in minerals have shown that the source of carbon in the natural processes of synthesis of perfect diamond crystals is mantle carbon dioxide,(СО2)Р=6.1МPаandδ13С=(-6.1±0.5)‰.A new mechanism for the synthesis of natural crystals of diamond,pyrope,magnetite,quartz,etc.has been developed.It is shown that under the influence of a powerful pulse of tectonogenic energy in some parts of the lithosphere that there are deep faults-tubes,which take root-migrating melt in the direction of the earth’s crust.During migration in the contact zone—“melt-lithosphere rocks”due to their contact interaction-friction,a high-voltage electric field of complex shape is formed,in which CO2 turns into an energy-excited state,its molecules decompose into individual radicals and atoms.In the melt-electrolyte under the influence of an electric field,ions-cations move in certain directions depending on the configuration of the field,which is due to magma,contact with rocks of the lithosphere and the speed of magma in the gap-tube.As they move,these ions undergo numerous collisions with the molecules present there,in particular,СО2 and its atoms and radicals,temporarily forming unstable compounds that fall into the zone with existing iron compounds,etc.OxygenСО2 poatomically detaches from the molecule and forms FeO·Fe2O3(magnetite),and the most energetically advantageous for chemically active carbon atoms in such an environment is that the melt bonds together form a diamond crystal.The isolated SiO2 molecules chemically form a group of garnets,quartz,and the like.

Mesozoic Volcanism Surrounding Songliao Basin,China: Implication for the Relationship with Evolution of Basin

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Cenozoic Volcanism in South China Sea and Its Vicinity and South China Sea Spreading

The rock series, rock types and Sr Nd isotopic dating of the Cenozoic volcanic rocks in the South China Sea are similar to those in its vicinity. On the basis of the spreading age of the South China Sea, the Cenozoic volcanic rocks are divided into three stages: the pre spreading stage, the spreading stage and the post spreading stage. The deep process characteristics of the asthenosphere and lithosphere may be inferred from the study on primary basaltic magma. The top layers of the asthenosphere both in the spreading stage and in the pre spreading stage are closer to the earth surface than that in the post spreading stage. From the pre spreading stage to the spreading stage, the top layer of the asthenosphere decreased in depth, while the amount of interstitial partial melts increased. The evolution of the primary basaltic magma shows a progressive evolution sequence of the rifting volcanism and a faster lithospheric spreading velocity. From the spreading stage to the post spreading stage, the top layer of the asthenosphere gradually increased in depth, but the amount of interstitial partial melts decreased. The evolution of primary basaltic magma shows a retrogressive evolution sequence of the rifting volcanism and a gradual decrease in the lithospheric spreading velocity. The depth recognized by the study on the Cenozoic volcanism demonstrates the deep environment for the formation and evolution of the South China Sea.

Destruction of the Northern Margin of the North China Craton in Mid-Late Triassic: Evidence from Asthenosphere-derived Mafic Enclaves in the Jiefangyingzi Granitic Pluton from the Chifeng Area, Southern Inner Mongolia

The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.

Study on Eogene Basalts: Implication of the Deep Process over the Bohaiwan Basin Evolution

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Late Cenozoic Tectonic Uplift Producing Mountain Building in Comparison with Mantle Structure in the Alpine-Himalayan Belt

Tectonic uplift producing recent mountain systems has spanned in the Alpine-Himalayan Belt the time interval from Oligocene to Recent (the last 30 - 35 Ma), being divided into two stages. During the first stage, local uplands, usually not higher than middle-elevated mountains, rose and their total area increased. During the second stage (the last 5 - 2 Ma) this process was accompanied by a total uplift of the greater part of the belt. As a result, the rate of vertical movements increased, the recent mountain systems were formed, and the coarse molasses accumulated in the adjacent basins. Uplift of the land surface resulting in formation of mountain topography is an isostatic reaction to decompaction of the upper spheres of the Solid Earth. Three factors of the decompaction are discussed in the paper. These are: I, collisional compression, resulting in deformational thickening of the Earth’s crust (folding, thrusting, etc.);II, partial replacing of the lithosphere mantle by the lower-dense asthenosphere material and, as a result, decompaction of the uppermost mantle;and III, retrograde metamorphism of high-metamorphosed rocks within the lower crust and near the crust-mantle boundary and, as a result, decompaction of these rocks. These processes were initiated or facilitated by the lateral asthenosphere flows. According to the seismic tomography data, the flows spread from the stationary developed zone of the rise of deep mantle material that is expressed in the recent structure as the Ethiopian-Afar super-plume. Reworking the 400 - 700-km deep transition layer of the mantle, the sub-lithosphere flows could be enriched in sources of aqueous fluids. The flows and their fluids initiated factors II and III of the tectonic uplift and caused softening and detachment of the lithosphere, facilitating deformational thickening of the Earth’s crust, i.e., the factor I. The latter produced uplands during the entire Oligocene-Quaternary development of the orogenic belt, while the factors II and III manifested themselves only during the second stage of mountain building. The detailed studies in the Central Tien Shan and the Greater Caucasus showed that the acceleration of uplift at the second stage was caused mainly by the factor II in the Central Tien Shan and the factor III in the Greater Caucasus.

Crustal and Upper Mantle Research in Pannonian Basin by Electromagnetic Induction:A Review

The review paper summarizes the main results of the electromagnetic inductionstudies carried out in the Pannonian Basin and Carpathians during the last30 years.The following conducting formations are discussed in detail:(1)Crustal conductors inthe crystalline basement of the sedimentary basin mainly due to graphitic schist blocksclearly connected to the fracture tectonics of the area;(2)Conducting layer in thelower crust probably due to free fluid deliberated by the dehydration process at tempera-ture of300—400℃during metamorphism;(3)Conducting asthenosphere due to par-tial melting at the bottom of the lithosphere;and(4)Conductivity increases due toolivine—spinel phase transition.All of these phenomena are strongly related to the spe-cial thermal state and tectonics of the Pannonian Basin and Carpathians.

Yanshanian Magma-Tectonic-Metallogenic Belt in East China of Circum-Pacific Domain(Ⅱ): Lithosphere-Asthenosphere System and Metallogenic Environment

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On Geophysical Background of Superlarge Deposits in the Chinese Continent

Based on the study of tens of geophysical profiles (seismic, geothermal flow and magnetotelluric sounding profiles) and 3-D shear wave velocity structures of the Chinese continent and its neighbouring regions, this paper describes the 3-D crustal and upper mantle structures and discusses briefly the deep geophysical background of superlarge ore deposits in the Chinese continent. Superlarge deposits are usually very few in number, but they are distributed still in certain forms such as 'point', 'zone' and 'area'. Most of the large-, medium- and small-sized deposits occur near the margins of different tectonic units; while the superlarge endogenic polymetallic deposits occur mostly in thinned mantle lithosphere, uplifts of the asthenosphere (vertical low-velocity zones) and the transformation zones of lateral inhomogeneity (weak zones) in the upper mantle. The superlarge endogenic polymetallic deposits are almost unevenly distributed in three major ore zones in China, corresponding to the boundaries of

The westward drift of the lithosphere:A tidal ratchet?

Is the westerly rotation of the lithosphere an ephemeral accidental recent phenomenon or is it a stable process of Earth's geodynamics? The reason why the tidal drag has been questioned as the mechanism determining the lithospheric shift relative to the underlying mantle is the apparent too high viscosity of the asthenosphere. However, plate boundaries asymmetries are a robust indication of the 'westerly'decoupling of the entire Earth's outer lithospheric shell and new studies support lower viscosities in the low-velocity layer(LVZ) atop the asthenosphere. Since the solid Earth tide oscillation is longer in one side relative to the other due to the contemporaneous Moon's revolution, we demonstrate that a non-linear rheological behavior is expected in the lithosphere mantle interplay. This may provide a sort of ratchet favoring lowering of the LVZ viscosity under shear, allowing decoupling in the LVZ and triggering the westerly motion of the lithosphere relative to the mantle.

THE CAUSE OF FORMATION OF THE LAYERS WITH LOW VELOCITY AND HIGH ELECTRICAL CONDUCTIVITY IN WESTERN TIBET

Comprehensive geophysical survey carried out in Western Tibet discovered that there is a layer with low velocity and high electrical conductivity embedded in the depth of 10～25km with a thickness of n km beneath the southern Gandise terrain and the southern Qiangtang terrain respectively. A low velocity body, simultaneously a high electrical conductivity body, exists in the depth of 40km with a thickness of 11～22km, expanding about 100km in NS direction beneath Dongco basin in the northern Gandise.In order to investigate how these layers were formed, more study on deep thermal status is needed.There is neither heat flow values measured on the spot nor thermal parameters measured of the typical rock in Western Tibet. The relations between heat flow values and other geological and geophysical parameters are analyzed. A method to calculate heat flow values and temperature distribution with the depth using the depth of Moho and the depth of the asthenosphere is suggested. In the area where there are both heat flow values measured and the two depths mentioned above, the heat flow values calculated using this method are very similar to the heat flow values measured.

The application of a gravimetric forward modelling of the lithospheric structure for an estimate of the average density of the upper asthenosphere

The average density of 3300 kg m-3 is often attributed for the asthenosphere. In this study, we inspect this value by estimating the average value of the(upper) asthenosphere based on applying the gravimetric forward modelling of major known lithospheric density structures. The LITHO1.0 global seismic model of the lithospheric density structure is used for this purpose, while considering that the lithosphere-asthenosphere boundary(LAB) is rheological, conventionally taken at the 1300C isotherm,above which the mantle behaves in a rigid fashion and below which it behaves in a ductile fashion.According to our result, the average density of the upper asthenosphere is roughly 3400 kg m-3. This density value closely agrees with the corresponding average value 3371 kg m-3 computed based on an empirical density model provided in the Preliminary Reference Earth Model(PREM), while using the LITHO1.0 LAB depth data. We also demonstrate that the sub-lithospheric mantle gravity map exhibits mainly a thermal signature. The most prominent features in this gravity map are mid-oceanic spearing ridges marked by gravity lows, while oceanic subductions in the West Pacific are characterized by the most pronounced gravity highs.

A numerical model for the gravimetric recovery of sub-lithospheric mantle structures

It is a well-known fact that the long-wavelength terrestrial geoid undulations are mainly attributed to deep mantle density heterogeneities,while more detailed features in the geoid geometry are associated with the topography and the lithospheric density structure.To enhance a gravitational signature of mantle density heterogeneities below the lithosphere,the gravitational contributions of topography and lithospheric density heterogeneities should be modelled and subsequently removed from Earth’s gravity field.The refined gravity field obtained after this numerical procedure is more suitable for a recovery of a mantle density structure(below the lithosphere).Following this idea,methods for a spherical harmonic analysis and synthesis of gravity field and lithospheric density structures are presented,and a theoretical relation between gravity field and mass density structure is formulated.Since a gravimetric recovery of inner density structure has a non-unique solution,we propose an alternative method based on a conversion of seismic velocities to mass densities.A forward modelling approach is then employed to find the mantle density configuration that generates the gravitational field that best approximates the corresponding refined gravitational field obtained from observed gravity field after subtracting the gravitational signal of the lithosphere.