Geometry of the neotectonic stress field in southern Italy: Geological and seismological evidence

The neotectonic regime in southern Italy has been evaluated by making a comparison between all the available structural and seismological data. The area investigated can be subdivided into four distinct zones which are characterized by different stress regimes. In the Southern Apennines the tensile axis of the stress field is oriented approximately NE-SW while the maximum principal stress (σ₁) is subvertical. In Northern Calabria, the tensile axis is ESE-WNW and the σ₁ axis is almost vertical. In the Catanzaro trough both the tensile axis and the σ₁ axis are subhorizontal and act E-W and N-S, respectively. Finally, the Strait of Messina zone is characterized by a tensile axis oriented E-W and by σ₁ being subvertical.     

Magnetic properties and neutron diffraction study of two manganese sulfosalts: monoclinic MnSb<Subscript>2</Subscript>S<Subscript>4</Subscript> and benavidesite (MnPb<Subscript>4</Subscript>Sb<Subscript>6</Subscript>S<Subscript>14</Subscript>)

Mn²⁺Sb₂S₄, a monoclinic dimorph of clerite, and benavidesite (Mn²⁺Pb₄Sb₆S₁₄) show well-individualized single chains of manganese atoms in octahedral coordination. Their magnetic structures are presented and compared with those of iron derivatives, berthierite (Fe²⁺Sb₂S₄) and jamesonite (Fe²⁺Pb₄Sb₆S₁₄). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb₂S₄ shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature. In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb₂S₄ interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]: jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams and persist down to 1.4 K.     

Enhancement of (0k0) reflections of clay minerals in a Guinier camera

In oriented aggregates of flake-like clay minerals the (0k0) planes tend to orient in such a way that their normals become aligned subparallel to the specimen layer. This property may be utilized to obtain enhanced (060) intensities provided that the normal of the clay layer and the primary beam intersect at an angle equal to the Bragg angle for (060). This condition may be satisfied in a Guinier camera.From the degree of orientation t(_00l) of the basal planes the enhancement factor t _(0k0) is calculated according to three models. For t _(00l) between 5 and 50 times the intensity of random orientation the enhancement t _(0k0) varies between 2 and 5.5 times.     

Preferential embrittlement of graphitic schists during extensional unroofing in the Alps: the effect of fluid composition on rheology in low-permeability rocks

Interlayered graphitic and non‐graphitic schists from the Tauern Window, Eastern Alps, record contrasting mechanical behaviour during extensional exhumation. Graphitic schists contain mesoscale extension fractures, pervasive microcracks in garnet, and abundant secondary fluid inclusion planes; all three types of structures are oriented perpendicular to the stretching lineation. Crack spacings in garnet from graphitic samples are tightly clustered around a mean of 180 μm. Non‐graphitic schists have fewer and more randomly oriented microcracks and fluid inclusion planes and maintained strain compatibility via crystal plasticity. The presence or absence of graphite appears to have exerted a fundamental control on rheology during unroofing. Calculations for a model graphitic rock at 500 °C and f_O2 = 10^?24 MPa show that the equilibrium metamorphic fluid evolves from X_CO2 = 0.07 to 0.38 during decompression from 700 to 400 MPa, in agreement with microcrack fluid inclusion data that show a change from X_CO2 < 0.1 to 0.45 in graphitic samples over the same pressure interval. This compositional shift results in >60% expansion of the pore fluid during decompression. H₂O‐rich fluid in non‐graphitic rocks expands <15% over the same pressure interval. The greater pore fluid expansion in low‐permeability graphitic horizons likely promoted tensile failure during unroofing. These results suggest that microcracking should be an inevitable consequence of decompression in many graphitic schists, whereas rocks that lack graphite are less likely to undergo microcracking. Microseismicity is predicted to be more common in graphitic than non‐graphitic rocks during unroofing of mountain belts.     

Compressional- and transpressional-stress pattern for Pliocene and Quaternary brittle deformation in fore arc and intra-arc zones (Andes of Central and Southern Chile)

Kinematic analysis of fault slip data for stress determination was carried out on Late Miocene to Quaternary rocks from the fore arc and intra-arc regions of the Chilean Andes, between 33° and 46° south latitudes. Studies of Neogene and Quaternary infilling (the Central Depression), as well as plutonic rocks of the North Patagonian Batholith along the Liquiñe–Ofqui Fault Zone, have revealed various compressional and/or transpressional states of stress. In the Pliocene, the maximum compressional stress (σ₁) was generally oriented east–west. During the Quaternary, the deformation was partitioned into two coeval distinctive states of stress. In the fore arc zone, the state of stress was compressional, with σ₁ oriented in a N–S to NNE–SSW direction. In the intra-arc zone the state of stress was transpressional with σ₁ striking NE–SW. Along the coast, in one site (37°30′S) the Quaternary strain deformation is extensional, with an E–W direction, which can be explained by a co-seismic crustal bending readjustment.     

Effect of Fe3+-bearing point defects on the UV-spectra of two natural olivines

Polarized near-UV spectra have been recorded on 20 μm diameter spots on oriented crystals of microprobe-analyzed olivines from Baikhal Rift, Fa_8.8 (I) and Seberget, Fa_9.3 (II), which have formed under different fO₂ and, therefore, are expected to contain Fe³⁺-bearing point defects in different concentrations. These should be reflected in the UV-spectra of such minerals (Cemic et al. 1986). The spectra obtained confirm these predictions: The difference in α _{Y, 26500} in both samples indicates a difference in Fe³⁺-site fractions of ΔX_Fe. = 1.78-10⁻⁴, which may be related to an fO₂ about ten times higher for the formation of olivine II compared to I.     

Ri-μi/μm-Ci dependent oblateness of deformed pebbles in the Baraitha conglomerate,Central India and tectonic implications

Strain analysis of the Baraitha conglomerate is attempted by direct measurements on extracted pebbles and by micrometric analysis. The overall deformation is of flattening type, with thek value lower by more than half in the matrix than in the pebbles. The viscosity contrast between pebbles and matrix (μ _i/μ_m) is in the ratio of 2:1 and the bulk deformation appears to be strongly controlled by C_i (concentration of pebbles expressed as percentage). The total shortening (≃35%) in the Baraitha conglomerate is comparable with the shortening accomplished in the folding of the overlying Bijawar Group volcanosedimentary sequence. The bulk strain axesX _t, Y_t andZ _t, as determined from the analysis of the deformed conglomerate, are unsymmetrically oriented with reference to folds formed by oblique flexural-slip with neitherX _t norY _tcoincident with the fold hinges. The lack of transection of folds by cleavage again suggests flattening deformation. The extension in theY _tdirection is greater in the matrix than in the pebbles.     

Intrafolial folds and associated structures in a progressive strain environment of Darjeeling-Sikkim Himalaya

The Dating rocks and Darjeeling gneisses, which constitute the Sikkim dome in eastern Himalaya, as well as the Gondwana and Buxa rocks of ‘Rangit Window’, disclose strikingly similar sequences of deformation and metamorphism. The structures in all the rocks belong to two generations. The structures of early generation are long-limbed, tight near-isoclinal folds which are often intrafolial and rootless. These intrafolial folds are associated with co-planar tight folds with variably oriented axes and sheath folds with arcuate hinges. Penetrative axial plane cleavage and mineral lineation are related structures; transposition of bedding is remarkable. This early phase of deformation (D ₁) is accompanied by constructive metamorphism. The structures of later generation are open, asymmetrical or polyclinal; a crenulation cleavage or discrete fracture may occur. The structures of early generation are distorted by folds of later generation and recrystallized minerals are cataclastically deformed. Recrystallization is meagre or absent during the later phase of deformation (D ₂). The present discussion is on structures of early generation and strain environment during theD ₁ phase of deformation. The concentration of intrafolial folds in the vicinity of ductile shear zones and decollement or detachment surface (often described as ‘thrust’) may be considered in this context. The rocks of Darjeeling-Sikkim Himalaya display minor structures other than intrafolial folds and variably oriented co-planar folds. The state of finite strain in the rocks, as observed from features like flattened grains and pebbles, ptygmatic folds and boudinaged folds indicate combination of flattening and constrictional type strain. The significance of the intrafolial folds in the same rocks is discussed to probe the environment of strain during progressive deformation (D ₁).     

Oriented transformation of grunerite to clinoferrosilite at 775° C and 500 bars Argon pressure

A member of the grunerite series (Fe_6.685Mn_0.142Ca_0.110Mg_0.096) (Si_7.968Al_0.016)O₂₂(OH)₂, has been transformed to clinoferrosilite, amorphous silica and water at 775° C and 500 bars Argon pressure. Single crystal photographs of an oriented intergrowth of the amphibole and pyroxene show that the clinoferrosilite retains the cristallographic a, b and c axes of the original grunerite in the I2/m orientation and has the cell dimensions: a=9.77, b=9.08, c=5.30 Å, =109.5°; space group P2₁/c. Mössbauer resonance spectroscopy confirmed the identity of the olinoferrosilite.A transformation mechanism requires a minimum of ionic movements in an acceptor region (7/8 of the total crystal), where pyroxene is formed by expulsion of protons and acceptance of Fe²⁺ ions; simultaneous destruction of donor regions provide the Fe²⁺ ions, the residue being silica and water. The formation of metastable clinoferrosilite rather than fayalite and quartz indicates the strong structural control imposed by the host grunerite structure on the nature of the transformation products.     

Thermal expansion along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 solid solutions

The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi₂O₆–NaFe³⁺Si₂O₆ and NaAlSi₂O₆–CaFe²⁺Si₂O₆ joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V ₀) = α(T − T ₀). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature and high-pressure strain are differently oriented.     

Stress tensor analysis of the 1998–1999 tectonic swarm of northern Quito related to the volcanic swarm of Guagua Pichincha volcano, Ecuador

The phreatic activity and the subsequent dacitic dome growth in 1998–1999 at Guagua Pichincha volcano, Ecuador, were associated with two seismic swarms: one located in the northern part of Quito (population: 1,500,000) and another one, just below the active volcano, about 15–20 km SW from the first one. Quito swarm tectonic events have high frequencies (from 1 to 10–15 Hz). We registered more than 3200 events (among which 2354 events of 1.4≤M_L≤4.2) between June 1998 and December 1999 at the −2- and −17-km depth. The volcanic events below the Guagua Pichincha caldera have high (from 1 to 10–15 Hz) and low (less than 3 Hz) frequencies. Approximately, 130,000 events were registered between September 1998 and December 1999 at the +2.4- and −3.5-km depth. Here, we study the stress tensors of these two swarms deduced from the polarities of P first motions and compare them to the regional stress tensor deduced from CMT Harvard focal mechanisms. The Quito swarm stress tensor is relatively close to the regional stress tensor (the σ₁ axis was oriented N117°E close to the N102°E direction of the plate motion found by the GPS measurement, and σ₃ is nearly vertical). The difference may be due to the action of the closely active Guagua Pichincha volcano. The Guagua Pichincha stress tensor is very different from the regional tectonic one. The σ₁ axis of the volcano is oriented N214°E, almost perpendicular to the σ₁ of the swarm of Quito and σ₃ is almost horizontal. Even if these two tensors are different, they can be explained in a more general tectonic scheme. The almost horizontal direction of σ₃ just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the Guagua Pichincha volcano. The movement of the fluids (magma, gas and/or groundwater) produced by the closely active Guagua Pichincha volcano seems to have an influence in the acceleration of the generation of seismic events.     

Polarized X-ray absorption spectroscopy of metal ions in minerals

We have made use of the nearly complete linear polarization of synchrotron radiation to study the polarization dependence of X-ray absorption near-edge structure (XANES) and extended fine structure (EXAFS) in oriented single crystals of gillespite (BaFe²⁺ Si₄O₁₀; Fe^{2 +} in square-planar coordination, point symmetry C ₄), anatase (TiO₂; Ti⁴⁺ in octahedral coordination, point symmetry D _2d), and epidote (Ca₂(Al, Fe³⁺)₃SiO₄)₃(OH); Fe³⁺ in distorted octahedral coordination, point symmetry (C _s). For gillespite, the Fe K-XANES spectrum varies strongly with E-vector orientation of the incident X-ray beam. When the E-vector lies in the plane of the FeO₄ group (i.e., perpendicular to the c-axis), multiple-scattering features at 7127 and 7131 eV intensify, whereas when the E-vector is perpendicular to the plane of the FeO₄ group (i.e., parallel to the c-axis), a strongly-polarized 1s to 4p bound state transition occurs at 7116 eV and a localized continuum resonance occurs at 7122 eV. The Fe-K-EXAFS spectrum of gillespite is also highly polarization dependent. When the E-vector is perpendicular to c, all four nearest-neighbor oxygens around Fe²⁺ contribute to the EXAFS signal; when E is parallel to c, the EXAFS signal from nearest-neighbors is reduced by at least 86%. The unpolarized Ti K-XANES spectrum of anatase has three relatively strong pre-edge features at 4967.1, 4969.9, and 4972.7 eV which have resisted definitive interpretation in past studies. The lowest energy feature has a strong xy polarization dependence, suggesting a large amount of 4p _x,y character, and it is also very sharp, indicating a well-defined transition energy. Both of these observations are consistent with an excitonic state with a binding energy of 2.8 eV. The two higher energy features, which are characteristic of octahedrally-coordinated Ti⁴⁺, show little polarization dependence and are probably due to 1s to 3d bound-state transitions, with a small degree of np character in the final state wavefunction. Interpretation of the polarization dependence of Fe K-XANES spectra for epidote is not as straightforward due to the lower space group symmetry (P2₁/m) relative to gillespite (P4/ncc) and anatase (I4₁/amd) and the lower point group symmetry (C _s) of the M(3) site which contains most of the Fe³⁺ in the epidote structure. However, the presence of a shoulder at 7121 eV in the E parallel to b spectrum and its absence in the E normal to bc spectrum are consistent with it being a 1s to 4p _z bound-state transition. Strong, weakly x, y polarized features near 7126 eV in both spectra are most likely due to localized continuum transitions. Also, the 1s to 3d pre-edge intensity varies in intensity with E-vector orientation which is consistent with displacement of Fe³⁺ from the center of the M(3) octahedral site. Analysis of EXAFS spectra of epidote in these two polarizations yields bond distances which are within 0.04 Å of previous single-crystal X-ray diffraction analysis. This study demonstrates the utility of polarized X-ray absorption spectroscopy in quantifying the energies and orbital compositions of final state wavefunctions associated with various X-ray induced transitions in transition-metal containing minerals. It also shows that reasonably accurate M-O distances can be obtained for individual bonds oriented in crystallographically non-equivalent directions.     

Estimation of Rock Cuttability from Shore Hardness and Compressive Strength Properties

Summary Shore hardness has been used to estimate some mechanical and physical properties of rocks for many years. This study differs from previous studies in a way that it is directly oriented to rock cuttability. Two Shore hardness values (SH ₁ andSH ₂) and a coefficient of deformation value (K) have been measured for 30 different rock samples. In the first stage of the study, optimum specific energy values for 16 different rock samples obtained from full-scale cutting tests were correlated with the Shore hardness values of the same rock samples changingSH ₁ values from 9 to 66 andSH ₂ values from 25 to 83, with deformation coefficient values changing from 26 to 195. In the second stage, the performance of a roadheader used in the Kü?üksu (Istanbul) tunnel was recorded in detail and the instantaneous cutting rate of the machine was determined. Then, the relationship between Shore hardness values, deformation coefficient and the instantaneous cutting rate of the machine was determined for different formations encountered. It is concluded that there is a relationship between Shore hardness values, optimum specific energy and compressive strength, which may be used to estimate the rock cuttability and the instantaneous cutting rates of roadheaders within certain limits of reliability.     

Interpretation of a set of faults across the hinge and a limb of a large-scale flexure in the Mount Isa district, Queensland, Australia, in terms of fractures related to the folding process

A revised interpretation of a number of faults across the hinge and western limb of a large-scale anticlinal flexure in the Mount Isa district has been made in terms of the faults following earlier-formed be joints. Such joints often develop in weakly or moderately folded competent sediments, as a result of either tensile stresses that were active at a late stage during folding or the influence of residual stresses generated during tectonic uplift. The joints are oriented such that on a stereographic projection their poles plot parallel to the a axis of a fabric cross and at 90° to the fold axis (b). bc joints are thus approximately normal to bedding and contain the fold axis, and hence they fan around the axial plane of the fold containing them. Across the hinge and western limb of a steeply N-plunging large-scale F₂ flexure in the Mount Isa district, a number of faults at high angles to bedding fan about the axial plane. Making use of the fold geometry and local bedding orientation it is possible to predict the orientation of ideal bc fractures at locations within the fold. These predictions fit well with the observed fault pattern. The movement on the faults, although apparently complex, appears consistent with continued shortening perpendicular to an axial-plane cleavage during the D₂ deformation or as part of a later D₂ deformation.     

Transport properties of high albite crystals,near-endmember feldspar and pyroxene glasses,and their melts to high temperature

Thermal diffusivity (D) was measured using laser-flash analysis (LFA) from oriented single-crystal albite and glasses near LiAlSi₃O₈, NaAlSi₃O₈, CaAl₂Si₂O₈, LiAlSi₂O₆ and CaMgSi₂O₆ compositions. Viscosity measurements of the supercooled liquids, over 2.6 × 10⁸ to 8.9 × 10¹² Pa s, confirm strongly non-Arrhenian behavior for CaAl₂Si₂O₈, and CaMgSi₂O₆, and near-Arrhenian behavior for the others. As T increases, D _glass decreases, approaching a constant near 1,000 K. Upon crossing the glass transition, D decreases rapidly. For feldspars, D for the melt is ~15% below D of the bulk crystal, whereas for pyroxenes, this difference is ~40%. Thermal conductivity (k _lat = ρC _P D) of crystals decreases with increasing T, but k _lat of glasses increases with T because heat capacity (C _P ) increases with T more strongly than density (ρ) and D decrease. For feldspars, k _lat for the melt is ~10% below that of the bulk crystal or glass, whereas this decrease for pyroxene is ~50%. Therefore, melting substantially impedes heat transport, providing positive thermal feedback that could promote further melting.     

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature

Thermal diffusivity (D) was measured using laser-flash analysis from oriented single-crystal low-sanidine (K_0.92Na_0.08Al_0.99Fe³⁺ _0.005Si_2.95O₈), and three glasses near KAlSi₃O₈. Viscosity measurements of the three supercooled liquids, in the range 10^6.8 to 10^12.3 Pa s, confirm near-Arrhenian behavior, varying subtly with composition. For crystal and glass, D decreases with T, approaching a constant near 1,000 K: D _sat ∼ 0.65 ± 0.3 mm² s⁻¹ for bulk crystal and ∼0.53 ± 0.03 mm² s⁻¹ for the glass. A rapid decrease near 1,400 K is consistent with crossing the glass transition. Melt behavior is approximated by D = 0.475 ± 0.01 mm² s⁻¹. Thermal conductivity (k _lat) of glass, calculated using previous heat capacity (C _P) and new density data, increases with T because C _P strongly increases with T. For melt, k _lat reaches a plateau near 1.45 W m⁻¹ K⁻¹, and is always below k _lat of the crystal. Melting of potassium feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in continental crust.     

Über Beanspruchung und Verformung von Gesteinen

A new real triaxial deformation apparatus for p ₁p ₂p ₃ tests and temperatures up to 700° C has been developed. In five creep tests over 8 hours the strain-time curves at 650° C for axial and orthorhombic symmetry of stress are plotted in the three main directions and compared with the petrofabric diagrams of the deformed material. In all tests the symmetry of the petrofabrics can be correlated with the symmetry of the external loading. From the strain-time curves it can be deduced that the intermediate loading p ₂ is of great influence in the stress-strain behavior.Syntectonic recrystallization is found to be common for all tests in the form of broad lensoid and irregular defined {01¯12} lamellae oriented favorably for twinning. Measurements of c-axes in newly recrystallized grains show preferential alingnement subparallel to the axis of maximum principal loading.

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Der Deutschen Forschungsgemeinschaft sei für die finanzielle Unterstützung der Untersuchungen besonders gedankt.     

Heavy-ion irradiation on crystallographically oriented cordierite and the conversion of molecular CO2 to CO: a Raman spectroscopic study

Crystallographically oriented sections of natural gemstone quality cordierite single-crystals have been irradiated with swift heavy ions of GeV energy and various fluences. Irradiation effects on the crystal lattice were investigated by means of Raman spectroscopy. Raman line scans along the trajectory of the ions reveal a close correlation of beam parameters (such as fluence and energy loss dE/dx along the ion path) to strain due to associated changes in lattice dimensions and defect concentration. The luminescence background also scales with the ion fluence and suggests the formation of point defects, which could also account for the macroscopically observable colouration of the irradiated samples. In addition, changes in the amount and nature of volatile species inside the structural channels are observed. They also scale with dE/dx and confirm the previously postulated irradiation-induced conversion of CO₂ to CO. Irradiations along the crystallographic a-, b- and c-axis reveal no significant anisotropy effect with respect to lattice alterations. The polarisation characteristics of the Raman-active modes confirm the preferred molecular alignment of CO and CO₂ along the a-axis direction.     

An EPR study of native radiation-induced paramagnetic defects in sudoite (di–trioctahedral Al–Mg chlorite) from the alteration halo related to unconformity-type uranium deposits

Natural radiation-induced defects were identified in specimens of sudoite (Al–Mg di-trioctahedral chlorite) related to unconformity-type uranium deposits at the base of the Athabasca Group (Saskatchewan, Canada), using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. X-band spectra indicate the presence of a main native defect, named the A_s-center, whose EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g _// = 2,051 and g _⊥ = 2,005, and a secondary defect with apparent component g = 2,025. The study of oriented specimens shows that the main defect has its g _// component perpendicular to the (ab) plane of sudoite. The A_s-center corresponds to an electron hole located on oxygen atoms of the structure and is likely associated with Si, according to the lack of hyperfine structure. The A_s-center in sudoite has EPR parameters similar to the A-center in kaolinite and dickite, and the A_i-center in illite. The saturation behavior of EPR spectra as a function of power demonstrates that native defects of sudoite are different from those known in other clays, such as kaolinite, dickite or smectite, but are similar to those of illite. The isochronal annealing data suggest that the main defect in sudoite is stable to more than 300°C. The corresponding defects characterized in sudoite may have the potential for tracing past radionuclide migration around unconformity-type uranium deposits.     

Magnetic Fabric Study of Late Holocene Sediments in Huangqihai Lake,Inner Mongolia and its Sedimentary Significance

The detailed magnetic susceptibility anisotropy study on the sediments of two sections, which are located in the lake-center and the lakeshore of the Huangqihai Lake,Inner Mongolia, revealed their hydrodynamics and sedimentary environment changes in the recent 2000 years.The results show that the sediments of two sections both display normal depositional magnetic fabrics,of which the minimum susceptibility axes（K₃） are oriented perpendicular to the bedding plane and the maximum magnetic susceptibility axes（K₁） lie parallel with the bedding plane.In addition,the lakeshore presents higher magnetic anisotropy degree（P）,magnetic foliation（F） and current factor （F_s） than the lake-center,showing that the lakeshore has higher flow velocity.For the west Huangqihai Lake（HQW） section in the lake-center,the magnetic matrix grain degree（Q） and the inclination of the minimum susceptibility axes sharply increased and decreased,respectively,at a depth of about 10 cm,24 cm,45 cm and 74 cm,which indicate abnormal depositional events with strong kinetic energy.Through comparative analysis,the HQW section can be divided into three stages from top to bottom.The upper stage was a stable depositional environment with strong hydrodynamic energy and low water level,which shows relatively higher F_s value and the Q value varies similarly with P and F.The middle stage was a stable depositional environment with high water level and low hydrodynamic energy,intermitted with high-energy abnormal events,which shows relatively lower F_s and the Q value was negatively correlated with P and F.The lower stage was an unstable depositional environment with low hydrodynamic energy and high water level,which shows relatively lower P,F,and F_s value.