Fault tectonics,neotectonic stresses,and hidden uranium mineralization in the area adjacent to the Strel’tsovka Caldera

The scheme of recent fault tectonics and neotectonic stresses of the area adjacent to the Strel’tsovka Caldera in the southeastern Transbaikal region has been compiled for the first time on the basis of structural and geomorphic study. The faults were ranked by criteria of slip direction stability along separate segments and their expression in topography. Neotectonic stresses of corresponding ranks were ascertained as well. The heterogeneity of neotectonic stress field is related to the mosaic development of compression, extension, and the three-axial stress state. Comparison of morphogenetic features of recent and older faults shows the different character of the deformation mechanism and orientation of tectonic displacements. It has been established that the Strel’tsovka Caldera and its northwestern segment, in particular, developed as an echeloned system of pull-apart grabens, but the caldera itself is situated in a recent rise, whereas the northwestern segment is located in a neotectonic depression corresponding to the Dry Urulyungui Basin filled with volcanic and sedimentary rocks. Such a structure markedly expands the outlook for discovery of hidden uranium mineralization in the studied area. The elaborated scheme of neotectonic faults and stresses reflects the postore geodynamic setting and completes the reconstruction of geodynamic conditions pertaining to the periods of preore preparation and ore-forming tectonomagmatic reactivation.     

Relationship between saline–alkali soil formation and neotectonic movement in Songnen Plain,China

In the Songnen Plain, China, salinization has become increasingly serious and desertification has increased rapidly since the middle of the twentieth century, restricting the economic growth of the area and threatening the environment. Many factors can cause the formation of saline–alkali soil, but none of them explain the origin of the substantial amount of soda that exists in the basin and its distribution pattern. This paper focuses attention on the relationship between the formation of saline–alkali soil and neotectonic movement, and the climate–tectonic cycle over the geological history of the region. Data interpreted by Thematic Mapper for two periods of time have been used to analyze changes in the saline–alkali soil. The results provide a useful tool for demonstrating the relationship between the saline–alkali soil and neotectonic movement, and for improving the technology and methods used to protect, manage, exploit and utilize the saline–alkali soil.     

南海西北部壳体新构造运动及其演化模式

本文根据南海西北部壳体的地形地貌、重磁场异常和地壳结构特征和岩石圈动力学环境，对穿过莺歌海盆地和西沙海槽的地震剖面进行解释。把本区新构造运动类型划分为拉张型、挤压型、平移剪切型和旋动型，并对其构造演化模式进行了初步分析。结果发现，南海西北部在漫长的地质历史中，曾经历复杂的动力学演变过程，从中生代到新生代，本区在周缘岩石圈壳体作用下，经历挤压、拉张、复杂应力调整和现代挤压收缩四个演化阶段。     

Geomorphic and structural evidences of neotectonic activity in the Sub-Himalayan belt of Nahan Salient,NW India

Neotectonism in the Sub-Himalayan belt is not new. Moreover, the word ‘Sub-Himalaya’ is almost synonymous with ‘neotectonic activity’. In the present paper, we report some of the most convincing geomorphic and structural evidences of neotectonic activity from the Sub-Himalayan belt in the Nahan Salient. The geomorphic evidences mainly include the four geomorphic surfaces identified from the transverse topographic profiles drawn parallel to the Himalayan front. These surfaces are commonly covered with terrace deposits that are tilted as well as faulted at a number of places. A number of faults, directly observable in the field, are normal in nature and they are oriented at high angles to the Himalayan Frontal Thrust (HFT). These faults are similar to the E-W extension in southern Tibet in response to the oblique convergence of India at ∼N20°E in the NW Himalaya. They are attributable to the kinematics of neotectonic compression along the HFT, the frontal ramp-oblique ramp-frontal ramp geometry of the thrust fault and related adjustments.     

New evidence from the southeastern U.S. for eustatic components in the late Holocene Sea levels

Changes in Holocene sea level through time have been attributed to eustatic, isostatic, and neotectonic processes. Eustatic changes imply global expression through linkage in world climate, or changes in ocean water or basin volume, while isostatic adjustment and neotectonic distortion involve regional or local geophysical parameters which must be ascertained. A Holocene sea level curve is being developed for the southeastern United States through a study of marsh stratigraphy and archaeologic sites located in marsh and interriverine areas. The curve is evaluated in light of intensive investigations of regional and local tectonic elements. Both major and some minor trends in sea level change are shown to include significant eustatic components.     

Neotectonics of the Deryugin Basin area (Sea of Okhotsk)

The data of the bottom “summit” surface were used for compiling the schematic structural-neotectonic map and map of the main neotectonic structural elements. Their comparison with the schematic paleogeographic maps of the lithophysical complexes for four periods (K₂-$ _{1 - 2} $ _{1 - 2} , $ \rlap{--} P_3 $ \rlap{--} P_3 -N₁¹, N₁^1–2, and N₁³-N₂) reveals that the largest part of the considered area was characterized by either a continental or relatively shallow-sea environment, except for the western areas occupied at that time by the relatively deep trough with its axis located substantially westward of the neotectonic Deryugin Basin and the Staritskii Trough. In the Late Pliocene, the deep paleotrough ($ \rlap{--} P_3 $ \rlap{--} P_3 -N₂²) and Deryugin Basin were likely occupied by shelf settings with continuing sedimentation. The paleogeographic environments of the area for the period from the terminal Pliocene to the late Riss (Taz) Glaciation (Q₂⁶; MIS6) are unknown so far. The most complete Quaternary section recovered by Core LV 28-34-2 consists of six units; the odd (1, 3, and 5) and even (2, 4, and 6) among them correspond to the warm and cold marine isotopic stages, respectively. Judging from the benthic foraminiferal assemblages, the water depths during cold periods were shallower as compared with the warm stages, which is explained by the respective ascending and descending bottom movements and, partially, by the eustatic sea level fluctuations. In the Late Pleistocene-Holocene (∼17 ka), the bottom of the Deryugin Basin and the summit part of the Institut Okeanologii Rise subsided with average rates of 8 and 3 cm/year, respectively.     

北京西山新构造运动的分期

根据北京西山若干新构造运动的标志及其地质年代测定资料，将该区新构造运动划分为“喜山期”和“西山期”两个阶段及其相应的１５个新构造幕（Ｈ１—Ｈ５和Ｗ１—Ｗ１０）。新生代以来，西山区新构造运动以不均衡的垂向差异性上升运动为主，兼有掀斜运动、断裂运动和水平运动。地壳运动以总体隆升背景上的脉动升降为特点．     

Stress orientation and tectonic regime in the northwestern Valencia Trough from borehole data

The orientation of the maximum horizontal stress S_H is obtained from the analysis of borehole breakouts, covering a depth range from 300 to 3415 m (below sea level) in twelve offshore exploration wells in the northwestern Valencia Trough. The orientation of S_H is roughly coincident with the strike of major extensional structures. From N to S it changes counterclockwise from a NE–SW orientation to a N–S orientation. Estimates of the tectonic regimes indicate that the area is characterised predominantly by normal-faulting with a strike-slip component. Both the stress orientations and the tectonic regimes are consistent with neotectonic studies in the nearby Catalan Coastal Ranges. An established method of estimating the tectonic regime by Moos and Zoback (1990) was modified by the inclusion of a nontrivial cohesion, but this changes the results insignificantly.     

Joints as fingerprints of stress in the quaternary carbonate deposits along coastal Saurashtra,Western India

Coastal cliffs and shore platforms are important geomorphic features of coastal areas of Saurashtra. These features are composed of medium to coarse grained carbonate sand and are designated as “Miliolitic limestones” that range in age from Middle to Late Pleistocene. Significant jointing has been observed in the Middle Pleistocene Miliolite Formation as well as in the younger shell limestone that comprises Chaya Formation of Late Pleistocene. Along with NE-SW trend which is the direction of maximum horizontal compressive stress [S_Hmax] for Indian sub-continent, other trends recorded are NNE-SSW, N-S, NW-SE and E-W. When compared with other regional studies, neotectonic episode in Saurashtra peninsula appears to be younger than at least 125ky. The present study on joint sets also indicates that they are important to understand stresses associated with anticlockwise rotation of the Indian plate.     

The Mesozoic to Early Cenozoic Magmatism of the Benue Trough (Nigeria); Geochemical Evidence for the Involvement of the St Helena Plume

The Benue Trough is a continental rift related to the openingof the equatorial domain of the South Atlantic which was initiatedin Late Jurassic-Early Cretaceous times. Highly diversifiedand volumetrically restricted Mesozoic to Cenozoic magmaticproducts are scattered throughout the rift. Three periods ofmagmatic activity have been recognized on the basis of ⁴⁰ Ar-³⁹Ar ages: 147–106 Ma, 97–81 Ma and 68–49 Ma.Trace element and Sr, Nd and Pb isotope determinations, performedon selected basaltic samples, allow two groups of basaltic rocksto be identified: (1) a group with a tholeiitic affinity, withZr/Nb=7–11.1; La/Nb = 0.77–1; ⁸⁷Sr/⁸⁶Sr; =0.7042–0.7065¹⁴³Nd/¹⁴⁴Nd;_i = 0.5125–0.5127; ²⁰⁶Pb/²⁰⁴Pb_i = 17.59–18.48;(2) a group with an alkaline affinity, with Zr/Nb = 3.6–6.8;La/Nb=0.53–0.66; ⁸⁷Sr/⁸⁶ Sr_i=0.7029–0.7037; ¹⁴³Nd/¹⁴⁴Nd_i=0.5126–0.5129;²⁰⁶Pb/²⁰⁴Pb_i = 18.54–20.42. The geochemical data leadto the conclusion that three types of mantle sources were involvedin the genesis of the Mesozoic to Cenozoic basaltic rocks ofthe Benue, without significant crustal contamination: (1) anenriched subcontinental lithospheric mantle from which the tholeiiticbasalts were derived; (2) a HIMU-type (plume) component fromwhich the alkaline basalticrocks originated; (3) a depletedasthenospheric mantle (N-MORB-type source), which was involvedin the genesis of the alkaline basaltic magmas. According to(1) the postulated location of the St Helena hot spot in theEquatorial Atlantic at about 130 Ma and (2) the isotopic compositionof the alkaline basaltic rocks of the Benue Trough and theirgeochemical similarity with the basalts of St Helena, we concludethat the St Helena plume was involved in the genesis of thealkaline magmatism of the Benue at the time of opening of theEquatorial Atlantic. Moreover, the geochemical similarity betweenthe alkaline magmatism of the Benue Trough and that of the CameroonLine suggests that both magmatic provinces were related to theSt Helena plume. Finally, the temporal change of the mantlesources observed in the Benue Trough can be accounted for bythe recent models of plume dynamics, in the general frameworkof opening of the Equatorial Atlantic. KEY WORDS: Benue Trough; Mesozoic to Cenozoic magmatism; Equatorial Atlantic; mantle sources; St Helena plume ^*;Corresponding author.     

Lithostratigraphic development and neotectonic significance of the Quaternary sediments along the Kachchh Mainland Fault (KMF) zone,western India

The Kachchh Mainland Fault (KMF) is a major E–W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow zone between the E–W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF. The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite. These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The tectonically controlled incision and dissection of the Quaternary deposits is the result of neotectonic activity that continues at present day. The overall nature, sedimentary characteristics and geomorphic setting of the sediments suggest that the KMF remained neotectonically active throughout the Quaternary period.     

Different modes of the Late Cretaceous–Early Tertiary inversion in the North German and Polish basins

Several selected seismic lines are used to show and compare the modes of Late-Cretaceous–Early Tertiary inversion within the North German and Polish basins. These seismic data illustrate an important difference in the allocation of major zones of basement (thick-skinned) deformation and maximum uplift within both basins. The most important inversion-related uplift of the Polish Basin was localised in its axial part, the Mid-Polish Trough, whereas the basement in the axial part of the North German Basin remained virtually flat. The latter was uplifted along the SW and to a smaller degree the NE margins of the North German Basin, presently defined by the Elbe Fault System and the Grimmen High, respectively. The different location of the basement inversion and uplift within the North German and Polish basins is interpreted to reflect the position of major zones of crustal weakness represented by the WNW-ESE trending Elbe Fault System and by the NW-SE striking Teisseyre-Tornquist Zone, the latter underlying the Mid-Polish Trough. Therefore, the inversion of the Polish and North German basins demonstrates the significance of an inherited basement structure regardless of its relationship to the position of the basin axis. The inversion of the Mid-Polish Trough was connected with the reactivation of normal basement fault zones responsible for its Permo-Mesozoic subsidence. These faults zones, inverted as reverse faults, facilitated the uplift of the Mid-Polish Trough in the order of 1–3 km. In contrast, inversion of the North German Basin rarely re-used structures active during its subsidence. Basement inversion and uplift, in the range of 3–4 km, was focused at the Elbe Fault System which has remained quiescent in the Triassic and Jurassic but reproduced the direction of an earlier Variscan structural grain. In contrast, N-S oriented Mesozoic grabens and troughs in the central part of the North German Basin avoided significant inversion as they were oriented parallel to the direction of the inferred Late Cretaceous–Early Tertiary compression. The comparison of the North German and Polish basins shows that inversion structures can follow an earlier subsidence pattern only under a favourable orientation of the stress field. A thick Zechstein salt layer in the central parts of the North German Basin and the Mid-Polish Trough caused mechanical decoupling between the sub-salt basement and the supra-salt sedimentary cover. Resultant thin-skinned inversion was manifested by the formation of various structures developed entirely in the supra-salt Mesozoic–Cenozoic succession. The Zechstein salt provided a mechanical buffer accommodating compressional stress and responding to the inversion through salt mobilisation and redistribution. Only in parts of the NGB and MPT characterised by either thin or missing Zechstein evaporites, thick-skinned inversion directly controlled inversion-related deformations of the sedimentary cover. Inversion of the Permo-Mesozoic fill within the Mid-Polish Trough was achieved by a regional elevation above uplifted basement blocks. Conversely, in the North German Basin, horizontal stress must have been transferred into the salt cover across the basin from its SW margin towards the basins centre. This must be the case since compressional deformations are concentrated mostly above the salt and no significant inversion-related basement faults are seismically detected apart from the basin margins. This strain decoupling in the interior of the North German Basin was enhanced by the presence of the Elbe Fault System which allowed strain localization in the basin floor due to its orientation perpendicular to the inferred Late Cretaceous–Early Tertiary far-field compression.     

Study of the Cuban fractures

With the help of aerial photographs, satellite photographs and imageries, contour maps, geological and geomorphological information (personal correspondence and unpublished works), geophysical regional data, and field work, it has been possible to map a network of fractures, alignments, and faults in 26 areas (distinguishing them quantitatively and hierarchically). Links with known regional structures were also studied. Interpretation of the linear relief elements confirms the very different density, dimensions, strikes, and function of the fracturation and also, from a microtectonic perspective, explains the activity of some active faults better. It has confirmed some previous results and improved on others; for example, the Oriente fault which is the most active in Cuba with two segments (Western: Cabo Cruz—Santiago de Cuba; Eastern: Santiago de Cuba—Punta de Maisí, the Western fault being the most active); the Nortecubana fault, forming the northern limit of the Cuban megablock, and divided into three segments; and the Cauto—Nipe fault, forming the limit of the neotectonic units, presenting two segments with three seismoactive knots.     

Geological structure of the Kashevarov Trough (central Sea of Okhotsk)

This paper reports the composition and age of rocks dredged from the Kashevarov Trough (central Sea of Okhotsk) during cruise 41 of the R/V Akademik M.A. Lavrentyev in 2006. It was found that the Late Cretaceous and Eocene volcanics from the Kashevarov Trough and Okhotsk-Chukotka volcanic belt, structures of which are traceable in the Sea of Okhotsk, have similar petrographic and geochemical features. The Cenozoic sedimentary cover consists of three different-age complexes: (1) the late Oligocene (∼28.2–24.0 Ma); (2) the terminal late Oligocene-early Miocene (24.0–20.3 Ma); (3) the terminal late Pliocene-early Pleistocene (2.0–1.0 Ma). The upper Oligocene-lower Miocene sediments were deposited in relatively shallow-water settings, whereas the late Pliocene-early Pleistocene complex was formed in deeper environments, which was probably determined by tectonic processes. The geological data indicate that the Kashevarov Trough and the surrounding underwater rises represented in the Oligocene-early Miocene a single shelf zone of the Sea of Okhotsk, which is underlain by a structurally integral Mesozoic basement and is now subsided to depths of 800–1000 m.     

Arsenic and mercury contamination in 31 cores taken in 1965, St. Anna Trough, Kara Sea, Arctic Ocean

 Several cores of 31 collected in 1965 in the St. Anna Trough, Kara Sea, have very high concentrations of Hg and As in surface/near-surface samples. Mercury contents range from 94 to 3915 ppb with a mean of 444 ppb and a baseline value of 314 ppb. Arsenic contents range from 5 to 710 ppm with a mean of 51 ppm and a baseline value of 23 ppm. The Hg and part of the As loading is likely anthropogenic from industrial activities in Siberia via atmospheric emission and deposition onto catchments. This is followed by mobilization into fluvial systems and is added to by industrial effluent discharge. Post-depositional diagenesis from depth in the cores contributes to high As values. A north-flowing bottom current transports Hg- and As-bearing suspended material from the Ob River sea discharge zone to depositional environments in the St. Anna Trough. Dumping of military materials and other wastes into the Kara Sea from the late 1940s to 1991 has likely added to Hg and As loading in the trough sediments. The bioavailability of mercury from suspended materials may be the reason why higher than normal levels of these potentially toxic elements are found in European Arctic seabirds, ringed seal and polar bear. Received: 12 December 1999 · Accepted: 23 May 2000     

Lithofacies zoning and titanium-zirconium potential of the Mansi and North Sos’va areas,Transural placer region

The lithofacies and morphostructural analyses of the Mansi and North Sos’va areas of the Transural placer region allowed us to establish factors of the spatial and lithostratigraphic control of titanium-zirconium placer potential. It was established that the placers are localized in sediments of the upper stage of the Oligocene-Miocene complex and rocks of Oligocene basin shows facies zoning. The most promising are the paleolittoral and shoal facies formed under moderate hydrodynamic activity. In tectonic aspect, the position of promising areas and their lithofacies composition are controlled by flank zones of local domes that experienced epeirogenic movements. Regressive regime in the Oligocene basin suggests the highest probability for the discovery of titanium-zirconium placers of the littoral type in inner zones of neotectonic domes.     

松辽盆地中南部及其邻区新构造运动与铀成矿

松辽盆地中南部及其邻区位于滨太平洋新构造域的内蒙 东北新构造区南部。晚第三纪以来 ,本区新构造运动比较强烈 ,最显著的特征是断块大幅度升降运动和强烈的火山活动。新构造所形成的巨型盆岭构造及其它微地貌为可地浸砂岩型铀矿成矿创造了有利的地质构造和地貌条件。新构造运动在铀成矿过程中发挥了积极作用 ,也产生了一些负面影响。松辽盆地东部和南部的盆缘区新构造发育 ,控矿明显 ,是寻找可地浸砂岩型铀矿的有利地段     

甘肃北山南部活动断裂的发现及其区域构造意义

在河西走廊北侧、 北山南缘新发现属于不同断裂系统的两条晚第四纪活动断裂,分别称之为旧井-板滩断裂和俄博庙断裂.其中,旧井-板滩断裂长约28 km,距玉门市约55 km,由4条分支断裂组成,呈复杂的"Y"字形分布.总体走向北东40°～50°,倾向北西,倾角60°～70°,控制了西侧两个晚新生代盆地的发育.俄博庙断裂长约1...     

吐哈盆地西南缘新构造控矿规律及十红滩铀矿床外围成矿有利区预测

本根据吐哈盆地西南缘新构造运动的表现特征,结合已知铀矿床、矿点的空间分布,认为该区新构造控矿规律主要体现在3个方面：(1)由新构造复活基底断裂形成的“断裂挠曲”控矿;(2)新构造褶皱形成的“坡中坡”转折区域控矿;(3)新断裂构造形成的地下水局部排泄源也参与了对铀矿化的控制作用。依据这些规律,笔预测十红滩北带之北带仍有成矿远景,并认为白咀山西侧及迪哈尔511线附近区域具有一定的成矿潜力。     

Microearthquakes and faulting in the southern Okinawa Trough

Southern Okinawa Trough represents an early stage of back-arc rifting and is characterized by normal faulting and microearthquakes. Earthquake distribution and deep structure of fault was investigated to clarify active rifting in the southern Okinawa Trough, where two parallel grabens are located. A network of ocean bottom seismometers (OBSs) that displayed the hypocenters of 105 earthquakes were observed for a period of 4 days in southern-graben (SG). Most of the microearthquakes occurred in a cluster about 7 km wide, which on a cross-section striking N45°E dips 48° to the southwest. Relocated hypocenters, which are recorded by a local seismic network, show scattered distribution around the southern-graben. There are no remarkable surface faults in the southern-graben. On the other hand, the recalculation of hypocenter locations of 1996 earthquakes swarm recorded by a local seismic network suggests that the swarm is associated with normal faulting on the southern side of northern-graben (NG). Thus, the undeveloped southern-graben is located to the south of the developed northern-graben. Southward migration of rifting, which may be caused by migration of volcanism, could thus be occurring in the southern Okinawa Trough. The extension rate computed for the southern Okinawa Trough from the fault model of the northern-graben is 4.6 cm/year, which is 59–102% of the extension rate (GPS measurements). This result indicates that the majority of extensional deformation is concentrated within the center of the northern-graben in the Okinawa Trough.