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1.
K. Satish Kumar S. Parveen Begum G. S. Srinivas M. Shri Hari Rao P. Prabhakara Prasad T. Seshunarayna R. K. Tiwari 《Journal of the Geological Society of India》2018,92(3):368-372
Ajmer-Sambar sector of Delhi fold belt, North-Central Rajasthan has got importance due to its litho characters, structure, metamorphism, magmatism, migmatisation, metallogeny and rich potential of base metal mineralization. This sector is comprised of Delhi sequence of rocks hosted by the Banded Gneisses Complex (BGC). In view of the significance of this region, ground magnetic survey was conducted along six regional profiles to understand the structural features, magnetic nature of the basement and depth to the basement. Analysis of the magnetic data has clearly identified two magnetic lineaments (a) L1 in WNW-ESE direction that appears to represent litho-contact between Kalyanpura sequences in the south to Anasagar migmatite in the north and (b) L2 in NNW to SSE direction south of Parvatsar which is inferred to be a structural control about which the quartzite rocks of Taragarh Formation culminate. An average depth to basement of 3.7 km is estimated through spectral analysis of magnetic data. The maximum depth of the basin 4.5 km is estimated in central part of the study area. The obtained depth results are in good agreement with the Cummulative Total Intensity Magnetic Anomaly field (CTIMAF) and Deep seismic stuides. 相似文献
2.
Magnetic observations over the area of the Transantarctic Mountains (TAM) and the Ross Sea have been compiled into a digital database that furnishes a new regional scale view of the magnetic anomaly crustal field in this key sector of the Antarctic continent. This compilation is a component of the ongoing IAGA/SCAR Antarctic Digital Magnetic Anomaly Project (ADMAP). The aeromagnetic surveys total 115 000 line km, and are distributed across the Victoria Land sector of the TAM, the Ross Sea, and Marie Byrd Land. The magnetic campaigns were performed within the framework of the national and international Italian–German–US Antarctic research programs and conducted with differing specifications during nine field seasons from 1971 until 1997. Generally flight line spacing was less than 5 km while survey altitude varied from about 610 to 4000 m above sea level for barometric surveys and was equal to 305 m above topography for the single draped survey. Reprocessing included digitizing the old contour data, improved levelling by means of microlevelling in the frequency domain, and re-reduction to a common reference field based on the DGRF90 model. A multi-frequency grid procedure was then applied to obtain a coherent and merged total intensity magnetic anomaly map. The shaded relief map covers an area of approximately 380 000 km2. This new compilation provides a regional image of the location and spatial extent of the Cenozoic alkaline magmatism related to the TAM–Ross Sea rift, Jurassic tholeiites, and crustal segments of the Early Palaeozoic magmatic arc. A linear, approximately 100-km wide and 600-km long Jurassic rift-like structure is newly identified. Magnetic fabric in the Ross Sea rift often matches seismically imaged Cenozoic fault arrays. Major buried onshore pre-rift fault zones, likely inherited from the Ross Orogen, are also delineated. These faults may have been reactivated as strike-slip belts that segmented the TAM into various crustal blocks. 相似文献
3.
《Gondwana Research》2014,25(1):358-367
The ice shield of Antarctica, which measures several kilometers in thickness, presents a challenge when attempting to unravel the subglacial geology. Here, we report about systematic airborne magnetic surveys conducted over the last decade, which investigated a significant part of Dronning Maud Land (DML), imaging for the first time the crustal architecture of the interior of this sector of East Antarctica. High-resolution data reveal parallel, elongated magnetic anomalies in southeastern DML. These NW–SE trending anomalies can be traced farther east into sparser Russian magnetic data sets. Several high amplitude magnetic anomalies with values above 400 nT have been observed in southwestern DML and Coats Land. They differ clearly in wavelength and amplitudes from the magnetic pattern found in the east and do not show any evidence of a Pan-African orogenic belt or suture zone connecting the Shackleton Range with eastern DML, as hypothesized in several studies. This leads to the assumption of the existence of a hitherto unrecognized large tectonic province in southeastern DML. Whereas an over 100 km long magnetic lineament in the interior of the Dronning Maud Land may reflect a major shear zone akin to the Pan-African age Heimefrontfjella shear zone. Both findings bring new evidences to the still open question about the amalgation of East and West Gondwana. In addition, the magnetic data allow mapping the eastern extent of the presumable cratonic province of Coats Land, a region considered as a key piercing point for reconstructions of Rodinia. Furthermore, the Beattie Magnetic Anomaly in southern Africa is assumed to continue into East Antarctica. Two magnetic highs in western DML are identified as possible eastward continuation of this prominent anomaly. 相似文献
4.
5.
A. V. Golynsky S. V. Alyavdin V. N. Masolov A. S. Tscherinov V. S. Volnukhin 《Tectonophysics》2002,347(1-3)
Airborne and marine magnetic observations in East Antarctica and adjacent seas of the Indian Ocean were compiled for a magnetic anomaly map of the Antarctic. For East Antarctica, over 260,000 line km of Russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5, 20 and 50 km. For the offshore areas, magnetic data from American, Australian, German, Japanese, and Russian marine expeditions were incorporated. Digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation. Local grids of these data were developed and merged into a regional grid at an interval of 5 km. The prime product of this compilation is a shaded-relief map that shows the most complete and coherent perspective to date of the region's magnetic character. In combination with other types of data, the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world. It maps out approximately 4300 km of the Antarctic Continental Margin Magnetic Anomaly (ACMMA) related to Gondwana breakup, new cratons and mobile belts, and large submarine igneous provinces. 相似文献
6.
Pramod Kumar Yadav P. K. Adhikari Shalivahan Anurag Tripathi Shailendra Singh Roshan K. Singh Ashish K. Bage 《Journal of the Geological Society of India》2017,89(6):705-710
Magnetic and radiometric surveys were carried out over a felsic dominated rifted margin of Proterozoic volcanic terrain of a mobile belt in the eastern India. The studies were made in blocks I and II of 0.65 sq km and 0.70 sq km respectively over a previously identified conductor in the northern fringe of Dalma Volcanics (DVs). In general, both the blocks show high magnetic signature associated with sulfide mineralisation. The interpretation of magnetic data suggests that nature of the causative source is mainly horizontal cylinder in both the blocks. The depth to the top of the causative source is about 25 m in both the blocks and extends upto 60 m in block I and 40m in block II. Gamma count rate exhibits about a factor of two to three enhancements above the field background for both the blocks. The obtained iso-rad maps are similar to uranium and copper belt in the Singhbhum shear zone south of the study area. The anomalous radiometric signature of the residual soil/rock of the area indicates towards hydrothermal alteration. The detailed magnetic surveys and preliminary iso-rads results seems quite encouraging and may be attributed to VMS setting in the area and potential sulfide mineralisation with uranium mineral association in the DVs province. 相似文献
7.
Muthamilselvan A 《地下水科学与工程》2021,9(3):256-268
The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India. It also aims to define depth to granitoid and structural elements which traverse the selected area. Magnetic data(n=84) measured, processed and interpreted as qualitative and quantitatively. The results of total magnetic intensities indicate that the area is composed of linear magnetic lows trending NE-SW direction and circular to semi-circular causative bodies. The magnetic values ranged from -137 nT to 2 345 nT with a mean of 465 nT. Reduction to equator shows significant shifting of causative bodies in the southern and northern directions. Analytical signal map shows exact boundary of granitic bodies. Cosine directional filter has brought out structural element trending NE-SW direction.Results of individual profile brought to light structurally weak zone between 90 m and 100 m in all the profile lines. Sudden decrease of magnetic values from 2 042 nT to 126 nT noticed in profile line 6 between 20 m and 30 m indicates fault occurrence. Magnetic breaks obtained from these maps were visualized,interpreted and identified two suitable sites for open and bore well. Radially averaged power spectrum estimates depth of shallow and deep sources in 5 m and 50 m, respectively. Euler method has also been applied to estimate depth of granitoid and structural elements using structural indexes 0, 1, 2, and 3 and found depth ranges from 10 m to 90 m. Study indicates magnetic method is one of the geophysical methods suitable for groundwater exploration and site selection for open and borewells. 相似文献
8.
Rajendra Sharma H. C. Gouda R. K. Singh B. V. Nagaraju 《Journal of the Geological Society of India》2012,79(1):11-29
The study of aeromagnetic data over parts of Assam-Meghalaya has delineated major discontinuities representing faults/ fractures/
contacts/ shears and magnetic body axes, which helped in understanding the regional and structural setup of the area. The
known Barapani and Dapsi Thrusts, Dudhnai Fault and three strong magnetic anomalies with reverse magnetisation have been delineated.
The quantitative analysis of aeromagnetic data brought out the depths of magnetic interfaces and the magnetic picture of different
layers, which also helped in understanding the regional and structural setup. The contact modeling across few profile sections
showed the depths to the top of contacts and the map of magnetic-basement-depth-model revealed the undulations of the basement.
Magnetic body axes of several magnetic anomalies and also several magnetic discontinuities representative of faults/ fractures/
contacts/ shears system in the area along with five potential blocks for mineral prospecting are the main outcome of this
exercise. The seismotectonic activity associated with the magnetic features has also been studied to understand the structural
setup. 相似文献
9.
Three long, strike-parallel, seismic-refraction profiles were made on the continental shelf edge, slope and upper rise off New Jersey during 1975. The shelf edge line lies along the axis of the East Coast Magnetic Anomaly (ECMA), while the continental rise line lies 80 km seaward of the shelf edge. Below the unconsolidated sediments (1.7–3.6 km/sec), high-velocity sedimentary rocks (4.2–6.2 km/sec) were found at depths of 2.6–8.2 km and are inferred to be cemented carbonates. Although multichannel seismic-reflection profiles and magnetic depth-to-source data predicted the top of oceanic basement at 6–8 km beneath the shelf edge and 10–11 km beneath the rise, no refracted events occurred as first arrivals from either oceanic basement (layer 2, approximately 5.5 km/ sec) or the upper oceanic crust (layer 3A, approximately 6.8 km/sec). Second arrivals from 10.5 km depth beneath the shelf edge are interpreted as events from a 5.9 km/sec refractor within igneous basement. Other refracted events from either layers 2 or 3A could not be resolved within the complex second arrivals. A well-defined crustal layer with a compressional velocity of 7.1–7.2 km/sec, which can be interpreted as oceanic layer 3B, occurred at 15.8 km depth beneath the shelf and 12.9 km beneath the upper rise. A well-reversed mantle velocity of 8.3 km/sec was measured at 18–22 km depth beneath the upper continental rise. Comparison with other deep-crustal profiles along the continental edge of the Atlantic margin off the United States, specifically in the inner magnetically quiet zone, indicates that the compressional wave velocities and layer depths determined on the U.S.G.S. profiles are very similar to those of nearby profiles. This suggests that the layers are continuous and that the interpretation of the oceanic layer 3B under the shelf edge east of New Jersey implies progradation of the shelf outward over the oceanic crust in that area. This agrees with magnetic anomaly evidence which shows the East Coast Magnetic Anomaly landward of the shelf edge off New Jersey and with previous seismic reflection data which reveal extensive outbuilding of the shelf edge during the Jurassic and Lower Cretaceous, probably by carbonate bank-margin accretion. 相似文献
10.
Mansour A. Al-Garni 《Arabian Journal of Geosciences》2018,11(6):133
The study area is located at the east of Qattara Depression at the north of the Western Desert of Egypt. The study area contains Abu Gharadig basin, which is the most petroliferous basin in the Egyptian Western Desert. Only three exploratory wells are presented in the study area, showing a thick sediment section overlying basement rocks. Magnetic data have been frequently used in geophysical exploration. Aeromagnetic data are mainly utilized to estimate the depth to the magnetic basement as well as to delineate the possible structures of the study area. The depth to magnetic basement has been estimated using the analytical solution of exponential equations obtained from the Fourier transformation of magnetic data, assuming multi-prisms. The depths obtained from this technique vary from 0.70 to 2.91 km with an average depth of 2.08 km. Local phase filters have been mainly used as edges detector where the possible occurrences structures can be delineated. Hyperbolic tilt angle, second-order tilt angle, and normalized total horizontal derivative (TDX) provide the best results for delineating the possible structures, showing the possible contacts within the basement of the study area. The edge enhancement filters show that the study area has been affected by different structural trends taking E-W, NE-SW, NNE-SSW, N-S, and ENE-WSW directions. 相似文献
11.
The Lugo gneiss dome, in the NW Iberian Massif (Spain) is a Variscan structure developed during late stages of orogenic collapse. Crustal extension was mainly accomplished by two kilometre-scale conjugate extensional shear zones and by the late development of the dome and a huge normal fault. These structures overprint previous contractional recumbent folds and a thrust fault. The Lugo dome and its southward continuation, the Sanabria dome, are the site of the conspicuous Eastern Galicia Magnetic Anomaly (EGMA), a N–S band, 50 km wide and 190 km long, with a maximum amplitude of 190 nT. Integrated potential field modelling of the EGMA and its corresponding gravity signature have been carried out aided by constraints provided by the measurement of c. 900 magnetic susceptibilities and by previous geophysical data, mainly seismic refraction and reflection profiles. Results suggest that a large volume of low-density migmatites and associated inhomogeneous granites are the main source of the magnetic anomaly. Small massifs of basic and ultrabasic rocks inside the migmatites and high-susceptibility iron ore bodies sparsely distributed in low-grade Middle Ordovician slates are also thought to contribute to the anomaly but to a minor extent. Although otherwise similar to other gneiss domes, the Lugo dome is accompanied by a striking magnetic anomaly whose origin is discussed in terms of the tectonic evolution of this structure and the provenance of the magnetite-bearing migmatites and inhomogeneous granites that core it. 相似文献
12.
新疆阿克苏地区中、上奥陶统碳酸盐岩磁化率与层序地层关系 总被引：1，自引：0，他引：1
通过对新疆阿克苏地区中、上奥陶统185块碳酸盐岩样品的磁化率测量和统计,结合碳酸盐岩微相分析和层序地层研究,探讨了碳酸盐岩磁化率变化与沉积环境、层序界面、准层序(组)等之间的关系。研究结果表明:深水低能环境下沉积的钙质泥岩、瘤状灰岩、泥灰岩等通常对应于磁化率低值,且磁化率曲线较为平直;浅水高能环境下形成的含鲕粒砂屑灰岩、鲕粒灰岩等通常对应于磁化率高值;碳酸盐岩地层中淹没型层序界面对应于磁化率测量值的明显减小;准层序(组)的上部单元碳酸盐岩磁化率值比下部单元明显增大,并且其曲线常呈高频振荡状。 相似文献
13.
The Curie point depth map of Eastern Iran was constituted from spectral analysis of the aeromagnetic data. The reduction to pole (RTP) was applied to the magnetic anomaly data. The Curie point depth values from 165 overlapping blocks, 100 × 100 km in size, have been estimated. The Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The centroid and top depth of the magnetic sources (respectively Z0 and Zt) is calculated from radially averaged log power spectrum for each block. Finally, the Curie point depth of Eastern Iran is obtained by Zb = 2Z0–Zt. The highest value of 24 km is located in eastern and western boundaries of the Lut block, and the lowest value of 12 km is located at north of study area. The shallow depths in the Curie-point depth map are well correlated with the young volcanic areas and geothermal potential fields. Geothermal gradient ranging from 24 to 45°C/km. The deduced thermal structure in eastern Iran has a relationship with orogenic collapse associated with delamination of thickened lithospheric root between the Lut and Afghan continental blocks. 相似文献
14.
尕林格矿区矿体和围岩磁性差异明显,磁法勘探是最直接而有效的方法.通过对尕林格Ⅳ矿群成矿地质条件、C4-4子异常地球物理特征的分析以及用解析法对ZK10001孔三分量磁测井曲线做定性、定量解释,推测出盲矿体的方位、埋深、距离钻孔位置,从而正确布钻,达到找矿目的. 相似文献
15.
16.
In order to evaluate the quality of the offshore magnetic data in the Earth Magnetic Anomaly Grid (2-arc-minute resolution)(EMAG2), the authors chose the aeromagnetic data at 1∶500 000 and 1∶1 000 000 scales of the southern section of the Kolbeinsey Ridge with a total area of 193 500 km2 to compare and analyze. Based on the EMAG2 data, the authors obtained the EMAG2 (downward continuation 4 km) and the aeromagnetic anomaly (upward continuation 4 km) using the analytical continuation method. Then, the correlation coefficients between the aeromagnetic anomaly (upward continuation 4 km) and the EMAG2, and the aeromagnetic anomaly and the EMAG2 (downward continuation 4 km) were calculated by the correlation analysis method. Finally, through comprehensive analysis of the features of these correlation coefficients and differences, the quality of the magnetic data of the southern section of the Kolbeinsey Ridge was evaluated in the database EMAG2. The results showed that the EMAG2 integrated a large number of the airborne or offshore magnetic data. The quality of the offshore magnetic data is relatively high in the offshore areas with dense lines. However, the quality of the offshore magnetic data is relatively low if the EMAG2 data at 4 km altitude is converted to the anomaly data at sea level. 相似文献
17.
2．5D磁法反演估算铁矿资源量,关键是在垂直磁异常走向上求拟合模型的截面积。该文利用一种常见模型拟合4种实测磁场,发现铁矿截面积与埋深和磁性大小有一定的规律：磁化强度一定时,截面积与埋深呈线性正相关;埋深一定时,截面积与磁化强度呈近似指数形式的反相关。固定深部或外围磁性体参数,单独考虑浅部或中问铁矿模型时也有这种规律。在无钻孔资料及磁性资料不清楚时,磁化强度100000×10^-3～150000×10^-3A／m为估算铁矿资源量的最佳磁参数。因磁法反演的多解性,此类方法适用于钻孔验证前的资源量估计。 相似文献
18.
I. Patra A. K. Chaturvedi P. K. Srivastava M. S. Ramayya 《Journal of the Geological Society of India》2013,81(3):299-308
The Mesoproterozoic Khariar basin, to the SE of Chhattisgarh basin, comprises 1000 m thick arenaceous-argillaceous sediments. For the first time, a multidisciplinary approach has been made to the integrate interpreted satellite imagery, aero-magnetic and aero-radiometric data with available ground exploration data sets with an objective to understand structural fabric and to establish various parameters for unconformity related uranium mineralization in the environs of Khariar basin. Total Magnetic Intensity (TMI) anomaly image has been useful to mark major faults (ENE-WSW), magnetic bodies and overall basement characteristics. Combination of first vertical derivative (1VD) and tilt derivative magnetic images brought out presence of NW-SE magnetic linear (dominant) with minor ENE-WSW and NNE-SSW trends. Basic dykes and quartz veins are the surface manifestations of NW-SE trend in basement. Radially averaged power spectrum indicates the approximate basement configuration. Enhanced Thematic Mapper satellite imagery (Landsat ETM+) interpretation has shown lineaments along NW-SE, NNE-SSW, ENE-WSW and ENW-WSE directions. These observations are corroborated by interpreted results of magnetic data. Analysis of both results indicate NW-SE and ENE-WSW trends as post depositional. Aero-radiometric images (U, Th, K and ternary U-Th-K) show overall radio-elemental distribution for various litho-units. Besides, Th and K images along with interpreted ETM+ satellite imagery (RGB: 432/752/751) are useful to map small outliers and to modify basement-sediment contact. Geochemical data from basement rocks around Khariar basin suggests the younger Bundeli granitoids and its equivalents are good source of uranium in the western margin. Presence of labile uranium is inferred from higher concentration of uranium in water samples. The Airborne gamma-ray spectrometry (AGRS) and hydro-geochemical anomalies fall along fault zones and intersection of fault zones. The western and southern margin of Khariar basin are also characterized by presence of paleosol at unconformity, which are favorable factors for unconformity type uranium mineralization. Based on the present study, part of western and southern margin emerge as potential target areas for further exploration of uranium. 相似文献
19.
Magnetic susceptibility measurements were conducted on 24 vibrocores obtained from an area located off the northeastern coast
of Lantau Island in Hong Kong. High intensities of magnetic susceptibility were detected in the uppermost sections of the
majority of the cores. Several magnetic parameters measured for one of the cores suggest that the variations in the magnetic
characteristics over depth are mainly due to varying concentrations of the magnetic minerals. Since a strong correlation has
been found between magnetic susceptibility and the heavy metals Pb, Cu, Zn and Cr, an anthropogenic contamination origin is
thought to be the cause. The present study shows that magnetic susceptibility is a fast, inexpensive and non-destructive method
for the detection and mapping of contaminated sediments.
Received: 12 August 1997 · Accepted: 18 November 1997 相似文献
20.
The present study is an attempt to determine the sedimentary cover, and structural trends in the central part of Sinai Peninsula, Egypt. This study has been implemented by the integration of gravity and magnetic methods. Gravity data has been used for 2D modelling along some profiles perpendicular to the main structural trends of the study area. Magnetic data will be analyzed to determine the depth to the basement surface. The depths obtained from magnetic data will be used as a control points in the gravity modelling in order to minimize the error and facilitate the iteration of the suggested models. The basement relief map from magnetic and gravity output has been produced. This map indicates that, the basement depths, generally, increases from south to north and from east to west direction of the study area. The sedimentary cover is about 1.5-2 km in the southern part and increases to more than 4 km in the northeastern and western parts and changes gradually in the other parts of the study area. Results of structural trend analysis indicate that, the study area is greatly affected by several structural trends; N-S, E-W, NW-SE, and NNE-SSW directions. These trends are associated with the Baltim fault trend, Tethyan trend, Gulf of Suez, and Aqaba trend, respectively. 相似文献