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1.
The magnitude of the in situ stresses in the Cooper–Eromanga Basins have been determined using an extensive petroleum exploration database from over 40 years of drilling. The magnitude of the vertical stress (Sv) was calculated based on density and velocity checkshot data in 24 wells. Upper and lower bound values of the vertical stress magnitude are approximated by Sv = (14.39 × Z)1.12 and Sv = (11.67 × Z)1.15 functions respectively (where Z is depth in km and Sv is in MPa). Leak-off test data from the two basins constrain the lower bound estimate for the minimum horizontal stress (Shmin) magnitude to 15.5 MPa/km. Closure pressures from a large number of minifrac tests indicate considerable scatter in the minimum horizontal stress magnitude, with values approaching the magnitude of the vertical stress in some areas. The magnitude of the maximum horizontal stress (SHmax) was constrained by the frictional limits to stress beyond which faulting occurs and by the presence of drilling-induced tensile fractures in some wells. The maximum horizontal stress magnitude can only be loosely constrained regionally using frictional limits, due to the variability of both the minimum horizontal stress and vertical stress estimates. However, the maximum horizontal stress and thus the full stress tensor can be better constrained at individual well locations, as demonstrated in Bulyeroo-1 and Dullingari North-8, where the necessary data (i.e. image logs, minifrac tests and density logs) are available. The stress magnitudes determined indicate a predominantly strike-slip fault stress regime (SHmax > Sv > Shmin) at a depth of between 1 and 3 km in the Cooper–Eromanga Basins. However, some areas of the basin are transitional between strike-slip and reverse fault stress regimes (SHmax > Sv ≈ Shmin). Large differential stresses in the Cooper–Eromanga Basins indicate a high upper crustal strength for the region, consistent with other intraplate regions. We propose that the in situ stress field in the Cooper–Eromanga Basins is a direct result of the complex interaction of tectonic stresses from the convergent plate boundaries surrounding the Indo-Australian plate that are transmitted into the center of the plate through a high-strength upper crust.  相似文献   

2.
This study defines the Mio-Pliocene to present-day stress regime acting at the northeastern corner of the eastern Mediterranean region along the Karasu Valley (i.e., the Amanos Range), taking in the Antakya, Osmaniye and Kahramanmaras provinces. The inversion slip vectors measured on fault planes and chronologies between striations indicate that the stress regime varied from transpressional initially to transtensional, having consistent NW- and NE-trending σHmax (σ1) and σHmin (σ3) axes, respectively; there are significantly different mean stress-ratio (Rm) values however. The older mean stress state is characterized by N151±11°E-trending σ1 and N59±12°E-trending σ3 axes, and by a mean arithmetic Rm value of 0.76, indicating that the regional stress regime is transpressional. The younger stress regime is characterized by N154±8°E-trending σ1 and N243±8°E-trending σ3 axes, and by a mean arithmetic Rm value of 0.17, indicating a transtensional character for this regional stress regime. The low R values of the stress deviators related to the recent stress state reflect normal-component slips. The earthquake focal mechanism inversions confirm that the younger stress regime continues into the Recent. The inversion identifies a transtensional stress regime representing strike-slip and an extensional stress state with a consistent NE-trending σHmin (σ3) axis. These stress states are characterized by N66°E and N249°E-trending σ3 axes, respectively. Both significant regional stress regimes induce left-lateral displacement along the southern part of the East Anatolian Fault (EAF, or Amanos Fault). The temporal change, probably in Quaternary time, within the regional stress regime—from transpression to transtension—resulted from the coeval influences of subduction processes in the west–southwest (i.e., along the Cyprus arc), continental collision in the east, and westward escape of the Anatolian block.  相似文献   

3.
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.  相似文献   

4.
Quaternary folding of the eastern Tian Shan, northwest China   总被引：3，自引：0，他引：3  
The Tian Shan, east–west trending more than 2000 km, is one of most active intracontinental mountain building belts that resulted from India–Eurasia collision during Cenozoic. In this study, Quaternary folding related to intracontinental mountain building of the Tian Shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images [Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM) and India Remote Sensing (IRS) Pan] combined with field geologic and geomorphic observations and seismic reflection profiles. Analyses of spatial–temporal features of Quaternary folded structure indicate that the early Quaternary folds are widely distributed in both piedmont and intermontane basins, whereas the late Quaternary active folds are mainly concentrated on the northern range-fronts. Field observations indicate that Quaternary folds are mainly characterized by fault-related folding. The formation and migration of Quaternary folding are likely related to decollement surfaces beneath the fold-and-fault zone as revealed by seismic reflection profiles. Moreover, analysis of growth strata indicates that the Quaternary folding began in late stage of early Pleistocene (2.1–1.2 Ma). Finally, tectonic evolution model of the Quaternary deformation in the Tian Shan is presented. This model shows that the Quaternary folding and faulting gradually migrate toward the range-fronts due to the continuous compression related to India–Eurasia collision during Quaternary time. As a result, the high topographic relief of the Tian Shan was formed.  相似文献   

5.
In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of ML 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude Mw 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes.Eight small earthquakes (3.0  ML < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 1012–5.04 × 1015 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.  相似文献   

6.
This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes (σ1, σ2 and σ3) and the ratio of the principal stress differences ( ) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first is characterized by NNW–SSE compression and ENE–WSW extension and related to Middle Miocene-Recent sinistral movement along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW–ESE compression and NNE–SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.  相似文献   

7.
Dissolution of the synthetic hydroxylapatite (HAP) and fluorapatite (FAP) in pure water was studied at 25 °C and 45 °C in a series of batch experiments. The XRD, FT-IR and SEM analyses indicated that the synthetic, microcrystalline HAP and FAP with apatite structure used in the experiments were found to have no obvious variation after dissolution except that the existence of OH groups in FT-IR spectra for FAP after 2880 h dissolution was observed. During the HAP dissolution (0–4320 h), the aqueous calcium and phosphate concentrations reached the maxima after 120 h and then decreased slowly with time. For the FAP dissolution in pure water, after a transient time of 1440 h (< 60 d), element concentrations and pH became constant suggesting attainment of a steady-state between the solution and solid. During early stages of the FAP dissolution reaction (< 72–120 h), mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P, Ca:F and P:F being lower than mineral stoichiometric ratios of Ca5(PO4)3F, i.e., 1.67, 5.0 and 3.0, respectively. This indicated that F were preferentially released compared to Ca from the mineral structure. The mean Ksp values were calculated by using PHREEQC for HAP of 10− 53.28 (10− 53.02–10− 53.51) and for FAP of 10− 55.71 (10− 55.18–10− 56.13) at 25 °C, the free energies of formation ΔGfo[HAP] and ΔGfo[FAP] were calculated to be − 6282.82 kJ/mol and − 6415.87 kJ/mol, respectively.  相似文献   

8.
We estimated the stress fields of the aftershocks of the 2000 western Tottori earthquake (Mw 6.6) and the northern Hyogo swarm (max Mw 5.2) by a stress tensor inversion of moment tensor solutions reported from the National Research Institute for Earth Science and Disaster Prevention (Japan). The maximum principal stress direction of the western Tottori sequence was estimated as N107°E with a strike–slip regime. In the northern Hyogo swarm, the orientations of the principal stress directions could not be well constrained by the observed data, but after examining the detailed characteristics of the solution, we obtained a most probable solution of N113°E for the σ1 direction. These solutions are consistent with the maximum horizontal directions roughly estimated from the strike directions of large earthquakes occurring geographically between these two seismic activities. We measured the angle between each fault–slip direction and maximum principal stress direction to investigate the frictional properties of earthquakes. The distribution of the angles was forward modeled to estimate the coefficient of friction and the stress ratio, assuming uniformly distributed fault orientations. For the western Tottori sequence, a homogeneous stress field with a coefficient of friction less than 0.4 was estimated. A high stress level was also suggested because very little change occurred in the stress field during the mainshock. For the northern Hyogo sequence, the coefficient of friction was estimated to be between 0.5 and 1.0.  相似文献   

9.
In normal faulting regimes, the magnitudes and orientations of the maximum and minimum principal compressive stresses may be known with some confidence. However, the magnitude of the intermediate principal compressive stress is generally much more difficult to constrain and is often not considered to be an important factor. In this paper, we show that the slip characteristics of faults and fractures with complex or nonoptimal geometry are highly sensitive to variation or uncertainty in the ambient effective intermediate principal stress (σ′2). Optimally oriented faults and fractures may be less sensitive to such variations or uncertainties. Slip tendency (Ts) analysis provides a basis for quantifying the effects of uncertainty in the magnitudes and orientations of all principal stresses and in any stress regime, thereby focusing efforts on the most important components of the system. We also show, for a normal faulting stress regime, that the proportion of potential surfaces experiencing high slip tendency (e.g., Ts ≥ 0.6) decreases from a maximum of about 38% where σ′2 = σ′3, to a minimum of approximately 14% where σ′2 is halfway between σ′3 and σ′1, and increases to another high of approximately 29% where σ′2 = σ′1. This analysis illustrates the influence of the magnitude of σ′2 on rock mass strength, an observation previously documented by experimental rock deformation studies. Because of the link between fault and fracture slip characteristics and transmissivity in critically stressed rock, this analysis can provide new insights into stress-controlled fault transmissivity.  相似文献   

10.
Bonini (2009, Structural controls on a carbon dioxide-driven mud volcano field in the Northern Apennines (Pieve Santo Stefano, Italy): relations with pre-existing steep discontinuities and seismicity. Journal of Structural Geology 31, 44–54) presents a 2D mechanical analysis to infer the failure conditions responsible for the seismicity distribution during an Mw = 4.6 seismic sequence nucleating during 2001 in the Northern Apennines. In my view the mechanical analysis presented in this paper has some weakness or is not well constrained, in particular: 1) the assumption of a dip angle of 50°, is not consistent with the activated structures; 2) the Pf = σ3 condition, difficult to be attained along a cohesionless fault dipping at 50°; 3) the isotropic stress state, i.e. σ2 = σ3, that is not consistent with the active or recent stress field in the area.  相似文献   

11.
The Odesan area in the eastern Gyeonggi Massif, South Korea, consists principally of migmatitic and porphyroblastic gneisses intruded by mangerite. Mafic mangerites with SiO2 contents from 52.40 to 54.20 wt.% have higher FeO* + MgO (14.98–18.28 wt.%) and CaO contents (5.80–7.84 wt.%) but lower total alkali contents (4.74 < Na2O + K2O < 5.80 wt.%) than felsic mangerites (55.9 < SiO2 < 60.61 wt.%, 9.51< FeO* + MgO < 11.62 wt.%, 3.28 < CaO < 5.68 wt.%, 6.72 < Na2O + K2O < 8.05 wt.%). Fe-numbers (FeO* / [MgO + FeO*]) are 0.44–0.47 for mafic mangerites and 0.38–0.42 for felsic mangerites. The mangerites show calc-alkaline affinities in an AFM plot and resemble high-Ba–Sr granitoids with low Rb / Sr ratios of 0.25–0.10. Their MORB-normalized compositions show enrichment in LILE (decoupled LIL/HFS pattern) and negative anomalies in Ti–Nb–Ta. Their geochemical characters are consistent with their formation by partial melting of a basaltic source at temperatures higher than 1025 °C. The mangerites of the present study differ from mangerite formed in a typical within-plate tectonic setting in their high mg# and Sr concentrations and negative Nb and Ta anomalies. Their LILE enrichment and negative Ti–Nb–Ta anomalies could well have been inherited from a pre-collision subduction event. A mean U–Pb zircon age of 257 Ma for the mangerite demonstrates that the tectonic belt connecting the Hongseong and Odesan areas represents a probable extension of the late Permian–Triassic collision belt between the North China and South China blocks into South Korea, with collision occurred earlier in South Korea.  相似文献   

12.
This study provides evidence for the existence of halite and sylvite solid inclusions in igneous quartz and feldspars, the first to be reported in intrusive rocks, and to partially constrain the physicochemical environment that lets halides crystallize under magmatic conditions.Halite and sylvite solid inclusions were found included in quartz and feldspars from a micrographic–granophyric assemblage in a miarolitic aplite and, rarer, in alkali-feldspar from a miarolitic monzogranite. Monzogranite and aplite represent I-type, K-enriched postcollisional rocks of the Late Cambrian–Early Ordovician Sierra Norte–Ambargasta batholith in the Eastern Sierras Pampeanas. Both granitoids fall among the most evolved felsic rocks of the batholith, with aplite approaching haplogranitic compositions. Halite is far more common than sylvite and the presence and distribution of one or both halides are erratic within the felsic intrusive bodies. Halides occur as small skeletal grains, commonly in cross-shaped aggregates of less than 50 μm. No K or Na was found at the detection limits of EDS in either halite or sylvite respectively. Textural relationships suggest that the alkali-chlorides separated from the melt near the minima along the quartz–feldspar cotectics of PH2O > 160 < 200 MPa in a silica-, and potassium-rich magmatic system at approximately 750–700 °C, prior to the H2O-vapor saturated miarole-forming stage.Computed ratios for the magmatic volatile phase (MVP) coexisting with melt at the early stage of aplite crystallization are: NaCl/HCl = 0.11–0.97 and KCl/HCl = 0.24–1.62, being the highest range of values (0.79–0.97 and 1.45–1.62, respectively) found in those alkali-chloride-bearing samples. Maximum HCl/ΣCl(MVP) (0.28 to 0.31) indicates higher total Cl concentration in the MVP of alkali-chloride-bearing aplites, which is much higher in the halite-free aplite samples (HCl/ΣCl(MVP) = 0.59 to 0.74). One miarolitic monzogranite sample, where halite solid inclusions are present, also yielded the highest ratios for NaCl/HCl(MVP) (0.91) and KCl/HCl(MVP) (1.46), and the HCl/ΣCl(MVP) is 0.30. A high HCl concentration in the fluid phase is suggested by the log f(HF)/f(H2O) = − 4.75 to − 4.95, log f(HCl)/f(H2O) = − 3.73 to − 3.86, and log f(HF)/f(HCl) = − 0.88 to − 1.22, computed at 750 °C after biotite composition. The Cl concentrations at 800 °C, computed with a Dv/lCl = 0.84 + 26.6P (P at 200 MPa), yielded values within the range of  70 to 700 ppm Cl in the melt and  4000 to 40 000 ppm Cl in the coexisting MVP. The preferential partitioning of Cl in the vapor phase is controlled by the Dv/lCl; however, the low concentration of Cl in the melt suggests that high concentrations of Cl are not necessary to saturate the melt in NaCl or KCl.Cl-saturation of the melt and coexisting MVP might have been produced by a drop in Cl solubility due to the near-haplogranitic composition of the granitoids after extreme fractionation, probably enhanced by fluctuating reductions of the emplacement pressure in the brittle monzogranite host. Liquid immiscibility, based in the differential viscosity and density among alkali-chloride saturated hydrosaline melt, aluminosilicate felsic melt, and H2O-rich volatiles is likely to have crystallized halite and sylvite from exsolved hydrosaline melt. High degrees of undercooling might have been important at the time of alkali-chloride exsolution. The effectiveness of alkali-chloride separation from the melt at magmatic temperatures is in line with the interpretation of “halite subtraction” as a necessary process to understand the origin of the “halite trend” in highly saline fluid inclusions from porphyry copper and other hydrothermal mineralizations, despite the absence of the latter in the Cerro Baritina aplites, where this process preceded the exsolution of halite-undersaturated fluids.Pervasive alteration of the monzogranite country rock as alkali-metasomatic mineral assemblages, the mineral chemistry of some species, and the association of weak molybdenite mineralization are compatible with the activity of alkaline hypersaline fluids, most likely exsolved during the earliest stages of aplite consolidation.  相似文献   

13.
A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ1−σ2)/(σ1−σ3) was calculated to be 0.64, indicating that σ2 lies closer to the midpoint between σ1 and σ3 than to σ3.  相似文献   

14.
The co-seismic deformations produced during the September 27, 2003 Chuya earthquake (Ms = 7.5) that affected the Gorny Altai, Russia, are described and discussed along a 30 km long segment. The co-seismic deformations have manifested themselves both in unconsolidated sediments as R- and R′-shears, extension fractures and contraction structures, and in bedrock as the reactivation of preexisting schistosity zones and individual fractures, as well as development of new ruptures and coarse crushing zones. It has been established that the pattern of earthquake ruptures represents a typical fault zone trending NW–SE with a width reaching 4–5 km and a dextral strike–slip kinematics. The initial stress field that produced the whole structural pattern of co-seismic deformations during the Chuya earthquake, is associated with a transcurrent regime with a NNW–SSE, almost N–S, trending of compressional stress axis (σ1), and a ENE–WSW, almost E–W, trending of tensional stress axis (σ3). The state of stress in the newly-formed fault zone is relatively uniform. The local stress variations are expressed in insignificant deviation of σ1 from N–S to NW–SE or NE–SW, in short-term fluctuations of relative stress values in keeping their spatial orientations, or in a local increase of the plunge angle of the σ1. The geometry of the fault zone associated with the Chuya earthquake has been compared with the mechanical model of fracturing in large continental fault zones with dextral strike–slip kinematics. It is apparent that the observed fracture pattern corresponds to the late disjunctive stage of faulting when the master fault is not fully developed but its segments are already clearly defined. It has been shown that fracturing in widely different rocks follows the common laws of the deformation of solid bodies, even close to the Earth surface, and with high rates of movements.  相似文献   

15.
The Temaguessine high-level subcircular pluton is intrusive into the LATEA metacraton (Central Hoggar) Eburnian (2 Ga) basement and in the Pan-African (615 Ma) granitic batholiths along a major NW–SE oriented major shear zone. It is dated here (SHRIMP U–Pb on zircon) at 582 ± 5 Ma. Composed of amphibole–biotite granite and biotite syenogranite, it comprises abundant enclaves: mafic magmatic enclaves, country-rock xenoliths and remarkable Fe-cordierite (#Fe = 0.87) orbicules. The orbicules have a core rich in cordierite (40%) and a leucocratic quartz–feldspar rim. They are interpreted as resulting from the incongruent melting of the meta-wacke xenoliths collapsed into the magma: the breakdown of the biotite + quartz assemblage produced the cordierite and a quartz–feldspar minimum melt that is expelled, forming the leucocratic rim. The orbicule generation occurred at T < 850° and P < 0.3 GPa. The Fe-rich character of the cordierite resulted from the Fe-rich protolith (wacke with 4% Fe2O3 for 72% SiO2). Strongly negative εNd (−9.6 to −11.2), Nd TDM model ages between 1.64 and 1.92 Ga, inherited zircons between 1.76 and 2.04 Ga and low to moderately high ISr (0.704–0.710) indicate a Rb-depleted lower continental crust source for the Temaguessine pluton; regional considerations impose however also the participation of asthenospheric material. The Temaguessine pluton, together with other high-level subcircular pluton, is considered as marking the end of the Pan-African magma generation in the LATEA metacraton, resulting from the linear delamination along mega-shear zones, allowing asthenospheric uprise and melting of the lower continental crust. This implies that the younger Taourirt granitic province (535–520 Ma) should be considered as a Cambrian intraplate anorogenic event and not as a very late Pan-African event.  相似文献   

16.
We conducted hydraulic fracturing (HF) in situ stress measurements in Seokmo Island, South Korea, to understand the stress state necessary to characterize a potential geothermal reservoir. The minimum horizontal principal stress was determined from shut-in pressures. In order to calculate the maximum horizontal principal stress (S Hmax) using the classical Hubbert–Willis equation, we carried out hollow cylinder tensile strength tests and Brazilian tests in recovered cores at depths of HF tests. Both tests show a strong pressure rate dependency in tensile strengths, from which we derived a general empirical equation that can be used to convert laboratory determined tensile strength to that suitable for in situ. The determined stress regime (reverse-faulting) and S Hmax direction (ENE–WSW) at depths below ~300 m agrees with the first order tectonic stress. However the stress direction above ~300 m (NE–SW) appears to be interfered by topography effect due to a nearby ridge. The state of stress in Seokmo Island is in frictional equilibrium constrained by optimally oriented natural fractures and faults. However, a severe fluctuation in determined S Hmax values suggests that natural fractures with different frictional coefficients seem to control stress condition quite locally, such that S Hmax is relatively low at depths where natural fractures with low frictional coefficients are abundant, while S Hmax is relatively high at depths where natural fractures with low frictional coefficients are scarce.  相似文献   

17.
New field, petrological, geochemical, and geochronological data (U–Pb and Sm–Nd) for Ordovician rock units in the southeastern Puna, NW Argentina, indicate two lithostratigraphic units at the eastern–northeastern border of salar Centenario: (1) a bimodal volcanosedimentary sequence affected by low- to medium-grade metamorphism, comprising metasediments associated with basic and felsic metavolcanic rocks, dated 485 ± 5 Ma, and (2) a plutonic unit composed of syenogranites to quartz-rich leucogranites with U–Pb zircon ages between 462 ± 7 and 475 ± 5 Ma. Felsic metavolcanic and plutonic rocks are peraluminous and show similar geochemical differentiation trends. They also have similar Sm–Nd isotopic compositions (TDM model ages of 1.54–1.78 Ga; εNd(T) values ranging from −3.2 to −7.5) that suggest a common origin and derivation of the original magmas from older (Meso-Paleoproterozoic?) continental crust. Mafic rocks show εNd(T) ranging from +2.3 to +2.5, indicating a depleted mantle source. The data presented here, combined with those in the literature, suggest Ordovician magmatism mainly recycles preexisting crust with minor additions of juvenile mantle-derived material.  相似文献   

18.
The local and geometrical structure around gold (III) e.g., Au3+ ions in aqueous solution with different OH−/Cl− molar ratios, has been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of [AuCln(OH)4−n]− solutions have been calculated and the multiple-scattering spectral features have been attributed to Cl d-states, axial water molecules and the replacement of Cl− ligands by OH− ligands. A square–planar geometry for [AuCln(OH)4−n]− with two axial water molecules has been identified. Moreover, a spectral correlation between XANES features and the type of planar atoms has been identified. By extended X-ray absorption fine structure spectra (EXAFS), the planar Au bond distances in the solutions have also been determined, e.g., 2.28 Å for Au–Cl and 1.98 Å for Au–O, respectively. The same EXAFS analysis provides evidence that the peak at about 4.0 Å in solutions with the lowest OH−/Cl− molar ratio arises from collinear Cl–Au–Cl multiple-scattering contributions. For the first time, a complete detailed reconstruction of the hydration structure of an Au ion at different pH values has been achieved.  相似文献   

19.
The Húsavík–Flatey Fault (HFF) is an oblique dextral transform fault, part of the Tjörnes Fracture Zone (TFZ), that connects the North Volcanic Zone of Iceland and the Kolbeinsey Ridge. We carry out stress inversion to reconstruct the paleostress fields and present-day stress fields along the Húsavík–Flatey Fault, analysing 2700 brittle tectonic data measured on the field and about 700 earthquake focal mechanisms calculated by the Icelandic Meteorological Office. This allows us to discuss the Latest Cenozoic finite deformations (from the tectonic data) as well as the present-day deformations (from the earthquake mechanisms). In both these cases, different tectonic groups are reconstructed and each of them includes several distinct stress states characterised by normal or strike-slip faulting. The stress states of a same tectonic group are related through stress permutations (σ1−σ2 and σ2−σ3 permutations as well as σ1−σ3 reversals). They do not reflect separate tectonic episodes. The tectonic groups derived from the geological data and the earthquake data have striking similarity and are considered to be related. The obliquity of the Húsavík–Flatey Fault implies geometric accommodation in the transform zone, resulting mainly from a dextral transtension along an ENE–WSW trend. This overall mechanism is subject to slip partitioning into two stress states: a Húsavík–Flatey Fault-perpendicular, NE–SW trending extension and a Húsavík–Flatey Fault-parallel, NW–SE trending extension. These three regimes occur in various local tectonic successions and not as a regional definite succession of tectonic events. The largest magnitude earthquakes reveal a regional stress field tightly related to the transform motion, whereas the lowest magnitude earthquakes depend on the local stress fields. The field data also reveal an early extension trending similar to the spreading vector. The focal mechanism data do not reflect this extension, which occurred earlier in the evolution of the HFF and is interpreted as a stage of structural development dominated by the rifting process.  相似文献   

20.
Neotectonic evolution of the Central Betic Cordilleras (Southern Spain)   总被引：1，自引：0，他引：1  
Paleostress orientations were calculated from fault-slip data of 36 sites located along a traverse through the Central Betic Cordilleras (southern Spain). Heterogeneous fault sets, which are frequent in the area, have been divided into homogeneous subsets by cross-cutting relationships observed in the field and by a paleostress stratigraphy approach applied on each individual fault population. The state of stress was sorted according to main tectonic events and a new chronology is presented of the Miocene to Recent deformation in the central part of the Betic Cordilleras. The deviatoric stress tensors fall into four distinct groups that are regionally consistent and correlate with three Late Oligocene–Aquitanian to Recent major tectonic events in the Betic Cordilleras. The new chronology of the neotectonic evolution includes, from oldest to youngest, the following main tectonic phases:
(1) Late Oligocene–Aquitanian to Early Tortonian: σ1 subhorizontal N–S, partly E–W directed, σ3 subvertical; compressional structures (thrusting of nappes, large-scale folding) and strike-slip faulting in the Alborán Domain and the External Zone of the Betic Cordilleras;
(2) Early Tortonian to Pliocene–Pleistocene: σ1 subvertical, σ3 subhorizontal NW–SE, partly N–S directed or E–W-directed (radial extension); large-scale normal faulting in the Central Betic Cordilleras and in the oldest Neogene formations of the Granada Basin related to the gravitational collapse of the Betic Cordilleras and the exhumation of the intensely metamorphosed rock series of the Internal Zones, at the same time formation of the Alborán Basin and intramontane basins such as the Granada Basin;
(3) Pleistocene to Recent: (3a) σ1 subvertical, σ3 subhorizontal NE–SW with prominent normal faulting, but coevally; (3b) σ1 subhorizontal NW directed, σ3 NE–SW subhorizontal with strike-slip faulting. Extensional structures and strike-slip faulting are related to the ongoing convergence of the Eurasian and African Plates and coeval uplift of the Betic Cordilleras. Reactivation of pre-existing fractures and faults was frequently observed. Phase 3 is interpreted as periodic strike-slip and normal faulting events due to a permutation of the principal stress axes, mainly σ1 and σ2.
Keywords: Neotectonics; Paleostress; Fault-slip data; Deformation history; Betic Cordilleras  相似文献   

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