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1.
Volcanic rocks occupy considerable regions in the western portion of India, attaining a maximum thickness of 7000′ near Igatpuri. These rocks are essentially basaltic in nature and are generally referred to as plateau basalts. An attempt has been made in this paper to present some results of geological and geophysical investigations carried out in the Deccan Traps. Three areas (Ajanta - Long. 75″41′ -75° 45′ E, Lat. 20° 32′ - 20° 35′ 15″ N, 18 sq. miles in area; Ellora -Long. 75″ 11′ - 75° 16′ E, Lat. 20° 1′ - 20° 9′ N, 80 sq. miles in area; and Chincholi - Long. 77° 22′ - 77° 30′ E, Lat. 17° 22′ -17° 30′ N, 50 sq. miles in area) have been chosen for this study because of their geological setting. A large number of field specimens have been collected for petrographic study. This is supplemented by examination of microsections and chemical analyses of a few traps. In the Chincholi area where the trap overlies the granites, limestones seem to intervene in between trap and granites. With a view to estimate the possible thickness of the limestone beds, the distribution of intensity of magnetic field in a portion of the area has been studied with a magnetometer. Magnetic susceptibilities in case of few specimens have also been studied. Elastic constants of Deccan Traps have been determined for fifty specimens, employing the Wedge Method. These are further correlated with textural features and porosity values. Such an integrated geological and geophysical investigation on Deccan Traps is bound to reveal some interesting results.  相似文献   

2.
Geochemistry of Pliocene to recent volcanic rocks from Los Humeros caldera (19°30′ N – 19°50′ N and 97°15° W – 97°35′ W) in East-Central mexico is described. The volcanic rocks from this area seem to represent both alkali and high-alumina basalt series, or both calcalkaline and high-K calc-alkaline sequences. The available bulk-chemical analyses (23 this study and 18 from unpublished literature) show that the entire sequence of rocks from basalts to rhyolites are present in this area. Different degrees of partial melting of the source region followed by extensive shallow-level crystal differentiation seem to have taken place before most volcanic eruptions. These processes are perhaps the most important mechanisms for magma genesis in Los Humeros caldera. Geophysical studies in this area are not sufficient and more detailed geophysical surveys and a better geological interpretation are needed in order to delimit the underlying magma chamber.  相似文献   

3.
Geology and volcanology of the Edd-Bahar Assoli area (Ethiopia)   总被引：1，自引：0，他引：1  
The paper presents geological and petrological data on one of the alkaline ranges developed along the borders of the Afar depression (Ethiopia). These alkaline ranges occur in a position transversal to the dominant NNW trend of the spreading zones of northern and central Afar which are characterized by magmas of tholeiitic affinity. The Edd-Bahar Assoli volcanic range consists of broad fields of basic lavas and numerous spatter cones outcropping in the area extending between 13°25′ and 13°75′ lat. N and 41°38′ and 42°15′ long. E. The mineralogical assemblage and the chemical data point to an alkaline nature for this range consisting mainly of alkali olivine basalts and basalts tending to hawaiites, the most evolved terms being largely subordinate. Petrologic differences between the Assab, Edd-Bahar Assoli and Erta Ale ranges are shown. The Edd-Bahar Assoli alkaline volcanism would be related to tectonic patterns trending both from NNW-SSE to N-S and from NE-SW to E-W. The supposed similarity with the transverse structure of the equatorial Atlantic ocean would thus not completely be ascertained in this zone. In Afar, the coexistence of an axial volcanism of tholeiitic affinity with an alkaline volcanism at the margin can better be explained by models based upon the upper mantle temperature distribution in a zone under oceanization.  相似文献   

4.
Two techniques, namely alternating-field demagnetization and thermal demagnetization, are widely being used for determining the stability of magnetization of a rock specimen. Recently a faster and simpler technique known as low-field hysteresis loop and memory-phenomenon test has been developed for determining the stability of magnetization directions of igneous rocks. In this paper the results of this new technique, after applying it to about 1000 specimens obtained from 250 oriented rock samples collected from 42 sites of Deccan Trap basalts from Mount Girnar (21°30′N; 70°30′E) and Mount Pavagarh (22°30′N; 73°30′E), India, are presented.The agreement between the mean natural remanent magnetization directions determined by this procedure and those computed after alternating-field demagnetization has been found to be very good. All the specimens from Mount Girnar and 94% of Mount Pavagarh specimens showed a stable line without any memory in a field ≈ 10 Oe. This indicates that the rocks from these two localities are highly stable and are most suitable ones for the determination of a precise palaeomagnetic direction.  相似文献   

5.
新疆天山地区壳幔S波速度结构特征及变形分析   总被引：1，自引：0，他引：1       下载免费PDF全文
天山地区地质构造复杂,地震活动频繁,其壳幔变形和深部结构一直受到学者们的高度关注.然而,由于天山地区地震台站资料较少,致使壳幔变形研究结果与解释存在诸多争议.本研究利用在天山地区（40°N-46°N,78°E-92°E）新布设的11个流动宽频带地震台站和该地区39个固定台站的观测资料,采用接收函数与面波联合反演方法,获得了研究区地壳厚度及壳幔S波速度结构.反演结果显示天山地区（41.5°N-44°N,78°E-88°E）平均地壳厚度为56 km,塔里木盆地（40°N-41.5°N,79°E-90°E）、准噶尔盆地（44°N-46°N,82°E-90°E）和吐鲁番盆地（42°N-43°N,88°E-90°E）具有较厚的沉积层,地壳平均厚度为43 km、53 km和46 km,整体表现为天山厚、盆地相对较薄的特征;在研究区南天山的最高峰（42°N,80.5°E）及北天山的最高峰（43.5°N,86°E）附近,中下地壳存在较厚的低速层,我们认为在强烈挤压作用下低速、低强度的中下地壳强烈变形可能是导致该区域快速隆升的主要原因.在研究区中部,位于塔里木盆地与准噶尔盆地之间的天山地区,中下地壳及上地幔均存在低速层,且盆地莫霍面向天山倾斜明显.结合前人的研究成果推测,在南北向构造挤压应力作用下,塔里木盆地与准噶尔盆地发生了向天山造山带方向的双向壳幔层间插入俯冲.在研究区东部,塔里木盆地东北缘与天山东部接触带的地壳内没有明显的低速层,推测应处在早期挤压变形状态,该区域的壳幔边界为缓变的速度梯度带,可能与上地幔热物质侵入或渗透有关.  相似文献   

6.
青藏高原岩石圈三维电性结构   总被引：3，自引：0，他引：3       下载免费PDF全文
本文报道通过综合大地电磁调查数据研究青藏高原岩石圈三维电阻率模型的初步成果.大地电磁法调查区域已经覆盖了高原大部分面积,为全区三维电阻率成像研究打下了可靠的基础.对多个测区大地电磁数据进行精细的同化处理和反演成像,取得了青藏高原可靠的岩石圈三维电阻率结构图像.成像的区域为28°N—35°N,80°E—104°E.三维反演计算时采用的网格尺寸为20km×20km,垂直方向不等间距剖分为26层.结果表明,青藏高原现今岩石圈电阻率扰动主要反映印度克拉通对亚欧大陆板块俯冲引起的热流体运动和大陆碰撞和拆离产生的构造.在岩石圈地幔,察隅地块、喜马拉雅地块和拉萨地块东部联成统一的高电阻率地块,它们反映了向北东俯冲的印度克拉通.雅鲁藏布江、班公—怒江和金沙江缝合带都有明显的低电阻率异常,表明岩石圈深处有热流体活动.雅鲁藏布江、班公—怒江和金沙江缝合带都有明显的低电阻率异常,也表明它们的岩石圈还有流体活动.青藏高原东部的低阻区沿100°E向地幔下方扩大,反映了金沙江断裂带有切穿岩石圈的趋势.地幔电阻率平面扰动的模式显示,青藏高原东西部的地体碰撞拼合形式和方向是不同的.在青藏高原西部,羌塘、拉萨和喜马拉雅等地体从北到南碰撞拼合.在青藏高原东部,羌塘—拉萨、察隅、印支、雅安和扬子等地体多方向拆离拼合,在地壳造成不正交的拆离带和压扭构造系.从高阻-低阻区的分布看,东部的地体拼合有地幔的根源,今后还会进一步发展.察隅地块岩石圈对青藏高原东部的楔入,使其北部和东部地块的岩石圈发生拆离撕裂,也造成热流体上涌的低电阻率异常.  相似文献   

7.
An en echelon suite of four fracture zones, trending approximately N40°E, has been discovered during a survey of the Southwest Indian Ocean Ridge between Bouvet Island and 14°E. The largest of these fracture zones, the Islas Orcadas and Shaka, are less than 30 km wide, have more than 3 km of vertical relief, and are respectively 100 and 200 km in length. The morphology of these and the Bouvet and Prince Edward fracture zones have been used to compute a pole for the relative motion between Africa and Antarctica. This pole, at 4°S and 32°W, is within the range of previously computed pole positions.Ridge basalts were dredged at three separate locations: at the Conrad fracture zone near 55°40′S and 3°51′W, at the Islas Orcadas fracture zone near 54°5′S and 6°4′E, and at the ridge crest near 11°E. In addition, samples from a probable upper mantle intrusion were recovered from one wall of the Islas Orcadas fracture zone. The opposite wall was very different consisting entirely of normal mid-ocean ridge basalt.  相似文献   

8.
本文采用天然地震近震走时反演地壳三维速度结构的方法获得了郯庐断裂带鲁苏皖段及附近地壳(30°N—37°N,113°E—122°E)三维速度结构.对地壳内分层速度结构的分析发现,郯庐断裂带鲁苏皖段存在速度的分段特征.郯庐断裂带鲁苏皖段浅层35.3°N以北,34.5°N—35.3°N间,33°N—34.5°N间呈现的速度分段和地表出露地层有关,与地质上安丘段、莒县—郯城段,新沂—泗洪段三个破裂单元相对应,且和各段的地震活动相呼应,表明郯庐带新沂到泗洪段可能是断裂的闭锁段.郯庐断裂带鲁苏皖段地壳速度结构自浅至深分为三段,大体位置是:南段(32.5°N—33°N以南),中段(32.5°N—33°N至35°N—35.3°N),北段(35°N—35.3°N以北).上地壳分段与苏鲁超高压变质岩带的插入有关,中、下地壳速度分段则可能和火山岩滞留有关.地壳各层速度结构不同段的速度差异反映了构造块体的速度差异,表明各构造块体在地壳下部仍有差异,郯庐带西侧速度总体高于东侧,反映了不同构造块体的形成和组成差别,也说明了该断裂带可能延伸到莫霍面.而不同深度的分段性可能反映了不同地质演化过程.  相似文献   

9.
This paper describes certain aspects of the F region storm morphology based on vertical incidence measurements at single ionosonde station Chilton (51°.60′N, 358°.70′E). The topics discussed include requirements for better understanding of the ionospheric F region morphology and its forecasting under geomagnetically quiet and disturbed conditions. A few common storms during the years of low (1996 and 1997) and high (2000 and 2001) solar activity are considered as well as the Short-Term Ionospheric Forecasting (STIF) method by using two representative examples. The merits are stressed of near-real-time use of data to provide more accurate specification of the geomagnetically disturbed ionosphere and forecast its structure few hours in advance.  相似文献   

10.
本文利用重力资料对兰州－天水地区的深部构造进行了研究。在计算中，采用Ｐａｒｋｅｒ－Ｏｌｄｅｎｂａｒｇ三维位场反演方法，反演前对重力资料进行了地形改和中新生低沉积层校正。根据反演结构，综合反演结果，综合分析了有关资料，认为该区为青藏块体过渡带，并且并且提出了陇中盆地为断块型构造盆地的新认识。  相似文献   

11.
Izvestiya, Physics of the Solid Earth - Abstract—The archaeomagnetic study of ceramic material from Veksa III archaeological site (φ = 59°17′ N, λ = 40°10′ E)...  相似文献   

12.
Analysis of wind, air temperature, humidity and rainfall data from Land Surface Processes Experiment (LASPEX) in the surface layer at Anand (22°35′N, 72°55′E) and Khandha (22°02′N, 73°11′E) during January to December 1997 is presented. Wind and temperature at various levels showed prominent diurnal variation. Progression of daily wind and temperature revealed the intra-seasonal, quasi-biweekly and 6–9 day oscillations indicated large-scale convection, transport of heat and water vapor from Arabian Sea towards these stations.Power spectrum of wind and humidity corroborated the planetary scale Madden–Julian oscillation in the surface layer. Periodic oscillations of 21, 6–9, 1 day and 12 h were prominent in the spectrum of all variables. Low-frequency spectral peaks showed the energy in wind is 2–3 times higher over Khandha than at Anand whereas temperature is 3 times higher at Anand than Khandha.  相似文献   

13.
Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.  相似文献   

14.
Age determination of paleotsunami sediment from Lombok Island, Indonesia, and surrounding area has been carried out using the 210 Pb method in BATAN Jakarta. The basic theory of this method assumes that weathering of sediments, including paleotsunami sediments, will result in 210 Pb enrichment. The principle of this method is to calculate 210 Pb contents accumulation in a particular sedimentation interval from the surface to the deeper buried sediments. The results are then converted into age or depositional time in years ago unit. The dating results from the paleotsunami sediments of the Gawah Pudak(S8°46’2.91’’, E115°56’34.23’’) and Gili Trawangan areas(S8°21’1.38’’, E116°2’36.6’’) indicate the Gawah Pudak sediments were deposited 37 years ago(c. in 1977)and 22 years ago(c. in 1992). Three paleotsunami sediments from Gili Trawangan were deposited 149 years ago(c. in 1865), 117 years ago(c. in 1897) and 42 years ago(c. in 1972). These results are then compared to the available Indonesian earthquake catalogue data. This study reveals that paleotsunami sediments around Lombok Islands, from older to younger, were caused by the 1857 earthquake(epicentre in Bali Sea; M7; S8°00’09.45’’,E115°29’56.41’’), 1897 earthquake(epicentre in Flores Sea;M5.5; S6°47’59.62’’, E120°48’03.5’’ or Sulu Sea earthquake; M8.5; 70 km NW of Basilan Island), the 1975 earthquake(Nusa Tenggara; S10°6’16.61’’, E123°48’09.39’’), 1977 earthquake(in Waingapu, Sumba; M8.0;S11°5’39.34’’, E118°27’50.86’’) and the 1992 earthquake(Flores; M7.8; S8°28’52.11’’, E121°53’44.3’’).  相似文献   

15.
The present study reports the analysis of GPS TEC prior to 3 earthquakes (M > 6.0). The earthquakes are: (1) Loyalty Island (22°36′S, 170°54′E) on 19 January 2009 (M = 6.6), (2) Samoa Island (15°29′S, 172°5′W) on 30 August 2009 (M = 6.6), and (3) Tohoku (38°19′N, 142°22′E) on 11 March 2011 (M = 9.0). In an effort to search for a precursory signature we analysed the land and ocean parameters prior to the earthquakes, namely SLHF (Land) and SST (Ocean). The GPS TEC data indicate an anomalous behaviour from 1–13 days prior to earthquakes. The main purpose of this study was to explore and demonstrate the possibility of any changes in TEC, SST, and SLHF before, during and after the earthquakes which occurred near or beneath an ocean. This study may lead to better understanding of response of land, ocean, and ionosphere parameters prior to seismic activities.  相似文献   

16.
This palaeomagnetic study is centered on agglomerates and volcanic rocks from the western margin of the Appalachian belt in the Drummondville-Actonvale-Granby area, Quebec (long.: 72°30′W, lat.: 46°00′N). It involves a total of 36 oriented samples (111 speciments) distributed over eleven sites. Both thermal and AF cleaning techniques were used to isolate residual remanent components. The dispersion of the directions is slightly reduced after AF cleaning and thermal treatment.The palaeopole position obtained is 191°E, 6°N (dm = 14°, dp = 7°) after thermal treatment and 164°E, 19°N (dm = 11°, dp = 6°) after AF cleaning. The polarity of most of the sites (two exceptions) are reversed. The thermal-treated data appear to be relatively stable and an approximate value of the primary magnetization is extracted from them. The palaeopole obtained does not lie close to the tentatively defined position of the Cambrian and Ordovician poles from rocks of the North American plate; it is located near the Upper Cambrian and Lower Ordovician poles from eastern Newfoundland and the Lower Ordovician pole from the Caledonides in Europe.  相似文献   

17.
In the Bohai Bay Basin and its adjacent regions(112°―124°E,34°―42°N),there exists abundant gas-petroleum while modern inter-plate seismic activity is robust.Although the tectonic structure of this region is very complicated,plenty of geological,geophysical and geochemical data and results are obtained through previous researches.On the basis of absorbing previous results,especially various kinds of geological and geophysical results,we collect and process the arrival time of P-wave phases of local events and tele-seismic events recorded by the station within this region from 1978 to 2004,build the responding initial model,and image the velocity structure of the crust and upper mantle of this region via tomography.The perturbation images of various depths and velocity profiles imply that the velocity structure of the crust and upper mantle in the Bohai Bay Basin and its adjacent regions is mainly influenced by the surface tectonic units,and is characterized by "Stripped along east-west,and zoned along south-north";some large-scaled faults penetrate Moho and lithosphere,and provide the channels for the basic lava or hot mass upwelling from the mantle.  相似文献   

18.
Kaoru  Sugihara  Naoto  Masunaga  Kazuhiko  Fujita 《Island Arc》2006,15(4):437-454
Abstract The taxonomic diversity of hermatypic corals decreases with increasing latitude, which correlates with sea‐surface temperatures. However, little is known about latitudinal changes in the taxonomic diversity and biogeographic patterns of larger benthic foraminifera, although their physiological requirements are similar to those of hermatypic corals because of their symbiotic relationships with microalgae. The present study examined how the abundance and taxonomic composition of larger foraminiferal assemblages in shallow‐water reef sediments change with latitude along the Ryukyu Islands (Ryukyus), which are located near the northern limit of coral‐reef distributions in the western Pacific Ocean. Three islands from different latitudes in the Ryukyus were selected to investigate latitudinal changes in larger foraminiferal assemblages: Ishigaki Island (24°20′N, 124°10′E), Kudaka Island (26°09′N, 127°54′E) and Tane‐ga‐shima Island (30°20′N, 131°E). Four sediment samples were taken at each of three topographic sites (beach, shallow lagoon and reef crest) on the reef flat of each island. Foraminiferal tests of a 2.0‐ to 0.5‐mm size fraction were selected, identified and counted. The variations in foraminiferal abundance in reef sediments from three latitudinally different islands exhibit two contrasting trends along reef flats: a shoreward decrease on Ishigaki and Tane‐ga‐shima Islands and a shoreward increase on Kudaka Island. A total of 25, 24 and 13 foraminiferal taxa were identified in Ishigaki, Kudaka and Tane‐ga‐shima Islands, respectively. Baculogypsina sphaerulata, Neorotalia calcar and Amphistegina spp. were dominant (i.e. >3% of foraminiferal assemblages) in the three islands. Calcarina gaudichaudii and Calcarina hispida were common on Ishigaki and Kudaka Islands but were absent on Tane‐ga‐shima Island. Larger foraminiferal assemblages from three different reef‐flat environments on Ishigaki Island can be distinguished, whereas those from the three environments on Kudaka and Tane‐ga‐shima Islands are similar in composition. These latitudinal changes in larger foraminiferal assemblages in reef sediments may possibly be caused by variations in the topography of reef flats, distributions and standing crops of living foraminifers on reef flats, and the northern limit of some calcarinid species in the northern Ryukyus.  相似文献   

19.
Measurements of both broadband and spectral UV radiation have been carried out at Lhasa (29°40′N, 91°08′E, 3648 m above sea level) on the Tibetan Plateau, using a moderate bandwidth filter instrument (NILUV) and a Fixed Imaging Compact Spectrometer (FICS). In this paper, the erythemal UV dose rates deduced from broadband measurements during the period from 1 July 1996 to 10 December 1997 are presented. The observed highest erythemal UV dose rate is 500 (or 458) mW/m2 in July 1996 (or 1997), and the corresponding daily erythemal UV dose can reach up to 7.60 (or 7.00) kJ/m2 and 9.18 (or 8.96) kJ/m2, respectively, for the monthly mean and the monthly maximum. Comparisons with the UV levels at other locations at similar latitudes show that both the monthly mean and monthly maximum erythemal UV doses at Lhasa can be higher by a factor of 1.3–1.5 than those at San Diego (32°05′N, 117°1′W) in summer (from May to August), and exceed the corresponding values at Perth (32°0′S, 115°8′E) in the southern hemisphere summer (from November to February) by a factor of 1.2–1.4. Comparisons of both the broadband measurements and spectral measurements with the outputs of a discrete ordinate method (DOM) radiative transfer model have also been conducted. The results from the comparisons of broadband measurements with model outputs show that a 15, 11 and 10% agreement may be achieved around solar noon (with solar zenith angle smaller than 60°), respectively, for global irradiances in the 305, 320 and 340 mm channels, whilst the corresponding agreements are about 8 and 4% for the erythemal UV dose rate and the 340–305 nm ratio, respectively. The comparisons of the measured spectral irradiance with model calculations indicate that large discrepancies may appear at wavelengths shorter than 310 nm and longer than 380 nm. However, a 10% agreement may be generally achieved in UVA for solar zenith angle lower than 55°C. The corresponding agreement is about 20 and 5%, respectively, for UVB and the erythemal UV dose rate.  相似文献   

20.
Two lower tropospheric inversion layers (named as LTI1 and LTI2) over Yichang (111°18′E, 30°42′N) were studied by using the data from intensive radiosonde observations in January 2007 on an eight-times-daily basis. Our observations reveal that both the inversion layers are closely related to the intensive inertial gravity waves propagating in winter tropospheric jets. However, their formation mechanisms are likely to be different. Gravity-wave-induced intensive turbulence via convective instability may yield a downward energy transport and finally form the LTI1, while we speculate that the reflection of gravity waves by the strong tropospheric jet is responsible for the LTI2.  相似文献   

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