The 3^(rd) International Earth Science Olympiad(www.ieso2009.tw/home/home.html)was organized by the National Taiwan Normal University at Taipei,Taiwan.Fifty students from 14 countries participated in the 3^(rd) IESO.F...The 3^(rd) International Earth Science Olympiad(www.ieso2009.tw/home/home.html)was organized by the National Taiwan Normal University at Taipei,Taiwan.Fifty students from 14 countries participated in the 3^(rd) IESO.Four other countries sent Observers.展开更多
The purpose of this study is to investigate the effect of Panoramic Virtual Reality(PVR)applied to online earth science classes on students’learning flow.To this end,a PVR learning material was made with a geology le...The purpose of this study is to investigate the effect of Panoramic Virtual Reality(PVR)applied to online earth science classes on students’learning flow.To this end,a PVR learning material was made with a geology learning site,which contains a core geologic concept contained in a high school curriculum in Korea.To this end,a PVR learning material was made at a geologic field site to provide an interactive and engaging way for students to grasp core geologic concepts according to the high school curriculum in Korea.The PVR was applied to online earth science classes with 45 high school students.In order to examine the effect of the PVR on students'learning flow,pre-post learning flow test papers were used,then matchedsample t-test analysis and students'responses were analyzed.The result shows online classes with PVR have positive effects on learning flow(p<0.05).And it was possible for the students to observe three-dimensional geologic structures effectively in online classes as in offline field trips.And the students'responded with positive feedbacks.These suggest that PVR in online classes can be used as an effective teaching method,which can improve students'flow and eventually understanding subjects.展开更多
Dilatancy is referred to the phenomenon of volume increase that occurs when a material is deformed.Dilatancy theory originated in geomechanics for the study of the behavior of granular materials.Later it is expanded t...Dilatancy is referred to the phenomenon of volume increase that occurs when a material is deformed.Dilatancy theory originated in geomechanics for the study of the behavior of granular materials.Later it is expanded to the case of more brittle materials like rocks when it is subjected to the load of varying effective stress and starts to crack and deform,then named the dilatancy-diffusion hypothesis.This hypothesis was developed to explain the changes in rock volume and pore pressure that occur prior to and during fault slip,which can influence earthquake dynamics.Dilatancy-fluid diffusion is a significant concept in understanding the seismogenic process and has served as the major theoretical pillar for earthquake prediction by its classic definition.This paper starts with the recount of fundamental laboratory experiments on granular materials and rocks,then conducts review and examination of the history for using the dilatancy-diffusion hypothesis to interpret the‘prediction’of the 1975 Haicheng Earthquake and other events.The Haicheng Earthquake is the first significant event to be interpreted with the dilatancy-diffusion hypothesis in the world.As one pivotal figure in the development of the dilatancy-diffusion hypothesis for earthquake prediction Professor Amos Nur of Stanford University worked tirelessly to attract societal attention to this important scientific and humanistic issue.As a deterministic physical model the dilatancy-diffusion hypothesis intrinsically bears the deficit to interpret the stochastic seismogenic process.With the emergence of deep learning and its successful applications to many science and technology fields,we may see a possibility to overcome the shortcoming of the current state of the theory with the addition of empirical statistics to push the operational earthquake forecasting approach with the addition of the physicallyinformed neural networks which adopt the dilatancy-diffusion hypothesis as one of its embedded physical relations,to uplift the seismic risk reduction to a new level for saving lives and reducing the losses.展开更多
The green energy transition relies heavily on critical metals,such as rare earth elements(REEs).However,their reserves are primarily focused in a few countries,such as China,which accounts for approximately 70%of glob...The green energy transition relies heavily on critical metals,such as rare earth elements(REEs).However,their reserves are primarily focused in a few countries,such as China,which accounts for approximately 70%of global production.Hence,several countries are currently looking for alternative resources for REEs.Alternative REE resources in the supply chain include recycling of e-waste,industrial waste like red mud and phosphogypsum,coal ash,mine tailings,ocean floor sediments,and even certain types of sedimentary deposits like phosphorites where REEs are present in lower concentrations but at larger volumes compared to primary ore deposits which are becoming targets by REEs industry.Currently,several studies are going on the development of eco-friendly REEs extraction technologies from phosphorite deposits.Consequently,advanced data analysis tools,such as Machine Learning(ML),are becoming increasingly important in mineral prospectivity and are rapidly gaining traction in the earth sciences.Phosphorite deposits are mainly used to manufacture fertilizers as these rocks are known for their significant phosphorus content.Moreover,these formations are considered a prospective resource of REEs.The different types of phosphorite deposits such as continental,seamount,and ore deposits worldwide reported concentrations of∑REE upto 18,000µg/g.Due to the augmented claim of REEs for various ultra-modern,and green technology applications that are required to switch over to a carbon-neutral environment,these phosphorite deposits have become an important target mostly because of their relatively higher content of REEs especially heavy rare earth elements(HREE).For example,Mississippian phosphorites reported ∑ HREE 7,000µg/g.To have a comprehensive understanding of the REEs potential of these phosphorite deposits which also include several Chinese phosphorite deposits,this study is undertaken to review the phosphorite deposits in the world and their REEs potential,in addition to some of the associated aspects such as applications and formation mechanisms for different types of phosphorite deposits such as igneous phosphate deposits,sedimentary phosphorite deposits,marine phosphorite deposits,cave phosphate deposits,and insular guano deposits.Other important aspects include their occurrences,types,geochemical characteristics,the REEs enrichment mechanisms,and various recovery methods adopted to recover REEs from different phosphorite deposits.The present review paper concludes that the recent studies highlight the global potential of phosphorite deposits to satisfy the increasing demand for REEs.Extracting REEs from phosphorite presents no significant technological or environmental difficulties,as long as radioactive elements are eliminated.In India,more comprehensive geological surveys,along with the advancement of new methods and evaluations,are required to locate phosphorite deposits with high concentrations of REEs.展开更多
In the present study, trace element(including rare earth element) chemical data has been interpreted with the aim to decipher the tectonic setting and paleo-redox conditions of the Post- to Neo-archean shales from the...In the present study, trace element(including rare earth element) chemical data has been interpreted with the aim to decipher the tectonic setting and paleo-redox conditions of the Post- to Neo-archean shales from the Singhbhum Mobile Belt, eastern India. The data show moderate enrichment of compatible elements [such as Cu(avg. 59.28 ppm), Ni(avg. 59.49 ppm), V(avg.234.24 ppm) and Cr(avg. 181.23 ppm)] relative to the Post-Archean Australian Shale. Their chondrite normalized light rare earth elements are moderately fractionated [(La/Sm)Nranges from 2.21 to 5.78], whereas heavy rare earth elements show a nearly flat pattern [(Gd/Lu)Nranges from0.74 to 1.68]; this indicates that the rare earth element(REE) concentrations, rather than being severely affected by the diagenesis and weathering processes, decreased gradually from Gd to Lu. The Post-Archean Australian Shale normalized multi-element diagram shows the slight enrichment of Cr, V, Zr, Y, U and Sc, whereas Sr, Pb, Hf and Th are depleted. The notable negative anomaly of Sr indicates the least accumulation of plagioclase, which is also supported by the negative Eu-anomaly in these rocks.The La–Th–Sc and Th–Zr–Sc tectonic setting diagrams indicate their continental arc setting. The geochemical parameters, such as U/Th, V/Cr, Ni/Co, and Cu/Zn, indicate that these shales were deposited under oxic to anoxic environmental conditions.展开更多
This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.I...This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.展开更多
In order to examine the factors which affect the range of heat transfer in earth surrounding subways, FLAC3D was adopted in this study to analyze these factors, under different conditions, in a systematic manner. When...In order to examine the factors which affect the range of heat transfer in earth surrounding subways, FLAC3D was adopted in this study to analyze these factors, under different conditions, in a systematic manner. When we compare these numerical tests, the results show that the main factors, affecting the heat transfer range are the thermal properties of the surrounding earth, the initial ground temperature and the temperature in the tunnel. The heat transfer coefficient between air and linings has little effect on the temperature distribution around the tunnel. The current results can provide a reference for improving the thermal environment in subways and optimizing the design of subwav ventilation and air conditioning.展开更多
Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those acti...Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming, through the infilling of seasonal （winter） thermal contraction-cracks in perma- frost by windblown sand, in present-day polar regions with a mean monthly air temperature range of 40 ~C and mean annual air temperatures of -20 ~C or lower. Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle. The seasonal （annual） oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas. Palaeomagnetic data determined directly for Prote- rozoic glacial deposits and closely associated rocks indicate low palaeolatitudes： Cryogenian deposits in South Australia accumulated at 〈10% most other Cryogenian deposits at 〈20~ and Palaeoproterozoic deposits at 〈15~ palaeolatitude. Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole, hence palaeolatitudes represent geographic latitudes. The Cry- ogenian glacial environment included glacier-flee, continental permafrost regions with ground frozen on a kyr time-scale, aeolian sand-sheets, extensive and long-lived open seas, and an active hydrological cycle. This palaeoenvironment confiicts with the ＇snowball Earth＇ and ＇slushball Earth＇ hypotheses, which cannot accommodate large seasonal changes of temperature near the equator. Consequently, their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian ＇auxiliary assumptions＇. However, non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial pro- cesses. Modelling of a strongly seasonal climate for a frozen-over Earth is invalidated by the evidence for persistent open seas and glacier-free continental regions during Cryogenian glaciations, and gives a mean monthly air temperature range of only 〈10 ~C for 〈10~ latitude. By contrast, a strongly seasonal climate in low palaeolatitudes, based on the actualistic interpretation of cryogenic sand wedges and other structures, is consistent with a high obliquity of the ecliptic （〉54°） during Proterozoic low-latitude glaciations, whereby the equator would be cooler than the poles, on average, and global seasonality would be greatly amplified.展开更多
The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolu...The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.展开更多
Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Gorges Area, South China. In this study, rare earth element geochemistry of eight phosphatic rock samples from the Hu...Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Gorges Area, South China. In this study, rare earth element geochemistry of eight phosphatic rock samples from the Hushan Section has been studied. All the samples display typical hat-shaped REE patterns, moderate negative Ce anomalies（Ce/Ce＊=0.55 to 0.67）, slightly positive Eu anomalies（Eu/Eu＊=1.05 to 1.22） and low Y/Ho ratios（38.2±5.6）. The hat-shaped REE patterns indicate diagenetic alteration of the primary REE signatures, which coincides with detrital siliciclastic sources of REE based on the Y/Ho ratios. The degree of Negative Ce anomalies and positive Eu anomalies may have recorded the redox features of diagenetic fluids, suggesting an anoxic environment during the phosphogenesis processes in Neoproterozoic Ediacaran Doushantuo Formation, South China. The geochemical comparison between the Lower Phosphorite Layer and Upper Phosphorite Layer at Hushan indicates a greater degree of diagenesis occurred in the Upper Layer than the Lower one. Besides the terrigenous sources of REE, organic materials could have also played a role on the REE characteristics.展开更多
Zhijin County in Western Guizhou is one of the most important production areas of phosphorites in China. In order to investigate genesis of the phosphorites, their REE compositions were analyzed by using inductively c...Zhijin County in Western Guizhou is one of the most important production areas of phosphorites in China. In order to investigate genesis of the phosphorites, their REE compositions were analyzed by using inductively coupled plasma emission mass spectrometry (ICP-MS) method. For comparison, phosphorites from the Lower Cambrian black rock series in Southern China, such as Zunyi in Guizhou and Zhangjiajie in Hunan Province, were also analyzed. The analytical data show that: (1) Xinhua phosphorites possess a quite high and greatly varied total rare earth elements (ΣREE), which varying between 164.23×10-6 and 1395.01×10-6 with average of 642.54×10-6, remarkable differentiation between light (LREE) and heavy rare earth elements (HREE), and the ΣLREE/ΣHREE ratios varying between 5.04 and 6.52. The ΣREE and ΣLREE/ΣHREE ratios of the Zunyi and Zhangjiajie phosphorites are 156.69×10-6～637.41×10-6 with average of 431 75×10-6 and 3.17～6.95 with average of 4.37 respectively; (2) All the phosphorites from Xinhua, Zunyi and Zhangjiajie show remarkable negative Ce anomalies. Besides, the Xinhua phosphorites possess lower δCe, which varying between 0.26 and 0.53 with average of 0.35, while δCe of the Zunyi and Zhangjiajie phosphorites are 0.30～0.66 with average of 0.47, suggesting that all of the phosphorites are typical marine sediments deposited mainly in ancient peri-continental seas, and the depositional position of the Xinhua phosphorite might be deeper; (3) Most phosphorites from Xinhua, Zunyi and Zhangjiajie possess unremarkable positive Eu anomaly, and only a few of samples show obvious ones. The δEu varies between 0.98 and 2.4, suggesting that hot (>200 ℃) and strong reductive hydrothermal fluids might have been involved in genesis of the phosphorites; (4) The Xinhua phosphorite is relatively depleted in HREE, and LaN/NdN and δY of most samples are >1 and >1.5 respectively. Besides, there exists no correlation between δY and δCe, suggesting that the phosphorite was subjected to quite strong weathering and leaching processes, and catagenesis do not greatly modify its REE compositions.展开更多
Trace element(TE) and rare earth element(REE) contents in red soils from the Dongting Lake area of China were determined to understanding the provenance and weathering characteristics of the red soils.The results show...Trace element(TE) and rare earth element(REE) contents in red soils from the Dongting Lake area of China were determined to understanding the provenance and weathering characteristics of the red soils.The results showed similar REE distribution patterns among red soils from the Dongting Lake area,Xiashu loess from Zhenjiang,loess and Pliocene red soil from the Loess Plateau.These patterns implied a similar provenance from dust-storms,except for red soil R5 which formed by bedrock weathering and had significant light REE(LREE) enrichment and heavy REE(HREE) depletion due to longer weathering periods and higher intensity of weathering.Trace element,especially the Rb/Sr and Li/Ba ratios,and REE,especially the LREE/HREE ratio and δEu could trace weathering intensity.Higher Rb/Sr,Li/Ba,and LREE/HREE ratios and negative Eu anomalies were present in the red soils from the Dongting Lake area.The weathering intensity was in the decreasing order of R5 in the Dongting Lake area > red soils from the Dongting Lake area(including reticulate red soil,weak reticulate red soil,and homogeneous red soil formed by dust storms) > Xiashu loess from Zhenjiang > loess-paleosol and Pliocene red soil from the Loess Plateau.Variations in the TE and REE contents of soil could be effectively used to study the provenance and the weathering intensity.展开更多
In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atm...In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian ＂explosion＂ of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth＇s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break- up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic （Huronian） carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off after the Great Oxidation Event of the Paleoproterozoic？ The answer may lie in the huge scar left by the -2023 Ma Vredefort impact in South Africa, and in the worldwide organic carbon-rich deposits of the Shunga Event, arresting to the near-extirpation of life and possible radical alteration of the course of Earth history.展开更多
We present a high-resolution seismic catalog for the 2021 M_(S)6.4/M_(W)6.1 Yangbi sequence.The catalog has a time range of 2021-05-01 to 2021-05-28,and contains~8,000 well located events.It captures the features of t...We present a high-resolution seismic catalog for the 2021 M_(S)6.4/M_(W)6.1 Yangbi sequence.The catalog has a time range of 2021-05-01 to 2021-05-28,and contains~8,000 well located events.It captures the features of the whole foreshock sequence and the early aftershocks.We designed a detection strategy incorporating both an artificial intelligent(AI)picker and a matched filter algorithm.Here,we adopt a hybrid AI method incorporating convolutional and recurrent neural network(CNN&RNN)for event detection and phase picking respectively(i.e.CERP),a light-weight AI picker that can be trained with small volume of data.CERP is first trained with detections from a STA/LTA and Kurtosis-based method called PAL,and then construct a rather complete template set of~4,000 events.Finally,the matched filter algorithm MESS augments the initial detections and measures differential travel times with cross-correlation,which finally results in precise relocation.This process gives 9,026 detections,among which 7,943 events can be well relocated.The catalog shows as expected power-law distribution of frequency magnitude and reveals detailed pattern of seismicity evolution.The main features are:(1)the foreshock sequence images simple fault geometry with consistent strike,but also show a variable event depth along strike;(2)the mainshock ruptures the same fault of the foreshock sequence and activate conjugate faults further to the southeast;(3)complex seismicity are developed in the post-seismic period,indicating complex triggering mechanisms.Thus,our catalog provides a reliable basis for further investigations,such as b-value studies,rupture process,and triggering relations.展开更多
The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and ...The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.展开更多
Data obtained by GRACE(Gravity Recovery and Climate Experiment) have been used to invert for the seismic source parameters of megathrust earthquakes under the assumption of either uniform slip over an entire fault or ...Data obtained by GRACE(Gravity Recovery and Climate Experiment) have been used to invert for the seismic source parameters of megathrust earthquakes under the assumption of either uniform slip over an entire fault or a point-like seismic source.Herein, we further extend the inversion of GRACE long-wavelength gravity changes to heterogeneous slip distributions during the 2011 Tohoku earthquake using three fault models:(Ⅰ) a constant-strike and constant-dip fault,(Ⅱ) a variable dip fault, and(Ⅲ) a realistically varying strike fault. By removing the post-seismic signal from the time series, and taking the effect of ocean water redistribution into account, we invert for slip models I, II, and III using co-seismic gravity changes measured by GRACE, de-striped by DDK3 decorrelation filter. The total seismic moments of our slip models, with respective values of 4.9×10^(22) Nm, 5.1×10^(22) Nm, and 5.0×10^(22) Nm, are smaller than those obtained by other studies relying on GRACE data. The resulting centroids are also located at greater depths(20 km, 19.8 km,and 17.4 km, respectively). By combining onshore GPS, GPS-Acoustic, and GRACE data, we obtain a jointly inverted slip model with a seismic moment of 4.8×10^(22) Nm, which is larger than the seismic moment obtained using only the GPS displacements. We show that the slip inverted from low degree space-borne gravimetric data, which contains information at the ocean region, is affected by the strike of the arcuate trench. The space-borne gravimetric data help us constrain the source parameters of a megathrust earthquake within the frame of heterogeneous slip models.展开更多
This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma...This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.展开更多
This research uses eigenvalue characteristics of nonlinear principal component analysis （NLPCA） and principal component analysis （PCA） to investigate total electron content （TEC） anomalies associated with Taiwan...This research uses eigenvalue characteristics of nonlinear principal component analysis （NLPCA） and principal component analysis （PCA） to investigate total electron content （TEC） anomalies associated with Taiwan＇s Chi-Chi earthquake of 21 September 1999 （LT） （M_w=7.6）. The transforms are used for ionospheric TEC from 01 August to 20 September 1999 （local time） using data from 13 GPS receivers. The data were collected at 22°N-26°N Lat. and 120°E-122°E Long.. Applying the NLPCA to the multi-channel total electron content records of GPS receivers, the earthquake-associated TEC anomalies were represented by large principal eigenvalues of NLPCA （〉0.5 in a normalized set） on 14 August and 17, 18, and 20 September, with allowance given for the Dst index, which was quiet for the study period. Comparisons were then made with other researchers who also found TEC anomalies on September 17, 18, and 19 associated with the Chi-Chi earthquake, which cannot be detected by PCA.Consideration is also given for reported ground level geomagnetic field activity that occurred between mid-August and late October, leading up to and including the Chi-Chi and Chia-Yi earthquakes, which are associated with the same series of faults. It is possible that Aug. 14 is representative of an earthquake-associated TEC anomaly. This is an interesting result given how much earlier than the earthquake it occurred.展开更多
This paper reports statistical results of Seismo-Ionospheric Anomalies(SIAs) of the Total Electron Content(TEC) in the Global Ionosphere Map(GIM) associated with 56 M≥6.0 earthquakes in China during 1998—2012.To det...This paper reports statistical results of Seismo-Ionospheric Anomalies(SIAs) of the Total Electron Content(TEC) in the Global Ionosphere Map(GIM) associated with 56 M≥6.0 earthquakes in China during 1998—2012.To detect SIA,a quartile-based(i.e.median-based) process is performed.TEC anomalies for the period of earthquakes without being led by magnetic storms about 10 days are further isolated and examined to confirm the SIP existence.Results show that SIA is the TEC significantly decrease in the afternoon period 2—9 days before the earthquakes in China,which is in a good agreement with the SIA appearing before the 12 May 2008 M 8.0 Wenchuan earthquake.展开更多
文摘The 3^(rd) International Earth Science Olympiad(www.ieso2009.tw/home/home.html)was organized by the National Taiwan Normal University at Taipei,Taiwan.Fifty students from 14 countries participated in the 3^(rd) IESO.Four other countries sent Observers.
基金supported by the research grant of the Kongju National University in 2023.
文摘The purpose of this study is to investigate the effect of Panoramic Virtual Reality(PVR)applied to online earth science classes on students’learning flow.To this end,a PVR learning material was made with a geology learning site,which contains a core geologic concept contained in a high school curriculum in Korea.To this end,a PVR learning material was made at a geologic field site to provide an interactive and engaging way for students to grasp core geologic concepts according to the high school curriculum in Korea.The PVR was applied to online earth science classes with 45 high school students.In order to examine the effect of the PVR on students'learning flow,pre-post learning flow test papers were used,then matchedsample t-test analysis and students'responses were analyzed.The result shows online classes with PVR have positive effects on learning flow(p<0.05).And it was possible for the students to observe three-dimensional geologic structures effectively in online classes as in offline field trips.And the students'responded with positive feedbacks.These suggest that PVR in online classes can be used as an effective teaching method,which can improve students'flow and eventually understanding subjects.
基金sponsored by the National Research Foundation of Korea(RS-2023-00220913).
文摘Dilatancy is referred to the phenomenon of volume increase that occurs when a material is deformed.Dilatancy theory originated in geomechanics for the study of the behavior of granular materials.Later it is expanded to the case of more brittle materials like rocks when it is subjected to the load of varying effective stress and starts to crack and deform,then named the dilatancy-diffusion hypothesis.This hypothesis was developed to explain the changes in rock volume and pore pressure that occur prior to and during fault slip,which can influence earthquake dynamics.Dilatancy-fluid diffusion is a significant concept in understanding the seismogenic process and has served as the major theoretical pillar for earthquake prediction by its classic definition.This paper starts with the recount of fundamental laboratory experiments on granular materials and rocks,then conducts review and examination of the history for using the dilatancy-diffusion hypothesis to interpret the‘prediction’of the 1975 Haicheng Earthquake and other events.The Haicheng Earthquake is the first significant event to be interpreted with the dilatancy-diffusion hypothesis in the world.As one pivotal figure in the development of the dilatancy-diffusion hypothesis for earthquake prediction Professor Amos Nur of Stanford University worked tirelessly to attract societal attention to this important scientific and humanistic issue.As a deterministic physical model the dilatancy-diffusion hypothesis intrinsically bears the deficit to interpret the stochastic seismogenic process.With the emergence of deep learning and its successful applications to many science and technology fields,we may see a possibility to overcome the shortcoming of the current state of the theory with the addition of empirical statistics to push the operational earthquake forecasting approach with the addition of the physicallyinformed neural networks which adopt the dilatancy-diffusion hypothesis as one of its embedded physical relations,to uplift the seismic risk reduction to a new level for saving lives and reducing the losses.
基金the Anusandhan National Research Foundation(ANRF),Science and Engineering Research Board(SERB),Department of Science&Technology,Government of India for a start-up research grant(M-14/0599,Sanction order no.SRG/2022/001478)Seed Grant under Institutions of Eminence(IoE),Banaras Hindu University(BHU)(Dev.Scheme No.6031)for financial assistance.
文摘The green energy transition relies heavily on critical metals,such as rare earth elements(REEs).However,their reserves are primarily focused in a few countries,such as China,which accounts for approximately 70%of global production.Hence,several countries are currently looking for alternative resources for REEs.Alternative REE resources in the supply chain include recycling of e-waste,industrial waste like red mud and phosphogypsum,coal ash,mine tailings,ocean floor sediments,and even certain types of sedimentary deposits like phosphorites where REEs are present in lower concentrations but at larger volumes compared to primary ore deposits which are becoming targets by REEs industry.Currently,several studies are going on the development of eco-friendly REEs extraction technologies from phosphorite deposits.Consequently,advanced data analysis tools,such as Machine Learning(ML),are becoming increasingly important in mineral prospectivity and are rapidly gaining traction in the earth sciences.Phosphorite deposits are mainly used to manufacture fertilizers as these rocks are known for their significant phosphorus content.Moreover,these formations are considered a prospective resource of REEs.The different types of phosphorite deposits such as continental,seamount,and ore deposits worldwide reported concentrations of∑REE upto 18,000µg/g.Due to the augmented claim of REEs for various ultra-modern,and green technology applications that are required to switch over to a carbon-neutral environment,these phosphorite deposits have become an important target mostly because of their relatively higher content of REEs especially heavy rare earth elements(HREE).For example,Mississippian phosphorites reported ∑ HREE 7,000µg/g.To have a comprehensive understanding of the REEs potential of these phosphorite deposits which also include several Chinese phosphorite deposits,this study is undertaken to review the phosphorite deposits in the world and their REEs potential,in addition to some of the associated aspects such as applications and formation mechanisms for different types of phosphorite deposits such as igneous phosphate deposits,sedimentary phosphorite deposits,marine phosphorite deposits,cave phosphate deposits,and insular guano deposits.Other important aspects include their occurrences,types,geochemical characteristics,the REEs enrichment mechanisms,and various recovery methods adopted to recover REEs from different phosphorite deposits.The present review paper concludes that the recent studies highlight the global potential of phosphorite deposits to satisfy the increasing demand for REEs.Extracting REEs from phosphorite presents no significant technological or environmental difficulties,as long as radioactive elements are eliminated.In India,more comprehensive geological surveys,along with the advancement of new methods and evaluations,are required to locate phosphorite deposits with high concentrations of REEs.
文摘In the present study, trace element(including rare earth element) chemical data has been interpreted with the aim to decipher the tectonic setting and paleo-redox conditions of the Post- to Neo-archean shales from the Singhbhum Mobile Belt, eastern India. The data show moderate enrichment of compatible elements [such as Cu(avg. 59.28 ppm), Ni(avg. 59.49 ppm), V(avg.234.24 ppm) and Cr(avg. 181.23 ppm)] relative to the Post-Archean Australian Shale. Their chondrite normalized light rare earth elements are moderately fractionated [(La/Sm)Nranges from 2.21 to 5.78], whereas heavy rare earth elements show a nearly flat pattern [(Gd/Lu)Nranges from0.74 to 1.68]; this indicates that the rare earth element(REE) concentrations, rather than being severely affected by the diagenesis and weathering processes, decreased gradually from Gd to Lu. The Post-Archean Australian Shale normalized multi-element diagram shows the slight enrichment of Cr, V, Zr, Y, U and Sc, whereas Sr, Pb, Hf and Th are depleted. The notable negative anomaly of Sr indicates the least accumulation of plagioclase, which is also supported by the negative Eu-anomaly in these rocks.The La–Th–Sc and Th–Zr–Sc tectonic setting diagrams indicate their continental arc setting. The geochemical parameters, such as U/Th, V/Cr, Ni/Co, and Cu/Zn, indicate that these shales were deposited under oxic to anoxic environmental conditions.
基金supported by the "Wenchuan Earthquake Fault Scientific Drilling" of the National Science Foundation of China
文摘This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.
基金Projects BK2007145 supported by the Jiangsu Natural Science Foundation of China NCET-04-0454 by the Program for New Century Excellent Talentsin Universities
文摘In order to examine the factors which affect the range of heat transfer in earth surrounding subways, FLAC3D was adopted in this study to analyze these factors, under different conditions, in a systematic manner. When we compare these numerical tests, the results show that the main factors, affecting the heat transfer range are the thermal properties of the surrounding earth, the initial ground temperature and the temperature in the tunnel. The heat transfer coefficient between air and linings has little effect on the temperature distribution around the tunnel. The current results can provide a reference for improving the thermal environment in subways and optimizing the design of subwav ventilation and air conditioning.
文摘Proterozoic （pre-Ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming, through the infilling of seasonal （winter） thermal contraction-cracks in perma- frost by windblown sand, in present-day polar regions with a mean monthly air temperature range of 40 ~C and mean annual air temperatures of -20 ~C or lower. Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle. The seasonal （annual） oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas. Palaeomagnetic data determined directly for Prote- rozoic glacial deposits and closely associated rocks indicate low palaeolatitudes： Cryogenian deposits in South Australia accumulated at 〈10% most other Cryogenian deposits at 〈20~ and Palaeoproterozoic deposits at 〈15~ palaeolatitude. Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole, hence palaeolatitudes represent geographic latitudes. The Cry- ogenian glacial environment included glacier-flee, continental permafrost regions with ground frozen on a kyr time-scale, aeolian sand-sheets, extensive and long-lived open seas, and an active hydrological cycle. This palaeoenvironment confiicts with the ＇snowball Earth＇ and ＇slushball Earth＇ hypotheses, which cannot accommodate large seasonal changes of temperature near the equator. Consequently, their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian ＇auxiliary assumptions＇. However, non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial pro- cesses. Modelling of a strongly seasonal climate for a frozen-over Earth is invalidated by the evidence for persistent open seas and glacier-free continental regions during Cryogenian glaciations, and gives a mean monthly air temperature range of only 〈10 ~C for 〈10~ latitude. By contrast, a strongly seasonal climate in low palaeolatitudes, based on the actualistic interpretation of cryogenic sand wedges and other structures, is consistent with a high obliquity of the ecliptic （〉54°） during Proterozoic low-latitude glaciations, whereby the equator would be cooler than the poles, on average, and global seasonality would be greatly amplified.
基金This paper was sponsored by the National Natural Science Foundation of China(grant No.40272049)Doctor Research Foundation of China University of Petroleum(Project No.Y020109).
文摘The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.
基金supported by projects from the National Natural Science Foundation of China (Nos. 41230102,41273009)the National 973 project (No. 2013CB835000)
文摘Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Gorges Area, South China. In this study, rare earth element geochemistry of eight phosphatic rock samples from the Hushan Section has been studied. All the samples display typical hat-shaped REE patterns, moderate negative Ce anomalies（Ce/Ce＊=0.55 to 0.67）, slightly positive Eu anomalies（Eu/Eu＊=1.05 to 1.22） and low Y/Ho ratios（38.2±5.6）. The hat-shaped REE patterns indicate diagenetic alteration of the primary REE signatures, which coincides with detrital siliciclastic sources of REE based on the Y/Ho ratios. The degree of Negative Ce anomalies and positive Eu anomalies may have recorded the redox features of diagenetic fluids, suggesting an anoxic environment during the phosphogenesis processes in Neoproterozoic Ediacaran Doushantuo Formation, South China. The geochemical comparison between the Lower Phosphorite Layer and Upper Phosphorite Layer at Hushan indicates a greater degree of diagenesis occurred in the Upper Layer than the Lower one. Besides the terrigenous sources of REE, organic materials could have also played a role on the REE characteristics.
文摘Zhijin County in Western Guizhou is one of the most important production areas of phosphorites in China. In order to investigate genesis of the phosphorites, their REE compositions were analyzed by using inductively coupled plasma emission mass spectrometry (ICP-MS) method. For comparison, phosphorites from the Lower Cambrian black rock series in Southern China, such as Zunyi in Guizhou and Zhangjiajie in Hunan Province, were also analyzed. The analytical data show that: (1) Xinhua phosphorites possess a quite high and greatly varied total rare earth elements (ΣREE), which varying between 164.23×10-6 and 1395.01×10-6 with average of 642.54×10-6, remarkable differentiation between light (LREE) and heavy rare earth elements (HREE), and the ΣLREE/ΣHREE ratios varying between 5.04 and 6.52. The ΣREE and ΣLREE/ΣHREE ratios of the Zunyi and Zhangjiajie phosphorites are 156.69×10-6～637.41×10-6 with average of 431 75×10-6 and 3.17～6.95 with average of 4.37 respectively; (2) All the phosphorites from Xinhua, Zunyi and Zhangjiajie show remarkable negative Ce anomalies. Besides, the Xinhua phosphorites possess lower δCe, which varying between 0.26 and 0.53 with average of 0.35, while δCe of the Zunyi and Zhangjiajie phosphorites are 0.30～0.66 with average of 0.47, suggesting that all of the phosphorites are typical marine sediments deposited mainly in ancient peri-continental seas, and the depositional position of the Xinhua phosphorite might be deeper; (3) Most phosphorites from Xinhua, Zunyi and Zhangjiajie possess unremarkable positive Eu anomaly, and only a few of samples show obvious ones. The δEu varies between 0.98 and 2.4, suggesting that hot (>200 ℃) and strong reductive hydrothermal fluids might have been involved in genesis of the phosphorites; (4) The Xinhua phosphorite is relatively depleted in HREE, and LaN/NdN and δY of most samples are >1 and >1.5 respectively. Besides, there exists no correlation between δY and δCe, suggesting that the phosphorite was subjected to quite strong weathering and leaching processes, and catagenesis do not greatly modify its REE compositions.
基金supported by the Science Foundation of Nanjing University of Information Science and Technology,China(No.20080328)the National Key Technology R&D Program (No.2006BAK21B02)+1 种基金the National Key Basic Research Program (973 Program) of China (No.2003CB415201)the National Natural Science Foundation of China (No.40671016)
文摘Trace element(TE) and rare earth element(REE) contents in red soils from the Dongting Lake area of China were determined to understanding the provenance and weathering characteristics of the red soils.The results showed similar REE distribution patterns among red soils from the Dongting Lake area,Xiashu loess from Zhenjiang,loess and Pliocene red soil from the Loess Plateau.These patterns implied a similar provenance from dust-storms,except for red soil R5 which formed by bedrock weathering and had significant light REE(LREE) enrichment and heavy REE(HREE) depletion due to longer weathering periods and higher intensity of weathering.Trace element,especially the Rb/Sr and Li/Ba ratios,and REE,especially the LREE/HREE ratio and δEu could trace weathering intensity.Higher Rb/Sr,Li/Ba,and LREE/HREE ratios and negative Eu anomalies were present in the red soils from the Dongting Lake area.The weathering intensity was in the decreasing order of R5 in the Dongting Lake area > red soils from the Dongting Lake area(including reticulate red soil,weak reticulate red soil,and homogeneous red soil formed by dust storms) > Xiashu loess from Zhenjiang > loess-paleosol and Pliocene red soil from the Loess Plateau.Variations in the TE and REE contents of soil could be effectively used to study the provenance and the weathering intensity.
基金supported by funds from the Natural Science and Engineering Council of Canada
文摘In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian ＂explosion＂ of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth＇s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break- up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic （Huronian） carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off after the Great Oxidation Event of the Paleoproterozoic？ The answer may lie in the huge scar left by the -2023 Ma Vredefort impact in South Africa, and in the worldwide organic carbon-rich deposits of the Shunga Event, arresting to the near-extirpation of life and possible radical alteration of the course of Earth history.
基金supported jointly by National Key R&D Program of China(No.2018YFC1503400)National Natural Science Foundation of China projects(Nos.41774067,U2039204,and 42074046)+2 种基金Science for Earthquake Resilience(No.XH20082Y)US National Science Foundation(No.1941719)University of California at Riverside.
文摘We present a high-resolution seismic catalog for the 2021 M_(S)6.4/M_(W)6.1 Yangbi sequence.The catalog has a time range of 2021-05-01 to 2021-05-28,and contains~8,000 well located events.It captures the features of the whole foreshock sequence and the early aftershocks.We designed a detection strategy incorporating both an artificial intelligent(AI)picker and a matched filter algorithm.Here,we adopt a hybrid AI method incorporating convolutional and recurrent neural network(CNN&RNN)for event detection and phase picking respectively(i.e.CERP),a light-weight AI picker that can be trained with small volume of data.CERP is first trained with detections from a STA/LTA and Kurtosis-based method called PAL,and then construct a rather complete template set of~4,000 events.Finally,the matched filter algorithm MESS augments the initial detections and measures differential travel times with cross-correlation,which finally results in precise relocation.This process gives 9,026 detections,among which 7,943 events can be well relocated.The catalog shows as expected power-law distribution of frequency magnitude and reveals detailed pattern of seismicity evolution.The main features are:(1)the foreshock sequence images simple fault geometry with consistent strike,but also show a variable event depth along strike;(2)the mainshock ruptures the same fault of the foreshock sequence and activate conjugate faults further to the southeast;(3)complex seismicity are developed in the post-seismic period,indicating complex triggering mechanisms.Thus,our catalog provides a reliable basis for further investigations,such as b-value studies,rupture process,and triggering relations.
基金Financial support from the Ministry of Earth Sci-ences,New Delhi for Excimer 193 nm LA system at CSIR-NGRI MoES/P.O.(Seismo)/1(245)/2014for the project on Singhbhum craton to S.D.,E.V.S.S.K.B.,B.S.and T.V.K(No.MoES/P.O.(Geosci)45/2015+1 种基金GAP-738-28EVB)part of the CSIR-NGRI projects INDEX(PSC0204) and GEOMET
文摘The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.
基金supported financially by the National Natural Science Foundation of China (No.41574021,41474059,41331066,41774088,and 41174063)a research grant from the Institute of Crustal Dynamics,China Earthquake Administration (No.ZDJ2017-23)+4 种基金the CAS/CAFEA International Partnership Program for Creative Research Teams (No.KZZD-EW-TZ-19)the Key Research Program of Frontier Sciences CAS (Chinese Academy of Sciences) (QYZDY-SSW-SYS003)the SKLGED foundation (SKLGED2014-1-1-E)the GOCE Italy Project (the Italian Space Agency and the European Space Agency Endorsement)the China Postdoctoral Science Foundation (No.133014)
文摘Data obtained by GRACE(Gravity Recovery and Climate Experiment) have been used to invert for the seismic source parameters of megathrust earthquakes under the assumption of either uniform slip over an entire fault or a point-like seismic source.Herein, we further extend the inversion of GRACE long-wavelength gravity changes to heterogeneous slip distributions during the 2011 Tohoku earthquake using three fault models:(Ⅰ) a constant-strike and constant-dip fault,(Ⅱ) a variable dip fault, and(Ⅲ) a realistically varying strike fault. By removing the post-seismic signal from the time series, and taking the effect of ocean water redistribution into account, we invert for slip models I, II, and III using co-seismic gravity changes measured by GRACE, de-striped by DDK3 decorrelation filter. The total seismic moments of our slip models, with respective values of 4.9×10^(22) Nm, 5.1×10^(22) Nm, and 5.0×10^(22) Nm, are smaller than those obtained by other studies relying on GRACE data. The resulting centroids are also located at greater depths(20 km, 19.8 km,and 17.4 km, respectively). By combining onshore GPS, GPS-Acoustic, and GRACE data, we obtain a jointly inverted slip model with a seismic moment of 4.8×10^(22) Nm, which is larger than the seismic moment obtained using only the GPS displacements. We show that the slip inverted from low degree space-borne gravimetric data, which contains information at the ocean region, is affected by the strike of the arcuate trench. The space-borne gravimetric data help us constrain the source parameters of a megathrust earthquake within the frame of heterogeneous slip models.
文摘This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.
文摘This research uses eigenvalue characteristics of nonlinear principal component analysis （NLPCA） and principal component analysis （PCA） to investigate total electron content （TEC） anomalies associated with Taiwan＇s Chi-Chi earthquake of 21 September 1999 （LT） （M_w=7.6）. The transforms are used for ionospheric TEC from 01 August to 20 September 1999 （local time） using data from 13 GPS receivers. The data were collected at 22°N-26°N Lat. and 120°E-122°E Long.. Applying the NLPCA to the multi-channel total electron content records of GPS receivers, the earthquake-associated TEC anomalies were represented by large principal eigenvalues of NLPCA （〉0.5 in a normalized set） on 14 August and 17, 18, and 20 September, with allowance given for the Dst index, which was quiet for the study period. Comparisons were then made with other researchers who also found TEC anomalies on September 17, 18, and 19 associated with the Chi-Chi earthquake, which cannot be detected by PCA.Consideration is also given for reported ground level geomagnetic field activity that occurred between mid-August and late October, leading up to and including the Chi-Chi and Chia-Yi earthquakes, which are associated with the same series of faults. It is possible that Aug. 14 is representative of an earthquake-associated TEC anomaly. This is an interesting result given how much earlier than the earthquake it occurred.
文摘This paper reports statistical results of Seismo-Ionospheric Anomalies(SIAs) of the Total Electron Content(TEC) in the Global Ionosphere Map(GIM) associated with 56 M≥6.0 earthquakes in China during 1998—2012.To detect SIA,a quartile-based(i.e.median-based) process is performed.TEC anomalies for the period of earthquakes without being led by magnetic storms about 10 days are further isolated and examined to confirm the SIP existence.Results show that SIA is the TEC significantly decrease in the afternoon period 2—9 days before the earthquakes in China,which is in a good agreement with the SIA appearing before the 12 May 2008 M 8.0 Wenchuan earthquake.
