New evidence for age variation and scale effects of permeabilities of young oceanic crust from borehole thermal and pressure measurements     

Keir Becker  Earl E. Davis 《Earth and Planetary Science Letters》2003,210(3-4):499-508

In 1996, long-term sealed-hole hydrological observatories with subseafloor temperature and pressure sensors were installed in four cased holes drilled by the Ocean Drilling Program into sedimented young oceanic crust east of the Juan de Fuca Ridge. Data recovered over a year later showed that all four holes displayed temperature profiles indicative of vertical fluid flow immediately prior to their being sealed. Warm water was being produced from basement in two cases, and cool ocean bottom water was being drawn into basement at the others. Linear flow rates of 60–200 m/h were estimated from the perturbation of the temperature profiles relative to undisturbed geothermal gradients at the sites. The pressure differentials driving the flow were also measured at the time of the observatory installations, allowing estimates of permeabilities of the upper crustal sections penetrated by the holes. Estimated permeabilities vary systematically with age, ranging from about 10⁻¹⁰ m² in the youngest site (0.9 Ma) to 10⁻¹² m² in the oldest site (3.6 Ma), confirming an apparent reduction of permeability with age determined with packer experiments at three of the same sites. Combined with other estimates of permeabilities in the same holes using methods with different scales of investigation, the new permeability estimates also provide evidence for a significant scale dependence of permeability in the upper oceanic crust.  相似文献   

The closing of a seaway: ocean water masses and global climate change     

Caroline H. Lear  Yair Rosenthal  James D. Wright 《Earth and Planetary Science Letters》2003,210(3-4):425-436

The Late Neogene witnessed various major paleoceanographic changes that culminated in intense Northern Hemisphere Glaciation (NHG). The cause and effects of these changes are still debated. We use a multiproxy approach to determine the relative timing of the closure of the Panama gateway, changes in Atlantic circulation, global cooling and ice sheet growth. Benthic foraminiferal Mg/Ca records from a Pacific and an Atlantic Site have been produced and are interpreted in terms of bottom water temperatures. These Mg-temperature records are combined with published benthic δ¹³C, δ¹⁸O and erosion records to reconstruct the flow of proto-North Atlantic Deep Water (proto-NADW) over the past 12 Ma. The results suggest that between 12.5 and 10.5 Ma, and again between about 8.5 and 6 Ma, a nutrient-depleted water mass that was colder (by 1–2°C) and fresher than the intervening deep water mass filled the Atlantic basin. This proto-NADW became warmer (by 1°C) and saltier between 6 and 5 Ma, coincident with the restriction of surface water flow through the Central American Seaway. The Mg-temperature records define a subsequent global cooling trend of 3.5°C between 5 Ma and today. Early NHG in the late Miocene was perhaps related to the formation of the relatively cold, fresh proto-NADW. The formation of the warmer and saltier proto-NADW in the early Pliocene may have initially limited Northern Hemisphere ice growth. However, the increased moisture released at high northern latitudes associated with formation of ‘warm’ proto-NADW, coupled with the global temperature decrease of deep (and hence polar surface) waters, likely helped initiate the intense NHG of the Plio–Pleistocene.  相似文献   

塔里木盆地中部志留-泥盆系沉积构造背景   总被引：6，自引：4，他引：6       下载免费PDF全文

宋文杰  李曰俊  王国林  胡剑风  闵磊  谢烈文 《地质科学》2003,38(4):519-528

我国陆上最深的钻井塔参1井位于塔里木盆地中央隆起,井深7200m,在井深3742～4001m钻遇志留泥盆系碎屑岩259m,包括下志留统125m,上泥盆统134m。在该段岩心采样23块(下志留统15块,上泥盆统8块),其全岩和微量元素地球化学分析表明,塔参1井的志留泥盆系碎屑岩均为稳定大陆克拉通内部的沉积,物源可能来自其底部以前震旦纪花岗岩为代表的古老陆壳基底。  相似文献   

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake     

Tatsuo Matsuda  Kentaro Omura  Ryuji Ikeda  Takashi Arai  Kenta Kobayashi  Koji Shimada  Hidemi Tanaka  Tomoaki Tomita  Satoshi Hirano   《Tectonophysics》2004,378(3-4):143

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.  相似文献   

卤水资源开发利用技术述评   总被引：18，自引：11，他引：18       下载免费PDF全文

李海民  程怀德  张全有 《盐湖研究》2003,11(3):51-64

总结并论述了国内外从卤水中提取钾、镁、锂、硼、溴等资源的分离提取技术 ,并对其技术的应用范围、优缺点及技术发展趋势进行了述评  相似文献   

中国科学深钻选址地球物理调查与大别-苏鲁岩石圈   总被引：13，自引：0，他引：13       下载免费PDF全文

杨文采  程振炎  张春贺 《地球学报》2003,24(5):391-404

本文简要地讨论了大别-苏鲁超高压变质带大陆科学钻探选址新采集的地球物理调查剖面及相关地球物理成果。这些剖面以深反射地震及大地电磁测量为研究岩石圈构造的主要方法，结合地质资料和区域重磁平面图，分析大别—苏鲁地体的深部地质构造与岩石圈主要特征，以及大陆科学钻探靶区选择的地质地球物理依据。同时讨论了大陆科学钻探的靶区(江苏东海县)的地壳构造与地热研究结果，并将深度偏移地震剖面与先导孔岩心钻探结果进行了对比。  相似文献   

The oxygen isotopic composition and temperature of Southern Ocean bottom waters during the last glacial maximum     

Mitchell J Malone  Jonathan B Martin  Ulysses S Ninnemann  Timothy S White 《Earth and Planetary Science Letters》2004,222(1):275-283

We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ¹⁸O_sw from the pore water δ¹⁸O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ¹⁸O_sw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ¹⁸O_sw of 1.0-1.1‰.Using the calculated bottom-water δ¹⁸O_sw, we have extracted the temperature component from the benthic foraminiferal δ¹⁸O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern.  相似文献   

中国大陆科学钻探工程项目进展综述   总被引：1，自引：0，他引：1       下载免费PDF全文

王达 《探矿工程》2002,(6):47-53

阐明了中国大陆科学钻探工程的意义与目标，论述了工程建设的主要内容和项目的组织管理，介绍了项目的进展情况。  相似文献   

大洋钻探与深海热液作用   总被引：2，自引：0，他引：2  

吴世迎 《地球科学进展》1995,10(3):223-228

在ＤＳＤＰ／ＯＤＰ的２６年钻探中，有近２０个航次钻遇到的热液作用踪迹或热液产物。强调了深海热液作用作为研究海底扩张，地幔物质上涌，新生洋壳生成及火山活动所构成的地壳演化过程，已经成了大洋钻探计划的核心内容之一，并由此在若干重大理论问题上，获得了突破性的发展。  相似文献   

井间地震层析成像技术及其在岩溶勘察中的应用     

孙跃军  俞国柱  石桂  刘文祥 《CT理论与应用研究》2001,10(4):10-13

地下岩溶的存在，会对各种建设工程带来极大的危害或隐患，井间地震层析成像（地震CT）技术能有效、精细地反演出井间岩层的不均匀分布，本文阐述了该技术的方法原理，并介绍了应用该技术的一个岩溶勘察工程实例，在该工程中，笔者用钻探取芯结果约束地震CT的反演结果，分析结果表明，地震CT有较高的精度和可信度，在工程地质勘察中能做到对地下介质的精细成像，远远优越于常规勘察方法。  相似文献