Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

In this work,we aim to investigate the origin of the magnetic carriers in the lunar crust and the intensity of the ancient dynamo field.The magnetization and depth range of magnetic carriers are studied under a weak and a strong magnetic anomaly in Mare Tranquillitatis and in Oceanus Procellarum,respectively,where the surface ages are 3.6 and 3.3 billion years.A sophisticated three-dimensional amplitude inversion software program from a geophysical survey is used to reconstruct the distributions of magnetization in the lunar crust.Because no globally measured surface magnetic field exists for the Moon,a crustal magnetic anomaly model with a grid resolution of 0.2°is used.The depth range of the magnetic source is fixed by the boundary identified by a relative criterion,which is 20%of the recovered maximum magnetization.The central burial depths of the magnetic carriers are approximately 15 km and 25 km under Reiner Gamma and Mare Tranquillitatis,respectively.The volumes of the two magnetic sources are at scales of 104 and 105 km3,respectively.The aforementioned differences may imply a hotter crust under Reiner Gamma than Mare Tranquillitatis by 3.3 billion years.The results support the view that the magma intrusions magnetized by an ancient magnetic field could be the origin of magnetic anomalies under Reiner Gamma and Mare Tranquillitatis.Compared with previous works,the maximum magnetization of 3 A/m under Reiner Gamma supports the intensity of the field being several microteslas.

An alternative 2D ICEEMDAN-based denoising method and its application in processing magnetic anomaly data

Due to environmental noise and human factors,magnetic data collected in the field often contain various noises and interferences that significantly affect the subsequent data processing and interpretation.Empirical Mode Decomposition(EMD),an adaptive multiscale analysis method for nonlinear and non-stationary signals,is widely used in geophysical and geodetic data processing.Compared with traditional EMD,Improved Complete Ensemble EMD with Adaptive Noise(ICEEMDAN)is more effective in addressing the problem of mode mixing.Based on the principles of 1D ICEEMDAN,this paper presents an alternative algorithm for 2D ICEEMDAN,extending its application to two-dimensional scenarios.The effectiveness of the proposed approach is demonstrated through synthetic signal experiments,which show that the 2D ICEEMDAN exhibits a weaker mode mixing effect compared to the traditional bidimensional EMD(BEMD)method.Furthermore,to improve the performance of the denoising method based on 2D ICEEMDAN and preserve useful signals in high-frequency components,an improved soft thresholding technique is introduced.Synthetic magnetic anomaly data testing indicates that our denoising method effectively preserves signal continuity and outperforms traditional soft thresholding methods.To validate the practical application of this improved threshold denoising method based on 2D ICEEMDAN,it is applied to ground magnetic survey data in the Yandun area of Xinjiang.The results demonstrate the effectiveness of the method in removing noise while retaining essential information from practical magnetic anomaly data.In particular,practical applications suggest that 2D ICEEMDAN can extract trend signals more accurately than the BEMD.In conclusion,as a potential tool for multi-scale decomposition,the 2D ICEEMDAN is versatile in processing and analyzing 2D geophysical and geodetic data.

Identification of the Caroline Plate boundary:constraints from magnetic anomaly

The Caroline Plate is located among the Pacific Plate,the Philippine Sea Plate,and the India Australia Plate,and plays a key role in controlling the spreading direction of the Philippine Sea Plate.The Caroline Submarine Plateau(or Caroline Ridge)and the Eauripik Rise on the south formed a remarkable T-shaped large igneous rock province,which covered the northern boundary between the Caroline Plate and the Pacific Plate.However,relationship between these tectonic units and magma evolution remains unclear.Based on magnetic data from the Earth Magnetic Anomaly Grid(2-arc-minute resolution)(V2),the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)technique was used to study the boundary of the Caroline Plate.Results show that the northern boundary is a transform fault that runs 1400 km long in approximately 28 km wide along the N8°in E-W direction.The eastern boundary is an NNW-SSE trending fault zone and subduction zone with a width of tens to hundreds of kilometers;and the north of N4°is a fracture zone of dense faults.The southeastern boundary may be the Lyra Trough.The area between the southwestern part of the Caroline Plate and the Ayu Trough is occupied by a wide shear zone up to 100 km wide in nearly S-N trending in general.The Eauripik transform fault(ETF)in the center of the Caroline Plate and the fault zones in the east and west basins are mostly semi-parallel sinistral NNW-SSE–trending faults,which together with the eastern boundary Mussau Trench(MT)sinistral fault,the northern Caroline transform fault(CTF),and the southern shear zone of the western boundary,indicates the sinistral characteristics of the Caroline Plate.The Caroline hotspot erupted in the Pacific Plate near the CTF and formed the west Caroline Ridge,and then joined with the Caroline transform fault at the N8°.A large amount of magma erupted along the CTF,by which the east Caroline Ridge was formed.At the same time,a large amount of magma developed southward via the eastern branch of the ETF,forming the northern segment of the Eauripik Rise.Therefore,the magmatic activity of the T-shaped large igneous province is obviously related to the fault structure of the boundary faults between the Caroline Plate and Pacific Plate,and the active faults within the Caroline Plate.

Investigation of Potential Factors on South Atlantic Magnetic Anomaly

The first part of this investigation analyzes the deep earthquake occurrences in Nazca subducting under South America. The depth taken is to get information about possible influences from the unknown materials and formations under the crust. The results revealed the presence of malleable material, which is unbreakable and, therefore, unable to trigger earthquakes. The structure of those elements is diamagnetic, attracting ionized particles from the Van Allen belt region in the ionosphere. The charged particles travel towards Earth’s surface, enhanced during the geomagnetic storms. The South Atlantic Magnetic Anomaly (SAMA) found that the deformation suffered by the anomaly moving from South Africa to South America is, possibly due to a bulge of unknown flexible material buried underneath the oceanic and continental crust. The continental part is strengthening in weakness because the background also has a high amount of diamagnetic material in this region, and it would not happen over the Atlantic Ocean, where part of the deformation is placed.

Preliminary geological interpretation of long-wavelength magnetic anomalies over China and surrounding regions

Long-wavelength(>500 km)magnetic anomalies originating in the lithosphere were first found in satellite magnetic surveys.Compared to the striking magnetic anomalies around the world,the long-wavelength magnetic anomalies in China and surrounding regions are relatively weak.Specialized research on each of these anomalies has been quite inadequate;their geological origins remain unclear,in particular their connection to tectonic activity in the Chinese and surrounding regions.We focus on six magnetic high anomalies over the(1)Tarim Basin,(2)Sichuan Basin(3)Great Xing’an Range,(4)Barmer Basin,(5)Central Myanmar Basin,and(6)Sunda and Banda Arcs,and a striking magnetic low anomaly along the southern part of the Himalayan-Tibetan Plateau.We have analyzed their geological origins by reviewing related research and by detailed comparison with geological results.The tectonic backgrounds for these anomalies belong to two cases:either ancient basin basement,or subduction-collision zone.However,the geological origins of large-scale regional magnetic anomalies are always subject to dispute,mainly because of limited surface exposure of sources,later tectonic destruction,and superposition of multi-phase events.

Regional magnetic anomaly fields:3D Taylor polynomial and surface spline models

We used data from 1960.0,1970.0,1980.0,1990.0,and 2000.0 to study the geomagnetic anomaly field over the Chinese mainland by using the three-dimensional Taylor polynomial（3DTP） and the surface spline（SS） models.To obtain the pure anomaly field,the main field and the induced field of the ionospheric and magnetospheric fields were removed from measured data.We also compared the SS model anomalies and the data obtained with Kriging interpolation（KI）.The geomagnetic anomaly distribution over the mainland was analyzed based on the SS and 3DTP models by transferring all points from 1960.0-1990.0 to 2000.0.The results suggest that the total intensity F anomalies estimated based on the SS and KI for each year are basically consistent in distribution and intensity.The anomalous distributions in the X-,Y-,and Z-direction and F are mainly negative.The 3DTP model anomalies suggest that the intensity in the X-direction increases from-100 nT to 0 nT with longitude,whereas the intensity in the Y-direction decreases from 400 nT to 20 nT with longitude and over the eastern mainland is almost negative.The intensity in the Z-direction and F are very similar and in most areas it is about-50 nT and higher in western Tibet.The SS model anomalies overall reflect the actual distribution of the magnetic field anomalies;however,because of the uneven distribution of measurements,it yields several big anomalies.Owing to the added altitude term,the 3DTP model offers higher precision and is consistent with KI.

Origin of Phosphorite Nodules of Lebedinsky Iron Deposit in Kursk Magnetic Anomaly (KMA) of the Russian Platform

Phosphorite has become increasingly important as the raw material for phosphatic fertilizer. Phosphorite nodules are widespread in the Kursk complex deposit (Russian platform). Genesis of these nodules has long been a matter of debate, and this has hampered understanding of the mechanism and controls in the formation of the nodules. In this paper, we report the petrographical, mineralogical, and geochemical data of the Lebedinsky phosphorite nodules. Petrographic study reveals complex phosphatic cement resulting in the replacement of apatite minerals around quartz grains. The main mineral composition consists of quartz, phosphate minerals (apatite, francolite mainly), feldspar, iron hydroxides and carbonate minerals. These results, when combined with available data, are used to address the origin of the phosphorite nodules. The nodules are characterized by the universal presence of biogenic and chemical signatures which is phosphorus crown around crystal grains. The structure of the nodules is massive. Their texture is depicted by basaltic cement and concretion, which consists mainly of apatite and its varieties, with general formula: Ca_10 (PO_4, CO_3) 6(F,OH,Cl). Variation of mineralogy appears dependent on geological setting. Microscopic observations of biogenic fossils in Lebedinsky phosphorite favor a chemical and biogenic origin of phosphorites. Weathering has been suggested to be capable of liberating as much as 20 %-35 % P_2O_5 from sedimentary rocks. Previous investigations demonstrate that weathering of the Proterozoic substratum was the main cause in the formation of Fe, Mo, Mn, Pb, Zn, and P in the Russian platform. We therefore suggest that both weathering and biochemical processes have been positive in the formation of the Lebedinsky phosporite nodules. However, whether continental weathering or oceanic bio-chemical processes are more relevant in the phosphorite accumulation remains undetermined.

An analysis of the characteristics of crustal magnetic anomaly in China based on CHAMP satellite data

Based on the observation data of CHAMP satellite from 2006 to 2009, a 2D crustal magnetic anomaly model in China is established to study the distribution characteristics of crustal magnetic anomaly. In this paper, the 2D anomaly model is derived from the Legendre polynomial expansion of harmonic term N =6-50. The result shows that many elaborate structures reflected in magnetic anomaly map well correspond to the geologic structures in China and its adjacent area. The magnetic anomaly at low satellite height behaves complexly, which is mainly caused by the magnetic disturbance of shallow rocks.In contrast, the magnetic field isolines at high satellite height are relatively sparse and only magnetic anomalies of deep crust are reflected. This fact implies that the 2D model of crustal magnetic anomaly provides an important method of the space prolongation of geomagnetic field, and is of theoretical and practice importance in geologic structure analysis and geophysical prospecting.

A two-dimensional lithospheric magnetic anomaly field model of Egypt using the measurements from Swarm satellites

We use magnetic field data observed by the Swarm mission from 2014 to 2020 to construct,for the first time,a two-dimensional(2 D)lithospheric magnetic anomaly model of Egypt and its surrounding area.Nighttime data during quiet geomagnetic conditions has been expanded in terms of the Legendre polynomial in harmonic terms N=6-50.The damped least square method has been used to estimate the model coefficients based on the lithospheric magnetic data.Modeled data at two different altitudes(438-448 km and 503-511 km)were compared with the CHAOS model.Results exhibit that the 2 D model is superior to the CHAOS model in the capability of extracting more information about small-scale crustal anomaly field.At low altitudes(438-448 km),the strength of the anomaly field increases,but the noise of the external fields has greatly reduced at high altitudes(503-511 km).Besides,the magnetic anomaly field at low altitudes has illuminated short-scale anomalies that didn’t appear at high altitudes.Both the total and vertical magnetic anomaly vectors showed their ability to reveal tectonic structures compared with Moho depth map and the geological maps.

Abnormally large short-term and impending earthquake geomagnetic anomaly implies a possibility of earthquake pre-warning

The study found that strong magnetic anomalies repeatedly took place before big earthquakes. Based on geomagnetic record analysis results,we discussed a possible pattern of the magnetic anomalies prior to earthquake. In meizoseismal area or epicenter,in a time period of 36 h to about 10 min before earthquake,the exceptional big geomagnetic change increases with the magnitude of earthquake. We calculated that,in a place of 1 km from the epicenter,the magnetic anomaly before destructive earthquakes of Ms 6～9 can reach to 102～104 nT(the magnitude of earth magnetic field is 104 nT) ,rather than the magnitude of 10 nT from seismomagnetic effect theories since 1960s. From this we speculated the abnormal magnetic ULF near epicenter before earthquake seems to be an "intermittent magnetic eruption". Accordingly,we proposed that geomagnetic induction earthquake alarm can be a new pre-warning method to surmount hardship in solving the puzzledom of earthquake imminent prediction.

Estimation of Curie Depth of Subei Basin by Magnetic Anomaly

The Curie point depth is the depth at which the ferromagnetic mineral loses paramagnetism,which corresponds to a temperature of 550-580 degrees Celsius.This parameter is of great significance for constraining the thermal state of the lithosphere and can be used as an important reference for the evaluation of the prospects for dry hot rock exploration.We use aeromagnetic anomaly radial power spectrum based on the fractal magnetization model to calculate the Curie depth in the Subei Basin.We use the conventional method to preprocess the aeromagnetic data and process aeromagnetic data with selecting the appropriate wave number,domain,window size and fractal parameters to calculate the depth of the bottom of the magnetic source in the Subei Basin,which is approximated as Curie depth.The Curie depth of Subei basin ranges from 18 km to 37 km,with an average Curie depth of 23 km.The Curie depth of Baoying(20 km)and Jianhu(22 km)area is relatively shallow,and that of the surrounding area is relatively deep.In most areas,the Curie depth corresponds to the terrestrial heat flow.

Magnetic Theory and Applications in the Naples Bay (Southern Tyrrhenian Sea, Italy): Magnetic Anomaly Fields and Relationships with Morpho-Structural Lineaments

Magnetic theory and application to a complex volcanic area located in Southern Italy are here discussed showing the example of the Gulf of Naples, located at Southern Italy Tyrrhenian margin. A magnetic anomaly map of the Gulf of Naples has been constructed aimed at highlighting new knowledge on geophysics and volcanology of this area of the Eastern Tyrrhenian margin, characterized by a complex geophysical setting, strongly depending on sea bottom topography. The theoretical aspects of marine magnetometry and multibeam bathymetry have been discussed. Magnetic data processing included the correction of the data for the diurnal variation, the correction of the data for the offset and the leveling of the data as a function of the correction at the cross-points of the navigation lines. Multibeam and single-beam bathymetric data processing has been considered. Magnetic anomaly fields in the Naples Bay have been discussed through a detailed geological interpretation and correlated with main morpho-structural features recognized through morpho- bathymetric interpretation. Details of magnetic anomalies have been selected, represented and correlated with significant seismic profiles, recorded on the same navigation lines of magnetometry. They include the continental shelf offshore the Somma-Vesuvius volcanic complex, the outer shelf of the Gulf of Pozzuoli offshore the Phlegrean Fields volcanic complex, the relict volcanic banks of Pentapalummo, Nisida and Miseno, the Gaia volcanic bank on the Naples slope, the western slope of the Dohrn canyon, the Magnaghi canyon’s head and the magnetic anomalies among the Ischia and Procida islands.

Study on the distribution characteristics of faults and their control over petroliferous basins in the China seas and its adjacent areas

As one of the main controlling factors of oil and gas accumulation,faults are closely related to the distribution of oil and gas reservoirs.Studying how faults control petroliferous basins is particularly important.In this work,we investigated the plane positions of major faults in the China seas and its adjacent areas using the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)of the Bouguer gravity anomaly,the fusion results of gravity and magnetic anomalies,and the residual Bouguer gravity anomaly.The apparent depths of major faults in the China seas and its adjacent areas were inverted using the Tilt-Euler method based on the Bouguer gravity anomaly.The results show that the strikes of the faults in the China seas and its adjacent areas are mainly NE and NW,followed by EW,and near-SN.Among them,the lengths of most ultra-crustal faults are in the range of 1000–3000 km,and their apparent depths lie between 10 km and 40 km.The lengths of crustal faults lie between 300 km and 1000 km,and their apparent depths are between 0 km and 20 km.According to the plane positions and apparent depths of the faults,we put forward the concept of fault influence factor for the first time.Based on this factor,the key areas for oil and gas exploration were found as follows:the east of South North China Basin in the intracontinental rift basins;the southeast region of East China Sea Shelf Basin,the Taixinan and Qiongdongnan basins in the continental margin rift basins;Zhongjiannan Basin in the strike-slip pull-apart basins;the Liyue,Beikang,and the Nanweixi basins in the rifted continental basins.This work provides valuable insights into oil and gas exploration,mineral resource exploration,and deep geological structure research in the China seas and its adjacent areas.

Structural Mapping of Kakobola and Its Surroundings by Analyzing Geomagnetic Data

This study focuses on the Kakobola region and its surroundings where cavities discovered in its basement may represent a major risk for the hydroelectric dam erected on the Lufuku River near the Kakobola city and the civil engineering works in the study area. In order to deepen the studies related to this understudied region and provide decision-makers with information that will enable them to make the necessary and appropriate decisions regarding the development of this area, a study based on the analysis of geomagnetic data was carried out using certain methods revealing more shallow than deep structures, and others highlighting the limits of both shallower and deeper structures. Total magnetic anomalies and reduced to equator (RTE) magnetic anomalies were used to map the subsurface of the Kakobola region and its surroundings. In order to detect the edges of magnetized structures, the horizontal gradient magnitude (HGM), the analytic signal (AS), the horizontal gradient of tilt angle (HGTA), the tilt angle (TA), the theta map (TM), the enhanced total horizontal derivative of the tilt angle (ETHDR), the tilt angle of the horizontal gradient (TAHG), and the tilt angle of analytic signal (TAAS) were used. The study area is characterized by two areas of low values of magnetic anomalies and two other sources of high magnetic anomalies located in the bed and the neighborhood of the two major rivers in the region. The shallow sources of magnetic anomalies are lying in the bed and the vicinity of the same rivers in the study area. The magnetic sources in the study area are connected and almost linear. Several magnetic lineaments identified in this region by different methods present several preferential directions, but the most predominant directions are NE-SW, NW-SE, W-E and NE-SW.

Interpretation of magnetic anomalies by horizontal and vertical derivatives of the analytic signal

Magnetic anomalies are often disturbed by the magnetization direction, so we can＇t directly use the original magnetic anomaly to estimate the exact location and geometry of the source. The 2D analytic signal is insensitive to magnetization direction. In this paper, we present an automatic method based on the analytic signal horizontal and vertical derivatives to interpret the magnetic anomaly. We derive a linear equation using the analytic signal properties and we obtain the 2D magnetic body location parameters without giving a priori information. Then we compute the source structural index （expressing the geometry） by the estimated location parameters. The proposed method is demonstrated on synthetic magnetic anomalies with noise. For different models, the proposed technique can both successfully estimate the location parameters and the structural index of the sources and is insensitive to noise. Lastly, we apply it to real magnetic anomalies from China and obtain the distribution of unexploited iron ore. The inversion results are consistent with the parameters of known ore bodies.

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.

Characteristics of Meso-Cenozoic Igneous Complexes in the South Yellow Sea Basin,Lower Yangtze Craton of Eastern China and the Tectonic Setting

The South Yellow Sea Basin is partially surrounded by the East Asian continental Meso- Cenozoic widespread igneous rocks belt. Magnetic anomaly and multi-channel seismic data both reveal the prevalent occurrence of igneous rocks. We preliminarily defined the coupling relation between magnetic anomalies and igneous rock bodies. Some igneous complexes were also recognized by using multi-channel seismic and drilling data. We identified various intrusive and extrusive igneous rock bodies, such as stocks, sills, dikes, laccoliths and volcanic edifice relics through seismic facies analysis. We also forecasted the distribution characteristics of igneous complexes. More than fifty hypabyssal intrusions and volcanic relics were delineated based on the interpretation of magnetic anomaly and dense intersecting multi-channel seismic data. It is an important supplement to regional geology and basin evolution research. Spatial matching relations between igneous rock belts and fractures document that extensional N-E and N-NE-trending deep fractures may be effective pathways for magma intrusion. These fractures formed under the influence of regional extension during the Meso- Cenozoic after the Indosinian movement. Isotopic ages and crosscutting relations between igneous rock bodies and the surrounding bedded sedimentary strata both indicate that igneous activities might have initiated during the Late Jurassic, peaked in the Early Cretaceous, gradually weakened in the Late Cretaceous, and continued until the Miocene. Combined with previous studies, it is considered that the Meso-Cenozoic igneous activities, especially the intensive igneous activity of the Early Cretaceous, are closely associated with the subduction of the Paleo-Pacific Plate.

Linear magnetic anomalies and tectonic development of the middle Okinawa Trough

By analyzing the magnetic anomalies,the linear magnetic anomalies in the middle Okinawa Trough are identified.It means that the crust along the spreading axis is broken,and new oceanic crust is formed.Geophysical data have revealed that a model of three extensive episodes occurs in the Okinawa Trough,which can be named as“doming episode” from the Middle to Late Miocene(Phase I),the episode from the Pliocence to Early Pleistocene(Phase Ⅱ),and the recent“spreading episode”(Phase Ⅲ).The magnetic anomalies in the middle Okinawa Trough are very similar to those found in the middle Red Sea,indicating that the Okinawa Trough is developing towards the “Red Sea stage”.Similar to the Red Sea,there are a “main trough”and a “axial trough”in the Okinawa Trough.

Vector transformation and reduction to the pole for regional magnetic data with variable field direction

The vector transformation and pole reduction from the total-field anomaly are signifi cant for the interpretation.We examined these industry-standard processing procedures in the Fourier domain.We propose a novel iteration algorithm for regional magnetic anomalies transformations to derive the vertical-component data from the total-field measurements with the variation in the core-fi eld direction over the region.Additionally,we use the same algorithm to convert the calculated vertical-component data into the corresponding data at the pole and realize the processing of diff erential reduction to the pole(DRTP).Unlike Arkani-Hamed’s DRTP method,the two types of iterative algorithms have the same forms,and DRTP is realized by implementing this algorithm twice.The synthetic model’s calculation results show that the method has high accuracy,and the fi eld data processing confi rms its practicality.

Structural characteristics of the KPR-CBR triple-junction inferred from gravity and magnetic interpretations,Philippine Sea Plate

The intersection of the Kyushu-Palau Ridge(KPR)and the Central Basin Rift(CBR)of the West Philippine Basin(WPB)is a relic of a trench-trench-rift(TTR)type triple-junction,which preserves some pivotal information on the cessation of the seafloor spreading of the WPB,the emplacement and disintegration of the proto-Izu-Bonin-Mariana(IBM)Arc,and the transition from initial rifting to steady-state spreading of the Parece Vela Basin(PVB).However,the structural characteristics of this triple-junction have not been thoroughly understood.In this paper,using the newly acquired multi-beam bathymetric,gravity,and magnetic data obtained by the Qingdao Institute of Marine Geology,China Geological Survey,the authors depict the topographic,gravity,and magnetic characteristics of the triple-junction and adjacent region.Calculations including the upward continuations and total horizontal derivatives of gravity anomaly are also performed to highlight the major structural features and discontinuities.Based on these works,the morphological and structural features and their formation mechanisms are analyzed.The results show that the last episode amagmatic extension along the CBR led to the formation of a deep rift valley,which extends eastward and incised the KPR.The morphological and structural fabrics of the KPR near and to the south of the triple-junction are consistent with those of the western PVB,manifesting as a series of NNE-SSW-and N-S-trending ridges and troughs,which were produced by the extensional faults associated with the initial rifting of the PVB.The superposition of the above two reasons induced the prominent discontinuity of the KPR in deep and shallow crustal structures between 15°N‒15°30′N and 13°30′N‒14°N.Combined with previous authors’results,we propose that the stress produced by the early spreading of the PVB transmitted westward and promoted the final stage amagmatic extension of the CBR.The eastward propagation of the CBR destroyed the KPR,of which the magmatism had decayed or ceased at that time.The destruction mechanism of the KPR associated with the rifting of the PVB varies along strike the KPR.Adjacent to the triple-junction,the KPR was destroyed mainly due to the oblique intersection of the PVB rifting center.Whereas south of the triple-junction,the KPR was destroyed by the E-W-directional extensional faulting on its whole width.