Geochemistry of subducted metabasites exhumed from the Mariana forearc: Implications for Pacific seamount subduction     

Jianghong Deng  Lipeng Zhang  He Liu  Haiyang Liu  Renqiang Liao  Abdul Shakoor Mastoi  Xiaoyong Yang  Weidong Sun 《地学前缘(英文版)》2021,12(3):101117

Seamounts on the drifting oceanic crust are inevitably carried by plate motions and eventually accreted or subducted. However, the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained. Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene (~52 Ma). The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes, providing exceptional opportunities to directly study the subducted oceanic crust and seamounts. The International Ocean Discovery Program (IODP) expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes, e.g., the Fantangisña and Asùt Tesoru seamounts. These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and Nd-Hf isotopes characteristics, suggesting different provenances and mantle sources. The tholeiites from the Fantangisña Seamount have trace element characteristics typical of mid-ocean ridge basalt. The Pacific-type Hf-Nd isotopic compositions, combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust. The alkali basalts-dolerites from the Fantangisña and Asùt Tesoru seamounts show ocean island basalt (OIB)-like geochemical characteristics. The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate. The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.Two types of OIBs have been recognized from alkali metabasites, one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province, and another is similar to the EMII-type OIBs from the Samoa Island in southern Pacific, with negative Nb-Ta-Ti anomalies and enriched Nd-Hf isotopes. Generally, these alkali metabasites are sourced from the heterogeneous mantle sources that are similar to the present South Pacific Isotopic and Thermal Anomaly. This study provides direct evidence for seamount subduction in the Mariana convergent margins. We suggest seamount subduction is significant to element cycling, mantle heterogeneity, and mantle oxidation in subduction zones.  相似文献   

Observations of Antarctic precipitable water vapor and its response to the solar activity based on GPS sensing     

Wayan Suparta  Zainol Abidin Abdul Rashid  Mohd. Alauddin Mohd. Ali  Baharudin Yatim  Grahame J. Fraser 《Journal of Atmospheric and Solar》2008,70(11-12):1419-1447

Predicting global climate change is a great challenge and must be based on a thorough understanding of how the climate system components behave. Precipitable water vapor (PWV) is one of the key components in determining and predicting the global climate system. It is well known that the local surface temperature and pressure have a direct influence on the production of PWV. However, the influence of solar activity on atmospheric dynamics and their physical mechanisms is still an open debate, where past studies are focused at mid-latitude regions. A new method of determining and quantifying the solar influence on PWV based on GPS observations to correlate the GPS PWV and total electron content (TEC) variations is proposed. Observed data from Scott Base (SBA) and McMurdo (MCM) stations from 2003 to 2005 have been used to study the response of PWV to solar activity. In the analysis, the effects of local conditions (wind speed and relative humidity) on the distribution of PWV are investigated. Results show significant correlation between PWV and solar activity for four geomagnetic storms, with correlation coefficients of 0.74, 0.77, 0.64 and 0.69, which are all significant at the 95% confidence level. There was no significant correlation between TEC and PWV changes during the absence of storms. On a monthly analysis, a strong relationship exists between PWV and TEC during storm-affected days, with correlation coefficients of 0.83 and 0.89 (99% confidence level) for SBA and MCM respectively. These indicate a statistically significant seasonal signal in the Antarctic region, which is very active (higher) during the summer and inactive (lower) for the winter periods.  相似文献   

Contribution of intercepted subsurface flow to road runoff and sediment transport in a logging‐disturbed tropical catchment     

J. N. Negishi  R. C. Sidle  A. D. Ziegler  S. Noguchi  N. Abdul Rahim 《地球表面变化过程与地形》2008,33(8):1174-1191

Hydrological and sediment fluxes were monitored for a 1 yr period in a tropical headwater catchment where a 3 yr old logging road caused substantial Hortonian overland flow (HOF) and intercepted subsurface flow (ISSF). On a 51·5 m road section, ISSF became an increasingly important component of total road runoff, up to more than 90% for large storms. The proportion of ISSF contributed by road cuts along more or less planar slopes compared with ISSF from a zero‐order basin (convergent slopes) truncated by the road declined with increasing rainfall. During the monitored storms that generated ISSF along the road, on average, 28% of sediment export and 79% of runoff from the road section were directly attributable to ISSF. Estimates of total sediment export from the road surface (170 t ha^?1 yr^?1) and suspended sediment export from the logging‐disturbed catchment (4 t ha^?1 yr^?1) were exceptionally high despite 3 yr of recovery. ISSF caused not only additional road‐generated sediment export, but also exacerbated HOF‐driven erosion by creating a poor foundation for vegetation recovery on the road surface. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Salt-water intrusion mapping by geoelectrical imaging surveys   总被引：7，自引：0，他引：7  

S.S. Abdul Nassir  M.H. Loke  C.Y. Lee  M.N.M. Nawawi 《Geophysical Prospecting》2000,48(4):647-661

The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore-water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt-water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh-water/saline-water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites.  相似文献   

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet,north-eastern Bangladesh     

Nasir Ahmed  Md.Bodrud-Doza  S.M.Didar-Ul Islam  Manzoor Ahmad Choudhry  Md.Iftakharul Muhib  Anwar Zahid  Shahadat Hossain  Md.Moniruzzaman  Nipa Deb  Md.Abdul Quaiyum Bhuiyan 《Acta Geochimica》2019,(3):440-455

To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC,DO, DOC, Na^+, K^+, Ca²⁺, Mg²⁺, Cl^-, SO_4^2-, NO_3^-,HCO_3^-, SiO_2^-, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO_3 is the dominant groundwater type. The mean value of temperature, EC,Na^+, K^+, Ca²⁺, Mg²⁺, Cl^-, NO_3^- and SO_4^2- were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3and 21.4 lg/L respectively, which varied from 0.03 to148 lg/L. From spatial distribution, it was found that Fe,Mn and As concentrations are high but patchy in northern,north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson's correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers,rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area.  相似文献   

Analytical Modeling of Well Design in Riverbank Filtration Systems     

Shaymaa Mustafa  Mohamad Darwish  Arifah Bahar  Zainal Abdul Aziz 《Ground water》2019,57(5):756-763

Analytical studies for well design adjacent to river banks are the most significant practical task in cases involving the efficiency of riverbank filtration systems. In times when high pollution of river water is joined with increasing water demand, it is necessary to design pumping wells near the river that provide acceptable amounts of river water with minimum contaminant concentrations. This will guarantee the quality and safety of drinking water supplies. This article develops an analytical solution based on the Green's function approach to solve an inverse problem: based on the required level of contaminant concentration and planned pumping time period, the shortest distance to the riverbank that has the maximum percentage of river water is determined. This model is developed in a confined and homogenous aquifer that is partially penetrated by the stream due to the existence of clogging layers. Initially, the analytical results obtained at different pumping times, rates and with different values of initial concentration are checked numerically using the MODFLOW software. Generally, the distance results obtained from the proposed model are acceptable. Then, the model is validated by data related to two pumping wells located at the first riverbank filtration pilot project conducted in Malaysia.  相似文献   

Crop Residues Mulch as Organic Weed Management Strategy in Maize          下载免费PDF全文

Azhar Mahmood  Muhammad Zahid Ihsan  Abdul Khaliq  Saddam Hussain  Zahid Ata Cheema  Muhammad Naeem  Ihsanullah Daur  Hafiz Athar Hussain  Fahad Alghabari 《洁净——土壤、空气、水》2016,44(3):317-324

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Supercritical Fluid CO2 Technique for Destruction of Pathogenic Fungal Spores in Solid Clinical Wastes          下载免费PDF全文

Efaq A. Noman  Nik N. N. A. Rahman  Mohammad Shahadat  Hideyuki Nagao  Adel Al‐Gheethi  Tengku N. T. Lah.  Abdul K. M. Omar 《洁净——土壤、空气、水》2016,44(12):1700-1708

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Countermeasure of river bend scour using a combination of submerged vanes and riprap     

Piya Biswas  Abdul Karim Barbhuiya 《国际泥沙研究》2018,33(4):478-492

A series of laboratory flume experiments were done in a large-scale 180° bend with non-cohesive sediment to find optimal or effective protection works at a bend. Detailed study of the scour and flow field dynamics with and without protection works was done. Spatially dense, high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three-dimensional(3 D)velocity throughout the bend. Characterizing the role of flow field dynamics on the pattern of deposition and erosion through experimental measurements provided valuable data about how such flow features contribute to scour and about the performance of the protection works. From the experimental results, it is revealed that for a perennial river it is not possible to protect from scour either with riprap or with submerged vanes alone. Protection from scour at a bend can be achieved with proper combination of these two works. First, submerged vanes can protect the toe, and, second, riprap can protect the upper part of the slope if it is not damaged through toe erosion. The experiments convincingly demonstrate the efficiency of this bank protection technique.  相似文献   

Metabolic and physiological regulation of Chlorella sp. (Trebouxiophyceae,Chlorophyta) under nitrogen deprivation     

Yong  Wai-Kuan  Lim  Phaik-Eem  Vello  Vejeysri  Sim  Kae-Shin  Abdul Majid  Nazia  Mustafa  Emienour Muzalina  Nik Sulaiman  Nik Meriam  Liew  Kan-Ern  Chen  Brenna Jia-Tian  Phang  Siew-Moi 《中国海洋湖沼学报》2019,37(1):186-198

Journal of Oceanology and Limnology - A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel...  相似文献