Sediment Characteristics of Tidal Deposits at Mandvi, Gulf of Kuchchh, Gujarat, India: Geophysical, Textural and Mineralogical Attributes

The textural and mineralogical characteristics of subsurface sediments along with Ground Penetrating Radar (GPR) data collected along the Western margin of India were used to understand the depositional environments and the provenance of sediments. Textural attributes such as mean, standard deviation, skewness and Kurtosis show fluctuations due to fluvio-marine interaction and it is well understood that the bottom sediments are enriched with muddy sand, which may be deposited by mean of tidal invasion. The abundance of very coarse silt to very fine sand indicates the prevalence of low energy environment. The Linear Discriminate Function analysis indicates the fluvio marine deposition of sediments under low energy condition. GPR data upto a depth of 5 m shows the stratigraphic sequences of very fine sands and coarse silt. Optically Stimulated Luminescence (OSL) dating of sediments implies that the tidal sediments had deposited between ~30 ± 1 and ~90 ± 4 years before Present. XRD studies results the dominance of K-feldspar and deficiency of clay minerals, indicating that most of the sediments are derived from hinterland. Studies indicate that the Provenance of sediments in the Mandvi area is not related to Indus delta even though a considerable part of Gulf sediments are deposited by the Indus River.

Magnetotelluric investigation of lithospheric electrical structure beneath the Dharwar Craton in south India:Evidence for mantle suture and plume-continental interaction

Broad-band and long period magnetotelluric measurements made at 63 locations along -500 km long Chikmagalur-Kavali profile,that cut across the Dharwar craton (DC) and Eastern Ghat Mobile Belt (EGMB) in south India,is modelled to examine the lithosphere architecture of the cratonic domain and define tectonic boundaries.The 2-D resistivity model shows moderately conductive features that intersperse a highly resistive background of crystalline rocks and spatially connect to the exposed schist belts or granitic intrusions in the DC.These features are therefore interpreted as images of fossil pathways of the volcanic emplacements associated with the greenstone belt and granite suite formation exposed in the region.A near vertical conductive feature in the upper mantle under the Chitradurga Shear Zone represents the Archean suture between the western and eastern blocks of DC.Although thick (-200 km) cratonic (highly resistive) lithosphere is preserved,significant part of the cratonic lithosphere below the western DC is modified due to plume-continental lithosphere interactions during the CretaceouseTertiary period.A west-verging moderately conductive feature imaged beneath EGMB lithosphere is interpreted as the remnant of the Proterozoic collision process between the Indian land mass and East Antarctica.Thin (-120 km) lithosphere is seen below the EGMB,which form the exterior margin of the India shield subsequent to its separation from East Antarctica through rifting and opening of the Indian Ocean in the Cretaceous.

New Data on the Mineralogy of Chromite from the Nuggihalli Schist Belt,Western Dharwar Craton,Karnataka,India:Petrogenetic Implications

The occurrence of rhythmic layering of chromite and host serpentinites in the deformed layered igneous complexes has been noticed in the Nuggihalli schist belt （NSB） in the western Dharwar craton, Karnataka, South India. For this study, the chromitite rock samples were collected from Jambur, Tagadur, Bhakatarhalli, Ranganbetta and Byrapur in the NSB. Petrography and ore microscopic studies on chromite show intense cataclasis and alteration to ferritchromite. The ferritchromite compositions are characterized by higher Cr number （Cr/[Cr＋AI]） （0.68-0.98） and lower Mg number （Mg/[Mg＋Fe]） （0.33-0.82） ratios in ferritchromite compared to that of parent chromite. The formation process for the ferritchromite is thought to be related to the exchange of Mg, AI, Cr, and Fe between the chromite, surrounding silicates （serpentines, chlorites）, and fluid during serpentinization.

Upper mantle anisotropy inferred from shear wave splitting beneath the Eastern Indian Shield region

We estimate the shear wave splitting parameters vis-a-vis the thicknesses of the continental lithosphere beneath the two permanent seismic broadband stations located at Dhanbad(DHN) and Bokaro(BOKR) in the Eastern Indian Shield region. Broadband seismic data of 146 and 131 teleseismic earthquake events recorded at DHN and BOKR stations during 2007-2014 were analyzed for the present measurements.The study is carried out using rotation-correlation and transverse component minimization methods. We retain our "Good", "Fair" and "Null" measurements, and estimate the splitting parameters using 13 "Good" results for DHN and 10 "Good" results for BOKR stations. The average splitting parameters(φ,δt)for DHN and BOKR stations are found to be 50.76°±5.46° and 0.82±0.2 s and 56.30°±5.07° and0.95 ± 0.17 s, and the estimated average thicknesses of the anisotropic layers beneath these two stations are ～94 and ～109 km,respectively. The measured deviation of azimuth of the fast axis direction(0)from the absolute motion of the Indian plate ranges from ～8° to 14°. The measured deviation of azimuth of the fast axis direction(0) from the absolute motion of the Indian plate ranges from ～8° to 14°. The eastward deviation of the fast axis azimuths from absolute plate motion direction is interpreted to be caused by induced outflow from the asthenosphere. Further, the delay time found in the present analysis is close to the global average for continental shield areas, and also coherent with other studies for Indian shield regions. The five "Null" results and the lower delay time of ～0.5-0.6 s might be indicating multilayer anisotropy existing in the mantle lithosphere beneath the study area.

Basin Groundwater Recharge and Discharge in the Gully Erosion Prone Areas of Anambra, Nigeria

Anambra State of Nigeria is ravaged by ecological hazards of gully erosion and landslides. Over 450 active gully and landslide sites with depths ranging from 5 m to over 120 m are concentrated on both sides of the Awka-Nanka-Umuchu-Orlu cuesta. The Idemili River and Odo River form the major drainage basins of the area. The geomorphic characteristic of the cuesta/escarpment is a major controlling factor in groundwater recharge and discharge within the drainage basins. Rise in aquifer levels result in hydrogeotechnical implications of gully development and landslides. The calculated values of hydraulic properties of conductivity and transmissivity range from 1.20×10^-1 to 5.93×10^-1 cm/s and 1.15×10^5-13.05×10.3 m^2/s respectively. The values of groundwater velocity and groundwater discharge were 82 m.yearl and 2.96×10^6 m^3.yearl The plasticity index of the soil in the gully prone areas is relatively low ranging from 12.50-36.57%. The unique features of the geologic formations together with obtained aquifer characteristics favour gully/landslide hazards in the area.

水库触发地震暨印度Koyna地震近期研究

人们研究水库人工蓄水触发地震已经有60余年历史。至今,全球已证实因水库蓄水诱发地震超过90例。人工蓄水触发地震的研究在大量文献和专著中已有论述。本文以Gupta编著的《水库诱发地震》(Gupta, H.K., 1992,《Reservoir-Induced Earthquake》,阿姆斯特丹Elsevier出版)为基础,该著作包含了 1990年以前水库地震领域的必要信息。此外,补充了过去十年间水库地震研究的新信息。印度Koyna仍然是人工蓄水触发地震的最佳试验场。20世纪90年代,在Koyna附近和最近开始蓄水的Wama水库发生了两次超过M5的地震和许多小震。对于这些地震开展了大量关于地震重定位、应力降、地震成核、地震迁移等方面的工作。在一个独特的实验中,在Koyna-Wama地震活跃区布置了 21个90~250m的深钻井,并对水位进行连续监控。在一些井中,监测到与MM4地震相关的数厘米的阶跃状同震变化。加利福利亚Oroville地震序列作为记录最好的触发地震,层析成像结果揭示了这一地震序列与东南倾向的低速区相关。类似的现象在Aswan显示浅层地震活动性和低的P波波速相关。自20世纪90年代以来,已经有一些新的蓄水库报告称触发了地震活动。最重要的一次是在泰国Srinagarind大坝,发生了 M 5.9地震,而且这次地震序列具有诱发地震序列的特点。新的理论工作,特别是孔隙流体压力对非均质岩石的影响和对触发地震活动的意义是一个重要的发展。但是,要充分认识人工蓄水库在触发地震中的作用,还需要进行更多的研究。