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.

Geochemistry of the Cenozoic Potassic Volcanic Rocks in the West Kunlun Mountains and Constraints on Their Sources

The geochemical characteristics of the Cenozoic volcanic rocks from the north Pulu, east Pulu and Dahongliutan regions in the west Kunlun Mountains are somewhat similar as a whole. However, the volcanic rocks from the Dahongliutan region in the south belt are geochemically distinguished from those in the Pulu region (including the north and east Pulu) of the north belt. The volcanic rocks of the Dahongliutan region are characterized by relatively low TiO2 abundance, but more enrichment in alkali, much more enrichment in light rare earth elements and large ion lithosphile elements than those from the Pulu region. Compared with the Pulu region, volcanic rocks from the Dahongliutan region have relatively low 87Sr/86Sr ratios, and high εNd, 207Pb/204Pb and 208Pb/204Pb. Their trace elements and isotopic data suggest that they were derived from lithospheric mantle, consisting of biotite- and hornblende-bearing garnet lherzolite, which had undertaken metasomatism and enrichment. On the primitive mantle-normalized patterns, they display remarkably negative Nb and Ta anomalies, indicating the presence of early-stage subducted oceanic crust. The metasomatism and enrichment resulted from the fluid released from the crustal materials enclosed in the source region in response to the uplift of asthenospheric mantle. Based on the previous experiments it can be inferred that the thickness of the lithosphere ranges from 75 to 100 km prior to the generation of the magmas. However, the south belt differs from the north one by its thicker lithosphere and lower degree of partial melting. The different thickness of the lithosphere gives rise to corresponding variation of the degree of crustal contamination. The volcanic rocks in the south belt are much more influenced by crustal contamination. In view of the tectonic setting, the generation of potassic magmas is linked with the uplift of asthenosphere resulted from large-scale thinning of the lithosphere after the collision of Indian and Eurasian plates, whereas the thinning of the lithosphere may result from delamination. The potassic magmas mainly resulted from partial melting of lithosphere mantle caused by the uplift of asthenosphere.

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.

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.

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.

Carboniferous Post-collisional Rift Volcanism of the Tianshan Mountains, Northwestern China

The Tianshan Carboniferous post-collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post-collisional rift basic lavas can be classified into two major magma types: (1) the low-Ti/Y type situated in the eastern-central Tianshan area, which exhibits low Ti/Y (<500), Ce/Yb (<15) and SiO2 (43-55%), and relatively high Fe2O3T (6.4-11.5%); (2) the high-Ti/Y type situated in the western Tianshan area, which has high Ti/Y (>500), Ce/Yb (>11) and SiO2 (49-55%), and relatively low Fe2O3T (5.8-7.8%). Elemental data suggest that chemical variations of the low-Ti/Y and high-Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB-like asthenospheric mantle source (87Sr/86Sr(t) ≈ 0.703-0.705, eNd(0 = +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post-collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post-collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle-melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel-garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient.

Reassessment of petrogenesis of Carboniferous—Early Permian rift-related volcanic rocks in the Chinese Tianshan and its neighboring areas

The Carboniferous-Early Permian rift-related volcanic successions, covering large areas in the Chinese Tianshan and its adjacent areas, make up a newly recognized important Phanerozoic large igneous province in the world, which can be further divided into two sub-provinces： Tianshan and Tarim. The regional unconformity of Lower Carboniferous upon basement or pre-Carboniferous rocks, the ages （360--351 Ma） of the youngest ophiolite and the peak of subduction metamorphism of high pressure-low temperature metamorphic belt and the occurrence of Ni-Cu-bearing mafic-ultramafic intrusion with age of ~352 Ma and A-type granite with age of ~358 Ma reveal that the final closure of the Paleo-Asian Ocean might take place in the Early Mississippian. Our summation shows that at least four criteria, being normally used to identify ancient asthenosphere upwelling （or mantle plumes）, are met for this large igneous province： （1） surface uplift prior to magmatism; （2） being associated with continental rifting and breakup events; （3） chemical characteristics of asthenosphere （or plume） derived basalts; （4） close links to large-scale mineralization and the uncontaminated basalts, being analogous to those of many ＂ore-bearing＂ large igneous provinces, display Sr-Nd isotopic variations between plume and EMI geochemical signatures, These suggest that a Carboniferous asthenosphere upwelling and an Early Permian plume played the central role in the generation of the Tianshan--Tarim （central Asia） large igneous province.

Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China

The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyroxene thermometer of Brey and Kohler （1990）, and using the oxybarometry of Nell and Wood （1991）, the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 （n = 8）, which is comparable to that of abyssal peridotites and the asthenospheric mantle. ThefO2 values of peridotites, together with their bulk rock compositions （e.g., Mg#, Al2O3, CaO, Ni, Co, Cr） and mineral compositions （e.g., Mg# of olivine and pyroxene, Cr# [=Cr/ [Cr＋Al]] and Mg# [=Mg/[Mg＋Fe2~] of spinel）, suggest that the present-day subcontinental lithospheric mantle （SCLM） beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements （PGE）, which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field （LVF） in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton （NCC） in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospberic mantle.

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

esozoic volcanic rocks developed on the basement of the Precambrian block and Hercynina orogenic belt surrounding Songliao basin. The volcanism was actived from Early Jurassic to Late Cretaceous with its peak time in J3-K1 and the rock types are dominated by high K calcalkaline series, partly consisting of shoshonitic and calcalkaline series. Mesozoic volcanism of studied area may result from decompression melting accompanying uneven extension wide spread at a large area corresponding to the formation of grabens without contemporaneous subduction in J3-K1. The basic volcanics and their differentiates came from an enriched lithospheric mantle. While in K2 the extensional center concentrated at Songliao basin and the equivalent products are basalts rich in Na and poor in K and the magma generated from the top of asthenosphere about 60 km. During this time large Songliao depression was developed.

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.

The principal characteristics of the lithosphere of China

The lithospheric structure of China and its adjacent area is very complex and is marked by several prominent characteristics. Firstly, China＇s continental crust is thick in the west but thins to the east, and thick in the south but thins to the north. Secondly, the continental crust of the Qinghai--Tibet Plateau has an average thickness of 60-65 km with a maximum thickness of 80 km, whereas in eastern China the average thickness is 30-35 km, with a minimum thickness of only 5 km in the center of the South China Sea. The average thickness of continental crust in China is 47.6 km, which greatly exceeds the global average thickness of 39.2 km. Thirdly, as with the crust, the lithosphere of China and its adja- cent areas shows a general pattern of thicker in the west and south, and thinner in the east and north. The lithosphere of the Qinghai--Tibet Plateau and northwestern China has an average thickness of 165 kin, with a maximum thickness of 180--200 km in the central and eastern parts of the Tarim Basin, Pamir, and Changdu areas. In contrast, the vast areas to the east of the Da Hinggan Ling-Taihang-Wuling Mountains, including the marginal seas, are characterized by lithospheric thicknesses of only 50-85 kin. Fourthly, in western China the lithosphere and asthenosphere behave as a ＂layered structure＂, reflecting their dynamic background of plate collision and convergence. The lithosphere and asthenosphere in eastern China display a ＂block mosaic structure＂, where the lithosphere is thin and the asthenosphere is very thick, a pattern reflecting the consequences of crustal extension and an upsurge of asthenospheric materials. The latter is responsible for a huge low velocity anomaly at a depth of 85--250 km beneath East Asia and the western Pacific Ocean. Finally, in China there is an age structure of ＂older in the upper layers and younger in the lower layers＂ between both the upper and lower crusts and between the crust and the lithospheric mantle.

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

The present paper describes the characteristics of Cenozoic basalt in the Bohaiwan basin and its implication of the control of deep process over the basin evolution. The large scale Eogene basalts lying on the basement of the Bohaiwan basin belong to alkaline series and subalkaline series. The basalt magma originates at a depth of 48-76 km and a temperature of 1 300-1 400 ℃ with the mantle partial melting degree of 8%-14%. In Eogene period, the rising of the top of asthenosphere from 100-140 km to 50-70 km led to the strong extension and thinning of the overlying lithosphere, which was stretched at an average rate of 0.41 cm/a and the β value from 1.9 to 2.3. At the same time, it triggered the great scale rifting in the earth crust, forming large rift basins.

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.

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.

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

The review paper summarizes the main results of the electromagnetic induction studies carried out in the Pannonian Basin and Carpathians during the last 30 years . The following conducting formations are discussed in detail : (1)Crustal conductors in the crystalline basement of the sedimentary basin mainly due to graphitic schist blocks clearly connected to the fracture tectonics of the area ; (2 ) Conducting layer in the lower crust probably due to free fluid deliberated by the dehydration process at temperature of 300-400℃during metamorphism ; (3 ) Conducting asthenosphere due to partial melting at the bottom of the lithosphere ; and (4) Conductivity increases due to olivine-spinel phase transition .All of these phenomena are strongly related to the special thermal state and tectonics of the Pannonian Basin and Carpathians.