华南地区岩石圈地壳速度结构数据处理

利用从地球物理综合剖面上取得的P波速度数据,进行数据处理归类,按照VP速度值的大小,结合地质分析,将华南地区岩石圈地壳划分出上、中、下地壳(上地壳P波速度<6.2 km/s,中地壳P波速度6.2～6.7 km/s,下地壳P波速度>6.7 km/s).计算出地壳各层的平均速度和厚度值,以及整个地壳的平均速度和厚度值,为进一步研究地球内部结构特征及其动力学过程提供重要的依据.     

青藏高原东北缘六盘山—鄂尔多斯盆地的地壳 速度结构特征

青藏高原东北缘六盘山—鄂尔多斯盆地深地震测深剖面沿近东—西向布设长约420km,跨越鄂尔多斯盆地、六盘山和秦祁地块。本文根据沿测线爆破地震的6炮记录截面图中,6个震相的到时资料,结合地震记录中的振幅信息,确定了沿剖面的二维纵波地壳速度结构。鄂尔多斯盆地的地壳平均速度为6.38~6.40km/s,地壳厚度为41.7~48.2km。六盘山地区的地壳平均速度最高为6.40~6.42km/s,地壳厚度最大为53~54km。六盘山以西秦祁地块的地壳平均速度最低为6.32~6.40km/s,地壳厚度为50.3~53km。整个莫霍面形态东浅西深,明显向西倾斜。鄂尔多斯盆地东侧的莫霍面深度最浅为41.7km,六盘山下方莫霍面的深度最深为54km。莫霍面首波Pn在220km之后出现,速度为7.8~8.1km/s。最后讨论了本区的深部特征和盆山结构关系。     

地幔岩简介

地球为一不均匀的球体,具有层圈构造,层与层之间的界线各地区不完全一致,因而不同的学者所提出的模式也不尽相同,大体可采用下列剖面: 地壳厚度在各地变化较大,我国地壳的厚度据1965年发表的资料为; 海洋地壳的厚度较小,太平洋与印度洋地壳平均厚度为13KM,大西洋的地壳厚度在10—14KM。在地壳莫氏面以下分布有厚度为2800KM的地幔层(Mantle),它组成了地球全部质量的67.2％,而地壳、水圈、大气圈只占地球重量的0.5％。近廿多年来人们对地球的研     

中国大陆主要成矿域地壳速度结构与成矿作用

文章汇集了中国11条地球科学断面和数十条人工地震剖面，对中国大陆的地壳结构进行了综合研究。获得了主要成矿域的地壳分层结构模型。根据各层的厚度和地震波速度差异，揭示出主要成矿域地壳速度结构的横向变化，勾绘出壳内低速层的分布特征。文中还探讨了中国大陆主要成矿域岩石圈的现今活动性，以及地壳厚度、壳内低速层、“墙式”地震剪切波垂向低速带和下地壳底部高速层(体)的分布特征以及与成矿作用的关系。     

关于岩石圈有效弹性厚度的地质理解

简要回顾了岩石圈均衡理论的发展及岩石圈区域均衡和挠曲理论在岩石圈动力学研究中起的作用,阐述岩石圈有效弹性厚度(Te)的概念和特征。强调Te的研究是地质学和地球物理学的紧密结合,即通过岩石圈挠曲理论和区域均衡原理,对地形和重力资料进行谱分析计算,来获取岩石圈的物理性质信息。计算的Te(和相应的挠曲刚度)是岩石圈等效的强度,与爆破地震、地震层析成像和大地电磁测深等方法观测到的岩石圈和地壳厚度不同,它们之间只有通过岩石圈的屈服刚度包络面(YSE)才能比较。大洋和大陆岩石圈YSE的理论计算,表明Te值显著小于地震学的地壳和岩石圈厚度。尤其对于大陆岩石圈,地壳厚度、热年龄和应变率均可显著影响岩石圈的强度。本文还以滇西为实例介绍了对相干值曲线计算的新认识和当前岩石圈Te研究的最新趋势。     

西藏高原亚东至当雄地带二维地壳结构的研究

本文采用中国科学院地球物理研究所1977年在西藏高原取得的人工地震资料，并根据国家自然科学基金项目、地质矿产部重点课题“亚东—格尔木地学断面”的要求，对亚东至当雄地带进行了二维地壳结构的处理和研究。除论文发表的部分结果外，对尚未发表的纳木湖至羊卓雍湖地带的两条相遇地震剖面记录图进行了研究，并采用Pg震相进行了浅层结构的处理。 研究结果给出了亚东至当雄地带的二维地壳结构和速度分布，该地带内地壳厚度为70 km左右，由康马往南地壳厚度逐渐变薄，地壳内存在有两个低速层。地壳浅层结构研究表明：莎马达附近有一条深断裂存在，是南喜马拉雅和北喜马拉雅的分界线，并存在着雅鲁藏布江断裂和当雄断裂，且有向深部延伸的趋势。利用该区纵波研究了Q值，并给出计算结果，综合该地区地壳结构和速度分布，并结合当雄地震区、羊八井地热田进行了研究。     

利用地球物理场特征探讨陕西省深部构造

陕西省,尤其是秦岭地区处于中国南北构造和东西构造的交汇部位,是中国地壳五大块体中的青藏块体、塔里木块体、华南块体和华北块体的分界部位,其地壳结构和地质构造都十分复杂。因此,利用区域地球物理场对陕西省深部构造进行研究十分必要。一、方法上地幔与地壳之间存在着一个物质界面—莫霍洛维奇不连续面,简称莫霍面。它可引起相当可观的重力异常。因此,由区域重力异常,通过反演计算可以获得莫霍面的起伏变化和地壳视厚度值。按王懋基等采用的方法,本文用40×40公里网格计算平均重力异常,用     

地壳厚度对中国金矿床空间分布规律的制约

圈定成矿远景区并进行矿产勘查,是新一轮找矿突破的重要内容。在当前大数据和深部地球的背景下,文章根据金矿床空间分布对所在的地壳厚度和地表高程进行了空间连接和相关统计分析,并初步圈定了金矿床的成矿远景区。研究结果表明,地壳厚度为35 km和高程为200 m左右的区域,是金矿床产出的有利区域,并且金矿床的地壳厚度极值和频率呈现分形关系,为金矿床靶区的预测,提供了基本的非线性深部矿产资源预测数学模型;根据金矿床和地壳厚度、高程等的关系,对金矿床的优势成矿远景区进行了预测。预测结果显示,松嫩盆地周边,济南-郑州-武汉-长沙-南宁沿线及周边,是金矿床产出的有利远景区域。     

中国满洲里-绥芬河地学断面地震学研究

满洲里－绥芬河地学断面域地震学研究表明：沿断面可划分额尔古纳－大兴安岭、松辽盆地－张广才岭和佳木斯－兴凯三个波速块体;纵向上地壳分为三层,地壳厚度２９～３８ｋｍ;Ｐ波平均速度６．２５～６．４０ｋｍ／ｓ;松辽盆地沉积盖层较厚,基底面下方附近低角度断层发育;Ｍｏｈｏ面厚度１．５～５．０ｋｍ,内部结构复杂;上地幔低速层埋深差异较大,松嫩块体埋深最浅;深源地震频度高、强度大、震源深,浅源地震相对较少和较弱,震源多位于地壳中上部;地壳构造应力场主压应力优势方向为北东—南西。     

福建地区地壳上地幔S波速度结构与泊松比

        利用在福建地区布置的 12 个宽频带数字地震流动台站和 8 个固定台站记录的远震 P 波波形数据进行接收函数计算, 运用H-k 搜索叠加方法得到了研究区的平均地壳厚度H 与波速比k（=VP/VS）,并运用接收函数反演方法得到了 0~80 km 范 围内的地壳和上地幔 S 波速度结构。H-k 叠加结果表明,福建地区地壳厚度在 28.4~32.8 km 范围内,从内陆到沿海变薄, 从南到北变厚;沿着 NW-SE 方向,泊松比分布有分带特征,沿海地区泊松比高于内陆地区;同时表明,该地区地壳可分 为上、中、下地壳,地壳结构横向差异较明显,多个台站下方可发现壳内低速层,沿海地区上地幔顶部平均速度相对低, 可能暗示了深部存在热异常区域。     

河南登封-鲁山地区地壳出露剖面岩石高压条件下地震波速特征的实验研究

首次给出了河南登封—鲁山一带地壳出露剖面岩石高压条件下纵波速度V_p值的实验测定结果。样品分别采自古元古代的安沟群及新太古代的登封群和太华群。静态压力自常压至3000MPa变化。结果表明,岩石的纵波速与岩性关系密切。上、中地壳岩石的V_p 随压力的增加变化范围明显大于下地壳岩石,变质等级的增加伴随着V_p的明显增大,经温度影响校正后的V_p值与位于邻近地区的QB-1地震测深剖面的解释结果吻合很好。     

Petrological model of the northern Izu–Bonin–Mariana arc crust: constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan

Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic–gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu–Bonin–Mariana (IBM) arc. The Vp values of the tonalitic–gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3–6.6 km/s for tonalites (56.4–71.1 wt.% SiO₂), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO₂), and 7.1–7.3 km/s for a hornblende gabbro (43.2–47.7 wt.% SiO₂). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1–6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1–7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3–7.7 km/s at 15–22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.     

Upper lithospheric seismic velocity structure across the Pripyat Trough and the Ukrainian Shield along the EUROBRIDGE'97 profile

We present new results on the structure resulting from Palaeoproterozoic terrane accretion and later formation of one of the aulacogens in the East European Platform. Seismic data has been acquired along the 530-km-long, N–S-striking EUROBRIDGE'97 traverse across Sarmatia, a major crustal segment of the East European Craton. The profile extends across the Ukrainian Shield from the Devonian Pripyat Trough, across the Palaeoproterozoic Volyn Block and the Korosten Pluton, into the Archaean Podolian Block. Seismic waves from chemical explosions at 18 shot points at approximately 30-km intervals were recorded in two deployments by 120 mobile three-component seismographs at 3–4 km nominal station spacing. The data has been interpreted by use of two-dimensional tomographic travel time inversion and ray trace modelling. The high data quality allows modelling of the P- and S-wave velocity structure along the profile. There are pronounced differences in seismic velocity structure of the crust and uppermost mantle between the three main tectonic provinces traversed by the profile: (i) the Pripyat Trough is a ca. 4-km-deep sedimentary basin, fully located in the Osnitsk–Mikashevichi Igneous Belt in the northern part of the profile. The velocity structure is typical for a Precambrian craton, but is underlain by a ca. 5-km-thick lowest crustal layer of high velocity. The development of the Pripyat Trough appears to have only affected the upper crust without noticeable thinning of the whole crust; this may be explained by a rheologically strong lithosphere at the time of formation of the trough. (ii) Very high seismic velocity and Vp/Vs ratio characterise the Volyn Block and Korosten Pluton to a depth of 15 km and probably also the lowest crust. The values are consistent with an intrusive body of mafic composition in the upper crust that formed from bimodal melts derived from the mantle and the lower crust. (iii) The Podolian Block is close to a typical cratonic velocity structure, although it is characterised by relatively low seismic velocity and Vp/Vs ratio. A pronounced SW-dipping mantle reflector from Moho to at least 70 km depth may represent the Proterozoic suture between Sarmatia and Volgo–Uralia, the structure from terrane accretion, or a later shear zone in the upper mantle. The sub-Moho P-wave seismic velocity is high everywhere along the profile, with the exception of the area above the dipping reflector. This velocity change further supports a plate tectonic origin of the dipping mantle reflector. The profile demonstrates that structure from Palaeoproterozoic plate tectonic processes are still identifiable in the lithosphere, even where younger metamorphic equilibration of the crust has taken place.     

http://www.sciencedirect.com/science/article/pii/S1674987113001369

The 3-D P- and S-wave velocity models of the upper crust beneath Southwest Iberia are determined by inverting arrival time data from local earthquakes using a seismic tomo~raphy method. We used a total of 3085 P- and 2780 S-wave high quality arrival times from 886 local earthquakes recorded by a per- manent seismic network, which is operated by the Institute of Meteorology （IM）, Lisbon, Portugal. The computed P- and S-wave velocities are used to determine the 3-D distributions of Vp/Vs ratio. The 3-D velocity and Vp/Vs ratio images display clear lateral heterogeneities in the study area. Significant veloc- ity variations up to ~6% are revealed in the upper crust beneath Southwest lberia, At 4 km depth, both P- and S-wave velocity take average to high values relative to the initial velocity model, while at 12 km, low P-wave velocities are clearly visible along the coast and in the southern parts. High S-wave velocities at 12 km depth are imaged in the central parts, and average values along the coast; although some scattered patches of low and high S-wave velocities are also revealed. The Vp/Vs rztio is generally high at depths of 4 and 12 km along the coastal parts with some regions of high Vp/Vs ratio in the north at 4 km depth, and low Vp/Vs ratio in the central southern parts at a depth of 12 km, The imaged low velocity and high Vp/Vs ratios are related to the thick saturated and unconsolidated sediments covering the region; whereas the high velocity regions are generally associated with the Mesozoic basement rocks.     

Lithospheric structure below transantarctic mountain using receiver function analysis of TAMSEIS data

The lithospheric structure of Antarctica has been investigated from P- (PRF) and S- receiver functions (SRF) using the seismological data from Trans-Antarctic Mountain Seismic Experiment (TAMSEIS). For the stations deployed on the thick ice sheet, estimation of crustal parameters from PRF may be erroneous as the Moho conversions may interfere with the reverberations within the thick ice sheet. However, the free surface multiples are well observed in PRF. On the other hand, in SRFs, the primary conversions of interest and multiples are separated by the mother S-phase. Therefore, it is advantageous to interpret PRF and SRF jointly for the regions where we have thick low velocity layer at the top such as ice or sediments. The crustal structure and corresponding parameters have already been estimated by various workers, but here we interpret the PRF and SRF jointly to minimize the ambiguity and map the lithospheric architecture below TAM. Our analysis reveals that the average crustal thickness beneath the east Antarctica craton is ～44 km with Vp/Vs ranging between ～1.7 and 1.9. Below Trans-Antarctic Mountain (TAM), the average crustal thickness is ～36 km with higher Vp/Vs of ～1.8–2.0. The rift and the volcanic affected coastal region show erratic depths and Vp/Vs, primarily due to the absence of either primary conversion or multiples in the receiver functions. A small number of stations far from the volcano show that the crust is thinnest (～26 to 34 km thick) in the coastal part. The contribution of this study is the mapping of the lithospheric configuration, not done so far using SRF. The SRF section along a profile spanning E-, W- Antarctica and TAM reveals that the lithospheric thickness in the coast is ～80 km and below TAM it is ～120 km. In the central thick ice cover region, the lithosphere thickens upto ～150 km towards Vostok highlands. The most intriguing feature in our SRF section is that the crust and lithosphere are shallow below TAM compared to the E- Antarctica. Further, we observe a mid-lithospheric low velocity layer confined mostly below TAM, suggesting that the thermal buoyancy could be the prime cause for the upliftment of TAM.     

Vp/Vs Anisotropy and Implications for Crustal Composition Identification and Earthquake Prediction

The ratio of P- to S-wave velocities (Vp/Vs) is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable constraints on its formation and evolution processes. Furthermore, the spatial and temporal changes in Vp/Vs before and after earthquakes are probably the most promising avenue to understanding the source mechanics and possibly predicting earthquakes. Here we calibrate the variations in Vp/Vs in dry, anisotropic crustal rocks and provide a set of basic information for the interpretation of future seismic data from the Wenchuan earthquake Fault zone Scientific Drilling (WFSD) project and other surveys. Vp/Vs is a constant (φ0) for an isotropic rock. However, most of crustal rocks are anisotropic due to lattice-preferred orientations of anisotropic minerals (e.g., mica, amphibole, plagioclase and pyroxene) and cracks as well as thin compositional layering. The Vp/Vs ratio of an anisotropic rock measured along a selected pair of propagation-vibration directions is an apparent value (φij) that is significantly different from the value for its isotropic counterpart (φ0). The usefulness of apparent Vp/Vs ratios as a diagnostic of crustal composition depends largely on rock seismic anisotropy. A 5% of P- and S-wave velocity anisotropy is sufficient to make it impossible to determine the crustal composition using the conventional criteria (Vp/Vs<1.756 for felsic rocks, 1.756l.944 fluid-tidied porous/fractured or partially molten rocks) if the information about the wave propagation-polarization directions with respect to the tectonic framework is unknown. However, the variations in Vp/Vs measured from borehole seismic experiments can be readily interpreted according to the orientations of the ray path and the polarization of the shear waves with respect to the present-day principal stress directions (I.e., the orientation of cracks) and the frozen fabric (I.e., foliation and lineation).     

Laboratory measurement of P-wave velocity in crustal and upper mantle xenoliths from Ichino-megata, NE Japan: ultrabasic hydrous lower crust beneath the NE Honshu arc

Ultrasonic laboratory measurements of P-wave velocity (Vp) were carried out up to 1.0 GPa in a temperature range of 25–400 °C for crustal and mantle xenoliths of Ichino-megata, northeast Japan. The rocks used in the present study cover a nearly entire range of lithological variation of the Ichino-megata xenoliths and are considered as representative rock samples of the lower crust and upper mantle of the back arc side of the northeast (NE) Honshu arc. The Vp values measured at 25 °C and 1.0 GPa are 6.7–7.2 km/s for the hornblende gabbros (38.6–46.9 wt.% SiO₂), 7.2 km/s for the hornblende-pyroxene gabbro (43.8 wt.% SiO₂), 6.9–7.3 km/s for the amphibolites (36.1–44.3 wt.% SiO₂), 8.0–8.1 km/s for the spinel lherzolites (46.2–47.2 wt.% SiO₂) and 6.30 km/s for the biotite granite (72.1 wt.% SiO₂). Combining the present data with the Vp profile of the NE Honshu arc [Iwasaki, T., Kato, W., Moriya, T., Hasemi, A., Umino, N., Okada, T., Miyashita, K., Mizogami, T., Takeda, T., Sekine, S., Matsushima, T., Tashiro, K., Miyamachi, H. 2001. Extensional structure in northern Honshu Arc as inferred from seismic refraction/wide-angle reflection profiling. Geophys. Res. Lett. 28 (12), 2329–2332], we infer that the 15 km thick lower crust of the NE Honshu arc is composed of amphibolite and/or hornblende (±pyroxene) gabbro with ultrabasic composition. The present study suggests that the Vp range of the lower crustal layer (6.6–7.0 km/s) in the NE Honshu arc, which is significantly lower than that obtained from various seismic measurements (e.g. the northern Izu-Bonin-Mariana arc: 7.1–7.3 km/s), is due to the thick hydrous lower crustal layer where hornblende, plagioclase and magnetite are dominant.     

Experimental study of the seismic properties of the Eastern Alps (Italy) along the Aurina–Tures–Badia Valleys transect

In order to better constrain the interpretation and the nature of the seismic reflectors, experimental measurements at high confining pressure (up to 300 MPa) and room temperature of the compressional wave velocity (Vp) on 10 samples representative of the most common lithologies along the Aurina (Ahrntal), Tures (Tauferer Tal), and Badia (Abtei Tal) Valleys profile (Eastern Alps, Italy) have been performed. For each sample, the speed of ultrasonic waves was measured in three mutually perpendicular directions, parallel and normal to the rock foliation and lineation.The main results are:(a) Good agreement between the calculated vs. measured modal compositions of the considered rocks, indicating that they were presumably equilibrated at the estimated P–T conditions; therefore, the seismic properties are representative of the crustal level indicated by the thermobarometry.(b) Measured and calculated average Vp are in good agreement, and are typical of mid-crustal level (6.0–6.5 km/s). Only the amphibolites show Vp typical of the lower crust (7.2 km/s).(c) The seismic anisotropy of metapelites is very high (12–27%), both with orthorhombic and transverse isotropy symmetry; amphibolites are transversely isotropic with an anisotropy of 8%; orthogneisses and granitoids are isotropic or weakly anisotropic.(d) The contacts between amphibolites and all other rock types may generate good reflections, provided they are not steeply inclined. Although the metamorphic foliation remains steeply inclined, discordant buried sub-horizontal igneous contacts may be detected.     

华南大陆东部壳幔结构的宽频带地震学探测

华南大陆是新元古代以来全球地质演化历史最复杂的地区之一, 也是欧亚板块东南缘地壳生长和大陆增生最活跃, 大规模构造变形、岩浆活动和多金属矿产资源最丰富的地区。揭示该区浅表构造与岩浆活动和成矿作用机制离不开对深部壳幔结构的研究。宽频带地震学是开展深部壳幔结构探测的重要手段, 基于宽频带地震学数据可以刻画地壳-岩石圈-上地幔-地幔过渡带不同深度和尺度的深部结构, 为深入理解研究区的深部构造、动力学过程、岩浆活动与成矿作用提供有效约束。本文较全面地总结了近二十年来在华南大陆东部地区开展的宽频带流动地震探测工作, 并对研究区的地壳厚度、Vp/Vs比值、岩石圈底界(LAB)深度、上地幔速度结构与各向异性等进行了分析与讨论。本文旨在为相关研究人员和团队提供未来在该区新布设地震探测台站时的参考, 也可为后续深入研究该区的深部结构与成矿过程提供一些深部要素约束。     

Poisson's ratio in the oceanic crust — a review

Laboratory samples from the upper oceanic crust (tholeiitic basalt flows) that have not been significantly weathered, hydrothermally altered or fractured have a typical Poisson's ratio of 0.30 ( ) and a compressional velocity of 6.0 km s⁻¹; from the middle crust (dolerite sheeted dykes) a ratio of 0.28 ( ) and a velocity of 6.7 km s⁻¹; from the lower crust (gabbro) a ratio of 0.31 ( ) and a velocity of 7.1 km s⁻¹; and from the uppermost mantle a ratio of 0.24 ( ) and a velocity of 8.4 km s⁻¹. These sample values are representative of the large scale insitu values for the middle and lower crust and for the upper mantle. The upper crust is modified by several processes that decrease the velocity and generally increase Poisson's ratio: (1) the formation of an irregular layer of low temperature weathering generally less than 50 m thick; (2) large scale porosity in the form of drained pillows and lava tubes, of talus and rubble and of large open fractures; (3) where there was a high sedimentation rate over the ridge that formed the crust, hydrothermal alteration and intercalation of basalt and sediments. The Poisson's ratios of both high velocity sediments and of crystalline continental crustal rocks generally are significantly lower than the ratios of oceanic crustal rocks of similar compressional wave velocity. Thus, the use of shear wave velocities should permit the separation of these different formations which frequently cannot be distinguished on the basis of compressional wave seismic refraction data alone.