East African topography and volcanism explained by a single,migrating plume

Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle plumes.Several models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east Africa.We devise paleogeographically constrained global models of mantle convection and,based on the evolution of flow in the deepest lower mantle,show that the Afar plume migrated southward throughout its lifetime.The models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system(EARS),which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone,over the last≈45 Myr.We further show that the age-progression of volcanism associated with the southward propagation of EARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African plate.The models suggest that the Afar plume became weaker as it migrated southwards,consistent with trends observed in the geochemical record.     

渤海地球物理场与深部潜在地幔热柱的异常构造背景

渤海是中国东部陆缘的一个裂谷型盆地，通过重力、航磁、古地磁、天然地震、地热、应力场、地壳与上地幔结构及地震层析成像等资料，对渤海湾及其周边地带的深部结构、地球物理场效应和深层物理过程进行了综合研究．这一盆地是由NNE－NE向、近EW向和NW向3组断裂组成，这3组断裂与3组地幔隆起带基本相对应，并在渤中坳陷交汇、渤海内部的现代构造运动以水平构造应力场作用下的走滑运动为主要特征，渤海区内地壳厚度仅28-29km，上地幔向上隆起，等温居里面埋深浅（为12km），并为较高区热流值区（56-77mW／m2）．该区岩石层厚度变化显著，庙岛西部中地壳中有一近似圆形的低速体，在120km深度仍为低速异常区．深大断裂可为深部热物质与气态物质上涌的通道．通过综合研究，提出渤海湾很可能是一个潜在的、尚在发展中的地幔热柱．     

Accurately measuring volcanic plume velocity with multiple UV spectrometers

A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the time varying structure of SO₂ concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s⁻¹. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements. Editorial responsibility: A. Woods     

Estimation of ecologically significant circulation features of the Columbia River estuary and plume using a reduced-dimension Kalman filter

A data assimilation method was used to estimate the variability of three ecologically significant features of the Columbia River estuary and plume: the size of the plume, the orientation of the plume, and the length of the salinity intrusion in the estuary. Our data assimilation method was based on a reduced-dimension Kalman filter that enables fast data assimilation of nonlinear dynamics in the estuary and plume. The assimilated data included measurements of salinity, temperature, and water levels at 13 stations in the estuary and at five moorings in the plume.     

黄河口羽状流对调水调沙的响应

本文基于2010年MODIS卫星遥感数据,研究了黄河口海域海表温度(SST)的季节性变化,分析了调水调沙期间黄河口羽状流向海扩展的时空变化,揭示了黄河口羽状流对调水调沙的响应。研究结果表明:海表温度主要受太阳辐射和临近大陆气候的影响,夏季秋季高,春季冬季低,四个季节羽状流扩散范围都较小。调水调沙期间,羽状流向海传输方向发生摆动,由北向逐渐向东偏转至正东方向,最后又转为北向。随着径流量的增加,羽状流扩散范围和传输距离也迅速增大,传输距离与径流量呈较好的对数线性关系。此外,潮汐变化也会影响羽状流的传输方向和输运距离。     

Circulation induced by subglacial discharge in glacial fjords: Results from idealized numerical simulations

The flow caused by the discharge of freshwater underneath a glacier into an idealized fjord is simulated with a 2D non-hydrostatic model. As the freshwater leaves horizontally the subglacial opening into a fjord of uniformly denser water it spreads along the bottom as a jet, until buoyancy forces it to rise. During the initial rising phase, the plume meanders into complex flow patterns while mixing with the surrounding fluid until it reaches the surface and then spreads horizontally as a surface seaward flowing plume of brackish water. The process induces an estuarine-like circulation. Once steady-state is reached, the flow consists of an almost undiluted buoyant plume rising straight along the face of the glacier that turns into a horizontal surface layer thickening as it flows seaward. Over the range of parameters examined, the estuarine circulation is dynamically unstable with gradient Richardson number at the sheared interface having values of <1/4. The surface velocity and dilution factors are strongly and non-linearly related to the Froude number. It is the buoyancy flux that primarily controls the resulting circulation with the momentum flux playing a secondary role.     

Long wavelength gravity anomalies over India: Crustal and lithospheric structures and its flexure

Long wavelength gravity anomalies over India were obtained from terrestrial gravity data through two independent methods: (i) wavelength filtering and (ii) removing crustal effects. The gravity fields due to the lithospheric mantle obtained from two methods were quite comparable. The long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere–asthenosphere boundary (LAB) and the Moho with appropriate densities, that are constrained from seismic results at certain points. Modeling of the long wavelength gravity anomaly along a N–S profile (77°E) suggest that the thickness of the lithosphere for a density contrast of 0.05 g/cm³ with the asthenosphere is maximum of ∼190 km along the Himalayan front that reduces to ∼155 km under the southern part of the Ganga and the Vindhyan basins increasing to ∼175 km south of the Satpura Mobile belt, reducing to ∼155–140 km under the Eastern Dharwar craton (EDC) and from there consistently decreasing south wards to ∼120 km under the southernmost part of India, known as Southern Granulite Terrain (SGT).The crustal model clearly shows three distinct terrains of different bulk densities, and thicknesses, north of the SMB under the Ganga and the Vindhyan basins, and south of it the Eastern Dharwar Craton (EDC) and the Southern Granulite Terrain (SGT) of bulk densities 2.87, 2.90 and 2.96 g/cm³, respectively. It is confirmed from the exposed rock types as the SGT is composed of high bulk density lower crustal rocks and mafic/ultramafic intrusives while the EDC represent typical granite/gneisses rocks and the basement under the Vindhyan and Ganga basins towards the north are composed of Bundelkhand granite massif of the lower density. The crustal thickness along this profile varies from ∼37–38 km under the EDC, increasing to ∼40–45 km under the SGT and ∼40–42 km under the northern part of the Ganga basin with a bulge up to ∼36 km under its southern part. Reduced lithospheric and crustal thicknesses under the Vindhyan and the Ganga basins are attributed to the lithospheric flexure of the Indian plate due to Himalaya. Crustal bulge due to lithospheric flexure is well reflected in isostatic Moho based on flexural model of average effective elastic thickness of ∼40 km. Lithospheric flexure causes high heat flow that is aided by large crustal scale fault system of mobile belts and their extensions northwards in this section, which may be responsible for lower crustal bulk density in the northern part. A low density and high thermal regime in north India north of the SMB compared to south India, however does not conform to the high S-wave velocity in the northern part and thus it is attributed to changes in composition between the northern and the southern parts indicating a reworked lithosphere. Some of the long wavelength gravity anomalies along the east and the west coasts of India are attributed to the intrusives that caused the breakup of India from Antarctica, and Africa, Madagascar and Seychelles along the east and the west coasts of India, respectively.     

一次飞机播撒吸湿性焰剂试验的微物理探测浅析

2011年夏季,北京市人工影响天气办公室组织了吸湿性焰剂的飞机播撒试验,选取八达岭长城西北的淡积云作为催化对象.试验期间,使用装备了云探测设备的运12飞机进行播撒及云微物理探测.在6月1日的试验中,运用差异化策略分别对不同的淡积云实施了催化,探测发现云中出现了符合暖云增雨概念模型的微物理反应.随后在晴空区实施了烟羽探测试验,通过在吸湿性焰剂烟羽区的穿刺飞行,获得了正在扩散的吸湿性焰剂的粒子谱,了解了播撒后扩散区的微物理特征.     

Nature of mantle source contributions and crystal differentiation in the petrogenesis of the 1.78 Ga mafic dykes in the central North China craton

Circa 1.78 Ga mafic dyke swarms and some coeval volcanic associations constitute a Large Igneous Province in the central North China craton. The 1st generation of dykes intruded at ca. 1780 Ma and is chemically delineated into 3 groups: the LT Group is gabbroic and has low-Fe–Ti contents, acting as parental magma; the NW Group is high in Fe–Ti-contents and doleritic with an iron-enriched trend; whereas the EW Group is doleritic to andesitic and crystallized from relict siliceous liquids with a silica-enriched trend. They have an EM-I type source and record integral magmatic processes. These include contamination of lithospheric material and assimilation of crustal melts with in-situ crystallization in a magma chamber (the LT Group) and fractional crystallization in magma channels (the NW Group) and even with additional alteration (the EW Group). The 2nd generation is slightly younger (ca. 1760 Ma) and scarcely distributed. It has high-Fe–Ti contents, originated from a mixing source of DM and EM-I types. The dykes could be associated with a palaeo-plume: the 1st generation represents lower mantle melts generated from the plume head, whereas the 2nd generation records extra melts from asthenosphere entrained by the plume tail.