Deformation history and U–Pb zircon geochronology of the high grade metamorphic rocks within the Klaeng fault zone,eastern Thailand     

《Journal of Asian Earth Sciences》2013

In eastern Thailand the Klaeng fault zone includes a high-grade metamorphic rock assemblage, named Nong Yai Gneiss, which extends about 30 km in a NW–SE direction along the fault zone. The rocks of this brittle-fault strand consist of amphibolite to granulite grade gneissic rocks. Structural analysis indicates that the rocks in this area experienced three distinct episodes of deformation (D₁–D₃). The first (D₁) formed large-scale NW–SE-trending isoclinal folds (F₁) that were reworked by small-scale tight to open folds (F₂) during the second deformation (D₂). D₁ and D₂ resulted from NE–SW shortening during the Triassic Indosinian orogeny before being cross-cut by leucogranites. D₁ and D₂ fabrics were then reworked by D₃ sinistral shearing, including shear planes (S₃) and mineral stretching lineations (L₃). LA–MC–ICP–MS U–Pb zircon dating suggested that the leucogranite intrusion and the magmatic crystallization took place at 78.6 ± 0.7 Ma followed by a second crystallization at 67 ± 1 to 72.1 ± 0.6 Ma. Both crystallizations occurred in the Late Cretaceous and, it is suggested, were tectonically influenced by SE Asian region effects of the West Burma and Shan-Thai/Sibumasu collision or development of an Andean-type margin. The sinistral ductile movement of D₃ was coeval with the peak metamorphism that occurred in the Eocene during the early phases of the India–Asia collision.  相似文献   

The effect of long-term soil irrigation by wastewater on organic matter, polycyclic aromatic hydrocarbons, and heavy metals evolution: case study of Zaouit Sousse (Tunisia)     

Khadhar Samia  Charef Abdelkarim  Hidri Yassin  Higashi Teruo 《Arabian Journal of Geosciences》2013,6(11):4337-4346

Irrigation by treated wastewater (TWW) can pollute the soil by different organic and inorganic compounds. The pollution level can depend on the irrigation period, soil nature, and wastewater characteristics. Since 1989, the Zaouit Sousse area (central Tunisian) has been irrigated by treated wastewater. The irrigation period and the mineralogy of soil composition change from one locality to another in Zaouit Sousse area. In this work, we are interested in organic compounds, polycyclic aromatic hydrocarbons (PAHs), and heavy metals (HMs) evolution. One control soil (S1) and four irrigated areas soil (S2, S3, S4, and S5) were chosen. The soil samples differ by the irrigation period and soil characteristics. Total PAHs content in control soil was 66.2 ng?g^?1 and in irrigated areas were between 46.23 and 129.51 ng?g^?1. The PAHs content in irrigated soil, except S5 which has been irrigated with wastewater for 20 years and contains the highest clay fraction percent, decreased with the irrigation period (from 0 to 20 years). The microbial degradation may decrease the PAHs concentrations in the soil thanks to bacterium brought by TWW and the important soil permeability. Concentration of heavy metals ranged from 24 to 1,320 μg?L^?1. The HMs (Cu, Cr, Zn, Fe, Ni, Pb, and Cd) contents decreased with the irrigation period (from 10 to 20 years). So, following the PAHs aerobic bio-degradation, this organic compound discharges their absorbed heavy metals which leached to deeper levels. The Cr, Cu, Al, Zn, and Cd mobility depend on the clay yield too. However, the PAHs and Pb mobility are also related to humic substance quantities. Cr and Cu have affinities both to clay and humic substance quantities.  相似文献   

First record of myrmecochorous diaspores removal by dung beetles in the Caatinga vegetation,a Brazilian semiarid ecosystem     

《Journal of Arid Environments》2013

Canthon (Francmonrosia) carbonarius is recognized as coprophagous and this paper describes, for the first time, the interaction between the dung beetle and seeds of Jatropha mollissima, in Pernambuco state, on the Caatinga vegetation. The observed activities were remotion of elaiosome parts, rolling and deposition of the diaspore on the beetle burial site. Interactions between myrmecochorous diaspores and dung beetle may have important ecological implications. These insects may also act as either predators or secondary dispersal agents of myrmecochorous seeds available in the environment. The findings of the present study serve as a starting point for future studies assessing the ecological implications on the use of this new type of resource by dung beetles in the Caatinga vegetation.  相似文献   

A quantitative assessment of vegetable farming on vacant lots in an urban fringe area in Metro Manila: Can it sustain long-term local vegetable demand?     

《Applied geography (Sevenoaks, England)》2013

The aim of this study was to quantitatively assess vegetable production and consumption in an urban fringe area in Metro Manila, the Philippines. We conducted field investigations into vegetable production at a farm within a subdivision, monitored customers for 1 week at the farm's vegetable stand, interviewed customers of the stand, and conducted household monitoring and interviews to identify purchasing behavior. We also conducted an object-based WorldView-2 image analysis of a larger area to identify current and potential future vegetable farming plots and a spatial analysis using GIS to visualize the vegetable production/consumption ratio. We found that about one-third of current vegetable demand could be supplied by greater promotion of vegetable farming in vacant lots and by setting up more vegetable stands at spatial intervals less than 1-km. Subdivision regulations also influenced vegetable farming because of the level of social acceptance of caretakers of vacant lots. The current planning and institutional framework does not consider social contexts in land use and planning. We suggested that a new framework is necessary; it should consider balancing the formation of social capital and formalize planning and institutional procedures to support sustainable local vegetable production.  相似文献   

泰国东南部Rayong省Klaeng地区的中-晚泥盆世放射虫     

Yoshihito KAMATA  Miyako KATO  Katsumi UENO  Akira MIYAHIGASHI  Thasinee CHAROENTITIRAT  Apsorn SARDSUD 《地球学报》2012,33(S1):33-35

Tectonic subdivision of mainland Thailand has been discussed by means of Paleozoic and Mesozoic stratigraphy, micropaleontology represented by fo-raminiferal and radiolarian biostratigraphy and paleo-biogeography, tectonic settings of granitoids, and ul-tramafic rocks that are distinctive of suture lines. Re-cently, Ueno (2002) and Ueno and Charoentitilat (2011) proposed a new tectonic scheme of mainland Thailand and divided it into three geotectonic units: the Sibu-masu Block, Sukhothai Zone, and Indochina Block from west to east, which are separated by the Mae Yuan Fault, the Chiang Rai Tectonic Line, and the Nan–Uttaradit Suture, respectively. In Northern Thai-land, moreover, the peculiar Inthanon Zone is recog-nized in the eastern part of the Sibumasu Block, where Paleo-Tethyan oceanic rocks are widely distributed as tectonic slices. These geotectonic subdivisions in Northern Thailand are relatively clear. However, the tectonic subdivisions of Central and Southeast Thai-land have not been well documented and are still con-troversial because there is short of information about basement rocks in those areas. In this circumstance, we have examined Paleozoic to Mesozoic stratigraphy, lithology, and radiolarian ages of siliceous rocks dis-tributed in Southeast Thailand to clarify the geotec-tonic belongings of this area and the southern exten-sions of geotectonic units consisting of Northern Thailand. In the course of this research, we could ob-tain Middle to Late Devonian radiolarians from well-bedded siliceous rocks distributed in southwest of Klaeng, Rayong Province. In this study, we report lithology and age of the radiolaria-bearing rocks and discuss their stratigraphy and geological correlation nearby the Klaeng region.  相似文献   

Granulite formation in a Gondwana fragment: petrology and mineral equilibrium modeling of incipient charnockite from Mavadi, southern India     

Takahiro Endo  Toshiaki Tsunogae  M. Santosh  Hisako Shimizu  E. Shaji 《Mineralogy and Petrology》2013,107(5):727-738

We report a new occurrence of incipient charnockite from Mavadi in the Trivandrum Granulite Block (TGB), southern India, and discuss the petrogenesis of granulite formation in an arrested stage on the basis of petrography, geothermobarometry, and mineral equilibrium modeling. In Mavadi, patches and lenses of charnockite (Kfs?+?Qtz?+?Pl?+?Bt?+?Grt?+?Opx?+?Ilm?+?Mag) of about 30 to 220 cm in length occur within Opx-free Grt-Bt gneiss (Kfs?+?Qtz?+?Pl?+?Bt?+?Grt?+?Ilm). The application of mineral equilibrium modeling on the charnockite assemblage in the NCKFMASHTO system to constrain the conditions of charnockitization defines a P–T range of 800 °C at 4.5 kbar to 850 °C at 8.5 kbar, which is broadly consistent with the results from the conventional geothermobarometry (810–880 °C at 7.7–8.0 kbar) on these rocks. The P–T conditions are lower than the peak metamorphic conditions reported for the ultrahigh-temperature granulites from this area (T?>?900 °C). The heterogeneity in peak P–T conditions within the same crustal block might be related to local buffering of metamorphic temperatures by the Opx-Bt-Kfs-Qtz assemblage. The result of T versus mole H₂O (M(H₂O)) modeling demonstrated that the Opx-free assemblage in the Grt-Bt gneiss is stable at M(H₂O)?=?0.3 to 1.5 mol%, and orthopyroxene occurs as a stable mineral at M(H₂O) <0.3 mol%, which is consistent with the petrogenetic model of incipient charnockite related to the lowering of the water activity and stabilization of orthopyroxene through the breakdown of biotite by dehydration caused by the infiltration of CO₂-rich fluid from external sources. We also propose a possible alternative mechanism to form charnockite from Grt-Bt gneiss through slight variations in bulk-rock chemistry (particularly for the K- and Fe-rich portion of Grt-Bt gneiss) that can enhance the stability of orthopyroxene rather than that of biotite, with K-metasomatism playing a possible role.  相似文献   

Genotoxicity in two bivalve species from a coastal lagoon in the south of Portugal     

《Marine environmental research》2013

DNA damage was evaluated by comet assay in the haemolymph of two bivalve species Ruditapes decussatus and Mytilus galloprovincialis from the Ria Formosa lagoon (south Coast of Portugal). Clams and mussels were sampled from sites close to each other to determine interspecific responses to similar environmental conditions, considering also seasonal and gender differences. Coupled with genotoxic effect, another damage biomarker (lipid peroxidation) was analysed to verify if the conditions that instigate DNA damage can be related with injury to cell membranes. For both species, DNA damage was low, reflecting the low levels of genotoxic contaminants in the lagoon, and no interspecific differences were found. However, seasonal differences were established for both bivalve species, reflecting higher environmental stress in summer. Regarding gender susceptibility, only clams showed differences in percentage of Tail DNA, with females more sensitive to DNA damage than males. Additionally, results for clams point out that factors responsible for LPO may not be the same as those causing genotoxicity. This study demonstrated that DNA damage is a sensitive biomarker to discriminate spatial, temporal and gender differences, being an appropriate biomarker for genotoxicity evaluation even in places of low contamination, such as the Ria Formosa lagoon.  相似文献   

Are small rodents key promoters of ecosystem restoration in harsh environments? A case study of abandoned croplands on Mongolian grasslands     

Y. Yoshihara  T. Okuro  J. Undarmaa  T. Sasaki  K. Takeuchi 《Journal of Arid Environments》2009,73(3):364-368

We focused on the potential contribution of fossorial rodents to recovery of degraded abandoned Mongolian croplands. From field observations and the literature, we determined that plant litter and soil crusting were the main factors preventing establishment or growth of the perennial grass Elymus chinensis (Poaceae) on these croplands. We hypothesized that small fossorial rodents such as Mongolian gerbils promote grass establishment and growth by clearing litter and destroying crusts. We designed a path model linking number of burrows to patch size and plant volume of E. chinensis. As we hypothesized, small rodents increased the patch size of E. chinensis through reduction of litter cover. However, unexpectedly, we could not find significant effects on E. chinensis via crust thickness. Our results suggest that litter removal by the rodents gave E. chinensis suitable space that was free of competitors; this allowed expansion of the E. chinensis patches. Any effect of soil crusting on plant volume could not be explained simply by the variables we used, probably because some other mechanism, such as temporal variation in the crust, was involved. We demonstrate that small rodents are key agents in the recovery of degraded grasslands.  相似文献   

Using postglacial sea level,crustal velocities and gravity-rate-of-change to constrain the influence of thermal effects on mantle lateral heterogeneities     

《Journal of Geodynamics》2009,47(3-5):104-117

Lateral heterogeneities in the mantle can be caused by thermal, chemical and non-isotropic pre-stress effects. Here, we investigate the possibility of using observations of the glacial isostatic adjustment (GIA) process to constrain the thermal contribution to lateral variations in mantle viscosity. In particular, global historic relative sea level, GPS in Laurentide and Fennoscandia, altimetry together with tide-gauge data in the Great Lakes area, and GRACE data in Laurentide are used. The lateral viscosity perturbations are inferred from the seismic tomography model S20A by inserting the scaling factor β to determine the contribution of thermal effects versus compositional heterogeneity and non-isotropic pre-stress effects on lateral heterogeneity in mantle viscosity. When β = 1, lateral velocity variations are caused by thermal effects alone. With β < 1, the contribution of thermal effect decreases, so that for β = 0, there is no lateral viscosity variation and the Earth is laterally homogeneous. These lateral viscosity variations are superposed on four different reference models which differ significantly in the lower mantle viscosity. The Coupled Laplace Finite Element method is used to predict the GIA response on a spherical, self-gravitating, compressible, viscoelastic Earth with self-gravitating oceans, induced by the ICE-4G deglaciation model.Results show that the effect of β on uplift rates and gravity rate-of-change is not simple and involves the trade-off between the contribution of lateral viscosity variations in the transition zone and in the lower mantle. Models with small viscosity contrast in the lower mantle cannot explain the observed uplift rates in Laurentide and Fennoscandia. However, the RF3S20 model with a reference viscosity profile simplified from Peltier's VM2 with the value of β around 0.2–0.4 is found to explain most of the global RSL data, the uplift rates in Laurentide and Fennoscandia and the BIFROST horizontal velocity data. In addition, the changes in GIA signals caused by changes in the value of β are large enough to be detected by the data, although uncertainty in other parameters in the GIA models still exists. This may encourage us to further utilize GIA observations to constrain the thermal effect on mantle lateral heterogeneity as geodetic and satellite gravity measurements are improved.  相似文献   

Reactive-transport modeling of fly ash–water–brines interactions from laboratory-scale column studies     

《Physics and Chemistry of the Earth》2014

Dynamic leaching tests are important studies that provide more insights into time-dependent leaching mechanisms of any given solid waste. Hydrogeochemical modeling using PHREEQC was applied for column modeling of two ash recipes and brines generated from South African coal utility plants, Sasol and Eskom. The modeling results were part of a larger ash–brine study aimed at acquiring knowledge on (i) quantification and characterization of the products formed when ash is in contact with water–brines in different scenarios, (ii) the mineralogical changes associated with water–brine–ash interactions over time, (iii) species concentration, and (iv) leaching and transport controlling factors. The column modeling was successfully identified and quantified as important reactive mineralogical phases controlling major, minor and trace elements’ release. The pH of the solution was found to be a very important controlling factor in leaching chemistry. The highest mineralogical transformation took place in the first 10 days of ash contact with either water or brines, and within 0.1 m from the column inflow. Many of the major and trace elements Ca, Mg, Na, K, Sr, S(VI), Fe, are leached easily into water systems and their concentration fronts were high at the beginning (within 0.1 m from the column inflow and within the first 10 days) upon contact with the liquid phase. However, their concentration decreased with time until a steady state was reached. Modeling results also revealed that geochemical reactions taking place during ash–water–brine interactions does affect the porosity of the ash, whereas the leaching processes lead to increased porosity. Besides supporting experimental data, modeling results gave predictive insights on leaching of elements which may directly impact on the environment, particularly ground water. These predictions will help develop scenarios and offer potential guide for future sustainable waste management practices as a way of addressing the co-disposal of brines within inland ash dams and heaps.  相似文献