Late- to post-orogenic exhumation of the Central Pyrenees revealed through combined thermochronological data and modelling

Apatite (U–Th)/He and fission track thermochronometry have been combined with 3D thermal modelling to constrain the late- to post-orogenic exhumation history of the Central Pyrenees, Spain. Data from four massifs immediately north and south of the present drainage divide of the mountain belt reveal a diachroneity in the transition from syn- to post-orogenic forcing of exhumation. Immediately south of the drainage divide, rapid exhumation of ∼1.5 mm year⁻¹ decelerated after ∼30 Ma to ∼0.03 mm year⁻¹. A similar transition occurred immediately north of the drainage divide at the same time. Further south, in the core of the Axial Zone antiformal stack of the Pyrenees, rapid (∼1 mm year⁻¹), syn-orogenic exhumation continued to ∼20 Ma, but slowed to ∼0.1–0.2 mm year⁻¹ soon after that time. This order of magnitude decrease in exhumation rates across the orogen records the diachronous transition into a post-orogenic state for the mountain belt. These data do not record rejuvenation of exhumation in Late Miocene or Pliocene times driven either by large-scale base-level change or an evolution to more erosive climatic conditions.     

Models of crustal flow in the India–Asia collision zone

Surface velocities in parts of the India–Asia collision zone are compared to velocities calculated from equations describing fluid flow driven by topographically produced pressure gradients. A good agreement is found if the viscosity of the crust is ∼10²⁰ Pa s in southern Tibet and ∼10²² Pa s in the area between the Eastern Syntaxis and the Szechwan Basin. The lower boundary condition of the flow changes between these two areas, with a stress-free lower boundary in the area between the Szechwan basin and the Eastern Syntaxis, and a horizontally rigid but vertically deformable boundary where strong Indian lithospheric material underlies southern Tibet. Deformation maps for olivine, diopside and anorthite show our findings to be consistent with laboratory measurements of the rheology of minerals. Gravitationally driven flow is also suggested to be taking place in the Indo–Burman Ranges, with a viscosity of ∼10¹⁹–10²⁰ Pa s. Flow in both southern Tibet and the Indo–Burman Ranges provides an explanation for the formation of the geometry of the Eastern Himalayan Syntaxis. The majority of the normal faulting earthquakes in the Tibetan Plateau occur in the area of southern Tibet which we model as gravitationally spreading over the Indian shield.     

The evolution of sedimentary basins on a viscoelastic lithosphere: theory and examples

Summary. A systematic approach is suggested for modelling the development of sedimentary basins. The theory, which partitions basin formation into initiating and isostatic adjustment processes, is applicable to all modes of basin formation if these processes are linear, or can he represented with sufficient accuracy in an incrementally linear form.
The dynamics of regional isostatic adjustment are characterized by the Heaviside space-time Green functions for the response of elastic and viscoelastic (Maxwell) thin plate models of the lithosphere. It is shown, by convolving the Heaviside—Green functions with cylindrical surface loads, that the rate of isostatic adjustment on a viscoelastic lithosphere is a function of the wavelength of the surface load, long wavelengths being compensated most rapidly.
Six archetypal initiating processes for sedimentary basin development are presented. These processes are those responsible for the subsidence of the Earth's surface which creates a depression in which water and sediments collect. Isostatic amplification of subsidence by sediment and water loads is cast in the form of an integral equation with isostatic Heaviside—Green functions as kernel.
Specific examples, the basins that result from a graben initiating process, are compared with the largest scale structure of the North Sea Basin, a basin that is known to be underlain by a graben system. A model, in which a 50-km wide graben subsides exponentially with a time constant of 5 × 10⁷yr during the interval 180–100 Myr bp , is shown to be consistent with the largest scale structure of the North Sea Basin if the underlying lithosphere is viscoelastic with a flexural rigidity of ∼5 × 10²⁵ Nm and relaxation time constant ∼ 10⁶ yr.     

Sediment transport to the Laptev Sea–hydrology and geochemistry of the Lena River

This study focuses on the fluvial sediment input to the Laptev Sea and concentrates on the hydrology of the Lena basin and the geochemistry of the suspended particulate material. The paper presents data on annual water discharge, sediment transport and seasonal variations of sediment transport. The data are based on daily measurements of hydrometeorological stations and additional analyses of the SPM concentrations carried out during expeditions from 1975 to 1981. Samples of the SPM collected during an expedition in 1994 were analysed for major, trace, and rare earth elements by ICP-OES and ICP-MS. Approximately 700 km³ freshwater and 27 times 10⁶ tons of sediment per year are supplied to the Laptev Sea by Siberian rivers, mainly by the Lena River. Due to the climatic situation of the drainage area, almost the entire material is transported between June and September. However, only a minor part of the sediments transported by the Lena River enters the Laptev Sea shelf through the main channels of the delta, while the rest is dispersed within the network of the Lena Delta. Because the Lena River drains a large basin of 2.5 times 10⁶ km², the chemical composition of the SPM shows a very uniform composition. In contrast, smaller rivers with more restricted catchment areas exhibit significant differences.     

Interplay between lithospheric flexure and river transport in foreland basins

ABSTRACT Foreland basins form by lithospheric flexure under orogenic loading and are filled by surface transport of sediment. This work readdresses the interplay between these processes by integrating in a 3D numerical model: the mechanisms of thrust stacking, elastic flexural subsidence and sediment transport along the drainage network. The experiments show that both crustal tectonic deformation and vertical movements related to lithospheric flexure control and organise the basin-scale drainage pattern, competing with the nonlinear, unpredictable intrinsic nature of river network evolution. Drainage pattern characteristics are predicted that match those observed in many foreland basins, such as the axial drainage, the distal location of the main river within the basin, and the formation of large, long-lasting lacustrine systems. In areas where the river network is not well developed before the formation of the basin, these lithospheric flexural effects on drainage patterns may be enhanced by the role of the forebulge uplift as drainage divide. Inversely, fluvial transport modifies the flexural vertical movements differently than simpler transport models (e.g. diffusion): Rivers can drive erosion products far from a filled basin, amplifying the erosional rebound of both orogen and basin. The evolution of the sediment budget between orogen and basin is strongly dependent on this coupling between flexure and fluvial transport: Maximum sediment accumulations on the foreland are predicted for a narrow range of lithospheric elastic thickness between 15 and 40 km, coinciding with the T _e values most commonly reported for foreland basins.     

Seismic moment release during slab rupture beneath the Banda Sea

The highest intermediate depth moment release rates in Indonesia occur in the slab beneath the largely submerged segment of the Banda arc in the Banda Sea to the east of Roma, termed the Damar Zone. The most active, western-part of this zone is characterized by downdip extension, with moment release rates (∼10¹⁸ Nm yr^–1 per 50 km strike length) implying the slab is stretching at ∼10⁻¹⁴ s⁻¹ consistent with near complete slab decoupling across the 100–200 km depth range. Differential vertical stretching along the length of the Damar Zone is consistent with a slab rupture front at ∼100–200 km depth beneath Roma propagating eastwards at ∼100 km Myr^–1. Complexities in the slab deformation field are revealed by a narrow zone of anomalous in-plane P -axis trends beneath Damar, where subhorizontal constriction suggests extreme stress concentrations ∼100 km ahead of the slab rupture front. Such stress concentrations may explain the anomalously deep ocean gateways in this region, in which case ongoing slab rupture may have played a key role in modulating the Indonesian throughflow in the Banda Sea over the last few million years.     

黄河中游流域地貌形态对流域产沙量的影响

在黄河中游地区 ,选择了 5 0多个面积约 5 0 0～ 2 5 0 0平方公里的水文测站流域 ,分别代表 6种不同自然地理类型 ,在流域沟壑密度、沟间地坡度小于 15°面积百分比等地貌形态指标量计的基础上 ,进行了流域产沙量与地貌形态指标相关分析。结果表明 ,对于不同类型流域 ,流域产沙量随流域地貌的变化遵循不同的响应规律 ,而且视流域其它下垫面环境条件的均一程度 ,其相关程度和响应速率各不相同。受地面物质、植被、地貌发育阶段等流域其它下垫面环境条件的制约 ,除沟壑密度外 ,流域产沙量与流域地貌形态的关系都没有人们以前所预期的好。     

The Climate and Hydrology of the Upper Blue Nile River

The Upper Blue Nile river basin is the largest in Ethiopia in terms of volume of discharge, second largest in terms of area, and contributes over 50 per cent of the long-term river flow of the Main Nile. This paper provides a review of the nature and variability of the climate and hydrology in the source region of the Blue Nile-the central Ethiopian Highlands. Annual rainfall over the basin decreases from the south-west (>2000 mm) to the north-east (around 1000 mm), with about 70 per cent occurring between June and September. A basin-wide time series of annual rainfall constructed from 11 gauges for the period 1900 to 1998 has a mean of 1421millimetres, minimum in 1913 (1148 mm) and maximum in 1903 (1757 mm). Rainfall over the basin showed a marked decrease between the mid-1960s and the late 1980s and dry years show a degree of association with low values of the Southern Oscillation Index (Sol). The October to February dry season in 1997/98 was the wettest on record and responsible for widespread flooding across Ethiopia and also parts of Somalia and Kenya. Available river flow records, which are sparse and of limited duration, are presented for the Blue Nile and its tributaries upstream of the border with Sudan. Runoff over the basin amounts to 45.9 cubic kilometres (equivalent to 1456 m₃s₋₁) discharge, or 261 millimetre depth (1961–1990), a runoff ratio of 18 per cent. Between 1900 and 1997 annual river flow has ranged from 20.6 cubic kilometres (1913) to 79.0 cubic kilometres (1909), and the lowest decade-mean flow was 37.9 cubic kilometres from 1978 to 1987. Annual river flow, like rainfall, shows a strong association with the SOI     

近50a来黑河流域水文及生态环境的变化

利用详实资料,对比分析了40年代以来不同时期黑河流域水文及生态环境的变化特征,并对不同时期流域水土资源开发利用规模及出山径流的变化进行对比分析,结果说明:本世纪40年代以来,流域中游地区地表水利用量增加了19倍,灌溉绿洲扩大了89.5%,使流域33条支流相继断流,干流下游水量减少了51%,终端湖泊干涸,水质恶化,土地盐碱化和沙漠化在全流域发展,沙漠化土地面积自1949年以来增加了4%~11%。人类对流域水土资源的大规模开发利用是产生这些变化的主要因素。     

Widespread syn-sedimentary deformation on a muddy deep-water basin-floor: the Vischkuil Formation (Permian), Karoo Basin, South Africa

The ∼380-m-thick mudstone–siltstone-dominated Vischkuil Formation represents the initiation phase of a 1.3-km-thick prograding basin floor to slope to shelf succession that marks a significant increase in the rate of siliciclastic sediment supply to the early Karoo Basin in the Permian. In the upper Vischkuil Formation three well exposed, widespread (∼3000 km²) 10–70-m-thick intervals of deformed strata are encased within undeformed sediments. Such chaotic mass movement deposits that are mappable over areas comparable with seismic-scale mass transport deposits are commonly associated with submarine slope settings. However, the surrounding lithofacies and the correlation of distinctive marker beds indicate that these deformation intervals developed in a distal low gradient basin floor setting. The deformed intervals comprise a lower division of tight down-flow verging folds dissected by thrust planes that sole out onto a highly sheared décollement surface that are interpreted as slides. The lower divisions are overlain by an upper division of chaotic lithofacies with large contorted clasts of sandstone supported by a fine-grained matrix interpreted as a debrite. The juxtaposition of these lithofacies, the distribution of thickness of the divisions, and their close kinematic relationships indicate that the emplacement of the debris-flows triggered and drove the underlying slide, in a low-gradient distal setting. Individual beds in the deformed intervals can be mapped laterally into undeformed strata indicating limited movement of the slide. Therefore, widespread zones of syn-sedimentary deformation in deep-water settings do not necessarily indicate a slope setting and should not be used as single criterion to determine depositional setting. When associated with major debrites they may be developed on a flat basin floor.     

Physiographically Controlled Allometry of Specific Sediment Yield in the Canadian Cordillera: A Lake Sediment-based Approach

It is generally supposed that specific sediment yield declines as the drainage basin area increases, as part of the mobilized sediment becomes trapped in the downstream cascade of storage zones. In British Columbia, using fluvial suspended sediment load data, Church and Slaymaker (Nature 1989, Vol 337, pp. 452–454) have observed a pattern of increasing specific sediment yield at all spatial scales up to 3×10⁴km². This trend has been attributed to the dominance of secondary remobilization of Quaternary sediments over primary denudation of the land surface. Using a larger data set of lake sediment-based estimates of long-term sediment yield, sub-regional patterns of specific yield have been investigated for the Canadian Cordillera. Between spatial scales of 0.9 and 190 km² sediment yield trends are differentiated by physiography, as indicated by the variable allometry observed in the specific sediment yield–drainage basin area relations. Highest sediment yields were observed in the Coast Mountains where specific sediment yields conform to the regional pattern described by Church and Slaymaker. However, in flat-lying plateau and major valley areas specific sediment yield decreases with increasing drainage area, thus conforming to the conventional model of sediment delivery. In several other sub-regions of intermediate relief there were no significant relations between specific yield and drainage area. These results suggest that no single model of sediment yield is adequate to describe sediment transfer processes in the Canadian Cordillera at the sub-regional scale.     

Stability of output fluxes of large rivers in South and East Asia during the last 2 million years: implications on floodplain processes

We compare the present-day sediment discharge (solid phase) of some of the largest rivers in Asia to the average discharge deduced from the mass accumulated in several sedimentary basins during the Quaternary. There is a very good correlation, especially for the largest rivers: the Ganges–Brahmaputra, the Changjiang, the Huanghe and, to a lesser extent, the Indus and the Zhujiang. This suggests that present-day average discharge at the outlet has remained constant throughout the Quaternary at least for very large rivers (drainage area of the order of 10⁵–10⁶ km²). This, in turn, suggests either that continental denudation of large Asian catchments has remained on average constant, implying a strong tectonic control on erosion during the Quaternary, or that the river network has the ability to buffer changes in hillslope erosion or in sea-level in order to conserve the total discharge at the outlet. We show how this buffering capacity relies on the characteristic reaction time-scale of Asian alluvial plains (of the order of 10^5–6 years), that is, much higher than the time-scales of the Quaternary climate oscillations (of the order of 10⁴ years). A short-term perturbation originating in hillslopes will be diluted by the floodplain. At the outlet the signal should have a longer time span and a smaller amplitude. In the same manner, an alluvial plain should not instantaneously react to a 10⁴-year sea-level drop because of its inertia. Along with long-term tectonic control we infer this buffering to be the main cause for the average constancy of sediment yield of large Asian rivers during the Quaternary.     

Land subsidence pattern controlled by old alpine basement faults in the Kashmar Valley, northeast Iran: results from InSAR and levelling

Fluid storage systems, such as oil, gas, magma or water reservoirs, are often controlled by the host rock structure and faulted terrain. In sedimentary basins, where no direct information about underlying structure is available, the pattern of ground deformation may allow us to assess the buried fault arrangement. We provide an example in the semi-arid area of Iran, in the Kashmar Valley, a region subject to land subsidence due to water overexploitation. Geodetically determined subsidence rates in the Kashmar Valley exceed 15–30 cm yr⁻¹. The pattern of surface deformation is strongly non-uniform and displays NE–SW elongated bowls of subsidence. The trend resembles old Cretaceous-to-Tertiary faults that evolved during early alpine tectonic deformation. Although these early alpine structures are considered tectonically inactive in the present day, the observed land subsidence pattern indicates significant structural control on the geometry of the aquifer basin and its deformation during reservoir drainage.     

A Pliocene–Quaternary compressional basin in the Interandean Depression, Central Ecuador

The segment of the Interandean Depression of Ecuador between Ambato and Quito is characterized by an uppermost Pliocene–Quaternary basin, which is located between two N-S trending reverse basement faults: the Victoria Fault to the west, and the Pisayambo Fault to the east. The clear evidence of E-W shortening for the early Pleistocene (between 1.85 and 1.21 Ma) favours a compressional basin interpretation. The morphology (river deviations, landslides, folded and flexure structures) demonstrates continuous shortening during the late Quaternary. The late Pliocene-Quaternary shortening reached 3400 ± 600 m with a rate of 1.4 ± 0.3 mm yr⁻¹. The E-W shortening is kinematically consistent with the current right-lateral reverse motion along the NE-SW trending Pallatanga Fault. The Quito-Ambato zone appears to act as a N-S restraining bend in a system of large right-lateral strike-slip faults. The compressive deformation which affects the Interandean Depression during the Pliocene is apparently coeval to the beginning subduction of very young oceanic lithosphere north of the Gulf of Guayaquil. The relatively buoyant new crust may have significantly increased the mechanical coupling in the subduction zone from Pliocene to Present.     

Regional variations of heat flow differences with depth in Alberta, Canada

Summary. Differences between estimated average heat flow values for the Mesozoic and Cenozoic formations ( Q ₁) and estimated average heat flow values for the Palaeozoic formations below the erosional unconformity ( Q ₂) are calculated for the Alberta part of the western Canadian sedimentary basin. Significant heat flow differences exist for these two intervals and the map of Δ Q = Q ₁– Q ₂ shows that Q ₂ is generally greater than Q ₁ in the western and south-western part of Alberta, while in the northern part of the province Q ₂ is generally less than Q ₁. The regional variations of Δ Q are large, with standard deviation of 26 mW m⁻² and average value –13.5 mW m⁻². A regional trend of Δ Q correlates with topographic relief and the hydraulic head variations in the basin. It is shown that there is a heat flow increase with depth in water recharge areas and a decrease in heat flow with depth in the low topographic elevation water discharge areas when comparing the average heat flow in Mesozoic + Cenozoic and Palaeozoic formations.     

40Ar-39Ar incremental heating studies on the Tudor Gabbro, Grenville Province, Ontario: its bearing on the North American apparent polar wander path in late Proterozoic times

Summary. ⁴⁰Ar-³⁹Ar incremental heating studies have been carried out on samples taken from the Tudor Gabbro, Grenville Province, Ontario. In an earlier K-Ar study, these rocks have yielded an isochron age of ∼700 Ma together with very high initial argon ratios. Age spectrum plots on whole-rock samples, in general, display a saddle-shaped character, with two of them exhibiting minima close to 700 Ma. No clear plateaus are observed for these rocks. A hornblende separate records the time ∼1110 Ma at which the stock finally cooled through the ∼590°C isotherm. The Tudor Gabbro was probably intruded into an area undergoing middle-amphibolite facies meta-morphism about 1180 Ma ago. The age spectra of two whole-rock samples together with that of their plagioclase separates, suggest that the stock cooled to ∼200–250°C at about 720 Ma. Slow cooling, averaging about 1°C Ma⁻¹ is indicated for this section of the Grenville Province for the period 1100–700 Ma. If the age of the Tudor Gabbro's palaeomagnetic pole position is taken to be 720 Ma, the Hadrynian Track Hypothesis leads to very high polar wander rates of > 20cm a⁻¹ for the period 820–720 Ma. If this hypothesis is rejected, the average drift rate for this period would be ∼4 cm a⁻¹, in much better agreement with published values of ∼5 cm a⁻¹ for the period 1400–820 Ma.     

Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses

The Turkana rifted zone in northern Kenya is a long‐lived and polyphased rift system where the lack of well‐marked rift morphology makes it difficult to identify the zone of active deformation. A high‐density river network is exceptionally well developed over the study area and shows evidence of drainage anomalies that suggest recent fault‐induced movements at various scales. Correlation of surface drainage anomalies with Landsat remote sensing and deep seismic reflection data permits to characterize the deep geometry of the inferred fault structures. Seismic stratigraphy further allows distinction between the inherited (Oligocene–Pliocene) and the newly formed (<3.7 Ma) origin of the recent deformation. Evidence for neotectonics are observed (1) along a large‐scale transverse (EW) fault rooted at depth along a steep basement discontinuity (Turkwell), (2) along a rift‐parallel (NS) fault zone probably emplaced during the Pliocene–Pleistocene and currently bounding the Napedet volcanic plateau to the west and (3) over a round‐shaped uplifted zone caused by positive inversion tectonics (Kalabata). The major contribution of this work is the recognition of a broad (80 km wide) zone of recent/active extensional deformation in the Turkana Rift in contrast with the narrow (20 km wide) N10°E‐trending axial trough forming the Suguta valley to the south, and the Chew Bahir faulted basin to the north. These along‐strike variations in structural style are partly controlled by the occurrence of rejuvenated Oligocene–Miocene rift faults and long‐lived transverse discontinuities in the Turkana Rift area. More generally, this study has implications for the use of river drainage network about recent/active extensional domains with subdued topography and slow deformation rate.     

Large-scale velocity field and strain tensor in Iran inferred from GPS measurements: new insight for the present-day deformation pattern within NE Iran

A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr⁻¹ at about N11°, 2 ± 1 mm yr⁻¹ of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr⁻¹ of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.     

基于水化学和稳定同位素定量评价巴音河流域地表水与地下水转化关系

以分析青海巴音河流域地表水与地下水转化关系为目标,2016年8月,沿巴音河采集了23组地表水样、13组地下水样和9组泉水样,室内分析得到了其对应的主要水化学离子和氘氧稳定同位素数据,运用统计分析、Piper三线图、Gibbs图分析了流域水化学特征;以溶解性总固体（TDS）、氯离子（Cl^-）和氧同位素（δ¹⁸O）作为示踪剂,定性分析了巴音河沿程地表水与地下水的转化关系;基于质量平衡法,运用δ¹⁸O定量计算了巴音河沿程地表水和地下水之间的转化量。研究结果表明：TDS、Cl^-、δ¹⁸O可用于定性分析巴音河流域不同河段地表水与地下水之间的转化关系,定量评估其转换强度;巴音河流域地表水和地下水的水化学类型主要为HCO₃·Cl-Ca·Mg,地下水水化学类型更为多样,地表水受控于岩石风化作用,地下水与泉水受到岩石风化与蒸发作用的影响;地表水与地下水水力联系密切,沿巴音河流向,二者相互转化频繁,上游河段,地下水主要接受地表水渗漏和沿途侧向径流补给,补给比例分别为65.33%、34.67%,至黑石山水库上游,地表水接受上游地下水和溢出泉水的补给,补给比例分别为49.54%、50.46%;中游河段,地下水接受地表水和北部山区侧向径流补给,补给比例分别为65%、35%;下游河段,地表水接受地下水和泉水补给,补给比例分别为53.12%、46.88%。研究结果有助于建立流域水循环模式、揭示水资源形成机制,可以为巴音河流域水资源可持续开发利用和生态环境保护提供理论和技术支持。     

Role of pore pressure generation in sediment transport within half-grabens

Sediment transport and overpressure generation are coupled primary through the impact of effective stress on subsidence and compaction. Here, we use mathematical modeling to explore the interactions between groundwater flow and diffusion-controlled sediment transport within alluvial basins. Because of lateral variation in permeability, proximal basin facies will have pore pressure close to hydrostatic levels while distal fine-grained facies can reach near lithostatic levels. Lateral variation in pore pressure leads to differential compaction, which deforms basins in several ways. Differential compaction reduces basin size, bends isochron surfaces across the sand–clay interface, restricts basinward progradation of sand facies, and reduces the amplitude of oscillation in the lateral position of the sand–clay interface especially in the deepest part of the section even when temporal sediment supply are held constant. Overpressure generation was found to be sensitive to change in sediment supply in permeable basins (at least 10⁻¹⁷ m² in our model). We found that during basin evolution, temporal variations in overpressure and sediment supply fluctuations are not necessarily in phase with each other, especially in tight (low permeability) basins (<10⁻¹⁷ m² in our model).