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1.
In many Precambrian provinces the understanding of the tectonic history is constrained by limited exposure and aeromagnetic data provide information below the surface cover of sediments,water,etc.and help build a tectonic model of the region.The advantage of using the aeromagnetic data is that the data set has uniform coverage and is independent of the accessibility of the region.In the present study,available reconnaissance scale aeromagnetic data over Peninsular India are analyzed to understand the magnetic signatures of the Precambrian shield and suture zones thereby throwing light on the tectonics of the region.Utilizing a combination of differential reduction to pole map,analytic signal,vertical and tilt derivative and upward continuation maps we are able to identify magnetic source distribution,tectonic elements,terrane boundaries,suture zones and metamorphic history of the region.The magnetic sources in the region are mainly related to charnockites,iron ore and alkaline intrusives.Our analysis suggests that the Chitradurga boundary shear and Sileru shear are terrane boundaries while we interpret the signatures of Palghat Cauvery and Achankovil shears to represent suture zones.Processes like metamorphism leave their signatures on the magnetic data:prograde granulites(charnockites)and retrograde eclogites are known to have high susceptibility.We fnd that charnockites intruded by alkali plutons have higher magnetization compared to the retrogressed charnockites.We interpret that the Dharwar craton to the north of isograd representing greenschist to amphibolite facies transition,has been subjected to metamorphism under low geothermal conditions.Some recent studies suggest a plate tectonic model of subductionecollisioneaccretion tectonics around the Palghat Cauvery shear zone(PCSZ).Our analysis is able to identify several west to east trending high amplitude magnetic anomalies with deep sources in the region from Palghat Cauvery shear to Achankovil shear.The magnetic high associated with PCSZ may represent the extruded high pressureeultra high temperature metamorphic belt(granulites at shallow levels and retrogressed eclogites at deeper levels)formed as a result of subduction process.The EW highs within the Madurai block can be related to the metamorphosed clastic sediments,BIF and mafc/ultramafc bodies resulting from the process of accretion. 相似文献
2.
Total field magnetic data were collected over the Krishna-Godavari basin covering 20, 000 sq.km with an average spacing of 8.5 km. This was mainly to study the long wavelength features related with the deep structures. Aeromagnetic map of the region compared well with the ground maps. The anomaly maps show a combination of NE-SW, NS/NNE-SSW and NW-SE trends. The anomalies of ground data are transformed to isolate the sources at different depths. The second vertical derivative and downward continuation maps bring out clearly the NE-SW and NS/NNE-SSW trends related to the coastal basin and Eastern Ghats implying that they are shallow. These are probably superposed on much deeper NW-SE trending structural features of Pre-Gondwana breakup as evidenced in the Horizontal Gradient of Pseudogravity and upward continuation maps. From the offshore magnetic data it appears that these trends extend up to the Ocean Continent Boundary. It is inferred that the deeper features are associated with rifting of Dharwar and Bastar cratons within the Indian plate, prior to the rifting of India from Gondwanaland. The superposed horst and graben structures are related to the formation of the pull-apart Krishna-Godavari basin as a result of rifting and drifting of India from Gondwanaland. These two structural features are associated with two different tectonic events. 相似文献
3.
Thermal perturbation during charnockitization and granulite facies metamorphism in southern India 总被引：1，自引：0，他引：1
Abstract We have deduced the steady-state lithospheric geotherm at c. 1 Ga in the south Indian shield area using the available data on the concentration of radioactive elements, and the P-T conditions of Proterozoic mantle xenoliths in the south Indian kimberlites as constraints. The geotherm was adjusted back to 2.5 Ga by keeping the surface temperature constant and calculating the temperature change at the top of convecting upper mantle. The reduced or mantle heat flux, which was treated as an adjustable parameter, was 20.9–21.3 mW/m2 at 1–2.5 Ga. Comparison of the calculated steady-state geotherm with the available P-T data of the Archaean (c. 2.5 Ga) charnockites and granulites from southern India suggests that the granulite facies metamorphism in this region had resulted from a major thermal perturbation, which was c. 400° C at 25 km. Seismic tomographic and gravity data essentially preclude any significant magma underplating of the granulitic crust in southern India. Previous workers have suggested that the formation of charnockites in this region was associated with copious CO2 influx from a deep-seated source, possibly the mantle. In this work, we have evaluated both the transient and steady-state thermal effects of the heat convected by CO2 outgassing from upper mantle. It is shown that the thermobarometric array of charnockites and granulites can be produced by the convective perturbation of the steady-state geotherm, and that a flux of CO2 of ±90 mol/m2 yr (corresponding to Darcy velocity of ±0.30 cm/yr) for a period of ±30 Ma was needed to produce the required perturbation. This is c. 150 times the average CO2 flux through the tectonically active area of the Earth's crust at the present time. There is, however, an uncertainty of a factor of 3 in this value. Seismic tomographic and gravity data independently suggest thickening of the crust beneath the granulite terrane compared with the adjacent Dharwar craton. This suggests thermal perturbation due to overthrusting as a major potential cause for the granulite facies metamorphism in south India. Overthrusting of a 30–35-km-thick thrust block was needed to produce the required thermal effect. The estimated thickness of the original crust from geobarometric and seismic tomographic data south of the orthopyroxene isograd or ‘transition zone’is compatible with the emplacement of a thrust block of this magnitude. However, the latter fails to match the estimated pre-uplift crustal thickness at the transition zone, if it is assumed that the crust has not thinned by non-erosional processes since the Archaean. Thus, we propose a combination of overthrusting and CO2 fluxing from a deep-seated source as the cause for the formation of charnockites in this zone. The required focusing of CO2 in this case is c. 40% of that estimated in the model where CO2 fluxing was considered to be the sole reason for thermal perturbation. This combined thrusting—CO2 fluxing model also helps explain the development of patchy charnockites in the transition zone from amphibolite facies rocks. 相似文献
4.
The Eastern Ghats are a prominent topographic feature on the Indian Peninsula, stretching from the southern tip of the peninsula to near Bhubaneswar (20°N, 86°E) along the east coast. The belt is characterised by occurrences of high grade metamorphic rocks such as pyroxene granulites, sillimanite gneisses, charnockites and gabbro-anorthosite masses. The gravity field over the Eastern Ghats is appreciably positive as compared to the surrounding low grade gneissic terrain.Analysis of the gravity field along the coastal and southern granulite terrain comprising the Eastern Ghats shows that a large number of gravity highs are associated with charnockites of basic and intermediate nature as well as gabbro-anorthosite masses. The lows appear to be associated with acid charnockites, syenite masses or granitic intrusives.The boundary between the Eastern Ghats terrain and the adjoining Dharwar/Bastar cratons appears to be a faulted one. The crust underneath the Eastern Ghats is inferred to be of a higher density than that of the Dharwar/Bastar cratons to its west. The gravity field over the Eastern Ghats is compared to that of similar terrains in other parts of the world. It is inferred that the Eastern Ghats are characterised by a crust of higher than normal density. 相似文献
5.
Abstract Two varieties of charnockites are recognized in the Dharwar craton of southern India. The style and sequence of structures in one charnockite variety, and related intermediate to basic granulites, are similar to those in the supracrustal rocks of the Dharwar Supergroup and the adjacent Peninsular Gneiss. This style has isoclinal folds with long limbs and sharp hinges with an axial planar fabric in some instances. Additional evidence of flattening is provided by pinch-and-swell and boudinage structures, with basic granulites forming boudins in the more ductile charnockites/enderbites in the limbs of isoclinal folds. These folds are involved in near-coaxial upright folding resulting in the bending of the axial planes of the isoclinal folds and the associated boudins. All these structures are overprinted by non-coaxial upright folds with axial planes striking nearly N–S. The map pattern of charnockites suggests that this sequence of structures is present not only on a mesoscopic scale, but also on a macroscopic scale. Charnockites of this variety provide, in some instances, evidence of having been migmatized to give rise to hornblende–biotite gneiss and biotite gneiss, which form a part of the Peninsular Gneiss terrane.
The second variety comprises charnockite sensu stricto with an entirely different structural style. This type occurs in the tensional domains of the hinge zones of the later buckle folds, in the necks of foliation boudinage, in shear zones and in release joints parallel to the axial planes of the later folds in the Peninsular Gneiss. Because the non-coaxial later folds are associated with a strain pattern different from, and later than, that of the isoclinal folds of the first generation, it follows that charnockites of the Dharwar craton have evolved in at least two distinct phases, separate both in time and in process. 相似文献
The second variety comprises charnockite sensu stricto with an entirely different structural style. This type occurs in the tensional domains of the hinge zones of the later buckle folds, in the necks of foliation boudinage, in shear zones and in release joints parallel to the axial planes of the later folds in the Peninsular Gneiss. Because the non-coaxial later folds are associated with a strain pattern different from, and later than, that of the isoclinal folds of the first generation, it follows that charnockites of the Dharwar craton have evolved in at least two distinct phases, separate both in time and in process. 相似文献
6.
重力异常图中的边界增强和提取技术 总被引：1，自引：0，他引：1
对比了重磁勘探领域中4种典型的边界增强方法：Tilt导数、Tilt导数的水平梯度、Theta角和归一化的标准偏差,它们都能放大与边界有关的高频异常。增强后异常幅值极大值与地质体边界对应的情况可用近似边界法自动提取,而异常幅值拐点与边界对应的情况可以引入Canny边界检测算子来提取。理论模型试验表明：用Canny算子提取Tilt导数图边界与用近似边界检测法提取其它边界增强图的边界相比,前者提取的边界位置与真实位置更吻合,虚假边界更少。应用该方法对梅山铁矿的局部重力异常进行了处理,勾画出铁矿的大致范围。 相似文献
7.
Aeromagnetic anomalies over Bastar craton and Pranhita-Godavari (P-G) basin in the south of central India could be attributed
to NW-SE striking mafic intrusives in both the areas at variable depths. Such intrusions can be explained considering the
collision of the Bastar and Dharwar cratons by the end of the Archaean and the development of tensile regimes that followed
in the Paleoproterozoic, facilitating intrusions of mafic dykes into the continental crust. The P-G basin area, being a zone
of crustal weakness along the contact of the Bastar and Dharwar cratons, also experienced extensional tectonics. The inferred
remanent magnetization of these dykes dips upwards and it is such that the dykes are oriented towards the east of the magnetic
north at the time of their formation compared to their present NW-SE strike. Assuming that there was no imprint of magnetization
of a later date, it is concluded that the Indian plate was located in the southern hemisphere, either independently or as
part of a supercontinent, for some span of time during Paleoproterozoic and was involved in complex path of movement and rotation
subsequently. The paper presents a case study of the utility of aeromagnetic anomalies in qualitatively deducing the palaeopositions
of the landmasses from the interpreted remanent magnetism of buried intrusive bodies. 相似文献
8.
M. Sridhar A. Markandeyulu A. S. Chawla A. K. Chaturvedi 《Journal of the Geological Society of India》2018,91(2):165-173
Aeromagnetic data overcome constrain of inadequate exposures and provide signatures of bodies beneath sediment cover. Present work on analysis of aeromagnetic data over western part of Kaladgi basin provided insight into the basement structures and their role in basin evolution. In the study area, the NW-SE and NE-SW are the major trends of magnetic lineament followed by E-W and N-S trends.Archean to Paleoproterozoic basement is manifested by two structural zones, NW-SE trends related to major lineaments within the basement and the NE-SW trends presumed intra-basinal fault systems which controlled the local depressions. The basin configuration deduced from depth to basement show that the Kaladgi basin is an open deep basin and divided into several sub-basins, separated by fault-controlled NE-SW and NW-SE oriented basement ridges. An intriguing find in the western part are the numerous scattered smaller-scale, circular or semicircular, distinct magnetic anomalies of moderate to strong magnetic signal with strong remenance. Analyses coupled with 3D inversions in combination with sub-surface probing reveal in-homogeneities within basement gneisses and supracrustal rocks of the Kaladgi basin, Dharwar craton. 3D inversions of these circular bodies, suggest that they are apophyses of the intrusions or alternatively as younger intrusive stocks. Sub-surface probing by boreholes over circular bodies revealed leucocratic granite with porphyritic texture emplaced as intrusive within the Chitradurga metasediments. This implies that these intrusives are post-Chitradurga schist and pre Badami sediments as they have not affected the latter. However, they can be presumed to be coeval to potassic granites, which intrude the eastern part of the western Dharwar craton in southern India, until geochronological data are available. 相似文献
9.
《International Geology Review》2012,54(4):689-695
The Magnitogorsk synclinorium, a major structure of the southern Urals, has pronounced positive gravity anomalies associated with numerous greenstone intrusives. It is bounded on the west by a gravity low which corresponds with the Ural-Tau and Bashkir anticlinorium and on the east by gravity minima corresponding to the East-Uralian anticlinorium with its numerous intrusives. The relationship between gravity anomalies and major south Uralian structure indicates the effect of deeper structure conditions. Magnetic data correlates with the gravity results in that the western and eastern zones have quiescent negative magnetic fields and the Magnitogorsk synclinorium shows a strongly differentiated magnetic field. Positive magnetic anomalies are related to ultrabasic and basic intrusives, though some large magnetic maxima correspond to lower Carboniferous acidic and alkalic intrusives. Gravity and magnetic anomalies give some idea of deeper structure of the area. Copper pyrite deposits are associated with linear magnetic anomalies and associated zones of crushing. Regionally, these deposits are definitely associated with positive gravity anomaly zones. Geologic and geophysical maps are included, showing major geologic features and related magnetic and gravity anomaly zones. — C. E. Sears. 相似文献
10.
文章针对在东昆仑祁漫塔格群力地区圈出的9处1:5 000高精度磁异常,通过初步解译,6条剖而的磁异常(△T)求解及磁性矿体的反演计算,结合测定的磁物性及野外地质观察结果,将在磁异常内发现的地表矿体、深部隐伏矿体进行对比分析后认为,M1、M4、M5、M6等磁异常,地表强度大,峰值高,但反映的只是浅部矿体的特征,而M0、M8两个弱磁异常,虽然磁异常强度小、峰值低,但这些磁异常规模比较大,反映的是深部磁异常的特征.提出在以后的找矿工作中应苇视对这种弱磁异常的评价. 相似文献
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12.
本文在对南阳盆地及造山带地球化学数据因子分析的基础上,对研究区与铁矿化相关的元素组合进行异常信息的提取与评价。结果表明:1)因子分析获得的F2因子(Co-Mn-Ti-V-Fe)能够很好地反映出与铁矿化相关的异常信息,可以作为寻找铁矿矿化的标志之一;2)从奇异性指数图可以看出,已经发现的铁(磁铁)矿床基本上位于奇异性指数a2的区域,南阳盆地西部地区异常较好、研究程度低,可以作为进一步开展矿产勘查工作的重点区域;3)S-A方法得到的背景图中高异常值主要分布在中-基性岩体的区域,异常图展示出较好的矿化异常,未出现大型铁矿床的原因可能是研究区中-基性岩在地表出露比较分散、不具规模,在该区域深部中-基性岩体中具有寻找大型隐伏铁矿床的可能。因此,基于奇异性理论和S-A法的综合异常提取方法对于寻找深部和隐伏的矿体具有帮助,可以为下一步的找矿工作提供参考。 相似文献
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14.
Southern India and Sri-Lanka are the places where "incipient charnockites",i.e.the local transformation of amphibolite-facies gneisses into orthopyroxene-bearing,igneous looking charnockites,have been discovered in the early sixties.The fact that some incipient charnockites occur along a network of brittle fractures,together with CO_2 remnants preserved in mineral inclusions,had called for the role of fluids during charnockite alteration.The present work presents new observations on fluid inclusions and microtextures of incipient charnockites from type localities in southern India.In addition to CO_2-rich fluid inclusions in quartz and feldspar,all of the occurrences have disrupted remnants of concentrated aqueous alkali chloride solutions.CO_2 inclusions are more abundant in paragneiss(Kerala)than in orthogneiss(Karnataka/Tamil Nadu).The finding of disrupted brine inclusions in the Kabbal charnockite is a key link between closely associated massive charnockites and Closepet Granite,both of which also share the brine remnants.All of the occurrences studied here have feldspar or feldspar-quartz microvein networks along grain boundaries of recrystallized quartz,feldspar and orthopyroxene.These metasomatic veins again indicate the action of alkali-exchanging fluids(i.e.,saline solutions).Feldspar microveins,which have been found in most "massive" charnockites,along with the CO_2-rich fluid inclusions,suggest a commonality of incipient charnockite and massive charnockite,both types differing in intensity of interaction with metasomatizing pore fluids. 相似文献
15.
黄沙坪矿田的综合找矿模式及其在隐伏矿床预测中的应用 总被引：3，自引：0，他引：3
黄沙坪矿田的综合找矿模式可概括为已知黄沙坪铅锌矿床成矿模式、地质地球化学及地球物理找矿标志以及最优找矿方法。黄沙坪铅锌矿床成矿母岩与中酸性高侵位岩体有关,倒转背斜轴部及其纵横断裂交汇处控制矿床,走向逆冲断裂带、间层断裂或虚脱带、岩体侵入接触带等控制矿体;矿床范围内有重力、磁力、电性、放射性等异常,出现成矿元素及重矿物指示标志;探查岩体(探岩)、圈定远景区(圈区)找矿床赋存部位(找位)、寻工业矿体(寻体)是最优找矿方法。此综合找矿模式在隐伏矿床预测中的应用经钻探验证取得了积极效果。 相似文献
16.
三维地质建模的用途、现状、问题、趋势与建议 总被引：4，自引：0，他引：4
文章论述了三维地质建模技术的用途、现状、存在问题、发展趋势和几点建议。笔者认为三维地质建模的用途是:1真三维的立体场景;2精准的储量计算;3平、剖面构造形态相容并联动编辑;4多源、异构数据的集成与同化;5各种三维空间分析与过程模拟;6便于向客户与领导介绍复杂的地质条件。从行业应用和国内软件发展两个方面论述了当前三维地质建模的应用现状,该技术应用中存在的问题:1软件操作太复杂,难以为基层广大地质作图人员所掌握;2三维建模约束条件太严苛,编辑工作量巨大;3没有三维地质模型数据标准,模型数据难以交换与共享;4勘探规范没有要求,地质队积极性不高;5三维地质模型的建模成本由谁支付。三维地质建模的发展趋势:1软件将更加成熟、稳定、易用;2由早期的注重形态建模向形态与属性建模并重的方向发展;3与地震、测井等物探数据结合更加紧密;4与矿藏描述、成藏模拟、沉积环境分析、构造演化分析、构造演化模拟等专业应用结合更加紧密;5融入大数据、云计算、物联网等IT主流技术。向国家相关主管部门、企业用户和软件开发商提出了几点建议:1国家应继续支持三维地质建模领域;2三维地质建模要与专业应用紧密结合;3加强相关标准的制定与维护;4逐步在勘探规范中增加对三维建模的要求;5软件开发者设法降低软件的操作复杂度,提高容错能力。 相似文献
17.
黑龙江大兴安岭地区HFU-09号航放异常特征及找矿意义 总被引：1，自引：0，他引：1
利用大兴安岭地区1/5万高精度航放资料,对圈定的HFU-09号航放异常开展了综合查证,采用的工作手段包括剖面、面积性查证及深部钻探验证。在钻孔中发现了低品位铀矿体、铀矿化体、铅锌矿化体及铌钽矿找矿线索。根据查证结果认为,1:5万航空物探调查圈定的航放异常与地面伽玛能谱测量圈定的U、Th异常对应性较好,异常再现性较明显。区内岩石破碎铁染发育部位一般存在矿化。在对赋存于花岗岩中的航放异常进行查证时,需结合岩石的具体矿化蚀变特征进行贵金属、有色金属矿产的评价,以期发现多金属矿床。 相似文献
18.
R. Ananda Reddy 《Journal of the Geological Society of India》2014,83(3):235-251
Widespread distribution of mafic dykes and scanty occurrence of ultrabasic intrusives of kimberlitic affinity around Proterozoic Cuddapah basin, parts of Eastern Dharwar craton of south India has been the focus of attention since their discovery, to understand the structural fabric in relation to their emplacement in geological time. Satellite Imagery, geomorphological, geophysical and radiometric age data of Narayanpet area, northwest of Cuddappah basin, have clearly displayed the alignments and structures of geological significance, such as deep seated fault / fracture / shear zones, stratigraphic / lithological contacts, basic / ultrabasic intrusives and younger granites etc,. Based on the field observations such as emplacement of mafic dykes, their cross cutting relationship, study of morphological and geophysical signatures, inferred linears drawn from satellite imagery, aeromagnetic and gravity maps are arranged in a chronological order. A system of long, narrow and widely spaced dykes trending NW-SE direction conformable to gneissic foliation, typically associated with migmatites in the southwestern part of the study area are the oldest. Followed by E-W dykes, cut across by the sparsely distributed dykes associated with NW-SE and N-S features and in turn off set by dykes of NE-SW trends are the youngest. Kimberlites of Narayanpet area, belongs to hypabysal facies, which are essentially controlled by E-W to ENE-WSW deep seated fault / fracture zone, their intersection with NW-SE, NE-SW to N-S trends, which may have been reactivated during Proterozoic period as indicated by the intrusion of mafic dykes (～2270 to 1701 Ma) and emplacement of kimberlitic magmatism (～1300 to 1100 Ma) suggesting different intrusive episodes. Kimberlite pipes of Narayanpet field, falls in an ellipsoid form trending WNW-ESE direction in the northern part of the area, associated with radial drainage / topographic high and a gravity low. In addition, physical properties such as density and magnetic susceptibilities of mafic dykes and kimberlites, their geophysical signatures, emplacement of kimberlites at the close vicinity of mafic dykes or at their intersections have also been discussed. 相似文献
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大兴安岭南段是我国重要的锡多金属成矿集中区,为促进区域锡多金属找矿突破,以在黄岗-甘珠尔庙地区多年的野外调查研究工作为基础,运用年代学测试、化学分析及地质模型等方法,分析了区域锡的成矿作用。认为二叠统基底地层及锡林郭勒杂岩是成矿物质的初始来源,经历的变质过程具有进一步富集的作用,大部分锡矿均遭受了多期次的火山-岩浆活动,最终决定锡多金属成矿的是燕山期酸性岩浆-热液成矿作用。同时成矿作用还受到控岩控矿构造、围岩性质、氧化-还原条件、开放-封闭环境的制约,认为在氧化性花岗岩浆侵入钙质地层条件下成矿作用以铁锡为主;还原性岩浆在侵入具开放性特征的围岩时,成矿作用以花岗岩外带围岩中的热液型脉状锡矿为主,而在侵入具封闭性特征的围岩时,成矿作用以花岗岩内带岩浆凸起部位的花岗岩型锡矿为主。因此,建议将主攻矿种由铅锌调整为锡银,部署重砂及化探方法圈定异常,针对硫化矿体部署电法,针对隐伏岩体部署磁法与重力,还可部署烃、汞、氧气测量等非常规化探方法预测隐伏岩体。 相似文献