Tectonic framework of Tiburon Basin,Gulf of California,from seismic reflection evidence

Tiburon Basin is characterized by a thick sedimentary fill that records the evolution of one of the rift segments of the East Pacific Rise. Its structure corresponds to an echelon pull-apart basin bounded by two dextral-oblique faults. Unlike basins in the southern Gulf of California that are underlain by oceanic crust, rift basins in the northern Gulf of California contain sedimentary thickness (up to 6 km) that masks the structure of the crust. To study the architecture of the Tiburon Basin, two-dimensional, multichannel seismic reflection data collected by Petróleos Mexicanos (PEMEX) in the early 1980s were used. The data base is a grid of lines, 5–20 km apart, with 6 s of record in 48 channels. Additional seismic data of the Ulloa 99 project were also interpreted. Our results indicate that the general structural pattern of the Tiburon Basin is controlled by two dextral-oblique faults: De Mar and Tiburon. De Mar lies to the east and ends in elevated basement transferring the stress to the Desemboque fault. The latter borders the incoming basement from the Sonora and Tiburon faults to the west, ending to the north in an antiform. Four structural domains are recognized: (1) the northern Tiburon domain is a high basement that divides the Delfin Basin to the northeast and exhibits extensional folds with their axes parallel to the basement and its flanks; (2) the Libertad domain is a sheared basement high along the margin of Sonora and forms the right step of the Tepoca Basin to the north; (3) the Tiburon central domain defines a broad sag cut by a dense NE-striking pattern of normal faults with opposed dips in the depocentre and abruptly ends to the west against the Tiburon fault; and (4) the southern Tiburon domain forms a basement ramp offshore Isla Tiburon and is controlled by a pattern of NNE-striking normal faults on the south that likely connect at an oblique angle (?60°) to the De Mar fault. We propose a rhombochasm basin model with more than 6 s of sedimentary record in the depocentre, in which the basement is not recorded. The NW-trending faults in the Libertad domain possibly continue towards the Sonora coastal plain. The principal NW-trending dextral faults and the secondary NNE-striking pattern of normal faults cut the shallow strata of this domain.     

Consag Basin: northern Gulf of California,evidence of generation of new crust,based on seismic reflection data

The Gulf of California is an excellent example of how new ocean basins form. Tectonically, the northern Gulf of California is an incipient ocean basin and studies on it have defined acoustic basement and reveal the presence of new oceanic crust and intrusive bodies. Some recent studies report fundamental differences between the basins of the northern and southern Gulf of California: that the latter have well-developed oceanic crust beneath a thin cover of sediments, whereas the northern basins show proto-ocean basins, which may reflect thermal insulation of the thick sedimentary cover, the presence of low-angle faults, and more diffuse and distributed deformation. During the 1970s, Petróleos Mexicanos (PEMEX) undertook a 2D seismic reflection survey in the northern Gulf of California, over many active rift basins, including the Consag Basin. Through the processing and interpretation of these data, we describe the structural characteristics of the Consag Basin beyond 2 km depths. Using seismic reflection data, we identified an intrusion in the central part of this basin that may represent new oceanic crust buried by more than 4 km of sediments.     

Structure of the rift basins in the central Gulf of California: Kinematic implications for oblique rifting

We use structural and seismostratigraphic interpretation of multichannel seismic reflection data to understand the structure and kinematic history of the central Gulf of California. Our analysis reveals that oblique strain in the central Gulf formed two tectono–sedimentary domains during distinct deformation stages. The eastern domain, offshore Sonora, is bounded by the East and West Pedro Nolasco faults that may constitute the southernmost segments of the Tiburón Fault System. Within this domain, the dip-slip Yaqui Fault controlled deposition of 3.9 km of sediments in the half-graben Yaqui Basin. The western domain, offshore Baja California, is bounded by the Guaymas Transform Fault, which controlled the accumulation of 1.45 km of sediments within a half-graben that formed the early Guaymas Basin. The tectono–sedimentary activity offshore Sonoran likely ranges from Late Miocene–Pliocene to Late Pliocene time, while activity in the Guaymas Basin commenced in Late Pliocene time. Extinction of the main faults offshore Sonora was nearly coeval to the initiation of the Guaymas Transform Fault. Our results suggest that oblique strain has been accommodated by strain partition since the onset of rifting in the central Gulf. The Guaymas Basin is now a nascent spreading center, but prior to this, it evolved as a half-graben controlled by the Guaymas Transform Fault; such drastic transition is not constrained, but likely occurred during the Pleistocene time and must be localized < 30 km north of the axial troughs. The faults within the central Gulf transpose the Miocene N–S oriented grabens of Basin and Range style preserved onshore in the conjugate rifted margins.     

Origin of lead in the Gulf of California Ecoregion using stable isotope analysis

The magnitude and sources of lead (Pb) pollution in the Gulf of California Ecoregion (GCE) in northwest Mexico were evaluated using various samples collected from urban and rural areas around two typical subtropical coastal ecosystems. Lead concentrations and isotopic compositions (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) were measured using high resolution inductively-coupled plasma mass spectrometry (HR-ICP-MS) and thermal ionization mass spectrometry (TIMS). Urban street dust (157 ± 10.1 μg g^− 1) was heavily enriched with Pb, compared to the Pb enrichment of agricultural soils (29.0 ± 16.0 μg g^− 1) and surface estuary sediments (35.6 ± 15.4 μg g^− 1), all of which contained higher Pb concentrations than found in the natural bedrock (16.0 ± 5.0 μg g^− 1). Pb concentrations in SPM (> 95% of total Pb) were significantly higher in sewage effluent (132 ± 49.9 μg g^− 1) than in agricultural effluents (29.3 ± 5.9 μg g^− 1), and river runoff (7.3 ± 4.2 μg g^− 1). SPM in estuary water column averaged 68.3 ± 48.0 μg g⁻¹. The isotopic composition of Pb (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb) in rural samples of aerosols (1.181 ± 0.001, 2.444 ± 0.003) and soil runoff (1.181 ± 0.003, 2.441 ± 0.004) was comparable to that of natural Pb-bearing bedrock (1.188 ± 0.005, 2.455 ± 0.008); while urban samples of aerosols, street dust, and sewage (1.190–1.207, 2.452–2.467) showed a significant contribution from automotive emissions from past leaded gasoline combustion (1.201 ± 0.006, 2.475 ± 0.005). The absence of lead from fertilizer (1.387 ± 0.008, 2.892 ± 0.005) suggests that this mixture is not representative of the GCE. A mixing model revealed that the Pb content in the environmental samples is predominantly derived from natural weathering and the past leaded gasoline combustion with the later influence of inputs from a more radiogenic source related with anthropogenic lead of North American origin (1.21 ± 0.02; 2.455 ± 0.02).     

Structure of the Cobar Basin,New South Wales,based on seismic reflection profiling

The Cobar Basin in central western New South Wales is a mineral‐rich Early Devonian basin typical of those that characterize the Siluro‐Devonian history of the Lachlan Orogen of southeastern Australia. One hundred and seventy kilometres of seismic profiling in three lines across the basin have shown it to be asymmetrical in shape with an east‐dipping western margin that is steeper than the moderately west‐dipping eastern margin. Maximum basin thickness is around 6 km, but there are significant thickness changes, especially from south to north, which reflect the effect of synsedimentary faulting. Seismic profiling suggests that the basin deformed by thin‐skinned tectonics; postulated strike‐slip effects were not visible on the sections. The seismic profiling has, for the first time, imaged the western synrift basin margin which is generally not exposed. Strain variations during deformation along this edge were taken up by the formation of a major jog ('dog‐leg') which has propagated into the basin as a tear fault. Intrabasinal tears, as well as thrusts, which link into one or more detachments, provide potential pathways for mineralizing fluids during basin inversion.     

Carbonates calibrated against oceanographic parameters along a latitudinal transect in the Gulf of California, Mexico

Trophic resources are an important control governing carbonate production. Though this importance has long been recognized, no calibration exists to quantitatively compare biogenic assemblages within trophic resource fields. This study presents a field calibration of carbonate producers in a range of settings against high‐resolution in situ measurements of nutrients, temperature and salinity. With its latitudinal extent from 30° to 23° N, the Gulf of California, Mexico, spans the warm‐temperate realm and encompasses nutrient regimes from oligo‐mesotrophic in the south to eutrophic in the north. Accordingly, from south to north carbonates are characterized by: (i) coral‐dominated shallow carbonate factories (5–20 m water depth) with average sea‐surface temperatures of 25 °C (min. 18 °C, max. 31 °C), average salinities of 35·06‰ and average chlorophyll a levels, which are a proxy for nutrients, of 0·25 mg Chl a m^?3 (max. 0·48, min. 0·1). (ii) Red algal‐dominated subtidal to inner‐shelf carbonate formation (10–25 m) in the central Gulf of California exhibiting average temperatures of 23 °C (min. 18 °C, max. 30 °C), average salinities of 35·25‰, and average Chl a levels of 0·71 Chl a m^?3 (max. 5·62, min. 0). (iii) Molluskan bryozoan‐rich inner to outer shelf factories in the northern Gulf of California (20–50 m) with average sea surface temperatures of only 20 °C (min. 13 °C, max 29 °C), average salinities of 35·01‰, and average contents of 2·2 mg Chl a m^?3 (max. 8·38, min. 0). By calibrating sedimentological data with in situ measured oceanographic information in different environments, the response of carbonate producers to environmental parameters was established and extrapolated to carbonates on a global scale. The results demonstrate the importance of recognizing and quantifying trophic resources as a dominant control determining the biogenic composition and facies character of both modern and fossil carbonates.     

Tectonic and liquefaction structures in the Loreto basin,Baja California (Mexico) : synsedimentary deformation along a fossil fault plane

Abstract

Complex fault assemblages associated to liquefaction structures have been analyzed in a Pliocene basin located along the Gulf of California. The studied outcrop shows a fossil fault plane formed ill soft flat lying sediments. The liquefaction and fluidification structures have been recognized in voleaniclastic layers deposited ill a lagoonal environment and are potentially related to seismic wave shaking and to successive dewatering along fractures. This strati-graphic record is explained by the progressive development of a seismic fault zone, related to the transtensional regime still active in the Gulf. The present analysis can he considered as an useful case study for the reconnaissance of the different types of structures formed during synsedimentary deformation in hydroplastic conditions.     

羌塘盆地石油地震反射新剖面及基底构造浅析

针对羌塘盆地地表地质条件复杂,地震资料信噪比低,取得高质量的地震剖面存在很大困难等问题,中国地质调查局在羌塘布设了总长约52km的试验剖面,初步摸索出一套适用于羌塘地区地震资料采集与处理的方法技术。处理后的地震叠加剖面上反射信息丰富,揭示出盆地基底以上各构造层的空间展布特征,为查明构造圈闭和构造界面,确定地层的组合等方面,提供了高质量数据。文中在对地震反射特征分析的基础上对两条剖面显示的盆地基底的埋深、形态等方面进行了初步研究。     

Climate and ocean variability during the middle and late Holocene recorded in laminated sediments from Alfonso Basin, Gulf of California, Mexico

A laminated sequence (core BAP96-CP 24°38.12′N, 110°33.24′W; 390 m depth) from the Alfonso Basin in Bay of La Paz, southern Gulf of California, contains a record of paleoceanographic and paleoclimatic changes of the past 7900 yr. Radiolarian assemblages and magnetic susceptibility are used as proxies of oceanographic and climatic variability. The records provide a regional scenario of the middle and late Holocene, suggesting two major climatic regimes and several millennial-scale events. Conditions relatively warmer and drier than today occurred from 7700 to 2500 cal yr BP, promoting the intensification of evaporation processes and the prevalence of the Gulf of California water in the Basin. These conditions correlate with strong droughts in the middle Holocene of North America and with minimal incursion of tropical waters into the Gulf of California. Proxies indicate a warm scenario and the dominance of the Equatorial Surface Water in the Alfonso Basin from 2400 to 700 cal yr BP, suggesting the intensification of ENSO cycles. A climatic signal between 1038 and 963 cal yr BP may be correlated with global signal of the “Medieval Warm Period.” Several cooling events are recognized at 5730, 3360, 2700, 1280 and 820 cal yr BP and are associated with intensification of northwest winds leading to upwellings and enhanced productivity in the Basin.     

Laminated sediments in the Bay of La Paz, Gulf of California: a depositional cycle regulated by pluvial flux

Abstract Core BAP96‐CP, sampled from the deepest part of the Bay of La Paz, Gulf of California, has been analysed sedimentologically taking into account regional climate and oceanography. Laminated sediments at the bottom of the bay are essentially not bioturbated by benthic fauna. A subanoxic condition (O₂ < 0·2 mL L^?1) inhibits the proliferation of benthic fauna. Within the bay, the relative abundances of terrigenous and biogenic inputs change periodically. The terrigenous input is greater than the biogenic input and apparently experiences larger fluctuations. The terrigenous input dominates in dark laminae, whereas the biogenic input mostly occurs in light laminae. Thus, it is assumed that, down the core, the alternation of dark and light laminae represents cycles in the extent of dilution of the biogenic input by terrigenous input. The terrigenous input into the Bay of La Paz is mostly regulated by pluvial runoff. Thus, its temporal fluctuation follows the periods shown by the regional pluvial regime, particularly the 11·2 year period. This is equal to the frequency of sunspot cycles.     

藏北羌塘盆地反射地震剖面与叠加速度研究

本文主要阐述藏北羌塘盆地龙尾错区块的二维反射地震试验的数据采集和处理的过程.分析两条剖面的反射特征,并对叠加剖面进行了初步解释:羌塘盆地中央隆起北侧存在大规模的深凹陷构造;盆地浅部不同方向的构造变形存在较大差异;出现较强的基底反射特征;中生代、古生代地层的反射特征差异较大.文中尝试对数据处理过程中的叠加速度变化进行研究,获得了与叠加剖面较一致的结果,并进一步对某探井的构造背景提出见解.     

Holocene laminated sediments from the southern Gulf of California: geochemical,mineral magnetic and microfossil study

Geochemical, magnetic mineral analyses and microfossils (radiolarians) are used to characterise a Holocene laminated sequence from the Alfonso Basin, northern Bay of La Paz, southern Gulf of California. In most cases, dark and light laminae show similar bulk chemical compositions and magnetic mineral properties. However, dark laminae contain relatively more terrigenous elements (Al, Si, Fe, K and Mg) supporting a pluvial origin related to the volcanic siliceous tuffs around the Bay of La Paz. In light laminae, calcium content is higher, representing biogenic input. The magnetic signal is dominated by low coercivity, fine‐grained low‐titanium titanomagnetites and magnetite. Hysteresis ratio parameters in domain state plots show that samples fall in the pseudo‐single domain field, indicating mixtures of single‐ and multi‐domain particles. Variations in hysteresis saturation magnetisation parameters for dark and light laminae reflect changes in relative mineral concentration. Results indicate a dominant volcanic source for magnetic minerals into the basin, associated with variable pluvial and/or aeolian transport. Low radiolarian abundance in dark laminae seems to be associated with larger penetration and longer residence time of oligotrophic subtropical waters into the bay that occurred during El Niño–Southern Oscillation (ENSO) events. Light laminae are the result of episodic pulses of high productivity. We suggest that dark/light laminae result from oceanographic and climatic cyclic processes, with main terrigenous input variation possibly associated with ENSO forcing of pluvial influx, and/or latitudinal migration of the Intertropical Convergence Zone. The laminated sequence of the Alfonso Basin formed a non‐annual depositional system, in contrast to the varved sediments characteristic of the central Gulf of California basins. Copyright © 2010 John Wiley & Sons, Ltd.     

Controls on forearc basin architecture from seismic and sequence stratigraphy of the Upper Cretaceous Great Valley Group,central Sacramento Basin,California

Seismic and sequence stratigraphic analysis of deep-marine forearc basin fill (Great Valley Group) in the central Sacramento Basin, California, reveals eight third-order sequence boundaries within the Cenomanian to mid-Campanian second-order sequences. The third-order sequence boundaries are of two types: Bevelling Type, a relationship between underlying strata and onlapping high-density turbidites; and Entrenching Type, a significantly incised surface marked by deep channels and canyons carved during sediment bypass down-slope. Condensed sections of hemipelagic strata draping bathymetric highs and onlapped by turbidites form a third important type of sequence-bounding element, Onlapped Drapes. Five tectonic and sedimentary processes explain this stratigraphic architecture: (1) subduction-related tectonic tilting and deformation of the basin; (2) avulsion of principal loci of submarine fan sedimentation in response to basin tilting; (3) deep incision and sediment bypass; (4) erosive grading and bevelling of tectonically modified topography by sand-rich, high-density turbidite systems; and (5) background hemipelagic sedimentation. The basin-fill architecture supports a model of subduction-related flexure as the principal driver of forearc subsidence and uplift during the Late Cretaceous. Subduction-related tilting of the forearc and growth of the accretionary wedge largely controlled whether and where the Great Valley turbiditic sediments accumulated in the basin. Deeply incised surfaces of erosion, including submarine canyons and channels, indicate periods of turbidity current bypass to deeper parts of the forearc basin or the trench. Fluctuations in sediment supply likely also played an important role in evolution of basin fill, but effects of eustatic fluctuations were overwhelmed by the impact of basin tectonics and sediment supply and capture. Eventual filling and shoaling of the Great Valley forearc during early Campanian time, coupled with dramatically reduced subsidence, correlate with a change in plate convergence, presumed flat-slab subduction, cessation of Sierran arc volcanism, and onset of Laramide orogeny in the retroarc.     

Late Quaternary climate change record from two long sediment cores from Guaymas Basin,Gulf of California

Modern Guaymas Basin (Gulf of California, Mexico) is a region of high diatom productivity where exceptional preservation factors maintain biannually alternating sediment deposition as annual varves. New sediment cores from Guaymas Basin (MD02‐2512 and MD02‐2515) present the opportunity to construct climate records from below the last glacial period. A low‐resolution age model has been constructed from oxygen isotope analysis, correlation with other dated short piston cores from Guaymas Basin and an estimate of sedimentation rate. MD02‐2512 from eastern Guaymas Basin has an age range from the Holocene to late marine isotope stage 6 (MIS 6); MD02‐2515 from western Guaymas Basin has an age range from ～8000 to 40 000 yr. Shipboard analyses of colour reflectance, magnetic susceptibility and sediment density are combined with continuous X‐ray fluorescence scans to reconstruct a picture of glacial climate in the Gulf of California. Eastern Guaymas Basin is affected by glacial sea level fall, which results in a drastic change in productivity rates and sediment type. The laminated record of MIS 5 allows comparison with the Holocene, showing a similarity of sedimentation patterns during deglaciation and a series of very rapid variations just prior to the last glaciation. In western Guaymas Basin there are a series of Younger Dryas‐like events during the glacial, typified by low productivity and high terrigenous input. Long‐term climate and productivity changes appear to be caused by the southward displacement of the Subtropical High pressure zone. Copyright © 2005 John Wiley & Sons, Ltd.     

Structural characteristics of the Altar Basin,Northwest Sonora,Mexico

Eight two-dimensional, multichannel seismic reflection lines were acquired, processed, and interpreted to study the structure of the Altar Basin, which is part of the Salton Trough tectonic province. We identified two basin-bounding zones characterized by different degrees of strain: the Cerro Prieto–Altar deformation zone (CPADZ) and the Altar–Caborca deformation zone (ACDZ). The CPADZ is bounded on the west by the Cerro Prieto fault and on the east by the Altar fault. To the north, the strike of both faults changes slightly from a NW to more NNW direction. In the CPADZ, the thickness of the crust decreases southward towards the Gulf of California, and is associated with a deformation-developing fault. The CPADZ has a rotation component orientating these faults in an oblique direction to the Cerro Prieto fault, whereas within the ACDZ, a geometric coherence of synthetic and antithetic faults exists, creating horsts and graben striking N37° W. The Altar fault is recognized by basement interruption, with a vertical component of ～1 km, striking at N37° W and dipping 83° SW. On the northeastern side of the Altar Basin, the basement configuration shows that the minimum time of basement record (～0.4 s of two-way travel time) and the time curve gradient decrease in the NE–SW direction. The depocentre is ～6 km deep in the central-west portion of the basin. We identified a graben between the Rosario and Tinajas Altas mountains (Rosario Basin). The extension–connection of the Altar and Rosario basins to the south is not well defined; nevertheless, these basins could represent the link between the Colorado River and the Gulf of California during the late Miocene, whereas this link was abandoned in the Pliocene as subsidence migrated towards the northwest into the Cerro Prieto and Laguna Salada basins.     

Isla San Pedro Nolasco as a Late Miocene intrusive record at the eastern margin of the Gulf of California: Insights from geological,geochemical and geochronological studies

Isla San Pedro Nolasco (ISPN) is a structural high bounded by inactive dextral oblique-slip faults in the east-central part of the Gulf of California rift zone and is composed of intrusive rocks not exposed on other Gulf of California islands. Here we present the reconnaissance results from geological mapping, as well as first geochemical and geochronological data for the ISPN intrusive complex. The intrusive rocks compose a sheet-like body of intermediate and felsic composition intruded by an intermediate and acidic dike swarm. All intrusive rocks (host and dikes) range in age from ca. 9 Ma to 10 Ma (⁴⁰Ar/³⁹Ar) and show a hydrous ferromagnesian mineral association (amphibole and biotite) with a calc-alkalic and transitional affinity. This hydrated mineralogical association has not been recognized in the coeval rocks along the onshore western margin of the North American plate (coastal Sonora). However, such hydrous mineralogical association is found in the coeval rift transitional volcanic rocks from the Baja California Microplate at Santa Rosalía and Bahía de Los Ángeles – Bahía de Las Ánimas. The ISPN continental block, at least 40 km long, has been pulled apart by transtensional faulting of the late Miocene Gulf of California shear zone before the westward migration of the North America-Pacific plate boundary at ca. 3–2 Ma. Eventually, ISPN became isolated as an island during the late Miocene flooding of the Gulf of California seaway.     

川东南涪陵地区石炭系黄龙组地震异常特征及其意义

涪陵地区位于川东南探区北部,通过该区石炭系黄龙组地震剖面测线逐条解释,识别出了四种典型异常反射结构：①地震同相轴波峰、波谷均表现为中振幅～弱振幅;②地震同相轴下拉波峰振幅有强有弱,上部波谷反射呈现强振幅～中振幅;③地震反射同相轴明显下拉,同时下拉同相轴上部反射呈现中振幅～弱振幅、下部反射振幅减弱;④地震同相轴反射为弱振幅,近空白反射或弱波谷反射。基于岩溶单元发育理论模型及该区沉积特征,对四种典型地震剖面反射异常地质成因解释进行了地球物理正演模拟,结果显示了与实际典型地震反射结构相吻合的地震剖面特征。其分别代表了岩溶高地峰丛与浅洼发育;被泥质充填或半充填的溶洞或孔隙性非常高的储层发育;高泥质含量充填物,或低速度、未被完全充填的缝洞体发育;7 m～9 m及以下的黄龙组地层。同时,基于特殊剖面结构研究成果,对该区可能发育的新型储层类型进行了预测,有效地指导了该区下部油气有利储层的寻找。     

库车前陆盆地与波斯湾盆地盐构造对比研究

通过对库车前陆盆地和波斯湾盆地的盐层发育状况、盐构造特征以及盐构造与油气关系的对比研究,认为盐底辟构造与油气密切相关。库车前陆盆地勘探程度较低,应注重寻找盐底辟构造,以及与其相关的圈闭。库车前陆盆地盐构造的形成机制与波斯湾盆地下法尔斯组/加奇萨兰组相似,与霍尔姆兹组不同。根据波斯湾盆地下法尔斯组/加奇萨兰组盐构造在油气成藏中的作用,认为库车前陆盆地南部盐层较厚的地区应加强盐下勘探的力度,寻找盐下圈闭。北部山前盐层欠发育地区应注重寻找盐上圈闭,同时兼顾盐下圈闭。库车前陆盆地具有良好的三叠系和侏罗系烃源岩,应该有很广阔的勘探前景。     

Low-frequency 3-D seismic survey of upper crustal magmatic intrusions in the northeastern Pannonian basin of Hungary

A specially designed 700-km² grid survey, deploying 1000 regularly distributed low-frequency seismic recording systems, successfully investigated one of the most complex geologic environments of the Pannonian basin. The wide-angle signals penetrated through over 1000 m of multi-phase igneous lithology and recognized, for the first time, the underlying enigmatic Permian to Early Triassic basement rocks. Tomographic inversion of the first arrival grid data resulted in determination of an accurate three-dimensional (3-D) velocity field, to a depth of 4 km. The anomalous changes of the spatial velocity data outline the regional extent of the Late Miocene magmatic intrusions, which are covered by over 2000 m of Mid-Miocene to Pleistocene clastics. Complex relationship was found between the surface potential data and the intrusive bodies. This multi-faceted geophysical data analysis established a functional technique for mapping a subsurface with intricate acoustic and structural complexity.     

青藏高原羌塘盆地中央隆起近地表速度结构的初至波层析成像试验

利用2条衔接并横过青藏高原羌塘盆地中央隆起的反射地震剖面探测数据,进行了初至波层析成像试验,以揭示羌塘中央隆起的表层结构特征。研究结果表明,大量的反射地震单炮记录初至清晰,长排列接收丰富了浅表构造趋势特征的信息,层析走时射线密度随地下构造的复杂程度而变化。层析反演得到的速度结构显示了高速层起伏剧烈的变化特征,其厚度与地表出露地层的年代负相关。深反射地震初至波走时层析成像可以提供丰富的地壳近地表结构信息。