Morphology of the Blanco Transform Fault Zone-NE Pacific: Implications for its tectonic evolution

The right-lateral Blanco Transform Fault Zone (BTFZ) offsets the Gorda and the Juan de Fuca Ridges along a 350 km long complex zone of ridges and right-stepping depressions. The overall geometry of the BTFZ is similar to several other oceanic transform fault zones located along the East Pacific Rise (e.g., Siquieros) and to divergent wrench faults on continents; i.e., long strike-slip master faults offset by extensional basins. These depressions have formed over the past 5 Ma as the result of continual reorientation of the BTFZ in response to changes in plate motion. The central depression (Cascadia Depression) is flanked by symmetrically distributed, inward-facing back-tilted fault blocks. It is probably a short seafloor spreading center that has been operating since about 5 Ma, when a southward propagating rift failed to kill the last remnant of a ridge segment. The Gorda Depression on the eastern end of the BTFZ may have initially formed as the result of a similar occurrence involving a northward propagating rift on the Gorda ridge system. Several of the smaller basins (East Blanco, Surveyor and Gorda) morphologically appear to be oceanic analogues of continental pull-apart basins. This would imply diffuse extension rather than the discrete neovolcanic zone associated with a typical seafloor spreading center. The basins along the western half of the BTFZ have probably formed within the last few hundred thousands years, possibly as the result of a minor change in the Juan de Fuca/Pacific relative motion.     

Fault pattern from seabeam processing: The western part of the Blanco Fracture Zone (NE pacific)

The Blanco Fracture Zone, which connects the Juan de Fuca and Gorda ridges, is structurally complex and contains numerous pull-apart basins and accretion centres. It terminates at its western end in two troughs where the Juan de Fuca Ridge progressively dies out. This unusual structure is studied in detail using bathymetric analysis which allows the fault pattern to be determined. The method developed to extract structural information involves numerical treatment of the gridded bathymetry derived from image processing methods. The detailed mapping of the fault pattern shows that the active zone corresponds to a N100° E strike-slip zone which connects the southern end of the Juan de Fuca Ridge with the northeastern edge of the Blanco Trough, via the northwestern wall of the Parks Plateau. The present day direction of the active zone comes after a previous one trending at N115° E, apparently within the same area. The Parks Plateau results from a jump of the plate boundary from the southern to northern limits of the plateau. Deformation over the past 2 Ma results from a northeastward displacement of the junction between the transform zone and the ridge.     

Recent tectonics of the Blanco Ridge,eastern blanco transform fault zone

Bathymetric, hydro-acoustic, seismic, submersible, and gravity data are used to investigate the active tectonics of the eastern Blanco Transform Fault Zone (BTFZ). The eastern BTFZ is dominated by the 150 km long transform-parallel Blanco Ridge (BR) which is a right-lateral strike-slip fault bordered to the east and west by the Gorda and Cascadia Depressions. Acoustic locations, fault-parameter information, and slip vector estimates of 43 earthquakes (M _w3.8) that occurred along the eastern BTFZ over the last 5 years reveal that the Blanco Ridge is a high-angle right-lateral strike-slip fault, with a small component of dip-slip motion, where the Juan de Fuca plate is the hanging wall relative to the Pacific plate. Furthermore, the Cascadia and Gorda basins are undergoing normal faulting with extension predominantly oblique to the transform trend. Seafloor submersible observations agree with previous hypotheses that the active transform fault trace is the elongate basin that runs the length of the BR summit. Brecciated and undeformed basalt, diabase, and gabbro samples were collected at the four submersible survey sites along the Blanco Ridge. These petrologic samples indicate the Blanco Ridge is composed of an ocean crustal sequence that has been uplifted and highly fractured. The petrologic samples also appear to show an increase in elevation of the crustal section from east to west along the Blanco Ridge, with gabbros exposed at a shallower depth farther west along the southern (Pacific plate side) BR ridge flank. Further supporting evidence for BR uplift exists in the seismic reflection profiles across the BR showing uplift of turbidite sequences along the north and south ridge base, and gravity and magnetics profiles that indicate possible basement uplift and a low-density zone centered on the ridge's Pacific plate side. The BR formation mechanism preferred here is first, uplift achieved partially through strike-slip motion (with a small dip-slip component). Second, seawater penetration along the fault into the lower crust upper mantle, which then enhanced formation and intrusion of a mantle-derived serpentinized-peridotite diapir into the shallow ocean crust, causing further uplift along the fault.     

Metalliferous Sediment and a Silica-Hematite Deposit within the Blanco Fracture Zone,Northeast Pacific

A Tiburon ROV dive within the East Blanco Depression (EBD) increased the mapped extent of a known hydrothermal field by an order of magnitude. In addition, a unique opal-CT (cristobalite-tridymite)-hematite mound was discovered, and mineralized sediments and rock were collected and analyzed. Silica-hematite mounds have not previously been found on the deep ocean floor. The light-weight rock of the porous mound consists predominantly of opal-CT and hematite filaments, rods, and strands, and averages 77.8% SiO₂ and 11.8% Fe₂O₃. The hematite and opal-CT precipitated from a low-temperature (≥ 115° C), strongly oxidized, silica- and iron-rich, sulfur-poor hydrothermal fluid; a bacterial mat provided the framework for precipitation.

Samples collected from a volcaniclastic rock outcrop consist primarily of quartz with lesser plagioclase, smectite, pyroxene, and sulfides; SiO₂ content averages 72.5%. Formation of these quartz-rich samples is best explained by cooling in an up-flow zone of silica-rich hydrothermal fluids within a low permeability system. Opal-A, opal-CT, and quartz mineralization found in different places within the EBD hydrothermal field likely reflects decreasing silica saturation and increasing temperature of the mineralizing fluid with increasing silica crystallinity.

Six push cores recovered gravel, coarse sand, and mud mineralized variously by Fe or Mn oxides, silica, and sulfides. Total rare-earth element concentrations are low for both the rock and push core samples. Ce and Eu anomalies reflect high and low temperature hydrothermal components and detrital phases.

A remarkable variety of types of mineralization occur within the EBD field, yet a consistent suite of elements is enriched (relative to basalt and unmineralized cores) in all samples analyzed: Ag, Au, S, Mo, Hg, As, Sb, Sr, and U; most samples are also enriched in Cu, Pb, Cd, and Zn. On the basis of these element enrichments, the EBD hydrothermal field might best be described as a base- and precious-metal-bearing, silica-Fe-oxide-barite deposit. Such deposits are commonly spatially and temporally associated with volcanogenic massive sulfide (VMS) ores. A plot of data for pathfinder elements shows a large hot spot at the northwestern margin of the field, which may mark a region where moderate to high temperature sulfide deposits are forming at depth; further exploration of the hydrothermal field to the northwest is warranted.     

Morphology and crustal structure of a small transform fault along the Mid-Atlantic Ridge: The Atlantis Fracture Zone

The Atlantis Fracture Zone (30° N) is one of the smallest transform faults along the Mid-Atlantic Ridge with a spatial offset of 70 km and an age offset of ~ 6 Ma. The morphology of the Atlantis Fracture Zone is typical of that of slow-slipping transforms. The transform valley is 15–20 km wide and 2–4 km deep. The locus of strike-slip deformation is confined to a narrow band a few kilometers wide. Terrain created at the outside corners of the transform is characterized by ridges which curve toward the ridge-transform intersections and depressions which resemble nodal basins. Hooked ridges are not observed on the transform side of the ridge-transform intersections. Results of the three-dimensional inversion of the surface magnetic field over our survey area suggest that accretionary processes are sufficiently organized within 3–4 km of the transform fault to produce lineated magnetic anomalies. The magnetization solution further documents a 15-km, westward relocation of the axis of accretion immediately south of the transform about 0.25 Ma ago. The Atlantis Transform is associated with a band of high mantle Bouguer anomalies, suggesting the presence of high densities in the crust and/or mantle along the transform, or anomalously thin crust beneath the transform. Assuming that all the mantle Bouguer anomalies are due to crustal thickness variations, we calculate that the crust may be 2–3 km thinner than a reference 6-km thickness beneath the transform valley, and 2–3 km thicker beneath the mid-points of the spreading segments which bound the transform. Our results indicate that crustal thinning is not uniform along the strike of the fracture zone. Based on studies of the state of compensation of the transform, we conclude that the depth anomaly associated with the fracture zone valley is not compensated everywhere by thin crust. Instead, the regional relationship between bathymetry and gravity is best explained by compensation with an elastic plate with an effective thickness of ~ 4 km or greater. However, the remaining isostatic anomalies indicate that there are large variations away from this simple model which are likely due to variations in crustal thickness and density near the transform.     

浅层地震在复杂断裂带探测中的应用研究

拟建中的潍河特大桥地处沂沭大断裂边缘。区内断裂发育,构造复杂,直接会影响大桥基础的稳定性,因而查清区内断裂带的准确位置与分布是大桥工程的关键。探测应用浅层地震折射波方法和选用追逐与相遇观测系统和大小排列相结合的工作方法,准确地查明了区内断裂的准确位置和特征,与钻井资料对比,十分吻合。     

青岛劈石口断裂的构造特征和现代活动性研究

通过野外地质观察和断裂平、剖面图的绘制,阐述了青岛劈石口断裂的空间展布、构造特征和构造作用.并应用地貌学、第四纪地质学、地震地质学和构造年代方法对劈石口断裂的现代活动性进行了研究,认为上述断裂自晚更新世以来,其活动性趋向稳定状态,属于晚第四纪不活动断裂.     

基于经验模式分解的希尔伯特变换包络提取在机械故障诊断中的应用

本文采用经验模式分解 (EMD)提取信号的内在模函数 (IMF) ,并利用希尔伯特变换对所得IMF进行包络分析 ,提取机械故障特征。与直接对原信号进行包络分析相比较 ,该方法提取的机械故障特征更明显。数值模拟和对故障轴承振动信号分析表明了该方法的有效性。     

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.     

池养长毛对虾体长与体重的关系

本文报道池养长毛对虾体长在６．８－１２３．９ｍｍ范围内的体长与体重的关系。池养长毛对虾雌、雄群体的生长特点是雌虾快于雄虾。由雌雄混合、雌虾、雄虾群体的体重对体长的相关曲线都很接近。     

Relationship between the oceanic geoid and the structure of the oceanic lithosphere

Data from the GEOS 3 and SEASAT Satellites have provided a very accurate geoid map over the oceans. Broad bathymetric features in the oceans such as oceanic swells and plateaus are fully compensated. For these features it can be shown that the geoid anomalies due to the density structure of the lithosphere are proportional to the first moment of the density distribution. Deepening of the ocean basins is attributed to thermal isostasy. The thickness of the oceanic lithosphere increases with age due to the loss of heat to the sea floor. Bathymetry and the geoid provide constraints on the extent of this heat loss. Offsets in the geoid across major fracture zones can also be used to constrain this problem. Geoid-bathymetry correlations show that the Hawaiian and Bermuda swells and the Cape Verde Rise are probably due to lithospheric thinning. A similar correlation for the Walvis Ridge and Agulhas Plateau indicates that these features are probably due to an anomalously light mantle lithosphere.     

两个凡纳滨对虾家系体重与体长的关系

凡纳滨对虾Litopeneaus vannamei家系的培育是遗传选育种的基础,其生长特性包括生长速度、体重与体长的关系等,是家系的表型特征。报道了凡纳滨对虾2个家系的体长与体重的关系。通过回归分析,凡纳滨对虾家系1体重(W)与体长(L)的关系为:W=0.0059L3.2809(R2=0.9931);家系2体重与体长的关系为:W=0.0059L3.2974(R2=0.9940),2个家系体重与体长的关系没有明显的变化,得出凡纳滨对虾体重与体长的关系为:W=0.0059L3.2895(R2=0.9934)。     

孤西断裂带下古生界褶皱-块断型潜山油气成藏模式

通过对孤西断裂带下古生界褶皱-块断型潜山油藏的综合研究，总结出孤西潜山带经历印支期挤压逆冲、燕山期拉张负反转和喜马拉雅期拉张断裂改造3个构造演化阶段，形成了受北西向孤西断裂控制的内幕褶皱-块断型潜山带，发育了不整合面风化壳型、潜山内幕孔洞型和构造裂缝型3种储集层类型，进一步厘定了高潜山和低潜山2大类5种潜山油气成藏模式，其中高潜山油气藏模式有风化壳型、反向断块内幕型和地层不整合型，低潜山油气藏模式有反向断块和顺向断块型2种，这对济阳坳陷潜山勘探及多样性潜山理论的完善具有重要意义，为实现成藏规律指导下的潜山勘探奠定了基础。     

The origin of bathymetric highs at ridge-transform intersections: A multi-disciplinary case study at the Clipperton Fracture Zone

Bathmetric highs on the old crust proximal to ridge-transform intersections (RTIs), termed intersection highs, are common but poorly understood features at offsets of fast to intermediate rate spreading centers. We have combined new reflection seismic, photographic, and geochemical data with previously published Seabeam, SeaMARC I, and SeaMARC II data to address the nature of the intersection highs at the Clipperton Fracture Zone. The Clipperton Intersection Highs are both topped by a carapace of young lavas at least 100 m thick. These lavas, which were erupted on the intersection highs, are chemically similar to their adjacent ridge segments and different from the surrounding older crust. At least some of the erupted magma traveled directly from the adjacent ridge at a shallow crustal level. Ridge-related magma covers and intrudes at least the upper 500 m of the transform tectonized crust at the RTI. We suspect that additional magma enters the intersection highs from directly below, without passing through the ridge. The young oceanic crust near the western Clipperton RTI is not thin by regional comparison. The 1.4 m.y. old crust near the eastern Clipperton RTI thickens approaching the transform offset. If the thermal effects of the proximal ridge were negligible, the eastern intersection high crust would appear to be in isostatic equilibrium. We believe that thermal effects are significant, and that the intersection high region stands anomalously shallow for its crustal thickness. This is attributable to increased temperature in the mantle below the ridge-proximal crust. Although ridge magma is injected into the proximal old crust, plate boundary reorganization is not taking place. Intersection high formation has been an ongoing process at both of the Clipperton RTIs for at least the past 1 m.y., during which time the plate boundary configuration has not changed appreciably. We envision a constant interplay between the intruding ridge magma and the disrupting transform fault motion. In addition, we envision a nearly constant input of magma from below the high, as an extension of the magma supply to the ridge from the mantle. Because the proximal ridge profoundly affects the juxtaposed crust at the RTI, sea floor fabric along the aseismic extensions of this fast-slipping transform fault is primarily a record of processes at work at the RTI rather than a record of transform tectonism.     

Relationship between salt diapirism and faulting in the central structural belt of the Dongying sag, Bohai Gulf basin, China

1 Introduction D iapiric structures are an im portant andw idespread structural style in m any tectonic settings(Ism ail-Zadeh etal.,2001),including m agm a diapirs,salt diapirs, m ud diapirs, and serpentinite diapirs.C om pared w ith the form ertw o,m ud diapirism in sedi-m ents is rarely reported and studied although it hasbeen know n for a long tim e both on land and underthe sea.H ow ever,w ith the geologicalinvestigations ofO D P and related on-land studies of accretionaryprism s, m ud…     

利用EMD方法和小波变换进行信号奇异性检测

本文采用经验模式分解 (EMD)与小波变换相结合的方法分析非平稳机械故障信号的奇异性 ,进行机械故障诊断。与直接对原信号进行小波分析相比较 ,该方法提取的奇异性特征明显。数值模拟和对故障轴承的振动信号分析表明了该方法的有效性。     

断块油藏储量计算中夹层的识别与剔除

岩性夹层和物性夹层在陆相沉积中非常普遍，通过岩性和物性特征识别取心井夹层，根据不同夹层的测井响应特征识别非取心井的夹层，并按照一定的标准剔除，能更加合理地确定有效厚度，精细表征油藏地质特征，取得客观的储量数据。     

Investigation of Fethiye-Marmaris Bay (SW Anatolia): seismic and morphologic evidences from the missing link between the Pliny Trench and the Fethiye-Burdur Fault Zone

New (2009) multi-beam bathymetric and previously published seismic reflection data from the NE-SW-oriented Fethiye Bay and the neighboring N-S-oriented Marmaris Bay off SW Anatolia were evaluated in order to interpret the seafloor morphology in terms of the currently still active regional tectonic setting. This area lies between the Pliny Trench, which constitutes the eastern sector of the subduction zone between the African and Eurasian plates in the Eastern Mediterranean, and the Fethiye-Burdur Fault Zone of the Anatolian Plate. The bathymetric data document the very narrow shelf of the Anatolian coast, a submarine plain between the island of Rhodes and Marmaris Bay, and a large canyon connecting the abyssal floor of the Rhodes Basin with Fethiye Bay. The latter are here referred to as the Marmaris Plain and Fethiye Canyon, respectively. Several active and inactive faults have been identified. Inactive faults (faults f1) delineate a buried basin beneath the Marmaris Plain, here referred to as the Marmaris Basin. Other faults that affect all stratigraphic units are interpreted as being active. Of these, the NE-SW-oriented Marmaris Fault Zone located on the Marmaris Plain is interpreted as a transtensional fault zone in the seismic and bathymetric data. The transtensional character of this fault zone and associated normal faults (faults f3) on the Marmaris Plain correlates well with the Fethiye-Burdur Fault Zone on land. Another important fault zone (f4) occurs along the Fethiye Canyon, forming the northeastern extension of the Pliny Trench. The transpressional character of faults f4 inferred from the seismic data is well correlated with the compressional structures along the Pliny Trench in the Rhodes Basin and its vicinity. These observations suggest that the Marmaris Fault Zone and faults f3 have evolved independently of faults f4. The evidence for this missing link between the Pliny Trench and the Fethiye-Burdur Fault Zone implies possible kinematic problems in this tectonic zone that deserve further detailed studies. Notably, several active channels and submarine landslides interpreted as having been triggered by ongoing faulting attest to substantial present-day sediment transport from the coast into the Rhodes Basin.     

The morphology and structure of the West O’Gorman Fracture Zone

The West O’Gorman Fracture Zone is an unusual feature that lies between the Mathematician Ridge and the East Pacific Rise on crust generated on the East Pacific Rise between 4 and 9 million years ago. We made a reconnaissance gravity, magnetic and Sea Beam study of the zone with particular emphasis on its eastern (youngest) portion. That region is characterized by an elongate main trough, a prominent median ridge and other, smaller ridges and troughs. The structure has the appearance of large-offset fracture zone, possibly in a slow spreading environment. However, magnetic anomalies indicate that the offset, if any, is quite small, and the spreading rate during formation was fast. In addition, the magnetic profiles do not support earlier models for a difference in spreading rate north and south of the fracture. The morphology of the fracture zone suggests that flexure may be responsible for some of the topography; but gravity studies indicate some of the most prominent features of the fracture zone are at least partially compensated. The main trough is underlain by a thin crust (or high density body), similar to large-offset fracture zones in the Atlantic, while the median ridge is underlain by a thickened crust. Sea Beam data does not unambiguously resolve between volcanism or serpentinization of the upper mantle as a mechanism for isostatic compensation. Why the West O’Gorman exists remains enigmatic, but we speculate that the topographic expression of a fracture zone does not require a transform offset during formation. Perhaps the spreading ridge was magma starved for some reason, resulting in a thin crust that allowed water to penetrate and serpentinize portions of the upper mantle.