阿尔金断裂带对青藏高原北部生长、隆升的制约

大量的同位素年代学证据表明(古)阿尔金断裂带可能形成于三叠纪,后又经历了侏罗纪、白垩纪的强烈左旋走滑活动,自印度板块与欧亚大陆碰撞后阿尔金断裂再次活动。主要的走滑活动发生在:(1)245~220Ma;(2)180~140Ma;(3)120~100Ma;(4)90~80Ma;(5)60~45Ma;(6)渐新世至中新世;(7)上新世至更新世以及(8)全新世。沿阿尔金断裂带,伴随左旋走滑活动形成一系列的逆冲断裂和正断裂,反映走滑过程中伴随隆升作用的存在,并且形成自北向南包括祁连山、大雪山、党河南山、柴北缘山、祁漫塔格山和昆仑山,表明阿尔金断裂带制约着青藏高原北部的生长和隆升。阿尔金断裂带东、西两端的白垩纪和新生代火山活动是断裂走滑活动的响应。     

Defining geologic Hazards for natural resources management using tree-ring analysis

Landslides, avalanches, floods, and other geologic hazards impair natural resources management by jeopardizing public safety, damaging or restricting resource utilization, and necessitating expenditures for corrective measures The negative impact of geologic hazard events can be reduced by tailoring resources management to hazard potential of an area This requires assessment of where and how frequently the events occur National forests and other managed wildlands often lack monitoring or historical records to compute frequency of hazard occurrence Tree-ring analysis, based on internal growth response to external events such as tilting and abrasion, can provide frequency data Two examples of the use of tree-ring analysis to date landslide activity illustrate advantages and limitations of the technique An example from the Fishlake National Forest in central Utah illustrates assessment for planning purposes An example from the Sierra National Forest in east-central California shows assessment applied to project design Many geologic hazards in addition to landslides are suited to tree-ring analysis to establish frequency of occurrence Hazard reduction efforts in natural resources management could be enhanced by careful application of tree-ring analysis     

Lead orthophosphates—III. Stabilities of fluoropyromorphite and bromopyromorphite at 25°C

The reactions of secondary lead orthophosphate with approximately 10^?1 M sodium fluoride and sodium bromide solutions have been investigated at 25°C. Interpretation of the solubility data resulted in solubility product constants for fluoropyromorphite and bromopyromorphite of 10^?71.6 and 10^?78.1, respectively. According to these constants, the stability sequence for lead pyromorphites is Pb₅(PO₄)₃Cl > Pb₅(PO₄)₃Br > Pb₅(PO₄)₃OH > Pb₅(PO₄)₃F. The derived free energy data have been used to evaluate the respective stabilities of fluoro-pyromorphite and bromopyromorphite within the systems PbF₂-PbO-P₂O₅-H₂O and PbBr₂-PbO-P₂O₅-H₂O and to predict the equilibrium behavior of the Pb₅(PO₄)₃F-Pb₅(PO₄)₃OH solid solution under aqueous conditions.     

Cloud height differences on Saturn

Spectrophotometry from 0.6–2.5 μm at 1.5% spectral resolution of Saturn's equator and visibly dark South Equatorial Belt near a 1980 ring-plane crossing shows substantially less absorption by methane over the equator than over the SEB. Model fits using Appleby's model atmosphere and a multiple scattering model lead to the conclusion that the pressure levels of the clouds in the two regions differ by 20%. The region of high clouds is coincident with the location of the equatorial fast jet observed by Voyager.     

西昆仑山前冲断带晚新生代构造地貌特征

在卫片解译、DEM数据处理、地形图分析与剖面制作的基础上,结合野外构造地貌考察与观测,对西昆仑山前冲断带的构造地貌特征进行了定量、半定量的研究。沿山前发育系统的水系变化、冲积扇变化、不对称背斜、大规模正断裂、不对称河流阶地等典型的构造地貌,表明这条由南向北逆冲的冲断带在扩展过程中存在着由西向东迁移的特征。冲断带的东西分段以桑株河为界,以西发育固满背斜,其构造样式为向北的逆冲伴随向南的反冲;以东发育一系列不对称的背斜,表现出明显的由南向北逆冲的特征,地表无明显的反冲构造出现。利用生长地层和河流阶地估算了西昆仑山的隆升速率:晚上新世—早更新世以来的最低隆升速率为0.21～0.25mm/a,100ka以来的隆升速率为1.5mm/a。     

Regional landslide evaluation: Two Utah examples

Landslide-susceptibility evaluations based on bedrock units, slope inclination, and aspect (slope orientation) incorporate the lithologic, stratigraphic, structural, and topographic passive conditions contributing to landsliding as outlined by Sharpe (1938). Generalized results based on passive condition analyses may define potential for failure over entire states or large parts of states, establishing an approximate landslide susceptibility for specific areas that are still in need of detailed study. This provides a preliminary susceptibility for use in land management and identifies high-priority areas for future detailed investigations. Landslides in the Bear River Range, north-central Utah, and the northern Wasatch Plateau, central Utah, illustrate application of these factors to regional landslide-susceptability evaluation. The greatest landslide potential exists on slopes of between 10 and 40%, with a westerly aspect, underlain by Wasatch or Salt Lake formations in the Bear River Range and on slopes of from 20 to 60% that are underlain by either North Horn or Price River formations in the northern Wasatch Plateau. Results from the two study areas are compared to a statewide landslide evaluation (Schroder 1971) in terms of passive conditions. Lithologic and stratigraphic conditions of the state and of the two study areas are nearly identical. Aspect data detect the presence or absence of structural conditions favoring failure in the two study areas rather than climatic factors as concluded in the statewide analysis. Topographic condition is more precisely stated in quantitative as opposed to qualitative terms to define failure-prone slopes in the two study areas.     

The occurrence of fungi on some rooted aquatics from the Chesapeake Bay

During 1975 and 1976, 433 isolates, representing 37 genera of fungi, were collected fromPotamogeton perfoliatus andRuppia maritima in the Chesapeake Bay. Seasonal distribution patterns of selected species are presented and their possible relationships to the declining host plant populations are discussed.     

THE PALEOSEISMIC SURFACE RUPTURE AT SOUTH OF CENTRAL ALTYN TAGH FAULT AND ITS TECTONIC IMPLICATION

In this study, we described a 14km-long paleoearthquakes surface rupture across the salt flats of western Qaidam Basin, 10km south of the Xorkol segment of the central Altyn Tagh Fault, with satellite images interpretation and field investigation methods. The surface rupture strikes on average about N80°E sub-parallel to the main Altyn Tagh Fault, but is composed of several stepping segments with markedly different strike ranging from 68°N~87°E. The surface rupture is marked by pressure ridges, sub-fault strands, tension-gashes, pull-apart and faulted basins, likely caused by left-lateral strike-slip faulting. More than 30 pressure ridges can be distinguished with various rectangular, elliptical or elongated shapes. Most long axis of the ridges are oblique(90°N~140°E)to, but a few are nearly parallel to the surface rupture strike. The ridge sizes vary also, with heights from 1 to 15m, widths from several to 60m, and lengths from 10 to 100m. The overall size of these pressure ridges is similar to those found along the Altyn Tagh Fault, for instance, south of Pingding Shan or across Xorkol. Right-stepping 0.5~1m-deep gashes or sub-faults, with lengths from a few meters to several hundred meters, are distributed obliquely between ridges at an angle reaching 30°. The sub-faults are characterized with SE or NW facing 0.5~1m-high scarps. Several pull-apart and faulted basins are bounded by faults along the eastern part of the surface rupture. One large pull-apart basins are 6~7m deep and 400m wide. A faulted basin, 80m wide, 500m long and 3m deep, is bounded by 2 left-stepping left-lateral faults and 4 right-stepping normal faults. Two to three m-wide gashes are often seen on pressure ridges, and some ridges are left-laterally faulted and cut into several parts, probably owing to the occurrence of repetitive earthquakes. The OSL dating indicates that the most recent rupture might occur during Holocene.
Southwestwards the rupture trace disappears a few hundred meters north of a south dipping thrust scarp bounding uplifted and folded Plio-Quaternary sediments to the south. Thrust scarps can be followed southwestward for another 12km and suggest a connection with the south Pingding Shan Fault, a left-lateral splay of the main Altyn Tagh Fault. To the northeast the rupture trace progressively veers to the east and is seen cross-cutting the bajada south of Datonggou Nanshan and merging with active thrusts clearly outlined by south facing cumulative scarps across the fans. The geometry of this strike-slip fault trace and the clear young seismic geomorphology typifies the present and tectonically active link between left-lateral strike-slip faulting and thrusting along the eastern termination of the Altyn Tagh Fault, a process responsible for the growth of the Tibetan plateau at its northeastern margin. The discrete relation between thrusting and strike-slip faulting suggests discontinuous transfer of strain from strike-slip faulting to thrusting and thus stepwise northeastward slip-rate decrease along the Altyn Tagh Fault after each strike-slip/thrust junction.