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1.
Yoann Quesnel Christophe Sotin Benoit Langlais Simona Costin Mioara Mandea Matthias Gottschalk Jérome Dyment 《Earth and Planetary Science Letters》2009,277(1-2):184-193
This paper proposes a model of serpentinization of the Southern martian crust that may explain the topographic dichotomy, the absence of an associated free-air gravity anomaly and the presence of strong magnetic anomalies in the Southern Hemisphere. The thermodynamical conditions for serpentinization were likely met in the lithosphere during the Noachian period. This process may have decreased the density in the Southern crust and created the topographic dichotomy. Different reactions of serpentinization that can form magnetite have been considered. Assuming an intense magnetic field (core dynamo), we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies. The pertinence and the implications of our model concerning the early thermal evolution of Mars are discussed, with emphasis on the intensity of the paleo-magnetic field. 相似文献
2.
Abstract Several linear magnetic anomalies over continental crust have been identified in and around the Japanese Islands. The anomalies are probably related to island arc tectonic structures, but identifying specific sources has been difficult. Several deep holes were drilled in and around Aso caldera, where a linear anomaly occurs along an active fault. One drillhole located on the linear anomaly encountered a zone of highly magnetized and altered basement rocks at least 100 m thick at a depth of ∼1000 m. The other hole was located away from the anomaly and did not encounter any high-magnetic zones. Rocks from the zone have exceptionally strong remanent magnetization (several tens of A/m) sub-parallel to the present field. AF demagnetization experiments indicated that the magnetization is hard and stable. Magnetic modeling indicates that the linear anomaly is caused mainly by this layer. Microscopic examination of core samples shows that the highly magnetized zone includes secondary magnetic minerals and abundant hydrothermal alterations. Temperatures determined by fluid inclusions and down-hole temperatures show that the temperature of the highly magnetized zone was elevated in the past relative to surrounding rocks. The high temperature could destroy primary magnetic minerals and replace them with secondary magnetic minerals. Thus, the past hydrothermal system may have enhanced thermo-chemical remanent magnetization. The results can produce a model indicating that there was a past hydrothermal system related to the tectonic structure. 相似文献
3.
根据波茨坦地磁场模型(POMME6.2),研究喜马拉雅东构造结周围地区地壳磁异常的空间分布、磁异常随高度的衰减特征.利用二维小波变换方法对地表磁异常进行分解,分析小波细节组合和逼近信号的异常特点.讨论磁异常与地质构造的联系.结果表明,研究区内地壳磁异常分布相当不均匀.喜马拉雅—东构造结—龙门山—大巴山地区分布着较强的负磁异常;四川盆地为正磁异常,其他地区磁异常较弱.东构造结对周围地区磁异常有重要影响,它及其周围地区的地壳磁异常都是在负磁或弱磁异常背景上,叠加着中短波长的正负磁异常.这些中小尺度磁异常由中、上层地壳磁性物质产生,走向与地质构造基本一致.沿金沙江、红河断裂带分布着清晰的弱磁异常带.龙门山断裂带、丽江—小金河断裂带和红河断裂带是磁异常强弱过渡带.青蒇高原中部东西向的磁异常,在东构造结弧顶地区呈弧形分布.青藏高原中部和滇中地块带状、团状磁异常具有相同的衰减规律. 相似文献
4.
Paleomagnetic studies of the basalt samples of Mid-Atlantic Ridge recovered during DSDP Leg 45 and the FAMOUS Project have led to a revision of our view of the oceanic igneous crust as a recorder of geomagnetic field reversals. The discovery of several magnetic polarity reversals with depth in the crust has indicated that oceanic igneous basement should not necessarily be considered magnetized uniformly in direction, or even polarity, in a given vertical cross section. Statistical arguments, based on the ratio of the average time of crustal formation to the average length of a magnetic polarity interval, indicate that magnetic reversals with depth are to be expected in typical ocean crust, but also that this does not conflict with current theories of plate tectonics or exclude the upper layers of the crust from making a major contribution to the overlying linear magnetic anomalies. Certain ratios of average crustal formation time to average polarity interval do, however, result in an effective zero magnetization for the oceanic crust and these conditions may be responsible for the reduced amplitude of magnetic anomalies in some areas. 相似文献
5.
化向地磁极(化极)是最基本的磁测资料处理方法之一,化极能消除或减少斜磁化影响,提高对磁测资料的认识程度和解释水平,对研究地壳产生的磁异常具有重要意义.但低纬度地区特别是磁赤道处,化极处理很不稳定甚至奇异,一直是位场研究的难点.针对地磁纬度较低特别是磁赤道地区磁异常化极的困难,利用从磁北极处垂直磁化向低纬度地区水平磁化方向转换稳定的特点,提出"狭义化赤"概念,并将其与低纬度磁异常"倒相"解释方法结合,提出专门用于磁赤道处化极的方法.该方法扩展了现有的化极理论,实现了磁赤道处的稳定化极.区别于目前任何方法,专门用于(近)水平磁化条件下的化极计算,具有原理简单,实现方便,收敛速度快等特点.对理论模型和实际资料计算表明这种针对磁赤道地区磁异常的化极处理方法是稳定、可靠的. 相似文献
6.
Crustal thermal regime inferred from magnetic anomaly data and its relationship to seismogenic layer thickness: The Japanese islands case study 总被引：2，自引：0，他引：2
The seismogenic layer thickness correlates with surface heat flow beneath the Japanese islands. However, this correlation is shown at restricted area, where seismic activity is high. In order to overcome this spatial limitation, we used another approach to estimate the regional thermal structure in the crust beneath the Japanese islands with more uniform coverage. The bottom depths of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. We applied this method to estimate the crustal thermal structure in square windows of 2.125° × 2.125°. The obtained depths ranging from 11 to 30 km with average value of 18 km, correlate with the seismogenic layer thickness. It suggests that the Curie point depth is a useful indicator of the crustal thermal structure in these regions. 相似文献
7.
New possibilities for the interpretation of long-period magnetic anomalies were opened up by the construction of their first satellite-based maps. The anomalies are due to lateral variations in the magnetic properties and thickness of the deep layers of magnetized rocks. The CHAMP orbital geometry is suitable for providing daily information on the magnetic field over the almost uniform grid above the Earth’s surface. These measurements favor calculation of the spherical harmonic model of the main magnetic field for each day separately. The distribution of regional lithospheric anomalies derived from the satellite measurements over the territory of Southeast Asia is analyzed. These lithospheric anomalies agree with the zonal-block crustal structure of this region revealed from geological assessments. 相似文献
8.
Field tests were conducted to determine representative total-intensity magnetic anomalies due to the presence of underground storage tanks and 55-gallon steel drums. Three different drums were suspended from a non-magnetic tripod and the underlying field surveyed with each drum in an upright and a flipped plus rotated orientation. At drum-to-sensor separations of 11 feet, the anomalies had peak values of around 50 gammas and half-widths about equal to the drum-to-sensor separation. Remanent and induced magnetizations were comparable; crushing one of the drums significantly reduced both. A profile over a single underground storage tank had a 1000-gamma anomaly, which was similar to the modeled anomaly due to an infinitely long cylinder horizontally magnetized perpendicular to its axis. A profile over two adjacent tanks had a smooth 350-gamma single-peak anomaly even though models of two tanks produced dual-peaked anomalies. Demagnetization could explain why crushing a drum reduced its induced magnetization and why two adjacent tanks produced a single-peak anomaly.
A 40-acre abandoned landfill was surveyed on a 50- by 100-foot rectangular grid and along several detailed profiles. The observed field had broad positive and negative anomalies that were similar to modeled anomalies due to thickness variations in a layer of uniformly magnetized material. It was not comparable to the anomalies due to induced magnetization in multiple, randomly located, randomly sized, independent spheres, suggesting that demagnetization may have limited the effective susceptibility of the landfill material. A different 6-acre site survey conducted on a 10- by 10-foot grid was analyzed to determine the maximum station spacing and line separation that could have been used. Essentially, all of the anomalies at this site would have been resolved by a survey conducted on a 20- by 20-foot grid and the larger anomalies would have been detected by a 50- by 50-foot grid. 相似文献
A 40-acre abandoned landfill was surveyed on a 50- by 100-foot rectangular grid and along several detailed profiles. The observed field had broad positive and negative anomalies that were similar to modeled anomalies due to thickness variations in a layer of uniformly magnetized material. It was not comparable to the anomalies due to induced magnetization in multiple, randomly located, randomly sized, independent spheres, suggesting that demagnetization may have limited the effective susceptibility of the landfill material. A different 6-acre site survey conducted on a 10- by 10-foot grid was analyzed to determine the maximum station spacing and line separation that could have been used. Essentially, all of the anomalies at this site would have been resolved by a survey conducted on a 20- by 20-foot grid and the larger anomalies would have been detected by a 50- by 50-foot grid. 相似文献
9.
《Physics of the Earth and Planetary Interiors》2005,148(2-4):149-156
Early in the history of planetary evolution portions of Martian crust became magnetized by dynamo-generated magnetic field. A lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo. This ambient field is capable of magnetizing portions of deeper crust that cools through its blocking temperatures in an absence of dynamo. We consider both magnetite (Fe3O4) and hematite (α-Fe2O3) as minerals contributing to the overall magnetization. Analysis of magnetization of magnetic minerals of various grain size and concentration reveals that magnetite grains less than 0.01 mm in size, and hematite grains larger than 0.01 mm in size can become effective magnetic source capable of magnetizing magnetic minerals contained in surrounding volume. Preexisting crustal remanence (for example ∼250 A/m relates to 25% of multi-domain hematite) can trigger a self-magnetizing process that can continue in the absence of magnetic dynamo and continue strengthening and/or weakening magnetic anomalies on Mars. Thickness of the primary magnetic layer and concentration of magnetic carriers allow specification of the temperature gradient required to trigger a self-magnetization process. 相似文献
10.
Electrical conductivity anomalies in the earth 总被引：1，自引：0，他引：1
Yoshimori Honkura 《Surveys in Geophysics》1978,3(3):225-253
Anomalies of short-period geomagnetic variations have been found in various regions over the world. It is known that such anomalies arise from electromagnetic induction within an electrical conductivity anomaly or from local perturbation of induced electric currents by a conductivity anomaly. In order to investigate a regional electric state in the Earth, conductivity anomaly (CA) studies based on anomalous behaviors of geomagnetic variations have been extensively undertaken, as well as studies based on magnetotelluries in which induced currents are directly used.Some of the geomagnetic variation anomalies, however, turned out to be caused by surface conductors, such as sea water and sediments. Anomalies of this sort have been intensively studied and classified into coast, island, peninsula, and strait effects in the case of sea effects. Three-dimensional conduction or channelling of induced electric currents is sometimes observed in the cases of sediments and some crustal conductivity anomalies. However, anomalies of such surface origins often provide some information of the underground conductivity structure.Electrical conductivity anomalies can be classified into two types: anomalies originating in the crust and in the upper mantle. Many of crustal anomalies are well correlated with metamorphic belts, fracture zones, and hydrated layers, and magnetic and gravity anomalies are also often found over the conductivity anomalies. Most of mantle anomalies have been interpreted mainly in terms of high temperature and partial melting, since conductivity anomalies coincide well with anomalies in heat flow and seismic wave velocities. 相似文献
11.
本文联合使用云南、四川和贵州地震台网的85个地震台站在2008年1月—2017年12月期间记录的49130个地震、317366个初至Pg震相绝对到时数据和2674110条高精度的相对到时数据,采用区域双差地震层析成像方法联合反演了川滇南部地壳三维P波速度结构和39621个地震的震源参数,探究了川滇南部中下地壳流和腾冲火山区岩浆囊的分布特征.研究结果表明：（1）川滇南部上地壳的速度异常特征与地表地形密切相关;（2）小江断裂带的中下地壳存在一条绵延近二百多公里的低速异常结构,最南端受到红河断裂带的阻挡而终止于断裂带南段北侧,这可能是川滇南部的一条中下地壳流,低速异常结构在红河断裂带南段转而向南东流动反映了红河断裂带可能为川滇菱形块体的西南边界;（3）红河断裂带各段速度异常存在明显的差异,重定位后的震源分布显示红河断裂带中段和南段虽然不如北段地震活动强烈,但地震震源深度分布较北段深;（4）腾冲火山区西侧和北侧下方10~20 km深度范围内存在的低速异常体推测为通过怒江断裂带形成的岩浆通道从中地壳涌入上地壳的岩浆囊,可能反映了自更新世延续至今的以橄榄玄武岩和安山岩为主要岩性的壳内岩浆活动,持续的岩浆活动为地表热活动提供了主要动力. 相似文献
12.
重-磁-震联合反演是获取地壳结构的重要方法.此次研究,我们主要基于全球最新的水深、重磁异常、沉积物厚度等数据,结合实测地震数据和前人研究成果,分析了中国海-西太平洋地区的莫霍面展布特征,并利用重磁震联合反演方法获得了跨越中国海-西太平洋典型剖面的地壳结构和异常体分布,揭示了陆壳到洋壳的典型变化规律.结果表明,从浙江地区到马里亚纳俯冲带,地壳结构大致呈现由厚到薄、由老到新、由复杂到简单的特征.浙江地区（扬子块体和华夏块体）地壳结构复杂,三层结构明显,地壳内断裂带发育,并伴有广泛的岩浆侵入;东海地区莫霍面起伏剧烈,地壳厚度变化较大,冲绳海槽地壳明显减薄,是其过渡壳性质的体现;西菲律宾海盆、九州-帕劳海脊、帕里西维拉海盆、马里亚纳俯冲带等构造单元地壳结构相对简单,二层结构明显.其中,西菲律宾海盆和帕里西维拉海盆地壳内部磁异常变化较为剧烈,海盆扩张过程中形成的磁异常体分布广泛,地壳厚度（5~8 km）明显小于陆壳;九州-帕劳海脊地壳厚度可达~20 km,缺失中地壳,表现为岛弧地壳结构;同源的西马里亚纳岛弧和东马里亚纳火山弧地壳结构相似,浅层磁异常体分布广泛,西马里亚纳岛弧地壳厚度（~17 km）略小于东马里亚纳火山弧（~20 km）,体现了裂离的不对称性;马里亚纳海槽具有正常的洋壳结构（~7 km）,但扩张中心未发生明显破裂.对比各构造单元地壳结构的异同点,我们进一步认识到,陆壳与洋壳之间不是孤立的,陆壳可能会演化出洋壳的结构或组分,板块的演化总是处于动态循环过程中.此研究加深了我们对中国海-西太平洋深部构造特征的整体理解,促进了我们对大陆边缘演化与板块相互作用的认识,深化了我国管辖海域及邻近地区的基础地质调查. 相似文献
13.
普里兹湾位于南极洲东部大陆边缘,其深部地壳结构特征对认识白垩纪冈瓦纳古陆裂解和新生代大陆边缘形成具有重要意义.本文利用重磁、多道反射地震、声纳浮标折射地震和ODP钻井数据对普里兹湾海域的深部地壳结构进行了研究.研究结果显示,普里兹凹陷表现为典型的盆地负重力异常特征,其沉积基底较深,而在四夫人浅滩为高幅重力正异常,其沉积基底普遍抬升.在大陆架中部存在SW-NE向条带状基底的抬升,且呈朝NE向逐渐变深的趋势.在中大陆架外侧,均衡残余重力异常呈V字形负异常条带状分布,其两翼分别与四夫人浅滩和弗拉姆浅滩外的大陆坡相连.该异常带在大陆架中部向陆的偏移可能是由于古大陆架边缘的地形影响,推测其与普里兹冲积扇同属于洋陆过渡带向陆的部分,在重力模拟剖面表现为地壳向海逐渐减薄.普里兹冲积扇的地壳厚度较薄,平均为6 km,最薄处可达4.6 km,并且根据洋陆过渡带向海端的位置,推测可能属于接近洋壳厚度的过渡壳.重力异常分区的走向与兰伯特地堑在普里兹湾的构造走向基本一致,可能主要反映了二叠纪-三叠纪超级地幔柱对普里兹湾的裂谷作用的影响.该区域的自由空间重力异常和均衡残余异常均表现为超过100×10-5m/s2的高幅正异常特征,可能由位于大陆架边缘的巨厚沉积体负载在高强度岩石圈之上的区域挠曲均衡作用所导致,可能与该区域第二期裂谷期之后的沉积间断以及快速进积加厚的演化过程有关.普里兹湾磁力异常的走向与重力异常明显不同,大致可分为东北高幅正异常区和西南低幅异常区.重磁异常在走向上的差异反映高磁异常主要来源于岩浆作用形成的铁镁质火成岩的影响,并且岩浆作用的时代不同于基底隆升的时代,而可能形成于前寒武纪或者南极洲和印度板块裂谷期间(白垩纪). 相似文献
14.
The high-amplitude wide magnetic anomaly that covers a large area of the north-eastern – central Adriatic Sea in the Croatian offshore is ∼100 km wide and extends NW–SE for ∼350 km. The anomaly is located between the Dinarides and Apennines chains, in an interesting geodynamic scenario. The presence of intruded gabbroid rocks in the Croatian archipelago also contributes to making this intriguing and still not extensively investigated anomaly potentially significant to the geologic and geophysical context in which it is located. In this work, we model the Bouguer and magnetic anomalies across the Adriatic Sea. The 2D geophysical modeling was produced across four cross sections considering surface heat flow data to calculate the Curie depth. The magnetic susceptibilities and densities used for the synthetic bodies are in agreement with the literature and with those derived by previous models. The results suggest the presence of an uplifted magnetized basement with high magnetic susceptibility (0.075 SI units) to be the main contributor to the observed magnetic anomaly. This magnetic susceptibility is interpreted as representative of a gabbroid-intruded basement. The high-susceptibility basement is in lateral continuity with a relatively low susceptibility basement (0.025–0.038 SI units). The results of the geophysical modeling are compared with a conceptual geological model realized from the integration of surface, well and geophysical data, the latter concerning seismic, tomographic, magnetic and gravimetric anomalies and heat flow data. These data have been merged in an integrated data-base using MOVE software, and the geophysical modeling was performed using GM-SYS. The comparison allowed to confirm the hypothesis that the magnetic anomaly is related to the basement and to its position in the complex geodynamic evolution of the Apennines–Adriatic–Dinarides system. 相似文献
15.
陆壳中的地震更危险,但其分布更具有弥散性,尤其在中国大陆地区;因此可靠且易用的地震警示信息显得非常重要.目前这类信息主要来自历史地震目录,大地测量及构造等资料,还需要补充其它的地学资料.本文提出一种来自卫星地壳磁场的约束.对于中国大陆的壳内地震(MS≥5.0),研究表明其大都(80％以上)位于卫星地壳磁场的垂向磁感应强度分量的零等值线上或附近,并且理论上可以用一作用于半无限磁弹性平面中的集中力所产生的磁场分布来进行相应解释.尽管存在许多不确定因素,这种新的独立于传统资料的约束,提供了更为详细的地震警示性信息.同时,在缺少历史地震目录,大地测量及构造资料的地区,这种约束可作为一种先导性的监测信息加以使用. 相似文献
16.
L.L Hood P.J Coleman Jr. C.T Russell D.E Wilhelms 《Physics of the Earth and Planetary Interiors》1979,20(2-4):291-311
Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate presently available magnetic anomaly maps — one covering a portion of the lunar near side and the other a part of the far side.
The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous, light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. An age for Cavalerius (and, by implication, for Reiner Gamma) of 3.2 ± 0.2 × 109 y is estimated. The main (30 × 60 km) Reiner Gamma deposit is nearly uniformly magnetized in a single direction, with a minimum mean magnetization intensity of 7 × 10−2 G cm3/g (assuming a density of 3 g/cm3), or about 700 times the stable magnetization component of the most magnetic returned samples. Additional medium-amplitude anomalies exist over the Fra Mauro Formation (Imbrium basin ejecta emplaced 3.9 × 109 y ago) where it has not been flooded by mare basalt flows, but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles.
The mean altitude of the far-side anomaly gap is much higher than that of the near-side map and the surface geology is more complex, so individual anomaly sources have not yet been identified. However, it is clear that a concentration of especially strong sources exists in the vicinity of the craters Van de Graaff and Aitken. Numerical modeling of the associated fields reveals that the source locations do not correspond with the larger primary impact craters of the region and, by analogy with Reiner Gamma, may be less conspicuous secondary crater ejecta deposits. The reason for a special concentration of strong sources in the Van de Graaff-Aitken region is unknown, but may be indirectly related to the existence of strongly modified crustal terrain which also occurs in the same region. The inferred directions of magnetization for the several sources of the largest anomalies are highly inclined with respect to one another, but are generally depleted in the north-south direction. The north-south depletion of magnetization intensity appears to continue across the far-side within the region of coverage.
The mechanism of magnetization and the origin of the magnetizing field remain unresolved, but the uniformity with which the Reiner Gamma deposit is apparently magnetized, and the north-south depletion of magnetization intensity across a substantial portion of the far side, seem to require the existence of an ambient field, perhaps of global or larger extent. The very different inferred directions of magnetization possessed by nearly adjacent sources of the Van de Graaff-Aitken anomalies, and the depletion in their north-south component of magnetization, do not favor an internally generated dipolar field oriented parallel to the present spin axis. A variably oriented interplanetary magnetizing field that was intrinsically strong or locally amplified by unknown surface processes is least inconsistent with the data. 相似文献
17.
基于全球EGM2008自由空气重力异常模型,本文计算了蒙古及周边地区的布格重力异常和AiryHeiskanen均衡重力异常.在此基础上,本文采用Crust 1.0地壳模型为参考,通过重力正演方法,对蒙古及周边地区不同深度地壳密度结构模型的重力异常进行了计算,并对得到的正演布格重力异常与实际重力异常进行了对比和分析.研究结果表明:蒙古西部杭爱山地区与阿尔泰山地区的构造变形差异性明显,现今均衡重力异常中杭爱山周边没有明显的均衡异常高值区,而阿尔泰山地区西南方向存在均衡重力异常高值分布,分析与新构造运动密切相关;Crust 1.0模型给出的壳幔横向密度不均匀体分布对于计算Moho面起伏引起的重力异常作用明显;Crust 1.0给出的地壳内界面变形可以反映深大活动断裂的深部构造变形.研究结果对于认识蒙古东西部构造特征差异,以及现今西部活动断裂的地球物理场特征具有参考意义,也可以为进一步应用Crust 1.0模型为参考开展三维密度结构反演提供一定帮助. 相似文献
18.
19.
Guoming Gao Lan Shi Guofa Kang Yingyan Wu Chunhua Bai Limin Wen Jing Hou 《Studia Geophysica et Geodaetica》2018,62(3):408-426
In this paper, the CHAMP satellite data from the last decade are used to map the lithospheric magnetic field in continental China at altitudes of 300 and 400 km using the spline function model technique. The results show that our model has higher amplitude than the spherical harmonic magnetic field model MF7. The resulting lithospheric anomaly distribution of continental China agrees with the geotectonic structure and crustal thermal structure. The magnetic anomaly distribution clearly indicates extrusion of the Tibetan Plateau towards the northeast and northwest directions. Northward movement is impeded by the relative rigid Tarim Basin featured with positive magnetic anomalies. The positive magnetic anomalies in Tarim basin extend to the northern Tibetan Plateau, suggesting that the southern part of Tarim Basin underthrusted the northern Tibetan Plateau. 相似文献
20.
Pearlyn C. Manalo Carla B. Dimalanta Noelynna T. Ramos Decibel V. Faustino-Eslava Karlo L. Queaño Graciano P. YumulJr. 《Surveys in Geophysics》2016,37(3):557-578
Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc–continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc–continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust–mantle interface. 相似文献