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41.
We use a simple approach to estimate the present-day thermal regime along the northwestern part of the Western Indian Passive Margin, offshore Pakistan. A compilation of bottom borehole temperatures and geothermal gradients derived from new observations of bottom-simulating reflections (BSRs) allows us to constrain the relationship between the thermal regime and the known tectonic and sedimentary framework along this margin. Effects of basin and crustal structure on the estimation of thermal gradients and heat flow are discussed. A hydrate system is located within the sedimentary deep marine setting and compared to other provinces on other continental margins. We calculate the potential radiogenic contribution to the surface heat flow along a profile across the margin. Measurements across the continental shelf show intermediate thermal gradients of 38–44 °C/km. The onshore Indus Basin shows a lower range of values spanning 18–31 °C/km. The Indus Fan slope and continental rise show an increasing gradient from 37 to 55 °C/km, with higher values associated with the thick depocenter. The gradient drops to 33 °C/km along the Somnath Ridge, which is a syn-rift volcanic construct located in a landward position relative to the latest spreading center around the Cretaceous–Paleogene transition. 相似文献
42.
Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m2) surrounded by a continuous bed of methanotrophic mussels (Bathymodiolus childressi) covering 434 m2 and a patchy bed covering an additional 214 m2 of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m3, while the middle and upper stages deposited 7700 and 20,400 m3, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ14C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages. 相似文献
43.
熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。 相似文献
44.
Gao2008、Crowley2013和Sigl2015火山强迫资料,均基于极地冰芯重建.由于每组重建使用的冰芯数据和分析方法等不同,因此结果存在差异,从而影响气候模式应用.文中详细梳理三组火山强迫资料在原始冰芯数据、信号识别提取和沉积通量计算等方面的差异;介绍重建中涉及的对未知火山事件发生季节、纬度及从极地硫酸盐沉积... 相似文献
45.
Chronostratigraphic constraints on Middle Pleistocene faunal assemblages and Acheulian industries from the Cretone lacustrine basin,central Italy
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46.
Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite. 相似文献
47.
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49.
Kevin Hall 《地球表面变化过程与地形》1982,7(1):45-51
Volcanic activity on sub-Antarctic Marion Island is found to have occurred only during the interglacials. The present volcano distribution is associated with a radial and peripheral fault system, the location of which appears to be related to the former glacier distribution. An hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice-covered and ice-free areas during isostatic uplift. The faulting initiates volcanism due to the location of the island within a volcanic region. 相似文献
50.
Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea 总被引:2,自引:0,他引:2
Dong-Chan Koh Kyung-Seok Ko Yongje Kim Seung-Gu Lee Ho-Wan Chang 《Hydrogeology Journal》2007,15(4):727-743
Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO4 and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO4 in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO4 originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO3–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry. 相似文献