Structural architecture of a highly oblique divergent plate boundary segment   总被引：1，自引：0，他引：1  

Amy E. Clifton  Simon A. Kattenhorn 《Tectonophysics》2006,419(1-4):27-40

The Reykjanes Peninsula in southwest Iceland is a highly oblique spreading segment of the Mid-Atlantic Ridge oriented about 30° from the direction of absolute plate motion. We present a complete and spatially accurate map of fractures for the Reykjanes Peninsula with a level of detail previously unattained. Our map reveals a variability in the pattern of normal, oblique- and strike-slip faults and open fractures which reflects both temporal and spatial strain partitioning within the plate boundary zone. Fracture density varies across the length and width of the peninsula, with density maxima at the ends and at the northern margin of the zone of volcanic activity. Fractures with similar strike cluster into distinct structural domains which can be related to patterns of faulting predicted for oblique extension and to their spatial distribution with respect to volcanic fissure swarms. Additional structural complexity on the Reykjanes Peninsula can be reconciled with magmatic periodicity and associated temporal strain partitioning implied by GPS data, as well as locally perturbed stress fields. Individual faults show variable slip histories, indicating that they may be active during both magmatic and amagmatic periods associated with different strain fields.  相似文献   

A comparative error analysis of manual versus automated methods of data acquisition for algebraic strain estimation   总被引：1，自引：0，他引：1  

Kingshuk Roy Choudhury  Kieran Mulchrone   《Tectonophysics》2006,421(3-4):209-230

This paper presents a statistical analysis of the algebraic strain estimation algorithm of Shimamoto and Ikeda [Shimamoto, T., Ikeda, Y., 1976. A simple algebraic method for strain estimation from deformed eillipsoidal objects: 1. Basic theory. Tectonophysics 36, 315–337]. It is argued that the error in their strain estimation procedure can be quantified using an expected discrepancy measure. An analysis of this measure demonstrates that the error is inversely proportional to the number of clasts used. The paper also examines the role of measurement error, in particular that incurred under (i) a moment based and (ii) manual data acquisition methods. Detailed analysis of these two acquisition methods shows that in both cases, the effect of measurement error on the expected discrepancy is small relative to the effect of the sample size (number of objects). Given their relative speed advantage, this result favours the use of automated measurement methods even if they incur more measurement error on individual objects. Validation of these results is carried out by means of a simulation study, as well as by reference to studies appearing in previous literature. The results are also applied to obtain an upper bound on the error of strain estimation for various studies published in the literature on strain analysis.  相似文献   

Strain softening of K0-consolidated Changi sand under plane-strain conditions     

D. Wanatowski  J. Chu 《Acta Geotechnica》2006,1(1):29-42

Experimental results are presented in this paper to study the strain softening behaviour of a marine dredged sand under plane-strain conditions. K₀ consolidated drained and undrained tests were conducted using a new plane-strain apparatus to characterize the strain softening behaviour of the sand under plane-strain conditions. For medium dense specimens, strain softening and shear bands were observed to occur under both drained and undrained conditions. For very loose specimens, no shear bands were observed and critical states were reached within the homogeneous deformation region in both drained and undrained tests. Strain softening was observed to occur at small strain for very loose specimens under undrained conditions. Two types of strain softening, the homogenous softening and banding softening, were identified and the conditions for strain softening were established. The results obtained from this study were compared with the studies by Han and Vardoulakis (Géotechnique 41(1):49–78, 1991), Finno et al. (J Geotech Eng ASCE 122(6):462–473, 1996, Géotechnique 47(1):149–165, 1997) and Mokni and Desrues (Mech Cohes-Frict Mat 4:419–441, 1998).  相似文献   

Sediment-Based Study of the Effects of Decreasing Mine Water Pollutionon a Heavily Modified, Nutrient Enriched Lake     

T. Kauppila 《Journal of Paleolimnology》2006,35(1):25-37

Ni and Cu mining and ore processing in Hitura, Western Finland, have resulted in emissions of metal-rich wastewaters into the nearby Kalajoki River since 1970. The wastewaters are discharged into the river 3 km upstream from the eutrophic Lake Pidisjärvi, which is a widening of the river by the town of Nivala. The water level of the lake was elevated by 1.5 m and the extensive macrophyte stands were cut in 1979, profoundly changing the environmental conditions. The effects of the decreasing metal emissions and nutrient concentrations since 1979 on the now open 3.9 km² lake were studied with paleolimnological techniques. A 2-m sediment core was taken from the lake in February 2004 and analysed for sediment chemistry and diatom assemblages. At the coring site, 13 cm of sediment had been deposited since 1979, on top of a bed of undecomposed macrophyte remains. When the sediment chemistry was compared with records of decreasing metal loading since 1979, no correlation was found because post-depositional mobility and changes in sediment characteristics affect the sediment metal profiles. Thus, the reduced emissions from the mine and the lower lake water phosphorus levels have not caused a corresponding decrease in sediment metal and P concentrations. However, both of these environmental variables accounted for a statistically significant percentage of variation in the sedimentary diatom assemblages in a redundancy analysis constrained to a single variable. This relationship persisted for Ni loading even in a partial analysis, while the importance of nutrients was confirmed by the good correlation between diatom-inferred and measured P concentrations. The results suggest that reductions in metal and nutrient loading have had an effect on the algal assemblages even though the sediment concentrations of Ni, Cu or P have not decreased.  相似文献   

Ground deformation of the southern sector of the Aeolian islands volcanic arc from geodetic data     

Alessandro Bonaccorso   《Tectonophysics》2002,351(3)

The deformation pattern and the dynamics of the southern sector of the Aeolian archipelago are investigated. A study on the ground deformation, measured over the last 20 years in the trilateration geodetic network between the islands of Vulcano and Lipari, has been conducted. Analysis of the relative displacements and the uniform strain tensor parameters, as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling, allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area. These phases, however, appear to be closely interrelated. The analysis of the deformation pattern allows to constrain the predominance of a roughly E–W trending extension and a N–S contraction at a regional scale. This regime is consistent with right-lateral movements along a NW–SE striking fault system.  相似文献   

饱和岩石的各向异性及非线性黏弹性响应   总被引：25，自引：2，他引：25       下载免费PDF全文

席道瑛  刘斌  田象燕 《地球物理学报》2002,45(1):109-118

在MTS伺服压机上对不同饱和状态的砂岩、大理岩标本进行了垂直层理和平行层理两个方向的正弦波加载试验,研究了饱和岩石的各向异性及非线性黏弹性行为. 在最大载荷低于岩石的屈服点时,获得的衰减、杨氏模量、泊松比、波速都表现出显著的各向异性,同时它们还具有较明显的应变振幅效应和频率效应. 随着应变振幅的增大,衰减近似呈线性增长,杨氏模量和泊松比近似呈线性下降. 在0.005-4Hz频段内除衰减不明显依赖频率以外,杨氏模量、泊松比、波速对频率的依赖性都较强; 当频段扩大到15Hz时,这4个参数都表现出较强的频率效应. 饱和岩石的衰减、杨氏模量、泊松比、波速均随饱和液体的黏滞系数增大而增大.  相似文献   

Tracking recent recovery from eutrophication in a high arctic lake (Meretta Lake, Cornwallis Island, Nunavut, Canada) using fossil diatom assemblages   总被引：4，自引：0，他引：4  

Neal Michelutti  Marianne S.V. Douglas  John P. Smol 《Journal of Paleolimnology》2002,28(3):377-381

Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a high arctic lake that received raw sewage for almost 50 years from the Canadian Department of Transport Base. The lake was sampled from 1968–72 during the International Biological Programme, as part of the Char Lake Project. As the number of users at the Transport Base declined throughout the 1990s, so too did the lake's nutrient levels, and Meretta Lake is now classified as oligotrophic. A previous diatom-based paleolimnological study revealed marked species assemblage shifts coincident with sewage inputs beginning in the late 1940s; however, because the core was taken at a time when nutrient levels were still relatively high (i.e., 1993), the diatom record did not yet track any signs of recovery. In this present study, we examined fossil diatom assemblages from a sediment core taken in 2001. Our results indicate a shift to the pre-impact diatom assemblages in the most recent sediments, indicating that the paleolimnological record is tracking the decreased nutrient inputs to this high arctic lake, and confirms that no significant lags exist in these largely ice-covered lakes.  相似文献   

Strain partitioning and preservation of Ar/Ar ages during Variscan exhumation of a subducted crust (Malpica–Tui complex, NW Spain)     

J. Rodr&#x;&#x;guez  M.A. Cosca  J.I. Gil Ibarguchi  R.D. Dallmeyer 《Lithos》2003,70(3-4):111-139

The Malpica–Tui complex (NW Iberian Massif) consists of a Lower Continental Unit of variably deformed and recrystallized granitoids, metasediments and sparse metabasites, overridden by an upper unit with rocks of oceanic affinities. Metamorphic minerals dated by the ⁴⁰Ar/³⁹Ar method record a coherent temporal history of progressive deformation during Variscan metamorphism and exhumation. The earliest stages of deformation (D1) under high-pressure conditions are recorded in phengitic white micas from eclogite-facies rocks at 365–370 Ma. Following this eclogite-facies peak-metamorphism, the continental slab became attached to the overriding plate at deep-crustal levels at ca. 340–350 Ma (D2). Exhumation was accompanied by pervasive deformation (D3) within the continental slab at ca. 330 Ma and major deformation (D4) in the underlying para-autochthon at 315–325 Ma. Final tectonothermal evolution included late folding, localized shearing and granitic intrusions at 280–310 Ma.

Dating of high-pressure rocks by the ⁴⁰Ar/³⁹Ar method yields ages that are synchronous with published Rb–Sr and Sm–Nd ages obtained for both the Malpica–Tui complex and its correlative, the Champtoceaux complex in the French Armorican Massif. The results indicate that phengitic white mica retains its radiogenic argon despite been subjected to relatively high temperatures (500–600 °C) for a period of 20–30 My corresponding to the time-span from the static, eclogite-facies M1 peak-metamorphism through D1-M2 eclogite-facies deformation to amphibolite-facies D2-M3. Our study provides additional evidence that under certain geological conditions (i.e., strain partitioning, fluid deficiency) argon isotope mobility is limited at high temperatures, and that ⁴⁰Ar/³⁹Ar geochronology can be a reliable method for dating high pressure metamorphism.  相似文献   

Deformation at Stromboli volcano (Italy) revealed by rock mechanics and structural geology     

A Tibaldi  C Corazzato  T Apuani  A Cancelli 《Tectonophysics》2003,361(3-4):187-204

We approach the reconstruction of the recent structural evolution of Stromboli volcano (Italy) and the analysis of the interplay between tectonics, gravity and volcanic deformation. By tying together structural, lithostratigraphic and rock mechanics data, we establish that since 100 ka BP, the edifice has faulted and jointed mainly along NE-striking planes. Faults mostly dip to the NW with normal displacement. Taking also into account the presence of a NW-trending regional least principal stress and of tectonic earthquake hypocenters inside the cone, we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone. Dyking concentrated along a main NE-trending weakness zone (NEZ) across the volcano summit, resembling a volcanic rift, whose geometry is governed by the tectonic field. In the past 13 ka, Stromboli experienced a reorganisation of the strain field, which was linked with the development of four sector collapses affecting the NW flank, alternating with growth phases. The tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders. We propose that tectonics control the geometry of dykes inside the cone and that these, in turn, contribute to destabilise the cone flanks.  相似文献   

Layer parallel shortening in salt-detached folds: constraint on cross-section restoration     

M. Sans  J. Vergs  E. Gomis  J. M. Pars  M. Schiattarella  A. Trav  F. Calvet  P. Santanach  A. Doulcet 《Tectonophysics》2003,372(1-2):85-104

Cleavage-fissility perpendicular to bedding is a common feature in the external part of fold-and-thrust belts. Three techniques were used to determine the internal distortion in the frontal Southern Pyrenees: the analysis of strain markers such as burrows and rain drops, the measurement of fissility, and the measurement of anisotropy of magnetic susceptibility (AMS). The comparison of the three techniques showed a good fit although they differ in sensitivity to penetrative strain variations in the range of deformation values explored in the study case. On the regional scale, the values of layer parallel shortening (LPS) derived from the markers analysis are very constant and account for 16–23% of shortening. These values are two to three times larger than the shortening values calculated from the restoration of the macroscopic scale structures and indicate a good decoupling above the Cardona salt Formation. This study permitted an accurate restoration of the low-amplitude el Guix detached anticline.  相似文献