重磁异常解释断裂构造的处理方法及图示技术

利用重磁异常解释断裂是地质构造研究的主要手段之一.重磁异常解释断裂通常是在等值线图或剖面平面图上进行的,而重磁异常在进行等值线网格化成图时会造成微弱信息丢失,这些原因造成重磁异常解释断裂的多解性.本文对重磁异常数据在化极、曲面延拓处理的基础上,采用水平梯度法提取延拓曲面上的重磁异常梯度带,之后对断裂带进行窄化处理,通过图示技术将重磁异常数据转换成灰度值,图像的灰度值以变密度显示,形成彩色的变密度图像,这样就提高了数据图像识别断裂的视觉效果.该方法应用在鄂尔多斯盆地不同层次(时间序列)的断裂研究中,提取和识别重磁异常特征所反映的断裂信息,效果较好.     

基于二阶导数的磁源边界与顶部深度快速反演

为实现磁异常反演,首先提出了磁异常非参数快速反演的概念,即无需提供先验信息.在Nabighian提出的磁场通用梯度公式的基础上,推导实现了基于磁异常垂向二阶导数的非参数快速反演(V2D_depth).它不仅可以获取场源的边界信息,同时可以反演场源的埋深.通过与Tilt_depth方法对比,本文方法计算的场源边界更清晰,反演的深度也更接近真实深度,同时较大程度上克服了Tilt_depth方法受叠加异常的影响.理论模型验证了方法的有效性,并通过准噶尔盆地某区块磁异常数据的处理,提取了受强大的区域背景场掩盖的石炭系火成岩产生的弱异常,突出了构造分区、断裂分布等信息,获取了火成岩的位置及埋深参数,为该区的火成岩油气藏勘探提供了有效的处理途径.     

低纬度磁异常化极的伪倾角方法改进

基于改造化极因子的低磁纬度频率域化极方法具有计算速度快、控制参数少、操作简单、化极稳定等优点.本文分析压制因子法和伪倾角法的化极因子特征及其控制参数的影响,在此基础上改进伪倾角法的化极因子,即在磁偏角垂直方向及附近采用伪倾角法化极因子,而在其他方向采用常规频率域化极因子.改进后的伪倾角法既能有效压制磁偏角垂直方向及附近化极因子的放大作用,使得化极稳定,又能减少其他方向有效信号的化极特征的损失,提高化极精度.理论模型数据试验表明本文改进方法有效.利用本文改进方法对南海海域磁总场异常数据进行了变磁倾角化极,得到南海海域化极磁异常,这为研究南海大地构造特征和岩浆活动提供重要的参考资料.     

基于卫星重磁资料的南海深部构造研究

南海深部构造对研究南海构造演化和油气勘探具有重要意义.本文对南海地区的自由空气重力异常进行布格校正、海水层校正和沉积层校正,得到布格重力异常,再对布格重力异常进行区域异常和局部异常分离,利用位场界面反演方法对区域布格异常进行反演计算得到研究区域的莫霍面深度分布;采用全变倾角化极方法对研究区域的卫星磁异常数据进行化极处理,并进一步对化极磁异常作向上延拓,得到延拓后化极磁异常结果.分析布格重力异常、莫霍面深度及化极磁异常特征,结合天然地震层析成像的证据,得到以下结论：推测南海北部陆缘的古俯冲带位置是从118.5°E,24°N沿北东向延伸至109°E,15°N;红河断裂入海后经过莺歌海盆地在海南岛南部转为南北向与越东断裂相接并延伸至万安盆地;推测中特提斯洋的部分闭合位置是从110°E,2°N到101°E,21°N.     

婆罗洲北部岩石密度和磁化率特征及其对南海南部前新生界岩性识别的约束

基于540块样品的体积磁化率-比重测量和矿物-岩性鉴定结果,分析了婆罗洲北部岩石类型、密度、磁化率特征,据此明确重磁资料对于南海南部中生界岩性识别的适用性.结果表明婆罗洲北部发育3类25种岩石,以发育中基性火成岩和外碎屑沉积岩为主,发育少量内源沉积岩、酸性火成岩和变质岩.具有极强磁性-强磁性,高密度-中等密度特征的岩石多为火成岩和凝灰质砂岩及其变质岩.弱磁性-无磁性、中等-极低密度特征的岩石多为砾岩、砂岩、粉砂岩、泥岩和煤等.弱-逆磁性、高-中等密度的岩石多为灰岩和硅质岩.新生界岩石具有密度较低、磁化率中等的特征.中生界岩石具有密度中等、磁化率中高的特征.前中生界岩石具有密度高、磁性低的特征.结合分布特征可知,前中生界岩石产生局部弱重力异常,中生界沉积岩产生区域性的负重力异常,火成岩产生区域性的正重力异常.南海南部的区域性高磁力异常来源于中生代的基性火成岩(及其变质岩),区域性中等磁力异常可能来源于酸性火成岩(及其变质岩).据此进行了南海南部中生界岩性的识别,结果表明南海南部存在大面积的中生界沉积岩分布区,认为南海南部中生界地层具有油气勘探潜力.     

南海大陆边缘构造活动与重磁场特征研究

南海是研究大陆边缘类型、大陆边缘成因机制的理想场所.本文对南海重力和磁力数据及其向上延拓处理结果所反映的地球物理场特征进行了分析.在综合前人关于南海地质、地球物理研究工作的基础上,论述了南海大陆边缘构造特征与重磁场特征、基底断裂体系及火成岩分布与性质.南海周边的大陆边缘类型各不相同,重磁场特征、基底断裂和火成岩分布直接...     

斜磁化磁异常处理方法分析

受斜磁化的影响,磁异常特征复杂、不便于解释.强剩磁的存在、低纬度化极的困难等问题常常迫使人们直接针对斜磁化磁异常开展处理与反演.为了减小斜磁化的影响,磁异常总梯度模、分量模、磁异常梯度张量等处理方法得到广泛应用.本文基于理论分析,结合模型实验,分析现有斜磁化磁异常处理方法的优缺点,指出磁异常总梯度模、分量模、磁异常梯度张量等处理方法可能引起错误的地质解释,而采用适当的化极计算则可以明显改善解释效果.     

南海共轭大陆边缘构造属性的综合地球物理研究

利用南海最新的重磁资料,在岩石物性分析和全海域分带变倾角化极磁异常反演磁性基底分布的基础上,选择6条典型剖面拟合反演其密度与磁性结构,在此基础上进行了深部结构的对比分析.反演中尽可能以海底地震仪探测数据(OBS)、多道地震等结果作为约束,其中FF'剖面层速度分析是利用“南海大陆边缘动力学及油气资源潜力”973项目200...     

低纬度磁异常化极方法——压制因子法

磁异常化极转换是磁异常解释的重要基础，针对频率域磁异常化极现状，本文对低纬度化极的困难原因进行了深入分析，并提出了针对性的化极措施——压制因子法. 与已有研究比较，该方法具有简单直观、控制参数少因而便于实际操作的特点，模型计算表明了方法的有效性. 在我国南海低磁纬度地区实测磁异常的计算解释中，应用该化极方法，取得了良好的效果.     

位场方法在非常规油气勘探中的应用

在常规油气勘探领域,高精度的重磁资料能够非常好的完成油气资源的远景评价,为地震勘探和钻井提供指导.在非常规油气勘探领域,重磁勘探方法显得尤为重要.因为非常规油气资源的地质结构、圈闭条件、储层评价、成藏机理、渗流特征等方面更加复杂和未知,地震勘探和钻井难以直接开展,亟需非地震方法的优选规划.由于重磁位场方法并不能"特异性"的揭示地下页岩分布和页岩气的资源潜力,从某种程度上说,重磁位场方法在常规油气和非常规油气的勘探技术是没有多大区分的,核心都是"综合"二字.其中,对重磁资料的处理要经过常规的延拓、剩余重力异常提取和磁异常化极等,以及重力异常剥皮、park反演、梯度反演等关键处理,能够获取特定地层的厚度与埋深和断裂信息.本文以页岩气资源的重磁位场勘探技术为中心,通过调研国内外重磁方法在非常规油气勘探阶段的应用实例,总结规律,构建利用位场方法开展页岩气等资源勘探的技术体系与流程.     

南海北部盆地基底岩性地震-重磁响应特征与识别

针对性选取东南沿海露头剖面18条,采集245件南海盆地基底可能出现的岩性样品,测定其密度和磁化率,建立各种岩性的密度-磁化率交会图版,以此约束过井地震剖面和重磁异常的地质解释,总结出南海北部盆地基底火山岩、侵入岩、变质岩和沉积岩4大类11亚类岩性的地震-重磁响应特征.应用重磁震-岩性解释模型逐一对南海盆地北部主干剖面进行地质-地球物理综合解释,从而实现了盆地基底岩性的平面填图.这种从盆缘剖面到盆地内部、从岩石物性测量到地质-地球物理综合解释的方法,在资料获取难度大、地质条件复杂的南海盆地基底地质研究中,业已证明是行之有效的,相信在其他盆地研究中也会有借鉴意义.     

南海前新生代残留盆地分布综合地球物理研究

为了对南海海域的前新生代残留盆地分布有个整体而全面的认识,本文开展了南海残留盆地宏观分布的综合地球物理研究.通过岩石物性分析,综合重、磁、震等地球物理方法,利用正演与反演方法,分区计算并求取了南海的重力基底和磁性基底埋深,得到了中生界及前中生界残余厚度,给出了整个南海前新生代残留盆地的宏观格架与残余厚度分布特征并讨论了...     

核磁共振测井在火成岩地层应用的适应性分析

火成岩岩石具有高磁化率特征,与沉积岩差别明显,岩石的高磁化率会对核磁共振信号产生显著影响,开展核磁共振测井在火成岩地层应用的适应性分析研究,为广泛使用核磁共振测井用于火成岩储层评价提供参考.采用理论模拟、实验分析及实际测井资料相结合的方法,分析了高磁化率岩石的核磁共振响应特征.分析结果表明,火成岩岩石具有很高的磁化率,从酸性火成岩到基性火城岩,岩石的磁化率一般是逐渐增大的.高磁化率岩石孔隙内部会产生强梯度磁场,孔隙内部的磁场梯度越强,核磁共振的T2谱前移越明显,核磁信号衰减幅度也越大,核磁分析孔隙度与常规分析的孔隙度误差也越大;相同岩石磁化率情况下,岩石孔径越小,岩石孔隙内部磁场梯度越强,核磁信号衰减越大,核磁共振测井计算的孔隙度也越低.因此,核磁共振测井与岩性有关系,核磁共振测井会受到高磁化率岩石的显著影响.核磁共振测井在部分火成岩,尤其在中基性火成岩和小孔径火成岩储层中应用具有很大的局限性.     

南海磁场特征研究

建立客观的磁力ΔT异常,获得可信的磁力ΔZ_⊥异常、居里面成果, 在此基础上开展综合地质地球物理研究,对于解决南海资源等相关的地质、地球物理问题意义重大.本文汇集我国历年在南海取得的磁力实测资料,重新处理、校正、整合,特别是追溯南海周边的国际地磁台的日变资料进行日变改正,形成的南海磁力ΔT异常,其资料品质得到了极大提高.采用全磁纬变倾角化极技术,获得磁力ΔZ_⊥异常,其与实测证实的磁性海山、海岛有非常好的匹配关系,建立起可以直接用于反演处理解释的南海磁力ΔZ_⊥异常.选择磁力ΔZ_⊥异常的小波多尺度分解四阶逼近,采用单一磁性界面反演技术进行深度反演,获得居里面又称磁性底界面.建立了认识、解释南海的磁场基础体系,证实了南海基性岩浆岩分布区与磁力ΔZ_⊥异常的正磁异常高密切相关,区域性的磁力ΔZ_⊥异常负磁异常区可能与居里面深度相关.     

Geochronological and petrological investigations of Miocene felsic igneous rocks in the Amakusa Islands,southwest Japan: Possible extension of the Setouchi Volcanic Belt

The opening of the Japan Sea led to the separation of southwest Japan from the Eurasian continent. Subsequent to this event, a diverse range of igneous activities occurred in southwest Japan. On the back-arc side of the region, igneous activity commenced at approximately 22 Ma and persisted for an extended period. In the trench-proximal region of southwest Japan, magmatism initiated around 15.6 Ma, immediately following the cessation of the Japan Sea opening, in correlation with the subduction of the Philippine Sea plate beneath southwest Japan. The Amakusa Islands in western Kyushu host felsic to intermediate igneous rocks with Miocene radiometric ages. There has been a debate regarding the attribution of the igneous rocks in Amakusa Island among the Miocene igneous rocks in southwest Japan. To address this issue, we conducted zircon U–Pb dating and analyzed the major- and trace-element compositions of felsic igneous rocks in the Amakusa Islands to elucidate their characteristics. The obtained U–Pb ages range from 14.5 to 14.8 Ma, suggesting contemporaneity between magmatism in the Amakusa Islands and the Setouchi Volcanic Rocks in the trench-proximal region of southwest Japan. The major and trace element compositions of the felsic igneous rocks exhibit similarities to the dacites of the Setouchi Volcanic Rocks. These findings support previous suggestions that the magmatism in the Amakusa Islands can be correlated with the Setouchi Volcanic Rocks, based on the discovery of a high-Mg andesite dike and paleo-stress analysis utilizing the direction of dikes and sills. Therefore, the Setouchi Volcanic Belt is proposed to extend further west than the previously identified Ohno volcanic rocks in eastern Kyushu. The subduction of the Shikoku Basin of the Philippine Sea plate toward western Kyushu supports the hypothesis that the Kyushu-Palau Ridge was positioned west of Kyushu at ~15 Ma.     

Major element, trace element, and Sr, Nd and Pb isotope studies of Cenozoic basalts from the South China Sea

The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh ba-saltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cu-mulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.     

南海地球物理场特征及基底断裂体系研究

南海海域主体可划分为南海北缘、中西沙、南沙南海海盆四块，各块具有明显不同的重磁场特征。反演得到的莫霍面总体趋势由陆向洋抬升，反映陆壳、拉伸陆壳、过渡壳、洋壳的分布。东沙高磁异常含一定的高频成份，与新生代玄武岩及中生代岩浆岩有关，而其低频成份可能反映了发育的下地壳高速层，南海海域断裂极为发育，可分为北东向断裂组、东西向断裂组、北西向断裂组和南北向断裂组，南海北缘、南缘均以北东向张性断裂与北西向张剪性、剪性断裂为主要格架，形成了、南北分带、东西分块”构造格局。     

岩浆岩磁组构的实验模拟研究

岩浆岩的模拟实验,由于其实验条件的可控性,能够较好地研究岩浆岩的影响因素及其机理．本文实验表明,岩浆岩的磁组构除与成岩时的流动有关外,还受地磁场及重力场的影响,当流动较强时,岩浆岩的磁线理与流动方向有很好的一致性;当流动较弱时,地磁场方向的影响更大．另外,由于岩浆岩较弱的磁各向异性,以及成岩后期各种因素的影响,使其机理呈现复杂性,主轴方位具有分散性．     

The inversion of density structure by graphic processing unit (GPU) and identification of igneous rocks in Xisha area

Organic reefs, the targets of deep-water petroleum exploration, developed widely in Xisha area. However, there are concealed igneous rocks undersea, to which organic rocks have nearly equal wave impedance. So the igneous rocks have become interference for future exploration by having similar seismic reflection characteristics. Yet, the density and magnetism of organic reefs are very different from igneous rocks. It has obvious advantages to identify organic reefs and igneous rocks by gravity and magnetic data. At first, frequency decomposition was applied to the free-air gravity anomaly in Xisha area to obtain the 2D subdivision of the gravity anomaly and magnetic anomaly in the vertical direction. Thus, the distribution of igneous rocks in the horizontal direction can be acquired according to high-frequency field, low-frequency field, and its physical properties. Then, 3D forward modeling of gravitational field was carried out to establish the density model of this area by reference to physical properties of rocks based on former researches. Furthermore, 3D inversion of gravity anomaly by genetic algorithm method of the graphic processing unit (GPU) parallel processing in Xisha target area was applied, and 3D density structure of this area was obtained. By this way, we can confine the igneous rocks to the certain depth according to the density of the igneous rocks. The frequency decomposition and 3D inversion of gravity anomaly by genetic algorithm method of the GPU parallel processing proved to be a useful method for recognizing igneous rocks to its 3D geological position. So organic reefs and igneous rocks can be identified, which provide a prescient information for further exploration.     

The inversion of density structure by graphic processing unit （GPU） and identification of igneous rocks in Xisha area

Organic reefs, the targets of deep-water petroleum exploration, developed widely in Xisha area. However, there are concealed igneous rocks undersea, to which organic rocks have nearly equal wave impedance. So the igneous rocks have become interference for future exploration by having similar seismic reflection characteristics. Yet, the density and magnetism of organic reefs are very different from igneous rocks. It has obvious advantages to identify organic reefs and igneous rocks by gravity and magnetic data. At first, frequency decomposition was applied to the free-air gravity anomaly in Xisha area to obtain the 2D subdivision of the gravity anomaly and magnetic anomaly in the vertical direction. Thus, the distribution of igneous rocks in the horizontal direction can be acquired according to high-frequency field, low-frequency field, and its physical properties. Then, 3D forward modeling of gravitational field was carried out to establish the density model of this area by reference to physical properties of rocks based on former researches. Furthermore, 3D inversion of gravity anomaly by genetic algorithm method of the graphic processing unit(GPU) parallel processing in Xisha target area was applied, and 3D density structure of this area was obtained. By this way, we can confine the igneous rocks to the certain depth according to the density of the igneous rocks. The frequency decomposition and 3D inversion of gravity anomaly by genetic algorithm method of the GPU parallel processing proved to be a useful method for recognizing igneous rocks to its 3D geological position. So organic reefs and igneous rocks can be identified, which provide a prescient information for further exploration.