One-Dimensional Thermal Modeling of the Eastern Pontides Orogenic Belt (NE Turkey)

The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine–Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590?±?60°C at a Moho depth of 35?km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29?km, which may correspond to the crustal magma chambers, is found 5–7?km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7?mW?m^?2. High mantle heat flow density value of 48?mW?m^?2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere.     

Magnetic Signatures and Curie Surface Trend Across an Arc–Continent Collision Zone: An Example from Central Philippines

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.     

New constraints on lithospheric thickness of the Iranian plateau using converted waves

The study of mantle lithosphere plays a key role to reveal predominant tectonic setting process of a region. The current geological and tectonic setting of Iran is due to the ongoing continental–continental collision of the Arabian and Eurasian plates. We applied a combined P and S receiver function analysis to the teleseismic data of nine permanent broadband seismic stations of the International Institute of Earthquake Engineering and Seismology located in different tectonic zones of Iranian plateau. More than 4 years of data were used to estimate the thickness of the crust and mantle lithosphere. According to our results, the crust is 50 km thick beneath the Zagros fold and thrust belt (ZFTB). We found the maximum Moho depth of approximately 70 km under the Sanandaj-Sirjan zone (SSZ) indicating the overthrusting of the crust of Central Iran onto the Zagros crust along the main Zagros thrust (MZT). Below the northeasternmost part of the Urumieh–Dokhtar Magmatic Arc (UDMA) and Central Iran, the Moho becomes shallower and lies at 40 km depth. Towards northeast, beneath the Alborz zone, the crust is 55 km thick. Based on S receiver functions, we provided new insights into the thickness of the Arabian and Eurasian lithospheres. The location of the boundary between these plates was estimated to be beneath the SSZ, which is slightly shifted northeastward relative to the surficial expression of the MZT. Furthermore, the Arabian plate is characterized by the relatively thick lithosphere of about 130 km beneath the ZFTB reaching 150 km beneath the SSZ, where the thickest crust was also observed. This may imply that the shortening across the Zagros is accommodated by lithospheric thickening. In contrast, UDMA and Central Iran are recognized by the thin lithosphere of about 80–85 km. This thin lithosphere may be associated with the asthenospheric upwelling caused by either lithospheric delamination or Neo-Tethys slab detachment beneath the Zagros collision zone.     

中国中南地区综合地质地球物理研究

利用重、磁和天然地震资料对中南地区进行了综合地质地球物理研究.根据研究区的重、磁异常的分布特征,可将其分为4个重力异常区、3个航磁异常区.根据重力资料反演计算得到的研究区的地壳厚度在295～41 km之间,总的趋势为西厚东薄,地壳厚度与地形起伏基本上呈镜像关系.根据磁力资料计算得到的研究区居里界面在12～40 km之间变化.地震层析成像结果表明研究区内的速度分布总体上体现了纵横交错的断块特征.在纵向尺度上,江汉－洞庭盆地以及周缘造山带的上地壳结构变化不大,中地壳和下地壳则普遍受到现今构造活动的改造,以致岩石的结构发生了一定的变化.它们主要表现为低速区域的扩大,尤其是在地壳下部尤为突出,这与断陷盆地的拉张以及造山带岩石层的底侵和拆沉作用密切相关.通过对研究区地球物理场的分析计算,在研究区共提取主要断裂带34条.根据岩石层板块大地构造理论,依据岩石层结构、地壳结构和结晶基底等深部结构的不同,将研究区中板内不同构造单元——块体作为一级构造单元,块体之间的深大断裂带作为块体的边界——块体结合带,据此原则在研究区中划分出两个一级构造单元,五个二级构造单元.     

Combined Gravimetric–Seismic Crustal Model for Antarctica

The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz’s inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48–50 km) and the Kottas Mountains (48–50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34–38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24–28 km), while in West Antarctica the Moho depth minima are along the West Antarctic Rift System under the Bentley depression (20–22 km) and Ross Sea Ice Shelf (16–24 km). The gravimetric result confirmed a maximum extension of the Antarctic continental margins under the Ross Sea Embayment and the Weddell Sea Embayment with an extremely thin continental crust (10–20 km).     

鲁西隆起重磁异常特征及其构造活动性分析

通过对鲁西隆起区重磁资料的分析和反演计算,研究了沂沭断裂带、齐河—广饶断裂带、聊城—兰考断裂带、丰沛断裂带以及地块内部断裂的重磁异常、莫霍面和居里面深度特征,并讨论了鲁西隆起的地质构造特征和构造活动性.结果显示:鲁西隆起基底广泛出露,沉积层主要分布在由断裂下降盘控制的凹陷内,区内断裂深度达20 km以上,其中蒙山断裂深入至上地幔,控制了蒙山金伯利岩型金刚石矿的产出;鲁西隆起区莫霍面深度为30—35 km,整体呈向西开口的箕形,地块中部地壳厚度较厚,除西侧地壳呈阶梯状增厚外隆起地块四周地壳逐渐减薄;居里面深度介于20—33 km之间,中部地区较深,为整体稳定的地块,断裂带分布位置对应于居里面梯度带;地震活动主要集中于断裂带与莫霍面梯度带交会区以及断裂带上的居里面突变区.      

川西高原重磁异常特征与构造背景分析

川西高原位于青藏高原东缘,是我国大陆地壳构造变形及地震活动最强烈的区域.利用最新重力、航磁资料,通过异常分析和反演计算,研究了该区鲜水河断裂、理塘断裂、金沙江断裂的重磁异常特征、莫霍面特征、居里面特征,分析得出了这些断裂的深部地质结构与构造背景.计算表明:川西高原莫霍面东南浅、西北深,地壳厚度在43~63km之间.居里面特征表现为条带状,深度在17~23km之间.其中,鲜水河断裂带对应莫霍面深度梯度带,居里面为高低起伏圈闭.理塘断裂带北段莫霍面局部隆坳相间,南段莫霍面逐渐抬升,居里面呈现由西向东加深的梯度带.金沙江断裂带,居里面形成局部抬升,深部可能存在高温地热异常源.综合分析认为,川西高原地壳结构主要特点为:增厚的下地壳,热-塑性变形的中地壳,脆性变形的上地壳.     

利用接收函数方法研究西秦岭构造带及其邻区地壳结构

根据西秦岭构造带及其周边地区117个宽频带地震台站的高质量波形数据, 利用远震P波接收函数的H-k叠加方法, 求得地壳厚度和平均波速比. 通过分析地壳厚度、 波速比及其关系和接收函数CCP叠加剖面, 研究了该区域的地壳结构特征. 结果表明, 研究区域内地壳结构差异大, 呈过渡带特征. 地壳厚度总体上呈北北西向分布, 自西南向东北逐渐减小. 羌塘块体地壳厚度为72 km, 渭河盆地附近为39 km. 西秦岭构造带的地壳厚度为42—56 km, 南北向莫霍界面平坦. 研究区域P波与S波波速比平均为1.74, 其中西秦岭构造带平均为1.72. 较低的波速比主要分布在西秦岭构造带、 祁连山块体、 松潘—甘孜地块北部以及香山—天景山断裂区域, 这可能是由于含长英质酸性岩组分的上地壳叠置增厚而导致的. 该区域缺少超高波速比, 表明这一区域发生岩浆底侵或上地壳熔融的可能性很小. 综合分析表明, 西秦岭构造带及邻区的地壳结构主要是由于青藏高原隆升并在向东北向扩张中受到周边块体的阻挡而引起的地壳构造变形所致. 西秦岭构造带的莫霍界面变化和波速比分布与该构造带经历碰撞地壳增厚后的伸展走滑运动有关.      

Velocity properties of the lithosphere in the ocean-continent transition zone in the Kamchatka region from seismic tomography data

Arrival times of P and S waves from local earthquakes in the Kamchatka area of the Kurile-Kamchatka Island Arc are used for calculating a spatial model of the elastic wave velocity distribution to a depth of 200 km. The lithosphere is shown to be strongly stratified in its velocity properties and laterally heterogeneous within the mantle wedge and seismic focal zone. A lower velocity layer (an asthenospheric wedge) is identified at depths of 70–130 km beneath the Eastern Kamchatka volcanic belt. The morphology of the Moho interface and the velocity properties of the crust are studied. The main tectonic structures of the region are shown to be closely interrelated with deep velocity heterogeneities. Regular patterns in the statistics of the earthquakes are analyzed in relation to variations in the elastic wave velocities in the focal layer. A mechanism of lithospheric block displacements along weakened zones of the lower crust and upper mantle is proposed.     

长江中下游成矿带及邻区三维Moho面结构:来自人工源宽角地震资料的约束

为深入理解长江中下游地区在中生代成矿的深部动力学过程,对跨越宁芜矿集区地质廊带内的非纵剖面反射/折射地震数据进行动校正和时深转换处理,获得了非纵方向的Moho面深度;联合纵测线和非纵测线上Moho面深度数据,获得了长江中下游成矿带及邻区的三维Moho面深度结构.结果显示宁芜矿集区下方的Moho面整体较浅,约32~34km,华北块体合肥盆地内Moho面整体较深,约34~35km.Moho面深度和区域布格重力异常变化趋势对应良好.宁芜矿集区下方Moho面呈上隆特征,支持长江中下游地区成矿模式中增厚岩石圈发生拆沉、软流圈的上隆及底侵作用等动力学过程.Moho面平行于成矿带走向的变化趋势,预示长江中下游成矿带地壳和上地幔在板块边界发生了NE-SW向的切向流动变形.郯庐断裂带两侧,Moho面深度变化较大,表明地表近陡立的郯庐断裂为深大断裂,深部可能切穿Moho面并延伸至上地幔.     

丽江-攀枝花-者海地带二维地壳结构及其构造意义

本文利用攀西地区通过攀枝花的东西向剖面爆炸地震资料,进行了震相的重新识别和二维射线追踪与理论图计算.结果表明,沿剖面地表附近有4个低速区和若干高速带,它们与地质和构造有很好的对应关系.渡口附近的高速岩体一直延伸到了上地壳的底部,形成一个统一的地垒状构造,该高速体与攀枝花成矿岩体相关,并推断华坪及其以西地带也是找矿的有利地区.中地壳下部有一厚度约9km的低速层,它可能是壳内的韧性剪切带.低速层顶部深度为27.0-29.5km,与研究地区的居里面深度及天然地震震源深度的分布基本符合.剖面东段中地壳顶部还有一层很薄的低速层,反映了构造带两侧运动的不对称性.地壳厚度为53-56km,构造带中部的Moho界面没有明显的上隆.     

四川地区的地震层析成像

由四川地震台网的P波数据所进行的层析成像研究得到了该区地壳及上地幔速度图像的新信息(结果表明:1.20^-km深度处的速度图像与地表构造特征密切有关,反映了地壳的岩性分布,呈现为断块结构;龙门山、鲜水河主要断裂及南北构造带和四川盆地清晰地成像在图上.一直被认为是隐伏存在的华蓥山断裂则鲜明地展现在20-85km深度的速度图像上.2.50±km深度处的速度图像则反映了该区的莫霍面深度明显起伏;四川盆地、徽（县）成（县）盆地和汉中盆地的地壳厚度小于50km,上地幔顶部速度约8.1km/s.龙门山以104°E为界,北段地壳厚度与四川盆地一样,中南段与川西相近.康滇地轴为四川地区地壳由东向西增厚的过渡地带.3.岩石层厚度显著变化,扬子准地台为比较活动的褶皱区,具有较厚的岩石层.4.速度结构与地震活动性存在一定的联系,该区1930年以来M≥6.0的强震震中在20^-km深度（上地壳）上的投影大都分布在速度梯度带上,成条带分布.考虑到强震的余震区大都偏高速体一侧,似乎表明,高速体有高于周围介质的剪切强度,它可能起沿断裂带凹凸体的作用.强震震中在50⁺km深度（上地幔顶部）上的投影几乎都分布在低速区及其边缘,那里壳幔间速度呈过渡关系,是软流层顶部较浅地区.     

远震P波接收函数揭示的张家口(怀来)—中蒙边境(巴音温多尔)剖面地壳厚度与泊松比

本文使用时间域迭代反褶积算法,从张家口(怀来)—巴音温多尔一线布设的41个宽频地震台站、1年期间记录的连续三分量数据中提取到高质量的P波接收函数1844个.用H-κ扫描方法获得了测线下方Moho深度与波速比值(VP/VS)进而计算出泊松比,用共转换点(CCP)叠加方法获得了沿测线Moho面起伏图像.结果显示:(1)测线下方Moho深度平均40km,仅各块体边界处出现Moho深度小尺度急剧变化.整体上,Moho面产状相对于索伦缝合带大致对称,在缝合带南侧的温都尔庙带和白乃庙带下方呈南倾趋势,在缝合带北侧的宝力道带、贺根山杂岩带下方呈北倾趋势.(2)华北克拉通北缘泊松比总体较高,兴蒙造山带整体较低;各次级块体内部泊松比分布相对稳定,块体分界带附近往往存在泊松比值的升降扰动.(3)整条测线地壳厚度和泊松比之间存在弱的负相关关系,表明存在构造作用的影响.(4)整条测线泊松比呈现以索伦缝合带南缘为对称轴的非线性分布.本文所获得的地壳上地幔结构以及泊松比分布特征,支持古亚洲(索伦)洋(南北)双向俯冲,最终沿林西断裂闭合的动力学模式.     

Study of crustal structure and geological implications of southwestern margin of Northeast India

It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average V_P/V_S ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38–45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of V_P/V_S ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson’s ratio (1.69–1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of V_P/V_S ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins.     

Mapping of magnetic basement in Central India from aeromagnetic data for scaling geology

The Central Indian region has a complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graben and some part of the Deccan Trap, the northern Singhbhum Orogen and the eastern Dharwar Craton. The region is well covered by reconnaissance‐scale aeromagnetic data, analysed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km, whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas the deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belt near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units, whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity, and intrusive bodies at different depths, which can be attributed to different thermo‐tectonic processes since Precambrian.     

3D Crustal and Lithospheric Structures in the Southeastern Mediterranean and Northeastern Egypt

Crustal and lithospheric thicknesses of the southeastern Mediterranean Basin region were determined using 3D Bouguer and elevation data analysis. The model is based on the assumption of local isostatic equilibrium. The calculated regional and residual Bouguer anomaly maps were employed for highlighting both deep and shallow structures. Generally, the regional field in the area under study is considered to be mainly influenced by the density contrast between the crust and upper mantle. Use of the gravity and topographic data with earthquake focal depths has improved both the geometry and the density distribution in the 3-D calculated profiles. The oceanic-continental boundary, the basement relief, Moho depth and lithosphere-asthenosphere boundary maps were estimated. The results point to the occurrence of thick continental crust areas with a thickness of approximately 32 km in northern Egypt. Below the coastal regions, the thickness of crust decreases abruptly (transition zone). An inverse correlation between sediment and crustal thicknesses shows up from the study. Furthermore, our density model reveals the existence of a continental crustal zone below the Eratosthenes Seamount block. Nevertheless, the crustal type beneath the Levantine basin is typically oceanic; this is covered by sedimentary sequences more than 14 km thick. The modeled Moho map shows a depth of 28–30 km below Cyprus and a depth of 26–28 km beneath the south Florence Rise in the northern west. However, the Moho lies at a constant shallow depth of 22–24 km below the Levantine Basin, which indicates thinning of the crust beneath this region. The Moho map reveals also a maximum depth of about 33–35 km beneath both the northern Egypt and northern Sinai, both of which are of the continental crust. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thinning beneath south Cyprus (LAB ~90 km depth), followed by thickening beneath the Eratosthenes seamount, Florence Rise, Levantine Basin and reaching to maximum thickness below Cyprian Arc (LAB ~115–120 km depth), and further followed by thinning in the north African margin plate and north Sinai subplate (LAB ~90–95 km depth). According to our density model profiles, we find that almost all earthquakes in the study area occurred along the western and central segments of the Cyprian arc while they almost disappear along the eastern segment. The active subduction zone in the Cyprian Arc is associated with large negative anomalies due to its low velocity upper mantle zone, which might be an indication of a serpentinized mantle. This means that collision between Cyprus and the Eratosthenes Seamount block is marked by seismic activity. Additionally, this block is in the process of dynamically subsiding, breaking-up and being underthrusted beneath Cyprus to the north and thrusted onto the Levantine Basin to the south.     

大兴安岭造山带及两侧邻区莫霍面深度与泊松比分布特征

利用2009～2016年内蒙古自治区数字地震台网宽频带固定地震台站的远震波形数据,采用接收函数H-k算法获得23个基岩台站下方的莫霍面深度和泊松比,同时,收集并筛选出277个已有探测台阵和流动台站的接收函数研究结果,综合分析给出大兴安岭造山带及两侧邻区莫霍面深度、泊松比的分布特征。研究表明,研究区域的莫霍面在整体上呈现自东向西逐渐加深的特征,莫霍面深度为25.0～42.3km,平均约为33.5km。莫霍面最浅的区域为松辽盆地(深度为27.0～35.0km),最深的区域为大兴安岭重力梯级带以西地区(深度为41.0～42.3km)。研究区域泊松比为0.19～0.33,平均值为0.26,大于全球大陆地壳的平均值。泊松比高值异常区集中在火山岩区及具有较厚沉积层的盆地。台站所处位置的海拔与莫霍面深度之间具有较强的正相关性,艾里补偿模式在研究区成立,莫霍面起伏与区域地形地貌特征间具有显著的镜像关系。大兴安岭地区的莫霍面深度与泊松比间存在显著的反相关关系,而在松辽盆地及周缘地区未发现明显的规律性,这也意味着松辽盆地在构造演化过程中经历了更为复杂的地壳改造过程。     

大别造山带地壳结构反演及其动力学意义

大别造山带是全球最大的碰撞造山带之一,三叠纪时期,扬子板块深俯冲至地幔的200km处,经历了超高压变质作用。白垩纪早期,该造山带发生了强烈的伸展和垮塌,以及大规模的后造山地幔源岩浆侵入和火山活动。本研究收集了大别造山带及其邻区(29°~34°N、114°~119°E)的震相资料,采用双差层析成像技术,对大别造山带地壳结构进行反演,研究地壳结构与后造山地幔源岩浆侵入和火山活动之间的关系。结果显示,大别造山带中上地壳存在低速结构,该低速结构可能是熔融的幔源侵入物质,由于俯冲板片断裂,或下地壳/岩石圈发生拆沉,导致软流圈物质上涌至地壳底部、侵入地壳中,形成大别造山带地壳中的低速结构;同时,合肥盆地显示为低速区,可能是受浅部沉积层影响。研究中横切大别山的4条剖面显示,该地区下方存在北向倾斜高速结构,该高速结构可能是襄樊-广济断层,或者是扬子板块向华北板块下方俯冲的遗迹。     

滇西三江构造带电性结构特征——以福贡—巧家剖面为例

为查明滇西三江构造带及邻区复杂的构造特征,并揭示该区深部电性结构,沿福贡—巧家布设了一条长约410 km的大地电磁剖面.共观测到61个物理点,其中宽频大地电磁测点41个,长周期大地电磁测点20个.通过对采集到的数据进行一系列的处理、反演,得到了沿剖面的壳幔电性结构模型.并结合研究区内区域地质资料及其他地球物理资料,对剖面所经过的各个主要地质构造单元及主要断裂带进行了综合解释.电性结构模型揭示沿剖面地壳电性层次复杂,深部电性结构由西往东呈分块展布,横向变化大,壳内广泛发育低阻异常.在中甸构造带(香格里拉地块)和盐源—永胜构造带深部壳幔存在大规模低阻异常,这可能与地下局部熔融体和地热流有关;康滇构造带壳幔存在大规模高阻异常,表明地壳中曾经有地幔物质侵入;在大凉山构造带地下10~50 km深处存在一呈横向“半月形”展布的低阻体,电阻率值不满10Ωm,结合地质资料与前人的研究成果,推测该低阻体成因应与青藏高原东南缘“地壳管道流”有一定关联.     

中国海陆莫霍面及深部地壳结构特征——以阿尔泰—巴士海峡剖面为例

中国海陆莫霍面及深部地壳结构特征研究是东亚地区宏观构造格架研究中的重点内容之一.本文以地震测深等数据为约束信息,以重力数据为基础,通过分区计算,反演了中国海陆莫霍面深度.依据地壳性质与莫霍面深度分布特征,划分了莫霍面深度梯级带与分区,并对各分区的莫霍面分布特点进行了归纳、总结.并选取阿尔泰—巴士海峡典型剖面进行了重、震反演,建立了密度结构.剖面上莫霍面深度和深部结构能够清晰地反映中国大陆"三横、两竖、两三角"构造格架中的两横和两竖,在昆仑—秦岭—大别以北的准噶尔地块和中朝地台莫霍面深度45~50 km,而其以南至贺兰山—龙门山之间的祁连、柴达木至松潘—甘孜的莫霍面呈"W"型起伏,莫霍面深度由祁连地块北部的50 km,加深至68 km,在柴达木盆地抬升至58 km,在阿尼玛卿山莫霍面降至68 km,向南逐渐抬升至四川盆地的44 km,经大兴安岭—太行山—武陵山这一竖的台阶式抬升至华南褶皱带的35 km,在江绍—南岭以南缓慢抬升至南海北部陆架区的20~25 km.在巴士海峡处南海沿马尼拉海沟向东俯冲,莫霍面形态较复杂.同时剖面上祁连—柴达木地块的中下地壳存在一个低速、低密度体,推测其可能是由于部分熔融引起的,是青藏高原东北缘壳内物质流动的通道.