Present rate of uplift in Fennoscandia from GRACE and absolute gravimetry

Fennoscandia is a key region for studying effects of glacial isostatic adjustment. The associated mass variations can be detected by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, which observes the Earth's gravity field since April 2002, as well as by absolute gravimetry field campaigns. Since 2003, annual absolute gravity (AG) measurements have been performed in Fennoscandia by the Institut für Erdmessung (IfE, Institute of Geodesy) of the Leibniz Universität Hannover, Germany, within a multi-national cooperation. This offers a unique opportunity for validation and evaluation of the GRACE results. In this preliminary study, the GRACE results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the FG5-220 gravimeter of the IfE.The results from GRACE monthly solutions provided by different analysis centres show temporal gravity variations in Fennoscandia. The included secular variations are in good agreement with former studies. The uplift centre is located west of the Bothnian Bay, the whole uplift area comprises Northern Europe. Nevertheless, the differences between the GRACE solutions are larger than expected and the different centre-specific processing techniques have a very strong effect on possible interpretations of GRACE results. The comparison of GRACE to the AG measurements reveals that the determined trends fit well with results from GRACE at selected stations, especially for the solution provided by the GFZ. Variations of land hydrology clearly influence results from GRACE and the AG measurements.     

The Fennoscandian uplift and late cenozoic geodynamics: geological evidence

The history of the recording and interpretation of the Fennoscandian uplift illustrates the main history of Earth sciences because the results obtained had (and still have) immediate impact of the interpretation of a large number of fundamental problems in Earth sciences. Thanks to a paper of De Geer in 1888, the glacial isostatic origin was established. Fennoscandia became the classic area of glacial isostasy, and its sea level records were used for geophysical calculations of the properties and dynamics of the mantle and crust. The varve dated sea level curve of Lidén (1938) from the center of uplift provided an exceptionally well dated record. With the radiocarbon method, the records of shorelines and shorelevel displacement curves were drastically improved providing a totally new basis for the understanding of the geodynamics of the Fennoscandian uplift and for the geophysical interpretation of the data obtained. This is especially true in combination with the repeated levelling data obtained during the last decades for Finland and Sweden.The Late Cenozoic long term movements of the Fennoscandian Shield are characterized by a considerable subsidence. The postglacial uplift of Fennoscandia is complex (an exponential and a linear factor) and caused by two different mechanisms. The total absolute movement in relation to the last glaciation is an elliptic uplift cone of 830 m height surrounded by a subsidence through of 170 m height. The mass in the uplift cone and in the subsidence through is as 1:1 with a volume 0.7 × 10⁶km³. The disappearence/appearance of mass give evidence of a mass transfer in a low viscosity asthenosphere. The properties and conditions of the asthenosphere are found to be: 1–10 × 10²⁰ Poises in viscosity, 3 × 10^–14 – 3 × 10^–16 sec^–1 in strain rates, 0.7% of the melting temperature, 3 mm in grain size, and 5–0.4 bar in stress. The main isostatic uplift (the exponential factor) originates from an asthenospheric dislocation glide process which in early-mid Holocene time changed over into a diffusion creep process. The present linear uplift factor (identified through the last 8000 yrs) seems to originate from mesospheric motions under the following approximate conditions: 0.6% of the melting temperature, 2 × 10²² Poises in viscosity, 3 × 10^–16 sec^–1 in strain rates and 8 bars in stress. Uplift irregularities and neotectonism are frequently established and often reveal an old geodynamic inheritance (e.g. the Pre-Baikalian/Gothian bedrock seam of high geodynamic activity). The peak rates of glacial isostasy are associated with intensive fracturing, faulting and seismic activity.     

Gravity change, geoid change and remaining postglacial uplift of Fennoscandia

The result obtained hitherto on the Fennoscandian land uplift gravity line indicates that the postglacial uplift process might be more complicated than a pure horizontal flow of mantle (‘Bouguer model’). Simple formulae, valid for a more arbitrary model, are developed for the change of the geoid and for the remaining land uplift. Numerical applications yield a geoid change of about 0.4 mm yr^-1 and a remaining land uplift of the order of 50 m, but the latter quantity is very difficult to determine with reasonable accuracy.     

The present rate of uplift of Fennoscandia implies a low-viscosity asthenosphere

The rate of displacement in Fennoscandia has been intensively discussed for many years. It is now widely accepted to be an isostatic response of the glacial history of the area. The Earth's present response to deglaciation in Fennoscandia is simulated using a three-dimensional (3D), viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value. The deglaciation history is considered to be known, and the C¹⁴-datings are converted to sidereal years. The pattern of the present uplift gives a firm match with the observed data when a low-viscosity asthenosphere is introduced. Assuming a 15,000 years load cycle, i.e. the glacier was applied to the surface for 15,000 years before the melting started, the best fitting earth viscosity model is a 10²⁴ Nm lithosphere overlying a 75 km-thick 2.0 × 10¹⁹ Pas asthenosphere and a 1.2 × 10²¹ Pas mantle. The simulations suggest a remaining maximum uplift of 40 m.     

Postglacial land uplift patterns of south Sweden and the Baltic Sea region

Comparison of the land uplift pattern for the last 10,300 years, shown by studies of raised shorelines of the Baltic Ice Lake, with the pattern of present-day land uplift of Fennoscandia, shows that significant regional changes of uplift pattern have taken place. Some of these changes seem to be related to a halt in ice retreat during the Younger Dryas cold stage. It is also probable that some observed anomalies in the present uplift are not of glacio-isostatic origin, but are possibly related to structures in the lower lithosphere and upper mantle or large scale tectonics.     

遥感影像地表温度反演与地热资源预测——以石家庄地区为例

热红外遥感技术可以反演地表温度信息,可在地热资源预测方面发挥重要作用.研究基于京津冀地区地热成藏模式,利用单窗算法反演出石家庄地区2015年3月6日地表温度,结合夜间热红外影像、遥感构造解译结果和剩余重力异常数据,综合分析,相互论证,圈定1处山地对流型地热远景区和2处沉积盆地型地热远景区.其中,平山县寺沟村昼夜地温值均...     

Autochthonous block fields in southern Norway: Implications for the geometry,thickness, and isostatic loading of the Late Weichselian Scandinavian ice sheet

The consistent geographical and altitudinal distribution of autochthonous block fields (mantle of bedrock weathered in situ) and trimlines in southern Norway suggests a multi-domed and asymmetric Late Weichselian ice sheet. Low-gradient ice-sheet profiles in the southern Baltic region, in the North Sea, and along the outer fjord areas of southern Norway, are best explained by movement of ice on a bed of deforming sediment, although water lubricated sliding or a combination of the two, may not be excluded. The ice-thickness distribution of the Late Weichselian Scandinavian ice sheet is not in correspondence with the modern uplift pattern of Fennoscandia. Early Holocene crustal rebound was apparently determined by an exponential, glacio-isostatic rise. Later, however, crustal movements appear to have been dominated by large-scale tectonic uplift of the Fennoscandian Shield, centred on the Gulf of Bothnia, the region of maximum lithosphere thickness.     

A consistent map of the postglacial uplift of Fennoscandia

A consistent map of the recent postglacial rebound of Fennoscandia is constructed on the basis of sea-level records, lake-level records and repeated high-precision levellings.
The uplift rates calculated from the sea-level series form a consistent framework of the map. The sea-level stations used are 56 reliable stations in the Baltic Sea and adjacent waters with series spanning 60 years or more, many of them about 100 years. Using a reference station in the Baltic Sea and another one outside the Baltic, all results are reduced to a common time span, the 100-year-period 1892–1991, in order to eliminate oceanographic changes. Inland, uplift differences are obtained from the repeated national levellings and, in four of the large lakes, from long water level series in pairs. The levellings, however, yield less accurate land uplift values than the sea-level and lake-level data.
The resultant map shows a fairly smooth phenomenon, with a maximum apparent uplift in the Gulf of Bothnia of 9.0 mm yr^-1. The standard error is typically 0.2 mm yr^-I close to the sea level stations, larger inland.
Finally the pattern of the present uplift as determined here is observed to be very similar to that of the past uplift as determined from ancient shore-lines of the Litorina Sea. However, the ratio between the past uplift and the present uplift rate tends to increase somewhat towards the uplift centre. This might reflect a non-uniform mantle viscosity. Also, the uplift maximum seems to have migrated towards NNE.     

The Barents Sea Ice Sheet — A model of its growth and decay during the last ice maximum

On the basis of geomorphological and sedimentological data, we believe that the entire Barents Sea was covered by grounded ice during the last glacial maximum. ¹⁴C dates on shells embedded in tills suggest marine conditions in the Barents Sea as late as 22 ka BP; and models of the deglaciation history based on uplift data from the northern Norwegian coast suggest that significant parts of the Barents Sea Ice Sheet calved off as early as 15 ka BP. The growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central Barents Sea, where ice caps may develop and expand to finally coalesce with the expanding ice masses from Svalbard and Fennoscandia.The outlined model for growth and decay of the Barents Sea Ice Sheet suggests a system which developed and existed under periods of maximum climatic deterioration, and where its growth and decay were strongly related to the fall and rise of sea level.     

Quaternary denudation of southern Fennoscandia – evidence from the marine realm

Throughout the last 1.1 million years repeated glaciations have modified the southern Fennoscandian landscape and the neighbouring continental shelf into their present form. The glacigenic erosion products derived from the Fennoscandian landmasses were transported to the northern North Sea and the SE Nordic Seas continental margin. The prominent sub‐marine Norwegian Channel trough, along the south coast of Norway, was the main transport route for the erosion products between 1.1 and 0.0 Ma. Most of these erosion products were deposited in the North Sea Fan, which reaches a maximum thickness of 1500 m and has nearly 40 000 km³ of sediments. About 90% of the North Sea Fan sediments have been deposited during the last 500 000 years, in a time period when fast‐moving ice streams occupied the Norwegian Channel during each glacial stage. Back‐stripping the sediment volumes in the northern North Sea and SE Nordic Seas sink areas, including the North Sea Fan, to their assumed Fennoscandian source area gives an average vertical erosion of 164 m for the 1.1–0.0 Ma time period. The average 1.1–0.0 Ma erosion rate in the Fennoscandian source area is estimated to be 0.15 mm a^?1. We suggest, however, that large variations in erosion rates have existed through time and that the most intense Fennoscandian landscape denudation occurred during the time period of repeated shelf edge ice advances, namely from Marine Isotope Stage 12 (c. 0.5 Ma) onwards.     

Newest results obtained in studying the Fennoscandian land uplift phenomenon

The Fennoscandian land uplift phenomenon has been studied using geodetic, gravimetric and seismologic material. Results obtained show that the greatest part of the phenomenon is of glaciological origin. In the geoid there is a depression approx. eight meters in depth. A seismic map showing data gathered over 500 years shows also a certain tectonic pattern.     

Detailed gravity studies over Jabera — Damoh region of the Vindhyan basin (Central India) and crustal evolution

Vindhyan Basin of Central India situated just north of SONATA rift zone, forms one of the major geotectonic segment of the Indian subcontinent which is associated with complex thermo-tectonic history. Southern part of this basin is known to contain favorable conditions for hydrocarbon entrapment. Keeping this in view, a detailed gravity survey network comprising 40 gravity bases and 1500 data points in an area of about 110 × 100 km² was planned in and around Jabera-Damoh region. Analysis of Bouguer and free air gravity anomaly maps, prepared using fractal based gridding method, indicates presence of two sedimentary basins (Jabera and Damoh) faulted on either sides beside ridge like features. However, well-known Jabera domal structure appeared to be a shallow feature only. Inversion of gravity data further reveals presence of 5 to 6 km thick Vindhyan sediments in the Jabera basin which are underlain by Mahakoshal/Bijawar group of rocks, resting directly over the lower crust, thereby indicating almost total absence of granitic crust from this region. It appears that due to an underlying thermal anomaly, the entire region may have been subjected to sustained uplift, deformation, erosion and consequent crustal extension during early to mid Proterozoics which brought high velocity mafic crust to such shallow levels.     

The Vetreny Poyas (Windy Belt) subprovince of southeastern Fennoscandia: An essential component of the ca. 2.5–2.4 Ga Sumian large igneous provinces

Ca. 2.5–2.4 Ga Sumian magmatism is widespread in the Karelia and Kola cratons of Fennoscandia and probably represents at least two intermixed large igneous provinces (LIPs). It is distinct from other Paleoproterozoic LIPs (Jatulian 2.22–2.1 Ga and Ludicovian 2.06–1.96 Ga) elsewhere in the Fennoscandian Shield. A poorly understood portion of Sumian magmatism is the Vetreny Poyas (Windy Belt) subprovince, which covers ∼75,000 km² in southeastern Fennoscandia. This subprovince consists of four genetically related complexes which developed at different levels in the crust: a volcanic complex (komatiitic basaltic lava flows on Golets, Levgora and Myandukha hills, and Victoria lava lake on Levgora hill), a subvolcanic complex (mafic–ultramafic sills and lopoliths including Ruiga, Kirichgora, Kozhozero and Undozero), plutonic complexes (Burakovsky and Vyzhiga) and a dyke complex (gabbronoritic Avdeyevo and Shala dykes and peridotitic Vinela and Koppalozero dykes). Similar patterns are present in other Sumian belts elsewhere in Karelia, for instance in southern Lapland and the Kola Peninsula.     

New gravity maps of the Eastern Alps and significance for the crustal structures

The deep seismic profile Transalp crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the Transalp-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between − 190 * 10^− 5 m/s² and + 25 * 10^− 5 m/s², with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10^− 5 m/s², with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses. At last a discussion of a 2D density model based on reflection seismic data and receiver functions is made.     

内蒙古西部银根-额济纳旗盆地重力场与 断裂构造的特征

为了研究银根-额济纳旗盆地的构造特征,为该区油气资源远景调查评价提供依据,系统地收集、研究了已有的重力调查资料,分析了研究区重力场的特征及其成因,推断了研究区的断裂构造体系。研究区区域重力异常主要是由莫霍面起伏变化引起的,剩余重力异常重力高与重力低相间分布的特征,可能一方面反映了研究区凹陷与隆起分布的范围及展布特征,另一方面反映了凹陷与隆起之间发育非对称的断裂。研究区主要发育北东东向(北东向)、北西西向2组断裂,这2组断裂对基底结构、性质、隆坳格架及中生代盆地展布起重要的控制作用。基底断裂将研究区分割成多个块体,使盆地形成凹、凸相间的结构特征。     

Holocene marine terraces on two salt diapirs in the Persian Gulf,Iran: age,depositional history and uplift rates

Slightly inclined Holocene marine terraces cover parts of two circular salt diapirs (Hormoz and Namakdan) in the Persian Gulf. Their relative altitude above present sea level results from a combination of general marine transgression/regression affecting the whole area, and of local uplift related to salt diapirism. Differential uplift rate of the studied diapirs in centre‐to‐rim profiles was calculated from results based on: (i) radiocarbon ages of skeletal remains of benthic faunas (19 samples), which originally grew close to sea level; (ii) original altitude of samples, estimated from general sea‐level oscillation curves for the last 10 kyr, and (iii) present sample altitude measured in the field. Calculated uplift rates increase from rim to centre on both diapirs in the range from: 2 mm yr^?1 at the rim to 5–6 mm yr^?1 at the interior of Hormoz, and 1–3 mm yr^?1 at the rim to 3–5 mm yr^?1 at the interior of Namakdan. Such uplift rate distributions fit into the parabolic profile of Newtonian fluid rather than to profiles typical for pseudoplastic fluids. The increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces. No tectonic dissections were found. The depositional history on both salt diapirs is similar although they are situated more than 100 km apart. Marine sedimentation started at about 9.6k cal. yr BP on Hormoz and at 8.6k cal. yr BP on Namakdan. Owing to rapid transgression, the sea partially truncated both salt diapirs and rapidly deepened, and carbonate mud was deposited on the peripheries of both salt diapirs. Between 7 and 5k cal. yr BP beach deposition replaced carbonate mud. Soon after 5k cal. yr BP, the sea retreated from most of the marine terraces on both salt diapirs. Copyright © 2006 John Wiley & Sons, Ltd.     

Glacial rebound and sea-level change in the British Isles

Observations of sea levels around the coastline of the British Isles for the past 10,000–15,000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the Late Devensian ice sheet. A high-resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea-level change and which demonstrates that the observations are the result of (i) the glacio-isostatic crustal rebound in response to the unloading of the ice sheet over Britain and, to a lesser degree, of the ice sheet over Fennoscandia, and (ii) the rise in sea-level from the melting Late Pleistocene ice sheets, including the response of the crust to the water loading (the hydro-isostatic effect). The agreement between model and observations is such that there is no need to invoke vertical crustal movements for Great Britain and Ireland of other than glacio-hydro-isostatic origin. The rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea-level change to approximate the eustatic sea-level rise. The observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation. Preliminary solutions are presented which indicate an upper mantle viscosity of (3–5)10²⁰ Pas, a lithospheric thickness of about 100 km or less, and an ice model that was not confluent with the Scandinavian ice sheet during the last glaciation and whose maximum thickness over Scotland is unlikely to have exceeded about 1500 m.     

Exposure ages from relict lateral moraines overridden by the Fennoscandian ice sheet

Lateral moraines constructed along west to east sloping outlet glaciers from mountain centred, pre-last glacial maximum (LGM) ice fields of limited extent remain largely preserved in the northern Swedish landscape despite overriding by continental ice sheets, most recently during the last glacial. From field evidence, including geomorphological relationships and a detailed weathering profile including a buried soil, we have identified seven such lateral moraines that were overridden by the expansion and growth of the Fennoscandian ice sheet. Cosmogenic ¹⁰Be and ²⁶Al exposure ages of 19 boulders from the crests of these moraines, combined with the field evidence, are correlated to episodes of moraine stabilisation, Pleistocene surface weathering, and glacial overriding. The last deglaciation event dominates the exposure ages, with ¹⁰Be and ²⁶Al data derived from 15 moraine boulders indicating regional deglaciation 9600 ± 200 yr ago. This is the most robust numerical age for the final deglaciation of the Fennoscandian ice sheet. The older apparent exposure ages of the remaining boulders (14,600-26,400 yr) can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle. Their potential exposure history, based on local glacial chronologies, indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5. Although numerous deglaciation ages were obtained, this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data.     

豫东平原区的地球物理特征及找煤远景

豫东平原区勘探手段多样，地质资料丰富，通过对豫东平原区重力场、磁力场、地震反射波等地球物理特征综合分析，并进行联合反演及钻探资料对比一区域地质研究和综合地质解释的成果表明，该区构造型式多样．挤压式、伸展式、走滑式均有表现，但以伸展式断裂为主；构造线可见三组发育方向，近EW向构造形成最早，NNE-NE向构造形成最晚，而NW向构造则介于二者之间，且具有左行平移走滑性质；该区总体恪局为“两坳夹一隆”，即开封坳陷、周口坳陷、通许隆起，其煤炭资源丰富，埋藏深度变化较大；隆、坳中发育很多结构不同的次级凸起和凹陷，正确认识这些隆、坳中的次级构造单元及结构，是预测找矿的关键。     

Onshore–offshore structure and hydrocarbon potential of the South Yellow Sea

Recent high-resolution airborne gravity data taken over the South Yellow Sea and its western onshore–offshore transition zone, combined with ground gravity data taken over the onshore area (Subei Basin), China, show that the South Basin of the South Yellow Sea and the Subei Basin correspond to the same gravity low anomaly. Magnetic data also support our interpretations. Both areas have similar strata, structures and hydrocarbon potential, and form a large Cenozoic terrestrial sedimentary basin controlled by the Tanlu Fault. Cenozoic terrestrial strata are well developed in the South Basin of the South Yellow Sea, and thick Meso–Paleozoic marine strata are preserved in the Central uplift area. Future hydrocarbon exploration in the South Yellow Sea should focus on the Cenozoic continental sequence, especially the Paleogene in the South Basin, as well as the Meso–Paleozoic marine rocks in the Central uplift area. The western part of the middle depression and middle and western parts of the north depression in the South Basin of the South Yellow Sea have the greatest potential for hydrocarbon accumulation.